JPH1047598A - Manufacture of dry ice and liquefied nitrogen and device thereof, and re-liquefying method of boil-off gas and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a liquefied nitrogen efficiently by utilizing the temperature of LNG effectively by cooling a combustion exhaust gas by utilizing the temperature of a discharged LNG, producing a dry ice by the solidification of carbon dioxide gas contained in the combustion exhaust gas and separating it, and compressing and cooling a residual exhaust gas further. SOLUTION: LNG 11 coming out from LNG storage 1 is heat exchanged with a compression gas 13 by a heat exchanger 2 and NG 12 is made by the heat exchange with a combustion exhaust gas 10 by a fluidized bed type heat exchanger 3. While, the combustion exhaust gas 10 is cooled to about -40 to -70 deg.C by the heat exchange with NG gas 12 and the minute particle shape powder body of a dry ice is generated in the fluidized bed and this is separated from the residual exhaust gas by a cyclone 21 and stored in a dry ice storage 20. Then, the residual exhaust gas is supplied to a gas compressor 4 through a filter 22 to form a compression gas 13 and cooled by the heat exchange to LNG 11 by the heat exchanger 2 and further, after being heat exchanged to the low temperature gas 17 and cooled by the low temperature air heat exchanger 9, its one part is made to a liquefied nitrogen 14 by a adiabatic expansion device 5 and stored in a storage 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to liquefied natural gas (LN).
G), a method and an apparatus for producing dry ice and liquefied nitrogen by using cold heat when supplying as natural gas (abbreviated as NG), and an apparatus for producing dry ice and liquefied nitrogen. Boil-off gas at the time of supply (LNG is vaporized and accumulated in the upper part of the LNG storage tank: abbreviated as BOG)
And a device for reliquefying LNG as LNG.

[0002]

2. Description of the Related Art LNG is stored in a cold storage tank, and is vaporized and pressurized at the time of NG supply and discharged as a thermal power plant or NG for city gas. LNG paid out at the time of demand for NG is normally disposed of by heat exchange with seawater to be heated and vaporized to make NG. Therefore, there is a problem that low-temperature seawater is generated and affects the environment.

[0003] The LNG tank is kept cool,
Part of LNG is constantly vaporized due to heat from the outside, or BOG is generated in an unsteady state when LNG is dispensed or received from a transport ship due to pre-cooling of piping and equipment. I do. The stationary BOG generation amount is about 0.001 to 0.1% / hr based on the storage amount. Thus, there has been a demand for an effective method of treating BOG that is constantly generated regardless of day or night.

Here, L obtained by reliquefying BOG is
The results of a review of the prior art BOG reliquefaction process from the perspective of returning NG to the LNG tank are shown below.

(A) Japanese Patent Application Laid-Open No. Sho 50-2 discloses a method utilizing a liquefaction cycle based on a combination of compression, cooling and expansion.
No. 2771 discloses a method using BOG itself as a working medium, and JP-A-57-65792 discloses a method using ammonia as an intermediate refrigerant.
No. 583 discloses a method based on a closed loop cycle using nitrogen as a working medium.

[0006] (b) JP-A-60-98300 discloses isopentane, which stores LNG cold in the daytime when gas supply load is high and re-liquefies BOG using cold storage in the night when light load is low. Japanese Patent Laid-Open Publication No. Hei 2-157583 discloses a method of using a hydrocarbon such as isobutane as a refrigerant and storing the cold using the sensible heat and latent heat. There is disclosed a method of storing cold using the same.

[0007] (c) As for the LNG vaporization operation at the time of gas supply and re-liquefaction of BOG using LNG cold heat, JP-A-4-370499 discloses that BOG is compressed, cooled, liquefied, and liquefied BOG. Japanese Patent Application Laid-Open No. Sho 62-147197 discloses a method for discharging gas and mixing it with LNG to constitute a BOG liquefaction cycle and refluxing liquefied BOG to a storage tank.

(D) A method for facilitating reliquefaction by adding a high-boiling component to BOG is disclosed in JP-A-2-240.
Japanese Patent Publication No. 499 discloses a method of adding a hydrocarbon having 2 to 4 carbon atoms after heating BOG, and Japanese Patent Application Laid-Open No. 3-41518 discloses a method of reliquefying heavy components of BOG to reduce the nitrogen concentration in BOG. A method for recycling into containers is disclosed.

In the above-mentioned processing method, the processing method (a) applies a liquefaction cycle to BOG, and can be operated regardless of the time zone, but is not an effective use process of LNG cold heat.

In the processing method (b), LNG cold energy is stored, so that BOG can be re-liquefied even at night when gas supply is interrupted or sharply reduced, and LNG cold energy is used, so that BOG is used.
Although the power cost for liquefaction can be reduced, there is a problem that the regenerator tank becomes large in view of the regenerative characteristics of the regenerator.

