JPH1038199A - Low-temperature liquefied gas storing facility and operating method for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption by reducing load of a compressor, and also to improve operating efficiency of a consumer by eliminating restriction of the operation of the consumer such as a thermal power plant. SOLUTION: A boosting means for boosting LNG 2 (low-temperature liquefied gas) extracted from a low-temperature tank 1 and for guiding it to an evaporator 5 is formed into a two-staged boosting method by pumps 8, 9, and a line 6' for guiding liquefied gas 2' generated in the low-temperature tank 1 to a compressor 7, a line 6 for joining gas 2' boosted by the compressor 7 to the outlet side of the evaporator 5, and a line 10 for extracting gas 2' from the low pressure stage of the compressor 7 and joining it to the outlet side of the pump 8 are provided. In the high-load operation, the line 10 is selected to liquefy gas 2' and dissolve it in LNG 2, while, in the low-load operation, gas 2' is accumulated on the gas phase of the low-temperature tank 1. The line 6 is selected to extract gas 2' from the low-temperature tank 1 only when pressure of gas phase is raised to the tank designed pressure value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature liquefied gas storage facility and a method of operating the same.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a general low-temperature liquefied gas storage facility. In FIG. 1, reference numeral 1 denotes a storage medium containing LNG2 (low-temperature liquefied gas) obtained by liquefying natural gas at about -162.degree. Low temperature tank 3 is the vaporized gas 2 ′ of the LNG2
Is a thermal power plant (demand destination) that uses LNG as fuel, and LNG 2 stored in the low-temperature tank 1 is referred to as LNG.
After being drawn out by the pump 4 and raised to a predetermined pressure, it is led to the vaporizer 5, where the vaporized gas is vaporized by heat exchange with seawater or the like to form the vaporized gas 2 ', and the vaporized gas 2' is converted into the thermal power plant 3 It is sent to and used.

On the other hand, with respect to the vaporized gas 2 'generated by natural heat input or the like in the low-temperature tank 1, a suction line 6' from the top of the low-temperature tank 1 in order to maintain the pressure in the low-temperature tank 1 at a certain value or less. Through the compressor 7, and the compressor 7 constantly extracts the gas to be supplied thereto.
(Pressure at the outlet side of the fuel cell), joins the outlet side of the vaporizer 5 through the compressor outlet line 6, and is sent to the thermal power plant 3 together with the vaporized gas 2 ′ from the vaporizer 5 for consumption. Like that.

[0004]

However, in recent years, there has been developed a combined cycle in which power is generated by a gas turbine and power is also generated by a steam turbine using steam generated by exhaust heat recovery of the gas turbine. The number of thermal power plants 3 is increasing, and in such a thermal power plant 3 of a combined cycle, the final supply gas pressure of the vaporized gas 2 ′ is about 30 kg / cm ² or more (a thermal power plant that does not employ a combined cycle). About 8 kg at the power station
/ Cm ² ), the pressure of the vaporized gas 2 ′ generated in the low-temperature tank 1 must be increased to about 30 kg / cm ² or more, but the load on the compressor 7 increases significantly. This has led to a significant increase in power costs.

[0005] Further, during nighttime when power consumption is greatly reduced, the demand for the vaporized gas 2 'on the thermal power plant 3 side is extremely reduced, so that the vaporization from the compressor outlet line 6, which is normally unnecessary, is required. The fact is that the gas 2 ′ is taken out on the side of the thermal power plant 3 so that the pressure in the low-temperature tank 1 does not rise and is inevitably consumed.
If unnecessary thermal gas 2 'generated inside the power plant 3 must be taken off at the thermal power plant 3, there is a risk that efficient operation of the whole power plant may be hindered.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims to reduce the load on the compressor to reduce the power cost, and to eliminate the restriction on the operation of the demand destination such as a thermal power plant, thereby reducing the demand. The aim is to improve the operational efficiency of.

