# US 11,112,173 B2 · Configurations and methods for small scale LNG production

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- Number: US 11,112,173 B2
- Document ID: US11112173B2
- Status: Granted
- Kind: B2
- Application number: 15/201,070
- Filed: 2016-07-01
- Published: 2018-01-04
- Granted: 2021-09-07
- Earliest claimed: 2016-07-01
- Assignees: Fluor Technologies Corporation
- Applicants: Fluor Technologies Corporation
- Inventors: John Mak
- Web page: https://patentgrep.com/patent/US11112173B2

## CPC

- F25J 1/0022: {Hydrocarbons, e.g. natural gas}
- F25J 1/004: {by flash gas recovery (F25J1/0267 takes precedence)}
- F25J 1/005: {by expansion of a gaseous refrigerant stream with extraction of work}
- F25J 1/0052: {by vaporising a liquid refrigerant stream}
- F25J 1/0072: {Nitrogen}
- F25J 1/0208: {in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop (F25J1/021 takes precedence)}
- F25J 1/0245: {Different modes, i.e. 'runs', of operation; Process control}
- F25J 1/0275: {adapted for special use of the liquefaction unit, e.g. portable or transportable devices}
- F25J 1/0288: {using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders}
- F25J 5/00: Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants (heat exchangers F28C, F28D, F28F)
- F25J 2210/60: Natural gas or synthetic natural gas [SNG]
- F25J 2220/66: Separating acid gases, e.g. CO2, SO2, H2S or RSH
- F25J 2220/68: Separating water or hydrates
- F25J 2230/60: the fluid being hydrocarbons or a mixture of hydrocarbons
- F25J 2240/40: Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
- F25J 2245/90: the recycled stream being boil-off gas from storage
- F25J 2270/16: with mutliple gas expansion loops of the same refrigerant
- F25J 2290/12: Particular process parameters like pressure, temperature, ratios
- F25J 2290/60: Details about pipelines, i.e. network, for feed or product distribution
- F25J 2290/62: Details of storing a fluid in a tank
- F25J: LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS {OR LIQUEFIED GASEOUS} MIXTURES BY PRESSURE AND COLD TREATMENT {OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE (cryogenic pumps F04B37/08; gas storage vessels, gas holders F17; filing vessels with, or discharging from vessels, compressed, liquefied or solidified gases F17C; refrigeration machines, plants, or systems F25B)}

## Abstract

An LNG plant comprises a cold box and a refrigeration unit fluidly coupled with a plurality of heat exchanger passes in the cold box. The refrigeration unit is configured to provide a first refrigerant stream to a first heat exchanger pass of the plurality of heat exchanger passes at a first pressure, a second refrigerant stream to a second heat exchanger pass at a second pressure, and a third refrigerant stream to a third heat exchanger pass at a third pressure. The second refrigerant stream comprises a first portion of the first refrigerant stream, and the third refrigerant stream comprises a second portion of the first refrigerant stream. The second pressure and the third pressure are both below the first pressure. The cold box is configured to produce LNG from a natural gas feed stream to the cold box using a refrigeration content from the refrigeration unit.

## Claims

### Claim 1

A method of generating LNG from a natural gas feed comprising:
passing a first refrigerant stream through a first heat exchanger pass of a plurality of heat exchanger passes in a cold box, wherein the first refrigerant stream is at a first pressure;
splitting the first refrigerant stream into a second refrigerant stream and a third refrigerant stream by passing the first refrigerant stream through a splitter downstream of the cold box;
expanding the second refrigerant stream to a second pressure in a first expander;
after expanding the second refrigerant stream, passing the second refrigerant stream through a second heat exchanger pass of the plurality of heat exchanger passes at the second pressure;
expanding the third refrigerant stream to a third pressure in a second expander;
after expanding the third refrigerant stream, passing the third refrigerant stream through a third heat exchanger pass of the plurality of heat exchanger passes at the third pressure, wherein the second pressure and the third pressure are both below the first pressure;
after passing the third refrigerant stream through the third heat exchanger pass, compressing, by a first compressor and then by a second compressor, the third refrigerant stream to a fourth pressure equal to or above the second pressure;
after compressing the third refrigerant stream, cooling the third refrigerant stream;
after cooling the third refrigerant stream, combining the second refrigerant stream and the third refrigerant stream downstream of the cold box to form a recycle stream;
compressing the recycle stream in a two-stage compressor to form the first refrigerant stream;
passing a natural gas feed stream through at least a fourth heat exchanger pass of the plurality of heat exchanger passes; and
liquefying at least a portion of the natural gas stream in the cold box using a refrigeration content provided by at least one of the second refrigerant stream and the third refrigerant stream to form an LNG stream,
wherein the first expander is disposed downstream from the splitter,
wherein the first expander is coupled to the first compressor, wherein the second expander is coupled to the second compressor.

### Claim 2 (depends on 1)

The method of claim 1, wherein combining the second refrigerant stream and the third refrigerant stream comprises combining the second refrigerant stream at the second pressure and the third refrigerant stream at the fourth pressure.

### Claim 3 (depends on 1)

The method of claim 1, wherein the first expander is coupled to the first compressor, wherein the second expander is coupled to the second compressor.

### Claim 4 (depends on 1)

The method of claim 1, wherein each of the first refrigerant stream, the second refrigerant stream, and the third refrigerant stream consists of one or more non-hydrocarbon refrigerants.

### Claim 5 (depends on 1)

The method of claim 1, wherein the second pressure is between 20% and 50% of the first pressure on an absolute scale, and wherein the third pressure is between 3% and 20% of the first pressure on an absolute scale.

### Claim 6 (depends on 1)

The method of claim 1, wherein the first pressure is between 1,000 psia and 2,000 psia.

### Claim 7 (depends on 1)

The method of claim 1, wherein a ratio of the second pressure to the third pressure is between 10:1 and 2:1.

### Claim 8 (depends on 1)

The method of claim 1, wherein a molar ratio of a flowrate of the second refrigerant stream to a flowrate of the first refrigerant stream is between 0.5 and 0.75.

### Claim 9 (depends on 1)

The method of claim 1, further comprising:
passing a boil-off gas received from a LNG transport through a fifth heat exchanger pass of the plurality of heat exchanger passes;
recovering refrigeration content from the boil-off gas in the cold box to form a heated boil-off gas.

### Claim 10 (depends on 9)

The method of claim 9, further comprising:
compressing the heated boil-off gas; and
combining a portion of the compressed heated boil-off gas with the natural gas stream.

### Claim 11 (depends on 9)

The method of claim 9, further comprising:
compressing the heated boil-off gas; and
passing a portion of the compressed heated boil-off gas to a LNG storage tank.

### Claim 12 (depends on 11)

The method of claim 11, further comprising:
moving, by the compressed heated boil-off gas, LNG from the storage tank to a LNG transport.