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

Abstract

A technique capable of preventing damage to a waste-heat-recovery heat exchanger is provided. An air compressor includes cooling heat exchangers that exchange heat between cooling water and compressed air, and a cooling-liquid pipe through which the cooling water flows. A waste heat recovery device includes waste-heat-recovery heat exchangers that exchange heat between waste-heat-recovery water and the compressed air, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery water flows, branch pipes that connect the cooling-liquid pipe and the waste-heat-recovery-liquid pipe, flow-path switching three-way valves that open and close the branch pipes, and a temperature controller that controls the flow-path switching three-way valves. When a temperature of the waste-heat-recovery water exceeds a threshold, the temperature controller controls the flow-path switching three-way valves to open the branch pipes.

Description

TECHNICAL FIELD

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

[0002] A gas compressor that sucks in a gas such as air and discharges a high-pressure gas such as compressed air by using a compression mechanism is known. In particular, an air compressor is used as an air source for a machine tool, a press machine, an air blow, or the like in a factory line or a work site. It is said that, among energy consumed in an entire factory, total energy consumed by a gas compressor corresponds to 20% to 25%, and therefore, an effect of recovering waste heat from a gas compressor is large. In particular, in order to achieve a reduction target of CO 2 emissions originating from a global warming issue, utilization of waste heat from a gas compressor may be regarded as increasingly important in the future.

[0003] A gas compressor includes a compressor main body that compresses a gas such as air, a cooling system that absorbs heat generated by compression, and a motor or the like that serves as a driving power source of the gas compressor. Further, in a gas compressor, when motor input power is set to 100%, an amount of heat absorbed by the cooling system corresponds to 90% or more thereof, and the amount of heat is usually released to outside air, so that a very large amount of energy is discharged into the atmosphere. In order to reduce a waste heat amount, improvement in efficiency of the compressor main body and the motor has been promoted; however, an effect thereof may be limited to several percent, and therefore, effective utilization of waste heat from a gas compressor is demanded.

[0004] Patent Document 1 exists as a conventional technology in this technical field. Patent Document 1 describes a waste heat recovery system including a temperature sensor disposed downstream of a waste-heat-recovery heat exchanger in a waste-heat-recovery-liquid pipe, a temperature control valve, and a temperature controller that controls an opening degree of the temperature control valve in accordance with a temperature of waste-heat-recovery water measured by the temperature sensor and a set recovery-water temperature.CITATION LISTPATENT DOCUMENT

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-96043SUMMARY OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In the technology described in Patent Document 1, waste-heat-recovery water flowing through a heat exchanger is cooled by being supplied to a waste-heat utilization side and used as a heat source. However, when a user does not use the waste-heat-recovery water as a heat source, the waste-heat-recovery water may return to the heat exchanger without being cooled, and therefore, a temperature of the waste-heat-recovery water may further increase. Since a temperature of compressed air may reach a maximum of approximately 170°C, when the temperature of the waste-heat-recovery water exceeds a boiling point, an internal pressure of piping of the heat exchanger increases, and the heat exchanger may be damaged.

[0007] Accordingly, an object of the present invention is to provide a technology capable of preventing damage to a heat exchanger for waste heat recovery.SOLUTIONS TO PROBLEMS

[0008] In order to solve the above-described problems, one representative waste heat recovery system of the present invention is a waste heat recovery system including a fluid machine main body through which a fluid flows, and a waste heat recovery device that recovers waste heat from the fluid. The fluid machine main body includes 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. The waste heat recovery device includes a waste-heat-recovery heat exchanger that exchanges heat between a waste-heat-recovery liquid and the fluid, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery liquid flows, a first bypass flow path that connects an upstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and an upstream side of the cooling heat exchanger in the cooling-liquid pipe, a second bypass flow path that connects a downstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and a downstream side of the cooling heat exchanger in the cooling-liquid pipe, 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 controller that controls the first valve and the second valve. The controller controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when a temperature of the waste-heat-recovery liquid exceeds a threshold.EFFECTS OF THE INVENTION

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

[0010] Other problems, configurations, and effects than those described above will be made apparent by the following description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a schematic diagram illustrating an example of an overall configuration of a waste heat recovery system according to the present embodiment. Fig. 2 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water in a normal state in the waste heat recovery system according to the present embodiment. Fig. 3 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water when a temperature of the waste-heat-recovery water exceeds a threshold in the waste heat recovery system according to the present embodiment. Fig. 4 is a flowchart illustrating an example of control performed by a temperature controller in the waste heat recovery system according to the present embodiment. Fig. 5 is a graph illustrating an example of a transition of a temperature of waste-heat-recovery water in the waste heat recovery system according to the present embodiment. MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a water-cooled packaged two-stage oil-free screw compressor that compresses air is described as an example of a gas compressor.

[0013] Fig. 1 is a schematic diagram illustrating an example of an overall configuration of the waste heat recovery system according to the present embodiment.

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

[0015] The air compressor 1 includes compressor main bodies 101 and 102, cooling heat exchangers 103 and 104, and an oil cooler 105, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the compressor main bodies 101 and 102 and other components are installed, and a box-shaped cover composed of a plurality of panels made of metal or the like that are installed on the base so as to cover the compressor main bodies 101 and 102 and other components, and the housing has excellent soundproof performance.

[0016] The waste heat recovery device 2 includes heat exchangers 201 and 202 and a temperature controller 206, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the heat exchangers 201 and 202 and other components are installed, and a box-shaped cover composed of a plurality of panels made of metal or the like that are installed on the base so as to cover the heat exchangers 201 and 202 and other components, and the housing has excellent soundproof performance.

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

[0018] The compressor main body 101 is a first-stage compressor main body disposed on an upstream side in an air flow, and the compressor main body 102 is a second-stage compressor main body disposed on a downstream side in the air flow with respect to the first-stage compressor main body 101.

[0019] Since the compressor main bodies 101 and 102 in the present embodiment are oil-free screw compressors, unlike a liquid-injection-type air compressor that injects a liquid such as oil or water into a compression working chamber, the compressor main bodies 101 and 102 tend to generate a large amount of heat due to heat generated during air compression. Further, since air after compression is at a high temperature, the compressed air may be unsuitable for use by a demand side of compressed air. Therefore, in the air compressor 1, cooling water is supplied to various portions. Further, as will be described later, the air compressor 1 of the present embodiment is configured to be capable of recovering waste heat generated when the compressor main bodies 101 and 102 compress air.

