A NEW METHOD FOR CO_2 CAPTURE: FROSTING CO_2 AT ATMOSPHERIC PRESSURE

摘要

CO_2 capture in the flue gas of energy production facilities shows a great advantage providing that it is performed at atmospheric pressure. Taking into account that the triple point of CO_2 is at 520 kPa and -56℃, the only possibility to capture CO_2 at atmospheric pressure is to freeze it on cold surface. This frosting is performed with a system consisting in an integrated cascade, which is a vapor compressor system using progressive distillation of a refrigerant blend in order to evaporate at low temperature (between -130 and -110℃) and at sufficient high pressure to keep an acceptable pressure ratio for a single stage compressor. The design and control of the frosting/defrosting on the heat exchanger surface permits the recovery of fusion heat when CO_2 changes from solid to liquid phase. This latent heat of fusion is used to cool down the liquid blend of refrigerants just prior to evaporation. The paper presents the global design of the system, the energy consumption and the coefficient of performance of this low temperature refrigerating system.