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With the continued development of sour gas fields around the world, the removal of mercaptans from gaseous and liquid hydrocarbon streams is becoming a challenge for today's gas processing plants. Key elements include meeting environmental regulatory standards, maximizing productivity and minimizing total lifecycle costs. A variety of mercaptans handling processes are available, and these processes have been generally applied based on the level of mercaptans in the feed gas. This variety may make it difficult for plant owners to select the best technology, given the project's demand for an optimized, fit-for-purpose scheme to meet economic, technological and environmental targets.
This article discusses proven mercaptans removal technologies in gas processing plants, as well as various options to process the captured mercaptans. It also suggests which combination of technologies best fits each application and offers the most cost-effective and environmentally friendly solution.
Natural gas from the wellhead contains hydrocarbons and water, and sometimes carbon dioxide (CO2), hydrogen sulfide (H2S) and other sulfur components, such as mercaptans (R-SH) and other impurities. Therefore, feed gas treatment may be required to make it suitable for the desired application. Whereas deep removal of CO2 and H2S has been mastered, R-SH removal from a sour feed stream still presents challenges, depending on the concentrations involved.
The primary motive for removing mercaptans in the gas processing plant is to meet a maximum total sulfur specification in the treated gas or natural gas liquids. To comply with environmental regulations and avoid problems with corrosion and damage to downstream equipment, typical total sulfur specifications generally range from 30 ppmv to 100 ppmv. Of course, the design objective is to eliminate or reduce the size of the treatment units, thereby minimizing costs.
A number of processes for removing mercaptans from natural gas and hydrocarbon liquid streams exist. However, the level of mercaptans in the feed gas is the primary influence in the selection of the most appropriate mercaptans removal method.
Mercaptans removal from feed gas. Conventionally, mercaptans have been removed by treating the natural gas feed stream with either a physical solvent, a hybrid solvent (i.e., a mixture of chemical and physical solvent) or a molecular sieve unit (MSU). However, where high levels of mercaptans in the feed gas are...