ASME Conference Presenter Attendance Policy and Archival Proceedings

2012;():i. doi:10.1115/GT2012-NS3.

This online compilation of papers from ASME Turbo Expo 2012: Turbine Technical Conference and Exposition (GT2012) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Cycle Innovations

2012;():1-7. doi:10.1115/GT2012-68132.

To relieve problems of high-energy consumption and poor corrosion-resistant during the conventional corrosive and thermal-sensitive material evaporation-concentration process, a closed low temperature heat pump evaporation-concentration scheme has been recommended. Through compared with the usual mechanical vapor recompression (MVR) heat pump evaporation-concentration process, a vitamin E solution evaporation-concentration scheme was analyzed as an example, key equipments size, cost, integrated thermodynamic performance and economic performance of the proposed system scheme have been explored. The results showed, compared with the MVR scheme, the closed low temperature heat pump evaporation-concentration scheme hold advantages in comprehensive performance. And raw material evaporation temperature selection affected integrated performance of the proposed scheme less. The comprehensive performance index is decreased with evaporation temperature for both of the two schemes. At the same evaporation temperature increase, the comprehensive performance is decreased less than that of the MVR scheme. Advantage of the proposed scheme became obvious when the evaporation temperature lower than 44 °C. Furthermore, thermodynamic performance of the proposed suggested worse than that of the MVR heat pump, while the key equipment- compressor of the proposed scheme was compact, cost less, and regardless considering the processed corrosive material causticity impaction.

Commentary by Dr. Valentin Fuster
2012;():9-18. doi:10.1115/GT2012-68133.

Geothermal power is becoming more and more significant in the renewable power mix of several countries in the world. The thermal conditions of the geothermal fluids exhausting from geothermal power plants shows additional potential for improved heat utilization through the integration of a low heat recovery system. This paper addresses the optimum integration of an Organic Rankine Cycle (ORC) as bottoming cycle with a geothermal steam power plant as topping cycle over a range of geothermal fluid interface temperatures.

A reference geothermal based steam turbine power plant of 50MW capacity with indirect cycle configuration has been chosen for the study. At design point of the reference plant, optimized Organic Rankine Cycles based on three working fluids n-pentane, R123, and R245fa have been integrated at the exhaust of the geothermal fluid leaving the geothermal plant. An overall optimization of the power plant has been carried out by downsizing and over sizing the topping cycle with the integration of the bottoming cycle. One of the optimization variables for the overall plant is the interface temperature, which is a consequence of the resizing of the topping cycle. The procedure is repeated for the three different organic working fluids. By applying this procedure, it is then possible to know within a given interface temperature range, the organic working fluid that will give optimum plant performance.

The choice of ORC integration option is not only driven by the best techno-economic solution but additionally by environmental, health and safety compliance.

Commentary by Dr. Valentin Fuster
2012;():19-30. doi:10.1115/GT2012-68158.

Recently, the expert engine diagnostic systems using the artificial intelligent methods such as Neural Networks, Fuzzy Logic and Genetic Algorithms have been studied to improve the model based engine diagnostic methods. Among them the Neural Networks is mostly used to engine fault diagnostic system due to its good learning performance, but it has a drawback due to low accuracy and long learning time to build learning data base if only use of the Neural Networks. In addition, it has a very complex structure due to finding effectively faults of single type faults and multiple type faults of gas path components.

This work builds inversely a base performance model of a turboprop engine to be used for a high altitude operation UAV using measuring performance data, and proposes a fault diagnostic system using the base performance model and artificial intelligent methods such as Fuzzy and Neural Networks. Each real engine performance model, which is named as the base performance model that can simulate a new engine performance, is inversely made using its performance test data. Therefore the condition monitoring of each engine can be more precisely carried out through comparison with measuring performance data.

The proposed diagnostic system identifies firstly the faulted components using Fuzzy Logic, and then quantifies faults of the identified components using Neural Networks leaned by fault learning data base obtained from the developed base performance model. In leaning the measuring performance data of the faulted components, the FFBP(Feed Forward Back Propagation) is used. In order to user’s friendly purpose, the proposed diagnostic program is coded by the GUI type using MATLAB.

The proposed program is verified by application of several case studies having the arbitrary implanted engine component faults as well as real engine performance data.

Commentary by Dr. Valentin Fuster
2012;():31-39. doi:10.1115/GT2012-68159.

Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to reduce CO2 emissions, improving power unit efficiency has become an issue of utmost significance. The development of technologies related to coal-fired power units does not focus solely on the steam parameters ahead of the turbine. Increasing the live steam parameters usually constitutes the greatest contribution to the rise in the efficiency of a power unit, but the sum of efficiency gains related to the application of other solutions can also be significant and can, in some cases, exceed the effects related to raising the temperature and steam pressure values. A paper presents thermodynamic and economic analysis of various configurations of the ultra-supercritical coal-fired 900 MW power unit with the auxiliary steam turbine. Main subject of research was a power unit considered within the Strategic Research Programme – Advanced Technologies for Energy Generation with the parameters of live and reheat steam: 30 MPa/650°C/670°C. The base configuration of the power unit has single steam reheat and electric drive boiler feed pump. Analysis of ultra-supercritical 900 MW power unit involves configuration with a single and double reheat. The following configurations of the auxiliary steam turbine will be presented and compared:

• extraction-backpressure steam turbine fed with steam from cold reheat line with bleed and steam outlet directed to the feed water heaters;

• extraction-backpressure steam turbine fed with steam from cold reheat line with bleed and steam outlet directed to the feed water heaters; the auxiliary turbine drives the boiler feed pump;

• backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the intermediate-pressure turbine; the auxiliary turbine drives the boiler feed pump.

The analysis of the operation of the 900 MW unit was carried out for three load levels: for the nominal mass flow of live steam, and for the partial mass flow of 75% and 50%. For all presented solutions thermodynamic and economic analysis was performed, which has taken into account the charge for CO2 emissions.

Topics: Steam turbines
Commentary by Dr. Valentin Fuster
2012;():41-50. doi:10.1115/GT2012-68180.

A novel electrical energy storage system based on cryogenic liquid nitrogen as storage medium was developed and investigated in order to integrate fluctuating wind energy into the electrical grid. In times of surplus electric power from wind turbines the electrical energy is used to generate very cold liquid nitrogen with an air separation unit which will be stored in cryogenic tanks. In times of electricity demand the energy which is stored in the coldness of the liquid nitrogen will be transferred into electrical energy by a Rankine cycle. The external heat input is solely supplied from the ambience because all changes of state of this cryogenic Rankine cycle are below the ambient temperature level. The cycle drives an expansion turbine for power generation with a power of 10 MW.

In this work two variants of the cryogenic Rankine cycle are presented.

The thermodynamic analyses show that the volumetric energy density of this liquid nitrogen energy storage system (LINESS) amounts > 50 kWh/m3, which is much higher than of many alternative energy storage systems. But the overall efficiency of this storage system is moderate and amounts 13%.

The investigations also show that the technical feasibility of the turbine is given, but a standard steam turbine cannot be adopted for this cycle. The main advantage of this novel storage system compared to compressed air or hydrogen power storage systems is that it can be built independent of geological premises due to the high volumetric energy density.

Commentary by Dr. Valentin Fuster
2012;():51-64. doi:10.1115/GT2012-68402.

Nowadays, the reduction of fuel consumption and pollutant emissions has become a top priority for society and economy. In the past decades, some of the environmental advantages of the gas turbine (such as inherently low CO and unburned HC) have led some car manufacturers to evaluate the potential of this type of engine as prime mover. This paper suggests a strategy to assess the fuel consumption of gas turbines applied in road vehicles. Based on a quasistatic approach, a model was created that can simulate road vehicles powered by gas turbines, and thereafter a comparison was established with reciprocating engines. Within this study, material and turbomachinery technology developments that have taken place in micro gas turbines since the 1960’s have been considered. A 30% efficiency improvement target has been identified with respect to making the gas turbine fuel competitive to a diesel engine powering an SUV. It is the authors’ view that several technologies that could mature sufficiently within the next 10–15 years exist, such as uncooled ceramic turbines. Such technologies could help bridge the fuel efficiency gap in micro gas turbines and make them commercially competitive in the future for low-emissions vehicular applications. Furthermore, the system developed also allows the simulation of hybrid configurations using gas turbines as range extenders, a solution that some car manufacturers consider to be the most promising in the coming years.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2012;():65-77. doi:10.1115/GT2012-68416.

Numerical modelling of aero engine combustors under relight conditions is a matter of continuously increasing importance due to the demanding engine certification regulations. In order to reduce the complexity and the cost of the numerical modelling, common practice is to replace the atomizer’s swirlers with velocity profiles boundary conditions, very often scaled down from nominal operating conditions assuming similarity of the swirler flowfield. The current numerical study focuses on the flowfield characteristics of an axially swirled atomizer operating within a windmilling engine environment. The scalability of the velocity profile from higher power settings is examined. Observations on the performance of the axial swirler under relight conditions are also made.

Experimental data was used as a validation platform for the numerical solver, after a grid sensitivity study and a turbulence model selection process. Boundary conditions for simulating the windmilling environment were extracted from experimental work.

The swirler axial and tangential velocity profiles were normalised using the swirler inlet velocity. Results showed that both profiles are only scalable for windmilling conditions of high flight Mach number (≥ 0.5). At low flight Mach numbers, the actual profile had a lower velocity than that predicted through scaling. The swirl number was found to deteriorate significantly with the flight velocity following a linear trend, reducing significantly the expected flame quality. As a consequence the burner is forced to operate at the edge of its stability loop with low certainty regarding its successful relight.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2012;():79-89. doi:10.1115/GT2012-68506.

For geographic regions where significant power demand and highest electricity prices occur during the warm months, a gas turbine inlet air cooling technique is a useful option for increasing output. Inlet air cooling increases the power output by taking advantage of the gas turbine’s feature of higher mass flow rate, due the compressor inlet temperature decays. Industrial gas turbines that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, the increases of the air density results in a higher air mass flow rate once the volumetric rate is constant. Consequently, the gas turbine power output enhances. Different methods are available for reducing compressor intake air temperature. There are two basic systems currently available for inlet cooling. The first and most cost-effective system is evaporative cooling. Evaporative coolers make use of the evaporation of water to reduce the gas turbine inlet air temperature. The second system employs two ways to cool the inlet air: mechanical compression and absorption. In this method, the cooling medium flows through a heat exchanger located in the inlet duct to remove heat from the inlet air. In the present study, a thermodynamic analysis of gas turbine performance is carried out to calculate heat rate, power output and thermal efficiency at different inlet air temperature and relative humidity conditions. The results obtained with this model are compared with the values of the condition without cooling herein named of Base-Case. Then, the three cooling techniques are computationally implemented and solved for different inlet conditions (inlet temperature and relative humidity). In addition, the gas turbine was performed under different cooling methods applied for two Brazilian sites, the comparison between chiller systems (mechanical and absorption) showed that the absorption chiller provides the highest increment in annual energy generation with lower unit energy costs. On the other hand, evaporative cooler offers the lowest unit energy cost but associated with a limited cooling potential.

Topics: Cooling , Gas turbines
Commentary by Dr. Valentin Fuster
2012;():91-97. doi:10.1115/GT2012-68540.

Solid oxide fuel cell (SOFC) is a complicated system with heat and mass transfer as well as electrochemical reactions. The flow configuration has great impact on the system performance. Based on the established one dimensional direct internal reforming SOFC mathematical model, with the consideration of the flow, thermal and electrical characteristic, this paper developed the two dimensional mathematical model for both counter-flow and cross-flow types. Plus, the comparison and analysis of the steady distribution are performed. The results reveal that on the geometry parameters and inlet conditions, the outlet temperatures of counter-flow SOFC are lower than that of cross-flow. However, the average temperature of PEN plate is higher than cross-flow, and both the operating voltage and electric efficiency are also higher than that of cross-flow. This will be beneficial for the structure design of SOFC.

Commentary by Dr. Valentin Fuster
2012;():99-107. doi:10.1115/GT2012-68568.

This study aims at the development of a software tool for supply and demand matching of electrical and thermal energy in an urban district.

In particular, the tool has been developed for E-NERDD, the experimental district that TPG-DIMSET is going to build in Savona, Italy.

E-NERDD is an acronym for Energy and Efficiency Research Demonstration District. It is one of the districts that will be used within the project to demonstrate how different software tools and algorithms perform in thermodynamic, economic and environmental terms.

The software tool originally developed for and implemented in this work, called E-NERDD Control System, is targeted on enabling the operation of the hardware, when connected in a district mode.

Supply and demand are matched to reach a thermoeconomic optimum. An optimization algorithm is organized into two different levels of optimization: a first level that resolves a constrained minimization problem in planning power supply for each generator on the basis of day-before forecasting; and a second level that distributes among the different machines the gap between planned and real-time demand.

The algorithm developed is demonstrated in four test cases in order to test it in different working conditions.

Topics: Optimization
Commentary by Dr. Valentin Fuster
2012;():109-117. doi:10.1115/GT2012-68580.

This paper describes the development and testing of a new algorithm to identify faulty sensors, based on a statistical model using quantitative statistical process history. Two different mathematical models were used and the results were analyzed to highlight the impact of model approximation and random error. Furthermore, a case study was developed based on a real micro gas turbine facility, located at the University of Genoa. The diagnostic sensor algorithm aims at early detection of measurement errors such as drift, bias, and accuracy degradation (increase of noise). The process description is assured by a database containing the measurements selected under steady state condition and without faults during the operating life of the plant. Using an invertible statistical model and a combinatorial approach, the algorithm is able to identify sensor fault. This algorithm could be applied to plants in which historical data are available and quasi steady state conditions are common (e.g. Nuclear, Coal Fired, Combined Cycle).

Commentary by Dr. Valentin Fuster
2012;():119-131. doi:10.1115/GT2012-68585.

This paper presents the development of a new experimental facility for analysis and optimization activities on smart polygeneration grids. The test rig is being designed and built in the framework of the European project “Energy-Hub for residential and commercial districts and transport” (E-HUB), which targets optimal energy management of residential and commercial districts.

The experimental rig, named “Energy aNd Efficiency Research Demonstration District” (E-NERDD), is located inside the University campus in Savona, and is based on four different prime movers able to produce both electrical and thermal energy: a 100 kWe micro gas turbine, a 20 kWe internal combustion engine, a 3 kWe Stirling engine, and a 450 kWe fuel cell/gas turbine hybrid system emulator based on the coupling of a micro gas turbine with a modular vessel. While the electrical side is based on the connection with the campus grid (further developments are planned for a local electrical grid including storage units), thermal energy is managed through a dual ring-based water distribution system. The facility is also equipped with thermal storage tanks and fan cooler units to study and optimize different thermal management algorithms generating different thermal load demands. The facility also includes an absorption chiller for cold water generation. As a result, trigeneration operation is possible in a physically simulated urban district. Moreover, the rig is equipped with six photovoltaic panels (significant for the electrical aspects) and 10 kWp of thermal solar panels to be integrated in the grid.

