JP2007232329A - Cold utilization method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold utilization method for miniaturizing a cold storage facility by efficiently utilizing cold which a low temperature fluid has. <P>SOLUTION: The method of utilizing cold of the low temperature fluid using a heat exchanger comprising third passages 3, 4, 25 coming in thermal contact with a low temperature fluid passage 1 and a high temperature fluid passage 2 is characterized in that (1) CO<SB>2</SB>-containing gas is supplied to the third passages 3, 25, and heat is moved from the CO<SB>2</SB>-containing gas to the lower temperature fluid to heat the low temperature fluid and to solidify CO<SB>2</SB>directly to be stored in the third passage 25 and that (2) heat is moved from the high temperature fluid to the stored solidified CO<SB>2</SB>to sublimate CO<SB>2</SB>and to cool the high temperature fluid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for effectively utilizing the cold energy of a cryogenic fluid, and more particularly to a method for transferring the cold energy of a cryogenic fluid to another heat medium for storage.

  In recent years, demand for natural gas has increased from the viewpoint of environmental problems. Natural gas is usually extracted from a gas field, pretreated such as desulfurization, decarbonation, dehydration, and dehumidification, cooled to about −160 ° C., liquefied, and then transported by a tanker or the like. The transported liquefied natural gas takes a large amount of heat from the outside (seawater, etc.) and gasifies it again for use. Conventionally, cold heat transferred to the outside (seawater or the like) has been discarded without being effectively used. In recent years, effective use of cold energy has been promoted from the viewpoint of effective use of energy. However, since the demand for liquefied natural gas is likely to fluctuate, it has been difficult to stably use cold heat. Thus, it has been proposed to use an appropriate cold storage agent and to use this cold energy by utilizing the solidification latent heat and sensible heat of the cold storage agent.

  For example, Patent Document 1 discloses a cold recovery method that stores cold during the daytime when the demand for natural gas increases and uses the cold stored during the night when the demand decreases. As a regenerator, ammonia, normal butane, normal hexane, normal heptane, and normal octane are disclosed.

  In Patent Document 2, as a cold storage agent for storing cold heat such as liquefied natural gas, lower hydrocarbons (normal pentane, normal hexane, normal heptane, etc.) and oxygen-containing organic compounds (methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone) , Diethyl ether) combinations are disclosed.

  Patent Document 3 discloses a method of storing cold heat during the day when the demand for natural gas increases, and liquefying the natural gas vaporized using the stored cold heat at night when the demand decreases. As a regenerator, a eutectic mixture of ethanol (91.2% by weight) and water (8.8% by weight) is disclosed.

  Patent Document 4 discloses a method in which natural gas is liquefied and stored and then vaporized and supplied again, and a mixture of methanol and 2-propanol is disclosed as a cold storage agent.

  Patent Document 5 discloses a method of storing and effectively using the cold heat of liquefied natural gas, and describes that alcohol or a mixture of alcohol and water is preferable as the cold storage agent.

  Patent Document 6 discloses a method in which generated evaporative gas is liquefied again and returned to a liquefied natural gas tank during a time period when the demand for natural gas decreases, and a mixture of normal hexane and normal pentane (or gasoline) as a cold storage agent. Is disclosed.

  Patent Document 7 discloses a method for using cold heat, which comprises temporarily storing cold heat of liquefied natural gas in the form of solidification latent heat and sensible heat by heat exchange in a cold storage agent, and applying the stored cold heat to a substance on the high temperature side by heat exchange. Has been. At that time, a regenerator is circulated in the process, one of the heat exchangers receives cold heat from the liquefied natural gas, and the other heat exchanger uses a method of giving the obtained cold heat to the high-temperature substance. And as a cold storage agent having fluidity that can store cold in a low temperature region, (1) a mixture of normal hexane and isopentane, (2) a mixture of normal hexane and normal pentane, (3) a mixture of normal hexane and gasoline, (4 ) A mixture of metaxylene and toluene, (5) a mixture of kerosene and gasoline, (6) a mixture of oxoxylene and toluene, (7) a mixture of ethanol and 1-propanol, (8) a mixture of methanol and 1-propanol, ( 9) A mixture of methanol and ethanol, (10) a mixture of 2-propanol and ethanol.

  Patent Document 8 discloses a method of storing cold heat of liquefied natural gas for effective use, and normal pentane is disclosed as a cold storage agent.