[0020] The waste-heat-recovery heat exchangers 201 and 202 perform heat exchange between waste-heat-recovery water, which is a waste-heat-recovery liquid sent from a heat treatment facility 4 on a utilization side of waste heat generated by the compressor main bodies 101 and 102, and compressed air discharged from the compressor main bodies 101 and 102.

[0021] The heat exchanger 201 is an intermediate-stage waste-heat-recovery heat exchanger disposed between the first-stage compressor main body 101 and the second-stage compressor main body 102, and the heat exchanger 202 is a discharge-stage waste-heat-recovery heat exchanger disposed on a discharge side (downstream side) of the second-stage compressor main body 102.

[0022] The heat treatment facility 4 cools waste-heat-recovery water by exchanging heat between the waste-heat-recovery water and cold water, and converts the cold water into hot water to be used by a user. However, the heat treatment facility 4 is not limited thereto, and the waste-heat-recovery water may exchange heat with oil or air, or the user may directly use the waste-heat-recovery water itself.

[0023] The cooling heat exchangers 103 and 104 perform heat exchange between cooling water, which is a cooling liquid sent from the cooling facility 3 provided outside the air compressor 1, and compressed air discharged from the compressor main bodies 101 and 102.

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

[0025] The cooling facility 3 cools cooling water by exchanging heat with outside air or the like outside the waste heat recovery system 100.

[0026] Between the first-stage compressor main body 101 and the second-stage compressor main body 102, an intermediate-stage waste-heat-recovery heat exchanger 201 and an intercooler 103 are disposed in this order from an upstream side. Further, on a discharge side of the second-stage compressor main body 102, a discharge-stage waste-heat-recovery heat exchanger 202 and an aftercooler 104 are disposed in this order from the upstream side. Depending on circumstances, a configuration in which an arrangement order of the waste-heat-recovery heat exchangers 201 and 202 and the intercooler 103 and the aftercooler 104 is reversed may also be adopted.

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

[0028] The above-described flow path is used during a load operation. During an unload operation (no-load operation), blow-off air flows through the first-stage compressor main body 101, the intermediate-stage waste-heat-recovery heat exchanger 201, the intercooler 103, the second-stage compressor main body 102, and the discharge-stage waste-heat-recovery heat exchanger 202, and thereafter, a check valve 109 is fully closed due to the unload operation, so that the blow-off air is discharged to the atmosphere from a blow-off pipe 107. Accordingly, even during the no-load operation, the blow-off air flows through the heat exchangers 201 and 202, and therefore, waste heat may be recovered regardless of an operating state, and a waste heat recovery rate may be improved.

[0029] Further, a waste-heat-recovery-liquid pipe 211 through which waste-heat-recovery water that exchanges heat with compressed air in the waste-heat-recovery heat exchangers 201 and 202 flows, and a cooling-liquid pipe 106 through which cooling water that exchanges heat with compressed air in the intercooler 103 and the aftercooler 104 flows are provided.

[0030] The waste-heat-recovery-liquid pipe 211 is supplied from the heat treatment facility 4 on a utilization side of waste heat by operation of a circulation pump 207, passes through the intermediate-stage waste-heat-recovery heat exchanger 201 and the discharge-stage waste-heat-recovery heat exchanger 202, and is connected to the heat treatment facility 4.

[0031] Further, a temperature sensor 205 that measures a temperature of waste-heat-recovery water, and a flow meter 209 that measures a flow rate of the waste-heat-recovery water are provided downstream of the heat treatment facility 4 in the waste-heat-recovery-liquid pipe 211.

[0032] The cooling-liquid pipe 106 is configured to branch from the cooling facility 3 into a first cooling-liquid pipe 106a, a second cooling-liquid pipe 106b, and a third cooling-liquid pipe 106c, and thereafter, the branched pipes merge and are connected to the cooling facility 3.

[0033] The first cooling-liquid pipe 106a is connected from the cooling facility 3 to the cooling facility 3 via the aftercooler 104. The second cooling-liquid pipe 106b is connected from the cooling facility 3 to the cooling facility 3 via the oil cooler 105, a cooling jacket provided in a casing of the second-stage compressor main body 102, and a cooling jacket provided in a casing of the first-stage compressor main body 101. The third cooling-liquid pipe 106c is connected from the cooling facility 3 to the cooling facility 3 via the intercooler 103.

[0034] An upstream side of the intercooler 103, the aftercooler 104, and the oil cooler 105 in the cooling-liquid pipe 106 is connected to an upstream side of the intermediate-stage waste-heat-recovery heat exchanger 201 in the waste-heat-recovery-liquid pipe 211 by a cooling-liquid inlet-side branch pipe 110.

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

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

[0037] At a connection point between the waste-heat-recovery-liquid pipe 211 and the cooling-liquid outlet-side branch pipe 111, an outlet-side flow-path switching three-way valve 204 that switches between a flow path toward a downstream side of the waste-heat-recovery-liquid pipe 211 and a flow path toward the cooling-liquid outlet-side branch pipe 111 is provided.

[0038] An upstream side of the inlet-side flow-path switching three-way valve 203 in the waste-heat-recovery-liquid pipe 211 and a downstream side of the outlet-side flow-path switching three-way valve 204 in the waste-heat-recovery-liquid pipe 211 are connected by a waste-heat-recovery-liquid circulation pipe 210, and a temperature control valve 208 that opens and closes the waste-heat-recovery-liquid circulation pipe 210 is provided.

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

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

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

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

[0043] Next, air cooled by the intercooler 103 (for example, approximately 40 ° C) is compressed by the second-stage compressor main body 102 in order to further increase pressure. Thereafter, compressed high-temperature air (for example, approximately 160 °C or higher) again exchanges a required amount of heat in the discharge-stage waste-heat-recovery heat exchanger 202, and is further cooled by the aftercooler 104. The air cooled by the aftercooler 104 (for example, approximately 40 °C) is then supplied to a demand side of compressed air.

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

[0045] Fig. 2 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water in a normal state in the waste heat recovery system 100 according to the present embodiment.

[0046] As indicated by a broken line, the waste-heat-recovery water flows in from the heat treatment facility 4 on a utilization side of waste heat by operation of the circulation pump 207, flows through the waste-heat-recovery-liquid pipe 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 facility 4 on the utilization side of waste heat.

