In-field Peanut Processing for Biodiesel Production

Authors: Butts, Christopher - Chris; Sorensen, Ronald - Ron; Nuti, Russell; Lamb, Marshall; Faircloth, Wilson

Submitted to: American Peanut Research and Education Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/10/2008
Publication Date: 7/14/2008
Citation: Butts, C.L., Sorensen, R.B., Nuti, R.C., Lamb, M.C., Faircloth, W.H. 2008. In-field Peanut Processing for Biodiesel Production. American Peanut Research and Education Society Proceedings.

Interpretive Summary: None required.

Technical Abstract: The costs and environmental impact for using petroleum-based fuels such as diesel, has triggered considerable interest in the development of sustainable, on-farm biodiesel production systems. Field studies have demonstrated that a peanut (Arachis hypogaea L.) can produce 1138 kg/ha of peanut oil at a cost of $0.38/kg ($0.35/L). If off-road diesel costs $0.92/L, then $0.57/L may be invested in combining, curing, storing, shelling, and crushing the peanuts, then processing the oil into a methyl ester. The average cost of combining ($124/ha), curing ($74/t), and shelling ($148/t) farmer stock peanuts results in an approximate processing cost of $0.66/L of available peanut oil. In an attempt to reduce these processing costs, a grain combine was used to harvest and shell peanuts from the 2007 crop that had been dug, inverted, windrowed, and allowed to cure in the windrow until a the kernel moisture content was less than 10%. Peanut plants were pitched into the corn header of the combine which then fed them into the threshing cylinder. Peanut material that was transferred into the grain tank was captured in a polypropylene bag, weighed, and analyzed. Cylinder speed (3 speeds), concave opening (3 settings), fan speed (5 speeds), and various sieve openings were used to thresh and shell peanuts in two separate tests. In test 1, the fan speed and sieve openings were held constant while cylinder speed and concave settings were varied. Concave setting had no significant effect on the proportion of peanuts that were shelled. The percent peanut kernels that were shelled and removed from the hulls increased as cylinder speed increased and ranged from 42 to 82%. Foreign material ranged from 8 to 25%. In the second test, the highest cylinder speed and the smallest concave setting were selected while fan speed and sieve settings were varied. The shelled peanut kernels ranged from 76 to 91% during these second series of tests with no apparent effect of fan speed or sieve opening. Percent foreign material tended to decrease as the fan speed increased and reach a lower limit of 7%. The maximum amount of foreign material obtained during the fan speed/sieve opening tests was 13%. Based on a visual observation, the vast majority of peanut kernels were split or broken with very few whole kernels. This is acceptable and may be desirable for oil production. Based on these performance tests, it may be feasible to use a grain combine with minimal modification to harvest and shell field-cured peanuts for use in the production of biodiesel. The typical operating cost for a grain combine is approximately $74/ha. Allowing peanuts to cure in the windrow, then harvesting with a grain combine will reduce the cost of harvesting, curing, and shelling from $0.66/L of available peanut oil to approximately $0.06/L.