The prevention of corrosion on boiler tube-walls has been a most difficult and cost intensive problem in WTE plants. This is specifically the case where the incineration boilers are operating with increased saturated steam temperatures and their corresponding pressures. In addition, variations in the garbage mixtures, with differing values of chemical content and varying waste composition give importance to the prevention of boiler tube corrosion. Several refractory lining systems and types have been installed over the previous 80 years and can be compared. In the early stages it began with simple concrete installations and only later was it developed to use heat resistant ceramic products, now essentially silicon carbide. 20 years ago cement or chemically bonded SiC monolithics (gunning, trowelling or casting materials) were usually installed to protect boiler walls, but today fabricated and fired SiC tiles, with their enhanced properties, are mainly used. A distinction is made between hanging and bolted tiles, as well as between oxide bonded and nitride bonded SiC material and between mortared, backfilled and rear ventilated tiles. All these systems were carefully examined and assessed. It proved possible to develop a revolutionary heat conduction and corrosion protection system utilising air. An air gap between the refractory SiC tiles and the boiler wall proved to be both simple and successful. By means of detailed and systematic documentation and monitoring, including J + G’ s “Air” tiling system, it has, for a few years, been possible to offer and recommend long lasting refractory linings with the aim of protecting boiler walls against corrosion, reducing operating costs and using the energy of the waste in an optimum manner.

Thermal treatment of waste using grate-based systems has gained world-wide acceptance as the preferred method for sustainable management of residual waste. However, in order to maintain this position and respond to new challenges and/or priorities, it is necessary to further develop innovative concepts that use safe process engineering technology in terms of climate and resource protection as well as reduction of environmental impacts. MARTIN, in collaboration with research institutes, successfully developed and optimized a multi-stage combustion process in the 1990s. Various pilot and full-scale studies and tests followed. Based on this knowledge, MARTIN and its cooperation partners COVANTA ENERGY (USA), CNIM (F) and Mitsubishi Heavy Industries (JP) developed the Very Low NO x (VLN) process as a large-scale primary measure for NO x reduction. MARTIN’s next step was to develop the Very Low NO x gasification mode (VLN-GM) process. This process has been implemented directly in continuous operation at an industrial-scale Energy-from-Waste (EfW) plant in Switzerland. In VLN-GM operation, the excess air rate in the gas above the grate is decreased from λ = 1.2 to about 0.8. The characteristics of municipal solid waste make it suitable for the generation of heat and power. While boiler concepts implemented in the past often focused on factors such as high availability, reduced downtimes and minimized maintenance costs, measures to increase the efficiency of the overall process are also growing in importance. Energy efficiency can be increased by optimizing boiler efficiency itself on the one hand, and on the other hand by improving peripheral plant devices, in particular by improving energy recovery through changes in the steam parameters. MARTIN has developed corrosion-protected wall and radiant superheater solutions, located in the upper furnace area, and installed these as prototypes in full-scale plants. As a result, steam can be heated about 35 °C (90 °F) in excess of the current state-of-the-art parameters without adversely affecting plant operation due to superheater corrosion. This paper documents that innovative concepts using MARTIN technology successfully provide solutions for a grate-based conversion technology (VLN-GM) as well as measures for increasing the energy efficiency of Energy-from-Waste plants.

