Exhaust heat recovery system

Abstract

To provide an exhaust heat recovery system capable of satisfying a demand of a demander.SOLUTION: The cooling unit 4 includes a bypass line 46 bypassing the evaporator 12, and a cooling device 47 interposed in the bypass line 46 and cooling the cooling water. When the hot-water temperature is higher than the predetermined temperature range, the controller 6 controls the bypass amount adjustment mechanism 48 so as to increase the flow rate of the cooling water flowing from the cooler 11 toward the cooling device 47. The compressor unit 2 includes an air release line 25 for releasing the compressed gas passing through the cooler 11 to the outside air. When the hot-water temperature is lower than the predetermined temperature range, the controller 6 increases the number of revolutions of the compressor 20 and controls the air release valve 26 so as to increase the amount of the compressed gas released to the outside air via the air release line 25.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust heat recovery system. [Background technology]

[0002] Patent Document 1 discloses a system that generates hot water by utilizing heat recovered from compressed air discharged from a compressor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6607960 Summary of the Invention [Problem to be solved by the invention]

[0004] The demand for compressed air and hot water fluctuates from time to time depending on the circumstances of the demanding party. The above system does not take into consideration fluctuations in the demand for compressed air. When the demand for compressed air and the demand for hot water are not balanced, there is a risk that the supply of either will be insufficient to meet the demand.

[0005] An object of the present invention is to provide an exhaust heat recovery system that can satisfy the demands of the user. [Means for solving the problem]

[0006] One aspect of the present invention is a heat pump unit including a compressor unit including an oil-free compressor and a cooler that cools compressed gas discharged from the compressor with cooling water; a refrigerant circulation line that circulates a refrigerant, an evaporator that evaporates the refrigerant, and a condenser that condenses the refrigerant, forming a refrigeration cycle; a cooling unit including a cooling water supply line that sends the cooling water heated in the cooler by heat exchange with the compressed gas to the evaporator, and a cooling water return line that returns the cooling water cooled in the evaporator by heat exchange with the refrigerant to the cooler; a hot water supply unit including a water line that sends water to the condenser and a hot water line that circulates hot water obtained by heating the water in the condenser by heat exchange with the refrigerant; and a pressure sensor that detects the discharge pressure of the compressor. a hot water temperature sensor that detects the temperature of the hot water; and a controller that controls the rotation speed of the compressor so that the discharge pressure detected by the pressure sensor is within a predetermined pressure range, wherein the cooling unit further includes a bypass line that bypasses the evaporator and connects the coolant feed line to the coolant return line, a cooling device that is interposed in the bypass line and cools the coolant, and a bypass amount adjustment mechanism that adjusts the bypass amount, which is the flow rate of the coolant flowing from the cooler to the cooling device, and the controller determines whether the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range, and controls the bypass amount adjustment mechanism to increase the bypass amount if the hot water temperature is higher than the predetermined temperature range.

[0007] According to the above configuration, the compressor unit can supply compressed gas discharged from the compressor to a demand destination. Furthermore, exhaust heat recovered from the compressed gas when the compressed gas is cooled is used as a heat source for a heat pump in the evaporator, and the heat pump unit generates hot water from water in the condenser. The hot water supply unit can supply the obtained hot water to a demand destination.

[0008] Here, the fact that the discharge pressure detected by the pressure sensor is within a predetermined pressure range means that the supply and demand of compressed gas are in balance. If the discharge pressure falls outside the predetermined pressure range due to fluctuations in the demand, the controller controls the compressor speed so that the discharge pressure falls within the predetermined pressure range. This adjusts the supply of compressed gas so that it is in balance with the demand.

[0009] The amount of hot water heat supplied depends on the amount of waste heat that can be recovered by the cooler, and the amount of waste heat depends on the amount of compressed gas supplied adjusted as described above. When the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range, it means that the supply of hot water heat is also balanced with the demand for compressed gas under conditions where the supply and demand for compressed gas are balanced.

[0010] If the hot water temperature is higher than the specified temperature range, it means that the supply of hot water heat is greater than the demand. When this situation (compressed gas supply and demand are balanced, but hot water heat is in excess supply) is detected, the controller increases the bypass amount. A portion of the cooling water sent from the cooler bypasses the evaporator and is cooled by the cooling device. This makes it possible to reduce the amount of waste heat supplied from the cooler to the heat pump unit while maintaining a balance between supply and demand of compressed gas. The supply of hot water heat is reduced and adjusted to balance with the demand.

[0011] The bypass amount adjustment mechanism may be configured by a three-way valve provided at the branch point between the cooling water supply line and the bypass line, and the controller may control the three-way valve to control the flow rate of the cooling water flowing from the cooler to the evaporator and the bypass amount when the hot water temperature is higher than the predetermined temperature range.

[0012] According to the above configuration, the amount of waste heat discarded by the cooling device can be minimized, and the amount of hot water heat supplied can be easily adjusted to match the amount of heat demanded.

[0013] The compressor unit may further include an air release line that releases the compressed gas that has passed through the cooler into the outside air, and an air release valve that adjusts the air release amount, which is the amount of compressed gas released into the outside air through the air release line, and the controller may control the air release valve to increase the rotation speed of the compressor and the air release amount when the hot water temperature is lower than the predetermined temperature range.

[0014] If the hot water temperature is lower than the specified temperature range, it means that the supply of hot water heat is less than the demand. When this situation (compressed gas supply and demand is balanced, but hot water heat is insufficient) is detected, the controller increases the compressor rotation speed. This increases the amount of compressed gas passing through the cooler, increasing the amount of waste heat that can be recovered by the cooler, i.e., the amount of waste heat that can be used by the heat pump unit. The supply of hot water heat increases and is adjusted to balance with the demand.

