Air compression system

Abstract

To provide an air compression system capable of preventing freezing of cooling liquid without separately providing a heater or the like.SOLUTION: An air compression system includes a compressor that performs a compression operation of compressing air to generate compressed air, and a flow path through which a coolant used for cooling a cooling target whose temperature has risen due to compression heat generated in the compression operation flows, and performs an anti-freezing operation of preventing freezing of the coolant using the compression heat when a predetermined condition is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an air compression system including a compressor for generating compressed air. [Background technology]

[0002] Conventionally, air compression systems equipped with a compressor that generates compressed air have been commonly used. The compressor performs a compression operation to compress air to generate compressed air, and the compressed air thus generated can be supplied to various devices and equipment that require compressed air.

[0003] Furthermore, to prevent the temperature from rising too high due to the heat of compression generated during the compression operation, an air compression system has been proposed in which cooling water is circulated to enable cooling, as disclosed in Patent Document 1. The air compression system disclosed in Patent Document 1 produces hot water by recovering the heat of compression using cooling water, thereby enabling the heat of compression to be used effectively. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-25119 Summary of the Invention [Problem to be solved by the invention]

[0005] In an air compression system that uses a coolant as described above, there is a risk that the coolant will freeze if the ambient temperature drops significantly during cold seasons. Freezing of the coolant can lead to a decrease in the performance of the air compression system or damage to the system. However, if a heater or other device is separately provided to warm the air compression system in order to prevent the coolant from freezing, this can result in problems such as increased costs and a more complicated system.

[0006] SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an air compression system that can prevent the cooling liquid from freezing without providing a separate heater or the like. [Means for solving the problem]

[0007] The air compression system of the present invention comprises a compressor that performs a compression operation to compress air to generate compressed air, and a circulation path through which a cooling liquid used to cool an object to be cooled whose temperature has risen due to the compression heat generated in the compression operation is circulated, and is configured to perform an anti-freeze operation that uses the compression heat to prevent the cooling liquid from freezing when predetermined conditions are met.

[0008] This configuration makes it possible to prevent the coolant from freezing without providing a separate heater, etc. Note that the "coolant" here is not limited to ordinary cooling water, but is a concept that includes various liquids that may freeze, such as water containing additives (brine).

[0009] More specifically, the above configuration may include a heat exchanger that exchanges heat between the object to be cooled and the cooling liquid, and an air release valve that allows the compressed air sent out from the compressor to be released, and when the specified conditions are met while the compression operation is stopped, the anti-freeze operation may be performed by performing the compression operation to generate the heat of compression and circulating the cooling liquid in the circulation path, and releasing the compressed air at the air release valve.

[0010] More specifically, the above configuration may be such that the heat exchanger is arranged so that the compressed air discharge path and the circulation path pass through, and exchanges heat between the compressed air to be cooled and the cooling liquid, and the air release valve is arranged downstream of the heat exchanger in the discharge path.

[0011] More specifically, the above configuration may include a heat exchanger that exchanges heat between the object to be cooled and the cooling liquid, and the circulation path is formed to circulate the supplied cooling liquid through the heat exchanger to a predetermined heat recovery destination, and a return path that returns the cooling liquid from the rear side of the heat exchanger to a return destination on the front side, and the operating mode during the compression operation is switchable between at least a heat recovery mode in which the cooling liquid that has passed through the heat exchanger is sent to the heat recovery destination, and a non-heat recovery mode in which the cooling liquid that has passed through the heat exchanger is returned through the return path, and when the predetermined condition is met when the operating mode is the heat recovery mode, the configuration may be such that the cooling liquid that has passed through the heat exchanger is returned through the return path as the anti-freeze operation.

[0012] More specifically, the above configuration may be an air compression system in which a cooling mechanism capable of performing a cooling operation to cool the cooling liquid is provided between the return destination and the heat exchanger in the distribution path, and the cooling operation is performed when the operating mode is the non-heat recovery mode, and when the specified condition is satisfied when the operating mode is the non-heat recovery mode, the system may be configured to perform the anti-freeze operation by stopping the cooling operation and returning the cooling liquid that has passed through the heat exchanger through the return path.

[0013] More specifically, the above configuration may include a first heat exchanger that exchanges heat between the object to be cooled and the first cooling liquid, and a second heat exchanger that exchanges heat between the object to be cooled and the second cooling liquid, and the flow paths may include a first flow path formed to flow the supplied first cooling liquid to a predetermined heat recovery destination via the first heat exchanger, and a second flow path formed to flow the supplied second cooling liquid to a predetermined destination via the second heat exchanger, and the operating mode during the compression operation may be switchable between at least a heat recovery mode in which the first cooling liquid flows through the first flow path and is sent to the heat recovery destination, and a non-heat recovery mode in which the second cooling liquid flows through the second flow path and is sent to the destination, and when the specified condition is met when the operating mode is the heat recovery mode, the second cooling liquid may be circulated through the second flow path as the anti-freeze operation.

[0014] More specifically, the above configuration may include a first heat exchanger that exchanges heat between the object to be cooled and the first cooling liquid, and a second heat exchanger that exchanges heat between the object to be cooled and the second cooling liquid, and the flow paths may include a first flow path formed to flow the supplied first cooling liquid to a predetermined heat recovery destination via the first heat exchanger, and a second flow path formed to flow the supplied second cooling liquid to a predetermined destination via the second heat exchanger, and the operating mode during the compression operation may be switchable between at least a heat recovery mode in which the first cooling liquid flows through the first flow path and is sent to the heat recovery destination, and a non-heat recovery mode in which the second cooling liquid flows through the second flow path and is sent to the destination, and when the specified condition is met when the operating mode is the non-heat recovery mode, the first cooling liquid may be circulated through the first flow path as the anti-freeze operation.

[0015] More specifically, the above configuration may include a temperature sensor that detects an ambient temperature, and the predetermined condition may be a condition that is satisfied when the detected ambient temperature falls below a set value. [Effects of the Invention]

[0016] According to the air compression system of the present invention, it is possible to prevent the coolant from freezing without providing a separate heater or the like. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram of an air compression system according to a first embodiment. [Figure 2] 1 is a schematic configuration diagram of a hot water producing system according to a first embodiment. [Figure 3] FIG. 10 is a schematic configuration diagram of an air compression system according to a second embodiment. [Figure 4] FIG. 10 is a schematic configuration diagram of a hot water producing system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] An air compression system according to each embodiment of the present invention will be described below with reference to the drawings.

[0019] 1. First embodiment First, a first embodiment of the present invention will be described. Fig. 1 is a schematic diagram of an air compression system AS1 according to the first embodiment. The air compression system AS1 includes a control device C, a temperature sensor TS, a compression unit 1 that produces compressed air, and a heat recovery unit 2 that can recover the heat of compression produced by the compression unit 1.

[0020] The control device C controls the operation of each part of the air compression system AS1. The temperature sensor TS continuously detects the ambient temperature of the air compression system AS1 and sends information about the detected ambient temperature to the control device C.

[0021] 1-1. Compression unit configuration Next, we will explain the configuration of the compression unit 1. The compression unit 1 includes a water-addition type compressor 3, a pre-separator 4 that separates the fluid discharged from the compressor 3 into water and air, an after-cooler 5 that cools the compressed air after water and air separation in the pre-separator 4, a water cooler 6 that cools the separated water after water and air separation in the pre-separator 4, and a separator tank 7 to which the compressed air and separated water that have passed through the coolers 5 and 6 are supplied.

[0022] The compressor 3 is a water-addition type air compressor. There is no particular restriction on the type of compressor 3, but it may be, for example, a screw type or a scroll type. In the water-addition type compressor 3, water (typically purified water (pure water) or softened water) is added to the air intake port, and the air is compressed and discharged while this added water is used for sealing the compression chamber and cooling the compression mechanism. When discharging the air, the added water is also discharged together with the compressed air.

[0023] In the example shown in FIG. 1 , the compressor 3 is driven by an electric motor 8, but it may be driven by another prime mover. For example, the compressor 3 may be driven by a steam motor (steam engine). The compressor 3 may also be on / off controlled, or its capacity may be controlled (output adjustment). For example, the compressor 3 is controlled by on / off control of the electric motor 8, or by inverter control of the rotation speed of the electric motor 8. Alternatively, in the case of a steam motor, the opening / closing or opening degree of a steam supply valve to the steam motor is controlled.

