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Dry Field Peas as Ethanol Feedstock

Growth of the corn-based ethanol production has contributed to increased corn demand and prices. In North Dakota for example, ethanol plants face great feedstock supply risk as corn production in the region is highly variable due to the state’s arid and northern climate. However, the state is a leading producer of dry field peas. Fractionated dry pea or field pea (Pissum sativum L.) are a potential ethanol feedstock replacement alternative for corn.

Fractionation is a process whereby the pea is separated into component parts, one high in protein and the other high in starch. The former is sold in traditional human and livestock consumption markets whereas the latter can be supplement corn to produce ethanol. An extensive body of research has been reported on the fractionation of peas for human consumption (Fedec, 2003). Dry peas can be fractionated by either wet milling or dry milling with air classification. Wet processing is used to produce more highly purified protein and starch, but this process is more difficult and requires higher amounts of energy for drying and refining of effluent streams. Dry milling is less expensive to build and operate, and is effluent free (Nichols et al., 2005).

Nichols et al., investigated the actual ethanol yield of starch-enriched field peas in a laboratory setting and found the yield to be 0.48 g ethanol/g pea starch), which is 85 percent of the theoretical yield. Therefore, if the whole pea were used, and assuming 46 percent starch on a dry basis, and allowing for the typical efficiencies of conversion, production of 3.4 gallons of ethanol from 100 pounds of field peas could be expected.  

Pryor, et al (2008), conducted fermentation analyses of blending pea starch with corn in a conventional dry-grind ethanol plant and found that the starch-enriched product from fractionated field peas had a neutral or slightly positive impact on ethanol production rates given similar initial starch loadings. Wilhemi, et al. (2009) constructed a detailed engineering process flow model of the process including a model of energy balances. Using this information, Gustafson, C., et al, (2008) developed a stochastic simulation model to evaluate economic feasibility and reduction of corn supply risks. Both engineering and economic analyses show that the investment and power costs for dry milling and air classifying equipment that is presently commercially available is prohibitively expensive. However, an even more significant factor are high pea feedstock prices, relative to corn. Corn prices would have to rise more than 20 percent before peas break even. An alternative approach not investigated was to mix whole or dehulled peas with corn without fractionation which might be more affordable.

 

References

Fedec, P. 2003. Air classification. Encyclopedia of food sciences and nutrition. San Diego, Calif., London Academic: 96-106.

Gustafson C., et al, “Economic Feasibility of Supplementing Corn Ethanol Feedstock with Fractionated Dry Peas: A Risk Perspective” Transition to a Bioeconomy: Risk, Infrastructure & Industry Evolution, Farm Foundation, Berkely, CA, June 24, 2008, 19pgs.

Nichols, N., B.S. Dien., Y.V. Wu., and M.A. Cotta. 2005. “Ethanol Fermentation of Starch from Field Peas.” Cereal Chemistry, AACC International, Inc 82(5): 554-558.

Pryor, S.W., Lenling, M, and D.P. Wiesenborn. 2008. Integrated Use of Field Pea Starch and Corn for Ethanol Production. ASABE International Meeting, July 1, 2008, Providence, RI.

Wilhelmi, A., D. Wiesenborn, C. Gustafson, S. Pryor. “Models for Fractionation of Field Peas to Supplement Corn Ethanol” Applied Engineering in Agriculture, 25(5), 2009:709-17

 

Author:

Cole Gustafson, North Dakota State University

Filed under: ,

NDSU, Dept. 7620

P.O. Box 6050

Fargo, ND  58108-6050

Phone: 701.231.7261

Fax: 701.231.1008

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