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.

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.

In a previous paper presented to the NAWTEC 12 Conference [1] we described the use of Multicomponent Infrared Gas Analyzers at Waste-to-Energy Facilities. In the subsequent eight years since the paper was presented, the state-of-the-art for the technology has advanced significantly. In addition, the user base has significantly expanded leading to more widespread use of the hot-wet multicomponent technology. Experience in dealing with recurring issues has helped develop best-practice approaches for rapid startup and minimal downtime during maintenance periods. This paper describes these technological advances and best practices incorporated into this competitively priced integrated CEM system design.

The efforts for reducing the emissions into the atmosphere start already in the furnace and are completed by an effective flue gas cleaning system. This implies the necessity for design developments of key components for a modern EfW plant. For the core component of the firing system — the grate — Fisia Babcock Environment (FBE) is using forward moving grates as well as roller grates. The moving grate, which is used in the great majority of all our plants, has specific characteristics for providing uniform combustion and optimal burnout. These include, amongst others: - Uniform air supply by means of specific grate bar geometry. - Two grate steps in direction of waste transport for optimum burnout. - Flexible adaptation of the combustion process to the respective conditions and requirements by zone-specific air distribution and transport velocity of waste on grate. - Combustion control adapted to the specific plant for ensuring a consistent combustion process and production of energy. In addition to these features influencing the emissions the moving grate exhibits also specific characteristics regarding the mechanical aspects allowing low-maintenance and reliable operation. For optimum flue gas burnout a good oxygen distribution after leaving the combustion zone is required. For ensuring this, the injection of secondary air is designed to produce a double-swirl, developed by FBE. Final reduction of the nitrogen constituents NO and NO 2 to the stipulated emission value is achieved by the SNCR process. As well in this respect, there is a great amount of experience available. Besides these measures regarding the combustion process, this paper also reports about flue gas cleaning systems. In this field the FBE CIRCUSORB ® process is presented and compared with the known dry absorption process. CIRCUSORB ® is a lime-based flue gas cleaning process with continuous recirculation of the moistened reaction product and simultaneous addition of fresh hydrated lime. The flue gas temperature downstream of the economizer can be selected very low and permits in this way maximized utilization of the energy. The evaporation of the moisture from the reaction product (flash evaporation) effects final cooling down of the flue gas to optimum process temperature and improves at the same time SO 2 separation. This reduces the technical investment required for the flue gas cleaning process. The total of all measures taken and the robust design of all components permit economical plant operation while complying with the stipulated emission limit values.

The past few years have produced significant variations in the U.S. economic climate. In turn, the revenues from the extraction and sale of both ferrous and non-ferrous metals from WTE plants have experienced wildly positive/negative swings in value. The revenue from sales of these metals and the capital costs for the process installation directly impacts financial payback, and answers the simple question: “should we do this project?” Some key criteria will be discussed: source reduction and curbside recycling and their impact on metals yield (projected vs. actual), plant size and “economy of scale”, and operating and maintenance costs. This paper will review six recent and planned metals recovery projects in the U.S. Technologies and scopes of work include simple addition of metals recovery equipment, complete systems and buildings at existing facilities, and planned systems and buildings at new facilities. The paper will summarize the criteria for metals revenue and project costs, which determine whether the project is a “Go” or a “No Go”.

When the current generation of U.S. waste-to-energy (WTE) facilities was developed during the 1980s and early 1990s, there were a large number of companies competing to design, build, operate and maintain them under a long term contract. Over the years, almost all of these firms have left the WTE business for a variety of reasons leaving essentially only two U.S. firms actively competing for renewed operating and maintenance (O&M) contracts for publicly owned WTE facilities. This consolidation has significantly reduced the level of competition for public owners who are interested in rebidding their WTE O&M contracts at the end of their initial or extended terms and, as a result, has the potential to increase the cost of service. Consolidation has likewise reduced the level of competition for potential new WTE projects in the U.S. This paper reviews the history of public sector operation of WTE facilities in the U.S., the unique challenges presented by public operation and whether it is time for more public owners to consider this alternative for existing WTE facilities in light of the lack of competition by private operating companies. Perceived risks and impediments to public operation of WTE facilities and suggestions on how to overcome them are presented as well as the benefits and opportunities available to public owners. The keys to a successful public WTE operating venture are also discussed based on the experiences of ecomaine, a consortium of 21 member municipalities in southern Maine that have operated and maintained their own 550 ton per day (tpd) WTE facility for more than 20 years. Public versus private operating practices for European WTE facilities are also explored as well as public ownership and operation of new WTE facilities including those based on alternative or emerging technologies.

