Waste Heat Recovery System, Waste Heat Recovery Unit, and Waste Heat Recovery Method

Abstract

A technique is provided that can prevent damage to a waste heat recovery heat exchanger. An air compressor includes cooling heat exchangers that perform heat exchange between cooling water and compressed air, and a cooling liquid pipe through which the cooling water flows. A waste heat recovery unit includes waste heat recovery heat exchangers that perform heat exchange between waste heat recovery water and compressed air, a waste heat recovery liquid pipe through which the waste heat recovery water flows, a waste heat recovery liquid inlet pipe and a waste heat recovery liquid outlet pipe that connect an auxiliary cooling facility and the waste heat recovery liquid pipe, flow path switching three-way valves that open and close the inlet and outlet pipes, and a temperature controller that controls the valves. When the temperature of the waste heat recovery water exceeds a threshold, the temperature controller opens the inlet and outlet pipes by controlling the three-way valves.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention

[0001] The present invention relates to a waste heat recovery system, a waste heat recovery unit, and a waste heat recovery method.2. Description of the Related Art

[0002] Gas compressors, which draw in air or other gases and discharge high-pressure gas such as compressed air using a compression mechanism, are known. In particular, air compressors are used as air sources for machine tools, press machines, air blowers, and the like in factory lines and worksites. It is said that among the total energy consumed in a factory, approximately 20-25% is consumed by gas compressors, and thus recovering waste heat from such compressors can have a significant impact. Especially in view of the need to reduce CO2 emissions due to global warming concerns, the utilization of waste heat from gas compressors is expected to become increasingly important.

[0003] A gas compressor includes a compressor body that compresses air or other gases, a cooling system that absorbs heat generated during compression, and a motor that serves as the drive source of the compressor. When assuming 100% motor input power, over 90% of that energy is absorbed as heat by the cooling system. This heat is typically released into the atmosphere, resulting in a significant energy loss. Although efforts are being made to increase the efficiency of compressor bodies and motors to reduce waste heat, their impact is limited to a few percent. Therefore, effective utilization of waste heat from gas compressors is in demand.

[0004] As prior art in this technical field, Japanese Laid-Open Patent Publication No. 2021-96043 discloses a waste heat recovery system comprising a temperature sensor installed 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 the opening angle of the temperature control valve based on the temperature of the waste heat recovery water measured by the sensor and a predetermined target temperature.

[0005] In the technique disclosed in Japanese Laid-Open Patent Publication No. 2021-96043, the waste heat recovery water flowing through the heat exchanger is cooled by being supplied to the utilization side and used as a heat source. However, if the customer does not use the waste heat recovery water as a heat source, and the water returns to the heat exchanger without being cooled, the temperature of the waste heat recovery water further increases. Since the temperature of the compressed air can reach up to approximately 170° C., if the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the heat exchanger piping rises, which may cause damage to the heat exchanger.

[0006] Accordingly, the present invention is directed to providing a technique capable of preventing damage to the heat exchanger used for waste heat recovery.SUMMARY OF THE INVENTION

[0007] To solve the above problem, a representative embodiment of the waste heat recovery system of the present invention includes a fluid machine body through which a fluid flows, and a waste heat recovery unit that recovers waste heat from the fluid.

[0008] The fluid machine body comprises:

[0009] a cooling heat exchanger that exchanges heat between a cooling liquid and the fluid; and

[0010] a cooling liquid pipe through which the cooling liquid flows.

[0011] The waste heat recovery unit comprises:

[0012] a waste heat recovery heat exchanger that exchanges heat between a waste heat recovery liquid and the fluid;

[0013] a waste heat recovery liquid pipe through which the waste heat recovery liquid flows;

[0014] a first bypass flow path that connects the upstream side of the waste heat recovery heat exchanger in the waste heat recovery liquid pipe to the outlet side of an auxiliary cooling device that is not connected to the cooling liquid pipe of the fluid machine body;

[0015] a second bypass flow path that connects the downstream side of the waste heat recovery heat exchanger in the waste heat recovery liquid pipe to the inlet side of the auxiliary cooling device;

[0016] a first valve that opens and closes the first bypass flow path;

[0017] a second valve that opens and closes the second bypass flow path; and

[0018] a control unit that controls the first and second valves.

[0019] The control unit opens the first and second bypass flow paths by controlling the first and second valves when the temperature of the waste heat recovery liquid exceeds a threshold.

[0020] According to the present invention, damage to the waste heat recovery heat exchanger can be prevented.

[0021] Other problems to be solved, configurations, and effects not mentioned above will become apparent from the following description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic diagram showing an example of the overall configuration of a waste heat recovery system according to a first embodiment.

[0023] FIG. 2 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water under normal operation in the waste heat recovery system of the first embodiment.

[0024] FIG. 3 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water when the temperature of the waste heat recovery water exceeds a threshold in the waste heat recovery system of the first embodiment.

[0025] FIG. 4 is a flowchart showing an example of control performed by a temperature controller in the waste heat recovery system of the first embodiment.

[0026] FIG. 5 is a graph showing an example of temperature transitions of the waste heat recovery water in the waste heat recovery system of the first embodiment.

[0027] FIG. 6 is a schematic diagram showing an example of the overall configuration of a waste heat recovery system according to a second embodiment.

[0028] FIG. 7 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water under normal operation in the waste heat recovery system of the second embodiment.

[0029] FIG. 8 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water when the temperature of the waste heat recovery water exceeds a threshold in the waste heat recovery system of the second embodiment.

[0030] FIG. 9 is a schematic diagram showing a variation of the overall configuration of the waste heat recovery system in the second embodiment.

[0031] FIG. 10 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water under normal operation in the variation of the second embodiment.

[0032] FIG. 11 is a diagram showing an example of the flow paths of waste heat recovery water and cooling water when the temperature of the waste heat recovery water exceeds a threshold in the variation of the second embodiment.

[0033] FIG. 12 is a flowchart showing an example of control performed by a temperature controller in the waste heat recovery system of the second embodiment.DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment 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.

[0035] FIG. 1 is a schematic diagram showing an example of the overall configuration of a waste heat recovery system according to a first embodiment.