[0024] When the compressor 3 is operated, outside air is drawn into the compressor 3 from an intake passage 10 via an air filter 9, and at this time, water is added at a set flow rate via an added water return passage 11 from the separator tank 7. The air compressed in the compressor 3 is discharged to the pre-separator 4 together with the added water. A check valve 13 is provided in a discharge passage 12 from the compressor 3 to the pre-separator 4.

[0025] The water-addition type compressor 3 can also be called a water-lubricated type or a water-injected type. In addition, although the compressor 3 of this embodiment has water added to the air inlet, it may also be provided with a water supply inlet in addition to the air inlet, and water may be added to this water supply inlet.

[0026] The pre-separator 4 receives the fluid discharged from the compressor 3 (compressed air discharged together with added water) and separates it into gas and water. That is, the fluid discharged from the compressor 3 is separated into compressed air and separated water in the pre-separator 4. Accordingly, the interior of the pre-separator 4 is separated into an upper gas phase and a lower liquid phase. The gas phase of the pre-separator 4 is connected to the gas phase of the separator tank 7 via a gas phase communicating passage 14, while the liquid phase of the pre-separator 4 is connected to the liquid phase of the separator tank 7 via a liquid phase communicating passage 15.

[0027] An aftercooler 5 is provided in the gas phase communication passage 14 from the pre-separator 4 to the separator tank 7. The aftercooler 5 is a means for cooling the compressed air after air-water separation in the pre-separator 4. Here, the aftercooler 5, which serves as a heat recovery heat exchanger 16 that recovers heat of compression, exchanges heat between the compressed air and the coolant F without mixing them. In the aftercooler 5, the compressed air is cooled by the coolant F, while the coolant F is warmed by the compressed air.

[0028] A water cooler 6 is provided in the liquid phase communication passage 15 from the pre-separator 4 to the separator tank 7. The water cooler 6 is a means for cooling the separated water after the air-water separation in the pre-separator 4. Here, the water cooler 6, which serves as a heat recovery heat exchanger 16 that recovers heat of compression, exchanges heat between the separated water and the coolant F without mixing them. In the water cooler 6, the separated water is cooled by the coolant F, while the coolant F is heated by the separated water.

[0029] The separator tank 7 receives the compressed air and separated water that have passed through the coolers 5 and 6, and separates the air into water and gas. The compressed air from the pre-separator 4 is cooled in the after-cooler 5 to condense the water, which is then removed in the separator tank 7. Therefore, the inside of the separator tank 7 is also separated into an upper gas phase and a lower liquid phase. The fluid is supplied from the pre-separator 4 to the separator tank 7 via the communication passages 14 and 15 by the discharge pressure of the compressor 3 and the head pressure difference.

[0030] In addition to the gas-phase communication passage 14, the gas-phase section of the separator tank 7 is also connected to a compressed air delivery passage 17 leading to the compressed air utilization section. The compressed air delivery passage 17 is provided with a primary pressure regulating valve 18 and a check valve 19, in that order from the separator tank 7 side. The primary pressure regulating valve 18 is a valve that maintains the pressure inside the separator tank 7 at or above a set pressure while the compressor 3 is in operation. Here, the primary pressure regulating valve 18 is a self-actuating valve that operates mechanically based on the pressure on the primary side (i.e., the separator tank 7 side). However, in some cases, the primary pressure regulating valve 18 may be an electrically operated valve that is controlled based on the detected pressure by monitoring the primary side pressure with a sensor. In addition, in this embodiment, the gas-phase section of the separator tank 7 is provided with a safety valve 20 and an air release valve 21 for exhausting air to the outside. The primary pressure regulating valve 18 and the check valve 19 may also be configured as an integrated valve mechanism.

[0031] In addition to the liquid phase communicating passage 15 described above, an added water return passage 11 to the compressor 3 is connected to the liquid phase section of the separator tank 7. An added water valve 22 and a water filter 23 are provided in the added water return passage 11, in this order from the separator tank 7 side. By opening the added water valve 22 while the compressor 3 is operating, the water stored in the separator tank 7 can be returned to the compressor 3 via the added water return passage 11. At that time, the added water can be returned from the separator tank 7 to the compressor 3 by suction into the compressor 3 due to the operation of the compressor 3 and pressurization inside the separator tank 7.

[0032] Furthermore, primary pressure regulating valve 18 maintains the pressure inside separator tank 7 at or above the set pressure, and as will be described later, the pressure inside compressed air delivery path 17 (and therefore the pressure inside separator tank 7) is maintained at a desired level, so that added water can be supplied to compressor 3 at a set flow rate while added water valve 22 functions as an orifice. Moreover, when added water is supplied from separator tank 7 to compressor 3, impurities can be removed by water filter 23.

[0033] Additionally, the separator tank 7 is provided with a water level detector 30. The water level detector 30 may have any configuration, but may be, for example, a float-type water level detector capable of detecting the water level of purified water and condensed water that do not contain ions. Furthermore, a pressure sensor 31 is provided in the compressed air delivery path 17 from the separator tank 7, downstream of the primary pressure regulating valve 18 and the check valve 19. This pressure sensor 31 makes it possible to monitor the discharge pressure of the compressed air (the pressure supplied to the compressed air utilization section).

[0034] 1-2. Heat recovery unit configuration Next, a description will be given of the configuration of the heat recovery unit 2. The heat recovery unit 2 is a unit that recovers heat by using the heat of compression of the compressor 3 to warm the coolant F, and is configured so that it can be switched between the on and off states of heat recovery.

[0035] The coolant F is not particularly limited, but is typically water. This water can be tap water, softened water, purified water (pure water), or the like, depending on the application. For example, when the heat recovery unit 2 is used to preheat the water supplied to the steam boiler, degassed softened water is used as described below. Hereinafter, the coolant F will be described as water, but the same applies to other liquids. In other words, in the following, the coolant F does not necessarily have to be water, but may be a liquid other than water (for example, brine).

[0036] The heat recovery unit 2 includes a heat recovery heat exchanger 16 (aftercooler 5, water cooler 6) that heats the coolant F (cooling water) using the heat of compression of the compressor 3, an inlet path 32 for the coolant F to the heat recovery heat exchanger 16, an outlet path 33 for the coolant F from the heat recovery heat exchanger 16, a return path 34 for the coolant F that connects the outlet path 33 and the inlet path 32, a switching means 35 (heat recovery valve 36, return valve 37) that switches between the liquid flow path and the circulation path described below, and a radiator 38 that cools the coolant F circulating through the circulation path.

[0037] In this embodiment, the heat recovery heat exchanger 16 is an aftercooler 5 and a water cooler 6. The aftercooler 5 exchanges heat between the compressed air and the coolant F, cooling the compressed air with the coolant F while heating the coolant F with the compressed air. Heat recovery can be achieved by using the heat of compression of the compressed air to heat the coolant F. On the other hand, the water cooler 6 exchanges heat between the added water (water separated in the pre-separator) and the coolant F, cooling the added water with the coolant F while heating the coolant F with the added water. Heat recovery can be achieved by using the heat of compression of the added water to heat the coolant F.

[0038] In this embodiment, the coolant F is passed through the aftercooler 5 and the water cooler 6 in that order. Therefore, the aftercooler 5 and the water cooler 6 are connected by a communication path 39. The coolant F flows from the inlet path 32, passes through the aftercooler 5, the communication path 39, and the water cooler 6 in that order, and then flows to the outlet path 33. Hereinafter, the aftercooler 5 and the water cooler 6 connected by the communication path 39 may be collectively referred to simply as the heat recovery heat exchanger 16.

[0039] A pump 40, a check valve 41, and a radiator 38 are provided in this order in an inlet passage 32 leading from the water supply source to the heat recovery heat exchanger 16. By operating the pump 40, the coolant F can be passed through the heat recovery heat exchanger 16. In this embodiment, the radiator 38 is air-cooled and exchanges heat between the coolant F and outside air (ventilated by a fan 38A). As will be described in detail later, for example, when the temperature of the coolant F on the inlet side of the radiator 38 is higher than the outside air temperature, the fan 38A of the radiator 38 can be operated to cool the coolant F by the ventilation provided by the fan 38A.

