KR101363565B1 - equipment and method for gas substitution of liquefied natural gas tank - Google Patents

Abstract

The present invention relates to a gas replacement facility and a gas replacement method of a liquefied natural gas tank, the replacement gas supply pipe 40 connected to the replacement gas pipe 30 through which the fuel gas (FG) flows is the center of the dome upper portion of the outer tank (10). It is installed through, the outer tank gas discharge pipe (50, 60) and the inner tank gas discharge pipe 70 is installed.
Gas replacement is performed in such a manner that the fuel gas fills the space of the outer tank 10 first, and then fills the space of the inner tank 20, and the fuel gas is not mixed with nitrogen gas inside the tank. By pressurizing the nitrogen gas downward in the discharge is made to the atmosphere.
Therefore, the time required for the replacement process is shortened, and the consumption of the replacement gas is reduced.

Description

Equipment and method for gas substitution of liquefied natural gas tank

The present invention relates to a gas replacement facility and a gas replacement method of a liquefied natural gas tank, and more particularly, to a gas replacement facility and a gas replacement method of a liquefied natural gas tank that can be carried out more quickly.

Liquefied natural gas (hereinafter referred to as LNG) that is unloaded from a transport ship is stored in a large tank of about 100,000 to 200,000 km3.

The LNG tank is a concrete structure built on the ground or underground, and includes an outer tank having a domed roof on the upper part of the cylindrical wall, and a cylindrical inner tank constructed inside the outer tank. LNG is stored in

Meanwhile, in order to store LNG in an LNG tank, first, oxygen and water present in the tank must be removed, and dry nitrogen gas (N ₂ ) is injected into the tank to remove the oxygen and water to the outside. . In other words, by replacing the air in the tank with nitrogen to remove oxygen and water in the tank.

After removing the oxygen and water as described above, by replacing the nitrogen gas with boil-off gas (BOG) again of the worm BOG (warm BOG) generated in the next cool down (Cool Down) process The gas replacement process (also called BOG substitution process) to increase the purity is carried out.

However, in the conventional gas replacement process, a large amount of BOG is vented and incinerated to the outside of the tank, thereby increasing the time and amount of BOG consumed to completely replace the tank with BOG.

In addition, since the inner portion of the outer tank is made of carbon material and has low temperature brittleness, the BOG supply pipe had to be connected to the inner tank to supply the BOG, and the BOG was mixed with nitrogen gas to escape into the outer tank space. Therefore, the gas replacement of the inner tank and the outer tank is made at the same time, and since the discharge and incineration of the mixed gas continues, the replacement speed becomes slower.

Accordingly, the present invention has been made to solve the above problems, the time required for the gas replacement process is shortened, and the gas replacement of the liquefied natural gas tank to reduce the consumption of the replacement gas used for nitrogen replacement Its purpose is to provide a facility and a gas replacement method.

Gas replacement equipment of the liquefied natural gas tank according to the present invention for achieving the above object,

A substitution gas supply pipe installed through the outer tank of the LNG tank;

An outer tank gas discharge pipe connecting an adjacent floor of the outer tank to the atmosphere;

An inner tank gas discharge pipe connecting the inner tank bottom proximal portion of the LNG tank to the atmosphere;

A first valve installed at the replacement gas supply pipe;

A second valve and a third valve respectively installed at the outer tank gas discharge pipe;

A fourth valve installed in the inner tank gas discharge pipe

.

In addition, the replacement gas supply pipe is characterized in that installed through the upper center portion of the outer tank.

In addition, the replacement gas pipe is characterized in that connected to the fuel gas (FG) pipe produced at the production base.

In addition, the fuel gas pipe is characterized in that the heat pipe is not insulated.

In addition, an incineration tube connected to a combustor is connected to a position before the fourth valve of the inner tank gas discharge pipe, and a fifth valve is installed in the incineration pipe.

In addition, the outer tank gas discharge pipe and the inner tank gas discharge pipe is characterized in that the methane concentration sensor is installed.

On the other hand, the gas replacement method of the liquefied natural gas tank according to the present invention,

An external tank gas replacement step of discharging nitrogen gas in the external tank to the atmosphere by injecting a substitution gas into the upper center of the external tank of the LNG tank;

When the gas replacement of the outer tank is finished, the inner tank gas replacement step of introducing the replacement gas into the inner tank of the LNG tank to discharge the nitrogen gas in the inner tank to the atmosphere

.

