JPH09303697A - Pressure suppression device for low temperature liquefied gas storage tank - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To suppress an increase in tank pressure even when the amount of vaporized gas delivered to the demand destination is suppressed more than before in a predetermined time period when the demand for the vaporized gas at the demand destination decreases. To get it. SOLUTION: A return nozzle 9 penetrating a tank roof 4 and having a discharge port opened in an upper region of the storage tank space 2, and a funnel portion 11 having a slit 13 opened to the upper region of the storage tank space 2 and surrounding the discharge port. An external circulation line having a lead pipe 12 provided at the upper end and extending at the lower end to the bottom of the storage space 2 and opened, and a pump 14 so that the stored liquid 3 can be extracted from the bottom of the storage space 2 outside the tank 1 and circulated to the return nozzle 9. A pressure suppression device for the low temperature liquefied gas storage tank 1 is constituted by 15 and. When the stored liquid 3 is externally circulated through the external circulation line 15, the vaporized gas 5 is sucked into the lead pipe 12 through the slit 13 due to the pressure drop when the stored liquid 3 flows down the lead pipe 12, and is liquefied again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressurization suppressing device for a low temperature liquefied gas storage tank that stores a low temperature liquefied gas such as LNG.

[0002]

2. Description of the Related Art Conventionally, in a low temperature liquefied gas storage tank for storing a low temperature liquefied gas such as LNG, in order to keep the tank pressure within a constant value, the vaporized gas generated by heat input into the tank is always used. A compressor is used to send it to the demand destination for consumption, but if the demand destination is a power plant, for example, the demand for vaporized gas will be extremely reduced during the nighttime when the power consumption is greatly reduced. It will be.

At this time, if the amount of vaporized gas consumed falls below the amount of vaporized gas generated in the tank at night, the tank pressure rises in an extremely short time and exceeds the upper limit of the control pressure. The reality is that vaporized gas is used in preference to other power generation fuels.

[0004]

However, if there is such a restriction that the vaporized gas generated in the tank in the nighttime zone should be preferentially used as described above, the efficient use in the demand destination such as a power plant is difficult. There was a risk that it would hinder operation.

The present invention has been made in view of the above-mentioned circumstances, and even if the delivery amount of vaporized gas to the demand destination is suppressed more than before in a predetermined time period when the demand of the vaporized gas at the demand destination decreases. The purpose is to suppress an increase in tank pressure.

[0006]

According to the present invention, there is provided a return nozzle which penetrates a tank roof and has a discharge port opened in an upper region of a storage tank space, and a discharge nozzle of the return nozzle which is partially opened in an upper region of the storage tank space. It has a lead tube having a funnel part surrounding the outlet at the upper end and having a lower end extending to the bottom of the storage space and opening, and a pump for extracting the stored liquid from the bottom of the storage space outside the tank and circulating it to the return nozzle. The invention relates to a pressurization suppressing device for a low temperature liquefied gas storage tank, which is provided with an external circulation line configured as described above.

Thus, in a predetermined time period when the demand for vaporized gas at the demand destination decreases, even if the amount of vaporized gas delivered to the demand destination is suppressed, the storage stored in the low temperature liquefied gas storage tank If the liquid is circulated externally by the external circulation line and the return nozzle and the lead pipe are made to flow down, gas is entrained as the stored liquid flowing from the outlet of the return nozzle to the funnel at the upper end of the lead pipe flows down in the lead pipe. And
The gas in the gas phase portion in the upper area of the storage space is entrained in the reed tube from the open portion of the funnel, and the gas entrainment phenomenon causes the gas taken in the reed tube to Since it is liquefied again under the liquid level due to heat exchange with the stored liquid or the like, it is possible to suppress an increase in tank pressure.

Further, a flow rate adjusting valve for adjusting the flow rate of the stored liquid circulating through the external circulation line and the flow rate of the stored liquid circulating through the external circulation line are measured, and the measured value of the flow rate becomes a predetermined set value. A flow meter for controlling the flow rate adjusting valve, a tank pressure gauge for measuring the pressure in the upper region of the storage space,
Externally circulate based on the pressure measured by the liquid level meter and the tank pressure gauge that measure the liquid level of the stored liquid, the consumption of vaporized gas required by the customer, and the liquid level measured by the liquid level meter. A control device for calculating an appropriate flow rate of the storage fluid to be set and setting it in the flow meter may be provided.

