The separation of CO2 from ambient air - A techno-economic assessment

This paper assesses the separation of CO2 from ambient air from a technical and economic standpoint. Reducing CO2 emissions and their sequestration from the atmosphere is vital to counteract ongoing climate change. The most promising technological options for CO2 separation are first identified by reviewing the literature and comparing the most important technical and economic parameters. The results point to amines/imines as adsorbing agents to separate CO2 from ambient air. A system layout is then designed and a technical analysis conducted by solving mass and energy balances for each component. An economic analysis is then performed by applying a specifically-developed model. The total energy demand of the system discussed here is calculated as 3.65 GJ/tCO2. This high energy demand mainly derives from the system-specific implementation of two compressors that compress air/CO2 and overcome the pressure losses. The second-law efficiency calculated ranges of 7.52-11.83 %, depending on the option of heat integration. The costs of avoiding CO2 emissions vary between $ 824 and 1333/tCO2, depending on the energy source applied. The results of this work present higher values for energy demand and costs compared to other values stated in literature. The reasons for this deviation are often insufficient and overoptimistic assumptions in other literature on the one hand, but also relate to the specific system design investigated in this paper on the other. Further case studies reveal that enormous land requirements and investments would be needed to reduce potential CO2 quantities in the atmosphere to contemporary levels. A comparison between CO2 removal from the atmosphere and carbon capture and storage technology for coal power plants shows that this technology is not yet able to economically compete with carbon capture and storage. Furthermore, the impact of CO2 separation on the production costs of industrial commodities like cement and steel demonstrates that CO2 removal from the atmosphere is not yet a viable alternative to solving the climate change problem. In the long-term, CO2 separation from ambient air may still play an important role in the sequestration of CO2 from diluted and dispersed sources, as the technology has the potential for significant further development and optimization.