KR100758666B1 - An extremely low temperature liquid fuel storage tank using the heat recovery cycle - Google Patents

Abstract

The present invention relates to a cryogenic liquid fuel storage tank for a vehicle using a heat recovery cycle.

The liquid fuel storage tank according to the present invention includes an inner tank for storing liquid fuel, an outer tank for accommodating the inner tank, an insulation pipe disposed between the outer tank and the inner tank, and disposed adjacent to the outer tank. And a hollow heat exchanger provided with an enclosed space therein, and both ends of the heat insulating pipe are connected to the heat exchanger through an outer tank, and a discharge pipe from which liquid fuel is discharged extends from the inner tank. The point of configuration is to pass through the inside of a heat exchanger.

Cryogenic Liquid Fuel, Dual Storage Tank, Insulation Pipe, Heat Exchanger

Description

Ultra low temperature liquid fuel storage tank using the heat recovery cycle

1 is a perspective view schematically showing the configuration of a liquid fuel storage tank for a conventional vehicle.

Figure 2 is a perspective view schematically showing the overall configuration of the cryogenic liquid fuel storage tank using a heat recovery cycle according to the present invention.

Figure 3 is a schematic cross-sectional view showing the overall configuration of the cryogenic liquid fuel storage tank using the heat recovery cycle according to the present invention.

Figure 4 is a cutaway perspective view showing the internal configuration of the liquid fuel storage tank according to the present invention.

5 is a view showing the operating state of the cryogenic liquid fuel storage tank according to the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... inner tank 20 ... outer tank

30 ... Insulation piping 40 ... Heat exchanger

50.Exhaust pipe

The present invention relates to a cryogenic liquid fuel storage tank for a vehicle, and more particularly, by disposing a heat insulating pipe between the outer tank and the inner tank of the liquid fuel storage tank of a double tank structure in which the inner tank is spaced apart from the inner tank. In the cryogenic liquid fuel storage tank for vehicles using a heat recovery cycle that can effectively block the heat invading from and increase the heat insulation effect, thereby preventing the liquid fuel vaporization as much as possible to further improve the storage period of the liquid fuel will be.

In general, a thermal insulation method that blocks external heat for long-term preservation of liquid fuel filled in a cryogenic liquid fuel storage tank, injects polyurethane foam between the inner and outer walls of the tank, perlite vacuum insulation, and multilayer Vacuum insulation (Multi-layer vacuum insulation, Super insulation, hereinafter referred to as 'super insulation') has been applied.

Among them, double vacuum insulation, which is called super-insulation method, is currently used for the storage of cryogenic fluids having a very low vaporization temperature such as liquid hydrogen (-253 ° C). This insulation method winds and stacks 30-50 sheets of thin silver foil called Mylar (Polyethylene tetraphthalate) to shield radiant heat between inner and outer tanks to maintain a high vacuum of 1 × 10 ^-5 Torr or higher. That's the way. The thermal conductivity value of this method is about 3.7 × 10 ^-5 W / mK, which is about 1/1000 of the polyurethane foam insulation method (k = 2.4 × 10 ^-2 W / mK), and the daily vaporization rate of the fluid stored inside the tank Can be kept within 5%.

However, in the case of a storage tank for liquid hydrogen (LH ₂ ) and a liquid natural gas (LNG) used as a passenger car or a large bus fuel, a more effective thermal insulation method is required to minimize fuel vaporization rate and to preserve fuel in the tank for a longer time. Is required. This is because minimizing the amount of vaporization of fuel is directly related to fuel efficiency and vehicle fuel efficiency when the vehicle is not operated.

To this end, recently, liquid air cylinders have been installed between the external and internal tanks of the conventional two-tank type fuel tanks to absorb / block heat from the outside, thereby storing liquid hydrogen for vehicles. A tank has been proposed, which has a structure as shown in FIG.

That is, Figure 1 is a perspective view schematically showing the configuration of a conventional liquid hydrogen storage tank for a vehicle, the conventional liquid hydrogen storage tank for vehicles is a triple cylinder structure. More specifically, the conventional liquid hydrogen storage tank for vehicles includes an inner cylinder (1) in which liquid hydrogen (-253 ° C), which is cryogenic liquid, is stored, a liquid air cylinder (3) intervening in the middle, and an outer cylinder (2). Consists of. Such a structure allows the liquid air cylinder 3 to intervene in the middle of a conventional two-cylinder type fuel tank, thereby absorbing / blocking intrusion heat from the outside, thereby improving the thermal insulation effect.

