Fixed-bed gasification of feedlot manure and poultry litter biomass
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The U.S. cattle industry is a $175 billion industry with an estimated 100 million cattle. About 10 million head of these cattle are in feedlots producing harvestable manure. At the same time, the U.S. poultry industry is the world's largest producer and exporter of poultry meat. Not surprisingly, one outcome is the production of a large quantity of manure byproducts, with approximately 60 million tons of dry harvestable animal manure produced annually from confined livestock and poultry. This article describes a method of extracting energy from feedlot manure or poultry litter biomass either individually or combined with each other. High-ash (approximately 45% dry weight basis) feedlot biomass (HFB) and poultry litter biomass (HLB) were gasified in a 10 kW (thermal) fixed-bed, counter-current atmospheric pressure gasifier to generate a mixture of combustible gases that could be further burned to generate heat. This article discusses the effect of the biomass particle size on the composition of the product gas leaving the gasifier, the temperature profiles in the fixed bed, and the ash fusion of HFB and HLB during gasification. Air-blown gasification of the biomass fuels yielded a low-Btu gas with a higher heating value of 4.4 0.4 MJ/m3and an average product gas composition (dry basis) of H2: 5.8 1.7%, CO: 27.6 3.6%, CH4: 1.0 0.5%, CO2: 6.7 4.3%, and N2: 59.0 7.1%. The overall average equivalence ratio was 2.82 0.43 on a dry ash-free basis. The experimental results also show that high-alkaline content fuels, such as HLB (Na2O + K2O = 16.7% of ash), can be gasified by blending with lower-alkaline content fuels, such as HFB (6.0%), to reduce agglomeration in the fuel bed without significantly affecting the heating value of the product gas. The gasification of HLB and HFB yields a low-Btu gas that can be combusted to generate heat for steam or power generation. The process has potential for reducing transportation costs for traditional cropland-based manure application in some regions.
