KR20130043255A - Efficient lng storage tank using waste heat - Google Patents

Abstract

PURPOSE: An ultralow-temperature liquid storage tank is provided to reduce the evaporation quantity of liquid fuel like LNG even through a waste heat recovery cycle device using a refrigerant and an existing insulation method in which pearlite powder is charged between an inner tank and an outer tank to maintain a low-vacuum state are combined. CONSTITUTION: An ultralow-temperature liquid storage tank comprises an inner tank(10) and an outer tank(12). An insulation material(30) is charged between the inner and outer tanks in a vacuum state. A waste heat recovery cycle device using a refrigerant is embedded between the inner and outer tanks so that heat infiltrated from the outside can be blocked by the insulation material. The refrigerant is vaporized by absorbing the infiltrated heat to prevent the evaporation of ultra-low temperature liquid stored in the inner tank. [Reference numerals] (AA) Used pipe;

Description

Cryogenic LNG Storage Tank Using Waste Heat

The present invention relates to a cryogenic liquid storage tank, and more particularly, to a cryogenic liquid storage tank having high efficiency of waste heat recovery for long-term storage of a cryogenic liquid fuel such as LNG and the like with maximum safety and thermal insulation effect.

Generally, cryogenic liquefied gas such as LNG is about 90% methane, and refers to a hydrocarbon-based mixture containing some ethane, propane, n-butane, iso-butane, nitrogen, etc. Although the physical and chemical properties are slightly different, it is known that liquefaction is possible around -160 ° C because most of them are methane.

Therefore, after removing impurities such as carbon dioxide, water, and sulfide from natural gas (NG), LNG is compressed, expanded, and heat exchanged at -162 ° C (at atmospheric pressure) to facilitate mass transportation and storage. It is liquefied and transported to ships and stored at LNG production bases.

Since the LNG is a cryogenic liquid of -160 ° C, if the LNG storage tank is not sufficiently insulated, liquid LNG may be continuously vaporized due to external heat inflow.

Recently, LNG charging stations for vehicles have been newly established for use in fuels such as buses and large container trucks, and the supply of tanks for storing LNG is increasing every year, but large-scale for storing natural gas such as LNG. There is no improvement in the performance of tanks and small and medium tanks.

Therefore, it is urgent to develop a highly efficient cryogenic liquid (liquefied gas) storage tank capable of storing liquefied gas for a longer period of time by increasing the thermal insulation effect of the tank for storing cryogenic liquefied gas such as LNG and enabling the use of liquefied gas safely. It is required.

Referring to Figure 6 attached to the structure of the cryogenic liquid storage tank, such as the conventional liquid nitrogen, a low-vacuum single material filled between the inner tank 10 and the outer tank 12, and the double inner and outer tank of 260mm thick Consists of perlite powder, the space between the perlite filled inner and outer tanks is maintained at a vacuum of 10 ^-2 Torr.

In other words, the tank storing LNG at -160 ° C maintains a vacuum degree of 10 ^-2 Torr in the pearlite powder in the same way as the existing cryogenic liquid storage tanks such as liquid nitrogen and liquid oxygen to block heat inflow from the outside atmosphere.

At this time, the pearlite is a solid powder, fine particles such as wheat flour, the thermal conductivity of the pearlite in a low vacuum state is 0.044W / mK when the density is 210kg / ㎥, if the density is high thermal conductivity It becomes bigger.

In particular, the pipe of the cryogenic liquid storage tank as described above is connected to a plurality of upper and lower portions of the inner tank for the inlet, out, pressure, decompression of the cryogenic liquid (LNG), and extends out of the outer tank.

In the existing cryogenic liquefied gas storage tank, there are various heat inflow paths such as heat inflow through a wall, heat inflow through a pipe, and heat inflow through a support system.

In other words, on the premise that sufficient insulation such as piping connected to the cryogenic liquid storage tank is sufficient, the main heat transfer of the tank is introduced through the wall, and also heat inflow through the pipe and heat inflow through the support system exist. For example, when 193 mm thick pearlite powder and 10 ^-2 Torr of low vacuum are used, the total heat flow in the existing storage tank is 1) wall heat flow: 1146.3W, 2) heat flow in the pipe: 1.8402W, 3 Heat inflow of the support system: 7.9294W.