Since the processing method (c) does not store cold,
BOG re-liquefaction is possible only when LNG is paid out.
There is a problem that BOG cannot be reliquefied at night when OG treatment is the most problematic.

[0012] The treatment method of (d) is the BO method at the time of BOG reliquefaction.
To increase the dew point of G, heavy hydrocarbons are added to BOG
It is only an auxiliary means for facilitating the re-liquefaction of BOG, and BOG can be re-liquefied only during LNG dispensing because it does not store cold. However, there is a problem that BOG re-liquefaction cannot be performed at night when BOG treatment is the most problematic. .

As described above, the conventionally proposed B
Among the OG processing methods, a preferred method is to cool the refrigerant or cold storage material using cold generated during the vaporization of LNG at the time of dispensing, and when the demand decreases or stops,
A method (b) in which BOG is re-liquefied by using the cooled heat of the cooled refrigerant or cold storage material and returned to the LNG tank (Japanese Patent Application Laid-Open No. 60-9 / 1985)
No. 8300). However, as described above, this method also has a problem that it is necessary to increase the size of the regenerator. In addition, as a peripheral technology related to BOG re-liquefaction, it is possible to mix with NG to be paid out or use it to liquefy air using cold heat and rectify it to produce liquefied nitrogen, liquefied oxygen, and liquefied argon together. It is well known that liquefied carbon dioxide and dry ice can be produced together by cooling carbon dioxide.

The above description is summarized below. L paid out as NG for thermal power plants and city gas
The amount of NG fluctuates greatly depending on the time zone and season. on the other hand,
BOG is constantly and unsteadily generated, including day and night, when LNG is received or stored in the LNG tank, or when NG is dispensed. During the daytime when the amount of LNG to be dispensed is large, processing can be performed by compressing the BOG and directly mixing and consuming it with the dispensed LNG, or indirectly mixing and re-liquefying it and returning it to the LNG tank. But,
When the payment of LNG is reduced or not at night or in the early morning, the BOG whose processing volume fluctuates irregularly can be processed stably, and the compact that can effectively use the LNG cold heat,
Further, further establishment of an energy-saving BOG processing technology is desired.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for effectively utilizing the cold heat of LNG and a method for efficiently liquefying BOG whose generation amount fluctuates without causing the above problems. It is to provide a device.

[0016]

Means for Solving the Problems The present inventors have conducted intensive studies on the peripheral technology of LNG processing in order to solve the above-mentioned problems. As a result, the latent heat of vaporization until LNG evaporates and becomes NG at a temperature close to the external temperature and / or Alternatively, using sensible heat as cold heat, it is possible to produce dry ice and liquefied nitrogen by cooling carbon dioxide and nitrogen contained in various types of combustion exhaust gas,
Further, the present inventors have found that an extremely efficient process can be constructed by storing the liquefied nitrogen produced in this manner and using the liquefied nitrogen to re-liquefy BOG during a period in which LNG is not required, thereby completing the present invention. Was.

That is, the present invention provides the following (1) to (1)
0). (1) Discharging the combustion exhaust gas using the cold heat of the discharged LNG, solidifying the carbon dioxide contained in the combustion exhaust gas to generate and separate dry ice, and further compressing the residual exhaust gas from which the dry ice has been separated. A method for producing dry ice and liquefied nitrogen, comprising producing liquefied nitrogen by cooling. (2) The method for producing dry ice and liquefied nitrogen according to (1), wherein the combustion exhaust gas is LNG or LPG combustion exhaust gas.

(3) Discharged LNG is heat-exchanged with compressed flue gas after separating dry ice in a heat exchanger for cooling compressed gas and then with flue gas dehumidified by a fluidized bed heat exchanger. On the other hand, the dehumidified combustion exhaust gas is heat-exchanged with the partially vaporized LNG through the compressed gas cooling heat exchanger in the fluidized bed heat exchanger to produce and separate dry ice. After compressing the residual exhaust gas from which the ice has been separated, heat is exchanged with LNG from the storage tank in the heat exchanger for cooling the compressed gas, or heat exchange is performed and then adiabatically expanded to produce liquefied nitrogen. The method for producing dry ice and liquefied nitrogen according to the above (1) or (2). (4) The method for producing dry ice and liquefied nitrogen according to (4), wherein the produced dry ice is separated by a cyclone.