[0015] If the amount of compressed gas passing through the cooler were supplied to the demand destination as is, the supply amount of compressed gas would be in excess of the demand amount. At this time, the discharge pressure detected by the pressure sensor is higher than the specified pressure range. Therefore, the controller increases the amount of released air. A portion of the compressed gas after passing through the cooler is released into the outside air. This makes it possible to suppress the supply amount of compressed gas relative to the amount passing through the cooler while maintaining a balance between supply and demand of hot water heat, thereby maintaining a balance between supply and demand of compressed gas.

[0016] One aspect of the present invention is a heat pump unit that configures a refrigeration cycle and includes a compressor unit including an oil-free compressor and a cooler that cools compressed gas discharged from the compressor with cooling water; a refrigerant circulation line that circulates a refrigerant, an evaporator that evaporates the refrigerant, and a condenser that condenses the refrigerant; a cooling unit that includes a cooling water supply line that sends the cooling water heated in the cooler by heat exchange with the compressed gas to the evaporator, and a cooling water return line that returns the cooling water cooled in the evaporator by heat exchange with the refrigerant to the cooler; and a hot water supply unit that includes a water line that sends water to the condenser and a hot water line that circulates hot water obtained by heating the water in the condenser by heat exchange with the refrigerant. and a controller that controls the rotation speed of the compressor so that the discharge pressure detected by the pressure sensor is within a predetermined pressure range, wherein the compressor unit further includes an air release line that releases the compressed gas that has passed through the cooler into the outside air, and an air release valve that adjusts the amount of air release, which is the amount of compressed gas released into the outside air through the air release line, and wherein the controller determines whether the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range, and, if the hot water temperature is lower than the predetermined temperature range, increases the rotation speed of the compressor and controls the air release valve to increase the amount of air release.

[0017] In the above configuration, the compressor unit can also supply compressed gas discharged from the compressor to a consumer. Furthermore, exhaust heat recovered from the compressed gas when it is cooled is used as a heat source for a heat pump in an evaporator, and the heat pump unit generates hot water from water in a condenser. The resulting hot water can be supplied to a consumer by a hot water supply unit.

[0018] When the discharge pressure detected by the pressure sensor is within a predetermined pressure range, it means that the supply and demand of compressed gas are balanced. The controller adjusts the supply of compressed gas to satisfy the demand by controlling the compressor rotation speed. Furthermore, when the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range, it means that the supply of hot water heat is balanced with the demand under the condition that the supply and demand of compressed gas are balanced.

[0019] If the hot water temperature is lower than the specified temperature range, it means that the supply of hot water heat is less than the demand. When this situation (compressed gas supply and demand are balanced, but hot water heat is insufficient) is detected, the controller increases the compressor rotation speed, increasing the amount of compressed gas passing through the cooler. This increases the supply of hot water heat, adjusting it to balance with the demand. The controller also increases the amount of air released, releasing some of the compressed gas after passing through the cooler into the outside air. This allows the supply of compressed gas to be restricted relative to the amount passing through the cooler while maintaining the balance between supply and demand of hot water heat, and the supply and demand of compressed gas is also maintained.

[0020] The compressor unit may further include a receiver tank that stores the compressed gas that has passed through the cooler, and the air release line may release the compressed gas in the receiver tank to the outside air.

[0021] The compressor unit may further include an expander provided in the gas release line and driven by the compressed gas, and a generator driven by the expander.

[0022] According to the above configuration, electrical energy can be recovered from the compressed gas released into the outside air, improving the efficiency of the exhaust heat recovery system. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an exhaust heat recovery system that can satisfy the demands of the consumer. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic configuration diagram of an exhaust heat recovery system according to a first embodiment. [Figure 2] 10 is a graph showing the amount of hot water heat supplied relative to the amount of compressed gas supplied. [Figure 3] 3 is a flowchart showing processing executed by a controller of the exhaust heat recovery system according to the first embodiment. [Figure 4] Flowchart continued from Figure 3. [Figure 5] Flowchart continued from Figure 3. [Figure 6] FIG. 10 is a schematic configuration diagram of an exhaust heat recovery system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments will be described with reference to the drawings. The same or corresponding elements are designated by the same reference numerals throughout the drawings, and detailed descriptions thereof will be omitted.

[0026] Referring to FIG. 1, an exhaust heat recovery system 1 according to the first embodiment includes a compressor unit 2, a heat pump unit 3, a cooling unit 4, and a hot water supply unit 5. The compressor unit 2 generates compressed gas and supplies it to a demand destination. The cooling unit 4 cools the compressed gas with cooling water and removes heat from the compressed gas. The heat pump unit 3 heats water using the exhaust heat recovered from the compressed gas to generate hot water. The hot water supply unit 5 supplies the hot water to a demand destination.

[0027] The compressor unit 2 includes a compressor 20 , a cooler 11 , and a receiver tank 22 .

[0028] In this embodiment, the compressor 20 is an oil-free two-stage compressor having a low-pressure stage compressor 20A and a high-pressure stage compressor 20B. However, the compressor 20 is not limited to a two-stage type, and may be a one-stage type or a three-stage or more type. The object to be compressed is not limited to air, and may be any gas other than air (for example, a refrigerant gas).

[0029] In this embodiment, the low-pressure stage compressor 20A and the high-pressure stage compressor 20B are screw-type compressors each having a pair of male and female screw rotors therein. The pair of male and female screw rotors are rotationally driven by a motor 21a. The rotation speed of the motor 21a, and therefore the rotation speed of the compressor 20, is adjusted by an inverter 21b electrically connected to the motor 21a. The number of pairs of motor 21a and inverter 21b may be one pair common to the multi-stage compressor 20, as in the illustrated example, or multiple pairs individual for each stage.

[0030] The cooler 11 uses cooling water to cool the compressed gas discharged from the compressor 20. The cooler 11 includes an intercooler 11A and an aftercooler 11B.

