Abstract
In upstream oil and gas operations, a considerable amount of hydrogen sulfide (H2S) is being emitted every year. Health issues associated with H2S that might be very serious vary dependent on the length of exposure. Furthermore, the gas is highly corrosive, which is a concern in the industry. A promising technique that can be used to remove this air pollutant from waste gas is photolysis, which has been successfully used in wastewater treatment processes. However, to the best knowledge of the author, no inclusive model has yet been developed for H2S gas phase photolysis. In this research study, a sophisticated simulation model was developed successfully to describe ultraviolet degradation of H2S from waste gas. The photochemical reactor has been modeled with 19 chemical species and a total of 47 chemical and photochemical reactions which includes a light field model, a chemical model, a flow pattern model and a mass transfer model.
Simulation shows that the UV degradation of H2S in waste gas is a highly efficient process. Simulations were run to investigate the process efficiency is a function of initial concentration, gas flow rate, and relative humidity. The model was also validated with some literature experimental data by applying the model to those experimental conditions, and comparing the results. Comparison of simulation results and the experimental data indicates that the model overestimates the removal efficiency to some extent; however, observing the same trends in two different cases of the effect of initial H2S concentration and the effect of gas flow rate validates the model with sufficient accuracy to establish the feasibility of the process.
Previously, it was found experimentally that the main photolysis (or photocatalysis) product is SO42- (or H2SO4) at very low concentration of H2S. The model also agrees with this result, and furthermore predicts SO2 as another photolysis product which is predominant at high
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concentration of H2S. Hence altogether, it can be concluded based on the model that the UV degradation technique is effective, and it decomposes H2S to less harmful products which are also easier to be treated.
Moreover, the capability of the model for modeling the degradation of multiple pollutants at the same time was tested by model extension with NOx reactions. According to the simulation results, adding H2S in the NOx photolysis system has positive effects on the degradation efficiency for both H2S and NOx. The extended model indicates that the proposed model can be used as the basis of a modular comprehensive model to predict removal efficiency for each species and moreover product analysis when more than one pollutant is present.
