Exhaust heat recovery system

Abstract

To provide an exhaust heat recovery system which recovers heat energy efficiently.SOLUTION: An exhaust heat recovery system having a plurality of gas compressors, a waste heat recovery device and a control device includes a waste heat recovery passage which connects the plurality of gas compressors and the waste heat recovery device, the plurality of gas compressors can select the use of waste heat recovery course or not based on an instruction from the control device and, in the waste heat recovery system, the control device compares a preset demanded water temperature and a supplied water temperature as the temperature of the supplied water to an outer part from the waste heat recovery device and, when the supplied water temperature is lower than the demanded water temperature, the use of the waste heat recovery course is indicated to at least one of the plurality of gas compressors.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a waste heat recovery system. [Background technology]

[0002] In recent years, the effective use of thermal energy has become increasingly important in response to energy conservation and environmental issues.

[0003] Patent Document 1 discloses a heat recovery compressor and a centralized control device, with one of the objectives being to use energy efficiently. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-168724 Summary of the Invention [Problem to be solved by the invention]

[0005] The system of Patent Document 1 does not recover waste heat from some of the gas compressors, and there is room for further improvement in terms of effective use of the thermal energy contained in that waste heat. Furthermore, the configuration described in Patent Document 1 is based on the premise that some of the gas compressors are not connected to a waste heat recovery device, and does not take into account a situation in which all of the gas compressors are connected to a waste heat recovery device.

[0006] Therefore, an object of the present invention is to effectively utilize thermal energy in a system in which all gas compressors are connected to a waste heat recovery device. [Means for solving the problem]

[0007] An example of a means for solving the above problem is as follows.

[0008] A waste heat recovery system having a plurality of gas compressors, a waste heat recovery device, and a control device, the waste heat recovery system having a waste heat recovery path connecting the plurality of gas compressors and the waste heat recovery device, the plurality of gas compressors being able to select whether or not to use the waste heat recovery path based on instructions from the control device, the control device comparing a set required water temperature with a supply water temperature, which is the temperature of water supplied from the waste heat recovery device to the outside, and if the supply water temperature is lower than the required water temperature, instructing at least one of the plurality of gas compressors to use the waste heat recovery path. [Effects of the Invention]

[0009] According to the present invention, waste heat is recovered from all gas compressors constituting the system, thereby making it possible to efficiently recover thermal energy.

[0010] Further configurations and effects of the present invention will become apparent throughout the entire specification below. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an example of a system configuration according to an embodiment of the present invention. [Figure 2] 1 is a flowchart of an embodiment of the present invention. [Figure 3] 3 is a flowchart illustrating the details of the process in step 107 of FIG. 2. [Figure 4] 3 is a flowchart illustrating the details of the process in step 106 of FIG. 2. [Figure 5] 1 is a diagram illustrating an example of a system configuration according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0012] The waste heat recovery system according to the present invention comprises a gas compressor that generates compressed gas, a waste heat recovery device that recovers heat generated in the process of generating the compressed gas, and a control device that oversees these devices, and operates in accordance with operating parameters.

[0013] In this specification, a gas compressor is defined as one that has an electric motor that drives the compressor body. A gas compressor that compresses air by mechanically controlling loading (producing compressed air) and unloading (idle operation and standby) driven by the electric motor is called a constant speed compressor.

[0014] A gas compressor that controls the rotation speed of the electric motor by changing the operating frequency using an inverter is called a variable speed compressor. When a variable speed compressor operates at full motor speed in response to a command from a control device or controller, it is called full speed operation.

[0015] Depending on the operating parameters, the gas compressors will first operate as frequency controlled variable speed machines, then as full speed variable speed machines, and finally as fixed speed machines, and then shut down in the same order.

[0016] In the embodiment described below, a waste heat recovery system including four gas compressors, one waste heat recovery device, and one control device that controls them will be described as an example.

