Tar conversion of biomass syngas in a downstream char bed

The catalytic conversion of biomass-derived tars over char during long tests (over 6 h) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 degrees C whereas the temperature of the secondary reactor was varied between 750 degrees C and 875 degrees C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 degrees C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 degrees C, the initial conversion of tar was above 70% and over 64% after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80% during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation.