ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V001T00A001. doi:10.1115/POWER2018-NS1.

This online compilation of papers from the ASME 2018 Power Conference (POWER2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Fuels, Combustion, and Material Handling

2018;():V001T01A001. doi:10.1115/POWER2018-7171.

Testing was performed on commercially available 1 kW spark ignition generators that were modified to operate on JP-8 and other heavy fuels. This approach is motivated by the US Military mandate that only one fuel, JP-8, be taken to the battlefield, and the increased electrical demands at the squad and platoon level. Small units require a portable power source that can meet their energy demands, particularly battery charging. While diesel engines can operate on JP-8, their weight limits their mobility at the platoon level. Spark ignition engines have better power density at the 1 kW level, but must be modified to burn logistically available fuel.

Multiple approaches have been pursued to enable these engines to operate on JP-8. In the present study, the longer term effects of three approaches are examined and compared to an unmodified spark ignition generator operating on gasoline. These approaches include A) chemically altering the fuel as it flows to the engine to create a higher octane mixture, B) modifying the carburetor and using ether starter fluid to preheat the cylinder, and C) electrically heating the cylinder while modifying the fuel system for direct injection. The different generators were characterized by oil sampling at 15 hour intervals. Oil testing included flash point, viscosity, wear elements, and additives. Oil quality and emissions vary with load. Different approaches to conversion perform better at different loads.

It was determined that multiple start-stop cycles with no load resulted in fuel dilution of the lubricating oil in several of the modified engines. Response varied with some of the modified engines maintaining low fuel dilution similar to the gasoline fueled engine while others indicated 15–20% fuel in the oil. During operation at full load, the modified JP-8 burning generators showed 3–5% fuel dilution in the oil while the unmodified gasoline generator was less than 1%.

These experiments illustrate the challenges in developing portable, reliable JP-8 burning power sources. While further research and development is needed in each approach, it was shown that converted spark ignition engines are a promising path to portable logistic power. Oil analysis was shown to identify future research and development efforts to improve this technology.

Commentary by Dr. Valentin Fuster
2018;():V001T01A002. doi:10.1115/POWER2018-7179.

Large eddy simulation/Flamelet progress variable approach is employed in current research to investigate how flame behaviour is influenced by bluff-body and coflow composition. We used Sydney bluff-body burner as the target burner. Computation grid in cylinder coordinates is approximately 2.7 million in total number, extended to the downstream location 80 times of jet diameter. Three coflow compositions with different oxygen ratio at the same inlet velocity are considered. Comparing to jet flames with hot and diluted coflow, instantaneous and statistical results showed that an introduction of bluff-body preheats the fuel and shortens the flame length. At lower oxygen ratio condition, a weaker reaction zone emerged, marked by lower temperature and OH concentration; the flame appeared lifted gradually, leading to a potential MILD combustion. Besides, bluff-body effect behaves differently in these flames: at lower oxygen ratio condition, a large-scale distribution of CH2O appeared as a marker of partial premixing and preignition reaction in recirculation area; on the contrary, in higher oxygen ratio case, the recirculation area brings out more reactive fuel at lower speed and higher temperature, hence ignitable in the vicinity of bluff-body.

Topics: Flames
Commentary by Dr. Valentin Fuster
2018;():V001T01A003. doi:10.1115/POWER2018-7202.

Homogeneous charge compression ignition (HCCI) is a combustion technology which has received increased attention of researchers in the combustion field for its potential in achieving low oxides of nitrogen (NOx) and soot emission in internal combustion (IC) engines. HCCI engines have advantages of higher thermal efficiency and reduced emissions in comparison to conventional internal combustion engines. In HCCI engines, ignition is controlled by the chemical kinetics, which leads to significant variation in ignition time with changes in the operating conditions. This variation limits the practical range of operation of the engine. Additionally, since HCCI engine operation combines the operating principles of both spark ignition (SI) and compression ignition (CI) engines, HCCI engine parameters such as compression ratio and injection timing may vary significantly depending on operating conditions, including the type of fuel used. As such, considerable research efforts have been focused on establishing optimal conditions for HCCI operation with both conventional and alternative fuels. In this study, numerical simulation is used to investigate the effect of compression ratio on combustion and emission characteristics of an HCCI engine fueled by pure biodiesel. Using a zero-dimensional (0-D) reactor model and a detailed reaction mechanism for biodiesel, the influence of compression ratio on the combustion and emission characteristics are studied in Chemkin-Pro. Simulation results are validated with available experimental data in terms of incylinder pressure and heat release rate to demonstrate the accuracy of the simulation model in predicting the performance of the actual engine. Analysis shows that an increase in compression ratio leads to advanced and higher peak incylinder pressure. The results also reveal that an increase in compression ratio produces advanced ignition and increased heat release rates for biodiesel combustion. Emission of NOx is observed to increase with increase in compression ratio while the effect of compression ratio on emissions of CO, CO2 and unburned hydrocarbon (UHC) is only marginal.

Commentary by Dr. Valentin Fuster
2018;():V001T01A004. doi:10.1115/POWER2018-7207.

In this work, the combustion characteristics of semi-coke, coal, and their blends under air conditions were studied. The influence of blending ratio on the combustion characteristics of blended fuels were investigated by thermogravimetric analysis. It was found that the co-combustion of semi-coke and bituminous coal was a complicated process rather than a simple linear superposition, with interaction effect occurring in the co-combustion process. The synergy occurred in the whole combustion process and it was analyzed quantitatively by comparing the interaction coefficient f and the relative root mean square error RMS. The combustion of semi-coke and the blends can be divided to three stages, as well as two stages of coal. In addition, the blends show better combustion behavior with enhancing bituminous coal proportion, and bituminous coal can improve the combustion behavior of semi-coke.

Topics: Coke , Coal , Co-firing
Commentary by Dr. Valentin Fuster
2018;():V001T01A005. doi:10.1115/POWER2018-7211.

Semi-coke is a specific solid fuel, which is mainly produced by upgrading low-rank coal. The poor reactivity of semi-coke makes a difficulty to its practical utilization in utility boilers. Previous research was mainly focused on the combustion behavior of semi-coke, while the industrial application has to be understood. In this paper, the effect of co-firing semi-coke and bituminous coal on the operation performance of pulverized boiler was numerically studied. The work was conducted on a 300 MW tangentially fired boiler, and the temperature distribution, the char burnout and NOx production were mainly examined. The results indicate that the incomplete combustion heat loss drops with the increase in semi-coke blending ratio. The NOx concentration increases from 186 mg/Nm3 for only firing the bituminous coal to 200, 214, and 255 mg/Nm3, when the blending ratio was 17%, 33% and 50%, respectively. With enhancing excess air coefficient for the co-firing condition, the combustion efficiency got improved, while NOx production increased very slightly. In general, the boiler is well adapted to co-firing semi-coke, and the semi-coke blending ratio of 1/3 with an excess air coefficient of 1.235 is recommended.

Commentary by Dr. Valentin Fuster
2018;():V001T01A006. doi:10.1115/POWER2018-7218.

For SCR (selective catalytic reduction) applications both aqueous ammonia and urea reagents are used for NOx reducing agents in exhaust systems. For both diesel engines and small boilers, the reagent injection systems often consist of a few, and in some cases, a single injector, located on the wall of the exhaust pipe or duct. Often numerical modeling is performed to determine the location and orientation of the injectors and to predict the NRMS (normalized root mean square) of the gas phase reducing specie distribution prior to the catalyst. Aqueous ammonia and aqueous urea have significantly different processes from the point of injection to the formation of the gas phase reducing species. Evaporation characteristics are important, but for urea, the molecule must also decompose into ammonia and isocyanic acid. For modeling purposes, a simplifying assumption is frequently made to treat the liquid reagent as liquid water and assume that the evaporation of liquid water satisfactorily emulates the processes of forming the gas phase reducing species for both aqueous ammonia and aqueous urea reagents. In reality, the reagent droplets are binary component mixtures and treating the droplets as a single component, namely water, may significantly depart from reality. Additionally, the evaporation processes for aqueous ammonia and aqueous urea have significantly different behaviors. This paper addresses the potential errors associated with using a single component water drop for emulating the evaporation of aqueous ammonia and aqueous urea. This is accomplished by analyzing binary component evaporation for both aqueous ammonia and aqueous urea. Additionally, the time for the gas phase chemical decomposition of urea into ammonia and isocyanic acid is evaluated for various conditions. Typical decomposition times are compared to droplet evaporation times. Finally, the paper attempts to provide guidelines for determining when treating the drops as a single component may be sufficiently accurate, and when the complexity of modeling binary component evaporation is necessary.

Topics: Evaporation
Commentary by Dr. Valentin Fuster
2018;():V001T01A007. doi:10.1115/POWER2018-7242.

This work extends the species sensitivity method of model reduction known as Alternate Species Elimination (ASE) to a stochastic version. The new Stochastic Species Elimination (SSE) approach allows for a linear reduction in the number of species retained in the course of reduction. It improves the computational cost and offers flexibility to the user in terminating the reduction process when an acceptable model size is attained. Larger chemical kinetic models, such as the recent literature model of n-octanol, are approached with the SSE method coupled with multiple species sampling. This further allows for a faster model reduction process. These modified approaches are applied to the reduction of selected chemical kinetic models based on ignition simulations: the n-heptane model by Mehl et al. (654 species, 5258 reactions), reduced using the SSE method (293 species, 2792 reactions) and the ASE method (245 species, 2405 reactions); the iso-octane model by Mehl et al. (874 species, 7522 reactions), reduced to an SSE version (315 species, 3037 reactions) and an ASE version (306 species, 2732 reactions); and the n-octanol model by Cai et al. (1281 species, 5537 reactions), with a reduced SSE version (450 species, 2532 reactions). Resulting skeletal models are shown to adequately predict ignition delay times as well as flame propagation when compared to the predictions of the detailed models. Burning velocity predictions are well-captured even though the reduction is based on ignition delay simulations.

