Influence of CaO additives on wheat-straw pyrolysis as determined by TG-FTIR analysis

摘要

The interest in utilization of biomass by CO_2 sorbent enhanced gasification is increasing due to the concerns about global warming and the wish to produce high purity hydrogen. Pyrolysis in the presence of abundant CaO additives is a fundamental step which determines primary product distribution, composition and properties. In this paper, pure wheat-straw pyrolysis and CaO catalyzed pyrolysis (loading various amounts of CaO additives) at different heating rates were compared using the thermogravimetric Fourier transform infrared (TG-FTIR) analysis. Results showed that CaO additives affected pyrolysis. In the main mass loss stage, the mass loss and maximum mass loss rate decreased with increasing amount of CaO additives. The temperature at the maximum mass loss rate shifted to lower value. CaO additives could not only absorb the released CO_2 but also restrain the CO and CH_4 yields and meanwhile catalyze the tar reduction reactions. Calculated activation energies at different heating rates were generally in close agreement with that of a previous study and the average activation energy was lowered. Unlike pure wheat-straw pyrolysis, a second mass loss stage mainly caused by calcium carbonate decomposition appeared in CaO catalyzed pyrolysis. The evolution of CO was found to be enhanced by CaO additives in this stage. The total mass loss decreased in the presence of CaO additives. CaO additives can play the roles of both CO_2 sorbent and tar reduction catalyst in sorbent enhanced biomass gasification.