  Patent Document 9 discloses a method for effectively storing and storing cold heat of liquefied natural gas, and discloses a mixture of methanol (42%) and ethanol (58%) as a cold storage agent.

  Patent Document 10 discloses a method of storing and utilizing the cold heat of liquefied natural gas. As a cold storage agent, a mixture of ethanol and water or a mixture of ethanol and methanol, preferably ethanol (55 wt%)-methanol (45 % By weight) are disclosed.

  Patent Document 11 discloses a method of storing cold heat of liquefied natural gas and liquefying boil-off gas in a time zone in which the demand for liquefied natural gas decreases using the stored heat, and HFC- 134a, HFC-23, HFC-32, propane and mixtures of these components are disclosed.

  Patent Document 12 discloses a method of storing cold energy of liquefied natural gas and liquefying boil-off gas in a time zone in which the demand for liquefied natural gas decreases using the stored heat. According to this, the cold storage tank is divided into two temperature ranges, and HFC-134a, HFC-23, HFC-32, ethane, propane, butane, pentane and these components are used as the cold storage agents used in the temperature range of −100 ° C. or lower. As a regenerator used in a temperature range of −100 ° C. to −50 ° C., methanol, ethanol, aqueous methanol solution, aqueous ethanol solution, and aqueous methanol-ethanol solution are disclosed.

  In Patent Document 13, a mixture obtained by adding water to an eutectic substance of ethanol (58 wt%)-methanol (42 wt%) as an alcohol-based cold storage agent having a solidification temperature of −150 ° C. and good fluidity at −135 ° C. Is disclosed.

  Patent Document 14 discloses a mixture of isopentane and normal hexane, a mixture of isopentane and normal heptane, a mixture of isohexane and normal hexane, and a mixture of isohexane and normal heptane as a cold storage agent having fluidity.

Patent Document 15 discloses a method in which carbon dioxide is used as a cold storage agent, and cold energy is stored using the latent heat of solidification of carbon dioxide.
Japanese Patent No. 2938878 Japanese Patent No. 2850247 Japanese Patent Laid-Open No. 03-236588 Japanese Patent No. 2688267 JP-A-4-251182 Japanese Patent Laid-Open No. 4-309783 Japanese Patent No. 2979704 Japanese Patent Laid-Open No. 5-263997 Japanese Patent No. 3385384 Japanese Patent No. 3358845 JP-A-11-108298 Japanese Patent Laid-Open No. 11-118099 JP 2000-144123 A JP 2003-73660 A Japanese Patent Laid-Open No. 11-14172

  The methods described in Patent Documents 1 to 14 have a problem in terms of safety because an organic compound corresponding to a dangerous substance specified by the Fire Service Act is used as a cold storage agent.

  Furthermore, in the methods described in Patent Documents 1 to 15, when the amount of cold generated increases, the scale of the container increases and the cold storage facility increases.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for using cold energy that can efficiently use the cold heat of a low-temperature fluid and can reduce the size of a cold energy storage facility.

As a result of intensive studies by the present inventors, CO ₂ is used as a cold storage agent, sublimation latent heat capable of storing and releasing more heat than solidification latent heat and latent heat of fusion is used, and the latent heat is further converted into liquid or gas. It has been found that by storing it in a solid state having a higher density than that, cold energy can be efficiently stored and released, and the cold energy storage facility can be miniaturized, and the present invention has been completed.

The method of using the cold of the present invention that has solved the above problems
A heat exchanger provided with a third flow path that is in thermal contact with the flow path for the low temperature fluid and the flow path for the high temperature fluid is used as a cold storage facility,
(1) A CO ₂ -containing gas is supplied to the third flow path, and heat is transferred from the CO ₂ -containing gas to the low-temperature fluid, whereby the low-temperature fluid is heated and the CO ₂ is directly solidified to make the third Stored in the flow path of
(2) It is characterized by sublimating CO ₂ and cooling the high-temperature fluid by transferring heat from the high-temperature fluid to the stored solidified CO ₂ . At that time, it is preferable to use natural gas as the low-temperature fluid, and examples of the high-temperature fluid include nitrogen gas, oxygen gas, argon gas, dry air, hydrogen gas, or a gas obtained by mixing two or more of these. Is preferably used. In addition, low temperature fluid is supplied to alternately repeat the low flow period and the high flow period,
It is also preferable that the supply amount of the CO ₂ -containing gas while the low-temperature fluid is in the low flow rate period is smaller than the supply amount of the CO ₂ -containing gas during the high flow rate period. Furthermore, it is also preferable to divide the heat exchanger into a plurality of regions in series along the low-temperature fluid flow path, and to change the partial pressure of the CO ₂ gas in the third flow path for each region.