[0017] FIG. 1 is a block diagram showing the configuration of the present invention. A waste heat recovery system 2 is connected to the gas compressor 3 via an output pipe 6 that supplies a heat transfer fluid to the gas compressor 3 and a return pipe 7 that takes in the heat transfer fluid from the gas compressor 3. Heat exchange occurs between the circulating water taken in via an input pipe 10 and the heat transfer fluid. The hot water obtained through the heat exchange is supplied via an output pipe 11. A control device 1 has a signal line 9 for RS485 communication with the waste heat recovery system 2 and a signal line 8 for RS485 communication with the gas compressor 3. It controls the operation of the present invention based on the operating state and temperature of the gas compressor 3 and controls the operation of each device according to a program stored internally. A gate solenoid valve 4 opens and closes in response to commands from the waste heat recovery system 2 to prevent the heat transfer fluid from flowing to a gas compressor not targeted for waste heat recovery. A check valve 5 prevents the heat transfer fluid returning to the waste heat recovery system 2 from flowing back into the gas compressor 3. Reference numeral 20 denotes an air storage device for compressed air produced by the gas compressor. In FIG. 1, the control device 1 is placed separately from the waste heat recovery device 2, but the case where they are configured as an integrated unit is also within the scope of the disclosure of this embodiment.

[0018] In the present invention, a waste heat recovery path is formed between the gas compressor 3 and the waste heat recovery device 2 by the output pipe 6 and the return pipe 7. In this case, the waste heat refers to the heat generated in the gas compressor 3 due to the operation of the gas compressor 3. Therefore, by recovering the heat generated in the gas compressor 3 through this waste heat recovery path, an improvement in energy efficiency is realized.

[0019] Furthermore, this heat recovery also functions as a cooling loop for the gas compressor 3. Therefore, in some cases, it may be possible to reduce the scale of the heat dissipation mechanism to be provided in the gas compressor 3, which in turn contributes to reducing the cost of the gas compressor 3 itself.

[0020] The gas compressor 3 of the present invention is configured to be able to select whether or not to use the waste heat recovery path. This selection can be realized, for example, by opening or closing a valve provided in the waste heat recovery path in the gas compressor 3, based on an instruction from the control device 1.

[0021] The present invention also includes a case in which a valve is provided between the gas compressor 3 and the waste heat recovery device 2, and whether or not to use the waste heat recovery path can be selected by opening or closing the valve.

[0022] In the configuration of Figure 1, for example, the control device 1 first compares the set required water temperature with the supply water temperature, which is the temperature of the supply water supplied from the waste heat recovery device 2 to the outside through the output piping 11, and if the supply water temperature is lower than the required water temperature, it instructs at least one of the multiple gas compressors to use the waste heat recovery path, thereby realizing a waste heat recovery system.

[0023] 5 shows an example in which the control device 1 determines whether or not to use the waste heat recovery path by controlling the opening and closing of the gate solenoid valve 4. Through the signal line 30, the control device 1 controls the opening and closing of the gate solenoid valve 4 corresponding to the gas compressor to be instructed, and as a result, at least one of a plurality of gas compressors is instructed to use the waste heat recovery path, thereby realizing a waste heat recovery system.

[0024] 1 and 5, for example, in the present invention and specification, expressions such as "the gas compressor can select whether to use the waste heat recovery path based on an instruction from the control device" or "an instruction is given to at least one of the gas compressors to use the waste heat recovery path" are essentially the same technical concept whether they are achieved by an instruction to the gas compressor itself or by opening or closing a valve in the waste heat recovery path. For this reason, expressions such as "the gas compressor can select whether to use the waste heat recovery path based on an instruction from the control device" or "an instruction is given to at least one of the gas compressors to use the waste heat recovery path" are used as expressions that include both instructions to the gas compressor itself and instructions to valves, etc.

[0025] 2 is a flowchart showing the operation of the present invention. The operation based on the flowchart is as follows.

[0026] Step 101 is a process of determining whether or not there is a stopped gas compressor 3 in accordance with the internal program of the control device 1. Specifically, the control device 1 communicates with the gas compressor 3 via RS485 to acquire the operating status. If there is a stopped gas compressor 3, the process proceeds to step 102. If there is no stopped gas compressor, the process proceeds to step 103.

[0027] Step 102 is a process for stopping the waste heat recovery performed by the waste heat recovery device 2 for the stopped gas compressor 3. Specifically, the gate solenoid valve 4 corresponding to the stopped gas compressor 3 is closed by a command from the waste heat recovery device 2, thereby cutting off the supply of heat transfer fluid from the waste heat recovery device 2 to the gas compressor 3 via the output piping 6.

[0028] In the present invention, the gate electromagnetic valve 4 may be built into the gas compressor 3 or may be provided separately.

