Retrofit Design of CO2 Compression and Purification Process Using Intensification with Cryogenic Air Separation Unit

The CO2 Compression and Purification Unit (CPU) is an auto refrigeration system that works based on the Joule-Thomson effect, which requires high energy for compression and refrigeration. Therefore, optimization of this system has been an attractive research field in recent years. However, this system is applied for capturing CO2 from Oxy-Fuel Combustion (OFC) flue gases. The OFC refers to fuel combustion with approximate pure oxygen which in practice is usually produced from a cryogenic air separation unit (ASU). In this study, CO2CPU system was redesigned based on oxygen stream effluent from cryogenic ASU. The results obtained by analyzing a sample of combustion gas showed that only the oxygen gas stream produced in the ASU unit, which is being prepared to enter the combustion chamber is sufficient to condense and refrigerate the CO2CPU system. The performance of the proposed design was compared with three recently proposed schemes for a given feed. The results showed that the proposed system can perform at lower operating pressure and needs a significantly smaller heat-transfer area. In addition, the integration of CPU and ASU decreased the number of compressors and reduced the heat exchange area of cold boxes by at least 79% and the compressor energy consumption by at least 29%. It also allowed the delivery of the final CO2 product in the subcooled liquid phase. Therefore, instead of the expensive compressor, the pump can be used to increase the pressure to transfer CO2. Furthermore, optimization and sensitivity analysis were performed on this system using the Response Surface Methodology (RSM), which indicated that the inlet pressure and the temperature of the second separator had the most significant effect on this system.