In addition, by applying the above cold energy utilization method,
Using a heat exchanger having a CO ₂ -containing gas channel that is in thermal contact with the low-temperature natural gas channel and the high-temperature hydrogen gas channel,
(1) cold natural gas and CO ₂ containing gas supply, as well as heat the cold natural gas by transferring heat to the cold natural gas from the CO ₂ containing gas, by solidifying the CO ₂ directly CO ₂ containing gas Stored in the flow path,
(2) The natural gas heated in the step (1) is treated by a steam reforming method to produce hydrogen gas,
(3) The hydrogen gas is purified and separated, and is divided into high-purity hydrogen gas and CO ₂ gas containing hydrogen gas,
(4) The CO ₂ gas containing the hydrogen gas obtained in the step (3) is used as the CO ₂ -containing gas in the step (1), and the high purity hydrogen gas obtained in the step (3) is used at a high temperature. Supply to the hydrogen gas flow path,
(5) By transferring heat from the solidified CO ₂ stored in the step (1) to the high-purity hydrogen gas, CO ₂ can be sublimated and the high-purity hydrogen gas can be cooled. Can be cooled. At that time, after having increased directly solidified allowed by the hydrogen concentration of CO ₂ using CO ₂ gas containing hydrogen gas obtained in the step (3) as a CO ₂ containing gas in the step (1), this hydrogen concentration The increased gas is preferably combined with the hydrogen gas obtained in the step (2) and purified in the step (3). Also, by collecting the gas of increased CO ₂ concentration by the CO ₂ sublimes in the above step (5), it can be produced CO ₂ gas efficiently.

According to the cold energy utilization method of the present invention, since the cold energy is stored by directly solidifying the CO ₂ gas, the amount of heat stored per unit volume can be remarkably increased, and the cold energy storage facility can be downsized. .

  In the cold heat utilization method of the present invention, the low temperature fluid flow path for flowing a low temperature fluid (for example, liquefied natural gas) and the high temperature fluid flow path for flowing a high temperature fluid (for example, nitrogen gas) are in thermal contact. The heat exchanger provided with the third flow path is used as a cold storage facility. FIG. 1 is a schematic perspective view showing an example of such a heat exchanger (cold energy storage facility). A heat exchanger (cold storage facility) 20 in FIG. 1 includes a substantially cylindrical container 25, a low-temperature fluid flow path 1 and a high-temperature fluid flow path 2 penetrating the container 25 in the axial direction. The outer wall of 25 is provided with ventilation ports 3 and 4 for supplying and exhausting gas into the container. The ventilation ports 3 and 4 and the inside of the container 25 form a third flow path, and the third flow path is in thermal contact with the low temperature fluid flow path 1 and the high temperature fluid flow path 2. is doing.

And the heat exchanger (cold energy storage equipment) 20 of FIG. 1 is drive | operated as follows. That is, a CO ₂ -containing gas as a cold storage agent is supplied to the inside of the container 25 from the ventilation port 3 or 4, and a low-temperature fluid (liquefied natural gas in the illustrated example) is circulated in the low-temperature fluid channel 1. As a result, heat exchange is performed between the low-temperature fluid (liquefied natural gas) and the CO ₂ -containing gas, and the low-temperature fluid (liquefied natural gas) can be heated (vaporized in the illustrated example). On the CO ₂ -containing gas side, the CO ₂ gas is directly solidified by being cooled by the low-temperature fluid (liquefied natural gas) and accumulated from the heat transfer surface of the low-temperature fluid flow path 1. Therefore, cold heat can be stored inside the container 25 in the form of dry ice.

  Further, in the heat exchanger 20 of FIG. 1, a high-temperature fluid (nitrogen gas in the illustrated example) can be circulated through the high-temperature fluid flow path 2, and the high-temperature fluid (nitrogen gas) is generated by dry ice stored in the container 25. Can be cooled. The dry ice deprived of cold heat by the high-temperature fluid is sublimated and discharged to the outside through the ventilation port 3 or 4.

