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Co-Firing Coal: Poultry Litter Biomass Blends in a Laboratory-Scale Boiler-Burner

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 55(2): 681-688. (doi: 10.13031/2013.41377) @2012
Authors:   B. F. Thien, B. D. Lawrence, J. M. Sweeten, K. Annamalai
Keywords:   Biomass, Coal, Co-firing, Combustion, Manure, Nitrous oxide, Poultry litter

Broiler chicken houses are an example of concentrated animal feeding operations that produce large amounts of animal waste that must be used or disposed of in an environmentally acceptable manner. Most of the collected poultry litter is used as fertilizer with or without intermediate storage (i.e., stockpiled). There are limits to the amount of manure that can safely be applied as fertilizer, and stored manure carries the risk of ground or surface water pollution. Combustion is proposed as an alternative method to safely dispose of excess poultry litter. The proposed disposal technique is mixing coal with poultry litter (e.g., 90:10 blend of coal:poultry litter by mass) and firing the resulting blended fuel in a convention utility boiler. This process is known as co-firing. The high temperatures produced by the coal allow the poultry litter to be completely combusted. Relative to coal, poultry litter biomass (LB) has a small heat value, high ash content, high sulfur content, and high nitrogen. All of these facts could lead to combustion and emissions problems when co-firing coal with litter biomass. In this research, the performance of a laboratory-scale boiler burner was evaluated while firing coal or coal:LB blends to determine the combustion performance. The carbon monoxide (CO) emissions for the fuels were similar, with the amount of CO produced being greater at lower excess air percentages. The burnt fraction for both of the fuels was between 0.80 and 0.95, showing that the addition of LB-based fuels does not adversely affect particle burnout. The pollutant emissions for the fuels were also evaluated, and the results show that the addition of litter biomass does not increase the emission of nitrous oxide (NO), even though the fuel nitrogen in the blended fuel is increased by 8% to 20% with the addition of 10% LB. The sulfur dioxide (SO2) emissions were also measured, but the results were inconclusive due to uncontrolled absorption of SO2 by the walls of the furnace. Overall, the results showed that switching from coal to a coal:LB blend does not result in a large decrease in boiler performance nor an increase in NO emissions, despite the relatively small reduction in fuel quality attributable to coal:LB blends.

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