(633f) Techno-Economic Evaluation of Amine-Based CO2 Capture: Exploring Post-Combustion Applications

To date, efforts to reduce CO₂ emissions have mainly focused on the power sector, with a phasing out of fossil fuels and replacement with renewable energy. The global power generation capacity of the existing coal fleet worldwide in 2017 was approximately 10,000 TWh. A third of this global power plant capacity is less than 10 years old, and thus, have potential for retrofit with amine-based CO₂ capture technology. Unlike power, key industries such as iron and steel or cement do not have a renewable technology substitute that is commercially available. Therefore, carbon capture and storage (CCS) technologies remains a potentially important option for the industrial sector. Although cost competitiveness of industrial products is a main concern, the prospects of post-combustion CO₂ capture in industry remain positive due possible cost savings provided by higher CO₂ concentration of the flue gases (> 10 %_mol).

The objective of this study is to explore opportunities for amine-based CO₂ capture across a comprehensive range of post-combustion applications. The techno-economic analysis considers a wide range of operating conditions that encompasses the majority of industrial post-combustion capture applications. Feed CO₂ concentrations between 2 and 42 %_mol, and feed flow rates between 1 and 1000 kg/s are evaluated, whilst considering capture rates between 70 and 99 %_mol. The process design and economics model was based on a published model^[1] with modifications to widen the range of applicability.

For feed CO₂ concentrations below 15 %_mol across all capture rates investigated, it was found that there was little benefit from economies of scale beyond 20 kg/s feed flow. The breakdown of capital and operating costs were also examined. For a given flow rate and amine lean loading, increasing the CO₂ content of the feed gas has a range of impacts. The cost of the absorber does not decrease as much as conventionally expected; although the height may be reducing, the increased amine circulation rate causes the diameter to increase. A rate-based sizing method was opted for both the absorber and stripper, and the ratio of cost between the absorber and stripper was found not to be constant, contrary to common practice.

At CO₂ concentrations above 8 %_mol, the marginal cost of capture as a function of CO₂ capture rate was found to be small. The cost of capture between 70 and 90 %_mol capture rate was essentially constant at a feed flow rate off 150 kg/s. From 90 to 99 %_mol the increase in capture cost is not prohibitive (≈ 5 US$/t_CO2), and this presents an opportunity for industrial emitters to capture substantially more of their CO₂ for little penalty. The greatest increase in capital costs is seen between 90 and 99 %_mol capture rate, with the cost of the absorber increasing significantly.

Along with the component-wise cost breakdown, the contributions of capital and operating cost to the total annualised cost were investigated. In many cases, operating costs contribute at least 50 % of the total annual cost and can be as high as 85 % in some cases. As steam is the greatest proportion of operating costs, its cost has a significant impact on capture cost in those cases.

The effect of the cost of capital on the capture cost was also explored. It was varied between 2 and 20 % to cover the range of public/government funding to privately funded. The greatest impact was seen at lower CO₂ concentrations (2 – 8 %_mol) and low feed flow rates (< 5 kg/s). This is due those scenarios being capital cost driven, i.e. the majority of their total annual cost is capital cost.

This study shows that amine absorption could be economically viable for industrial post-combustion capture applications over a wide range of conditions. In many cases, the difference in cost to capture 90 % of emitted CO₂ is very similar to 70 %, and 99 % capture rate is also within reach. This will be important in the context of a net-zero carbon future, and may encourage the deployment of amine-based post-combustion capture in industry.

References

[1] – Danaci, D., Bui, M., Mac Dowell, N., & Petit, C. (2020). Exploring the limits of adsorption-based CO₂ capture using MOFs with PVSA - from molecular design to process economics. Molecular Systems Design & Engineering, 5(1), 212-231. doi:10.1039/c9me00102f