JP2020148211A - Lng cold recovery system - Google Patents

Abstract

To provide an LNG cold recovery system that can be applied to an existing LNG satellite, and can recover a large amount of cold of LNG with a simple structure and without depending on other systems.SOLUTION: An LNG cold recovery system comprises: a first pipeline temperature sensor 16 for measuring temperature of LNG inside a first pipeline 14; an LNG storage tank put-out isolation valve 18; a second pipeline 22 connecting an LNG vaporizer 20; a third pipeline 24 connecting the LNG vaporizer 20 and the first pipeline 14; a fourth pipeline 28 connecting the LNG vaporizer 20 and a cascade capacitor 26; a fifth pipeline 32 connecting the cascade capacitor 26 and a refrigerant circulation pump 30; a sixth pipeline 34 connecting the refrigerant circulation pump 30 and the LNG vaporizer 20; and a control unit 44 for controlling an opening degree of the LNG storage tank put-out isolation valve 18 and activation of the refrigerant circulation pump 30 from measured values of the first pipeline temperature sensor 16 and the sixth pipeline temperature sensor 36.SELECTED DRAWING: Figure 1

Description

The present invention relates to an LNG cold heat recovery system that recovers cold heat discharged when NG (natural gas) is generated from LNG (liquefied natural gas).

NG is a gas at room temperature, and when the production area and consumption area are in remote areas where it cannot be transported by pipeline, it is cooled to about -162 ° C and liquefied to generate LNG, and the volume is about 600. It is common to reduce the volume to one-third and transport it by a large dedicated carrier.

This LNG is transported to the consumption area by a dedicated carrier, then transferred to an LNG tank, returned to NG according to demand, and then consumed in a power plant, a boiler, or the like.

In addition, a part of LNG stored in the LNG tank is transferred to the LNG lorry in the state of LNG and sent to LNG consumers such as factories in various places.

LNG transported by LNG lorry is generally temporarily stored in a facility called an LNG satellite base on or near the premises of LNG consumers, and sequentially generates and consumes gas NG from LNG according to demand. Will be done.

In order to convert LNG, which is a low-temperature liquefied fluid, into NG, which is a gas, an air-heated vaporizer or a vaporizer that uses a heat source such as hot water or steam is often used.

However, some LNG consumers with carburetors may require cold heat for systems such as air conditioning in buildings and factories, and cooling processes in factories.

If the cold heat of LNG can be used for other systems that require cold heat, there are two energy savings: reduction of energy consumed as fuel for NG generation and reduction of cold production energy for other systems. Can be realized at the same time.

Therefore, as described in Patent Document 1, a low-temperature liquefied gas vaporizer and an operation method thereof for recovering the cold heat of the low-temperature liquefied gas and using it in a cold heat utilization facility have been proposed.

Japanese Unexamined Patent Publication No. 2004-324716

However, since the low-temperature liquefied gas vaporizer and its operating method described in Patent Document 1 mainly assume the use of water as a heat medium for generating a gas from the low-temperature liquefied gas, it is necessary to heat it to about room temperature with water. It is said that the temperature difference is small and the heat exchanger becomes large compared to the gas, and the configuration is completely different from the existing vaporizer, so it is necessary to construct a new vaporizer and it is a double investment, so the cost increases. There are challenges.

In view of the above problems, it is an object of the present invention to provide an LNG cold heat recovery system in which the apparatus is small and can be used as it is even if there is an existing vaporizer.

(1) The LNG cold heat recovery system according to the present invention is an LNG cold heat recovery system that recovers the cold heat of LNG generated by cooling natural gas, the first pipe through which LNG flows and the fluid inside the pipe of the first pipe. On the first pipe temperature sensor installed for measuring the temperature, the LNG storage tank discharge shutoff valve installed on the first pipe and downstream of the first pipe temperature sensor, and on the first pipe. There is a second pipe that branches on the upstream side of the LNG storage tank discharge shutoff valve and connects the first pipe and the LNG evaporator, and the first pipe on the downstream side of the LNG storage tank discharge shutoff valve. A third pipe connecting the LNG evaporator and the first pipe, a fourth pipe connecting the LNG evaporator and a cascade condenser to transfer a fluid, and a third pipe connecting the cascade condenser and a suction side of a fluid circulation pump. The fifth pipe, the sixth pipe connecting the discharge side of the refrigerant circulation pump and the LNG evaporator, and the sixth pipe temperature sensor installed in the sixth pipe to measure the fluid temperature inside the sixth pipe. It is provided with a control unit for controlling the opening degree of the LNG storage tank discharge shutoff valve and the start of the fluid circulation pump based on the measured values of the first pipe temperature sensor and the sixth pipe temperature sensor. It is a feature.