[0047] As indicated by a dotted line, the cooling water flows in from the cooling facility 3, flows through the cooling-liquid pipe 106, branches into the first cooling-liquid pipe 106a, the second cooling-liquid pipe 106b, and the third cooling-liquid pipe 106c, 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 thereafter merges and flows out toward the cooling facility 3.

[0048] Here, when a user does not cause the heat treatment facility 4 to exchange heat between 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 in the heat treatment facility 4. Therefore, a temperature of the waste-heat-recovery water circulating in the waste-heat-recovery-liquid pipe 211 increases. When the temperature of the waste-heat-recovery water exceeds a boiling point, an internal pressure of the waste-heat-recovery-liquid pipe 211 increases, and the waste-heat-recovery heat exchangers 201 and 202 may be damaged.

[0049] Accordingly, in the present embodiment, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds a preset threshold, the temperature controller 206 switches the flow-path switching three-way valves 203 and 204 and opens the temperature control valve 208, thereby switching flow paths of the waste-heat-recovery water and the cooling water.

[0050] Fig. 3 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water when the temperature of the waste-heat-recovery water exceeds the threshold in the waste heat recovery system 100 according to the present embodiment.

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

[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 third cooling-liquid pipe 106c 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 thereafter merges and flows out toward the cooling facility 3.

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

[0054] Further, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds the threshold, the temperature controller 206 opens the temperature control valve 208. Accordingly, as indicated by a broken line, the waste-heat-recovery water flows in from the heat treatment facility 4 on a utilization side of waste heat, flows through the waste-heat-recovery-liquid pipe 211, passes through the waste-heat-recovery-liquid circulation pipe 210, and flows out toward the heat treatment facility 4 on the utilization side of waste heat without passing through the waste-heat-recovery heat exchangers 201 and 202.

[0055] According to the present embodiment, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds the threshold, the temperature controller 206 switches the flow-path switching three-way valves 203 and 204 and uses cooling water from the cooling facility 3 for heat exchange with compressed air in the waste-heat-recovery heat exchangers 201 and 202. Accordingly, an increase in the temperature of the waste-heat-recovery water may be prevented, and damage to the waste-heat-recovery heat exchangers may be prevented.

[0056] Fig. 4 is a flowchart illustrating an example of control performed by the temperature controller 206 in the waste heat recovery system 100 according to the present embodiment.

[0057] In Fig. 4, at a start of processing, the waste-heat-recovery water and the cooling water are assumed to flow through the normal flow paths illustrated in Fig. 2.

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

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

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

[0061] In step S304, the temperature controller 206 switches the inlet-side flow-path switching three-way valve 203 to allow cooling liquid in the cooling-liquid pipe 106 to flow into the waste-heat-recovery-liquid pipe 211 via the cooling-liquid inlet-side branch pipe 110. At the same time, the temperature controller 206 switches the outlet-side flow-path switching three-way valve 204 to allow the cooling liquid 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 cooling-liquid outlet-side branch pipe 111.

[0062] In step S305, the temperature controller 206 opens the temperature control valve 208, thereby opening the waste-heat-recovery-liquid circulation pipe 210 and enabling circulation of waste-heat-recovery water from the heat treatment facility 4.

[0063] In step S306, after executing steps S304 and S305, the temperature controller 206 waits for a preset time. The waiting time is set to be sufficient for the temperature of the waste-heat-recovery water exceeding 95 °C to decrease.

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

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

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

[0067] In step S311, the temperature controller 206 stops operation of the circulation pump 207 installed in the waste-heat-recovery-liquid pipe 211, the air compressor 1, and the waste heat recovery device 2, and ends the process.

[0068] On the other hand, when the temperature of the waste-heat-recovery water does not exceed 95 °C in step S308, the process proceeds to step S309.

[0069] In step S309, the temperature controller 206 determines whether the temperature of the waste-heat-recovery water acquired in step S307 is lower than 40 °C. When the temperature of the waste-heat-recovery water is not lower than 40 °C in step S309, the process returns to step S306 and waits for a preset time.

[0070] On the other hand, when the temperature of the waste-heat-recovery water is lower than 40 °C in step S309, the process proceeds to step S312.

[0071] In step S312, the temperature controller 206 switches the inlet-side flow-path switching three-way 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 flow-path switching three-way 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 step S313, the temperature controller 206 closes the temperature control valve 208, thereby closing the waste-heat-recovery-liquid circulation pipe 210.

[0073] In step S314, the temperature controller 206 waits in a normal state for a preset time, and then returns to step S302.

[0074] Fig. 5 is a graph illustrating an example of a transition of the temperature of the waste-heat-recovery water in the waste heat recovery system 100 according to the present embodiment.

[0075] In Fig. 5, a vertical axis indicates the temperature of the waste-heat-recovery water measured by the temperature sensor 205, and a horizontal axis indicates an elapsed time.

[0076] When a user does not cause the heat treatment facility 4 to exchange heat between 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 in the heat treatment facility 4. Therefore, a temperature of the waste-heat-recovery water circulating in the waste-heat-recovery-liquid pipe 211 increases.

[0077] When the temperature of the waste-heat-recovery water exceeds 95 °C, the temperature controller 206 performs the control illustrated in Fig. 4, thereby switching the flow-path switching three-way valves 203 and 204 and opening the temperature control valve 208.

[0078] Accordingly, the waste-heat-recovery water circulates through a flow path that does not pass through the waste-heat-recovery heat exchangers 201 and 202 illustrated in Fig. 3. Therefore, an increase in the temperature of the waste-heat-recovery water may be prevented, and damage to the waste-heat-recovery heat exchangers may be prevented.

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

[0080] Accordingly, the waste-heat-recovery water circulates through a flow path that passes through the waste-heat-recovery heat exchangers 201 and 202 illustrated in Fig. 2. Therefore, heat exchange between compressed air and the waste-heat-recovery heat exchangers 201 and 202 is performed, and waste heat of the air compressor 1 may be recovered.

[0081] Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications are included therein. For example, the above-described embodiment has been described in detail in order to facilitate understanding of the present invention, and the present invention is not necessarily limited to an embodiment including all the components described above.

[0082] For example, in the embodiment, the waste-heat-recovery-liquid pipe 211 is configured to be connected 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. However, the configuration is not limited thereto. That is, a plurality of waste-heat-recovery-liquid pipes 211 corresponding to a plurality of waste-heat-recovery heat exchangers may be provided, and each of the plurality of waste-heat-recovery-liquid pipes may be provided as a separate and independent path in the housing.

