JP4255151B2 - Pressure drop method for medium pressure LNG storage tank - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention reduces the pressure in the storage tank on the LNG replenishment side when the LNG is fed from a lorry vehicle or the like using a pressure difference into a storage tank to which LNG should be replenished, among a plurality of installed medium pressure LNG storage tanks. The present invention relates to a method for reducing the pressure of an intermediate pressure LNG storage tank.
[0002]
[Prior art]
In an LNG satellite base or the like, when replenishing LNG from a lorry vehicle or the like to an intermediate pressure LNG storage tank, the pressure in the storage tank (hereinafter referred to as a supplement side storage tank) to which LNG is to be replenished is reduced. LNG is fed using the difference.
[0003]
Conventionally, in order to reduce the pressure in the replenishment side storage tank, it is common to dissipate the vaporized gas accumulated in the upper part of the LNG in the replenishment side storage tank into the atmosphere or to reduce the pressure in a large-capacity hydrated holder. there were. As a result, the internal pressure of the replenishment-side storage tank is made lower than the internal pressure of a tank such as a lorry vehicle, and LNG is fed.
[0004]
There was also a method of dropping the pressure of the LNG storage tank using a BOG compressor.
[0005]
[Problems to be solved by the invention]
However, the above-described pressure reduction method for releasing the vaporized gas into the atmosphere has a problem that waste is generated from the viewpoint of energy consumption because the gas usable as fuel is released into the atmosphere. In particular, along with the recent increase in size of medium-pressure LNG storage tanks, LNG gas tends to be diffused into the atmosphere and energy loss tends to increase, which is not economically preferable.
[0006]
In addition, methane, which is a main component of the LNG vaporized gas, is a kind of global warming gas and is not environmentally preferable.
[0007]
Furthermore, since methane is vaporized when the pressure is reduced, there is also a problem that methane evaporates from LNG and LNG is concentrated (the calories of LNG increase).
[0008]
Therefore, the present invention has been devised to solve the above-described problems, and the object of the present invention is to reduce the pressure of the medium-pressure LNG storage tank without dissipating the vapor of LNG into the atmosphere. An object of the present invention is to provide a method for reducing the pressure of an intermediate pressure LNG storage tank.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a LNG replenishment side for supplying LNG using a pressure difference from a lorry vehicle into a storage tank to which LNG should be replenished among a plurality of medium-pressure LNG storage tanks installed. Spraying low-temperature LNG in another storage tank having a higher liquid level than the other storage tank from the upper part of the storage tank on the LNG replenishment side using the pressure difference between the two storage tanks, and reducing the pressure in the storage tank on the LNG replenishment side It is.
[0010]
According to the above method, the low temperature LNG in the other storage tank cools the relatively high temperature gas in the upper part of the storage tank on the LNG replenishment side to condense and liquefy it. Can be pressed.
[0011]
After the gas in the storage tank on the LNG replenishment side flows into a discharge pipe or a low pressure holder connected to each medium pressure LNG storage tank, the pressure in the storage tank is reduced, and then LNG is introduced from the other storage tank and sprayed. Those that do are preferred.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a schematic view showing an intermediate pressure LNG storage facility for carrying out the method of lowering the pressure of an intermediate pressure LNG storage tank according to the present invention.
[0014]
First, the configuration of the medium pressure LNG storage facility will be described.
[0015]
As shown in the figure, a plurality of medium-pressure LNG storage tanks 1 and 2 are provided on the ground. In this embodiment, an example in which two medium-pressure LNG storage tanks are provided will be described.
[0016]
Below each of the medium pressure LNG storage tanks 1 and 2, a discharge pipe 3 is provided that feeds gas after adjusting the amount of heat in a pipe (not shown) connected to each household. On the bottom surface of the medium pressure LNG storage tanks 1 and 2, a lower discharge pipe 4 connected to the discharge pipe 3 and for discharging the LNG in the storage tank is provided. The discharge pipe 3 is provided with a vaporizer 5 and a pressure reducing valve 6. After the LNG is vaporized by the vaporizer 5, the pressure is reduced by the pressure reducing valve 6, and propane gas or the like is added to the vaporized gas. After adjustment, it is sent as city gas. Each lower discharge pipe 4 is provided with a discharge valve 7.
[0017]
On the upper surface of each of the intermediate pressure LNG storage tanks 1 and 2, an upper discharge pipe 8 for discharging the vaporized gas of LNG to the downstream side of the pressure reducing valve 6 of the discharge pipe 3 is provided. Each upper discharge pipe 8 is provided with a discharge valve 9.
[0018]
An upstream portion of the lower discharge pipe 4 of the one intermediate pressure LNG storage tank 1 above the discharge valve 7 extends to the upper surface of the other intermediate pressure LNG storage tank 2 to transfer the LNG in the intermediate pressure LNG storage tank 1 to the intermediate pressure LNG storage tank 2. An LNG introduction pipe 11 for introducing the gas phase 14 above the LNG is provided. Similarly, an LNG introduction pipe 11 extending to the upper surface of the intermediate pressure LNG storage tank 1 is provided upstream of the discharge valve 7 of the lower discharge pipe 4 of the intermediate pressure LNG storage tank 2.