Using the heat exchanger 20 as described above is extremely safe because cold heat can be stored with CO ₂ . CO ₂ does not fall under the dangerous goods specified by the Fire Service Act, but rather functions as a digestive agent at the fire site.

Further, in the above method, since CO ₂ is directly solidified to store cold heat, the heat exchanger (cold heat storage facility) can be downsized. That general, the amount that can be stored cold heat per unit volume (referred to as a cold storage density, latent heat value obtained by the product of the density of the refrigerant 13A) are water (solidification temperature: 0 ° C.) in which the at 334MJ / m ³ to, for example, in the normal pentane about 74MJ / ^{m 3} (solidification temperature: about -130 ° C.), in ethanol of about 87MJ / ^{m 3} (solidification temperature: about -117 ° C.) are, of water 1 / 5-1 / 3 And much lower. Therefore, even when the same amount of cold energy is stored, if these organic compounds are used as a cold storage agent, an amount 3 to 5 times that of water is required, and the scale of the container increases. On the other hand, although water is excellent in cold storage density as described above, it has a high solidification temperature (0 ° C.), so that it can store cold heat from a cryogenic substance such as liquid natural gas (−120 ° C. or less). It is inappropriate. In order to effectively use the cold energy stored in the ice state, it is necessary to melt the ice with a high-temperature fluid, and the range of use is limited. Therefore, it is desired to lower the solidification temperature. For example, when a hydrophilic organic compound (for example, ethanol) is added to water to lower the solidification temperature, the cold storage density is lowered.

On the other hand, in the utilization method of the cold of the present invention, the sublimation latent heat of CO ₂ is utilized, and the cold storage density is about 900 MJ / m ³ [0.573 MJ / kg (sublimation latent heat of carbon dioxide) × 1570 kg. / M ³ (density of dry ice)], 10 times or more of the organic compound and 2.5 times or more of water. Therefore, even when storing the same amount of cold energy, the volume of the cold storage agent can be reduced to 1/10 or less compared to the organic compound and 2/5 or less compared to water, and a heat exchanger (cold storage facility) 20 can be reduced in size. Further, the sublimation temperature of CO ₂ is about −78.5 ° C. (in the case of normal pressure), which is very suitable for storing cold heat from a cryogenic substance.

  By the way, natural gas has a large demand in the daytime and a small demand in the nighttime. Therefore, when natural gas is used as a low-temperature fluid, the supply of cold heat is excessive during the daytime, and there is a tendency for the cold heat to remain. Even in such a case, according to the cold energy utilization method of the present invention, it is possible to store the excessive cold energy in the daytime in the form of dry ice. At night, the high temperature fluid (nitrogen gas) can be cooled by dry ice stored in the daytime, and cold energy can be used constantly.

When the supply amount of low-temperature fluid repeats the low flow period and high flow period alternately (periodically) as described above (for example, when the supply amount of low-temperature fluid varies between daytime and nighttime), the low-temperature fluid has a low flow rate. the supply amount of CO ₂ containing gas between (e.g. at night) in the period, it is recommended to reduce between (eg daylight) than the supply amount of CO ₂ containing gas in a high flow rate stage.

Specifically, when the supply of cold heat is excessive in the high flow period of the low-temperature fluid, it is desirable to supply the CO ₂ -containing gas sufficiently in the third flow path in order to store the cold heat reliably. .

On the other hand, when the supply of cold heat is insufficient due to the low flow rate of the low-temperature fluid, it is desirable to restrict (particularly stop) the supply of the CO ₂ -containing gas.

The heat exchanger (cold storage facility) 20 is divided into a plurality of regions (thermally independent regions) in series along the low-temperature fluid channel 1 (and the high-temperature fluid channel 2). The partial pressure of CO ₂ in the three flow paths may be changed. Among them as located downstream of the cryogen (liquefied natural gas), it is recommended to adjust so that the partial pressure of CO ₂ is high. The lower the temperature of the low-temperature fluid, the higher the temperature from CO ₂ . If the partial pressure of CO ₂ is increased as it is located downstream of the low-temperature fluid, the sublimation temperature of CO ₂ can be increased as the temperature of the low-temperature fluid increases as it goes downstream. The sublimation latent heat of CO ₂ can always be used. Therefore, the heat exchanger can be made extremely compact.