(2) Further, in the LNG cold heat recovery system according to the present invention, in the LNG cold heat recovery system according to (1), the temperature measured by the first pipe temperature sensor of the control unit is equal to or lower than a preset temperature. In such a case, the refrigerant circulation pump is started, and the control is performed to gradually close the LNG storage tank discharge shutoff valve until the temperature measured by the sixth pipe temperature sensor becomes equal to or lower than a preset temperature.

(3) Further, in the LNG cold heat recovery system according to the present invention, in the LNG cold heat recovery system according to (1) or (2), the temperature measured by the sixth pipe temperature sensor is preset in the control unit. When the temperature falls below the temperature, the LNG storage tank discharge shutoff valve is gradually opened.

(4) Further, the LNG cold heat recovery system according to the present invention is installed at the LNG side outlet of the LNG evaporator in the LNG cold heat recovery system according to any one of (1) to (3), and is the LNG evaporator. It is provided with an LNG evaporator temperature sensor that measures the internal temperature and transmits it to the control unit, and a fourth pipe temperature sensor that is installed on the fourth pipe and measures the fluid temperature inside the pipe and transmits it to the control unit. In the control unit, when the temperature measured by the LNG evaporator temperature sensor is higher than the preset temperature, the temperature difference between the temperatures measured by the fourth pipe temperature sensor and the sixth pipe temperature sensor is When the temperature difference is smaller than a preset temperature difference, the LNG storage tank discharge shutoff valve is fully opened and the refrigerant circulation pump is stopped.

According to the LNG cold heat recovery system described in (1), the fact that the LNG in the liquid phase has a temperature gradient when the phase changes to the NG in the gas phase is utilized, and the use load of LNG is generated and the cold heat is used. It is possible to realize a simple system in which the presence or absence of cold heat demand in equipment can be determined only by measuring with two temperature sensors.

By using methylene chloride or the like as the refrigerant for recovering LNG cold heat, the cold heat of LNG (both latent heat and sensible heat) is recovered as sensible heat only, and a cascade condenser is used to recover the sensible heat of the refrigerant. Heat is exchanged as latent heat by sensible heat transfer to a refrigerant such as carbon dioxide in the tank.

As a result, when the temperature of the refrigerant such as methylene chloride is not sufficiently lowered, even if the refrigerant is circulated by the refrigerant circulation pump, heat exchange is not performed in the cascade capacitor (heat transfer due to evaporation does not occur), so that the heat is cooled. No thermal load is applied to the equipment used.

Therefore, even with this simple configuration, it has a remarkable effect that the cold heat of LNG can be effectively recovered.

Furthermore, even if there is an existing LNG satellite base, it can be added later, and it operates as an independent system without depending on information from other systems, so it has the effect of high system stability. ..

According to the LNG cold heat recovery system described in (2), the value measured by the first pipe temperature sensor and the flow rate of LNG flowing in the first pipe have a certain degree of correlation, so that when the refrigerant circulation pump is started. By arbitrarily setting the temperature of LNG, the flow rate of LNG to start cold heat recovery can be freely set.

Further, by controlling the opening degree of the LNG storage tank discharge shutoff valve based on the value measured by the sixth pipe temperature sensor, it is possible to freely set the amount of cold heat recovered by the LNG.

According to the LNG cold heat recovery system described in (3), when the value measured by the sixth pipe temperature sensor falls below a preset temperature, the LNG storage tank discharge shutoff valve is gradually opened to flow to the LNG cold heat recovery system. It is possible to limit the amount of LNG, prevent freezing of the refrigerant, and at the same time, recover the maximum amount of cold heat that can be recovered by the LNG cold heat recovery system.

According to the LNG cold heat recovery system described in (4), when the value measured by the LNG evaporator temperature sensor becomes equal to or higher than the preset temperature (that is, the flow rate of LNG has decreased). , If the temperature difference between the 4th pipe temperature sensor and the 6th pipe temperature sensor becomes less than the preset temperature (that is, the refrigerant side cannot recover any more cold heat), the LNG storage tank discharge shutoff is blocked. Fully open the valve (ie, do not allow LNG to flow into the LNG cold heat recovery system) and stop the refrigerant circulation pump. As a result, it is possible to reliably grasp that the flow rate of LNG that can be recovered has fallen below the specified value and that the cold heat recovery with the refrigerant has been completed.