Commentary by Dr. Valentin Fuster
2018;():V001T01A008. doi:10.1115/POWER2018-7255.

Development of alternative, clean and renewable energy production from different hydrocarbon materials helps to partially replace the limited resources of fossil fuels and also help reduce carbon emissions from fossil fuels that drives global warming. Biomass and bio-wastes are renewable and sustainable hydrocarbon resources, which can be used for energy and fuels production along with permanent disposal of plastic wastes. Landfills of wastes is unsustainable with additional problems of non-degradability and growing burden to the environment and society. Co-pyrolysis and co-gasification of biomass with different types of plastic wastes has shown to provide enhanced product yields and quality for syngas and liquid fuel production. To date, limited information is available on the understanding of chars produced from co-pyrolysis. The effect of co-pyrolysis on the type, quality and yield of chars produced is essential for efficient utilization of a wide variety of biomass, bio-waste and plastic waste resources.

This paper provides information on the effect of plastic addition to the pyrolysis of biomass as well as the quality and quantity of char produced with different amounts of plastic waste added at different pyrolysis temperatures. TGA reactor was used for all these investigations and the quality of char produced was examined from the perspective of char combustion for energy production. Char is commonly produced as a by-product from pyrolysis and gasification reactors. Carbonization temperatures investigated were in the range of 573–773 K for 30 min using pinewood biomass, while recycled polyethylene terephthalate was used as plastic waste. The investigations revealed that chars produced from co-pyrolysis especially for carbonization temperature (Tc) of 673 K and above behaved completely differently than the chars produced from separate pyrolysis of biomass and plastic waste under the same pyrolysis conditions. These chars produced from co-pyrolysis were more uniform in their behavior in oxidation environment, with higher heat flow for almost similar quantities of chars during oxidation. This was conjectured to be from enhanced quality of chars produced having increased C content (from increased heavy aromatics and efficient loss of volatiles) during co-pyrolysis without any loss of char yield. The char yield was found to be equal or higher during co-pyrolysis compared to the weighted aggregate of individual pyrolysis. These investigations provided novel results on the behavior and capabilities of chars produced from co-pyrolysis of biomass and plastic wastes to provide a new avenue for the quality enhancement of bio-chars and efficient utilization of carbonaceous solid waste resources.

Commentary by Dr. Valentin Fuster
2018;():V001T01A009. doi:10.1115/POWER2018-7341.

Reduced mechanisms are needed for use with computational fluid dynamic codes (CFD) utilized in the design of combustors. Typically, the reduced mechanisms are created from the detailed mechanisms which contain numerous species and reactions that are computationally difficult to handle using most CFD codes. Recently, it has been shown that the detailed Aramco 2.0 mechanism well predicted the available experimental data at high pressures and in high-CO2 diluted methane mixtures. Further, a 23-species gas-phase mechanism is derived from the detailed Aramco 2.0 mechanism by path-flux-analysis method (PFA) by using CHEM-RC. It is identified that the reaction CH4+HO2⇔ CH3+H2O2 is very crucial in predicting the ignition delay times under current conditions. Further, it is inferred that species C2H3 and CH3OH are very important in predicting the ignition delay time of lean sCO2 methane mixtures. Also, the 23-species mechanism presented in this work is performing on par with the detailed Aramco 2.0 mechanism in-terms of simulating ignition delay times, perfectly-stirred-reactor estimates under various CO2 dilutions and equivalence ratios, and prediction of turbulence chemistry interactions. It is observed that the choice of equation-of-state has no significant impact on the ignition delay times of supercritical CH4/O2/CO2 mixtures but it influences supercritical H2/O2/CO2 mixtures considered in this work.

Commentary by Dr. Valentin Fuster
2018;():V001T01A010. doi:10.1115/POWER2018-7414.

The objective of this paper is to elucidate the recently observed strong correlation between derived cetane number (DCN) and lean blow out (LBO) characteristics for both petroleum-derived and alternative jet fuels, as well as their blends. In order to evaluate the variability of fuel physical and chemical properties for petroleum-derived jet fuels, the fuel property database appearing in the DSIC-PQIS 2013 report are rigorously analyzed and compared against fuel-specific data for 17 petroleum-derived and alternative jet fuels and their blends obtained previously in our works. The global combustion characteristics of each fuel for fuel/air mixture were characterized experimentally by determining their combustion property targets (CPTs) — the hydrogen to carbon molar ratio (H/C ratio), the derived cetane number (DCN), the average molecular weight (MW), and surrogate fuel mixtures and threshold sooting index (TSI). Surrogate mixtures of known hydrocarbon species were blended to match the CPTs of target real fuel. The known chemical functional group distributions of the surrogate mixtures for each fuel or fuel blend were then used to predict well-known fundamental combustion behaviors — reflected shock ignition delay times and laminar flame speeds — through quantitative structure-property relationship (QSPR) regression analyses developed from a validation base of single component, binary and ternary mixture database. The results show that the DCN is capable of representing ignition propensity and flame propagating characteristics for both petroleum-derived and alternative jet fuels as well as their mixtures with high fidelity. Finally, the chemical functional group distributions of the real fuels themselves were directly measured using 1H nuclear magnetic resonance (NMR) spectra results. QSPR predictions based upon the experimental NMR functional group measurements are shown to provide a rapid, small sample, characterization tool for predicting the above global combustion behaviors of petroleum derived and alternative jet fuel candidates as well as their blends. Through combustor as well as stirred reactor experiments, fuel DCN has been identified as having major influence on LBO in devices that are sensitive to fuel chemical properties.

Commentary by Dr. Valentin Fuster
2018;():V001T01A011. doi:10.1115/POWER2018-7432.

As alternative jet fuels continue to be developed, their impact on combustor performance remains of utmost importance. Alternative jet fuels generally contain few aromatics and differ in alkylated compositions, yielding different chemical and physical properties from those of conventional jet fuels; understanding how these property differences impact combustor performance near limiting conditions is important in certifying their use in blending with petroleum derived fuels or as complete substitutes. Ignition and extinction properties that are associated with Lean Blowout (LBO) are areas of focus for jet fuel certification as they are important safety metrics bounding combustor stability. Previous results for 23 different test fuels in a referee combustor show a strong correlation of Lean Blowout (LBO) with fuel Derived Cetane Number (DCN). This previous study involved fuels with compositions similar to conventional fuels. However, fuels with properties differing significantly from conventional fuels were found to have a weaker correlation with DCN and higher LBO equivalence ratios overall. The surrogate fuels and blends that show the largest discrepancy from the earlier correlation were blends involving highly volatile, low DCN components such as iso-octane prevalent in the early stages of distillation, and less volatile, high DCN normal alkane components such as n-hexadecane, prevalent in the final stages of distillation. Thus, significant differences in fuel reactivity along the distillation curve from those of conventional petroleum derived fuels appeared to exhibit differing LBO character. From these observations, three hypotheses, preferential vaporization, relative droplet lifetimes, and thermal quenching, are proposed and investigated by utilizing the available data. Using normalized power law regressions, distillation simulation methods and Quantitative Structure Property Relation (QSPR) results, the DCN at 34% distillation recovery show a stronger correlation with LBO than the DCN determine for the fuel itself. In this paper, we apply findings to propose fuel compositions to investigate the noted hypotheses by utilizing reactive low molecular weight molecules and a less reactive high molecular weight fuel. The suggested fuel to stress test this hypothesis is a blend of 30 (molar)% n-heptane and 70 (molar)% Gevo Alcohol-to-Jet (ATJ), which is essentially composed of (primarily) 2,2,4,6,6 iso-dodecane and isocetane. If preferential vaporization is significant, then this fuel should be more stable than the “DCN-Law,” i.e. fuels are no more stable than the corresponding DCN allows, would predict.

Commentary by Dr. Valentin Fuster
2018;():V001T01A012. doi:10.1115/POWER2018-7433.

Historically, combustion modeling is important for many transportation- and ground-based applications. More recently, modeling has been offered as an early screening tool in the evaluation of a potential alternative aviation jet fuel. This combustion evaluation path would in theory be conducted by gas turbine Original Equipment Manufacturers (OEMs) on proprietary geometries and conditions. Ideally, OEMs would have access to the latest combustion theory models and would thus have the highest predictive confidence in their model predictions. Unfortunately, the latest combustion theory codes are not written for commercial purposes.