[0007]

According to the present invention, a boosting means for boosting a low-temperature liquefied gas extracted from a low-temperature tank and guiding it to a vaporizer is constituted as a two-stage boosting system using a primary pump and a secondary pump. A suction line for introducing the vaporized gas generated in the low-temperature tank to the compressor, a compressor outlet line for joining the vaporized gas pressurized by the compressor to the outlet side of the vaporizer, and vaporization from a low-pressure stage of the compressor. A low-temperature liquefied gas storage facility, characterized in that a bypass line for extracting gas and joining the outlet side of the primary pump is provided, and the bypass line and the compressor outlet line can be selectively switched. It is related.

When operating such a low-temperature liquefied gas storage facility, the low-temperature liquefied gas extracted from the low-temperature tank is pressurized in two stages by a primary pump and a secondary pump, and the pressurized low-temperature liquefied gas is discharged. During normal high-load operation where the demand for the low-temperature liquefied gas required by the demand destination is sufficiently large while the vaporized gas is sent to the demand destination by the vaporizer, the bypass line is selected to generate the vaporized gas generated in the low-temperature tank. Is increased to approximately the same level as the outlet pressure of the primary pump by the compressor and mixed with the low-temperature liquefied gas from the primary pump to liquefy, and the compressor is stopped during low-load operation where the demand of the demand destination is small. And waits until the demand of the demand destination recovers while accumulating the vaporized gas in the gas phase in the low-temperature tank, and the demand does not recover sufficiently. Only when the pressure of the gas phase in the low-temperature tank has risen to near the tank design pressure value, the compressor outlet line is selected, the vaporized gas is extracted from the low-temperature tank, and the vaporized gas is vaporized by the compressor. It is preferable to increase the pressure to about the same as the pressure on the outlet side and mix it with the vaporized gas from the vaporizer.

Therefore, in the present invention, the vaporized gas generated in the low-temperature tank during the normal high-load operation in which the demand for the low-temperature liquefied gas required by the customer is sufficiently large is substantially equal to the outlet pressure of the primary pump by the compressor. To the bypass line, and liquefy and dissolve in the low-temperature liquefied gas from the primary pump.In the liquid phase that is easily pressurized, the pressure is increased by the secondary pump and vaporized by the vaporizer. It is possible to easily obtain a proper supply gas pressure (outlet pressure of the vaporizer).

[0010] Further, during low load operation in which the demand of the demand destination is small, the apparatus waits until the demand of the demand destination recovers while accumulating the vaporized gas in the gas phase in the low-temperature tank, and the demand of the demand destination fully recovers. Then, by operating the bypass line again and extracting vaporized gas from the low-temperature tank, there is a restriction that unnecessary vaporized gas generated in the low-temperature tank during low-load operation must be collected at the demand side. And the compressor can be stopped during low-load operation when the demand of the demand destination is small.

When the pressure of the gas phase in the low-temperature tank rises to near the tank design pressure value before the demand of the demand destination is not fully recovered for some reason, the compressor outlet line is selected and the low-temperature tank is selected. If the vaporized gas is extracted from the tank, it is possible to avoid a situation where the pressure of the gas phase in the low-temperature tank exceeds the tank design pressure value.

[0012]

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

FIGS. 1 and 2 show an example of an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIG. 3 represent the same components.

As shown in FIG. 1, in the low-temperature liquefied gas storage facility according to this embodiment, the LN
The boosting means for boosting G2 and guiding it to the vaporizer 5 is configured as a two-stage boosting method using a primary pump 8 and a secondary pump 9.

Further, in this low-temperature liquefied gas storage facility, a suction line 6 'for guiding a vaporized gas 2' generated in the low-temperature tank 1 to a compressor 7, and a vaporized gas 2 'pressurized by the compressor 7, A compressor outlet line 6 which joins the outlet side of the vaporizer 5 is provided in the same manner as in the related art, and the vaporized gas 2 ′ is extracted from the low-pressure stage of the compressor 7 and is provided to the outlet side of the primary pump 8. Merging bypass line 10
The compressor 11 is connected to the bypass line 10 and the compressor outlet line 6 by a valve 11, so that the two lines 6, 10 can be selectively switched.
12 are provided respectively.