In addition, by using the fuel gas produced at the production base as the replacement gas to prevent mixing with the nitrogen gas in the LNG tank, it is characterized in that the nitrogen gas under pressure by the piston effect caused by the replacement gas discharged. .

Further, after each of the external tank gas replacement step and the internal tank gas replacement step, measuring the methane concentration of the exhaust gas discharged from the tank to perform a gas replacement completion determination step of determining that the corresponding gas replacement step is completed. It features.

In addition, when the internal tank gas replacement step is completed, by supplying the exhaust gas of the inner tank to the combustor characterized in that to incinerate the fuel gas contained in the exhaust gas.

In addition, the fuel gas is characterized in that the temperature is higher and the specific gravity is lower than the nitrogen gas inside the LNG tank.

According to the present invention as described above, irrespective of whether the dome material of the outer tank has low temperature brittleness, the replacement gas can be injected through the upper portion of the dome center of the outer tank.

In addition, by supplying the fuel gas having a higher temperature and specific gravity than the nitrogen gas as the replacement gas, mixing with the nitrogen gas is prevented, and as described above, the supply of the replacement gas at the upper portion of the outer tank starts the replacement gas to the piston effect. By pressurizing the nitrogen gas it can be discharged more smoothly.

In addition, by replacing the inner tank after the completion of the replacement of the outer tank, the replacement of the two tanks are made in stages, thereby increasing the piston effect is more rapid nitrogen gas discharge.

In addition, the exhaust gas is not mixed with the nitrogen gas and is discharged in the above manner (discharge method by the piston effect), thereby reducing the consumption of fuel gas used as the replacement gas.

1 is a view showing the installation state of the gas replacement system and the external tank replacement step of the gas replacement method according to the present invention,
2 is a view showing the internal tank replacement step of the gas replacement method according to the present invention,
3 is a flowchart of a gas substitution method according to the present invention.

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

As shown in FIG. 1, the LNG tank includes an outer tank 10 and an inner tank 20. The outer tank 10 is a cylindrical structure formed in the upper portion of the dome (dome), the inner tank 10 is a cylindrical structure having a flat top. Between the outer tank 10 and the inner tank 20, there is a space that functions as a space in which the insulating space of the inner tank 20 and the boil-off gas of LNG stored in the inner tank 20 is filled. In addition, the lower portion of the outer tank 10 supports the load of the entire structure including the inner tank 20, there is a structural layer to insulate the inner tank 20 to the ground.

Gas replacement system of the LNG tank according to the present invention, the replacement gas supply pipe 40 is installed through the interior of the outer tank 10, the outer tank gas discharge pipe connecting the atmosphere near the bottom of the outer tank 10 and the atmosphere 50 and 60, an inner tank gas discharge pipe 70 connecting the bottom portion of the inner tank 20 to the atmosphere, a first valve 41 installed in the replacement gas supply pipe 40, and the outside And a second valve 51 and a third valve 61 installed in the tank gas discharge pipes 50 and 60 and a fourth valve 71 provided in the inner tank gas discharge pipe 70.

The replacement gas supply pipe 40 is connected to a replacement gas pipe 30 through which a replacement gas (hereinafter referred to as a replacement gas) flows into the LNG tank for nitrogen gas replacement in the LNG tank, and the replacement gas supply pipe 40, the first valve 41 is installed to open and close it.

In addition, the replacement gas supply pipe 40 is installed through the upper center portion of the dome of the outer tank 10, the end of which is located under the inner side of the dome to supply the replacement gas to the lower space of the dome. .

In addition, the replacement gas supply pipe 40 may be provided with an auxiliary opening and closing valve 42 adjacent to the replacement gas pipe 30 side.

The replacement gas pipe 30 is preferably an FG pipe through which a fuel gas (hereinafter, FG; fuel gas) produced in the production base flows. The FG is a fuel gas for heating the compressed BOG and NG in a heater and then supplying the inside of the base and the supply control station. Since the replacement gas pipe 30 is a non-insulated tube, the temperature of the FG is Affected by atmospheric temperature. Therefore, the FG has a much higher temperature than the nitrogen gas injected into the LNG tank to remove moisture and oxygen.