(5) LNG storage tank, heat exchanger for cooling compressed gas, fluidized bed heat exchanger, cyclone, dry ice storage tank, adiabatic expansion device, liquefied nitrogen storage tank, gas compression device, LNG discharged from LNG storage tank In a heat exchanger for cooling compressed gas, heat is exchanged with compressed flue gas after separating dry ice, and further heat exchange with flue gas dehumidified in a fluidized bed heat exchanger to form NG. The dehumidified combustion exhaust gas is heat-exchanged with the partially vaporized LNG through the compressed gas cooling heat exchanger in the fluidized bed heat exchanger to generate dry ice, and the generated dry ice is separated by a cyclone and dried. The residual exhaust gas stored in the ice storage tank and separated from the dry ice is compressed by a gas compression device, and the LNG from the LNG storage tank is further compressed by a heat exchanger for cooling compressed gas.
Dry ice and liquefaction, characterized in that liquefied nitrogen is produced by heat-exchanging with NG or heat-exchanged and then adiabatically expanded to produce liquefied nitrogen and storing the obtained liquefied nitrogen in a liquefied nitrogen storage tank. Nitrogen production equipment.

(6) Discharging The combustion exhaust gas is cooled by utilizing the cold heat of the LNG, and the carbon dioxide gas contained in the combustion exhaust gas is cooled and solidified to produce and separate dry ice. Is further compressed and cooled to produce and store liquefied nitrogen, and the liquefied nitrogen is used to liquefy BOG. (7) The method for reliquefying BOG according to the above (6), wherein dry ice and liquefied nitrogen are produced during the LNG demand period, and BOG is liquefied during the LNG non-demand period.

(8) The discharged LNG is heat-exchanged with the compressed flue gas after separating dry ice in a heat exchanger for cooling compressed gas and then with the flue gas dehumidified by the fluidized bed heat exchanger. On the other hand, the dehumidified combustion exhaust gas is heat-exchanged with the partially vaporized LNG through the heat exchanger for cooling compressed gas in the fluidized bed heat exchanger to produce and separate dry ice, thereby separating dry ice. After compressing the generated and separated residual exhaust gas, the compressed gas-cooling heat exchanger
Heat exchange with LNG from the NG storage tank, or after heat exchange, further adiabatic expansion to produce and store liquefied nitrogen;
The method of (6) or (7), wherein the BOG is liquefied using the liquefied nitrogen. (9) The method for reliquefying BOG according to the above (8), wherein the produced dry ice is separated by a cyclone.

(10) LNG storage tank, heat exchanger for cooling compressed gas, fluidized bed heat exchanger, cyclone, dry ice storage tank, adiabatic expansion device, liquefied nitrogen storage tank, gas compression device, BO
It consists of a G compressor and a BOG liquefaction heat exchanger. The LNG discharged from the LNG storage tank is compressed gas cooling heat exchanger.
After separating dry ice, heat exchange is performed with the compressed flue gas, and further, heat exchange is performed with the flue gas dehumidified in the fluidized bed heat exchanger to form NG. On the other hand, the dehumidified flue gas is converted into the fluidized bed type flue gas. The heat exchanger exchanges heat with the partially vaporized LNG through the heat exchanger for cooling the compressed gas to generate dry ice, separates the generated dry ice by a cyclone, and removes the residual exhaust gas from the dry ice to a gas compressor. And then heat exchange with LNG from the LNG storage tank by a heat exchanger for compressed gas cooling or heat exchange and then adiabatic expansion to produce liquefied nitrogen, and the obtained liquefied nitrogen is transferred to the liquefied nitrogen storage tank. Storing and compressing the BOG by a BOG compression device, and then exchanging heat with the liquefied nitrogen in a BOG liquefaction heat exchanger to liquefy the BOG; Location.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS LNG has a slightly different composition depending on the place of production.
Of saturated hydrocarbons at normal pressure or under pressure.
It is cooled to 0 to -170 ° C, liquefied and stored, and its vaporization temperature at normal pressure is about -161 ° C. Therefore, it is possible to produce dry ice, liquefied air or liquefied nitrogen, which has a great demand for a coolant or the like, by utilizing latent heat of vaporization and / or sensible heat until LNG is vaporized to become NG at an external temperature as cold heat. it can. Further, the liquefied air or liquefied nitrogen produced by this method can be stored and used to re-liquefy the BOG when needed.

Since liquefied nitrogen has a relatively large amount of cold storage heat per unit weight, it can be stored in a small facility, which is preferable. That is, liquefied nitrogen at 1 atm under saturation is
It also retains 103.0 kcal / kg of cold heat compared to gaseous nitrogen at 25 ° C., also at 1 atmosphere.

BOG stays in the upper part of the LNG storage tank at almost normal pressure, its temperature is -100 to -160 ° C,
The main component is methane, the liquefaction temperature at normal pressure is about -161 ° C, and the liquefaction temperature when compressed to 30 kg / cm ² G is about 145 ° C.

In the present invention, the payout LNG is LN
The demand period is the period during which LNG is paid out for the above-mentioned applications, and the amount of LNG that is paid out to the above-mentioned applications during the non-demand period is significantly reduced. Or, it means a period that is 0. 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.

