Theoretical Heat Needs for Digestion of Raw and Diluted Sand-Laden Dairy Manure

摘要

Pairing sand-laded dairy manure (SLDM) and anaerobic digestion requires removal of stall bedding sand prior to or within the digestion chamber. Passive and mechanical sand separation devices require raw SLDM to be diluted. Dilution of SLDM prior to digestion increases the heat requirements required to reach digester operational temperature. The objectives of this analysis were to determine the theoretical required heat, biogas production, and heat available from biogas utilization for a digester processing raw and diluted SLDM at different influent temperatures. Referenced values and reasonable assumptions were used to calculate theoretical required heat, biogas production, and available heat for 100 lactating dairy cows. Dilution ratio and digesterinfluent temperature had a greater effect on heat required to reach operation temperature than the mass of sand in the digester influent. An engine-generator set and biogas boiler produce enough heat from biogas generated in an anaerobic digester to raise raw SLDM from a temperature of 0-37.7 deg C. A biogas boiler produces enough heat to increase diluted SLDM at a ratio of 2 to 1 from a temperature of 0 -37.7 deg C. An engine-generator set provides enough heat to raise SLDM at a 1 to 1 dilution ratio from a temperature of 18.3 -37.7 deg C. On the basis of heat required, digestion of raw and diluted SLDM was shown to be feasible if 1) digesters are reasonably efficient at converting biologically available volatile solids to biogas and 2) dilution water to separate sand from manure is kept to a minimum.