(98c) Influence of Coal-Biomass Feed Mixtures on Gasification Products

The United States Department of Energy's National Energy Technology Laboratory (NETL) is working to develop technologies that allow for the efficient conversion and utilization of domestically abundant resources in an effort to mitigate environmental issues, improve national security and develop greater fuel independence. Coal, an abundant natural resource, can be utilized by thermochemical processes to produce electricity, hydrogen, liquid fuels or other chemicals. Co-gasification of coal and non-food oriented biomass can prolong national fossil energy resources while reducing many environmental issues. Gasification can often be considered a two-stage process at low heating rates and a single stage process (simultaneous pyrolysis and gasification reactions) at high heating rates. Pyrolysis, a devolatilization reaction involving the breakdown of the macromolecular structure of carbonaceous fuel material and the release of volatile gases (CO, CO2, H2, CH4, H2O, etc.) and liquid products, first occurs during heat-up. After devolatilization is complete, the residual solid (char) is free to react by gasification reactions to produce syngas components. In order to further understand gasification phenomena, both reactions will be investigated at various feed compositions and reactor conditions. The focus of this paper is on the first and most complex pyrolysis reaction.

An experimental study on co-pyrolysis of Illinois#6 coal and switch grass was done in a batch reactor at conditions consistent with an entrained gasifier. Co-pyrolysis experiments were performed in an effort to gain an understanding of the effect of coal-biomass co-fed products on reaction kinetics and gaseous, liquid and solid product distributions. Coal and biomass were fed to the reactor with varying feed ratios (100%, 85%, 70%, 50% and 0% coal, balance biomass). Primary gaseous products (CO, CO2, CH4, H2 and H2O) were monitored and analyzed online using quadrupole mass spectrometry. Trace gaseous products were collected as a batch and analyzed using gas chromatography/mass spectrometry. Tar/liquid product analysis was done using gas chromatography/mass spectrometry and residual solid analysis was done with inductively coupled plasma optical emission spectroscopy. Initial results indicate that the addition of small quantities of biomass to coal can improve gaseous product yield and decrease product sulfur species.