Waste heat recovery system, waste heat recovery unit, and waste heat recovery method

Abstract

Provided is a technique capable of preventing the damage of heat exchangers for waste heat recovery. An air compressor 1 is provided with: heat exchangers 103, 104 for cooling that exchange heat between cooling water and compressed air; and a cooling liquid pipe 106 through which the cooling water circulates. A waste heat recovery machine 2 is provided with: heat exchangers 201, 202 for waste heat recovery that exchange heat between waste heat recovery water and the compressed air; a waste heat recovery liquid pipe 211 through which the waste heat recovery water circulates; branch pipes 110, 111 that connect the cooling liquid pipe 106 and the waste heat recovery liquid pipe 211; flow path switching three-way valves 203, 204 that open and close the branch pipes 110, 111; and a temperature controller 206 that controls the flow path switching three-way valves 203, 204. The temperature controller 206 controls the flow path switching three-way valves 203, 204 to open the branch pipes 110, 111 when the temperature of the waste heat recovery water exceeds a threshold.

Description

Waste heat recovery system, waste heat recovery unit, and waste heat recovery method

[0001] The present invention relates to a waste heat recovery system, a waste heat recovery unit, and a method for recovering waste heat.

[0002] Gas compressors are known that take in gases such as air and expel high-pressure gases such as compressed air using a compression mechanism. Air compressors, in particular, are used on factory lines and at work sites as an air source for machine tools, presses, air blowers, and the like. It is said that the total energy consumed by gas compressors accounts for 20 to 25% of the total energy consumed in a factory, making the recovery of waste heat from gas compressors highly effective. In particular, the use of waste heat from gas compressors is expected to become even more important in the future, especially in order to achieve CO2 emission reduction targets stemming from the issue of global warming.

[0003] A gas compressor is composed of a compressor body that compresses a gas such as air, a cooling system that absorbs the heat generated by the compression, and a motor that drives the compressor. Furthermore, in a gas compressor, if the motor input power is taken as 100%, the amount of heat absorbed by the cooling system is equivalent to more than 90% of the power. This heat is usually released into the outside air, resulting in a significant amount of energy being emitted into the atmosphere. To reduce the amount of waste heat, efforts have been made to improve the efficiency of the compressor body and the motor, but the effect is limited to a few percent. Therefore, effective utilization of the waste heat from gas compressors is required.

[0004] Prior art in this technical field is disclosed in Patent Document 1. Patent Document 1 describes an exhaust heat recovery system that includes a temperature sensor installed downstream of a heat exchanger for exhaust heat recovery in an exhaust heat recovery liquid pipe, a temperature control valve, and a temperature regulator that controls the opening / closing angle of the temperature control valve in accordance with the temperature of the exhaust heat recovery water measured by the temperature sensor and a set recovered water temperature.

[0005] Japanese Patent Application Laid-Open No. 2021-96043

[0006] In the technology described in Patent Document 1, the waste heat recovery water flowing through the heat exchanger is cooled by being supplied to the waste heat utilization side and used as a heat source, but if the customer does not use the waste heat recovery water as a heat source, the temperature of the waste heat recovery water will rise further if it returns to the heat exchanger without being cooled.Since the temperature of compressed air can reach a maximum of approximately 170 degrees, if the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the heat exchanger piping will increase, and there is a risk of damaging the heat exchanger.

[0007] Therefore, an object of the present invention is to provide a technique capable of preventing damage to a heat exchanger for recovering waste heat.

[0008] In order to solve the above problems, one representative waste heat recovery system of the present invention is a waste heat recovery system comprising a fluid machine main body through which a fluid flows and a waste heat recovery machine that recovers waste heat from the fluid, wherein the fluid machine main body comprises a cooling heat exchanger that exchanges heat between a cooling liquid and the fluid and a cooling liquid pipe through which the cooling liquid flows, and the waste heat recovery machine comprises a waste heat recovery heat exchanger that exchanges heat between the waste heat recovery liquid and the fluid, a waste heat recovery liquid pipe through which the waste heat recovery liquid flows, and a cooling liquid pipe between the waste heat recovery liquid pipe upstream of the waste heat recovery heat exchanger and the cooling liquid pipe. The system includes a first bypass flow path connecting the liquid piping upstream of the cooling heat exchanger, a second bypass flow path connecting the waste heat recovery liquid piping downstream of the waste heat recovery heat exchanger and the cooling liquid piping downstream of the cooling heat exchanger, a first valve for opening and closing the first bypass flow path, a second valve for opening and closing the second bypass flow path, and a control unit for controlling the first valve and the second valve, wherein the control unit controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when the temperature of the waste heat recovery liquid exceeds a threshold value.