This work identifies and develops a conduit for OEM usage of latest flamelet theory for use in the evaluation of alternative jet fuel combustion properties. A so-called “common format routine” (CFR) software with two low-dimensional manifold combustion models that can be used for laminar and turbulent applications is developed, which can be implemented by OEMs on proprietary hardware. The two models are the flamelet prolongation of the intrinsic low-dimensional manifold (FPI), used for premixed combustion, and the flamelet progress variable (FPV), utilized for nonpremixed combustion. The three branches of combustion are computed using a hybrid tool that combines homotopic flamelet calculations with scaling laws and the two- and one-point flamelet continuation methods in order to resolve bifurcations. The mixture fraction and progress variable definitions can be chosen to be any summation of atomic and species composition, respectively. Diffusivity coefficients can be computed using unity Lewis number, mixture-averaged and multicomponent species composition. The turbulence-chemistry interaction is tabulated a priori using Beta probability density function (PDF) for the mixture fraction and Beta or Dirac-delta PDF for the progress variable. Parallel computing is necessary for industrial quality tabulation. The tabulated table can be used for k-ε and k-ω RANS, SAS, DES, and LES simulations. The software can also interact with liquid spray and exchange mass between the liquid and gaseous phase. The software is verified against previous numerical simulations of canonical triple flames, piloted flames and single-cup combustor. The numerical results are validated against experimental measurements of temperature and species mass fractions. The CFR software advances Cantera 2.3. Hence, the software contains an inner layer of C++ code, an intermediate layer of Python wrappers, and an upper layer (GUI) of C# code. The pre-tabulated chemistry is used for CFD simulations. The tables are bi-linearly interpolated for laminar simulations and tri-linearly interpolated for turbulent simulations. The tabulated chemistry can be hooked to commercial software such as Fluent through C and Scheme codes. The simulated flames presented here were computed with this software. The developed software is reliable for modeling and simulation of complex combustion phenomena.

Commentary by Dr. Valentin Fuster
2018;():V001T01A013. doi:10.1115/POWER2018-7497.

Urban solid waste generation has drastically grown around the world, requiring creative, ecologically correct and sustainable solutions to be developed. This work considers a problem of thermodynamic optimization of extracting the most energy from a stream of hot exhaust produced by urban solid waste incineration, considering a stoichiometric combustion model, when the contact heat transfer area is fixed. For that, a mathematical model is introduced to evaluate the rate of heat generation due to the waste incineration process, and the exergetic (power) rate captured by a heat recovery steam generator (heat exchanger). The numerical results show that when the (cold) receiving stream boils in the counterflow heat exchanger; the thermodynamic optimization consists of locating the optimal capacity rate of the cold current. At the optimum, the cold side of the heat transfer surface is divided into three sections: preheating of liquid, boiling and superheating of steam. Experimental results are in good qualitative and quantitative agreement with the numerically calculated mathematical model results. Microalgae cultivated in large-scale vertical tubular compact photobiorreactors are investigated to treat the emissions produced by the incineration, and to increase the efficiency of the global system via cogeneration of co-products with high aggregated commercial value.

Commentary by Dr. Valentin Fuster
2018;():V001T01A014. doi:10.1115/POWER2018-7537.

Over the past decade, several technical developments (such as hydraulic fracturing) have led to an exponential increase in discovering new domestic natural gas reserves. Raw natural gas composition can vary substantially from source to source. Typically, methane accounts for 75% to 95% of the total gas, with the rest of the gas containing ethane, propane, butane, other higher hydrocarbons, and impurities, with the most common including H2O, CO2, N2, and H2S. All natural gas requires some treatment, if only to remove H2O; however, the composition of natural gas delivered to the commercial pipeline grids is tightly controlled. Sub-quality natural gas reserves, which are defined as fields containing more than 2% CO2, 4% N2, or 4 ppm H2S, make up nearly half of the world’s natural gas volume. The development of sub-quality, remote, and unconventional fields (i.e. landfill gas) can present new challenges to gas separation and purification methods. Adsorbent technologies, such as the use of activated carbons, zeolites, or metal-organic frameworks (MOFs), may hold the key to more efficient and economically viable separation methods.

This work proposes to prove the applicability of the multi-component potential theory of adsorption (MPTA) to a real world natural gas adsorbent system to properly characterize the adsorbent’s selectivity for an individual gas component using only the single component isotherms. Thus, the real-world gas separation/purification application of a specific adsorbent for a given gas stream can be obtained simply and effectively without the need for large experimental efforts or costly system modifications until after an initial computational screening of perspective materials has been completed. While the current research effort will use natural gas, which is the world’s largest industrial gas separations application, to validate the MPTA, the tools gained through this effort can be applied to other gas separation effort.

Commentary by Dr. Valentin Fuster

Combustion Turbines Combined Cycles

2018;():V001T02A001. doi:10.1115/POWER2018-7129.

A series of experiments were performed on a vertical EV burner with a constant coflow air of 873 L /min to generate turbulent lean premixed flow in order to study the impact of the addition of Acetylene/Argon mixture to the liquefied petroleum gas (LPG) on the temperature field and flame structure. The fluidics mechanism was inserted at a fixed position inside the entry section of the EV burner assembly. The flow rates of fuel (LPG/C2H2/ Ar) and air were measured using calibrated rotameters. The different volume ratios of the fuel constituents (at a specified fuel flow rate) were admitted via three solenoid valves at the entry section of each stream prior to mixing and monitored using a labview program. The axial temperature profiles at different operating conditions were measured using a bare wire Pt-Pt -10% Rh (type S) thermocouple of wire diameter 250 μm. Flame images were obtained — before and after fluidics insertion — using a high resolution Canon 6D 20MP digital camera. The selection of the different considerated cases was based on flame stability. The experimental program aims at identifying and analyzing the changes in flame characteristics (flame length, axial profiles of mean gas temperature, NOx concentration and overall combustion efficiency) resulting from the insertion of fluidics while considering different proportions of the fuel constituents) (including pure LPG, as a reference case). In all experiments flame stabilization was ensured. The results obtained indicate the following: it was noticed that in most cases of pure LPG only, and other mixtures the images shows increase in both the length and luminosity of the flame as a result of higher degrees of swirl due to the fluidics insertion while the temperature profiles of the different flames were changed. It was indicated that NOx trend was decreased by 52% while the combustion efficiency was improved by 2.5%.

Topics: Turbulence , Flames
Commentary by Dr. Valentin Fuster
2018;():V001T02A002. doi:10.1115/POWER2018-7146.

Combined Cycle Gas Turbine (CCGT) power plant offer operators both environmental and economic benefits. The high efficiency achievable across a wide load range reduces both fuel costs and CO2 emissions to atmosphere. However, the scale of the power generation plays a major role in determining both cost and efficiency: a modern large centralized CCGT of 600MW output or more will have a full load efficiency in excess of 60% and a very competitive installed cost on a US$/kW basis. The smaller gas turbines required for distributed power applications are not optimized for combined cycle operation, with potential full load efficiencies of a combined cycle scheme ranging from a little over 40% to the high 50s depending on the power output of the gas turbine, the exhaust gas conditions and the plant configuration, while the installed cost is around twice that of a large centralized CCGT on a US$/kW basis.

The drawback of a conventional combined cycle plant design is the need for water, which is a scarce commodity in some regions. Air cooling of the CCGT plant can be used to reduce water consumption, but make-up water will still be required for the steam system to compensate for steam losses, blowdown etc.

While the lower exhaust gas temperatures of the smaller gas turbines impact the combined cycle efficiencies achievable, they do allow Organic Rankine Cycle (ORC) technology to be considered for an alternative combined cycle configuration. This paper compares both the capital and operating costs and performance of combined cycle power plants for distributed power applications in the 30MW to 250MW power range based on conventional steam and various different ORC configurations.

Commentary by Dr. Valentin Fuster
2018;():V001T02A003. doi:10.1115/POWER2018-7173.

The Kemper County Project has demonstrated Transport Integrated Gasification (TRIG™) at a 2-on-1 Integrated Gasification Combined-Cycle (IGCC) facility located in Kemper County, Mississippi. Kemper is the largest IGCC project in the world, the first to use lignite as fuel, the first to capture and sell CO2, and the first to produce multiple byproducts from initial startup. The facility features two Siemens SGT6-5000F gas turbines, each capable of operating on a high-hydrogen syngas produced in the Transport Gasifiers from locally mined lignite.

Using high-hydrogen syngas requires unique modifications to the combustion turbine design. Flame-diffusion combustors, rather than dry low-NOX designs, prevent flashback caused by the high hydrogen content of the syngas. Also, ports added to the turbine compressor casing allow air to be extracted from the compressor and used elsewhere in the plant, supplying up to one half of the air required by the gasifier.

The Kemper facility has achieved the integrated operation of both gasifiers, including the production of electricity from syngas by both combustion turbines. Turbine operation on the high hydrogen syngas was smooth both during normal operations and during transitions, with efficiencies meeting or exceeding expectations. This paper describes the Kemper plant design, focusing on the combustion turbine design unique to Kemper. The paper also discusses turbine design challenges specific to Kemper, provides an overview of the robust control scheme used on both syngas and natural gas co-firing operations, and provides preliminary operational and performance results, including inspection findings.

Commentary by Dr. Valentin Fuster
2018;():V001T02A004. doi:10.1115/POWER2018-7192.

Renewable energy has a significant role to play in helping the world achieve the greenhouse gas emission reduction necessary to achieve the pathway to a 2°C increase in global temperature. Electricity generation from wind and solar resources can contribute immensely to the decarbonization of power generation, but these resources are intermittent. High penetration of intermittent renewable power generation can cause grid stability and control issues for network operators, with fast response fossil fuel power plant necessary to provide security of supply and maintain grid stability. Increasingly natural gas-fueled distributed power generation is being installed to provide the necessary grid support.