FIG. 3 is a schematic perspective view showing an example of a heat exchanger having a plurality of regions. In the heat exchanger 21 of FIG. 3, a total of three heat exchange units (thermally independent regions) 8, 9, and 10 are serially arranged along the low temperature fluid flow path 1 (and the high temperature fluid flow path 2). These three heat exchange units 8, 9, 10 constitute a single heat exchanger (cold storage facility) 21 as a whole. Each of the heat exchange units 8, 9, and 10 has the same configuration as that of the heat exchanger 20 shown in FIG. 1, and can supply CO ₂ -containing gas independently of each other.

The operating conditions for processing a low-temperature fluid (for example, liquefied natural gas at about −140 ° C.) using the heat exchanger 21 of FIG. 3 will be described with reference to the CO ₂ state diagram shown in FIG. . That is, in the first heat exchange unit 8 located on the most upstream side of the low-temperature fluid, the partial pressure of CO ₂ is set to about 0.01 to 0.05 MPa, for example. If this partial pressure is set, the sublimation temperature of CO ₂ can be set to about −90 to −100 ° C., and the cold heat of the low-temperature fluid (about −140 ° C.) flowing into the first heat exchange unit can be changed to CO _2. Can be stored using the latent heat of sublimation. In the next second heat exchange unit 9, the partial pressure of CO ₂ is set to about 0.05 to 0.2 MPa. With this partial pressure, the sublimation temperature of CO ₂ can be set to about −90 to −70 ° C. Since the temperature of the liquefied natural gas leaving the first heat exchange unit and flowing into the second heat exchange unit is about −90 to −100 ° C., this cold heat also uses the sublimation latent heat of CO _2. Can be stored. Further, in the third heat exchange unit 10 located on the most downstream side, the partial pressure of CO ₂ is set to about 0.2 to 0.5 MPa. If this partial pressure is set, the sublimation temperature of CO ₂ can be set to about −57 to −70 ° C., and the cold heat of natural gas is changed to CO ₂ as in the case of the second heat exchange unit 9. Can be stored using the latent heat of sublimation.

If the heat exchanger 21 of FIG. 3 is used as described above, the sublimation latent heat of CO ₂ can be used in all regions (heat exchange units 8, 9, 10), so the heat exchanger 21 can be made compact. Can do.

  In FIG. 3, the heat exchanger 21 having a configuration in which the three heat exchange units (thermally independent regions) 8, 9, and 10 are connected is shown. What is necessary is just to select suitably according to the quantity of the cold which has, for example, it can select from the range of about 1-10 pieces, and it is preferable that it is about 2-5 pieces.

The partial pressure of CO ₂ in each heat exchange unit (thermally independent region) is not particularly limited as long as the sublimation latent heat of CO ₂ in the unit (region) can be used. Preferably, the most upstream heat exchanger located on the side of the unit in (thermal independent area), CO ₂ partial pressure to CO ₂ at +. 5 to + 50 ° C. of about temperatures for temperature sublimation of the cryogen cold fluid adjust the, in subsequent heat exchange unit (thermal independent area), CO ₂ minutes as CO ₂ at a temperature of +. 5 to + 50 ° C. of about with respect to the temperature of the cryogen flowing into the unit (area) is sublimated It is recommended to adjust the pressure.

The external shape (container shape) of the heat exchanger (including the heat exchange unit) is not limited to the cylindrical shape as shown in FIGS. 1 and 3, and various shapes can be used. For example, a plate fin heat exchanger that can secure a large amount of heat exchange per unit volume as described in FIG. 3 of JP-A-7-243760 can be used. Further, the penetration direction of the flow path for the low temperature fluid and the flow path for the high temperature fluid is not particularly limited, and these may be branched in the middle. Further, the number of ventilation ports may be one or more, but preferably two or more. If two or more, can be made to flow CO ₂ containing gas in a constant direction, it can be efficiently supplied and discharged the CO ₂ containing gas. Moreover, you may form the 4th flow path for flowing other fluids as needed.

The low-temperature fluid is not limited to the above-mentioned liquefied natural gas, and various fluids can be used as long as the fluid has a temperature lower than the theoretical maximum value of the sublimation temperature of CO ₂ (−56.5 ° C .: refer to the triple point in FIG. 2). Can be used. The temperature of the cryogenic fluid is preferably −60 ° C. or lower, more preferably −80 ° C. or lower, and even more preferably about −100 ° C. or lower. The lower limit of the temperature of the cryogenic fluid is not particularly limited, but is usually about −180 ° C. (for example, about −150 ° C.).

