Single mixed refrigerant, closed loop process for liquefying natural gas

A process for cooling a fluid feed material from an initial temperature to a level from over 200 Farenheit degrees to over 300 Farenheit degrees therebelow and consisting essentially of the steps of:

• providing a single mixed refrigerant composition capable of cooling said material and containing a number of refrigerant constituents having a wide range of successively lower boiling points;
• passing said refrigerant composition through a single closed loop refrigeration cycle consisting essentially of compression, partial condensation, multiple path heat exchange and expansion zones;
• maintaining the flowing constituents of the refrigerant composition and the relative proportions thereof identical throughout said compression, partial condensation, multiple path heat exchange and expansion zones of the single closed loop cycle,
• the total mixed refrigerant composition being successively directed
• (1) from the compression zone to the partial condensation zone for partial condensation of the refrigerant by an external cooling medium to produce a vapor phase and a liquid phase,
• (2) the vapor phase and the liquid phase from the condensation zone are combined,
• (3) the combined phases are directed to the heat exchange zone for flow without change in composition along
• (a) a first path therethrough, next
• (b) to the expansion zone, and then
• (c) back to the heat exchange zone for flow along a second path therethrough in countercurrent, thermal interchange relationship to refrigerant flow along said first path, and
• (4) the refrigerant composition is then returned to the compression zone;
• directing the fluid feed material through said heat exchange zone along a third path in concurrent flow thermal interchange relationship to the refrigerant flowing along said first path and countercurrent to the refrigerant flow along said second path to effect the required cooling of the fluid feed material in said heat exchange zone by only the refrigerant composition of said single closed loop cycle,
• at least one of the refrigerant constituents having a boiling point in the second path lower than the temperature level to which the fluid feed material is lowered in said heat exchange zone,
• the constituents of the refrigerant composition in admixture having freezing points below said temperature level to which the feed material is lowered, and
• said refrigerant composition being characterized by the properties of
• (1) at least a portion thereof being vaporizable across said expansion zone,
• (2) substantially all of the refrigerant becoming liquid along said first path through the heat exchange zone, and
• (3) substantially all of the composition undergoing vaporization along said second path through the heat exchange zone at the respective temperatures and pressures of the refrigerant existing along said first and second paths;
• providing a total of at least five refrigerant constituents in said refrigerant composition in
• (1) relative quantities and of
• (2) respective relative boiling points and
• (3) circulating the refrigerant composition in said closed loop cycle at a sufficiently higher rate than the flow of feed material along said third path through the heat exchange zone, to
• (a) lower the temperature level of said fluid feed material in the heat exchange zone as it flows therethrough from more than 200 Fahrenheit degrees to over 300 Fahrenheit degrees below its initial temperature as directed to the heat exchange zone, while
• (b) maintaining a minimal temperature difference between the fluid feed material and the refrigerant composition in thermal interchange relationship thereto throughout the length of the heat exchange zone, and at the same time to
• (c) cause the combined cooling curve of the fluid feed material flowing along said third path and the refrigerant flowing along said first path and the heating curve of the refrigerant flowing along said second path to both be of relatively straight, closely adjacent, generally matched configuration throughout the respective flow paths of the refrigerant and said feed material through the heat exchange zone;
• and
• passing a cooling medium in heat exchange relationship with the refrigerant composition flowing through said partial condensation zone,
• said cooling medium being at a temperature from more than 200 Fahrenheit degrees to over 300 Fahrenheit degrees above the temperature of the fluid feed material exiting from said heat exchange zone,
• at least one other of the refrigerant constituents having a boiling point to cause only partial condensation of the refrigerant in said partial condensation zone at the temperature and pressure of the refrigerant composition as it flows through said partial condensation zone from the compression zone to the heat exchange zone.