Environmental and economic evaluations of energy recovery from agricultural and forestry residues

Abstract

Agricultural and forestry residues have been converted to energy for centuries. The technologies employed range from straightforward approaches such as combustion to produce heat to more involved approaches such as pyrolysis of the residues to produce medium-Btu synthetic gas, charcoal, and oil. Thus there is no one technology that can be characterized as the best or most promising for conversion of agricultural and forestry residues into energy. Therefore, to accurately assess the potential of agricultural and forestry residues as energy resources, an array of current conversion options should be addressed. Four conversion methods and five residues are examined in this report, which describes six model systems: hydrolysis of corn residues, pyrolysis of corn residues, combustion of cotton-ginning residues, pyrolysis of wheat residues, fermentation of molasses, and combustion of pulp and papermill wastes. Estimates of material and energy flows for those systems are given per 10/sup 12/ Btu of recovered energy. Regional effects are incorporated by addressing the regionalized production of the residues. A national scope cannot be provided for every residue considered because of the biological and physical constraints of crop production. Thus, regionalization of the model systems to the primary production region for the crop from which the residue is obtained has been undertaken. The associated environmental consequences of residue utilization are then assessed for the production region. In addition, the environmental impacts of operating the model systems ae examined. On the basis of estimates found in the literature, capital, operating, and maintenance cost estimates are given for the model systems. The study indicates that the most serious environmental impacts arise from residue removal rather than from conversion.