Continuous Improvement of Hybrid-Solvent Solutions through a Smarter Formulation

This paper presents how the optimization of the solvent composition provides significant OPEX reduction and simplifies process management. Removing mercaptans from natural gas is becoming a tough work for operating companies due to the tightening of commercial specifications for sulfur-containing molecules in the final products. Beside this, about 40% of the known gas reserves are sour; some of them contain H2S and mercaptans. To commercialize these gas fields in a profitable way, smart process solutions focused on energy efficiency are needed. Classical gas sweetening units are based on chemical absorption by means of aqueous alkanolamines to remove CO2 and H2S from natural gas. These solvents have limited mercaptans removal capacity, requiring supplementary removal processes. This has a negative impact on the overall gas processing costs. To face this challenge, TOTAL has developed a new series of hybrid solvents able to remove, in a one- step operation, CO2, H2S and mercaptans. Process performances can be improved without plant modification. The first solvent formulation was based on DiEthanolAmine (DEA) and was implemented in the sweetening units of the Lacq plant (France), demonstrating the benefits of the new hybrid solvents at industrial scale. DEA solvent is a widely used and easy-to operate/monitor solvent. However, DEA has the drawback to be sensitive to chemical and thermal degradation. Moreover, DEA regeneration is quite energy demanding. To overcome these problems, the amine components have been changed. The choice of new components is driven by following characteristics: good solvent stability, low regeneration energy demand, high CO2 and H2S removal efficiency. A mixture of MethylDiEthanolamine and Piperazine (MDEA+PZ) has been adopted as the solution to replace the DEA based solvent. The choice has been made thanks to the good chemical stability of MDEA and the high performance of PZ as an activator to boost the rate of the absorption process. This paper presents the operational feedback with this new formulation. The first benefit of the hybrid solvent formulated with MDEA+PZ is that it was implemented in the existing unit without plant modification. Other advantage is the improved chemical and thermal stability. This solvent swap allows to decrease the reboiler duty of the solvent regeneration, to reduce the chemicals consumption, while keeping the final product quality unchanged. The benefits of the solvent swap will be supported by operating data collected before and after the solvent swap.