It is an overall schematic diagram of the LNG cold heat recovery system which concerns on this invention. It is a flow chart at the time of starting of the LNG cold heat recovery system which concerns on this invention. It is a schematic diagram of the LNG load and the temperature sensor at the time of starting the LNG cold heat recovery system which concerns on this invention. It is a flow chart at the time of stopping of the LNG cold heat recovery system which concerns on this invention. It is a schematic diagram of the LNG load and the temperature sensor at the time of stopping of the LNG cold heat recovery system which concerns on this invention.

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. Such an embodiment is merely an example for facilitating the understanding of the invention, and does not limit the present invention unless otherwise specified.

In the present specification and the drawings, elements having substantially the same function and configuration are designated by the same reference numerals to omit duplicate description, and elements not directly related to the present invention are not shown.

FIG. 1 is a schematic diagram showing a system configuration of the LNG cold heat recovery system 100.

First, the system configuration of the LNG cold heat recovery system 100 will be described.

The LNG cooled to about -162 ° C. is stored in the LNG storage tank 10. A first pipe temperature sensor 16 installed for measuring the fluid temperature inside the pipe is installed on the first pipe 14 through which LNG connecting the LNG storage tank 10 and the LNG vaporizer 12 flows.

An LNG storage tank discharge shutoff valve 18 is installed on the first pipe 14 and downstream of the first pipe temperature sensor 16, and LNG is sent to the LNG cold heat recovery system 100 by opening and closing the LNG storage tank discharge shutoff valve 18. Alternatively, it is possible to select whether to send LNG directly from the LNG storage tank 10 to the LNG vaporizer 12.

This is because the difference in flow path resistance due to the LNG evaporator described later being provided in the LNG cold heat recovery system 100 is utilized.

The second pipe 22 connecting the first pipe 14 and the LNG evaporator 20 is branched on the first pipe 14 on the upstream side of the LNG storage tank discharge shutoff valve 18, and the LNG outlet side of the LNG evaporator is LNG. The evaporator temperature sensor 21 is installed.

The LNG evaporator 20 and the first pipe 14 are connected by a third pipe 24 on the first pipe 14 on the downstream side of the LNG storage tank discharge shutoff valve 18.

The LNG evaporator 20 is connected to the cascade condenser 26 by a fourth pipe 28 for transferring the refrigerant. As this refrigerant, a refrigerant such as methylene chloride that recovers cold heat by sensible heat without phase change is used.

Further, a fourth pipe temperature sensor 29 is installed in the fourth pipe 28 to measure the temperature of the refrigerant inside the pipe.

The cascade condenser 26 and the suction side of the refrigerant circulation pump 30 are connected by a fifth pipe 32, and the discharge side of the refrigerant circulation pump 30 and the LNG evaporator 20 are connected by a sixth pipe 34.

A sixth pipe temperature sensor 36 is installed to measure the fluid temperature inside the sixth pipe 34.

The cascade condenser 26 is connected to the receiver tank 38 by a gas pipe 40 and a condensate pipe 42.

The refrigerant side of the cascade capacitor 26 is heat exchange by sensible heat such as methylene chloride, but carbon dioxide or the like is used as the other fluid.

This enables sensible heat on the refrigerant side and heat exchange on the other fluid by latent heat (that is, heat exchange by evaporation).

The measured values of the first pipe temperature sensor 16, the LNG evaporator temperature sensor 21, the fourth pipe temperature sensor 29, and the sixth pipe temperature sensor 36 are transmitted to the control unit 44, and the control unit 44 is based on the transmitted values. It is possible to control the opening degree of the LNG storage tank discharge shutoff valve 18 and control the start and stop of the refrigerant circulation pump 30.

Next, the operation at the time of starting the LNG cold heat recovery system 100 will be described with reference to FIGS. 1 to 3.

First, in the initial state, LNG is stored in the LNG storage tank 10 at a low temperature of about −162 ° C., and the first pipe 14 connecting the LNG vaporizer 12 is also filled with LNG.

