Liquefaction apparatus and liquefaction method
By incorporating low-temperature gas lines to pre-cool raw material gases before circulation, the liquefaction cycle reduces compressor power consumption and costs while enhancing heat exchange, achieving efficient liquefaction without enlarging equipment.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- IWATANI CORP
- Filing Date
- 2025-01-16
- Publication Date
- 2026-07-29
AI Technical Summary
Existing gas liquefaction cycles, such as the Claude cycle, face high power consumption and increased costs due to inefficient heat exchange and increased load on compressors when liquefying gases at room temperature, particularly when the flow rate in the branch expansion line increases.
A configuration that includes a low-temperature gas line and a raw material gas diversion line, where low-temperature gases are used to pre-cool the raw material gas before it enters the circulation line, enhancing heat exchange and reducing the temperature of gases entering the circulation compressor and expansion valve.
This configuration reduces power consumption of the compressors, lowers liquefaction costs, and increases the liquefaction rate by optimizing heat exchange and maintaining a low temperature for the return gas, thus avoiding the need for larger heat exchangers.
Smart Images
Figure 2026122548000001_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a liquefaction device suitable for liquefying industrially useful gases, such as gases used as fuels.
Background Art
[0002] As a liquefaction cycle used in a gas liquefaction device, a Claude cycle using a compressor, an expansion valve, and an expander is known. In addition to creating a low-temperature state with a compressor and an expansion valve, this cycle uses adiabatic expansion by an expander to generate a large amount of cold and perform liquefaction efficiently. Specifically, for example, as shown in Patent Document 1 below, in a precooling line, a high-pressure gas stream after boosting the pressure of a raw material gas with a circulation compressor is cooled through a group of heat exchangers arranged in series, and then is expanded isentropically by an expansion valve to be liquefied. Liquefaction is not performed on the entire amount, and a part of the raw material gas that is not liquefied and is at a low temperature and low pressure (return gas) returns to the circulation compressor in the precooling line through the group of heat exchangers in a circulation line. Since the return gas is at a low temperature, it cools the raw material gas in the precooling line by heat exchange. However, since it cannot generate cold, in addition to the above circulation, a part of the precooled high-pressure raw material gas is decompressed and its temperature is lowered by adiabatic expansion by an expander through a branch expansion line branched between the heat exchangers in the precooling line, and is merged into the upstream side of the circulation line.
[0003] Such a liquefaction cycle is widely used for liquefying oxygen, nitrogen, helium, hydrogen, etc. However, when the raw material gas is at room temperature, the power consumption of the compressor increases, resulting in high costs. Also, although it is a Claude cycle that generates a large amount of cold by adiabatic expansion by the expander in the branch expansion line, if the flow rate in the branch expansion line increases too much, the power consumption of the circulation compressor will increase instead. That is, the temperature of the gas entering the expansion valve can be lowered and the liquefaction amount per cycle increases, but the gas returning to the circulation line decreases, and the heat exchange amount by the heat exchanger performed upstream of the confluence point with the branch expansion line in the circulation line decreases. Then, the temperature of the gas entering the circulation compressor approaches room temperature, and the load on the circulation compressor increases.
[0004] Even if a gas is useful, commercialization is impossible if the cost is too high. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Special Publication No. 61-3459 [Overview of the project] [Problems that the invention aims to solve]
[0006] Therefore, the main objective of this invention is to reduce liquefaction costs by suppressing the power consumption of the compressor. [Means for solving the problem]
[0007] The liquefaction apparatus for achieving this objective has the following configuration: A low-temperature gas line is provided through which a low-temperature liquefied gas or low-temperature gas (hereinafter referred to as "low-temperature gas, etc.") with a lower boiling point than the raw material gas flows; the upstream end of a raw material gas diversion line, which diverts a portion of the raw material gas, is connected upstream of the circulating compressor in the pre-cooling line; and the downstream end of the raw material gas diversion line is connected upstream of the heat exchanger located at the uppermost position in the circulation line. Furthermore, the liquefaction apparatus is equipped with a diversion gas cooling heat exchanger that exchanges heat between the low-temperature gas line and the raw material gas diversion line to lower the temperature of the raw material gas in the raw material gas diversion line.
