Calcium Based Sulfur Recovery Process for Kraft Black Liquor Gasification - Proof of Concept, 1998 International Chemical Recovery Conference Proceedings

This paper describes a novel process for use in black liquor gasification systems to recover sulfur from the product gas by reaction with lime. A sulfur-rich white liquor stream is produced by reaction of the resulting calcium sulfide with sodium hydroxide. Equilibrium calculations suggest that industrial feasible conditions will result in a concentrated solution of NaHS and NaOH with insignificant byproduct formation. Bench-scale experiments were conducted to investigate the sulfur removal and conversion operations. Eighty-percent conversion of CaS to NaHS was achieved in 60 minutes at 95°C with 100 g/L initial NaOH concentration. Complete conversion was attained within 240 minutes at 90-95°C with 50-100 g/L alkali. Only trace amounts of oxidized sulfur species were detected by ion chromatography. Industrial lime samples of 79 to 595 pm were reacted with H2 S to form 62-69% CaS, compared with the commercial 99.2% pure CaS powder (sub- 4 µm) used in most of the experiments. Conversion of the industrial lime was as good or better than the commercial CaS; suggesting the proposed sulfur recovery process will operate well with bed material from a fluidized, product gas desulfurizer.