For the waste disposal of urban areas and major cities at the North American market place rather large scale energy from waste (EfW) plants are needed. This implies a mechanical input of approx. 40 Mg/h [39.36 tn l./h] and thermal input by waste per unit of 110 MW [375.3 MBTU/h] and more. There are basic design criteria that feature large scale EfW plants: - Layout of boiler with horizontal or vertical orientation of convective part. - Top or bottom suspension of boiler. - Flexible design of stoker regarding large throughput figures and heating values of waste with water or air cooled grate bars. - Design and geometry of combustion furnace in order to optimize the flow pattern. - Optimization of boiler steel structure: integrated steel structure for boiler and boiler house enclosure. - Optimization of corrosion protection and maintainability of large scale boilers: cladding versus refractory lining. - Maintenance aspects of the boiler. The paper gives information on the pros and cons regarding the design features with special focus on optimized solutions for large scale EfW plants. For the core component of the combustion system — the grate — Fisia Babcock Environment (FBE) is using forward moving grates as well as roller grates. The moving grate in STEINMÜLLER design, which is used in the great majority of all our plants, has specific characteristics for providing uniform combustion and optimal burnout. The automatic combustion rate control system is the key component in the combustion process in order to receive good burn out quality in slag and flue gas as well as constant steam production and oxygen content of flue gas. This paper includes a detailed report on a modern control system with focus on a simple and efficient control structure. Besides these measures regarding the combustion process, this paper also reports about the respective aspects and concepts for the flue gas cleaning systems. In this field the FBE CIRCUSORB ® process was presented in previous papers and is now compared with a multistage wet flue gas cleaning system. The latter is relevant in case of very low emission requirements.

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 (NO x ) emissions, although slightly higher following the upgrade, are still within the NO x 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.

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.

Biomass is likely to be a significant energy resource in the future. A common way to recover energy from biomass is through gasification where synthesis gas is produced; by-products of this process are tar and ash/char. This research investigates the potential to use the ash/char as a catalyst by understanding the properties of char generated under different gasification conditions. Specifically, it is desired to produce a porous char which could be used as a catalyst or as a support for more catalytically active metals. In this work, poplar wood was gasified under CO 2 , steam, and air at different reaction temperatures. Experiments were done in a fluidized bed reactor at temperatures of 500°C, 750°C and 920°C and char was recovered. BET-surface area measurements showed that gasification under CO 2 has the potential to produce char with a higher surface area than char produced from steam gasification. Higher temperature or longer gasification times resulted in the production of a more porous char. TGA experiments showed that gasification under CO 2 resulted in a higher mass loss compared to gasification with steam. Gasification with steam/CO 2 mixtures yielded a mass loss similar to that of steam only which could be indicative of competitive reactions between steam and CO 2 . Experiments done in an ESEM allowed for visual observation of the changes in physical properties of the biomass during gasification. With CO 2 , physical changes were observed at temperatures as low as 400°C whereas physical changes were not observed under steam at this temperature.

The dominant technology for large Waste-to-Energy (WTE) facilities is combustion on a moving grate of “as-received” municipal solid wastes (MSW). However, there are circumstances where a low-capacity plant (<100,000 tons per year) is required. This study examines the technical, economic, and environmental aspects of some small-scale WTE technologies currently in operation. The Energos technology was developed in Norway, in order to provide relatively small communities with an economically efficient alternative to mass-burn incineration with equally low emissions to the atmosphere and flexibility in feedstock. All operating plants treat MSW plus additional streams of commercial or industrial wastes. Prior to thermal treatment, the materials are shredded in a high-torque, low-rpm shredder and ferrous metals are removed magnetically. The feedstock is partially oxidized on a moving grate in the gasification chamber where the fixed carbon is completely burnt off. The volatilized gases are fully combusted in a second chamber and the heat is transferred to a heat recovery system for steam generation. The Energos gasification technology is currently in operation at six plants in Norway, one in Germany, and one in the UK. As expected, the capital cost per ton of annual ton of capacity increases with decreasing plant capacity, while there is a linear relationship between energy recovery and capacity. Some other small-scale technologies are investigated in this study and will be reported at the NAWTEC meeting. Low capacity (<80,000 tons) WTE facilities require a relatively small footprint (1.5 to 2 acres; <1 hectare) and it is believed that these facilities can be built at a capital cost per ton that is as low, or lower, than that of large mass burn WTE facilities.