[0008] In this configuration, a portion of the raw material gas before pressurization passes through a raw material gas diversion line and is pre-cooled between it and the low-temperature gas line before joining the circulation line upstream of the heat exchanger group. The temperature of the gas in the joining raw material gas diversion line can be made to be approximately the same as the temperature of the gas returning to the circulation line, and the flow rate can be increased. As a result, the amount of heat exchanged in the heat exchanger upstream of the point where it joins the branch expansion line in the circulation line can be increased. Consequently, the amount of gas diverted to the branch expansion line is reduced, and the temperature of the gas entering the circulation compressor and the gas entering the expansion valve can be lowered. [Effects of the Invention]
[0009] According to this invention, a configuration is adopted in which a portion of the raw material gas before pressurization is cooled and merged upstream of the heat exchanger group in the circulation line to increase the amount of heat exchanged in the heat exchanger. This reduces the amount of gas diverted to the branch expansion line, and thus lowers the temperature of the gas drawn in by the circulation compressor. As a result, the power consumption of the circulation compressor can be reduced, and liquefaction costs can be lowered.
[0010] Furthermore, it is possible to lower the temperature of the gas entering the expansion valve and ensure a sufficient amount of gas passes through the expansion valve, thus contributing to a reduction in liquefaction costs by increasing the amount of liquefaction.
[0011] Furthermore, because the system employs a configuration that effectively utilizes low-temperature gases, it is possible to operate with ample cooling capacity for pre-cooling the raw material gas, thus avoiding the need for larger heat exchangers. [Brief explanation of the drawing]
[0012] [Figure 1] System diagram of the liquefaction system. [Figure 2] System diagram of a liquefaction apparatus in another example. [Modes for carrying out the invention]
[0013] One embodiment for carrying out this invention will be described below with reference to the drawings.
[0014] Figure 1 shows a system diagram of a liquefaction apparatus 11 that liquefies gas. This liquefaction apparatus 11 is suitable for liquefying gases that do not liquefy simply by compression and cooling, such as industrially useful gases like oxygen, nitrogen, helium, hydrogen, and natural gas, especially gases at room temperature. In addition to using the raw material gas to be liquefied, the apparatus employs a configuration that utilizes low-temperature gases, etc., to reduce liquefaction costs.
[0015] The types of gases used, such as the raw material gas and cryogenic gas, are not fixed and are selected as appropriate depending on the purpose and environment. Examples of raw material gases include biogas and synthetic methane obtained by methanation, which are currently expected to see increased use. For cryogenic gases used as heat transfer fluids, it is preferable to use cryogenic liquefied gases such as liquefied hydrogen, liquefied nitrogen, or liquefied helium, from the viewpoint of effectively utilizing the latent heat of vaporization. In the illustration in Figure 1, the type of raw material gas to be liquefied is represented by the symbol "X", and the type of gas such as cryogenic gas is represented by the symbol "Y", with the gases being represented by the symbols "GX" and "GY", and the liquids by the symbols "LX" and "LY".
[0016] The liquefaction unit 11 has three lines that constitute the Claude cycle, namely the pre-cooling line 12, the circulation line 13, and the branched expansion line 14, as well as two additional lines (a low-temperature gas line 15 and a raw material gas diversion line 16).
[0017] First, let's explain the three basic lines: the pre-cooling line 12, the circulation line 13, and the branched expansion line 14.
