(404e) Pressure Swing Adsorption Process for Pre-Combustion CO2 Capture

The IGCC technology (Integrated Gasification Combined Cycle) with pre-combustion CO2 capture is a promising approach for near-zero CO2 emission power plants to be realized in the near future. A key challenge within this technology is the separation of the CO2 / H2 gas mixture resulting form the gasification of coal followed by the water gas shift reaction. In this work pressure swing adsorption (PSA) is investigated as a possible method for CO2 capture.

Among the existing commercial adsorbents zeolites and activated carbon are suitable to separate CO2 and H2. The latter will be used in this work as a base case to be compared with newly developed tailored adsorbents to reach the required high purity.

One important characteristic of every adsorbent is its equilibrium adsorption isotherm, which can be measured by a gravimetric method using a Rubotherm magnetic suspension balance (Rubotherm, Bochum, Germany) [1]. Adsorption isotherm measurements of pure CO2 and H2 were performed at pressures up to 150 bar and in a temperature range of 25 - 140°C and 25 - 65°C, respectively. Also binary adsorption isotherms of different CO2 / H2 mixtures will be measured following the method described earlier [2].

Due to its short cycle times, a pressure swing adsorption process is well suitable for this application. In this process CO2 is the more retained component and required at high purity, whereas the purity of H2 is less stringent. Therefore a conventional stripping PSA scheme (e.g. a Skarstrom cycle) may not be suitable. In this case a different process concept has to be developed. Rectifying or dual reflux PSA processes as well as various combinations of the different PSA steps can be considered to obtain the more retained component at high purity [3, 4]. For the development, optimization and design as well as its comparison to other alternatives, the process is modeled and simulated.

In order to measure the dynamic adsorption behavior and to evaluate the developed model, a lab-scale adsorption column is used. In this setup all different steps of an adsorption cycle, i.e. adsorption, pressurization, desorption and blowdown, can be investigated and analyzed by on-line measurement of pressures at the column in- and outlet, temperatures inside the column and at the in- and outlet as well as composition of the outlet gases.

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

References

[1] R. Pini, S. Ottiger, A. Rajendran, G. Storti, M. Mazzotti, Adsorption 14, 133 (2008).

[2] S. Ottiger, R. Pini, G. Storti, M. Mazzotti, Langmuir 24, 9531 (2008).

[3] D. Diagne, M. Goto, T. Hirose, J. Chem. Eng. Jpn. 27, 85 (1994).

[4] R. Kumar, W.C.Kratz, D.E. Guro, D.L. Rarig, W.P. Schmidt, Sep. Sci. Technol. 27, 509 (1992).