The simplified logic and execution flow of the program is visualised in Figure . For each calculation step / unit operation considered i.e., compression, cooling, pumping, the fluid state is recorded both in and out of each operation as well as any required power input (compressor/pump) or heat exchanged (coolers/heat exchangers). The simplest calculation is if no refrigeration/liquefaction/pumping (i.e. via P liq ) is specified as well as if no pressure drop dP in compression stages/coolers is specified and only compression is considered from inlet conditions P in to the final desired pressure P comp = P f inal . The compression process with n stages is calculated one stage at a time with a fixed pressure ratio P ratio . For each stage i, until the final stage is reached i.e., i = n, the stage inlet conditions are updated from the previous stage output and each stage is calculated in an iterative way. Liquefaction and pumping is activated if P liq < P f inal and P liq is below the critical pressure of the CO 2 stream. The liquefaction temperature, T liq , is calculated at P liq and a CO 2 vapour fraction (VF) equal to 0. The process includes calculation of the required refrigeration cycle, where the coefficient of performance (COP) is the key output that enables scaling of the refrigeration cycle energy/power requirements based on the latent heat of the CO 2 condensation. The diagram does not show the complexity of the inclusion of the economizer (heat exchanger) upstream the liquefaction process. In case P liq is set above the critical pressure, a refrigeration process may still be invoked by specifying a cooling temperature, T liq , for cooling the supercritical CO 2 exiting the last compression stage into the dense liquid region. This is only invoked if the specified T liq is below the refrigeration cycle condenser temperature, T cond and below the the coolant temperature pinch, T cool + 10 K.