However, hybrid power plants comprised of a fossil fuel power generating system, a renewable power generation system and energy storage can provide both the low CO2 electricity required to meet environmental constraints, and the despatchability and stability required by grid operators. Integrated Solar Combined Cycle Power Plants (ISCCs), comprising a Concentrated Solar Power plant and a natural gas fired combined cycle plant, have the potential to simultaneously reduce fossil fuel consumption, provide secure, highly predictable electricity generation, and reduce the cost of integrating renewable energy into a power system.

While a number of ISCCs have been built at a larger scale (above 150MW power output), the concept has rarely been adopted for smaller scale distributed power applications. In addition, the traditional ISCC concept uses a steam bottoming cycle, which consumes water, and often locations where distributed ISCC could be utilized suffer from a scarcity of fresh water.

This paper evaluates whether replacing the steam bottoming cycle with an Organic Rankine Cycle (ORC) alternative can provide a simpler, lower cost distributed ISCC solution that can be utilized on smaller and island grid systems, or mini- and micro-grids, to provide an affordable, water-free, low carbon power generation system.

Commentary by Dr. Valentin Fuster
2018;():V001T02A005. doi:10.1115/POWER2018-7328.

The method of specific entropy generation (SEG) is employed to show how the thermal efficiency of a combined cycle power plant can be improved. SEG is defined as the total entropy generation rate associated with the operation of a power plant per unit flowrate of the fuel burnt in the combustor. In a recent article published in Journal of Energy Resources and Technology, it is shown that the thermal efficiency of a gas turbine cycle inversely correlates with SEG. In this work, we extend the analysis to show that the same relation between the thermal efficiency and SEG is also valid for a combined cycle. The topping cycle consists of a compressor, a combustor and a gas turbine, whereas the bottoming cycle includes a heat recovery steam generator, a steam turbine, a condenser, a deaerator, a condensate pump and a feed water pump.

It is shown that the minimization of SEG is identical to the maximization of thermal efficiency. An illustrative example is presented using the SEG method to improve the efficiency of the combined cycle. The results reveal that 89% of the inefficiencies takes place in the gas turbine cycle. A modified design is then proposed to reduce the efficiency losses in the topping cycle. In the modified design, the thermal energy of the flue gases is first used in a heat exchanger to preheat the air before the combustor. The flue gases leaving the heat exchanger is then directed to the HRSG for producing steam. With this modification, the thermal efficiency and the power output of the combined cycle increase 2.7 percentage points and 20.9 kW per unit molar flowrate of the fuel. Recovering the thermal energy of the flue gases for both preheating the air and producing the steam appears to be more efficient than just producing the steam. Despite the net power production of the bottoming cycle decreases in the modified design, the overall efficiency of the combined cycle increases due to the improvement in the efficiency of the topping cycle.

Commentary by Dr. Valentin Fuster
2018;():V001T02A006. doi:10.1115/POWER2018-7551.

With the everlasting increase in the population, a huge surge in the electricity consumption can be noticed. Thus, the power and electricity generating power plants need to augment their performance to cope with this uprising problem. The main goal for most gas turbine power plants is to increase their efficiency and performance which can be achieved by increasing the turbine inlet temperature (TIT). However, increasing the TIT requires cooling of the turbine blades to extend its lifetime and avoid thermal stresses and oxidation rates. Usually, there are two routes to improve the turbine blade cooling, either scientist focus on the parameters that effect the cooling process such as the film cooling effectiveness, shape of holes and angle of injection, or the problem is approached from a thermodynamic point of view. It is well known that the air used to cool the turbine blades is bled from the compressor which causes a severe penalty on the thermodynamic efficiency and power output of the gas turbine. This paper main objective is to improve the gas turbine performance by lowering the temperature of the coolant lines bled from the compressor for turbine blade cooling resulting in a reduction in the amount of coolant mass flow rate required for turbine cooling which will reduce the penalty on the overall efficiency increasing it. For this purpose, three different configurations of Maisotsenko desiccant cooling systems were proposed to cool down coolant lines as well as the inlet air temperature. Optimization analysis was performed to determine the best operating parameters of the gas turbine as well as the cooling systems. Sensitivity analysis was conducted as well to investigate the effect of various variables on the gas turbine overall efficiency and the coolant mass flow rate. The results showed an increase in the overall efficiency from 42.57% to 43.83%, reduction in the amount of coolant mass flow rate that is bled from the compressor from 4.584 kg/s to 3.607 kg/s and in the cooling fraction from 4.72% to 3.9%.

Commentary by Dr. Valentin Fuster

Boilers and Heat Recovery Steam Generators

2018;():V001T03A001. doi:10.1115/POWER2018-7278.

Nitrogen oxide (NOx) emitted from boilers in coal-fired power plant may be reduced by 90 percent through the application of the selective catalytic reduction (SCR). However, the escaped ammonia from the SCR systems could react with sulfur oxides (SOx) in the flue gas to form ammonium bisulfate (ABS) in exhaust systems. The blockage and corrosion caused by ABS seriously impact the rotary air preheater (RAPH), which would not only increase operating cost on ash-blowing and cleaning but also lead to unplanned outage. To solve the problem, in this paper a novel preheater system is proposed. A single preheater is split into two sub-preheaters, between which the main flue gas flow is mixed with the recirculated flue gas from outlet of the lower-temperature preheater. After the mixing point, a reaction chamber and a precipitator are installed. A numerical finite difference method (FDM) is employed to model the RAPH and obtain the accurate temperature distribution of fluid and heat transfer elements. The initial formation temperatures of (NH4)2SO4 and ABS are 200 °C and 170 °C, respectively, according to the flue gas composition in this work. By calculation, this split design of the RAPH is believed to be effective in reducing deposition of ABS.

Topics: Design
Commentary by Dr. Valentin Fuster

Virtual Plant and Cyber-Physical Systems

2018;():V001T04A001. doi:10.1115/POWER2018-7315.

Energy based Cyber-physical systems (CPS) find their greatest popularity in smart grid applications, where a complex computational algorithm imparts “intelligence” to a supervisory control and data acquisition (SCADA) system used for balancing load distributions. In contrast to this static application of CPS technology, research conducted jointly by U.S. Department of Energy’s, National Energy Technology Laboratory (NETL) and Ames Laboratory proposes a new paradigm in which CPS is used as a core technology in energy system development, design, and deployment. The goal is to speed up the development and deployment of advanced concept power plants, reduce the cost and thereby encouraging private and public investment, and substantially reduce the risk of failure. The current technology development paradigm generally starts with models and bench-scale tests, leading to a pilot plant demonstration of the technology before construction of a commercial system. The concept proposed by NETL and Ames incorporates CPS before and during the construction of a pilot plant — arguably the highest risk part of implementing new energy technologies — and then extends the cyber physical infrastructure to the full-scale plant creating a fully functional and coupled digital twin. The creation of a cyber-physical platform as a part of the advanced energy system design and deployment has the potential to enable the “customization” of energy systems to meet local needs and resources. This will reduce cost and environmental impact of energy production and use. Examples of how the technology development process can be changed in the energy sector will be discussed using fuel cell turbine hybrids as an example.

Commentary by Dr. Valentin Fuster
2018;():V001T04A002. doi:10.1115/POWER2018-7346.

The emphasis on traditional control in power systems has traditionally focused on the application of first order transfer functions to develop gains in distributed PI or PID control. The application of traditional PI or PID control in fuel cell turbine hybrid power systems for setpoint tracking or disturbance rejection during transient operation has proved to be challenging because the interaction and nonlinearities. In this work, a systematic approach to specifying ideal gains for PID control was established and then applied to hybrid systems using the cyber-physical emulation facility at the National Energy Technology Laboratory. Through testing on hardware, it was proved that the control variable response to actuator modulation was not first order. By developing second order transfer functions to specify gains, the response of the system was predicted as expected by simulation. Testing of a hot air bypass valve to control fuel cell cathode airflow setpoint tracking and disturbance rejection was effectively demonstrated with response behaviors as expected, rise times under 3.5 seconds, and overshoot predicted for the underdamped case.

Commentary by Dr. Valentin Fuster
2018;():V001T04A003. doi:10.1115/POWER2018-7425.

Increased accuracy of solids flow meters can be achieved with sensor fusion; the combination of solids velocity measurement with other process sensors to define the process state of the solids while they flow. In a circulating fluidized bed aeration flow, temperature measurements, and pressure differentials are routinely measured to ensure stable process operations. These process measurements were used as input to real-time model of the standpipe where the velocity measurement was taken to determine the actual solids bed density. The model development and implementation are described with the objective of updating the measured flows continuously in real time. Real time optimization techniques use the pressure measurements for inferring voidage and apply the inferred values to estimate the pressure profile and aeration split. In essence, the approach becomes solving nonlinear least squares problem and closure of mass balance of gas in real time.

Commentary by Dr. Valentin Fuster
2018;():V001T04A004. doi:10.1115/POWER2018-7486.