According to such a liquid tank storage tank, the liquid hydrogen stored in the inner cylinder (1) is evaporated while passing through the heat exchanger (4) when supplied to the outside of the cylinder (3), the air in contact with the atmosphere is very low temperature (-193) The vaporization of the liquid fuel stored in the inner cylinder 1 is delayed by absorbing / blocking heat injected into the liquid air cylinder 2, which is liquefied in the intermediate cylinder, and enters from the outside. Here, the liquid air can be injected into the liquid air cylinder 2 because the pressure inside the cylinder is lowered due to the low temperature.

However, the prior art as described above has the disadvantage that the moisture or carbon dioxide contained in the air is continuously condensed and injected into the cylinder while the air in the atmosphere is injected into the liquid air cylinder 2. This causes a problem that the heat exchanger is clogged during the liquid air circulation, the heat exchanger performance, and further the overall performance of the device is degraded, the production is very difficult as a three-cylinder structure, which has a large manufacturing cost.

The present invention has been made in view of the above-described problems of the prior art, and the heat insulating pipe between the outer tank and the inner tank of the cryogenic liquid fuel storage tank of the double tank structure in which the inner tank is spaced inside the outer tank. By arranging one heat exchange cycle, it is easy to manufacture as a simple structure, and it can effectively absorb / block heat invading from the outside and at the same time increase the heat insulating effect. It is an object of the present invention to provide a cryogenic liquid fuel storage tank for a vehicle using a heat recovery cycle that can further improve the storage period of the fuel.

According to an embodiment of the present invention for achieving the above object, as a fuel tank for storing cryogenic liquid fuel, an inner tank for storing liquid fuel, an outer tank for receiving the inner tank, the outer tank and the inner And a heat exchanger disposed between tanks, and a hollow heat exchanger disposed adjacent to the outer tank and provided with a sealed space therein, and both ends of the insulation pipe connected to the heat exchanger through an outer tank. The discharge pipe for discharging the liquid fuel provides a cryogenic liquid fuel storage tank for a vehicle using a heat recovery cycle, characterized in that it extends from the inner tank and passes through the heat exchanger.

Preferably, the heat insulation pipe may have a configuration in which a copper tube having a circular or elliptical cross section is wound in an annular shape on the inner wall of the inner tank, or alternatively, may be configured in the form of a cylindrical drum on the outer wall of the inner tank.

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

2 and 3 are a perspective view and a cross-sectional view schematically showing the overall configuration of the cryogenic liquid fuel storage tank using the heat recovery cycle according to the present invention, Figure 4 is an internal configuration of the liquid fuel storage tank according to the present invention Incision perspective to show.

2 to 3, the cryogenic liquid fuel storage tank according to the present invention is a liquid fuel having a vaporization point of ultra-low temperature, specifically, liquid hydrogen (-253 ℃) or liquefied natural gas (LNG, -193 ℃) and In order to store the same cryogenic liquid fuel for a longer time, it is provided with an inner tank 10 in which the liquid fuel is stored and an outer tank 20 accommodating the inner tank 10. An insulation pipe 30 is disposed between the outer tank 20 and the inner tank 10 to absorb / block heat invading from the outside, and a space enclosed therein is located outside the outer tank 20. The provided hollow heat exchanger 40 is arranged adjacently.

At this time, both ends of the heat insulating pipe 30 are connected to the heat exchanger 40 via the outer tank 20, the discharge pipe 50 for discharging the liquid fuel is extended from the inner tank 10 to the outside of the tank Via the inside of the heat exchanger 40 disposed in the. Therefore, the cryogenic liquid fuel stored in the inner tank 10 undergoes heat exchange with the refrigerant charged in the insulation pipe 30 while passing through the heat exchanger 40 when it is sent out through the discharge pipe 50.

The configuration of the present invention as described above will be described in more detail.

The inner tank 10 is filled with cryogenic liquid fuel and stored. The inner tank 10 is stably supported with a predetermined space with an inner wall of the outer tank 20 via a plurality of ribs (or brackets).

The heat insulating pipe 30 is installed in close contact with the outer wall of the inner tank 10 to absorb / block heat introduced from the outside through the outer tank 20. The heat insulating pipe 30 is a general structure sealed after the refrigerant is filled therein, the outer wall is protected by a mylar silver foil (not shown) wound in multiple layers on the outer wall.

Here, the refrigerant may vary depending on the type of liquid fuel stored in the inner tank 10. For example, when the liquid fuel stored in the inner tank 10 is liquid hydrogen, liquid nitrogen having a high liquefaction point or liquid nitrogen gas may be used as the refrigerant.

Copper or steel pipes having a circular or elliptical cross section may be used as the heat insulating pipe 30, and a tube formed with a groove (Groove or Wick) may be used therein for smooth flow of the refrigerant.

