Optimal Design and Operating Conditions of the CO2 Liquefaction Process, Considering Variations in Cooling Water Temperature

Ship transportation of liquid CO2 is now considered as an alternative transport option to pipelines, in the absence of any suitable onshore storage locations. The compressors for a liquefaction process in the transport chain account for a significant portion of the total energy consumption. The temperature of seawater as an intercooling medium has a very significant effect on the energy consumption of the multistage compressors. Although several studies for the optimal design and operation of liquefaction process have been proposed, they do not consider the seasonal and locational variations in the cooling water temperature; therefore, further improvement in the energy efficiency in the CO2 liquefaction process is necessary. In this study, the variations in the operational energy and other operational issues of the CO2 liquefaction process, according to the actual seawater temperature in the range of 5-30 degrees C was investigated. Moreover, the optimal discharge pressure of the final stage compressor before the Joule-Thomson (J-T) expansion and the pressure ratio of multistage compressors are provided, given the seawater temperature, to minimize the total compressor power consumption. Furthermore, the optimal number and position of multistream heat exchangers are investigated. The total compressor power consumption is similar to 90-140 kW(h)/ton CO, in the seawater temperature range of 5-30 degrees C.