[0009] According to the present invention, damage to a heat exchanger for recovering waste heat can be prevented.

[0010] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0011] Fig. 1 is a schematic diagram showing an example of the general configuration of the waste heat recovery system of the present embodiment. Fig. 2 is a diagram showing an example of the circulation paths of waste heat recovery water and cooling water in the waste heat recovery system of the present embodiment under normal conditions. Fig. 3 is a diagram showing an example of the circulation paths of waste heat recovery water and cooling water in the waste heat recovery system of the present embodiment when the temperature of the waste heat recovery water exceeds a threshold value. Fig. 4 is a flowchart showing an example of control performed by a temperature controller in the waste heat recovery system of the present embodiment. Fig. 5 is a graph showing an example of the transition of the temperature of the waste heat recovery water in the waste heat recovery system of the present embodiment.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a water-cooled, package-type, two-stage, oil-free screw compressor for compressing air will be described as an example of a gas compressor.

[0013] FIG. 1 is a schematic diagram showing an example of the general configuration of a waste heat recovery system according to this embodiment.

[0014] As shown in FIG. 1 , the waste heat recovery system 100 includes an air compressor 1 that compresses air, and a waste heat recovery machine 2 that recovers waste heat from the compressed air discharged from the air compressor 1 .

[0015] The air compressor 1 includes compressor bodies 101 and 102, heat exchangers 103 and 104 for cooling, and an oil cooler 105, all of which are arranged in a housing. Although not shown, the housing has a base on which the compressor bodies 101 and 102 and other components are installed, and a box-shaped cover made up of multiple panels of metal or the like that is installed on the base so as to cover the compressor bodies 101 and 102 and other components, and has excellent soundproofing properties.

[0016] The waste heat recovery machine 2 includes heat exchangers 201 and 202 and a temperature controller 206, and these devices are arranged in a housing. Although not shown, the housing has a base on which the heat exchangers 201 and 202 and other devices are installed, and a box-shaped cover made of a plurality of panels made of metal or the like that is installed on the base so as to cover the heat exchangers 201 and 202 and other devices, and has excellent soundproofing properties.

[0017] Each of the compressor bodies 101, 102 includes a screw rotor consisting of one male rotor and one female rotor (not shown). The compressor bodies 101, 102 are configured to be driven by a main motor (not shown) located inside a housing, for example, via a power transmission mechanism. The power source for the compressor bodies 101, 102 is not limited to an electric motor, but may also be an internal combustion engine or the like.

[0018] Compressor body 101 is a first-stage compressor body located upstream of the air flow, and compressor body 102 is a second-stage compressor body located downstream of the air flow relative to first-stage compressor body 101.

[0019] The compressor bodies 101, 102 in this embodiment are oil-free screw compressors. Unlike liquid-feed air compressors that inject liquids such as oil or water into the compression working chamber, the compressor bodies 101, 102 tend to generate heat due to the heat generated during air compression. Furthermore, since the compressed air is hot, it may not be suitable for use by the compressed air consumer. For this reason, cooling water is supplied to each component of the air compressor 1. Furthermore, as will be described later, the air compressor 1 in this embodiment is configured to recover waste heat generated when the compressor bodies 101, 102 compress air.

[0020] The heat exchangers 201, 202 for waste heat recovery exchange heat between the compressed air discharged from the compressor bodies 101, 102 and waste heat recovery water, which serves as a waste heat recovery liquid and is sent from the heat treatment equipment 4 on the user side of the waste heat generated by the compressor bodies 101, 102.

[0021] Heat exchanger 201 is a heat exchanger for recovering intermediate-stage waste heat that is located between the first-stage compressor body 101 and the second-stage compressor body 102, and heat exchanger 202 is a heat exchanger for recovering discharge-stage waste heat that is located on the discharge side (downstream side) of the second-stage compressor body 102.

[0022] The heat treatment equipment 4 cools the waste heat recovery water by exchanging heat with cold water and converts the cold water into hot water for use by users, but is not limited to this; the waste heat recovery water may be heat exchanged with oil or air, or users may use the waste heat recovery water itself.

