For the last decades, continuous global trend towards more stringent safety, commercial and environmental specifications kept processing sour natural gas containing acid gas such as H2S and/or CO2 a growing challenge. If mercaptans are present in the sour natural gas, the limited mercaptans absorption capacity of the well known alkanolamine solvents can be a major problem. The operating companies have to upgrade their production units to comply with these specification and environmental constraints evolutions. Additional treatment steps are often required to achieve the total sulfur specification in the sales gas, adding process complexity and further increasing cost.
An efficient solution to solve the problem would be to replace the usual alkanolamine aqueous solvent by a hybrid formulation allowing simultaneous removal on mercaptans and acid gases. This approach has been rarely considered because of the side effects of traditional hybrid solvents: hydrocarbon co-absorption, negative impact on the downstream sulfur recovery units. It may be necessary also to replace the internals of the absorber column in the Acid gas Removal Units.
To address this issue, TOTAL is now using a new dedicated hybrid formulation since 2007. This new solvent has been developed by TOTAL by taking advantage of its intensive know-how and experience in gas processing. The hybrid solvent is obtained by addition of a physical component into a generic alkanolamine-water solvent. The final solvent composition is determined to optimize mercaptans removal and minimize hydrocarbon coabsorption, without affecting acid gas removal capabilities.
Without any plant modification, this hybrid solvent can be implemented in existing unit to remove mercaptans with the acid gases, with no detrimental impact on downstream SRU. It allows operating cost reduction of the existing downstream units. Last but not least, the energy consumption of the acid gas removal units can be lowered by 10- 15%.
This paper presents several applications cases where the benefit of using the hybrid solvent is demonstrated.