[0036] As shown in FIG. 1, the waste heat recovery system 100 includes an air compressor 1 that compresses air, and a waste heat recovery unit 2 that recovers waste heat from the compressed air discharged from the air compressor 1.

[0037] The air compressor 1 includes compressor bodies 101 and 102, cooling heat exchangers 103 and 104 for cooling, and an oil cooler 105. These components are housed within an enclosure. Although not shown in the drawings, the enclosure includes a base on which the compressor bodies 101 and 102 and other components are installed, and a box-shaped cover composed of multiple panels made of metal or the like, which are placed on the base so as to cover the compressor bodies 101 and 102 and other components. The enclosure provides excellent sound insulation performance.

[0038] The waste heat recovery unit 2 includes heat exchangers 201 and 202, and a temperature controller 206. These components are housed within an enclosure. Although not shown in the drawings, the enclosure includes a base on which the heat exchangers 201 and 202 and other components are installed, and a box-shaped cover composed of multiple panels made of metal or the like, which are placed on the base so as to cover the heat exchangers 201 and 202 and other components. The enclosure provides excellent sound insulation performance.

[0039] Each of the compressor bodies 101 and 102 includes a screw rotor composed of one male rotor and one female rotor (not shown). The compressor bodies 101 and 102 are configured to be driven by a main electric motor (not shown) arranged within the enclosure, for example via a power transmission mechanism. Note that the power source for the compressor bodies 101 and 102 is not limited to an electric motor and may instead be an internal combustion engine or the like.

[0040] The compressor body 101 is a first-stage compressor body disposed on the upstream side of the airflow, and the compressor body 102 is a second-stage compressor body disposed downstream of the first-stage compressor body 101 in the direction of the airflow.

[0041] Since the compressor bodies 101 and 102 in the present embodiment are oil-free screw compressors, they tend to generate a significant amount of heat during air compression, unlike liquid-injection type air compressors in which a liquid such as oil or water is injected into the compression chamber. Furthermore, because the compressed air becomes high in temperature, it may not be suitable for use by the end user of the compressed air. Therefore, in the air compressor 1, cooling water is supplied to various components. Additionally, as will be described later, the air compressor 1 in this embodiment is configured to allow recovery of the waste heat generated when the compressor bodies 101 and 102 compress air.

[0042] The waste heat recovery heat exchangers 201 and 202 perform heat exchange between waste heat recovery water, which serves as a waste heat recovery liquid and is supplied from a heat treatment facility 4 on the utilization side, and compressed air discharged from the compressor bodies 101 and 102.

[0043] The heat exchanger 201 is an intermediate-stage waste heat recovery heat exchanger disposed between the first-stage compressor body 101 and the second-stage compressor body 102, and the heat exchanger202 is a discharge-stage waste heat recovery heat exchanger disposed on the discharge side (downstream side) of the second-stage compressor body 102.

[0044] The heat treatment facility 4 cools the waste heat recovery water by exchanging heat with cold water, thereby converting the cold water into hot water that can be used by the user. However, this is not limited thereto; the waste heat recovery water may alternatively exchange heat with oil or air, or the user may directly use the waste heat recovery water itself.

[0045] The cooling heat exchangers 103 and 104 perform heat exchange between cooling water, which serves as a cooling liquid and is supplied from a cooling facility 3 provided outside the air compressor 1, and compressed air discharged from the compressor bodies 101 and 102.

[0046] The heat exchanger 103 (hereinafter referred to as the intercooler) is a cooling heat exchanger disposed between the first-stage compressor body 101 and the second-stage compressor body 102. The heat exchanger 104 (hereinafter referred to as the aftercooler) is a cooling heat exchanger disposed on the discharge side of the second-stage compressor body 102.

[0047] The cooling facility 3 cools the cooling water by exchanging heat with the outside air or other external environment of the waste heat recovery system 100.

[0048] Between the first-stage compressor body 101 and the second-stage compressor body 102, the intermediate-stage waste heat recovery heat exchanger 201 and the intercooler 103 are arranged in this order from upstream to downstream. On the discharge side of the second-stage compressor body 102, the discharge-stage waste heat recovery heat exchanger 202 and the aftercooler 104 are arranged in this order from upstream to downstream. In some cases, the arrangement order between the waste heat recovery heat exchangers 201 and 202, and the intercooler 103 and aftercooler 104 may be reversed.

[0049] The first-stage compressor body 101, the intermediate-stage waste heat recovery heat exchanger 201, the intercooler 103, the second-stage compressor body 102, the discharge-stage waste heat recovery heat exchanger 202, and the aftercooler 104 are connected by an air pipe 108 through which the air to be compressed flows.

[0050] The above-described flow path corresponds to the loaded operation (operation under load). During unloaded operation (operation without load), the blow-off air flows through the first-stage compressor body 101, the intermediate-stage waste heat recovery heat exchanger 201, the intercooler 103, the second-stage compressor body 102, and the discharge-stage waste heat recovery heat exchanger 202. Then, due to the check valve 109 being fully closed by the unloaded operation, the blow-off air is discharged to the atmosphere through a blow-off pipe 107. Because the blow-off air flows through the heat exchangers 201 and 202 even during unloaded operation, waste heat recovery can be performed regardless of the operating state, thereby improving the waste heat recovery rate.

[0051] A waste heat recovery liquid pipe 211, through which waste heat recovery water flows to exchange heat with compressed air in the waste heat recovery heat exchangers 201 and 202, and a cooling liquid pipe 106, through which cooling water flows to exchange heat with compressed air in the intercooler 103 and the aftercooler 104, are also provided.

[0052] The waste heat recovery liquid pipe 211 is supplied with waste heat recovery water from a heat treatment facility 4 on the utilization side 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 back to the heat treatment facility 4.

[0053] A temperature sensor 205 that measures the temperature of the waste heat recovery water and a flow meter 209 that measures the 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.

[0054] The cooling liquid pipe 106 branches 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 is configured such that these pipes merge and connect back to the cooling facility 3.

[0055] The first cooling liquid pipe 106a connects the cooling facility 3 to the aftercooler 104 and then back to the cooling facility 3. The second cooling liquid pipe 106b connects the cooling facility 3 to the oil cooler 105, then through the cooling jacket provided in the casing of the second-stage compressor body 102 and the cooling jacket provided in the casing of the first-stage compressor body 101, and then back to the cooling facility 3. The third cooling liquid pipe 106c connects the cooling facility 3 to the intercooler 103 and then back to the cooling facility 3.

