Current Status of Global WTE

This paper is based on data compiled in the course of developing, for InterAmerican Development Bank (IDB), a WTE Guidebook for managers and policymakers in the Latin America and Caribbean region. As part of this work, a list was compiled of nearly all plants in the world that thermally treat nearly 200 million tons of municipal solid wastes (MSW) and produce electricity and heat. An estimated 200 WTE facilities were built, during the first decade of the 21st century, mostly in Europe and Asia. The great majority of these plants use the grate combustion of as-received MSW and produce electricity. The dominance of the grate combustion technology is apparently due to simplicity of operation, high plant availability (>90%), and facility for training personnel at existing plants. Novel gasification processes have been implemented mostly in Japan but a compilation of all Japanese WTE facilities showed that 84% of Japan’s MSW is treated in grate combustion plants. Several small-scale WTE plants (<5 tons/hour) are operating in Europe and Japan and are based both on grate combustion and in implementing WTE projects. This paper is based on the sections of the WTE Guidebook that discuss the current use of WTE technology around the world. Since the beginning of history, humans have generated solid wastes and disposed them in makeshift waste dumps or set them on fire. After the industrial revolution, near the end of the 18th century, the amount of goods used and then discarded by people increased so much that it was necessary for cities to provide landfills and incinerators for disposing wastes. The management of urban, or municipal, solid wastes (MSW) became problematic since the middle of the 20th century when the consumption of goods, and the corresponding generation of MSW, increased by an order of magnitude. In response, the most advanced countries developed various means and technologies for dealing with solid wastes. These range from reducing wastes by designing products and packaging, to gasification technologies. Lists of several European plants are presented that co-combust medical wastes (average of 1.8% of the total feedstock) and wastewater plant residue (average of 2% of the feedstock).

Comparison of Environmental Performance Expectations: Gasification Versus Mass-Burn WTE Facilities Currently Under Construction in North America

In recent years, factors including limited landfill capacity, increasing costs of fossil fuels, and increased pressure to actively recover value from waste in the form of materials and energy have encouraged municipalities throughout North America to advance waste management strategies that utilize waste-to-energy (WTE) technologies as an alternative to landfilling. Currently, utilization of alternative conversion technologies, including gasification, is limited to small-scale or pilot municipal solid waste (MSW) to energy facilities in North America. Though limited history of environmental performance when using MSW as a primary feedstock has delayed public acceptance of facility proposals, municipalities are now moving forward with alternative conversion technology applications. In Florida, two entities have received permits from the Department of Environmental Protection to proceed with construction of gasification facilities — Geoplasma, Inc. in St. Lucie County, and INEOS New Planet BioEnergy in Vero Beach. In Edmonton, Alberta, Canada, Enerkem GreenField Alberta Biofuels has received a permit from Alberta Environment to begin construction of a gasification facility that will produce bioethanol from post-recycled MSW. Since 1996, no new greenfield MSW-processing mass burn facility has been constructed in the U.S., though facilities in Hillsborough County, FL; Lee County, FL; and Olmstead County, MN have undergone expansions, and in Honolulu, FL, a 900 TPD unit is currently under construction. In recent years, two municipalities have received permits to proceed with construction of mass burn WTE facilities and have made significant progress toward implementation: The municipalities of Durham and York, Ontario, Canada and The Solid Waste Authority of Palm Beach County, Florida. This paper will provide a direct comparison of the expected environmental performance of the recently permitted gasification facilities to the expected environmental performance of the recently permitted mass burn WTE facilities, as established by permit applications and emissions modeling studies. Comparison of emissions of particulate matter, sulfur dioxide, nitrogen oxides, carbon monoxide, volatile organic compounds, and hydrogen chloride will be performed on the basis of one ton of feedstock processed. Emission of these pollutants at the recently permitted facilities discussed above will be contrasted with emissions experienced at currently operating WTE facilities within North America.

Rapid Growth of WTE in China: Current Performance and Impediments to Future Growth

China has the largest population (1.33 billion) on Earth and a 2010 GDP of $5.4 trillion. This nation has experienced rapid economic growth in the last decade that has been accompanied by the generation of an enormous amount of municipal solid wastes. From 2000 to 2009, the reported MSW increased by 33% to 157 million tons. This paper presents the current situation in MSW generation, characterization, and means of disposal, based on the results of studies by WTERT (www.wtert.org) in China. The landfills serving the large cities of China are reaching or have already reached full capacity and there is strong government support for the waste to energy (WTE) alternative, resulting in over 90 WTE plants built or under construction. The thermal treatment technologies are based mostly on imported or domestic grate combustion technologies and on fluid bed combustion of shredded wastes. Of particular interest to the WTERT studies have been the Air Pollution Control systems used in Chinese plants and their performance, in particular the dioxin and furan levels attained, in view of continuing public opposition to WTE in Beijing and some other cities. The cities of Guangzhou, Shanghai, and Beijing were visited to examine any obstacles to further expansion of the WTE industry in China. There are extreme differences in the composition of MSW as well as waste management from region to region. It is believed that one of the reasons for public opposition to WTE projects is inadequate transparency as to the emissions of WTE plants. Also, it appears that some WTE facilities tend to cut down costs at the expense of adequate emission control. The paper concludes with discussion of the economics of Chinese WTE plants built in the last six years.