[0031] When the motor 21a operates, the low-pressure stage compressor 20A and the high-pressure stage compressor 20B are driven. The low-pressure stage compressor 20A compresses the gas that it draws in to generate compressed gas. The intercooler 11A cools the compressed gas discharged from the low-pressure stage compressor 20A. The high-pressure stage compressor 20B draws in the compressed gas cooled by the intercooler 11A and further compresses the drawn compressed gas. The aftercooler 11B cools the compressed gas discharged from the high-pressure stage compressor 20B. The compressed gas cooled by the aftercooler 11B is pressure-fed to the receiver tank 22.

[0032] Receiver tank 22 stores the compressed gas that has passed through cooler 11 and separates drainage from the compressed gas. Receiver tank 22 is connected to pipe 23a, which leads to aftercooler 11B, and pipe 23b, which extends toward the consumer. Pipe 23a is equipped with a check valve 24a, and pipe 23b is equipped with a discharge valve 24b. When discharge valve 24b opens, the compressed gas after drainage separation is supplied from receiver tank 22 to the consumer through pipe 23b.

[0033] The compressor unit 2 further includes an air release line 25 and an air release valve 26 .

[0034] The air release line 25 releases the compressed gas that has passed through the cooler 11 to the outside air. In this embodiment, the air release line 25 is connected to the receiver tank 22 and releases the compressed gas in the receiver tank 22 to the outside air.

[0035] The air release valve 26 adjusts the amount of compressed gas (hereinafter referred to as the "air release amount") released to the outside air via the air release line 25. The air release valve 26 is, for example, a flow control valve disposed in the air release line 25. When the air release valve 26 is fully closed, the air release amount is zero. By increasing the opening of the air release valve 26 to increase the air release amount, the supply amount of compressed gas to the demand side can be adjusted by reducing the supply amount relative to the amount of compressed gas generated in the compressor 20 (in other words, the amount of compressed gas passing through the cooler).

[0036] The heat pump unit 3 includes a refrigeration cycle including a refrigerant circulation line 30 through which a refrigerant circulates, a refrigeration compressor 31, a condenser 13, an expansion valve 32, and an evaporator 12. The refrigeration compressor 31, the condenser 13, the expansion valve 32, and the evaporator 12 are arranged in this order on the refrigerant circulation line 30 along the flow direction of the refrigerant.

[0037] The refrigeration compressor 31 compresses the refrigerant evaporated in the evaporator 12. The condenser 13 condenses the refrigerant compressed in the refrigeration compressor 31. The expansion valve 32 expands and cools the refrigerant condensed in the condenser 13. The evaporator 12 evaporates the refrigerant expanded in the expansion valve 32.

[0038] The cooling unit 4 shares a cooler 11 with the compressor unit 2 and an evaporator 12 with the heat pump unit 3. The cooling unit 4 includes a cooling water circulation line 40 through which cooling water circulates, a water pump 43, an oil cooler 44, and a main body cooling mechanism 45.

[0039] The cooling water circulation line 40 includes a cooling water feed line 41 that sends cooling water from the cooler 11 to the evaporator 12, and a cooling water return line 42 that returns cooling water from the evaporator 12 to the cooler 11. A water pump 43 pumps cooling water along the cooling water circulation line 40.

[0040] The cooler 11 exchanges heat between the compressed gas and cooling water, thereby cooling the compressed gas. The cooling water is heated in the cooler 11 by heat exchange with the compressed gas. The cooling water heated in the cooler 11 is sent to the evaporator 12 through a cooling water supply line 41. The evaporator 12 exchanges heat between the refrigerant and the cooling water, thereby evaporating the refrigerant. The cooling water is cooled in the evaporator 12 by heat exchange with the refrigerant. The cooling water cooled in the evaporator 12 is sent to the cooler 11 through a cooling water return line 42.

[0041] The intercooler 11A, aftercooler 11B, oil cooler 44, and main body cooling mechanism 45 are connected in parallel between the downstream part of the cooling water return line 42 and the upstream part of the cooling water supply line 41. The cooling unit 4 recovers exhaust heat not only from the compressed gas but also from the oil and the main body of the compressor 20, and supplies the recovered exhaust heat to the heat pump unit 3.

[0042] The oil cooler 44 uses cooling water to cool the oil used for lubricating the compressor 20. The main body cooling mechanism 45 has a low-pressure stage jacket 45a and a high-pressure stage jacket 45b provided on the main bodies of the low-pressure stage compressor 20A and the high-pressure stage compressor 20B, respectively. The cooling water flows from the cooling water return line 42, passes through the low-pressure stage jacket 45a and the high-pressure stage jacket 45b in this order, and then flows into the cooling water feed line 41.

[0043] The cooling unit 4 further includes a bypass line 46 , a cooling device 47 , and a bypass amount adjustment mechanism 48 .

[0044] A bypass line 46 is added to the cooling water circulation line 40 to bypass the evaporator 12 and connect the cooling water delivery line 41 to the cooling water return line 42 .

[0045] The cooling water supply line 41 has a branch point with the bypass line 46, and the cooling water supply line 41 forms a downstream section 41a that connects the branch point to the evaporator 12. The cooling water return line 42 has a junction with the bypass line 46, and the cooling water return line 42 forms an upstream section 42a that connects the evaporator 12 to the junction point. The water pump 43 is interposed in the cooling water return line 42 downstream of the junction point.

[0046] The cooling water circulation line 40 forms two routes through which the cooling water flows between the branching point and the merging point. The first route is a main line 40m consisting of a downstream portion 41a and an upstream portion 42a, and the evaporator 12 is located in the main line 40m. The second route is a bypass line 46. A cooling device 47 is located in the bypass line 46. The cooling device 47 is, for example, a cooling tower, and cools the cooling water flowing through the bypass line 46.

[0047] The cooling water heated by the cooler 11 etc. (including the oil cooler 44 and the main body cooling mechanism 45) mainly flows through the main line 40m to the evaporator 12, where it is cooled and reaches the confluence point. The cooling water heated by the cooler 11 etc. may partially flow through the bypass line 46 to the cooling device 47, where it is cooled and reaches the confluence point.