Further technologies to be considered for the E-NERDD are power plants based on other renewable resource (e.g. with biomass fuel). These systems are planned to be analyzed through real plants (remote connection with the field) or through virtual models based on real-time dynamic approaches.

Experimental tests related to the performance of the micro gas turbine are reported and discussed in this paper. The focus here is on machine correction curves essential to evaluate factors for quantifying ambient temperature influence on machine performance. This analysis is essential for setting the thermal distribution grid and for future optimization tests.

Commentary by Dr. Valentin Fuster
2012;():133-142. doi:10.1115/GT2012-68586.

Gas turbine combined cycles (GTCC) using a steam bottoming cycle are a widely used technology for electric power generation. From [1] it is known that the best current large GTCC’s loose around 25% of the fuel exergy just by combusting the fuel while all other exergy losses sum up to around 15%. For the net efficiency of such plants 60% is remaining. This paper shows thermodynamic calculation results of GTCC’s with variable pressure ratio and turbine inlet temperature (TIT) aimed at understanding the efficiency potential associated with further increases of the TIT thus reducing the exergy loss by combustion. The assumptions of these calculations correspond to published industrial experience and standard assumptions in two different scenarios. The results are curves showing net efficiency and specific power as functions of TIT. Other data like the related pressure ratio and compressor exit temperature are shown too. The conclusion shows that a net efficiency of 63…65% is feasible with a hot gas temperature of around 1750°C based on the two scenarios. The winning cycle arrangement uses an adiabatic compressor. A GTCC with GT-compressor having one intercooling stage is clearly less favorable in several respects.

Topics: Cycles
Commentary by Dr. Valentin Fuster
2012;():143-153. doi:10.1115/GT2012-68599.

The present work deals with a high temperature proton exchange membrane (SPEEK-type) fuel cell (HT-PEMFC) energy system fuelled with hydrogen obtained by reforming of ammonia (NH3) and coupled with a bottoming Organic Rankine Cycle (ORC) energy system. This system was designed for distributed electric power generation, mainly for production of electric power systems with potential future applications in smart-grid.

The use of ammonia as hydrogen rich gas source allows to avoid hydrogen tanking with metal hydrides, giving the opportunity to lighten and simplify the storage section of the system with respect to the pure hydrogen fed systems.

The hybrid fuel cell/ORC configuration allows to increase the efficiency of standard power generation technologies. In other words, the ORC subset represents the most appropriate solution, in terms of sustainability, for extracting the excess heat produced during the H2 combustion maintaining the PEMFC working temperature at 120°C and for reducing the temperature of the exhausts.

The objective of the work is to optimize the electric output of the system (PEMFC + ORC), thus improving the overall efficiency. To this end, a numerical model is implemented and tested. A validation of the numerical scheme is carried out comparing the prediction of the reforming phase with experimental results obtained by the authors. The thermal and electrical energy balance is also assessed. Furthermore, the operation conditions of the reformer are studied in detail to determine the settlements leading to a proper ammonia cracking to produce nitrogen and hydrogen. Furthermore, the calculations take into account also the auxiliary equipments such as pumps, compressors and heat exchangers.

Commentary by Dr. Valentin Fuster
2012;():155-164. doi:10.1115/GT2012-68697.

Power generation with a supercritical CO2 closed regenerative Brayton cycle has been successfully demonstrated using a bench scale test facility. A set of a centrifugal compressor and a radial inflow turbine of finger top size is driven by a synchronous motor/generator controlled using a high-speed inverter. A 110 W power generating operation is achieved under the operational condition of rotational speed of 1.15kHz, CO2 flow rate of 1.1 kg/s, and respective thermodynamic states (7.5 MPa, 304.6 K) at compressor and (10.6 MPa, 533 K) at turbine inlet. Compressor work reduction owing to real gas effect is experimentally examined. Compressor to turbine work ratio in supercritical liquid like state is measured to be 28% relative to the case of ideal gas. Major loss of power output is identified as rotor windage. It is found the isentropic efficiency depends little on compressibility coefficient. Off design performance of gas turbine working in supercritical state is well predicted by a Meanline program. The CFD analysis on compressor internal flow indicates that the presence of backward flow around the tip region might create a locally depressurized region leading eventually to the onset of flow instability.

Topics: Brayton cycle
Commentary by Dr. Valentin Fuster
2012;():165-173. doi:10.1115/GT2012-68754.

Growing concerns regarding fluctuating fuel costs and pollution targets for gas emissions, have led the aviation industry to seek alternative technologies to reduce its dependency on crude oil, and its net emissions. Recently blends of bio-fuel with kerosine, have become an alternative solution as they offer “greener” aircraft and reduce demand on crude oil. Interestingly, this technique is able to be implemented in current aircraft as it does not require any modification to the engine. Therefore, the present study investigates the effect of blends of bio-synthetic paraffinic kerosine with Jet-A in a civil aircraft engine, focusing on its performance and exhaust emissions. Two bio-fuels are considered: Jatropha Bio-synthetic Paraffinic Kerosine (JSPK) and Camelina Bio-synthetic Paraffinic Kerosine (CSPK); there are evaluated as pure fuels, and as 10% and 50% blend with Jet-A. Results obtained show improvement in thrust, fuel flow and SFC as composition of bio-fuel in the blend increases. At design point condition, results on engine emissions show reduction in NOx, and CO, but increases of CO is observed at fixed fuel condition, as the composition of bio-fuel in the mixture increases.

Commentary by Dr. Valentin Fuster
2012;():175-184. doi:10.1115/GT2012-68822.

Compressed air and steam are perhaps the most significant industrial utilities after electricity, gas and water, and are responsible for a significant proportion of global energy consumption. Microturbine technology, in the form of a Gas Turbine Air Compressor (GTAC), offers a promising alternative to traditional, electrically driven air compressors providing low vibration, a compact size, reduced electrical consumption and potentially reduced greenhouse gas emissions. With high exhaust temperatures, gas turbines are well suited to the cogeneration of steam. The compressed air performance can be further increased by injecting some of that cogenerated steam or by conventional recuperation.

This paper presents a thermodynamic analysis of various forms of the GTAC cycle incorporating steam cogeneration, steam injection (STIGTAC) and recuperation. The addition of cogeneration leads to improved energy utilisation, while steam injection leads to a significant boost in both the compressed air delivery and efficiency. As expected, for a low pressure ratio device, recuperating the GTAC leads to a significant increase in efficiency. The combination of steam injection and recuperation forms a recuperated STIGTAC with increased compressed air performance over the unrecuperated STIGTAC at the expense of reduced steam production. Finally, an analysis using a simplified model of the STIGTAC demonstrates a significant reduction in CO2 emissions, when compared to an equivalent air compressor driven by primarily coal-based electricity and a natural gas fired boiler.

Commentary by Dr. Valentin Fuster
2012;():185-194. doi:10.1115/GT2012-68825.

This paper presents a model based, off-line method for analysing the performance of individual components in an operating gas turbine. As with other studies, a least squares approach is employed. The component models are physics-based where possible. In its most general form, the method permits simultaneous inference of the combustor efficiency and stagnation pressure loss, the hot-end heat losses and associated heat transfer coefficients, the turbine inlet temperature and the turbine’s isentropic efficiency. As part of this, combustion of unburnt fuel within the turbine is modelled.

The method is demonstrated on a so-called ‘Gas Turbine Air Compressor (GTAC)’ test rig built by the group, a micro-turbine whose compressor supplies air for both the cycle and external applications, but produces no shaft work. The method is also formulated for other gas turbines. The highest order models are tested first, and then the model order is progressively reduced to determine adequate component model complexity. Since the GTAC is a micro-gas turbine, heat losses are found to be significant. It is also shown that care must be taken to distinguish between variations in the performance of different components, since the performance of several components can have similar effects on the complete, operating device.

Commentary by Dr. Valentin Fuster
2012;():195-205. doi:10.1115/GT2012-68856.

Accurate and reliable component life prediction is crucial to ensure safety and economics of gas turbine operations. In pursuit of such improved accuracy and reliability, model-based creep life prediction methods have become more and more complicated and therefore demand more computational time although they are more flexible in applications, in particular for new gas turbine engines. Therefore, there is a need to find an alternative approach that is able to provide a quick solution to creep life prediction for production engines while at the same time maintain the same accuracy and reliability as that of the model-based methods. In this paper a novel creep life prediction approach using Artificial Neural Networks is introduced as an alternative to the model based creep life prediction approach to provide a quick and accurate estimation of gas turbine creep life. Multilayer feed forward back propagation neural networks have been utilised to form three neural network-based creep life prediction architectures known as the Range Based, Functional Based and Sensor Based architectures. The new neural network creep life prediction approach has been tested with a model single spool turboshaft gas turbine engine. The results show that good generalisation can be achieved in all three neural network architectures. It was also found that the Sensor-Based architecture is better than the other two in terms of accuracy, with 98% of the post-test samples possessing prediction errors within ± 0.4%. Overall, it can be concluded that the proposed neural network approach in creep life prediction is able to provide a good alternative to the more complicated model-based creep life prediction algorithms and can be applied to different types of gas turbine engines.

Commentary by Dr. Valentin Fuster
2012;():207-215. doi:10.1115/GT2012-68868.

The gas turbine engine has many advantages such as low investment costs, low emissions and a low water consumption. This fact allows its application in many power engineering systems, for example as parts of gas and oil transport systems. It is possible to increase the efficiency of gas turbines through the use of combined cycles. For this purpose, the steam cycle is used most frequently. These systems are highly efficient in terms of energy, but they are very complex and have a high water consumption. An alternative to steam cycles are gas-air systems, referred to as the ABC’s (Air Bottoming Cycles), which use hot combustion gases as a heat source for the air cycle. ABC’s are composed of a gas turbine powered by natural gas, an air compressor and an air turbine coupled to the system by means of a heat exchanger, referred to as the AHX (Air Heat Exchanger).

The paper presents an application of gas-air systems with example configurations, together with thermodynamic characteristics. Two technological structures are taken into consideration — a simple system of the ABC and an ABC with air intercooling. A parametric analysis of these systems is performed using a special computer program with real gas properties for enthalpy and entropy calculations. A basic comparative analysis of gas turbine air bottoming cycle and combined gas-steam cycle has been also done. Other important calculations are related to the heat exchanger, which is one of the most important components in this system because it couples the gas and air parts. The efficiency of the whole cycle depends on a rationally designed heat exchanger. The calculations are performed for a shell-and-tube exchanger, as well as for a plate heat exchanger. For all investigations an purchase cost of machines and devices is also determined.

Commentary by Dr. Valentin Fuster
2012;():217-225. doi:10.1115/GT2012-68996.

This paper presents a reduced-order through-flow expander design for the Humid Air Turbine (HAT) also called the Evaporative Gas Turbine (EvGT). The HAT cycle is an innovative gas turbine cycle that uses humid air to enhance efficiency and power output. This means that there will be a higher water vapour content in the exhaust gases than for a simple cycle. This high water content affects the design of the HAT expander. The design of a wet expander is presented and compared with the results obtained with an expander working under dry exhaust gas conditions. The study was conducted using the reduced-order turbine design tool LUAX-T, developed at Lund University, which is freely available for academic use upon request. LUAX-T allows a flow-path analysis of the expander by specifying important flow-path parameters such as blade root stress and wall-hade angle. The HAT cycle enables cooling flow to the expander under different conditions and design differences for three different options are presented. The first cooling air bleeding point evaluated is the original position, where air is bled from the compressor discharge. The second position is just before the humidification tower, where the air has been cooled down to a low temperature. The third position is just after the humidification tower, where the air has been humidified thus changing its thermodynamic properties. Results in this paper shows that there is a need for an additional turbine stage in a humid expander compared to a dry expander. There are also results indicating that the compressor power can be reduced depending on which cooling strategy is used which can yield an increased total efficiency for a HAT cycle.

Topics: Turbines
Commentary by Dr. Valentin Fuster
2012;():227-238. doi:10.1115/GT2012-69141.

This study aims to present various design aspects and realizable performance of the natural gas fired semi-closed oxy-fuel combustion combined cycle (SCOC-CC). Design parameters of the cycle are set up on the basis of component technologies of today’s state-of-the-art gas turbines with a turbine inlet temperature between 1400°C and 1600°C. The most important part in the cycle analysis is the turbine cooling which affects the cycle performance considerably. A thermodynamic cooling model is introduced to predict the reasonable amount of turbine coolant to maintain the turbine blade temperature of the SCOC-CC at the levels of those of conventional gas turbines. Optimal pressure ratio ranges of the SCOC-CC for two different turbine inlet temperature levels are searched. The performance penalty due to the CO2 capture is examined. Also investigated are the influences of the purity of oxygen provided by the air separation unit on the cycle performance. A comparison with the conventional combined cycle adopting a post-combustion CO2 capture is carried out taking into account the relationship between performance and CO2 capture rate.

Topics: Combustion , Fuels , Design , Cycles
Commentary by Dr. Valentin Fuster
2012;():239-247. doi:10.1115/GT2012-69232.

The tendency for environmentally friendlier aeronautic engines, led to the re-examination of the contra rotating open rotor (CROR) as a more efficient and less polluting propulsion system, thanks to its noticeably high propulsive efficiency. The geometrical and operational characteristics of these contra rotating propellers are examined in order to optimize the noise emissions, given the challenging regulation context for such an unducted concept. For this research, computational techniques have been used to develop a numerical model for prediction of noise levels generated by CRORs propellers. An extended database of unsteady CFD simulations, generated with innovative methods, namely a non-linear harmonic flow solver and an acoustic propagation model based on the Ffowcs Williams–Hawkings approach, have been used to assess the noise spectra measured in the certification points. Sound pressure levels and frequencies have been afterwards converted into EPN levels along the aircraft flight path, according to the ICAO regulation. The whole procedure has been applied to 102 different cases to establish the influence of several independent parameters on noise emissions. A surface response model has finally been developed, providing an easy tool of fast utilization to be implemented in optimization platforms.

Commentary by Dr. Valentin Fuster
2012;():249-255. doi:10.1115/GT2012-69258.

A hybrid system based on an existing recuperated microturbine and a pre-commercially available high temperature tubular solid oxide fuel cell is modeled in order to study its performance. Individual models are developed for the microturbine and fuel cell generator and merged into a single one in order to set up the hybrid system. The model utilizes performance maps for the compressor and turbine components for the part load operation. The full and partial load exergetic performance is studied and the amounts of exergy destruction and efficiency of each hybrid system component are presented, in order to evaluate the irreversibilities and thermodynamic inefficiencies. Moreover, the effects of various performance parameters such as fuel cell stack temperature and fuel utilization factor are investigated. Based on the available results, suggestions are given in order to reduce the overall system irreversibility. Finally, the environmental impact of the hybrid system operation is evaluated.