BOG is paid out as NG for thermal power plants and city gas during the demand period, but is generated at a substantially constant speed due to external heat during the non-demand period, and when the LNG is received from a transport ship or the like, the storage tank wall is discharged. A large amount of BOG is generated in a relatively short time due to the pre-cooling of pipes,
Since it stays in the upper part of the storage tank, B
The OG needs to be reliquefied by the cryogenic heat of liquefied nitrogen. In the present invention, there is no need to worry about a pressure increase due to the containment of BOG in the LNG storage tank.

The combustion exhaust gas targeted in the present invention is LNG,
It is a combustion exhaust gas of LPG, petroleum, coal, refuse and the like, and is preferably a combustion exhaust gas of LNG and LPG. For example, dry ice and liquefied nitrogen can be produced by using the discharged NG combustion exhaust gas and utilizing the cold heat of LNG at the time of dispensing, and BOG reliquefaction is performed by using the produced liquefied nitrogen. It can be performed.

Hereinafter, the present invention will be described in detail by taking as an example the case where the combustion exhaust gas is LNG combustion exhaust gas. The components of the flue gas are mainly carbon dioxide, nitrogen and moisture,
Contains small amounts of oxygen and trace amounts of nitrogen oxides. Therefore, if water is mainly removed from the combustion exhaust gas, it becomes suitable as a raw material for dry ice and liquefied nitrogen,
Even if nitrogen after reliquefaction of BOG with liquefied nitrogen is released to the atmosphere, it is originally a combustion exhaust gas, so there is little economic loss and there is no problem in environmental conservation. Further, these gases are nonflammable, and even if the device is damaged, there is little danger of causing a disaster by mixing with LNG or BOG.

As the combustion exhaust gas for liquefaction, a gas from which the moisture in the combustion exhaust gas has been removed in advance after purifying treatment such as dust collection and filtration as necessary is used. For example, heat exchange with NG after passing through the fluidized bed heat exchanger in the present invention can remove in advance the moisture in the combustion exhaust gas.

At the time of demand for NG, LNG discharged from the LNG storage tank exchanges heat with the compressed gas (nitrogen) in the heat exchanger for cooling the compressed gas, and further exchanges heat with the exhaust gas dehumidified in the fluidized bed heat exchanger. NG, and it is paid out as NG for thermal power plants and city gas.

The dehumidified combustion exhaust gas is supplied to the lower part of the fluidized bed heat exchanger, exchanges heat with a mixed fluid of LNG and NG, and is cooled to produce dry ice. The fluidized bed heat exchanger includes a vessel in which a fluidized bed is formed, and a heat exchange pipe or panel provided in the vessel. LNG and / or NG (usually a mixed fluid) is provided in the heat exchange pipe or panel. )
Flows as a coolant, and a fluidized bed medium is added to the space forming the fluidized bed.

As the fluidized bed medium, silica sand, metal particles, ceramic particles, and other particles can be used, and the shapes thereof are spherical, angular, hollow, tubular, and annular. When particles are used as the fluidized bed medium, the fluidized bed medium particles flow and circulate in the fluidized bed with the combustion exhaust gas rising in the fluidized bed, and are cooled by a cooling pipe through which LNG or NG flows, The carbon dioxide in the combustion exhaust gas is solidified and adheres to the particles as dry ice on the particles, but the dry ice on the particles is peeled off due to the collision friction between the flowing particles and becomes dry ice powder, which is conveyed to the airflow. You.

The diameter and specific gravity of the particles are selected so as to meet operating conditions such that the flue gas ascending in the fluidized bed flows and circulates in the fluidized bed so that even if dry ice adheres, it can flow sufficiently. Although depending on the shape and size of the fluidized bed, the linear velocity of the combustion exhaust gas is 0.05 to 5 m / sec, preferably,
0.1 to 1.0 m / sec. Therefore, preferred examples of the fluidized bed medium particles include those having a specific gravity of about 2 to 10 such as silica sand and metal particles, and those having a particle diameter of 10 μm to 1 mm. The shape of the particles is preferably spherical, angular, hollow, or amorphous such as sand.

The medium particles not only cool the flue gas to produce dry ice, but also pulverize the dry ice formed on the particles, the cooling pipe of the fluidized bed heat exchanger and the wall surface of the fluidized bed into powder. And has the function of scraping.

The upper or upstream portion of the fluidized bed is used to circulate the fluidized bed medium particles through the fluidized bed or to separate fine particles generated by crushing dry ice deposited on the fluidized bed medium particles. Can be provided with a separator such as a cyclone. Even if these separators are used, the fluidized bed medium particles and the generated fine particles of dry ice are easily separated due to a difference in specific gravity and the like.

