JP7108168B2 - Liquid cold heat recovery system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid cold heat recovery system for recovering cold heat discharged when a low-temperature liquid, which is gas at room temperature but is liquefied at low temperature, is converted to gas.

Cryogenic liquids include LNG (liquefied natural gas), liquid nitrogen, liquid oxygen, and the like, and are usually used in gaseous states as NG (natural gas), nitrogen, and oxygen, respectively.

For example, in the case of NG, if the production area and the consumption area are in remote areas that cannot be transported by pipeline, LNG is generated by cooling to about -162 ° C and liquefying, and the volume is reduced to about 600 minutes. It is common to reduce the volume to 1 of 1 and transport it by a large dedicated carrier.

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

Also, part of the LNG stored in the LNG tank is transferred to an LNG truck in the state of LNG and sent to LNG consumers such as factories in various places.

LNG transported by LNG tanker is temporarily stored in a facility called an LNG satellite station, which is generally located on the premises of the LNG consumer or nearby, and according to demand, NG, which is a gas, is generated from LNG and consumed. be done.

Nitrogen and oxygen are also often produced from air using cryogenic separation processes, so the nitrogen and oxygen are often produced first as liquid nitrogen and liquid oxygen. However, even in the case of liquid nitrogen and liquid oxygen, it is common to convert them into gas when consumers consume them.

When LNG, liquid nitrogen, and liquid oxygen, which are low-temperature liquefied fluids, are converted to NG, nitrogen, and oxygen, which are gases, an air heating type vaporizer or a vaporizer using a heat source such as hot water or steam is used. There are many.

However, some consumers of low-temperature liquefied fluids with vaporizers need cold energy for systems such as air conditioning in buildings and factories, cooling processes in factories, etc. If it can be used in other systems, two energy savings can be achieved: a reduction in the energy consumed as fuel for gas generation and a reduction in cold production energy for other systems.

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

JP-A-2004-324761

However, in the low-temperature liquefied gas vaporizer and its operating method in Patent Document 1, it is assumed that water is mainly used as a heat medium for generating gas from the low-temperature liquefied gas, so it is necessary to heat it to about room temperature with water. The difference in temperature is small compared to normal gas, and the heat exchanger becomes large. Also, because the structure is completely different from the existing vaporizer, it is necessary to build a new vaporizer, which is a double investment, which increases the cost. I have a problem.

In view of the above problems, an object of the present invention is to provide a liquid cold heat recovery system that is small in size and that can utilize existing vaporizers.

(1) A liquid cold heat recovery system according to the present invention is a liquid cold heat recovery system installed on a liquid main pipe that connects a liquid storage tank and a liquid vaporizer to recover cold heat, in which the liquid cold heat recovery system branches from the liquid main pipe, a liquid second pipe connected to a liquid inlet of a liquid evaporator; a liquid third pipe connecting a liquid outlet provided in the liquid evaporator and the liquid main pipe; a liquid first control valve provided between a second pipe branch and a connecting portion of the liquid third pipe; a liquid second control valve provided on the liquid second pipe; a liquid temperature sensor provided in the liquid evaporator; a refrigerant first pipe that connects the refrigerant outlet provided in the liquid evaporator and the cold heat utilization equipment; a refrigerant second pipe that connects the cold heat utilization equipment and the refrigerant circulation pump; A third refrigerant pipe connecting the refrigerant circulation pump and the refrigerant inlet of the liquid evaporator; a fourth refrigerant pipe branching from the third refrigerant pipe and connecting the second refrigerant pipe; A refrigerant temperature sensor provided, a refrigerant first control valve provided on the third refrigerant pipe and on the refrigerant inlet side of the branch portion of the fourth refrigerant pipe, and on the fourth refrigerant pipe Based on the provided refrigerant second control valve, the liquid temperature sensor, and the measured values of the refrigerant temperature sensor, the liquid first control valve, the liquid second control valve, the refrigerant first control valve, and the refrigerant second control valve and a control unit for controlling the degree of opening of each of the two control valves.

