JP3303101B2 - Supercritical gas liquefaction method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for liquefying a supercritical gas, and more particularly to a method for liquefying various gases having a pressure higher than a critical pressure and a temperature higher than a critical temperature, such as nitrogen, oxygen and methane. Method and apparatus.

[0002]

2. Description of the Related Art Various systems have been known as means for liquefying various gases. For example, JP-A-61-
The method for liquefying a supercritical gas (permanent gas in the publication) described in Japanese Patent No. 105086 employs a configuration as shown in FIG.

That is, in the above liquefaction method, the supercritical gas cooled to extremely low temperature in the heat exchanger 1 is isenthalpy-expanded continuously by at least three pressure-reducing valves 2 and 2, and the resulting flash gas is The liquid is separated from the liquid by the gas-liquid separators 3 provided at the subsequent stage of each pressure reducing valve 2, and other liquids except the liquid separated by the final gas-liquid separator are expanded by the next pressure reducing valve 2. As a fluid, at least a part of the flash gas separated by the gas-liquid separators 3, 3 is introduced into the heat exchanger 1,
Heat exchange is performed with the supercritical gas.

[0004]

Although the above-mentioned method is excellent in liquefaction efficiency, it has a disadvantage that at least three gas-liquid separators for separating flash gas and liquid after isenthalpy expansion are required. have. That is, as an industrial control method of these gas-liquid separators, a method of controlling the liquid level in the gas-liquid separator is used, but the controllability and the liquid from the heat exchanger at the time of stoppage are used. In consideration of the flow, a gas-liquid separator sized to store the liquid flow for several minutes is generally required.

[0005] Therefore, when at least three gas-liquid separators of such a size are installed, the capacity thereof is large relative to other devices such as heat exchangers, and the liquefaction apparatus becomes large. It is not economical and has disadvantages such as a large heat loss.

Accordingly, the present invention provides a method and apparatus for liquefying a supercritical gas, which can reduce the number of gas-liquid separators used in a liquefaction apparatus as much as possible without reducing the liquefaction efficiency, thereby making the equipment economical. It is an object.

[0007]

In order to achieve the above-mentioned object, a method for liquefying a supercritical gas according to the present invention comprises the steps of cooling a high-pressure supercritical gas to a temperature lower than its critical temperature, and then partially cooling the supercritical gas. A pre-cooling step of expanding the supercritical gas by isenthalpy expansion, and a main cooling step of further cooling the low-temperature supercritical gas after the pre-cooling step to a lower temperature,
A decompression step of decompressing the supercritical gas after the main cooling step, wherein the main cooling step is a part of the low-temperature supercritical gas before or after each cooling step introduction or after derivation. And has two or more cooling steps which are isenthalpy expanded and used as a cooling source of the cooling step. At least one of the cooling steps branches a part of the supercritical gas before the introduction of the cooling step. Is a cooling source, and after isenthalpy expansion in a cooling step at a later stage of two or more cooling steps
Pressure after the isenthalpy expansion in the previous cooling step
Characterized in that the pressure is lower than the pressure , and further, in one or more of the pre-cooling step and the main cooling step, the cooled supercritical gas is separated into flash gas and liquid after isenthalpy expansion, The method is characterized in that the separated flash gas is used as a cooling source of the supercritical gas, and a step of introducing the separated liquid into the next cooling step is inserted.

[0008] The supercritical gas liquefaction apparatus of the present invention comprises:
After a high-pressure supercritical gas is cooled to a temperature lower than its critical temperature, and a part of the low-temperature supercritical gas derived from the heat exchanger is branched and isenthalpy-expanded by a pressure reducing valve, A pre-cooling circuit introduced as a cooling source to the heat exchanger, a heat exchanger for further cooling the low-temperature supercritical gas derived from the pre-cooling circuit to a lower temperature, and a low-temperature superconductor before or after introduction of the heat exchanger. After a part of the critical gas is branched and subjected to isenthalpy expansion by a pressure reducing valve, a cooling circuit of two or more circuits is introduced into the heat exchanger as a cooling source of the low-temperature supercritical gas.
A main cooling circuit having a road, seen including a decompression circuit for decompressing the supercritical gas deriving main cooling circuit, of the main cooling circuit
Pressure-reducing valve in the cooling circuit at the subsequent stage in two or more cooling circuits
The pressure after the isenthalpy expansion at
Set lower than the pressure after isenthalpy expansion at the pressure reducing valve
Was that characterized by, further wherein the pre-cooling circuit and one or more positions either of the main cooling circuit, the gas-liquid separator for separating the isenthalpic expansion with supercritical gas and flash gas and liquid provided, separated A circuit for introducing a flash gas as a cooling source of the supercritical gas into a heat exchanger of a preceding cooling circuit and a circuit for introducing a separated liquid to a next cooling circuit are inserted.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the present invention and shows a basic configuration of the present invention. Also,
FIG. 2 is a TS diagram illustrating a state change.