[0048] Hereinafter, the flow rate of the cooling water flowing from the cooler 11 to the evaporator 12 will be referred to as the "main flow rate." The flow rate of the cooling water flowing from the cooler 11 to the cooling device 47, bypassing the evaporator 12, will be referred to as the "bypass amount."

[0049] The bypass amount adjustment mechanism 48 adjusts the bypass amount. The bypass amount adjustment mechanism 48 includes, for example, a flow control valve interposed in the bypass line 46. A valve on the main line 40m can also constitute the bypass amount adjustment mechanism 48. The valve on the main line 40m may be an on-off valve or a flow control valve, and is fully open unless otherwise specified. When the flow control valve on the bypass line 46 is fully closed, the bypass amount becomes zero and the mainstream amount is maximized. Increasing the opening of the flow control valve on the bypass line 46 increases the bypass amount and decreases the mainstream amount. A portion of the exhaust heat recovered in the cooling water is discarded in the cooling device 47, thereby reducing the amount of exhaust heat used in the heat pump unit 3.

[0050] The hot water supply unit 5 shares the condenser 13 with the heat pump unit 3. The hot water supply unit 5 includes a water line 51 that sends water to the condenser 13 and a hot water line 52 that circulates the hot water obtained in the condenser 13. The condenser 13 performs heat exchange between the refrigerant and the water, thereby cooling and condensing the refrigerant. The water is heated in the condenser 13 through heat exchange with the refrigerant, thereby producing hot water. The term "water" refers to the object to be heated, and "hot water" refers to water that has been heated, and is not limited by water temperature. That is, the water may be, for example, cold water (e.g., 5 to 15°C), room temperature water (e.g., 20 to 30°C), or high temperature water (e.g., 50°C or higher).

[0051] The hot water line 52 extends from the condenser 13 to the demand destination and supplies hot water to the demand destination. At the demand destination, the heat of the hot water is consumed according to demand. As a result, the temperature of the hot water drops and it returns to water. The water line 51 extends from the demand destination to the condenser 13 and sends the water after heat consumption to the condenser 13. In this way, the water line 51 and the hot water line 52 form a closed-loop path through which water circulates.

[0052] The exhaust heat recovery system 1 includes a controller 6, a pressure sensor 71, and a hot water temperature sensor 72.

[0053] The controller 6 is configured by hardware such as a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory), and software implemented therein. The controller 6 is connected to a pressure sensor 71, a hot water temperature sensor 72, inverters 21b and 31b, an air release valve 26, and a bypass amount adjustment mechanism 48.

[0054] The pressure sensor 71 detects the discharge pressure of the compressor 20. As an example, the pressure sensor 71 is provided in the receiver tank 22 and detects the internal pressure of the receiver tank 22. The hot water temperature sensor 72 is provided in the hot water line 52 and detects the temperature of the hot water.

[0055] The controller 6 controls the rotation speed, air release amount, and bypass amount of the compressor 20 based on the discharge pressure detected by the pressure sensor 71 and the hot water temperature detected by the hot water temperature sensor 72 so that the supply amount of compressed gas is balanced with the demand amount at the demand destination and the supply amount of hot water heat is balanced with the demand amount at the demand destination. The controller 6 controls the rotation speed of the compressor 20 through control of the inverter 21b. The controller 6 controls the air release amount through control of the air release valve 26. The air release valve 26 may be a flow control valve or an on-off valve. The controller 6 controls the bypass amount through control of the bypass amount adjustment mechanism 48.

[0056] Control for balancing the supply and demand of compressed gas and the supply and demand of hot water heat quantity will be described below with reference to Figures 2 to 5. Figure 2 is a graph showing the relationship between the supply amount of compressed gas and the supply amount of hot water heat quantity. Figures 3 to 5 are flowcharts showing the processing executed by controller 6.

[0057] 3, first, the supply and demand of compressed gas is balanced. The pressure sensor 71 detects the discharge pressure (step S1), and the controller 6 controls the rotation speed of the compressor 20 so that the discharge pressure is within a predetermined pressure range (step S2). That is, the capacity of the compressor 20 is controlled.

[0058] In this regard, if the supply amount of compressed gas exceeds the demand amount, the discharge pressure detected by the pressure sensor 71 will be relatively high. Conversely, if the supply amount of compressed gas is insufficient compared to the demand amount, the discharge pressure detected by the pressure sensor 71 will be relatively low. When the supply amount of compressed gas is balanced with the demand amount, the discharge pressure detected by the pressure sensor 71 will fall within a predetermined pressure range.

[0059] Therefore, in step S2, the controller 6 determines whether the discharge pressure is within a predetermined pressure range. If the discharge pressure is higher than the predetermined pressure range (there is an excess supply of compressed gas), the controller 6 reduces the rotation speed of the compressor 20. This reduces the amount of compressed gas produced, and the supply of compressed gas is reduced to match the demand, thereby balancing the supply and demand of compressed gas. If the discharge pressure is lower than the predetermined pressure range (there is an insufficient supply of compressed gas), the controller 6 increases the rotation speed of the compressor 20. This increases the amount of compressed gas produced, and the supply of compressed gas is increased to match the demand, thereby balancing the supply and demand of compressed gas.

[0060] Once the supply and demand of compressed gas is balanced in this manner, the controller 6 controls the capacity of the refrigeration compressor 31 (step S3). The refrigeration compressor 31 is driven by a motor 31a, and the controller 6 controls the inverter 31b electrically connected to this motor 31a. This makes it possible to adjust the rotation speed of the refrigeration compressor 31. When the rotation speed of the compressor 20 changes in step S2, the controller 6 changes the rotation speed of the refrigeration compressor 31 accordingly. The rotation speed of the refrigeration compressor 31 is positively correlated with the rotation speed of the compressor 20. When the rotation speed of the compressor 20 increases, the rotation speed of the refrigeration compressor 31 also increases.

[0061] Next, the controller 6 executes control to balance the supply and demand of hot water heat. Before explaining this control, the relationship between the supply amount of hot water heat and the supply amount of compressed gas, and the relationship between the demand amount of hot water heat and the hot water temperature detected by the hot water temperature sensor 72 will be explained.

