JPH11118099A - Cold accumulating device, cold accumulating method, and method for reliquefying bog - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold accumulating device usable to accumulate cold of a material having very low temperature <=-100 deg.C, having a large cold accumulating amount per unit mass, and using a cold accumulating agent having high heat transferring performance; a cold accumulating method of it; and a reliquefying method of BOG by the cold of LNG. SOLUTION: A first cold accumulating tank 4 capable of accumulating cold as sensible heat or latent heat of solidification in a pressure vessel in the temperature range <=-100 deg.C and filled with a first cold accumulating agent selected from a group of HFC-134a, HFC-23, HFC-32, ethane, propane, butane and pentane, and a second cold accumulating tank 7 capable of accumulating cold as sensible heat or latent heat of solidification in a pressure vessel in the temperature range of -100 deg.C to -50 deg.C and filled with a second cold accumulating agent of methanol, ethanol, a mixture of methanol and water a mixture of ethanol and water, or a mixture of methanol, ethanol and water are connected in series. LNG is allowed to flow the cold accumulating tanks in order, and cold is accumulated by heat exchanging through respective cold accumulating agents via partition walls to reliquefy BOG by making use of accumulated cold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to liquefied natural gas (LN).
G) and natural gas (NG)
A method and an apparatus for storing cold energy in a regenerator tank filled with a regenerator, and a method for regenerating boil-off gas (abbreviated as BOG) as LNG when NG is not supplied using the accumulated cold energy. The present invention relates to a method and an apparatus for liquefaction.

[0002]

2. Description of the Related Art LNG is stored in a cold storage tank and is dispensed as a thermal power plant or NG for city gas. NG
LNG that is paid out at the time of demand for NG
Therefore, there was a problem that low-temperature seawater was generated and affected the environment. In addition, the LNG tank is kept cool, but BOG is generated when part of LNG is constantly vaporized by heat from the outside, or partially when LNG is paid out or received from a transport ship. . The amount of BOG generated is about 0.001 to 0.1% / hr based on the stored amount.
It is. To recover and liquefy BOG with LNG, use LN
It is thermally advantageous to use the cold heat at the time of dispensing G, but at night or late at night when the amount of LNG to be dispensed is low.
BOG cannot be directly liquefied using the cold heat at the time of dispensing NG.

[0003] As a processing method of BOG, L
Refrigerant is cooled by utilizing cold generated when NG is vaporized, and when shipment is reduced or stopped, BOG is re-liquefied using the cooled refrigerant and returned to the LNG tank (Japanese Patent Laid-Open No. Japanese Patent Application Laid-Open No. 98300/98), and a method of mixing and using the NG to be paid out is known. Also, LNG
For example, Japanese Patent Application Laid-Open No. 60-98300 and Japanese Patent Application Laid-Open No.
No. 3997 discloses isopentane (freezing point −160 ° C.) having a low freezing point and high boiling point, and isobutane (freezing point −14).
A technique is disclosed in which 5 ° C.) or propane (freezing point −187.1 ° C.) is used as a regenerator, and the regenerator is used by flowing through a heat exchanger. However, since the regenerator does not solidify in these regenerators, only the sensible heat can be used for the regenerator, and a large-scale regenerator is required to store a large amount of cold energy of LNG. In Japanese Patent Application Laid-Open No. Hei 5-263997, there is a material such as n-pentane (freezing point-129.7 ° C.) that can be solidified and utilize sensible heat and latent heat near the freezing point. That is, in a region of about -100 ° C. or higher, only a sensible heat having a small regenerative capacity can be used, and there is a problem that the regenerative equipment becomes large.