However, the conventional cryogenic liquid storage tank is a pearlite powder having a thermal conductivity of 0.033 W / mK and a vacuum insulation (vacuumity of 10 ^-2 Torr) between the inner tank and the outer tank, which is a double tank, and stored in the tank. The liquid is evaporating considerably faster.

At this time, the amount of vaporization of the liquid is less than 2.5% a day, based on the tank certification value of the Gas Safety Corporation, but is usually known as about 1.5 ~ 2%, and usually the pearlite powder vacuum insulation tank as described above is 1 ~ 2 It is known that% vaporization occurs.

However, since the LNG is a cryogenic liquid at -162 ° C, heat is continuously introduced from the outside during storage in the storage tank, and the stored liquid is vaporized into gas, and the vaporized gas is set to a safety valve set pressure of 10kg / cm2 or more for safety. It is then released to the atmosphere.

Therefore, since vaporized natural gas is an explosive substance, it is essential to be stored in a liquid state for a long time in a storage tank for safety. Therefore, it is urgently required to develop a cryogenic liquid (LNG, etc.) storage tank with adiabatic efficiency. It is becoming.

The present invention has been made in view of the above point, in order to solve the problem that the evaporation is continuously generated by the external heat inflow unless the thermal insulation of the storage tank for storing cryogenic liquid fuel of -160 ℃, the insulation effect It is an object of the present invention to provide a cryogenic liquid storage tank capable of storing cryogenic liquid (LNG) for a longer period of time and increasing the use of cryogenic liquid safely.

In order to achieve the above object, the present invention provides a cryogenic liquid storage tank including an inner tank and an outer tank, wherein the inner and outer tanks have a super insulation insulation in a vacuum state between the inner tank and the outer tank. By installing a waste heat recovery cycle device using a refrigerant between them, the super insulation insulation blocks the heat invading from the outside, and the refrigerant of the waste heat recovery refrigerant waste cycle device is sucked in and vaporized, thereby vaporizing the cryogenic liquid stored in the inner tank. It provides a cryogenic liquid storage tank, characterized in that to prevent it from being.

According to the present invention, the waste heat recovery cycle apparatus comprises: a closed circulation refrigerant pipe arranged in a screw or spiral in a space between an inner and an outer tank; A heat exchanger which is connected to both ends of the refrigerant pipe so as to communicate with each other and at the top of the space between the inner and outer tanks so that the liquefied gas (liquid) discharge pipe extending from the inner tank passes; Characterized in that consisting of.

In particular, the insulating material for super insulation is wrapped around the outer surface of the inner tank of polyethylene terephthalate (Mylar) or aluminum film, which is a highly reflective material, in between, one selected from glass fiber, paper, nylon fiber as interlayer By inserting, it is characterized in that the vacuum is maintained at 1 × 10 ^-5 Torr or less.

Preferably, the inner tank is made of STS304, STS316-based material that can withstand cryogenic temperatures, and the outer tank is made of SS400 material.

In addition, the refrigerant charge tube is further connected to the outside of the outer tank to the inside of the heat exchanger to charge any one of the refrigerant selected from R22, R134a.

Through the above-mentioned means for solving the problems, the present invention provides the following effects.

According to the present invention, by adopting a super-insulation insulation method for arranging insulation such as polyethylene terephthalate (Mylar) between the inner and outer tanks and maintaining the high vacuum, the waste heat recovery cycle apparatus using a refrigerant is applied together to liquefy. The amount of vaporization of liquid fuels such as oxygen (LO ₂ ), liquefied nitrogen (LN ₂ ), liquefied argon (LAR), and LNG (LNG) can be greatly reduced, resulting in safe use for long-term storage of cryogenic liquids such as LNG. Can provide the effect.

Alternatively, by combining perlite powder between the inner tank and the outer tank to maintain low vacuum, a combination of a waste heat recovery cycle system using a refrigerant can greatly reduce the amount of vaporization of liquid fuels such as LNG. Can be.

In addition, by adopting the waste heat recovery cycle technology and the super insulation insulation method using the refrigerant, it can contribute to the diffusion and commercialization of the high efficiency liquid storage tank having a vaporization rate of less than 0.2%.

