Black liquor gasification is a thermochemical conversion process in which black liquor—the aqueous, alkaline spent cooking liquor generated during chemical pulping and containing dissolved lignin-derived organic matter together with inorganic sodium- and sulfur-containing pulping chemicals—is converted under substoichiometric oxidizing conditions into a combustible product gas and an inorganic recovery stream ^[1][2]. Unlike conventional black-liquor recovery-boiler operation, which primarily combusts the organic fraction, gasification uses controlled partial oxidation, with oxygen, air, steam, or their combinations as gasifying agents, to form a synthesis-gas mixture principally containing carbon monoxide, hydrogen, carbon dioxide, water vapor, and, depending on process conditions, methane and sulfur-bearing gases ^[1].

The concept encompasses gasifier configurations that process concentrated liquor at elevated temperature, including entrained-flow, fluidized-bed, and supercritical-water systems, provided that conversion of the liquor’s organic fraction to gas is coupled with retention or recovery of its inorganic chemical constituents ^[2][3]. It excludes simple combustion and gasification of solid biomass not derived from pulping liquor.