The apparatus of this embodiment has three heat exchangers 11, 1
2, 13 and four pressure reducing valves 21, 22, 23, 24 are combined, and first, a high-pressure supercritical gas is introduced into the first heat exchanger 11 from the pipe 1, The supercritical gas is cooled to a temperature lower than the critical temperature of the supercritical gas by a later-described return fluid serving as a cooling source (preliminary cooling step). The cooled supercritical gas having a temperature equal to or lower than the critical temperature is led out to the pipe 2,
A part thereof branches into the tubes 3 and 4, and the remaining low-temperature supercritical gas is introduced into the second heat exchanger 12.

The low-temperature supercritical gas branched to the pipe 3 isenthalpy-expanded by the pressure reducing valve 21 into a fluid in a gas-liquid mixed state, introduced into the first heat exchanger 11 as a return fluid, and introduced into the first heat exchanger 11. It is a cooling source for supercritical gas. The process up to the cooling process by isenthalpy expansion in the pressure reducing valve 21 is referred to as a preliminary cooling process.

The low-temperature supercritical gas branched to the pipe 4 isentropically expanded by the pressure reducing valve 22 to become a fluid in a gas-liquid mixed state, and flows from the second heat exchanger 12 in a direction countercurrent to the low-temperature supercritical gas. And serves as a cooling source for the low-temperature supercritical gas introduced from the pipe 2 to the second heat exchanger 12. The process after this process is referred to as a main cooling process.

The low-temperature supercritical gas which is further cooled to a lower temperature in the second heat exchanger 12 and is led from the second heat exchanger 12 to the pipe 5 is partially branched into the pipe 6 while remaining in the pipe 6. Is introduced into the third heat exchanger 13.

The low-temperature supercritical gas branched into the pipe 6 isenthalpy-expanded by the pressure reducing valve 23 to become a gas-liquid mixed fluid, and is returned as the second heat exchanger 12 and the first heat exchanger 11. And is a cooling source for the supercritical gas introduced from the pipe 1.

The heat is introduced from the pipe 5 to the third heat exchanger 13,
The low-temperature supercritical gas further cooled by the return gas passing through the pressure reducing valve 23 and led out to the pipe 7 is isenthalpy expanded by the pressure reducing valve 24, liquefied and taken out.

That is, the high-pressure supercritical gas supplied from the pipe 1 is sufficiently cooled in the heat exchangers 11, 12, and 13 and then liquefied by being depressurized by the pressure reducing valve 24, so as to be liquefied. Becomes At this time, flash gas may be partially generated depending on the reduced pressure.

This will be described as a state change on the TS diagram of nitrogen. In FIG. 2, line ABCD is an isobar that cools gas compressed to supercritical pressure, line UVW shows where nitrogen is in a two-phase state of liquid and gas, and point B is the first heat exchanger 11. , Point C indicates the outlet of the second heat exchanger 12, and point D indicates the outlet of the third heat exchanger 13. Line BEFG, line CHIJ, line DKLM, and line XN indicate isenthalpy lines, and line OP, line QR, and line ST are equal pressure lines of gaseous nitrogen.

Here, in the method shown in FIG. 1, the supercritical gas is cooled down to a middle temperature between points D and Z along the isobar of ABCD, and then decompressed by the pressure reducing valve 24 to be liquefied. It is sent out from a point corresponding to the state (pressure, temperature) after decompression.

The gas as the cooling source branches off from the supercritical gas at points B and C on the line AD, and the pressure reducing valves 21 and
Due to 22 , 23 , the pressure gradually expands as shown in FIG.
Then , after a liquid-gas mixed fluid having an equal enthalpy change by the lines BEF, BEF ', and CHJ, respectively, it rises while performing heat exchange with the supercritical gas to be cooled along the isobars of the lines FOP, F'QR, JST. Warm and return to room temperature.

FIG. 3 shows a second embodiment of the present invention.
In the first embodiment, instead of the path for branching to the pipe 6 and expanding with the pressure reducing valve 23 before being introduced into the third heat exchanger 13, the low temperature led to the pipe 7 from the third heat exchanger 13 is used. A part of the supercritical gas is branched into a pipe 8, subjected to isenthalpy expansion by a pressure reducing valve 25, and then introduced into a third heat exchanger 13 as a cooling source.

