JP2020148210A - Lng cold recovery system - Google Patents

Abstract

To provide an LNG cold recovery system that can be applied to an existing LNG vaporizer, 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 fluid inside an LNG pipeline; an LNG storage tank put-out isolation valve 18 provided nearer a downstream side than the first pipeline temperature sensor 16; a second pipeline temperature sensor 26 for measuring temperature of fluid inside a second pipeline 22; an LNG vaporizer temperature sensor 28 for measuring temperature inside an LNG vaporizer; a refrigerant circulation pump 38 for feeding a refrigerant to a cold utilization facility 32; and a control unit 46 for controlling an opening degree of the LNG storage tank put-out isolation valve 18 and activation and deactivation of the refrigerant circulation pump 38, based on measured values of the first pipeline temperature sensor 16, the second pipeline temperature sensor 26, and the LNG vaporizer temperature sensor 28.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, in which LNG installed between the LNG storage tank and the LNG vaporizer flows. One pipe, a first pipe temperature sensor installed to measure the pipe temperature of the first pipe, and an LNG storage tank payout installed on the first pipe and downstream of the first pipe temperature sensor. The shutoff valve, the 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, and the internal fluid temperature of the second pipe. The second pipe temperature sensor installed to measure the temperature, the LNG evaporator temperature sensor installed at the LNG outlet of the LNG evaporator and measuring the temperature inside the LNG evaporator, and the first pipe. A third pipe connecting the LNG evaporator and the first pipe on the downstream side of the LNG storage tank discharge shutoff valve, a fourth pipe connecting the LNG evaporator and cold heat utilization equipment to transfer a refrigerant, and the above. It is composed of a fifth pipe connecting the cold heat utilization equipment and the suction side of the refrigerant circulation pump, and a sixth pipe connecting the discharge side of the refrigerant circulation pump and the LNG evaporator, the first pipe temperature sensor, and the second. It is characterized by including a control unit that controls the opening degree of the LNG storage tank discharge shutoff valve and the start and stop of the refrigerant circulation pump based on the measured values of the pipe temperature sensor and the LNG evaporator temperature sensor.

(2) The LNG cold heat recovery system according to the present invention is the LNG cold heat recovery system according to (1), in which the control unit has a temperature measured in advance by the first pipe temperature sensor or the second pipe temperature sensor. When the temperature is below the set temperature and the temperature measured by the LNG evaporator temperature sensor is below the preset temperature or within the preset time, the predetermined temperature drop is measured. It is characterized in that the refrigerant circulation pump is started after the lapse of time and the control is performed to close the LNG storage tank discharge shutoff valve.

(3) The LNG cold heat recovery system according to the present invention is the LNG cold heat recovery system according to (1) or (2), in which the fourth pipe measures the fluid temperature inside the pipe and transmits the fourth pipe to the control unit. The sixth pipe is provided with a pipe temperature sensor, the sixth pipe is equipped with a sixth pipe temperature sensor that measures the fluid temperature inside the pipe and transmits the temperature to the control unit, and the control unit has a temperature measured by the LNG evaporator temperature sensor. When the temperature is equal to or higher than the preset temperature and the temperature difference between the fourth pipe temperature sensor and the sixth pipe temperature sensor is equal to or lower than the preset value, the fluid circulation pump is stopped and the above. It is characterized by controlling the opening of the LNG storage tank discharge shutoff valve.

(4) The LNG cold heat recovery system according to the present invention is the LNG cold heat recovery system according to any one of (1) to (3), wherein the control unit has a preset value measured by the sixth pipe temperature sensor. When the value is lower, the LNG storage tank discharge shutoff valve is fully closed, and when the measured value of the sixth pipe temperature sensor is higher than the preset value, the LNG storage tank discharge shutoff valve is gradually opened. And.

(5) The LNG cold heat recovery system according to the present invention is the LNG cold heat recovery system according to (4), in which a cold heat recovery unit shutoff valve for opening / closing control by the control unit is installed in the second pipe, and the control is performed. The unit is characterized in that when the temperature measured by the fourth pipe temperature sensor falls below a preset temperature, the LNG storage tank discharge shutoff valve is fully opened and the cold heat recovery unit shutoff valve is fully closed. And.