The design of optimal control architectures and the optimal selection of controlled variables represents a critical task for maximizing the economic profitability of operating plants. Traditionally, controlled variables are selected based on heuristics or past experiences. For cyber-physical systems (CPS), where physical and virtual components can be integrated in the same unit to evaluate the dynamic response of innovative power cycles past experiences may not be available. Trial-and-error methods can be time-consuming and costly. Besides, the selected controlled variables may not be optimal from the economic perspective. A systematic approach to the selection of controlled variable for cyber physical systems is presented here. The method is applied to a solid oxide fuel cell (SOFC)-gas turbine (GT) CPS at the National Energy Technology Laboratory (NETL) in Morgantown, WV. The main result of this work is the synthesis of optimal controlled variable sets for a cyber physical system exhibiting trade offs between economics as well as controllolability of variables.

Commentary by Dr. Valentin Fuster

Plant Development and Construction

2018;():V001T05A001. doi:10.1115/POWER2018-7141.

Gas turbine engine prices vary widely. Any organisation planning to invest in a project involving the use of gas turbine engines, as prime mover, must perform a robust economic analysis to guide the organisations investment decisions. One major element that could greatly influence the outcome of an economic analysis, and eventual organisational decisions and planning, is gas turbine engine acquisition price.

This study applies artificial neural networks to estimate gas turbine engine price. A supervised network learning strategy has been adopted to train the network from a dataset of historical records of gas turbine engine performance parameters and engine price. Numerical gradient checking has been performed to validate the computed cost function with quantified similarity obtained in the order of 10−9. The challenge of neural network overfitting has been minimized by applying a regularization technique. As such, the developed network closes reflects real world observations. To validate the network predictions, the developed neural network has been used to estimate the price of known gas turbine engine units with 95% to 99.9% accuracy.

Commentary by Dr. Valentin Fuster
2018;():V001T05A002. doi:10.1115/POWER2018-7142.

In this paper, an economic model is presented for the evaluation of gas turbine total productive life cost and profitability. The model utilizes input from gas turbine engine performance, emissions and lifing models to provide quantitative information on the economic implications of an investigated system or investment option.

In this study, the proposed model is used to conduct economic analysis on a turbojet engine, repurposed for alternative profitable use in electrical power generation. Results from the analysis are compared against competitor units to determine the models economic feasibility, benefits and limitations over competitors. Results obtained from the investigation reveal that the repurposed unit is economically feasible and favours profitability at minimal investment costs, with least burden on consumers. At a discount rate of 2.5%, investing in the repurposed engine model offers an investment base 13% lower, NPV 6% higher and an LCOE 24% higher in simple cycle than in combined cycle operation.

Commentary by Dr. Valentin Fuster
2018;():V001T05A003. doi:10.1115/POWER2018-7466.

This paper attempts to quantify global development of coal- and natural gas-based power between 2003 and 2016 by analyzing the progression of individual coal and natural gas power units of 100 megawatts or greater as reported by S&P Global Platts. About 1,000 gigawatts (GW) of new coal capacity entered service worldwide in this period, nearly doubling the world coal power fleet. About 96% of this new capacity was built in 10 countries led by China and India. The momentum of global coal power development has slowed since 2014 with cancelled, deferred, or delayed capacity in 2016 more than quintupling that reported in 2013. This slowdown occurred mainly in China and India, where 426 GW of coal capacity were cancelled during 2015 and 2016, while only 26 GW was built. The vast majority of the new coal capacity built in Germany, Japan, and South Korea since 2003, and the majority in China since 2008, use supercritical or ultra-supercritical (USC) technologies. Subcritical technology still prevails among units constructed in developing countries, but USC units are being built in all the top 10 countries except the United States, where no new coal power plant is currently under construction.

Commentary by Dr. Valentin Fuster

Renewable Energy Systems

2018;():V001T06A001. doi:10.1115/POWER2018-7109.

The paper investigates the cavitation in micro-turbomachinery, using a small-sized water system. Unsteady numerical model is architected to predict cavitating flows through a 7.5 cm axial hydro-turbine working at 2.8 m water head. Based on the validated simulations, specific turbine designs (regular design and rim-drive turbines) are simulated with cavitating flow conditions including different rotation speeds (1000–5000 rpm) and outlet pressures (0, -24, -48, -96, kPa gage). Phase change interactions (liquid water and vapor) were considered by adding the physics models of Volume of Fluid (VOF) multiphase, cavitation, and Large Eddy Simulation (LES) turbulence. Records featured spatial variation in the cavitation pattern between the two designs. Rim-drive turbine stands against cavitation along the rim integration lines, but it starts the hub cavitation earlier than the regular turbine. The proposed rim-drive bests the regular geometry before cavitation, and the relative efficiency gap increased to be 16% at extreme cavitation condition.

Commentary by Dr. Valentin Fuster
2018;():V001T06A002. doi:10.1115/POWER2018-7159.

Totally enclosed air to air cooled (TEAAC) generator with IC6A1A6 (as per IEC 60034-6) cooling is a widely accepted generator cooling solution for squirrel cage induction generators (SCIG) used in wind power generation, where the generator has two cooling systems, internal and external. The internal cooling is a closed loop system, where a shaft mounted mechanical fan helps in recirculating air inside the generator, and transfers the heat from the generator into an air-to-air heat exchanger. The external cooling system is a separate ventilation system creating airflow from the nacelle through the heat exchanger and removing the heat outside the nacelle with the help of an electrical fan mounted near the non-drive end of the generator. Cooling improvement of generator and bearing windings for performance enhancement is a well known research topic in turbo-generation as well as wind energy. Various winding design effort has been made in past for efficient generator cooling for turbogenerator as well as for wind turbine generator. With the increasing demand of power output, winding and bearing temperature class reaching its limit. Challenge is to come up with a solution for improving the performance of generator in terms of reducing temperature experienced by windings and at the same time reducing the cost. Detailed testing has been done on a test turbine to compare results obtained from open ventilated solution IC3A1 (as per IEC60034-6) and IC6A1A6 cooling for the squirrel cage induction generator. Paper presents advantages in case of using IC3A1 cooling where temperature of windings reduced substantially in comparison with IC6A1A6 cooling. To avoid contamination led windings and bearings hotspots, presented IC3A1 cooling configuration uses a unique design with inlet duct, filters, outlet duct and wire mesh.

Commentary by Dr. Valentin Fuster
2018;():V001T06A003. doi:10.1115/POWER2018-7177.

In order to pursue superior cycle efficiency and lower power generation cost for the CSP plants, two S-CO2–Brayton–cycle–based power cycles with different utilization methods of the residual heat recover of the top S-CO2 Brayton cycle (SCBC) are investigated to seek alternatives to the stand-alone S-CO2 cycle as the power block of concentrated solar power plants. The residual heat released by the top S-CO2 cycle are either utilized to drive a LiBr absorption chiller (AC) for further chilling of the CO2 fluids exiting the precooler before entering the main compressor inlet temperature or recovered by an organic rankine cycle (ORC) for generating electricity. Thermo-economic analysis and optimization are performed for the SCBC–AC and SCBC–ORC, respectively. The results show that the thermal and exergetic efficiencies of the SCBC–AC are comparable with those of the SCBC–ORC in low pressure ratio conditions (PR<2.7) but are apparently lower than SCBC–ORC when PR is over 2.7. The LCOE of the CSP plant integrated with SCBC–AC is more sensitive to the change of PR. The optimal PR to maximum the cycle efficiency or minimize the plant LCOE for the SCBC–ORC is higher than that for the SCBC–AC, while the optimal recuperator effectiveness to minimize the LCOE of CSP plant integrated with SCBC–ORC is lower than that of SCBC–AC. The optimization results show that the thermo-economic performance of the SCBC–AC is comparable to that of the SCBC–ORC. Significant ηex improvement and LCOE reduction can be obtained by both the two combined cycles relative to the stand-alone S-CO2 cycle. The maximal ηex improvements obtained by the SCBC–ORC and SCBC–AC are 6.83% and 4.12%, respectively. The maximal LCOE reduction obtained by the SCBC-ORC and SCBC–AC are 0.70 ȼ / (kW·h) and 0.60 ȼ / (kW·h), respectively.

Commentary by Dr. Valentin Fuster
2018;():V001T06A004. doi:10.1115/POWER2018-7183.

Renewable energy is best utilized when partnered with energy storage to balance the variable supply with daily and seasonal grid demands. At the distribution level, in addition to meeting power demands, there is a need to maintain system voltage and reactive power / VAR control. Rotating machinery is most effective for VAR control at the substation level. This paper presents a patented MW-scale system that provides power from a hydrogen-oxygen-fueled combined cycle power plant, where the hydrogen and oxygen are generated from electrolysis using renewable wind or solar power. The steam generated from combustion is the working fluid for the power plant, in a closed loop system. Also presented is a discussion on a patented strategy for safe combustion and handling of hydrogen and oxygen, as well as how to use this combustion strategy for flame and post flame temperature control. Finally, a preliminary benefits analysis illustrates the various energy storage and distributed generation benefits that are possible with this system. Depending on the storage approach, energy storage — charge and discharge durations — of 4 to greater than 24 hours are possible, much longer than most battery energy storage systems. Benefits include not only peak shaving and VAR control, but also grid balancing services to avoid the “spilling” of excess renewable power when supply exceeds demand and fast ramping in the evening hours.

Commentary by Dr. Valentin Fuster
2018;():V001T06A005. doi:10.1115/POWER2018-7189.

