Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2010
Publication Date: 9/14/2010
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. Industrial and Engineering Chemistry Research. 49:10125-10131.
Interpretive Summary: A skid-mounted commercial pyrolysis system was used to produce combustible gas and biochar from chicken litter, swine solids, and swine solids blended with rye grass. The skid-mounted reactor system heated the manures to 620 degrees Celsium without presence of oxygen. When swine solids were pyrolyzed, they produced gas with the highest heating value followed by the mixture of swine solids with rye grass and chicken litter. The heating value of the gas from pyrolyzing swine solids was slightly lower than that of natural gas. About 43 to 49 percent of original manures were converted to biochar. The heating values of the biochar made from swine solids and the mixture were similar to coals; the heating value of chicken litter biochar was slightly below that of coal due to high level of ash. The manure biochars contained high levels of phosphorous and potassium, which could be used as a low-grade fertilizer. Swine solids are usually wet and require a lot of energy for drying before proessing; however, mixing the dewatered swine solids with dried rye grass almost eliminated the need for external energy.
Technical Abstract: In this study, we used a commercial pilot-scale pyrolysis reactor system to produce combustible gas and biochar at 620 degrees Celsium 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 sulfur-containing gases were produced; dimethyl sulfide and methyl mercaptan concentrations were higher than the Occupational Safety and Health Administration's permissible exposure limits. Biochar yield ranged from 43 to 49 percent based on dry weight with about 53 percent 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 percent of the feedstock energy was retained in biochar and 25 percent in produced gases. Manure biochars contained higher concentrations of phosphorus and potassium 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 million joule/kilogram) was required to make 1 kilogram of biochar from wet swine manure with 97 percent moisture content (MC). However, dewatering of the wet swine manure to 75 percent 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.