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

[0084] According to such a configuration, waste-heat-recovery water at a plurality of different temperatures may be obtained and utilized from each of the plurality of waste-heat-recovery-liquid pipes. Accordingly, it becomes possible to accommodate a plurality of facilities or the like that require waste-heat-recovery water at different temperatures.

[0085] Further, in the embodiment, the cooling-liquid pipe 106 is configured to branch from the cooling facility 3 into the first cooling-liquid pipe 106a, the second cooling-liquid pipe 106b, and the third cooling-liquid pipe 106c, and thereafter, the branched pipes merge and are connected to the cooling facility 3. However, the configuration is not limited thereto.

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

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

[0088] Further, in the embodiment, flow paths of the waste-heat-recovery water and the 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. However, the configuration is not limited thereto, as long as the flow paths may be controlled in accordance with the temperature of the waste-heat-recovery water. For example, instead of using the temperature sensor 205 and the temperature controller 206, a self-actuated automatic temperature control valve that does not require auxiliary power such as air pressure, water pressure, hydraulic pressure, or electricity may be used.

[0089] Further, in the embodiment, the air compressor 1 is specifically applicable to a screw compressor. However, the present invention is not limited thereto. That is, in the embodiment, screw rotors are used in the compressor main bodies 101 and 102, but the compressor main bodies are not limited thereto, and various types of compression means such as turbo-type compression means including centrifugal-type and axial-flow-type compression means, and positive-displacement-type compression means including scroll-type, reciprocating-type, and claw-type compression means may be used.

[0090] Further, in the embodiment, a single-screw-type rotor is used, but a twin-screw-type rotor or a triple-screw-type rotor may be used.

[0091] Further, in the embodiment, the number of stages of the compressor main bodies 101 and 102 is two. However, the number of stages is not limited thereto, and may be a single stage or three or more stages.

[0092] Further, in the embodiment, the air compressor 1 is an oil-free screw compressor. However, the air compressor 1 is not limited thereto, and may be a liquid-injection-type air compressor that injects oil or water into a compression working chamber. Further, although the gas to be compressed has been described as air, the gas is not limited thereto, and may be nitrogen or the like.

[0093] Further, the threshold of the temperature of the waste-heat-recovery water used in the control of the embodiment is not limited thereto.

[0094] Further, in the embodiment, cooling water whose temperature has increased is configured to be cooled by exchanging heat with outside air in the cooling facility 3. However, the configuration is not limited thereto, and heat of the cooling water whose temperature has increased may be recovered and utilized.

[0095] Further, a part of a configuration of one embodiment may be replaced with a configuration of another embodiment, and a configuration of another embodiment may be added to a configuration of one embodiment. Further, for each embodiment, addition, deletion, or replacement of another configuration may be performed with respect to a part of the configuration.REFERENCE SIGNS LIST

[0096] 1: air compressor, 2: waste heat recovery device, 3: cooling facility, 4: heat treatment facility, 100: waste heat recovery system, 101: first-stage compressor main body, 102: second-stage compressor main body, 103: cooling heat exchanger (intercooler), 104: cooling heat exchanger (aftercooler), 105: oil cooler, 106: cooling-liquid pipe, 107: blow-off pipe, 108: air pipe, 109: check valve, 110: cooling-liquid inlet-side branch pipe, 111: cooling-liquid outlet-side branch pipe, 201: intermediate-stage waste-heat-recovery heat exchanger, 202: discharge-stage waste-heat-recovery heat exchanger, 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 control valve, 209: flow meter, 210: waste-heat-recovery-liquid circulation pipe, 211: waste-heat-recovery-liquid pipe.

Examples

Embodiment Construction

[0012]Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a water-cooled packaged two-stage oil-free screw compressor that compresses air is described as an example of a gas compressor.

[0013]Fig. 1 is a schematic diagram illustrating an example of an overall configuration of the waste heat recovery system according to the present embodiment.

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

[0015]The air compressor 1 includes compressor main bodies 101 and 102, cooling heat exchangers 103 and 104, and an oil cooler 105, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the compressor main bodies 101 and 102 and other components are installed, and a box-shaped cover compos...

TECHNICAL FIELD

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

[0002] A gas compressor that sucks in a gas such as air and discharges a high-pressure gas such as compressed air by using a compression mechanism is known. In particular, an air compressor is used as an air source for a machine tool, a press machine, an air blow, or the like in a factory line or a work site. It is said that, among energy consumed in an entire factory, total energy consumed by a gas compressor corresponds to 20% to 25%, and therefore, an effect of recovering waste heat from a gas compressor is large. In particular, in order to achieve a reduction target of CO 2 emissions originating from a global warming issue, utilization of waste heat from a gas compressor may be regarded as increasingly important in the future.

[0003] A gas compressor includes a compressor main body that compresses a gas such as air, a cooling system that absorbs heat generated by compression, and a motor or the like that serves as a driving power source of the gas compressor. Further, in a gas compressor, when motor input power is set to 100%, an amount of heat absorbed by the cooling system corresponds to 90% or more thereof, and the amount of heat is usually released to outside air, so that a very large amount of energy is discharged into the atmosphere. In order to reduce a waste heat amount, improvement in efficiency of the compressor main body and the motor has been promoted; however, an effect thereof may be limited to several percent, and therefore, effective utilization of waste heat from a gas compressor is demanded.

[0004] Patent Document 1 exists as a conventional technology in this technical field. Patent Document 1 describes a waste heat recovery system including a temperature sensor disposed downstream of a waste-heat-recovery heat exchanger in a waste-heat-recovery-liquid pipe, a temperature control valve, and a temperature controller that controls an opening degree of the temperature control valve in accordance with a temperature of waste-heat-recovery water measured by the temperature sensor and a set recovery-water temperature.CITATION LISTPATENT DOCUMENT

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-96043SUMMARY OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In the technology described in Patent Document 1, waste-heat-recovery water flowing through a heat exchanger is cooled by being supplied to a waste-heat utilization side and used as a heat source. However, when a user does not use the waste-heat-recovery water as a heat source, the waste-heat-recovery water may return to the heat exchanger without being cooled, and therefore, a temperature of the waste-heat-recovery water may further increase. Since a temperature of compressed air may reach a maximum of approximately 170°C, when the temperature of the waste-heat-recovery water exceeds a boiling point, an internal pressure of piping of the heat exchanger increases, and the heat exchanger may be damaged.

