CO2 capture for backup power plants: Entrained flow Calcium Looping using Ca(OH)2

Abstract

Calcium-Looping is a suitable post-combustion CO₂ capture technology for deep decarbonization of flue gases coming from power plants and industrial processes. A novel concept, which uses Ca(OH)₂ instead of CaO as CO₂ capture sorbent and entrained flow reactors instead of fluidized beds, enables the flexible operation to decarbonize backup power plants during low renewable energy generation. Therefore, experiments were carried out in an electrically heated entrained flow reactor at the University of Stuttgart, investigating the CO₂ uptake of Ca(OH)₂ powders and the possible degree of decarbonization in realistic flue gas conditions. High CO₂ capture efficiencies of over 90 % were achieved within only four seconds of gas–solid reaction time while showing that the sorbent excess needed for this decarbonization is comparably low (Ca-to-CO₂ ratios <1.5). Additionally, a model was fitted based on the experimental results, showing that 99 % CO₂ capture would be possible with a Ca-to-CO₂ ratio of 2.29. This presents an increased reactivity of the carbonation of Ca(OH)₂ compared to CaO, which enables the operation in small entrained flow reactors. Furthermore, comparably low temperatures of 550 °C decrease the systems energy penalty while enabling higher CO₂ capture efficiencies. Thus, the findings of this study demonstrate the suitability of Ca(OH)₂ as a CO₂ capture sorbent in entrained flow reactors and prove the potential for a large-scale application to decarbonize backup power plants.