JP2001526376A - Liquefaction process and equipment - Google Patents

Abstract

(57) [Summary] An apparatus for liquefying natural gas, comprising a series of heat exchangers for cooling natural gas in a counter-current heat exchanger with a refrigerant, and a compressor for compressing the refrigerant. Means and expansion means for adiabatically expanding at least two separate streams of compressed refrigerant, said expanded stream of refrigerant being at the lower temperature end of each heat exchanger. Connected and prior to feeding to the series of heat exchangers, pre-cooling the natural gas to a temperature of 0 ° C. or less and before feeding back to the series of heat exchangers or the expansion means, A pre-cooling refrigeration system for pre-cooling the compressed refrigerant discharged from the hotter end of the heat exchanger to a temperature of 0 ° C or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a liquefaction process and apparatus.

[0002] During the liquefaction of natural gas by a refrigerant, attempts are made to match the cooling curve of the natural gas with the heating curve of the refrigerant by splitting the refrigerant into two streams cooled to different temperatures. It is well known. For example, the inventor's patent WO-A-95
27179 describes this.

The inventor's patent WO-A-9713108 discloses a small liquefied natural gas plant for use in offshore liquefaction of natural gas. FIG. 1 of the accompanying drawings is a general type of natural gas liquefier disclosed in WO-A-9713108. However, the device of FIG. 1 differs from the device of WO-A-9713108 in several respects.

In the case of FIG. 1, natural gas preheated passes through conduit 101 for about 8 hours.
. It is sent to the heat exchanger 166 at a pressure of 3 MPa. In one embodiment, the natural gas in conduit 101 has the following composition: That is, it has the following composition: 4.2 mol% nitrogen; 85.1 mol% methane; 8.2 mol% ethane; 2.5 mol% propane. The natural gas in the conduit 101 is cooled within a temperature range of about 5-10 ° C. by a heat exchanger using cooling water, and is discharged into the conduit 102.

[0005] Natural gas exiting heat exchanger 166 passes through conduit 102 through CWH
E (the coiled heat exchanger) is fed to the hotter end. CWHE1
50 comprises one shell housing two separate heat exchanger bundles 151 and 152. Within CWHE 150, natural gas is cooled by a countercurrent heat exchanger using a nitrogen refrigerant. The cooled natural gas is CWH at a temperature of about -90 ° C.
Exiting E150, it passes through conduit 104 to another heat exchanger 153.
As the heat exchanger 153, aluminum PFHE (plate-fin heat exchanger) can be used. Natural gas is cooled in heat exchanger 153 to a temperature of about -150 ° C., exits the cooler end of heat exchanger 153 and exits conduit 10.
Sent to 6.

The natural gas in conduit 106 is sent to the hot end of heat exchanger 154, where it is cooled to a temperature of about −160 ° C., and the cold end of heat exchanger 154 is cooled. And is sent to conduit 107. Natural gas in conduit 107 is sent to the top of nitrogen recovery tower column 157. High nitrogen content of feed gas
If the required composition of the liquefied natural gas product cannot be obtained by a two-stage or two-stage flash separation drum, the column 157 is required. The use of a heat exchanger 154 to provide the reboil heat from the natural gas in the conduit 106 aids the recovery process. LNG is sent from column 157 to conduit 167,
From there it is sent to the cooler end of the heat exchanger 154. The heat exchanger 154
Warm the LNG to a temperature of about -160C. The LNG exits the hotter end of the heat exchanger 154 and is sent to the conduit 168 and back to the column 157 through the conduit.

[0007] The LNG from the bottom of column 157 is sent to conduit 111 and then
It is sent to the transfer pump 158. The pump 158 supplies LNG to the conduit 112.
To the LNG storage tank 186.