The low-temperature supercritical gas branched to the pipe 8 is converted into a liquid-gas mixed fluid whose isenthalpy has changed by the line DKL in FIG.
The temperature is raised while performing heat exchange with the supercritical gas to be cooled along the isobar of ST, and the temperature is returned to room temperature.

FIG. 3 shows a third embodiment of the present invention.
During the process, the gas-liquid mixed fluid after the enthalpy expansion of the cooled supercritical gas is separated into a flash gas and a liquid, and the separated flash gas is used as a cooling source for the supercritical gas. This shows an example in which a step to be introduced into the next cooling step is inserted.

In the embodiment shown in FIG. 4, in the second embodiment, the cooled supercritical gas led out from the first heat exchanger 11 to the pipe 2 is entirely branched without branching.
And undergoes isenthalpy expansion, becomes a fluid in a gas-liquid mixed state, is introduced into the gas-liquid separator 32, and is separated into gas and liquid. The flash gas separated by the gas-liquid separator 32 is supplied to the pipe 3
3 and is introduced as a fluid back into the first heat exchanger 11 and serves as a cooling source for the high-pressure supercritical gas.

On the other hand, the liquid in the gas-liquid separator 32 is
And after branching partially into the tube 35, as described above,
After being sequentially introduced into the second heat exchanger 12 and the third heat exchanger 13 and sufficiently cooled, they are expanded by the pressure reducing valve 24 and taken out. The gas branched to the pipe 35 is supplied to a pressure reducing valve 36.
After being subjected to isenthalpy expansion in step (1), the heat is sequentially used as a cooling source of the second heat exchanger 12 and then as a cooling source of the first heat exchanger 11.

After the liquid is led out from the second heat exchanger 12 to the pipe 5, it is the same as the second embodiment except that the fluid is a liquid. I do.

That is, in the method shown in FIG. 4, in FIG. 3, the supercritical gas is changed to the point B along the isobar of the line AB.
After cooling to the line BE
It expands along the isenthalpy line of F and reaches point F. Next, the liquid-gas mixed fluid at the point F is supplied to the gas-liquid separator 3.
2 separates the liquid at the point X and the flash gas at the point O. The separated liquid at the point X is cooled down to the intermediate temperature between the points K and Z along the isobar of the line XHKZ, and then depressurized by the pressure reducing valve 24, liquefied and according to the state (pressure, temperature) after the pressure reduction. Sent out from the point.

On the other hand, the gas as a cooling source branches from the liquid from the points X and K on the line UV, and the lines XN and K
After the enthalpy expansion by L, the lines NQR, L
The isobar in ST and the flash gas at the point O are heated along the isobar in the line OP while performing heat exchange with the supercritical gas to be cooled and / or the liquid to be cooled, and returned to room temperature.

FIG. 5 shows a fourth embodiment of the present invention as a specific apparatus configuration. Hereinafter, the present embodiment will be described in accordance with the procedure for liquefying nitrogen gas.

From tube 51, 40 ° C., 1.1 ata, 2
A raw material nitrogen gas of 000 Nm ³ / h is introduced, and compressed to 40 ° C. and 38.0 ata by the multi-stage compressor 71.
Each stage of the multi-stage compressor 71 includes pipes 52, 5 described later.
Nitrogen gas reduced to the suction pressure of each stage from 3, 54 is introduced and compressed together with the raw material nitrogen gas. At this time, when the pressure of the source nitrogen gas is about the suction pressure of the middle stage of the multi-stage compressor 71, the source nitrogen gas can be introduced from a stage corresponding to the pressure.

The nitrogen gas compressed to a critical pressure of 40.degree. C. or higher than 38.0 ata is branched from a pipe 55 to a pipe 56 and a pipe 57, and introduced into pressurizing blowers 74 and 75 directly connected to expansion turbines 72 and 73, respectively. Then, the pressure is raised to a pressure higher than the critical pressure. The nitrogen gas pressurized by one pressurizing blower 74 is cooled by an after cooler 76 and
The supercritical nitrogen gas at 61 ° C. and 61 ata is led out to the pipe 58 and the nitrogen gas pressurized by the other pressurizing blower 75 is
Cooled by aftercooler 77, 40 ℃, 55ata
And becomes the supercritical pressure nitrogen gas.

The supercritical nitrogen gas in the pipe 58 is introduced into the cold box 80 and cooled by the first heat exchanger 81. This supercritical nitrogen gas is cooled to a critical temperature (-147.1 ° C.) or lower except that a part thereof branches to the pipe 60 on the way, and becomes a supercritical nitrogen gas at −165 ° C. and 61 ata, for example.