[0056] The upstream sides of the intercooler 103, aftercooler 104, and oil cooler 105 in the cooling liquid pipe 106 are connected to the upstream side of the intermediate-stage waste heat recovery heat exchanger 201 in the waste heat recovery liquid pipe 211 via a branch pipe 110 on the cooling liquid inlet side.

[0057] The downstream side of the discharge-stage waste heat recovery heat exchanger 202 in the waste heat recovery liquid pipe 211 is connected to the downstream sides of the intercooler 103, aftercooler 104, and oil cooler 105 in the cooling liquid pipe 106 via a branch pipe 111 on the cooling liquid outlet side.

[0058] 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 three-way flow switching valve 203 is provided to switch between the flow path from the upstream side of the waste heat recovery liquid pipe 211 and the flow path from the branch pipe 110 on the cooling liquid inlet side.

[0059] At the connection point between the waste heat recovery liquid pipe 211 and the branch pipe 111 on the cooling liquid outlet side, an outlet-side three-way flow switching valve 204 is provided to switch between the flow path toward the downstream side of the waste heat recovery liquid pipe 211 and the flow path toward the branch pipe 111 on the cooling liquid outlet side.

[0060] The upstream side of the inlet-side three-way flow switching valve 203 and the downstream side of the outlet-side three-way flow switching 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 is provided to open and close the circulation pipe 210.

[0061] The temperature controller 206 controls the flow switching three-way valves 203 and 204 and the temperature control valve 208 based on the temperature measured by the temperature sensor 205 and a preset temperature.

[0062] Although not shown in the drawings, the oil cooler 105 is a water-cooled heat exchanger that cools lubricating oil used to lubricate the bearing portions of the compressor bodies 101 and 102, as well as the power transmission mechanism and other components. The lubricating oil cooled by the oil cooler 105 lubricates the bearing portions and other parts of the compressor bodies 101 and 102, and is then stored in an oil reservoir (not shown). Thereafter, the lubricating oil is delivered to the oil cooler 105 by a delivery mechanism such as an oil pump (not shown), where it is cooled and circulates through this lubrication path.

[0063] Next, the operation of the waste heat recovery system 100 configured as described above will be explained.

[0064] In FIG. 1, the air compressor 1 draws in air through a capacity control valve (not shown) disposed upstream of the first-stage compressor body 101 and compresses the air in the first-stage compressor body 101. The compressed high-temperature air (for example, approximately 160° C.) then undergoes heat exchange in the intermediate-stage waste heat recovery heat exchanger 201 and is further cooled in the intercooler 103. In the intermediate-stage waste heat recovery heat exchanger 201, heat exchange occurs between the high-temperature compressed air and the waste heat recovery water. In the intercooler 103, heat exchange occurs between the compressed air, which was cooled in the intermediate-stage waste heat recovery heat exchanger 201, and the cooling water.

[0065] Next, the air cooled in the intercooler 103 (for example, to approximately 40° C.) is further compressed by the second-stage compressor body 102 to increase the pressure. The resulting high-temperature compressed air (for example, approximately 160° C. or even higher) then undergoes additional heat exchange in the discharge-stage waste heat recovery heat exchanger 202 and is subsequently cooled in the aftercooler 104. The air cooled in the aftercooler 104 (for example, to approximately 40° C.) is then supplied to the consumer of the compressed air.

[0066] Next, the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 will be explained.

[0067] FIG. 2 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water during normal operation in the waste heat recovery system 100 according to the first embodiment.

[0068] As indicated by the dashed line, the waste heat recovery water flows in from the heat treatment facility 4 on the utilization side 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 the 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.

[0069] As indicated by the dotted line, the cooling water flows in from the cooling facility 3, branches from the cooling liquid pipe 106 into the first cooling liquid pipe 106a, the second cooling liquid pipe 106b, and the third cooling liquid pipe 106c, and flows through them. It exchanges heat with the compressed air in the intercooler 103 and the aftercooler 104, or with the lubricating oil in the oil cooler 105, then merges and flows out toward the cooling facility 3.

[0070] Here, if the user does not use the heat treatment facility 4 to perform heat exchange between the waste heat recovery water and the cold water, the waste heat recovery water that has exchanged heat with the compressed air in the waste heat recovery heat exchangers 201 and 202 will not be cooled in the heat treatment facility 4. As a result, the temperature of the waste heat recovery water circulating through the waste heat recovery liquid pipe 211 increases. If the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the waste heat recovery liquid pipe 211 increases, which may cause damage to the waste heat recovery heat exchangers 201 and 202.

[0071] Therefore, 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 switching three-way valves 203 and 204 and opens the temperature control valve 208, thereby switching the flow paths of the waste heat recovery water and the cooling water.

[0072] FIG. 3 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 according to the first embodiment, in a case where the temperature of the waste heat recovery water exceeds the threshold.

[0073] 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 switching three-way valves 203 and 204. As a result, as indicated by the dotted line, the 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 branch pipe 110 on the cooling liquid inlet side.

[0074] The cooling water that has flowed 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 the compressed air in the intercooler 103 and the aftercooler 104, or with the lubricating oil in the oil cooler 105, then merges and flows out toward the cooling facility 3.

[0075] The cooling water that has flowed 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 the compressed air in the waste heat recovery heat exchangers 201 and 202, then passes through the branch pipe 111 on the cooling liquid outlet side, merges into the cooling liquid pipe 106, and flows out toward the cooling facility 3.

[0076] In addition, 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. As a result, as indicated by the dashed line, the waste heat recovery water flows in from the heat treatment facility 4 on the utilization side, flows through the waste heat recovery liquid pipe 211, flows through the waste heat recovery liquid circulation pipe 210, bypassing the waste heat recovery heat exchangers 201 and 202, and flows out toward the heat treatment facility 4 on the utilization side.

[0077] 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 switching three-way valves 203 and 204, so that the cooling water from the cooling facility 3 is used for heat exchange with the compressed air in the waste heat recovery heat exchangers 201 and 202. This prevents the temperature of the waste heat recovery water from rising and makes it possible to prevent damage to the waste heat recovery heat exchangers.

