JP3551397B2 - Gas liquefaction method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas liquefaction method, and more particularly, to a method of compressing various gases, for example, oxygen, nitrogen, methane, etc., to a critical pressure or higher and then cooling and liquefying the same.
[0002]
[Prior art]
Conventionally, various methods have been used as a method for liquefying various gases. FIG. 4 shows an example of this, which will be described below in accordance with a procedure for liquefying nitrogen gas.
[0003]
Raw material nitrogen gas is introduced from a pipe 1 and compressed by a multi-stage compressor 2 to, for example, 28 kg / cm ² abs. Into the multistage compressor 2, for example, nitrogen gas of 6 kg / cm ² abs passing through a pipe 3 described later is introduced and compressed together with the raw material nitrogen gas.
[0004]
After the compressed nitrogen gas is cooled by the aftercooler 4, it passes through a pipe 5, branches into a pipe 6 and a pipe 7, and is introduced into pressurizing blowers 10 and 11 directly connected to expansion turbines 8 and 9, respectively. The pressure is raised to a pressure higher than the critical pressure.
[0005]
The pressurized nitrogen gas passing through one pipe 6 is pressurized by a pressurizing blower 10 and cooled by an aftercooler 12, and then becomes a pressurized nitrogen gas having a critical pressure of, for example, 42 kg / cm ² abs or more. Introduced into box 14. This pressurized nitrogen gas is introduced into the liquefaction line 16 of the heat exchanger 15 and cooled, and a part of the nitrogen gas is branched to the pipe 17, and the remaining nitrogen gas passes through the pipe 18 and reaches a critical temperature of -147.1 ° C. or lower. (For example, -173.0 ° C., 42 kg / cm ² abs). After the cooled nitrogen gas is led out of the heat exchanger 15 to the pipe 19, it is subjected to JT expansion (equal enthalpy expansion) to a required pressure (for example, 6 kg / cm ² abs) at the expansion valve 20, and then to the pipe 21. Through a gas-liquid separator (not shown), and is separated into flash gas and liquefied nitrogen. The flash gas merges with, for example, nitrogen gas flowing through a pipe 26 described later, and liquefied nitrogen is collected as a product. Is done.
[0006]
The nitrogen gas passing through the pipe 17 branched from the liquefaction line 16 is isentropically expanded to, for example, 6 kg / cm ² abs from a pressure of, for example, 42 kg / cm ² abs by the expansion turbine 8 and then cooled.
[0007]
On the other hand, the pressurized nitrogen gas pressurized by the pressurized blower 11 is cooled by the after cooler 22, becomes a pressurized nitrogen gas having a critical pressure of, for example, 38 kg / cm ² abs or more, and is introduced into the cold box 14 through the pipe 23. You. The pressurized nitrogen gas is cooled by the cooling line 24 of the heat exchanger 15, and then isentropically expanded to, for example, 6 kg / cm ² abs in the expansion turbine 9 through the pipe 25 to lower the temperature. The expanded and cooled nitrogen gas is introduced as a cooling source gas into the heat exchanger 15 through the pipe 26, and heat-exchanges with the warm fluid in the liquefaction line 16 and the cooling line 24 through the pipe 27 to increase the temperature. Further, it joins with the nitrogen gas passing through the pipe 28 expanded and cooled by the expansion turbine 8, and the temperature is raised to the pipe 3 and the pressure of the multi-stage compressor 2 is returned to an appropriate stage, recompressed and circulated. I do.
[0008]
[Problems to be solved by the invention]
The conventional gas liquefaction method including such a process is mainly designed to reduce the power per unit flow rate of the product liquefied gas (power consumption unit). The efficiency varies depending on the efficiency of the gas turbine (expansion turbine, compressor, etc.), the efficiency of the heat exchanger, etc., and these efficiencies depend on the process for liquefying gas.