[0023] The cooling heat exchangers 103 and 104 exchange heat between cooling water as a coolant sent from a cooling facility 3 provided outside the air compressor 1 and compressed air discharged from the compressor bodies 101 and 102.

[0024] The heat exchanger 103 is a cooling heat exchanger arranged between the first stage compressor body 101 and the second stage compressor body 102 (hereinafter, the heat exchanger 103 will be referred to as an intercooler), and the heat exchanger 104 is a cooling heat exchanger arranged on the discharge side of the second stage compressor body 102 (hereinafter, the heat exchanger 104 will be referred to as an aftercooler).

[0025] The cooling equipment 3 cools the cooling water by exchanging heat with the atmosphere outside the waste heat recovery system 100 .

[0026] Between the first-stage compressor body 101 and the second-stage compressor body 102, an intermediate-stage waste heat recovery heat exchanger 201 and an intercooler 103 are arranged in this order from the upstream side. Also, on the discharge side of the second-stage compressor body 102, a discharge-stage waste heat recovery heat exchanger 202 and an aftercooler 104 are arranged in this order from the upstream side. Note that, in some cases, the arrangement order of the waste heat recovery heat exchangers 201, 202, the intercooler 103, and the aftercooler 104 may be reversed.

[0027] The first stage compressor body 101, the heat exchanger 201 for intermediate stage waste heat recovery, the intercooler 103, the second stage compressor body 102, the heat exchanger 202 for discharge stage waste heat recovery, and the aftercooler 104 are connected by an air pipe 108 through which the air to be compressed flows.

[0028] During unloaded operation, the vent air flows through the first-stage compressor body 101, intermediate-stage waste heat recovery heat exchanger 201, intercooler 103, second-stage compressor body 102, and discharge-stage waste heat recovery heat exchanger 202, and then, because unloaded operation causes check valve 109 to be fully closed, the vent air is released into the atmosphere through vent pipe 107. As a result, because the vent air flows through heat exchangers 201 and 202 even during unloaded operation, waste heat can be recovered regardless of the operating state, and the waste heat recovery rate can be improved.

[0029] In addition, there are provided a waste heat recovery liquid pipe 211 through which waste heat recovery water flows to exchange heat with compressed air in heat exchangers 201 and 202 for waste heat recovery, and a cooling liquid pipe 106 through which cooling water flows to exchange heat with compressed air in an intercooler 103 and an aftercooler 104 for cooling.

[0030] The waste heat recovery liquid piping 211 is sent from the heat treatment equipment 4 on the waste heat utilization side by operating the circulation pump 207, and is connected to the heat treatment equipment 4 via a heat exchanger 201 for intermediate stage waste heat recovery and a heat exchanger 202 for discharge stage waste heat recovery.

[0031] Further, downstream of the heat treatment equipment 4, the waste heat recovery liquid pipe 211 is provided with a temperature sensor 205 for measuring the temperature of the waste heat recovery water, and a flow meter 209 for measuring the flow rate of the waste heat recovery water.

[0032] The cooling liquid piping 106 is configured to branch from the cooling equipment 3 into a first cooling liquid piping 106a, a second cooling liquid piping 106b, and a third cooling liquid piping 106c, which then merge and connect to the cooling equipment 3.

[0033] The first coolant pipe 106a connects to the cooling equipment 3 from the cooling equipment 3 via the aftercooler 104. The second coolant pipe 106b connects to the cooling equipment 3 from the cooling equipment 3 via the oil cooler 105, a cooling jacket provided on the casing of the second-stage compressor body 102, and a cooling jacket provided on the casing of the first-stage compressor body 101. The third coolant pipe 106c connects to the cooling equipment 3 from the cooling equipment 3 via the intercooler 103.

[0034] The upstream of the intercooler 103, aftercooler 104, and oil cooler 105 on the coolant piping 106 and the upstream of the heat exchanger 201 for intermediate-stage waste heat recovery on the waste heat recovery liquid piping 211 are connected by a branch piping 110 on the coolant inlet side.

[0035] In addition, the downstream side of the heat exchanger 202 for discharge stage waste heat recovery in the waste heat recovery liquid piping 211 is connected to the downstream side of the intercooler 103, aftercooler 104, and oil cooler 105 in the cooling liquid piping 106 by a branch piping 111 on the cooling liquid outlet side.