JP-A-3-236588 and JP-A-4
Japanese Patent No. 251182 discloses that a eutectic mixture of ethanol / water is used as a regenerator, a tube is provided inside a regenerator filled with the regenerator, and BOG is flowed through the tube. A method for reliquefying BOG is disclosed. By using the eutectic mixture of ethanol / water as the regenerator, the regenerator can utilize not only sensible heat but also latent heat during crystallization of the eutectic mixture for regenerative storage. However, since the freezing point of ethanol is −114.4 ° C. and the freezing point of water is 0 ° C., the freezing point of the ethanol / water mixture is high, and the regenerator alone has a high regenerative temperature level, which is advantageous in terms of regenerative temperature. Hard to say.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for accumulating cold energy of LNG without causing the above-mentioned problems, and to provide an LNG system utilizing the method.
It is an object of the present invention to provide a method and an apparatus for liquefying BOG generated when NG is not required.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies and found that such a problem can be solved.
The present invention has been completed.

That is, a first aspect of the present invention is a first regenerator containing a first regenerator capable of storing cold heat as sensible heat and latent heat of solidification in a temperature range of -100 ° C. or less in a pressure vessel. Inside the pressure vessel, connected in series with a second cold storage tank filled with a second cold storage agent capable of storing cold heat as sensible heat and latent heat of solidification in a temperature range of -100 ° C or more and -50 ° C or less, The present invention relates to a cool storage device characterized in that a heat medium is circulated through the cool storage tank in order so that heat can be exchanged with each of the cool storage agents via partition walls.
Thereby, for example, it is possible to store the cold heat of the dispensed LNG as a sensible heat and a latent heat in a cool storage tank filled with a cool storage agent, and it is possible to reduce the size of the cool storage tank as compared with the case where the cool storage is performed only with the sensible heat. Moreover, the cold of LNG is reduced by -1.
Since the cold storage can be performed at two temperature levels of 00 ° C. or lower and −100 ° C. or higher, the thermal efficiency is high.

A second aspect of the present invention is that the first regenerator is HFC
-134a, HFC-23, HFC-32, ethane, propane, butane and pentane. The cold storage device according to the first aspect of the present invention, characterized in that the cold storage agent is at least one selected from the group consisting of: . Third of the present invention
Means that the first regenerator is HFC-134a / HFC-23
And the molar fraction of each component is 0.8 to 0.4 / 0.2.
A mixture of 0.6 or HFC-134a / HF
In the mixture of C-32, the mole fraction of each component is 0.8 to 0.5.
The present invention relates to the cold storage device according to the second aspect of the present invention, wherein the cold storage agent is any one of a mixture of /0.2 to 0.5. A fourth aspect of the present invention is characterized in that the second regenerator is any one of methanol, ethanol, a methanol / water mixture, an ethanol / water mixture, and a methanol / ethanol / water mixture. First
The present invention relates to a cool storage device according to any one of (1) to (3).
These provide a cool storage agent that can be used specifically,
The required regenerator can be selected.

According to a fifth aspect of the present invention, using the regenerator according to any one of the first to fourth aspects of the present invention, LNG is circulated from the first regenerator to the second regenerator, the first regenerator and the second regenerator. The present invention relates to a method for storing LNG cold energy, wherein the cold energy of LNG is stored in a first regenerator and a second regenerator by exchanging heat with the regenerator through a partition. Thereby, for example, it is possible to store the cold heat of the dispensed LNG as a sensible heat and a latent heat in a cool storage tank filled with a cool storage agent, and it is possible to reduce the size of the cool storage tank as compared with the case where the cool storage is performed only with the sensible heat. In addition, the cold heat of LNG is -100
The thermal efficiency is high because cold can be stored at two temperature levels of below -100 ° C and above -100 ° C.

