Dual-stage acid gas combustion to increase sulfur recovery and decrease the number of catalytic units in sulfur recovery units

•Sulfur recovery units (SRUs) must achieve sulfur recovery efficiency (SRE) near 98–99.99% to meet environmental standards.•A SRU process modification is proposed to increase SRE and reduce number of catalytic units.•The modification involves dual-stage combustion with the withdrawal of S and H2O.•The SRE in the thermal section increases from 63 to 75% with the modified process.•The modification reduces number of catalytic units from three to two to reach a desired SRE. Sulfur compounds in crude oil and gas are absorbed as acid gas (H2S and CO2), and converted to sulfur in sulfur recovery units (SRUs). To meet environmental standards, SRUs must achieve sulfur recovery efficiency (SRE) near 98–99.99%. The existing technologies for high SRE induce high costs to the economically deficient SRUs. To reduce their operating cost, a process modification is proposed that increases SRE and reduces the number of expensive catalytic units. The modification involves dual-stage acid gas combustion occurring in two Claus furnaces along with the intermediate withdrawal of sulfur and H2O. The conventional and the modified thermal sections are simulated using industrial plant data and a detailed reaction mechanism. The SRE in the thermal section increased from 63% with the conventional process to 75% with the modified process. To determine the overall efficiency, the 2-stage and 3-stage catalytic units combined with the conventional and modified thermal sections are simulated. The overall SRE of the modified thermal section with 2-stage catalytic unit was higher than that of the conventional thermal section with 3-stage catalytic unit, which indicates that the number of catalytic units and the operating cost of SRUs can be reduced with the suggested process modifications.