Covanta Energy, in cooperation with United Technologies Corporation (UTC), has evaluated, designed, and is in the process of installing an Organic Rankine Cycle (ORC) system at its Haverhill Energy from Waste (EfW) Facility to improve heat recovery and energy efficiency, and to generate more clean renewable energy. ORC systems have been applied in geothermal applications and some other industrial processes to recover low grade and waste energy to generate electricity. This paper describes the design and integration of the ORC system into the Haverhill EfW steam cycle, and the landfill gas engine system, which also operates at the facility. The anticipated energy efficiency improvements and increased net power output have been analyzed and simulated. The results show that the integration of the ORC system could lead to a potential increase in the net power output by as much as 305 kWe in the summer and by 210 kWe in normal weather. It is also anticipated that with the ORC system the facility has the potential to improve the overall plant energy efficiency, as well as save city water.

A greenfield Refuse Derived Fuel (RDF) facility in Alliance Ohio will process 2,400 Tons Per Day (TPD) of Municipal Solid Waste (MSW) and Construction & Demolition Debris (C&D). The Ohio EPA has issued the final air permit for the facility. There will be two equipment trains to handle the material each consisting of Riley Power’s Advanced Stoker™ boiler, Turbosorp® dry scrubber, and Regenerative Selective Catalytic Reduction (RSCR®) nitrogen oxides (NOx) control system. The key parts of the “chute to stack” equipment represent a significant advancement in technology when compared to past facilities, as demonstrated by the designation by the State of Ohio as an “Advanced Energy Project”. The Riley Advanced Stoker™ boiler has unique design features to ensure high efficiency, corrosion resistance, and fuel flexibility while at relatively low cost. The use of the Turbosorp will result in lower emissions of lead, other volatile heavy metals, and mercury than for a typical spray dryer/baghouse (SDA) system. Acid gas removal is also superior to an SDA system while utilizing less lime reagent and power. The RSCR follows the Turbosorp as a “low dust” SCR but with auxiliary energy consumption about 85% lower than a typical low dust, tail end SCR. The RSCR will reduce NOx and Carbon Monoxide (CO) emissions to low values when compared to other facilities producing energy from waste. This paper will describe the design basis for the system including fuels to be processed, steam flow and conditions, and emissions. A detailed description of the technologies will also be presented.

Municipal solid waste (MSW) gasification/pyrolysis enhancement using CO 2 as gasification medium has been studied to understand the performance under various reaction conditions. MSW gasification/pyrolysis has been characterized thermo-gravimetrically under various atmospheres covering the gasification/pyrolysis process, which has been used as a basis for scale-up experimental work using a flow-through reactor (FTR) and drop tube reactor (DTR) (0.5 g/min of sample, 4–5 sec residence time, 500°C-1000°C). For example, FTR has been used to carry out the fast pyrolysis process having a nominal heating rate of 800°C/min. Oils produced from the FTR have been condensed and analyzed with GC/MS. Among identified chemical species in the pyrolysis sample, the 10 most abundant compounds (benzene, toluene, styrene, limonene, 2,3-dimethyl-1-heptene, benzoic acid, ethylbenzene, indole, xylene, and d-allose) in the pyrolysis oil sample were determined and quantified. These 10 abundant chemical species are substantially reduced in the presence of CO 2 . This leads to a substantial increase of C 1–5 hydrocarbons in gaseous (non-condensable) products and a reduction of pyrolysis oil (∼20%) as well. In addition, MSW samples have been tested in the DTR at a temperature range from 500°C and 1000°C under various atmospheres with CO 2 concentrations of 0% and 30%. The release of all chemical species from the DTR was determined using μ-GC. For example, CO (∼30%), H 2 (∼25%), and CH 4 (∼10%) under the presence of CO 2 were generated and introducing CO 2 into the gasification process substantially enhanced syngas production. Finally, steam gasification using different ratios of biomass to polyethylene has been explored to better understand the enhanced steam gasification of MSW that is mostly composed of biomass and polymer. Overall thermal degradation trend is the similar, but steam gasification of MSW needs a relatively long residence time and high temperature as compared to biomass.

