Selective hydrogen sulfide (H2S) removal in the presence of carbon dioxide (CO2), based on the novel co-current ProPure gas-liquid contactor and a regenerative solvent.
The key CAP technology is the ProPure co-current contactor, which is a gas flow driven “oneshot” contactor. The co-current contactor replaces the counter-current tower in a conventional amine plant. The small liquid droplets generated promote high gas-liquid mass transfer rates at low to intermediate permanent pressure drops.
CAP’s H2S-selectivity is achieved by a short retention time combined with the high gas-solvent exposure area throughout the contactor. Compared to countercurrent contactors the gas residence time is considerably shorter, typically 30–60 times shorter. Therefore, CO2 co-absorption is significantly reduced, allowing higher solvent H2S-loading capacity. Tertiary amines such as MDEA yield selective H2S-removal, as the solvent proton reaction with H2S is instantaneous whereas the reaction with CO2 undergoes several (slow) intermediate reactions. The higher the ratio
between CO2 and H2S concentrations, the more competitive CAP becomes as compared to conventional counter-current contactor technology.
Due to the contactor operating at high gas velocities, its size is much smaller compared to conventional equipment. The selective nature results in significantly lower circulation rates, which reduces the amine regeneration system’s overall size.
Economics: For a case with inlet concentrations of 5% CO2, 10–20 ppmv H2S and H2S-outlet specification of 2 ppmv, a reduction in installed weight of 60% is estimated compared to conventional technology. This is mainly due to the reduced amine circulation rate. The limited foot-print requirement makes CAP feasible for retrofit installations on existing offshore fields.