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WTE Plant Operations and Retrofit Projects

2009;():1-11. doi:10.1115/NAWTEC17-2301.

The incorporation of municipal solid waste combustor (MWC) ash into bituminous pavements has been investigated in the United States since the middle 1970s. Thus far, most, if not all of these projects, have attempted to answer the questions: Is it safe? Is it feasible? Or does it provide an acceptable product? Polk County Solid Waste located in Northwest Minnesota has now completed three Demonstration Research Projects (DRP) utilizing ash from its municipal solid waste combustor as a partial replacement of aggregate in asphalt road paving projects. The results of these projects show no negative environmental or worker safety issues, and demonstrate improved structural performance and greater flexibility from the ash-amended asphalt as compared to conventional asphalt. Polk County has submitted an application to the Minnesota Pollution Control Agency (MPCA) to obtain a Case-Specific Beneficial Use Determination (CSBUD), which would allow for continued use of ash in road paving projects without prior MPCA approval. However, concerns from the MPCA Air Quality Division regarding a slight increase in mercury emissions during ash amended asphalt production has resulted in a delay in receiving the CSBUD. Polk County decided to take a different approach. In January 2008, Polk submitted and received approval for their fourth ash utilization DRP. This DRP differs from the first three in that the ash will be used as a component in the Class 5 gravel materials to be used for a Polk County Highway Department road rebuilding project. The project involves a 7.5 mile section of County State Aid Highway (CSAH) 41, which conveniently is located about 10 miles south of the Polk County Landfill, where the ash is stored. The CSAH 41 project includes the complete rebuilding and widening of an existing 7.5 mile paved road section. Ash amended Class 5 gravel would be used in the base course under the asphalt paving, and also in the widening and shouldering sections of the road. The top 2 inches of the widening and shouldering areas would be covered with virgin Class 5 and top soil, so that all ash amended materials would be encapsulated. This has been the procedure followed in previous projects. No ash will be used in the asphalt mix for this project. This paper discusses production, cost, performance and environmental issues associated with this 2008 demonstration research project.

Commentary by Dr. Valentin Fuster
2009;():13-18. doi:10.1115/NAWTEC17-2303.

The COUNCIL OF THE EUROPEAN UNION has enacted laws to improve the quality of the ambient air: The “COUNCIL DIRECTIVE 1999/30/EC of 22 April 1999 relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air” and the “DIRECTIVE 2008/50/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 21 May 2008 on ambient air quality and cleaner air for Europe”. The Member States had to bring into force the laws, regulations and administrative provisions necessary to comply with these Directives. These Directives are raising the expectations on the reduction of fine particulate matter on the potential emitters, mainly public traffic, industry and waste-to-energy (WtE) plants. Although there is currently no European regulation on stack emissions of fine particulate matter, local regulatory authorities have tightened the emission limits of total particulate matter. For example, quite a number of Italian WtE plants are expected to meet dust emission levels of less than 2 mg/m3 . In order to assure compliance strong efforts and large investments have been made to optimize the efficiency of their APC system. Different dust filtration technologies will be compared and the filtration principles of depth filtration and surface filtration will be detailed. A comparison of an experimental study and the practical performance of the different technologies are discussed. Special focus will be given to the development and application of High Efficiency Membrane Filter Laminates for retention of fine particulate matter. These filter materials consist of micro-porous expanded PolyTetraFluoroEthylene (ePTFE) membranes laminated onto suitable backing materials, retention rates of > 99.99% of PM2.5 have been achieved. A number of large European WtE plants have already completed their APC upgrades by using the High Efficiency Membrane Filter Laminates. Some of them are on operation for a couple of years, performance reviews will be detailed.

Commentary by Dr. Valentin Fuster
2009;():19-22. doi:10.1115/NAWTEC17-2319.

Steam or compressed air continue to be the typical cleaning mediums for long retractable (IK) sootblowers used to clean the convection section of the boiler. Advancements in steam/air nozzle technology have lead to improved cleaning in areas such as the secondary superheater, but due to issues with boiler tube erosion, advanced nozzles have not been routinely used in the convection section. Boiler tube erosion and the resulting forced outages due to tube leaks have consistently been an operational issue for many boilers. Sonic cleaning has offered the hope of cleaning without tube erosion, but cleaning results have been mixed. The energy created by sonic devices is more than an order of magnitude less than a sootblower jet and as a result have not been able to remove many types of deposits.

Topics: Pressure , Boilers
Commentary by Dr. Valentin Fuster
2009;():23-27. doi:10.1115/NAWTEC17-2321.

This paper discusses the retrofit injection of humid gas from sludge dryer with secondary air in the WTE furnaces in Québec City. In 1992, a municipal sludge treatment plant was added in the WTE building. Three sludge dryers, each connected to a furnace, were added. Direct contact with hot furnace gas was used to dry sludge in a rotary drum. Humid gas from the dryer was returned to the rear wall of the furnace just above the finishing grate. CFD modeling showed cold flow of humid gas on the rear furnace wall, restriction of the combustion area on the principal grate, and stratification of the flow inside the boiler. A retrofit of the first chamber of the boiler was designed using injection of humid gas from the sludge dryer with secondary air on the front and rear walls. The main purpose of the retrofit was to maintain CO levels of under 57 mg/m3 on a 4 hour mobile average. The first boiler was retrofitted in winter 2008 and results have been very encouraging.

Commentary by Dr. Valentin Fuster
2009;():29-35. doi:10.1115/NAWTEC17-2322.

In September of 2007, a new 636TPD Municipal Waste Combustor was brought on line at the Lee County WTE Facility in Fort Myers, FL operated by Covanta Energy. This unit was the first new Waste to Energy unit built in the United States in a number of years and included a lower permitted daily average NOx emissions requirement of 110ppm @ 7%O2 while maintaining ammonia slip to less than 10ppm. To meet this new stringent NOx emissions requirement, the boiler was designed with advanced combustion controls including Flue Gas Recirculation combined with a urea based Selective Non-Catalytic Reduction Process to provide a combined NOx reduction of approximately 70% while maintaining the required ammonia slip. The SNCR System provided by Fuel Tech was designed with 3 levels of seven wall injectors installed in the upper furnace. Both boiler load and Furnace Gas Temperature were used as a feed forward control with the CEM NOx signal as a feed back to automatically select the injector levels and reagent feed rates to maintain the targeted NOx while also maintaining ammonia slip control. This paper will outline the design considerations, the details of the process and the operation of the systems on this unit.

Commentary by Dr. Valentin Fuster
2009;():37-41. doi:10.1115/NAWTEC17-2334.

