Boyle off gas cooling method and apparatus

摘要

The present invention is an improvement of the common single mixed refrigerant (SMR) cycle for LNG reliquefaction, which enables, among other things, the use of a cost effective lubricating screw compressor in a mixed refrigerant system. Compared to typical configurations, the present invention enables reduced complexity, fewer devices, and reduced capital costs. Fig. 6 illustrates a method of cooling a boil-off gas (BOG) stream from a liquefied gas tank, the method comprising at least the step of heat exchanging the BOG stream with the SMR in the liquefied heat exchanger system to provide a cooled BOG stream An SMR is provided in the SMR recirculation system, wherein the SMR recirculation system includes at least: (a) compressing the SMR using at least one lubricated screw compressor to provide a compressed SMR stream; (b) Separating the compressed SMR stream to provide an oil-based stream and a first SMR vaporized gas stream; and (c) delivering the first SMR vaporized gas stream into the liquefaction heat exchanger system to generate the first SMR vaporized gas stream. Cooling, providing a cooled first SMR vaporized gas stream; (d) extracting the cooled first SMR vaporized gas stream from the liquefaction heat exchanger system (E) separating the cooled first SMR vaporized gas stream to provide a liquid phase SMR stream and an oil free SMR vaporized gas stream; (f) heat the oil free SMR vaporized gas stream to liquefy Passing through the exchanger system to provide condensed SMR stream; (g) expanding the condensed SMR stream and passing through the liquefaction heat exchanger system for heat exchange with the BOG stream Providing the SMR stream.