With this configuration, the control device can calculate an appropriate flow rate of the stored liquid to be circulated externally and set it in the flow meter, so that the stored liquid can be externally controlled so as to suppress an increase in tank pressure. It becomes possible to automatically perform the circulating operation.

That is, if the pressure in the upper region of the storage space at the start of operation is measured by the tank pressure gauge, the amount of change in the tank pressure until the tank pressure reaches the upper limit of the control pressure can be set. Based on the pressure change amount, the allowable gas change amount in the gas phase portion in the upper region of the storage space can be obtained.

This permissible gas change amount is obtained by subtracting the absorbed amount of the vaporized gas liquefied by the external circulation and the consumed amount of the vaporized gas in the customer from the generated amount of the vaporized gas in the tank in a predetermined time period. Of these, the amount of vaporized gas generated in the tank is empirically known, and the amount of vaporized gas consumed by the demand destination is determined by the operation of the demand destination. Once the amount of change is determined, the minimum required absorption amount of vaporized gas that must be liquefied by external circulation is naturally determined.

Here, there is a correlation between the absorption level of the vaporized gas that is liquefied by being caught in the lead tube when the stored liquid is circulated at a constant flow rate and the liquid level of the stored liquid in the tank. Has been confirmed by the inventor of the present application, and as described above, if the minimum required absorption amount of vaporized gas is determined,
The circulating flow rate of the stored liquid required to achieve the absorbed amount of the vaporized gas is determined based on the liquid level of the stored liquid measured by the liquid level gauge.

Further, it is preferable that the return nozzle is arranged so as to penetrate through the central position of the tank roof.
Since it is possible to arrange the lead tube at a position where the height dimension is the maximum in the storage tank space and to make the height dimension of the lead tube as large as possible, the drop rate of the stored liquid flowing down in the lead tube can be significantly increased. It becomes possible to accelerate, and it becomes possible to efficiently entrain the vaporized gas in the lead tube and liquefy it.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show an example of a mode for carrying out the present invention.

In the figure, 1 indicates a low temperature liquefied gas storage tank,
A low-temperature liquefied gas such as LNG is stored as a storage liquid 3 in a storage space 2 formed inside the low-temperature liquefied-gas storage tank 1 and is formed in a dome shape on the upper portion of the low-temperature liquefied gas storage tank 1. The tank roof 4 is connected to a gas discharge line 8 that extracts the vaporized gas 5 in the upper region of the storage tank space 2 and guides it to a demand destination 7 such as a power plant via a compressor 6.

Further, a return nozzle 9 is provided at a central position on the tank roof 4 of the low temperature liquefied gas storage tank 1, and as shown in FIG. 2, the lower end of the return nozzle 9 is
A discharge port 10 is opened in the upper region of the storage space 2.

Immediately below the return nozzle 9 in the storage space 2 of the low temperature liquefied gas storage tank 1, there is provided a funnel portion 11 surrounding the discharge port 10 of the return nozzle 9 at the upper end and the lower end up to the bottom of the storage space 2. Lead tube 1 that is extended and opened
2 are arranged upright, and the funnel portion 11 has
A plurality of open slits 13 are opened in the upper area of the storage space 2.

Further, outside the low temperature liquefied gas storage tank 1, there is provided an external circulation line 15 having a pump 14 so that the stored liquid 3 can be extracted from the bottom of the storage space 2 and circulated to the upper end of the return nozzle 9. A flow meter 16 for measuring the circulation flow rate of the storage liquid 3 and a flow rate adjusting valve 17 for adjusting the circulation flow rate of the storage liquid 3 are provided at appropriate positions of the external circulation line 15. An opening adjustment signal 20 is output from the flow meter 16 to the flow rate adjusting valve 17 so that the flow rate value measured by the meter 16 becomes a set value set by the setting signal 19 from the control device 18. Has become.

