Kadam, Kiran (PureVision Technology, Inc.511 McKinley Ave., Fort Lupton, CO, 80621; Phone: 303-857-4530; Fax: 303-857-0323; Email: Carl@PureVisionTechnology.com)
Greenhouse Gas Reduction Opportunities via Processing Agricultural Residues in Rural Biorefineries
K.L. Kadam *, E.R. Lehrburger, C.H. Lehrburger
A new biorefining process referred to as “reactive fractionation” is presented in the context of greenhouse gas (GHG) reduction using corn stover and wheat straw as feedstocks. This closed-loop process is under development and is being optimized using a continuous 10-kg/hr process development unit. The novel biomass fractionation technology relies on an extruder apparatus that minimizes reagent and water use and accomplishes biomass fractionation in a relatively short time compared to traditional biomass pretreatment or pulping processes. This two-stage approach dissolves and separates hemicellulose and lignin from biomass in sequential stages, leaving relatively pure cellulose. Enzymatic hydrolysis of this cellulose stream requires significantly lower enzyme loadings for hydrolysis with a corresponding reduction in production costs. The hemicellulose sugars captured in the hydrolyzate liquor and cellulose-derived glucose are used to produce ethanol. Ethanol produced from lignocellulosic feedstocks can be used as a renewable fuel or fuel oxygenate. The non-sulfur lignin is highly reactive and can be used for value-added products or for on-site co-generation of steam and electricity. This paper quantifies the GHG reduction potential in such a process using agricultural residues. The offset credits attributable to the bio-products and bio-energy generated in the proposed biorefinery configuration are computed by comparing, on an energy-equivalent basis, ethanol vs. gasoline combustion, electricity generation from lignin vs. coal, and biogas vs. natural gas combustion. Environmental impacts will be discussed in terms of net CO2 emissions and the total greenhouse gas potential from major GHGs, i.e., CO2, CH4, and N2O. Greenhouse gas reduction would stem from the following attributes of the biorefinery scenario: proposed process is a net producer of energy, a portion of the total energy consumption is from renewable sources, and the fossil-derived CO2 emissions are lower because the carbon dioxide released from ethanol, methane and lignin combustion is eventually recycled via photosynthesis. Potential monetization of CO2 offset credits will be reported based on current clearing prices at the Chicago Climate Exchange. The results for criteria pollutants such as carbon monoxide, non-methane hydrocarbons, SOx, NOx, and particulates will also be generally discussed. Besides affecting global issues of climate change and conservation of natural resources, e.g., fossil reserves, the proposed biorefinery scenario also impinges positively on local air quality. Results will be presented for a commercial scenario based on a single biorefinery configuration, which will be extrapolated to full market penetration defined by corn stover and wheat straw availability on a sustainable and economic basis in the Central Great Plains (U.S.). The projected impacts for utilizing a portion of these abundant feedstocks will be reported to emphasize the potential impact of the proposed technology in reducing GHG emisions. Although specific for the agricultural states in the American Midwest, such information should also be generically applicable to other regions of North America and elsewhere in processing of waste/excess biomass via the biorefinery scenario. Successful commercialization of such projects will result in similar positive environmental impact.