Gas liquefaction process and apparatus

Claim 2

A gas liquefaction process according to claim 1 in which natural gas comprises said feed gas.

Claim 3

A gas liquefaction process according to claim 1 in which natural gas comprises said feed gas and nitrogen comprises said refrigerant gas.

Claim 4

A gas liquefaction process according to claim 1 in which nitrogen comprises said feed gas.

Claim 5

A gas liquefaction process according to claim 1 in which said refrigerant and feed gases are of the same composition.

Claim 6

A gas liquefaction process according to claim 1 in which the partially cooled high pressure feed gas is cooled in a first intermediate heat exchanger and thereafter additionally cooled in a second intermediate heat exchanger in part by said cold work expanded refrigerant gas having been partially warmed in said cold heat exchanger; another part of said partially cooled remaining compressed refrigerant gas from said warm heat exchanger is further cooled in said first intermediate heat exchanger to lower temperature, work expanded to pressure above said low pressure and colder temperature between said intermediate temperature of said warm work expanding and said lower-than-intermediate temperature of said cold work expanding; and progressively warmed by said high pressure feed gas in said second intermediate heat exchanger, said another part of said partially cooled remaining compressed refrigerant gas and said high pressure feed gas in said first intermediate heat exchanger, and said remaining compressed refrigerant gas and high pressure feed gas in said warm heat exchanger; and recompressed and recycled as part of said compressed refrigerant gas, all of the process refrigeration being provided by the three work expansions.

Claim 7

A nitrogen liquefaction process comprising the steps of: a. providing nitrogen feed gas and nitrogen recycle gas at sub-critical pressure and mixing same; b. compressing a first portion of the mixed nitrogen to supercritical pressure; c. warm work expanding a second portion of said mixed nitrogen to intermediate temperature and low pressure; d. partially cooling the supercritical pressure first portion and remaining mixed nitrogen portion in a warm heat exchanger in part by the warm work expanded second portion; e. cold work expanding at least part of the partially cooled remaining mixed nitrogen from said warm heat exchanger to lower-than-intermediate temperature and said low pressure, all of the process refrigeration being supplied by work expansion of gas other than heat of compression; f. further cooling the partially cooled super-critical pressure first portion from said warm heat exchanger by the cold work expanded mixed nitrogen at relative pressures such that the specific heat ratio of said first portion to said cold work expanded mixed nitrogen is 1.5-15 and thereby partially warming said mixed nitrogen in a cold heat exchanger; g. throttling the further cooled first portion from said cold heat exchanger to form product liquid nitrogen; h. further warming the cold work expanded mixed nitrogen from said cold heat exchanger by heat exchange with said supercritical pressure first portion and remaining mixed nitrogen portion in said warm heat exchanger; i. recompressing the further warmed work expanded second and work expanded mixed nitrogen from said warm heat exchanger as said nitrogen recycle gas; and j. controlling the warm and cold work expansion steps to deliver said process refrigeration of the expanded gases to regions of the cooling supercritical pressure first portion where such gas has substantially constant specific heat.

Claim 8

A process according to claim 8 in which the partially cooled supercritical pressure first portion is cooled in a first intermediate heat exchanger and thereafter additionally cooled in a second intermediate heat exchanger in part by said cold work expanded mixed nitrogen having been partially warmed in said cold heat exchanger; another part of said partially cooled remaining mixed nitrogen from said warm heat exchanger is further cooled in said first intermediate heat exchanger to lower temperature, work expanded to colder temperature between said intermediate temperature of said warm work expanding and said lower-than-intermediate temperature of said cold work expanding but higher pressure than said warm and cold work expanding; and progressively warmed by said supercritical pressure first portion in said second intermediate heat exchanger, said another part of said partially cooled remaining mixed nitrogen and said supercritical pressure first portion in said first intermediate heat exchanger, and said remaining mixed nitrogen portion and said supercriticAl pressure first portion in said warm heat exchanger; and recompressed as part of said nitrogen recycle gas, all of the process refrigeration being provided by the three work expansions.

Claim 9

A process according to claim 1 in which the power generated by said cold work expanding is recovered to compress said feed gas to first intermediate pressure above said subcritical pressure and the power generated by said warm work expanding is recovered to further compress said feed gas from said first to second higher intermediate pressure.

Claim 10

A process according to claim 1 in which said feed gas is combined with said further warmed work expanded refrigerant gas, the combined gas is recompressed in step (h) and a first portion of the compressed combined gas is further compressed in step (a) to high pressure as said feed gas.

Claim 11

A process according to claim 1 in which said warm work expanded gas portion and the partially warmed cold work expanded refrigerant gas are combined at the cold end of said warm heat exchanger for the step (c) partial cooling and step (g) partial warming.

Claim 12

A process according to claim 8 wherein the work expansions are controlled so as to maintain the average temperature difference between the warming and cooling gases in the heat exchangers at below about 10* C.

Claim 13

Gas liquefaction apparatus comprising: a. means for compressing feed gas from subcritical to high pressure; b. a first work expander for expanding a compressed refrigerant gas portion from subcritical pressure below the feed gas high pressure to low pressure and intermediate cold temperature; c. a relatively warm heat exchanger having separate passageways for partially cooling the high pressure feed gas and remaining compressed refrigerant gas by the low pressure intermediate cold temperature refrigerant gas from said first work expander; d. a second work expander for expanding at least part of the partially cooled remaining compressed refrigerant gas from said warm heat exchanger from said subcritical pressure to said low pressure and lower-than-intermediate temperature, said work expanders providing all of the refrigeration needed for said gas liquefaction other than heat of compression; e. a relatively cold heat exchanger having separate passageways for further cooling said high pressure feed gas from said warm heat exchanger by the low pressure lower-than-intermediate temperature refrigerant gas from said second work expander; f. valve means for throttling the further cooled feed fluid from said cold heat exchanger and thereby forming product liquid; g. passageway means in said warm heat exchanger for further warming the low pressure refrigerant gas partially warmed in said cold heat exchanger, by heat exchange with said high pressure feed gas and remaining compressed refrigerant gas; h. means for recompressing the further warmed low pressure refrigerant gas from said warm heat exchanger to subcritical pressure below said feed gas high pressure; i. conduit means for recycling the recompressed refrigerant gas to said first work expander; j. feed gas supply conduit means joining refrigerant gas recompression means (h) to form recompressed feed-refrigerant gas; and k. first branch conduit means joining the discharge side of recompression means (h) to feed gas compression means (a) to form said high pressure feed gas, second branch conduit means joining the discharge side of recompression means (h) to said first work expander for expansion of recompressed feed-refrigerant gas as said low pressure intermediate cold temperature refrigerant gas, and third branch conduit means joining the discharge side of recompression means (h) to passageway means in warm heat exchanger (c) for partial cooling said feed-refrigerant gas as said remaining compressed refrigerant gas.

Claim 14

A process according to claim 1 wherein said feed gas is multi-component and said high pressure of (a) is at least 85 percent of the feeD gas critical pressure.