Practical Experience on Optimization of Combustion With Expert Systems From 12 WTE Plants in Europe and China

Process optimization of Waste to Energy plants (WtE plants) is of particular interest because control performance is crucial for the profitability of the overall operation of the plant. WtE plants represent very large investments and an optimal efficiency in operation is crucial for the return of the investment. Process optimization including optimal control of the abnormal operating situations when the waste quality is out of the normal range is thus very attractive in order to increase the profitability and efficiency of the waste incineration operations. This presentation will describe how high-level control based on expert system can be used in a practical and convenient way to provide a more efficient operation of a WtE plant and provide a capacity increase of 3–6% or more and thereby be a very attractive investment for an existing or new WtE plant operator.

Carbon Monoxide Emission Improvements From Combustion System Upgrades at the Wheelabrator Portsmouth Refuse Derived Fuel Plant

Wheelabrator Technologies Inc. (WTI) operates a waste-to-energy facility in Portsmouth, Virginia. At full capacity, a total of 2,000 tons/day of refuse derived fuel (RDF) can be fired in four identical boilers to generate a total of 600,000 lb/hr of steam and 60 MW of electricity. The boilers were originally designed to co-fire RDF and coal; however, coal burning capability was removed a few years after commissioning. The plant provides all of the process/heating steam and the majority of the electrical power to the nearby Norfolk Naval Shipyard. Historically, the boilers had not been able to reliably achieve carbon monoxide (CO) emissions compliance. CO emissions experienced during normal boiler operation would be more than twice the mandated emission limit. WTI’s goal was to improve the boilers’ CO emissions performance while achieving sustained boiler operation at higher steam generation and RDF firing rates. WTI contracted Jansen Combustion and Boiler Technologies, Inc. (JANSEN) to evaluate the operation of the boilers, to assess the overall feasibility of meeting WTI’s goals, and to develop design concepts to overcome boiler limitations. The project was initiated by an engineering site visit where boiler operating data was collected and evaluated to develop a baseline of boiler operation. Current and new combustion system arrangements were evaluated with Computational Fluid Dynamics (CFD) modeling. The results confirmed that the root cause of the poor CO emissions performance was the inadequate penetration and mixing of the original overfire air (OFA) system (comprised of multiple rows of small ports on the front and rear furnace walls). CFD modeling also showed increased CO emissions to result from non-uniform RDF delivery profiles generated by the original fuel distributors that were installed at a high elevation over the grate. Modeling of the furnace with larger and fewer OFA nozzles placed on the side walls in an interlaced pattern, and the installation of “new-style” RDF distributors at a lower elevation where the boiler’s original coal distributors formerly were located was shown to significantly improve CO burnout. From December 2010 to May 2011, the new combustion systems were installed on all four boilers. Subsequent testing has shown that CO levels have been lowered by more than 70% and boiler availability has been significantly improved. Nitrogen oxides (NOx) emissions, although slightly higher following the upgrade, are still within the NOx compliance limit. This paper describes the process that led to a successful project, including: data collection and analyses, CFD modeling, equipment design and supply, operator training, and start-up assistance.

Resource Recovery: The Contribution of Energy-From-Waste Plants

Energy-from-Waste plants using grate-based systems have gained world-wide acceptance as the preferred method for the sustainable treatment of waste. Key factors are not only the reduction of waste volume and mass and the destruction or separation of pollutants but also the efficient production and use of energy (electricity, district heating/cooling, process steam), compliant disposal and the recovery of resources from combustion residues (e.g. metals, rare earths). International requirements relating to energy efficiency and materials recovery by means of thermo-recycling in Energy-from-Waste plants call for the continuing development and optimization of existing technologies and concepts. The technologies and processes for the recovery of reusable materials from dry-discharged bottom ash and from filter ash point to the key role that Energy-from-Waste plants are able to play in the efficient conservation of resources. It is primarily thermal treatment with dry discharge and subsequent processing of the bottom ash fractions that enables Energy-from-Waste plants to justify their status as universal recyclers. In addition to recovery of the energy inherent in the waste, the treatment of dry-discharged bottom ash is an important contribution to compliance with raw material and climate policies and to the promotion of closing the material cycle in general. Furthermore, dry bottom ash discharge represents a further step towards waste-free operation and “after-care-free” landfills. This paper documents the potential of Energy-from-Waste plants for the recovery of resources and provides examples of recent developments and large-scale implementations of innovative recovery technologies in Europe.

