The SEWGS process

The Sorption Enhanced Water Gas Shift process (SEWGS) is a technology that combines the water-gas shift reaction with CO2 capture at high temperature. The feed to the SEWGS unit is syngas, which is produced by reforming and high temperature shift. The products are a pure CO2 stream at low pressure and a H2-rich stream at high pressure and high temperature. The CO2 can be compressed and transported to a suitable storage location, e.g. geological formations. In a reactor CO is converted with H2O to CO2 and H2 (water-gas shift reaction). Simultaneously, CO2 is removed from the gas by sorption on a promoted hydrotalcite-like material. The sorbent is regenerated by purging counter currently with steam at low pressure. Since adsorption of CO2 is thermodynamically favored at high pressure and desorption at low pressure, parallel reactors are operated in pressure swing cycles.

 

Power production with CO2 capture by SEWGS.
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Power production with CO2 capture by SEWGS.

Power is generated by gas turbines (GT) and steam turbines (ST), heat is recovered for steam generation (HRSG). Steam is needed for auto thermal reforming and water gas shift (ATR/WGS), and for CO2 removal by SEWGS.

 

 

SEWGS principle
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SEWGS principle: (upper) adsorption and reaction at high pressure (lower) desorption at low pressure.

 

Sorbent material, hydrotalcites, can be used in the sorption enhanced water gas shift based capture system. The experiments with the SEWGS single column proofed good long term stability of the hydrotalcite sorbents for CO2 capture. In 2007 combined WGS and CO2 capture experiments in the single column unit (column is fi lled with mixture of WGS catalyst and CO2 sorbent) also confi rmed the technical feasibility of the SEWGS process for pre combustion CO2 capture. In 2008, continuous SEWGS experiments have been performed on the multi column SEWGS test rig. A so-called CO2 rinse cycle was tested. CO2 rinse means that CO2 at 30 bar is used to remove the gas from a reactor that is saturated with CO2 at the end of the hydrogen production step of the cycle. This cycle yielded a relatively pure hydrogen product, which means a high CO2 capture ratio.

 


CO2 slip in product gas during operation of SEWGS-1 without (dark blue line) and combined with water gas shift (light blue line). The combined water gas shift CO2 capture experiments show nearly 100% CO conversion at 400oC, while capturing/absorbing almost all CO2. After 300 cycles steady state is attained and CO2 slip is still negligible.