[0029] Step 103 is a process of determining whether or not waste heat recovery is necessary in accordance with the internal program of the waste heat recovery device 2. Specifically, the user can set whether or not waste heat recovery is necessary by operating the waste heat recovery device 2, and this setting value is recorded in the internal memory of the waste heat recovery device 2. If it is determined that waste heat recovery is necessary, the process proceeds to step 104. If it is determined that waste heat recovery is not necessary, the process ends.

[0030] Step 104 is a process of determining whether the required amount of heat has been recovered through waste heat recovery in accordance with the internal program of the waste heat recovery device 2. Specifically, when operating the waste heat recovery device 2, the user can set the desired water temperature, and this set value is recorded in the internal memory of the waste heat recovery device 2. The waste heat recovery device 2 obtains the water temperature from an internal temperature sensor and makes a determination by comparing it with the desired water temperature set by the user. If it is determined that the water temperature desired by the user is met, the process proceeds to step 105. If it is determined that the water temperature is not met, the process proceeds to step 107.

[0031] Step 105 is a process that determines whether the amount of heat being recovered is excessive for the water temperature requested by the user according to the internal program of the waste heat recovery device 2. Specifically, it compares the water temperature obtained from the temperature sensor with the requested water temperature set by the user, and determines whether the water temperature is rising by calculation. If it is determined that the amount of heat is excessive, the process proceeds to step 106. If it is determined that the amount of heat is not excessive, the process ends.

[0032] Step 106 is a process for reducing the number of gas compressors 3 from which waste heat is recovered. Specifically, the gate solenoid valve 4 corresponding to the gas compressor 3 from which waste heat is recovered is closed in response to a command from the waste heat recovery device 2, thereby cutting off the supply of heat transfer fluid from the waste heat recovery device 2 to the gas compressor 3 via the output piping 6, and the process ends.

[0033] Step 107 is a process for increasing the number of gas compressors 3 from which waste heat is recovered. Specifically, the gate solenoid valve 4 corresponding to the gas compressor 3 from which waste heat is recovered is opened in response to a command from the waste heat recovery device 2, thereby supplying the heat transfer fluid from the waste heat recovery device 2 to the gas compressor 3 via the output piping 6, and then the process is completed.

[0034] Fig. 3 is a flowchart showing a process for determining the priority of which of a plurality of gas compressors 3 should be subjected to waste heat recovery when the process of step 107 in Fig. 2 is executed. This is an example of the details of the process executed in step 107.

[0035] Step 201 is a process in which the control device 1 acquires the operating state of the gas compressor 3 via the signal line 8 by RS485 communication.

[0036] Step 202 is a process of referring to the operating state acquired in step 201 and determining whether the state is loaded or unloaded in accordance with the internal program of the control device 1. If the state is loaded, the process proceeds to step 203. If the state is unloaded, the process proceeds to step 210.

[0037] Step 203 is a process of determining whether or not a constant speed gas compressor 3 is present according to an internal program of the control device 1. Specifically, when operating the control device 1, the user registers in advance whether the gas compressor 3 connected to the control device 1 is a constant speed or variable speed compressor, and this setting value is recorded in the internal memory of the control device 1. If a constant speed gas compressor 3 is present, the process proceeds to step 209. If not, the process proceeds to step 204.

[0038] Step 204 is processing in which the control device 1 determines, according to an internal program, whether or not there is a gas compressor 3 that is a variable speed machine and is operating at full speed. Specifically, when operating the control device 1, the user registers in advance whether the gas compressor 3 connected to the control device 1 is frequency controlled or operating at full speed, and this setting value is recorded in the internal memory of the control device 1. If there is a gas compressor 3 operating at full speed, the process proceeds to step 208. If there is not, the process proceeds to step 205.

[0039] Step 205 is a process of referencing the operating state acquired in step 201 and determining, according to an internal program, whether there is any gas compressor 3 whose rotation speed is less than that required for waste heat recovery. Specifically, the control device 1 acquires the operating state of the inverter inside the gas compressor 3 via RS485 communication and compares it with the minimum motor operating frequency X [Hz] required for waste heat recovery, which is calculated by the internal program for the required water temperature recorded in the internal memory. If there is any gas compressor 3 whose motor operating frequency is less than X [Hz], the process proceeds to step 206. If there is not, the process proceeds to step 211.

