Tar Generation in Open-Top and Closed-Top Downdraft Gasifiers

Biomass gasification converts solid fuel to combustible gases along with tar. Tar removal is the major practical challenge for use of gaseous fuel produced in the gasification process in any applications. Gasifier types, operating conditions, and fuel properties have an important role for tar generation. Tar generation is estimated for two types of downdraft gasifiers. The tar concentration decreases with the increase of air mass fluxes in case of an open-top downdraft gasifier. In the case of closed-top gasifiers, tar concentration decreases with the increase of biomass consumption rate. The study observed that higher bed temperature increases the thermal cracking of the pyrolysis products and resulted in lower tar concentration in the output gas. Two-stage air supplies in case of open-top downdraft gasifier resulted in lower tar generation.