Integrating DAC into renewable heat supply

Kurzfassung

Direct Air Capture (DAC) is a method of capturing CO2 from the atmosphere to lower its concentration and making it available for downstream processes or underground storage. The required energy is quite high as in any CO2 extraction from the atmosphere, mainly needed for the regeneration of the sorbent material. In the presented concept, CO2 capture is combined with long-term energy storage and renewable heat generation to utilise part of the invested energy, increasing the overall efficiency. Basis of this concept is the technical lime cycle. Slaked lime can capture CO2 from the atmosphere in ambient conditions. By burning the formed limestone at temperatures of around 900-1200°C, called calcination, CO2 can be released as a pure stream, and be provided for subsequent processes. In order to use renewable energies, dynamic calcination is required, operated according to availability. Before using the lime as a CO2 sorbent again, the formed burnt lime can be used to provide heat by utilising the exothermic reaction from burnt lime with water, which can be used for hot water and space heating. The uncharged storage material can then be used as CO2 sorbent again as in other DAC systems. As the reaction takes place in ambient conditions, this is the speed-determining step of the overall system and is investigated at a test rig. In this contribution, experimental results of the reaction will be presented, as well as the resulting overall mass and energy balances of a combined DAC and energy storage system, providing pure CO2.