Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2006
Publication Date: November 5, 2006
Citation: Holt, G.A., Blodgett, T.L., Nakayama, F.S. 2006. Physical and combustion characteristics of pellet fuel from cotton gin by-products produced by select processing treatments. Industrial Crops and Products. 24(3):204-213. Interpretive Summary: A process designed to add value to byproducts from cotton processing facilities, known as the COBY Process, was used to manufacture six different fuel pellet treatments. The fuel pellets produced were sent to two laboratories for analytical analyses of heating value, ash content, bulk density, and proximate and ultimate analyses. In addition to the lab analyses, the pellets were fired in a commercially available pellet stove and the gaseous and particulate emissions were measured and compared to a premium grade wood pellet. The air-to-fuel ratio for the pellet stove was not modified from the factory settings. Therefore, the stove was designed and optimized to burn wood pellets and not the biomass pellets evaluated in the study. The purpose for not modifying the stove was to evaluate whether or not the emissions from burning the gin waste pellets would be within a respectable level of the wood pellets without major adjustments to the stove. Most of the gin waste fuel pellets were comparable to the wood pellets in heating value, pellet length, and bulk density. The one characteristic of the gin waste pellets that was significantly higher than the wood pellets was the ash content. The ash content of the gin waste pellets ranged from 4.9 to 9.8 percent compared to wood at 0.5 percent. Since the stove was not optimized to burn the gin waste pellets, the gaseous and particulate emissions were higher than they were for the wood pellets. Overall, byproducts from cotton processing facilities can be utilized as a fuel that has economic potential, but work remains in reducing the ash content of the fuel and/or optimizing the combustion process to reduce emissions within levels that are within specified regulatory limits.
Technical Abstract: Agricultural plant wastes, when properly processed into useful commodities, can become an economic asset. It has been estimated that over 2.04 million Mg of cotton byproducts are generated each year in the United States. On average, disposal of these byproducts costs the cotton gin approximately $1.65 (U.S.) per Mg. One means of changing a financial liability into a potential revenue generator is to process the byproducts into renewable, compact pellet-type fuel that can be used at the site or transported to the consumer. Furnaces and water heaters that can burn pelletized plant materials have become popular and their safety, low pollution, and reasonable operational costs have been demonstrated. Also, the drastic increases in the price of liquified fuel and its uncertain supply place a premium for finding and using alternate, low-cost, cellulose-based fuels. The objectives of our study were to fabricate pellet fuel from cotton gin byproducts using select processing techniques, determine its physical properties, and measure the emissions when fired in a commercial pellet stove used for residential heating. Byproducts from two cotton gins were collected and processed into fuel pellets. A total of seven different pellet fuels were evaluated, six from cotton gin byproducts and one from wood. The treatments resulted from using different material streams from the ginning process as well as varying quantities of starch and/or crude cottonseed oil during the fuel pellet manufacturing process. The fuel pellet density from the various treatments ranged from 488 to 678 kg/m3. The various treatments were burned in a conventional pellet stove (four replications) and the gaseous and particulate emissions measured. The average calorific value of the pellets ranged from 17.9 to 20.9 MJ/kg (HHV). The ash content for the various treatments ranged from a low of 4.88% to a high of 9.75%. The sodium content indicated concentration ranges from 91 to 282 ppm depending on the treatment. The emissions from the cotton gin byproduct pellets were higher than for a premium grade wood pellet. The emissions measured during testing were CO, NO, NO2, SO2, and particulates. The pellet stove was set up following the manufacturer’s recommendation to burn wood pellets, but was not adjusted for the cotton gin fuel pellets. By utilizing various additives and processing techniques, cotton gin byproducts could be used to manufacture a pellet fuel that has commercial potential. However, work remains to minimize the ash content and determine the optimal settings for maximizing combustion.