Liquefaction process
OwnerChristopher Alfred Dubarinventor
Life of this patent
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Abstract
A process for producing a liquefied natural product such as LNG is described where a single phase nitrogen refrigerant is used in such a way that the refrigerant stream (10) is divided into at least two separate portions (12, 14) which are passed through separate turbo-expanders (106, 108) before being admitted to separate heat exchangers (103, 104) so that the warming curve of the refrigerant more closely matches the cooling curve of the product being liquefied so as to minimize thermodynamic inefficiencies and hence power requirements involved in operation of the method.
Claims29
A natural gas liquefaction process, characterized in that the process comprises the steps of passing natural gas through a series of heat exchangers in countercurrent relationship with a single phase refrigerant gas circulated through a cooling cycle, substantially isentropically expanding portions of refrigerant to different cooling temperatures at which said refrigerant portions are supplied to respective heat exchangers for cooling the natural gas through corresponding temperature ranges, whereby the warming curve for the refrigerant comprising all said portions has sections of different gradients, discharging cooled natural gas from a final heat exchanger at an exit temperature in the range -160.degree. C. to -140.degree. C., and supplying to the final heat exchanger of said series a refrigerant portion at a cooling temperature and in an amount selected in the range of 20 to 50% of the circulated refrigerant so that the part of the refrigerant warming curve relating to the final heat exchanger is closely matched to and has substantially the same slope as the part of the natural gas cooling curve extending over the temperature range from said exit temperature to -100.degree. C.
Apparatus for liquefying natural gas by cooling with a single phase refrigerant consisting substantially of nitrogen, comprising a series of heat exchangers, and a compressor having an inlet connected to receive warmed refrigerant from the heat exchanges and an outlet connected to deliver refrigerant to further compressor means driven by turbo expanders through which portions of compressed refrigerant are isentropically expanded and cooled to different temperatures for use with different heat exchangers, said turbo expanders having refrigerant outlets connected to respective heat exchangers for delivering the different cooled portions of the refrigerant to respective heat exchangers for passage therethrough in countercurrent relationship with the natural gas, wherein the warming curve for the refrigerant comprises sections having different gradients and a part of the refrigerant warming curve relating to passage through a final heat exchanger is closely matched to and has substantially the same gradient as a part of the natural gas cooling curve extending over the same temperature range of the final heat exchanger.
Dependencies are inferred from the claim text.