Waste-to-Energy boilers, including mass-fired, RDF-fired, and biomass-fired boilers, produce very corrosive and erosive environments which can significantly reduce the life of furnace, super heater, boiler, and in-bed tubes. Combustion products from municipal waste refuse are very corrosive. This corrosion is typically caused by chloride compounds which deposit on the furnace, superheater, and boiler tubes. Due to high flue gas velocities and soot blowing required to remove ash and slag deposits, and BFB media, these tubes are also subject to substantial erosion. Since 2000, Inconel weld overlays have been used for corrosion and erosion protection on boiler tubes. During this period, many other materials have also been tested in waste-to-energy boilers with mixed results. This paper will provide an overview of the materials that have been tested on in-bed, furnace, superheater, and boiler tubes in waste-to-energy boilers. The test results will be based on laboratory analysis used to evaluate these corrosion and erosion protection solutions. In addition, field results will be reviewed from various waste-to-energy sites to support the laboratory analysis.

Commentary by Dr. Valentin Fuster
2009;():43-62. doi:10.1115/NAWTEC17-2335.

Owners and operators of waste-to-energy (WTE) facilities have a keen interest in the performance of their facilities since it drives the overall success and cost effectiveness of their projects. There are a number of parameters that are commonly used to gauge the performance of a WTE facility and, in many cases, the contract operator. This paper compares historical data from a number of mass burn WTE facilities to establish benchmarks for various performance criteria. This paper also discusses how these benchmarks compare with performance standards that were used as the basis of design for the existing generation of mass burn WTE facilities and operating contracts and discusses how to set performance expectation levels for new projects.

Commentary by Dr. Valentin Fuster
2009;():63-69. doi:10.1115/NAWTEC17-2339.

Combustion of the municipal waste generates highly corrosive gases (HCl, SO2 , NaCl, KCl and heavy metals chlorides) and ashes containing alkaline chlorides and sulphates. Currently, corrosion phenomena are particularly observed on superheater’s tubes. Corrosion rates depend mainly on installation design, operating conditions i.e. gas and steam temperature and velocity of the flue gas containing ashes. This paper presents the results obtained using an innovative laboratory-scale corrosion pilot, which simulates MSWI boilers conditions characterized by a temperature gradient at metal tube on the presence of corrosive gases and ashes. The presented corrosion tests were realized on carbon steel at fixed metal temperature (400°C). The influence of the flue gas temperature, synthetic ashes composition and flue gas flow pattern were investigated. After corrosion test, cross section of tube samples were characterised to evaluate thickness loss and estimate corrosion rate while the elements present in corrosion layers were analysed. Corrosion tests were carried out twice in order to validate the accuracy and reproducibility of results. First results highlight the key role of molten phase related to the ash composition and flue gas temperature as well as the deposit morphology, related to the flue gas flow pattern, on the mechanisms and corrosion rates.

Commentary by Dr. Valentin Fuster
2009;():71-75. doi:10.1115/NAWTEC17-2363.

Babcock Power Environmental (BPE), a Babcock Power Inc. company, has developed a new, innovative, high-efficiency NOx reduction technology designed to greatly reduce the NOx emissions from waste to energy (WTE) boilers at relatively low cost. This “tail-end” system uses Selective Catalytic Reduction (SCR) to achieve the high reduction performance. Conventional SCR catalyst cannot be used in the traditional “high-dust” location, downstream of the economizer because constituents in the ash would poison the catalyst quickly, rendering it useless. Thus, the Regenerative Selective Catalytic Reduction (RSCR® ) system is designed to operate at the end of the plant before the flue gas is discharged to the stack. The process utilizes a reactant (usually aqueous ammonia) to be added to the flue gas stream upstream of the RSCR to reduce NOx to harmless reaction products, N2 and H2 O. The RSCR combines the efficient heat recovery, temperature control, reactant mixing, and catalyst into a single unit and provides the maximum NOx reduction and heat recovery practical. The paper will describe the overall predicted performance of a typical WTE boiler plant using this new technology. The paper will also provide actual operating data on the RSCR, which has been retrofitted to four biomass-fired units.

Commentary by Dr. Valentin Fuster
2009;():77-82. doi:10.1115/NAWTEC17-2364.

The paper will present available De-NOx technologies as well as the paper will present the operational experience in European countries where the technology has been operating for approx. 10–15 years. The experience is based on Ramboll’s experience with NOx control on advanced WtE plants in Europe. Technical SCR solutions will be discussed and specific technical obstacles and specific precautions to be taken will be highlighted and illustrated by showcases. Investment and operating costs for SNCR versus SCR will be presented. Finally it will be evaluated which effect De-NOx at WtE facilities will have compared to the energy sector in general.

Commentary by Dr. Valentin Fuster
2009;():83-87. doi:10.1115/NAWTEC17-2372.

Over the last two and a half years, Covanta Energy, working with their technology partner, Martin GmbH of Germany, has developed and commercialized a new technology for reducing NOx emissions from Energy from Waste (EfW) facilities. NOx levels below 60 ppm (7% O2) have been reliably achieved, which is a reduction of 70% below the current EPA standard and typical levels of today’s EfW facilities in the United States. This technology represents a significant step forward in NOx control for the EfW industry. The technology, known as VLN™, employs a unique combustion system design, which in addition to the conventional primary and secondary air streams, also features a new internal stream of “VLN™-gas,” which is drawn from the combustor and re-injected into the furnace. The gas flow distribution between the primary and secondary air, as well as the VLN™-gas, is controlled to yield the optimal flue gas composition and furnace temperature profile to minimize NOx formation and optimize combustion. The VLN™ process is combined with conventional, aqueous ammonia SNCR technology to achieve the superior NOx performance. The SNCR control system is also integrated with the VLN™ combustion controls to maximize NOx reduction and minimize ammonia slip. A simplified version of the process, known as LN™, was also developed and demonstrated for retrofit applications. In the LN™ process, air is used instead of the internal VLN™ gas. The total air flow requirement is higher than in the VLN™ process, but unchanged compared to conventional systems, minimizing the impact on the existing boiler performance and making it ideal for retrofit applications. Covanta first demonstrated the new VLN™ and LN™ processes at their Bristol, Connecticut facility. One of Bristol’s 325 TPD units was retrofitted in April of 2006 to enable commercial scale testing of both the VLN™ and LN™ processes. Since installing and starting up the new system, Bristol has operated in both VLN™ and LN™ modes for extended periods, totaling more than one year of operation at NOx levels at or below 60 ppm (7% O2). The system is still in place today and being evaluated for permanent operation. Based on the success of the Bristol program, Covanta installed LN™ NOx control systems in a number of other existing units in 2007 and 2008 (total MSW capacity of over 5000 TPD), and is planning more installations in 2009. All of these retrofits utilize the Covanta LN™ system to minimize any impacts on existing boiler performance by maintaining existing excess air levels. Going forward, Covanta is making the LN™ technology available to its existing client base and is working with interested facilities to complete the necessary engineering and design modifications for retrofit of this innovative technology. For new grassroots facilities, Covanta is offering the VLN™ system with SNCR as its standard design for NOx control. An additional feature, particular to VLN™, is the reduced total combustion air requirement, which results in improved boiler efficiency. This translates into increased energy recovery per ton of waste processed. In addition to introducing the VLN™ and LN™ processes, this paper will provide an overview of the Bristol development and demonstration project. NOx and NH3 slip data from Bristol will be presented, illustrating the extended operating experience that has been established on the system. Other operating advantages of the new technology will also be discussed, along with lessons learned during the start-up and initial operating periods. The VLN™ technology has been demonsrated to decrease NOx emissions to levels well below any yet seen to date with SNCR alone and is comparable to SCR-catalytic systems. The result is a significant improvement in NOx control for much less upfront capital cost and lower overall operating and maintenance costs. VLN™ also also goes hand in hand with higher energy efficiency, whereas SCR systems lower energy efficiency due to an increased pressure drop and the need for flue gas reheat. The commercialization of the VLN™ and LN™ processes represents a significant step forward in the reduction of NOx emissions from EfW facilities.