The outer tank gas discharge pipe (50, 60) is disposed at a lower end position close to the bottom of the outer tank 10, the upper end is disposed outside the outer tank (20). The outer tank gas discharge pipe (50, 60) is installed in a state passing through the edge portion of the dome of the outer tank (10).

In addition, a second valve 51 and a third valve 61 capable of opening and closing respective pipes are provided at outer portions of the outer tank 20 of the outer tank gas discharge pipes 50 and 60, respectively.

The inner tank gas discharge pipe (70) is L-shaped, the lower horizontal portion is disposed in a position close to the bottom of the inner tank 20, the vertical portion penetrates the inner tank 20 and the outer tank (10) The upper end is disposed outside the outer tank 10. In particular, the lower opening of the inner tank gas discharge pipe 70 is disposed at the central portion of the inner tank 20.

In addition, a fourth valve 71 for opening and closing the inner tank gas discharge pipe 70 is installed at an outer portion of the outer tank 20 of the inner tank gas discharge pipe 70.

In addition, an incineration tube (80) connected to a combustor (not shown) is installed in the inner tank gas discharge pipe (70) before (lower) the installation position of the fourth valve (71), and the incineration pipe (80) Edo fifth valve 81 for opening and closing the pipe is installed.

On the other hand, the replacement gas supply pipe 40 is provided with a temperature sensor 43 and a pressure sensor 44 to know the temperature and pressure of the replacement gas supplied into the LNG tank.

In addition, the outer tank gas discharge pipe (50, 60) and the inner tank gas discharge pipe 70, the gas discharged from the LNG tank, methane concentration measurement sensor (52, 62, 72) for measuring the methane concentration in the discharged gas Are installed respectively.

In addition, all the pipes may be provided with a pump (not shown) for promoting the movement of the gas through the pipes respectively.

By the above configuration, in order to remove moisture and oxygen, the heterogeneous replacement gas (FG) can be injected into the LNG tank in a state where the LNG tank is replaced with dry nitrogen gas.

The nitrogen gas present in the LNG tank may be discharged to the outside of the LNG tank through the external tank gas discharge pipes 50 and 60 and the internal tank gas discharge pipe 70. That is, the FG substitution of the LNG tank is made. FG inflow from the outer tank 10 to the inner tank 20 is made through a balancing hole (21) formed in the upper (Suspend Deck) of the inner tank (20).

In addition, the second valve 51 and the third valve 61 of the outer tank gas discharge pipe (50, 60), the fourth valve 71 and the incineration pipe (80) of the inner tank gas discharge pipe (70) The opening and closing control of the fifth valve 81 and the first valve 41 of the replacement gas supply pipe 40 may be performed according to the measurement results of the methane concentration measurement sensors 52, 62, and 72. To this end, the first to fifth valves 41, 51, 61, 71, and 81 may be configured as electronic control valves, and the electronic control may be performed according to the measurement result of the methane concentration sensor 52, 62, 72. An electronic control unit may be provided to control the opening and closing of the valves.

FG in the gas discharged through the incineration tube 80 is supplied to a combustor connected to the incineration tube 80 to be incinerated.

In addition, by adjusting the operation of the pump installed in the replacement gas supply pipe 40 and the opening degree of the first valve 41 it can always supply a replacement gas to the external tank 10 at a constant pressure. This helps to prevent mixing of the FG and nitrogen gas supplied to the substitution gas.

Now, the gas replacement method of the LNG tank using the gas replacement equipment of the LNG tank including the above configuration will be described with reference to FIGS.

The LNG tank carrying out the FG replacement is nitrogen-substituted to remove oxygen and water, and the inside is filled with nitrogen gas.

In this state, the first valve 41 is first opened. (S10)

The FG is injected into the outer tank 10 by opening the first valve 41. (S20) Since the injected FG is affected by atmospheric temperature as described above, the FG is injected into the nitrogen gas inside the LNG tank. It is relatively high temperature (ex; April ~ May, FG temperature is formed in the range of 9 ~ 17 ℃. Even if the air temperature drops below freezing in winter, it is much higher than the nitrogen gas injected into LNG tank. In addition, the density of nitrogen (N ₂ ) is 1.251kg / m ³ and the density of methane (CH ₄ ), which is a component of FG, is 0.717kg / m ^3, which is smaller than that of nitrogen. That is, since the specific gravity of the FG injected is smaller than the nitrogen filled in the LNG tank, the protons are not mixed and a boundary layer is formed between the protons.