1 and 2 is a diagram showing a cryogenic liquid storage tank according to the present invention,
3 to 5 is a graph showing the results of performing adiabatic experiment by installing the super insulation of the cryogenic liquid storage tank according to the present invention,
6 is a diagram showing a conventional cryogenic liquid storage tank,

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The cryogenic liquid storage tank according to the present invention includes an internal tank 10 for storing liquid fuel (liquefied oxygen (LO ₂ ), liquefied nitrogen (LN ₂ ), liquefied argon (LAR), LNG (LNG), etc.), It consists of an outer tank 12 that is spaced apart while wrapping the inner tank 10, the insulation for the super insulation 30 and the waste heat recovery cycle device 20 is installed in the space between the inner and outer tanks (10, 12) There is a characteristic in point.

To this end, the cryogenic liquid storage tank is manufactured through the design of the inner tank and the outer tank, the refrigerant heat exchanger design, piping design.

The inner tank 10 is a tank capacity using a material of SUS304, STS304, STS316 series that can withstand cryogenic temperatures to store liquid fuel (for example, LNG) having a temperature of -162 ℃, pressure 10kg / ㎠: It is manufactured to be 10N㎥.

At this time, the thickness of the inner tank is determined by calculating the appropriate thickness in accordance with the design pressure and the material properties.

The outer tank 12 is designed in consideration of the thickness of the super insulation insulation filled in the space between the inner tank 10, the outside of the outer tank is applied with atmospheric pressure and the inside of the vacuum such as 1 × 10 ^-2 Torr Since it is caught, the external tank should be designed so as not to be damaged by the compression by external atmospheric pressure, and it is made of SS400 material because cryogenic liquid such as cryogenic liquid nitrogen or LNG does not directly contact.

In this case, a plurality of pipes are connected to the inner tank 10, and external heat may be transferred to the liquid fuel in the inner tank 10 through the pipes.

As shown in FIG. 1, the pipe type is connected to the upper and lower ends of the inner tank 10 from a liquid inlet to inject liquid fuel into the inner tank N1. And liquid lower injection pipe N2; A gas discharge pipe N4 connected to an upper end of the inner tank 10 to discharge the vaporized liquid fuel for safety; A liquid discharge pipe N3 connected to a lower end of the inner tank 10 to discharge the liquid fuel in the inner tank 10 to a place of use; A liquid filled test tube (N5) extending from the upper end of the inner tank (10) to the level of full charge therein to test that the liquid filling in the inner tank (10) is completed; Pressure measuring upper pipe (N6) and pressure measuring lower pipe (N7) connected to the upper and lower ends of the inner tank (10), respectively, to measure the pressure inside the upper and lower ends of the inner tank (10); A liquid pump discharge pipe N8 for pumping and discharging the liquid in the inner tank 10; A liquid pump recovery pipe N9 for pumping and returning liquid in the inner tank 10 is included.

In particular, the upper end of the outer tank 12 is connected to the refrigerant filling tube (N10) for injecting the refrigerant into the heat exchanger 24 to be described later.

As such, in the state in which the inner tank 10 and the outer tank 12 and various pipes are connected, the external heat may be transferred to the cryogenic liquid in the inner tank 10. (12) and the wall of the inner tank 10, various pipes, supports (not shown) installed for interconnection between the inner tank and the outer tank, and the like, as an example, the wall heat flow rate 820 W, Heat inflow: 1.84W, heat inflow of support 7.9294W, etc. A total of 829.77W of heat can be introduced.

At this time, if the total heat inflow amount of 829.77W is calculated as the LNG evaporation amount, the latent heat per 1kg of LNG is 135 kcal / kg, so 127kg of LNG is evaporated per day. do.

The present invention adopts a high vacuum super-insulation insulation method in the space between the inner and outer tanks 10 and 12 to minimize the amount of liquid fuel such as LNG vaporized as described above, and uses a waste heat recovery cycle apparatus using a refrigerant. It is characteristic in that they are applied together.

That is, a waste heat recovery cycle apparatus using a refrigerant between the inner tank 10 and the outer tank 12 while incorporating the super insulation insulation 30 in a vacuum state between the inner tank 10 and the outer tank 12. By internally forming the super-insulation, external heat (for example, sunlight) penetrating through the walls of the outer tank 12 and the inner tank 10, various pipes N1 to N9, a support body, and the like can be superposed. By blocking the heat insulating material 30 firstly and allowing the refrigerant of the refrigerant waste cycle to suck external heat in advance, vaporization of the cryogenic liquid stored in the inner tank 10 may be prevented by external heat. Will be.