A flash gas containing methane and a high percentage of nitrogen exits the top of column 157 and enters conduit 109. The flash gas in conduit 209 at a temperature of about -167 ° C is sent to the cooler end of heat exchanger 155, where it is warmed to a temperature of about -40 ° C. The warmed gas is sent from the hotter end of heat exchanger 155 to conduit 110 and from there to multi-stage fuel gas compressor 180. The compressor 180 has at least four compression stages and an internal cooling section between each stage using cooling water. Flash gas is
The pressure in the compressor 180 is slightly higher than the atmospheric pressure, usually 2.7-5.5M.
It is compressed to a pressure in the range of Pa and sent to the turbine 173 of the refrigerant compressor 159, as described in more detail below. If the turbine is an aero-derivative turbine, a high compression ratio in the turbine will require a high fuel gas pressure. Therefore, the fuel gas compressor 180 has significant power requirements due to the high discharge pressure and the high nitrogen content that the gas contains, and therefore, usually for economic reasons, replaces the gas motor instead of the electric motor drive. A turbine drive is used. As described below, the flash gas sent through conduit 110 is used to supply the bulk fuel gas requirements of the liquefaction plant.

Hereinafter, a nitrogen cooling cycle for cooling to a temperature at which natural gas is liquefied will be described. The nitrogen refrigerant is discharged into the conduit 132 at a temperature of about 5 ° C. from the hotter end of the CWHE 150. Nitrogen is supplied to at least one internal cooling device 17.
1 and at least two compressor stages 1 together with aftercooler 172
It is sent to a multi-stage compressor unit 159 comprising 69 and 170. Compressor stages 169 and 170 are driven by gas turbine 173. The operation of the compressor unit 159 consumes almost all the power required by the nitrogen refrigeration cycle. Gas turbine 173 is driven by fuel gas from conduit 110.

[0010] The compressed nitrogen is released from the compressor unit 159 into the conduit 133 at a pressure of about 5.1 MPa. Conduit 133 has two conduits 1
Connected to 34 and 135, between these two conduits, the nitrogen from conduit 133 is split according to the power absorbed by the compressor. Nitrogen in conduit 134 is sent to compressor 162 where it is approximately 8.5.
MPa, and then from the compressor 162 to the conduit 136
Sent to The nitrogen in the conduit 135 is sent to the compressor 163 where it is compressed to a pressure of about 8.5 MPa and then from the compressor 163 to the conduit 137. The nitrogen in both conduits 136 and 137 is sent to conduit 138 and then to heat exchanger 164 where it is cooled to ambient temperature. Nitrogen is passed from heat exchanger 164 through conduit 139 to heat exchanger 165, where it is cooled by cooled water to a temperature of 5-10 ° C. The cooled nitrogen is supplied from heat exchanger 165 to two conduits 120 and 14
Sent to conduit 140, which is connected to 1. The nitrogen flowing through conduit 140 is split into conduits 120 and 141 such that approximately 2% of the nitrogen in conduit 140 flows through conduit 141.

The nitrogen flowing through conduit 141 is sent to the hotter end of heat exchanger 155, where it is flushed by countercurrent heat exchanger with flash gas from column 157.
Cool to a temperature of about -123 ° C. Cooled nitrogen is discharged into the conduit 142 from the cooler end of the heat exchanger 155.

Conduit 120 is connected to the hotter end of CWHE 150,
Therefore, nitrogen is sent to the hotter end of the heat exchanger bundle 151.
Nitrogen from conduit 120 is cooled to about −13 ° C. in heat exchanger bundle 151. Most of the nitrogen refrigerant is recovered from CWHE 150 through conduit 122 after passing through heat exchanger bundle 151. The rest of the nitrogen refrigerant
Through the bundle 152, it is cooled to a temperature of about −90 ° C. and discharged from the CWHE 150 into the conduit 124.

The nitrogen in conduit 122 is sent to turboexpander 160 where it is expanded to a pressure of about 1.9 MPa and a temperature of about −95 ° C. The expanded nitrogen is released from the turboexpander 160 to the conduit 128. The nitrogen in conduit 124 is mixed with the nitrogen in conduit 142 and then sent to turboexpander 161 where it expands to a pressure of about 1.9 MPa and to a minimum temperature of nitrogen of about -151 ° C. Is done. The expanded nitrogen is released from the turbo expander 161 to the conduit 126. Turbo expander 160 is arranged to drive compressor 162, and turbo expander 161 is arranged to drive compressor 163. In this way, those processed and manufactured by the turbo expanders 160 and 161 can be collected.

