How does the Claus process recover sulfur from acid gas?

Claus process converts H2S to elemental sulfur in two steps: (1) Thermal stage - partial combustion of H2S: H2S + 1.5O2 = SO2 + H2O at 1000-1400C in furnace. Produces 60-70% of sulfur. (2) Catalytic stages - H2S + SO2 = S + H2O over alumina catalyst at decreasing temperatures (300C, 240C, 200C in successive stages). Each stage followed by condenser to remove sulfur. Overall: 2H2S + SO2 = 3S + 2H2O. Standard 3-stage Claus achieves 95-97% recovery. Tail gas treatment (SCOT, Beavon) reaches 99.9%. Feed gas from amine regeneration. Air flow controls H2S/SO2 ratio (critical 2:1). COS and CS2 hydrolyzed in first catalyst bed. Sulfur product is liquid, sold or stored in solid form.