Commentary by Dr. Valentin Fuster
2012;():257-268. doi:10.1115/GT2012-69433.

This paper presents a method of modelling contra-rotating turbomachinery components for engine performance simulations. The first step is to generate the performance characteristics of such components. In this study, suitably modified one-dimensional mean line codes are used. The characteristics are then converted to three-dimensional tables (maps). Compared to conventional turbomachinery component maps, the speed ratio between the two shafts is included as an additional map parameter and the torque ratio as an additional table. Dedicated component models are then developed that use these maps to simulate design and off-design operation at component and engine level.

Using this approach, a performance model of a geared turbofan with a Contra-Rotating Core (CRC) is created. This configuration was investigated in the context of the European program NEWAC (NEW Aero-engine core Concepts). The core consists of a seven-stage compressor and a two-stage turbine without inter-stage stators and with successive rotors running in opposite direction through the introduction of a rotating outer spool. Such a configuration results in reduced parts count, length, weight and cost of the entire HP system. Additionally, the core efficiency is improved due to reduced cooling air flow requirements.

The model is then coupled to an aircraft performance model and a typical mission is carried out. The results are compared against those of a similar configuration employing a conventional core and identical design point performance. For the given aircraft-mission combination and assuming a 10% engine weight saving when using the CRC arrangement over the conventional one, a total fuel burn reduction of 1.1% is predicted.

Commentary by Dr. Valentin Fuster
2012;():269-279. doi:10.1115/GT2012-69455.

The cooling of high temperature gas turbines has been the subject of intensive work over the past few decades. Analysis of the metal temperature of cooled blades requires the solution of the equations governing the heat flow through the blade given the internal and external distributions of the boundary gas temperatures and heat transfer coefficients. An analytical model to investigate the influence of Water Air Ratio (WAR) on turbine blade heat transfer and cooling processes (and thus the blade creep life) of industrial gas turbines is presented. The method is based on a blade with convective cooling and a thermal barrier coating (TBC). The approach is based on engine performance, heat transfer models (hot side and cold side model), in addition to a method that accounts for the changes in thermal conductivity, viscosity, density and the gas properties of moist air as a function of WAR. The evaluation of heat transfer data in this model is considered by using non-dimensional parameters namely: Reynolds number, Nusselt number, Stanton number, Prandtl number and other related parameters. The aim of this paper is to present an analytical model to investigate the influence of humidity on the turbine blade heat transfer and cooling processes which, in turn, affect blade creep life. The developed model can be used to assess the main parameters that influence blade cooling performance, such as cooling methods, alternative cooling fluids, blade geometry, gas properties and material and thermal barrier coatings. For a given off-design point, the WAR was varied from dry to humid air (air/water vapour mixtures). The whole cooled blade row is regarded as a heat exchanger with the presence of TBC subjected to a mainstream hot gas flow from the combustion chamber.

Commentary by Dr. Valentin Fuster
2012;():281-288. doi:10.1115/GT2012-69462.

The determination of the rate of heat transfer from the turbine blade in a cross flow is important in hot section gas turbine life assessment. For design purposes, the rate of heat transfer is normally fixed by semi-empirical correlations. These correlations require knowledge of fluid properties which depend on temperature. For gases these properties are normally available only for the dry state, thus the possible effect of the water vapour content has been overlooked. Many gas turbines operate in environments in which air humidity is very low and therefore has little influence on gas turbine performance. However humidity becomes more important in hot, humid climates where there are large variations in ambient absolute humidity, especially in hot and humid climates. The aim of this paper is to investigate and present the effect of humidity at different operating conditions on the turbine blade coolant heat transfer and blade creep life. The effect of humidity was considered only on the air coolant side. he The heat transfer coefficient on the hot side was calculated for dry hot gas. This avoided the balancing effect of each other (heat transfer coefficient coolant side and hot side). The WAR at each operating point is quantified based on the ambient temperature and the relative humidity (0%–100%). Results showed that with increasing WAR the blade inlet coolant temperature reduced along the blade span. The blade metal temperature at each section was reduced as WAR increased, which in turn increased the blade creep life. The increase in WAR increased the specific heat of the coolant and increased the heat transfer capacity of the coolant air flow. Different operating points were also evaluated at different WAR and Tamb to identify the effect of WAR on the creep life. The results showed that an increase in WAR increased the blade creep life. The creep life of the blade at each section of interest was obtained as a function of the blade section stress and the blade metal section temperature using the LMP approach.

Commentary by Dr. Valentin Fuster
2012;():289-297. doi:10.1115/GT2012-69470.

The aim of this study was to compare single- and twin-shaft oxy-fuel gas turbines in a semi-closed oxy-fuel combustion combined cycle (SCOC-CC). This paper discussed the turbomachinery preliminary mean-line design of oxy-fuel compressor and turbine. The conceptual turbine design was performed using the axial through-flow code LUAX-T, developed at Lund University. A tool for conceptual design of axial compressors developed at Chalmers University was used for the design of the compressor. The modeled SCOC-CC gave a net electrical efficiency of 46% and a net power of 106 MW. The production of 95% pure oxygen and the compression of CO2 reduced the gross efficiency of the SCOC-CC by 10 and 2 percentage points, respectively. The designed oxy-fuel gas turbine had a power of 86 MW. The rotational speed of the single-shaft gas turbine was set to 5200 rpm. The designed turbine had four stages, while the compressor had 18 stages. The turbine exit Mach number was calculated to be 0.6 and the calculated value of AN2 was 40·106 rpm2m2. The total calculated cooling mass flow was 25% of the compressor mass flow, or 47 kg/s. The relative tip Mach number of the compressor at the first rotor stage was 1.15. The rotational speed of the twin-shaft gas generator was set to 7200 rpm, while that of the power turbine was set to 4500 rpm. Twin-shaft turbine designed with five turbine stages to maintain the exit Mach number around 0.5. The twin-shaft turbine required a lower exit Mach number to maintain reasonable diffuser performance. The compressor turbine was designed with two stages while the power turbine had three stages. The study showed that a four-stage twin-shaft turbine produced a high exit Mach number. The calculated value of AN2 was 38·106 rpm2m2. The total calculated cooling mass flow was 23% of the compressor mass flow, or 44 kg/s. The compressor was designed with 14 stages. The preliminary design parameters of the turbine and compressor were within established industrial ranges. From the results of this study it was concluded that both single- and twin-shaft oxy-fuel gas turbines have advantages. The choice of a twin-shaft gas turbine can be motivated by the smaller compressor size and the advantage of greater flexibility in operation, mainly in off-design mode. However, the advantages of a twin-shaft design must be weighed against the inherent simplicity and low cost of the simple single-shaft design.

Commentary by Dr. Valentin Fuster
2012;():299-307. doi:10.1115/GT2012-69488.

This study is based on a complete hybrid system emulator test rig developed at the University of Genoa (Savona laboratory) by the Thermochemical Power Group (TPG). The plant is mainly composed of a 100 kW recuperated micro gas turbine coupled with both anodic and cathodic vessels for high temperature fuel cell emulation. The test rig was recently equipped with a real-time model for emulating components not physically present in the laboratory (SOFC block, reformer, anodic circuit, off-gas burner, cathodic blower). This model is used to fully evaluate thermodynamic and electrochemical performance related to solid oxide fuel cell systems. Using a UDP based connection with the test rig control and acquisition software, it generates a real-time hardware-in-the-loop (HIL) facility for hybrid system emulation. Temperature, pressure and air mass flow rate at the recuperator outlet (downstream of the compressor) and rotational speed of the machine are inputs from the plant to the model. The turbine outlet temperature (TOT) calculated by the model is fed into the machine control system and the turbine electric load is moved to match the model TOT values.

In this study various tests were carried out to characterize the interaction between the experimental plant and the real-time model; double step and double ramp tests of current and fuel provided the dynamic response of the system.

The control system proved to be fast, compared to the slow thermal response of the SOFC stack, and also reliable. The hybrid systems operated at 90% of nominal power with electrical efficiency of about 56% based on natural gas LHV.

Commentary by Dr. Valentin Fuster
2012;():309-318. doi:10.1115/GT2012-69491.

This paper focuses on emission prediction for plants which use gas turbines for electrical power generation. A Techno-Economic, Environmental and Risk Analysis (TERA) framework, developed at Cranfield University, is used as the modelling philosophy. Thermodynamic performance simulation is at the core of the study whilst the risk, lifing, economics and environmental modules are built around the performance. Recently, the public agenda has emphasised environmental issues and new restrictive legislation on emissions can be expected. It means electrical power generation companies will have to look for ways to reduce their emissions. The replacement of out-dated and/or obsolete machinery having lower overall energy efficiency is one way. However, selection of new machinery will not only require economic and technical risk assessment but also its environmental impact. In-house software (Turbomatch) is used to calculate thermodynamic performance and an adaptable aviation emissions model, to fit industrial applications is presented here with the emissions model focusing on NOx, CO2, H2O, CO and unburned hydrocarbons. Then, the environmental module has been fed by the levels of NOx, CO2 and H2O to estimate the damage the engine will cause to the environment over several years with respect to global warming. Based on both field and public domain data two hypothetical engine configurations are investigated. One of them, a 165MW single shaft industrial machine, is used as the baseline to compare against the second one which is a 30MW aeroderivative single shaft machine.

The results predict that the 165MW single shaft engine model is more sensitive to an increase in ambient temperature than the 30MW aeroderivative single shaft engine model. The larger engine thermal efficiency reduces by 4%, for 30°C increase in ambient temperature above design point. That of the smaller engine model decreases by 2 1/2%. The loss in shaft power is also sharper for the 165MW engine model; however the significantly greater stability shown for the 30MW engine with respect to ambient temperature variation comes at a price. This engine emits higher levels of all pollutants, especially NOx, compared to the 165MW engine due to relatively higher firing temperature in relation to the engine size. This paper helps to establish the basis of a methodology to analyse GT emissions for power generation. The other aim is to integrate these findings into a system which will act as optimiser for TERA analysis. The effectiveness of the system is that it will allow designers and users to compare between alternative possibilities for turbomachinery selection and replacement. There are other models being developed at Cranfield University which combine systems to give an overall evaluation in terms of technical, economic, environmental and risk perspectives for power generation [1].

Commentary by Dr. Valentin Fuster
2012;():319-328. doi:10.1115/GT2012-69495.

This paper looks at some of the financial implications of generating electricity using a 165 MW gas turbine based power plant operating in a warm coastal environment. The engine performance model is developed using the Turbomatch in-house software package capable of simulating engine performance at both design and off-design conditions. Given the long operational life of the power plant, the economic model uses the Net Present Value (NPV) technique to simulate and account for the time value of money. This allows techno-economic comparisons between various modes of operation and variations in power demand to be made. The modelling will be used to optimise operation using key economic and performance parameters. The modelling is based on the Techno-Economic, Environmental and Risk Analysis (TERA) philosophy which allows for a broad and multidimensional analysis of the problem to aid plant operation and equipment selection. The analysis shows that 30 °C increase in ambient temperature above the design point results in 11.5% increase in the levelized cost of electricity (LCOE). The analysis also shows that the LCOE is increased by 4.3 as a result of 5% degradation in turbine compressor.

Commentary by Dr. Valentin Fuster
2012;():329-336. doi:10.1115/GT2012-69548.

Research is being carried out at the Technological Institute of Aeronautics to provide the support for the design of high performance gas turbines, including noise prediction by means of theoretical and empirical methods. Emphasis is given to new engines noise prediction, to anticipate problems at very early design stage and to take the necessary actions to guarantee that the engine noise is below the imposed limits. Noise prediction is part of the high fidelity engine performance prediction computer program, which provides the designer, at any time during the design phases, with information on the noise levels generated by each component and by the engine. Research indicates that the combustor and the propelling nozzle are major noise sources, so that these two components of a turbojet engine were dealt with in this work. The far-field one-third octave band sound pressure levels, (SPL), and overall sound pressure level (OASPL) are calculated, for several observer positions and engine rotational speeds. A 5 kN turbojet engine under development serves as the basis for the noise prediction. The influence of the observer position on SPL and OASPL for steady engine operation, as well as the effect of the engine rotational speeds on the engine noise generated by the combustor and the propelling nozzle are presented, which are in agreement with the noise of similar engines. Ground reflection and atmospheric attenuation were not considered. A high fidelity engine performance prediction computer code incorporates the noise prediction methodology whose results are reported in this paper.

Commentary by Dr. Valentin Fuster
2012;():337-347. doi:10.1115/GT2012-69579.

This work analyzes the efficiency and economic performance of different configurations of a coal-fed Integrated Gasification Fuel Cell (IGFC) plant with CO2 capture. Our analysis evaluates novel configurations, providing a detailed economic assessment for each case.

The plants studied here are based on a pressurized Solid Oxide Fuel Cell (SOFC) based power cycle integrated with a Shell coal gasifier. The design variations focus on syngas cleaning and pre-processing upstream of the SOFC power island. In particular, we have designed, simulated and optimized three main system configurations; two with a partial methanation process upstream of the SOFC (‘TREMP’ and ‘HICOM’ cases, respectively) and one without (‘DIRECT’ case). Depending on the specific plant layout, carbon capture is accomplished either before or after the SOFC power island, or both.

The best performance, both thermodynamic and economic, was achieved by the HICOM case, whose coal-to-electricity conversion efficiency is 50.6% (lower heating value basis). In addition to outperforming the other IGFC configurations analysed, compared to a conventional IGCC-CCS plant, the ‘HICOM’ case produced over 20% reduction in the levelized-cost-of-electricity (LCOE) delivered by the power plant.

Commentary by Dr. Valentin Fuster
2012;():349-361. doi:10.1115/GT2012-69583.

This work focuses on the development and application of a generic methodology targeting the design of optimum rotorcraft operations in terms of fuel burn, gaseous emissions and ground noise impact. An integrated tool capable of estimating the performance and emitted noise of any defined rotorcraft configuration within any designated mission has been deployed. A comprehensive and cost-effective optimization strategy has been structured. The methodology has been applied to two generic–baseline missions representative of current rotorcraft operations. Optimally designed operations for fuel burn, gaseous emissions and ground noise impact have been obtained. A comparative evaluation has been waged between the acquired optimum designs. The respective trade-off arising from the incorporation of flight paths optimized for different objectives has been quantified. Pareto front derived models for fuel burn and emitted noise have been structured for each mission. The Pareto models have been subsequently deployed for the design of operations optimized in a multidisciplinary manner.

The results have shown that the proposed methodology is promising with regards to achieving simultaneous reduction in fuel burn, gaseous emissions and ground noise impact for any defined mission. The obtainable reductions are found to be dependent on the designated mission. Finally, the potential to design optimum operations in a multidisciplinary fashion using only a single design criterion is demonstrated.

Topics: Design
Commentary by Dr. Valentin Fuster
2012;():363-373. doi:10.1115/GT2012-69661.

