(552b) Techno-Economic Comparison of Fixed and Fluidized Bed Adsorption Processes for CCS from an Ngcc Plant

Adsorption processes using solid sorbents is currently being explored by several research groups as an alternative to amine-based processes for CO₂ capture. The process relies on the differences in the affinities of the different gases towards the solid and has been implemented on a large scale for several gas separation applications. Adsorption processes are broadly classified into two types based on the mode of regeneration of the sorbent: Pressure/vacuum swing adsorption (PSA/VSA) where the solid is regenerated by lowering the pressure of the column and temperature swing adsorption (TSA) process where the solid is regenerated by the supply of heat directly or indirectly. The former is widely used for high CO₂ concentrations of 15% or more, while the latter is more suited for low CO₂ concentrations of 3-5%, such as the flue gas from a natural gas combined cycle (NGCC) power plant.

In fixed bed applications (the preferred configuration for sorbent-based adsorption today), TSA processes are usually slow due to the long heating and cooling times, and this is especially a drawback as it lowers the productivity of the process. This is a major challenge in the case of CO₂ capture due to the large volumes of gases involved in the separation problem. One way to improve the productivity is the use of novel structured sorbents like monoliths, laminates, or hollow fibers [1]. More recently, a rotary column TSA process with cycle times of a minute is being advocated for CCS applications [2]. As an alternative, fluidized bed-based processes can be implemented where the sorbent is transferred between adsorption and desorption columns in a similar manner as traditional solvent-based post-combustion CO₂ capture processes. In such applications, sorbents promise lower energy penalties and smaller vessels, but circulating the sorbent and exchanging sensible heat is considerably more difficult with a powder than a liquid.

The current work aims to compare fixed bed (parallel fixed columns or a rotary bed) TSA processes to fluidized bed processes for CO₂ capture from an NGCC power plant. The adsorbents chosen for this study are Zeolite 13X and an amine containing sorbent, shaped as hollow fibres or monoliths for fixed bed applications or a powder for fluidized beds. The processes are simulated using a standardized 1D modelling approach using consistent input data on sorbent isotherms and kinetics. An integrated techno-economic optimization methodology based on Bayesian optimization is implemented to find the parameter settings returning the minimum levelized cost of electricity (LCOE) from each process. Aside from the LCOE, other important performance indicators such as the CO₂ avoidance cost, CO₂ capture energy penalty, CO₂ capture efficiency, and specific primary energy for CO₂ avoidance will also be compared between the different processes.

References

1. Parallel passage contactor having active layers Patent No WO2021/240476 A1
2. Nik et al., Rapid Cycle Temperature Swing Adsorption Process Using Solid
   Structured Sorbent for CO₂ capture from Cement Flue Gas, Proceedings of the GHGT-15 conference, 15^th-18^th March 2021, Abu Dhabi