The nitrogen in the conduit 126 is sent to the cold end of the heat exchanger 153 where it cools the natural gas with a countercurrent heat exchanger. In heat exchanger 153, the nitrogen is warmed to an intermediate nitrogen temperature of about -95C. Nitrogen exits the hotter end of heat exchanger 153 and is fed to the cooler end of CWHE 150 before
It is mixed with the nitrogen in conduit 128. The nitrogen in the CWHE 150 cools the natural gas therein by a countercurrent heat exchanger.

The heat exchangers 153, 154 and 155, and the column 157 are arranged in the cold box 181.

The inlet combustion air for the gas turbine 173 is sent to a heat exchanger 182 where it is cooled to 5-10 ° C. by a heat exchanger using chilled water. after,
The combustion air is discharged into the conduit 183 and sent to the turbine 173.

[0017] Cooling the inlet air supplied to the gas turbine increases power when ambient air temperature is high.

As in most large-scale LNG plants, the most expensive of the equipment are gas turbine drives and compressors, and major equipment such as bundles 151 and 152, which are usually made of aluminum. It is a CWHE cooling heat exchanger.

One object of the present invention is to increase the efficiency of prior art processes and to lower capital costs for liquefying natural gas.

The present invention is directed to a method and apparatus for liquefying natural gas. The above device
Refrigerant and compression means for compressing the refrigerant, and expansion means for adiabatically expanding at least two separate streams of the compressed refrigerant, in a countercurrent heat exchanger for cooling natural gas. A series of heat exchangers. In this case, the expanded flow of the refrigerant is in communication with the cold end of each heat exchanger.

One important feature of the present invention is a pre-cooled refrigeration for pre-cooling natural gas to a low temperature of 0 ° C. or less before feeding to the hot end of the series of heat exchangers. You are using the system. The pre-cooled refrigeration system is also used to pre-cool the high pressure refrigerant to a temperature of 0 ° C. or less before feeding to any of the heat exchangers in the series, or expansion means. It has been found that such pre-cooling can significantly reduce the power requirements of the liquefier and significantly reduce the number of components in the device. Conveniently, all refrigerant in the cooling cycle is pre-cooled by a pre-cooling refrigeration system.

It is desirable to cool the refrigerant in the first of the separate refrigerant streams with at least one of a series of heat exchangers. This cooling occurs after the refrigerant has been pre-cooled in the pre-cooling refrigeration system. In addition, the use of a pre-cooled refrigeration system eliminates the need to cool one or more of the refrigerant streams in a series of heat exchangers. Therefore, it is preferable that the flow of each refrigerant other than the flow of the first refrigerant is directly supplied to each expansion means without being further cooled by a series of heat exchangers.

The refrigerant in the flow of the refrigerant can be pre-cooled before or after splitting into the above-mentioned flow. However, pre-cooling before splitting is both convenient and economical. Preferably, the refrigerant is split into two streams of refrigerant.

Surprisingly, it has been found that by using a pre-cooled refrigeration system, it is sufficient to use only two of the series of heat exchangers. These two numbers are less than the number of heat exchangers in WO-A-9527179 and WO-A-9713108. Therefore, the manufacturing cost, operation cost, and maintenance cost of the heat exchanger could be significantly reduced.

Thus, in a preferred embodiment, two of a series of heat exchangers are used to divide the refrigerant into first and second refrigerant streams, Is cooled in the first hottest heat exchanger of the two heat exchangers. Therefore, if two refrigerant streams are used, the first refrigerant stream can be fed through the hottest heat exchanger of the series of heat exchanger interior heat exchangers, The two refrigerant streams can be fed directly to the expansion means without passing through a series of heat exchangers. By doing so, the heat transfer area of the first heat exchanger can be reduced by 35% as compared with the apparatus of FIG. 1, and the structure of the apparatus is simplified. This makes it easier to use a cheaper type of heat exchanger, such as aluminum PFHE or printed circuit heat exchanger (PCHE), instead of CWHE.