A sixth aspect of the present invention is the LN according to the fifth aspect of the present invention.
The BOG is circulated from the second regenerator to the first regenerator using the first regenerator and the second regenerator stored by the cold energy storage method, and the second regenerator and the first regenerator are stored. The present invention relates to a method for reliquefying BOG, wherein the BOG is liquefied by exchanging heat with the agent through partition walls. Thereby, if necessary, BOG can be re-liquefied by utilizing the cold heat stored, and -1
Since heat is exchanged in two stages of 00 ° C or lower and -100 ° C or higher, thermal efficiency is high, and almost all of BOG can be reliquefied when LNG is not supplied.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION LNG is usually composed of a saturated hydrocarbon having 1 to 5 carbon atoms and containing methane as a main component, and cooled to about -160 to -180 ° C under normal pressure or pressure to liquefy. It is stored and the vaporization temperature at normal pressure is -16
1 ° C. Therefore, the latent heat of evaporation and / or the sensible heat until the LNG evaporates and becomes NG at the outside temperature can be stored as cold heat. Further, the BOG can be re-liquefied using the stored cold heat. As described above, natural gas is a multi-component mixture containing methane as a main component, and its composition slightly varies depending on the place of production. Therefore, the boiling point and dew point of BOG also differ depending on the type of natural gas, but the boiling points show almost the same value. BOG accumulates in the upper part of the LNG tank at almost normal pressure, and its temperature is about -160.
-100 ° C, the main component is methane, the boiling point at normal pressure is about -161 ° C, the liquefaction temperature in the state of being compressed to 4 atm is about -140 ° C, and the liquefaction temperature in the state of being compressed to 40 atm. The boiling point is about -81 ° C.

In the present invention, the dispensing LNG is defined as N L for a thermal power plant or city gas from a cooled LNG tank.
LNG is paid out as G, and the demand period is LNG
NG refers to the period during which the NG is paid out for the use, and the non-demand period refers to the period during which the amount paid out for the use is reduced or zero. Therefore, for example, the demand period is daytime, and the non-demand period is nighttime or early morning or a shutdown period of a thermal power plant or the like. When necessary, for example, when cold is used to liquefy BOG. BOG is paid out as NG for thermal power plants and city gas during demand periods, but is generated at a substantially constant rate due to external heat during non-demand periods and accumulates in the upper part of the LNG tank. To re-liquefy the BOG by the regenerator. Therefore, in the present invention, BOG is changed to LNG.
There is no need to store large quantities in the upper part of the tank.

The BOG may be compressed by a compressor and liquefied by a regenerator, or may be precooled and then liquefied by a regenerator. As a method of pre-cooling, a temperature of about −50 ° C. higher than the temperature of the regenerator used in the present invention is used.
It can exchange heat at normal temperature, and cools the LNG that has been heat-exchanged by the regenerator in the present invention until it is dispensed and becomes NG (about 5 ° C.) (for example, provided between the second regenerator and the superheater). ) Can be stored and used. Further, when the pump power required for discharging BOG and increasing the pressure to the pressure of NG is larger than the pump power required for liquefaction of BOG, the BOG is utilized by utilizing the cold stored in cold storage during LNG discharge such as during the day. It may be liquefied.

Thereafter, LNG and N generated by heating LNG are heated.
G, BOG or working fluid may be generically referred to as fluid. The first regenerator used in the first regenerator in the present invention is-
Cold storage at 100 ° C or less, preferably -120 ° C or more
A regenerator suitable for use at about -200 ° C. The freezing agent has a freezing point of -100 ° C or lower, and is a medium in which cold heat is stored as sensible heat and solidifying latent heat of the cool storage agent. It is in a liquid state at a temperature, and has high heat transfer efficiency even during solidification.

As the first regenerator, HFC-134 is used.
a, HFC-23, HFC-32, ethane, propane,
A regenerator comprising at least one selected from the group consisting of butane, pentane and a mixture thereof is used. In particular, H
The mixture of FC-134a / HFC-23, in which the molar fraction of each component is 0.8 to 0.4 / 0.2 to 0.6, contains a eutectic point and thus exhibits a decrease in melting point. Most of the liquids are kept in a liquid state up to about -160 ° C., and when they reach a freezing point, they solidify and cool. HFC-134a / HFC
-32, wherein the molar fraction of each component is 0.8 to 0.5 /
The same applies to a mixture having a concentration of 0.2 to 0.5, and most of the regenerator keeps a liquid state up to about -160 ° C, and solidifies and cools when reaching a freezing point. In the two examples of the above-mentioned eutectic mixture, the melting point of the regenerator can be optionally changed by changing the composition of the mixture. Similarly HFC
-134a to which HFC-23 and HFC-32 are added is also a eutectic mixture, exhibits a melting point drop, and can be used in the same manner as described above. Ethane, propane, butane, pentane and mixtures thereof have high solubility in HFC-134a, and a mixture containing at least one of these hydrocarbon components and HFC-134a has a temperature of -120 ° C.
Liquid state at temperatures up to room temperature above -120 ° C
A solid solution can be formed below.

