US 6,298,688 B1 · Process for nitrogen liquefaction

Abstract

A process for gas liquefaction, particularly nitrogen liquefaction, which combines the use of a nitrogen autorefrigeration cooling cycle with one or more closed-loop refrigeration cycles using two or more refrigerant components. The closed-loop refrigeration cycle or cycles provide refrigeration in a temperature range having a lowest temperature between about −125° F. and about −250° F. A nitrogen expander cycle provides additional refrigeration, a portion of which is provided at temperatures below the lowest temperature of the closed-loop or recirculating refrigeration cycle or cycles. The lowest temperature of the nitrogen expander cycle refrigeration range is between about −220° F. and about −320° F. The combined use of the two different refrigerant systems allows each system to operate most efficiently in the optimum temperature range, thereby reducing the power consumption required for liquefaction.

A method of providing refrigeration for the liquefaction of a feed gas which comprises:

(a) providing a first refrigeration system comprising at least one recirculating refrigerant circuit, wherein the first refrigeration system utilizes a mixed refrigerant comprising two or more components and provides refrigeration in a first temperature range, and operating the first refrigeration system by utilizing steps which include
(a1) compressing a gaseous mixed refrigerant to provide a compressed mixed refrigerant;
(a2) cooling and at least partially condensing the compressed mixed refrigerant in a first heat exchanger to provide a cooled mixed refrigerant;
(a3) further cooling at least a portion of the cooled mixed refrigerant in a second heat exchanger to provide a further cooled mixed refrigerant;
(a4) reducing the pressure of the further cooled mixed refrigerant to provide a reduced-pressure mixed refrigerant;
(a5) warming and vaporizing the reduced-pressure mixed refrigerant in the second heat exchanger to provide a portion of the refrigeration required for the liquefaction of the feed gas and yield a vaporized mixed refrigerant;
and
(a6) recirculating the vaporized mixed refrigerant to provide at least a portion of the gaseous mixed refrigerant in (a1);
and
(b) providing a second refrigeration system in which a cooled and pressurized refrigerant stream is work expanded to generate a cold refrigerant stream, and warming the cold refrigerant stream in the second heat exchanger to provide another portion of the refrigeration required for the liquefaction of the feed gas, wherein the cooled and pressurized refrigerant stream comprises feed gas and has the same composition as the feed gas;
wherein the first refrigeration system comprises a recirculating refrigeration circuit which is operated by steps which include:
(1) compressing a gaseous mixed refrigerant to form a compressed gaseous mixed refrigerant;
(2) cooling and at least partially condensing a first portion of the compressed gaseous mixed refrigerant to form a first cooled mixed refrigerant;
(3) reducing the pressure of the first cooled mixed refrigerant to a first pressure level to form a first reduced-pressure mixed refrigerant;
(4) vaporizing the first reduced-pressure mixed refrigerant of (3) to provide a first portion of the refrigeration in the first temperature range and yield a first vaporized refrigerant;
(5) cooling and at least partially condensing a second portion of the compressed gaseous mixed refrigerant to form a second cooled mixed refrigerant;
(6) reducing the pressure of the second cooled mixed refrigerant to a second level to form a second reduced-pressure mixed refrigerant;
(7) vaporizing the second reduced-pressure mixed refrigerant to provide a second portion of the refrigeration in the first temperature range and form a second vaporized refrigerant;
(8) compressing the second vaporized refrigerant and combining it with the first vaporized refrigerant to form a combined compressed vaporized refrigerant;
and
(9) further compressing the combined vaporized refrigerant to provide the gaseous mixed refrigerant of (1).

18 more elements

Process for nitrogen liquefaction

Life of this patent

Process for nitrogen liquefaction

Life of this patent

Abstract

Claims14