The dry ice produced in the fluidized bed is powdery snow, has a bulk specific gravity of 0.2 to 0.8, and a particle size of 5 to 5
0 μm, at the above linear velocity, the residual exhaust gas mainly composed of nitrogen is carried away from the upper part of the fluidized bed and supplied to the cyclone for dry ice separation, where most of the dry ice fine particles are removed from the exhaust gas flow. However, fine particles (powder) of dry ice powder remaining in the exhaust gas and entrained are separated by a filter such as a bag filter. A bag filter is suitable as a filter for separating dry ice fine particles. Here, it is necessary to remove the dry ice fine particles to such an extent that the dry ice fine particles remaining in the exhaust gas accumulate in the gas compressor and the pipe and do not cause blockage or rotational imbalance. The material and structure of the filter are selected in consideration of low-temperature heat shrinkage and prevention of clogging due to dry ice adhesion.

Further, the lower part of the cyclone and the backfill
A dust collecting device is provided below the filter
Ice powder is collected. Apply this dry ice powder layer to 3
0-40kg / cm^TwoDensity by pressing
1600-1700kg / m ^ThreeDry ice molded body and
can do.

The component of the remaining exhaust gas (residual exhaust gas) separated from the dry ice is almost nitrogen, and is compressed to ²⁰ to 40 kg / cm ² in order to liquefy it. The compression of the residual exhaust gas (nitrogen) may be performed by repeating multi-stage compression and cooling such as two to four stages. For cooling, the NG held by the NG after passing through the heat exchanger for cooling the compressed gas is recovered, the residual exhaust gas (nitrogen) is pre-cooled, and L is further cooled to liquefy the residual exhaust gas.
Use the NG cold.

The compressed nitrogen (residual exhaust gas) is chilled to -100 to -160 ° C. by LNG in a compressed gas heat exchanger. The compressed and chilled nitrogen can be further heat-exchanged and liquefied in a cryogenic gas heat exchanger if necessary, and the unliquefied cryogenic gas can be cooled by adiabatic expansion and cooled. The part can be liquefied. Liquefied nitrogen is separated from gas,
It is stored in a liquefied nitrogen storage tank, and after the gas is cooled, it is heat-exchanged by the cryogenic gas heat exchanger.For example, it is recycled to the preceding stage of the gas compressor, or for removing moisture in the combustion exhaust gas. Released to atmosphere after use.

An expansion turbine is installed between the compressor and the liquefied nitrogen storage tank, and a part of the compressed nitrogen is supplied to the expansion turbine to be reversibly expanded and cooled, and is driven by power recovered from the compressed nitrogen. Nitrogen newly introduced by the turbine may be further compressed, while expanded and cooled unliquefied nitrogen may be supplied to a cryogenic gas heat exchanger or the like as cryogenic nitrogen to be recycled.

The method for producing liquefied nitrogen may be a method utilizing the simplest Joule-Thomson effect,
The nitrogen liquefaction method itself for cooling the compressed nitrogen using the cold heat of LNG may be performed by the Linde method, the Claude method, or any of these improved methods.

B generated in the LNG storage tank when NG is not required
OG is compressed to 5 to 30 kg / cm ² by a BOG compressor, and is used as a BOG liquefaction heat exchanger to exchange heat with liquefied nitrogen produced and stored by utilizing the cold heat of LNG when demanding NG to LNG. It is reliquefied and stored in the LNG storage tank as reliquefied BOG. Liquefied nitrogen is used for liquefaction of BOG or stored as excess liquefied nitrogen and used for another purpose. When used for liquefaction of BOG,
Nitrogen that is used in cooling the BOG in the G liquefaction heat exchanger and is vaporized is released to the atmosphere as exhaust gas. Note that N
BOG generated at the time of demand of G is 5 to 5 by the BOG compressor.
After being compressed to 30 kg / cm ² , it can be mixed with the dispensed LNG and used.

In the present invention, a heat exchanger for cooling a compressed gas, a fluidized bed heat exchanger, a heat exchanger for liquefying BOG and, if necessary, a cryogenic gas heat exchanger are used. As such a heat exchanger, a conventional shell and tube type or a plate fin type when the temperature difference is small can be used.

FIG. 1 is a flow sheet showing one embodiment of the present invention. In FIG. 1, a solid line indicates a flow when NG is required, and a broken line indicates a flow when NG is not required. Referring to FIG. 1 as an example of the present invention, a method for producing dry ice and liquefied nitrogen using the cold heat of discharged LNG, storing it, and reliquefying BOG will be described below. LNG storage tank 1 (capacity 2 to 100,000 k1
LNG is currently used).
Is stored at normal pressure and at about -161 ° C., and BOG is placed on top of LNG at normal pressure or slightly pressurized 0.2 kg / cm.
^{It is} about ² G and stays at -100 to -160 ° C. L
NG payout amount is, for example, 100t during daytime NG demand
/ Hr, the pressure is increased to 10 to 50 kg / cm ² by a pump and the amount is paid out.
10 to 10 t / hr. BOG generation is always 7t on average
/ Hr.