Commentary by Dr. Valentin Fuster
2009;():89-100. doi:10.1115/NAWTEC17-2373.

Great River Energy operates a waste-to-energy plant in Elk River, Minnesota. The plant burns 850 tons per day of refuse derived fuel (RDF) in three boilers, and its three steam turbines can produce 32 MW of electricity. In the largest of the three units, the No. 3 Boiler, steam generation was restricted by carbon monoxide (CO) and nitrogen oxides (NOx ) emission limits. The plant had an interest in improving the combustion performance of the unit, thereby allowing higher average RDF firing rates while staying within emissions compliance. The project was initiated by an engineering site visit and evaluation. The boiler had a history of unstable burning on the stoker grate, which required periodic natural gas co-firing to reduce CO levels. As an outcome to the evaluation, it was decided to install a new overfire air (OFA) system to improve burnout of combustible gases above the grate. Current and new OFA arrangements were evaluated via Computational Fluid Dynamics (CFD) modeling. The results illustrated the limitations of the original OFA system (comprised of multiple rows of small OFA ports on the front and rear furnace walls), which generated inadequate mixing of air and combustible gases in the middle of the boiler. The modeling illustrated the advantages of large and fewer OFA nozzles placed on the side walls in an interlaced pattern, a configuration that has given excellent performance on over 45 biomass-fired boilers of similar design upgraded by Jansen Combustion and Boiler Technologies, Inc. (JANSEN). Installation of the new OFA system was completed in April of 2008. Subsequent testing of the No. 3 Boiler showed that it could reliably meet the state emission levels for CO and NOx (200 ppm and 250 ppm, respectively, corrected to 7% dry flue gas oxygen) while generating 24% more steam than a representative five month period prior to the upgrade. This paper describes the elements that led to a successful project, including: data collection, engineering analyses, CFD modeling, system design, equipment supply, installation, operator training, and startup assistance.

Commentary by Dr. Valentin Fuster

Conversion Technologies and Climate Change

2009;():101-106. doi:10.1115/NAWTEC17-2310.

Taunton, Massachusetts (City) is a city of 55,000 people located in Southeast Massachusetts, approximately 35 miles from Boston. Currently it hosts a regional landfill that will reach capacity in 2013. Beginning in 2005, the City began the process of searching for a solid waste management technology to replace the landfill. The focus for the search has been on conversion technologies capable of recovering materials and producing electricity or fuels, and maximizing diversion of waste from landfilling. Technologies being considered include both traditional and emerging technologies; e.g., composting, co-composting, thermal gasification, aerobic and anaerobic digestion, hydrolysis and mechanical means of waste separation into useful products. Landfilling and traditional waste-to-energy technology are not being considered.

Commentary by Dr. Valentin Fuster
2009;():107-113. doi:10.1115/NAWTEC17-2316.

This presentation provides an overview of conversion technologies, their potential benefits and applicability to solid waste management, and the efforts to develop conversion facilities around the country and specifically, California, including Los Angeles County’s model for development. The Southern California Demonstration Project spearheaded by Los Angeles County is a unique project that proposes to develop up to four conversion technology demonstration facilities throughout Southern California, potentially the first of their kind anywhere in the U.S. These facilities will be collocated with material recovery facilities and will be designed specifically to process municipal solid waste residuals.

Commentary by Dr. Valentin Fuster
2009;():115-116. doi:10.1115/NAWTEC17-2318.

“Energy cost increases are expected to continue.... The impact of these energy cost increases on attractiveness of energy recovery could be significant.” “A number of new technological developments have been underway over the past few years that are now becoming available as full-scale systems and that are greatly expanding the opportunities for energy recovery from mixed municipal waste.” These sound like statements from today’s headlines or the latest marketing brochures reflecting the promise of emerging waste management technologies. The reality is that these statements were made over thirty years ago. Communities planning on implementing any new technology as part of their solid waste management program should proceed with caution. After all, the second quote above was followed by the following statement. “These systems have generally been developed by firms in private industry as new business ventures. Monsanto, Union Carbide, Devco, Garrett Research and Development (a division of Occidental Petroleum), Hercules, Black-Clawson, Horner-Schiffrin and Combustion Equipment Associates have been some of the most active firms.” Although many communities relied upon performance and financial guarantees offered by these companies, none of projects developed by them were successful. Similarly, there was a wave of optimism and projects that were implemented in the 1990’s involving numerous mixed municipal waste biological (i.e., composting) projects that also failed for economic or technical reasons. From these prior experiences, lessons can be drawn to assist communities evaluate the risks and rewards in procuring and contracting for today’s emerging technologies. The waste being delivered to these failed projects, unlike some of the salespersons, did not go away. These failed projects had to be redeveloped and replacement projects implemented to deal with the daily tide at the curb. A number of consultants, including the authors, started in the solid waste business redeveloping some of these failed initial efforts. From these prior experiences, lessons can be drawn to assist communities evaluate the risks and rewards in procuring today’s emerging technologies. New thermal conversion, pyrolysis, gasification, and bioconversion technologies are being proposed for projects throughout the U.S. based on experience in North America, Europe, the Middle East and Asia. Many communities have issued RFP’s to include emerging technologies in their integrated solid waste management systems. To successfully procure and finance a project involving one of these emerging technologies, the project sponsor or developer will need to: • Locate a politically suitable site for the project; • Acquire waste supply commitments; • Develop energy and material sales approaches and agreements; • Arrange for residue disposal; • Obtain permits to operate; and • Arrange for the financing. In addition to the above components, the efficacy of the technology and the financial backing provided by the technology supplier are critical to a successful project. Not unlike the early 1970’s and 1990’s companies are promoting the advantages and successful applications of new approaches to solid waste management. In doing so, some companies are asking communities to provide a suitable site (usually adjacent to or near an exiting permitted landfill or other solid waste management facility), supply waste, dispose of any residue, and assist in the permitting of a new project. The company may take the responsibility to arrange for energy and material markets, obtain the permits, and finance the project. The company’s objective is to develop a demonstration of their technology using mixed municipal solid waste, or a portion of the waste stream, in a U.S. community from which it can build its business. Before entering into long term obligations associated with such arrangements, it is important that a community consider the following: • How much will it cost to deliver waste to the new facility? • What impact will it have on the balance of the solid waste management system? • If the new system does not work, is there an alternative location, both in the short- and long-run to process/dispose of the waste? • If there are odor or other environmental problems that cannot be mitigated, is there a way to terminate the operation of the facility? • If the project does not succeed, will the company be responsible for razing the facility and returning a clean site? What other obligations will the company have? • What are the obligations of the community if the project does succeed? • What is the definition of success? • How long must the project be successfully demonstrated before it is converted into a fully commercial operation? • If this involves an expansion of the project, is the community obligated to proceed? This presentation compares and contrasts the experiences of the past with the current approaches being taken by firms promoting these technologies and communities implementing them in the hope of learning from our past.. Case studies will be discussed to support the conclusions and recommendations presented.

