(501c) Decomposition of Hydrogen Sulfide in a Nonthermal-Plasma Pulsed Corona Discharge Reactor

Gas streams containing H₂S are encountered in almost all current and potential fossil fuel energy extraction and processing systems. Sulfur must be removed from such streams for compliance with environmental regulations and to avoid corrosion of processing equipment. The conventional treatment method for H₂S is the Claus process, which produces sulfur and water. Besides sulfur recovery limitations, another major disadvantage of the Claus process is that the valuable potential product hydrogen (H₂) is converted into water. At current H₂S generation rates (approximately 6 million tons per year), Claus chemistry is estimated to result in a loss of 125 billion SCF per year of potential hydrogen, equivalent to 75 trillion BTU or approximately $450 million per year. The economics of industries that produce H₂S, such as petroleum refining or natural gas production from sour wells, could be altered dramatically if the H₂S could be economically decomposed into hydrogen and sulfur. The hydrogen could be recycled to petroleum refineries for use in hydrogenation operations (since most refineries currently use methane steam reforming to meet much of their hydrogen requirements) or it could be used as a clean fuel in fuel cells or in direct combustion applications. Clearly, there is a strong incentive to develop more cost-effective and environmentally benign alternatives to the Claus process, such as the proposed direct dissociation of H₂S into H₂ and sulfur. Many methods have been investigated to dissociate H₂S into its constituent elements. Nonthermal plasma has the advantage of being a partially ionized gas, which is a good source of chemically active species, including radicals, excited states and ions, that can promote chemical reactions at ambient temperatures. Therefore, direct dissociation of H₂S using various nonthermal plasma processing technologies, including microwave plasma, glow discharge, silent discharge, gliding discharge, and pulsed corona discharge, has been attempted. Our recent investigation found that H₂S decomposition in a pulsed corona discharge reactor (PCDR) has the lowest energy consumption compared to other types of nonthermal plasma discharge. In this work, the effects of various factors, such as charge voltage, pulse frequency, charge capacitance, and gas flowrates, on H₂S conversion in a nonthermal plasma reactor are reported in order to further optimize operating conditions. A newly designed PCDR with seven view ports for plasma diagnosis has been fabricated and used to dissociate H₂S into hydrogen and sulfur. A highly nonuniform corona discharge is formed. For constant power input, charge voltage and frequency have a weak effect on H₂S conversion rate at fixed charge capacitance. However, the charge capacitance has a large effect on H₂S conversion rates at a constant power input. H₂S conversion rates decrease with increasing charge capacitance. These observations can be explained by our proposed corona discharge mechanism.