ROLE OF BENZENE, TOLUENE AND XYLENE TO ACID GAS DESTRUCTION IN THERMAL STAGE OF CLAUS REACTORS
Gupta, Ashwani K.
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Crude oil and natural gas often contain acid gases (H2S and CO2) and trace amounts of benzene, toluene and xylene (BTX) and these are all harmful to human health, environment and industrial equipment. Acid gases in chemical industry and vehicles cause corrosion to parts of engines, refinery equipment and catalysts deactivation in catalytic processes. Human exposure to H2S, even in low concentrations, causes burning of eyes, headache, dizziness, dyspnea, and skin irritations. Inhalation of high doses of BTX may cause skin and respiratory tract irritation. Increased energy demand and exploitation of sourer feedstock have made regulatory agencies worldwide to promulgate stricter regulations on sulfur emissions. US EPA requires a reduction of sulfur in gasoline from 30ppm to 10ppm by 2017. Crude oil and gas must be subjected to more efficient desulfurization processes. The separated acid gases and BTX is further processed in Claus process for chemical and energy recovery. Currently, BTX poses several technical and operational problems that result in higher operational costs and increased toxic gas emissions in Claus plants. BTX destruction in the thermal stage of Claus process was identified as the solution. Acid gas and BTX combustion in thermal stage of Claus reactor, which provides simultaneous recovery of both sulfur and thermal energy, is the subject of this research. Effect of BTX in H2S fueled flames on sulfur chemistry in thermal stage of a Claus reactor was characterized. Reactor conditions that promote BTX destruction are presented. Oxygen enriched combustion air for the destruction of BTX and acid gas is examined. Chemical kinetic pathways of BTX destruction under high temperature conditions of the Claus reactor are evaluated. Intermediate radicals and stable species formed during the combustion process are characterized using flame emission spectroscopy and gas chromatography (GC). Role of multiple contaminants, CO2 and benzene, toluene or xylene in H2S combustion is also investigated. Chemical kinetic pathways and reactor conditions that promote/hinder the formation of mercaptans (such as COS and CS2) is addressed. The results presented here assist in the design guidelines of advanced Claus reactors for enhanced sulfur capture in the thermal stage and to mitigate environmental issues.