According to the LNG cold heat recovery system described in (1), the LNG cold heat recovery system can be started only by measuring the temperature of LNG with three temperature sensors. Further, even if there is an existing LNG satellite base, the LNG cold heat recovery system according to the present invention does not depend on information from other systems, so that it can be retrofitted and can be introduced inexpensively and early.

LNG is a mixture of methane and ethane, and unlike boiling water when the phase changes from liquid phase to gas phase (in the case of water, it is about 100 ° C under normal pressure), it utilizes the fact that it has a temperature gradient. Because it is.

According to the LNG cold heat recovery system described in (2), the use of LNG is surely started by detecting that LNG has started to flow by the temperature of the temperature sensor installed in the pipe or the temperature drop within a certain period of time. It is possible to start the LNG cold heat recovery system after confirming that it has been done.

According to the LNG cold heat recovery system described in (3), the temperature of the LNG evaporator temperature sensor became higher than the predetermined temperature (that is, the amount of LNG used decreased), or the temperature difference between the going and returning of the refrigerant pipe. It is possible to safely stop the LNG cold heat recovery system by detecting the temperature at which the temperature has decreased (that is, the cold heat utilization equipment no longer requires cold heat) with only the temperature sensor.

According to the LNG cold heat recovery system described in (4), it is possible to maximize the recovery amount of LNG cold heat simply by measuring the return temperature of the refrigerant with a temperature sensor.

According to the LNG cold heat recovery system described in (5), it is possible to detect a state in which too much LNG cold heat is present only by the refrigerant temperature, and it is possible to safely stop the LNG cold heat recovery system.

It is a schematic diagram which shows the whole structure of the LNG cold heat recovery system. It is a flow chart which shows the start condition of the LNG cold heat recovery system. It is a flow chart which shows the stop condition of the LNG cold heat recovery system. It is a flow chart which shows the system protection of the LNG cold heat recovery system.

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.

As an embodiment, the configuration of the LNG cold heat recovery system 100 will be described with reference to FIG.

The LNG storage tank 10 is a container for temporarily storing LNG installed in a factory or the like, which is a customer of LNG, and is kept cold in order to absorb external heat and prevent the internal pressure from increasing.

The inside of the LNG storage tank 10 is filled with LNG, and is connected to the LNG vaporizer 12 by a first pipe 14.

A first pipe temperature sensor 16 is installed in the first pipe 14 to measure the fluid temperature inside the pipe, and an LNG storage tank discharge shutoff valve 18 is located downstream of the first pipe temperature sensor 16 in the first pipe 14. is set up.

The first pipe 14 is provided with a second pipe 22 that branches on the upstream side of the LNG storage tank discharge shutoff valve 18 and connects the first pipe 14 and the LNG evaporator 20, and the second pipe 22 recovers cold heat. A unit shutoff valve 24 and a second pipe temperature sensor 26 for measuring the fluid temperature inside the pipe are installed.

An LNG evaporator temperature sensor 28 that measures the temperature inside the LNG evaporator is installed at the LNG outlet of the LNG evaporator 20, and the LNG evaporator 20 is located downstream of the LNG storage tank discharge shutoff valve 18 of the first pipe 14. And the first pipe 14 are connected by the third pipe 30.

A fourth pipe 34 that connects the LNG evaporator 20 and the cold heat utilization facility 32 to transfer the refrigerant, and a fourth pipe temperature sensor 36 that measures the pipe temperature are installed in the fourth pipe 34.

The cold heat utilization facility 32 and the suction side of the refrigerant circulation pump 38 are connected by a fifth pipe 40, and the discharge side of the refrigerant circulation pump 38 and the LNG evaporator 20 are connected by a sixth pipe 42.

A sixth pipe temperature sensor 44 is installed in the sixth pipe 42 to measure the pipe temperature.

