Co-Firing Coal: Litter Biomass Blends in a Laboratory Scale Boiler-Burner
Ben Thiena, Ben Lawrenceb and Kalyan Annamalaic
Texas A&M University, College Station, TX, 77843-3123, USA.
abenfthien@yahoo.com
blawrence030182@tamue.edu
ckannamalai@tamu.edu
ABSTRACT
Chicken houses are an example of concentrated animal feeding operations that produce large amounts of animal waste that must be safely used or disposed. Some animal manure is used as fertilizer, and some is stockpiled, but there are limits to the amount of manure that can safely be used as fertilizer and stored manure carries the risk of ground or water pollution. In order to safely dispose of excess manure, it is proposed that it be mixed with coal and then fired in convention utility boilers in a 90:10 blend by mass, a process know as co-firing. The high temperatures produced by the coal will allow the manure to be completely combusted. Unfortunately, biomass has a low heating value, a high ash content, a high sulfur content, and a high nitrogen content, which can lead to combustion problems. In this research the performance of a laboratory scale boiler burner was evaluated while firing coal and coal:manure blends to determine the combustion performance when switching from coal to biomass fuel blends. The 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 .80 and .95, showing that the addition of animal based fuels will not adversely affect particle burnout. The pollutant emission for the fuels were also evaluated, and the results show that the addition of litter biomass will not increase the emission of NO even though the fuel nitrogen in the blended fuel is increased by 8-20 percent with the addition of 10% animal manure. The 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 to a coal:manure blend will not result in a large decrease in boiler performance or increase in pollutant emissions, despite the reduction in fuel quality.
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