Pressure swing adsorption (PSA)


The IGCC technology (Integrated Gasification Combined Cycle) with pre-combustion CO2 capture presents a promising approach for near-zero CO2 emission power plants to be realized in the near future. A key challenge within this process is the separation of the CO2 / H2 gas mixture resulting from the gasification of coal with subsequent shift reaction. The efficiency of this step is critical to minimize the energy penalty of the capture process and enable this strategy.

The feed stream for this separation process is already at high pressure (35-40 bar) with a CO2 fraction of about 40%. These conditions are well suitable for a pressure swing adsorption (PSA) process. Therefore in our lab this PSA process is investigated experimentally and by numerical simulations including all the required aspects using commercial and new materials. Among the existing commercial adsorbents activated carbon is able to separate CO2 and H2 and will be used in this work as a base case to be compared with new adsorbents developed by SINTEF materials and chemistry (Oslo) to reach the required high purity.
One important characteristic of every adsorbent is its equilibrium adsorption isotherm. For the selected adsorbents pure and mixture isotherms of the main gases in the process, namely CO2, H2, and N2, will be measured by a gravimetric or gravimetric-chromatographic method, respectively. The dynamic characteristics of the process are investigated using a one or two column lab setup to measure the breakthrough behavior as well as complete PSA cycles.

As CO2, the strongly adsorbing heavy component, is required at rather high purity (>95%) and high recovery (>90% CO2 capture desired), whereas the purity of the light component namely H2 is less stringent, a conventional stripping PSA process like the Skarstrom cycle is most probably not applicable and a different process concept has to be developed. For the development, optimization and design as well as its comparison to other alternatives, the process is modeled and simulated in Fortran applying mass, energy and momentum balances. The model is validated using the equilibrium and dynamic experiments.
Furthermore a concept for the preliminary removal of impurities, above all sulfur components, and water has to be developed, as they may cause problems in the adsorption part.

This work is part of the European Union Framework Program 7 project DECARBit (“Decarbonise it”, 2008-2011).


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