Joule
Volume 5, Issue 8, 18 August 2021, Pages 2047-2076
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Article
A comparative energy and costs assessment and optimization for direct air capture technologies

https://doi.org/10.1016/j.joule.2021.05.023Get rights and content
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Highlights

  • Three DAC processes were compared on the basis of exergy demand and productivity

  • Solid sorbent-based processes perform better than solvent-based processes

  • CO2 capture costs below 200 $/tCO2 are achievable for all technologies

  • Adsorption/desorption kinetics and H2O affinity strongly affect solid sorbent process

Context & scale

Artificial removal of CO2 from the atmosphere will be pivotal for the realization of CO2-net-zero plans and policies. Among the few available solutions, the direct extraction from air—or direct air capture (DAC)—features the highest removal potential. Although energy and economic expenditure are high, DAC is still in its infancy, and a large potential exists for its optimization. To scale up the production, the different processes should be consistently evaluated, their design and operation optimized, and the needs for further development identified. Surprisingly, this is missing in the literature. In this study, we discuss the optimal process design and performance for the main DAC technologies, starting from publicly available unit designs and data and by using advanced simulation tools. Moreover, we identify the open challenges that need addressing and compute the CO2 capture cost as a function of energy and equipment costs, showing the combinations that would allow for cheaper DAC units.

Summary

This work provides a comparative technical assessment of three technologies for CO2 removal from air: two aqueous-scrubbing processes and one solid sorbent process. We compute productivity and exergy and energy consumption using process simulations and mathematical optimization. Moreover, we evaluate the cost range and discuss the challenges for large-scale deployment. We show that all technologies can provide high-purity CO2 and that the solid-based process has the potential to offer the best performance, owing to an exergy demand of 1.4–3.7 MJ.kgCO21 and a productivity of 3.8–10.6 kgCO2.m3.h1. Translating productivity and energy into cost of CO2 capture via a simple model, we show that the capital cost is the main cost driver. All technologies have the potential to operate below 200 $.tonCO21 under favorable, yet realistic, energy and reactor costs. The solid-sorbent process achieves this under a broader range of conditions and is less dependent on the installation cost when a high mass transfer is achieved.

Keywords

CDR
negative emissions technologies
direct air capture
DAC
tecno-economic assessment
CCS
net zero emissions
process modelling
optimization
solid sorbents

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These authors contributed equally

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