  Specific examples of the cryogenic fluid include natural gas and propane gas. These cryogenic fluids may be any of gas, liquid, and gas-liquid mixture. A preferred cryogenic fluid is natural gas, particularly liquefied natural gas.

  The high temperature fluid is not particularly limited as long as it is a fluid having a temperature higher than that of the low temperature fluid. Preferred high-temperature fluid includes nitrogen gas, oxygen gas, argon gas, dry air, hydrogen gas, or a gas obtained by mixing two or more of these.

Components other than CO ₂ contained in the CO ₂ containing gas is also particularly but not limited to, for example, hydrogen, methane, and the like. The CO ₂ concentration in the CO ₂ -containing gas is, for example, about 30 mol% to 70 mol%, preferably about 40 mol% to 60 mol%.

The above-described cold utilization method (heat exchanger, cold storage facility) of the present invention can be applied to, for example, a low-temperature natural gas (liquefied natural gas) processing plant. That is, according to the cold heat utilization method (heat exchanger) of the present invention, low-temperature natural gas (liquefied natural gas, etc.) is used as the low-temperature fluid, hydrogen gas is used as the high-temperature fluid, and CO ₂ -containing gas is used as the regenerator. Since these are all natural gas or natural gas-derived substances, it is possible to efficiently use cold energy in one processing plant.

  FIG. 4 is a flowchart showing an example of a processing plant to which the heat exchanger (cold storage facility) is applied. The plant of FIG. 4 is roughly divided into a natural gas main supply system 100 and a cold heat utilization system 101 using surplus natural gas. The supply system 100 includes natural gas main supply lines 50a, 50b, and 51, and a first heat exchanger 14 provided in the middle of the main supply lines 50a and 50b. The gas (such as liquefied natural gas) is heated (vaporized) by the heat exchanger 14 and then supplied to a general customer through the supply line 51. The first heat exchanger 14 is distinguished from the heat exchanger (cold storage facility) of the present invention in that it does not include a cold storage unit (dry ice storage unit).

By the way, the demand for natural gas during the daytime is much greater than during the night, and a large amount of natural gas is supplied to the general customers through the main supply lines 50a, 50b, 51 during the daytime. If the balance of quantity is lost, low temperature natural gas will be left over. Therefore, the plant of FIG. 4 is provided with a cold heat utilization system 101 in order to efficiently use the surplus low temperature natural gas (cold heat) during the daytime. This cold heat utilization system 101 is branched from the supply line 50a, and a second heat exchanger (directly connected to the take-out line 52) and a take-out line 52 for taking out excess low-temperature natural gas through the valve B1 in the middle. A cold storage facility) 21, a steam reformer 11 for steam reforming the natural gas heated (vaporized) in the heat exchanger 21, and steam reformed gas (usually about 50 mol% of CO ₂ , Hydrogen refining / separating apparatus [hydrogen pressure swing adsorption (PSA) apparatus] for separating H ₂ (containing about 30 mol% and methane about 15 mol%) into high-purity hydrogen gas and off-gas (main component CO ₂ ) 12 It is constituted by. The heat exchanger (cold energy storage facility) 21 corresponds to the above-described heat exchanger (cold energy storage facility) of the present invention. In the example of FIG. 4, the heat exchanger (cold energy storage facility) 21 of FIG. Is used.

By using such a cold energy utilization system 101, the off-gas generated in the hydrogen refining / separating device 12 can be used as a regenerator (CO ₂ -containing gas) of the heat exchanger (cold energy storage facility) 21, and hydrogen refining and separation. The high purity hydrogen gas generated in the device 12 can be used as a high temperature fluid of the heat exchanger (cold storage facility) 21. Since heat can be exchanged using liquefied natural gas and its derived components (hydrogen gas and off-gas), resources can be used effectively. Furthermore, since heat energy is exchanged between low-temperature natural gas and CO ₂ and hydrogen generated in the steam reformer, the supply of heat energy from the outside or the discharge of heat energy to the outside can be reduced. Excellent in terms of effective use. That is, it can be said that the cold energy utilization system 101 shown in FIG. 4 is environmentally friendly in terms of both resources and thermal energy.