When the initial generation of U.S. municipal waste combustor (WTE) facilities was developed during the 1980s and early 1990s, the only tools that were included in the service agreement to deal with a contract operator that was not meeting the contract terms was either dispute resolution or default and termination. After 20 years of administering these service agreements, those two provisions have proved inadequate for publicly owned WTE facilities particularly as it relates to ongoing maintenance. Additional provisions have recently been developed and incorporated into the next generation of service agreements to address this need. Contract operators of publicly owned WTE facilities typically focus their attention on facility performance and less on long-term facility asset preservation, especially for the portions of the facility that are not critical to production. If a contract operator is meeting all of its performance guarantees, but is falling behind on the general upkeep of facility buildings and/or infrastructure, owners will likely not invest the time and money in dispute resolution to try to get those items repaired. Additionally, neglect of those items does not rise to the level that the operator can be defaulted and terminated. As a result, conditions generally deteriorate to the point where the relations between the owner and contract operator are adversely affected. If the deferral of maintenance continues until the end of the service agreement term, the public owner will be faced with added capital costs and/or increased operating costs under a new service agreement for items that he already paid the previous operator for. This paper describes the new contractual provisions that have been developed in the latest generation of service agreements aimed at helping public owners of WTE facilities resolve these types of problems at minimal cost. Instead of only having the “nuclear weapons” (e.g., formal—and expensive—dispute resolution or default and termination), a series of mechanisms have been developed that provide owners with some “small arms weapons” to assure that the timely and proper maintenance is performed on all aspects of the WTE facility, thereby assuring its long-term preservation. This paper also sets forth case studies of three WTE facilities in the Tampa Bay, Florida area where these latest contractual provisions are being implemented and the results to date.

Fireside corrosion management in energy-from-waste (EfW) boilers is the leading cost of boiler maintenance. The combustion of refuse-derived fuel (RDF) processed from municipal solid waste in a boiler for power generation produces a very corrosive environment for boiler tube materials. Water wall corrosion has been greatly reduced by the use of Alloy 625 overlay in the highest corrosion areas. This paper will describe the progression of water wall corrosion up the boiler walls and novel attempts to reduce this problem. This paper presents an updated case study conducted at the Great River Energy plant in Elk River, MN from 2003–2009 on corrosion management. Areas to be addressed are protection of exposed carbon steel water wall tubes, management of Alloy 625 weld overlay on the water walls and corrosion in the high temperature superheat sections. Methods for testing and maintaining the corrosion resistant Alloy 625 cladding are reviewed. High temperature superheat material selection and shielding are reviewed with information leading to a cost effective solution that requires superheat replacement every three years with very few tube failures between replacements.

As Energy-from-Waste (EfW) facilities make the leap into the twenty-first (21 st ) century, so does the demand for cost efficient air pollution control technology. In an effort to meet this rising demand, companies have to develop concepts that remove acid gases in an efficient, sustainable, and reliable way. The current market trend to provide the best available control technology (BACT) leads people searching for technologies that are: • Proven and have extensive records of success. • Highly efficient, resulting in low emission to the atmosphere, but requiring minimal investment. • Compact in design, simple, and low maintenance. • Offering high availability, low reagent consumption, and low residue levels. • Resulting in either clean or suppressed liquid effluents. This paper will specifically discuss the three main types of acid gas control technologies available in today’s marketplace, which include dry, semi-dry, and wet scrubbers. It will first focus on the acid gas control technology most commonly used in the US, the spray dryer absorber, followed by a typical Ring Jet® wet scrubber with packed bed, and finally, the Turbosorp® system. For each of the above technologies, this paper will present the concepts, advantages and disadvantages, achievable emissions, and capital and operating costs. It will then look at how each of these technologies is utilized at existing EfW facilities operating throughout the world and provide information on how each facility has been operating. Lastly, it will look towards the future of acid gas control technologies and provide insight into what advances are being made to meet the most stringent air emission regulation all over the world.

Over the last few years an increase in the calorific value of the waste has been observed at our waste-to-energy facilities. Wheelabrator Technologies, Inc. in conjunction with Von Roll/Inova decided to install a zone of water-cooled grate blocks at the Millbury Massachusetts waste-to-energy facility as a pilot program. Common in Europe these water-cooled grate blocks address the issue of higher BTU waste and increase the overall life expectancy of the blocks compared to regular air-cooled grate blocks. This technical paper provides an overview on the installation, operation, and maintenance of a zone of water-cooled grate blocks. Discussed are the procedures for evaluating the overall project and some of the challenges we resolved.

The seemingly endless possibilities, which are offered for the refractory lining in WTE plants, have effected that new lining concepts have been developed and introduced again and again during the last decades. The objective of all lining systems from the start has been to reduce corrosion on the boiler walls to a minimum and to regulate heat loss in the first flue in such a way that all requirements according the 17 th Federal Emission Laws are fulfilled.