[0040] A heat recovery valve 36 is provided in the outlet path 33 from the heat recovery heat exchanger 16. When the compressor 3 is in operation, the heat recovery valve 36 is opened and the pump 40 is operated to pass the coolant F through the heat recovery heat exchanger 16, thereby recovering the heat of compression and sending the coolant F to a hot water destination. In this embodiment, the heat recovery valve 36 is configured as an electrically operated valve with an adjustable opening.

[0041] The outlet passage 33 upstream of the heat recovery valve 36 and the inlet passage 32 upstream of the pump 40 are connected by a return passage 34. In this embodiment, a storage tank 42 for the coolant F is provided at the connection point between the inlet passage 32 and the return passage 34. However, the installation of the storage tank 42 may be omitted in some cases. Furthermore, the storage tank 42 may be provided downstream of the connection point with the return passage 34 within the inlet passage 32 (preferably upstream of the pump 40). Note that the pump 40 may be provided downstream of the connection point with the return passage 34 within the inlet passage 32, or may be provided in the communication passage 39 or the outlet passage 33, upstream of the connection point with the return passage 34.

[0042] A return valve 37 is provided in the return path 34. In this embodiment, the return valve 37 is configured as an electric valve. Although details will be described later, by selectively opening either the heat recovery valve 36 or the return valve 37, it is possible to switch between returning the coolant F after passing through the heat recovery heat exchanger 16 to the inlet path 32 via the return path 34 or sending it downstream of the outlet path 33 without passing through the return path 34.

[0043] In this embodiment, the switching means 35 is composed of a heat recovery valve 36 and a return valve 37. By switching between opening and closing the heat recovery valve 36 and the return valve 37, the flow path of the coolant F can be switched between a liquid passage path and a circulation path, which will be described below.

[0044] The liquid passage path is realized by opening the heat recovery valve 36 while closing the return valve 37. The liquid passage path includes the inlet path 32, the heat recovery heat exchanger 16, and the outlet path 33, but does not include the return path 34. When the pump 40 is operated in the liquid passage path, the coolant F from the inlet path 32 passes through the heat recovery heat exchanger 16 and the heat recovery valve 36 of the outlet path 33, and is discharged (heat recovery implementation state). At this time, water is supplied to the storage tank 42 as needed from the water supply source. In other words, while the pump 40 is operating in the liquid passage path, water is supplied to the inlet path 32 from the water supply source.

[0045] The circulation path is realized by opening the return valve 37 while closing the heat recovery valve 36. The circulation path includes the inlet path 32 downstream of the connection point with the return path 34, the heat recovery heat exchanger 16, the outlet path 33 upstream of the connection point with the return path 34, and the return path 34. When the pump 40 is operated in the circulation path, the coolant F from the pump 40 is returned to the pump 40 via the heat recovery heat exchanger 16 and the return path 34 and circulated. At that time, the radiator 38 can be operated to cool the circulating coolant F in the radiator 38 (heat recovery stopped state). Note that while the coolant F is circulating in the circulation path, there is no need to supply new water from the water supply source to the storage tank 42.

[0046] An outlet hot water temperature sensor 43 is provided in the outlet path 33 on the outlet side of the heat recovery valve 36. Meanwhile, a feed water temperature sensor (not shown) is provided in the inlet path 32 on the inlet side of the radiator 38. The feed water temperature sensor may detect the water temperature of the feed water source in some cases, as long as it is located in the inlet path 32 on the upstream side of the radiator 38. However, if a storage tank 42 is provided in the inlet path 32, it is preferable that the feed water temperature sensor be located in the inlet path 32 at or downstream of the storage tank 42 and upstream of the radiator 38.

[0047] 1-3.Air compression system operation Next, the operation of the air compression system AS1 will be described. When there is a request for compressed air from the load equipment, the control device C drives the compressor 3 to produce compressed air so that the compressed air is supplied to the load equipment, but when there is no such request, it stops the compressor 3 so that compressed air is not supplied to the load equipment. Also, when the compressor 3 is driven, when there is a request for hot water from the hot water supply destination (heat recovery destination), the control device C executes heat recovery operation so that hot water is supplied to the hot water supply destination, but when there is no such request, it does not execute heat recovery operation.

[0048] Furthermore, when a predetermined condition α is satisfied, the control device C performs antifreeze operation to prevent the cooling liquid F and added water from freezing by using the heat of compression of the compressor 3. In this embodiment, the predetermined condition α is a condition that is satisfied when the ambient temperature detected by the temperature sensor TS falls below a set value (e.g., 1°C). That is, in this embodiment, the ambient temperature detected by the temperature sensor TS is monitored, and when this ambient temperature falls below the set value, the antifreeze operation is executed.

[0049] The control device C can switch the operating mode of the air compression system AS1 between a first operating mode in which compressed air is supplied to the load equipment and a heat recovery operation is performed, a second operating mode in which compressed air is supplied to the load equipment but a heat recovery operation is not performed, and a third operating mode in which compressed air is not supplied to the load equipment. Next, each of these operating modes will be described in more detail.

[0050] 1-3-1. First operation mode First, the first operating mode will be described. In the first operating mode, the compressor 3 draws in air through the air filter 9, compresses it, and discharges it. The compressed air discharged from the compressor 3 is sent from the compressed air delivery path 17 to the compressed air utilization section via the pre-separator 4, aftercooler 5, and separator tank 7. However, since the compressed air delivery path 17 is provided with a primary pressure regulating valve 18, when the pressure in the separator tank 7 is low, such as immediately after starting operation, the primary pressure regulating valve 18 is closed and compressed air is not delivered to the compressed air utilization section. When the pressure on the primary side of the primary pressure regulating valve 18 (i.e., the separator tank 7 side) reaches or exceeds the set pressure, the primary pressure regulating valve 18 opens and compressed air is delivered to the compressed air utilization section. The air release valve 21 is closed.

[0051] During operation of the compressor 3, the compressor 3 is controlled so as to maintain the pressure detected by the pressure sensor 31 at the target pressure. For example, the electric motor 8 of the compressor 3 is on / off controlled or inverter controlled. The target pressure is higher than the set pressure of the primary pressure regulating valve 18. Therefore, thereafter, the pressure inside the separator tank 7 is basically maintained at the target pressure.

[0052] By opening the added water valve 22 while the compressor 3 is operating, water can be added to the suction port of the compressor 3 at a set flow rate. This allows for sealing, cooling, and lubrication of the compressor 3. The compressed air from the compressor 3 is discharged to the pre-separator 4 together with the added water. The pre-separator 4 then separates the air into water and steam. The compressed air after separation in the pre-separator 4 is cooled in the after-cooler 5, then further separated into water and steam in the separator tank 7, and then discharged to the outside through the compressed air delivery path 17. Meanwhile, the separated water in the pre-separator 4 is cooled in the water cooler 6, then stored in the separator tank 7, and can be supplied to the compressor 3 via the added water return path 11.

[0053] Furthermore, the pump 40 is operated to pass the coolant F (cooling water) through the heat recovery heat exchanger 16. As a result, in the heat recovery heat exchanger 16, the fluid (compressed air and added water) discharged from the compressor 3 can be cooled, and the coolant F can be heated by the heat of compression from the discharged fluid. The hot water produced in this way has a flow path that can be switched by the switching means 35 depending on whether or not there is a hot water request from the hot water supply destination. In the first operating mode (when there is a hot water request), this hot water flow path (hot water flow path) is set as the liquid passage.

[0054] This liquid flow path is formed by closing the return valve 37 and opening the heat recovery valve 36. In this case, the coolant F from the water supply source is heated in the heat recovery heat exchanger 16 and sent to the hot water supply destination downstream of the outlet path 33. At this time, if the opening of the heat recovery valve 36 is adjusted so that the temperature detected by the outlet hot water temperature sensor 43 is maintained at the set temperature, hot water at the set temperature can be supplied to the hot water supply destination. In addition, the fan 38A of the radiator 38 is operated.