(2) The liquid cold energy recovery system according to the present invention is the liquid cold energy recovery system according to (1), wherein the controller controls the temperature measured by the liquid temperature sensor to be higher than a preset upper temperature limit. If it is high, the refrigerant circulation pump is stopped, the liquid first control valve is closed, the liquid second control valve and the refrigerant first control valve are opened, the opening degree of the refrigerant second control valve is minimized, and the The refrigerant circulation pump is activated when the temperature measured by the liquid temperature sensor falls below a preset temperature upper limit.

(3) The liquid cold heat recovery system according to the present invention is the liquid cold heat recovery system according to (1) or (2), wherein the control unit changes the temperature measured by the refrigerant temperature sensor to a preset temperature When the temperature measured by the refrigerant temperature sensor is higher than the upper limit of the preset temperature, the degree of opening of the first refrigerant control valve is throttled and the second refrigerant control valve is opened at the same time. When it becomes equal to or less than the upper limit, the opening degree of the second refrigerant control valve is throttled and at the same time, control is performed to open the first refrigerant control valve.

(4) The liquid cold heat recovery system according to the present invention is the liquid cold heat recovery system according to any one of (1) to (3), wherein the control unit presets the temperature measured by the refrigerant temperature sensor. When the temperature falls below the lower limit of the set temperature, control is performed to open the liquid first control valve and at the same time reduce the degree of opening of the liquid second control valve.

(5) The liquid cold heat recovery system according to the present invention is the liquid cold heat recovery system according to any one of (1) to (4), wherein the control unit presets the temperature measured by the liquid temperature sensor. When the temperature falls below the lower limit of the set temperature, control is performed to open the liquid first control valve and at the same time reduce the degree of opening of the liquid second control valve.

(6) The liquid cold heat recovery system according to the present invention is the liquid cold heat recovery system according to any one of (1) to (5), wherein the control unit presets the temperature measured by the refrigerant temperature sensor. When the temperature is higher than the lower limit, the first liquid control valve is closed, the degree of opening of the second refrigerant control valve is minimized, and the second liquid control valve and the first refrigerant control valve are fully opened. It is characterized by performing control to do.

According to the liquid cold heat recovery system described in (1), the liquid cold heat recovery system can be added to the liquid main pipe connecting the liquid storage tank and the liquid vaporizer provided in the existing liquid satellite base. It can be installed at a low cost without wasting the investment made so far. In addition, the liquid cold heat recovery system according to the present invention can operate as an independent system without receiving signals from other equipment, so it has the effect of not being affected by the reliability of other equipment. Moreover, it is possible to recover heat with a simple configuration in which four control valves are controlled based on the measurement results from two temperature sensors, a liquid temperature sensor and a refrigerant temperature sensor.

According to the liquid cold heat recovery system described in (2), it is determined whether the cold heat amount of the liquid is sufficient only by measuring the liquid outlet temperature from the liquid evaporator, and if the cold heat amount is sufficient, the heat is recovered. It is possible to start the refrigerant pump and start heat recovery.

According to the liquid cold energy recovery system described in (3), in order to prevent adverse effects on the cold energy utilization equipment when the recovered cold energy is insufficient, the refrigerant is circulated in the liquid cold energy recovery system to increase the refrigerant temperature sufficiently. can be cooled to

According to the liquid cold heat recovery system described in (4), if the amount of liquid cold heat is too large, troubles such as freezing and clogging of the refrigerant may occur. In such a case, it is possible to limit the amount of liquid flowing into the liquid cold heat recovery system and avoid troubles in the liquid cold heat recovery system.

According to the liquid cold energy recovery system described in (5), if the liquid temperature drops too much for some reason, trouble occurs in the liquid cold energy recovery system by limiting the amount of liquid sent to the liquid cold energy recovery system as in (4). can be avoided.

According to the liquid cooling energy recovery system described in (6), when the liquid cooling energy can be recovered, it is possible to recover as much liquid cooling energy as possible.