Therefore, after the boundary layer gradually descends and the dome lower space is replaced with the FG, the FG flows into an annular space surrounding the side space of the outer tank 10, that is, the side of the inner tank 20. It will replace the annular space.

At this time, the FG is a large space rather than flowing through the balancing hole 21 of the inner tank 20, so that the FG is moved to the annular space having a relatively low resistance, so that the replacement of the annular space is larger than the inner space of the inner tank 20. This is done first.

Nitrogen gas filled in the outer tank 10 during the FG replacement of the outer tank 10 is discharged into the atmosphere through the outer tank gas discharge pipes 50 and 60, wherein the methane concentration of the exhaust gas is It is measured by the methane concentration sensor 52,62.

If the methane concentration measured by the methane concentration measuring sensor (52, 62) exceeds the set value, it is determined that the external tank is completely replaced by FG. (S30) The set value of the methane concentration in the state that almost no nitrogen in the exhaust gas As a value, for example, it can be set to 95 vol%.

When it is determined that the replacement of the outer tank 10 is completed, the second valve 51 and the third valve 61 of the outer tank gas discharge pipes 50 and 60 are blocked.

After the second valve 51 and the third valve 61 are blocked as described above, the FG injected into the lower space of the dome is injected into the inner tank 20 through the balancing hole 21 and the inner tank 20. ) Gas replacement is performed (S50).

Since the gas replacement of the inner tank 20 also does not mix the injected FG and the nitrogen gas inside the inner tank 20, the upper FG gradually expands downwardly with a boundary layer formed therebetween. In this case, the nitrogen gas is pushed downward and discharged into the atmosphere through the inner tank gas discharge pipe 70.

As described above, the FG layer formed on the upper side does not mix with the lower nitrogen gas and pressurizes the nitrogen gas downwardly, that is, the gas discharged during the FG substitution by the piston effect (Piston Effect) is FG. It is rarely included. Therefore, there is an effect that the air emissions of the FG is significantly reduced compared to the conventional. This effect occurs equally when replacing the inner tank 20 as well as replacing the outer tank 10.

While the replacement of the inner tank 20 is in progress, the methane concentration sensor 72 installed in the inner tank gas discharge pipe 70 continuously measures the methane concentration in the exhaust gas.

Thereafter, when the methane concentration measured by the methane concentration measurement sensor 72 is equal to or higher than a set value (the same as the set value for determining the completion of the external tank replacement), it is determined that the replacement of the inner tank 20 is completed.

When it is determined that the replacement of the inner tank 20 is completed as described above, the fourth valve 71 is blocked to prevent the discharge of the exhaust gas into the air, and the fifth valve 81 of the incineration tube 80 is opened. (S80)

Therefore, the exhaust gas is supplied to the combustor and the FG contained in the exhaust gas is incinerated.

Thereafter, the fifth valve 81 is blocked to stop unnecessary incineration of the FG, and the first valve 41 is blocked to stop the FG injection into the LNG tank.

This terminates the FG replacement of the LNG tank.

According to the LNG tank gas replacement method according to the present invention as described above, the nitrogen gas is more rapidly due to the piston effect when the substitution gas and nitrogen gas is not mixed by using FG having a higher temperature and specific gravity than the nitrogen as the replacement gas. Is discharged.

In addition, the use of FG eliminates the risk of damage due to low temperature embrittlement of the dome inner surface material, thereby allowing the replacement gas to be injected through the upper peak of the LNG tank, thereby increasing the piston effect. The gas can be released more quickly.

In addition, as described above, the replacement gas is injected from the upper apex of the LNG tank, and then the external tank 10 is first replaced, and then the internal tank 20 is replaced. Since the area for pressurizing the nitrogen gas layer is reduced compared to when the entire LNG tank is replaced at the same time, even though the FG is injected at the same pressure, the piston effect is increased, so that nitrogen gas can be discharged more easily and quickly.

In addition, since the FG is rarely mixed with the nitrogen gas, it is possible to minimize the amount of FG discharged with the nitrogen gas. In other words, it is possible to minimize the amount of atmospheric emissions and incineration of the replacement gas, thereby reducing the consumption of the replacement gas.

As described above, according to the present invention, the process time required for the gas replacement process of the LNG tank is reduced, and the consumption of the replacement gas is reduced.

