(657i) Techno-Economic Analysis of Rotary Temperature Swing Adsorption (RTSA) Process for Post-Combustion CO2 Capture

Carbon capture and storage has been advocated as a near-term solution for mitigating the negative effects of climate change with the use of fossil fuels. Point sources such as power plants emit large volumes of CO₂ and therefore, they can be the primary targets for capturing CO₂. Adsorption with porous solids, absorption with amines, and CO₂ capture using membranes are possible technologies advocated for carbon capture applications. The capture technologies can be implemented before the combustion of the fuel (pre-combustion) or after the combustion of the fuel (post-combustion). From a retrofitting aspect, post-combustion carbon capture is advantageous. Typically, in a post-combustion scenario, the concentration of CO₂ ranges from 4-22% (Natural gas power plant - cement plant), depending on the type of the fuel and process used. In general, capturing large amounts of CO₂ from lower concentration streams poses a significant challenge due to the energy demand for capturing a certain fraction of CO₂ and the large flue gas stream that needs to be processed.

Adsorption separation processes utilize the affinity of the different gas molecules to separate the constituents of a gas mixture. The processes are broadly classified into pressure (PSA) and temperature swing adsorption (TSA) processes based on the modes of regeneration. For low CO₂ concentrations, TSA processes offer the benefits of high CO₂ product purity but suffer from long cycle times, which can have a significant impact on the footprint. Combining novel sorbent shapes like laminates or monoliths¹ and switching to novel process concepts such as the rotary TSA² such as the one shown in Figure 1. Such processes are gaining increased attention in the adsorption community. These processes can offer the advantages of simultaneous heating and cooling of the solid bed shaped in the form of a rotor. This is advantageous as the process can operate continuously and unlike packed beds does not need idle or hold times for continuous operation. This can potentially improve the productivity of the process, thereby potentially reducing the capture footprint^3-6.

In this work, a simple 4-step rotary TSA process comprising of adsorption, heavy reflux with light reflux product, counter-current steam purge, and light reflux was selected. The process was simulated using a 1D non-isothermal non-isobaric model. For this work, Lewatit sorbent shaped in the form of a monolith was considered to capture CO₂ from a natural gas combined cycle flue gas with 5% CO₂. First the process was optimized to evaluate the maximum purity and recovery values achievable from the 4-step process. It was seen that from a 5% CO₂ feed, the 4-step cycle was able to achieve 95% CO₂ purity on a dry basis and 90% of the CO₂ was recovered. In the next step process optimization was carried out to identify the minimum specific primary energy consumption for CO₂ avoided (SPECCA) and the levelized cost of electricity (LCOE) for purity and recovery targets of 95% and 90%, respectively. Furthermore, the impact of sorbent lifetime and cost of the sorbent on the LCOE and SPECCA were studied. The rotary TSA process was then benchmarked with a fixed bed 4-step TSA cycle with steam purge containing Lewatit beads and comparison of the SPECCA and LCOE values were made. These results will be covered in this presentation.

References

1. Parallel passage contactor having active layers Patent No WO2021/240476 A1.
2. https://www.svanteinc.com/carbon-capture-technology/
3. Herraiz et al., Frontiers in Energy, 2020.
4. Ghosh and Gupta, Int J. Greenh gas con, 2014.
5. Nik et al., Proceedings of the GHGT-15 conference, 2021.
6. Wang et al., Int J Green Energy, 2023