As concentrating solar power technologies moves to maturity progressively, large-scale solar thermal power plants have gained increasing attention. The exergetic and exergoeconomic analyses allow indicating energy degradation of the component quantitatively and establishing the monetary value to all material and energy flows. Therefore, they have strong theoretical implications to the system optimization. A thermodynamic simulation model of a 50 MW parabolic trough solar power generation system and the related exergetic and exergoeconomic analyses were presented in this paper. The results of exergetic analysis showed that the component of the lowest exergy efficiency was solar field, and the efficiency only had approximate 22%. Moreover, the exergy efficiencies of thermal energy storage and power block were about 81% and 58% respectively. According to the exergoeconomic analysis, the exergoeconomic cost of electricity and output thermal energy of solar field and thermal energy storage varied respectively in the ranges of 0.1277–0.1322 $/kWh, 0.0427–0.0503 $/kWh, and 0.0977–0.1074 $/kWh when thermal energy storage capacity ranged from 4 hours to 12 hours.

Commentary by Dr. Valentin Fuster
2018;():V001T06A006. doi:10.1115/POWER2018-7195.

Offshore structures are subject to severe environmental conditions and require high operating and maintenance costs. At the design stage of an offshore structure, it is necessary to perform load analysis and to consider representative environmental conditions characterized by statistical models. However, many available joint distribution models of the environmental parameters can only describe the correlation of these parameters in a very restricted form. The use of simple probabilistic models without correctly addressing their correlation may lead to significant bias in the reliability analysis. Here, the correlation between three offshore environmental parameters including the significant wave height, wave peak period, and mean wind speed is described by copula. The copula density functions and theoretical derivations of copula correlation parameters using actual sea state data are provided for general applications of reliability analysis of offshore structures. Hindcast data of two representative sites are used to fit the best copula. The developed copula-based joint distribution can be used for accurate reliability analysis of offshore structures considering long-term fatigue loads and extreme responses.

Commentary by Dr. Valentin Fuster
2018;():V001T06A007. doi:10.1115/POWER2018-7213.

A numerical model was developed in the TRNSYS environment (a transient simulation software) for Tri-Sol, a novel three-in-one solar energy system that produces electricity, hot water, and daylight for commercial buildings, to simulate its annual performance in terms of the three useful energy streams. Even though this model was developed for Tri-Sol, it can also be used for calculating the annual performance of similar concentrating PV/thermal (PV/T) and daylighting systems for various geographical locations. The model simultaneously calculates the codependent electrical and thermal performances, and calculates the useful daylight harvested by the building. The model is versatile and flexible in that any configuration of the modeled system can be properly designed using by changing parameters and inputs inside of TRNSYS.

This model was used to predict the annual performance a single Tri-Sol PV/T module and a single Tri-Sol unit with five such modules as a function of its tilt and geographical location. Then, this model was used to compute the monthly performance of a Tri-Sol array for a 10,000 ft.2 building for varying geographical locations at a fixed tilt angle. These results show the utility and the power of the model for designing combined PV/T-daylighting solar technologies such as Tri-Sol.

Commentary by Dr. Valentin Fuster
2018;():V001T06A008. doi:10.1115/POWER2018-7221.

The ideal gas equation of state is defined for a theoretical gas composed of molecules that have perfect elastic collisions and no intermolecular interchange forces. However, it has been widely reported that such an ideal model may not be a realistic representation under certain circumstances, in particular when the compressibility factor (Z) is not close to unity, and the consideration of other equations of state (real models) is imperative.

This study investigates the effect of using different equations of state, namely, the van der Waals, Redlich-Kwong, and Peng-Robinson equations, in the ideal isothermal analysis of a rotary displacer Stirling engine with the most commonly used gases, helium and air. The results are obtained numerically considering two major SE applications (cryocooling and distributed power generation) and two sets of operating conditions, and plotted in the form of Pressure-Volume diagrams. The amount of work per cycle based on the ideal gas model is taken as reference to compare the results from other models. The data show that at low pressure or high temperature conditions (corresponding to low density), the ideal gas equation is suitable for both gases, and using different models has no significant impact in the overall analysis. Additionally, while the use of ideal gas model is rather practical and fast, implementation of other models necessitate intensive computational processes.

Commentary by Dr. Valentin Fuster
2018;():V001T06A009. doi:10.1115/POWER2018-7270.

In this work, a computational study on four different types of helically grooved absorber tubes namely, semi-circular, rectangular, trapezoidal, and triangular has been carried out for their possible application in parabolic trough solar collector. In order to conduct the work, absorber tube of 2 m length with 19 mm inner and 25 mm outer diameter is selected. Flow velocities have been calculated by fixing the Reynolds number of the flow as 4000 i.e., turbulent flow. A constant heat flux of 818.5 W/m2 is provided at the lower surface of the absorber tube, facing the reflector. The simulation is performed using the finite volume based tool ANSYS FLUENT 17.1. The standard k-ε RNG turbulence model is used for simulation. The values of friction factors for semi-circular, rectangular, trapezoidal, and triangular absorber tube are 0.0511, 0.0889, 0.0929, and 0.0352, respectively. Nusselt numbers for these tubes are calculated as 68.91, 65.69, 72.05, and 85.49. Hence, it can be concluded from the present study that the thermal performance of the absorber tube with triangular groove is superior to the other groove types. The pressure drop for the same tube is also lowest.

Commentary by Dr. Valentin Fuster
2018;():V001T06A010. doi:10.1115/POWER2018-7271.

A shell and tube heat storage (1 MJ) has been designed computationally to enhance the heat transfer rate from heat transfer fluid (HTF) to the storage media. Concrete and water are considered as the sensible storage material and HTF, respectively. The system can be used to store the solar energy in the day time, which will be available in the absence of sunlight. Finite element based software, named COMSOL Multiphysics, is used for the study. The parameters analyzed, are tube outside diameter, radial distances between the tubes, number of tubes and inlet temperature of HTF. After a simulation time of 3000s, the increase of tube diameter from 1.03 to 1.71 cm is found to increase the average storage bed temperature by 6.3%. For the radial distances between the tubes to be 6 cm, the stored energy is maximum. The stored energies for 5 and 4 cm are 2.4 and 12.4% less than 6 cm, respectively, after duration of 6000s. The average bed temperature reaches to the steady state condition at 5147s with 19 tubes, whereas, with 25 tubes it takes 30.2% less time. Finally, the shell and tube heat storage has been optimized for higher heat transfer rate.

Commentary by Dr. Valentin Fuster
2018;():V001T06A011. doi:10.1115/POWER2018-7291.

The synergy between solar photovoltaic (PV) systems and behind-the-meter battery storage to reduce utility costs in buildings has drawn increasing attention. This paper presents results of a case study involving an economic analysis of battery-supported PV systems for an existing two-story commercial building in Albuquerque, New Mexico under different utility rate tariffs. The building, with 17,430 ft2 conditioned area, has been modeled in a detailed building energy simulation program, and hourly building electricity demand data and electricity demand generated using Typical Meteorological Year 2 (TMY2) weather file. The effect of strategies leading to demand leveling and demand limiting have also been discussed. Parametric analysis using System Advisor Model (SAM) software has been performed to determine the optimal sizing of the PV and battery systems for the given electric demand profiles under the assumed utility rate tariffs which will result in largest net present value (NPV). The results have been found to be highly sensitive to the costs of the PV systems and battery packs. Under the assumed realistic circumstances, we find that the inclusion of a battery pack in either a new or existing PV system does not improve the NPV even when the cost of battery storage is reduced from its current $250/kWh down to an unrealistic $50/kWh.

Commentary by Dr. Valentin Fuster
2018;():V001T06A012. doi:10.1115/POWER2018-7311.

With renewable energy and wind energy in particular becoming mainstream means of energy production, the reliability aspect of wind turbines and their sub-assemblies has become a topic of interest for owners and manufacturers of wind turbines. Operation and Maintenance (O&M) costs account for more than 25% of total costs of onshore wind projects and these costs are even higher for offshore installations. Effective management of O&M costs depends on accurate failure prediction for turbine sub-assemblies. There are numerous models that predict failure times and O&M costs of wind farms. All these models have inputs in the form of reliability parameters. These parameters are usually generated by researchers using field failure data. There are several databases that report the failure data of operating wind turbines and researches use these failure data to generate the reliability parameters through various methods of statistical analysis. However, in order to perform the statistical analysis or use the results of the analysis, one must understand the underlying assumptions of the database along with information about the wind turbine population in the database such as their power rating, age, etc. In this work, we analyze the relevant assumptions and discuss what information is required from a database in order to improve the statistical analysis on wind turbines’ failure data.

Commentary by Dr. Valentin Fuster
2018;():V001T06A013. doi:10.1115/POWER2018-7312.

Access to both electricity and clean drinking water is challenging in many remote communities. A self-powered water disinfection system, currently under development, can potentially address this challenge. In the proposed design, energy from water flowing through the system is harnessed using a pico turbine (nominal output power of 60 W) and used to power an electrochemical disinfection process. The characteristics of turbines at the pico-scale (less than 5kW) required for this system are not well researched, and off-the-shelf designs are either too bulky or too inefficient for this application. This paper presents a model developed to evaluate a new class of efficient pico-scale Francis turbines for this water disinfection system. A computational fluid dynamics (CFD) model of the turbine was developed in ANSYS® CFX® 17.1. The CFD model exploits the rotational symmetry of the turbine and draft tube fluid regions to reduce the computational cost in terms of time and memory. The turbine model is coupled with models of the electric generator and electrochemical cell to determine the balanced operating points. When validated against experimental data, the combined model showed good predictive ability despite its low computational cost: the modeled turbine efficiency is within 5% of the measured values across the operating range of the device. The current turbine design has a hydraulic efficiency above 60 % in its operating range, which is high for a compact turbine at this scale. The combined model was used with a parameterized version of the turbine geometry to identify key performance sensitivities, particularly with the blade trailing edge angle. Turbine efficiency was improved by more than 2 % across the allowable flow rates. The low computational cost of the combined model made it well suited for iterative design optimization, supplanting the need for lengthy experimental trials. Overall, the modeling approach presented here shows good promise for use in picoturbine design.