[0078] FIG. 4 is a flowchart illustrating an example of the control performed by the temperature controller 206 in the waste heat recovery system 100 according to the first embodiment.

[0079] In FIG. 4, at the start of the process, it is assumed that the waste heat recovery water and the cooling water are flowing through the flow paths under normal operation shown in FIG. 2.

[0080] When the air compressor 1 starts operating, power is supplied to the temperature controller 206, and control is initiated.

[0081] In step S302, the temperature controller 206 acquires the temperature of the waste heat recovery water in the waste heat recovery liquid pipe 211, as measured by the temperature sensor 205.

[0082] 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. If the temperature exceeds 95° C. in step S303, the process proceeds to step S304. On the other hand, if the temperature does not exceed 95° C. in step S303, the process proceeds to step S314, where it waits in the normal state for a predetermined period of time before returning to step S302.

[0083] In step S304, the temperature controller 206 switches the inlet-side flow switching three-way valve 203 to direct the cooling liquid from the cooling liquid pipe 106 into the waste heat recovery liquid pipe 211 via the branch pipe 110 on the cooling liquid inlet side. At the same time, the temperature controller 206 switches the outlet-side flow switching three-way valve 204 to direct the cooling liquid, having passed through the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202, into the branch pipe 111 on the cooling liquid outlet side.

[0084] In step S305, the temperature controller 206 opens the temperature control valve 208 to open the waste heat recovery liquid circulation pipe 210, thereby enabling the circulation of the waste heat recovery water from the heat treatment facility 4.

[0085] In step S306, after executing steps S304 and S305, the process waits for a predetermined period of time.

[0086] The waiting time is set to a duration sufficient for the temperature of the waste heat recovery water, which has exceeded 95° C., to decrease.

[0087] 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, as measured by the temperature sensor 205.

[0088] 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. If the temperature exceeds 95° C. in step S308, the process proceeds to step S310.

[0089] In step S310, the temperature controller 206 outputs a critical failure signal.

[0090] In step S311, the temperature controller 206 stops the operation of the circulation pump 207 installed in the waste heat recovery liquid pipe 211, the air compressor 1, and the waste heat recovery unit 2, and terminates the process.

[0091] On the other hand, if the temperature of the waste heat recovery water does not exceed 95° C. in step S308, the process proceeds to step S309.

[0092] In step S309, it is determined whether the temperature of the waste heat recovery water acquired in step S307 is below 40° C. If the temperature is not below 40° C. in step S309, the process returns to step S306 and waits for a predetermined period of time.

[0093] On the other hand, if the temperature of the waste heat recovery water is below 40° C. in step S309, the process proceeds to step S312.

[0094] In step S312, the temperature controller 206 switches the inlet-side flow 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 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.

[0095] In step S313, the temperature controller 206 closes the temperature control valve 208 to shut off the waste heat recovery liquid circulation pipe 210.

[0096] In step S314, the process waits in the normal state for a predetermined period of time and then returns to step S302.

[0097] FIG. 5 is a graph showing an example of the temperature variation of the waste heat recovery water in the waste heat recovery system 100 according to the first embodiment.

[0098] 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 elapsed time.

[0099] If the user does not use the heat treatment facility 4 to perform heat exchange between the waste heat recovery water and the cooling water, the waste heat recovery water that has exchanged heat with the compressed air in the waste heat recovery heat exchangers 201 and 202 is not cooled by the heat treatment facility 4, and therefore the temperature of the waste heat recovery water circulating through the waste heat recovery liquid pipe 211 increases.

[0100] 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 switching three-way valves 203 and 204 and to open the temperature control valve 208.

[0101] As a result, the waste heat recovery water circulates through a flow path that bypasses the waste heat recovery heat exchangers 201 and 202, as shown in FIG. 3. This prevents the temperature of the waste heat recovery water from rising and protects the waste heat recovery heat exchangers from damage.

[0102] 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 switching three-way valves 203 and 204 and closes the temperature control valve 208.

[0103] As a result, the waste heat recovery water circulates through the flow path that passes through the waste heat recovery heat exchangers 201 and 202, as shown in FIG. 2. Accordingly, the waste heat recovery water exchanges heat with the compressed air in the heat exchangers 201 and 202, making it possible to recover waste heat from the air compressor 1.

[0104] While 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 explained in detail to facilitate understanding of the invention and are not necessarily limited to including all of the described components.

[0105] For example, in the embodiment, the waste heat recovery liquid pipe 211 is configured to connect the heat treatment facility 4 to the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202, and then back to the heat treatment facility 4. However, the configuration is not limited to this. That is, multiple waste heat recovery liquid pipes may be provided corresponding to multiple waste heat recovery heat exchangers, and each of the waste heat recovery liquid pipes may be independently installed as a separate flow path within the casing.

[0106] Here, the multiple waste heat recovery heat exchangers may include the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202. Alternatively, the multiple waste heat recovery heat exchangers may be configured as a plurality of heat exchangers connected in series, which serve as the intermediate-stage waste heat recovery heat exchanger 201 (or the discharge-stage waste heat recovery heat exchanger 202).

[0107] According to such a configuration, it is possible to obtain and use waste heat recovery water having different temperatures from each of the plurality of waste heat recovery liquid pipes. This makes it possible to accommodate multiple facilities or the like that require waste heat recovery water at different temperatures.

[0108] In the embodiment, the cooling liquid pipe 106 is configured such that it branches 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 then merges again to connect to the cooling facility 3. However, the invention is not limited to this configuration.

[0109] For example, a plurality of cooling liquid pipes 106 may be provided in correspondence with a plurality of cooling heat exchangers, and each of the cooling liquid pipes may be provided as a separate and independent path within the housing.

[0110] Here, the plurality of cooling heat exchangers may include 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) is connected in series.

[0111] In the embodiment, the 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, and it is sufficient that the flow path can be controlled based on the temperature of the waste heat recovery water. For example, instead of using the temperature sensor 205 and the temperature controller 206, a self-operated automatic temperature control valve that does not require auxiliary power such as pneumatic, water-pressure-based, oil-pressure-based, or electric power may be used.