In addition, the heat insulating pipe 30 may be formed in an annular shape, that is, spirally wound on the outer wall of the inner tank 10 as shown in FIG. 4. Alternatively, although not shown in the drawing, the inner tank outer wall may be formed. It may be configured to have a configuration adjacent to the cylindrical drum (Cylinder).

Both ends of the heat insulating pipe 30 surrounding the inner tank 10 as described above are connected to the heat exchanger 40 via the outer tank 20. Specifically, the refrigerant inlet 42 and the outlet 44 are formed in one upper portion and the other lower portion of the heat exchanger 40, respectively, so that one end of the heat insulating pipe 30 is an inlet 42 of the upper portion of the heat exchanger 40. ) And the other end is connected to the outlet 44 of the other lower side of the heat exchanger.

Therefore, the vaporized refrigerant absorbing the external heat while passing around the inner tank 10 flows into the sealed heat exchanger 40 through the refrigerant inlet 42, and moves to the outside through the heat exchanger 40. The refrigerant phase-converted into the liquid phase while dissipating heat flows into the heat insulating pipe 30 through the refrigerant outlet 44 by its own weight and collects on the bottom surface of the heat exchanger 40.

Meanwhile, the discharge pipe 50 through which the liquid fuel is discharged extends from the inner tank 10 and passes through the heat exchanger 40 disposed outside the tank. At this time, part of the discharge pipe via the heat exchanger 40 inside the discharge pipe 50 takes the shape of continuously bent up, down, left, right in the heat exchanger 40 like the general heat exchanger.

Operation and effects of the present invention configured as described above will be described in detail with reference to the accompanying drawings.

5 is a view showing the operating state of the cryogenic liquid fuel storage tank according to the present invention, showing the circulation process of the refrigerant in the heat exchanger and heat insulating pipe according to the discharge of the cryogenic liquid fuel filled in the inner tank. In the present embodiment, a case where the liquid fuel filled in the inner tank is a liquid hydrogen having a vaporization temperature of -253 ℃.

Looking at the operation and effect of the present invention with reference to Figure 5, in the case of the liquid hydrogen storage tank after the liquid nitrogen or a high pressure nitrogen gas is filled with a high liquefied point than the liquid hydrogen as the storage liquid in the tank inside the heat insulating pipe 30 It is sealed and the liquid hydrogen discharged from the inner tank 10 passes through the heat exchanger 40.

Therefore, the cryogenic fluid (-253 ° C. liquid hydrogen) of the inner tank 10 undergoes heat exchange with nitrogen gas in the heat insulating pipe 30 while passing through the heat exchanger 40 when it is sent out. The refrigerant charged in the insulation pipe 30, that is, nitrogen gas, is liquefied under the influence of the cryogenic fluid, and passes from the outside while passing between the inner tank 10 and the outer tank 20 along the insulation pipe 30. Absorbs / blocks heat invading to prevent vaporization of liquid fuel, ie, liquid hydrogen, filled in the inner tank 10 as much as possible.

In more detail, the refrigerant inside the sealed heat exchanger 40, that is, liquid nitrogen, is continuously vaporized by heat inflow from the outside atmosphere. The vaporized nitrogen gas rises inside the heat exchanger at the same time as the vaporization and heat exchanges with the liquid hydrogen at -253 ° C passing through the heat exchanger 40 to become -196 ° C liquid nitrogen. The liquefied nitrogen flows into the heat insulating pipe 30 through the inlet 42 of the heat exchanger by gravity and flows in from the outside while passing around the inner tank by gravity, similarly to the principle of the other heat insulating pipe 30. Absorb / Block

At this time, the internal pressure of the heat insulating pipe 30 is a vacuum is formed by the liquefaction of the refrigerant, that is, liquid nitrogen. Therefore, a part of the liquid nitrogen inside the heat insulating pipe 30 due to continuous external heat inflow is vaporized again and performs a continuous heat insulating function through the cycle liquefied in the heat exchanger (40).

On the other hand, the liquid hydrogen heat-exchanged with the nitrogen gas is raised to a gas state when the temperature rises and is sent to the vehicle fuel.

The effects according to the present invention operating as described above will be described through specific examples below.

<Example>

The outer wall of the insulation pipe is multi-layered in Mylar foil.

Maintain a high vacuum of 1 × 10 ^-5 Torr or higher between inner and outer tanks.

For example, a heat transfer amount of a 100 liter vehicle fuel tank having the following conditions is calculated as follows.

