Cofiring Animal-Tissue Biomass in Coal-Fired Boilers to Dispose of Specified Risk Materials and Carcasses

摘要

The objective of the project was to demonstrate the technical viability of cofiring ATB in a coal-fired 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 deactivation/pathogen destruction.rnOverall, the project successfully demonstrated that carcasses and SRMs can be cofired with coal in a bubbling FBC. Feeding ATB into the FBC did, however, present several new challenges not encountered with other types of feedstocks previously tested in Penn State's FBC. Specifically, handling/feeding issues were encountered during the testing that 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 overture air ports used to ensure complete combustion.rnEmissions of SO_2 were reduced when firing ATB since the overall sulfur content in the fuel decreased with the addition of ATB. However, in a full-scale system, limestone is used for SO_2 control, whereas it was not for the pilot-scale testing, hence, SO_2 emissions would be similar in both scenarios. As expected, emissions of NO_x were reduced as the level of flue gas recirculation was increased.