Commentary by Dr. Valentin Fuster
2009;():117-118. doi:10.1115/NAWTEC17-2330.

Renewed interest in waste-to-energy (WTE) has spurred a number of plans for facility expansions, retrofits and in several cases, new facilities. Complex federal and state regulations governing stationary air pollution sources challenge projects to develop and implement a compliance strategy that meets current and emerging regulatory requirements and which consists of commercially available and technically feasible control technologies, while managing the financial viability of the project. Past experience in the WTE industry is indicative of current challenges, and the deliberate development of WTE in the United States over the last 15 years now creates challenges when technologies developed and implemented elsewhere must be considered. One example is control of nitrogen oxides. Individual projects are subject to regulatory requirements differently, with net emissions increases, location and other attributes establishing the basis for regulatory compliance. This paper will discuss the complex New Source Review permitting requirements that typically apply to WTE projects, review commercially available air pollution control technologies, and discuss, through the use of a case study, the decision-making process used to develop the air pollution control strategy for the York County Resource Recovery Center expansion, one recent development of new WTE capacity in the United States.

Commentary by Dr. Valentin Fuster
2009;():119-120. doi:10.1115/NAWTEC17-2347.

The U.S. Environmental Protection Agency’s Office of Research and Development (US EPA ORD) has developed a “Municipal Solid Waste Decision Support Tool”, or MSW-DST, for local government solid waste managers to use for the life cycle evaluation of integrated solid waste management options. The MSW-DST was developed over a five year period (1994–1999) with the assistance of numerous outside contractors and organizations, including the Research Triangle Institute, North Carolina State University, the University of Wisconsin-Madison, the Environmental Research and Education Foundation, Franklin Associates and Roy F. Weston. The MSW-DST can be used to quantify and evaluate the following impacts for each integrated solid waste management alternative: • Energy consumption, • Air emissions, • Water pollutant discharges, • Solid Waste disposal impacts. Recently, the MSW-DST was used by the U.S. EPA to identify solid waste management strategies that would help to meet the goal of the EPA’s “Resource Conservation Challenge.” In this effort, ten solid waste management strategies were evaluated for a hypothetical, medium-sized U.S. community, with a population of 750,000 and a waste generation rate of approximately 3.5 pounds per person per day. (Table 1). The assumed waste composition was based on national averages. A peer-reviewed paper on this research was published in 2008 by the American Society of Mechanical Engineers (ASME).

Commentary by Dr. Valentin Fuster
2009;():121-135. doi:10.1115/NAWTEC17-2348.

Countless proposals for conversion technologies applied to municipal solid waste (MSW), such as gasification, many of which include mechanical processing of the MSW prior to the thermal conversion steps, have generated significant interest and press over the past few years. Many community groups and local officials are being pressured by developers to view these technologies as better and more politically acceptable alternatives to mass burn waste-to-energy facilities. From a historical perspective, most (but not all) of the basic technologies being promoted today are not new, but are variations of technologies that were evaluated and tested during the 1970s for use in processing and converting MSW. This paper presents overviews and several case studies of the MSW conversion technologies that were developed and tested during the 1970s including MSW processing and gasification technologies, and sets forth: • Lessons learned from those experiments. • Based upon the lessons learned, recommended rules of engagement for those contemplating evaluation or use of a processing and/or conversion technology. • A practical application of the above lessons learned and rules of engagement to the plasma arc gasification technology currently being promoted by a number of developers. The contents of this paper should be carefully considered by anyone contemplating the merits and feasibility of any MSW processing and/or conversion technology being promoted today or in the future.

Commentary by Dr. Valentin Fuster
2009;():137-143. doi:10.1115/NAWTEC17-2350.

Over the past 15 years, South Korea has been actively pursuing a sustainable waste management strategy, which includes the thermal treatment of non-recyclable waste. Over 18,000 tons/day of waste are thermally treated in South Korea in over 40 plants. Since municipalities are not allowed to export waste outside of their respective jurisdictions, plants range in size from 25 ton/day to over 500 tons/day. There are currently 7 plants on 6 sites using gasification technology in South Korea, with the first plant in operation since 2001. The purpose of this paper is to describe how the downdraft gasification technology works, integration of the technology into a complete energy from waste facility, operating history, availability, emission levels and lessons learned. Synopsis of the technology: Curbside Municipal Solid Waste (MSW) is rough shredded and fed into the primary chamber through an air lock. The gasification occurs in the low temperature negative pressurized primary chamber where the MSW goes through drying, pyrolysis and gasification stages. The resulting syn-gas is filtered through the char bed into a secondary chamber where combustion takes place, producing a hot inert flue gas. A Heat Recovery Steam Generator (boiler) is used to recover the thermal energy from the flue gas. The char at the bottom of the primary chamber is oxidized, creating the heat for the gasification process. The air pollution control system is located after the Boiler and consists of carbon and lime injection followed by a bag filter. Operating history, availability and emission levels are presented.

Commentary by Dr. Valentin Fuster
2009;():145-151. doi:10.1115/NAWTEC17-2356.