[0040] Step 206 is a process of referring to the operating state acquired in step 201 and determining according to an internal program whether or not there is a gas compressor 3 with a rotation speed equal to or greater than that required for waste heat recovery. The specific process is the same as step 205. If there is a gas compressor 3 with an operating frequency of the motor equal to or greater than X [Hz], the process proceeds to step 207. If there is not, the process proceeds to step 210.

[0041] Step 207 shows that, through the processing of steps 205 and 206, the configuration of the gas compressor according to the present invention is a configuration in which gas compressors 3 with motor operating frequencies below X [Hz] and gas compressors 3 with motor operating frequencies above X [Hz] are mixed. Since it is considered that gas compressors 3 with motor operating frequencies below X [Hz] can only recover a small amount of heat even in a loaded state, the gas compressors 3 with motor operating frequencies below X [Hz] are excluded from the target for waste heat recovery, and waste heat recovery is prioritized for gas compressors 3 with a large amount of recoverable heat.

[0042] Step 208 is a process in which, since a gas compressor 3 operating at full speed can recover a greater amount of heat than a gas compressor 3 under rotation control, gas compressors 3 other than the gas compressor 3 operating at full speed are excluded from the target for waste heat recovery, thereby prioritizing waste heat recovery from the gas compressor 3 with the greater amount of heat.

[0043] Step 209 is a process in which the gas compressor 3 of a constant speed machine is excluded from the target for waste heat recovery, and waste heat recovery is prioritized from the gas compressor 3 of a constant speed machine, because the gas compressor 3 of a constant speed machine stops later than the gas compressor 3 of a variable speed machine, the time available for waste heat recovery is longer, and stable waste heat recovery is possible.

[0044] In step 210, when waste heat cannot be recovered and the water temperature required by the user cannot be met, a message "below set temperature" is displayed on the display of the control device 1, and the process ends.

[0045] In step 211, waste heat recovery is started by opening the gate solenoid valve 4 corresponding to the gas compressor 3 to be stopped last, in accordance with the internal program of the control device 1. The specific processing is the same as in step 107. By stopping the gas compressor 3 last, the time available for waste heat recovery can be extended.

[0046] Fig. 4 is a flowchart showing a process for determining the priority of which of a plurality of gas compressors 3 to stop waste heat recovery when the process of step 106 in Fig. 2 is executed. This is an example of the details of step 106 in Fig. 2.

[0047] Step 301 is a process in which the control device 1 acquires the operating state of the gas compressor 3 via the signal line 8 by RS485 communication.

[0048] Step 302 is a process of determining whether or not there is a gas compressor 3 under frequency control in accordance with an internal program of the control device 1. The specific process is the same as step 204. If there is a gas compressor 3 under frequency control, the process proceeds to step 303. If there is not, the process proceeds to step 304.

[0049] Step 303 is a process in which the gas compressor 3 under frequency control is given priority for stopping waste heat recovery, since the amount of heat produced by the gas compressor 3 during frequency control varies depending on the operating state, making stable waste heat recovery difficult.

[0050] In step 304, waste heat recovery is stopped by closing the gate solenoid valve 4 corresponding to the gas compressor 3 that is to be stopped first, in accordance with the internal program of the control device 1. The specific processing is the same as in step 106. By leaving the gas compressor 3 that is to be stopped last, the time available for waste heat recovery can be extended.

[0051] In the above embodiment, the determination is made based on the load / unload and frequency of the operating state of the gas compressor, but the present invention can also be used in a similar manner with processing that references, for example, the discharge temperature or discharge pressure. Specifically, in step 205, it can be replaced by determining whether waste heat recovery is performed if the discharge pressure is high and whether waste heat recovery is not performed if the discharge pressure is low, or whether waste heat recovery is performed if the discharge temperature is high and whether waste heat recovery is not performed if the discharge temperature is low.

[0052] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, some of the configurations of the embodiments can be added, deleted, or replaced with other configurations. Information such as programs that realize each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0053] Furthermore, the technical idea of ​​the present invention can also be expressed as a thermal energy recovery device when focusing on the control device 1 and the waste heat recovery device 2. Furthermore, one example of the invention disclosed in the above-mentioned specification of the present application can also be expressed as follows.