The insulation material for super insulation 30 is wound around the outer surface of the inner tank 10, polyethylene terephthalate (Mylar) or aluminum film of a high reflection material, dozens of layers of polyethylene teleterrate (Mylar) wound Or it is wrapped between the aluminum film by inserting one selected from glass fiber, paper, nylon fiber as interlayer paper, wherein the space between the inner tank 10 and the outer tank 12 is filled with the insulating material for super insulation (30). The degree of vacuum is maintained at 1 × 10 ^-5 Torr or less.

Therefore, the external heat is transferred to the inner tank 10 by the super insulation insulation 30 filled in the space between the inner tank 10 and the outer tank 12 maintained at a vacuum degree of 1 × 10 ⁻⁵ Torr or less. It can be blocked first.

The waste heat recovery cycle apparatus 20 is a device for secondarily preventing the cryogenic liquid in the inner tank 10 from vaporizing by absorbing external heat, and being disposed in a space between the inner and outer tanks 10 and 12. The internal and external tanks 10 allow the refrigerant pipe 22 and both ends of the refrigerant pipe 22 to communicate with each other, and also allow the liquefied gas (liquid) discharge pipe N3 extending from the internal tank 10 to pass therethrough. And 12) a heat exchanger 24 embedded in the space therebetween.

In more detail, the closed circulation refrigerant pipe 22 is arranged in the space between the inner and outer tanks 10 and 12, but is arranged in a screw or spiral from the upper end to the lower end of the inner tank 10, the closed circulation refrigerant pipe ( The inlet end 22a and the outlet end 22b of the 22 are communicatively connected to one side and the other side of the heat exchanger 24.

In addition, the heat exchanger 24 may be manufactured in a small tank, or may be manufactured in an intermediate tank type spaced apart while surrounding the inner tank 10, and the inside of the heat exchanger 24 may be cryogenic from the inner tank 10. The liquid discharge pipe N3 through which the liquid is discharged passes.

Therefore, even though the external heat is transferred to the inner tank 10, the liquid in the liquid state flowing through the closed circulation refrigerant pipe 22 of the waste heat recovery cycle apparatus 20 absorbs the external heat and the refrigerant as the external heat is absorbed. Is vaporized and enters the heat exchanger 24 through the inlet end 22a. At this time, since the cryogenic liquid flows in the liquid discharge pipe N3 passing through the heat exchanger 24, the vaporization is caused by the temperature of the cryogenic liquid. The refrigerant is liquefied again, discharged to the outlet end 22b, and recycled.

At this time, the cryogenic liquid in the liquid discharge pipe (N3) passing through the heat exchanger (24) can be vaporized due to the heat is taken away by the refrigerant, the vaporized liquid gas is backfired toward the inner tank (10) inner tank (10) As the pressure of Nm may increase, some of the liquid gas vaporized from the cryogenic liquid may be installed by mounting the check valve 40 at the position of the liquid discharge pipe N3 before passing through the heat exchanger 24 as shown in FIG. It is to prevent the back to the inner tank (10).

In this way, the internal tank by repeating the vaporization step according to the external heat absorption of the refrigerant and the liquefaction step through heat exchange with the cryogenic liquid in the liquid discharge pipe (for example, the refrigerant vaporized by cryogenic LNG cold heat is liquefied). The phenomenon that the cryogenic liquid in the inside is vaporized can be easily prevented.

On the other hand, the refrigerant used in the waste heat recovery cycle device 20 is a latent latent heat of evaporation, liquefaction and evaporation is easy, irrespective of ozone layer destruction, high critical temperature (critical point), specific volume of steam and Considering conditions such as a low specific heat ratio and proper heat of vapor and liquid, and suitable refrigerants such as R134a, R141, r123, but R134a which is widely used in consideration of price and ease of purchase It is preferable to use.

Here, an example of conducting a liquid nitrogen evaporation test by the insulating material for super insulation 30 as an experimental example of the present invention will be described.

That is, after applying a high vacuum of 10 ^-5 Torr between the inner and outer tanks (10, 12), filling the liquid nitrogen into the inner tank (10), the polyethylene teleterrate that is not sensitive to the inner tank ( Mylar) was tested to determine the amount of reduction of liquid nitrogen over time while changing the longevity and vacuum degree of the film, the results are as shown in Figures 3 to 5 attached.