In the present invention, the first regenerator used in the first regenerator is a pure substance or a mixture. In the case of a mixture, the vapor pressure is reduced or the ignition is reduced as compared with the case where each component is a pure substance. Flammability, and in some cases can be non-flammable. In addition, the regenerator has little corrosiveness to metals, and can be used for a long time by being enclosed in a metal pressure-resistant container. Further, the regenerator of the present invention has low ozone destruction properties and high safety even when leaked to the outside.

Next, the second regenerator used in the second regenerator according to the present invention will be described.
Is at least one selected from the group consisting of methanol, ethanol, water and mixtures thereof. The melting point of these components is methanol-9 for pure components.
Since the temperature is 7.8 ° C., ethanol is 114.4 ° C., and water is 0 ° C., by adjusting the composition of these mixtures, the melting point is −
It can be set to 100 ° C. or higher. Therefore, the cold storage temperature of the first cold storage tank is set to -160 to -100 ° C, and the cold storage temperature of the second cold storage tank is higher than the cold storage temperature of the first cold storage tank by -1.
By setting the temperature to 00 to -50 ° C, the cold heat of LNG can be stored at two temperature levels, and if necessary, the BOG can be re-liquefied using the stored heat. That is, according to the present invention, utilization of LNG cold energy is improved.

The material and thickness of the pressure vessel constituting the first and second regenerators are selected according to the conditions of use. However, cooling and heating are repeatedly performed between a low temperature such as −100 ° C. or lower and normal temperature, and the device can be used for a long time, preferably for 10 years or more. Further, those having good thermal conductivity are preferable from the viewpoint of cold storage and reuse of cold heat. Examples of the material include aluminum, aluminum alloy, copper, copper-nickel alloy, chromium-nickel alloy, nickel, iron, stainless steel, austenitic stainless steel, titanium, and titanium alloy. The surface of the pressure vessel may be coated with glass, ceramic, graphite or the like to increase corrosion resistance. Further, the pressure vessel may have a pattern such as unevenness on its surface, may be magnetized, or may be provided with an oxide film, if necessary.

A regenerator is filled in the above-mentioned pressure vessel.
The regenerator may be cooled and sealed in a liquid state, or may be sealed by cooling the pressure vessel with gas. The amount of the cold storage agent sealed in the pressure-resistant container is determined based on the expansion coefficient of the cold storage agent. For those with a large expansion coefficient during solidification, the capacity of
A safety factor of 0% may be expected. The filling port when the regenerator is sealed in the pressure vessel can be closed by welding, screwing, or the like.

In the present invention, "a first cold storage tank filled with a first cold storage agent for a first cold storage tank and a second cold storage tank filled with a second cold storage agent are connected in series. LNG is exchanged between the first regenerator and the second regenerator via the partition wall. "
The description will be made about the "heat exchange via the partition wall" in the above. The first regenerator and the second regenerator have a partition wall, for example, a tube, through which a fluid for heat exchange with the regenerator is provided inside the regenerator, and a regenerator is filled outside the tube inside the regenerator. You. The number of tubes is the number required for heat exchange. The shape of the tube may be a straight shape, a snake-like tube or a spiral shape. Therefore, in this case, the regenerator has a shape like a shell-and-tube heat exchanger. The partition is not limited to a tube. For example, a plurality of plate-shaped partitions may be provided inside the regenerator to form a fluid passage, and LNG or the like may be passed through the passage. As described above, the phrase “perform heat exchange through the partition walls” means that the cold storage agent is mixed with LNG or NNG.
Since G or BOG means that heat exchange is performed by heat conduction across the partition, the regenerator does not mix with LNG, NG, or BOG.

