Conditioning of a pipeline CO₂ stream for ship transport from various CO₂ sources

Abstract

In this work, the closed-cycle and open-cycle process design for the conditioning of a CO₂-stream for ship transport are compared in terms of the minimum specific energy demand. In contrast to other works, a high-pressure pipeline CO₂-stream is assumed as an input stream rather than a low pressure CO₂-stream from a capture plant. An output temperature of -50 °C is selected, which corresponds to an output pressure of 6.75 bar for pure CO₂ and output pressures of less than 25 bar for typical Post-Combustion and Oxyfuel CO₂-streams. It is shown that the minimum specific energy demand for closed-cycle refrigeration processes can be significantly reduced by a 2-stage or 3-stage temperature cascade. With approximately 46 kJ/kgCO₂, the minimum energy demand of the 3-stage open-cycle process is almost the same as for the 3-stage closed-cycle process. It is shown that the open-cycle process design cannot be used for CO₂-streams with impurities, unless the stream is purified in the refrigeration process. The results for typical Post-Combustion and Oxyfuel CO₂-streams show that the minimum specific energy demand slightly increases with an increasing impurity concentration. For the 1-stage closed-cycle process, it rises from 82.1 kJ/kgCO₂ for pure CO₂ to 83.4 kJ/kgCO₂ for an Oxyfuel stream with 98% CO₂ purity. That increase is smaller for the 2-stage closed-cycle and even smaller for the 3-stage process.