At the time of demand for NG, the LN exiting the LNG storage tank 1
G11 exchanges heat with the compressed gas [compressed gas of residual exhaust gas (nitrogen)] 13 in the compressed gas cooling heat exchanger 2, and further exchanges heat with the combustion exhaust gas 10 after dehumidification in the fluidized bed heat exchanger 3. As a result, NG 12 is paid out as NG pressurized to 30 to 80 kg / cm ² for thermal power plants and city gas.

On the other hand, the flue gas 10 from which water has been removed by a dehumidifier (not shown) exchanges heat with NG via the cooling pipe and the fluidized bed particles in the fluidized bed heat exchanger 3 to undergo about -40 to -40.
After cooling to 70 ° C., fine powder of dry ice is produced in the fluidized bed, separated from the fluidized bed particles with the residual exhaust gas, and transported to the cyclone 21. The fine powder of dry ice supplied to the cyclone is separated from residual exhaust gas in the cyclone and stored in the dry ice storage tank 20. The residual exhaust gas that has passed through the cyclone accompanies a small amount of dry ice fine particles, so that the dry ice fine particles are further removed by the filter 22 and then supplied to the gas compressor 4 as residual exhaust gas 26. In the case where the residual exhaust gas 26 contains oxygen gas or other trace gas, if necessary, in a preferred step by a conventional method, oxygen and other trace gas are separated by adsorption, desorption operation, etc., and then subjected to a compression / liquefaction step. You may send it.

The residual exhaust gas 26 (nitrogen) is pressurized to ²⁰ to 40 kg / cm ² by the gas compressor 4 to become a compressed gas 13, which is discharged by the heat exchanger 2 for cooling the compressed gas.
After being cooled by exchanging heat with the cryogenic gas 17 in the cryogenic air heat exchanger 9, a part thereof becomes liquefied nitrogen 14 by the adiabatic expansion device 5 and is stored in the liquefied nitrogen storage tank 6. , A part of which becomes a cryogenic gas 17, which is heat-exchanged with the compressed gas 13 in the cryogenic gas heat exchanger 9 and then recycled to the preceding stage of the gas compressor or a fluidized bed heat exchanger (not shown) After being used for removing moisture in the combustion exhaust gas by a dehumidifier through 3 if necessary, it is released to the atmosphere as exhaust nitrogen gas 23.

When NG is not required, the BOG 15 is compressed by the BOG compressor 8 to 5 to 30 kg / cm ² ,
The liquefied heat exchanger 7 exchanges heat with liquefied nitrogen to be reliquefied into LNG and stored in the LNG storage tank 1 as reliquefied BOG 16. The liquefied nitrogen is vaporized in the BOG liquefaction heat exchanger 7 and released to the atmosphere as exhaust nitrogen gas 24 or excess liquefied nitrogen 25
Used for other uses as.

[0050]

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. 1, LNG is stored in an LNG storage tank 1 at normal pressure and at -161 ° C. LN
The amount of G to be dispensed is 100 t / hr at the time of daytime demand, the pressure is increased to 30 kg / cm ² G by a pump, and the G is dispensed.
The payout amount during non-demand at night is 0 t / hr. At the time of demand for NG, the LNG discharged is heat-exchanged with the compressed gas 13 in the heat exchanger 2 for cooling the compressed gas, and further heat-exchanged with the combustion exhaust gas 10 after dehumidification in the fluidized-bed heat exchanger 3 to be dehumidified (Not shown) and became NG12, which was paid out for the thermal power plant.

On the other hand, 39 t / hr of flue gas discharged from the LNG combustion equipment and containing 71% of nitrogen, 9% of carbon dioxide, 3% of oxygen, 17% of moisture and 120 ppm of NOx are
The flue gas 10 is dehumidified to a water content of about 10 ppm or less through a dehumidifier (not shown), and is supplied to the fluidized bed heat exchanger 3 so that the superficial linear velocity of the gas in the fluidized bed becomes 0.25 m / sec. Supplied. The fluidized bed heat exchanger 3 is filled with silica sand having an average particle size of 180 μm. The exhaust gas 10 exchanged heat with LNG in the fluidized bed heat exchanger 3 and was cooled to about -140 ° C to produce fine powder of dry ice. The obtained fine powder of dry ice has a particle size of about 5 to 50 μm, and is transported to the cyclone 21 by the residual exhaust gas 26,
It was separated by a cyclone, collected in a dust collector below the cyclone, and stored in a dry ice storage tank 20. The residual exhaust gas accompanied by a small amount of dry ice fine particles was separated from the dry ice fine particles by a filter 22 (here, a bag filter), and then the residual exhaust gas 26 was supplied to the compressor 4. The separated dry ice fine particle powder was stored in the dry ice storage tank 20 together with the dry ice separated by the cyclone 21, and the amount of the obtained dry ice was 5.5 t / hr.