Commentary by Dr. Valentin Fuster
2018;():V001T06A014. doi:10.1115/POWER2018-7336.

The small solar thermal power plant is being developed with funding from EU Horizon 2020 Program. The plant is configured around a 2-kWel Organic Rankine Cycle turbine and solar field, made of Fresnel mirrors. The solar field is used to heat thermal oil to the temperature of about 240 °C. This thermal energy is used to run the Organic Rankine Cycle turbine and the heat rejected in its condenser (about 18-kWth) is utilized for hot water production and living space heating.

The plant is equipped with a latent heat thermal storage to extend its operation by about 4 hours during the evening building occupancy period. The phase change material used is Solar salt with the melting/solidification point at about 220 °C. The total mass of the PCM is about 3,800 kg and the thermal storage capacity is about 100 kWh. The operation of the plant is monitored by a central controller unit. The main components of the plant are being manufactured and laboratory tested with the aim to assemble the plant at the demonstration site, located in Catalonia, Spain. At the first stage of investigations the ORC turbine will be directly integrated with the solar filed to evaluate their joint performance. During the second stage of tests, the Latent Heat Thermal Storage will be incorporated into the plant and its performance during the charging and discharging processes will be investigated. It is planned that the continuous filed tests of the whole plant will be performed during the 2018–2019 period.

Commentary by Dr. Valentin Fuster
2018;():V001T06A015. doi:10.1115/POWER2018-7374.

This paper presents the operating principle of a novel solar rotary crank-less heat engine. The proposed engine concept uses air as working fluid. The reciprocating motion is converted to a rotary motion by the mean of unbalanced mass and Coriolis effect, instead of a crank shaft. This facilitates the engine scaling and provides several degrees of freedom in terms of structure design and configuration. Unlike classical heat engines (i.e. Stirling), the proposed engine can be fixed to the ground which significantly reduce the generation unit cost.

Firstly, the engine’s configuration is illustrated. Then, order analysis for the engine is carried out. The combined dynamics and thermal model is developed using ordinary differential equations which are then numerically solved by Simulink™. The resulting engine thermodynamics cycle is described. It incorporates the common thermodynamics processes (isobaric, isothermal, isochoric processes). Finally, the system behavior and performance are analyzed along with studying the effect of various design parameters on operating conditions such as engine speed, output power and efficiency.

Commentary by Dr. Valentin Fuster
2018;():V001T06A016. doi:10.1115/POWER2018-7376.

Thermoacoustic technology potentially offers a sustainable and reliable solution to help address the continuing demand for electric power. Thermoacoustic devices, operating on the principle of standing or traveling acoustic waves, can be designed as a heat pump or a prime mover system. This technical strategy is environmentally friendly as it utilizes noble gases, or air, as the working fluid and does not directly produce harmful emissions. However, heating and cooling sources are required to create the required thermal gradient. Due to the inherit simplicity and limitation of moving components, thermoacoustic devices require little maintenance and have a forecasted long operational lifespan. This paper will present the design considerations necessary to construct a traveling wave thermoacoustic heat engine. The modeling, analysis, fabrication, and testing with integrated sensors will be discussed to offer insight into the capabilities and subtleties. A case study with system operation at 54 Hz and 7.8% thermal to acoustic efficiency will be presented.

Commentary by Dr. Valentin Fuster
2018;():V001T06A017. doi:10.1115/POWER2018-7378.

Solar trackers are rising in popularity; they benefit a wide range of applications since distributed solar energy generation can reduce electricity costs and support energy independence. In this paper, a simple solar tracking system is introduced. The system is a package unit that can be mounted on any solar panel. The system consists of an electrical motor connected directly to a sliding mass on a linear bearing. The electrical motor is controlled to slide the weight along the shafts in controlled steps. As a result, the photovoltaic panels are rotated automatically under the effect of controlled weight unbalance in fine angle increments to track solar trajectory without the need for traditional complex or costly mechanisms. Two light dependent resistors (LDR) sensors, mounted onto the surface of the solar photovoltaic panel, are exposed to solar irradiance and used to feed signals to a controller. A model of the solar tracking system is developed using ordinary differential equations, and numerically solved by MATLAB/Simulink™. The power consumption and tracking strategy of the proposed tracking system are estimated under realistic operating conditions (e.g. wind and brakes), and the power consumption is compared to the power generated by the photovoltaic panels. Optimum values for the sliding mass are suggested. Two photovoltaic modules are used to calculate the output parameters of the proposed tracking mechanism.

Commentary by Dr. Valentin Fuster
2018;():V001T06A018. doi:10.1115/POWER2018-7388.

Growing concerns about global warming and depletion of fossil fuel have resulted in exploring alternative energy solutions such as renewable energy resources. Among those, marine and hydrokinetic and in particular wave energy have drawing more interest. Ocean waves are predictable, less variable, and offer higher energy density values. As per National Oceanic and Atmospheric Administration (NOAA), North Carolina ranks 6th with total 484 km coastline length. In this work, six-year National Data Buoy Center (NDBC) wave data from five stations along the North Carolina shore including Wilmington Harbor, Mansonboro Inlet, Oregon Inlet, and Duck FRF (17 and 26 m) are collected. The wave parameters such as wave height and period are analyzed and the potential wave power density values are calculated. The power production from the resource is estimated using wave energy converters. Storing excess energy in the form of hydrogen can be used for a variety of applications. Hence, the cost-performance analysis using the cost per unit method is conducted to obtain the maximum and average hydrogen production from the studied site. The results will be useful to a wide range of development activities in both academia and industry.

Commentary by Dr. Valentin Fuster
2018;():V001T06A019. doi:10.1115/POWER2018-7389.

Wave Energy is a predictable and stable form of renewable energies. In this work, the wave energy potential along the North Carolina shore is calculated using six-year (2012–2017) National Buoy Database (NDBC). The wave data from two buoys (US 192 and US 430) were collected and the average significant wave height (HS) and corresponding time period (T) were determined. The Reference Model 3 (RM3) defined by Department of Energy (DOE) was used to explore the potential power generation from wave energy. Simulations were setup on WEC-Sim, an open-source code based on MATLAB developed by the DOE. A six-degree of freedom solver was used to obtain the results for heave and pitch forces for the float. Dynamic responses were calculated by solving equations of motion based on Cummins’ equation about the body center of gravity. Waves were modeled as irregular ocean waves using North Carolina shore wave data. The preliminary results obtained the heave and surge forces on RM3 and the body reaction forces. The results from this work can be used for determination of RM3 performance for NC shore.

Commentary by Dr. Valentin Fuster
2018;():V001T06A020. doi:10.1115/POWER2018-7391.

Our recent progress on studying wave interaction with a lift-type rotor is discussed in this paper. The particular focus is on characterization of the rotor’s unidirectional responsiveness in waves. The rotor consists of six hydrofoil blades in two sets. One blade set has three blades laid out as a vertical-axis wind turbine of the Darrieus type. The other blade set has three blades configured like a Wells turbine. In combination, the formed rotor can be driven by flows in any direction to perform unidirectional rotation about its vertically mounted shaft. This unidirectional responsiveness of the rotor also holds in waves, making the rotor a valuable device for wave energy conversion. For parametric study of the rotor, hydrofoil blades using different cross sectional profiles and chord lengths have been employed to configure the rotor. The rotor was then tested in a wave flume under various wave conditions in a freewheeling mode. Experimental results were analyzed and discussed. The yielded research findings will greatly enhance the fundamental understanding on the rotor performance in waves, and effectively guide the prototype rotor development for practical applications.

Topics: Waves , Rotors , Blades , Hydrofoil
Commentary by Dr. Valentin Fuster
2018;():V001T06A021. doi:10.1115/POWER2018-7397.

In this paper, a numerical simulation of three-dimensional motion of tether undersea kites (TUSK) for power generation is studied. TUSK systems includes a rigid-winged kite, or glider, moving in an ocean current in which a tethered kite is connected by a flexible tether to a fixed structure. Kite hydrodynamic forces are transmitted through the tether to an electrical generator on the fixed structure. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. In order to resolve the boundary layer near the kite surface, adequate grid resolution is needed which increases the computational run time drastically especially in 3D simulations. Therefore, in this study a slip boundary condition is implemented at the kite interface to accurately predict the total drag, with lower grid resolution. In order to reduce the numerical run times, a moving computational domain method is also used. A PID controller is used to adjuste the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases. A baseline simulation study of a full-scale TUSK system is conducted in which the expected cross-current, figure-8 motions during a kite reel-out phase is captured. The effect of the tether drag on the kite motion and resulting power output is also investigated and compared with the results of the baseline simulation.

Commentary by Dr. Valentin Fuster
2018;():V001T06A022. doi:10.1115/POWER2018-7405.