[0036] At the connection point between the waste heat recovery liquid pipe 211 and the branch pipe 110 on the cooling liquid inlet side, an inlet-side flow path switching three-way valve 203 is provided to switch between the flow path from the upstream of the waste heat recovery liquid pipe 211 and the flow path from the branch pipe 110 on the cooling liquid inlet side.

[0037] In addition, at the connection point of the waste heat recovery liquid pipe 211 with the branch pipe 111 on the coolant outlet side, an outlet-side flow path switching three-way valve 204 is provided to switch between the flow path downstream of the waste heat recovery liquid pipe 211 and the flow path to the branch pipe 111 on the coolant outlet side.

[0038] The upstream side of the flow path switching three-way valve 203 on the inlet side of the waste heat recovery liquid piping 211 and the downstream side of the flow path switching three-way valve 204 on the outlet side of the waste heat recovery liquid piping 211 are connected by a waste heat recovery liquid circulation piping 210, and a temperature control valve 208 is provided that can open and close the waste heat recovery liquid circulation piping 210.

[0039] The temperature controller 206 controls the flow path switching three-way valves 203 and 204 and the temperature adjustment valve 208 in accordance with the temperature measured by the temperature sensor 205 and the set temperature.

[0040] Although not shown, the oil cooler 105 is a water-cooled heat exchanger for cooling the lubricating oil that lubricates the bearings of the compressor bodies 101 and 102, the power transmission mechanism, etc. The lubricating oil cooled by the oil cooler 105 lubricates the bearings of the compressor bodies 101 and 102, etc., and is then stored in an oil reservoir (not shown). The lubricating oil is then guided to the oil cooler 105 by a conveying mechanism such as an oil pump (not shown) and cooled, and is configured to circulate through this lubrication path.

[0041] Next, the operation of the waste heat recovery system 100 configured as above will be described.

[0042] 1 , air compressor 1 draws air through a capacity control valve (not shown) arranged upstream of first-stage compressor main body 101 and compresses the air in first-stage compressor main body 101. The compressed high-temperature air (for example, approximately 160°C) then exchanges the required amount of heat in intermediate-stage waste heat recovery heat exchanger 201 and is further cooled in intercooler 103. Here, compressed high-temperature air and waste heat recovery water flow through intermediate-stage waste heat recovery heat exchanger 201 to exchange heat, and compressed air whose temperature has been reduced by heat exchange in intermediate-stage waste heat recovery heat exchanger 201 flows through intercooler 103 to exchange heat with cooling water.

[0043] Next, the air cooled by the intercooler 103 (for example, to about 40°C) is compressed by the second-stage compressor body 102 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 heat exchanger 202 for recovering discharge-stage waste heat, and is further cooled by the aftercooler 104. The air cooled by the aftercooler 104 (for example, to about 40°C) is then sent to the source of demand for compressed air.

[0044] Next, the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 will be described.

[0045] FIG. 2 is a diagram showing an example of the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 of this embodiment under normal conditions.

[0046] As shown by the dashed line, the waste heat recovery water flows in from the heat treatment equipment 4 on the waste heat utilization side by operating the circulation pump 207, flows through the waste heat recovery liquid piping 211, has its temperature measured by the temperature sensor 205, exchanges heat with compressed air in the waste heat recovery heat exchangers 201 and 202, and then flows out toward the heat treatment equipment 4 on the waste heat utilization side.

[0047] As shown by the dotted line, the cooling water flows in from the cooling equipment 3, branches off from the cooling liquid pipe 106 to the first cooling liquid pipe 106a, the second cooling liquid pipe 106b, and the second cooling liquid pipe c, exchanges heat with compressed air in the intercooler 103 and the aftercooler 104, or exchanges heat with lubricating oil in the oil cooler 105, and then joins together and flows out toward the cooling equipment 3.

[0048] If the user does not use the heat treatment facility 4 to exchange heat between the waste heat recovery water and cold water, the waste heat recovery water that has exchanged heat with compressed air in the waste heat recovery heat exchangers 201, 202 will not be cooled by the heat treatment facility 4, and the temperature of the waste heat recovery water circulating through the waste heat recovery liquid piping 211 will rise. If the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the waste heat recovery liquid piping 211 will increase, and there is a risk that the waste heat recovery heat exchangers 201, 202 will be damaged.