[0007] Accordingly, an object of the present invention is to provide a technology capable of preventing damage to a heat exchanger for waste heat recovery.SOLUTIONS TO PROBLEMS

[0008] In order to solve the above-described problems, one representative waste heat recovery system of the present invention is a waste heat recovery system including a fluid machine main body through which a fluid flows, and a waste heat recovery device that recovers waste heat from the fluid. The fluid machine main body includes 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. The waste heat recovery device includes a waste-heat-recovery heat exchanger that exchanges heat between a waste-heat-recovery liquid and the fluid, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery liquid flows, a first bypass flow path that connects an upstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and an upstream side of the cooling heat exchanger in the cooling-liquid pipe, a second bypass flow path that connects a downstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and a downstream side of the cooling heat exchanger in the cooling-liquid pipe, 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 controller that controls the first valve and the second valve. The controller controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when a temperature of the waste-heat-recovery liquid exceeds a threshold.EFFECTS OF THE INVENTION

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

[0010] Other problems, configurations, and effects than those described above will be made apparent by the following description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a schematic diagram illustrating an example of an overall configuration of a waste heat recovery system according to the present embodiment. Fig. 2 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water in a normal state in the waste heat recovery system according to the present embodiment. Fig. 3 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water when a temperature of the waste-heat-recovery water exceeds a threshold in the waste heat recovery system according to the present embodiment. Fig. 4 is a flowchart illustrating an example of control performed by a temperature controller in the waste heat recovery system according to the present embodiment. Fig. 5 is a graph illustrating an example of a transition of a temperature of waste-heat-recovery water in the waste heat recovery system according to the present embodiment. MODE FOR CARRYING OUT THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a water-cooled packaged two-stage oil-free screw compressor that compresses air is described as an example of a gas compressor.

[0013] Fig. 1 is a schematic diagram illustrating an example of an overall configuration of the waste heat recovery system according to the present embodiment.

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

[0015] The air compressor 1 includes compressor main bodies 101 and 102, cooling heat exchangers 103 and 104, and an oil cooler 105, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the compressor main bodies 101 and 102 and other components are installed, and a box-shaped cover composed of a plurality of panels made of metal or the like that are installed on the base so as to cover the compressor main bodies 101 and 102 and other components, and the housing has excellent soundproof performance.

[0016] The waste heat recovery device 2 includes heat exchangers 201 and 202 and a temperature controller 206, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the heat exchangers 201 and 202 and other components are installed, and a box-shaped cover composed of a plurality of panels made of metal or the like that are installed on the base so as to cover the heat exchangers 201 and 202 and other components, and the housing has excellent soundproof performance.

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

[0018] The compressor main body 101 is a first-stage compressor main body disposed on an upstream side in an air flow, and the compressor main body 102 is a second-stage compressor main body disposed on a downstream side in the air flow with respect to the first-stage compressor main body 101.

[0019] Since the compressor main bodies 101 and 102 in the present embodiment are oil-free screw compressors, unlike a liquid-injection-type air compressor that injects a liquid such as oil or water into a compression working chamber, the compressor main bodies 101 and 102 tend to generate a large amount of heat due to heat generated during air compression. Further, since air after compression is at a high temperature, the compressed air may be unsuitable for use by a demand side of compressed air. Therefore, in the air compressor 1, cooling water is supplied to various portions. Further, as will be described later, the air compressor 1 of the present embodiment is configured to be capable of recovering waste heat generated when the compressor main bodies 101 and 102 compress air.

[0020] The waste-heat-recovery heat exchangers 201 and 202 perform heat exchange between waste-heat-recovery water, which is a waste-heat-recovery liquid sent from a heat treatment facility 4 on a utilization side of waste heat generated by the compressor main bodies 101 and 102, and compressed air discharged from the compressor main bodies 101 and 102.

[0021] The heat exchanger 201 is an intermediate-stage waste-heat-recovery heat exchanger disposed between the first-stage compressor main body 101 and the second-stage compressor main body 102, and the heat exchanger 202 is a discharge-stage waste-heat-recovery heat exchanger disposed on a discharge side (downstream side) of the second-stage compressor main body 102.

[0022] The heat treatment facility 4 cools waste-heat-recovery water by exchanging heat between the waste-heat-recovery water and cold water, and converts the cold water into hot water to be used by a user. However, the heat treatment facility 4 is not limited thereto, and the waste-heat-recovery water may exchange heat with oil or air, or the user may directly use the waste-heat-recovery water itself.

[0023] The cooling heat exchangers 103 and 104 perform heat exchange between cooling water, which is a cooling liquid sent from the cooling facility 3 provided outside the air compressor 1, and compressed air discharged from the compressor main bodies 101 and 102.

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

[0025] The cooling facility 3 cools cooling water by exchanging heat with outside air or the like outside the waste heat recovery system 100.

[0026] Between the first-stage compressor main body 101 and the second-stage compressor main body 102, an intermediate-stage waste-heat-recovery heat exchanger 201 and an intercooler 103 are disposed in this order from an upstream side. Further, on a discharge side of the second-stage compressor main body 102, a discharge-stage waste-heat-recovery heat exchanger 202 and an aftercooler 104 are disposed in this order from the upstream side. Depending on circumstances, a configuration in which an arrangement order of the waste-heat-recovery heat exchangers 201 and 202 and the intercooler 103 and the aftercooler 104 is reversed may also be adopted.

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

[0028] The above-described flow path is used during a load operation. During an unload operation (no-load operation), blow-off air flows through the first-stage compressor main body 101, the intermediate-stage waste-heat-recovery heat exchanger 201, the intercooler 103, the second-stage compressor main body 102, and the discharge-stage waste-heat-recovery heat exchanger 202, and thereafter, a check valve 109 is fully closed due to the unload operation, so that the blow-off air is discharged to the atmosphere from a blow-off pipe 107. Accordingly, even during the no-load operation, the blow-off air flows through the heat exchangers 201 and 202, and therefore, waste heat may be recovered regardless of an operating state, and a waste heat recovery rate may be improved.