[0112] FIG. 6 is a schematic diagram illustrating an example of the general configuration of a waste heat recovery system according to a second embodiment. In FIG. 6, the same reference numerals are used for components that are identical to those in the first embodiment shown in FIG. 1, and redundant descriptions thereof are omitted.

[0113] The waste heat recovery system 100 according to the second embodiment differs from that of the first embodiment in that an auxiliary cooling facility 3a is provided in addition to the cooling facility 3. The cooling facility 3 cools the waste heat recovery water by exchanging heat with external air or other external sources outside the waste heat recovery system 100.

[0114] Furthermore, in the waste heat recovery system 100 of the second embodiment, a waste heat recovery liquid outlet pipe 114 to the auxiliary cooling facility is provided in place of the branch pipe 111 of the first embodiment. This outlet pipe connects the outlet-side flow path switching three-way valve 204 to the inlet side of the auxiliary cooling facility 3a. Furthermore, in the waste heat recovery system 100 of the second embodiment, a waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility 3a is provided in place of the branch pipe 110 of the first embodiment. This pipe connects the outlet side of the auxiliary cooling facility 3a to the inlet-side flow path switching three-way valve 203. A auxiliary cooling pump 207a is provided on the waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility.

[0115] Next, the flow paths of the waste heat recovery water and the cooling water in the waste heat recovery system 100 according to the second embodiment will be described.

[0116] FIG. 7 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water under normal operation in the waste heat recovery system 100 according to the second embodiment.

[0117] The inlet-side flow switching three-way valve 203 closes the flow path from the auxiliary cooling facility 3a to the intermediate-stage waste heat recovery heat exchanger 201 and opens the flow path from the heat treatment facility 4 to the intermediate-stage waste heat recovery heat exchanger 201. In addition, the outlet-side flow switching three-way valve 204 closes the flow path from the discharge-stage waste heat recovery heat exchanger 202 to the auxiliary cooling facility 3a and opens the flow path from the discharge-stage waste heat recovery heat exchanger 202 to the heat treatment facility 4.

[0118] As indicated by the broken line, the waste heat recovery water flows in from the heat treatment facility 4 on the waste heat utilization side 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, and, after exchanging heat with the compressed air in the waste heat recovery heat exchangers 201 and 202, flows out toward the heat treatment facility 4 on the waste heat utilization side.

[0119] As indicated by the dotted line, the 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, and the third cooling liquid pipe 106c. It then flows to the intercooler 103 and the aftercooler 104, where it exchanges heat with the compressed air, or to the oil cooler 105, where it exchanges heat with the lubricating oil. Thereafter, the flows merge and the cooling water flows out toward the cooling facility 3.

[0120] The auxiliary cooling pump 207a is stopped, and the auxiliary cooling facility 3a, the waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility, and the waste heat recovery liquid outlet pipe 114 to the auxiliary cooling facility are not used.

[0121] If the user does not use the heat treatment facility 4 to exchange heat between the waste heat recovery water and the cooling water, the waste heat recovery water that has exchanged heat with the compressed air in the waste heat recovery heat exchangers 201 and 202 will not be cooled by the heat treatment facility 4. As a result, the temperature of the waste heat recovery water circulating through the waste heat recovery liquid pipe 211 will increase. If the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the waste heat recovery liquid pipe 211 may rise, potentially causing damage to the waste heat recovery heat exchangers 201 and 202.

[0122] In this 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, operates the supplementary cooling pump 207a, and opens the temperature control valve 208, thereby switching the flow paths of the waste heat recovery water and the cooling water.

[0123] FIG. 8 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water when the temperature of the waste heat recovery water exceeds a threshold in the waste heat recovery system 100 of the second embodiment.

[0124] 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. The inlet-side flow path switching three-way valve 203 opens the flow path from the auxiliary cooling facility 3a to the intermediate-stage waste heat recovery heat exchanger 201, and closes the flow path from the heat treatment facility 4 to the intermediate-stage waste heat recovery heat exchanger 201. The outlet-side flow path switching three-way valve 204 opens the flow path from the discharge-stage waste heat recovery heat exchanger 202 to the auxiliary cooling facility 3a, and closes the flow path from the discharge-stage waste heat recovery heat exchanger 202 to the heat treatment facility 4.

[0125] The waste heat recovery water that exchanges heat in the heat exchangers 201 and 202 flows in from the auxiliary cooling facility 3a, as indicated by the dash-dot line. It passes through the waste heat recovery liquid inlet pipe 113, flows through the waste heat recovery liquid pipe 211, and exchanges heat with the compressed air in the heat exchangers 201 and 202. After that, it flows out to the auxiliary cooling facility 3a via the waste heat recovery liquid outlet pipe 114. The waste heat recovery liquid, after exchanging heat, bypasses the heat treatment facility 4 and is cooled by the auxiliary cooling facility 3a. It then continues the cooling of the high-temperature compressed air by circulating through the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202 in the waste heat recovery unit 2.

[0126] 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. As indicated by the broken line, the waste heat recovery water from the waste heat utilization side heat treatment facility 4 flows into the waste heat recovery liquid pipe 211, passes through the waste heat recovery liquid circulation pipe 210, bypasses the waste heat recovery heat exchangers 201 and 202, and flows out toward the waste heat utilization side heat treatment facility 4.

[0127] The flow path of the cooling water flowing in from the cooling facility 3 when the temperature of the waste heat recovery water exceeds the threshold is, as indicated by the dotted line, the same as the water flow path under normal operation shown in FIG. 7.

[0128] According to the second 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 activates the auxiliary cooling pump 207a. As a result, the cooling water from the auxiliary cooling facility 3a is used to perform heat exchange with the compressed air in the waste heat recovery heat exchangers 201 and 202, thereby preventing the temperature of the waste heat recovery water from rising and avoiding damage to the waste heat recovery heat exchangers.

[0129] According to the configuration of the second embodiment, when the temperature of the waste heat recovery water exceeds a predetermined threshold, the waste heat recovery water is passed through the auxiliary cooling facility 3a, which is independent of the cooling facility 3 of the air compressor 1. This allows the waste heat recovery water to be cooled without altering its water quality by mixing the waste heat recovery water with the cooling water supplied to the cooling facility 3.

