STUDIES ON THERMAL DEGRADATION AND GASIFICATION OF BIOMASS

Abstract

Biomass materials like agricultural, agro-processing and forestry residues are available in abundance in India. Some of them pose disposal problems due to their low fodder and fertilizer values, e.g. pine needles, bagasse, and press mud (a waste from sugar industry), etc. Thermal gasification for energy utilization of such waste biomass materials is an attractive proposition. The present experimental study was undertaken to understand the fluidization behaviour, thermal degradation behaviour and kinetics of press mud, pine needles and bagasse abundantly available in India. Attempts to fluidize a biomass material alone as a single component bed charge indicated that a low bulk density (bulk density < 250 kgm-3), complex shaped biomass material was not fluidizable easily and that an inert solid (carrier solid) must be added to the bed charge to make a binary mixture to facilitate its fluidization. Significant hysteresis was observed in the plots of pressure drop versus superficial air velocity (increasing and decreasing mode). For binary mixtures of carrier solid and biomass, •it was observed that the minimum fluidization velocity increased with increase in H/D ratio. TG, DTG and DTA curves showed the number of distinct zones during thermal degradation process of the biomass. Generally two zones of thermal degradation were very prominent and third zone of char degradation in case pyrolysis in nitrogen atmosphere was not very prominent. The first zone showed the degradation of hemicellulose and the second zone exhibited the degradation of cellulose. The lignin degradation occurred throughout the degradation zone. The residue in case of oxidizing atmosphere was less as compared to that in case of nitrogen atmosphere. The model of kinetic analysis giving highest correlation coefficient was taken into consideration and it was found that in case of pyrolyis of the three biomass materials taken, the diffusion related models dominated over the limiting surface reaction in both phases models and Agrawal Sivasubrananian model. Among the diffusion models, one-way transport diffusion model and Zhuravlev model were governing models in case of pyrolysis in nitrogen atmosphere.