PROPERTIES OF GAS AND CHAR FROM MICROWAVE PYROLYSIS OF PINE SAWDUST

摘要

In this paper, pyrolysis of pine sawdust was carried out respectively using microwave and conventional electrical heating at different temperatures in order to understand the properties of pyrolytic products from microwave pyrolysis of biomass. Because the pyrolytic chars can absorb microwave radiation dramatically, the local temperature of biomass particles was higher than the surrounding's, which facilitated the biomass pyrolysis process. Therefore, compared to conventional heating method, fewer chars were obtained by microwave pyrolysis at the same temperature. While comparing the components of the pyrolytic gases, analyzed by a gas chromatograph, it was revealed that the microwave pyrolysis gas usually had higher H_2, CO contents and lower CH_4, CO_2 content than those obtained by conventional pyrolysis at the same temperature. The textural properties of the microwave pyrolysis chars were determined by SEM and BET methods, the results showed that the chars would melt and the pores would shrink at high temperatures, and hence, the specific surface areas of the chars decreased with increasing temperature. Which similarly caused that the reactivity of the char, determined by char-CO_2gasification rate on a thermal balance at 1000°C, was remarkably reduced when the microwave pyrolysis temperature exceeded 600°C. Furthermore, the chars produced from microwave pyrolysis were likely to havelower reactivity than that for conventional pyrolysis. In addition, the GC/MS analysis result of the pyrolytic tar from microwave pyrolysis of pine sawdust indicated that the quality of the liquid product from biomass pyrolysis could be improved via microwave heating.