  Since the demand for natural gas decreases at night, the flow rate of low-temperature natural gas in the extraction line 52 decreases (in some cases, the flow rate becomes zero). On the other hand, high-purity hydrogen gas is generated from the hydrogen purification / separation apparatus 12 even at night. Even in such a case, according to the cold energy utilization system 101 of FIG. 4, since the cold energy is stored as dry ice in the heat exchanger (cold energy storage facility) 21 in the daytime, the stored dry ice is used. Thus, the high-purity hydrogen gas at night can be cooled.

  The high-purity hydrogen gas cooled in the daytime and at night is liquefied by the hydrogen liquefier 13 in the example of FIG. And in the example of FIG. 4, since high purity hydrogen gas can be cooled regardless of day and night, liquefied hydrogen can be manufactured stably.

  In the example of FIG. 4, the high-purity hydrogen gas discharge line 65 extending from the hydrogen purification / separation device 12 includes a line 66 heading to the first heat exchanger 14 and a second heat exchanger (cold storage facility). The high-purity hydrogen gas is cooled by both the first and second heat exchangers 14 and 21. The hydrogen gas cooled by the first heat exchanger 14 is also connected to the line 68 through the high-purity hydrogen gas discharge line 67, and together with the high-purity hydrogen gas cooled by the second heat exchanger 21, It is liquefied by the hydrogen liquefier 13.

In the example of FIG. 4, the off-gas discharge line 60 extending from the hydrogen purification / separation apparatus 12 branches into three off-gas supply lines 31, 32, and 33 immediately before the heat exchanger 21. 21 are connected to the heat exchange units 8, 9, and 10 constituting the 21. Valves B2, B3, and B4 are attached to the off-gas supply lines 31, 32, and 33. By adjusting the opening degree of the valves B2, B3, and B4, the heat exchange units 8, 9, and 10 are provided. The partial pressure of CO ₂ can be controlled independently. However, when it is necessary to increase the pressure, the pressure is increased by a compressor or the like (not shown in FIG. 4) and then supplied to the heat exchange unit. When the flow rate of the low-temperature natural gas flowing into the heat exchanger 21 decreases (for example, at night), the valve B5 provided upstream of the branch point of each off gas supply line 31, 32, 33 is closed. As a result, the supply of off-gas to the heat exchanger 21 can be stopped. The remaining off gas can be discharged to the outside through the open line 61 by stopping the supply of the off gas.

Further, in the example of FIG. 4, the ventilation port (exhaust port) of the second heat exchanger (cold storage facility) 21 is connected to one line (recycle line 63) via valves B6, B7, B8. The recycle line 63 is joined to a line (transfer line 62) for transferring the steam reformed gas from the steam reformer 11 to the hydrogen purification / separation apparatus 12. Therefore, hydrogen contained in the off gas can be recycled. For example, when the amount of low-temperature natural gas (cold heat) processed in the second heat exchanger (cold storage facility) 21 is large (for example, during the daytime), CO ₂ is removed from the off-gas as dry ice. Hydrogen concentration increases. By treating the off-gas with an increased hydrogen concentration again with the hydrogen purification / separation apparatus 12, the hydrogen recovery rate can be increased.

In addition, in the example of FIG. 4, the recycle line 63 coming out from the ventilation port (exhaust port) of the second heat exchanger (cold heat utilization device) 21 branches to the CO ₂ recovery line 64 via the valve B9. . Therefore, for example, when the processing amount of the low-temperature natural gas (cold heat) in the second heat exchanger (cold storage facility) 21 is small (for example, at night), the valve B5 is closed and the off gas is supplied to the heat exchanger 21. the stop, from the heat exchanger 21 by CO ₂ gas obtained by sublimation of dry ice is discharged through the ventilation opening (exhaust port). Then, the valve B10 is closed, the valve B9 is opened, and this CO ₂ gas is recovered through the CO ₂ recovery line 64, whereby high-purity CO ₂ gas can be obtained.

  The first heat exchanger of the supply system 100 is not limited to the illustrated example, and various types can be used. For example, the second heat exchanger (cold energy storage facility) 21 of the cold energy utilization system 101 is used. It may be used. Furthermore, in a processing plant for low-temperature natural gas (such as liquefied natural gas), the supply system 100 is not necessarily required, and the natural gas heated by the cold energy utilization system 101 may be supplied to general customers.

  The installation position of the valve is not limited to the illustrated example, and can be installed at an appropriate location as long as it has an equivalent function. Various flow rate control means can be used instead of the valve.