Referring to FIG. 1 as an example of the present invention, a description will be given of a method of accumulating the cold heat of the dispensed LNG and utilizing this to re-liquefy BOG. LNG tank 1 (capacity 10
10,000 kl), LNG is at normal pressure or about 0.15 kgf / cm ²
With slight pressure, stored at around -160 ° C, LN
BOG on the top of G at normal pressure or slightly pressurized -160 ~
Storing at -100 ° C. The amount of LNG paid out is, for example, 100 t / hr during daytime demand, and 30
It is dispensed by being pressurized to kgf / cm ² , and the dispensed amount at the time of non-demand at night is almost 0 t / hr. The amount of BOG generated is always 2 t / hr on average. The first regenerator 4 is a shell-and-tube type pressure vessel. Discharge LNG2 is distributed to the tube side, and a space other than the LNG distribution tube in the regenerator, that is, the shell side is filled with a regenerator.
The first regenerator 5 filled in the first regenerator 4 is HFC-
134a, HFC-23, HFC-32, ethane, propane, butane, pentane and a mixture thereof. The second regenerator 7 is also a shell-and-tube type pressure vessel, and LNG and / or NG after passing through the first regenerator 4 is circulated on the tube 12 side, and the LN in the second regenerator is
The space other than the G circulation tube, that is, the shell side is filled with the second regenerator. The second regenerator 13 is methanol, ethanol, a mixture of methanol / water, a mixture of ethanol / water, or a ternary mixture of methanol / ethanol / water.

At the time of demand, the discharged LNG 2 that has left the LNG tank 1 is supplied to the LNG distribution tube 6 of the first regenerator 4 and stored in the first regenerator 5. The LNG and / or NG that has left the first cold storage tank 4 is supplied to the second cold storage tank 7,
Cold heat on the higher temperature side is stored. The NG that has exited the second regenerator 7 is supplied to the superheater 8 to have a predetermined temperature, and is discharged as NG. As the superheater 8, a system for spraying seawater is used. Next, at the time of demand, the BOG 3 stored in the upper part of the LNG tank 1 is compressed by the BOG compressor 10 to 3 to 20 kgf / cm ^2, and the discharged LNG is discharged.
Dispensing LNG2, which is reliquefied by being directly mixed with BOG 2 and combined with BOG, passes through the first cold storage tank 4 and the second cold storage tank 7 in this order, and gives the cold energy to the cold storage agent in each cold storage tank,
The NG 2 itself is vaporized, and becomes NG further heated to a 5 ° C. level by the superheater 8.

On the other hand, at the time of non-demand, BOG 3 accumulated in the upper part of LNG tank 1 is reduced by BOG compressor 10 to 3
２０20 kgf / cm ² , as shown by the dotted line in FIG.
After being supplied to the second regenerator 7 and cooled, the first regenerator 4
Is supplied to the LNG distribution tube 6 and cooled by the regenerator 5 to become a reliquefied BOG 11 and returned to the LNG tank 1.

[0024]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. (Embodiment 1) In the apparatus shown in FIG.
Has LNG stored at normal pressure and -161 ° C.
BOG accumulates at -160 ° C. at normal pressure in the upper part of NG. LNG payout is 100t / h during daytime demand
At r, the pump is pressurized to 30 kgf / cm ² by the pump and paid out, and the payout amount at night when there is no demand is 0 t / hr.
The first regenerator 4 has a diameter of 3 m, a length of 13 m, and a volume of 70 m.
^This is a regenerator tank (volume of the regenerator including the tube volume), in which an LNG circulation tube is provided. The shell side space other than the LNG circulation tube in the first regenerator is filled with the regenerator shown in Table 1. Have been. Further, an NG flow tube is provided in the second regenerator 7, and the N
A space other than the G circulation tube is filled with a mixed regenerator (second regenerator) of ethanol / water. On demand, L
The delivery LNG 2 that has left the NG tank 1 is stored in the first regenerator 4
And stored in the cold storage agent 5 surrounding the outside of the tube. NG out of the first regenerator 4
Was supplied to the second regenerator 7, and cold heat of a higher temperature was stored. The NG that exited the second regenerator 7 was supplied to a seawater sprinkler superheater 8, set to a predetermined temperature, and discharged as NG. Table 1 shows the results. The transfer of cold from the LNG to the regenerator was good.