[0062] The amount of hot water heat supplied, i.e., the amount of heat given from the refrigerant to the water in the condenser 13, depends on the capacity of the refrigeration compressor 31 and the amount of heat given from the cooling water to the refrigerant in the evaporator 12. This amount of heat depends on the amount of waste heat recovered from the compressed gas to the cooling water in the cooler 11, and the amount of waste heat depends on the amount of compressed gas supplied. The capacity of the refrigeration compressor 31 also depends on the amount of compressed gas supplied.

[0063] Therefore, the amount of hot water heat supplied is determined based on the amount of compressed gas supplied. Referring to Figure 2, the dashed line rising to the right indicates that, under conditions where the bypass volume is zero and the air release volume is zero, the amount of hot water heat supplied is uniquely determined once the amount of compressed gas supplied is determined. If the amount of compressed gas supplied is zero, the amount of hot water heat supplied will also be zero. If the compressor 20 is operating at rated speed and the amount of compressed gas supplied is at its maximum value (100%), the amount of hot water heat supplied will also be the maximum value (100%) achieved by this exhaust heat recovery system 1. The amount of hot water heat supplied is proportional to the amount supplied by the compressor 20.

[0064] Even if the supply and demand of compressed gas is balanced, the supply of hot water heat, which is determined based on the supply of compressed gas at that time, does not necessarily balance with the demand. When the demand for hot water heat is less than the supply, the amount of heat removed from the hot water at the demand destination decreases, and the temperature of the water flowing through water line 51 rises. The hot water temperature also rises accordingly. Conversely, when the demand for hot water heat is greater than the supply, the amount of heat removed from the hot water at the demand destination increases, and the temperature of the water flowing through water line 51 decreases. The hot water temperature also decreases accordingly.

[0065] When the supply of hot water heat is in balance with the demand, the hot water temperature detected by the hot water temperature sensor 72 falls within a predetermined temperature range. When the supply of hot water heat exceeds the demand, the hot water temperature detected by the hot water temperature sensor 72 becomes higher than the predetermined temperature range. When the supply of hot water heat is insufficient compared to the demand, the hot water temperature detected by the hot water temperature sensor 72 becomes lower than the predetermined temperature range.

[0066] In light of the above circumstances, as shown in Fig. 3, the hot water temperature sensor 72 detects the hot water temperature (step S4), and the controller 6 determines whether the hot water temperature is within a predetermined temperature range (step S5). That is, under the condition where the supply and demand of compressed gas is balanced in step S2, the controller 6 determines whether the hot water heat quantity is in balance, in excess of supply, or insufficient.

[0067] If the hot water temperature is within the predetermined temperature range (S5: YES_supply and demand balance), the controller 6 maintains the rotation speed of the compressor 20 (step S11), maintains the bypass amount (step S12), and maintains the release air amount (step S13). At this point, the process ends.

[0068] If the hot water temperature is higher than the predetermined temperature range (S5: NO — excess supply), as shown in Fig. 4, the controller 6 determines whether or not compressed gas is being released to the outside air via the air release line 25 (step S21). In other words, the controller 6 determines whether or not the air release valve 26 is fully closed. That is, in this step, it is determined whether or not the discharge pressure is within a predetermined pressure range.

[0069] If the gas is not being released, i.e., if the gas release valve 26 is fully closed and the amount of released gas is zero (S21: NO), the controller 6 first maintains the rotation speed of the compressor 20 (step S22). This maintains the supply amount of compressed gas, and keeps the supply and demand of compressed gas in balance. Next, the controller 6 controls the bypass amount adjustment mechanism 48 so that the bypass amount increases (step S23). The bypass amount is increased by increasing the opening of the flow control valve on the bypass line 46.

[0070] As a result, the amount of compressed gas generated, the amount passing through the cooler, and the amount supplied are maintained, and the amount of exhaust heat recovered by the cooler 11 is also maintained, while the amount of exhaust heat supplied to the evaporator 12 is suppressed in accordance with an increase in the bypass amount (a decrease in the main flow rate). The amount of hot water heat generated by the heat pump unit 3 decreases. The supply amount of hot water heat decreases to match the demand. Note that the exhaust heat not supplied to the evaporator 12 is discarded in the cooling device 47.

[0071] At this point, the process ends. When the process resumes, the supply and demand balance of compressed gas is maintained in step S2, and then a supply and demand determination of hot water temperature is made (step S5). If the supply rate of hot water heat is still not reduced sufficiently and the hot water temperature is still higher than the predetermined temperature range (S5: NO — excessive supply), the bypass amount is increased until the hot water temperature falls within the predetermined temperature range (step S23). When the hot water temperature falls to the predetermined temperature range (S5: YES — supply and demand balance), the bypass amount at that time is maintained (step S12), and the discharged air amount is maintained at zero (step S13).

[0072] If the hot water temperature is lower than the predetermined temperature range (S5: NO_insufficient supply), as shown in FIG. 5, the controller 6 determines whether or not the cooling water is flowing through the bypass line 46 (step S31).

[0073] If the bypass is in progress, i.e., if the bypass amount is not zero (S31: YES), the controller 6 maintains the rotation speed of the compressor 20 (step S34) and controls the bypass amount adjustment mechanism 48 to reduce the bypass amount (step S35). As a result, the amount of exhaust heat supplied to the evaporator 12 increases in accordance with the reduction in the bypass amount (increase in the main flow rate), and the amount of hot water heat generated by the heat pump unit 3 increases. The supply amount of hot water heat increases to match the demand.

[0074] At this point, the process ends. When the process resumes, the supply and demand balance of compressed gas is maintained in step S2, and then a supply and demand determination of hot water temperature is made (step S5). If the increase in the supply rate of hot water heat is still insufficient and the hot water temperature is still lower than the predetermined temperature range (S5: NO — insufficient supply), the bypass amount is reduced until the hot water temperature falls within the predetermined temperature range (step S35). When the hot water temperature rises to fall within the predetermined temperature range (S5: YES — supply and demand balance), the bypass amount at that time is maintained (step S12), and the discharged air amount is maintained at zero (step S13).