[0029] Further, a waste-heat-recovery-liquid pipe 211 through which waste-heat-recovery water that exchanges heat with compressed air in the waste-heat-recovery heat exchangers 201 and 202 flows, and a cooling-liquid pipe 106 through which cooling water that exchanges heat with compressed air in the intercooler 103 and the aftercooler 104 flows are provided.

[0030] The waste-heat-recovery-liquid pipe 211 is supplied from the heat treatment facility 4 on a utilization side of waste heat by operation of a circulation pump 207, passes through the intermediate-stage waste-heat-recovery heat exchanger 201 and the discharge-stage waste-heat-recovery heat exchanger 202, and is connected to the heat treatment facility 4.

[0031] Further, a temperature sensor 205 that measures a temperature of waste-heat-recovery water, and a flow meter 209 that measures a flow rate of the waste-heat-recovery water are provided downstream of the heat treatment facility 4 in the waste-heat-recovery-liquid pipe 211.

[0032] The cooling-liquid pipe 106 is configured to branch from the cooling facility 3 into a first cooling-liquid pipe 106a, a second cooling-liquid pipe 106b, and a third cooling-liquid pipe 106c, and thereafter, the branched pipes merge and are connected to the cooling facility 3.

[0033] The first cooling-liquid pipe 106a is connected from the cooling facility 3 to the cooling facility 3 via the aftercooler 104. The second cooling-liquid pipe 106b is connected from the cooling facility 3 to the cooling facility 3 via the oil cooler 105, a cooling jacket provided in a casing of the second-stage compressor main body 102, and a cooling jacket provided in a casing of the first-stage compressor main body 101. The third cooling-liquid pipe 106c is connected from the cooling facility 3 to the cooling facility 3 via the intercooler 103.

[0034] An upstream side of the intercooler 103, the aftercooler 104, and the oil cooler 105 in the cooling-liquid pipe 106 is connected to an upstream side of the intermediate-stage waste-heat-recovery heat exchanger 201 in the waste-heat-recovery-liquid pipe 211 by a cooling-liquid inlet-side branch pipe 110.

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

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

[0037] At a connection point between the waste-heat-recovery-liquid pipe 211 and the cooling-liquid outlet-side branch pipe 111, an outlet-side flow-path switching three-way valve 204 that switches between a flow path toward a downstream side of the waste-heat-recovery-liquid pipe 211 and a flow path toward the cooling-liquid outlet-side branch pipe 111 is provided.

[0038] An upstream side of the inlet-side flow-path switching three-way valve 203 in the waste-heat-recovery-liquid pipe 211 and a downstream side of the outlet-side flow-path switching three-way valve 204 in the waste-heat-recovery-liquid pipe 211 are connected by a waste-heat-recovery-liquid circulation pipe 210, and a temperature control valve 208 that opens and closes the waste-heat-recovery-liquid circulation pipe 210 is provided.

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

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

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

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

[0043] Next, air cooled by the intercooler 103 (for example, approximately 40 ° C) is compressed by the second-stage compressor main body 102 in order to further increase pressure. Thereafter, compressed high-temperature air (for example, approximately 160 °C or higher) again exchanges a required amount of heat in the discharge-stage waste-heat-recovery heat exchanger 202, and is further cooled by the aftercooler 104. The air cooled by the aftercooler 104 (for example, approximately 40 °C) is then supplied to a demand side of compressed air.

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

[0045] Fig. 2 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water in a normal state in the waste heat recovery system 100 according to the present embodiment.

[0046] As indicated by a broken line, the waste-heat-recovery water flows in from the heat treatment facility 4 on a utilization side of waste heat by operation of the circulation pump 207, flows through the waste-heat-recovery-liquid pipe 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 facility 4 on the utilization side of waste heat.

[0047] As indicated by a dotted line, the cooling water flows in from the cooling facility 3, flows through the cooling-liquid pipe 106, branches into the first cooling-liquid pipe 106a, the second cooling-liquid pipe 106b, and the third cooling-liquid pipe 106c, 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 thereafter merges and flows out toward the cooling facility 3.

[0048] Here, when a user does not cause the heat treatment facility 4 to exchange heat between 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 in the heat treatment facility 4. Therefore, a temperature of the waste-heat-recovery water circulating in the waste-heat-recovery-liquid pipe 211 increases. When the temperature of the waste-heat-recovery water exceeds a boiling point, an internal pressure of the waste-heat-recovery-liquid pipe 211 increases, and the waste-heat-recovery heat exchangers 201 and 202 may be damaged.

[0049] Accordingly, in the present embodiment, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds a preset threshold, the temperature controller 206 switches the flow-path switching three-way valves 203 and 204 and opens the temperature control valve 208, thereby switching flow paths of the waste-heat-recovery water and the cooling water.

[0050] Fig. 3 is a diagram illustrating an example of flow paths of waste-heat-recovery water and cooling water when the temperature of the waste-heat-recovery water exceeds the threshold in the waste heat recovery system 100 according to the present embodiment.

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

[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 third cooling-liquid pipe 106c 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 thereafter merges and flows out toward the cooling facility 3.

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

[0054] Further, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds the threshold, the temperature controller 206 opens the temperature control valve 208. Accordingly, as indicated by a broken line, the waste-heat-recovery water flows in from the heat treatment facility 4 on a utilization side of waste heat, flows through the waste-heat-recovery-liquid pipe 211, passes through the waste-heat-recovery-liquid circulation pipe 210, and flows out toward the heat treatment facility 4 on the utilization side of waste heat without passing through the waste-heat-recovery heat exchangers 201 and 202.

[0055] According to the present embodiment, when the temperature of the waste-heat-recovery water measured by the temperature sensor 205 exceeds the threshold, the temperature controller 206 switches the flow-path switching three-way valves 203 and 204 and uses cooling water from the cooling facility 3 for heat exchange with compressed air in the waste-heat-recovery heat exchangers 201 and 202. Accordingly, an increase in the temperature of the waste-heat-recovery water may be prevented, and damage to the waste-heat-recovery heat exchangers may be prevented.

[0056] Fig. 4 is a flowchart illustrating an example of control performed by the temperature controller 206 in the waste heat recovery system 100 according to the present embodiment.

[0057] In Fig. 4, at a start of processing, the waste-heat-recovery water and the cooling water are assumed to flow through the normal flow paths illustrated in Fig. 2.

