Feasibility study for anaerobic digestion of agricultural crop residues. Final report

This study provides cost estimates for the pretreatment/digestion of crop residues to fuel gas. Agricultural statistics indicate that the crop residues wheat straw, corn stover, and rice straw are available in sufficient quantity to provide meaningful supplies of gas. Engineering economic analyses were performed for digestion of sheat straw, corn stover, and rice straw for small farm, cooperative, and industrial scales. The results of the analyses indicate that the production of fuel gas from these residues is, at best, economically marginal, unless a credit can be obtained for digester effluent. The use of pretreatment can double the fuel gas output but will not be economically justifiable unless low chemical requirements or low-cost chemicals can be utilized. Use of low-cost hole-in-the-ground batch digestion results in improved economics for the small farm size digestion system, but not for the cooperative and industrial size systems. Recommendations arising from this study are continued development of autohydrolysis and chemical pretreatment of agricultural crop residues to improve fuel gas yields in an economically feasible manner; development of a low-cost controlled landfill batch digestion process for small farm applications; and determination of crop residue digestion by-product values for fertilizer and refeed

Feasibility study for anaerobic digestion of agricultural crop residues. Dynatech report No. 1935

The objective of this study was to provide cost estimates for the pretreatment/digestion of crop residues to fuel gas. A review of agricultural statistics indicated that the crop residues wheat straw, corn stover, and rice straw are available in sufficient quantity to provide meaningful supplies of gas. Engineering economic analyses were performed for digestion of wheat straw, corn stover, and rice straw for small farm-, cooperative-, and industrial scales. The small farm scale processed the residue from an average size US farm (400 acres), and the other sizes were two and three orders of magnitude greater. The results of the analyses indicate that the production of fuel gas from these residues is, at best, economically marginal, unless a credit can be obtained for digester effluent. The use of pretreatment can double the fuel gas output but will not be economically justifiable unless low chemical requirements or low cost chemicals can be utilized. Additional development is necessary in this area. Use of low cost hole-in-the-ground batch digestion results in improved economics for the small farm size digestion system, but not for the cooperative and industrial size systems. Recommendations arising from this study are continued development of autohydrolysis and chemical pretreatment of agricultural crop residues to improve fuel gas yields in an economically feasible manner; development of a low cost controlled landfill batch digestion process for small farm applications; and determination of crop residue digestion by-product values for fertilizer and refeed