[0018] The pre-cooling line 12 has a circulating compressor 31 on the upstream side that pressurizes the introduced raw material gas GX, and an expansion valve 32 on the downstream side that liquefies the high-pressure, low-temperature raw material gas GX. Between these, a heat exchanger group 33 consisting of multiple heat exchangers is arranged in series. In other words, the raw material gas GX flowing through the pre-cooling line 12 is pressurized by the circulating compressor 31, then gradually cooled as it passes through the heat exchanger group 33, and partially liquefied by isenthalpic expansion by the expansion valve 32, which consists of Joule-Thomson valves.
[0019] There are four heat exchangers arranged in the precooling line 12. Among them, the two middle heat exchangers 33b and 33c exchange heat with the circulation line 13, and the two heat exchangers 33a and 33d on both sides exchange heat with the low-temperature gas line 15. The two middle heat exchangers 33b and 33c are, in order from the upstream side of the precooling line 12, the second heat exchanger 33b and the third heat exchanger 33c. On the other hand, the heat exchanger on the upstream side of the precooling line 12 is the first heat exchanger 33a, and the heat exchanger on the downstream side of the precooling line 12 is the subcooling heat exchanger 33d.
[0020] The first heat exchanger 中間の is a heat exchanger on the upstream side of the branch point of the branch expansion line 14 in the precooling line 12. In the illustrated example, there is one, but if there are multiple, at least one of them exchanges heat with the low-temperature gas line 15.
[0021] The downstream end of the precooling line 12 is connected to a liquefied gas storage tank 34 in which the liquefied raw material gas LX is stored.
[0022] The circulation line 13 is a line that returns the low-temperature and low-pressure raw material gas (also referred to as "return gas") that was not liquefied by the isenthalpic expansion by the expansion valve 32 to the circulation compressor 31 through the heat exchanger group 33. The upstream end of the circulation line 13 is connected to the liquefied gas storage tank 34, passes through the third heat exchanger 33c and the second heat exchanger 33b in order among the heat exchangers of the heat exchanger group 33, and the downstream end is connected to the upstream stage of the circulation compressor 31 in the precooling line 12. A compressor 35 is provided between the second heat exchanger 33b and the downstream end to adjust the pressure of the raw material gas GX entering the circulation compressor 31. Instead of providing the compressor 35 in the circulation line 1,, a pressure reducing valve (not shown) can also be provided at the upstream stage of the circulation compressor 31 in the precooling line 12 and upstream of the connection position of the circulation line 13.
[0023] It should be noted that there seems to be a typo in the original text where "中間の" appears in the description of the first heat exchanger in . It might be a misspelling or an incorrect expression. I translated it as it is for the sake of following the translation rules strictly. If this is an important error, it may need to be corrected in the original text for a more accurate translation.The branch expansion line 14 is a line that generates cold using a part of the pre-cooled raw material gas. The upstream end is connected between the heat exchangers in the pre-cooling line 12, in this example, between the first heat exchanger 33a and the second heat exchanger 33b, and the downstream end is connected to the upstream side of the circulation line 13, in this example, between the second heat exchanger 33b and the third heat exchanger 33c. It has a branch flow expander 36 for generating cold, and a flow rate adjustment valve 37 is provided on the upstream side of the branch flow expander 36. The above-mentioned "upstream side of the circulation line 13" means the upstream side of the heat exchanger (the second heat exchanger 33b in the illustrated example) in front of the position where the upstream end of the branch expansion line 14 in the pre-cooling line 12 is connected.
[0024] In this branch expansion line 14, a part of the high-pressure raw material gas pre-cooled by the first heat exchanger 33a is diverted, and the raw material gas is adiabatically expanded to the low-pressure side pressure by the branch flow expander 36 and then merged into the low-temperature and low-pressure return gas. Thereby, the cooling capacity by the return gas is improved.
[0025] Next, the low-temperature gas line 15 and the raw material gas diversion line 16 will be described.