The intercooler 171 of FIG. 1 is expensive because of the high design pressure, tight area requirements, and the need to manufacture parts in contact with the seawater cooling medium from titanium. become. When the apparatus of the present invention is used, it is not necessary to use the intermediate cooling device 171 of FIG. This is because the compressed refrigerant discharged from the compression means is in a normal region.

Furthermore, the structure of the compression means can be simplified by using the present invention. This is because the temperature of the refrigerant is low, so the head requirements are low, the number of wheels of the compressor can be reduced, or the diameter of the wheels can be reduced. In addition, the required number of nozzles on the compressor case is 4
From 2 to 2, and the cost can be further reduced.
Another advantage is that for the same natural gas capacity, the power requirement of the compression means is about 16%
It can be lower, thereby lowering the rating of the turbine used to power the compressor. Thus, instead of the two compressors / internal refrigeration unit of FIG. 1, only one compressor stage is required and no internal refrigeration unit is required.

Preferably, the expanded refrigerant in the first refrigerant stream is supplied to the lower temperature end of the second heat exchanger, preferably the second refrigerant. The expanded refrigerant in the stream is preferably supplied to the lower temperature end of the first heat exchanger. Preferably, the expanded refrigerant in the second refrigerant stream is separated from the higher temperature of the second heat exchanger before being supplied to the lower temperature end of the first heat exchanger. Preferably, it mixes with the expanded refrigerant in the first refrigerant stream discharged from the end.

[0029] Two of the above series of heat exchangers can be installed separately or in a single heat exchanger shell containing two heat exchange bundles inside. it can. Each bundle corresponds to one of the heat exchangers in the series. The use of a single heat exchanger has the advantage that it does not have a significant adverse effect on efficiency and does not require the use of a cold box.

[0030] Preferably, the pre-cooled refrigeration system is provided with natural gas and refrigerant at 0 ° C to -40 ° C.
It is preferred to pre-cool to a temperature in the range of -10 ° C, preferably -10 ° C to -30 ° C. Preferably, the natural gas and refrigerant are cooled to about the same temperature as the pre-cooled refrigeration system. The refrigerant is usually at a temperature of -20 ° C or less,
Emitted from the hotter end of the hotter heat exchanger.

To pre-cool the streams of nitrogen and natural gas in two or more stages,
Industry standard refrigeration systems can be used. The number of cooling stages in the system is selected by the final pre-cooling temperature and by optimizing the cooling system's power requirements for increased costs when using a larger number of equipment items.

As pre-cooling heat exchangers, only a range of types of heat exchangers can be used. For example, as a pre-cooling heat exchanger, an aluminum core-in-
Kettle type or aluminum plate fin heat exchanger, PFHE
, Or PCHE can be used. However, for economic reasons, it is preferred that the pre-cooling heat exchanger use a conventional kettle-type tubular cooler made of carbon steel.

The refrigerant pre-cooling system uses separate pre-cooling refrigerants to pre-cool both natural gas and natural gas refrigerant. As the pre-cooling refrigerant, for example, propane, propylene, ammonia, or Freon refrigerant can be used. Preferably,
Preferably, R410a Freon is used as the pre-cooling refrigerant. This is because this refrigerant has a high capacity but is relatively safe and environmentally friendly.

In the case of the present invention, the pre-cooled refrigerant is advantageously driven by a pre-cooled gas turbine without the use of a plurality of separate electric motor-driven refrigeration units shown in FIG. 1A. It is compressed by one compression unit with two or more compression stages. Usually, a two-stage cooling system is suitable for this application, but in some cases a three-stage or four-stage cooling system may be more advantageous. Pre-cooled gas turbines can be used in generators as well as compression units for pre-cooled refrigeration systems, as the need for electric motor-driven chiller units has been eliminated, thus reducing the overall power requirements of the plant. Power can be supplied economically. This generator can meet all the usual power requirements of the device of the present invention and can significantly reduce the investment required for a separate gas turbine driven generator required for the device of FIG. .

