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

Kurzfassung

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 CO2 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 CO2-negative heat supply. Since CO2 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 CO2 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 CO2 from the atmosphere.