Analysis of direct combustion characteristics of pig manure based on thermogravimetry

Abstract: Pig manure causes severe environmental pollution due to inappropriate treatment. Utilization of energy from pig manure could reduce the environmental pollution, and provide large amounts of energy. At present, the energy utilized from pig manure is limited to anaerobic fermentation, which needs large investment and causes secondary pollution. Direct combustion technology is a new technology to generate energy by utilizing pig manure. To investigate the feasibility of this technology, piglets, fattening pig and sows were fed on corn-soybean meal diets and their fresh manure was collected in this study. The content of moisture and calorific value were measured. Lignocellulose including cellulose, hemicellulose and lignin were estimated through Van-Soest detergent analysis. The flammability index Cb, combustion stability index G and comprehensive combustion index SN of pig manure were investigated using a thermogravimetric method analysis. Because the fresh manure has higher moisture content, and honeycomb briquette type of manure could be easily dried by air, the compressive strength and combustion characteristics of the manure burned in boiler were also studied. The results showed that the moisture content from the piglets manure (76.85%) was higher than those from fattening pig (74.76%) and sows (74.28%). The highest and lowest calorific values of the fresh pig manure were 16.72-17.65 MJ/kg and 14.24-15.34 MJ/kg, respectively. The amounts of cellulose, hemicellulose and lignin in sow manure were the highest, and values from the piglets manure were lower than the other two groups. The values of Cb, G and SN of three fresh manure were (1.552-1.652)×10-5 mg/(min·℃2), (1.393-1.466)×10-6 mg/(min·℃2) and (6.480-7.305) ×10-9 mg2/(min2·℃3) respectively. The values of Cb, G and SN under the coal control were 0.092×10-5 mg/(min·℃2), 0.798×10-6 mg/(min·℃2) and 0.118×10-9 mg2/(min2·℃3) respectively, they were lower than those from the fresh manure. Our study also indicated that the fresh pig manure could be molded easily and had good formability. The compressive strength of the end face of pig manure pressed into honeycomb briquette type was 475 N per block. The combustion experiments showed that fresh pig manure had a good combustion performance with a volatile combustion state in boiler. In conclusion, our results demonstrated that the amount of energy from the fresh pig manure is slightly lower than that from the coal, but the pig manure had better combustion characteristics than coal. This study could provide a basis and reference to use pig manure as an ideal biomass energy through direct combustion. With this technology, pig manure could be eliminated on the spot and large amount of energy could be provided for heating pig farms. In order to improve the feasibility of pig manure burning for energy, it is necessary to further develop new equipments for pig manure processing and new boiler according to combustion characteristics of pig manure, and study the effects of the combustion exhaust components on environment.