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Simulation of double Claus furnace to increase sulfur recovery and reduce the number of catalytic units in sulfur recovery units

Abstract

Sulfur compounds present in crude oil and gas are absorbed primarily in the form of acid gas (H2S and CO2) and then converted to elemental sulfur in the sulfur recovery units (SRU). To comply with the increasing environmental standards on sulfur emissions, SRUs are required to achieve Sulfur recovery efficiency ranging from 98% to 99.99%. The existing technologies for higher sulfur recovery induce very high cost additions to an already economically deficient SRU. To reduce the SRU costs, a modified thermal section is proposed in this study to increase the sulfur recovery efficiency in the relatively inexpensive Claus furnace in order to reduce the number of expensive catalytic units required to meet the environmental standards. The modified SRU is based on double-stage acid gas combustion taking place in two Claus furnaces, along with the intermediate withdrawal of sulfur and H2O exiting the first furnace. The SRU’s conventional and modified thermal sections are simulated using industrial plant data and a detailed reaction mechanism. Compared to the conventional thermal section, Sulfur recovery efficiency increased from 63% to 75% due to a shift in the Claus equilibrium reactions towards Sulfur production (2H2S + SO2 ⇌ 3S + 2H2O), as both H2O and sulfur were withdrawn in the modified case. To determine the overall Sulfur recovery efficiency, the 2-stage and 3-stage catalytic sections combined with the conventional or modified thermal sections were simulated. In comparison, the overall Sulfur recovery efficiency (thermal + catalytic sections) in the modified thermal section increased remarkably from 96.5% to 98% with the 2-stage and from 97.6% to 98.6% with the 3-stage catalytic units. The higher amount of sulfur captured in the modified thermal section resulted in the decreased concentrations of H2S, SO2, H2, CO and H2O in the effluent gas, which helped to reduce the processing load/requirements in catalytic units. These results will assist in providing guidelines to reduce the number of expensive catalytic units to decrease the operating cost of SRUs.