Further, in the low temperature liquefied gas storage tank 1, a tank pressure gauge 21 for measuring the pressure of the gas phase portion in the upper region of the storage tank space 2 and a liquid level gauge for measuring the liquid level of the stored liquid 3 in the tank. 22 are provided respectively, and the tank pressure gauge 2
The pressure signal 23 from 1 and the liquid level signal 24 from the liquid level gauge 22 are input to the control device 18.

Further, in the control device 18, a consumption amount signal 25 of the vaporized gas 5 introduced from the demand destination 7 is also inputted, and this consumption amount signal 25 and the tank pressure gauge 21 are supplied. Based on the pressure signal 23 and the liquid level signal 24 from the liquid level meter 22, an appropriate flow rate of the stored liquid 3 to be circulated externally is calculated and output as the setting signal 19 to the flow meter 16. is there.

The operation of the present embodiment thus constructed will be described below. Before proceeding to the detailed description including the control system, the stored liquid 3 is extracted from the bottom of the storage tank space 2 and the external circulation line 15 is used. The significance of circulating the return nozzle 9 and the lead pipe 12 to the return nozzle 9 and returning the return nozzle 9 and the lead pipe 12 to the bottom of the storage space 2 will be described.

For example, when the consumption amount of the vaporized gas 5 decreases at night in a demand destination 7 such as a power plant, if the consumption amount of the vaporized gas 5 becomes lower than the generation amount of the vaporized gas 5 in the tank 1, The tank pressure rises in a very short time and exceeds the control pressure. This is because only the surface of the stored liquid 3 follows the pressure of the gas phase portion in the tank 1 in a very short time and shifts to the equilibrium state. It is due to being lost.

On the other hand, since the liquid phase portion has a large heat capacity, it takes a considerable amount of time for the entire liquid phase portion to reach an equilibrium state. This means that as a result of actually measuring the temperature inside the liquid phase, it takes a short time. It was also confirmed that there was no change in temperature.

Therefore, if the vaporized gas 5 generated in the tank 1 is returned to the liquid phase portion and is dispersed and absorbed in the entire liquid phase portion by taking advantage of the enormous heat capacity of the liquid phase portion itself, the tank pressure It is possible to suppress the rise temporarily.

Therefore, as shown in the present embodiment, the stored liquid 3 contained in the low temperature liquefied gas storage tank 1 is externally circulated through the external circulation line 15 so that the return nozzle 9 and the reed tube 12 flow down. By doing so, while the stored liquid 3 flowing from the discharge port 10 at the lower end of the return nozzle 9 into the funnel portion 11 at the upper end of the lead tube 12 flows down in the lead tube 12,
The vaporized gas 5 in the vapor phase portion in the upper region of the storage space 2 is caught in the lead tube 12 through the slit 13 of the funnel portion 11. Due to the entrained phenomenon of the vaporized gas 5, the vaporized gas 5 is taken into the lead tube 12. The vaporized gas 5 thus liquefied is liquefied again under the liquid level of the storage liquid 3 due to heat exchange with the storage liquid 3 or the like, so that the rise in tank pressure can be temporarily suppressed.

Further, particularly in the present embodiment, the control device 18 can calculate an appropriate flow rate of the storage liquid 3 to be circulated externally and set it in the flow meter 16. A method for obtaining an appropriate circulating flow rate of the liquid 3 will be described in detail below.

For example, when the consumption amount of the vaporized gas 5 at the demand destination 7 such as a power plant decreases in the night zone, the change in the tank pressure in the night zone can be expressed by the following mathematical expression 1 (relational expression).

[0029]

## EQU1 ## ΔP = (zRT / V) ΔW × θ (Equation 1) ΔP: Change in tank pressure z: Gas compression coefficient R: Gas constant T: Gas phase in tank 1 Temperature V: Volume of vapor phase portion in tank 1 ΔW: Amount of gas change in vapor phase portion of tank 1 θ: Circulation operation time of stored liquid 3

In Equation 1, the amount of change in tank pressure Δ
P, absorption amount W _{L of} vaporized gas 5 liquefied by external circulation
Other than the above, the values are determined by the physical constants and the operating conditions of the equipment. Therefore, the operating time θ for circulating the storage liquid 3 is set by the number of hours corresponding to the nighttime zone, and the allowable tank pressure within this operating time θ By setting the change amount ΔP, the gas change amount ΔW of the gas phase portion in the tank 1 can be obtained.