[0075] If the hot water temperature is lower than the predetermined temperature range and the bypass amount is zero (S31: NO), first, the controller 6 increases the rotation speed of the compressor 20 until the hot water temperature falls within the predetermined temperature range (step S32). As the rotation speed of the compressor 20 increases, the amount of compressed gas generated and the amount passing through the cooler increase, and the amount of waste heat recovered by the cooler 11 increases. Because the bypass amount is maintained at zero, the amount of waste heat supplied to the evaporator 12 increases, and the amount of heat of the hot water generated by the heat pump unit 3 increases. Therefore, the hot water temperature rises. When the hot water temperature rises to fall within the predetermined temperature range, the supply of hot water heat balances with the demand.

[0076] By the above control, even if the supply amount of hot water heat, which is uniquely determined by the supply amount of compressed gas, is less than the demand amount, the amount of compressed gas passing through the cooler is increased, thereby making up for the shortage of hot water heat. If the compressed gas were supplied to the demand destination as is, the supply amount of compressed gas would be in excess of the demand amount.

[0077] Therefore, the controller 6 controls the air release valve to increase the amount of air released until the discharge pressure detected by the pressure sensor 71 falls within a predetermined pressure range (step S33). This allows a portion of the compressed gas after passing through the cooler to be released to the outside air while maintaining the amount passing through the cooler, and the supply amount of compressed gas is suppressed relative to the amount passing through the cooler. A balance between supply and demand of compressed gas is achieved while maintaining a balance between supply and demand of hot water heat quantity.

[0078] At this point, the process ends. When the process resumes, the supply and demand balance of compressed gas is maintained in step S2, and then a supply and demand determination of hot water temperature is made (step S5). The hot water temperature is within the predetermined temperature range (S5: YES_supply and demand balance), the bypass amount is maintained at zero (step S12), and the release air amount at that time is maintained (step S13).

[0079] Returning to FIG. 4, if the hot water temperature is higher than the predetermined temperature range and air is being released (S21: YES), the controller 6 reduces the rotation speed of the compressor 20 until the hot water temperature falls within the predetermined temperature range (step S24).

[0080] As the rotation speed of the compressor 20 decreases, the amount of compressed gas produced and the amount passing through the cooler decrease, and the amount of waste heat recovered by the cooler 11 decreases. The amount of waste heat supplied to the evaporator 12 decreases, and the amount of heat in the hot water produced by the heat pump unit 3 decreases. As a result, the hot water temperature decreases. When the hot water temperature decreases to within a predetermined temperature range, the supply of hot water heat balances with the demand.

[0081] On the other hand, the supply amount of compressed gas falls short of the demand amount, and the discharge pressure detected by the pressure sensor 71 decreases. Therefore, the controller 6 controls the air release valve 26 to decrease the amount of air released until the discharge pressure detected by the pressure sensor 71 falls within a predetermined pressure range (step S25). This achieves a balance between the supply and demand of compressed gas while maintaining a balance between the supply and demand of hot water heat quantity.

[0082] At this point, the process ends. When the process resumes, the supply and demand balance of compressed gas is maintained in step S2, and then a supply and demand determination of hot water temperature is made (step S5). The hot water temperature is within the predetermined temperature range (S5: YES_supply and demand balance), the bypass amount is maintained at zero (step S12), and the release air amount at that time is maintained (step S13).

[0083] In step S24, the rotation speed of the compressor 20 may reach the minimum rotation speed before the hot water temperature falls within the predetermined temperature range. If the compressor 20 is controlled to stop when its rotation speed falls below the minimum rotation speed, it is preferable to proceed to step S25 rather than reducing the rotation speed to a value lower than the minimum rotation speed so as not to stop the compressor 20. That is, in step S24, if the rotation speed of the compressor 20 reaches the minimum rotation speed before the hot water temperature falls within the predetermined temperature range, the rotation speed of the compressor 20 may be maintained at the minimum rotation speed and the process may proceed to step S25. In step S25, the discharged air volume decreases to zero. At this point, the process temporarily ends. When the process resumes, the rotation speed of the compressor 20 is adjusted in step S2 so as to maintain the balance between supply and demand of compressed gas, and then a supply and demand determination of the hot water temperature is made (step S5). The hot water temperature is still higher than the predetermined temperature range (S5: NO_excess supply) and the amount of released air is zero (S21: NO), so the supply and demand of the hot water heat quantity is balanced by increasing the bypass amount (step S23).

[0084] The exhaust heat recovery system 1 of this embodiment comprises a compressor unit 2 including an oil-free compressor 20 and a cooler 11 that cools the compressed gas discharged from the compressor 20 with cooling water; a heat pump unit 3 that includes a refrigerant circulation line 30 that circulates the refrigerant, an evaporator 12 that evaporates the refrigerant, and a condenser 13 that condenses the refrigerant, thereby forming a refrigeration cycle; a cooling unit 4 that includes a cooling water supply line 41 that sends cooling water heated by heat exchange with the compressed gas in the cooler 11 to the evaporator 12, and a cooling water return line 42 that returns cooling water cooled by heat exchange with the refrigerant in the evaporator 12 to the cooler 11; and a hot water supply unit 5 that includes a water line 51 that sends water to the condenser 13 and a hot water line 52 that circulates hot water obtained by heating water by heat exchange with the refrigerant in the condenser 13.

[0085] The compressor unit 2 allows the compressed gas discharged from the compressor 20 to be supplied to the demand destination. In addition, the exhaust heat recovered from the compressed gas when it is cooled is used as a heat source for the heat pump unit 3 in the evaporator 12, and the heat pump unit 3 generates hot water from water in the condenser 13. The hot water obtained can be supplied to the demand destination by the hot water supply unit 5. By using a heat pump, hot water with a high calorific value can be obtained without providing multiple heat exchangers in the compressor unit 2. In addition, pressure loss is suppressed, improving the operating efficiency of the compressor. Because the compressor 20 is oil-free, the temperature of the compressed gas is high and a large amount of exhaust heat can be recovered.

