Mechanical Engineering
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Item ROLE OF BENZENE, TOLUENE AND XYLENE TO ACID GAS DESTRUCTION IN THERMAL STAGE OF CLAUS REACTORS(2015) Ibrahim, Salisu; Gupta, Ashwani K.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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.Item CHARACTERISTICS AND CHEMICAL KINETICS OF HYDROGEN SULFIDE COMBUSTION IN THERMAL CLAUS REACTOR(2012) Selim, Hatem Mohamed Mohiy Elden; Gupta, Ashwani K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrogen sulfide is a hazardous gas from both environmental safety and human health perspectives. Hydrogen sulfide presence in any combustion application results in the formation of acidic gases that affects ozone layer and causes acidic precipitation. Exposure to H2S levels at 100 ppm or higher can endanger human life. Hydrogen sulfide is commonly found to exist in crude natural gas and oil wells. With the decrease in fossil fuels reserves around the world, we will have to rely on extracting energy from wells that contain higher amounts of H2S. In addition, environmental regulations strictly regulate the H2S discharge into the atmosphere. Subsequently, efficient hydrogen sulfide treatment becomes of increasing importance with time. Hydrogen sulfide treatment is typically a chemical reaction process (Claus process) in which hydrogen sulfide is combusted to end-products of sulfur and water. Hydrogen sulfide combustion in thermal Claus reactor has been investigated in this research. A reduced reaction mechanism for H2S oxidation has been developed using a novel error-propagation-based approach for reduction of detailed reaction mechanisms. The reduced mechanism has been used for detailed investigation of chemical kinetics mechanistic pathways in Claus process. Experimental examination of H2S combustion in different flames, methane/air and hydrogen/air, is provided. Chemical kinetics pathways and reaction conditions responsible for sulfurous compounds formation (SO2, CS2, and COS) are addressed. Hydrogen sulfide flame emissions have been investigated for intermediate species identification using chemiluminescence flame spectroscopy. Effect of acid gas composition (H2S, CO2 and N2) on hydrogen sulfide combustion and Claus process efficiency is also provided. Finally, examination of the quality of captured sulfur with respect to reactor conditions is presented.