Advancements in Grate Cooling Technology

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.

Concepts and Experiences for Higher Plant Efficiency With Modern Advanced Boiler and Incineration Technology

The efforts for reducing CO2 Emissions into atmosphere and increasing costs for fossil fuels concepts are the drivers for Energy from Waste (EfW) facilities with higher plant efficiency. In the past steam parameters for EfW were requested mainly at 40 bars and 400 °C (580 psi and 752 F). In case of coal fired power plants at the same location as the EfW facilities higher steam parameters at 90 bar, 520 °C (1305 psi, 968 F) have been used for the design of stoker and boiler. This long-term experience with higher steam parameters is the platform for the todays and future demand in higher plant efficiency. Increase in EfW plant efficiency is achievable by increasing temperature and pressure of live steam going along with optimized combustion conditions when using well proven grate technology for waste incineration. On the other hand higher steam parameters result in higher corrosion rates on the boiler tubes and the optimization of the combustion conditions are limited by the burn out quality requirements of slag and flue gas. Advantages and disadvantages have therefore to be balanced carefully. This paper will present different measures for optimized boiler and combustion conditions compared to an EfW plant with live steam at 40 bars and 400 °C (580 psi and 752 F) and 60% excess of combustion air. Plants operated at these conditions have very low maintenance costs created by corrosion of boiler tubes and show performance with very high availability. The following parameters and experiences will be evaluated: - reduction of excess air; - flue gas temperature at boiler outlet; - higher steam parameters (pressure and temperature); - heating surfaces for steam superheating in the radiation boiler section; - steam reheating; - external superheaters using auxiliary fuels. The comparison of the different methods for increasing the efficiency together with resulting technology challenges incorporates the experiences from modern EfW reference facilities built in Naples/Italy, Ruedersdorf (Berlin)/Germany and Heringen/Germany.

Bio Green Waste-to-Energy: An Old Technology With a New Future

After 17 years of quiet dormancy, modern incineration, now known as “municipal waste combustion,” is headed for a big comeback here in America. These modern combustion facilities often include energy recovery, and are known as “Waste-to-Energy” plants, or “WTE” plants for short.

A Risk Assessment Framework for Evaluating Health Risks From New and Emerging Waste Management Technologies

Until recently, landfills and waste-to-energy (WTE) facilities were the two basic technologies available to process residual (post-recycled) municipal solid waste. These technologies have both advantages and drawbacks, and their relative merits have been debated many different ways. Risk assessments of both technologies have been used to examine their potential threats to human health and the environment, and have found both landfills and WTE facilities can be operated in an environmentally acceptable manner. Neither alternative, however, has gained general public acceptance, and planned projects are often controversial. There remains considerable skepticism, for example, that landfill liners will be effective over long periods of time, and a general uneasiness over the safety of waste combustion. The interest in emerging conversion technologies, such as gasification and anaerobic digestion, as an alternative to conventional landfills and WTE facilities is thus understandable. However, there is some concern that the environmental impacts of conversion technologies are not well understood, as no commercial facilities exist in the United States. Development of a risk assessment framework for evaluating conversion technologies will serve two purposes. First, it will ultimately facilitate objective evaluation of potential risks to health and the environment as well as comparative evaluation with respect to traditional landfill and WTE technologies. Second, it will initiate a conceptual model of environmental impacts that will be useful in identifying key emissions and data gaps. Our presentation will set forth an initial risk assessment framework, focusing on the emissions and residuals of conversion technologies, and using available data to characterize and project health risk impacts.

Palm Beach County WTE Expansion Model

Palm Beach County (Florida) Solid Waste Authority built an integrated solid waste management system in the 1980s and 1990s around an 1,800 tpd Refuse Derived Fuel (RDF) Waste-to-Energy (WTE) facility. The system included a network of five regional transfer stations, Subtitle D sanitary landfill, recovered materials processing facility, composting facility, metals processing facility and household hazardous waste collection program. The WTE, which became operational in 1989, was built with two 900 tpd RDF combustion units. Space was provided for the addition of a third combustion unit, a second turbine-generator and an extra flue was installed in the facility’s stack. By 2004, the WTE was fifteen years old. It had been running at over 125% availability and well above its nominal capacity for almost a decade. Landfill capacity was being consumed at a rate which would see it filled in less than 20 years. The County had been hit with repeated hurricanes in recent years and the County’s population was continuing to grow making landfill capacity projections far from certain. The Authority began an assessment of its long term capacity options which included renovation of its existing WTE facility, expansion of that facility, development of a new WTE facility, development of a new Subtitle D Landfill and several out-of-county options. This paper will focus on the results of this assessment with emphasis on the current efforts to develop a new Mass Burn WTE facility with a capacity of 3,000 tpd and a commercial operations date of 2015. It will be the largest new WTE built in North America in more than 20 years. The choice of Mass Burn technology, facility and combustion module sizing, air pollution control technology, facility site selection, environmental permitting, public outreach program, project financing and procurement and contracting approach will be discussed.