Opening control of the LNG storage tank discharge shutoff valve 18 based on the measured values of the first pipe temperature sensor 16, the second pipe temperature sensor 26, the LNG evaporator temperature sensor 28, the fourth pipe temperature sensor 36, and the sixth pipe temperature sensor 44. A control unit 46 capable of controlling the start and stop of the refrigerant circulation pump 38 is provided.

Next, FIG. 2 shows the flow at the time of starting the LNG cold heat recovery system.

When the temperature measured by the first pipe temperature sensor 16 or the second pipe temperature sensor 26 is equal to or lower than the preset temperature (-130 ° C or lower in FIG. 2), and is measured by the LNG evaporator temperature sensor 28. When the set temperature is below the preset temperature (-40 ° C or less in FIG. 2) or when the predetermined temperature drop is measured within the preset time (2 ° C or more drop within 10 minutes in FIG. 2). Since it can be determined that the use of LNG has started, the control unit 46 starts the refrigerant circulation pump 38 after a predetermined time (20 minutes in FIG. 2) set to prevent frequent start and stop, and discharges the LNG storage tank. Control is performed to close the shutoff valve 18.

By this control, LNG is sent to the LNG evaporator 20 through the second pipe 22, and heat exchange (that is, heating) with the refrigerant in the LNG evaporator 20 to change from the liquid phase to the gas phase.

As described above, the LNG cold heat recovery system 100 detects the start of use of LNG according to the flow shown in FIG. 2 and autonomously starts the cold heat recovery operation.

The LNG cold heat recovery system 100 according to the present invention does not recover all the cold heat of LNG, but it is sufficient if a certain amount of cold heat can be recovered. The LNG that cannot be completely vaporized by the LNG cold heat recovery system 100 is sent to the LNG vaporizer 12, and all of it is vaporized.

Methylene chloride (dichloromethane) or the like is used as the refrigerant, and the refrigerant is determined in consideration of the temperature used and the distance between the LNG cold heat recovery system 100 and the cold heat utilization facility 32.

FIG. 3 shows a flow in which the LNG cold heat recovery system 100 goes from the cold heat recovery operation to the stopped state, and a flow for maximizing the cold heat recovery amount and protecting the equipment.

First, in the flow from the cold recovery operation to the stop of the cold recovery operation, the temperature measured by the LNG evaporator temperature sensor 28 exceeds the preset temperature (more than -40 ° C in FIG. 3). When the temperature difference between the 4th pipe temperature sensor 36 and the 6th pipe temperature sensor 44 became less than or equal to the preset value (0.5 ° C or less in FIG. 3), the amount of LNG used decreased. Alternatively, it can be determined that the use of LNG has been stopped.

Therefore, the control unit 46 stops the refrigerant circulation pump 38 and controls to open the LNG storage tank discharge shutoff valve 18.

As a result, even if LNG is used, it does not flow to the LNG evaporator 20 due to the pressure loss in the flow path, but is directly input to the LNG vaporizer 12 through the first pipe 14, and the LNG cold heat recovery system 100 is stopped. It becomes a state.

On the other hand, if the temperature measured by the LNG evaporator temperature sensor 28 is equal to or lower than the preset temperature (−40 ° C. or lower in FIG. 3), it can be determined that LNG is still used.

In this case, if the measured value of the sixth pipe temperature sensor 44 is higher than the preset value (−45 ° C. in FIG. 3), the LNG cold heat recovery system 100 still has room for recovering cold heat, so the control unit 46 is LNG. The storage tank discharge shutoff valve 18 is fully closed.

As a result, the entire amount of LNG is passed through the LNG cold heat recovery system 100, and the cold heat of the LNG cold heat can be recovered to the maximum extent.

However, when the measured value of the sixth pipe temperature sensor 44 is lower than the preset value (−45 ° C. in FIG. 3), the LNG storage tank payout shutoff valve 18 is gradually opened. By this control, a part of LNG does not pass through the LNG cold heat recovery system 100 and is sent to the LNG vaporizer 12 as it is.

This avoids excessive cold heat recovery and prevents the refrigerant from freezing and equipment damage that may occur when the temperature of the refrigerant drops too low.

