ARS | Publication request: High-temperature pyrolysis of blended animal manures for producing renewable energy and value-added biochar

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 28, 2010
Publication Date: November 19, 2010
Citation: Ro, K.S., Cantrell, K.B., Hunt, P.G. 2010. High-temperature pyrolysis of blended animal manures for producing renewable energy and value-added biochar. In: Proceedings of the First International Conference on Green and Sustainable Technology: Research and Workforce Development, November 18-19, 2010, Greensboro, North Carolina. 4 pp.

Technical Abstract: In this study, we used a commercial pilot-scale, skid-mounted pyrolysis reactor system to produce combustible gas and biochar at 620ºC from three sources (chicken litter, swine solids, mixture of swine solids with rye grass). Pyrolysis of swine solids produced gas with the greatest higher heating value (HHV) followed by the mixture of swine solids with rye grass and chicken litter. Relatively high S-containing gases were produced; dimethyl sulfide and methyl mercaptan concentrations were higher than the OSHA PEL limits. Biochar yield ranged from 43 to 49% based on dry weight with about 53% of carbon recovery. While the HHV of the chicken litter biochar was slightly below that of low rank coals, swine-based biochars had HHVs between high and low rank coals. Approximately 50% of the feedstock energy was retained in biochar and 25% in produced gases. Manure biochars contained higher concentrations of P and K than that of original manure feedstocks. Consequently these could be used as a low-grade fertilizer to improve soil fertility and crop yields. Extremely high energy (232.3 MJ/kg) was required to make 1 kg of biochar from wet swine manure with 97% MC. However, dewatering of the wet swine manure to 75% MC substantially reduced the external energy requirement by 19 folds. Mixing of dried biomass such as rye grass with the dewatered swine solids almost eliminated the need for external energy. If one can co-pyrolyze wet animal wastes with additional feedstock that are drier and more energy dense than rye grass such as waste plastic pellets, it may be possible to produce both valuable biochar and extra power. In addition, applications of the biochar as a soil amendment and as a precursor for activated carbon will also be discussed at the meeting.