1 is a schematic diagram showing the entire liquid cold heat recovery system; FIG. It is a schematic diagram which shows the collection|recovery range of LNG cold-heat, and the temperature measurement value in a sensor. FIG. 3 is a schematic diagram showing a cold recovery range of liquid nitrogen or liquid oxygen and a temperature measurement value with a sensor;

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Such embodiments are merely examples for facilitating understanding of the invention, and do not limit the invention unless otherwise specified.

In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to omit redundant description, and elements that are not directly related to the present invention are omitted from the drawings.

A configuration of an embodiment of the present invention will be described with reference to the drawings.

As a first embodiment, a case of recovering cold energy from LNG, which is a low-temperature liquid, will be described.

FIG. 1 is a diagram showing the overall configuration of a liquid cryogenic heat recovery system 100 (the portion surrounded by a dotted line) and the relationship between other facilities provided in a typical LNG satellite base.

The liquid cryogenic heat recovery system 100 is installed on a liquid main pipe 130 connecting a liquid storage tank 110 and a liquid vaporizer 120 provided in an LNG satellite terminal (the overall structure is not shown).

A liquid second pipe 14 branched from the liquid main pipe 130 and connected to the liquid inlet 12A of the liquid evaporator 12, and a liquid third pipe connecting the liquid outlet 12B provided in the liquid evaporator 12 and the liquid main pipe 130. 16 are provided.

A liquid first control valve 18 is provided on the liquid main pipe 130 and between the branched portion with the liquid second pipe 14 and the connection portion with the liquid third pipe 16. A liquid second control valve 20 and a liquid temperature sensor 22 are provided in the liquid third pipe 16, respectively.

The liquid evaporator 12 is provided with a refrigerant outlet 12C, a first refrigerant pipe 24 connecting the cold heat utilization equipment 140 from the refrigerant outlet 12C, and a second refrigerant pipe 28 connecting the cold heat utilization equipment 140 to the refrigerant circulation pump 26. ing.

A third refrigerant pipe 30 connecting the refrigerant circulation pump 26 and the refrigerant inlet 12D of the liquid evaporator 12, and a fourth refrigerant pipe 32 branching from the third refrigerant pipe 30 and connecting the second refrigerant pipe 28 are provided. . This fourth refrigerant pipe functions as a bypass pipe for the cold heat utilization equipment 140 and also as a minimum flow line for the refrigerant circulation pump 26 .

A refrigerant temperature sensor 34 is provided on the first refrigerant pipe 24, and a first refrigerant control valve 36 is provided on the third refrigerant pipe 30 and on the refrigerant inlet 12D side of the branch of the fourth refrigerant pipe 32. .

A second refrigerant control valve 38 is provided on the fourth refrigerant pipe 32 .

Based on the measured values of the liquid temperature sensor 22 and the refrigerant temperature sensor 34, the opening degrees of the first liquid control valve 18, the second liquid control valve 20, the first refrigerant control valve 36, and the second refrigerant control valve 38 is provided with a control unit 40 for controlling the

In this way, the liquid cold heat recovery system 100 is installed on the liquid main pipe 130, but does not require signal exchange from the liquid storage tank 110, the liquid vaporizer 120, and the cold heat utilization equipment 140, and is independent from other systems. It is an independent system.

Next, the operation of the liquid cryogenic heat recovery system 100 will be described with reference to FIG.

2, the upper figure shows the LNG load and time, the middle figure shows the measured value and time of the liquid temperature sensor 22 when the LNG load fluctuates in the upper figure, and the lower figure shows the refrigerant temperature sensor when the LNG load fluctuates in the upper figure. 34 is a schematic diagram showing the relationship between measured values of 34 and time.

As shown in the upper diagram of FIG. 2, the liquid cold energy recovery system 100 according to the present invention is not intended to recover all the cold energy of the low temperature liquid.

