Single-fuel steam gasification of switchgrass and coal in a bubbling fluidized bed: A comprehensive parametric reference for co-gasification study

• Gasification of Vancouver Island coal resulted in high H2/CO molar ratio (>1).
• Steam gasification of biomasses rich in potassium resulted in H2/CO molar ratios <1.
• The steam-carbon reaction was in equilibrium for biomass and coal gasification.
• The Gibbs reactor simulation was not able to predict the syngas composition.
• The kinetically enhanced model was a reliable tool for composition estimation.

Recent regulatory sharp curbs on coal power plants have compelled industries to adopt alternative sources of fuels. Biomass/fossil fuel co-gasification could be a pathway through more sustainable energy production technologies. As a basis for co-gasification study, the characteristics of single-fuel switchgrass and coal steam gasification in an atmospheric pilot scale bubbling fluidized bed reactor were studied. Increasing the steam-to-fuel ratio at 860 °C caused a moderate increase in the H2 and CO2 concentrations and decreases in the CO and CH4 concentrations, due to more steam-CH4 reforming and water–gasification reaction of CO. With increasing reactor temperature, the H2 concentration increased, whereas the CO, CH4, and CO2 concentrations fell slightly. Fall switchgrass gasification resulted in higher carbon, hydrogen and cold gas efficiencies than spring harvest gasification, possibly due to higher potassium concentration and hence, greater reactivity of the fall switchgrass. The equilibrium model was unable to predict the syngas composition properly. Adding an extra methanator stoichiometric reactor to produce methane based on the empirical CH4 concentration, and removing part of the carbon, hydrogen and steam before introducing the feed and gas agent streams to the reactor based on experimental carbon, hydrogen, and steam efficiencies, the kinetically modified model predicted the syngas composition accurately.