[0054] <Part 1> A waste heat recovery system having a plurality of gas compressors, a waste heat recovery device, and a control device, a waste heat recovery path connecting the plurality of gas compressors and the waste heat recovery device; the plurality of gas compressors are capable of selecting whether or not to use the waste heat recovery path based on an instruction from the control device, The control device compares the set required water temperature with the supply water temperature, which is the temperature of water supplied from the waste heat recovery device to the outside, and if the supply water temperature is lower than the required water temperature, instructs at least one of the multiple gas compressors to use the waste heat recovery path.

[0055] <Part 2> In the waste heat recovery system described in <No. 1>, The control device instructs any one of the gas compressors using the waste heat recovery path to stop using the waste heat recovery path when the supply water temperature is higher than the required water temperature.

[0056] <Part 3> In the waste heat recovery system described in <No. 1>, When the control device instructs gas compressors that are not using the waste heat recovery path to use the waste heat recovery path, if the gas compressors that are not using the waste heat recovery path include a constant speed machine, the control device instructs the constant speed machine to use the waste heat recovery path with priority.

[0057] <Part 4> In the waste heat recovery system described in <No. 1>, When the control device instructs a gas compressor that is not using the waste heat recovery path among the gas compressors to use the waste heat recovery path, If the gas compressors not using the waste heat recovery path do not include a constant speed machine and include a variable speed machine operating at full speed, the waste heat recovery system gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path.

[0058] <Part 5> In the waste heat recovery system described in <No. 1>, When the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, A waste heat recovery system that, when a gas compressor using the waste heat recovery path includes a variable speed machine under frequency control, gives priority to the variable speed machine under frequency control and instructs the use of the waste heat recovery path to be stopped.

[0059] <Part 6> In the waste heat recovery system described in <No. 1>, When the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, In a case where the gas compressors using the waste heat recovery path do not include a variable speed machine under frequency control, but include a variable speed machine operating at full speed, the waste heat recovery system gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path to be stopped.

[0060] <Part 7> In the waste heat recovery system described in <No. 1>, The control device instructs the use of the waste heat recovery path by giving priority to a gas compressor that can recover a large amount of heat.

[0061] <Part 8> A thermal energy recovery system having a waste heat recovery system and a control system, the control device instructs the plurality of gas compressors whether or not to use a waste heat recovery path between the gas compressor and the waste heat recovery device; The control device compares the set required water temperature with a supply water temperature, which is the temperature of water supplied from the waste heat recovery device to the outside, and when the supply water temperature is lower than the required water temperature, a thermal energy recovery device that instructs at least one of the plurality of gas compressors to utilize the waste heat recovery path;

[0062] <No. 9> In the thermal energy recovery device according to <Item 8>, The control device instructs any one of the gas compressors using the waste heat recovery path to stop using the waste heat recovery path when the supply water temperature is higher than the required water temperature.

[0063] <Part 10> In the thermal energy recovery device according to <Item 8>, When the control device instructs gas compressors that are not using the waste heat recovery path among the gas compressors to use the waste heat recovery path, if the gas compressors that are not using the waste heat recovery path include a constant speed machine, the control device instructs the constant speed machine to use the waste heat recovery path with priority.

[0064] <Part 11> In the thermal energy recovery device according to <Item 8>, When the control device instructs a gas compressor that is not using the waste heat recovery path among the gas compressors to use the waste heat recovery path, If the gas compressors not using the waste heat recovery path do not include a constant speed machine and include a variable speed machine operating at full speed, the thermal energy recovery device gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path.

[0065] <Part 12> In the thermal energy recovery device according to <Item 8>, When the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, A thermal energy recovery device that, when a gas compressor using the waste heat recovery path includes a variable speed machine under frequency control, gives priority to the variable speed machine under frequency control and instructs the use of the waste heat recovery path to be stopped.

[0066] <Part 13> In the thermal energy recovery device according to <Item 8>, When the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, If the gas compressors using the waste heat recovery path do not include a variable speed machine under frequency control, but include a variable speed machine operating at full speed, the thermal energy recovery device gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path to be stopped.