10: outer tank 20: inner tank
21: balancing hole 30: substitution gas piping
40: replacement gas supply pipe 50,60: external tank gas discharge pipe
70: inner tank gas discharge pipe 80: incineration pipe
41,42,51,61,71,81: valve

Claims (11)

It is provided with an outer tank, the inner tank is disposed inside the outer tank and has a balancing hole in the upper portion, the gas replacement equipment of the LNG tank having a space between the outer tank and the inner tank,
It is installed through the outer tank, the end of the replacement gas supply pipe disposed between the outer tank and the inner tank,
Between the outer tank and the inner tank, the outer tank gas discharge pipe connecting the bottom of the outer tank and the atmosphere,
An inner tank gas discharge pipe connecting the inner tank bottom proximal part to the atmosphere;
A first valve installed at the replacement gas supply pipe;
A second valve and a third valve respectively installed at the outer tank gas discharge pipe;
Gas replacement system for a liquefied natural gas tank comprising a fourth valve installed in the inner tank gas discharge pipe. The method according to claim 1,
The replacement gas supply pipe is a gas replacement system of a liquefied natural gas tank, characterized in that installed through the upper center portion of the outer tank. The method according to claim 1,
The replacement gas supply pipe is connected to the replacement gas pipe through which the replacement gas is injected into the LNG tank,
The replacement gas pipe is a gas replacement system of a liquefied natural gas tank, characterized in that connected to the fuel gas pipe produced at the production base. The method according to claim 3,
The fuel gas pipe is a gas replacement system of a liquefied natural gas tank, characterized in that the non-insulated tube. The method according to claim 1,
An incineration tube connected to a combustor is connected to a position before the fourth valve of the inner tank gas discharge pipe, and a fifth valve is installed in the incineration pipe. The method according to claim 1,
The gas tank of the liquefied natural gas tank, characterized in that the methane concentration sensor is installed in the outer tank gas discharge pipe and the inner tank gas discharge pipe. The gas tank of the LNG tank having an outer tank, an inner tank disposed inside the outer tank and having a balancing hole formed thereon, and having a space between the outer tank and the inner tank,
A substitution gas supply pipe installed through the outer tank and having an end thereof disposed in a space between the outer tank and the inner tank;
Between the outer tank and the inner tank, an outer tank gas discharge pipe connecting the bottom of the outer tank and the atmosphere;
An inner tank gas discharge pipe connecting the inner tank bottom proximal part to the atmosphere;
A first valve installed at the replacement gas supply pipe;
A second valve and a third valve respectively installed at the outer tank gas discharge pipe;
Gas replacement method of the liquefied natural gas tank using the gas replacement equipment of the liquefied natural gas tank including the fourth valve installed in the inner tank gas discharge pipe,
An external tank gas replacement step of injecting a replacement gas into the external tank through the replacement gas supply pipe and discharging nitrogen gas in a space between the external tank and the internal tank to the external tank gas discharge pipe into the atmosphere;
When the gas replacement in the space between the outer tank and the inner tank is terminated, the second valve and the third valve are shut off, and the replacement gas is introduced into the inner tank through the balancing hole to allow nitrogen gas in the inner tank. Gas replacement method of a liquefied natural gas tank comprising an internal tank gas replacement step of discharging to the atmosphere through the inner tank gas discharge pipe. The method of claim 7,
The fuel gas produced at the production base is used as the replacement gas to prevent mixing with the nitrogen gas in the LNG tank, and the nitrogen gas is pressurized and discharged by the piston effect caused by the replacement gas. Gas replacement method of gas tank. The method of claim 7,
After completion of the external tank gas replacement step and the internal tank gas replacement step, by measuring the methane concentration of the exhaust gas discharged from the tank to perform a gas replacement completion determination step to determine that the corresponding gas replacement step is completed Gas replacement method of liquefied natural gas tank to be. The method according to claim 8,
The gas replacement method of the liquefied natural gas tank, characterized in that to incinerate the fuel gas contained in the exhaust gas by supplying the exhaust gas of the inner tank to the combustor when the internal tank gas replacement step is completed. The method according to claim 8,
The fuel gas is a gas replacement method of a liquefied natural gas tank, characterized in that the temperature is higher and the specific gravity is lower than the nitrogen gas inside the LNG tank.

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