[0025]

[Table 1]

(Embodiment 2) The BOG accumulated in the upper layer of the LNG tank is compressed to a pressure of 35 kgf / cm ² when the LNG is not required, and the pre-cooling is performed in the cold storage device obtained in the first embodiment. BO pre-cooled to -50 ° C by equipment (not shown, for example, provided between the second regenerator and superheater)
G can be continuously supplied at 2 t / hr for about 6 hours, and the entire amount of the supplied BOG can be liquefied and returned to the LNG tank 1.

[0027]

According to the present invention, it is possible to store the chilled heat of the dispensed LNG as sensible heat and latent heat in a regenerator filled with a regenerator, and to reduce the size of the regenerator as compared with the case where only the sensible heat is used. can do. Furthermore, the first
The cold storage temperature of the cold storage tank is set to -100 ° C or lower, the cold storage temperature of the second cold storage tank is set to -100 ° C or higher, which is higher than the cold storage temperature of the first cold storage tank, and the cold heat of LNG is stored at two temperature levels. If necessary, BOG can be re-liquefied using the cold storage heat. In addition, by utilizing the cold energy stored and cooled, almost all of the BOG is reliquefied when LNG is not supplied, and
It can be returned to the NG storage tank.

[Brief description of the drawings]

FIG. 1 LNG cold heat storage and BO using cold storage heat
It is a flowchart which shows the reliquefaction of G. The dashed line is B when not in demand
5 shows the flow of OG after compression.

[Explanation of symbols]

 Reference Signs List 1 LNG tank 2 Dispensing LNG 3 BOG 4 First regenerator 5 First regenerator 6 LNG distribution tube 7 Second regenerator 8 Superheater 9 NG 10 BOG compressor 11 Reliquefied BOG 12 NG distribution tube 13 Second regenerator Agent

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Haruma Asakawa 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Heavy Industries, Ltd.

Claims (6)

[Claims] 1. A first cold storage tank filled with a first cold storage agent capable of storing cold heat as sensible heat and latent heat of solidification in a temperature range of −100 ° C. or less, inside a pressure vessel, and inside the pressure vessel. And a second regenerator filled with a second regenerator capable of storing cold heat as sensible heat and latent heat of solidification in a temperature range of -100 ° C or higher and -50 ° C or lower. A regenerator, wherein a medium is circulated so that heat can be exchanged with each of the regenerators via partition walls. 2. The method according to claim 1, wherein the first regenerator is HFC-134a,
The regenerator according to claim 1, wherein the regenerator is at least one selected from the group consisting of FC-23, HFC-32, ethane, propane, butane, and pentane. 3. The method according to claim 1, wherein the first regenerator is HFC-134a / H.
In the mixture of FC-23, the mole fraction of each component is 0.8 to 0.1.
A mixture of 4 / 0.2-0.6, or HFC-13
In the mixture of 4a / HFC-32, the mole fraction of each component was 0.1.
The regenerator according to claim 2, wherein the regenerator is any one of a mixture of 8 to 0.5 / 0.2 to 0.5. 4. The regenerator according to claim 1, wherein the second regenerator is any one of methanol, ethanol, a methanol / water mixture, an ethanol / water mixture, and a methanol / ethanol / water mixture. A cold storage device according to any one of the above. 5. Using the cool storage device according to claim 1, flowing LNG from the first cool storage tank to the second cool storage tank,
LNG cold energy storage characterized by storing cold energy of LNG in the first cold energy storage medium and the second cold energy storage medium by exchanging heat with the first cold energy storage medium and the second cold energy storage medium through the partition walls, respectively. Method. 6. BOG is circulated from the second regenerator to the first regenerator using the first regenerator and the second regenerator stored by the method for storing LNG cold energy according to claim 5.
A method for reliquefying BOG, comprising liquefying BOG by exchanging heat with a second regenerative agent and a first regenerative agent through respective partition walls.