The estimated annual U.S. supply of fed-cattle SRMs, cow carcasses from packinghouses, on-farm mortalities, and cull cow SRMs is 850, 75, 2500, and 650 million pounds, respectively [1, 2]. With heating values ranging from 2300 to 6200 Btu/lb as fired, approximately 15 trillion Btu of energy is available for use as a fluidized-bed boiler fuel [1, 2]. Figure 1 illustrates the energy value of various boiler feedstocks, both fossil fuels and biofuels, which have been tested and/or characterized at Penn State [3]. Feedstocks with energy densities as low as 4000 Btu/lb (e.g., poultry litter) are fired in boilers as sole fuels while fuels with even lower energy densities are successfully cofired with coal [3].
With the implementation of USDA’s recently launched enhanced BSE (bovine spongiform encephalopathy) surveillance program (effective June 1, 2004), the need for additional cost-effective options for carcass disposal is necessary [1]. Additionally, the need for large-scale carcass disposal should a catastrophic event occur needs to be developed [4]. The National Agricultural Biosecurity Center Consortium USDA-APHIS (Animal Plant and Health Inspection Service) Cooperative Agreement Project, Carcass Disposal Working Group [5] reviewed 8 disposal options for carcasses/SRMs, including burial, incineration, composting, rendering, lactic acid fermentation, alkaline hydrolysis, anaerobic digestions, and novel technologies. This study did not review combustion in boilers, which was definitely an oversight. EPA (Fran Kremer and Paul Lemiuex, July 2004) have subsequently noted that: there are several design options for industrial and utility boilers available offering significant capacity for utilizing carcasses and SRMs; boilers have good control over combustion processes; and they provide particulate matter and acid gas control [6]. Although Kremer and Lemieux identified disadvantages of this technique in that fluidized-bed boilers are not permitted to burn wastes, they lack suitable feeding equipment, and there will be permit issues dealing with biocontaminants, they also stated that no technical issues appear to be insurmountable. Handling the carcasses/SRMs is not considered problematic. Fluidized-bed combustors have historically utilized low-grade fuels such as paper mill sludge, coal-water mixtures/pastes, waste coal, and others [3, 7]. A variety of handling equipment is available for these fuels. Similarly, the rendering industry processes and handles carcasses and other animal-tissue biomass (ATB); consequently, the handling, grinding, and delivery of the ATB into a boiler is not an issue. Also, fluidized-bed boilers have been used to combust hazardous wastes, plastics, and waste oils with complete combustion achieved. Fluidized-bed combustion is a proven technology for low- grade fuels and is ideal for utilizing carcasses and SRMs.
Although the disposal technologies listed above are being considered by industry and regulatory agencies, Cargill Taylor Beef, with the assistance from Penn State, has been exploring the possibility of cofiring ATB in coal-fired boilers as an additional disposal option. In July 2004, Penn State, Cargill Taylor Beef, and McDonalds Corporation hosted a workshop at Penn State to discuss and develop strategies to utilize ATB as a fuel in industrial and utility boilers, brainstorm on the development of a national infrastructure that could utilize ATB as a fuel on both a routine and large- scale emergency basis, and stimulate public-private collaboration [8]. Representatives from federal and state government, meatpacking and rendering industries, food industry and service, banking, equipment supply, cogeneration companies, fluidized-bed boiler manufacturing, and academia attended the workshop. The workshop consisted of presentation that outlined the issues of carcass and tissue disposal and provided overviews of the technology of energy generation from fluidized- bed boilers, followed by breakout sessions that addressed the issues of concept-to-commercialization, logistics, and economics and incentives. A major highlight of the presentations was that the boiler vendors informed the audience that the concept of cofiring ATB with coal was technically sound. One of the key points and future action items developed during the workshop included performing pilot-scale testing to demonstrate to regulatory agencies, USDA, FDA, and industry the technical viability of this option [8]. It was determined that this is necessary prior to securing funding for a full-scale demonstration cofiring carcasses/SRMs with coal.
The objectives of this study were to demonstrate the technical viability of cofiring animal tissue biomass in a coal-fired fluidized-bed combustor as an option for disposing of Specified Risk Materials (SRMs) and carcasses.
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