In a preferred embodiment, the natural gas emitted from the series of heat exchangers is sent to a nitrogen recovery column. Natural gas released from the series of heat exchangers can be sent to a heat exchanger in a recovery column located near the bottom of the nitrogen recovery column to provide reboil heat to the column. Apart from this, it is preferred that no other heat exchange takes place on the natural gas emitted from the series of heat exchangers before being sent to the recovery column.

The recovery column produces a gaseous top product containing nitrogen and methane, which preferably powers a turbine to drive compression means for the refrigerant. Is preferably used as a fuel gas. Preferably, the top product is compressed in a fuel gas compressor prior to feeding to the turbine, preferably to the top product before feeding to the fuel gas compressor.
It is preferable not to perform any heat exchange.

When the recovery column of the present invention is used, the size of the low-temperature box can be reduced as compared with the low-temperature box 181 in FIG. 1, and the number of devices can be reduced. (Or, if a series of heat exchangers are housed in a single heat exchanger shell, the cold box can be dispensed with.) In addition, no intermediate fuel gas is used and the top product is Feeding directly to the gas compressor lowers the suction temperature of the fuel gas compressor, thereby reducing power requirements and simplifying construction. Using the present invention, the fuel gas compressor can comprise a single stage compressor or a two stage compressor with one internal cooling device, and the compressor 18 of FIG.
When compared to zero, power requirements can be reduced by about 50%. In addition, electric motor driven compressors can be used instead of more expensive gas turbines.

The refrigerant is preferably nitrogen, preferably a gaseous refrigerant after passing through a refrigerant cycle.

[0039] The relative flow rates of the first and second refrigerant streams can be controlled such that the natural gas cooling curve and the nitrogen heating curve match as closely as possible. WO-A-971
3108 and WO-A-9527179 describe this in more detail.

The apparatus of the present invention can be used in offshore units for liquefying natural gas, as described in WO-A-9713108. In this embodiment, the device can be mounted on a support structure (eg, a ship) that can float on the sea or at least partially support it above sea level. it can.

Using the apparatus of FIG. 1, to produce 1 ton of LNG per day, about 1 ton
5.8 kW of power is required. Using the apparatus of the present invention, the production of one ton of LNG per day requires about 14.75 KW of power. It can be seen that this is a significant power savings and the above capital cost savings.

In the case of FIG. 2, pretreated natural gas is passed through conduit 201 for approximately 8
. It is supplied to the first pre-cooling heat exchanger 266 at a pressure of 3 MPa. In one embodiment, the natural gas in conduit 201 has the following composition: 4.2 mol% nitrogen; 85.1 mol% methane; 8.2 mol% ethane; 2.5
It has a composition of mol% propane. The heat exchanger 266 is a kettle-type cooling device made of carbon steel using R410a as a refrigerant. The natural gas in the conduit 201 is cooled to −19 ° C. in the heat exchanger 266 and discharged into the conduit 202.

The natural gas present in heat exchanger 266 is sent through conduit 202 to the hotter end of first heat exchanger 250. The heat exchanger 250 is a CWHE
And comprises one shell, which incorporates one heat exchanger bundle 251. Natural gas is supplied to heat exchanger 250 by a countercurrent heat exchanger using nitrogen refrigerant.
Cooled within. The cooled natural gas exits the heat exchanger 250 at a temperature of about -95C and passes through the conduit 204 to the second heat exchanger 253. Throttle valve 285 is located in conduit 204, through which natural gas expands, if desired. The natural gas is cooled in the heat exchanger 153 to a temperature of about −152 ° C., exits the cooler end of the heat exchanger 253 and enters the conduit 206.

The natural gas in conduit 206 is fed directly into heat exchanger device 254 located in nitrogen recovery column 257. The natural gas sent to the heat exchanger device 254 is
Heat is provided at the bottom of the column 257 and is cooled by natural gas at the bottom of the column 257. Natural gas is discharged from heat exchanger device 254 and enters conduit 207 through which natural gas is passed to nitrogen recovery column 257.
Sent to the top of Throttle valve 256 is located within conduit 207, through which natural gas can expand if desired.

LNG is discharged from the bottom of column 257 and enters conduit 211 before entering pump 258. Pump 258 delivers LNG to conduit 212 and to LNG storage tank 286.