[0009]
Accordingly, the present invention provides a method of cooling a gas having a critical pressure or higher to a temperature lower than a critical temperature, in a process in which an expansion turbine and a refrigerator are combined, without power liquefaction of a part of the gas at an outlet of the expansion turbine. It is an object of the present invention to provide a gas liquefaction method capable of reducing the basic unit.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a gas liquefaction method of the present invention is a method of liquefying a gas compressed to a critical pressure or higher by cooling the gas to a critical temperature or lower. A step of introducing pressure into a blower directly connected to a cold expansion turbine , increasing the pressure, branching the pressurized gas, and introducing one of the gases into a cooling line of a heat exchanger to cool, and introducing a cooling gas into the cold expansion turbine. after expansion cooling without liquefied at the outlet of the cold expansion turbine Te, introduced as a cooling source gas into the heat exchanger, corresponding to the cooling source gas after heating derived from the heat exchanger the compressor A step of introducing the gas into the pressure stage to recompress it, a step of introducing the other pressurized gas branched from the pressurized gas to be directly connected to the thermal expansion turbine and increasing the pressure above the critical pressure , and further branching the gas further pressurized. Before one of them A step of introducing and cooling into a liquefaction line of the heat exchanger, and cooling the other branched gas of the further pressurized gas with a refrigerator, and then introducing the gas into an equivalent temperature portion in the liquefaction line of the heat exchanger. Merging, or introducing into the corresponding pressure stage of the compressor after the cold recovery in the heat exchanger, withdrawing a part of the gas from the middle of the liquefaction line and introducing it to the thermal expansion turbine , expand and lower the temperature After that, a step of merging with a cooling source gas of the heat exchanger at a substantial temperature portion, and a step of extracting the gas cooled to a critical temperature or lower in a liquefaction line of the heat exchanger by JT expansion with an expansion valve and extracting it as a liquefied gas. , Are included.
[0011]
Furthermore, the present invention is characterized and Turkey be boosted above the critical pressure before Symbol compressed gas in the blower to be directly connected to the cold expansion turbine.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 shows an example of a nitrogen gas liquefaction process to which the present invention is applied. The same elements as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0013]
A raw material nitrogen gas of, for example, 10 ° C., 1.1 kg / cm ² abs, and 10,000 Nm ³ / h is introduced from the pipe 1, and compressed by the multi-stage compressor 2 to, for example, 26 kg / cm ² abs. The multi-stage compressor 2 uses one or more compressors, and for example, a circulating nitrogen gas of, for example, 6 kg / cm ² abs passing through a pipe 3 described later is introduced into the multi-stage compressor 2 and compressed together with the raw material nitrogen gas.
[0014]
The compressed nitrogen gas passes through the aftercooler 4 and the pipe 5, and is pressurized to, for example, 31 kg / cm ² abs by the booster blower 11 directly connected to the low-temperature side expansion turbine, that is, the cold expansion turbine 9, and the after-cooler 22. After being cooled, it branches from the pipe 51 to a pipe 52 and a pipe 53.
[0015]
The pressurized nitrogen gas branched to one pipe 52, for example, a pressurized nitrogen gas of about 60%, is introduced into a high-temperature side expansion turbine, that is, a pressurization blower 10 directly connected to the thermal expansion turbine 8, and further pressurized to a pressure equal to or higher than the critical pressure. Is done. This further pressurized nitrogen gas is cooled by the aftercooler 12 and then branched from the pipe 54 into a pipe 55 and a pipe 56. One nitrogen gas, usually 50% or more, branched into the pipe 55 is decompressed by the valve 57, introduced into the cold box 14 through the pipe 58, and flows into the liquefaction line 16 of the heat exchanger 15. I do. On the other hand, the nitrogen gas branched to the pipe 56 is cooled by the refrigerator 59, then introduced into the cold box 14 through the pipe 60, and the temperature of the nitrogen gas coincides with the nitrogen gas flowing through the liquefaction line 16 of the heat exchanger 15. Join at a location where
[0016]
A portion of the nitrogen gas having a pressure equal to or higher than the critical pressure flowing through the liquefaction line 16 branches into the pipe 17 in the middle of the heat exchanger 15, and the remaining nitrogen gas passes through the pipe 18, and has a critical temperature of -147.1 ° C or lower. (For example, -173.0 ° C., 42 kg / cm ² abs). The cooled nitrogen gas undergoes isenthalpy expansion (JT expansion) to a required pressure (for example, 6 kg / cm ² abs) at an expansion valve 20 through a pipe 19, and then passes through a pipe 21 to a gas-liquid separator ( (Not shown), is separated into flash gas and liquefied nitrogen, and the flash gas is recirculated by, for example, merging with the nitrogen gas flowing through the pipe 26, and 10,000 Nm ³ / h of liquefied nitrogen is collected as a product. Is done. Further, the nitrogen gas branched to the pipe 17 isentropically expanded to, for example, 6 kg / cm ² abs from a pressure of, for example, 42 kg / cm ² abs by the thermal expansion turbine 8 to lower the temperature.
