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Potential of Summer Legumes for Thermochemical Conversion to Synthetic Fuel

Cantrell, Keri B., Bauer, Philip J., Ro, Kyoung S.
Paper 2009 no.096758
Crotalaria juncea, energy crops, crop rotation, biomass, energy content, potassium, calcium, magnesium, sulfur, pyrolysis, chemical degradation, temperature, volatile compounds, energy conversion, thermogravimetry, thermal analysis, cowpeas, Vigna, summer, growing season, bioenergy, energy density, South Carolina
Summer legumes are commonly used worldwide in crop rotations as a nitrogen source. One particular legume, sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding, tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume---cowpeas, sunn hemp was superior in biomass yield (kg ha-1) and subsequent energy yield (GJ ha-1). Interlinked with energy yield, the sunn hemp energy content (MJ kg-1) at the greatest maturity sampled (after 12 weeks) was 19.0 MJ kg-1. This was 6% greater than that of cowpeas. Even though sunn hemp had a greater amount of ash, plant nutrient concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release more volatile matter. This volatile matter would be amenable to downstream conversion processes to generate either heat or synthetic fuels.