A flash gas containing methane and a high percentage of nitrogen exits the top of column 257 and enters conduit 209. The flash gas in conduit 209 at a temperature of about -165 ° C is sent to fuel gas compressor 280. The compressor 280 is a one-stage compressor or a two-stage compressor including one internal cooling device. Compressor 280 is driven by a 3 MW electric motor. The flash gas is typically supplied in the compressor 280 at a pressure slightly above atmospheric pressure,
It is compressed to a pressure in the range of 2.7-5.5 MPa. High pressure fuel gas is released from the compressor 280 into the conduit 210. As described below, the gas containing methane from the conduit 210 is used to supply the bulk fuel gas requirements of the liquefaction plant.

The following describes a nitrogen cooling cycle that cools natural gas to a temperature at which it can be liquefied. Nitrogen refrigerant is discharged from the hotter end of heat exchanger 250 and enters conduit 232 at about -26 ° C. Nitrogen is a single-stage compressor 259
Sent to Unlike the device of FIG. 1, there is only one compressor stage, so no internal cooling device is required. The compressor 259 is driven by the gas turbine 273. An RR Trent @ 54 MW can be used as the gas turbine. The operation of the compressor 259 consumes almost all the power required by the nitrogen cooling cycle.

The compressed nitrogen is discharged from the compressor 259 into the conduit 287 at a pressure of about 5.2 MPa. Nitrogen in conduit 287 is sent to heat exchanger 288, where the compressed nitrogen is cooled to ambient temperature by a countercurrent heat exchanger using seawater. The compressed nitrogen is passed from heat exchanger 288 to conduit 233
Released into

Conduit 233 is connected to conduits 234 and 235, between which the nitrogen from conduit 233 is split by the power absorbed by the compressor. The nitrogen in the conduit 234 is sent to a compressor 262 where it is compressed to a pressure of about 8.5 MPa,
2 to conduit 236. Nitrogen in conduit 235 is supplied to compressor 263 where it is compressed to a pressure of about 8.5 Mpa before being sent from compressor 263 to conduit 237. The nitrogen in both conduits 236 and 237 is sent to conduit 289, whereupon heat exchanger 290
Where it is cooled to ambient temperature by a countercurrent heat exchanger using seawater.

The nitrogen is released from the heat exchanger 290 into a conduit 238 through which it is sent to a second pre-cooled heat exchanger 264. Nitrogen is passed from heat exchanger 264 through conduit 239 to a third pre-cooling heat exchanger 265. Heat exchangers 264 and 265 are similar to heat exchanger 266. That is, these heat exchangers are shell kettle type cooling devices made of carbon steel using R410a as a refrigerant. The compressed nitrogen is cooled to about 7 ° C. in heat exchanger 264 and to about −19 ° C. in heat exchanger 265.

The cooled and compressed nitrogen is discharged from heat exchanger 265 to conduit 240 which connects to two conduits 220 and 222, respectively. Conduits 220 and 222 split the nitrogen into first and second refrigerant streams.
Conduit 220 is connected to the hotter end of heat exchanger 250. Nitrogen passing through heat exchanger 250 is heated to about -95 ° C before being discharged into conduit 221.
Is cooled.

The nitrogen in conduit 222 is sent to turboexpander 260 where it is
It is work expanded to a pressure of about 1.9 MPa and a temperature of about -100 ° C. The expanded nitrogen is released from the turboexpander 260 into the conduit 228. Nitrogen in conduit 221 is sent to turboexpander 261 where it is 1.9M
It is work expanded to a pressure of Pa and the lowest temperature of nitrogen, about -154 ° C.
The expanded nitrogen is released from the turbo expander 261 to the conduit 226. Turbo expander 260 is arranged to drive compressor 262, and turbo expander 261 is arranged to drive compressor 263. In this way, the turboexpanders 260 and 261 can recover most of the processed and expanded ones.