Here, L flowing through the primary pump 8
The relationship between the flow rate W1 of the NG2, the flow rate W2 of the vaporized gas 2 'flowing through the bypass line 10 (in terms of liquid), and the flow rate W3 of the LNG2 flowing through the secondary pump 9 is based on the Mollier diagram of FIG. , Bypass line 1
0 from the primary pump 8
It is appropriately set so that it is reliquefied and completely dissolved in NG2.

That is, in FIG. 2, an inner area A surrounded by a state curve x is in a gas-liquid mixed state, an area B on the left side of the area A is in a liquid phase state, and an area C on the right side of the area A is in a liquid phase state. Each shows a gas phase state. When the pressure at the outlet side of the primary pump 8 is P1 and the enthalpy is i1 (see the figure), the pressure of the vaporized gas 2 'from the bypass line 10 is reduced to P1 by the compressor 7. After increasing pressure, enthalpy i2
Will mix into LNG2 (see figure),
The flow rates W1, W2, and W3 are determined so that the LNG2 after the mixing has an enthalpy i3 such that the LNG2 stays in the region B in the liquid phase under the condition of the pressure P1 and a heat balance is established.

More specifically, the flow rates W1, W2, W3

W1 = W1 + W2 (Equation 1) holds, and the flow rates W1, W2, W3
Heat balance based on

## EQU2 ## The following relationship holds: W3i3 = W1i1 + W2i2 (Equation 2)

Therefore, according to Equations 1 and 2, the flow rate W2 is based on the flow rate W1.

W2 = [(i3-i1) / (i2-i3)] × W1 (Equation 3) Similarly, the flow rate W3 is equal to the flow rate W
Based on 2

W3 = [(i2-i1) / (i3-i1)] × W2 (Equation 4)

The compressor 7 and the valves 11, 12
Is a command signal 7 from the control device 13 disposed at a required place.
a, 11a, and 12a, and the demand of LNG 2 'demanded by the thermal power plant 3 is input to the control device 13 as a load signal 3a. The total flow rate of the vaporized gas 2 ′ is measured by the flow meter 14 and input as a flow signal 14 a, and the pressure of the gas phase in the low-temperature tank 1 is measured by the pressure gauge 15 and input as a pressure signal 15 a. It is supposed to be.

When operating such a low-temperature liquefied gas storage facility, the LNG extracted from the low-temperature tank 1 is
2 is boosted in two stages by a primary pump 8 and a secondary pump 9, and the boosted LNG 2 is supplied to the thermal power plant 3 as a vaporized gas 2 ′ by the carburetor 5, while requesting the thermal power plant 3 During daytime high load operation when the demand for LNG 2 is sufficiently large, the valve 11 is opened and the valve 12 is closed to select the bypass line 10, and the vaporized gas 2 ′ generated in the low-temperature tank 1 is supplied to the primary pump 8 by the compressor 7. And is mixed with LNG 2 from the primary pump 8 to be liquefied.

At this time, the compressor 7 and the valves 11, 12
Are operated by command signals 7a, 11a,
The controller 13 determines the operation mode in which the bypass line 10 is selected based on the load signal 3a from the thermal power plant 3 and after confirming the flow signal 14a from the flow meter 14. You.

During low-load operation at night when the demand for the thermal power plant 3 is low, the compressor 7 is stopped and the valve 1 is turned off.
1 and 12 are closed, and while the vaporized gas 2 ′ is stored in the gas phase in the low-temperature tank 1, the system waits until the demand of the thermal power plant 3 recovers. After a sufficient recovery, only the valve 11 is opened, the bypass line 10 is selected, the compressor 7 is restarted, and the high-load operation described above may be resumed.

The switching of the operation mode at this time is also performed by the control device 13, and by monitoring changes in the load signal 3a from the thermal power plant 3 and the flow signal 14a from the flow meter 14, an appropriate operation is performed. Mode is selected.