The environmental impact and potential for utilization of the billions of tons of used products and materials discarded each year by humanity is immense. The sheer magnitude of the materials and complexity of waste management and reuse make the issue of quantifying impacts and best practices all the more difficult. In recognition of this task, the Earth Engineering Center (EEC) of Columbia University and the Environmental Engineering Group of North Carolina State University combined resources in 2008 to form a research organization that is focused on defining and promoting best practices for sustainable waste management. This is the Center for Sustainable Use of Resources (SUR; wwwSURcenter.org) and its mission is to quantify the greenhouse gas emissions and other life cycle impacts of various “waste” management practices; and use this information for advancing the best practical means for managing used materials, in the U.S. and globally. The SUR Center builds on the strengths of past research at Columbia and North Carolina State on recycling, composting, waste-to-energy, and landfilling. This paper describes some of the research work completed and underway at the Center.

Commentary by Dr. Valentin Fuster

Innovative Projects and Management Practices

2009;():153-159. doi:10.1115/NAWTEC17-2320.

The maximum environmental benefits from a new Energy from Waste (EFW) facility may require locating the new plant close to both the source of the waste and the potential energy customers. This paper will present design features that were incorporated into several new EFW facilities to allow them to be located directly into urban environments while minimizing their impact on the community and often improving the quality of life for the surrounding communities. Locating the EFW facility directly into an urban community: • Minimizes the cost and the environmental impact of waste transport. • Allows electrical power to be generated at the point of consumption. • Provides thermal energy for district heating and cooling. • Reduces the dependence on imported fossil fuel for electrical generation and for heating / cooling. • Provides secure and well paying jobs for members of the community. • Reduces the carbon foot print of the community. • An EFW plant typically leads to higher recycling rate, both pre and post combustion. Some of the specific measures that have been considered for EFW plants in urban environment have included architectural enhancements, more stringent noise and odor control, significant reduction or even elimination of visible plumes. The two case studies included in this paper will be the new Isséane EFW plant in Paris and the recently awarded Riverside EFW plant in London.

Commentary by Dr. Valentin Fuster
2009;():161-163. doi:10.1115/NAWTEC17-2338.

After sixteen years of operation, it became apparent that the pit fire protection system installed during construction of the Spokane Regional Waste to Energy (WTE) Facility (1989–1991) was inadequate. A risk analysis was performed by Creighton Engineering Inc., a fire protection consulting firm, hired by the Spokane Regional Solid Waste System (Regional System) and Wheelabrator Spokane Inc. With input from Spokane County Fire District 10 and the City of Spokane Fire Department, a replacement supplemental fire protection system was designed and ultimately installed. This paper will describe the problems with the once state of the art fire system and the planning, design and installation of the new system.

Commentary by Dr. Valentin Fuster
2009;():165-166. doi:10.1115/NAWTEC17-2342.

The Mojave Desert and Mountain Recycling Authority is a California Joint Powers Authority (the JPA), consisting of nine communities in California’s San Bernardino County high desert and mountain region. In August 2008 the JPA contracted with Gershman, Brickner & Bratton, Inc. (GBB) to prepare the Victor Valley Resource Management Strategy (Resource Management Strategy). Working with RRT Design and Construction, Inc. (RRT), GBB prepared a coordinated forward-looking strategy to guide the JPA’s future program and facilities decisions. The Resource Management Strategy focused on the Town of Apple Valley, population 70,092, and the City of Victorville, population 107,408, the two largest JPA member communities, which have a combined total of more than 130,000 tons per year of material entering the JPA’s recycling system and the Victorville Landfill. The Resource Management Strategy is underpinned by a characterization of waste loads delivered to the Victorville Landfill. A visual characterization was carried out by RRT in September/October 2008. RRT engineers identified proportions of materials recoverable for recycling and composting among all loads collected from residential and non-residential generators for a full week, nearly 300 loads total. The JPA financed and manages the operations contract for the highly automated Victor Valley Material Recovery Facility (MRF). The MRF today receives and processes an average of 130 tons per day (tpd), five days per week, of single stream paper and containers and recyclable-rich commercial waste loads. The waste characterization indicated that as much as 80 percent of loads of residential and commercial waste currently landfilled could be processed for recycling and composting in a combination manual and automated sorting facility. Residue from the MRF, which is predominated by paper, would provide potential feedstock for an energy recovery project; however, the JPA has two strategies regarding process residue. The first strategy is to reduce residue rates from existing deliveries, to optimize MRF operations. An assessment of the MRF conducted by RRT indicated that residue rates could be reduced, although this material would continue to be rich in combustible materials. The second strategy is to increase recovery for recycling by expanding the recyclable-rich and organics-dense waste load deliveries to the MRF and/or a composting facility. The Resource Management Strategy provided a conceptual design and cost that identified projected capital and operations costs that would be incurred to expand the MRF processing system for the program expansion. Based on the waste composition analysis, residue from a proposed system was estimated. This residue also would be rich in combustible materials. The December 2008 California Scoping Plan is the roadmap for statewide greenhouse gas emission reduction efforts. The Scoping Plan specifically calls out mandatory commercial recycling, expanded organics composting (particularly food residue), and inclusion of anaerobic digestion as renewable energy. The Resource Management Strategy sets the stage for JPA programs to address Scoping Plan mandates and priorities. California Public Resources Code Section 40051(b) requires that communities: Maximize the use of all feasible source reduction, recycling, and composting options in order to reduce the amount of solid waste that must be disposed of by transformation and land disposal. For wastes that cannot feasibly be reduced at their source, recycled, or composted, the local agency may use environmentally safe transformation or environmentally safe land disposal, or both of those practices. Moreover, Section 41783(b) only allows transformation diversion credit (10 percent of the 50 percent required) if: The transformation project uses front-end methods or programs to remove all recyclable materials from the waste stream prior to transformation to the maximum extent feasible. Finally, prior to permitting a new transformation facility the California Integrated Waste Management Board is governed by Section 41783(d), which requires that CIWMB: “Hold a public hearing in the city, county, or regional agency jurisdiction within which the transformation project is proposed, and, after the public hearing, the board makes both of the following findings, based upon substantial evidence on the record: (1) The city, county, or regional agency is, and will continue to be, effectively implementing all feasible source reduction, recycling, and composting measures. (2) The transformation project will not adversely affect public health and safety or the environment.” The Resource Management Strategy assessed two cement manufacturers located in the high desert region for their potential to replace coal fuel with residue from the MRF and potentially from other waste quantities generated in the region. Cement kilns are large consumers of fossil fuels, operate on a continuous basis, and collectively are California’s largest source of greenhouse gas emissions. The Resource Management Strategy also identified further processing requirements for size reduction and screening to remove non-combustible materials and produce a feasible refuse derived fuel (RDF). A conceptual design system to process residue and supply RDF to a cement kiln was developed, as were estimated capital and operating costs to implement the RDF production system. The Resource Management Strategy addressed the PRC requirement that “all feasible source reduction, recycling and composting measures” are implemented prior to approving any new “transformation” facility. This planning effort also provided a basis for greenhouse gas reduction analysis, consistent with statewide initiatives to reduce landfill disposal. This paper will report on the results of this planning and the decisions made by the JPA, brought current to the time of the conference.