The LNG vaporizer 12 is not LNG but is in a substantially NG state, and the temperature of the NG is about room temperature.

The inside of the first pipe 14 is not LNG but almost NG, and the temperature becomes higher as it gets closer to the vaporizer 12. In the initial state, the LNG storage tank discharge shutoff valve 18 is fully open.

When the LNG storage tank discharge shutoff valve 18 is fully open, LNG hardly passes through the LNG evaporator 20 due to the flow path resistance, and flows to the LNG vaporizer 12 through the first pipe 14.

When the NG user starts using NG, the pressure on the NG user side decreases, so that LNG starts to flow from the LNG storage tank 10 toward the LNG vaporizer 12. When LNG flows into the LNG vaporizer 12, it is heated to a specified temperature, becomes NG, and is sent to an NG user.

Here, since LNG is a mixture of methane, ethane, propane, etc., it has a temperature gradient unlike water or the like when the phase changes from LNG, which is a liquid phase, to NG, which is a gas phase.

Therefore, as the flow rate of LNG increases, the temperature measurement value of the first pipe temperature sensor 16 installed in the first pipe 14 begins to decrease.

As shown in FIG. 2, when the use of LNG is started from the standby state, if the temperature of the first pipe temperature sensor 16 becomes equal to or lower than the preset temperature (−130 ° C. in FIG. 2), the control unit 44 controls the refrigerant. At the same time as starting the circulation pump 30, the closing control of the LNG storage tank discharge shutoff valve 18 is started (point A in FIG. 3). At this time, the LNG storage tank discharge shutoff valve 18 is not fully closed, but the opening degree is controlled to increase the resistance of the flow path of the first pipe 14, and the LNG can flow into the LNG evaporator 20. It will be possible.

As a result, the refrigerant (methylene chloride or the like) starts circulating between the LNG evaporator 20 and the cascade condenser 26, and at the same time, the recovery of LNG cold heat also starts.

Immediately after the start of circulation, the temperature of the refrigerant has not dropped sufficiently, but since the other fluid in the cascade condenser 26 exchanges latent heat with carbon dioxide or the like, it remains a gas while the temperature of the refrigerant is high and heat exchange occurs. Does not occur.

When the refrigerant temperature drops, the other fluid in the cascade capacitor 26 starts to condense, and the condensed fluid flows to the receiver tank 38 through the condensate pipe 42.

At the same time, gas from the receiver tank 38 is drawn into the cascade condenser 26 through the gas pipe 40, exchanges heat with the refrigerant, and condenses.

By using a cascade capacitor with sensible heat on the refrigerant side and latent heat on the other side in this way, heat exchange does not occur while the refrigerant temperature is high, and cold heat can be supplied to the cold heat utilization equipment only when the refrigerant temperature is low. ing. That is, although it has a simple configuration in which only the temperature of LNG is measured and the refrigerant circulation pump 30 is started, it is possible to recover the cold heat without imposing a burden such as taking cold heat from the cold heat utilization equipment at the time of starting.

Next, when the temperature of the sixth pipe temperature sensor 36 exceeds a preset temperature (−45 ° C. in FIG. 2), the control unit 44 closes and controls the LNG storage tank payout shutoff valve 18. This is to maximize the amount of cold heat recovered.

Next, when the temperature of the sixth pipe temperature sensor 36 is equal to or lower than the preset temperature, the control unit 44 opens and controls the LNG storage tank discharge shutoff valve 18. Since LNG has a low temperature of about -162 ° C., this is to prevent the trouble of clogging due to freezing of the refrigerant.

In FIG. 3, it corresponds to between BC. As described above, the LNG cold heat recovery system 100 according to the present invention does not try to recover all the cold heat of LNG.

This is because the LNG vaporizer 12 often exists as an existing one, and cost effectiveness is taken into consideration.

Next, the operation when the LNG cold heat recovery system 100 is stopped will be described with reference to FIGS. 4 and 5.

As shown in FIG. 4, when the LNG evaporator temperature sensor 21 exceeds a preset temperature (-40 ° C in FIG. 4), the temperature difference between the fourth pipe temperature sensor 29 and the sixth pipe temperature sensor 36. When is within the preset temperature (0.5 ° C. in FIG. 4), the control unit 44 fully opens the LNG storage tank discharge shutoff valve 18 and stops the refrigerant circulation pump 30. As a result, the LNG cold heat recovery system 100 is stopped.