[0026] The low-temperature gas line 15 is provided independently of the pre-cooling line 12, the circulation line 13, and the branch expansion line 14, and extends from a heat medium storage tank 51 that stores a low-temperature liquefied gas (liquid heat medium LY, preferably liquefied hydrogen) as a low-temperature gas or the like.
[0027] Upstream of the low-temperature gas line 15, the aforementioned supercooling heat exchanger 33d is provided to exchange heat with the pre-cooling line 12. This supercooling heat exchanger 33d is located upstream of the expansion valve 32 on the pre-cooling line 12. Downstream of the low-temperature gas line 15, the aforementioned first heat exchanger 33a is provided to exchange heat with the pre-cooling line 12. Between the supercooling heat exchanger 33d and the first heat exchanger 33a in the low-temperature gas line 15, a split-flow gas cooling heat exchanger 52 is provided. The split-flow gas cooling heat exchanger 52 exchanges heat with the raw material gas split-flow line 16. Upstream of the split-flow gas cooling heat exchanger 52 in the low-temperature gas line 15, an expander 53 is provided to enhance the cooling capacity of the low-temperature gas GY by its cold energy.
[0028] The raw material gas diversion line 16 is a line that diverts a portion of the raw material gas before pressurization and rejoins it with the return gas. Its upstream end is connected upstream of the confluence point of the circulation line 13 in the pre-cooling line 12, and its downstream end is connected to the heat exchanger located at the uppermost position in the circulation line 13, i.e., before the third heat exchanger 33c. The raw material gas diversion line 16 is equipped with the aforementioned heat exchanger 52 for cooling the diverted gas, which cools the raw material gas GX that is to be rejoined with the return gas by heat exchange with the low-temperature gas GY. A flow control valve 54 is provided upstream of the heat exchanger 52 for cooling the diverted gas in the raw material gas diversion line 16, and a pressure reducing valve 55 is provided downstream to match the pressure of the return gas.
[0029] In the liquefaction apparatus 11 configured as described above, a portion of the raw material gas GX before it is pressurized by the circulating compressor 31 is diverted, and the gas, which has been cooled by heat exchange with a low-temperature gas with a lower boiling point than the raw material gas GX, is merged upstream of the heat exchanger group 33 of the return gas that returns to the circulating compressor 31. This increases the amount of heat exchanged by the heat exchanger group 33 and suppresses the amount of gas that undergoes adiabatic expansion and merges with the return gas, i.e., the diverted flow rate that generates cold.
[0030] Specifically, in the pre-cooling line 12, the high-pressure raw material gas, pressurized by the circulating compressor 31, is gradually cooled as it flows through the first heat exchanger 33a, the second heat exchanger 33b, and the third heat exchanger 33c, and then a portion of it is liquefied by the expansion valve 32. In parallel with this, the cooling capacity of the heat exchangers is enhanced by the gas flowing through the branch expansion line 14 and the raw material gas diversion line 16. In other words, in the branch expansion line 14, a portion of the raw material gas pre-cooled in the first heat exchanger 33a after pressurization generates cold through adiabatic expansion by the branch flow expander 36. The depressurized and temperature-reduced gas then joins the return gas that has passed through the third heat exchanger 33c. Meanwhile, in the raw material gas diversion line 16, a portion of the raw material gas before pressurization is cooled by the diversion gas cooling heat exchanger 52 and joins the stage before the third heat exchanger 33c in the circulation line 13. The cooling temperature of the raw material gas by the cooling heat exchanger 52 is set to be at or above the temperature of the low-temperature return gas that could not be liquefied by the expansion valve 32.
[0031] The gas passing through the branched expansion line 14 increases the amount of heat exchanged by the second heat exchanger 33b, and the gas passing through the raw material gas diversion line 16 increases the amount of heat exchanged by the third heat exchanger 33c and the second heat exchanger 33b. This two-stage merging of low-temperature gases maintains a low temperature for the return gas in the circulation line 13 and ensures a sufficient flow rate for the return gas.