Commentary by Dr. Valentin Fuster
2009;():167-176. doi:10.1115/NAWTEC17-2343.

When local governments evaluate the environmental benefits and costs of alternatives for managing non-recyclable municipal solid waste, the relative costs of modern waste-to-energy (WTE) technology can be a significant stumbling block despite WTE technology’s environmental benefits. Although the preceding point is an important economic reality that has constrained WTE development in the United States, fortunately there is a highly effective means — the use of municipal solid waste “flow control” (or “facility designation”) authority — to overcome WTE’s perceived cost disadvantage. The relationship between flow control and WTE development, including significant encouragement for use of flow control as a result of the U.S. Supreme Court’s recent decision in United Haulers Association v. Oneida-Herkimer Solid Waste Management Authority, 127 S.Ct. 1786 (2007), is the focus of this paper, which will address the following topics: Policy Basis for Flow Control — Absent government intervention, management of municipal solid waste will seek the lowest cost (i.e., short-term cost) and frequently less environmentally protective alternatives. Flow control can counter the tendency to choose alternatives with lower short-term costs and at the same time facilitate implementation of the environmentally-preferable waste management alternatives a local government selects, such as WTE technology and other aspects of “integrated waste management.” Flow Control and the Courts — While the authority of a given local government to use flow control is grounded in state law, flow control also implicates matters that arise under federal law, such as Commerce Clause issues, given the possibility that solid waste regulation in one state can affect commercial interests in solid waste management in another state. Although concerns regarding claims of impact on interstate commerce prompted a negative Supreme Court response to flow control in C&A Carbone, Inc. v. Town of Clarkstown, 511 U.S. 383 (1994), the Court’s decision 13 years later in the Oneida-Herkimer case was in many ways just the opposite. WTE’s Correlation with Flow Control and Practical Guideposts — WTE development can be significantly advanced by the use of flow control. That conclusion is borne out by empirical data. The concluding portion of this paper addresses that topic as well as corollary issues, such as public-private collaboration for WTE development and other practical guideposts for implementing flow control ordinances.

Commentary by Dr. Valentin Fuster
2009;():177-180. doi:10.1115/NAWTEC17-2345.

Currently, over 70% of the non-hazardous solid waste generated in Ontario is disposed of in landfills. Approximately 45% of Ontario’s waste is disposed of in landfills located in Michigan. Disposal of residual waste in Ontario is undergoing a major shift. Pursuant to agreements made in 2006 between Ontario municipalities and federal and state representatives of Michigan, waste from Ontario municipalities will no longer be disposed in Michigan landfills post 2010. That has put enormous pressure on Ontario municipalities to seek alternative disposal solutions for the waste remaining after they reduce, reuse and recycle.

Commentary by Dr. Valentin Fuster
2009;():181-186. doi:10.1115/NAWTEC17-2346.

Oahu has special needs and requirements when it comes to dealing with solid waste on the island. The City and County of Honolulu has successfully addressed this problem in the past and is working on solutions for the future. Five percent of the island’s electrical power has been generated reliably from the 2000 tons per day of waste processed by their H-POWER Waste-to-Energy Facility. The facility has been processing waste for nearly twenty years and the volume of refuse going to the landfill is reduced by 90 percent. Honolulu is considering the best solutions for the island’s waste for the coming years. Waste-to-energy works in partnership with recycling to reduce the island’s increasing waste volumes. Recycling programs are in place and additional recycling measures are being considered. Landfill space is limited and questions exist regarding the ongoing use of the existing landfill and what will happen when it is closed. In an island setting, some alternatives available to other areas such as long haul to distant landfills are not available to bridge solid waste issues. Therefore practical solutions must be found and implemented in a timely manner. A number of initiatives and plans are in development. Measures are underway to prepare the H-POWER facility for future emission requirements and operation for the next twenty years. Steps have been taken toward expansion of the existing facility. Permitting and negotiations with agencies and utilities are under way. This paper will explore and expand upon these issues showing how they are interrelated to one another.

Commentary by Dr. Valentin Fuster

WTERT: Research and Technology Sessions

2009;():187-193. doi:10.1115/NAWTEC17-2304.

CarbonTech, LLC is the business vehicle to commercialize the licensed CATO Research Corporation process (US Patent No. 7,425,315) to generate an energy rich source of carbon from wastes such as municipal solid waste (MSW) and automobile shredder residue (ASR). With a focus on renewable energy technology, CarbonTech is in a unique position to reduce waste to landfills by 90%, generate a coal equivalent source of sustainable fuel to help reduce our dependence on fossil fuels, and recover metals for scrap recycling purposes.

Commentary by Dr. Valentin Fuster
2009;():195-203. doi:10.1115/NAWTEC17-2315.

Biomass is one of the most important sources of renewable energy. One aim of Biomass gasification is to convert a solid feedstock into a valuable syngas for electricity or liquid fuel production. Actual industrial auto-thermal gasification processes achieve a production of syngas mainly polluted by products such as dust, nitrogen oxides, sulfur dioxide and tars. Tars remain, one of the main drawbacks in using the gasification process since they are capable of condensing at low temperature. This could lead to fouling, corrosion, attrition and abrasion of downstream devices such as gas turbines or engines. Tars are often removed from the syngas, decreasing the internal energy of the syngas itself. These tars are heavy aromatic hydrocarbons whose treatment remains difficult by thermal, catalytic or even physical methods. They can condense or polymerize into more complex structures, and the mechanisms responsible for their degradation are not completely identified and understood. Turboplasma© is a thermal process, proposed by Europlasma. The main principle of operation relies on the use of thermal plasma for the cracking of tars inside a syngas produced in an auto-thermal gasification step. Basically, it consists of a degradation chamber where the syngas is heated by a plasma torch. The plasma plume provides a high temperature gas (around 5000K) to the system and enables heating of the incoming stream (above 1300K) and also generates high temperature zones (above 1600 K) inside the device. Due to both high temperature and long residence times of the syngas in the vessel, cracking of the tars occurs. Finally, the species released are mainly CO and H2 , leading to an increase in the Lower Heating Value of the syngas. The work presented here describes the design of a high temperature gasification system assisted by thermal plasma. It was performed using a CFD computation implemented with a full chemical model for the thermal degradation of tars. The objectives were to understand the aerodynamic behavior of the vessel and to propose enhancement in its design. We present here some results of this study.