In this work, the “HRSC Optimizer”, a recently developed optimization methodology for the design of Heat Recovery Steam Cycles (HRSCs), Steam Generators (HRSGs) and boilers, is applied to the design of steam cycles for three interesting coal fired, gasification based, plants with CO2 capture: a Fischer-Tropsch (FT) synthesis process with high recycle fraction of the unconverted FT gases (CTL-RC-CCS), a FT synthesis process with once-through reactor (CTL-OT-CCS), and an Integrated Gasification Combined Cycle (IGCC-CCS) based on the same technologies. The analysis reveals that designing efficient HRSCs for the IGCC and the once-through FT plant is relatively straightforward, while designing the HRSC for plant CTL-RC-CCS is very challenging because the recoverable thermal power is concentrated at low temperatures (i.e., below 260 °C) and only a small fraction can be used to superheat steam. As a consequence of the improved heat integration, the electric efficiency of the three plants is increased by about 2 percentage points with respect to the solutions previously published.

Commentary by Dr. Valentin Fuster
2012;():375-383. doi:10.1115/GT2012-69676.

Conceptual turbine and compressor designs have been established for the semi-closed oxy-fuel combustion combined cycle and the Graz cycle. Real gas effects are addressed by extending cycle and conceptual design tools with a fluid thermo-dynamic and transport property database. Maximum compressor efficiencies are established by determining optimal values for stage loading, degree of reaction and number of compressor stages. Turbine designs are established based on estimates on achievable blade root stress levels and state of the art design parameters. The work indicates that a twin shaft geared compressor is needed to keep stage numbers to a feasible level. The Graz cycle is expected to be able to deliver around 3% net efficiency benefit over the semi-closed oxy-fuel combustion combined cycle at the expense of a more complex realization of the cycle.

Topics: Combustion , Fuels , Cycles
Commentary by Dr. Valentin Fuster
2012;():385-394. doi:10.1115/GT2012-69778.

This work presents an analysis of the application of Direct Carbon Fuel Cells (DCFC) to large scale, coal fuelled power cycles. DCFCs are a type of high temperature fuel cell featuring the possibility of being fed directly with coal or other heavy fuels, with high tolerance to impurities and contaminants (e.g. sulphur) contained in the fuel.

Different DCFC technologies of this type are developed in laboratories, research centres or new startup companies, although at kW-scale, showing promising results for their possible future application to stationary power generation.

This work investigates the potential application of two DCFC categories, both using a “molten anode medium” which can be (i) a mixture of molten carbonates or (ii) a molten metal (liquid tin) flowing at the anode of a fuel cell belonging to the solid oxide electrolyte family.

Both technologies can be considered particularly interesting for the possible future application to large scale, coal fuelled power cycles with CO2 capture, since they both have the advantage of oxidizing coal without mixing the oxidized products with nitrogen, thus releasing a high CO2 concentration exhaust gas. After a description of the operating principles of the two DCFCs, it is presented a lumped-volume thermodynamic model which reproduces the DCFC behaviour in terms of energy and material balances, calibrated over available literature data. We consider then two plant layouts, using a hundred-MW scale coal feeding, where the DCFC generates electricity and heat recovered by a bottoming steam cycle, while the exhaust gases are sent to a CO2 compression train, after purification in appropriate cleaning processes. Detailed results are presented in terms of energy and material balances of the proposed cycles, showing how the complete system may surpass 65% LHV electrical efficiency with nearly complete (95%+) CO2 capture, making the system very attractive, although evidencing a number of technologically critical issues.

Commentary by Dr. Valentin Fuster
2012;():395-404. doi:10.1115/GT2012-69787.

This paper focuses on an air-blown gasification-based combined cycle where CO2 is removed from the coal-derived gas before fuelling the combustion turbine. On the basis of public information from Mitsubishi Heavy Industries (MHI), the air-blown gasifier was modeled and its performance was investigated by the authors in a previous study. Here, with reference to a possible IGCC power plant with such a gasification technology, the possibility of removing CO2 from the coal-derived fuel gas is considered. The main differences between the two IGCCs, without and with CO2 capture, are gas used for coal loading (N2 or CO2), the layout of the syngas cooling and treatment sections (owing to the presence of watergas shift reactions and CO2 absorption process) and the composition of the fuel used in the combustion turbine. The results highlight that IGCC efficiency reduces by about 10.8% points when realizing CO2 capture, mainly due to the steam consumption in shift reactors and CO2 solvent regeneration and to power consumption for CO2 compression. However, the calculated efficiency penalty is in line with the values typical of IGCCs with oxygen-blown gasifier and CO2 capture.

The power balances of the assessed cases are reported in detail and the main technical issues are discussed in the paper. The results of a sensitivity analysis are also reported to assess the effects of different steam to carbon ratios in the shift reactors.

Commentary by Dr. Valentin Fuster
2012;():405-414. doi:10.1115/GT2012-69835.

The channels formed between adjacent blades in a turbine/compressor are nothing more than a variable section duct. Hence, the first step of turbomachinery design is to understand the physical processes experienced by a certain fluid when flowing through these nozzles and diffusers. In the main, nozzles are easier to understand since the fluid flows impelled by a favourable pressure gradient whereas for diffusers the flow has to face an adverse pressure gradient. This latter situation brings about the occurrence of stall (boundary layer detachment from the wall) which makes it more complicated to design and operate the component (both the individual stages and the entire compressor). It is thus essential to characterise the performance of diffusers of any type, which is influenced by several parameters such as geometry, Mach and Reynolds number, inlet total pressure and aspect of the boundary layer at the inlet section. Dolan and Runstadler generated very valuable information in 1973 (Pressure recovery performance of conical diffusers at high subsonic Mach numbers, NASA CR-2299) by providing performance maps for the flow of air in diffusers. This work is aimed at complementing the previous one by giving maps that apply to the flow of supercritical carbon dioxide in similar devices. By doing so, an important step towards the design of thermal turbomachinery specific of this singular fluid is taken.

Commentary by Dr. Valentin Fuster
2012;():415-421. doi:10.1115/GT2012-69836.

A small 5-kN thrust gas turbine, designed and manufactured having in mind a thorough source of validation data, serves as basis for the study. The engine is an uncooled turbine, 5:1 pressure ratio axial flow compressor, delivering 8.1 kg/s air mass flow, whose control is made by a FADEC. Cold runs of the jet engine version have already been completed. The engine characteristics are being developed using the technology indicated in the paper. Accelerations and decelerations from idle to full power in a prescribed time interval and positive surge margin are the limitations imposed to the control system. In order to accomplish such requirements, a proportional, integral and derivative (PID) has been implemented to control the variable geometry transients, which proved to drive the engine to the required operating points. Compressor surge is avoided during accelerations or decelerations, imposing operation limits to the surge margin. In order to simulate a jet engine under transient operation, use was made of high-fidelity in-house developed software. The results presented in the paper are related to the compressor inlet guide vane (VIGV) transients. The engine transient calculations were predicted with the IGV settings varying with time, and the results are being used for the initial calibration of the transfer functions for the real time control.

Commentary by Dr. Valentin Fuster
2012;():423-430. doi:10.1115/GT2012-69896.

The advantage of higher turbine inlet temperatures as a way to increase cycle efficiency is potentially outweighed by the efficiency losses caused by the increased secondary air extracted from the compressor discharge to cool turbine components. Higher cooling effectiveness schemes could be used, but pressure head required to drive the coolant flow through the hot section components may be higher than those available due to combustor pressure losses. This paper looks to determine the potential effects on the overall cycle efficiency caused by an intentional pressure drop across the combustor, allowing more aggressive cooling schemes with a lower amount of cooling air, based on data of state of the art cooling schemes (coolant flow ratio, pressure head and cooling effectiveness) and a parametric analysis of a simple cycle turbine. Results suggest that coolant flow reduction can actually result in a lower pressure drop across the cooling passages, given the decreased flow velocity ending up in higher efficiency and specific work. Enhanced cooling schemes can also allow higher turbine inlet temperatures for a given coolant flow, resulting in improved performance.

Topics: Pressure , Cooling , Turbines
Commentary by Dr. Valentin Fuster
2012;():431-439. doi:10.1115/GT2012-69988.

Future fossil-fueled power generation systems will require emission control technologies such as carbon capture and sequestration (CCS) to comply with government greenhouse gas regulations. The three prime candidate technologies which permit carbon dioxide (CO2) to be captured and safely stored include pre-combustion, post-combustion capture and oxy-fuel (O-F) combustion. For more than a decade Clean Energy Systems, Inc. (CES) has been designing and demonstrating enabling technologies for oxy-fuel power generation; specifically steam generators, hot gas expanders and reheat combustors.

Recently CES has partnered with Florida Turbine Technologies, Inc. (FTT) and Siemens Energy, Inc. to develop and demonstrate turbomachinery systems compatible with the unique characteristics of oxy-fuel working fluids. The team has adopted an aggressive, but economically viable development approach to advance turbine technology towards early product realization. Goals include short-term, incremental advances in power plant efficiency and output while minimizing capital costs and cost of electricity.

Phase 2 of this development work has been greatly enhanced by a cooperative agreement with the U.S. Department of Energy (DOE). Under this program the team will design, manufacture and test a commercial-scale intermediate-pressure turbine (IPT) to be used in industrial O-F power plants. These plants will use diverse fuels and be capable of capturing 99% of the produced CO2 at competitive cycle efficiencies and cost of electricity. Initial plants will burn natural gas and generate more than 200MWe with near-zero emissions.

To reduce development cost and schedule an existing gas turbine engine will be adapted for use as a high-temperature O-F IPT. The necessary modifications include the replacement of the engine’s air compressor with a thrust balance system and altering the engine’s air-breathing combustion system into a steam reheating system using direct fuel and oxygen injection.

Excellent progress has been made to date. FTT has completed the detailed design and issued manufacturing drawings to convert a Siemens SGT-900 to an oxy-fuel turbine (OFT). Siemens has received, disassembled and inspected an SGT-900 B12 and ordered all necessary new components for engine changeover. Meanwhile CES has been working to upgrade an existing test facility to support demonstration of a “simple” oxy-fuel power cycle. Low-power demonstration testing of the newly assembled OFT-900 is expected to commence in late 2012.

Topics: Fuels , Turbomachinery
Commentary by Dr. Valentin Fuster
2012;():441-448. doi:10.1115/GT2012-69999.

Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC) is expected to be the most efficient power generation system in coal fired power generation systems [1,2]. However, more energy efficient power generation system has to be developed to decrease CO2 emission in the middle and long term. Thus, the authors have proposed Advanced Integrated Coal Gasification Combined Cycle (A-IGCC) and Advanced IGFC (A-IGFC) systems, which utilize exhaust heat from solid oxide fuel cells (SOFC) and / or a gas turbine as a heat source of gasification (exergy recuperation) [3]. Previously A-IGCC [4] and A-IGFC [5] without CO2 capture option were analyzed with the process simulator HYSYS®.Plant (Aspen technology Inc.) to calculate thermal efficiencies of the proposed systems. Then IGCC and A-IGCC with CO2 capture option [6, 7] were analyzed with Amine process simulator AMSIM(DBR), a module in PRO/II® (Invensys Process Systems Japan, Inc) combined with HYSYS®.Plant model. It shows in the results of thermal efficiency with CO2 capture option that the penalty of A-IGCC case is larger than that of IGCC case, indicating somewhat scope for increase of exergy recuperation in A-IGCC case [6]. This study deals in the analyses of A-IGFC with CO2 separation unit.

Commentary by Dr. Valentin Fuster
2012;():449-456. doi:10.1115/GT2012-70020.

The design of a small gas turbine in the range of 5 kN thrust / 1.2 MW shaft power is being made in association with industry, aiming at distributed power generation and cogeneration. The gas turbine was constructed and its gas generator is being prepared for development tests. The results will be used for the final specification of the power section. The gas turbine design has been carried out using indigenous software, developed specially to fulfill the requirements of the engines design, as well as the support for validation of research work. The work reported in this paper deals with the design methodology of a 5:1 pressure ratio, 5-stage axial flow compressor with VIGV and a single stage axial flow turbine. These components were designed and their maps synthesized and fed to the gas turbine performance simulation program. The engine performance results were analyzed and verified. The calculated behavior compares with similar engines’, indicating they are qualitatively correct.

Commentary by Dr. Valentin Fuster


2012;():457-461. doi:10.1115/GT2012-68140.

In a course of thermodynamics, in general, and gas turbine analysis, in particular as stand alone or within a cogeneration situation, teaching within the concepts of energy or exergy has become controversial particularly since most teachers of thermodynamics at the undergraduate level are not too familiar with the advantages of exergy analysis and thus do not cover the material from that point of view. In this paper, we will go through the pedagogical implications of teaching thermodynamics using both approaches and attempt to show and convince people that exergetic analyses are superior to any other approach in the teaching of thermodynamics. The bottom line and the ultimate goal is the precise teaching of the subject matter.

Commentary by Dr. Valentin Fuster
2012;():463-469. doi:10.1115/GT2012-68438.

It is common practice to install wind-monitoring stations in geographical locations having high winds to estimate power production prior to installing large-scale wind farms. For the current study, a wind-monitoring program was developed as an educational tool for undergraduate engineering students at West Virginia University. The focus of this paper is not on the results of the assessment, but rather on how this program was used as a hands-on approach for educating students about wind energy and availability. The objective of the student/industry collaborative project was to determine the feasibility of constructing a wind farm to power a federal prison facility located in an area with an abundant wind resource in North Central West Virginia, while educating students on wind energy.

This paper presents a description and assessment of this program as an undergraduate senior design project. As part of the program, students played a key role from the developmental stages of the project, to the assessment of the results. During the first semester of the senior design project, students procured a wind monitoring station based on down-select criteria, selected the site for construction, installed the wind monitoring station, commissioned the sensor suite, and performed quality assurance/quality control (QA/QC) of and evaluated the initial data sets. Students logged data through the second semester of the program, performed data quality monitoring, processed average wind speed and direction data into frequency distributions and wind roses, analyzed monthly and diurnal averages in wind resources and performed power production calculations. Several different methodologies were employed, including application of fluid control volume energy analysis to derive Betz’ limit, turbine efficiency curves with operational limits and Weibull statistics to employ online power production estimators. The program successfully introduced students to the applicability of their engineering education to the area of renewable energy.

Commentary by Dr. Valentin Fuster
2012;():471-478. doi:10.1115/GT2012-69419.

This paper describes the design considerations and calculations of a mobile low-cost test cell for small gas turbine engines (GTE). The test bed was designed for the TS-20 jet engine, originated in a gas turbine starter and should be used mostly for educational purposes and for experimental validation of analytical computations. Limitations of the project were the engine air mass flow rate, low noise emissions for possibility of performance close to urban area, low cost and good mobility of the test cell. The design of the test cell structure, inlet and exhaust silencers from the aero-thermodynamic and sound suppression point of view is presented. The calculation results and respective design solutions are offered.