[0055] When the predetermined condition α is satisfied in the first operating mode, anti-freeze operation is started as follows: The return valve 37 is opened, while the heat recovery valve 36 is closed. This allows the coolant F and added water to be heated by the heat of compression of the compressor 3, and the coolant F and added water to be circulated while preventing the heated coolant F from flowing out of the outlet passage 33. This makes it possible to raise the temperature of the air compression system AS1 above that before the anti-freeze operation was started. In this way, it is possible to prevent the coolant F and added water from freezing.

[0056] During anti-freeze operation, the heat recovery valve 36 is closed, temporarily stopping the supply of heated coolant F to the hot water supply destination (hot water supply from the air compression system AS1). Therefore, it is desirable to take measures to minimize problems with the use of hot water even when the hot water supply is temporarily stopped. As will become clear from the explanation below, the hot water production system HS1 (see Figure 2), which is configured to include the air compression system AS1, is configured with this in mind.

[0057] 1-3-2. Second operation mode Next, the second operation mode will be described. In the second operation mode, the operation of the compression unit 1 is basically the same as in the first operation mode. On the other hand, in the operation of the heat recovery unit, in the second operation mode (when there is no hot water demand), the hot water flow path described above is set to a circulation path.

[0058] This circulation path is formed by closing the heat recovery valve 36 and opening the return valve 37. Furthermore, the pump 40 is operated, and the fan 38A of the radiator 38 is also operated. In this case, the coolant F heated in the heat recovery heat exchanger 16 is returned to the inlet path 32 via the return path 34, cooled in the radiator 38, and then supplied to the heat recovery heat exchanger 16 again. In other words, the coolant F is circulated through the heat recovery heat exchanger 16, while the radiator 38 releases heat into the outside air.

[0059] When the predetermined condition α is satisfied in the second operating mode, anti-freeze operation is started as follows: That is, the fan 38A of the radiator 38 is stopped. As a result, the coolant F and the added water are heated by the heat of compression of the compressor 3, and the coolant F and the added water are circulated while preventing the coolant F heated by the heat of compression of the compressor 3 from being cooled by the radiator 38. This makes it possible to raise the temperature of the air compression system AS1 above that before the anti-freeze operation was started. In this way, it is possible to prevent the coolant F and the added water from freezing.

[0060] 1-3-3.Third operation mode Next, the third operating mode will be described. In the third operating mode, the compressor 3 is stopped, the air release valve 21 is opened, and the water addition valve 22 is closed. By keeping the air release valve 21 open while the compressor 3 is stopped, reverse rotation of the compressor 3 can be prevented. The heat recovery valve 36 is opened when there is a hot water request from the hot water supply destination, and is closed when there is no hot water request. Furthermore, since no heat of compression is generated in the compressor 3, the return valve 37 is closed, the pump 40 is stopped, and the circulation of the coolant F is stopped. Furthermore, the fan 38A of the radiator 38 is stopped.

[0061] When the predetermined condition α is satisfied in the third operating mode, anti-freeze operation is initiated as follows: That is, the compressor 3 is driven at low output (for example, 50% output) to intentionally generate heat of compression, the added water valve 22 is opened, and the pump 40 is operated. The air release valve 21 is left open. The heat recovery valve 36 is closed, and the return valve 37 is opened.

[0062] As a result, by circulating the coolant F and the added water while warming them with the heat of compression from the compressor 3, the temperature of the air compression system AS1 can be raised above that before the start of anti-freeze operation. In this way, it is possible to prevent the coolant F and the added water from freezing. Also, because the air release valve 21 is open at this time, the compressed air generated by the compressor 3 is released by the air release valve 21, preventing unnecessary compressed air from flowing into the load equipment.

[0063] In either operating mode, if it is determined that there is no longer any risk of the coolant F or added water freezing after the anti-freeze operation has started, the anti-freeze operation is terminated. For example, the control device C monitors the discharge temperature of the compressed air in the air compression system AS1 while the anti-freeze operation is being performed, and terminates the anti-freeze operation when this temperature reaches a predetermined value (for example, 50°C).

[0064] 1-4.Application example to hot water production system The air compression system AS1 described above can also be applied as a component of the hot water production system HS1 shown in Fig. 2. This hot water production system HS1 will be described below.

[0065] 2, in addition to air compression system AS1, hot water production system HS1 has control unit 215, pump 221, accumulator 222, first control valve 223, buffer tank 224, second control valve 225, outlet hot water temperature sensor 226, water line L1, and makeup water line L2. Hot water supply destination 201 has water supply tank 201a and boiler body 201b. Note that first control valve 223 corresponds to heat recovery valve 36 in FIG. 1, and outlet hot water temperature sensor 226 is a component equivalent to outlet hot water temperature sensor 43 in FIG. 1.

[0066] The control unit 215 controls each unit of the hot water production system HS1. The control unit 215 may be realized by the control device C that controls the operation of the air compression system AS1, or may be realized by another device that can cooperate with the control device C.

[0067] The water line L1 is connected to the water supply tank 201a from the buffer tank 224, in this order via the pump 221, the air compression system AS1, and the first control valve 223. In the water line L1, an accumulator 222 is disposed between the pump 221 and the air compression system AS1, and an outlet hot water temperature sensor 226 is disposed between the first control valve 223 and the water supply tank 201a.

[0068] One end of makeup water line L2 is connected to position P1 on water line L1 between accumulator 222 and air compression system AS1, and the other end is connected to position P2 on water line L1 between outlet hot water temperature sensor 226 and water supply tank 201a. A second control valve 225 is provided midway on makeup water line L2.

[0069] Make-up water is supplied from the outside as needed to the buffer tank 224, and the buffer tank 224 stores this make-up water as service water Wa. The supply of make-up water to the buffer tank 224 is controlled by the control unit 215 so that the amount of service water Wa stored in the buffer tank 224 falls within a predetermined range.

[0070] In the air compression system AS1, the upstream side of the water line L1 is connected to the inlet passage 32, and the downstream side of the water line L1 is connected to the outlet passage 33. As a result, the air compression system AS1 can use the water Wa that flows from the water line L1 into the inlet passage 32 as the coolant F, and can cause the coolant F after heat recovery to flow out from the outlet passage 33 to the water line L1 as the water Wa.

[0071] The opening degree of the first control valve 223 can be adjusted by the control unit 215, and the first control valve 223 serves to adjust the flow rate of the water Wa in the water line L1. When the first control valve 223 is opened while the pump 221 is operating, the water Wa is supplied to the air compression system AS1, enabling a heat recovery operation to cool the air compression system AS1, and also enabling the water Wa whose heat has been recovered in the air compression system AS1 to be supplied to the water supply tank 201a.

[0072] The second control valve 225 can be opened and closed under the control of the control unit 215. When the second control valve 225 is opened while the pump 221 is operating, the water Wa that has not passed through the air compression system AS1 (water Wa for which heat has not been recovered) is supplied to the water supply tank 201a.

[0073] The hot water supply destination 201 functions as a boiler facility that supplies the service water Wa stored in the water supply tank 201a to the boiler main body 201b as boiler feedwater and heats the service water Wa in the boiler main body 201b to generate steam. The hot water supply destination 201 monitors the amount of service water Wa stored in the water supply tank 201a based on a detection signal from, for example, a water level sensor (not shown), and if the amount of storage is below a predetermined reference value (reduced water value), it sends a signal to the control unit 215 indicating that there is a demand for the service water Wa, and if the amount of storage has reached an upper limit value (full water value), it sends a signal to the control unit 215 indicating that there is no demand for the service water Wa. The control unit 215 receives this signal and can recognize whether there is a demand for the service water Wa at the hot water supply destination 201.

[0074] When there is a demand for water Wa at hot water supply destination 201, control unit 215 operates pump 221 and controls first control valve 223 to an open state. This allows water Wa to be supplied to air compression system AS1, enabling heat recovery operation. Note that control unit 215 may also control the opening of first control valve 223 so that the temperature detected by outlet hot water temperature sensor 226 becomes a target temperature (i.e., so that water Wa supplied to water supply tank 201a is kept constant at a required temperature).