In accumulating the vaporized gas 2 ′ in the gas phase in the low-temperature tank 1, it is needless to say that the pressure resistance design of the low-temperature tank 1 is of course higher than in the prior art.
In the case where the demand for the vaporized gas 2 ′ is the thermal power plant 3, the vaporized gas 2 ′ can be stored in the gas phase in the low-temperature tank 1 at least for the time corresponding to the night time zone. deep.

However, if the pressure of the gas phase in the low-temperature tank 1 rises to near the tank design pressure during the night when the demand for the thermal power plant 3 does not sufficiently recover due to some circumstances, the valve 11 is opened. The compressor outlet line 6 is selected by closing and opening the valve 12, the vaporized gas 2 ′ is extracted from the low-temperature tank 1, and the pressure is increased to approximately the same as the outlet pressure of the vaporizer 5 by the compressor 7. 5 is mixed with the vaporized gas 2 'from step 5 to avoid a situation where the pressure of the gas phase in the low-temperature tank 1 exceeds the designed pressure value of the tank.

That is, in the operation mode in which the vaporized gas 2 ′ is accumulated in the gas phase in the low-temperature tank 1, the controller 13 controls the pressure of the gas phase in the low-temperature tank 1 based on the pressure signal 15 a from the pressure gauge 15. It is constantly monitored, and when it is confirmed that the pressure of the gas phase in the low-temperature tank 1 has increased to near the tank design pressure value, the other load signal 3a or the flow signal
An operation mode in which the vaporized gas 2 ′ is extracted from the low-temperature tank 1 is selected in preference to the determination based on “a”.

Therefore, according to the above embodiment, the thermal power plant 3
During the high-load operation in the daytime when the demand for LNG 2 required in the above is sufficiently high, the vaporized gas 2 ′ generated in the low-temperature tank 1 is boosted by the compressor 7 to approximately the same as the outlet pressure of the primary pump 8, and the bypass line 10 and is liquefied and dissolved in LNG 2 from the primary pump 8 so that the secondary pump 9 can be easily pressurized.
And the vaporized gas is vaporized by the vaporizer 5 to easily obtain the final feed gas pressure (pressure on the outlet side of the vaporizer 5). The load on the compressor 7 can be significantly reduced as compared with the case where the pressure is increased to the final supply gas pressure, and the power cost can be significantly reduced.

Further, during nighttime low load operation when the demand for the thermal power plant 3 is low, the evaporating gas 2 ′ is stored in the gas phase in the low temperature tank 1 while waiting until the demand for the thermal power plant 3 recovers. When the demand of the thermal power plant 3 is sufficiently recovered in the daytime of the next day, the bypass line 10 is selected again and the operation is performed so as to extract the vaporized gas 2 ′ from the inside of the low-temperature tank 1. It is possible to eliminate the restriction that the unnecessary vaporized gas 2 ′ generated in the thermal power plant 3 must be taken off at the thermal power plant 3 side, and to improve the operation efficiency of the thermal power plant 3.

Further, by operating the compressor 7 in this manner, the compressor 7 can be stopped during the low-load operation at night when the demand for the thermal power plant 3 is small, so that the power cost of the compressor 7 is further reduced. be able to.

Further, when the pressure of the gas phase in the low temperature tank 1 rises to near the tank design pressure during the night when the demand of the thermal power plant 3 does not sufficiently recover due to some circumstances, the compressor outlet line Since the vaporized gas 2 'can be extracted from the low-temperature tank 1 by selecting 6, the situation in which the pressure of the gas phase in the low-temperature tank 1 exceeds the design pressure value of the tank can be avoided.

The low-temperature liquefied gas storage equipment and the method of operating the same according to the present invention are not limited to the above-described embodiment, and the demand for the vaporized gas is not limited to the thermal power plant. Of course, other than LNG, various changes may be made without departing from the scope of the present invention.

[0033]

According to the low-temperature liquefied gas storage equipment of the present invention and the method of operating the same, various excellent effects as described below can be obtained.

