Technical demonstration of the novel Fraunhofer ISE biomass gasification process for the production of a tar-free synthesis gas

Abstract

A novel fixed-bed biomass gasification process (Fraunhofer ISE gasification process) for the production of tar-free synthesis gas was developed and demonstrated in a small-scale 50kWLHV (biomass) pilot plant. The process consists of four zones. Separated by moving grates to control the residence time in every zone. Thermal cracking of all higher hydrocarbons and tars occurs due to temperatures in the cracking zone of up to 1000°C, ensured via partial combustion of the raw gas. In addition, coke in the cracking zones acts catalytically. In order to increase the heating value of the product gas all remaining carbon is partially oxidized and the produced CO/CO2 is blended with the product gas. To demonstrate feasibility of the process, a pilot plant was designed, commissioned and tested. The gasifier produced a combustible gas with a lower heating value of 5.8MJ/Nm3 and CO, H2 and CH4 concentrations of 24, 14 and 2vol.%, respectively. Tar contents below 50mg/Nm3 were achieved in continuous operation. The results suggested a considerable effect of the temperature and the bed height in the tar cracking zone on the reduction of the tar content in the produced gas.