In the summer of 2009, Governor John P. DeJongh, Jr. announced that the Virgin Islands Water and Power Authority (WAPA) had just signed two 20-year Power Purchase Agreements, and the Virgin Islands Waste Management Authority (VIWMA) had signed two 20-year Solid Waste Management Services Agreements with affiliates of Denver-based Alpine Energy Group, LLC (AEG) to build, own, and operate two alternative energy facilities that will serve the residents of St. Croix, St. John, and St. Thomas. The alternative energy facilities, to be built on St. Croix and St. Thomas, have a projected cost of $440 million and will convert an estimated 146,000 tons per year of municipal solid waste into refuse-derived fuel (RDF) using WastAway Services® technology, which will be combined with petroleum coke as fuel in fluidized bed combustion facilities to generate steam and electric power. These sustainable projects will provide 33 MW of electric power to St. Thomas and St. John and 16 MW of electric power to St. Croix, and will help to provide long-term cost stability for electric power and solid waste management in the Territory. Construction is expected to start in spring 2010 with an anticipated completion date during the fourth quarter of 2012. This procurement is a significant achievement for the U.S. Virgin Islands. When the projects are fully implemented, they will allow the Territory to reduce its dependence on oil, recover the energy value and certain recyclable materials from its municipal solid waste, and divert this waste from landfill. Since VIWMA has the responsibility to collect and/or dispose of solid waste year-round, having a system incorporating multiple solid waste processing lines and an adequate supply of spare parts on hand at all times is crucial to meeting the daily demands of waste receiving and processing, and RDF production. Also, with the location of the US Virgin Islands in a hurricane zone, and with only one or two combustion units available in each Project, the ability to both stockpile waste pre-RDF processing and store the produced RDF is very important. Gershman, Brickner & Bratton, Inc. (GBB)’s work has included a due diligence review of the Projects and providing professional support in VIWMA’s negotiations with AEG. GBB’s initial primary assignment centered on reviewing the design and operations of the RDF processing systems that will be built and operated under the respective Service Contracts. VIWMA needed to undertake a detailed technical review of the proposed RDF processing system, since this was the integration point of the waste collection system and waste processing/disposal services. GBB, in association with Maguire, was requested to provide this review and present the findings and opinions to VIWMA. In the completion of this effort, which included both a technical review and participation in negotiations to advance the Service Contracts for the Projects, GBB made direct contact with the key equipment suppliers for the Projects proposed by AEG. This included Bouldin Corporation, the primary RDF processing system supplier, with its patented WastAway technology, and Energy Products of Idaho, the main thermal processing equipment supplier, with its fluidized bed combustion technology and air pollution control equipment. Additionally, since the combustion systems for both Projects will generate an ash product that will require marketing for use and/or disposal over the term of the Service Contracts, GBB made contact with LA Ash, one of the potential subcontractors identified by AEG for these ash management services. Due to the nature of the contract guarantees of VIWMA to provide 73,000 tons per year of Acceptable Waste to each Project for processing, VIWMA authorized GBB to perform a current waste stream characterization study. Part of this effort included waste sorts for one week each in February 2009 on St. Croix and March 2009 on St. Thomas, with the results shared with VIWMA and AEG, as compiled. The 2009 GBB waste stream characterization study incorporated historical monthly waste weigh data from both the Bovoni and Anguilla Landfills that were received from VIWMA staff. The study has formed a basis for continuing to augment the waste quantity information from the two landfills with the additional current monthly results compiled by VIWMA staff going forward following the waste sorts. The final GBB report was published in December 2009 and includes actual USVI landfill receipt data through August 31, 2009. The information contained in this document provides the underpinnings to allow for better tracking and analysis of daily, weekly and monthly waste quantities received for recycling, processing and disposal, which are important to the overall waste processing system operations, guarantees and cost projections. GBB’s annual projections are that the total waste on St. Croix is currently over 104,000 tons per year and over 76,000 tons per year on St. Thomas. The thermal processing technology selected for both Projects is a fluidized bed process, employing a heated bed of sand material “fluidized” in a column of air to burn the fuel — RDF and/or Pet Coke. As such, the solid waste to be used in these combustion units must be size-reduced from the myriad of sizes of waste set out at the curb or discharged into the large roll-off boxes or bins at the many drop-off sites in the US Virgin Islands. While traditional RDF would typically have several days of storage life, the characteristics of the pelletized RDF should allow several weeks of storage. This will be important to having a sound and realistic operating plan, given the unique circumstances associated with the climate, waste moisture content, island location, lack of back-up disposal options and downtime associated with the Power Generation Facility. During the negotiations between AEG and VIWMA, in which GBB staff participated, in addition to RDF and pelletized RDF as the waste fuel sources, other potential fuels have been discussed for use in the Projects and are included as “Opportunity Fuels” in the Service Contracts. These Opportunity Fuels include ground woody waste, dried sludges, and shredded tires, for example. Therefore, the flexibility of the EPI fluidized bed combustion boilers to handle multi-fuels is viewed as an asset over the long term, especially for an island location where disposal options are limited and shipping materials onto and off of each island is expensive. This presentation will provide a unique behind-the-scenes review of the process that led to this historic agreement, from the due diligence of the proposed technologies, to implementation planning, to the negotiations with the contractor. Also discussed will be the waste characterization and quantity analysis performed in 2009 and the fast-track procurement planning and procurement of construction and operating services for a new transfer station to be sited on St. Croix.