[0086] The exhaust heat recovery system 1 according to this embodiment includes a pressure sensor 71 that detects the discharge pressure of the compressor 20, and a controller 6 that controls the rotation speed of the compressor 20 so that the discharge pressure detected by the pressure sensor 71 falls within a predetermined pressure range. This adjusts the supply amount of compressed gas to be balanced with the demand amount.

[0087] The exhaust heat recovery system 1 according to this embodiment includes a hot water temperature sensor 72 that detects the temperature of the hot water. The cooling unit 4 further includes a bypass line 46 that bypasses the evaporator 12 and connects the coolant feed line 41 to the coolant return line 42, a cooling device 47 that is interposed in the bypass line 46 and cools the coolant, and a bypass amount adjustment mechanism 48 that adjusts the bypass amount, which is the flow rate of the coolant flowing from the cooler 11 to the cooling device 47. The controller 6 determines whether the hot water temperature detected by the hot water temperature sensor 72 is within a predetermined temperature range, and, if the hot water temperature is higher than the predetermined temperature range, controls the bypass amount adjustment mechanism 48 to increase the bypass amount.

[0088] Referring to Figure 3, point A is on the dashed line and represents a state in which the supply and demand of compressed gas and the supply and demand of hot water heat are balanced under conditions where the bypass volume is zero and the discharged air volume is zero. From this state, assume that the demand for hot water heat decreases from point A to point B. For ease of explanation, the horizontal coordinate value of point B is the same as the horizontal coordinate value of point A, and the supply and demand of compressed gas remain unchanged.

[0089] The hot water heat supply becomes excessive, and the hot water temperature becomes higher than the specified temperature range. This increases the bypass amount, suppressing the supply of hot water heat. As a result, the points representing the supply of compressed gas and hot water heat do not move along the horizontal axis but move downward along the vertical axis, transitioning from point A to point B. In other words, the supply of hot water heat decreases to match the demand, while the supply of compressed gas remains unchanged. While maintaining the balance between supply and demand of compressed gas, the supply and demand of hot water heat is also balanced. Note that the distance ΔY between points A and B along the vertical axis corresponds to the amount of heat wasted by the cooling device 47 to balance the supply and demand of hot water heat.

[0090] The compressor unit 2 further includes an air release line 25 that releases the compressed gas that has passed through the cooler 11 into the outside air, and an air release valve 26 that adjusts the amount of air release, which is the amount of compressed gas released into the outside air through the air release line 25. When the hot water temperature is lower than a predetermined temperature range, the controller 6 increases the rotation speed of the compressor 20 and controls the air release valve 26 to increase the amount of air release.

[0091] Referring to Figure 3, point P, like point A, is on the dashed line and represents a state in which the supply and demand of compressed gas and the supply and demand of hot water heat are balanced under conditions in which the bypass volume is zero and the discharged air volume is zero. From this state, it is assumed that the demand for hot water heat increases from point P to point R. For ease of explanation, it is assumed that the horizontal coordinate value of point R is the same as the horizontal coordinate value of point P, and the supply and demand of compressed gas remain unchanged.

[0092] The supply of hot water heat becomes insufficient, and the hot water temperature falls below the specified temperature range. This causes the rotation speed of the compressor 20 to increase, increasing the amount of compressed gas passing through the cooler. As a result, the point representing the supply of compressed gas and the supply of hot water heat moves along the dashed line. The increase in the rotation speed of the compressor 20 stops when a balance is achieved between the supply and demand of hot water temperature. In other words, the point representing the supply of compressed gas and the supply of hot water heat moves from point P to point Q, which has the same vertical coordinate value as point R and is on the dashed line. This achieves a balance between the supply and demand of hot water heat. On the other hand, the supply of compressed gas also increases to ensure the supply of hot water heat, which could result in an oversupply of compressed gas.

[0093] As a result, the amount of released air increases and the amount of compressed gas supplied is suppressed. As a result, the points representing the amount of compressed gas supplied and the amount of hot water heat supplied do not move along the vertical axis but move to the negative side (left side) of the horizontal axis, transitioning from point Q to point R. In other words, the amount of hot water heat supplied remains unchanged, while the amount of compressed gas supplied decreases to match the demand. While maintaining a balance between the supply and demand of hot water heat, a balance is also achieved for the supply and demand of compressed gas. The distance ΔX between points Q and R on the horizontal axis corresponds to the amount of released air.

[0094] Next, with reference to FIG. 6, an exhaust heat recovery system 1 according to a second embodiment will be described, focusing on the differences from the first embodiment.

[0095] In this embodiment, the bypass amount adjustment mechanism 48 is configured as a three-way valve provided at the branch point of the cooling water supply line 41 and the bypass line 46. This three-way valve is a flow-control type three-way valve. When the amount of cooling water flowing into the flow-control type three-way valve is 100, the amount of cooling water flowing through each flow path can be adjusted by setting the mainstream flow rate to 10 and the bypass amount to 90, or by setting the mainstream flow rate to 50 and the bypass amount to 50. When the hot water temperature is higher than a predetermined temperature range, the controller 6 controls the three-way valve to adjust the main flow rate and the bypass amount. That is, the controller 6 decreases the mainstream flow rate and increases the bypass amount. This minimizes the amount of heat wasted by the cooling device 47 and makes it easier to adjust the supply amount of hot water heat to match the demand amount. The three-way valve may also be an on-off type three-way valve that, when the amount of cooling water flowing into the three-way valve is 100, sets the mainstream flow rate to 100 and the bypass amount to 0, or sets the main flow rate to 100 and the bypass amount to 0.