[0075] The water Wa used for heat exchange in the air compression system AS1 is supplied to the water supply tank 201a, but the water supply flow rate may be temporarily increased for the water supply tank 201a when the storage volume reaches a lower limit. In this case, the second control valve 225 is controlled to be open so that more water Wa is supplied to the water supply tank 201a via the makeup water line L2.

[0076] On the other hand, the control unit 215 controls the first control valve 223 to be closed when there is no demand for the water Wa at the hot water supply destination 201. Even if the first control valve 223 is closed, the control unit 215 can control the second control valve 225 to be open, thereby making it possible to urgently supply the water Wa to the water supply tank 201a without passing through the air compression system AS1.

[0077] The air compression system AS1 provided in the hot water production system HS1 can be configured to switch between performing and not performing heat recovery operation when the compressor 3 is running, depending on whether there is demand for the water Wa at the hot water supply destination 201. Specifically, when there is demand, the air compression system AS1 can be configured to operate in a first operating mode in which the heat recovery operation is performed, and when there is no demand, the air compression system AS1 can be configured to operate in a second operating mode in which the heat recovery operation is not performed.

[0078] As already explained, when the air compression system AS1 is performing anti-freeze operation in the first operating mode, the supply of hot water from the air compression system AS1 is temporarily stopped. However, even in this case, the hot water production system HS1 can supply water to the water supply tank 201a by opening the second control valve 225. In this way, the hot water production system HS1 is designed to minimize problems with the use of hot water even if the supply of hot water from the air compression system AS1 is temporarily stopped.

[0079] 2. Second embodiment Next, a second embodiment of the present invention will be described below. Fig. 3 is a schematic diagram of an air compression system AS2 according to the second embodiment.

[0080] 2-1.Air compression system configuration As shown in Fig. 3, the air compression system AS2 includes a compressor 102, a control device C, and a temperature sensor TS. The control device C controls the operation of each part of the air compression system AS2. The temperature sensor TS continuously detects the ambient temperature of the air compression system AS2 and sends information about the detected ambient temperature to the control device C. In this embodiment, the air compression system AS2 is applied to a water-cooled two-stage oil-free screw compressor.

[0081] The compressor 102 is, for example, a screw type, and is configured to be driven by an electric motor. Note that the power source is not limited to an electric motor, and may be an internal combustion engine or the like. The compressor 102 has a first-stage compressor body 121 arranged upstream of the air flow, and a second-stage compressor body 122 arranged downstream of the first-stage compressor body 121 in the air flow.

[0082] Because the air compression system AS2 of this embodiment is an oil-free screw compressor, unlike a liquid-feed air compressor that injects a liquid such as oil or water into the compression working chamber, the compressor 102 tends to generate heat due to the heat generated during air compression. Furthermore, because the compressed air is hot, it may not be suitable for use by the load equipment (destination for compressed air). For this reason, a coolant F is supplied to each component of the air compression system AS2. Furthermore, as will be described later, the air compression system AS2 of this embodiment is configured to enable heat recovery operation in which the heat of compression generated during the air compression process of the compressor 102 is recovered.

[0083] The air compression system AS2 includes a heat recovery heat exchanger 103. The heat recovery heat exchanger 103 exchanges heat between low-temperature circulating water F1 (first coolant F) returning from a hot water user (e.g., a heating facility) and compressed air discharged from the compressor 102. The high-temperature circulating water F1 after heat exchange is sent to the hot water user by a circulation pump (not shown). The heat recovery heat exchanger 103 includes a primary heat recovery heat exchanger 131 disposed between the first-stage compressor body 121 and the second-stage compressor body 122, and a secondary heat recovery heat exchanger 132 disposed on the discharge side (downstream) of the second-stage compressor body 22.

[0084] The air compression system AS2 also includes a cooling heat exchanger 105. The cooling heat exchanger 105 exchanges heat between low-temperature circulating water F2 (second cooling liquid F) returning from a compression heat release destination (e.g., a cooling tower) and the compressed air discharged from the compressor 102. The high-temperature circulating water F2 after heat exchange is sent to the compression heat release destination by a circulation pump (not shown). The cooling heat exchanger 105 includes an intercooler 151 arranged between the first-stage compressor body 121 and the second-stage compressor body 122, and an aftercooler 152 arranged on the discharge side of the second-stage compressor body 122.

[0085] A primary heat recovery heat exchanger 131 and an intercooler 151 are arranged in this order from the upstream side between the first-stage compressor body 121 and the second-stage compressor body 122. Furthermore, on the discharge side of the second-stage compressor body 122, a secondary heat recovery heat exchanger 132 and an aftercooler 152 are arranged in this order from the upstream side.

[0086] The first-stage compressor body 121, the heat exchanger 131 for primary heat recovery, the intercooler 151, the second-stage compressor body 122, the heat exchanger 132 for secondary heat recovery, and the aftercooler 152 are connected by an air pipe 106 through which air to be compressed flows. A primary pressure regulating valve 111 is provided in the air pipe 106 at a position downstream of the aftercooler 152. An air release pipe (reference numeral omitted) provided with an air release valve 112 is connected to a branch point α in the air pipe 106 between the aftercooler 152 and the primary pressure regulating valve 111. The air release valve 112 is basically always closed except during execution of anti-freeze operation in a third operation mode, which will be described later.

[0087] The first coolant pipe 107 is configured to connect an inlet 171 through which low-temperature circulating water F1 returning from a hot water usage destination flows in, to an outlet 172 through which high-temperature circulating water F1 flows out after passing through the primary heat recovery heat exchanger 131 and the secondary heat recovery heat exchanger 132 and being sent toward the hot water usage destination. The first coolant pipe 107 forms part of a circulation path for the first circulating water F1, including the hot water usage destination. At least one of the inlet 171 and the outlet 172 is provided with an on-off valve (not shown) that can stop the first circulating water F1 flowing through the first coolant pipe 107.

[0088] The second coolant pipe 108 is configured to branch from an inlet 180 into a first branch pipe 181, a second branch pipe 182, and a third branch pipe 183, which then merge and connect to an outlet 184. The second coolant pipe 108 forms part of a circulation path for the second circulating water F2, including a destination for discharging the heat of compression. The cooling tower, which is the destination for discharging the heat of compression, is a device that cools the second circulating water F2 by exchanging heat with the atmosphere, and this cooling can be promoted by rotating a fan.

[0089] The outlet 184 is an outlet through which the second circulating water F2 flows out and is sent toward the cooling tower. The second coolant pipe 108 forms part of a circulation path for the second circulating water F2, including the cooling tower. At least one of the inlet 180 and the outlet 184 is provided with an on-off valve (not shown) that can stop the second circulating water F2 from flowing through the second coolant pipe 108.

[0090] The first branch pipe 181 runs from the inlet 180 through the aftercooler 152 and connects to the outlet 184. The second branch pipe 182 runs from the inlet 180 through the oil cooler 109, a cooling jacket provided on the casing of the second-stage compressor body 122, and a cooling jacket provided on the casing of the first-stage compressor body 121, and connects to the outlet 184. The third branch pipe 183 runs from the inlet 180 through the intercooler 151 and connects to the outlet 184.

[0091] Although not shown, the oil cooler 109 is a water-cooled heat exchanger for cooling the lubricating oil that lubricates the bearings of the compressor 102 and the power transmission gears. The lubricating oil cooled by the oil cooler 109 lubricates the bearings of the compressor 102 and the like, and is then stored in an oil sump (not shown) in the gear box. The lubricating oil is then guided to the oil cooler 109 by a conveying mechanism such as an oil pump (not shown) and cooled, and is configured to circulate through this lubrication path.

[0092] 2-2.Air compression system operation Next, the operation of the air compression system AS2 will be described. When there is a request for compressed air from the load equipment, the control device C drives the compressor 102 to produce compressed air so that the compressed air is supplied to the load equipment, but when there is no such request, it stops the compressor 102 so that compressed air is not supplied to the load equipment. Also, when the compressor 102 is driven, when there is a request for hot water from the hot water supply destination (heat recovery destination), the control device C executes heat recovery operation so that hot water is supplied to the hot water supply destination, but when there is no such request, it does not execute heat recovery operation.

