Effect of torrefaction pretreatment on the fast pyrolysis behavior of biomass: Product distribution and kinetic analysis on spruce-pin-fir sawdust

Abstract

Torrefaction pretreatment is of great significance to the enhancements of biomass characteristics. Product distribution and kinetics analysis of spruce-pin-fir (SPF) sawdust and its torrefaction samples were studied during the fast pyrolysis process. Under anaerobic conditions, torrefied biomass was prepared at different temperatures in a slot-rectangular spouted bed reactor. Fast pyrolysis experiments were conducted in a tube furnace with online mass spectrometry. The effects of torrefaction degree and pyrolysis temperature on product distribution were discussed. The main gaseous products, ie. CO, CO2, H2, and CH4, were investigated, and kinetic data of gaseous product formation was solved based on the isoconversional method. Other volatiles were the main product during the fast pyrolysis process, and the char yield was the lowest. With the increase of torrefaction degrees, the yield of char increased from 19.80 % to 22.09 % at 800 °C. The pyrolysis gas yield decreased from 25.78 % to 17.18 % as the torrefaction temperature increased from 240 °C to 300 °C. The gaseous products were mainly CO and CO2. The content of CO tended to increase, and the content of CO2 decreased when the pyrolysis temperature increased. The order of activation energy was E (CO2)>E (H2) >E (CO) >E (CH4) during the fast pyrolysis of SPF. The activation energy of the CO2, CH4, and H2 increased with the increase of the torrefaction temperature. According to different evaluation indexes, the optimal setting of reaction conditions is determined.