Topics: Design , Gas turbines
Commentary by Dr. Valentin Fuster
2012;():479-487. doi:10.1115/GT2012-69983.

The use of laboratory exercises in the training of engineering students is of paramount importance to give the students the possibility to gain practical experience on real hardware and on real test data. Recent trends in the education of engineers at the Department of Energy Technology at KTH go towards an increasing share of distant-based education, which is put in place to educate students at different geographic locations, not only locally (such as for example with engineers in industry) but also internationally (i.e. with students in different countries). In order to provide the possibility to follow a course at a distance without compromising on learning objectives and learning quality, a number of remotely operated laboratory exercises have been developed and implemented in the engineering curriculum at the department. Among these, to mention the work carried out by Navarathna et al. [11] on a remotely operated linear cascade test facility. The present laboratory exercise is integrated in a course on turbomachinery and gives the students the possibility to interactively learn about the operation of pumps at various speeds, various mass flow rates, parallel operation and serial operation. Students access the laboratory exercise using a web-based interface, perform measurements and finally have test data sent to an initially specified email address for further analysis.

Commentary by Dr. Valentin Fuster
2012;():489-499. doi:10.1115/GT2012-69987.

The preliminary design tools, for the design and performance analysis of axial flow compressors, has been developed based on reduced-order throughflow model. The in-house numerical tools developed specially for turbomachinery preliminary sizing and calculation of its operational characteristics is being an interesting experience in both under- and graduate lectures. Appropriate loss correlations have been selected aiming at good geometrical initial sizing. Flow properties distribution has been obtained using meanline code combined with a quasi-3D streamline curvature code. Any number of sections from hub to tip of each blade can be used for the determination of the blade shape. The compressor operation map calculated is validated against published test data. Details of the developed methodology and implementation are discussed.

Commentary by Dr. Valentin Fuster
2012;():501-512. doi:10.1115/GT2012-70025.

During a gas turbine development phase an important engineer task is to find the appropriate engine design point that meet the required specifications. This task can be very arduous because all possible operating points in the gas turbine operational envelope need to be analyzed, for the sake of verification of whether or not the established performance might be achieved. In order to support engineers to best define the engine design point that meet required performance a methodology was developed in this work. To accomplish that a computer program was written in Matlab®. In this program was incorporated the thermoeconomic and thermodynamic optimization. The thermodynamic calculation process was done based in enthalpy and entropy function and then validated using a commercial program. The methodology uses genetic algorithm with single and multi-objective optimization. The micro gas turbine cycle chosen to study was the recuperated. The cycle efficiency, total cost and specific work were chosen as objective functions, while the pressure ratio, compressor and turbine polytropic efficiencies, turbine inlet temperature and heat exchange effectiveness were chosen as decision variables. For total cost were considered the fixed costs (equipment, installation, taxes, etc.) and variable costs (fuel, environmental and O&M). For emissions were taken into account the NOx, CO and UHC. An economic analysis was done for a recuperated cycle showing the costs behavior for different optimized design points. The optimization process was made for: single-objective, where each objective was optimized separately; two-objectives, where they were optimized in pairs; three-objectives, where it was optimized in trio. After, the results were compared each other showing the possible design points.

Commentary by Dr. Valentin Fuster
2012;():513-523. doi:10.1115/GT2012-70095.

Despite the need for highly qualified experts, multi-disciplinary gas turbine conceptual design has not been a common study topic in traditional post-graduate curriculums. Although many courses on specialised topics in gas turbine technology take place, limited attention is given on connecting these individual topics to the overall engine design process. Teaching conceptual design as part of a post-graduate curriculum, or as an intensive short course, may help to address the industrial need for engineers with early qualifications on the topic i.e., prior to starting their careers in the gas turbine industry.

This paper presents details and lessons learned from: (i) the integration of different elements of conceptual design in an existing traditional MSc course on gas turbine technology through the introduction of group design tasks, and (ii) the development of an intensive course on gas turbine multi-disciplinary conceptual design as a result of an international cooperation between academia and industry.

Within the latter course, the students were grouped in competing teams and were asked to produce their own gas turbine conceptual design proposals within a given set of functional requirements. The main concept behind the development of the new design tasks, and the new intensive course, has been to effectively mimic the dynamics of small conceptual design teams, as often encountered in industry. The results presented are very encouraging, in terms of enhancing student learning and developing engineering skills.

Commentary by Dr. Valentin Fuster
2012;():525-536. doi:10.1115/GT2012-70154.

The education of engineers largely relies on traditional classroom teaching in which a teacher instructs a subject using a variety of techniques ranging from the traditional blackboard (nowadays also whiteboard), over overhead to computer-based presentations. In order to deepen knowledge and get hands-on experience, students are often given practical exercises or case studies to perform, be it individually or in group in the form of a seminar. It is experienced that black- (or white) board based lectures are having an advantage over overheads / slide shows as knowledge is built up instantaneously at a natural pace rather than confronting students with pages of prepared material. The present paper presents a new technique herein referred to as “podcasted whiteboard lectures” in which lectures are given in a traditional lecture hall setup but with having the teacher lecturing by means of an electronic whiteboard. A key advantage of this technique is that it can be recorded and made available to students afterwards, which is here done using podcasting. It is experienced that the technique is very efficient for maximizing the students’ learning experience as one is given the possibility to follow a subject ubiquitous and at preferred pace. Another advantage is that animations and simulations can be integrated right into the lecture and into the same medium used for lecturing. The technique is thereby equally applicable to campus as well as distance-based teaching.

Topics: Engineers , Teaching
Commentary by Dr. Valentin Fuster

Electric Power

2012;():537-545. doi:10.1115/GT2012-68169.

Siemens Energy, Inc. was awarded a contract by the U.S. Department of Energy for the first two phases of the Advanced Hydrogen Turbine Development Program. The 3-Phase, multi-year program goals are to develop an advanced syngas, hydrogen and natural gas fired gas turbine fully integrated into coal-based Integrated Gasification Combined Cycle (IGCC) plants.

The program goals include demonstrating:

• A 3–5% point improvement in combined cycle efficiency above the baseline,

• 20–30% reduction in combined cycle capital cost

• Emissions of 2 ppm NOx @ 15% O2 by 2015.

Siemens is currently well into Phase 2 of the program and has made significant progress in several areas. This includes the ability to attain the 2015 Turbine Program performance goals by developing component and systems level technologies, developing and implementing validation test plans for these systems and components, performing validation testing of component technologies, and performance demonstration through system studies.

Siemens and the Advanced Hydrogen Turbine Program received additional funds from the American Recovery and Reinvestment Act (ARRA) in 2010. The additional funding serves to supplement budget shortfalls in the originally planned spend rate.

The development effort has focused on engine cycles, combustion technology development and testing, turbine aerodynamics/cooling, modular component technology, materials/coatings technologies and engine system integration/flexibility considerations. High pressure combustion testing continues with syngas and hydrogen fuels on a modified premixed combustor. Advanced turbine airfoil concept testing continues. Novel manufacturing techniques were developed that allow for advanced castings and faster time to market capabilities. Materials testing continues and significant improvements were made in lifing for Thermal Barrier Coatings (TBC’s) at increased temperatures over the baseline. Studies were conducted on gas turbine/IGCC plant integration, fuel dilution effects, varying air integration, plant performance and plant emissions. The results of these studies and developments provide a firm platform for completing the advanced Hydrogen Turbine technologies development in Phase 2.

Topics: Turbines , Hydrogen
Commentary by Dr. Valentin Fuster
2012;():547-556. doi:10.1115/GT2012-68299.

Cost of electricity (COE) is the most widely used metric to quantify the cost-performance trade-off involved in comparative analysis of competing electric power generation technologies. Unfortunately, the currently accepted formulation of COE is only applicable to comparisons of power plant options with the same annual electric generation (kilowatt-hours) and same technology as defined by reliability, availability and operability. Such a formulation does not introduce a big error into the COE analysis when the objective is simply to compare two or more baseloaded power plants of the same technology (e.g., natural gas fired gas turbine simple or combined cycle, coal fired conventional boiler steam turbine, etc.) and the same (or nearly the same) capacity. However, comparing even the same technology class power plants, especially highly flexible advanced gas turbine combined cycle units with cyclic duties, comprising a high number of daily starts and stops in addition to emissions-compliant low-load operation to accommodate the intermittent and uncertain load regimes of renewable power generation (mainly wind and solar) requires a significant overhaul of the basic COE formula.

This paper develops an expanded COE formulation by incorporating crucial power plant operability and maintainability characteristics such as reliability, unrecoverable degradation, and maintenance factors as well as emissions into the mix. The core impact of duty cycle on the plant performance is handled via effective output and efficiency utilizing basic performance correction curves. The impact of plant start and load ramps on the effective performance parameters is included. Differences in reliability and total annual energy generation are handled via energy and capacity replacement terms. The resulting expanded formula, while rigorous in development and content, is still simple enough for most feasibility study type of applications. Sample calculations clearly reveal that inclusion (or omission) of one or more of these factors in the COE evaluation, however, can dramatically swing the answer from one extreme to the other in some cases.

Topics: Power stations
Commentary by Dr. Valentin Fuster
2012;():557-568. doi:10.1115/GT2012-68301.

Even though almost all components of an Integrated Gasification Combined Cycle (IGCC) power plant are proven and mature technologies, the sheer number of them, the wide variety of competing technologies (e.g., gasifiers, gas clean-up systems, heat recovery options), system integration options (e.g., cryogenic air separation unit and the gas turbine) including the recent addition of carbon capture and sequestration (CCS) with its own technology and integration options render fundamental IGCC performance analysis a monumental task. Almost all published studies utilize highly complex chemical process and power plant heat balance software, including commercially available packages and in-house proprietary codes. This makes an objective assessment of comparable IGCC plant designs, performance (and cost) and other perceived advantage claims (IGCC versus other technologies, too) very difficult if not impossible.

This paper develops a coherent simplified parametric model based on fully physics-based grounds to be used for quick design performance assessment of a large variety of IGCC power plants with and without CCS. Technology parameters are established from complex model runs and supplemented by extensive literature search. The model is tested using published data to establish its confidence interval and is satisfactory to carry conceptual design analysis at a high level to identify promising alternatives, development areas and assess the realism in competing claims.

Commentary by Dr. Valentin Fuster
2012;():569-576. doi:10.1115/GT2012-68363.

This paper addresses the engineering evaluation of F-Class hot section components from an owner/operator perspective, with the practical objective of extending their interval of useful service beyond the limits recommended by the OEM. Starting with the first stage, the initial aim is to extend operation from two to three intervals. A multi-disciplinary approach to hot section life management is described, which is used to assess the component condition and possible risks involved with extending the active service life. The assessment draws from many sources: design analysis (durability, weak points, material and coating limitations), inspection (when, where, limits and tolerances), service (base load, cycling, turbine inlet temperature and hours) and repair techniques (welding, brazing, heat treatments). Results of the modeling, damage tracking, NDT and metallurgical and mechanical testing are summarized.

Commentary by Dr. Valentin Fuster
2012;():577-585. doi:10.1115/GT2012-68435.

Unexpected outages and maintenance costs reduce plant availability and can consume significant resources to restore the unit to service. Although companies may have the means to estimate cash flow requirements for scheduled maintenance and on-going operations, estimates for unplanned maintenance and its impact on revenue are more difficult to quantify, and a large fleet is needed for accurate assessment of its variability. This paper describes a study that surveyed 388 combined-cycle plants based on 164 D/E-class and 224 F-class gas turbines, for the time period of 1995 to 2009. Strategic Power Systems, Inc. (SPS®), manager of the Operational Reliability Analysis Program (ORAP®), identified the causes and durations of forced outages and unscheduled maintenance and established overall reliability and availability profiles for each class of plant in 3 five-year time periods. This study of over 3,000 unit-years of data from 50 Hz and 60 Hz combined-cycle plants provides insight into the types of events having the largest impact on unplanned outage time and cost, as well as the risks of lost revenue and unplanned maintenance costs which affect plant profitability. Outage events were assigned to one of three subsystems: the gas turbine equipment, heat recovery steam generator (HRSG) equipment, or steam turbine equipment, according to the Electric Power Research Institute’s Equipment Breakdown Structure (EBS). Costs to restore the unit to service for each main outage cause were estimated, as were net revenues lost due to unplanned outages. A statistical approach to estimated costs and lost revenues provides a risk-based means to quantify the impact of unplanned events on plant cash flow as a function of class of gas turbine, plant subsystem, and historical timeframe. This statistical estimate of the costs of unplanned outage events provides the risk-based assessment needed to define the range of probable costs of unplanned events. Results presented in this paper demonstrate that non-fuel operation and maintenance costs are increased by roughly 8% in a typical combined-cycle power plant due to unplanned maintenance events, but that a wide range of costs can occur in any single year.

Commentary by Dr. Valentin Fuster
2012;():587-598. doi:10.1115/GT2012-68573.

The power generation mix is in transition with more and more electricity generated by renewable sources. Combined cycle power plants will have to partner with renewable sources and compensate for their fluctuating nature. In preparation for the next generation combined cycles, gas turbine technology development needs to continue to lower the lifecycle costs through increased efficiency, extended maintenance cycles, and reduced emissions. It must now also develop fast ramping capability, account for a wider variation in fuel composition and provide an emission effective part load operation. These needs will be met by refining state of the art technologies and by adding new technologies. This paper provides an overview of the research and development activities and resulting trend in Alstom gas turbine technologies.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2012;():599-606. doi:10.1115/GT2012-68574.

MHI recently developed a 1600°C class J-type gas turbine, utilizing some of the technologies developed in the National Project to promote the development of component technology for the next generation 1700°C class gas turbine.

This new frame is expected to achieve higher combined cycle efficiency and will contribute to reduce CO2 emissions.

The target combined cycle efficiency of the J type gas turbine will be above 61.5% (gross, ISO standard condition, LHV) and the 1on1 combined cycle output will reach 460MW for 60Hz engine and 670MW for 50Hz engine.

This new engine incorporates:

1) A high pressure ratio compressor based on the advanced M501H compressor, which was verified during the M501H development in 1999 and 2001.

2) Steam cooled combustor, which has accumulated extensive experience in the MHI G engine (> 1,356,000 actual operating hours).

3) State-of-art turbine designs developed through the 1700°C gas turbine component technology development program in Japanese National Project for high temperature components.

This paper discusses the technical features and the updated status of the J-type gas turbine, especially the operating condition of the J-type gas turbine in the MHI demonstration plant, T-Point.

The trial operation of the first M501J gas turbine was started at T-point in February 2011 on schedule, and major milestones of the trial operation have been met. After the trial operation, the first commercial operation has taken place as scheduled under a predominantly Daily-Start-and-Stop (DSS) mode. Afterward, MHI performed the major inspection in October 2011 in order to check the mechanical condition, and confirmed that the hot parts and other parts were in sound condition.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2012;():607-619. doi:10.1115/GT2012-68788.