To reduce the cost by reducing the size of the heat exchanger by not recovering all of the cold heat of the low-temperature liquid, and by mainly recovering the latent heat of vaporization and not recovering part of the sensible heat, and The purpose is to position the cryogenic heat recovery system 100 as a preheater for the existing liquid vaporizer 120 so as not to impair the reliability of the entire system for generating gas from liquid.

As shown in the upper diagram of FIG. 2, the design capacity of the liquid cold heat recovery system 100 is set to be smaller than the design capacity of the liquid load of the liquid vaporizer 120. This is the result of considering the merits and costs related to cold heat recovery. be.

FIG. 2 shows daily fluctuations in the amount of LNG used by LNG consumers (mainly factories) using LNG satellite bases and the associated sensor measurement values.

First, the portion described as the cold heat non-recovery range on the left side of the upper diagram of FIG. 2 indicates that the factory is in a stopped state at night or the like and the LNG load is low.

When the LNG load is low, the load on the cold heat utilization equipment 140 that requires LNG cold heat is also low, so the need to recover the LNG cold heat at a cost is low.

Here, LNG is a mixture containing methane, ethane, propane, etc., and has a temperature gradient even when accompanied by a phase change, so the temperature of LNG itself rises as the LNG load decreases.

2 indicates that the LNG temperature measured by the liquid temperature sensor 22 is high, that is, the LNG load is low.

Since the LNG temperature measured by the liquid temperature sensor 22 is equal to or higher than the preset temperature upper limit between DA and DA, the control unit 40 stops the refrigerant circulation pump 26 .

Even when the refrigerant circulation pump 26 is in a stopped state, the control unit 40 performs control to close the first liquid control valve 18 and open the second liquid control valve 20 . This is to allow even a small amount of LNG to flow into the liquid cryogenic heat recovery system 100 to maintain the low temperature state of the system and prepare for a prompt restart.

At the same time, the control unit 40 opens the first refrigerant control valve 36 and minimizes the opening degree of the second refrigerant control valve 38 . This is because when the value measured by the liquid temperature sensor 22 falls below the preset temperature upper limit (that is, when the LNG load increases), the system can be started immediately.

Since the fourth refrigerant pipe 32 provided with the second refrigerant control valve 38 also functions as a minimum flow pipe for the refrigerant circulation pump 26, the opening degree of the second refrigerant control valve 38 when the opening degree is minimum is It will be determined in consideration of the required flow rate at the minimum flow.

Point A in the middle diagram of FIG. 2 indicates a state where the liquid load begins to increase. For example, in the morning, when the plant starts up, the LNG load increases sharply. Along with this, the LNG temperature measured by the liquid temperature sensor 22 also drops sharply.

In order to recover the LNG cold heat, the control unit 40 starts the refrigerant circulation pump 26 at point A when the temperature measured by the liquid temperature sensor 22 falls below the preset temperature upper limit, and the liquid evaporator 12 cools the liquid. is heat-exchanged with the refrigerant and recovery is started.

Since the refrigerant exchanges heat with the extremely low temperature of about -160°C of LNG, it is preferable to use methylene chloride or the like having a low freezing point.

The control between da in FIG. 2 will be described. Between DA and A in FIG. 2, the liquid cold heat recovery system 100 is maintained at a low temperature by allowing a small amount of LNG to flow into the liquid cold heat recovery system 100, but the refrigerant is connected to the cold heat utilization equipment 140 via piping. Therefore, the temperature may rise while the LNG load is low, exceeding the preset upper temperature limit for the refrigerant. In that case, if the refrigerant is allowed to flow into cold heat utilization equipment 140 , cold heat utilization equipment 140 may be adversely affected.

Therefore, when the temperature measured by the refrigerant temperature sensor 34 exceeds the set temperature upper limit as between d and a in FIG. Control to open the second control valve 38 is performed. This increases the amount of refrigerant circulating in the liquid cold heat recovery system 100 and lowers the refrigerant temperature. Note that this control is applied with priority over the control between DA.

