(281g) Development and Optimization of Temperature Swing Adsorption Cycles for CO2 Capture and Utilization

Cyclic adsorption processes for gas separations have been extensively studied for the purification of the light components, since purities as high as 99.999% can be achieved with limited energy consumption. Examples of these processes are pressure swing adsorption (PSA) for H₂-purification, or temperature swing adsorption (TSA) for the drying of gases [1]. Contrary to that of the light product, the purity of the heavy product is thermodynamically limited in traditional (stripping) cycles which are characterized by the production of the light product at high pressures/low temperatures during the feed step, and by the desorption and production of the heavy product at low pressures/high temperatures [2]. Therefore, the design of cycles aimed at enriching the heavy product still remains a challenge.

A niche of applications for TSA cycles for CO₂ recovery lies in the chemical industry, where CO₂ is often emitted together with N₂ in the flue gas of reformers or boilers, but where CO₂ also represents a valuable reactant for the synthesis of chemicals. Examples of which are the synthesis of urea and that of methanol, where CO₂ is limiting with respect to the ammonia or hydrogen, respectively. In such applications the choice of a thermal regeneration allows a partial recovery of the sensible heat of the flue gas, which will lower the effective energy consumption of the process.

In this work we present a comprehensive investigation of TSA cycles for the recovery of CO₂ in post-combustion applications with downstream CO₂ utilization based on a detailed 1D adsorption column model [3]. Appropriate performance indicators are established, which define a theoretical performance limit: the minimal total volume of adsorbent required, and the minimal thermal energy requirement. The influence of the operating step duration and operating conditions on the region of attainable specifications and on the process performance are elucidated, and the effect of constraints such as the temperature of the flue gas is reported. This extensive analysis leads to the elaboration of heuristics for the development and optimization of TSA cycles for CO₂ recovery. Since the total volume of adsorbent required depends on the idle times of the cycle, hence on its scheduling, we further report the effect of different scheduling constraints on the limits of the attainable performances for a novel TSA process.

References

1. Ruthven, D., Ind. Eng. Chem. Res. (2000), 39, 2127—2131
2. Ebner, A. D. and Ritter, J. A., AIChE Journal (2002), 48(9), 1679—1691
3. Casas N., Schell J., Pini, R. and Mazzotti M., Adsorption (2012), 18, 143—161