  The second heat exchanger (cold storage facility) is not limited to the illustrated example, and various heat exchangers (cold storage facility) included in the present invention can be used.

FIG. 1 is a schematic perspective view showing an example of a heat exchanger used in the method for utilizing cold energy according to the present invention. FIG. 2 is a state diagram of CO ₂ . FIG. 3 is a schematic perspective view showing an example of a heat exchanger having a plurality of regions used in the cold energy utilization method of the present invention. FIG. 4 is a flowchart showing an example of a processing plant to which the heat exchanger of FIG. 3 is applied.

Explanation of symbols

1. 1. Flow path for cryogenic fluid High temperature fluid flow path 3, 4. Ventilation opening8. Thermally independent area (first heat exchange unit)
9. Thermally independent area (second heat exchange unit)
10. Thermally independent area (third heat exchange unit)
11. Steam reformer 12. 12. Hydrogen purification / separation apparatus Hydrogen liquefier 14. 1st heat exchanger 20,21. Heat exchanger 25. Containers 31, 32, 33. Off-gas supply lines 50a, 50b, 51. Main supply line 52. Take-out line 60. Off-gas discharge line 61. Open line 62. Transfer line 63. Recycle line 64. CO ₂ recovery line 65, 66. High purity hydrogen gas discharge line 67,68. High purity hydrogen gas discharge line 100. This supply system 101. Cold heat utilization systems B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11. valve

Claims (8)

Using a heat exchanger having a third flow path that is in thermal contact with the flow path for the low temperature fluid and the flow path for the high temperature fluid,
(1) Supplying a CO ₂ -containing gas to the third flow path, and transferring heat from the CO ₂ -containing gas to a low-temperature fluid, thereby heating the low-temperature fluid and directly solidifying CO ₂ 3 in the flow path,
(2) A method for utilizing cold energy of a low-temperature fluid, wherein heat is transferred from the high-temperature fluid to the stored solidified CO ₂ to sublimate the CO ₂ and cool the high-temperature fluid.   The cold utilization method according to claim 1, wherein the low-temperature fluid is natural gas.   The cold utilization method according to claim 1 or 2, wherein the high-temperature fluid is nitrogen gas, oxygen gas, argon gas, dry air, hydrogen gas, or a gas obtained by mixing two or more of these. The low-temperature fluid is supplied so as to alternate between the low flow rate period and the high flow rate period,
The supply amount of the CO ₂ -containing gas while the low-temperature fluid is in the low flow rate period is made smaller than the supply amount of the CO ₂ -containing gas during the high flow rate period. The method of using cold energy as described in 1. The heat exchanger according to claim 1 is divided into a plurality of regions in series along the flow path for the low-temperature fluid, and the cold heat that changes the partial pressure of the CO ₂ gas in the third flow path for each region. How to Use. Using a heat exchanger having a CO ₂ -containing gas channel that is in thermal contact with the low-temperature natural gas channel and the high-temperature hydrogen gas channel,
(1) cold natural gas and CO ₂ containing gas supply, as well as heat the cold natural gas by transferring heat to the cold natural gas from the CO ₂ containing gas, by solidifying the CO ₂ directly CO ₂ containing gas Stored in the flow path,
(2) The natural gas heated in the step (1) is treated by a steam reforming method to produce hydrogen gas,
(3) The hydrogen gas is purified and separated, and is divided into high-purity hydrogen gas and CO ₂ gas containing hydrogen gas,
(4) The CO ₂ gas containing the hydrogen gas obtained in the step (3) is used as the CO ₂ -containing gas in the step (1), and the high purity hydrogen gas obtained in the step (3) is used at a high temperature. Supply to the hydrogen gas flow path,
(5) wherein by moving the heat from the solidified CO ₂ which has been in a high purity hydrogen gas stored in step (1), hydrogen cooling, characterized in that to cool the high-purity hydrogen gas with sublimating the CO ₂ Law. The CO ₂ gas containing hydrogen gas obtained in the step (3) is used as the CO ₂ -containing gas in the step (1) to directly solidify CO ₂ to increase the hydrogen concentration, and then the gas having an increased hydrogen concentration. Is combined with the hydrogen gas obtained in the step (2) and purified in the step (3). A method for producing CO ₂ gas, comprising collecting a gas having an increased CO ₂ concentration as a result of sublimation of CO _{2 in} step (5) according to claim 6.

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