Co-gasification of blended lignite and wood pellets in a dual fluidized bed steam gasifier: The influence of lignite to fuel ratio on NH3 and H2S concentrations in the producer gas

Abstract

Co-gasification of coal and biomass has recently attracted great attention because it has potential to offer combined benefits of coal for high energy density and biomass for clean and renewable resources. However, the presence of ammonia (NH3) and hydrogen sulfide (H2S) in the producer gas is one of the main technical challenges because they poison the catalysts used in the downstream applications. This research investigated the influence of lignite to fuel (L/F) mass ratio on the NH3 and H2S concentrations in the producer gas as well as the conversions of fuel-nitrogen (N) and fuel-sulfur (S) to form NH3 and H2S. Experiments were performed in a 100kW dual fluidized bed (DFB) steam gasifier at 800°C with blended lignite and radiata pine wood with the L/F ratio ranging from 0% to 100%. The blends were in pellet form while the pure lignite was tested in particles. The results showed that the NH3 and H2S concentrations increased exponentially with the L/F ratio. This influence was attributed to higher contents of N and S in lignite compared with those in wood. Moreover, non-linear relationships between the conversions of fuel-N or fuel-S and the L/F ratio were observed. The non-linear relationships of the NH3 and H2S concentrations, and the fuel-N and fuel-S conversions as a function of the L/F ratio showed a synergetic effect of the blended lignite and wood pellets.