BIOSYN BIOMASS GASIFICATION PROCESS FOR THE PRODUCTION OF A TAR-FREE SYNTHESIS GAS

摘要

A novel fixed-bed biomass gasification process (“BioSyn gasifier”) for the production of tar-freesynthesis gas was developed and demonstrated at Fraunhofer ISE. The process consists of four zones, namelygasification, partial combustion, cracking and a reduction/oxidation (redox) zone. The zones are separated by movinggrates to control the residence time of the biomass in every step. Thermal cracking of all higher hydrocarbons andtars is achieved by temperatures in the cracking zone up to 1000 °C, ensured via a partial combustion of the raw gas.Besides, the coke in the cracking zones acts autocatalytically. In order to increase the heating value of the product gasand hence, the overall efficiency of the process, all remaining carbon is oxidized and CO from the reduction zone ismixed with the product gas. The produced gas is used for combined heat and power production with a gas engine.To demonstrate the feasibility of the process a pilot plant with 50 kWLHV(biomass) was designed, commissioned andtested with wood pellets. The gasifier produced a combustible gas with a lower heating value of 5,8 MJ/m~3 and CO,H_2 and CH_4 concentrations of 26, 15 and 2%, respectively. Tar contents below 30 mg/ m~3N could be achieved incontinuous operation. The results suggested a considerable effect of the temperature and the bed height in the tarcracking zone on the reduction the CH_4 concentration which is associated with the decrease of the tar content in theproduced gas. After knowing the optimal gasification parameters for the operation with wood pellets, other biomasssuch as biocoal was tested.