Natural gas liquefaction processes

Abstract

This paper presents Axens efforts to compare LiquefinTM with the competing process, specially the reputed most efficient ones: C3/MR, C3/MR followed by nitrogen cycle, dual mixed refrigerant process with spiral wound exchangers. To compare properly one process to another, it must be done with the same gas, with the same site conditions, with the same gas turbines and with the same cooling medium temperature (air or water). That done, to compare processes like for like is still not that easy. For instance, it seems fair to take the same efficiencies for the compressors, however, axial and centrifugal compressors do have different efficiencies. Similarly, equal basis leads to have the same temperature approach for the air-cooler (or water coolers), however between mixed refrigerant and propane, the heat exchange area will be much lower for mixed refrigerant if the approach is kept identical. The end flash vapour quantity has also a big influence on the process efficiency, but each process has a different fuel gas consumption. Those added factors may lead to wide differences. Axens has calculated the effect of all those parameters on efficiency. The equipment characteristics play also an important role in the comparison: the limitations of axial compressors, of centrifugal compressors (Mach number) and possibly spiral-wound exchangers maximum size do have to be taken into account. Even the gas turbines or alternative drivers chosen can be well adapted to one process, but not to the other. Another important parameter is the LPG recovery: a large LPG recovery will decrease the efficiency of any process, but not to the same extent. For Liquefin, the efficiency decrease is not very big. This paper shows the detailed results of those comparison studies, and the effect of several parameters on Liquefin efficiency.