Carbon dioxide removal from industrial gases using an indirectly heated and cooled temperature swing adsorption process
In addition to absorption and membrane processes, adsorption processes offer the possibility of capturing and recovering CO2 from fossil fueled power plants. Because of the long heating and cooling times required in a TSA process and because during desorption the recovered component is diluted, an indirectly heated and cooled TSA process is proposed for CO2 capture. The suitability of the indirectly heated and cooled temperature swing adsorption process for CO2 capture is investigated in this work. The heat transfer characteristics of an adsorbent packed bed with and without convection are investigated, since heat transfer plays a major role in this process. The adsorption characteristics of an indirectly heated and cooled adsorber is also an important topic in this work. A multidimensional mathematical model is derived in order to simulate the indirect heated and cooled temperature swing adsorption process. The heat conductivity of the solid particle and the wall Biot number are important model parameters and are required for modeling the indirect heated and cooled TSA process. The convective contribution to the radial heat conductivity at low Peclet numbers showed a similar relationship to the relationship that is postulated in the literature for higher Peclet numbers. Contrary to the radial heat conductivity, the convective contribution to the wall heat transfer coefficient shows no clear relationship. The reasons for this are the correlation between the parameters and that the non-convective contribution dominates over the range of Peclet numbers that are used in this work. To investigate the adsorption characteristics, an isotherm is scaled by comparing the experimental loading value that is measured with a breakthrough curve and the loading obtained by the isotherm. This is necessary since the same activation procedure cannot be achieved during the in situ activation of the bed. The model is validated and kinetic parameters are calculated. Moreover, the agreement between the model and the measurements is strong, especially for the CO2 concentration. The small discrepancies between the measured and predicted temperature profiles can be explained on one hand by flow disturbances and on the other hand by the uncertainty caused by scaling the isotherm. The recoveries obtained by the model are within the range of the experimental error and show the same dependency of the recovery with the regeneration temperature. The average purity of the recovered CO2 is also within the experimental error. Using the derived model and the determined kinetic parameters, a parametric sweep is conducted in order to see the influence of different parameters on the process. The influence is measured by three different key performance indicators: the average purity of the recovered CO2, the CO2 recovery, and the specific energy required. The numerical study shows that promising results are obtained by reducing the radial thermal resistance. Using optimal parameters, high recoveries and purities can be achieved and specific energy requirements that are lower than the benchmark process (amine wash). This work shows, that the indirectly heated and cooled TSA process offers a promising alternative to CO2 capture.
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