Simultaneous Steam Reforming of Tar and Steam Gasification of Char from the Pyrolysis of Potassium-Loaded Woody Biomass

Abstract

This paper proposes a two-stage conversion of biomass into gas, which consists of pyrolysis at 500–600 °C and steam reforming/gasification at 600–700 °C, and has a special feature of recycling of the potassium (K) catalyst. The proposed process was simulated experimentally employing K-loaded cedar as the feedstock and char from its pyrolysis as the catalyst for tar reforming. Tar from the pyrolysis was reformed over the char in a sequence of carbon deposition onto the pore surface and K-catalyzed steam gasification of the deposit, while K-catalyzed char gasification created active pores simultaneously. At the steam/carbon molar ratio of 0.55–1.10, the catalysis of K simultaneously realized the concentration of heavy tar (boiling point temperature > 336 °C) in the product gas as low as 20 mg m 3 N dry and progress of the char gasification as fast as that of char formation by the pyrolysis. The concentration of hydrogen in the product gas exceeded 50 vol % dry. A portion of K was released from the pyrolyzing cedar, fully captured by the char bed of the reformer, and involved in the steam reforming and gasification. A major portion of K retained in/on the spent char was extracted with water. The resulting aqueous solution of K was ready to be used as spray for K loading on the feedstock.