[0049] Therefore, in this embodiment, if the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds a predetermined threshold value, the temperature controller 206 switches the flow path switching three-way valves 203 and 204 and opens the temperature adjustment valve 208, thereby switching the flow paths of the waste heat recovery water and cooling water.

[0050] FIG. 3 is a diagram showing an example of the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 of this embodiment when the temperature of the waste heat recovery water exceeds a threshold value.

[0051] When the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds a threshold value, the temperature controller 206 switches the flow path switching three-way valves 203 and 204, and the cooling water flows in from the cooling equipment 3, as shown by the dotted line, and branches from the cooling liquid pipe 106 to the first cooling liquid pipe 106a, the second cooling liquid pipe 106b, the second cooling liquid pipe c, and the branch pipe 110 on the cooling liquid inlet side.

[0052] The cooling water that flows from the cooling liquid pipe 106 into the first cooling liquid pipe 106a, the second cooling liquid pipe 106b, or the second cooling liquid pipe c exchanges heat with compressed air in the intercooler 103 or the aftercooler 104, or exchanges heat with lubricating oil in the oil cooler 105, and then joins together and flows out toward the cooling equipment 3.

[0053] The cooling water that flows from the cooling liquid pipe 106 into the branch pipe 110 on the cooling liquid inlet side flows through the waste heat recovery liquid pipe 211, exchanges heat with compressed air in the heat exchangers 201 and 202 for waste heat recovery, then merges with the cooling liquid pipe 106 via the branch pipe 111 on the cooling liquid outlet side and flows out toward the cooling equipment 3.

[0054] In addition, if the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds the threshold value, the temperature controller 206 opens the temperature control valve 208, and the waste heat recovery water flows in from the heat treatment equipment 4 on the waste heat utilization side, as shown by the dashed line, flows through the waste heat recovery liquid piping 211, passes through the waste heat recovery liquid circulation piping 210, and flows out toward the heat treatment equipment 4 on the waste heat utilization side without passing through the heat exchangers 201 and 202 for waste heat recovery.

[0055] According to this embodiment, if the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds the threshold value, the temperature controller 206 switches the flow path switching three-way valves 203, 204, and the cooling water from the cooling equipment 3 is used for heat exchange with the compressed air in the waste heat recovery heat exchangers 201, 202, thereby preventing the temperature of the waste heat recovery water from rising and preventing damage to the waste heat recovery heat exchangers.

[0056] FIG. 4 is a flowchart showing an example of control performed by the temperature controller 206 in the waste heat recovery system 100 of this embodiment.

[0057] In FIG. 4, it is assumed that at the start of treatment, the waste heat recovery water and cooling water flow through the normal flow paths shown in FIG.

[0058] When the air compressor 1 starts operating, power is supplied to the temperature controller 206 and control begins.

[0059] In S302 , the temperature controller 206 acquires the temperature of the waste heat recovery water in the waste heat recovery liquid pipe 211 measured by the temperature sensor 205 .

[0060] In S303, the temperature controller 206 determines whether the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds 95° C. If the temperature of the waste heat recovery water exceeds 95° C. in S303, the process proceeds to S304. On the other hand, if the temperature of the waste heat recovery water does not exceed 95° C. in S303, the process proceeds to S314, where the system waits in a normal state for a preset time, and then returns to S302.

[0061] In S304, the temperature controller 206 switches the inlet-side flow path switching three-way valve 203, and uses the branch pipe 110 on the coolant inlet side to cause the coolant in the coolant pipe 106 to flow into the waste heat recovery liquid pipe 211. At the same time, the temperature controller 206 switches the outlet-side flow path switching three-way valve 204, and causes the coolant that has passed through the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202 to flow into the branch pipe 111 on the coolant outlet side.

[0062] In S305, the temperature controller 206 opens the temperature adjustment valve 208 to open the waste heat recovery liquid circulation pipe 210, thereby enabling the waste heat recovery water from the heat treatment equipment 4 to circulate.

[0063] In S306, after S304 and S305 are executed, the process waits for a preset time period, which is set to a time period sufficient for the temperature of the waste heat recovery water, which has exceeded 95°C, to decrease.

[0064] In S307, the temperature controller 206 acquires again the temperature of the waste heat recovery water in the waste heat recovery liquid pipe 211 measured by the temperature sensor 205.

[0065] In S308, the temperature controller 206 determines whether the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds 95° C. If the temperature of the waste heat recovery water exceeds 95° C. in S308, the process proceeds to S310.