[0093] Furthermore, when a predetermined condition α is satisfied, the control device C performs anti-freeze operation to prevent the cooling liquid F (the first circulating water F1 and the second circulating water F2 when the water is stopped) from freezing by using the heat of compression of the compressor 102. In the example of this embodiment, this predetermined condition α is a condition that is satisfied when the ambient temperature detected by the temperature sensor TS falls below a set value (e.g., 1°C). That is, in this embodiment, the ambient temperature detected by the temperature sensor TS is monitored, and when this ambient temperature falls below the set value, anti-freeze operation is performed.

[0094] The control device C can switch the operating mode of the air compression system AS2 between a first operating mode in which compressed air is supplied to the load equipment and a heat recovery operation is performed, a second operating mode in which compressed air is supplied to the load equipment but a heat recovery operation is not performed, and a third operating mode in which compressed air is not supplied to the load equipment. Next, each of these operating modes will be described in more detail.

[0095] 2-2-1. First operation mode First, the first operating mode will be described. The air compression system AS2 draws in air through a capacity control valve (not shown) located upstream of the first-stage compressor main body 121 and compresses the air in the first-stage compressor main body 121. The compressed high-temperature air (for example, approximately 160°C) then exchanges the required amount of heat in the primary heat recovery heat exchanger 131 and is further cooled in the intercooler 151. Here, the compressed high-temperature air and the first circulating water F1 flow through the primary heat recovery heat exchanger 131 to exchange heat, and the compressed air whose temperature has been reduced by heat exchange in the primary heat recovery heat exchanger 131 flows through the intercooler 151 to exchange heat with the second circulating water F2.

[0096] Next, the air cooled by the intercooler 151 (for example, to about 40°C) is compressed by the second-stage compressor body 122 to further increase the pressure. Thereafter, the compressed high-temperature air (for example, to about 160°C or even higher) exchanges the required amount of heat again in the secondary heat recovery heat exchanger 132, and is further cooled by the aftercooler 152. The air cooled by the aftercooler 152 (for example, to about 40°C) is then sent to the load equipment.

[0097] On the other hand, the first circulating water F1 flows in from the hot water user via the inlet 171, flows through the first coolant pipe 107, exchanges heat with compressed air in the primary heat recovery heat exchanger 103, and then flows out toward the hot water user from the outlet 172. Therefore, the hot water user can use the first circulating water F1 with an increased temperature as a heat source for heating, heating treatment, etc.

[0098] In this embodiment, the first circulating water F1 returning from the hot water user is medium-temperature water having a temperature of, for example, about 40 to 50° C. The first circulating water F1, which is room temperature water, is reheated to, for example, about 70 to 90° C. by heat exchange with compressed air in the heat recovery heat exchanger 103, and is then supplied to the hot water user. In the first operating mode, the second circulating water F2 flowing through the second coolant pipe 108 is stopped.

[0099] When the predetermined condition α is satisfied in the first operating mode, anti-freeze operation is initiated as follows. Specifically, the second circulating water F2 is stopped so that the second circulating water F2 flows through the second coolant pipe 108, and the first circulating water F1 flowing through the first circulating water pipe 107 is stopped. As a result, the second circulating water F2, which has been warmed by the heat of compression of the compressor 102, is circulated through a circulation path including the second coolant pipe 108, thereby raising the temperature of the air compression system AS2 above that before the anti-freeze operation was initiated. In this way, it is possible to prevent the coolant F from freezing. Note that when the anti-freeze operation is performed, it is desirable to stop the cooling tower fan to prevent a drop in the temperature of the circulating second circulating water F2.

[0100] During anti-freeze operation, the first circulating water F1 is stopped from flowing, and therefore the supply of the heated first circulating water F1 to the hot water user (hot water output from the air compression system AS2) is temporarily stopped. Therefore, even if the hot water output is temporarily stopped in this manner, it is desirable to take measures to minimize problems with the use of hot water. As will become clear from the explanation below, the hot water production system HS2 (see Figure 4), which is configured to include the air compression system AS2, is configured with this in mind.

[0101] 2-2-2. Second operation mode Next, the second operating mode will be described. In the second operating mode, the compressor 102 is driven to produce compressed air according to the demand (air load) of the load equipment, as in the first operating mode. Also, in the second operating mode, the first circulating water F1 flowing through the first coolant pipe 107 is stopped. On the other hand, the second circulating water F2 flowing through the second coolant pipe 108 is not stopped. As a result, the second circulating water F2 flows in from, for example, a cooling tower (not shown) through the inlet 180, flows through the second coolant pipe 108, cools the compressed air and other components in the cooling heat exchanger 105, and then flows out toward the cooling tower from the outlet 184. The second circulating water F2, whose temperature has increased, is cooled by heat exchange with the atmosphere in the cooling tower. Other operations are basically the same as in the first operating mode.

[0102] When the predetermined condition α is satisfied in the second operating mode, anti-freeze operation is initiated as follows. That is, the first circulating water F1 is released from the cutoff state to allow the first circulating water F1 to flow through the first coolant pipe 107, and the second circulating water F2 flowing through the second coolant pipe 108 is cut off. As a result, the first circulating water F1, which has been heated by the heat of compression of the compressor 102, is circulated through a circulation path including the first coolant pipe 107, thereby raising the temperature of the air compression system AS2 to a level higher than before the anti-freeze operation was initiated. In this way, it is possible to prevent the coolant F from freezing. Note that, as shown in FIG. 4, when the hot water user (heat recovery destination) is a hot water tank, the temperature of the first circulating water F1 in the first coolant pipe 107 can be raised in a short time if there is no demand for hot water and there is a sufficient amount of hot water remaining in the hot water tank.

[0103] 2-2-3.Third operation mode Next, the third operation mode will be described. In the third operation mode, the compressor 102 is stopped, the first circulating water F1 flowing through the first coolant pipe 107 is stopped, and the second circulating water F2 flowing through the second coolant pipe 108 is also stopped. When a predetermined condition α is satisfied in the third operation mode, anti-freeze operation is started as follows. That is, the compressor 102 is driven at low output (e.g., 50% output), the air release valve 112 is opened, and the first circulating water F1 and the second circulating water F2 are passed through the pipes 107, 108 in turn to circulate them.

[0104] As a result, by circulating the first circulating water F1 and the second circulating water F2 while heating them with the heat of compression of the compressor 3, the temperature of the air compression system AS2 can be raised above that before the start of anti-freeze operation. In this way, it is possible to prevent the coolant F from freezing. Also, because the air release valve 112 is open at this time, the compressed air generated by the compressor 102 is released by the air release valve 112, preventing unnecessary compressed air from flowing into the load equipment. The order in which water is passed through the first coolant pipe 107 and the second coolant pipe 108 is arbitrary, but when the waste heat utilization side is a hot water tank as shown in FIG. 4, it is preferable to give priority to passing water through the second coolant pipe 108 over the first coolant pipe 107, which can pass hot water from the hot water storage tank.

[0105] In either operating mode, if it is determined that there is no longer any risk of water freezing after the anti-freeze operation has started, the anti-freeze operation is terminated. For example, the control device C monitors the discharge temperature of the compressed air in the air compression system AS2 while the anti-freeze operation is being performed, and terminates the anti-freeze operation when this temperature reaches a predetermined value (for example, 50°C).

[0106] 2-3.Example of application to hot water production system The air compression system AS2 described above can also be applied as a component of the hot water production system HS2 shown in Fig. 4. This hot water production system HS2 will be described below.

[0107] 4, in addition to the air compression system AS2, the hot water producing system HS2 includes a hot water tank 330, a circulation line L20, a circulation state switching means 320, and a control unit 360. The control unit 360 controls each unit of the hot water producing system HS2. The control unit 360 may be realized by a control device C that controls the operation of the air compression system AS2, or may be realized by another device that can cooperate with the control device C.

[0108] The hot water tank 330 stores hot water W3 to be used in the hot water utilization facility 400. This hot water W3 is supplied from the hot water tank 330 to the hot water utilization facility 400 via a water distribution line L30. The hot water utilization facility 400 is, for example, a steam boiler device, and uses the hot water W3 as boiler feed water. If the hot water utilization facility 400 is a device that extracts only hot heat, such as a heating facility, the water distribution line L30 is a hot water loop piping, and the hot water W3 is circulated.

