Gasification of Raw and Torrefied Cotton Gin Wastes in an Auger System

Abstract

Abstract. A 10 kW thermal externally heated auger gasification reactor was constructed and tested in the Rice Research and Extension Center, University of Arkansas, Stuttgart, Arkansas. The reactor was used to achieve thermal decomposition of cotton gin wastes (CGW) into producer gas and biochar. Raw and torrefied CGW were gasified to assess the effects of the torrefaction process on the producer gas composition and yield. The effects of reactor temperature (750°C, 850°C, and 950°C) and cotton wastes pretreatment (raw and torrefied) on the producer gas, biochar and condensable liquids quality and quantity were investigated. Torrefying cotton gin wastes reduced their moisture content and volatile solids by 39.0% and 6.7%, respectively whereas it increased their bulk density, heating value and stoichiometric air required for complete combustion from 390 to 426 kg m -3 , from 16.6 to 17.2 MJ kg -1 and from 4.28 to 4.74 kg kg -1 CGW , respectively. Increasing the reactor temperature resulted in an increase in the producer gas production rate and a decrease in char production rate. The maximum gas production rate reached 31 L min -1 at STP (standard temperature and pressure) during gasification of raw CGW at reactor temperature of 950°C. At the reactor temperature of 950°C, the biochar production rate decreased by 21% and 10% during gasification of raw and torrefied CGW, respectively as compared to those at the reactor temperature of 750°C. Gasification of torrefied CGW produced biochar with lower moisture content (46.3%), volatile solids (48.4%), fixed carbon (2.9%), and higher heating value (7.8%) as compared to those from gasification of raw CGW. The maximum higher heating value of gas reached 5.4 MJ m -3 from torrefied CGW. The values of the cold gas efficiency and carbon conversion did not exceed 43.0% and 55.3%, respectively. The potential green electricity generation from raw and torrefied CGW during the ginning season (1500 h) would be about 5.0 MWe and 4.7 MWe, respectively, based on a 40 bale per hour ginning facility.