Commentary by Dr. Valentin Fuster
2009;():205-206. doi:10.1115/NAWTEC17-2317.

In recent years, Covanta Energy has successfully executed contracts with two Florida communities, Hillsborough and Lee County, to construct 50% processing capacity expansions to the existing 1200 TPD solid waste energy recovery facilities Covanta originally built and currently operates for each of these communities. Under new Service Agreements that commence following the completion of each expansion project, Covanta will continue to meet operating, maintenance and environmental performance standards established with Lee and Hillsborough Counties for these expanded facilities for another 10 and 20 years, respectively.

Commentary by Dr. Valentin Fuster
2009;():207-216. doi:10.1115/NAWTEC17-2328.

The amount of municipal solid waste is still increasing and the calorific value of the waste is steadily growing. The combined result is an increasing demand for new thermal treatment capacities. An alternative solution to new waste-to-energy projects is an expansion and technical upgrade of existing incineration plants. This is an advantageous option for waste management companies because they avoid the NIMBY syndrome and the difficulties in getting permits for green field projects. Furthermore, the investment cost per tonne burned waste is less than that for a new incineration line. This paper will present the basic ideas and principles used in upgraded projects. The core of the technology is a combination of a new furnace design, new water cooled wear zones and combustion grates and new control systems. Moreover, CFD modelling is an important tool in the design phase, and the paper gives a demonstration of the flow design process applied at Babcock & Wilcox Vo̸lund. CFD gives the designer the possibility of checking the design for a large number of critical factors such as velocities, mixing of combustion products and secondary air, oxygen and CO concentration, temperature, surface temperature, corrosion etc. This ability is extremely valuable in the case of expansion of existing incineration plants because many of the process parameters have to be within the limits of the old plant.

Commentary by Dr. Valentin Fuster
2009;():217-221. doi:10.1115/NAWTEC17-2340.

A large amount of paper is recycled in China, that generates a significant amount of sludge and residue during the paper production process. Energy recovery by means of combustion in Waste-to-Energy (WTE) plants can be a possible candidate for sludge elimination. Currently, two incineration methods, distinguished as either direct incineration of partially dewatered sludge (generally 80% water content) or dried sludge incineration (dried to about 40% water content), are available. Research on comparison of fixed cost, operating cost and pollutant emissions between the two systems is presented. Fixed cost and steam consumption increase for the dried sludge incineration system though this method possesses many advantages, these include the decrease in consumption of auxiliary coal, service power and flue gas purificants. Moreover, main pollutant emission, such as SO2 and NOx , is significantly reduced. Chinese WTE managing regulations recommend no less than a 4:1 weight ratio of waste to auxiliary fuel fed into the incinerator. For a partially dewatered sludge direct incineration system, this weight ratio is about 5:1. However it reduces to 3.6:1 in a dried sludge incineration system. This is offset by a decrease in consumption of auxiliary coal and the overall weight ratio based on the entire plant increases to 7.5:1. The result suggests not only the technical and economic feasibility of a dried sludge incineration method, but also the feasibility of adopting the weight ratio of waste to auxiliary fuel based on entire WTE plant in the future regulation in China.

Commentary by Dr. Valentin Fuster
2009;():223-230. doi:10.1115/NAWTEC17-2344.

The Air Force Research Laboratory, Airbase Technologies Division (AFRL/RXQ) is engineering and evaluating the Transportable Waste-to-Energy System (TWES). This trailer mounted system will convert military base waste and biomass waste streams to useful heat and power. The Department of Energy (DOE) Federal Energy Management Program (FEMP) is a TWES funding partner. The first stage of the project is a suspension-type combustor (furnace). The furnace has been built and tested. A key feature of the furnace system is its unique patented combustion coil design. The design is intended to maximize ablative heat transfer by increasing particle residence time near a radiant ignition source. The innovative features of the design are targeted at ensuring that the system can be highly fuel-flexible to convert a variety of biomass and other waste streams to energy while demonstrating very low emissions. In 2008, the unit underwent two days of emissions stack testing using established Environmental Protection Agency (EPA) testing protocols. During the testing, extensive real-time data were also collected. This paper presents the data and corresponding analysis of the recent emissions testing performed while utilizing dry wood chips as a control fuel. Detailed emission comparisons are presented using publicly available information from commercial units and from a similarly sized experimental system for small biomass combustion. Key combustion efficiency factors, such as carbon monoxide emissions and nitrogen oxide emissions are presented. The authors also provide commentary on the results for next generation units and the use of this mode of energy conversion for small scale systems.

Commentary by Dr. Valentin Fuster
2009;():231-236. doi:10.1115/NAWTEC17-2351.

The Municipal Solid Waste (MSW) gasification process is a promising candidate for both MSW disposal and syngas production. The MSW gasification process has been characterized thermo-gravimetrically under various experimental atmospheres in order to understand syngas production and char burnout. This preliminary data shows that with any concentration of carbon dioxide in the atmosphere the residual char is reduced about 20% of the original mass (in an inert atmosphere) to about 5%, corresponding to a significant amount of carbon monoxide production (0.7% of CO was produced from a 20mg sample with 100ml/min of purge gas at 825°C). Two main steps of thermal degradation have been observed. The first thermal degradation step occurs at temperatures between 280∼350°C and consists mainly of the decomposition of the biomass component into light C1–3 -hydrocarbons. The second thermal degradation step occurs between 380∼450°C and is mainly attributed to polymer components, such as plastics and rubber, in MSW. The polymer component in MSW gave off significant amount of benzene derivatives such as styrene. In order to identify the optimal operating regime for MSW gasification, a series of tests covering a range of temperatures (280∼700°C), pressures (30∼45 Bar), and atmospheres (100% N2, 0∼20%CO2 +Bal. N2 with/without steam) have been done and the results are presented here.

Commentary by Dr. Valentin Fuster
2009;():237-243. doi:10.1115/NAWTEC17-2358.

Chemical rate and heat transfer theory indicates that the combustion performance and productivity of a moving grate waste-to-energy boiler should be enhanced by means of pre-shredding of the MSW, thus reducing the average particle size, homogenizing the feed, and increasing its bulk density by an estimated 30%. However, the capital, operating and maintenance costs of the shredding equipment should be low enough so that existing or new WTE facilities consider pre-shredding of the MSW. In cases where MSW is transported to a central WTE from a number of Waste Transfer Stations (WTS), pre-shredding may take place at the WTS, thus increasing density and decreasing transportation costs. This is a mechanical engineering study that examined the evolution and present state of shredding equipment since 1994 when the last WTE shredder in the U.S. was installed at the SEMASS facility. The quantitative benefits realized through the pre-processing of MSW by means of modern shredding equipment are evaluated both for the traditional high speed hammermills and the new generation of low-rpm, high-torque shredders. The combustion characteristics of shredded MSW were analyzed and compared to those of the “as-received” material that is presently combusted in mass burn WTEs. The emphasis of the project has been on equipment that can be integrated in the traditional flowsheet of a WTE and serviced readily. The most important criterion in the final design will be that the economic and energy benefits of pre-shredding be clearly greater than the conventional operation of combusting as received MSW.

