Development of a New Ultra-Selective Solvent to Reduce the Cost to Capture CO2 from a H2S-Rich Natural Gas

Abstract

The contribution of CO2 present in natural gas to the total GHG emissions of the gas plant can be significant (up to 20% for Middle East Gas). When both H2S and CO2 are present, the CO2 capture cost is currently very high. The method developed to tackle this challenge is an innovative architecture of the acid gas treatment chain based on a new ultra-selective absorption process. The redesigned acid gas treatment architecture is detailed and compared with available technologies on the market. The technical cost of avoided CO2 can be reduced by up to 70% by using the new ultra-selective process compared to the available CO2 capture technology. This new acid gas treatment architecture can reduce by up to 20% the energy consumption to capture CO2. A new ultra-selective solvent has been developed using computational screening tools combined with experiments measuring physical, operational, thermodynamic, and kinetic properties. Those serve as input of a process simulation tool validated with medium-pressure absorber and regenerator pilot plant data. The new solvent is currently at TRL4 validation, a selectivity of more than 75% (CO2 slippage) has been observed on the pilot plant, with a H2S specification in the treated gas kept around 5 ppm. This result is the consequence of both a new solvent formulation (selective amine) and optimal operating conditions. There is, moreover, no increase in regeneration duty for the new solvent.

Selective H2S Absorption in Aqueous Tertiary Alkanolamine Solvents: Experimental Measurements and Quantitative Kinetic Model

“…To simultaneously respect the asymmetrical H 2 S (<4 ppm) and CO 2 (<2.0–2.5 vol %) specification, a selective solvent can be used that preferentially absorbs H 2 S over CO 2. Techno-economic studies have shown that a further increase of the selectivity might lower the cost of CO 2 capture from natural gas containing H 2 S. , …”

“…Physical solvents can be used for bulk selective H 2 S removal. Many molecules can be used, ,, and common examples are the Rectisol, Purisol, and Selexol processes. The selectivity is thermodynamic …”

“…Natural gas can contain significant amounts of acid gas (typically 0−30 vol % CO 2 , 0−30 vol % H 2 S), but the specifications of treated natural gas are very similar to biogas (around 4 ppm H 2 S and 50 ppm or 2.0−2.5 vol % CO 2 for LNG or pipeline, respectively) and can be reached with solely an amine scrubber, thanks to the high operating pressure of the absorption column. To simultaneously respect the asymmetrical H 2 S (<4 ppm) and CO 2 (<2.0−2.5 vol %) specification, a selective solvent can be used that preferentially absorbs H 2 S over CO 2. economic studies have shown that a further increase of the selectivity might lower the cost of CO 2 capture from natural gas containing H 2 S. 4,5 Low-pressure selective absorption is also applied in the natural gas industry, for example, in the acid gas enrichment (AGE) unit or the tail gas treatment unit (TGTU), in the upstream and downstream Claus sulfur recovery units, respectively. The main driving forces to improve the selectivity of the solvents in both TGTU and AGE are the reduction of CO 2 emissions, Claus unit optimization (only for AGE), and lower SO 2 emissions.…”