Updated Case Study of Fireside Corrosion Management in an RDF Fired Energy-From-Waste Boiler

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.

Experimental Research on Microwave Induced Thermal Decomposition of Printed Circuit Board Wastes

As a result of electronic industry development in China, significant amount of Printed Circuit Board (PCBs) wastes are generated. The thermal decomposition via combustion or pyrolysis/gasification is considered to be a feasible disposal way for PCBs. To understand the consequences of pyrolysis, gasification or combustion in WTE facilities, thermo-gravimetric analysis (TGA) has been carried to characterize the thermal decomposition mechanisms and extract the kinetic parameters in various atmospheres (N2, CO2 and air) to simulate different regions in WTE applications. TGA tests in N2 atmosphere showed there was only one significant reaction in the low temperature range of 270∼350°C, which was the decomposition of epoxy resin in PCBs. The behavior in CO2 atmosphere was similar with that in N2. However, the PCBs oxidation process in air atmosphere showed two thermal decomposition steps. One was the thermal decomposition similar to the volatilization in N2 atmosphere and the second step showed oxidation behavior. Some pre-processing was investigated to explore possible benefits in WTE combustion. PCBs waste was pyrolyzed using a microwave tubular furnace. The liquid product were collected and then identified by means of gas chromatography–mass spectrometry (GC–MS). Most of the Br contained in PCBs was released into non-condensable gas in the form of HBr. The liquid product contained a large amount of phenolic compounds, bisphenol A and other aromatic compounds that can be used to produce related chemical products or used in WTE facilities. The experimental results including the thermal kinetic parameters and microwave induced pyrolysis indicate the complex mechanisms that take place during the pyrolysis of PCBs wastes.

Analysis of Thermal Plasma-Assisted Waste-to-Energy Processes

Thermal plasma torches convert electricity to high-temperature thermal energy by applying a high voltage across a flowing gas stream. Plasma torches are used extensively for producing metallic and ceramic coatings and also for vitrifying hazardous materials, such as asbestos-contaminated wastes. In the last decade, several thermal plasma processes have been proposed for treating municipal solid wastes (MSW). This research is based on a critical analysis of previous work by the Earth Engineering Center and on published reports and examines the possibilities for the proposed thermal plasma (TP) processes to be recover energy from MSW as an alternative to the conventional waste-to-energy (WTE) by grate combustion. In particular, this study will investigate two prominent thermal plasma technologies that are presently under development: The Alter NRG “Westinghouse” process in the U.S. and the Europlasma process in France. The environmental impacts and the technical economic aspects of plasma-assisted WTE processes will be compared to the traditional process of MSW combustion on a moving grate.

Ultrafine Particles From WTE and Other Combustion Sources

The size of combustion generated particles ranges from a few nanometers up to 1 micron, whereas the size of naturally occurring PM such as pollens, plant fragments, and sea salt is generally larger than 1 micron. Particles generated by photochemical processes in the atmosphere are generally smaller than 1 micron. Ultrafine particles (UFP), also called “nanoparticles”, are <0.1 micron and in recent yearshave attracted attention due to potential adverse health effects associated with them. The contribution of UFP to the total PM mass is very small. However, they dominate the total number of particles in urban aerosols. Their sources are both mobile and stationary combustion sources and also gas-to-particle conversions. In coal and waste combustion systems, UFP are hypothesized to be generated mainly by nucleation of metal vapors. Coal naturally contains a vast range of inorganic elements among which are heavy metals. Sources of heavy metals in MSW include batteries, electronic devices, light bulbs, house dust and paint chips, food containers, used motor oils, plastics, yard wastes and some papers. The input of these metals into WTE facilities can be controlled by better source-separation of metal-containing materials. In 2007 almost 50% of the approximately 4.16 billion MWh generated in the United States was produced by coal power plants whereas only 0.3% was generated by the WTE industry. A preliminary study has shown that in terms of contribution to UHF in the atmosphere, MSW combustion has a minor effect in comparison to coal-fired power plants in the U.S. This paper will report on the results of this investigation.

Generating Renewable Electric Power and Reducing Carbon Footprint by Converting Low-Grade Heat to Electrical Energy

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.