Residual exhaust gas 26 after separation of dry ice
Is repeatedly compressed and cooled by the three-stage gas compressor 4,
It becomes a compressed gas 13 of 45 ° C. and 31 kg / cm ² , heat-exchanges with the discharged LNG 11 in the heat exchanger 2 for cooling the compressed gas, and further heat-exchanges with the cryogenic gas heat exchanger 9. Part of the liquefied nitrogen became 18.5 t / hr and was stored in the liquefied nitrogen tank 6. After the adiabatic expanded remaining cryogenic gas 17 undergoes heat exchange in the cryogenic gas heat exchanger 9, part of the gas is recycled to the preceding stage of the gas compressor 4, and the other part flows into the fluidized bed heat exchanger 3. The exhaust gas was released to the atmosphere after being used for pre-cooling and further as a cold source for dehumidification.

(Embodiment 2) In the apparatus shown in FIG.
In the NG storage tank 1, LNG is stored at normal pressure and at -161 ° C, and BOG remains at normal pressure and at -160 ° C above LNG. LNG payout amount is 10 during daytime demand.
At 0 t / hr, the pressure is increased to 30 kg / cm ² G by a pump, and the pump is paid out.
hr. The amount of BOG generated is 7 t / hr on average.

Using the liquefied nitrogen produced in Example 1, BOG was reliquefied into LNG at night when NG was not required. BOG generated at an average of 7 t / hr when NG is not required
15 was compressed to 11 kg / cm ² by a BOG compressor 8, and heat-exchanged with 15 t / hr of liquefied nitrogen in a BOG liquefaction heat exchanger 7, almost all of which was reliquefied and stored in the LNG storage tank 1. The composition, boiling point and dew point of LNG used in Examples 1 and 2 are as shown in Table 1.

[0055]

[Table 1]

The pressure is 30 kg / cm ² G and 40 kg.
/ NG L evaporation curve (or condensation curve) at / cm ² G
FIG. 2 shows the nitrogen evaporation curves (or condensation curves) at 20 kg / cm ² G and 30 kg / cm ² G.
FIG. 2 clearly shows that the temperature of the LNG is lower than the liquefaction temperature of the nitrogen gas under pressure, and thus the LNG (or N
G) and heat exchange between nitrogen (or liquefied nitrogen)
It can be seen that there are operating conditions under which the nitrogen gas (the main component of the combustion exhaust gas) can be liquefied by the cold heat of NG, and conversely, there are operating conditions under which the BOG can be liquefied by the cold heat of the liquefied nitrogen.

[0057]

According to the present invention, LNG is paid out LNG.
Dry ice and liquefied nitrogen could be produced from LNG or LPG combustion exhaust gas, etc. by utilizing the cold heat of the above. Also, the amount of LNG dispensed greatly differs between daytime demand and nighttime non-demand, but by using the above liquefied nitrogen, almost all of the BOG generated during nighttime LNG non-demand is reliquefied to LNG. We were able to return to storage tank.

[Brief description of the drawings]

FIG. 1 is a process flow sheet showing one embodiment of the present invention.

FIG. 2 is a diagram showing temperature versus enthalpy curves of LNG and nitrogen.

[Explanation of symbols]

1. LNG storage tank 2. Heat exchanger for compressed gas cooling
3. 3. Fluidized bed heat exchanger Gas compressor 5. Adiabatic expansion device 6. 6. Liquefied nitrogen storage tank 7. BOG liquefaction heat exchanger BOG compressor
9. Chill gas heat exchanger 10. 10. Combustion exhaust gas after dehumidification Payout LNG 1
2. NG 13. Compressed gas 14. Liquefied nitrogen 15. BOG
16. Reliquefied BOG 17. Chilled gas 20. Dry ice storage tank 21.
Cyclone 22. Filter 23. 13. Exhaust nitrogen gas (uncondensed) 25. Exhaust nitrogen gas (after BOG cooling) Excess liquefied nitrogen (multipurpose use) 26. Residual exhaust gas after removing moisture and carbon dioxide

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Furuichi 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanishi Heavy Industries, Ltd. (72) Inventor Satoshi Ogawa 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanishi Heavy Industries Co., Ltd.

Claims (10)

