Thermodynamics, economics and systems thinking: What role for air capture of CO2?

Air capture has recently been advanced by several parties as a solution to the problem of constraining - and ultimately reducing - atmospheric CO2 in response to climate change. However, there are significant barriers pertaining to scale, energy needs and cost, which will hugely challenge the effectiveness and practicality of air capture. This paper examines the thermodynamics, energetics and economics and politics of air capture. These compare unfavourably with alternative approaches to atmospheric greenhouse gas reduction. An analysis is made of the energy cost of the one favoured DAC technology for which experimental results are available in the open literature - temperature/vacuum swing adsorption, and of one point source capture technology - oxyfiring of refinery FCCUs. We also examine the engineering effort required to implement atmospheric capture on a scale at which it could significantly reduce atmospheric levels of CO2; and questions are addressed regarding its practicability and appropriateness. The analysis demonstrates that air capture remains at best a peripheral activity, at worst a distraction, until point sources of greenhouse gas emissions such as power stations, industrial flue gases, shale gas wellheads, anaerobic digestion plants and landfill sites have been completely decarbonised. When these and so many other unaddressed factors are affecting our global climate, the pursuit air capture, the ultimate “end-of-pipe” solution, is inappropriate.