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.

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.

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 NO x emissions from Energy from Waste (EfW) facilities. NO x 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 NO x 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 NO x formation and optimize combustion. The VLN™ process is combined with conventional, aqueous ammonia SNCR technology to achieve the superior NO x performance. The SNCR control system is also integrated with the VLN™ combustion controls to maximize NO x 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 NO x 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™ NO x 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 NO x 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. NO x and NH 3 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 NO x 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 NO x 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 NO x emissions from EfW facilities.

This paper focuses on recent advancements in the areas of imaging technology and flue gas temperature measurement which are providing new insights for plant engineers into combustion conditions and operation in Energy-from-Waste (EfW) facilities. The paper describes how Covanta Energy, an operator of over 30 EfW facilities and Enertechnix, a manufacturer of advanced combustion products and services, are developing new technologies in these following areas: Infra-red (IR) imaging using a mobile camera to provide active viewing of the boiler and combustion conditions; Digital recording of images of slagging, waste stream movement, and refractory inspection; Online inspection in back pass convection areas with a video camera that extends up to 20 feet into boiler. Furnace Exit Gas Temperature (FEGT) measurement integrating proven acoustic pyrometer technology to replace inherently inaccurate contact temperature methods such as thermocouples. The paper examines how each of these technologies is being introduced into EfW facilities operated by Covanta Energy. Actual results are used to evaluate the potential these new methods have for improving combustion, reducing maintenance costs and providing plant operators with useful tools for operating EfW facilities. Video images of the furnace and convection sections will be provided and discussed. FEGT data from comparative technologies is presented. The data is interpreted in order to compare the accuracy of the acoustic pyrometer measurement against other methods. Potential and determined benefits are presented and outlined. The paper attempts to provide a framework to help facilities understand the importance and impact of accurate FEGT measurement in the combustion process.

The Algonquin Power Energy-From-Waste (APEFW) facility is located in the suburban Toronto, Ontario city of Brampton. It receives approximately 140,000 metric tonnes (154,000 tons) of MSW per year from the Region of Peel (Region) and approximately 10,000 metric tonnes (11,000 tons) per year of international airport waste from the area’s two international airports. The APEFW facility commenced initial operations in 1992 and included four, 91 tonne (100 ton) per day Consumat two stage incinerators with heat recovery boilers and a dual-train air pollution control (APC) system consisting of evaporative cooling towers, venturi reactors and fabric filter baghouses. The APEFW facility expanded its capacity in 2001 with the addition of a fifth 91 tonne (100 ton) per day modular incinerator and heat recovery boiler. One of the stipulations in the permitting process was that the entire expanded facility meet more stringent emission standards that included a significantly lower nitrogen oxides (NOx) emission rate. After a review of several available NOx control technologies, the APEFW facility chose to install a Selective Catalytic Reduction (SCR) system. While SCR systems are fairly common on EFW facilities in Europe, the APEFW facility is the only EFW facility in North America that currently operates with an SCR system and as such has gained valuable insight into the application and performance of this technology that is very relevant to the North American EFW industry. This paper discusses the operation and maintenance of the SCR system, compares pre- and post-SCR NOx emissions and presents capital and operating costs for the SCR including the cost per tonne of waste processed and the cost per tonne of NOx removed.

This paper presents the preliminary results of one of the key financial liability issues raised by the operating companies during the competitive procurement process for the long-term operation and maintenance of the 24-year old Pinellas County 3,000 tpd waste-to-energy facility.

The Miami-Dade 3,000 tpd Refused-Derived Fuel (RDF) facility is located in Miami-Dade County, FL and is operated by Montenay Power, a Veolia Environmental Services Company. A team composed of plant staff and outside experts underwent a thorough equipment-by-equipment review of the Air Pollution Control (APC) system and identified a series of low cost design and operational improvements to the lime slakers, the spray dryers and the baghouses. These improvements were implemented over the course of several months and resulted in a drop in lime consumption, in the economy of one and a half air compressor units, and in reduced APC related plant downtime and maintenance costs. This paper describes several key improvement projects (including the upgrade of the spray nozzles, the change in slaking water quality and the fly ash fluidization project), detailing the initial problem, the chosen solution, the difficulties encountered during implementation and the achieved benefits.

This paper discusses one of the key lessons learned from administering the first generation of service agreements for public owners of waste-to-energy (WTE) facilities over the past 22 years and how those experiences were incorporated into a new service agreement for the operation and maintenance of Pinellas County’s 24 year old, 3,000 tpd WTE Facility to better protect the county’s interests. Additionally, a major issue raised by the operating companies during the competitive procurement process for continue operation of the facility is discussed and how that concern was addressed in the new service agreement is also presented. Capitalized words or terms used in this paper are defined within the new service agreement.