(10c) Syngas Compositions From Coal/Biomass Co-Gasification

Co-gasification of coal and biomass helps to mitigate some of the non-technical barriers impeding the development of independent coal or biomass gasification technologies. Co-gasification of coal and biomass can be considered as a potential fuel base for future energy needs. By mixing coal and biomass together, a renewable component is added to coal gasification to offset fossil CO2 emissions and biomass can be used at a much larger scale to improve process economics. When integrated with appropriate downstream process, syngas obtained from coal/biomass co-gasification could surface as the technology of choice for economically producing a variety of fuels and chemicals (methanol, mixed alcohols, gasoline etc.). The difference in the chemical properties of coal and biomass provides an opportunity to tailor the syngas composition by changing the operating parameters (temperature, pressure and coal/biomass ratio) as per the requirement of the end product.

The chemical and physical property differences between coal and biomass contribute to the technical challenges associated with co-gasification. Higher hydrogen to carbon ratio and oxygen content in biomass compared to coal makes it more reactive leading to less severe (lower temperature and pressure) conditions for gasification. Unfortunately, the lower severity for biomass gasification also leads to tar formation that is a major gas cleanup challenge in these processes. The trace elements in coal and biomass are quite different leading to different gas cleanup requirements for each solid feedstock. Sulfur and other heavy metals like As, Cd, Hg and Pb are major concern for coal gasification but char and tars more important for biomass gasification.

RTI's Center for Energy Technology has been conducting R&D associated with coal gasification for over 15 years. In the present research, a detailed parametric coal/biomass co-gasification study was conducted varying temperature, pressure and coal/biomass ratio. Effect of above process parameters on syngas composition was determined at atmospheric and high pressure in entrained flow gasification systems. Data collected from the parametric gasification testing were used to develop empirical correlations to interpret the effect of feedstock, coal/biomass blending ratio, and process conditions on measured product gas, liquid, and solid concentrations and composition. These results will be presented and discussed.