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 m3N 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.