A search of websites for firms in the United States and Canada identifying themselves as gasification or pyrolysis system suppliers indicates that there are a number of existing facilities where their technologies are installed. According to the websites, the companies’ existing installations focus on processing biomass and industrial residuals, rather than mixed refuse. The biomass processed, according to the websites includes yard waste, wood, and wastewater treatment sludge. The existence of these facilities provides a potential opportunity for communities in areas with a high density of development, who experience difficulties in siting “traditional” facilities for processing these biomass wastes. Such traditional facilities include yard waste and sludge composting, wood mulching, sludge drying, chemical treatment or pelletization, and combustion-based waste-to-energy. As a result of these facility siting difficulties, these communities often resort to long-haul trucking of the biomass wastes to processing facilities or landfills. Certain potential advantages associated with gasification and pyrolysis technologies could ease the siting difficulties associated with the traditional technologies, due to smaller facility footprints, reduced odors, and the potential for energy production through combustion of syngas/synfuel to power internal combustion engines or produce steam using boilers. Lower stack emissions may result as compared to direct combustion of biomass wastes. Locally sited biomass gasification facilities could reduce the environmental impacts associated with long-haul trucking and generate an energy product to meet nearby demand. Research has been conducted by the Author on behalf of client communities to identify gasification and pyrolysis facilities in the United States and Canada that are in actual operation in order to assess their potential for processing biomass wastes and for providing the advantages listed above. Website reviews, interviews with company representatives, and facility visits were conducted in order to assess their potential for development to meet the biomass management objectives of the communities. The information sought regarding design and operating parameters included the following: • Year of start-up. • Availability. • Process description. • Design throughput. • Actual throughput. • Energy product. • Energy generation capability and technology. • Residuals production and characteristics. • Emissions. • Construction and operating costs. In addition, the system suppliers’ business status was addressed in terms of their readiness and capabilities to participate in the development of new facilities. Confidentiality requirements imposed by the system suppliers may prevent the identification of the company name or facility location and certain details regarding the system designs.

A new WTE (Waste-to-Energy) power plant configuration combining municipal solid waste and gas turbines or landfill gas engines is proposed. The system has two objectives: increase the thermodynamic efficiency of the plant and avoid the corrosion in the MSW (Municipal Solid Waste) boiler caused by high tube metal temperatures. The difference between this concept and other existing configurations, such as the Zabalgarbi plant in Bilbao, Spain, is lower natural gas consumption, allowing an 80% waste contribution to the net energy exported or more. This high efficiency is achieved through four main steps: 1 . introducing condensing heat exchangers to capture low temperature heat from the boiler flue gases; the stack temperature can drop to 70°C; 2 . high steam temperatures in external superheaters using hot clean gases heated with duct burners; 3 . mixing the exhaust gases of a small gas turbine with hot air preheated in a specially designed heat exchangers. The resulting temperature of this gas mixture is almost the same as a standard gas turbine but with the flow similar to that of a large machine with a higher O 2 content; 4 . After the duct burner and heat exchangers, the oxygen content of the clean gas mixture is still high, nearly 18%, and the temperature is approximately 200°C. The gas is then used as combustion air to the MSW boiler such that all the energy stays in the system. The efficiency can be as high as 33% for the MSW part of the plant and 49% for the natural gas system. Since the natural gas consumption is almost ten times less than the existing designs, it can be replaced by landfill gas or gasified ethanol or biodiesel. Currently an 850 ton/day plant is being designed in Brazil in partnership with a large power company. Other advantages include, self generation of internal power and lower steam superheating temperatures in the MSW boiler. This concept can be used with any grate design.