[0019]
These LNG introduction pipes 11 are each provided with an introduction valve 12. An upper end portion of the LNG introduction pipe 11 slightly protrudes into the gas phase 14, and a tip 15 for injecting the introduced LNG to the gas phase 14 and the inner wall of the storage tank is provided at the end portion.
[0020]
In each of the above-described medium pressure LNG storage tanks 1 and 2, one intermediate pressure LNG storage tank 1 is a discharge side storage tank 16 in which a large amount of LNG is stored, and the other medium pressure LNG storage tank 2 has a storage amount of LNG. It becomes the replenishment side storage tank 17 which should replenish this few. The payout-side storage tank 16 and the replenishment-side storage tank 17 alternate with each other depending on the amount of LNG stored therein. In the state of FIG. 1, the intermediate pressure LNG storage tank 1 on the left side is the discharge side storage tank 16, and the intermediate pressure LNG storage tank 2 on the right side is the replenishment side storage tank 17.
[0021]
Next, a method for reducing the pressure of the intermediate pressure LNG storage tank according to the present invention will be described.
[0022]
Here, a case where the normal LNG storage tank operating pressure is 0.5 to 0.6 MPa will be described below.
[0023]
First, after closing the discharge valve 7 of the replenishment side storage tank 17, the discharge valve 9 of the upper discharge pipe 8 provided in the replenishment side storage tank 17 is opened, and the vaporized gas in the replenishment side storage tank 17 is caused to flow to the discharge pipe 3. The internal pressure of the replenishment side storage tank 17 is slightly lowered.
[0024]
Thereafter, the introduction valve 12 of the LNG introduction pipe 11 protruding into the gas phase 14 of the replenishment side storage tank 17 is opened. At this time, since the internal pressure of the replenishment side storage tank 17 is lower than the internal pressure of the discharge side storage tank 16, LNG at the bottom of the discharge side storage tank 16 is introduced into the gas phase 14 of the replenishment side storage tank 17 by the pressure difference. And sprayed through the tip 15 at the tip (indicated by a broken line in the figure).
[0025]
The temperature of the gas phase 14 is about −100 ° C. to −140 ° C. (lowering from the upper side to the lower side). The gas phase 14 is supplied with LNG at about −150 ° C. at the bottom of the discharge side storage tank 16. And by spraying on the inner wall of the storage tank, the vaporized gas is effectively cooled, and its heat is taken away and liquefied. Therefore, the vaporized gas weight is reduced, and the pressure inside the replenishment side storage tank 17 is reduced.
[0026]
In this way, LNG can be sprayed and dropped in the replenishment-side storage tank 17 by slightly flowing the vaporized gas in the replenishment-side storage tank 17 downstream of the pressure reducing valve 6 of the discharge pipe 3. Is not required to be released into the atmosphere, and methane can be prevented from being released into the atmosphere, and energy loss can be prevented. Moreover, methane does not evaporate from LNG, and the increase in the calories can also be prevented.
[0027]
Furthermore, according to the above method, since the pressure is reduced by using only the movement of thermal energy in the storage tank, there is no need to use a pump or the like, and no momentum is given to LNG from the outside. Energy such as electricity is unnecessary.
[0028]
After that, when the internal pressure of the replenishment side storage tank 17 decreases by approximately 0.2 MPa and becomes approximately 0.3 to 0.4 MPa, liquid feeding from the lorry wheel 18 is started. Since the internal pressure of the tank 19 of the lorry wheel 18 is approximately 0.5 to 0.6 MPa, the LNG of the lorry wheel 18 can be used without using a pump or the like due to the pressure difference between the internal pressure of the replenishment side storage tank 17 and the tank 19. The liquid is automatically fed to the replenishment side storage tank 17.
[0029]
In the present embodiment, the LNG vaporized gas is caused to flow to the discharge pipe 3 by the upper discharge pipe 8, but it may be supplied to a low pressure holder (not shown) as a pressure reducing destination.
[0030]
In this embodiment, two medium-pressure LNG storage tanks are provided, but a larger number may be used.
[0031]
【The invention's effect】
In short, according to the present invention, an excellent effect is achieved in that the pressure in the medium pressure LNG storage tank can be reduced without dissipating the LNG vapor into the atmosphere.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a medium-pressure LNG storage facility for carrying out the method for lowering the pressure of a medium-pressure LNG storage tank according to the present invention.
[Explanation of symbols]
1, 2 Medium pressure LNG storage tank 3 Discharge pipe 16 Discharge side storage tank 17 Replenishment side storage tank 18 Roller

Claims (2)

When sending LNG using a pressure difference from a lorry vehicle or the like to a storage tank to which LNG should be replenished among a plurality of medium pressure LNG storage tanks, Spraying the LNG in the storage tank from the upper part of the storage tank on the LNG replenishment side using the pressure difference between the two storage tanks to reduce the pressure in the storage tank on the LNG replenishment side, and reducing the pressure of the medium pressure LNG storage tank . The gas in the storage tank on the LNG replenishment side is caused to flow through a discharge pipe or a low-pressure holder connected to each medium-pressure LNG storage tank, the pressure in the storage tank is reduced, and then LNG is introduced from the other storage tank and sprayed. The method for reducing the pressure of an intermediate pressure LNG storage tank according to claim 1.

Images