Integration of a biomass fluidized bed gasifier in a coal oxy-combustion plant

Paper in proceeding, 2012

Integration of biomass gasification in a coal oxy-combustion plant is analyzed. In such a scenario, pure oxygen and flue gas from the oxyboiler (having high concentration of CO2) are available as gasification agents. Firstly, biomass gasification with CO2/O2 mixtures is analyzed, comparing it with H2O/O2 as a gasification agent. Secondly, the particular operation of a fluidized bed gasifier (FBG) coupled to an oxyboiler, where the gasification agent is a mixture of CO2/H2O/O2/N2, is analyzed using a previously developed model. Two cases, using either wet or dry flue gas from the oxyboiler, are analyzed. A 3 MWth demonstration plant constructed in Spain is taken as a reference for the analysis. It is concluded that a recycling ratio of wet flue gas of 0.7 (kg flue gas/kg biomass input) is a good choice for the gasification process, yielding a gas (dry) with 30% CO2 concentration, a ratio H2/CO (mol/mol) of 0.7, and a lower heating value of 9.5 MJ/Nm3. Co-firing of the gas in the oxyboiler seems to be the most promising application, allowing high conversion of biomass to electricity, while capturing green CO2 from the biomass.