[0130] For example, in some heat treatment facilities such as boilers, the waste heat recovery water supplied thereto may be required to be water with adjusted quality, such as softened water. On the other hand, cooling water is generally industrial water, which is relatively lower in quality but more economical. Therefore, there are cases where mixing the cooling water with the waste heat recovery water is undesirable.

[0131] FIG. 9 is a schematic diagram illustrating a modification of the configuration of the waste heat recovery system according to the second embodiment. In FIG. 9, components that are the same as those in the second embodiment shown in FIG. 6 are denoted by the same reference numerals, and a description thereof is omitted.

[0132] In the waste heat recovery system 100 shown in FIG. 9, the waste heat recovery liquid inlet valve 212 and a waste heat recovery liquid auxiliary cooling inlet valve 213 are provided instead of the inlet-side flow path switching three-way valve 203 in FIG. 6. Additionally, in the waste heat recovery system 100 shown in FIG. 9, a waste heat recovery liquid outlet valve 214 and a waste heat recovery liquid auxiliary cooling outlet valve 215 are provided instead of the outlet-side flow path switching three-way valve 204 in FIG. 6. That is, instead of the two three-way valves provided on the inlet and outlet sides in FIG. 6, two two-way valves are provided on each of the inlet and outlet sides.

[0133] The waste heat recovery liquid inlet valve 212 is provided on the waste heat recovery liquid pipe 211 upstream of the intermediate-stage waste heat recovery heat exchanger 201, and controls the inflow of the waste heat recovery liquid from the outlet side of the heat treatment facility 4 into the waste heat recovery liquid pipe 211.

[0134] The waste heat recovery liquid outlet valve 214 is provided on the waste heat recovery liquid pipe 211 downstream of the discharge-stage waste heat recovery heat exchanger 202, and controls the outflow of the waste heat recovery liquid from the waste heat recovery liquid pipe 211 to the heat treatment facility 4.

[0135] The waste heat recovery liquid auxiliary cooling inlet valve 213 is provided between a branch inlet pipe 115, which branches from the waste heat recovery liquid pipe 211 upstream of the intermediate-stage waste heat recovery heat exchanger 201, and a waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility. It controls the inflow of the waste heat recovery liquid from the auxiliary cooling facility 3a into the waste heat recovery liquid pipe 211.

[0136] The waste heat recovery liquid auxiliary cooling outlet valve 215 is provided between a branch outlet pipe 116, which branches from the waste heat recovery liquid pipe 211 downstream of the discharge-stage waste heat recovery heat exchanger 202, and a waste heat recovery liquid outlet pipe 114 to the auxiliary cooling facility. It controls the outflow of the waste heat recovery liquid from the waste heat recovery liquid pipe 211 to the auxiliary cooling facility 3a.

[0137] Next, the flow paths of the waste heat recovery water and the cooling water in a modification of the waste heat recovery system 100 according to the second embodiment will be described.

[0138] FIG. 10 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water under normal operation in the waste heat recovery system 100 according to the second embodiment.

[0139] The auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215 are closed, while the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214 are open.

[0140] As indicated by the broken line, the waste heat recovery water flows in from the heat treatment facility 4 on the waste heat utilization side 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 the compressed air in the waste heat recovery heat exchangers 201 and 202, and then flows out toward the heat treatment facility 4 on the waste heat utilization side.

[0141] As indicated by the dotted line, the cooling water flows in from the cooling facility 3, branches from the cooling liquid pipe 106 into the first cooling liquid pipe 106a, the second cooling liquid pipe 106b, and the third cooling liquid pipe 106c, and flows through them. It exchanges heat with the compressed air in the intercooler 103 and the aftercooler 104, or with the lubricating oil in the oil cooler 105. Thereafter, the flows merge and the cooling water flows out toward the cooling facility 3.

[0142] The auxiliary cooling pump 207a is stopped, and the auxiliary cooling facility 3a, the waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility, and the waste heat recovery liquid outlet pipe 114 to the auxiliary cooling facility are not used.

[0143] Here, 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 the compressed air in the waste heat recovery heat exchangers 201 and 202 will not be cooled by the heat treatment facility 4. As a result, the temperature of the waste heat recovery water circulating through the waste heat recovery liquid pipe 211 increases. If the temperature of the waste heat recovery water exceeds its boiling point, the internal pressure of the waste heat recovery liquid pipe 211 may rise, potentially causing damage to the waste heat recovery heat exchangers 201 and 202.

[0144] 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 opens the auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215, closes the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214, operates the auxiliary cooling pump 207a, and opens the temperature control valve 208, thereby switching the flow paths of the waste heat recovery water and the cooling water.

[0145] FIG. 11 is a diagram illustrating an example of the flow paths of the waste heat recovery water and the cooling water when the temperature of the waste heat recovery water exceeds a threshold in a modification of the waste heat recovery system 100 according to the second embodiment.

[0146] When the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds a threshold, the temperature controller 206 opens the auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215, closes the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214, and activates the auxiliary cooling pump 207a.

[0147] As a result, the waste heat recovery water that performs heat exchange in the heat exchangers 201 and 202 flows in from the auxiliary cooling facility 3a, as indicated by the dash-dot line, passes through the waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility, the inlet-side branch pipe 115 of the waste heat recovery liquid, and the waste heat recovery liquid pipe 211, exchanges heat with the compressed air in the waste heat recovery heat exchangers 201 and 202, and then flows out toward the auxiliary cooling facility 3a through the outlet-side branch pipe 116 of the waste heat recovery liquid and the waste heat recovery liquid outlet pipe 114 to the auxiliary cooling facility. The waste heat recovery liquid that has exchanged heat in the heat exchangers 201 and 202 is sent to the auxiliary cooling facility 3a without passing through the heat treatment facility 4, where it is cooled and then recirculated to the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202 in the waste heat recovery unit 2 to continue cooling the high-temperature compressed air.

[0148] In addition, 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, whereby the waste heat recovery water from the heat treatment facility 4 flows in from the heat treatment facility 4 on the waste heat utilization side, as indicated by the dashed line, flows through the waste heat recovery liquid pipe 211, passes through the waste heat recovery liquid circulation pipe 210, bypasses the waste heat recovery heat exchangers 201 and 202, and flows out toward the heat treatment facility 4 on the waste heat utilization side.

