Process For Improved Mercaptan Removal

Abstract

Abstract Removing mercaptans from sour natural gas has always been considered as a challenge. This is becoming an even more important issue with the global trend towards more stringent specifications for commercial gases. Amines have been extensively used because of their ability to meet the most severe H2S and CO2 specifications and their very high acid gas selectivity over hydrocarbons, but present very limited mercaptans removal performances. They require an additional treatment step to achieve the total sulfur content specification in the exported gas. Hybrid solvents are more efficient in removing mercaptans, but have the disadvantage of poor acid gas selectivity over hydrocarbons, resulting in hydrocarbon losses with the separated acid gases. Total, taking advantage of its extensive know-how and experience in acid gas removal with amine mixtures, has developed the HYSWEET® process, using a new hybrid solvent formulation allowing simultaneous absorption of acid gases and of mercaptans, with limited coabsorption of hydrocarbons. The solvent was selected at the laboratory scale, with a particular attention given to operation related constraints e.g., cost, corrosion, foaming, degradation…etc. The new solvent's acid gas and mercaptans removal performances were then validated on a pilot rig. The performance of the HYSWEET® process has been assessed for several field applications, and compared with the performances of conventional amine processes. This allowed evaluating the potential gain achievable by the implementation of the new hybrid solvent. The study leads to identify the application cases for which the new hybrid solvent will allow an economic and complete mercaptan removal without any additional treatment, and a perspective of reduction of the additional treatments for the other cases. Besides an economical mercaptan removal, the new hybrid solvent allows a significant reduction in the energy consumption. The results of the techno-economic evaluation of the HYSWEET® process have been confirmed during the first successful industrial application at the Lacq sour gas plant in 2008. Half of the gas production is now treated with the hybrid solvent, allowing the plant to achieve high global mercaptans removal. These results are fully documented in the paper, demonstrating that the newly developed process is a good contender for the development of new sour gas fields to achieve the increasingly stringent commercial gas specifications.