Characteristics and Environmental Fate of Mercury in Municipal Waste Combustor Ash Before and After Implementation of the “Maximum Achievable Control Technology” Air Standards

Mercury emissions from waste-to-energy facilities have been a source of public concern for more than ten years following release in the early 1990s of the EPA’s inventory of anthropogenic sources of mercury that listed MWCs as a significant source of mercury air emissions. Since 1990, source reduction, product reformulation, and increasingly effective battery recycling programs reduced mercury in trash by about 90%, according to the EPA. Pollution control equipment on waste-to-energy plants thereafter remove greater than 90% of the remaining mercury in the waste stream that is used as a fuel to generate power. The use of mercury by U.S. manufacturers will decline even further due to the virtual elimination of mercury from alkaline batteries and aggressive recycling and product substitution at hospitals, homes, and businesses. The Clean Air Act regulations promulgated in 1995 under the Maximum Available Control Technology standards have ensured that mercury emissions from waste-to-energy plants nationwide represent less than 3% of the U.S. inventory of man-made mercury sources, according to EPA, (or less than 1% of mercury emissions from all sources). Furthermore, health risk assessments completed over the past several years for new and existing waste-to-energy plants consistently reveal that the levels of mercury emissions result in exposures which are 100 times less than the threshold health effects standard established by federal and state regulatory agencies. Nonetheless, certain environmentalists and critics claim that the significant reduction in mercury air emissions has resulted in a transformation of the metal into the ash. In other words, the questions posed is whether what is not now going up the stack is instead finding its way into the ash. This paper answers that question with a resounding “no.” Based on an analysis of test data, mercury in MWC ash has not increased despite a greater than 90% reduction in mercury emissions.

Environmental Characterization of Ash From the Combustion of Wood and Tires for Beneficial Use in Florida

Non-hazardous industrial solid wastes are frequently proposed for beneficial use rather than being disposed in MSW landfills. An example of such an industrial waste is waste-to-energy (WTE) ash. Proposed beneficial use projects for WTE ash often involve some form of land application. Prior to the land application of any solid waste, the possible risk to human health and the environment should be assessed. The Florida Department of Environmental Protection (FDEP) has developed a beneficial use guidance document that provides WTE ash generators with the testing requirements that must be demonstrated before a particular beneficial use scenario is determined appropriate (FDEP 2001). For WTE ash to be deemed safe for land application, the risk associated with two separate pathways should be assessed: direct human exposure and the contamination of groundwater via leaching. While organic pollutants (e.g. dioxins) might be a concern, heavy metals are typically the pollutants that most limit the potential for reuse; heavy metals are the focus of the discussion in this paper.

Long-Term Operating Results: Ash Monofill

An ash monofill was studied from 1997 to 2001. Monitoring results of the lined landfill showed viability of liner since groundwater standards were not exceeded. Raw leachate of RCRA heavy metal leachate results show Chromium reaching groundwater standards while Lead, Cadmium and Zinc slightly exceed these standards. An upset incident of premature set-up of lime-laden ash caused a back-up and overflow condition in 1994. Adding water of solubilization and field compaction achieves optimal geo-technical properties and reduces heavy metal leachate. This water addition would have also reduced fugitive dust concerns. These principles of sound engineering management of MWC residues were well-known and widely publicized. If the landfill operator had applied these principles the upset incident could have been avoided. Long-term trends of RCRA heavy metal leachate results show compliance with groundwater standards, although Lead, Cadmium and Zinc exceed these standards. Application of sound engineering placement practice would have reduced these long-term trends. USA Regulatory officials should consider incorporating these principles into residue management recommendations, following Environment Canada’s example. Recognition and implementation of these principles would confirm that incinerator ash can be properly managed — to alleviate concerns — justifying their beneficial reuse.