[0109] Hot water tank 330 receives makeup water from the outside as needed and stores this makeup water as service water. The supply of makeup water to hot water tank 330 is controlled by control unit 360 so that the amount of service water stored in hot water tank 330 falls within a predetermined range. As a result, makeup water is appropriately supplied to hot water tank 330 in accordance with the demand of hot water utilization facility 400.

[0110] A circulation line L20 is connected to the hot water tank 330. The circulation line L20 is a circuit for circulating the service water (cold water) stored in the hot water tank 330 to the air compression system AS2. The circulation line L20 is made up of an outgoing path L21 to the air compression system AS2 and a returning path L22 from the air compression system AS2. In the following description, the service water circulating through the circulation line L20 may also be referred to as circulating water W2.

[0111] The outgoing line L21 is connected to an inlet 171 of the air compression system AS2, and the returning line L22 is connected to an outlet 172 of the air compression system AS2. As a result, the circulating water W2 flows into the air compression system AS2 as the first circulating water F1. Furthermore, the air compression system AS2 outputs the waste heat recovery water F1, which has been heated by the heat of compression of the compressor 102, to the returning line L22 as the circulating water W2.

[0112] The circulation line L20 is provided with a circulation state switching means 320 that switches the circulating water W2 between a circulation running state and a circulation stopped state. The circulation state switching means 320 is composed of a circulation pump 321 arranged on the outgoing line L21 and a control valve 322 arranged on the return line L22. An accumulator 323 is connected to the discharge side of the circulation pump 321. The control valve 322 is controlled to open and close by a drive signal from a control unit 360, which will be described later.

[0113] The hot water tank 330 is equipped with a heat storage amount detection means 331 and a pressure switch 333. The heat storage amount detection means 331 detects the temperature of the stored water. In this embodiment, the heat storage amount detection means 331 is configured as a temperature switch (thermostat). This temperature switch turns off when it detects, for example, a lower set temperature T1 (first set amount, for example 50°C), and turns on when it detects a higher set temperature T2 (second set amount, for example 70°C). Note that instead of a temperature switch, the heat storage amount detection means 331 can also use a temperature sensor that uses a thermocouple, a thermistor, or the like.

[0114] The pressure switch 333 detects a low water level (drought state) of the stored water. The pressure switch 333 turns on when it detects, for example, a higher set pressure, and turns off when it detects a lower set pressure.

[0115] The control unit 360 controls the circulation state switching means 320 based on the amount detected by the heat storage amount detection means 331, thereby performing water heating control. [A1] When the amount detected by the heat storage amount detection means 331 drops to the first set amount (lower set temperature T1), the circulation state switching means 320 switches to the circulation execution state. Specifically, when the OFF operation of the temperature switch is detected, the control valve 322 is opened and the circulation pump 321 is driven. This starts the flow of circulating water W2 to the air compression system AS2. [A2] When the amount detected by the heat storage amount detection means 331 rises to a second set amount (higher set temperature T2) higher than the first set amount, the circulation state switching means 320 switches to the circulation stop state. Specifically, when the on operation of the temperature switch is detected, the circulation pump 321 is stopped and the control valve 322 is closed. This stops the flow of circulating water W2 to the air compression system AS2.

[0116] Furthermore, while the circulation state switching means 320 is being switched to the circulation execution state, the control unit 360 preferably detects a dry state in the hot water tank 330 and prevents the circulation pump 321 from running dry. Specifically, when the pressure switch 333 detects a lower set pressure corresponding to a low water level while the circulation pump 321 is running, the control unit 360 forcibly stops the circulation pump 321 and then closes the control valve 322.

[0117] The air compression system AS2 provided in the hot water production system HS2 can be configured to switch between performing and not performing heat recovery operation when the compressor 102 is running, depending on the switching state of the circulation state switching means 320. Specifically, when the circulation state switching means 320 is in the circulation execution state, the air compression system AS2 can be configured to be in a first operation mode in which heat recovery operation is performed, and when the circulation state switching means 320 is in the circulation stop state, the air compression system AS2 can be configured to be in a second operation mode in which heat recovery operation is not performed.

[0118] As already explained, when the air compression system AS2 is performing anti-freeze operation in the first operating mode, the supply of hot water from the air compression system AS2 is temporarily stopped. However, even in this case, the hot water production system HS2 is able to supply water from the hot water tank 330 to the hot water utilization facility 400, and is also able to supply make-up water in response to a drop in the water level in the hot water tank 330. In this way, the hot water production system HS2 is designed to minimize problems with the use of hot water even if the supply of hot water from the air compression system AS2 is temporarily stopped.

[0119] 3. Summary As described above, the air compression systems AS1, AS2 of each embodiment include the compressors 3, 102 that perform a compression operation to compress air to generate compressed air, and a flow path (flow path for the coolant F) that circulates the coolant F used to cool the object to be cooled whose temperature has been increased by the heat of compression generated in the compression operation. When the predetermined condition α is satisfied, the air compression systems AS1, AS2 perform anti-freeze operation that uses the heat of compression to prevent the coolant F in the air compression systems AS1, AS2 from freezing.

[0120] Therefore, according to the air compression systems AS1 and AS2 of the respective embodiments, it is possible to prevent the cooling liquid F from freezing by utilizing the heat of compression generated in the compressor, without providing a separate heater or the like. Note that the "object to be cooled" here corresponds to the compressor itself, the compressed air, the added water in the first embodiment, and the like.

[0121] The air compression systems AS1 and AS2 in each embodiment are equipped with a temperature sensor TS that detects the ambient temperature, and the predetermined condition α is a condition that is met when the detected ambient temperature falls below a set value. This makes it possible to appropriately determine whether or not anti-freeze operation is required based on the ambient temperature, which is directly related to the susceptibility of the coolant F to freezing. However, the content of the predetermined condition α is not limited to this, and as an example, the predetermined condition α may be a condition that is met when an operator or the like performs a predetermined operation on the air compression systems AS1 and AS2 (such as pressing a button to start anti-freeze operation).

[0122] Furthermore, the air compression systems AS1 and AS2 of each embodiment include a heat exchanger 16, 103, or 105 that exchanges heat between the object to be cooled and the coolant F, and an air release valve 21 or 112 that allows the compressed air sent out from the compressor to be released. When a predetermined condition α is satisfied while the compression operation is stopped (third operation mode), anti-freeze operation is performed by performing a compression operation to generate compression heat and circulating the coolant F through the coolant F flow path, and the air release valve 21 or 112 releases the compressed air. Therefore, with the air compression systems AS1 and AS2 of each embodiment, anti-freeze operation can be performed using the coolant F heated by the compression heat, even while the compression operation is stopped. Furthermore, the air release valve 21 or 112 releases the compressed air, preventing unnecessary compressed air from flowing into the load equipment.

[0123] Furthermore, in the air compression systems AS1 and AS2 of each embodiment, the heat exchangers 16, 103 and 105 are provided so that the compressed air delivery path and the coolant F flow path pass through each other, and exchange heat between the compressed air to be cooled and the coolant F, and the air release valves 21 and 112 are provided in the delivery path downstream of the heat exchangers 16, 103 and 105. Therefore, the air compression systems AS1 and AS2 of each embodiment prevent the compressed air from being released before it is heat exchanged with the coolant F in the heat exchangers 16, 103 and 105, and make it possible to reliably warm the coolant F with the compressed air.

[0124] In the first embodiment, the air compression system AS1 includes a heat recovery heat exchanger 16 that exchanges heat between the cooling target and the coolant F. The coolant F flow path is configured to circulate the supplied coolant F through the heat recovery heat exchanger 16 to a predetermined heat recovery destination, and includes a return path (including a return path 34) that returns the coolant F from the downstream side of the heat recovery heat exchanger 16 to a return destination (storage tank 42) upstream of the heat recovery heat exchanger 16. The operation mode during compression is switchable between at least a first operation mode (heat recovery mode) in which the coolant F that has passed through the heat recovery heat exchanger 16 is sent to the heat recovery destination, and a second operation mode (non-heat recovery mode) in which the coolant F that has passed through the heat recovery heat exchanger 16 is returned through the return path. Furthermore, when a predetermined condition α is satisfied while the operation mode is the first operation mode, an anti-freeze operation is performed in which the coolant F that has passed through the heat recovery heat exchanger 16 is returned through the return path.