[0149] When the temperature of the waste heat recovery water exceeds the threshold, the flow path of the cooling water flowing in from the cooling facility 3 is the same as the flow path under normal operation shown in FIG. 10, as indicated by the dotted line.

[0150] According to the modified example of the second embodiment, when the temperature of the waste heat recovery water measured by the temperature sensor 205 exceeds the threshold, the auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215 are opened, the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214 are closed, and the auxiliary cooling pump 207a is operated. As a result, the cooling water from the auxiliary cooling facility 3a is used for heat exchange with the compressed air in the waste heat recovery heat exchangers 201 and 202, thereby preventing the temperature of the waste heat recovery water from rising and avoiding damage to the waste heat recovery heat exchangers.

[0151] According to the configuration of the second embodiment, when the temperature of the waste heat recovery water exceeds a predetermined threshold, the waste heat recovery water is passed through the auxiliary cooling facility 3a, which is separate from the cooling facility 3 of the air compressor 1. This allows the waste heat recovery water to be cooled without altering its water quality due to mixing with the cooling water supplied to the cooling facility 3.

[0152] Furthermore, according to the modification of the second embodiment, since two-way valves, which have a simple internal structure, are easy to maintain, and are inexpensive, are used for switching the flow paths, the manufacturing and maintenance costs can be reduced compared to the case of using three-way valves.

[0153] FIG. 12 is a flowchart illustrating an example of the control performed by the temperature controller 206 in the waste heat recovery system 100 according to the second embodiment.

[0154] In FIG. 12, at the start of the process, it is assumed that the waste heat recovery water and the cooling water are flowing through the flow paths under normal operation shown in FIG. 7 or FIG. 10.

[0155] When the air compressor 1 starts operating, power is supplied to the temperature controller 206, and control begins. In step S501, the temperature controller 206 acquires the temperature of the waste heat recovery water in the waste heat recovery liquid pipe 211 as measured by the temperature sensor 205.

[0156] In step S502, 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 step S502, the process proceeds to step S503. On the other hand, if the temperature of the waste heat recovery water does not exceed 95° C. in step S502, the process proceeds to step S515, where it waits under normal operation for a predetermined period of time before returning to step S501.

[0157] In step S503, the temperature controller 206 switches the inlet-side and outlet-side valves. In the second embodiment, the inlet-side flow path switching three-way valve 203 is switched to use the branch pipe 110 on the cooling liquid inlet side, thereby allowing cooling liquid from the cooling liquid 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 to direct the cooling liquid, which has passed through the intermediate-stage waste heat recovery heat exchanger 201 and the discharge-stage waste heat recovery heat exchanger 202, into the branch pipe 111 on the cooling liquid outlet side. In the modification of the second embodiment, the auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215 are opened, and the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214 are closed.

[0158] In step S504, the temperature controller 206 opens the temperature control valve 208, thereby opening the waste heat recovery liquid circulation pipe 210 and enabling circulation of the waste heat recovery water from the heat treatment facility 4.

[0159] In step S505, the auxiliary cooling pump 207a is operated to cause the waste heat recovery water to flow from the auxiliary cooling facility 3a into the waste heat recovery liquid inlet pipe 113 from the auxiliary cooling facility.

[0160] In step S506, after executing steps S503 and S504, the process waits for a predetermined period of time. The waiting time is set to a duration sufficient for the temperature of the waste heat recovery water, which has exceeded 95° C., to decrease.

[0161] In step S507, the temperature controller 206 again acquires the temperature of the waste heat recovery water in the waste heat recovery liquid pipe 211, as measured by the temperature sensor 205.

[0162] In step S508, 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 step S508, the process proceeds to step S510.

[0163] In step S510, the temperature controller 206 outputs a critical failure signal. In step S511, the temperature controller 206 stops the operation of the circulation pump 207 installed in the waste heat recovery liquid pipe 211, the auxiliary cooling pump 207a, the air compressor 1, and the waste heat recovery unit 2, and terminates the process.

[0164] On the other hand, if it is determined in step S508 that the temperature of the waste heat recovery water does not exceed 95° C., the process proceeds to step S509. In step S509, it is determined whether the temperature of the waste heat recovery water obtained in step S507 falls below 40° C. If the temperature of the waste heat recovery water does not fall below 40° C. in step S509, the process returns to step S506 and waits for a predetermined period of time.

[0165] On the other hand, if it is determined in step S509 that the temperature of the waste heat recovery water falls below 40° C., the process proceeds to step S512.

[0166] In step S512, the temperature controller 206 switches the inlet-side and outlet-side valves. In the second embodiment, the inlet-side flow path switching three-way valve 203 is switched 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. In the modified example of the second embodiment, the auxiliary cooling inlet valve 213 and the auxiliary cooling outlet valve 215 are closed, and the waste heat recovery liquid inlet valve 212 and the waste heat recovery liquid outlet valve 214 are opened.

[0167] In step S513, the temperature controller 206 closes the temperature control valve 208, thereby closing the waste heat recovery liquid circulation pipe 210. In step S514, the auxiliary cooling pump 207a is stopped. In step S515, the system waits for a preset period of time under normal operation and then returns to step S501.

[0168] In the embodiment, the air compressor 1 is specifically applicable to a screw compressor; however, the present invention is not limited thereto. That is, although screw rotors are used in the compressor bodies 101 and 102 in the embodiment, the invention is not so limited. Various types of compression mechanisms may be used, including turbo types such as centrifugal and axial compressors, and positive displacement types such as scroll, reciprocating, and claw compressors.

[0169] In the embodiment, a single-screw rotor is used; however, a twin-screw or triple-screw rotor may also be used.

[0170] In the embodiment, the number of stages of the compressor bodies 101 and 102 is two; however, the present invention is not limited thereto, and a single-stage configuration or a configuration with three or more stages may also be used.

[0171] In the embodiment, the air compressor 1 is an oil-free screw compressor; however, the present invention is not limited thereto, and a liquid-injection type air compressor that injects oil or water into the compression chamber may also be used. Furthermore, although air has been described as the gas to be compressed, the present invention is not limited to this and may also be applicable to other gases such as nitrogen.

[0172] The threshold temperature of the waste heat recovery water used in the control of the embodiment is not limited to the value described above.

