Direct air capture : is it the solution to the CO2 crisis ?

Climate change due to an increasing greenhouse gases concentration in the atmosphere is a challenging issue that humanity will have to address promptly. To limit global warming to 1.5°C, as set out in the Paris agreements during COP21, drastic reductions in our emissions by 2030 followed by achieving emissions neutrality in 2050 is recommended. Even if its heat trapping ability is far from being the highest, the abundance of carbon dioxide in the atmosphere makes it the major source of warming. Furthermore, it also has the disadvantage to have a very long lifetime; making past, present and future emissions, long-term contributors to global warming. To counter this, carbon dioxide removal technologies are presented as ways to artificially decreased CO2 concentration in the atmosphere. Among them, Direct Air Capture (DAC) is a promising technology at early stage of development. It described the process of extracting carbon dioxide directly from the atmosphere by chemically trapping it. The concentrated stream is then either geologically stored or used in industrial processes. Although the project looks great at first sight, its high energy consumption and other environmental pressures such as land and water use could limit DAC positive impact or even make it detrimental to the climate cause. It is precisely this ambiguity that motivates this work. Throughout this thesis, the two main DAC technologies, using solid or liquid capture medium, will be discussed by means of a life cycle analysis. After a literature review including a technical description of how the two capture methods work, they are compared on the basis of a reference case. Then, in order to take into account uncertainties related to the choice of the model as well as the limited information available concerning the few plants in operation, a sensitivity analysis is carried out. Based on these results, three location scenarios are established to illustrate them while deepening the analysis by adding the use of the obtained CO2 in the LCA scope.