Here, the amount of change ΔP of the tank pressure allowable within the operating time θ is determined by measuring the pressure in the upper region of the storage space 2 at the start of the operation with the tank pressure gauge 21. Since it can be calculated as the amount of change in the tank pressure until the upper limit is reached, it can be automatically set by the control device 18 that is adapted to receive the pressure signal 23 from the tank pressure gauge 21, and the mathematical expression 1 The gas change amount ΔW of the gas phase portion in the tank 1 obtained by
It can be automatically calculated by programming the calculation logic in the controller 18 in advance.

Further, the gas change amount ΔW of the gas phase portion in the tank 1 obtained by the mathematical formula 1 can be expressed by the following mathematical formula 2.

[0033]

[Formula 2] ΔW = W _BOG − (W _C + W _L ) ... (Equation 2) W _BOG : Amount of vaporized gas generated in the tank 1 W _C : Consumption of vaporized gas 5 at the demand destination 7 W _L : Absorption of vaporized gas 5 liquefied by external circulation

That is, the gas change amount ΔW of the vapor phase portion in the tank 1 is _calculated from the generated amount W _BOG of the vaporized gas 5 in the tank 1,
Absorption amount W _L of the vaporized gas 5 liquefied by the external circulation,
The consumption amount W _C of the vaporized gas 5 at the demand destination 7 is subtracted, but the generated amount W _BOG of the vaporized gas 5 in the tank 1 is empirically known, and the vaporization at the demand destination 7 is performed. Since the consumption amount W _C of the gas 5 is determined from the operational aspect of the demand destination 7, the minimum required absorption amount W _L of the vaporized gas 5 that must be liquefied by external circulation is the consumption amount from the demand destination 7. The signal 25 can be automatically calculated by the control device 18 adapted to be input.

Here, when the stored liquid 3 is circulated at a constant flow rate, the absorption amount W _L of the vaporized gas 5 that is caught in the lead tube 12 and liquefied, and the liquid level of the stored liquid 3 in the tank 1 It has been confirmed by the inventor of the present application that there is a correlation between and as shown in FIG. 3, and by utilizing this correlation, the flow rate at the time of external circulation of the stored liquid 3 at a predetermined liquid level can be determined. The absorption amount W _L of the vaporized gas 5 that can be liquefied in the storage liquid 3 can be set by appropriately setting it.

Therefore, if the minimum necessary absorption amount W _L of the vaporized gas 5 is calculated as described above, the circulation flow rate of the storage liquid 3 required to achieve the absorption amount W _L of the vaporized gas 5 is
The liquid level signal 24 from the liquid level meter 22 can be automatically calculated by the control device 18 and is output to the flow meter 16 as the setting signal 19 to appropriately set the circulating flow rate of the stored liquid 3. be able to.

As described above, by appropriately setting the circulation flow rate of the storage liquid 3 and performing the external circulation, it is possible to suppress the generation amount of the vaporized gas 5 in the tank 1 for about half a day.

The vaporized gas 5 absorbed in the stored liquid 3 by externally circulating the stored liquid 3 at night, for example, is increased from the gas discharge line 8 to a tank by increasing the rate of the compressor 6 during the day. 1, so that the saturated pressure (enthalpy) of the stored liquid 3 can be lowered and the vaporized gas 5 can be absorbed again at night.
By doing this, continuous operation is possible throughout the year.

Therefore, according to the above-described embodiment, even if the delivery amount of the vaporized gas 5 to the demand destination 7 is suppressed more than before in the predetermined time period when the demand of the vaporized gas 5 at the demand destination 7 decreases, Since the rise in tank pressure can be suppressed, there is no restriction that the customer 7 must consume the vaporized gas 5 in preference to other fuels, which brings about an advantage that the range of operation at the customer 7 is greatly expanded. .

Furthermore, since the controller 18 can calculate an appropriate flow rate of the stock solution 3 to be externally circulated and set it in the flow meter 16, the stock solution 3 is externally circulated so as to suppress an increase in tank pressure. Driving can be done automatically.

