Catalytic cracking of tars from biomass gasification

An experimental setup was designed to test the performances of three catalysts on cracking tars produced from a downdraft gasifier. The three catalysts were: alumina extrudes, dolomite, and olivine. In addition, experimental runs using silica microcrystals were used as a control. Tar collected from earlier gasification tests was vaporized in flowing nitrogen and reacted over these catalysts at various temperatures and flow rates. Alumina was tested at a lower temperature ranging between 300 and 500 °C and with a gas flow rate of 0.5–2.4 L/min. Dolomite, olivine and silica were tested between 400–800 °C and 0.5–2.4 L/min. Dolomite and olivine catalysts showed higher cracking rates than alumina or silica. Under optimum conditions, at 800 °C and 0.5 L/min, the dolomite catalyst cracked 92 % (±3 %) of all tars. The olivine catalyst also achieved optimum performance at 800 °C and 0.5 L/min, cracking approximately 89 % (±4 %) of all tars. In comparison, the alumina extrude catalyst showed only 71 % tar cracking efficiency, but at a significantly lower temperature of 400 °C. Silica had a maximum tar cracking efficiency of only 66 %, at 800 °C. All three catalysts showed no observable deactivation in the life runs.