The nitrogen in the conduit 226 is supplied to the cooler end of the heat exchanger 253, inside which the natural gas is cooled by a countercurrent heat exchanger. In heat exchanger 253, the nitrogen is heated to an intermediate nitrogen temperature of about -100C. Nitrogen exits the hotter end of heat exchanger 253 and is mixed with nitrogen in conduit 228 before being fed to the cooler end of heat exchanger 250. The nitrogen in the heat exchanger 250 cools the natural gas therein by the countercurrent heat exchanger.

The heat exchanger 253, the throttle valve 256, and the column 257 are located in the cold box 298.

Gas turbine 273 is driven by fuel gas from conduit 210. Turbine combustion air is sent to a fourth pre-cooling heat exchanger 282, where it is heated to about one
Cool to 0 ° C. Inlet air is discharged from heat exchanger 282 to a conduit 283 that connects to an air inlet of turbine 273. The heat exchanger 282 is connected to the R41
This is a finned tube heat exchanger using Oa as a refrigerant.

FIG. 3 is a modification of the apparatus of FIG. Many of the components shown in FIG. 3 are similar to the components shown in FIG. Similar parts have similar reference numbers.

The differences between the embodiment of FIG. 2 and the embodiment of FIG. 3 are as follows.

(I) Instead of the first and second heat exchangers 250 and 253, one CWHE 350 with one shell containing the first and second heat exchanger bundles 351 and 353 is used. is being done.

(Ii) The low temperature box 289 is not used.

FIG. 4 is a pre-cooled refrigeration system for heat exchangers 264, 265, 266 and 282 providing cooling at -23 ° C. and 3 ° C. temperature levels. Heat exchanger 264,
265, 266 and 282 can be considered as first, second, third and fourth pre-cooling heat exchangers, respectively. This system is a gas turbine 4
It includes a two-stage, single-case, API-type refrigeration compressor unit 410 driven by 12. The compressor unit 410 comprises two compressor stages 4
14 and 416. In this case, the cooling system has two stages,
In other cases, it may be advantageous to use a three or four stage cooling system.
The pre-cooled refrigerant is R410a, but other refrigerants, including other freons, such as R134a, could alternatively be used. The turbine 412 also drives an electric generator G that satisfies most of the respective electrical power requirements shown in FIGS.

It should be understood that the invention described above can be modified in various ways.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a conventional type of natural gas liquefaction apparatus described in WO-A-9713108.

FIG. 2 is a schematic diagram of one embodiment of the device of the present invention.

FIG. 3 is a schematic diagram of another embodiment of the device of the present invention.

FIG. 4 is a schematic diagram of one embodiment of a pre-cooled refrigeration system for use with the embodiments of FIGS. 2 and 3;

Claims (23)