[0066] In S310, the temperature controller 206 outputs a serious malfunction signal.

[0067] In S311, the temperature controller 206 stops the operation of the circulation pump 207, the air compressor 1, and the waste heat recovery machine 2, which are installed in the waste heat recovery liquid piping 211, and ends the process.

[0068] On the other hand, if it is determined in S308 that the temperature of the waste heat recovery water does not exceed 95°C, the process proceeds to S309.

[0069] In S309, it is determined whether the temperature of the waste heat recovery water obtained in S307 is below 40° C. If the temperature of the waste heat recovery water is not below 40° C. in S309, the process returns to S306 and waits for a preset time.

[0070] On the other hand, if the temperature of the waste heat recovery water is below 40° C. in S309, the process proceeds to S312.

[0071] In S312, the temperature controller 206 switches the inlet-side three-way flow path switching valve 203 to send the waste heat recovery water from the heat treatment facility 4 to the waste heat recovery heat exchangers 201 and 202. At the same time, the temperature controller 206 switches the outlet-side three-way flow path switching valve 204 to send the waste heat recovery water from the waste heat recovery heat exchangers 201 and 202 to the heat treatment facility 4.

[0072] In S313 , the temperature controller 206 closes the temperature adjustment valve 208 to close the waste heat recovery liquid circulation pipe 210 .

[0073] In S314, the process waits in a normal state for a preset time, and then returns to S302.

[0074] FIG. 5 is a graph showing an example of the transition of the temperature of the waste heat recovery water in the waste heat recovery system 100 of this embodiment.

[0075] In FIG. 5, the vertical axis indicates the temperature of the waste heat recovery water measured by the temperature sensor 205, and the horizontal axis indicates the passage of time.

[0076] If the user does not use the heat treatment equipment 4 to exchange heat between the waste heat recovery water and cold water, the waste heat recovery water that has exchanged heat with compressed air in the waste heat recovery heat exchangers 201 and 202 is not cooled by the heat treatment equipment 4, and the temperature of the waste heat recovery water circulating through the waste heat recovery liquid piping 211 rises.

[0077] When the temperature of the waste heat recovery water exceeds 95° C., the temperature controller 206 performs the control shown in FIG. 4 to switch the flow path switching three-way valves 203 and 204 and open the temperature adjustment valve 208 .

[0078] As a result, the waste heat recovery water circulates through a circulation path that does not pass through the waste heat recovery heat exchangers 201 and 202 shown in Figure 3, thereby preventing the temperature of the waste heat recovery water from rising and preventing damage to the waste heat recovery heat exchangers.

[0079] Thereafter, when the temperature of the waste heat recovery water measured by the temperature sensor 205 falls below 40° C., the temperature controller 206 switches the flow path switching three-way valves 203 and 204 and closes the temperature adjustment valve 208 .

[0080] As a result, the waste heat recovery water circulates through a flow path that passes through the waste heat recovery heat exchangers 201 and 202 shown in Figure 2, and exchanges heat with the compressed air in the waste heat recovery heat exchangers 201 and 202, thereby recovering the waste heat of the air compressor 1.

[0081] Although the embodiments have been described above, 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 having all of the described configurations.

[0082] For example, in the embodiment, the waste heat recovery liquid pipe 211 is configured to connect from the heat treatment facility 4 to the heat treatment facility 4 via the intermediate stage waste heat recovery heat exchanger 201 and the discharge stage waste heat recovery heat exchanger 202, but is not limited to this. That is, a plurality of waste heat recovery liquid pipes 211 may be provided corresponding to a plurality of heat exchangers for waste heat recovery, and each of the plurality of waste heat recovery liquid pipes may be provided within the housing as a separate, independent path.

[0083] Here, the multiple heat exchangers for waste heat recovery may be a heat exchanger 201 for intermediate stage waste heat recovery and a heat exchanger 202 for discharge stage waste heat recovery. Alternatively, the multiple heat exchangers for waste heat recovery may be configured as multiple heat exchangers in which the heat exchanger 201 for intermediate stage waste heat recovery (or the heat exchanger 202 for discharge stage waste heat recovery) is connected in series.

[0084] With this configuration, it is possible to obtain and use waste heat recovery water at a plurality of different temperatures from each of the plurality of waste heat recovery liquid pipes, thereby making it possible to accommodate a plurality of facilities, etc., that require waste heat recovery water at different temperatures.

