A low-energy chilled ammonia process exploiting controlled solid formation for post-combustion CO₂ capture

A new ammonia-based process for CO₂ capture from flue gas has been developed, which utilizes the formation of solid ammonium bicarbonate to increase the CO₂ concentration in the regeneration section of the process. Precipitation, separation, and dissolution of the solid phase are realized in a dedicated process section, while the packed absorption and desorption columns remain free of solids. Additionally, the CO₂ wash section applies solid formation to enable a reduction of the wash water consumption. A rigorous performance assessment employing the SPECCA index (Specific Primary Energy Consumption for CO₂ Avoided) has been implemented to allow for a comparison of the overall energy penalty between the new process and a standard ammonia-based capture process without solid formation. A thorough understanding of the relevant solid-solid-liquid-vapor phase equilibria and an accurate modeling of them have enabled the synthesis of the process, and have inspired the development of the optimization algorithm used to screen a wide range of operating conditions in equilibrium-based process simulations. Under the assumptions on which the analysis is based, the new process with controlled solid formation achieved a SPECCA of 2.43 MJ kg_CO^-1, corresponding to a reduction of 17% compared to the process without solid formation (with a SPECCA of 2.93 MJ kg_CO^-1). Ways forward to confirm this significant improvement, and to increase the accuracy of the optimization are also discussed.