When the temperature of the refrigerant measured by the refrigerant temperature sensor 34 becomes equal to or lower than the preset temperature upper limit, the control unit 40 reduces the degree of opening of the second refrigerant control valve 38 and closes the first refrigerant control valve 36 at the same time. Open control is performed to reduce the refrigerant circulation amount, the refrigerant is sent to the cold energy utilization equipment 140, and the cold energy utilization equipment 140 uses the recovered cold energy.

The section bc in FIG. 2 will be described.

Between bc, the temperature measured by the refrigerant temperature sensor 34 is lower than the preset lower temperature limit, so if left as it is, the refrigerant may freeze or block. This is a state in which the LNG load exceeds the design capacity of the liquid cold heat recovery system 100, and corresponds to the cold heat non-recovery range in the state where the liquid load is high in the upper diagram of FIG.

In this case, in order to protect the system, the controller 40 opens the first liquid control valve 18 and, at the same time, controls the degree of opening of the second liquid control valve 20 to be throttled. This limits the amount of LNG flowing into the liquid cryogenic heat recovery system 100 and prevents troubles such as freezing of the refrigerant.

Next, the control between BC will be explained.

BC control is an emergency protection system. If the temperature measured by the liquid temperature sensor 22 falls below the set temperature lower limit for some reason, the controller 40 opens the liquid first control valve 18 and at the same time throttles the opening degree of the liquid second control valve 20 for system protection. control. This limits the amount of LNG flowing into the liquid cryogenic heat recovery system 100 and prevents troubles such as freezing of the refrigerant.

Next, the control between cd will be explained.

Between c and d, the refrigerant temperature measured by the refrigerant temperature sensor is between the upper limit and the lower limit of the set temperature. Specifically, the control unit 40 closes the first liquid control valve 18 and minimizes the degree of opening of the second refrigerant control valve 38, and at the same time, fully opens the second liquid control valve 20 and the first refrigerant control valve 36. conduct.

The upper and lower limit values of the set temperature measured by the liquid temperature sensor 22 and the upper and lower limit values of the set temperature measured by the refrigerant temperature sensor 34 trigger the control of the control unit 40. However, by changing the respective upper and lower limits, it becomes possible to freely set the starting temperature of the liquid cold energy recovery system 100 and the amount of cold energy recovered.

Effects of the present invention according to the first embodiment will be described.

The liquid cold heat recovery system 100 according to the present invention has a simple configuration in which the temperature of the LNG outlet from the liquid evaporator 12 and the outlet temperature of the refrigerant are measured by sensors, and four control valves are controlled based on the measurement results. , a self-sustaining system that is completely separated from other equipment is realized, a protection system is also realized, the recoverable liquid cold heat is recovered as much as possible, and the set temperature of the liquid and refrigerant By changing the upper limit value and the lower limit value, there is an effect that the recovery amount of LNG cold heat can be freely changed.

Next, as a second embodiment, a case of recovering cold heat from liquid nitrogen or liquid oxygen will be described only in points different from the first embodiment.

FIG. 3 shows daily fluctuations in the consumption of liquid nitrogen or liquid oxygen by a customer and the associated sensor readings.

Since liquid nitrogen or liquid oxygen contains almost no other substances, the value measured by the liquid temperature sensor 22 is a constant temperature during the phase change regardless of the load of liquid nitrogen or liquid oxygen ( Fig. 3 middle diagram). However, even in that case, the value measured by the refrigerant temperature sensor 34 fluctuates according to the load fluctuation of liquid nitrogen or liquid oxygen (lower diagram in FIG. 3).

However, the control of the control unit 40 of the second embodiment is basically the same as that of the first embodiment.

The first embodiment and the second embodiment have been described above. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope described in the claims, and these also belong to the technical scope of the present invention. Understood.

INDUSTRIAL APPLICABILITY The present invention can be used as a liquid cold heat recovery system capable of recovering cold heat discharged when gas is generated from a low temperature liquefied fluid.

