There has been a recent discovery of a previously unknown exothermic reaction between CO2 and H2S. It’s a reaction that may fundamentally alter the hydrocarbon industry. Work continues. It’s called the Stenger-Wasas Process (SWAP) developed by Ray Stenger and Jim Wasas. And it may make obsolete traditional petroleum methods, such as the Claus Process and its variants.
The SWAP: Unrefined sour natural gas is fed into the catalytic reactor, where the SWAP reaction occurs between CO2 and H2S. Refined gas flows past the separator. CO2 and H2S are converted into water, sulfur and carbon in the collector. In a reaction that can start in less than one second at very moderate temperatures, the result of the SWAP is refined natural gas.
Brief Overview
Sulfur contaminants such as hydrogen sulfide (H2S), carbonyl sulfide (COS), and mercaptans in gas streams can create unacceptable levels of sulfur emissions in power applications or poison catalysts used in chemical synthesis. Sulfur contaminants are usually reduced to less than 300 ppm for power generation and considerably lower (<1 ppm) for the synthesis of methanol, ammonia, and Fischer-Tropsch (FT) liquids.
Sulfur recovery unit (courtesy: C&I)
Sulfur Recovery Processes
Removing sulfur from a natural gas or syngas process stream is only part of the story. The residual sulfur present in an acid gas stream must then be recovered to prevent environmental and safety harms, as well as meet operator permit requirements. Two main technologies have traditionally been used commercially to recover sulfur: the Claus process (partial combustion) for high levels of sulfur, and catalytic Redox processes, for relatively low levels of sulfur. In recent years, bio-chemical based technology, the Thiopaq Process, has been developed and commercially implemented. Other recent developments include the development of hybrid processes that combine Claus and Redox technology and are used for tailgas cleanup in Claus plants.
The SWAP has been verified by gas chromatography in the laboratory to reduce H2S to below the limit of detection (about 4ppb) in a single pass through the SWAP column.
The SWAP in the laboratory
Classified as hazardous waste by the EPA, H2S disposal requires expensive processing, i.e. the Claus Process. The SWAP may reduce related capital costs for the H2S disposal resulting from crude oil desulfurization, while simultaneously eliminating substantial amounts of CO2.
CLAUS PROCESS
Technology Description
In the Claus process, a high H2S concentration stream is the feedstock for recovery to elemental sulfur. Roughly 1/3 of the H2S is burnt (partial combustion) to form sulfur dioxide (SO2). The remaining H2S reacts with the synthesized SO2 over an alumina or bauxite catalyst to produce elemental sulfur. Depending on their concentrations, the unreacted components (tail gas), such as residual SO2, CO2, and H2S, are either emitted, thermally oxidized, or further treated in an additional recovery process.
(US Environmental Protection Agency, AP42, 5th Edition, “Compilation of AirPollutant Emissions Factors Volume 1: Stationary Point and Area Sources, 1995) The Claus process is thermodynamically limited to ~97 percent sulfur recovery, although additional treatment steps, such as tail gas sulfur recovery, can increase the recovery rate.
Commercial Manufacturers and Applications
The Claus process is the oldest commercial sulfur treatment process, with development dating back to the late 19th century. Today, Claus processes are the main step used for elemental sulfur production worldwide-in fact, 90 percent to 95 percent of the sulfur recovered in the United States was from the Claus process. Almost 40 companies operate over 1000 Claus processes in the United States, recovering nearly 9 million tons per year of sulfur. The petroleum and natural gas industries are the main users of the technology, with IGCC applications making up a small but growing segment of the user population.
With catalytic refining, environmental footprint and operational costs can be lowered. This and other breakthroughs may change the landscape of hydrocarbon refining. www.swapsol.com
This month, editors at Hydrocarbon Engineering Magazine, Europe’s premiere refining trade publication, took a look at the SWAP’s application in cleaning sour gas which has potential for dramatic savings for refiners. A new outside report shows the SWAP can beat costs of traditional methods (Claus) by as much as 70 percent.
