Engineering Economics of Cotton Stalk Supply Logistics Systems for Bioenergy Applications
Cotton stalk (CS), which is usually left in the field, can be a potential bioenergy feedstock if it can be economically harvested and delivered to a bioenergy plant. The objectives of this study were to systematically assess the spatial and temporal availability of harvestable quantities of CS and evaluate the least expensive supply system among various biomass supply logistics options. The availability of harvestable CS in the U.S. was estimated at the county level using cotton yield data with the best farm management practices. Six supply logistics options for CS were evaluated to estimate delivered cost and energy usage for each option: large rectangular bale (LReB), large round bale (LRoB), small round bale (SRoB), chops, modules, and single-pass bio-baler. The average annual availability of CS in the U.S. was estimated as about 14.4(±0.05) dry Tg, with an economically harvestable amount of 5.6 (±0.03) dry Tg and a minimal harvestable stalk yield of 2.5 dry Mg ha -1 . Among the six supply logistics options evaluated, LReB was the least expensive option, with an average delivered cost of $60 dry Mg -1 (100 km round trip) and energy input of 462 MJ dry Mg -1 . Sensitivity analysis of the LReB supply logistics system demonstrated that the total delivered cost can be further reduced by up to 30% if the overall machine capacity, field efficiency, and bale bulk density can be increased by 20%.