[0032] Furthermore, the raw material gas in the pre-cooling line 12 is cooled not only by heat exchange between the third heat exchanger 33c and the second heat exchanger 33b, but also by the first heat exchanger 33a and the supercooling heat exchanger 33d. Specifically, the supercooling heat exchanger 33d is cooled by low-temperature liquefied gas, and the first heat exchanger 33a is cooled by the low-temperature gas remaining after the low-temperature liquefied gas has vaporized. As a result, cooling can be performed more efficiently by making maximum use of latent heat and sensible heat than cooling by gas passing through the circulation line 13.
[0033] Because the raw material gas in the pre-cooling line 12 is effectively cooled, the temperature of the gas exiting the third heat exchanger 33c can be brought close to the saturation temperature, and this gas is further cooled in the supercooling heat exchanger 33d located upstream of the first heat exchanger 33a in the low-temperature gas line 15. This cooling further cools the saturated gas into a supercooled state. The high-pressure raw material liquid, now in a supercooled state, is reduced in pressure to the internal pressure of the storage tank 34 by the expansion valve 32. The liquefaction rate when the supercooled raw material gas is reduced in pressure is high, resulting in efficient liquefaction.
[0034] In this way, the temperature of the gas entering the compressor 35 and the circulating compressor 31 can be lowered, thereby reducing the power consumption of the compressor 35 and the circulating compressor 31.
[0035] Furthermore, the increased heat exchange rate by the heat exchanger suppresses the flow rate of the branch expansion line 14, thereby maintaining the cycle. This also reduces the power consumption of the compressor 35 and the circulating compressor 31.
[0036] Furthermore, in addition to the increased cooling capacity provided by the branched expansion line 14 and the raw material gas diversion line 16, the supercooling heat exchanger 33d supercools the gas entering the expansion valve 32, thereby further increasing the liquefaction rate due to isenthalpic expansion and achieving more efficient liquefaction.
[0037] Furthermore, since the configuration aims to improve efficiency by increasing the heat exchange rate of the heat exchanger, there is no need to increase the size of the heat exchanger, and increasing the liquefaction rate will not lead to an increase in the size of the equipment.
[0038] The above configuration is one embodiment for carrying out this invention, and this invention is not limited to the above configuration; other configurations can be adopted.
[0039] For example, the number of heat exchangers may be increased.
[0040] The expander 53 of the low-temperature gas line 15 can be omitted.
[0041] The expander 53 of the low-temperature gas line 15 may be moved between the heat exchanger 52 for cooling the branch gas and the first heat exchanger 33a. In this case, even if the low-temperature gas is in a low-temperature liquefied gas state at the outlet of the supercooling heat exchanger 33d, the heat exchanger 52 for cooling the branch gas intervenes to raise the temperature of the low-temperature gas entering the expander 53. This has the advantage of making maximum use of the cold energy of the low-temperature gas (hydrogen) while suppressing the premature deterioration of the turbine blades of the expander 53.
[0042] The branched flow expander 36 of the branched expansion line 14 may be replaced with a pressure reducing valve.
[0043] The upstream end of the raw material gas diversion line 16 may be connected downstream of the confluence point of the circulation line 13 in the pre-cooling line 12.
[0044] The pressure reducing valve 55 of the raw gas diversion line 16 can also be installed upstream of the heat exchanger 52 for cooling the diversion gas, that is, between the flow rate control valve 54 and the heat exchanger 52 for cooling the diversion gas.
[0045] An ejector may be provided at the point where the circulation line 13 merges with the pre-cooling line 12. By configuring the system to merge the return gas through the ejector, pressure reducing valves and compressors for pressure adjustment can be omitted. If the compressor can be omitted, power consumption can be further reduced, thereby significantly reducing the overall power consumption of the process.
