STUDIES INTO THE EFFECT OF TORREFACTION ON GASIFICATION OF BIOMASS

Abstract

The utilization of biomass sources can reduce greenhouse gas emission. Presently, biomass is being considered as a potential energy resource to substitute fossil fuel for large-scale power generation through combustion as well as a chemical feedstock. Gasification can turn biomass into convenient product gas that could be used for both energy conversion and chemical production. Biomass gasification is being recognized as an alternative to combustion for the production of clean energy and provision of syn gas for production of chemicals. However, major limitation of the biomass gasification is the tar produced during the process and the high-energy cost associated with its removal from the product gas. Torrefaction is a new pretreatment method for biomass that has positive features such as reduced the storage, transportation cost, increased energy density, easier grinding. The torrefaction process partially removes the low quality volatiles matter thereby making the gas cleaning simpler and increasing energy density of the biomass. Furthermore, it lowers the O/C ratio of biomass fuel making it more favorable for gasification.

To examine the above potential steam-gasification of raw biomass char and torrefied biomass char was investigated and studied their product gas composition and its other attributes. In this study, poplar wood was torrefied at 250oC and 275oC for 1 hour and gasified at different gasification temperatures (700-950oC). Measured and analyzed syngas gas yield, syngas composition and heating value. The kinetics of the process was also studied and it showed that torrefied (250oC with 1 hour residence time) biomass char had activation energy of 92.30 kJ/mol. Furthermore, SEM analysis of the char produced from the torrefied biomass and raw biomass was conducted to observe any difference in the microstructure their structure. The gasification experiments indicated that torrefied biomass produces slightly higher concentration of hydrogen and lower concentration of carbon dioxide than untreated biomass. Furthermore, this study showed that torrefaction has minor reduction in syngas yield, but major reduction in tar production. Overall combination of torrefaction and gasification of biomass is a promising technology for the future energy generation.