100: liquid cold heat recovery system, 110: liquid storage tank, 120: liquid vaporizer, 130: liquid main pipe, 140: cold heat utilization equipment, 12: liquid evaporator, 12A: liquid inlet, 12B: liquid outlet, 12C: refrigerant outlet , 12D: refrigerant inlet, 14: liquid second pipe, 16: liquid third pipe, 18: liquid first control valve, 20: liquid second control valve, 22: liquid temperature sensor, 24: refrigerant first pipe, 26 : refrigerant circulation pump, 28: second refrigerant pipe, 30: third refrigerant pipe, 32: fourth refrigerant pipe, 34: refrigerant temperature sensor, 36: first refrigerant control valve, 38: second refrigerant control valve, 40: control unit

Claims (5)

In a liquid cold heat recovery system installed on a liquid main pipe that connects a liquid storage tank and a vaporizer to recover cold heat,
a liquid second pipe branched from the liquid main pipe and connected to a liquid inlet of a liquid evaporator;
a liquid third pipe connecting the liquid outlet provided in the liquid evaporator and the liquid main pipe;
a liquid first control valve provided on the liquid main pipe and between the connecting portion of the liquid second pipe branch and the liquid third pipe;
a liquid second control valve provided on the liquid second pipe;
a liquid temperature sensor provided on the liquid third pipe;
a refrigerant first pipe that connects a refrigerant outlet provided in the liquid evaporator and cold heat utilization equipment;
A refrigerant second pipe that connects the cold heat utilization equipment and the refrigerant circulation pump;
a refrigerant third pipe connecting the refrigerant circulation pump and the refrigerant inlet of the liquid evaporator;
a fourth refrigerant pipe branching from the third refrigerant pipe and connecting the second refrigerant pipe;
a refrigerant temperature sensor provided on the first refrigerant pipe;
a refrigerant first control valve provided on the third refrigerant pipe and closer to the refrigerant inlet than the branch portion of the fourth refrigerant pipe;
a second refrigerant control valve provided on the fourth refrigerant pipe;
opening degrees of the first liquid control valve, the second liquid control valve, the first refrigerant control valve, and the second refrigerant control valve based on the measured values of the liquid temperature sensor and the refrigerant temperature sensor; and a control unit for controlling the
When the temperature measured by the liquid temperature sensor is higher than a preset temperature upper limit, the control unit stops the refrigerant circulation pump, closes the first liquid control valve, and controls the second liquid. valve and the first refrigerant control valve, the opening of the second refrigerant control valve is minimized, and when the temperature measured by the liquid temperature sensor is equal to or lower than the preset temperature upper limit, the refrigerant circulation A liquid cryogenic heat recovery system characterized by activating a pump. When the temperature measured by the refrigerant temperature sensor is higher than a preset temperature upper limit, the control unit reduces the degree of opening of the first refrigerant control valve and simultaneously opens the second refrigerant control valve. Control is performed, and when the temperature measured by the refrigerant temperature sensor is equal to or lower than the preset temperature upper limit, the degree of opening of the second refrigerant control valve is reduced and the first refrigerant control valve is opened. The liquid cold heat recovery system according to claim 1 , characterized in that: When the temperature measured by the refrigerant temperature sensor falls below a preset temperature lower limit, the control unit opens the liquid first control valve and simultaneously reduces the opening degree of the liquid second control valve. 3. The liquid cold heat recovery system according to claim 1 or 2, characterized in that throttling control is performed. When the temperature measured by the liquid temperature sensor falls below a preset temperature lower limit, the control unit opens the liquid first control valve and simultaneously reduces the opening degree of the liquid second control valve. 4. The liquid cold heat recovery system according to any one of claims 1 to 3, characterized in that throttling control is performed. When the temperature measured by the refrigerant temperature sensor is higher than a preset temperature lower limit, the control unit closes the first liquid control valve and minimizes the degree of opening of the second refrigerant control valve. 5. The liquid cold heat recovery system according to any one of claims 1 to 4, wherein control is performed to fully open the second liquid control valve and the first refrigerant control valve at the same time.

Images