(434b) High Temperature Steam Gasification of Algae and Switchgrass in a Transport Tube Reactor

Steam gasification of algae and switchgrass to produce synthesis gas (CO, CO2 H2) was performed at high temperature (1273-1673 K) in an externally heated transport tube reactor. High temperature with external heating was investigated because of its applicability to gasification processes using concentrated solar thermal energy. Conventional gasification generally operates at lower temperature and partially oxidizes the biomass to provide the heat of reaction. This either requires an oxygen plant or dilutes the product stream with nitrogen; in either case the heating value of the synthesis gas is lower than the feedstock due to the combustion process. In addition, low temperature often leads to the production of unwanted tars that are costly to remove in downstream processing. Concentrated solar thermal energy offers a solution to both of these issues by providing a low cost, renewable source of high temperature thermal energy. The combination of domestically produced biomass feedstocks with gasification using a renewable heat source offers a viable path to sustainable production of transportation fuels. Algae and switchgrass were studied because of their high land utilization and the growing interest in large scale production using marginal land. The effect of temperature, steam addition, and carrier gas flow rate on conversion efficiency and product distribution was studied in a laboratory scale reactor. Proof of concept experiments were run at NREL's High Flux Solar Furnace to evaluate the performance using concentrated solar thermal energy.