In the past 20 years, the equipment manufacturers have made significant strives to develop better and more cost effective products: gas turbines, steam turbines, Heat Recovery Steam Generators (HRSG), water treatment, fuel treatment equipment etc. Consequently, the Combined Cycle Power Plants (CCPP) have become, due to many technological breakthroughs, the most efficient form of electrical power generation from fossil fuel, reaching or exceeding net efficiencies of 60%. We are also witnessing a substantial penetration of Renewable in the power generation mix. The Renewable intermittent nature of generation associated with new grid requirements for spinning reserves and/or frequency control must be considered when new CCPP are conceptually designed.

The paper will examine several CCPP configurations, involving one, two, and three gas turbines. Substantial improvements in the efficiency are usually associated with an increased gas turbines electrical output. Various scenarios of plant configurations with targeted, sensible level of integration will be examined.

The challenges of major equipment selection (gas turbines, heat recovery steam generator steam turbines, heat sink) for each of the configurations will be examined from an EPC (Engineering, Procurement, Construction) Contractor perspective, based on the lessons learned from the development and execution of more than 30 advanced CCPPs.

A special emphasis will be given to the strategy of providing the CCPP with fast start-up, capability, rapid load changes, without negatively impacting part-load efficiencies and emissions. The effect of plant configuration on plant reliability, maintenance requirements and recommended spare parts will also be discussed.

Finally the paper describes the lessons learned, in plant configuration selection that can be successfully employed on future projects through judicious equipment selection at the development phase, design optimization and proper project management at the execution phase.

Commentary by Dr. Valentin Fuster
2012;():621-631. doi:10.1115/GT2012-69103.

Turbine manufacturers place limits on the service life of gas turbine (GT) rotors/discs based on either the number of hours of operation or the number of start-stop cycles. A significant number of gas turbine rotors are either condemned or slated for replacement during a future outage. Some turbines experience premature cracking which results in the replacement of select rotor components. Examples of such cases are GE Frame 7EA compressor disc cracking, Frame 7FA/9FA turbine disc air-feed slot and post cracking, and Frame 6001B turbine disc rabbet cracking Many Alstom 11N and Siemens W-501 rotors and discs are also replaced based on design life limitations. This experience prompted EPRI, sponsored by gas turbine owners to conduct projects in this area. Under this program, TurboMet International and AccTTech,LLC conducted metallurgical evaluation of cracked discs to understand the crack initiation and propagation mechanisms, detailed structural engineering analysis to understand the root cause of cracking and developed solutions; and to provide recommendations to turbine owners to mitigate such failures. Condition and remaining life analysis of several turbine models was conducted using rigorous engineering analysis to provide objective technical recommendations to turbine users to safely extend the life of the rotors. This collective experience has result in guidelines for safe reinspection intervals to mitigate future risk. In order to obtain pertinent material properties needed for such detailed engineering analysis, retired rotors and discs were obtained from both compressor and turbine sections. Nondestructive examinations (NDE) and materials testing were conducted to assess component condition and mechanical properties such as tensile, fracture toughness, crack growth, creep, low-cycle fatigue, etc. This paper provides an overview of an integrated rotor condition and life assessment approach including several examples of component evaluations.

Topics: Gas turbines , Rotors
Commentary by Dr. Valentin Fuster
2012;():633-645. doi:10.1115/GT2012-69615.

Currently, high efficiency and low emissions are most important requisites for the design of modern gas turbines due to the strong environmental restrictions around the world. In the past years, alternative fuels have been considered for application in industrial gas turbines. Therefore, combustor performance, pollutant emissions and the ability to burn several fuels became of much concern and high priority has been given to the combustor design.

This paper describes a methodology focused on the design of stationary gas turbines combustion chambers with the ability to efficiently burn conventional and alternative fuels. A simplified methodology is used for the calculations of the equilibrium temperature and chemical species in the primary zone of a gas turbine combustor. Direct fuel injection and diffusion flames, together with numerical methods like Newton-Raphson, LU Factorization and Lagrange Polynomials, are used for the calculations. Diesel, ethanol and methanol fuels were chosen for the numerical study.

A computer code sequentially calculates the main geometry of the combustor. From the numerical simulation it is concluded that the basic gas turbine combustor geometry, for some operating conditions and burning diesel, ethanol or methanol, are of similar sizes, because the development of aerodynamic characteristics predominate over the thermochemical properties.

It is worth to note that the type of fuel has a marked effect on the stability and combustion advancement in the combustor. This can be seen when the primary zone is analyzed under a steady-state operating condition. At full power, the pressure is 1.8 MPa and the temperature 1,000 K at the combustor inlet. Then, the equivalence ratios in the primary zone are 1.3933 (diesel), 1.4352 (ethanol) and 1.3977 (methanol) and the equilibrium temperatures for the same operating conditions are 2,809 K (diesel), 2,754 K (ethanol) and 2,702 K (methanol). This means that the combustor can reach similar flame stability conditions, whereas the combustion efficiency will require richer fuel/air mixtures of ethanol or methanol are burnt instead of diesel.

Another important result from the numerical study is that the concentration of the main pollutants (CO, CO2, NO, NO2) is reduced when ethanol or methanol are burnt, in place of diesel.

Commentary by Dr. Valentin Fuster
2012;():647-656. doi:10.1115/GT2012-69761.

This paper describes the aero-thermal design and validation of an advanced axial flow turbine. This turbine, which has evolved from the existing and proven GT26/GT24 design consists of an optimised annulus flow path using high lift airfoil profiles and improved aerodynamic matching between the turbine stages. A major design feature of the turbine has been to control and reduce the aerodynamic losses, with particular attention being devoted to minimising the secondary, trailing edge and blade tip losses. The advantages of these design changes to the overall turbine efficiency has been verified by extensive controlled experimentation in high-speed cascade test facilities; by the utilisation of 3D multi-row computational fluid dynamics analysis tools, and via engine tests.

In addition to the aerodynamic design modifications of the turbine, the thermal designs of the turbine vanes, blades and heat-shields were also optimised. For the first stage film cooled vane and blade airfoils and platforms, both the film cooling layout and operating characteristics were improved. And for all the internally cooled airfoils, the internal heat transfer design features were additionally optimised, which allowed for more homogenous metal temperature distributions on the airfoil and endwall surfaces. The verification and validation of the thermal designs of the turbine components was confirmed via extensive dedicated testing in high-speed cascades for the film cooling performances, and in scaled perspex models for the internal heat transfer coefficients and local flow distributions.

The complete turbine was further tested and validated in the GT26 Test Power Plant in Birr, Switzerland via a dedicated turbine thermal paint test run and a subsequent performance and mapping testing phase.

Topics: Design , Turbines
Commentary by Dr. Valentin Fuster

Fans and Blowers

2012;():657-664. doi:10.1115/GT2012-68056.

Future development of more efficient volute casing depends on improving understanding of the design and flow analysis of the volute casing. This paper reviews different aspects of design and flow behavior inside the volute casing. It describes advantages and disadvantages of the different designs, the relation between flow and geometry, the impact on the impeller and the flow behavior inside the volute. The main purpose is to provide an insight into the flow structure that can be used later to improve the performance or remediate some problems. The use of CFD is also discussed for the flow domain.

Topics: Design
Commentary by Dr. Valentin Fuster
2012;():665-673. doi:10.1115/GT2012-68130.

Experimental measurements and simulations are carried out to study the performances and the unsteady internal flow fields of a cross-flow fan (CFF), which uses a kind of porous stabilizers proposed by the authors in an attempt to control the noise. The performance curve and sound radiation of the fan as well as instantaneous pressure fluctuations in the flowfield are measured and analysed. Transient calculations of the flowfield are carried out to study the vortical flows inside the fan as well as in the porpous stabilizers. The results show that the porous stabilizers have not produced considerable effect on the cross-flow fan’s performance curve, but the amplitude of the pressure fluctuation and the level of radiated noise are affected. This qualitative study indicates the cross-flow fan noise may be controlled by using the porous stabilizers if the porosity is properly selected.

Commentary by Dr. Valentin Fuster
2012;():675-684. doi:10.1115/GT2012-68186.

Squirrel-cage fans are centrifugal fans with forward-curved blades. A large number of short blades of thin circular arc sheet metal provide a low diameter drum-type rotor of high axial length. Cross-flow fans have a similar rotor design. However, the flow passes the rotor in radial direction two times. One consequence of the forward-curved blades is that there is more or less no pressure rise in the rotor and the casing has to convert the high absolute rotor exit velocity into a global pressure rise. Both types are used in applications requiring low size, relative high volume flow rates, low costs and low noise at the drawback of relative low efficiency. Volume flow rate, specific isentropic enthalpy difference, rotor outer diameter and rotational speed of a single stage fan can be transformed to speed number and diameter number. For axial, radial and mixed flow fans, a single relationship (CORDIER-diagram) exists and it is well accepted that this line represents “optimum” fan designs with high efficiency. The paper provides a theoretical interpretation of the CORDIER-lines for squirrel-cage and cross-flow fans, since they differ considerably from the classical relationship. Based on velocity triangles and energy transfer, CORDIER-line of squirrel-cage fans depends on absolute inlet flow angle, relative exit flow angle, rotor inlet to exit diameter ratio, relative axial rotor width and circumferential efficiency. Additionally, the CORDIER-line of cross-flow fans depends on the degree of admission. At a distinguished pressure coefficient, a maximum speed number is found, corresponding to maximum volume flow rate.

Topics: Fans , Cross-flow
Commentary by Dr. Valentin Fuster
2012;():685-694. doi:10.1115/GT2012-68266.

Rotating instability in various types of fans, compressors, and pumps is considered as one of the symptoms of unsteady phenomena such as rotating stall or surge, and it is observed before a rotating stall as an amplitude increase in the power spectra of velocity fluctuation and/or radiated noise. In this paper, the cause of rotating instability in a centrifugal blower with a shrouded impeller is investigated through both experiments and numerical simulations. Experimental results show that the rotating instability may be attributed to unsteady vortices rotating along the impeller periphery and that a discrete noise component induced by the rotating instability is mainly caused by the interaction between unsteady vortices and the impeller discharge flow. A significant amplitude increase within a frequency band at almost half the blade passing frequency is found to be caused by an irregular change in the vortex rotating speed as well as by an irregular time interval in the train of generated vortices. In the numerical study, the structure and circumferential characteristics of the rotating vortices are investigated by a visualization technique using Q-definition. Circumferential characteristics of the rotating vortices may be largely influenced by the steady characteristics of the impeller discharge flow field, which are determined by the geometric configuration of the impeller and the scroll casing.

Topics: Impellers
Commentary by Dr. Valentin Fuster
2012;():695-703. doi:10.1115/GT2012-68528.

A multi-objective optimization of a sirocco fan for residential ventilation has been carried out in the present work. A hybrid multi-objective evolutionary algorithm combined with response surface approximation is applied to optimize the total-to-total efficiency and total pressure rise of the sirocco fan for residential ventilation. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume method and solved on hexahedral grids for the flow analysis. Numerical results are validated with the experimental data for the total-to-total efficiency and total pressure. The total-to-total efficiency and total pressure rise of the sirocco fan are used as objective functions for the optimization. In order to improve the total-to-total efficiency and total pressure rise of the sirocco fan, four variables defining the scroll cut-off angle, scroll diffuser expansion angle, hub ratio and the blade exit angle, respectively, are selected as the design variables in this study. Latin-hypercube sampling as design-of-experiments is used to generate the design points within the design space. A fast non-dominated sorting genetic algorithm with an ε–constraint strategy for the local search is applied to determine the global Pareto-optimal solutions. The trade-off between two objectives is determined and discussed with respect to the representative clustered optimal solutions in the Pareto-optimal solutions compared to the reference shape.

Commentary by Dr. Valentin Fuster
2012;():705-716. doi:10.1115/GT2012-69042.

Stall induced vibrations place fundamental limitations on a fan stage performance and remains a persistent problem in the development of axial compressor and fan stages. Rotating stall is purely a fluid mechanic instability, whilst blade flutter, stall and surge flutter, and their variants, are aeroelastic instabilities that involve coupled fluid-structure interaction. Stall oscillation frequency lays in a relatively low-frequency band (less than 0.7–0.5 shaft frequency), whilst mild surge oscillation frequency occurs usually in a much lower-order of frequency (typically <0.25–0.30) in high solidity industrial power fans. These mild surge oscillations can couple with fan blade aeroelastic modes. A loss in efficiency and high aeroelastic blade vibrations characterises fan performance in stall that can significantly increase stress levels in the blade.

In this paper, the authors conducted an experimental study to investigate rotating stall recovery patterns in a high solidity axial power fan using different strategies. The authors drove the fan to stall at the design stagger-angle setting and then: i) operated a variable pitch mechanism in order to recover the unstable operation or ii) recover from stall by increasing rotational speed. In both cases the recovery patterns entails the modification of the operating point of the fan along the throttle line of the system. They measured pressure fluctuations in the fan tip region using flush-mounted probes. The authors studied the flow mechanisms for the stall recovery associated with the two proposed methods. They cross-correlated pressure fluctuations and analysed cross-spectra in order to clarify the influence of blade pitch, end-wall flow, rotational speed and tip-leakage flow on stall recovery.

Topics: Blades
Commentary by Dr. Valentin Fuster
2012;():717-729. doi:10.1115/GT2012-69046.

The development of industrial fans traditionally relies upon the use of empirical correlations and experimental analyses to validate both aerodynamic and acoustic aspects of fan performance. This paper presents the development of a computational based method focused on the prediction of unsteady aerodynamics and modeling of aero-acoustic sources. The authors applied the study to a single fan from a new range of large tunnel ventilation axial flow fans. The fan specification required mechanical and aerodynamic properties that would enable it to operate in the forward direction under ambient conditions to provide cooling air to the tunnel under routine operation, and in the reverse direction at 400°C under emergency conditions in the event of a tunnel fire. The final aerodynamic and mechanical design was additionally required to generate no more than 80 db during reverse operation, to ensure members of the emergency service could still communicate in the event of a fire. The simulations were carried out using the open source code Open-Foam, within which the authors implemented a (Very) Large Eddy Simulation (V)LES based on an one-equation sub-grid scale SGS model to solve a transport equation for the modeled (sub-grid) turbulent kinetic energy. This improvement of the sub-grid turbulence model is here considered as a remedial strategy in VLES of high-Reynolds industrial flows able to tackle the otherwise insufficient resolution of turbulent spectrum. The VLES of the industrial fan permits to detect the flow features such as three-dimensional separation and secondary flows. Predicted noise emissions, in terms of sound pressure level spectra, are compared with experimental results, and found to agree within the uncertainty of the measurements.

Commentary by Dr. Valentin Fuster
2012;():731-742. doi:10.1115/GT2012-69048.