[0096] In this embodiment, the receiver tank 22 of the compressor unit 2 is provided with an air release line 25, and further includes an expander 27 driven by the compressed gas and a generator 28 driven by the expander 27. In this case, electrical energy can be recovered from the compressed gas released into the outside air, improving the efficiency of the exhaust heat recovery system 1.

[0097] Although the embodiment has been described above, the above configuration is merely an example and can be modified as appropriate within the scope of the present invention.

[0098] The bypass amount adjustment mechanism 48 may be configured according to the first embodiment, and the air discharge line 25 of the compressor unit 2 may be configured according to the second embodiment. The bypass amount adjustment mechanism 48 may be configured according to the second embodiment, and the air discharge line 25 of the compressor unit 2 may be configured according to the first embodiment.

[0099] The gas release line 25 is only required to be able to release the compressed gas after passing through the cooler to the outside air, and is not necessarily connected to the receiver tank 22. For example, the gas release line 25 may branch off from the pipe 23a or the pipe 23b. [Explanation of symbols]

[0100] 1. Waste heat recovery system 2 Compressor unit 3 Heat pump unit 4 Cooling Unit 5 Hot water supply unit 6 Controller 11 Cooler 11A Intercooler 11B Aftercooler 12 Evaporator 13 Condenser 20 Compressor 20A low pressure stage compressor 20B high pressure stage compressor 21a motor 21b Inverter 22 Receiver tank 23a Piping 23b Piping 24a Check valve 24b Discharge valve 25 Ventilation line 26 Air release valve 27 Expander 28 Generator 30 Refrigerant circulation line 31 Refrigeration compressor 31a Motor 31b Inverter 32 Expansion valve 40 Cooling water circulation line 40m main line 41 Cooling water supply line 41a downstream 42 Cooling water return line 42a upstream part 43 Water Pump 44 Oil cooler 45 Body cooling mechanism 45a low pressure stage jacket 45b High pressure stage jacket 46 Bypass Line 47 Cooling device 48 Bypass amount adjustment mechanism 51 Water Line 52 Hot water line 71 Pressure Sensor 72 Hot water temperature sensor ΔX, ΔY interval

Claims

1. a compressor unit including an oil-free compressor and a cooler that cools compressed gas discharged from the compressor with cooling water; a heat pump unit that includes a refrigerant circulation line that circulates a refrigerant, an evaporator that evaporates the refrigerant, and a condenser that condenses the refrigerant, and that constitutes a refrigeration cycle; a cooling unit including a cooling water supply line for supplying the cooling water heated by heat exchange with the compressed gas in the cooler to the evaporator, and a cooling water return line for returning the cooling water cooled by heat exchange with the refrigerant in the evaporator to the cooler; a hot water supply unit including a water line for supplying water to the condenser and a hot water line for circulating hot water obtained by heating the water through heat exchange with the refrigerant in the condenser; a pressure sensor for detecting a discharge pressure of the compressor; a hot water temperature sensor for detecting the temperature of the hot water; a controller that controls the rotation speed of the compressor so that the discharge pressure detected by the pressure sensor is within a predetermined pressure range; Equipped with The cooling unit is a bypass line that bypasses the evaporator and connects the cooling water delivery line to the cooling water return line; a cooling device interposed in the bypass line and cooling the cooling water; a bypass amount adjustment mechanism that adjusts a bypass amount, which is a flow rate of the cooling water flowing from the cooler to the cooling device, The controller determining whether the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range; When the hot water temperature is higher than the predetermined temperature range, the bypass amount adjustment mechanism is controlled to increase the bypass amount. Waste heat recovery system.

2. the bypass amount adjustment mechanism is configured by a three-way valve provided at a branch point between the cooling water feed line and the bypass line, When the hot water temperature is higher than the predetermined temperature range, the controller controls the three-way valve to control the flow rate of the cooling water flowing from the cooler to the evaporator and the bypass amount. The exhaust heat recovery system according to claim 1 .

3. The compressor unit is an air release line that releases the compressed gas that has passed through the cooler into the outside air; Further includes an air release valve that adjusts the amount of compressed gas released to the outside air through the air release line, When the hot water temperature is lower than the predetermined temperature range, the controller increases the rotation speed of the compressor and controls the air release valve to increase the amount of air released. The exhaust heat recovery system according to claim 1 or 2.

4. a compressor unit including an oil-free compressor and a cooler that cools compressed gas discharged from the compressor with cooling water; a heat pump unit that includes a refrigerant circulation line that circulates a refrigerant, an evaporator that evaporates the refrigerant, and a condenser that condenses the refrigerant, and that constitutes a refrigeration cycle; a cooling unit including a cooling water supply line for supplying the cooling water heated by heat exchange with the compressed gas in the cooler to the evaporator, and a cooling water return line for returning the cooling water cooled by heat exchange with the refrigerant in the evaporator to the cooler; a hot water supply unit including a water line for supplying water to the condenser and a hot water line for circulating hot water obtained by heating the water through heat exchange with the refrigerant in the condenser; a pressure sensor for detecting a discharge pressure of the compressor; a hot water temperature sensor for detecting the temperature of the hot water; a controller that controls the rotation speed of the compressor so that the discharge pressure detected by the pressure sensor is within a predetermined pressure range; Equipped with The compressor unit is an air release line that releases the compressed gas that has passed through the cooler into the outside air; Further includes an air release valve that adjusts the amount of compressed gas released to the outside air through the air release line, The controller determining whether the hot water temperature detected by the hot water temperature sensor is within a predetermined temperature range; When the hot water temperature is lower than the predetermined temperature range, the rotation speed of the compressor is increased and the air release valve is controlled to increase the amount of air released. Waste heat recovery system.

5. the compressor unit further includes a receiver tank that stores the compressed gas that has passed through the cooler, and the release line releases the compressed gas in the receiver tank to the outside air. The exhaust heat recovery system according to claim 4.

6. The compressor unit is an expander provided in the gas release line and driven by the compressed gas; and a generator driven by the expander. The exhaust heat recovery system according to claim 4 or 5.

Images