Conversion of cotton plant and cotton gin residues to fuels by the extruder ʹfeeder liquefaction process

Cotton is planted on a large scale in the USA, and is a major crop in Arizona. A large amount of cotton plant residue and cotton gin waste is produced annually, and these present a disposal problem. This material is comprised of cotton stalks, along with the upper portion of the taproot, and cotton gin trash. Cotton plant residues are a greater problem in the warmer regions of the USA as they serve as an overwintering site for insect pests, and thus must be destroyed. Presently they are buried. Most field operations used to bury the residue are high energy consumers and tend to destroy soil structure, thereby increasing the potential for erosion. This burial process is considered to be detrimental to the soil. One option to change the negative value of this biomass to a positive one is to harvest the cotton plants and combine them with other cotton wastes to produce a feedstock for liquefaction purposes. A process for harvesting and transporting the roots and stalks is being developed at the University of Arizona. In this paper we propose a combined harvesting/liquefaction system. This system would harvest and liquefy cotton wastes into oil and densified solid fuels with higher economic values. The extruder-feeder liquefaction process was developed at the University of Arizona in the 1980s under the sponsorship of the U.S. Department of Energy, with the goal to convert wood to a clean, 16 000 btu/lb liquid fuel. The process has been redirected to other organic wastes using additional processing to yield ‘value-added’ byproducts. Cotton wastes are good candidates for this process. By combining the harvesting and fuel processing operations, a negative value biomass would become a positive value biomass by (a) solving a disposal problem, and (b) producing high value fuels.