[0125] In the first embodiment, the air compression system AS1 is provided with a radiator 38 (cooling mechanism) capable of performing a cooling operation to cool the coolant F, between the return destination (storage tank 42) in the flow path of the coolant F and the heat recovery heat exchanger 16, and this cooling operation is performed when the operation mode is the second operation mode. Furthermore, if a predetermined condition α is satisfied when the operation mode is the second operation mode, an anti-freeze operation is performed in which the fan 38a of the radiator 38 is stopped (i.e., the cooling operation is stopped) and the coolant F that has passed through the heat recovery heat exchanger 16 is returned through the return path.

[0126] In the second embodiment, the air compression system AS2 comprises a heat recovery heat exchanger 103 (first heat exchanger) that exchanges heat between the object to be cooled and the first circulating water F1 (first cooling liquid F), and a cooling heat exchanger 105 (second heat exchanger) that exchanges heat between the object to be cooled and the second circulating water F2 (second cooling liquid F), and as a circulation path for the cooling liquid F, comprises a first circulation path formed to circulate the supplied first circulating water F1 to a predetermined heat recovery destination via the heat recovery heat exchanger 103, and a second circulation path formed to circulate the supplied second circulating water F2 to a predetermined destination (cooling tower) via the cooling heat exchanger 105. Furthermore, the air compression system AS2 is capable of switching the operating mode during compression operation between at least a first operating mode (heat recovery mode) in which the first circulating water F1 flows through a first circulation path and is sent to a heat recovery destination, and a second operating mode (non-heat recovery mode) in which the second circulating water F2 flows through a second circulation path and is sent to a cooling tower, and when a predetermined condition α is satisfied when the operating mode is the first operating mode, an operation is performed in which the second circulating water F2 flows through the second circulation path as anti-freeze operation.

[0127] In addition, in the second embodiment, when the operating mode is the second operating mode and a predetermined condition α is satisfied, the air compression system AS2 performs anti-freeze operation in which the second circulating water F2 circulates through the first circulation path.

[0128] Although the embodiments of the present invention have been described above, the above embodiments are illustrative in all respects and should not be considered limiting. The technical scope of the present invention is defined by the claims, not by the description of the above embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims. [Industrial Applicability]

[0129] The present invention can be used in an air compression system equipped with a compressor.

[0130] <Contribution to the United Nations-led Sustainable Development Goals (SDGs)> The air compression system disclosed herein improves energy efficiency by incorporating a heat recovery mechanism, and can contribute to achieving Goal 7 of the SDGs (Sustainable Development Goals), "Affordable and clean energy." [Explanation of symbols]

[0131] 1. Air Compression System 2. Heat recovery system 3. Compressor 4 Pre-separator 5 Aftercooler 6 Water Cooler 7 Separator Tank 8 motors 9. Air Filter 10 Intake passage 11 Added water return path 12 Discharge path 13 Check valve 14 Gas-phase connecting passage 15 Liquid phase communication passage 16 Heat recovery heat exchanger 17 Compressed air outlet 18 Primary pressure regulating valve 19 Check valve 20 Safety valve 21 Air release valve 22 Additive water valve 23 Water Filter 30 Water level detector 31 Pressure Sensor 32 Entrance road 33 Exit path 34 Return Route 35 Switching Method 36 Heat recovery valve 37 Return valve 38 Radiator 38A fan 39 Access Road 40 Pump 41 Check valve 42 Storage Tank 43 Outlet water temperature sensor 102 Compressor body 103 Heat recovery heat exchanger 105 Cooling heat exchanger 106 Air piping 107 First coolant pipe 108 Second coolant pipe 109 Oil cooler 111 Primary pressure regulating valve 112 Air release valve 121 First stage compressor body 122 Second stage compressor body 131 Primary heat recovery heat exchanger 132 Secondary heat recovery heat exchanger 151 Intercooler 152 Aftercooler AS1, AS2 Air Compression System C Control device F coolant F1 First circulating water (first coolant) F2 Second circulating water (second coolant) HS1, HS2 hot water production system TS Temperature Sensor

Claims

1. a compressor that performs a compression operation to compress air and generate compressed air; a flow path through which a cooling liquid used to cool the object to be cooled whose temperature has increased due to heat of compression generated in the compression operation flows; An air compression system that performs anti-freeze operation to prevent the cooling liquid from freezing by using the heat of compression when predetermined conditions are met.

2. a heat exchanger that exchanges heat between the object to be cooled and the coolant; An air release valve that allows the compressed air sent out from the compressor to be released, If the predetermined condition is satisfied while the compression operation is stopped, 2. The air compression system according to claim 1, wherein the anti-freeze operation comprises performing the compression operation to generate the heat of compression, circulating the coolant through the circulation path, and releasing the compressed air through the air release valve.

3. The heat exchanger comprises: The cooling system is provided so that a delivery path for the compressed air and the circulation path pass through each other, and heat is exchanged between the compressed air to be cooled and the cooling liquid, The air release valve is The air compression system according to claim 2, wherein the heat exchanger is provided downstream of the heat exchanger in the delivery path.

4. a heat exchanger that exchanges heat between the object to be cooled and the cooling liquid, The distribution channel is a return path formed to circulate the supplied cooling liquid through the heat exchanger to a predetermined heat recovery destination, and to return the cooling liquid from a downstream side of the heat exchanger to a return destination on an upstream side, an operating mode during the compression operation can be switched between at least a heat recovery mode in which the cooling liquid that has passed through the heat exchanger is sent to the heat recovery destination, and a non-heat recovery mode in which the cooling liquid that has passed through the heat exchanger is returned through the return path; If the predetermined condition is satisfied when the operation mode is the heat recovery mode, The air compression system according to claim 1 , wherein the freeze prevention operation is an operation in which the coolant that has passed through the heat exchanger is returned through the return path.

5. a cooling mechanism capable of performing a cooling operation to cool the cooling liquid is provided between the return destination and the heat exchanger in the distribution path; 5. The air compression system of claim 4, wherein the cooling operation is performed when the operating mode is the non-heat recovery mode, If the predetermined condition is satisfied when the operation mode is the non-heat recovery mode, The air compression system performs the anti-freeze operation by stopping the cooling operation and returning the coolant that has passed through the heat exchanger through the return path.

6. a first heat exchanger that exchanges heat between the object to be cooled and the first cooling liquid, and a second heat exchanger that exchanges heat between the object to be cooled and the second cooling liquid, The distribution channels include: a first circulation path formed to circulate the supplied first cooling liquid to a predetermined heat recovery destination via the first heat exchanger, and a second circulation path formed to circulate the supplied second cooling liquid to a predetermined delivery destination via the second heat exchanger, an operating mode during the compression operation is switchable between at least a heat recovery mode in which the first cooling liquid flows through the first flow path and is sent to the heat recovery destination, and a non-heat recovery mode in which the second cooling liquid flows through the second flow path and is sent to the destination, If the predetermined condition is satisfied when the operation mode is the heat recovery mode, The air compression system according to claim 1 , wherein the antifreeze operation is an operation in which the second coolant flows through the second flow path.

7. a first heat exchanger that exchanges heat between the object to be cooled and the first cooling liquid, and a second heat exchanger that exchanges heat between the object to be cooled and the second cooling liquid, The distribution channels include: a first circulation path formed to circulate the supplied first cooling liquid to a predetermined heat recovery destination via the first heat exchanger, and a second circulation path formed to circulate the supplied second cooling liquid to a predetermined delivery destination via the second heat exchanger, an operating mode during the compression operation is switchable between at least a heat recovery mode in which the first cooling liquid flows through the first flow path and is sent to the heat recovery destination, and a non-heat recovery mode in which the second cooling liquid flows through the second flow path and is sent to the destination, If the predetermined condition is satisfied when the operation mode is the non-heat recovery mode, The air compression system according to claim 1 , wherein the antifreeze operation is an operation in which the first coolant flows through the first flow path.

8. A temperature sensor is provided to detect the ambient temperature.

8. The air compression system according to claim 1, wherein the predetermined condition is satisfied when the detected ambient temperature falls below a set value.

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