[0067] <Part 14> In the thermal energy recovery device according to <Item 8>, The control device is a thermal energy recovery device that instructs the use of the waste heat recovery path by giving priority to a gas compressor that can recover a large amount of heat. [Explanation of symbols]

[0068] 1: Control device 2: Waste heat recovery device 3: Gas compressor 4: Gate solenoid valve 5: Check valve 6: Output piping 7: Return pipe 8: Signal line 9: Signal line 10: Input piping 11: Output piping 20:Air tank 30: Signal line

Claims

1. A waste heat recovery system having a plurality of gas compressors, a waste heat recovery device, and a control device, a waste heat recovery path connecting the plurality of gas compressors and the waste heat recovery device; the plurality of gas compressors are capable of selecting whether or not to use the waste heat recovery path based on an instruction from the control device, The control device compares the set required water temperature with a supply water temperature, which is the temperature of water supplied from the waste heat recovery device to the outside, a waste heat recovery system that instructs at least one of the plurality of gas compressors to use the waste heat recovery path when the supply water temperature is lower than the required water temperature;

2. 2. The waste heat recovery system according to claim 1, wherein when the supply water temperature is higher than the required water temperature, the control device: A waste heat recovery system that instructs any one of the gas compressors that uses the waste heat recovery path to stop using the waste heat recovery path.

3. 2. The waste heat recovery system according to claim 1, wherein when the control device instructs one of the gas compressors that is not using the waste heat recovery path to use the waste heat recovery path, the control device If the gas compressors not using the waste heat recovery path include a constant speed machine, the waste heat recovery system gives priority to the constant speed machine and instructs it to use the waste heat recovery path.

4. 2. The waste heat recovery system according to claim 1, wherein when the control device instructs one of the gas compressors that is not using the waste heat recovery path to use the waste heat recovery path, the control device If the gas compressors not using the waste heat recovery path do not include a constant speed machine and include a variable speed machine operating at full speed, the waste heat recovery system gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path.

5. 2. The waste heat recovery system according to claim 1, wherein when the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, A waste heat recovery system that, when a gas compressor using the waste heat recovery path includes a variable speed machine under frequency control, gives priority to the variable speed machine under frequency control and instructs the use of the waste heat recovery path to be stopped.

6. 2. The waste heat recovery system according to claim 1, wherein when the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, In a case where the gas compressors using the waste heat recovery path do not include a variable speed machine under frequency control, but include a variable speed machine operating at full speed, the waste heat recovery system gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path to be stopped.

7. 2. The waste heat recovery system according to claim 1, wherein the control device instructs the use of the waste heat recovery path to give priority to a gas compressor that can recover a large amount of heat.

8. A thermal energy recovery system having a waste heat recovery system and a control device, the control device instructs the plurality of gas compressors whether or not to use a waste heat recovery path between the gas compressor and the waste heat recovery device; The control device compares the set required water temperature with a supply water temperature, which is the temperature of water supplied from the waste heat recovery device to the outside, a thermal energy recovery device that instructs at least one of the plurality of gas compressors to use the waste heat recovery path when the supply water temperature is lower than the required water temperature;

9. 9. A thermal energy recovery device according to claim 8, wherein the control device instructs any one of the gas compressors using the waste heat recovery path to stop using the waste heat recovery path when the supply water temperature is higher than the required water temperature.

10. 9. The thermal energy recovery system according to claim 8, wherein when the control device instructs the gas compressors that are not using the waste heat recovery path to use the waste heat recovery path, the control device If the gas compressors not using the waste heat recovery path include a constant speed machine, the thermal energy recovery device instructs the constant speed machine to use the waste heat recovery path with priority.

11. 9. The thermal energy recovery system according to claim 8, wherein when the control device instructs the gas compressors that are not using the waste heat recovery path to use the waste heat recovery path, the control device If the gas compressors not using the waste heat recovery path do not include a constant speed machine and include a variable speed machine operating at full speed, the thermal energy recovery device gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path.

12. 9. The thermal energy recovery system according to claim 8, wherein when the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, A thermal energy recovery device that, when a gas compressor using the waste heat recovery path includes a variable speed machine under frequency control, gives priority to the variable speed machine under frequency control and instructs the use of the waste heat recovery path to be stopped.

13. 9. The thermal energy recovery system according to claim 8, wherein when the control device instructs the gas compressor using the waste heat recovery path among the gas compressors not to use the waste heat recovery path, If the gas compressors using the waste heat recovery path do not include a variable speed machine under frequency control, but include a variable speed machine operating at full speed, the thermal energy recovery device gives priority to the variable speed machine operating at full speed and instructs the use of the waste heat recovery path to be stopped.

14. 9. The thermal energy recovery system according to claim 8, wherein the control device instructs the use of the waste heat recovery path by giving priority to a gas compressor that can recover a large amount of heat.

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