Commentary by Dr. Valentin Fuster
2009;():245-251. doi:10.1115/NAWTEC17-2366.

The dominant waste-to-energy technology is combustion of “as-received” municipal solid wastes (MSW) on a moving grate. By far, the largest cost item in the operation of such plants is the repayment of the initial capital investment of $600 to $750 per annual metric ton of capacity which results in capital charges of $60–75 per ton of MSW processed. On the average, such plants generate about 650 kWh of electricity per metric ton of MSW combusted. Therefore, on the basis of 8,000 hours of operation per year (90% availability), the capital investment in WTE facilities ranges from $7,500 to $9,000 per kW of electric capacity. This number is three times higher than the present cost of installing coal-fired capacity (about $2,500 per kW). Of course, it is understood that WTE plants serve two purposes, environmental disposal of solid wastes and generation of electricity; in fact, most WTE plants would not exist if the fuel (i.e. the MSW) had to be paid for, as in the case of coal, instead of being a source of revenue, in the form of gate fees. However, the question remains as to why WTE plants are much more costly to build, per kWh of electricity generated, than coal-fired plants, even when the coal supply is lignite of calorific value close to that of MSW (about 10 MJ/kg). This study intends to examine the possible contributing causes, one by one, in the hope that the results may lead to the design of less costly WTE plants. Some of the factors to be examined are: Feed-stock handling; heat generation rate per unit volume of combustion chamber; heat transfer rate per unit area of boiler surfaces; % excess air and, therefore, volume of gas to be treated in Air Pollution per kW of electricity; differences in gas composition and high temperature corrosion in boiler that limit steam temperature and pressure and thus thermal efficiency; cost of APC (air pollution control) system because of the need to remove volatile metals and dioxin/furans from the process gas; and the handling of a relatively large amount of ash. In seeking the answers to the above questions, the study also compares the operational performance characteristics and engineering design of various existing WTE plants. This study is at its very beginning and it is presented at NAWTEC 17 in the hope of generating useful discussion that may lead to significant improvements in the design of future WTE facilities. The WTEs built in the U.S. until 1995 were designed for efficient and environmentally benign disposal of MSW, with energy recovery being a secondary consideration. There have been three principal changes since then: (a) the capital cost of WTEs, per daily ton of capacity has doubled and in some cases nearly tripled, (b) energy recovery per unit of carbon dioxide emitted has become an important consideration, and (c) the price of renewable electricity has increased appreciably. All these three factors point to the need for future WTEs to become more compact, less costly to build, and more energy-efficient. It is believed that this can be done by combining developments that have already been tested and proven individually, such as shredding of the MSW, higher combustion rate per unit surface area of the grate, oxygen enrichment, flue gas recirculation and improved mixing in the combustion chamber, superior alloys used for superheaters, and steam reheating between the high-pressure and low-pressure sections of the steam turbine. For example, oxygen enrichment is practiced at the Arnoldstein, Austria, WTE where parts of the primary air stream are enriched between 23% and 31% oxygen; steam reheating has been proven at the Waste Fired Power Plant of AEB Amsterdam where electricity production for the grid has been increased to over 800 kWh per ton MSW.

Commentary by Dr. Valentin Fuster
2009;():253-258. doi:10.1115/NAWTEC17-2367.

Flow, mixing, and, size segregation of Municipal Solid Waste (MSW) particles on the traveling grate of a mass-burn waste-to-energy (WTE) combustion chamber is analyzed for understanding those parameters that control the combustion processes and for designing the chamber. In order to quantify these phenomena, a full-scale physical model of the reverse acting grate was built and used for investigating the effects of the motion of the reverse acting grate under a MSW packed bed with tracer particles ranging from 6 – 22 cm in diameter. Based on these experimental data, a stochastic model of MSW particle within the packed bed on a traveling grate was applied for simulating the MSW particle behavior. The result shows that the motion of the traveling grate, whose speed ranged from 15 to 90 reciprocations/hour, increases the mean residence time of small and medium particles by 68% and 8%, respectively, while decreasing the mean residence time of large particles by 17%. This is because of size segregation of particles known as the Brazil Nut Effect. When the ratio of particle diameter to the height of moving bar, d/h, increases from 0.46 to 1.69, the mixing diffusion coefficient, De at 60/hour., decreases from 96 to 38.4. This indicates that the height of the moving bars should be greater than the diameter of targeted particles.

Commentary by Dr. Valentin Fuster
2009;():259-262. doi:10.1115/NAWTEC17-2375.

In a large-scale pilot plant, studies on wet-mechanical treatment of bottom ash using the SYNCOM-Plus process were carried out by MARTIN GmbH in the SYNCOM waste-to-energy plant in Arnoldstein, Austria (approx. 11000 kg/h waste throughput). Granulate of > 2 mm and fine fraction of < 5 mm were produced by dry screening, washing and wet screening. Additionally, sludge was separated from the wash water. The fine fraction and sludge as well as the boiler ash were recirculated into the furnace. In conclusion, the SYNCOM-Plus process meets all requirements which need to be complied with in an optimized and effluent-free commercial residue treatment process for the recovery of industrial products. This paper documents successful continuous operation of the SYNCOM-Plus process in direct connection with bottom ash discharge as well as the effects on combustion, flue gas composition and residue qualities.

Commentary by Dr. Valentin Fuster
2009;():263-271. doi:10.1115/NAWTEC17-2381.

Mid 2007 the Amsterdam Waste and Energy Company (AEB) commenced initial operations of their new Waste Fired Power Plant© (WFPP). The unit processes 530,000 metric tons of unsorted municipal solid waste producing electricity with a net efficiency of 30%. (Picture 1)The major contributor to the efficiency increase from the conventional 22% to 30% is a new and patented technology, whereby steam from the high pressure turbine is reheated by steam, rather than flue gas, before entering the low pressure turbine. The WFPP facility has operated successfully throughout 2008 and to this date. Also, for a period of nearly three years, AEB operated a commercial scale pilot plant, with a maximum capacity of 50 tons per hour, to develop the necessary process steps, to recover ferrous, non-ferrous, as well as precious metals from the bottom ash. In this recycling process, heavy metals and other toxicants are removed from the ash, rendering it suitable as a raw material for use in building materials, leaving less than 5% material to be landfilled. The operating results of both experiences are presented in this paper.

Commentary by Dr. Valentin Fuster

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