The supercritical nitrogen gas led from the first heat exchanger 81 to the pipe 61 is enthalpy-expanded to 9.5 ata by the pressure reducing valve 91 to form a gas-liquid mixed fluid. Introduced into 78 and separated into flash gas and liquid. The liquid separated by the gas-liquid separator 78 is led out to the pipe 62, and a part of the liquid is introduced into the second heat exchanger 82 except that it branches from the pipe 63 to the pressure reducing valve 92, and is cooled to −175 ° C. Except that it is introduced into the third heat exchanger 83 except that a part thereof branches off from the pipe 65 to the pressure reducing valve 93 and is further cooled to -190 ° C. The liquid nitrogen of 9.5 ata which was discharged to the pipe 66 at −190 ° C.
4 at -190 ° C, 2ata, 20,000N
It is withdrawn from the tube 67 as m ³ / h product liquefied nitrogen.

On the other hand, the supercritical nitrogen gas at 40 ° C. and 55 ata, which has been pressurized by the pressurizing blower 75 and passed through the aftercooler 77, is introduced into the cold box 80 through the pipe 59, After being cooled to 100 ° C., the supercritical pressure nitrogen gas isentropically expanded to 9.5 ata by the expansion turbine 73, and the supercritical pressure nitrogen gas branched from the pipe 58 to the pipe 60 is converted to 9.5 ata by the expansion turbine 72.
Expands isentropically up to Both expansion turbines 72, 7
The nitrogen gas expanded to 9.5 at 3 in
8 and 69, into the return flow path of the flash gas separated by the gas-liquid separator 78, at a rate commensurate with each temperature, and from the pipe 52 to the suction stage where the pressure of the multi-stage compressor 71 is equal. Will be returned.

The liquefied nitrogen branched from the pipe 62 to the pipe 63 is isenthalpy-expanded to 6 ata by the pressure reducing valve 92, and then becomes a cooling source for the second heat exchanger 82 and the first heat exchanger 81. The pipe 53 is sequentially introduced as a return fluid,
Is returned to the suction stage where the pressure of the multi-stage compressor 71 is equal.
Similarly, the liquefied nitrogen branched from the pipe 64 to the pipe 65 isentropically expanded to 1.1 ata by the pressure reducing valve 93,
The third heat exchanger 83, the second heat exchanger 82, and the first
Is sequentially introduced as a return fluid serving as a cooling source to the heat exchanger 81, and is returned from the pipe 54 to a suction stage of the multistage compressor 71 having the same pressure.

The state of this embodiment will be described with reference to FIG. 2 as follows. The supercritical gas introduced from the pipe 58 is supplied to the first line along the isobar of the line AB.
Is cooled to the point B (−165 ° C., 61 ata) by the heat exchanger 81, and expanded along the isenthalpy line of the line BEF by the pressure reducing valve 91 to reach the point F (9.5 ata). This gas-liquid mixed fluid is separated by the gas-liquid separator 78 into the liquid at the point X and the flash gas at the point O. The liquid at the point X is cooled by the second and third heat exchangers 82 and 83 to the point K along the isobar of the line XHK, expanded by the pressure reducing valve 94 through the isenthalpy line of the line KL, and expanded at the point L (−). 190
° C, 2 data).

On the other hand, the flash gas at the point O
The temperature is increased along the isobar of the line OP in the heat exchanger 81 of
The liquid at the point X branched to the pipe 63 is isenthalpy expanded by the line XN at the pressure reducing valve 92, and the liquid at the point H branched to the pipe 65 is expanded by the line HJ at the pressure reducing valve 93.
After reaching point N (6 ata) and point J (1.1 ata),
Return each heat exchanger along the isobar lines NQR, JST.

As described above, by combining the multi-stage compressor 71, the expansion turbines 72, 73, and the booster blowers 74, 75 of the expansion turbines 72, 73, the raw material nitrogen gas can be efficiently liquefied.

As is clear from the above embodiment, by providing one gas-liquid separator 78, the heat exchanger 81 has a pressure of the fluid to be cooled of 55 ata (the pressurized nitrogen gas to the expansion turbine 73 is 61 ata). Whereas the heat exchanger 8
In 2, 83, the pressure of the fluid to be cooled is reduced to 9.5 ata by the pressure reducing valve 91. Therefore, the heat exchanger 8
2 and 83 and the pressure reducing valves 92 and 93 may have a pressure-resistant structure against 9.5 ata, and the cost is increased by the provision of one gas-liquid separator 78. However, as shown in FIGS. As a whole, the cost is reduced as compared with the case where all of the heat exchanger and the valve have a high pressure pressure resistant structure.