Application of Unifuse Overlay Tubes in the Convection Section of Waste-to-Energy Boilers

The modern weld overlay applied by automatic gas-metal-arc welding (GMAW) process using Ni-Cr-Mo-Nb alloy 625 has been extremely successful in providing corrosion and erosion/corrosion protection for the waterwalls of waste-to-energy (WTE) boilers for over a decade. Without alloy 625 weld overlay protection, the carbon steel waterwall of a waste-to-energy boiler would be corroded through in a matter of months. The overlaid waterwalls for numerous WTE boilers have shown excellent performance results with services up to 10 years or more. Welding Services Inc. has developed a patented process for manufacturing weld overlay bimetallic tubes involving GMAW/GTAW process. Unifuse® 625 overlay tubing with carbon steel substrate has been successfully used as screen tubes, superheater tubes and generating banks in the convection section. The overlay tubes have successfully replaced such corrosion protection methods as stainless steel tube shields and refractories.

2nd Year Comparison of Superheater Metal Wastage Rates Utilizing Various Boiler Tube Alloys in a Waste-to-Energy Facility

The SEMASS Resource Recovery Facility (SEMASS) is a processed refuse fuel (PRF) waste-to-energy plant serving Southeastern Massachusetts. The plant consists of three 1000 ton per day boilers that generate steam at 765 F and 650 psig for use in a steam turbine/generator set. Over the past several years there have been a series of plant improvements made in order to achieve compliance with the MACT emission standards. Unfortunately, metal wastage rates due to fire side corrosion of pressure containing components, have increased significantly during this same time period. In an attempt to reduce overall maintenance costs and unscheduled down time due to tube failures, a test of various alloy tube materials was undertaken in 2001 (see NAWTEC#10 paper-1021) in the primary superheater section of boiler #1. The materials tested were SA213-T22 (original spec.), SA213-T22-Heavy Wall, SA213-TP310H, SB-423 Incoloy 825, and Inconel 625 spiral weld overlay of SA213-T22 base material. This paper will summarize the results of the second year of testing including wastage rate tables and annualized costs for the various tube materials.

Lee County Resource Recovery Facility Expansion Project

Municipal solid waste from Lee County and Hendry County is processed at the Lee County Solid Waste Resource Recovery Facility (the “Facility”). Lee County (the “County”) owns the Facility, which began commercial operation in December 1994. The Facility’s current permitted capacity is 1,320 tons per day (tpd), provided by two 660-tpd boiler units, at a reference waste of 5,000 Btu. Covanta Energy of Lee, Inc. operates and maintains the Facility under the terms of a Service Agreement with the County that runs through 2014. Covanta also designed and constructed the Facility. The expansion of this Facility will be the first new construction of a municipal waste combustion (MWC) unit since the New Source Performance Standards were adopted. Despite the County’s comprehensive recycling program, the amount of solid waste the County delivers to the Facility has increased each year since the Facility began operation, primarily due to population growth. In 1999, this amount reached the Facility’s guaranteed annual capacity of 372,300 tons. In 2000, the Facility processed over 392,000 tons of municipal solid waste, while the County landfilled nearly 44,000 additional tons of processible waste. Current population projections for Lee and Hendry Counties suggest that processible solid waste generation will continue to increase, reaching nearly 550,000 tons by 2010. Rather than landfilling processible waste generated in excess of the Facility’s current capacity, it is the County’s intention to expand the Facility by adding a third 660-tpd boiler unit which would increase the Facility’s permitted capacity to 1,980-tpd. The original application for the Facility’s Power Plant Site Certification anticipated such an expansion, including provisions for a third 660-tpd MWC unit. Certain provisions for this third unit were incorporated into the Facility’s design and construction as well. These included providing the physical space for the third unit, the physical space for an additional flue for the third unit, and sizing the tipping floor, refuse pit, and certain common equipment for three units. The expansion will require a second turbine-generator unit and expanded switchyard, an extension to the existing turbine-generator building, as well as the addition of a third boiler unit and air pollution control equipment. The expansion will also require modifications to certain equipment and systems common to all boiler units in order to meet the additional capacity requirements of the expanded Facility. As of February 2003, the County is waiting for the Florida Department of Environmental Protection to issue a draft PSD Air Permit and is on scheduled to go before the Power Plant Siting Board in September 2003.