[Claims] 1. A method of cooling a combustion exhaust gas by utilizing the cold heat of a discharged liquefied natural gas, solidifying carbon dioxide contained in the combustion exhaust gas to produce and separate dry ice, and separating the dry ice. A method for producing dry ice and liquefied nitrogen, further comprising compressing and cooling the exhaust gas to produce liquefied nitrogen. 2. The method for producing dry ice and liquefied nitrogen according to claim 1, wherein the combustion exhaust gas is a combustion exhaust gas of liquefied natural gas or liquefied petroleum gas. 3. The discharged liquefied natural gas is heat-exchanged with a compressed flue gas after separating dry ice by a heat exchanger for cooling a compressed gas, and is further exchanged with the flue gas dehumidified by a fluidized bed heat exchanger. Exchanged into natural gas, while the dehumidified flue gas was heat-exchanged with partially vaporized liquefied natural gas through the compressed gas cooling heat exchanger in the fluidized bed heat exchanger to produce dry ice. After separating and drying the residual exhaust gas from which dry ice has been separated, heat is exchanged with the liquefied natural gas from the storage tank in the heat exchanger for cooling the compressed gas, or heat exchange is performed and then adiabatically expanded to produce liquefied nitrogen. The method for producing dry ice and liquefied nitrogen according to claim 1 or 2, wherein: 4. The method for producing dry ice and liquefied nitrogen according to claim 3, wherein the produced dry ice is separated by a cyclone. 5. A liquefied natural gas storage tank, a heat exchanger for cooling compressed gas, a fluidized bed heat exchanger, a cyclone, a dry ice storage tank, an adiabatic expansion device, a liquefied nitrogen storage tank, and a gas compression device. The discharged liquefied natural gas is heat-exchanged with the compressed flue gas after separating dry ice in a compressed gas cooling heat exchanger, and then heat-exchanged with the dehumidified flue gas in a fluidized bed heat exchanger. On the other hand, the dehumidified combustion exhaust gas is heat-exchanged with the partially liquefied natural gas through the heat exchanger for cooling the compressed gas in the fluidized bed heat exchanger to produce dry ice, thereby producing dry ice. Ice is separated by a cyclone and stored in a dry ice storage tank, the residual exhaust gas from which the dry ice is separated is compressed by a gas compressor, and then liquefied natural gas storage is performed by a heat exchanger for cooling compressed gas. Heat-exchanged with liquefied natural gas, or heat-exchanged and then adiabatically expanded to produce liquefied nitrogen, and the obtained liquefied nitrogen is stored in a liquefied nitrogen storage tank. Equipment for producing dry ice and liquefied nitrogen. 6. The combustion exhaust gas is cooled by utilizing the cold heat of the discharged liquefied natural gas, and the carbon dioxide gas contained in the combustion exhaust gas is cooled and solidified to produce and separate dry ice. A method for reliquefying a boil-off gas, comprising compressing and cooling the exhaust gas to produce and store liquefied nitrogen, and liquefying the boil-off gas using the liquefied nitrogen. 7. The reliquefaction of a boil-off gas according to claim 6, wherein dry ice and liquefied nitrogen are produced during a demand period of the liquefied natural gas, and the boil-off gas is liquefied during a non-demand period of the liquefied natural gas. Method. 8. The discharged liquefied natural gas is heat-exchanged with a compressed flue gas after separating dry ice in a compressed gas cooling heat exchanger, and further exchanged with the flue gas dehumidified in a fluidized bed heat exchanger. The natural gas is exchanged, and the dehumidified combustion exhaust gas is heat-exchanged with the partially naturalized liquefied natural gas through the compressed gas cooling heat exchanger in the fluidized bed heat exchanger to produce and separate dry ice. After compressing the residual exhaust gas that has produced and separated dry ice, the compressed gas cooling heat exchanger exchanges heat with liquefied natural gas from the liquefied natural gas storage tank, or heat-exchanges and further adiabatically expands to liquefy. 8. The method for reliquefying a boil-off gas according to claim 6, wherein nitrogen is produced and stored, and the boil-off gas is liquefied using the liquefied nitrogen. 9. The method according to claim 8, wherein the produced dry ice is separated by a cyclone. 10. Liquefied natural gas storage tank, heat exchanger for cooling compressed gas, fluidized bed heat exchanger, cyclone, dry ice storage tank, adiabatic expansion device, liquefied nitrogen storage tank, gas compression device, boil-off gas compression device, boil-off gas The liquefied natural gas discharged from the liquefied natural gas storage tank is separated from dry ice by a liquefied natural gas storage heat exchanger and then heat-exchanged with the compressed flue gas after being separated from the dry ice. Liquefied natural gas that has been partially vaporized through the compressed gas cooling heat exchanger in the fluidized bed heat exchanger with the dehumidified combustion exhaust gas is heat-exchanged with the dehumidified combustion exhaust gas to form natural gas. Heat exchange to produce dry ice,
The generated dry ice is separated by a cyclone and stored in a dry ice storage tank, the residual exhaust gas from which the dry ice is separated is compressed by a gas compressor, and then the liquefied natural gas from the liquefied natural gas storage tank is compressed by a heat exchanger for cooling compressed gas. Liquefied nitrogen is produced by heat-exchange or heat-exchanged and then adiabatically expanded to produce liquefied nitrogen.The obtained liquefied nitrogen is stored in a liquefied nitrogen storage tank, and the boil-off gas is compressed by a boil-off gas compression device and then liquefied. A boil-off gas reliquefaction apparatus, which is configured to liquefy by exchanging heat with the liquefied nitrogen in a heat exchanger.