[0173] In the embodiment, the heated cooling water is cooled by exchanging heat with the atmosphere in the cooling facility 3. However, the invention is not limited to this configuration, and it is also possible to recover and utilize the heat from the heated cooling water.

[0174] In the embodiment, the air compressor 1 is described as a water-cooled type in which the compressor bodies, the intercooler, the aftercooler, and the oil cooler are cooled with cooling water. However, the invention is not limited to this, and it may also be an air-cooled type that includes a cooling fan for drawing in outside air and air-cooled components such as an intercooler, aftercooler, and oil cooler cooled by the cooling air generated by the cooling fan.

[0175] It is also possible to replace part of the configuration of one embodiment with that of another embodiment, or to add the configuration of another embodiment to that of one embodiment. Furthermore, it is possible to add to, remove from, or replace part of the configuration of each embodiment with another configuration.

Claims

1. A waste heat recovery system comprising:a fluid machine body through which a fluid flows, anda waste heat recovery unit that recovers waste heat from the fluid,wherein the fluid machine body includes:a cooling heat exchanger that performs heat exchange between a cooling liquid and the fluid; anda cooling liquid pipe through which the cooling liquid flows,wherein the waste heat recovery unit includes:a waste heat recovery heat exchanger that performs heat exchange 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 to an outlet side of an auxiliary cooling facility that is not connected to the cooling liquid pipe of the fluid machine body;a second bypass flow path that connects a downstream side of the waste heat recovery heat exchanger in the waste heat recovery liquid pipe to an inlet side of the auxiliary cooling facility;a first valve that opens and closes the first bypass flow path;a second valve that opens and closes the second bypass flow path; anda control unit that controls the first and second valves,wherein the control unit opens the first and second bypass flow paths by controlling the first and second valves 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 is provided downstream of the second valve and upstream of the first valve in the waste heat recovery liquid pipe, and that performs heat exchange between the waste heat recovery liquid and a refrigerant.

3. The waste heat recovery system according to claim 2,wherein the control unit closes the first and second bypass flow paths by controlling the first and second valves when a temperature of the waste heat recovery liquid falls below a second threshold.

4. The waste heat recovery system according to claim 2,wherein the first valve comprises a first three-way valve that switches between a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger and a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a second three-way valve that switches between a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe and a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by switching the first and second three-way valves.

5. The waste heat recovery system according to claim 2,wherein the first valve comprises a first two-way valve that opens and closes a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger, and a second two-way valve that opens and closes a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a third two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe, and a fourth two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by closing the first and third two-way valves and opening the second and fourth two-way valves.

6. A waste heat recovery unit that recovers waste heat from a fluid discharged from a fluid machine body comprising:a cooling heat exchanger that performs heat exchange between a cooling liquid and the fluid; anda cooling liquid pipe through which the cooling liquid flows,a waste heat recovery heat exchanger that performs heat exchange 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 to an outlet side of an auxiliary cooling facility that is not connected to the cooling liquid pipe of the fluid machine body;a second bypass flow path that connects a downstream side of the waste heat recovery heat exchanger in the waste heat recovery liquid pipe to an inlet side of the auxiliary cooling facility;a first valve that opens and closes the first bypass flow path;a second valve that opens and closes the second bypass flow path; anda control unit that controls the first and second valves,wherein the control unit opens the first and second bypass flow paths by controlling the first and second valves when a temperature of the waste heat recovery liquid exceeds a threshold.

7. The waste heat recovery unit according to claim 6, further comprising: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, and that performs heat exchange between the waste heat recovery liquid and a refrigerant.

8. The waste heat recovery unit according to claim 7,wherein the control unit closes the first and second bypass flow paths by controlling the first and second valves when a temperature of the waste heat recovery liquid falls below a second threshold.

9. The waste heat recovery unit according to claim 7,wherein the first valve comprises a first three-way valve that switches between a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger and a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a second three-way valve that switches between a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe and a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by switching the first and second three-way valves.

10. The waste heat recovery unit according to claim 7,wherein the first valve comprises a first two-way valve that opens and closes a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger, and a second two-way valve that opens and closes a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a third two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe, and a fourth two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by closing the first and third two-way valves and opening the second and fourth two-way valves.

11. A waste heat recovery method in a waste heat recovery system comprising a fluid machine body through which a fluid flows and a waste heat recovery unit that recovers waste heat from the fluid,wherein the fluid machine body includes:a cooling heat exchanger that performs heat exchange between a cooling liquid and the fluid; anda cooling liquid pipe through which the cooling liquid flows,wherein the waste heat recovery unit includes:a waste heat recovery heat exchanger that performs heat exchange 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 to an outlet side of an auxiliary cooling facility that is not connected to the cooling liquid pipe of the fluid machine body;a second bypass flow path that connects a downstream side of the waste heat recovery heat exchanger in the waste heat recovery liquid pipe to an inlet side of the auxiliary cooling facility;a first valve that opens and closes the first bypass flow path;a second valve that opens and closes the second bypass flow path; anda control unit that controls the first and second valves,wherein the control unit opens the first and second bypass flow paths by controlling the first and second valves when a temperature of the waste heat recovery liquid exceeds a threshold.

12. The waste heat recovery method according to claim 11,wherein the fluid machine body includes: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, and that performs heat exchange between the waste heat recovery liquid and a refrigerant.

13. The waste heat recovery method according to claim 12,wherein the control unit closes the first and second bypass flow paths by controlling the first and second valves when a temperature of the waste heat recovery liquid falls below a second threshold.

14. The waste heat recovery method according to claim 12,wherein the first valve comprises a first three-way valve that switches between a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger and a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a second three-way valve that switches between a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe and a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by switching the first and second three-way valves.

15. The waste heat recovery method according to claim 12,wherein the first valve comprises a first two-way valve that opens and closes a flow path from the waste heat recovery liquid pipe to the waste heat recovery heat exchanger, and a second two-way valve that opens and closes a flow path from the auxiliary cooling facility to the waste heat recovery heat exchanger;wherein the second valve comprises a third two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the waste heat recovery liquid pipe, and a fourth two-way valve that opens and closes a flow path from the waste heat recovery heat exchanger to the auxiliary cooling facility; andwherein the control unit opens the first and second bypass flow paths by closing the first and third two-way valves and opening the second and fourth two-way valves.

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