Further, if the return nozzle 9 is arranged so as to penetrate through the center of the tank roof 4 as in the present embodiment, the reed tube 12 is arranged at the position where the height dimension is maximum in the storage tank space 2. Since the height of the lead tube 12 can be made as large as possible, the falling speed of the storage liquid 3 flowing down in the lead tube 12 can be greatly accelerated, and the vaporized gas 5 can be efficiently introduced into the lead tube 12. It can be engulfed well and liquefied.

The pressurization suppressing device for a low temperature liquefied gas storage tank according to the present invention is not limited to the above-described embodiment, and the funnel portion may be partially opened to the upper region of the storage tank space. It is not limited to the shape and opening position of the slit in the illustrated example, and the operation of externally circulating the stored liquid so as to suppress the rise of the tank pressure may be performed manually, and further, the low temperature liquefied gas storage tank Needless to say, it may be an underground type or an above-ground type, and other various changes may be made without departing from the scope of the present invention.

[0043]

EFFECTS OF THE INVENTION The pressurization suppressing device for a low temperature liquefied gas storage tank of the present invention described above can exhibit various excellent effects as described below.

(I) In a predetermined time period when the demand for vaporized gas at the demand destination decreases, even if the delivery amount of the vaporized gas to the demand destination is suppressed as compared with the conventional case, the rise in tank pressure can be suppressed. Therefore, the restriction that the vaporized gas must be consumed prior to other fuels at the demand destination is eliminated, and there is an advantage that the range of operation at the demand destination is greatly expanded.

(II) According to the invention described in claim 2 of the present invention, an appropriate flow rate of the storage liquid to be externally circulated can be calculated by the control device and set in the flow meter. The operation of externally circulating the stored liquid can be automatically performed so as to suppress the rise.

(III) According to the third aspect of the present invention, the lead tube is arranged at a position where the height dimension is maximum in the storage tank space, and the height dimension of the lead tube is maximized. As a result, the rate of fall of the stored liquid flowing down in the lead pipe can be greatly accelerated, and the vaporized gas can be efficiently entrained in the lead pipe and liquefied.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a cross-sectional view showing details of the return nozzle and the lead tube in FIG.

FIG. 3 is a graph showing the correlation between the amount of vaporized gas absorbed and the liquid level of the stored liquid when the stored liquid is circulated at a constant flow rate.

[Explanation of symbols]

 1 Low-temperature liquefied gas storage tank 2 Storage space 3 Storage liquid 4 Tank roof 5 Vaporized gas 7 Demand 9 Return nozzle 10 Discharge port 11 Funnel part 12 Reed pipe 13 Slit 14 Pump 15 External circulation line 16 Flowmeter 17 Flow control valve 18 Control Device 21 Tank pressure gauge 22 Liquid level gauge

Claims (3)

[Claims] 1. A return nozzle that penetrates the tank roof and has a discharge port opened in the upper region of the storage tank space, and a funnel portion that partially opens in the upper region of the storage tank and surrounds the discharge port of the return nozzle. And a lead pipe having a lower end extending to the bottom of the storage space and opening, and an external circulation line having a pump for extracting the stored liquid from the bottom of the storage space outside the tank and circulating it to the return nozzle. A device for suppressing pressure increase in a low-temperature liquefied gas storage tank, comprising: 2. A flow rate adjusting valve for adjusting a flow rate of a stored liquid circulating through an external circulation line, and a flow rate of the stored liquid circulating through the external circulation line, and the measured value of the flow rate becomes a predetermined set value. Flow meter for controlling the flow rate adjusting valve, a tank pressure gauge for measuring the pressure in the upper region of the storage tank, a liquid level meter for measuring the liquid level of the stored liquid, the pressure measured by the tank pressure gauge, the demand A controller for calculating an appropriate flow rate of the stored liquid to be circulated externally and setting the flow rate meter on the basis of the consumption amount of the vaporized gas and the liquid level measured by the liquid level gauge, which are required by the preceding The pressurization suppression device for a low temperature liquefied gas storage tank according to claim 1. 3. The pressurization suppressing device for a low temperature liquefied gas storage tank according to claim 1 or 2, wherein the return nozzle is arranged at a central position of the tank roof.