FIG. 3 is a thermal conductivity test result according to the vacuum pressure of the super insulation insulation. When the vacuum pressure was lowered at room temperature and liquid nitrogen temperature, the thermal conductivity rapidly decreased at 0.1 Torr or less, but at 1 × 10 ^-5 Torr or less. Very low thermal conductivity value of 14 ~ 78W / mK was found, and finally it is preferable to apply high vacuum of 10 ^-5 Torr while filling super insulation insulation between inner and outer tanks (10, 12). Could.

4 is a graph showing the results of experiments on the insulation effect of the longevity of the polyethylene teleterrate (Mylar) film and the longevity of the paper (paper) of the super insulation insulation material, and the degree of vacuum 1 × 10 ^-5 Torr, polyethylene telephthalate ( The best time for evaporating 0.8 kg of liquid nitrogen from 40 layers of Mylar) film + paper (paper) was 500 minutes.

FIG. 5 is a graph illustrating the results of experiments of the longevity of polyethylene terephthalate (Mylar) film and the longevity of PE (polyester) film of super insulation insulation, and a graph of polyethylene terephthalate (Mylar) film + liver paper ( PE) It shows the evaporation time of liquid nitrogen according to the degree of vacuum when it is 40 layers, and the result shows that the evaporation time of 0.8 kg of liquid nitrogen is 480 minutes, and the thermal insulation effect is higher than that of polyethylene terephthalate (Mylar) film + paper. Low value was found.

As a result of this experiment, it can be seen that the super insulation insulation material can use paper and PE as interlayer paper for polyethylene terephthalate (Mylar) film, and preferably use paper as interlayer paper for polyethylene terephthalate (Mylar) film. there was.

10: inner tank
12: outer tank
20: waste heat recovery cycle device
22: closed circulation refrigerant pipe
22a: entrance
22b: exit
24: Heat exchanger
30: insulation for super insulation
N1: liquid upper injection pipe
N2: liquid bottom injection pipe
N3: liquid discharge pipe
N4: gas discharge pipe
N5: Liquid filling test tube
N6: Upper pipe for pressure measurement
N7: bottom pipe for pressure measurement
N8: liquid pump discharge pipe
N9: liquid pump return pipe
N10: Refrigerant Filling Tube

Claims (5)

In the cryogenic liquid storage tank comprising an inner tank 10 and an outer tank 12,
A waste heat recovery cycle apparatus 20 using a refrigerant between the inner tank 10 and the outer tank 12 while internally embedding the super insulation insulation 30 in a vacuum state between the inner tank 10 and the outer tank 12. ), The super-insulation insulation 30 blocks the heat invading from the outside, and the cryogenic liquid stored in the internal tank 10 A cryogenic liquid storage tank, characterized in that to prevent vaporization.
The method according to claim 1,
The waste heat recovery cycle device 20 is:
A closed circulation refrigerant pipe (22) arranged in a screw or spiral manner in a space between the inner and outer tanks (10, 12);
Both ends of the refrigerant pipe 22 are connected in communication with each other and extend from the inner tank 10 to allow the liquefied gas (liquid) discharge pipe N3 having the check valve 40 to pass through the inner and outer tanks ( A heat exchanger (24) installed in the uppermost space of the space between 10 and 12;
Cryogenic liquid storage tank, characterized in that consisting of.
The method according to claim 1,
The insulating material for super insulation 30 is wound around the outer surface of the inner tank of polyethylene terephthalate (Mylar) or aluminum film, which is a highly reflective material, in between, selected between glass fiber, paper, nylon fiber as interlayer A cryogenic liquid storage tank, wherein one is inserted and maintained at a vacuum degree of 1 × 10 ⁻⁵ Torr or less.
The method according to claim 1,
The inner tank 10 is made of a material of STS304, STS316 series that can withstand cryogenic temperatures, the outer tank 12 is a cryogenic liquid storage tank, characterized in that made of SS400 material.
The method according to claim 1,
Ultra-low temperature, characterized in that the refrigerant filling tube (N10) is further connected to the charge of any one selected from the R22, R134a, R141, r123 from the outside of the outer tank 12 to the inside of the heat exchanger (24) Tank for liquid storage.

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