Performance of entrained flow and fluidised bed biomass gasifiers on different scales

This biomass gasification process study compares the energetic and economic efficiencies of a dual fluidised bed and an oxygen-blown entrained flow gasifier from 10 MW_th to 500 MW_th. While fluidised bed gasification became the most applied technology for biomass in small and medium scale facilities, entrained flow gasification technology is still used exclusively for industrial scale coal gasification. Therefore, it is analysed whether and for which capacity the entrained flow technology is an energetically and economically efficient option for the thermo-chemical conversion of biomass. Special attention is given to the pre-conditioning methods for biomass to enable the application in an entrained flow gasifier. Process chains are selected for the two gasifier types and subsequently transformed to simulation models. The simulation results show that the performance of both gasifier types is similar for the production of a pressurised product gas (2.5 MPa). The cold gas efficiency of the fluidised bed is 76-79% and about 0.5-2 percentage points higher than for the entrained flow reactor. The net efficiencies of both technologies are similar and between 64% and 71% depending on scale. The auxiliary power consumption of the entrained flow reactor is caused mainly by the air separation unit, the oxygen compression, and the fuel pulverisation, whereas the fluidised bed requires additional power mainly for gas compression. The costs for the product gas are determined as between 4.2 cent/kWh (500 MW_th) and 7.4 cent/kWh (10 MW_th) in the economic analysis of both technologies. The study indicates that the entrained flow reactor is competitive technology for biomass gasification also on a smaller scale.