Patent ID: 6751984
Filing Date: 2004-06-22
Classification: F25J

Abstract:
Method of cooling and optically liquefying a product gas comprising hydrocarbon-containing gases or nitrogen, comprising the steps of:directing the product gas to be cooled to counterflow heat exchange with a multicomponent refrigerant through at least two serially connected two-flow plate heat exchangers which are primary heat exchangers, with compressing of the refrigerant in an oil lubricated compressor subsequent to each cooling cycle; removing heat absorbed by the refrigerant in the cooling by heat exchange, then passing the cooled refrigerant into at least one phase-separator for separating the multicomponent refrigerant into a more volatile fraction which constitutes a high level refrigerant and a less volatile fraction which constitutes a low level refrigerant; cooling the more volatile fraction in counterflow heat exchange by a low level refrigerant, by passing through at least one two-flow plate heat exchanger, which is a secondary heat exchanger, arranged in parallels with respect to flow of low level refrigerant, with a primary heat exchanger, so that the primary and secondary heat exchangers are arranged in pairs; and throttling the less volatile fraction to become part of a low level refrigerant, and splitting the low level refrigerant into two separate partial flows, with a partial flow provided to a primary heat exchanger of a pair and to a secondary heat exchanger of said pair, to cool and optionally liquefy the product gas in at least two serially arranged primary heat exchangers, and to cool and partially liquefy the high level refrigerant in at least one secondary heat exchanger, wherein the less volatile fraction from a first of the at least one phase separator constitutes a part of the low level refrigerant in a primary and secondary heat exchanger pair working at the highest temperature and is split between the primary and the secondary heat exchanger pair in a predetermined ratio.