According to the World Health Organization, nearly 3 billion people burn wood, crop wastes, charcoal, coal and animal dung to meet their day to day energy needs and among these nearly 1.3 billion people do not have electricity access. More than 80% of the population suffering from energy poverty are living in rural areas of developing countries, such as in East Africa. On the other hand, the potential of renewable energy resources in East African countries is huge. However, such resources are usually intermittent and therefore the use of renewable energy sources to provide modern energy access with a good reliability level, for the remote locations with lack of energy access, is still an issue. With this regard, one of the emerging technologies to solve accessibility of energy in rural and remote areas is DC-microgrids. This paper assessed the use of off-grid systems in different developing countries and presents the results in improving energy access, especially in rural and remote locations. The results indicate that the experience of some Asian countries and Tanzania in East Africa could be a good example for other East African countries to invest in off-grid systems and address energy access problems in their rural and remote locations. On the other hand, there are challenges related to financing and lack of trained man power in East African countries.

Topics: Microgrids
Commentary by Dr. Valentin Fuster
2018;():V001T06A023. doi:10.1115/POWER2018-7428.

At present, the lithium-ion battery (LIB) is the most important candidate for electrical energy storage for different applications, including electric and hybrid vehicles and aircraft. Although many studies have been done so far to evaluate performance and durability of LIB cells and packs for vehicle application, there is no study for the application of LIBs in electric and hybrid aircraft. In this paper, the cycle life and calendar life of a typical aftermarket LIB are studied through an empirical modeling method. The degradation rate of the battery for a typical light-weight passenger aircraft with a flight range of less than 1000 km is presented. The real duty-cycle of the battery for this aircraft is used for the cycle-life analysis.

Commentary by Dr. Valentin Fuster
2018;():V001T06A024. doi:10.1115/POWER2018-7430.

To advance the utilization of the solar energy and coal resources as well as improve the flexibility of coal-based power plant, an improved solar-coal hybrid system for methanol production and power generation is proposed and thermodynamically analyzed. In the proposed system, the concentrated solar energy at high-temperature is used for heating the coal gasification to produce syngas for methanol synthesis; the waste material and heat from coal-to-methanol process are efficiently recovered in the conjunct power generation system; and the surplus electric power is optionally used for methanol synthesis by electrolysis process during the off-peak period. Through employing the proposed system, the solar energy and electricity (optional) could be effectively converted into methanol as stable chemical energy together with a preferable overall system thermal efficiency. The thermodynamic analysis results showed that, the overall energy and exergy efficiencies reaches 48.6 and 47.3%, respectively; the equivalent solar-to-methanol conversion efficiency can soar to 66.2%; and the net electricity-to-methanol efficiency reaches 61.6% with the power load reducing from 48.7% to 31.0%.

Commentary by Dr. Valentin Fuster
2018;():V001T06A025. doi:10.1115/POWER2018-7474.

Numerical models for the evaluation of cryo-adsorbent based hydrogen storage systems for fuel cell vehicles were developed and validated against experimental data. These models simultaneously solve the conservation equations for heat, mass, and momentum together with the equations for the adsorbent thermodynamics. The models also use real gas thermodynamic properties for hydrogen. Model predictions were compared to data for charging and discharging both MOF-5™ and activated carbon systems. Applications of the model include detailed finite element analysis simulations as well as full vehicle-level system analyses. The present work provides an overview of the compacted adsorbent MOF-5™ storage prototype system, as well as a detailed computational analysis and its validation using 2-liter prototype test system. The results of these validated computational analyses are then projected to a full scale vehicle system, based on an 80 KW fuel cell with a 20 kW battery.

This work is part of the Hydrogen Storage Engineering Center of Excellence (HSECoE), which brings materials development and hydrogen storage technology efforts address onboard hydrogen storage in light duty vehicle applications. The HSECoE spans the design space of the vehicle requirements, balance of plant requirements, storage system components, and materials engineering. Theoretical, computational, and experimental efforts are combined to evaluate, design, analyze, and scale potential hydrogen storage systems and their supporting components against the Department of Energy (DOE) 2020 and Ultimate Technical Targets for Hydrogen Storage Systems for Light Duty Vehicles.

Commentary by Dr. Valentin Fuster
2018;():V001T06A026. doi:10.1115/POWER2018-7476.

A well-designed battery management system along with a set of voltage and current sensors is required to properly measure and control the battery cell operational variables for Hybrid Electric Aircrafts (HEAs). Some critical functions of the battery including State-Of-Charge (SOC) and State-Of-Health (SOH) estimations, over-current, and over-/under-voltage protections are mainly related to current and voltage sensor measurements. Therefore, in case of battery faults occur in HEA, designing a reliable and robust diagnostic procedure is essential. In this study, for Li-ion batteries, a new and fast fault diagnosis technique via collecting data is proposed. Finally, the effectiveness of the proposed diagnostic method is validated, and the results show how overcharge, over-discharge and sensor faults can be accurately detected.

Commentary by Dr. Valentin Fuster
2018;():V001T06A027. doi:10.1115/POWER2018-7488.

Wind energy has become a dominant source of renewable energy during the past decade. Current hybrid wind turbines are primarily designed and manufactured based on a combination of aerodynamic properties for both Darrieus and Savonius turbines. In this work, the aerodynamic performance characteristics of a smart vertical axis wind turbine (VAWT) with an electro-magnetic switch mechanism for dis-/engagement mechanism is studied analytically and numerically. The proposed novel VAWT offers a high start-up torque by a Savonius turbine and high power coefficient values by a Darrieus turbine. The switch mechanism can further improve the system efficiency by running the turbines together or independently. The proposed hybrid VAWT was modeled as a combined Savonius-type Bach turbine and a 3-bladed H-Darrieus turbine. The hybrid turbine has a self-startup feature and reaches a coefficient of power (Cp) of over 40%. The turbine is also estimated to cover a wide operational range up to TSR 6. The follow on research phases of the project include studying the proposed smart VAWT experimentally and validating the results with those obtained through computational analysis.

Commentary by Dr. Valentin Fuster
2018;():V001T06A028. doi:10.1115/POWER2018-7525.

Based on a real-world scenario in Central America, this work is to plan and design a solar-powered microgrid for the rural communities who have had no access to electric power due to their distance from the grid as well as the mountainous terrain. The minimum spanning tree method is used to generate the initial grid topology and the difference between the results with and without the consideration of actual terrain effects is shown. The design of solar generation and energy storage has 3 options: a centralized solar park powering all communities, each community with a solar plant, and distributed generation at household level. Using dc power flow, we develop optimization algorithm to improve the solutions and compare the designs in terms of feasibility and resilience (against power congestion) or robustness (against structural damage). Through this case, it is demonstrated that our methodology can inform and assist the planning of solar-powered microgrids for remote communities.

Commentary by Dr. Valentin Fuster
2018;():V001T06A029. doi:10.1115/POWER2018-7538.

Renewable energy is one of the most promising solutions to energy shortage that may occur in the future particularly in remote areas. Solar cells suffer from the problem of high temperature, which reduces the electrical efficiency and operational life. In this study we investigate a new hybrid technique of cooling and voltage induction. A set of small generators installed on the back of a solar panel operating under the influence of heat and magnetic energy are called thermo-magneto-electric generators (TMEG). A modeling study was done using COMSOL Multiphysics5.2a (COMSOL) software as a package to simulate the physical states of the system. This study showed that a TMEG has the ability to improve the efficiency as a result of reducing the temperature. An induction voltage is also an output of the system and can be combined with the output of the solar panel composing the hybrid system.

Commentary by Dr. Valentin Fuster
2018;():V001T06A030. doi:10.1115/POWER2018-7548.

In this paper, the performance of Parabolic Trough Solar Collector (PTSC)-based power generation plant is studied. The effect of adding an Organic Rankine Cycle (ORC), and a Thermal Energy Storage (TES) system on the performance and financial metrics of the PTSC-power plant is investigated. Moreover, multiple organic working fluids for the ORC are compared in terms of the thermal and exergetic efficiencies, as well as the pumping power, and the most efficient fluid is selected. Further, the TES system is characterized by two-tank storage system with a storage period of 7 hours/24 hours. A yearly, monthly, and daily performance analyses are presented based on the Typical Meteorological Year (TMY) values for the city of Abu Dhabi, to study the improvement caused by the ORC and TES system. The simulation results show that Benzene is the most efficient organic fluid, as it showed the highest thermal and exergetic efficiency, and the lowest pumping power when compared to other organic fluids. In addition, the presence of the ORC increased the annual energy output of the power plant by 4%, while the addition of the TES increased the annual energy output by 68% and decreased the LCE by 29%. In the case where both the ORC and TES are added, the annual energy output increased by 72%, while the LCE decreases by almost 31%.

Commentary by Dr. Valentin Fuster
2018;():V001T06A031. doi:10.1115/POWER2018-7558.

The Wells turbine is a self-rectifying device that employs a symmetrical blade profile, and is often used in conjunction with an oscillating water column to extract energy from ocean waves. The effects of solidity, angle of attack, blade shape and many other parameters have been widely studied both numerically and experimentally. To date, several 3-D numerical simulations have been performed using commercial software, mostly with steady flow conditions and employing various two-equation turbulence models. In this paper, the open source code Open-FOAM is used to numerically study the performance characteristics of a Wells turbine using a two-equation turbulence model, namely the Menter SST model, in conjunction with a transient fluid solver.

Commentary by Dr. Valentin Fuster

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