(I) During normal high-load operation where the demand for the low-temperature liquefied gas required by the demand destination is sufficiently large, the vaporized gas generated in the low-temperature tank is reduced by the compressor to approximately the same as the outlet pressure of the primary pump. By raising the pressure and flowing to the bypass line, and liquefying and dissolving in the low-temperature liquefied gas from the primary pump, the secondary pump is pressurized in a liquid phase that is easily pressurized, and is vaporized by the vaporizer and finally fed. Since the gas pressure (outlet pressure of the vaporizer) can be easily obtained, the load on the compressor is lower than in the conventional case where the vaporized gas is pressurized to the final supply gas pressure by the compressor alone. Can be significantly reduced, and the power cost can be greatly reduced.

(II) At the time of low load operation in which the demand of the demand destination is small, while waiting for the demand of the demand destination to recover while accumulating the vaporized gas in the gas phase in the low-temperature tank, the demand of the demand destination is sufficiently satisfied. After recovery, unnecessary bypass gas generated in the low-temperature tank during low-load operation must be collected by the demand side by selecting the bypass line again and operating to extract the vaporized gas from the low-temperature tank. The operating efficiency of the thermal power plant can be improved by eliminating restrictions, and the compressor can be stopped during low-load operation when demand at the destination is small, further reducing the power cost of the compressor. can do.

(III) When the pressure of the gas phase in the low-temperature tank rises to near the tank design pressure value before the demand of the demand destination is not fully recovered for some reason,
By selecting the compressor outlet line and extracting the vaporized gas from the low-temperature tank, it is possible to prevent a situation in which the gas phase pressure in the low-temperature tank exceeds the tank design pressure value.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an embodiment of the present invention.

FIG. 2 is a Mollier diagram illustrating a heat balance when revaporizing a vaporized gas.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Low temperature tank 2 LNG (low temperature liquefied gas) 2 'Vaporized gas 3 Thermal power plant (demand destination) 5 Vaporizer 6 Compressor outlet line 6' Suction line 7 Compressor 8 Primary pump 9 Secondary pump 10 Bypass line

Claims (2)

[Claims] A low-pressure liquefied gas extracted from a low-temperature tank is pressurized and guided to a vaporizer by means of a two-stage pressure raising method using a primary pump and a secondary pump, and the vaporized gas generated in the low-temperature tank is provided. A suction line leading to the compressor, a compressor outlet line for joining the vaporized gas pressurized by the compressor to the outlet side of the vaporizer, and a vaporized gas extracted from a low-pressure stage of the compressor. A low-temperature liquefied gas storage facility, comprising: a bypass line that merges with an outlet side; and a structure that can selectively switch between the bypass line and the compressor outlet line. 2. The method for operating a low-temperature liquefied gas storage facility according to claim 1, wherein the low-temperature liquefied gas extracted from the low-temperature tank is pressurized in two stages by a primary pump and a secondary pump, and the pressure is increased. While the low-temperature liquefied gas is sent to the customer as a vaporized gas by a vaporizer,
During normal high-load operation where the demand for the low-temperature liquefied gas demanded by the demand destination is sufficiently large, the bypass line is selected and the vaporized gas generated in the low-temperature tank is substantially equal to the outlet pressure of the primary pump by the compressor. And liquefied by mixing in the low-temperature liquefied gas from the primary pump, and at the time of low-load operation where the demand of the demand destination is small, the compressor is stopped to accumulate the vaporized gas in the gas phase in the low-temperature tank. Waiting until the demand of the demand destination recovers, and only when the pressure of the gas phase in the low-temperature tank has risen to near the tank design pressure value before the demand has recovered sufficiently, the compressor outlet line is disconnected. Selecting and extracting the vaporized gas from the low-temperature tank, increasing the vaporized gas to approximately the same level as the outlet pressure of the vaporizer by a compressor, and mixing the vaporized gas with the vaporized gas from the vaporizer. The method of operating a low temperature liquefied gas storage facility that.