The fact that the LNG evaporator temperature sensor 21 exceeds a preset temperature indicates that the flow rate of LNG has decreased or is not flowing.

Further, the fact that the temperature difference between the fourth pipe temperature sensor 29 and the sixth pipe temperature sensor 36 is within the preset temperature indicates that the cold heat cannot be recovered by the refrigerant.

The range that satisfies these two conditions corresponds to the area between DE and E in FIG.

By this operation, it is possible to detect that the LNG is not flowing enough to recover the cold heat, and at the same time, detect that the refrigerant is not able to recover the cold heat, so that the system can be reliably stopped while maximizing the amount of cold heat recovered. It will be possible.

In this way, the LNG cold heat recovery system 100 realizes not only start and stop but also maximization of cold heat recovery of LNG only by the temperature sensor in the system.

Therefore, it does not depend on information from other systems, and even if an existing LNG satellite exists, it has a remarkable effect that it can be installed later.

The embodiment has been described above. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, and these also naturally belong to the technical scope of the present invention. Understood.

The present invention can be used as an LNG cold heat recovery system capable of recovering cold heat discharged when natural gas is generated from LNG.

10: LNG storage tank, 12: LNG vaporizer, 14: first pipe, 16: first pipe temperature sensor, 18: LNG storage tank discharge shutoff valve, 20: LNG evaporator, 21: LNG evaporator temperature sensor, 22: No. 2 pipes, 24: 3rd pipe, 26: cascade condenser, 28: 4th pipe, 29: 4th pipe temperature sensor, 30: refrigerant circulation pump, 32: 5th pipe, 34: 6th pipe, 36: 6th pipe Piping temperature sensor, 38: Receiver tank, 40: Gas piping, 42: Condensate piping, 44: Control unit, 100: LNG cold heat recovery system

Claims (4)

In an LNG cold heat recovery system that recovers the cold heat of LNG generated by cooling natural gas.
The first pipe through which LNG flows and
The first pipe temperature sensor installed to measure the fluid temperature inside the first pipe,
An LNG storage tank discharge shutoff valve installed on the first pipe and downstream of the first pipe temperature sensor.
A second pipe that branches on the first pipe and is branched on the upstream side of the LNG storage tank discharge shutoff valve and connects the first pipe and the LNG evaporator.
A third pipe that connects the LNG evaporator and the first pipe on the first pipe and on the downstream side of the LNG storage tank discharge shutoff valve.
The fourth pipe that connects the LNG evaporator and the cascade capacitor and transfers the refrigerant, and
The fifth pipe connecting the cascade condenser and the suction side of the refrigerant circulation pump,
A sixth pipe connecting the discharge side of the refrigerant circulation pump and the LNG evaporator,
It is composed of a sixth pipe temperature sensor installed in the sixth pipe to measure the fluid temperature inside the sixth pipe.
The LNG is provided with a control unit that controls the opening degree of the LNG storage tank discharge shutoff valve and the start of the refrigerant circulation pump based on the measured values of the first pipe temperature sensor and the sixth pipe temperature sensor. Cold heat recovery system. The control unit starts the refrigerant circulation pump when the temperature measured by the first pipe temperature sensor becomes equal to or lower than a preset temperature, and the temperature measured by the sixth pipe temperature sensor is a preset temperature. The LNG cold heat recovery system according to claim 1, wherein the control is performed to gradually close the LNG storage tank discharge shutoff valve until the following. 1 or claim 1, wherein the control unit controls to gradually open the LNG storage tank discharge shutoff valve when the temperature measured by the sixth pipe temperature sensor falls below a preset temperature. 2. The LNG cold heat recovery system according to 2. An LNG evaporator temperature sensor installed at the LNG side outlet of the LNG evaporator, measuring the temperature inside the LNG evaporator and transmitting the temperature to the control unit.
A fourth pipe temperature sensor installed on the fourth pipe, measuring the fluid temperature inside the pipe and transmitting it to the control unit, is provided.
In the control unit, when the temperature measured by the LNG evaporator temperature sensor is higher than the preset temperature, the temperature difference between the temperature measured by the fourth pipe temperature sensor and the sixth pipe temperature sensor is According to any one of claims 1 to 3, the LNG storage tank discharge shutoff valve is fully opened and the refrigerant circulation pump is controlled to stop when the temperature difference is smaller than a preset temperature difference. The LNG cold heat recovery system described.

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