Induced draft fans extract coal-fired boiler exhaust gases in the form of a two-phase flow with a dispersed solid phase made of unburnt coal and fly-ash. As a consequence of the particles that comprise the fly-ash, the axial fan blades are subject to erosion resulting in material wear at the leading edge, trailing edge and blade surface. Erosion results in a loss of the blade aerodynamic profile, a reduction of blade chord and effective camber that together degrade aerodynamic performance.

In this paper, the authors use a numerical study to predict the aerodynamic performance of the as-new blade and the same blade as-eroded after 9,000 hours in-service. The authors predicted fan performance and stall margin for both the as-new and as-eroded blade, and evaluated the impact for fan operation at a constant duty point. The authors calculated particle trajectories using an in-house Computational Fluid Dynamic (CFD) solver coupled with a particle cloud tracking model predicting solver based on an original finite element interpolation scheme. The numerical study clarifies the influence of fan aerodynamic operation to the determination of the erosion regimes and patterns. The authors also investigate the coupling between the three-dimensional flow structure at high- and low-volume flow rate and the particle motion to provide insight into the performance degradation process, and the risk that continued operation poses to the fan’s mechanical integrity.

Commentary by Dr. Valentin Fuster
2012;():743-752. doi:10.1115/GT2012-69081.

A set of aeroacoustic optimization strategies for axial fans is presented. Their efficiency is demonstrated for small axial fans. Thereby, the generated noise could be reduced significantly while retaining or even improving the aerodynamic performance.

In particular, we discuss the following two optimization strategies in detail: Firstly, we consider the design of winglets using a parametric model for genetic optimization. The resulting winglet geometry helps to control the tip vortex over a large range of operating points, thereby reducing the generated noise. In addition, the power consumption of the fan could be reduced. Various choices of geometrical parameter sets for optimization are evaluated.

Secondly, we discuss the reduction of fan noise via contour optimized turbulators. For axial fans it is desirable to reduce sound emission across a broad operating range, not just for the design point. However, operation in off-design points may be accompanied by flow separation phenomena, which contribute predominantly to noise generation and reduce the aerodynamic performance of the fan. Turbulators can help to minimize these adverse effects. The advantages of various contoured turbulator geometries are discussed for off-design operating points.

The optimization of the above mentioned strategies was driven by aeroacoustic measurements via physical tests as well as numerical analysis based on the Lattice-Boltzmann method. The merits of either method are discussed with respect to the two optimization strategies.

Commentary by Dr. Valentin Fuster
2012;():753-761. doi:10.1115/GT2012-69347.

A new spray axial-flow fan with a ring-shaped spray-generating device in the upstream of the rotor is proposed in this paper. The characteristics of the new spray axial-flow fan were tested in detailed according to the international performance test standard. The experimental results showed that the characteristics of the new fan operating with working fluid which having a high water-air mass ratio have been improved obviously, compared with those of the existing spray fan with the conventional spray-generating device. The new spay fan considerably expands the limit on the water-air mass ratio of the working fluid, beyond which the motor of the spray fan may be over loaded, due to its much lower decrease slope of total pressure efficiency and much lower increment slope of shaft power against the increase in the water-air mass ratio of the working fluid. In addition, its utilization factor of sprayed water also increases obviously. Numerical investigations on this new fan with working fluid under the air phase or the mixed air-water phase were also conducted. The results indicated that the numerical results agree well with the experimental data with air as the working fluid. This verified the validity of computational models. However, the numerical results using the discrete phase model available in the Fluent program for the mixed air-water working fluid showed an evident deviation from the experimental results. The numerical simulations underestimate the deteriorating effect of the characteristics of the spay fan with water added, which means it cannot well simulate and analyze the complex flow filed inside the spay fan. Further research is needed to explore the mechanism for the deteriorated characteristics of the spray fan.

Topics: Sprays , Axial flow
Commentary by Dr. Valentin Fuster
2012;():763-770. doi:10.1115/GT2012-69369.

Low solidity circular cascade diffuser abbreviated by LSD was proposed by Senoo et al. showing a high blade loading or a high lift coefficient without stall even under small flow rate conditions. These high performances were achieved by that the flow separation on the suction surface of the LSD blade was successfully suppressed by the secondary flow formed along the side walls. The higher performance of the LSD was achieved in both pressure recovery and operating range by adopting the tandem cascade because the front blade of the tandem cascade was designed suitably for small flow rates while the rear blade of the tandem cascade was designed suitably for large flow rates.

In order to clarify the reason why the tandem cascade could achieve a high pressure recovery in a wide range of flow rate, the flow in the LSD with the tandem cascade is analyzed numerically in the present study by using the commercial CFD code of ANSYS-CFX 13.0. The behavior of the secondary flow is compared between the cases with the single cascade and the tandem one. It is found that the high blade loading of the front blade is achieved at the small flow rate by formation of the favorable secondary flow which suppresses the flow separation on suction surface of the front blade, and the flow separation on pressure surface of the front blade appeared at the design flow rate can be suppressed by the accelerated flow in the gap between the trailing edge of the front blade and the leading edge of the rear blade, resulting in the positive lift coefficient in spite of a large negative angle of attack.

Commentary by Dr. Valentin Fuster
2012;():771-785. doi:10.1115/GT2012-69733.

The heat transfer characteristics of industrial air-cooled heat exchangers (ACHEs) are dependent on the ability of the fan system to deliver sufficient cooling air. However, under normal operating conditions, variable flow direction and strength often subject peripheral fans to distorted inlet conditions with an attendant reduction in overall volumetric flow rate and cooling capacity. In this paper, a design methodology for single-rotor axial flow fans, appropriate for use in large industrial ACHE’s is presented. The primary motivation for this work was to address the issues of robust off-design performance, in particular, distorted inlet flow tolerance. Using this methodology, two 8-bladed prototype fans (B1 and B2) were designed, built and tested in accordance with BS 848 (Type A) standards. The two B-fans have a hub-tip ratio of xh = 0.4 and employ the Clark Y and NASA LS airfoil profiles respectively. Measured performance characteristics were compared to commercial fan designs (V-, DL- and L-fan) used in existing ACHEs. Results indicate that the B-fans have a higher design point operating efficiency. The B-fans also show a steeper fan static pressure rise characteristic compared to the commercial fans, except for the DL-fan, implying a greater tolerance to pressure fluctuations caused by distorted inflows.

Commentary by Dr. Valentin Fuster
2012;():787-794. doi:10.1115/GT2012-69920.

This paper presents a parametric design of fully reversible jet-fan blades for ventilation and smoke control use in road tunnels. The blade design variables are tip solidity, twist and camber distribution. The authors base the design methodology on a sensitivity analysis which they obtained from a response surface approximation. They construct the latter using high-fidelity computational analysis tools for four experimental cases which they generated using an experimental design approach. The sensitivity analysis calculates a rank and a weight for each design variable that affects the jet-fan performance parameters thrust and efficiency, and thus facilitates insight into each design’s relative performance. Finally, the authors present a redesign of an existing reversible jet-fan blade by following the design guidelines obtained from the sensitivity analysis. The authors study and discuss the aerodynamic and structural characteristics of the redesigned blade and compared it to that of the baseline design configuration.

Topics: Blades
Commentary by Dr. Valentin Fuster
2012;():795-802. doi:10.1115/GT2012-70024.

In vacuum cleaners radial impellers with high rotational speed are very often used. A high rotational speed is connected with a best efficiency point of the radial impeller at a high flow rate. This is contrary to the working point of the whole system. Thus there is need for a radial impeller designs having a high efficiency at low flow rates under the restriction of a high rotational speed. One important parameter connected to the hydraulic efficiency characteristics of the radial impeller is the blade inflow angle β1. In order to shift the best efficiency point towards lower flow rates radial impellers with double curved blades and a linear β1 distribution were designed and CFD simulations were done in order to investigate the effect of this approach. A linear variation of the inflow angle β1 enables the designer to shift the efficiency characteristics of the impeller towards lower flow rates with a gain in hydraulic efficiency and pressure increase.

Topics: Impellers , Design
Commentary by Dr. Valentin Fuster
2012;():803-812. doi:10.1115/GT2012-70103.

An overview is given on the research maintained by the author about design aspects of three-dimensional blade passage flow in low-speed axial flow industrial fan rotors, affected by spanwise changing design blade circulation due to controlled vortex design (CVD), blade forward sweep (FSW), and their combination.

It was pointed out that, comparing the CVD method to free vortex design, the fluid in the blade suction side boundary layer has increased inclination to migrate radially outward, increasing near-tip blockage and loss. It was concluded that the benefit of FSW, in terms of moderating loss near the tip, can be better utilized for rotors of CVD, in comparison to free vortex design.

Compared to free vortex design, FSW applied to blades of CVD was found especially beneficial in loss reduction also away from the endwalls, via shortening the flow paths on the suction side — being anyway elongated by the radially outward flow due to CVD —, and thus, reducing the effect of wall skin friction. The necessity of correcting the swept blades was pointed out for matching with the prescribed CVD circulation distribution.

Topics: Design , Rotors , Vortices , Blades
Commentary by Dr. Valentin Fuster

Industrial and Cogeneration

2012;():813-825. doi:10.1115/GT2012-68057.

There are numerous gas turbine applications in power generation and mechanical drive service where power drop during the periods of high ambient temperature has a very detrimental effect on the production of power or process throughput. Several geographical locations experience very high temperatures with low coincident relative humidities. In such cases media evaporative cooling can be effectively applied as a low cost power augmentation technique. Several misconceptions exist regarding their applicability of evaporative cooling the most prevalent being that they can only be applied in extremely dry regions. This paper provides a detailed treatment of media evaporative cooling, discussing aspects that would be of value to an end user including selection of climatic design points, constructional features of evaporative coolers, thermodynamic aspects of its effect on gas turbines and approaches to improve reliability. It is hoped that this paper will be of value to plant designers, engineering companies and operating companies that are considering the use of media evaporative cooling.

Commentary by Dr. Valentin Fuster
2012;():827-834. doi:10.1115/GT2012-68118.

This paper describes efforts required to operate condensing-extraction steam turbine generators with flexible rotor design on a slow-roll (also called, true stand-by) mode of operation. This mode of operation became necessary as a result of changing steam demand from the refinery and the resulting decreased performance of the existing steam turbine generators and the associated economic losses for the cogeneration facility. Design modifications implemented to achieve slow-roll of steam turbine generators and produce maximum power output obtainable with new steam flow conditions without affecting reliability and availability of the entire cogeneration facility are discussed in this paper. Successful implementation of the proposed design approach was demonstrated through extensive field testing completed in the summer of 2011. A simple life cycle economic analysis shows that the payback period associated with the proposed design modifications implemented to two steam turbine generators at the plant is approximately six (6) months.

Commentary by Dr. Valentin Fuster
2012;():835-846. doi:10.1115/GT2012-68137.

As electricity demand from individual power plants is expected to fluctuate increasingly due to the growing share of renewables, operators of large Combined Cycle Gas Turbine power plants will have to deal with increasing load variations and rapid load changes. To keep up reliability and availability of the plants, it is useful to accurately keep track of plant performance by comparing actual cycle data with a steady state base case model. This paper presents various aspects of the performance modeling of Alstom’s GT26 gas turbine as recently installed in the Netherlands. The modeling environment is GSP, a component based zero-dimensional software tool. Firstly, the modeling strategy is presented, taking into account the specific features of this sequential combustion gas turbine. Secondly, the method of processing field measurements to model inputs is shown and furthermore, the influence of measurement uncertainty on model parameter estimation is assessed. Procedures will be proposed to use this model in daily operation, to keep track of actual component loading. Later on, the recorded performance data can be used to evaluate maintenance as a function of actual operational history, as a basis for future strategies.

Commentary by Dr. Valentin Fuster
2012;():847-858. doi:10.1115/GT2012-68332.

There exist a widespread interest in the application of gas turbine power augmentation technologies in both electric power generation and mechanical drive markets attributable to deregulation in the power generation sector, increased electric rates during peak demand period, and need for a proper selection of the gas turbine in a given application. In this study detailed thermo-economic analyses of various power augmentation technologies, implemented on a selected gas turbine, have been performed to identify the best techno-economic solution depending on the selected climatic conditions.

The presented results show that various power augmentation technologies examined have different payback periods. Such a techno-economic analysis is necessary for proper selection of a power augmentation technology.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2012;():859-869. doi:10.1115/GT2012-68346.

Integrated Gasification Combined Cycle (IGCC) power plants are energy systems mainly composed of a gasifier and a combined cycle power plant. Since the gasification process usually requires oxygen as the oxidant, an Air Separation Unit is also part of the plant. Moreover, a producer gas cleaning unit is always present between the gasifier and the gas turbine.

With respect to Natural Gas Combined Cycles (NGCCs), IGCCs are characterized by a consistent loss in the overall plant efficiency due to the conversion of the raw fuel in the gasifier and the electrical power parasitized for fuel production which considerably reduces plant net electric power. In order to reduce this loss, synergies among the different components of the plant should be improved.

In this paper, an analysis of state-of-the-art IGCC plant components is presented. Particular interest is given to characteristic energy and flow streams in order to evaluate possible synergies and optimizations. Moreover, a simulation model of an IGCC plant, built in a commercial energy system simulation environment, is set up and the influence of ambient conditions on IGCC net power output is analyzed. The suggestions gained from the current paper and the simulation model will be used in the Part II of this paper to evaluate the capability of a strategy for IGCC power augmentation, based on ASU discharged nitrogen utilization.

Commentary by Dr. Valentin Fuster
2012;():871-881. doi:10.1115/GT2012-68352.

Integrated Gasification Combined Cycles (IGCCs) are energy systems mainly composed of a gasifier and a combined cycle power plant. Since the gasification process usually requires oxygen as the oxidant, the plant also has an Air Separation Unit (ASU). Moreover, a producer gas cleaner unit is always present between the gasifier and the gas turbine. Since these plants are based on gas-steam combined cycle power plants they suffer from a reduction in performance when ambient temperature increases.

In this paper, an innovative system for power augmentation in IGCC plants is presented. The system is based on gas turbine inlet air cooling by means of liquid nitrogen spray. In fact, nitrogen is a product of the ASU, but is not always exploited. In the proposed plant, the nitrogen is first chilled and liquefied and then it can be used for inlet air cooling or stored for a postponed use.

This system is not characterized by the limits of water evaporative cooling (where the lower temperature is limited by air saturation) and refrigeration cooling (where the effectiveness is limited by pressure drop in the heat exchanger).

A thermodynamic model of the system is built by using a commercial code for the simulation of energy conversion systems. A sensitivity analysis on the main parameters (e.g. ambient air temperature, inlet air temperature difference, etc.) is presented. Finally the model is used to study the capabilities of the system by imposing the real temperature profiles of different sites for a whole year.

Commentary by Dr. Valentin Fuster
2012;():883-889. doi:10.1115/GT2012-68668.

