Separation and Storage of Carbon Dioxide from Various Mixtures by Using a Cryogenic Approach

In this study, a thermodynamic analysis using computer programming was conducted to investigate the separation process and the quantity and quality of CO₂ produced by the cryogenic approach. Correlations are developed based on heat transfer fundamentals to predict performance parameters and desired quantities. The effects of temperature, pressure, and the amount of cryogenic fluid required for CO₂ separation, particularly in a CO₂-containing mixture, are investigated. For analysis, pure CO₂, 20%CO₂– 80%CH₄, 30%CO₂–70%CH₄, 40%CO₂–60%CH₄, and 50%CO₂–50%CH₄ combinations are considered_. The mass of liquid nitrogen (as a cryogenic fluid) is considered to be in the range of 1 kg to 100 Kg. It is observed that the mass of solid CO₂ can be produced by direct sublimation by rejecting heat to liquid nitrogen for both pure and mixed. A specific amount of liquid nitrogen is required to sublimate the CO₂. As the percentage of CO₂ decreases in the mixture, the fluid nitrogen requirement increases for complete sublimation. In the case of liquid CO₂, the gas is first compressed above the triple point pressure of CO₂; then, using liquid nitrogen, the sensible and latent heat are removed for liquefaction. It is observed that the compression pressure should be in the lower range for complete liquefaction of CO₂ for a particular amount of liquid nitrogen. Increasing the compression pressure will result in low CO₂ liquefaction and increase compression power and outlet compression temperature. It is predicted that the pressure range should be 6 to 20 bars for complete conversion, and low power is required for all considered mixtures. The study also supports the effectiveness of heat exchangers and the efficiency of a compressor in reducing CO₂ emissions.