[0017]
On the other hand, the pressurized nitrogen gas branched to the pipe 53 is introduced into the cooling line 24 of the heat exchanger 15, cooled, and then led out to the pipe 25 halfway through the heat exchanger 15, where it is cooled by the cold expansion turbine 9. For example, the temperature is reduced by isentropic expansion to 6 kg / cm ² abs. The expanded and cooled nitrogen gas is introduced as a cooling source gas into a pipe 27 of the heat exchanger 15 through a pipe 26. Further, the nitrogen gas branched from the liquefaction line 16 to the pipe 17 isentropically expanded to, for example, 6 kg / cm ² abs in the thermal expansion turbine 8 to lower the temperature, and then the nitrogen gas flowing through the pipe 27 through the pipe 28 At a position where the temperature and the temperature coincide with each other, the temperature is increased by exchanging heat with the nitrogen gas in the liquefaction line 16 and the cooling line 24 in the heat exchanger 15, and the temperature is led out to the pipe 3. The pressure is returned to the appropriate stage, recompressed and circulated. Further, the nitrogen gas after expansion and cooling flowing through the pipe 28 is not merged with the pipe 27 as described above, but after collecting the cold through the pipe 29 indicated by the broken line, the nitrogen gas is returned to the corresponding pressure stage of the multi-stage compressor 2. It may be introduced.
[0018]
Thus, in the method of cooling and liquefying a gas compressed above the critical pressure to below the critical temperature, a step of compressing the raw material gas by the multi-stage compressor 2 and a step-up blower 11 directly connecting the compressed gas to the cold expansion turbine 9 And pressurized gas below the critical pressure, the pressurized gas is branched into a pipe 52 and a pipe 53, and one pressurized gas branched into the pipe 53 is introduced into the cooling line 24 of the heat exchanger 15 to be cooled. After the process and the cooling gas derived from the cooling line 24 are introduced into the cold expansion turbine 9 to expand and lower the temperature, the cooling gas is introduced into the pipe 27 of the heat exchanger 15 as a cooling source gas. Introducing the cooling source gas after the temperature rise derived to the above to the corresponding pressure stage of the multi-stage compressor 2 to recompress it, and supplying the other pressurized gas branched to the pressurized gas pipe 52 to the thermal expansion turbine 8. Directly connected A step of further increasing the pressure to a pressure higher than the critical pressure by introducing the gas into the pressure increasing blower 10; A step of introducing the gas into the liquefaction line 16 of the exchanger 15 for cooling, and a step of cooling the gas having a pressure equal to or higher than the other critical pressure branched to the pipe 56 by the refrigerator 59, A step of introducing the gas into the temperature portion and joining it, and extracting a part of the gas into the pipe 17 from the middle of the liquefaction line 16 and introducing the gas into the thermal expansion turbine 8 to expand and lower the temperature. Of joining the cooling source gas flowing through the pipe 27 of the heat exchanger 15 at a corresponding temperature portion, or introducing the cooling gas into the corresponding pressure stage of the multi-stage compressor 2 after collecting the cold in the pipe 29 of the heat exchanger 15 without merging. When As shown in FIG. 2, the temperature of the gas cooled in the heat exchanger 15 is reduced by performing JT expansion of the gas cooled to a critical temperature or lower in the liquefaction line 16 of the heat exchanger 15 by the expansion valve 20 and extracting the liquefied gas. The temperature difference between the fluid and the cold fluid can be made closer overall as compared with the conventional one shown in FIG.
[0019]
In general, the efficiency of the heat exchanger is higher when the temperature difference between the hot fluid and the cold fluid is closer.Therefore, by applying the method of the present invention, heat exchange between the hot fluid and the cold fluid can be performed efficiently. it can. Further, by introducing a gas having a pressure lower than that of the conventional gas into the cold expansion turbine 9, the turbine efficiency can be improved without liquefying a part of the gas at the turbine outlet.