[0085] In addition, in the embodiment, the cooling liquid piping 106 is configured to branch from the cooling equipment 3 into a first cooling liquid piping 106a, a second cooling liquid piping 106b, and a third cooling liquid piping 106c, which then merge and connect to the cooling equipment 3, but this is not limited to this.

[0086] For example, a plurality of coolant pipes 106 may be provided corresponding to a plurality of heat exchangers for cooling, and each of the plurality of coolant pipes may be provided as a separate, independent path within the housing.

[0087] Here, the plurality of heat exchangers for cooling may be an intercooler 103 and an aftercooler 104. Alternatively, the plurality of heat exchangers for cooling may be configured as a plurality of heat exchangers in which the intercoolers 103 (or the aftercoolers 104) are connected in series.

[0088] In addition, in the embodiment, the flow paths of the waste heat recovery water and cooling water are controlled by the temperature sensor 205, the temperature controller 206, the flow path switching three-way valves 203 and 204, and the temperature control valve 208, but this is not limited to this and it is sufficient if the flow paths can be controlled based on the temperature of the waste heat recovery water.For example, it may be a self-powered automatic temperature control valve that does not use the temperature sensor 205 or the temperature controller 206 and does not require auxiliary power such as air pressure, water pressure, hydraulic pressure, or electricity.

[0089] In addition, although the air compressor 1 in the embodiment is specifically applicable to a screw compressor, the present invention is not limited to this. That is, although the embodiment uses screw rotors in the compressor bodies 101 and 102, the present invention is not limited to this, and various types of compression means may be used, such as turbo types such as centrifugal types and axial flow types, and positive displacement types such as scroll types, reciprocating types, and claw types.

[0090] Furthermore, although a single screw rotor is used in the embodiment, a twin or triple screw rotor may also be used.

[0091] In addition, in the embodiment, the compressor bodies 101 and 102 have two stages, but this is not limitative and the compressor bodies may have a single stage or three or more stages.

[0092] In the embodiment, the air compressor 1 is an oil-free screw compressor, but is not limited to this and may be a liquid-feed air compressor in which oil or water is injected into the compression working chamber. Also, although the gas to be compressed is described as air, it is not limited to this and may be nitrogen or the like.

[0093] Furthermore, the threshold value of the temperature of the waste heat recovery water used in the control of the embodiment is not limited to this.

[0094] In addition, in the embodiment, the cooling water whose temperature has risen is cooled by heat exchange with the atmosphere in the cooling equipment 3, but this is not limited to this, and it is also possible to recover and utilize the heat of the cooling water whose temperature has risen.

[0095] It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment.It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0096] 1: air compressor, 2: waste heat recovery machine, 3: cooling equipment, 4: heat treatment equipment, 100: waste heat recovery system, 101: first stage compressor body, 102: second stage compressor body, 103: cooling heat exchanger (intercooler), 104: cooling heat exchanger (aftercooler), 105: oil cooler, 106: cooling liquid piping, 107: vent piping, 108: air piping, 109: check valve, 110: cooling branch pipe on the coolant inlet side, 111: branch pipe on the coolant outlet side, 201: heat exchanger for intermediate stage waste heat recovery, 202: heat exchanger for discharge stage waste heat recovery, 203: inlet side flow path switching three-way valve, 204: outlet side flow path switching three-way valve, 205: temperature sensor, 206: temperature controller, 207: circulation pump, 208: temperature adjustment valve, 209: flow meter, 210: waste heat recovery liquid circulation pipe, 211: waste heat recovery liquid pipe

Claims

1. A waste heat recovery system comprising a fluid machine main body through which a fluid flows, and a waste heat recovery machine that recovers waste heat from the fluid, wherein the fluid machine main body comprises: a cooling heat exchanger that exchanges heat between a cooling liquid and the fluid, and a cooling liquid piping through which the cooling liquid flows; the waste heat recovery machine comprises: a waste heat recovery heat exchanger that exchanges heat between the waste heat recovery liquid and the fluid, a waste heat recovery liquid piping through which the waste heat recovery liquid flows, a first bypass flow path connecting the upstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the upstream of the cooling heat exchanger on the cooling liquid piping, a second bypass flow path connecting the downstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the downstream of the cooling heat exchanger on the cooling liquid piping, a first valve that opens and closes the first bypass flow path, a second valve that opens and closes the second bypass flow path, and a control unit that controls the first valve and the second valve, The control unit controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when the temperature of the waste heat recovery liquid exceeds a threshold value.