However, if three or more gas-liquid separators are provided as in the conventional apparatus shown in FIG. 6, the cost is increased as a whole as described above. Therefore,
By setting an appropriate expansion pressure and an appropriate number of gas-liquid separators in each expansion stage, it is possible to reduce the apparatus cost with substantially the same liquid efficiency.

Various kinds of gases capable of creating a supercritical state can be used as the raw material gas. The degree of pressure reduction at each pressure reducing valve and the amount of branching to the pressure reducing valve depend on the type of the target gas. The amount, temperature, pressure, and flow rate of each flow path inevitably change according to these conditions.

[0042]

As described above, according to the present invention,
An economical supercritical gas can be liquefied without reducing the liquefaction efficiency while minimizing equipment having a large volume such as a gas-liquid separator.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of the present invention.

FIG. 2 is a TS diagram for explaining the method of the present invention.

FIG. 3 is a system diagram showing a second embodiment of the present invention.

FIG. 4 is a system diagram showing a third embodiment of the present invention.

FIG. 5 is a system diagram showing a fourth embodiment of the present invention.

FIG. 6 is a system diagram showing an example of a conventional liquefaction apparatus.

[Explanation of symbols]

11, 12, 13, 81, 82, 83 ... heat exchangers 21, 22, 23, 24, 25, 31, 36, 91, 9
2, 93, 94 ... pressure reducing valve 32, 78 ... gas-liquid separator 71 ... multi-stage compressor 72, 73 ... expansion turbine 74, 75 ... step-up blower

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F25J 1/00-5/00

Claims (4)

(57) [Claims] 1. A pre-cooling step in which a high-pressure supercritical gas is cooled to a temperature lower than its critical temperature, and a part of the pre-cooling step is isenthalpy-expanded as a cooling source for the supercritical gas. A main cooling step of further cooling the low-temperature supercritical gas after completion of the main cooling step, and a decompression step of reducing the pressure of the supercritical gas after the main cooling step, wherein the main cooling step comprises: The process includes two or more cooling steps in which a part of the low-temperature supercritical gas before or after introduction of each cooling step is branched and isenthalpy-expanded to serve as a cooling source of the cooling step. at least one is a step in which the cooling step before introduction of branches a part of the supercritical gas and cooling source, the subsequent in two or more cooling steps cooling
The pressure after the isenthalpy expansion in the process
Liquefaction method of supercritical gas, characterized in that the pressure after the expansion of isenthalpy is lower than the pressure . 2. The method for liquefying a supercritical gas according to claim 1, wherein one of the pre-cooling step and the main cooling step is performed.
More than once, the cooled supercritical gas is isenthalpy-expanded and then separated into a flash gas and a liquid.The separated flash gas is used as a cooling source for the supercritical gas, and the separated liquid is introduced into the next cooling step. A method for liquefying a supercritical gas, comprising the step of: 3. A heat exchanger for cooling a high-pressure supercritical gas to a temperature lower than its critical temperature, a part of the low-temperature supercritical gas derived from the heat exchanger is branched, and isenthalpy is reduced by a pressure reducing valve. After expansion, a pre-cooling circuit to be introduced as a cooling source to the heat exchanger, a heat exchanger for further cooling the low-temperature supercritical gas derived from the pre-cooling circuit to a lower temperature, and before or before introduction of the heat exchanger After a part of the derived low-temperature supercritical gas is branched and isenthalpy-expanded by a pressure reducing valve, it is introduced into the heat exchanger twice as a cooling source for the low-temperature supercritical gas.
It is seen containing a main cooling circuit having a road or more cooling circuits, and a decompression circuit for decompressing the supercritical gas deriving main cooling circuit, before
Subsequent cooling in two or more cooling circuits of the main cooling circuit
The pressure after isenthalpy expansion at the pressure reducing valve
Pressure after isenthalpy expansion at pressure reducing valve in stage cooling circuit
A supercritical gas liquefaction apparatus characterized by being set lower than the above . 4. The supercritical gas liquefaction apparatus according to claim 3, wherein one of the pre-cooling circuit and the main cooling circuit is provided.
In more than one place, a gas-liquid separator is provided to separate the supercritical gas expanded isenthalpy into a flash gas and a liquid, and the separated flash gas is used as a cooling source of the supercritical gas in a heat exchanger of a cooling circuit in a preceding stage. An apparatus for liquefying a supercritical gas, wherein a circuit for introducing a liquid and a circuit for introducing a separated liquid to a next cooling circuit are inserted.