Recent technological developments in expander design and next generation refrigerants have made implementation of the Organic Rankine Cycle (ORC) a viable strategy for converting low grade heat into valuable amounts of recoverable, green electrical power. This green process reduces the typical plants carbon footprint. A brief review of the technical drivers of a typical ORC design will be followed with examples of waste heat energy sources in a typical 50 MMGPY biofuels plant. A Case History will be presented for potential energy sources to drive the process that will include 1.) 15 psig steam / condensate return 2.) Boiler stack gas 3.) Dryer stack gas emissions with expected converted electrical energy yields. Impact of energy savings and reducing total plant carbon emissions will also be addressed.

In March 2008, Keppel Seghers started the engineering, supply, construction and commissioning of a Combined Heat and Power (CHP) Waste-to-Energy (WtE) plant in A˚motfors (Sweden). When completed in 2010 the plant will process close to 74,000 tons per year of household waste (average LHV = 10.5 MJ/kg) and limited quantities of (demolition) wood resulting in a yearly production of about 108,700 MWh of steam, 12,100 MWh of heat and 13,400 MWh of electricity. Herewith, the A˚motfors WtE-CHP is sized to meet the joined energy needs of the local paper production, neighboring industries and buildings at an overall net plant efficiency of almost 65%. The WtE-CHP will offer state-of-the-art combustion and energy recovering technology, featuring Keppel Seghers’ proprietary Air-Cooled Grate, SIGMA combustion control and integrated boiler. Waste is fed into the combustion line with an automatic crane system. To surpass the stringent EU emission requirements, a semi-dry flue gas cleaning system equipped with Keppel Seghers’ Rotary Atomizer was selected as economic type of process for purifying the combustion gas from the given waste mixture. Furthermore a low NOx-emission of 135 mg/Nm 3 (11%O2, dry) as imposed by Swedish law is achieved by SNCR. The plant engineering is described with a focus on the overall energy recovery. As stable steam supply to the paper mill and the district heating system needs to be assured under all conditions the design includes for supporting process measures such as combustion air preheating, steam accumulation, turbine bypassing, buffering of the main condenser and back-up energy supply from an auxiliary fuel boiler. Additionally, external conditions can trigger distinct plant operation modes. A selected number of them are elaborated featuring the WtE-plant’s capability to conciliate a strong fluctuating steam demand with the typical intrinsic inertia of a waste-fired boiler. With prices for fossil fuels increasing over the years, the cost for generating process steam and heat has become dominant and for paper mills even makes the overall difference in viability. As will be documented in this paper, the decision to build the A˚motfors WtE-CHP was taken by Nordic Paper after a quest for significant cost-cutting in the production of process energy. Moreover, the use of industrial and household waste as fuel brings along the advantage of becoming largely independent from evolutions on the international oil and gas markets. By opening up the possibility for a long-term secured local (waste) fuel supply at fixed rates, WtE-technology offers a reliable alternative to maintain locally based industrial production sites. The Nordic Paper mills in A˚motfors are therefore now the first in Sweden to include a waste-fired CHP on a paper production site.

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 SO 2 and NO x , 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.

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.

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 C 1–3 -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%CO 2 +Bal. N 2 with/without steam) have been done and the results are presented here.

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.

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.