Kawasaki Heavy Industries (KHI) will launch the first unit of the L30A gas turbine, rated output of 30.9MW, and 41.2% of thermal efficiency. The L30A is a twin-shaft gas turbine designed for combined heat and power application (CHP) with lower emissions. The newly developed 14-stage compressor has a pressure ratio of 24.5 with an air flow of 86.5 kg/sec. KHI’s proven dry low emission (DLE) technologies are adapted to the combustion design, and NOx emission of 15 ppm (15% = O2) has been achieved. Also, the newly designed 2-stage gas generator turbine (GGT) employs the proven cooling design with conjugate heat transfer and flow (CHT) analysis, and 3-stage power turbine (PT) has the inter-locking type tip shroud which reduces vibration level for wide operating range of PT with lower pressure losses. The in-house verification tests have been conducted since 2010, to confirm design targets such as performance, emission, vibrations and temperatures were verified in exclusive test facility for the L30A. This paper describes the technical features of the L30A, the development activities and some verification test results.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2012;():891-901. doi:10.1115/GT2012-68727.

An industrial gas turbine had a reoccurring failure with its accessory gearbox. The gearbox would run for a few days and then begin to show increased vibrations. The vibration level would gradually increase until the turbine alarm and trip signals operated. Studies at the time suggested alignment and accessory coupling issues were the cause. After many realignments and gears being changed the problem persisted. Eventually the gearbox replaced as it was suspected the original had internal alignment issues. This proved to be unsuccessful and the problem continued.

At the time of the unit’s last overhaul it was discovered the generator’s non-drive-end bearings insulation had failed and could not be rectified in time for its return to operation. It was then decided to install a second rotor earthing brush to the non-drive-end of the generator.

The writer reviewed all the historical and current date including a site inspection of the plant. Initial inspection of the gear damage indicated excessive misalignment and gear tooth overload. Finally, examination of the shell bearing liners had indications consistent with Electrical Static Discharge [ESD]. This had been overlooked; interpretation of the marking was due to unusual misalignment and the gear shaft.

Commentary by Dr. Valentin Fuster
2012;():903-912. doi:10.1115/GT2012-68765.

The product development process for gas turbines relies upon the understanding of the existing engine fleet. For this reason, performance measurement data are regularly collected. The processed data show a remaining scatter, which complicates the direct use of the fleet evaluation results. This scatter can be attributed to e.g. the measurement chain, existing hardware condition, and hardware installation. To understand the true engine performance, the contributing factors behind the scatter must be addressed.

This paper describes the influence of compressor blading clearances on gas turbine performance. Fleet evaluation results are first presented. The scatter in the resulting parameters (i.e.: compressor efficiency and mass flow rate, turbine efficiency) cannot be explained simply by uncertainty in the performance measurement data. Therefore, an empirical model has been developed which correlates measured compressor clearances with deviations in component efficiencies in order to understand the end effect on engine performance.

The evaluation shows a correlation between the weighted average clearances and compressor blading efficiencies. Thus, one of the contributors to the data scatter has been identified and quantified by using the empirical model and statistical analysis. The result demonstrates a method to reduce uncertainties in the fleet data and consequently improve the component understanding.

Commentary by Dr. Valentin Fuster
2012;():913-923. doi:10.1115/GT2012-68808.

Air cooling via evaporation of water droplets injected at the compressor intake duct is the process known as Fogging System, which is among the most used technologies for increasing output power of gas turbines nowadays. The optimal design of this system must consider numerous variables, such as: air temperature (Ta), air relative humidity (RH), duct geometry, amount of water injected (mw), droplets size (Dd), and nozzles location. Since there are so many variables the flow under study is very complicated. In consequence the analytical determination of an optimal Fogging System design is not feasible. In this paper, a numerical model was developed in order to characterize the injection of water at the air intake duct of a Gas Turbine. First, the expressions characterizing the model were included in the CFD software ANSYS CFX v-11 and simulated in a simple geometry (rectangular duct). Validation of CFD results was carried out by comparison with experimental data. Good agreement between numerical results of a control case and experimental data was achieved (deviation < 2%). Then, the influence of key parameters such as: Ta, RH, Dd, mw over the performance of the air cooling system was investigated. Finally, the model was used to design a Fogging System for an existing 120 MW Gas Turbine. For this gas turbine operating under real conditions, the model predicts a net power increment of 2% [7].

Commentary by Dr. Valentin Fuster
2012;():925-937. doi:10.1115/GT2012-68846.

In this paper, a thorough flow simulation of a small turbojet engine has been carried out to predict the engine performance as a result of water injected at the compressor inlet. Wet compression will not only change compressor performance characteristic map, but also has effects on both the combustor and the turbine sections. The match between the turbojet engine components, that is the compressor, combustor and turbine, will shift to a new operating point. In this paper, we present a steady-state numerical simulation of the entire gas turbine with wet compression in order to evaluate the effects on the gas turbine performance.

Compared with the dry case, the results of wet cases show increased values of compressor compression ratios, turbine expansion ratios, intake mass flowrates and engine thrusts including decreased amount of specific fuel consumption. The wet compression reduces NOx production in the combustor, which is also simulated and results presented. The study also indicates that the water mass flowrate and droplet diameter are key factors impacting the engine performance.

Commentary by Dr. Valentin Fuster
2012;():939-948. doi:10.1115/GT2012-68894.

The present study deals with the integration between a Thermo-Photo-Voltaic generator (TPV) and an Organic Rankine Cycle (ORC) named here TORCIS (Thermo-photo-voltaic Organic Rankine Cycle Integrated System). The investigated TORCIS system is suitable for CHP applications, such as residential and tertiary sector users. The aim of the research project on this innovative system is the complete definition of the components design and the pre-prototyping characterization of the system, covering all the unresolved issues. This paper shows the results of a preliminary thermodynamic analysis of the system. More in details, TPV is a system to convert into electric energy the radiation emitted from an artificial heat source (i.e., combustion of fuel) by the use of photovoltaic cells; in this system, the produced electric power is strictly connected to the thermal one, as their ratio is almost constant and cannot be changed without severe loss in performance; the coupling between TPV and ORC allows to overcome this limitation and to realize a cogenerative system which can be regulated with a large degree of freedom changing the electric-to-thermal power ratio. The paper presents and discusses the TORCIS achievable performance, highlighting its potential in the field of distributed generation and cogenerative systems.

Commentary by Dr. Valentin Fuster
2012;():949-960. doi:10.1115/GT2012-68988.

The paper presents the optimization of an energy supply system for an industrial area. The system is mainly composed of a district heating network (DHN), of a solar thermal plant with long term heat storage, of a set of combined heat and power units (CHP) and of additional thermal/cooling energy supply machines. The thermal vector can be produced by solar thermal modules, by fossil-fuel cogenerator or by conventional boilers. The optimization algorithm is based on a Mixed Integer Linear Programming (MILP) model and it has to determine the optimal structure of the energy system and the size of the components (solar field area, heat storage volume, machines sizes, etc.). The model allows to calculate the economical and environmental benefits of the solar thermal plant compared to the cogenerative production, as well as the share of the thermal demand covered by renewable energies. The aim of the paper is to identity the optimal energy production mix able to meet the user energy demands and furthermore how the solar thermal energy integration affects the optimal energy system configuration. The average costs of the heat produced for the users have been evaluated for different optimal configurations, and it emerges that the solution including some cogenerators located in strategic production units, the district heating network, the long term heat storage and a solar plant of proper size, allows achieving the lowest cost of the heat. Thus, the integrated solution turns out to be the best from both the economical and environmental point of view.

Commentary by Dr. Valentin Fuster
2012;():961-977. doi:10.1115/GT2012-69133.

The rotor blade tip leakage flow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated.

The evaluation of results on various performance parameters such as total pressure ratio, inlet flow capacity and adiabatic efficiency combined with contours of total pressure losses, entropy, Mach No., and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection flow rate and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.

Commentary by Dr. Valentin Fuster
2012;():979-992. doi:10.1115/GT2012-69158.

Generally, droplets are injected into air at inlet or interstage of a compressor. However, both cases did not consider how to utilize the kinetic energy of these moving droplets. Under the adverse pressure gradient of compressor, the lower energy fluids of blade surfaces and endwalls boundary layers would accumulate and separate. Kinetic droplets could accelerate the lower energy fluids and eliminate the separation. This paper mainly investigate the effective positions where to inject water and how to utilize the droplets’ kinetic energy. Four different injecting positions, which located on the suction surface and endwall, are chosen. The changes of vortexes in the compressor cascade are discussed carefully. In addition, the influences of water injection on temperature, total pressure losses and Mach number are analyzed. Numerical simulations are performed for a highly loaded compressor cascade with ANSYS CFX software.

Commentary by Dr. Valentin Fuster
2012;():993-1002. doi:10.1115/GT2012-69621.

The first Siemens SGT5-8000H had extensively been tested in Simple Cycle in Irsching during 2008 and 2009. About 3000 sensors had been installed for monitoring of the engine operation, the results demonstrated that all performance targets have been exceeded.

Detailed measurements of pressure, temperature and flow were performed in the turbine flow path at various locations in circumferential and radial direction. The experimental test results in the turbine flow path have been used for additional detailed analysis of the fluid dynamics operation by a High Fidelity 3D CFD whole turbine model. This standardized whole turbine CFD process forms an important element in the Siemens design chain. The model was set up with all geometrical details to resolve all relevant flow features such as shrouds, cavities, coating, fillets etc.

This paper summarizes and compares the experimental test results with predicted CFD design values for overall thermodynamic operation and aerodynamics data at turbine outlet.

Besides the results from the Simple Cycle prototype test phase, performance test results are presented from recent measurements during customer acceptance testing in Combined Cycle in 2011. These results show a confirmation of the previously measured overall performance values after complete rebuild and re commissioning of the engine for combined cycle operation.

Commentary by Dr. Valentin Fuster
2012;():1003-1011. doi:10.1115/GT2012-69660.

The University of Central Florida Cogeneration Facility is a state of the art chilled water CHP system using a natural gas fueled high efficiency 60 Hz medium speed reciprocating engine as the prime mover. The facility features one lean burn 5.5 MW 18KU30GSI (MACH II-SI) spark ignition engine, generator, controls, auxiliaries, multi-effect absorption chiller, secondary cooling, and an advanced emissions control system that includes selective catalytic reduction (SCR) system and oxidation catalyst (OC).

The cogeneration system is located on a constrained site in Orlando, Florida at the second largest university in the United States with a student enrollment of over 56,000. The site is adjacent to a sensitive environmental area to the east, a main thoroughfare to the south, student dormitories to the west, and a lecture hall to the north. The architecture of the new combined heat and power plant was carefully designed to blend with the surrounding campus architecture and sound attenuation methods were employed to minimize noise pollution from the power plant.

The new chilled water system was interconnected to the existing campus chilled water facility, therefore requiring coordination with existing chilled water infrastructure as well as other existing electrical, water, sewer, and storm water utilities on the campus.

This paper describes the plant load profile, design criteria, engine performance, chilled water production heat balance, and emissions requirements. The economic benefit to the University is discussed including both the impact of self generating power and augmentation of the existing chilled water system. In addition, the benefits of using modern 3-dimensional design tools are outlined for a brown-field location such as the subject site.

Commentary by Dr. Valentin Fuster
2012;():1013-1023. doi:10.1115/GT2012-69847.

Inlet filtration on a gas turbine strongly influences the performance degradation and life of the turbine. The inlet filtration system must have a diverse set of stages to remove the contaminants present in various phases (gas, liquid, and solid). Filters for gas turbine filtration systems are currently classified using one of three standards: ASHRAE 52.2, EN 779, or EN 1822. These standards measure the performance of filters in the dry state and do not consider the performance of the filter when wet (saturated with water). Many locations where gas turbines operate, experience conditions where the filter can be dampened or saturated which can significantly influence the filter’s performance. In addition, if soluble particles, such as sodium chloride, are captured by the filter, then there is a potential for the soluble particles to be carried by the water through the filter and into the gas turbine. In order to understand the performance of a filter with water present, a procedure is being developed. This procedure intends to quantify the effects of water and salt on the performance of filters. The procedure has been written, and a series of preliminary validation tests have been completed. The results of the preliminary validation testing show that a change can be observed in the filter’s performance when salt and water are introduced into the flow stream. In addition, the preliminary validation testing revealed many areas where the test procedure could be improved.

Commentary by Dr. Valentin Fuster
2012;():1025-1034. doi:10.1115/GT2012-70086.

Power plants are complex systems consisting of thousands of heterogeneous components. The maintenance policy of such systems includes grouping the maintenance actions of different components. This grouping of the maintenance actions together with functional interactions between the components results in system level models that are highly coupled. Accurate models of the maintenance process would allow plant managers and system designers to generate cost-effective maintenance policies. A system level model with explicit accounting of all components, interactions and maintenance policy groupings would provide the desired accuracy, but the creation of such a model is infeasible or very expensive. In this paper, a bottom-up modeling procedure that allows for the creation of the maintenance model is introduced. This approach reduces the complexity of the modeling process while still capturing all the relevant characteristics. Each component type present in the system is modeled separately, but each model includes an aggregated representation of the effects of the rest of the system on the modeled component type. This procedure applied to both a midsize-system and to a gas turbine engine. Simulations are used to illustrate how the created models are used and to verify the level of accuracy by comparing the results to system-level models.

Commentary by Dr. Valentin Fuster
2012;():1035-1042. doi:10.1115/GT2012-70096.

At present, the attention of the market in Stirling engines is increasing for small size applications of electrical power generation. These engines are based on a simple principle of functioning and could employ renewable energy sources. Two main configurations are available on the market: the first is a four-cylinder engine with wobble yoke mechanism and the second is represented by the single-cylinder free-piston concept. The paper is aimed at investigating several multi-cylinder configurations for the improvement of the engine performances. These are evaluated by means of numerical simulations taking into account the dynamics of the mechanism and the thermal aspects of the cycle. In particular the attention of the authors is focused on the design of a new configuration with a higher number of cylinders.

Topics: Machinery , Design , Cylinders
Commentary by Dr. Valentin Fuster
2012;():1043-1052. doi:10.1115/GT2012-70097.

Gas turbine inlet fogging and overspray (high-fogging) have been considered the most cost-effective means of boosting a gas turbine’s total power output, especially under hot or dry weather conditions. The result of employing fogging or overspray is indisputably clear — total power output is increased; however, development of the theory and explanation of the phenomena associated with fogging and overspray are not always consistent and are sometimes misleading and incorrect. This paper focuses on reviewing several interesting features and commonly discussed topics, including (a) entropy production of water evaporation, (b) the effect of centrifugal force on water droplets, and (c) whether water droplets can survive the journey in the compressor and enter the combustor. Furthermore, three turbine myths: that fogging/overspray increases the air density in the compressor, reduces the compressor power consumption, and noticeably enhances the gas turbine efficiency, are examined and discussed.

Some common mistakes in describing the compressor work are identified and corrected. A newly constructed multiphase T-S diagram is used to explain the physics of water droplet evaporation process and corresponding entropy production during wet compression.

Commentary by Dr. Valentin Fuster

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