Combined system of renewable heat supply and DAC based on the technical lime cycle

A novel concept is proposed and analyzed, in which long-term thermochemical energy storage based on CaO is combined with direct air capture (DAC) by utilizing the carbonation of Ca(OH) 2 under ambient conditions. With a theoretical heat storage density of approximately 320 kWh/t CaO and an intrinsic DAC functionality with a CO 2 storage capacity of 44 wt%, the technical lime cycle offers two storage functions and thus promotes flexibility in energy networks with the goal to enable CO 2 -negative heat supply. Since CO 2 uptake is the rate-determining step in the closed technical lime cycle, the parameters affecting the carbonation of powdered Ca(OH) 2 are identified and analyzed to assess the feasibility of the proposed concept. Influence of CO 2 concentration, layer thickness and air flow are experimentally investigated, each showing a dependency on the carbonation rate. With a 2.0 mm Ca(OH) 2 layer, 72.3% carbonation could be achieved in 62 h. Based on these experimental results, initial system estimates indicate that with a hydration efficiency of 95%, 240 kWh of heat on demand, corresponding to the heating demand of an average week, require 0.78 t of CaO and could capture up to 430 kg CO 2 from the atmosphere.