[0020]
Therefore, the gas liquefaction efficiency can be greatly improved by improving the heat exchange efficiency and the turbine efficiency. For example, in the above-described process of producing 10000 Nm ³ / h of liquefied nitrogen, the unit power consumption is lower than in the past. Can be reduced by about 4.2%.
[0021]
In the above example, the pressure of the gas introduced into the cold expansion turbine 9, that is, the pressure of the gas pressurized by the pressure booster 11 directly connected to the cold expansion turbine 9 is set to be equal to or lower than the critical pressure. The pressure may be raised to a pressure higher than the critical pressure, and the inlet temperature and expansion ratio of the cold expansion turbine 9 may be set appropriately so that the gas does not liquefy at the turbine outlet.
[0022]
【The invention's effect】
As described above, in the gas liquefaction method of the present invention, the raw material gas compressed and pressurized to a predetermined pressure is raised to a critical pressure or lower by a blower directly connected to a cold expansion turbine, and the pressurized gas is further supplied to a thermal expansion turbine. While the pressure is raised above the critical pressure by a directly connected blower, the gas on the high pressure side, which is raised above the critical pressure by the blower directly connected to the thermal expansion turbine, is introduced into the liquefaction cooling path of the heat exchanger, and part of it is liquefied. While taking out as a gas, the remainder is introduced into a warm expansion turbine at an intermediate temperature to expand and lower the temperature, as a part of a cooling source gas, and a low-pressure side gas which is pressurized by the blower directly connected to the cold expansion turbine. the cooled in the heat exchanger to a predetermined temperature, the gas to be liquefied by expansion cooling to not liquefied in the cold expansion turbine outlet as a cooling source for cooling below the critical temperature By there, the gas at higher than conventional efficiency can be heat exchange, it is possible to reduce the power consumption rate required for the liquefaction of the gas.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an example of a gas liquefaction apparatus to which the present invention is applied.
FIG. 2 is a QT diagram of a heat exchanger in a gas liquefaction apparatus to which the present invention is applied.
FIG. 3 is a QT diagram of a heat exchanger in a conventional gas liquefaction apparatus.
FIG. 4 is a system diagram showing an example of a conventional gas liquefaction apparatus.
[Explanation of symbols]
2: Multistage compressor, 8: Hot expansion turbine, 9: Cold expansion turbine, 10, 11: Booster blower, 14: Cold box, 15: Heat exchanger, 16: Liquefaction line, 20: Expansion valve, 24: Cooling line , 59… Refrigerator

Claims (2)

In a method of cooling and liquefying a gas compressed above a critical pressure below a critical temperature, a step of compressing a raw material gas with a compressor (2) and a blower (11) directly connecting the compressed gas to a cold expansion turbine (9 ) And pressurizing the gas, branching the pressurized gas, introducing one of the gas into a cooling line (24) of a heat exchanger (15) to cool the gas, and supplying the cooling gas to the cold expansion turbine (9) . after expansion cooling without liquefied at the outlet of the cold expansion turbine is introduced (9), introduced as a cooling source gas to said heat exchanger (15), heat exchanger (15) the derived temperature was raised from Introducing the cooling source gas into the corresponding pressure stage of the compressor (2) to recompress it, and a blower (10) for directly connecting the other pressurized gas branched from the pressurized gas to the thermal expansion turbine (8 ). a step of boosting the critical pressure or higher is introduced, the Further branching the boosted gas, while the heat exchanger (15) a step of cooling by introducing the liquefied line (16) of the refrigerator the branched other gas of said and further boosted gas (59 ) , The mixture is introduced into the liquefaction line (16 ) of the heat exchanger (15) at a corresponding temperature and merged, or after the cold recovery in the heat exchanger (15) , the compressor (2) is cooled. And a step of extracting a part of the gas from the middle of the liquefaction line (16) , introducing the gas into the thermal expansion turbine (8) , and expanding and lowering the temperature. Then, the heat exchanger (15) And a gas cooled to a critical temperature or lower in a liquefaction line (16) of the heat exchanger (15) is expanded by JT with an expansion valve (20) and taken out as a liquefied gas. And a process. Scan method of liquefaction. The gas liquefaction method according to claim 1 , wherein the pressure of the compressed gas is raised to a critical pressure or higher by the blower (11) .

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