2. A waste heat recovery system as claimed in claim 1, further comprising a waste heat recovery liquid heat exchanger disposed downstream of said second valve and upstream of said first valve in said waste heat recovery liquid piping, for exchanging heat between said waste heat recovery liquid and a refrigerant.

3. A waste heat recovery system as claimed in claim 2, further comprising a coolant heat exchanger disposed downstream of a connection point of the coolant piping with the second bypass passage and upstream of a connection point of the coolant piping with the first bypass passage, for exchanging heat between the coolant and a refrigerant.

4. A waste heat recovery system as described in claim 2, wherein the control unit controls the first valve and the second valve to close the first bypass flow path and the second bypass flow path when the temperature of the waste heat recovery liquid falls below a second threshold value.

5. A waste heat recovery unit for recovering waste heat from a fluid discharged from a fluid machine body, the waste heat recovery unit comprising a cooling heat exchanger for exchanging heat between a cooling liquid and a fluid, and a cooling liquid piping through which the cooling liquid flows, the waste heat recovery unit comprising: a waste heat recovery heat exchanger for exchanging heat between the waste heat recovery liquid and the fluid, a waste heat recovery liquid piping through which the waste heat recovery liquid flows, a first bypass flow path connecting the upstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the upstream of the cooling heat exchanger on the cooling liquid piping, a second bypass flow path connecting the downstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the downstream of the cooling heat exchanger on the cooling liquid piping, a first valve for opening and closing the first bypass flow path, a second valve for opening and closing the second bypass flow path, and a control unit for controlling the first valve and the second valve, The control unit controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when the temperature of the waste heat recovery liquid exceeds a threshold value.

6. A waste heat recovery unit as claimed in claim 5, further comprising a waste heat recovery liquid heat exchanger disposed downstream of the second valve and upstream of the first valve in the waste heat recovery liquid piping, for exchanging heat between the waste heat recovery liquid and a refrigerant.

7. A waste heat recovery unit as claimed in claim 6, further comprising a coolant heat exchanger provided downstream of a connection point of the coolant piping with the second bypass flow path and upstream of a connection point of the coolant piping with the first bypass flow path, for exchanging heat between the coolant and a refrigerant.

8. A waste heat recovery unit as described in claim 6, wherein the control unit controls the first valve and the second valve to close the first bypass flow path and the second bypass flow path when the temperature of the waste heat recovery liquid falls below a second threshold value.

9. A waste heat recovery method for a waste heat recovery system including a fluid machine main body through which a fluid flows and a waste heat recovery machine that recovers waste heat from the fluid, wherein the fluid machine main body includes a cooling heat exchanger that exchanges heat between a cooling liquid and the fluid, and a cooling liquid piping through which the cooling liquid flows, and the waste heat recovery machine includes a waste heat recovery heat exchanger that exchanges heat between the waste heat recovery liquid and the fluid, a waste heat recovery liquid piping through which the waste heat recovery liquid flows, a first bypass flow path connecting the upstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the upstream of the cooling heat exchanger on the cooling liquid piping, a second bypass flow path connecting the downstream of the waste heat recovery heat exchanger on the waste heat recovery liquid piping to the downstream of the cooling heat exchanger on the cooling liquid piping, a first valve that opens and closes the first bypass flow path, and a second valve that opens and closes the second bypass flow path, A waste heat recovery method comprising the steps of: when a temperature of the waste heat recovery liquid exceeds a threshold value, controlling the first valve and the second valve to open the first bypass flow path and the second bypass flow path.

10. A waste heat recovery method as claimed in claim 9, further comprising a waste heat recovery liquid heat exchanger provided downstream of the second valve and upstream of the first valve in the waste heat recovery liquid piping, for exchanging heat between the waste heat recovery liquid and a refrigerant.

11. A waste heat recovery method according to claim 10, further comprising a heat exchanger provided downstream of a connection point of the cooling liquid piping with the second bypass flow path and upstream of a connection point of the cooling liquid piping with the first bypass flow path, for exchanging cooling liquid heat between the cooling liquid and a refrigerant.

12. A waste heat recovery method according to claim 10, wherein when the temperature of the waste heat recovery liquid falls below a second threshold value, the first valve and the second valve are controlled to close the first bypass flow path and the second bypass flow path.

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