FIG. 4 is a flow showing equipment protection when there is too much LNG cold heat.

When the temperature measured by the fourth piping temperature sensor 36 falls below the preset temperature (-60 ° C in FIG. 4), the control unit 46 fully opens the LNG storage tank discharge shutoff valve 18 and opens the cold heat recovery unit shutoff valve 24. Fully closed.

When the amount of LNG cold heat is too large due to this control, LNG is not flowed to the LNG cold heat recovery system 100, and the entire amount is sent from the LNG storage tank 10 to the LNG vaporizer 12. This control makes it possible to protect equipment in an emergency.

As described above, the LNG cold heat recovery system 100 according to the present invention can be started and stopped autonomously without depending on information from other systems. Further, even if the existing LNG vaporizer 12 exists, it does not interfere with the existing system, so that it can be introduced inexpensively and quickly.

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: 1st pipe, 16: 1st pipe temperature sensor, 18: LNG storage tank discharge shutoff valve, 20: LNG evaporator, 22: 2nd pipe, 24: Cold heat recovery unit Shutoff valve, 26: 2nd pipe temperature sensor, 28: LNG evaporator temperature sensor, 30: 3rd pipe, 32: Cold heat utilization equipment, 34: 4th pipe, 36: 4th pipe temperature sensor, 38: Refrigerator circulation pump , 40: 5th pipe, 42: 6th pipe, 44: 6th pipe temperature sensor, 46: control unit, 100: LNG cold heat recovery system

Claims (5)

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, which is installed between the LNG storage tank and the LNG vaporizer,
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 second pipe temperature sensor installed to measure the fluid temperature inside the second pipe,
An LNG evaporator temperature sensor installed at the LNG outlet of the LNG evaporator and measuring the temperature inside 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 cold heat utilization equipment and transfers the refrigerant, and
The fifth pipe connecting the cold heat utilization equipment and the suction side of the refrigerant circulation pump,
It is composed of a sixth pipe connecting the discharge side of the refrigerant circulation pump and the LNG evaporator.
Control to control the opening degree of the LNG storage tank withdrawal shutoff valve and start and stop of the refrigerant circulation pump based on the measured values of the first pipe temperature sensor, the second pipe temperature sensor, and the LNG evaporator temperature sensor. An LNG cold heat recovery system characterized by having a unit. In the control unit, when the temperature measured by the first pipe temperature sensor or the second pipe temperature sensor becomes equal to or lower than a preset temperature, the temperature measured by the LNG evaporator temperature sensor is in advance. When a predetermined temperature drop is measured below a set temperature or within a preset time, the refrigerant circulation pump is started after a predetermined time has elapsed, and control is performed to close the LNG storage tank discharge shutoff valve. The LNG cold heat recovery system according to claim 1, characterized by this. The fourth pipe is provided with a fourth pipe temperature sensor that measures the fluid temperature inside the pipe and transmits it to the control unit.
The sixth pipe is provided with a sixth pipe temperature sensor that 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 becomes equal to or higher than a preset temperature, the temperature difference between the fourth pipe temperature sensor and the sixth pipe temperature sensor is preset. The LNG cold heat recovery system according to claim 1 or 2, wherein when the value is equal to or less than the value, the refrigerant circulation pump is stopped and the LNG storage tank discharge shutoff valve is controlled to be opened. When the measured value of the sixth pipe temperature sensor is lower than the preset value, the control unit fully closes the LNG storage tank discharge shutoff valve, and the measured value of the sixth pipe temperature sensor is higher than the preset value. The LNG cold heat recovery system according to any one of claims 1 to 3, wherein the LNG storage tank discharge shutoff valve is gradually opened in the case of the case. A cold heat recovery unit shutoff valve for opening / closing control by the control unit is installed in the second pipe.
When the temperature measured by the fourth pipe temperature sensor falls below a preset temperature, the control unit controls to fully open the LNG storage tank discharge shutoff valve and fully close the cold heat recovery unit shutoff valve. The LNG cold heat recovery system according to claim 4.

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