Diameter and length of outer cylinder for 100Liter vehicles: 450mm, 1250mm

Inner cylinder diameter: 350mm

Outer cylinder temperature: 300K (27 ℃)

Internal cylinder temperature: 20K (-253 ℃)

Insulation piping temperature: 77K (-196 ℃)

Latent heat of liquid hydrogen evaporation: 105.78 kcal / kg

Liquid hydrogen density: 70.79 kg / m ³

Calculation of heat quantity:

Cylinder

Q =-2 π L k (To-Ti) / ln (ro / ri)

=-(2) (3.14) (1.25m) (3.7 x 10 ^-5 W / mK) (27 + 196) / ln (0.225m / 0.175m)

= 0.2577 W

-Side section

      Q =-k A (To-Ti) / X

=-(3.7 x 10 ^-5 W / mK) [(0.225m) 2π] (27 + 253) / (0.05m)

         = 0.033 W

Total external heat flux: Qt = 0.2577 + 0.033 = 0.2907 W

                   = 0.2907 J / s x 3600 s / h = 1.0466 kJ / h = 0.2504 kcal / h

Amount of liquid hydrogen evaporated by heat inflow:

-Evaporation mass and volume per hour:

      m = (0.2504 / 105.78) = 0.00237 kg / h

      V = (0.00237 kg) x (1 / 70.79) x (1000 Liter) = 0.033 Liter / h

-Daily vaporized liquid amount:

0.033 Liter / hx 24h = 0.8 Liter

-Daily vaporization rate in total:

(0.8 Liter / 100 Liter) x 100 = 0.8%

As described above, according to the cryogenic liquid fuel storage tank according to the embodiment of the present invention, the daily vaporization rate is about 0.8%, the heat insulation effect is very excellent.

According to the present invention described above, the inner tank 10, which is filled with the liquid fuel in the outer tank 20 is stored spaced apart, the heat insulating pipe between the outer tank 20 and the inner tank 10 ( Only by hypothesis 30) it is possible to obtain a more improved thermal insulation effect than the prior art.

As a result, according to the present invention, it is possible to greatly improve the workability compared to the conventional triple tank structure, the outside air moisture or carbon dioxide is accumulated in the tank in the process of liquefied by the outside air while the liquid fuel as the storage fluid passes through the heat exchanger It can eliminate the disadvantages.

In the above description, the present invention has been described using only a vehicle fuel storage tank as an example. However, the present invention may be equally applicable to a cryogenic liquid storage tank such as liquid hydrogen and liquid nitrogen, and a transport vehicle for cryogenic fluid as well as a vehicle fuel storage tank. It would be obvious to him.

In addition, the present invention described above may be variously modified and may take various forms, and the detailed description of the present invention has been described with reference to only one embodiment thereof. It is to be understood, however, that the present invention is not limited to one form referred to in the description, but rather includes all modifications, equivalents, and substitutes within the spirit and scope of the invention as defined by the appended claims. Should be.

As described above, according to the ultra low temperature liquid fuel storage tank for vehicles using the heat recovery cycle of the present invention, a sealed insulation pipe filled with liquid or gas is disposed between the inner tank and the outer tank, thereby filling the insulation pipe. The fluid, ie, the refrigerant, absorbs external invading heat and vaporizes, thereby absorbing and blocking external heat. Accordingly, the thermal insulation effect is greatly improved, and as a result, the cryogenic liquid fuel filled in the tank can be stored for a long time.

Moreover, the present invention can obtain an improved heat insulation effect compared to the conventional art only by installing a heat insulating pipe between the tanks of the double structure, which can greatly improve the workability of the conventional triple tank structure. As a result, the production cost can be reduced and improved productivity can be expected, and outside moisture or carbon dioxide does not accumulate inside the cylinder, thereby improving product reliability.

Claims (3)

Fuel tank for storing cryogenic liquid fuel, Internal tanks for storing liquid fuel, An outer tank accommodating the inner tank; An insulation pipe disposed between the outer tank and the inner tank; A hollow heat exchanger disposed adjacent to the outer tank and provided with an enclosed space therein; Both ends of the heat insulating pipe are connected to the heat exchanger via an outer tank, and the discharge pipe for discharging liquid fuel extends from the inner tank to pass through the heat exchanger. Fuel storage tank. The method of claim 1, The heat insulating pipe is a cryogenic liquid fuel storage tank for a vehicle using a heat recovery cycle, characterized in that the copper or steel pipe having a circular or elliptical cross section is wound in an annular shape on the outer wall of the inner tank. The method of claim 1, The thermal insulation pipe is a cryogenic liquid fuel storage tank for a vehicle using a heat recovery cycle, characterized in that the cylindrical tank is installed on the outer wall of the inner tank.

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