A Kinetic Simulation Study to Decrease Carbon Monoxide CO Emission from Sulfur Recovery Units SRU

To meet the regulations on the emission of toxic gases such as carbon monoxide (CO) and Hydrogen Sulfide (H2S) from the Sulphur Recovery Units (SRUs), a high amount of fuel gas is burnt in the incinerator to oxidize them that increases the sulfur production cost and CO2 emissions. This study investigates the major reactions that cause CO emissions and recommends possible solution to mitigate its formation in the SRU. The SRU simulations were conducted using a well validated and detailed reaction mechanism that captures the chemistry of CO and Sulfur species in the Claus furnace. The Claus reaction mechanism, containing 290 species and 1900 reversible reactions for the oxidation of H2S and the formation and destruction of COS, CO, CO2, hydrocarbons, and CS2 was used for reactor simulations, which was validated successfully using industrial plant data and the experimental data from lab-scale setups. The process parameters were varied to find the set of conditions that minimize CO production in the SRUs. The CO production in Claus furnace occurred through the high temperature decomposition of CO2 and CH4 present in the acid gas stream. The production of COS occurred from the reactions of CO with sulfur. The inlet temperatures of the feed gas streams (air and acid gas) were varied systematically to observe their effect on sulfur recovery and emissions of CO, SO2, COS, and aromatics. Upon decreasing the furnace temperature (by decreasing inlet air temperature) from 1105°C to 1050°C, CO emission from the SRU decreased by up to 60%, while sulfur recovery efficiency increased by 0.2%. However, the emission of aromatics (mainly benzene) increased by 3.5 ppm, while the more detrimental toluene, ethylbenzene and xylene were completely oxidized. Thus, maintaining an optimal feed temperature was found to minimize CO emissions from the SRUs, while maintaining high sulfur recovery. The simulation results predict the cost-effective solutions of minimizing CO and SO2 emissions from SRUs through the variation in process parameters that will help in reducing the consumption of fuel gas in the SRU incinerator.