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

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

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

[0061] In step S304, the temperature controller 206 switches the inlet-side flow-path switching three-way valve 203 to allow cooling liquid in the cooling-liquid pipe 106 to flow into the waste-heat-recovery-liquid pipe 211 via the cooling-liquid inlet-side branch pipe 110. At the same time, the temperature controller 206 switches the outlet-side flow-path switching three-way valve 204 to allow the cooling liquid 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 cooling-liquid outlet-side branch pipe 111.

[0062] In step S305, the temperature controller 206 opens the temperature control valve 208, thereby opening the waste-heat-recovery-liquid circulation pipe 210 and enabling circulation of waste-heat-recovery water from the heat treatment facility 4.

[0063] In step S306, after executing steps S304 and S305, the temperature controller 206 waits for a preset time. The waiting time is set to be sufficient for the temperature of the waste-heat-recovery water exceeding 95 °C to decrease.

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

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

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

[0067] In step S311, the temperature controller 206 stops operation of the circulation pump 207 installed in the waste-heat-recovery-liquid pipe 211, the air compressor 1, and the waste heat recovery device 2, and ends the process.

[0068] On the other hand, when the temperature of the waste-heat-recovery water does not exceed 95 °C in step S308, the process proceeds to step S309.

[0069] In step S309, the temperature controller 206 determines whether the temperature of the waste-heat-recovery water acquired in step S307 is lower than 40 °C. When the temperature of the waste-heat-recovery water is not lower than 40 °C in step S309, the process returns to step S306 and waits for a preset time.

[0070] On the other hand, when the temperature of the waste-heat-recovery water is lower than 40 °C in step S309, the process proceeds to step S312.

[0071] In step S312, the temperature controller 206 switches the inlet-side flow-path switching three-way 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 flow-path switching three-way 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 step S313, the temperature controller 206 closes the temperature control valve 208, thereby closing the waste-heat-recovery-liquid circulation pipe 210.

[0073] In step S314, the temperature controller 206 waits in a normal state for a preset time, and then returns to step S302.

[0074] Fig. 5 is a graph illustrating an example of a transition of the temperature of the waste-heat-recovery water in the waste heat recovery system 100 according to the present embodiment.

[0075] In Fig. 5, a vertical axis indicates the temperature of the waste-heat-recovery water measured by the temperature sensor 205, and a horizontal axis indicates an elapsed time.

[0076] When a user does not cause the heat treatment facility 4 to exchange heat between 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 in the heat treatment facility 4. Therefore, a temperature of the waste-heat-recovery water circulating in the waste-heat-recovery-liquid pipe 211 increases.

[0077] When the temperature of the waste-heat-recovery water exceeds 95 °C, the temperature controller 206 performs the control illustrated in Fig. 4, thereby switching the flow-path switching three-way valves 203 and 204 and opening the temperature control valve 208.

[0078] Accordingly, the waste-heat-recovery water circulates through a flow path that does not pass through the waste-heat-recovery heat exchangers 201 and 202 illustrated in Fig. 3. Therefore, an increase in the temperature of the waste-heat-recovery water may be prevented, and damage to the waste-heat-recovery heat exchangers may be prevented.

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

[0080] Accordingly, the waste-heat-recovery water circulates through a flow path that passes through the waste-heat-recovery heat exchangers 201 and 202 illustrated in Fig. 2. Therefore, heat exchange between compressed air and the waste-heat-recovery heat exchangers 201 and 202 is performed, and waste heat of the air compressor 1 may be recovered.

[0081] Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications are included therein. For example, the above-described embodiment has been described in detail in order to facilitate understanding of the present invention, and the present invention is not necessarily limited to an embodiment including all the components described above.

[0082] For example, in the embodiment, the waste-heat-recovery-liquid pipe 211 is configured to be connected 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. However, the configuration is not limited thereto. That is, a plurality of waste-heat-recovery-liquid pipes 211 corresponding to a plurality of waste-heat-recovery heat exchangers may be provided, and each of the plurality of waste-heat-recovery-liquid pipes may be provided as a separate and independent path in the housing.

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

[0084] According to such a configuration, waste-heat-recovery water at a plurality of different temperatures may be obtained and utilized from each of the plurality of waste-heat-recovery-liquid pipes. Accordingly, it becomes possible to accommodate a plurality of facilities or the like that require waste-heat-recovery water at different temperatures.

[0085] Further, in the embodiment, the cooling-liquid pipe 106 is configured to branch from the cooling facility 3 into the first cooling-liquid pipe 106a, the second cooling-liquid pipe 106b, and the third cooling-liquid pipe 106c, and thereafter, the branched pipes merge and are connected to the cooling facility 3. However, the configuration is not limited thereto.

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

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

[0088] Further, in the embodiment, flow paths of the waste-heat-recovery water and the 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. However, the configuration is not limited thereto, as long as the flow paths may be controlled in accordance with the temperature of the waste-heat-recovery water. For example, instead of using the temperature sensor 205 and the temperature controller 206, a self-actuated automatic temperature control valve that does not require auxiliary power such as air pressure, water pressure, hydraulic pressure, or electricity may be used.

[0089] Further, in the embodiment, the air compressor 1 is specifically applicable to a screw compressor. However, the present invention is not limited thereto. That is, in the embodiment, screw rotors are used in the compressor main bodies 101 and 102, but the compressor main bodies are not limited thereto, and various types of compression means such as turbo-type compression means including centrifugal-type and axial-flow-type compression means, and positive-displacement-type compression means including scroll-type, reciprocating-type, and claw-type compression means may be used.

[0090] Further, in the embodiment, a single-screw-type rotor is used, but a twin-screw-type rotor or a triple-screw-type rotor may be used.

[0091] Further, in the embodiment, the number of stages of the compressor main bodies 101 and 102 is two. However, the number of stages is not limited thereto, and may be a single stage or three or more stages.

[0092] Further, in the embodiment, the air compressor 1 is an oil-free screw compressor. However, the air compressor 1 is not limited thereto, and may be a liquid-injection-type air compressor that injects oil or water into a compression working chamber. Further, although the gas to be compressed has been described as air, the gas is not limited thereto, and may be nitrogen or the like.

[0093] Further, the threshold of the temperature of the waste-heat-recovery water used in the control of the embodiment is not limited thereto.

[0094] Further, in the embodiment, cooling water whose temperature has increased is configured to be cooled by exchanging heat with outside air in the cooling facility 3. However, the configuration is not limited thereto, and heat of the cooling water whose temperature has increased may be recovered and utilized.