[Claims] An apparatus for liquefying natural gas, comprising a series of heat exchangers for cooling natural gas in a countercurrent heat exchanger with a refrigerant, and compression means for compressing the refrigerant. And expansion means for expanding the two separate streams of compressed refrigerant in an adiabatic manner, wherein the expanded stream of refrigerant is connected to the lower temperature end of each heat exchanger. Before feeding the series of heat exchangers, the natural gas is brought to 0 ° C.
Released from the hotter end of the series of heat exchangers before pre-cooling to the following temperature and before feeding back to the series of heat exchangers or the expansion means:
A pre-cooling refrigeration system for pre-cooling the compressed refrigerant to a temperature of 0 ° C or lower. 2. The apparatus of claim 1, wherein substantially all of the refrigerant discharged from the hotter end of the series of heat exchangers is sent through the pre-cooled refrigeration system. apparatus. 3. The apparatus according to claim 1, wherein a first stream of the separate refrigerant streams is cooled inside at least one of the series of heat exchangers, and An apparatus wherein a cooling refrigeration system is arranged to pre-cool the refrigerant before cooling the first refrigerant stream with the series of heat exchangers. 4. The apparatus of claim 3, wherein the series of heat exchangers includes two heat exchangers, and wherein the first refrigerant flow is a first of the two heat exchangers. A device that is cooled by the hotter heat exchanger. 5. The apparatus according to claim 3 or 4, wherein the pre-cooled refrigerant in the or each refrigerant stream other than the first refrigerant stream does not receive any further cooling. A device that is sent directly to the inflation means. 6. Apparatus according to claim 1, wherein said compression means comprises a single compression stage. 7. The apparatus according to any of the preceding claims, wherein the pre-cooling refrigeration system is arranged to pre-cool natural gas and the refrigerant to a temperature in the range of -10 ° C to -30 ° C. Equipment. 8. The apparatus according to claim 1, wherein said pre-cooling refrigeration system comprises one compression unit having two or more compression stages driven by a pre-cooling gas turbine. Equipment to be equipped. 9. The apparatus according to claim 1, further comprising a recovery column including a heat exchanger at or near a bottom thereof, wherein the arrangement supplies reboil heat to the recovery column. An apparatus for supplying cooled natural gas discharged from the series of heat exchangers to a heat exchanger of the recovery column, and then to the recovery column. 10. The apparatus according to claim 9, wherein an upper end of the recovery column is connected to a fuel gas inlet of a turbine for driving the refrigerant compression means, whereby the recovery column is connected to the recovery column. An apparatus wherein the top product supplies fuel to the turbine. 11. The apparatus of claim 10, further comprising a compressor for compressing a top product from the recovery column prior to feeding the fuel gas inlet, wherein the pre-cooling refrigeration system comprises: Apparatus arranged to pre-cool the top product after being compressed. 12. The apparatus according to any one of the preceding claims, wherein the series of heat exchangers are arranged in a heat exchanger shell having a number of heat exchanger bundles, each bundle comprising: Is a device corresponding to each of the heat exchangers. 13. A method for liquefying natural gas, comprising passing natural gas in countercurrent through a series of heat exchangers by a refrigerant circulated through a processing expansion cycle that compresses the refrigerant; Splitting and cooling the refrigerant to form at least first and second cooled refrigerant flows; expanding the first refrigerant to a first refrigerant temperature in a substantially adiabatic state; In the step of expanding the flow of the second refrigerant to a second refrigerant temperature higher than the first refrigerant temperature, the refrigerant in the flow of the first and second refrigerant, through a corresponding temperature range Sending the natural gas to 0 ° C. in the pre-cooling refrigeration system before feeding it to the series of heat exchangers to cool the natural gas.
Pre-cooling to the following temperature, before compression and expansion, or before feeding back to the series of heat exchangers, the refrigerant released from the hotter end of the series of heat exchangers, In the pre-cooling refrigeration system, a device that pre-cools to a temperature of 0 ° C or less. 14. The method of claim 13, wherein substantially all of the refrigerant discharged from the hotter end of the series of heat exchangers is sent through the pre-cooled refrigeration system. . 15. The method of claim 13 or claim 14, wherein a first one of the refrigerant streams is cooled within at least one of the series of heat exchangers, and wherein the pre-cooled refrigeration is provided. A method wherein the system is arranged to pre-cool the refrigerant before cooling the first refrigerant stream with the series of heat exchangers. 16. The method of claim 15, wherein the series of heat exchangers includes two heat exchangers, and wherein the first refrigerant flow is a first of the two heat exchangers. Cooling in the higher temperature heat exchanger. 17. The method of claim 15 or claim 16, wherein the pre-cooled refrigerant in the or each refrigerant stream other than the first refrigerant stream comprises:
A method of expanding within the working expansion cycle without receiving any further cooling. 18. The method according to claim 13, wherein the compression means comprises a single compression stage. 19. The method according to any one of claims 13 to 18, wherein natural gas released from said series of heat exchangers supplies reboil heat to said recovery column. At the bottom of or near the bottom of the recovery column, without any further heat exchange, from the heat exchanger to the recovery column. 20. The method according to claim 19, wherein gaseous top products from the recovery column are supplied to a fuel gas inlet of a turbine to drive compression of the refrigerant. 21. The method of claim 20, wherein the top product is compressed and then cooled by the pre-cooling refrigeration system before being supplied to the fuel gas inlet. 22. The method of claim 21, wherein the top product does not undergo any heat exchange before being compressed. 23. An offshore natural gas liquefaction plant comprising an apparatus according to any one of claims 1 to 12, and at least part of which can float or otherwise be at sea level A support structure that can be supported.