Novel air-liquid contacting concepts for direct air capture of CO2
Project duration: July 2023–June 2026
Dr Ali Kiani
Mohamed Abdellah, Ali Pourkhesalian, Ehsan Soroodan Miandoab, Nouman Mirza, Aaron Cottrell, Sanger Huang and Paul Feron.
Direct air capture (DAC) methods using liquids for transfer of carbon dioxide (CO2) face several current process and equipment challenges, including high operational and capital costs.
Current gravity-operated equipment has a high liquid-to-gas (L/G) ratio (>0.2 kg/kg) and its ‘packed column’ architecture (where the carrier gas is forced through the packing) imposes pressure drops, both of which increase energy requirements. The optimum L/G ratio for effective transfer of CO2 from the air to a liquid absorbent is around 0.01 kg/kg with a pressure drop half that of current levels. Overall cost is also determined by the efficient contact between the large air flow and the small amount of liquid needed to capture CO2 at 400+ parts per million (ppm) concentration. This combination is inherently difficult to realise. In essence, the equipment for it doesn’t yet exist.
The successful development of innovative air–liquid contactor processes and equipment with optimum performance for the overall DAC process will address these challenges, and constitute a large step forward in removing cost obstacles and significantly enhancing the potential application of DAC. The technology could also be used in conjunction with geological storage and mineralisation, providing two significant pathways towards realisation of net-zero emissions. The early stage of research and development in the field makes it an ideal area for discovery science that will significantly increase CSIRO’s capabilities and business opportunities in the net-zero economy.
Our project aims to develop innovative air-liquid contacting concepts and equipment that enable CO2 capture from the atmosphere at much lower L/G ratios and gas-side pressure drops. This will result in lower energy requirements for moving liquid and air, and consequently lower costs for DAC.
Based on our previous work, there are two concepts that show great potential for energetically-optimised and effective mass transfer of CO2 from air to liquid.
We’ll assess the performance of both concepts, including effective capture of CO2 aerosol emissions at the back end of the system, and validate the results with modelling. These results are critical for subsequent design activities.
In the system design and construction phase, we’ll investigate different flow modes and rates for their potential to lower L/G ratio and pressure drop, and for successful recovery of droplets from the air stream to prevent aerosol emissions. Based on the results of the experimental work, we’ll develop detailed designs for new contactor processes and equipment that are simple, low cost, and with low energy input. This would enable DAC technology to be deployed before the end of the decade.
There are a number of technical challenges to overcome. One is to provide the efficient contact between the large air flow and the small amount of liquid that will enable a lower L/G ratio and energy-efficient movement of air and liquids. The second is to generate droplets of a sufficiently small size at acceptable energy consumption that are easily recoverable from the air stream in an overall device that provides sufficient residence time for the transfer of CO2 to the liquid. And the third relates to packed columns, which tend to be avoided in many applications that remove components at low concentration because of the relatively high pressure drop. They remain attractive, however, due to their ability to provide significant surface area for CO2-transfer at low cost.
To address these challenges, we’ve identified concepts for investigation that have the ability to operate at low air–liquid ratio and low pressure drop, and with known potential for enhanced contact and residence time, mass transfer rate and removal of droplets from the air stream.
Kiani, A., Lejeune, M., Li, C., Patel, J., & Feron, P. (2021). Liquefied synthetic methane from ambient CO2 and renewable H2-A technoeconomic study. Journal of Natural Gas Science and Engineering, 94, 104079.
Commonwealth Scientific and Industrial Research Organisation. (2021). Methane Fuel Carrier Project – knowledge sharing report.