[0095] Further, a part of a configuration of one embodiment may be replaced with a configuration of another embodiment, and a configuration of another embodiment may be added to a configuration of one embodiment. Further, for each embodiment, addition, deletion, or replacement of another configuration may be performed with respect to a part of the configuration.REFERENCE SIGNS LIST

[0096] 1: air compressor, 2: waste heat recovery device, 3: cooling facility, 4: heat treatment facility, 100: waste heat recovery system, 101: first-stage compressor main body, 102: second-stage compressor main body, 103: cooling heat exchanger (intercooler), 104: cooling heat exchanger (aftercooler), 105: oil cooler, 106: cooling-liquid pipe, 107: blow-off pipe, 108: air pipe, 109: check valve, 110: cooling-liquid inlet-side branch pipe, 111: cooling-liquid outlet-side branch pipe, 201: intermediate-stage waste-heat-recovery heat exchanger, 202: discharge-stage waste-heat-recovery heat exchanger, 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 control valve, 209: flow meter, 210: waste-heat-recovery-liquid circulation pipe, 211: waste-heat-recovery-liquid pipe.

Examples

Embodiment Construction

[0012]Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a water-cooled packaged two-stage oil-free screw compressor that compresses air is described as an example of a gas compressor.

[0013]Fig. 1 is a schematic diagram illustrating an example of an overall configuration of the waste heat recovery system according to the present embodiment.

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

[0015]The air compressor 1 includes compressor main bodies 101 and 102, cooling heat exchangers 103 and 104, and an oil cooler 105, and these components are disposed in a housing. Although not illustrated, the housing includes a base on which the compressor main bodies 101 and 102 and other components are installed, and a box-shaped cover compos...

Claims

1. A waste heat recovery system comprising a fluid machine main body through which a fluid flows, and a waste heat recovery device 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 device comprises a waste-heat-recovery heat exchanger that exchanges heat between a waste-heat-recovery liquid and the fluid, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery liquid flows, a first bypass flow path that connects an upstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and an upstream side of the cooling heat exchanger in the cooling-liquid pipe, a second bypass flow path that connects a downstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and a downstream side of the cooling heat exchanger in the cooling-liquid pipe, 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 controller that controls the first valve and the second valve, and wherein the controller controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when a temperature of the waste-heat-recovery liquid exceeds a threshold.

2. The waste heat recovery system according to Claim 1, further comprising: a waste-heat-recovery-liquid heat exchanger that exchanges heat between the waste-heat-recovery liquid and a refrigerant, wherein the waste-heat-recovery-liquid heat exchanger is provided downstream of the second valve and upstream of the first valve in the waste-heat-recovery-liquid pipe.

3. The waste heat recovery system according to Claim 2, further comprising: a cooling-liquid heat exchanger that exchanges heat between the cooling liquid and a refrigerant, wherein the cooling-liquid heat exchanger is provided downstream of a connection point of the cooling-liquid pipe with the second bypass flow path and upstream of a connection point of the cooling-liquid pipe with the first bypass flow path.

4. The waste heat recovery system according to Claim 2, wherein the controller 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 becomes lower than a second threshold.

5. A waste heat recovery unit for recovering waste heat from the fluid discharged from a fluid machine main body comprising a cooling heat exchanger that exchanges heat between a cooling liquid and a fluid, and a cooling-liquid pipe through which the cooling liquid flows, the waste heat recovery unit comprising a waste-heat-recovery heat exchanger that exchanges heat between a waste-heat-recovery liquid and the fluid, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery liquid flows, a first bypass flow path that connects an upstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and an upstream side of the cooling heat exchanger in the cooling-liquid pipe, a second bypass flow path that connects a downstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and a downstream side of the cooling heat exchanger in the cooling-liquid pipe, 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 controller that controls the first valve and the second valve, wherein the controller controls the first valve and the second valve to open the first bypass flow path and the second bypass flow path when a temperature of the waste-heat-recovery liquid exceeds a threshold.

6. The waste heat recovery unit according to Claim 5, further comprising: a waste-heat-recovery-liquid heat exchanger that exchanges heat between the waste-heat-recovery liquid and a refrigerant, wherein the waste-heat-recovery-liquid heat exchanger is provided downstream of the second valve and upstream of the first valve in the waste-heat-recovery-liquid pipe.

7. The waste heat recovery unit according to Claim 6, further comprising: a cooling-liquid heat exchanger that exchanges heat between the cooling liquid and the refrigerant, wherein the cooling-liquid heat exchanger is provided downstream of a connection point of the cooling-liquid pipe with the second bypass flow path and upstream of a connection point of the cooling-liquid pipe with the first bypass flow path.

8. The waste heat recovery unit according to Claim 6, wherein the controller 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 becomes lower than a second threshold.

9. A waste heat recovery method for a waste heat recovery system comprising a fluid machine main body through which a fluid flows and a waste heat recovery device 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 device comprises a waste-heat-recovery heat exchanger that exchanges heat between a waste-heat-recovery liquid and the fluid, a waste-heat-recovery-liquid pipe through which the waste-heat-recovery liquid flows, a first bypass flow path that connects an upstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and an upstream side of the cooling heat exchanger in the cooling-liquid pipe, a second bypass flow path that connects a downstream side of the waste-heat-recovery heat exchanger in the waste-heat-recovery-liquid pipe and a downstream side of the cooling heat exchanger in the cooling-liquid pipe, 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, the waste heat recovery method comprising controlling the first valve and the second valve to open the first bypass flow path and the second bypass flow path when a temperature of the waste-heat-recovery liquid exceeds a threshold.

10. The waste heat recovery method according to Claim 9, wherein the waste-heat-recovery liquid exchanges heat with a refrigerant by using a waste-heat-recovery-liquid heat exchanger that is provided downstream of the second valve and upstream of the first valve in the waste-heat-recovery-liquid pipe.

11. The waste heat recovery method according to Claim 10, wherein the cooling liquid exchanges heat with the refrigerant by using a cooling-liquid heat exchanger provided downstream of a connection point of the cooling-liquid pipe with the second bypass flow path and upstream of a connection point of the cooling-liquid pipe with the first bypass flow path.

12. The waste heat recovery method according to Claim 10, wherein the first valve and the second valve are controlled to close the first bypass flow path and the second bypass flow path when the temperature of the waste-heat-recovery liquid becomes lower than a second threshold.

Images