Why is this research needed?

Direct air capture (DAC) is widely recognised for its indispensable role as one of few negative emissions technologies (NETs) available that can be deployed to eliminate the emissions from the most recalcitrant or expensive sources of greenhouse gas emissions. DAC systems compare favourably to other NETs in many aspects, such as their significantly lower land and water requirements, smaller impact on biodiversity and food security, and inherent flexibility of siting locations. It is estimated that to deliver Paris Agreement targets, global CO₂ DAC capacities required by 2030, 2040 and 2050 should reach 470, 4,798 and 15,402 Mt-CO₂/annum, respectively, while the UK needs to achieve a least capacity of 5 Mt-CO₂ per year by 2050 if to meet its legally binding net-zero targets. However, the current high cost of direct air capture, which varies typically from $250 to $600/ton-CO₂ captured, presents a major barrier to overcome to unleash the essentially unlimited DAC capacities for negative emissions.

Two main types of DAC technologies are being developed and commercially exploited at various stages, including absorption-based systems (e.g. Carbon Engineering), which requires temperatures of around 900^oC to regenerate the solvent, and adsorption-based systems (e.g. Climeworks, Global Thermostat) which usually require much lower operation temperatures. Techno-economic and lifecycle assessments have demonstrated that adsorption-based DACs compare favourably to absorption-based systems, due to major cost reduction potentials by utilising low grade waste heat, high modularity, and no demand for water supply. The average energy requirements of adsorption-based DACs are found generally comparable, being 50-80% thermal for sorbent regeneration and 20-50% electrical mainly used by electrical fans for air circulation. The electrical energy demand in air circulation can translate into more than 50% of the energy-related cost per ton-CO₂ captured. Studies found that the operational and maintenance costs are generally dominated by the fan power used to overcome the system pressure drop, which could be a decisive inherent factor preventing further major cost reductions after all possible efficiency measures, such as more efficient fans and optimised contactor and sorbent structures. Consequently, trade-offs often have to be made between air velocity (pressure drop) and process efficiency so to reduce fan power demand. In addition, the high electrical demand of today’s DAC systems (ca. 650 kWh electricity/ton-CO₂), also serve an impeding factor for large scale deployment of DAC.

To overcome the performance challenges, a novel concept of heat-driven DAC system, which can potentially operate on harvesting essentially any sources of waste heat at above ambient temperatures, is proposed for the flexible funding call to carry out a proof-of-concept feasibility study. The proposed DAC process works on a principle of using heat as the driving force for air circulation in structured contactors for adsorption, thus drastically reduce the electrical energy consumption and hence the cost of direct air capture. The heat-driven DAC system can be configured flexibly either for centralised large-scale applications or distributed small scale DAC units.

What is this research investigating?

The proposed study aims to conduct a feasibility study of a new proof-of-concept of direct air capture (DAC) for major cost reductions with potentials of energy autonomy. The specific objectives include:

• to validate a heat-driven DAC concept through small scale laboratory tests and process modelling;
• to evaluate and optimise the preparation and topology/morphology-controlled assembling of CO₂ capture materials; and
• to perform a preliminary performance evaluation of the new DAC concept against existing DAC technologies based on published data.

What does the research hope to achieve?

In alignment with UKCCSRC’s research needs identified recently (e.g. low concentration residual waste, containment challenges for smaller emitters, and cost reductions of CCS etc), this study aims to examine the feasibility of a new DAC technology that can potentially deliver major cost reductions by harvesting and using essentially any sources of waste heat at above ambient temperatures, filling a knowledge/technology gap that has never been investigated. The research will contribute to the UK accomplishing its zero-emissions target by developing new direct air capture technologies that can be deployed to eliminate the emissions from the hard-to-decarbonise emission sources. It is also expected that the research will generate high quality peer-reviewed publication(s) in top international journals, contributing to the UK’s international leadership in the vital areas of greenhouse gas removal.