Changing Waste-to-Energy in Nashville, Tennessee

For almost 30 years, the Metropolitan Government of Nashville and Davidson County has been relying on one of the more innovative approaches to waste management. Since the early 1970s, the now 1,000 tons per day WTE facility has been the primary energy source for supplying steam and chilled water for a downtown district energy system serving some 39 buildings. A recent review of alternatives has resulted in Metro deciding to close the facility and replace it with a more traditional district energy supply system and at the same time re-engineer its solid waste management programs to include more efficient collection and recycling programs. This paper will present the planning process and analysis that were done; describe the key factors that led to Metro Nashville’s decisions; detail the procurement and development process that has been initiated; and outline the timetable for implementing the decided upon changes. The authors believe this case study will provide insights for other WTE projects that from time to time struggle with peaceful co-existence with other elements of integrated solid waste management. The authors have been serving as advisors to Metro throughout this process. Mr. Gershman has recently been designated by Metro as its overall Project Manager for its District Energy System.

Ways to Improve the Efficiency of Waste to Energy Plants for the Production of Electricity, Heat and Reusable Materials

Up to now the emissions of waste-to-energy plants have been of major concern for the operators of waste incineration plants and the public. In Germany the emission standards for waste incineration plants have been very strict for more than 10 years, more stringent than for coal fired power plants, for example. Now the member states of the European Union are following suit with the same standards in accordance with European directive 2000/76/EC on the incineration of waste. Within a couple of years all European waste incineration plants will have to comply with the emission limits of directive 2000/76/EC. There is also legislation in the pipeline restricting landfilling of untreated waste. In view of the discussions about CO2 reductions the efficiency of today’s Waste to Energy (WTE) plants should be improved, even though — or rather because — waste is regarded to some extent as “green power”. With the same goal in mind the recovery rate of reusable materials from the incineration of waste or flue gas treatment should be improved. This will make it possible to reduce the amount of CO2 generated by the production of these materials from natural resources and to conserve natural resources.

Continued Performance and Economic Issues for the Polk County Minnesota Bituminous County Road Constructed With Municipal Solid Waste Combustor Ash

This paper is a follow up to previous installments presenting environmental, construction, performance and economic issues associated with Polk County CSAH 13. The CSAH 13 project was a demonstration of the use of municipal waste combustor (MWC) ash in bituminous. New structural and cost data is presented. The incorporation of MWC ash into bituminous pavements has been investigated in the United States since the middle 1970s. Thus far, most, if not all of these projects, have attempted to answer the questions: Is it safe? Is it feasible? Or does it provide an acceptable product? The presented project answers these questions on a new level. MWC ash amended bituminous was used to construct a portion of 2.25 miles of road in Northwest Minnesota. Significant environmental and structural testing was performed prior to, during and after construction. Environmental testing on this project has shown that the use of MWC ash in bituminous pavement, as performed, is safe. In addition, economic analysis shows important financial advantages by using ash-amended bituminous. Structural testing showed a 36% increase in stability, 19% increase in flow and a 17% increase in spring season axle load capacity. Improvement in resistance to freeze-thaw cracking was also shown.

Collier County, Florida: Consideration of Gasification as a Long-Term Waste Management Solution

Collier County, Florida (“County”) is in the midst of developing an integrated waste management program. Unlike many counties, Collier County owns a landfill with sufficient long-term landfill capacity to last another 15 years. However, due to the Board of County Commissioner’s (“Board”) desire to have a 50-year solution for solid waste, the County has set upon a course to divert waste from the landfill to the maximum extent possible. In doing so, the County solicited long-term waste management solutions from private companies capable of processing the majority of the municipal solid waste generated in the County. Over the past two years, the County has considered several of these alternatives ranging from MSW composting to mass-burn waste-to-energy; however, based on an evaluation of a wide range of impacts, gasification was selected as the preferred alternative. With this focus, the County issued a Request for Proposal (“RFP”) in November 2001 for a design, build, own, operate, and finance gasification project. The County received three proposals in April 2002 in response to the RFP. To date, the County has completed the proposal evaluation process and has ranked the top two responsive firms: Interstate Waste Technologies (“IWT”) and Brightstar Environmental (Florida), LLC (“Brightstar”) based on experience, technical approach, business arrangement, and cost. If implemented, this project will be the only commercial gasification project operating in the United States. This paper will provide insight into various stages of the project, from development through to the current status of the project, as well as the strategic policy, financial, and technical considerations that make this opportunity a good fit for the County. An emphasis will also be placed on comparing and contrasting the benefits and drawbacks of each technology, such as processing methodology, cost, redundancy, and scalability.