Aero-Shields: New Product Improves Boiler Performance and Maintenance

Aero-Shields were developed by Covanta Energy in 2005 to address excessive fouling and accelerated tube metal wastage in certain heat transfer areas of a large Municipal Solid Waste (MSW) fired boiler. Computational Fluid Dynamic (CFD) modeling and a Cold Flow model were used to investigate flue gas flow distribution, velocities, temperatures, and other parameters in specific areas of the boiler. The intent of this effort was to identify the problematic areas and develop a solution to better distribute gas flow within these specific areas of the boiler. The result of this development effort was named “Aero-Shield”. The Aero-Shield provides a dual benefit of being a tube-shield and gas baffling device by incorporating extended tapered sides. The shape, size and installation location was developed through the use of CFD modeling. Initial testing of the shields was performed in December 2005 at the Lee County facility Boiler#2 at the top and bottom of the third pass. The Lee County boiler is a typical horizontal boiler design using Martin GMBH technology to process solid waste. This paper demonstrates how CFD modeling plays an extremely important role in designing and optimizing Aero-Shields for new applications. It also describes additional applications which have been tested in multiple facilities and boilers types since 2005. It covers design guidelines for the material, geometry, and installation procedure. The paper will also highlight a number of benefits which have been confirmed through extensive field testing which include: • Significant heat transfer increase in a targeted boiler area. This increases boiler efficiency and generates additional MWs at the same fuel rate. • In Energy-from-Waste (EfW) applications, capital and maintenance costs are often more important than saving fuel. Aero-Shield applications provide significant savings by requiring less heat surface for the same heat recovery in a targeted boiler component. • Reduced ash deposits which results in reduced maintenance. • Improved gas flow distribution allows Aero-Shields to reduce peak gas temperatures and velocities, resulting in lower wastage rates for critical boiler components. • Simple, quick, and economical installation: typically performed in a few hours. Covanta currently has a patent pending on this application and product. Additional testing is ongoing to address other areas within the boiler that may benefit from this technology recognizing that the “Aero-Shield” is a customized solution for each application.

Effect of Methyl Chloride on Landfill Gas Dry Reforming

Landfills are the second-largest source of anthropogenic methane emissions in the U.S., accounting for 22% of CH4 emissions. Landfill gas (LFG) is primarily composed of CH4 and CO2, and currently only 18% of this is used for energy. Because landfills will continue to be used for the foreseeable future, complete utilization of LFG is becoming more important as the demand for energy increases. Catalytically reforming LFG produces syngas (H2 and CO) that can be converted to liquid fuels or mixed into the LFG stream to produce a more reactive, cleaner burning fuel. It has been demonstrated that injecting 5% syngas into a simulated LFG mixture prior to engine combustion decreases CO, UHC, and NOx emissions by 73%, 89%, and 38%, respectively. One barrier to using LFG in a catalytic system is the contaminant content of the LFG, including chlorine and sulfur compounds, higher order hydrocarbons, and siloxanes that have the potential to poison a catalyst. Chlorinated compounds are present in LFG at 10–100ppm levels and are often found as chlorocarbons. This research explores the effect of methyl chloride on the activity of a Rh/γ-Al2O3 catalyst while dry reforming LFG to syngas. It has been found that methyl chloride acts as a reversible poison on the dry reforming reaction, causing a loss in dry reforming activity, decrease in syngas production, and increase in H2/CO ratio while CH3Cl is present in the feed. CH3Cl exposure also decreases the acidity of the catalyst which decreases carbon formation and deactivation due to coking.

Restructuring Plant Operations and Contracts to Make a First Generation RDF Plant Competitive in a Cost-Driven Market

In 1989, United Power Association (now Great River Energy) and Northern States Power (now Xcel Energy) formed a partnership and entered a 20 year contract with five local counties to turn MSW (municipal solid waste) into RDF (Refuse Derived Fuel) and combust the RDF in converted grate-fired boilers in Elk River, MN. Great River Energy owned and operated the Energy Recovery Station (ERS) and Xcel Energy operated the Resource Processing Plant (RPP) a few miles away. The Resource Processing Plant processed 400,000 tons/year of MSW into RDF for the Energy Recovery Station and other RDF plants owned by Xcel Energy. The project was successful, but required significant subsidies from the counties to maintain competitive tipping fees. At the end of the original 20 year contract, a number of the counties wanted to reduce or end any subsidies and restructure the contracts. In the fall of 2009, lack of contracted MSW created difficult financial conditions that threatened to end the project and divert 400,000 tons/year of MSW to area landfills. In May of 2010, Great River Energy purchased the Resource Processing Plant and reorganized the project to be able to better control operating costs and maintain competitive electric rates for its customers. In 2011, Great River Energy restructured processing contracts with three of the original counties and also directly contracted with the regional MSW haulers while implementing sweeping changes in the processing of MSW. A cleaning system was installed to increase the value of the ferrous material collected during the production of RDF. The installation of a bulky waste shredder and processing changes increased the efficiency of converting MSW to RDF. In addition, the recovery of non-ferrous materials from the MSW and heavy residue was optimized. In one year of operation, the Resource Processing Plant has increased RDF production from 84% to over 95% and decreased landfilling to near zero while increasing the revenue from recovered materials. County subsidies have been significantly reduced and will phase out after 2015, tipping fees have been adjusted to be competitive with local landfills, and electric costs have been stabilized at comparable renewable energy rates.