[0046] Figure 2 shows an example in which a heat exchanger has been added. Specifically, the liquefaction unit 11 has a fourth heat exchanger 33e, which performs heat exchange with the low-temperature gas line 15, located upstream of the circulating compressor 31 in the pre-cooling line 12.
[0047] In this fourth heat exchanger 33e, the raw material gas entering the circulating compressor 31 is cooled by heat exchange with the low-temperature gas, further reducing the power consumption of the circulating compressor 31. In particular, omitting the compressor 35 in the circulation line 13 and providing an ejector (not shown) at the junction with the pre-cooling line 12, as described above, is even more effective in reducing power consumption. [Explanation of symbols]
[0048] 11...Liquefaction device 12…Pre-cooling line 13…Circulation line 14… Branching expansion line 15…Cold gas line 16… Raw material gas diversion line 31... Circulating compressor 32...Expansion valve 33...Heat exchanger group 33a...First heat exchanger 33d…Supercooling heat exchanger 36... Branching flow expander 52… Heat exchanger for flow-dividing gas cooling
Claims
1. A liquefaction apparatus comprising: a pre-cooling line in which a group of heat exchangers consisting of multiple heat exchangers is arranged in series between a circulating compressor that pressurizes the raw material gas and an expansion valve that liquefies the high-pressure, low-temperature raw material gas; a circulation line that passes the low-temperature, low-pressure raw material gas that was not liquefied by isenthalpic expansion by the expansion valve back to the circulating compressor through the group of heat exchangers; and a branch expansion line that branches off from between the heat exchangers in the pre-cooling line and is connected to the upstream side of the circulation line, causing adiabatic expansion of a portion of the pre-cooled raw material gas to merge with the low-temperature, low-pressure raw material gas, A low-temperature gas line is provided through which a low-temperature liquefied gas or low-temperature gas with a lower boiling point than the raw material gas flows, Upstream of the circulating compressor in the pre-cooling line, the upstream end of a raw material gas diversion line, which diverts a portion of the raw material gas, is connected. The downstream end of the aforementioned raw material gas diversion line is connected to the upstream stage of the heat exchanger located at the uppermost position in the circulation line. A heat exchanger for cooling the flow gas is provided between the low-temperature gas line and the flow gas diversion line to exchange heat and lower the temperature of the flow gas in the flow gas diversion line. Liquefaction equipment.
2. A supercooling heat exchanger is provided upstream of the expansion valve in the precooling line, which exchanges heat with a position upstream of the heat exchanger for cooling the diversion gas in the low-temperature gas line. The liquefaction apparatus according to claim 1.
3. At least one of the heat exchangers upstream of the branching point of the branched expansion line in the pre-cooling line exchanges heat with the low-temperature gas line. The liquefaction apparatus according to claim 1 or claim 2.
4. The cryogenic liquefied gas or cryogenic gas flowing through the aforementioned cryogenic gas line is hydrogen. The liquefaction apparatus according to claim 1 or claim 2.
5. The raw material gas is methane. The liquefaction apparatus according to claim 1 or claim 2.
6. A liquefaction method comprising: pressurizing a raw material gas in a circulating compressor; sequentially cooling it in a heat exchanger group consisting of multiple heat exchangers arranged in series and liquefying it with an expansion valve; returning the low-temperature, low-pressure return gas that has not been liquefied by the expansion valve back to the circulating compressor through the heat exchanger group; and generating coldness through adiabatic expansion using a portion of the raw material gas being cooled by the heat exchanger group, and then joining it with the return gas. The aforementioned circulating compressor separates a portion of the raw material gas before it is pressurized, and the gas, which has been cooled by heat exchange with a low-temperature liquefied gas or low-temperature gas with a lower boiling point than the raw material gas, is merged upstream of the heat exchanger group of the return gas returning to the circulating compressor. This increases the amount of heat exchanged by the heat exchanger group and suppresses the amount of gas that undergoes adiabatic expansion and merges with the return gas. Liquefaction method.