Demonstrate the Technical Feasibility of Cofiring Animal-Tissue Biomass (SRMs and Carcasses) With Coal in a Pilot-Scale Bubbling Fluidized-Bed Combustor

Findings: The objective of the project was to demonstrate the technical viability of cofiring ATB in a coal-fired fluidized-bed combustor (FBC) as an option for disposing of SRMs and carcasses. This testing is necessary to demonstrate to the regulatory agencies, USDA, FDA, and industry the technical viability of this disposal option prior to securing funding for a full-scale demonstration. The purpose of this testing was to assess technical issues of feeding/combusting the animal-tissue biomass and not to investigate prion/pathogen destruction. Overall, the project successfully demonstrated that carcasses and SRMs can be cofired with coal in a bubbling FBC. Feeding ATB into the FBC presented several new challenges not encountered with other types of feedstocks previously tested at Penn State. Specifically, handling/feeding issues were encountered during the testing; however, they were primarily artifacts of the small scale of the equipment and the specific feeders available for use with such a heterogeneous material. These issues would not be expected at the full scale since full-scale units routinely handle low-quality fuels. After several feeder modifications and trials at different injection locations in the pilot-scale FBC, an overbed feed system was selected for the testing. In addition, a 4-inch diameter screw feeder was used and this large feed size, relative to the combustor diameter of 1 foot, resulted in fuel slugging into the combustor. This slugging, in turn, resulted in fluctuating carbon monoxide and total hydrocarbon emissions, which are indicators of incomplete combustion. However, the average emissions from ATB cofiring tests in many cases were similar to the average emissions from coal baseline testing, indicating that under the conditions tested in the small-scale unit, the ATB performed similarly to coal. In a full-scale unit, the disproportionate ratio of feed line size to unit diameter would be eliminated thereby eliminating feed slugging. Also, the ATB would either be injected into the bed, thereby ensuring uniform mixing and complete combustion or the ATB would be injected directly above the bed with overfire air ports used to ensure complete combustion. In summary, the objectives of the project were met in that cofiring carcasses and SRMs with coal was successfully demonstrated. While the test conditions were not optimum, due to the equipment limitations, performance of the ATB cofire tests was comparable to coal baseline testing. Statistically it was shown that the ATB feed location had a greater effect on CO emissions, which were used as an indication of combustion performance, than the fuel type due to feeding difficulties. Baseline coal (fed about 2 feet above the bed) tests and tests cofiring ATB1 into the bed were statistically indistinguishable. This indicates that a demonstration at the full scale, which is the next activity in demonstrating this concept, should be successful since equipment limitations would not be a factor. Hence, emissions cofiring ATB with coal would be expected to be similar to that when firing coal only.