Exhaust heat recovery system and exhaust heat recovery method

Abstract

An exhaust heat recovery system 1 comprises: a gas compressor unit 10 for producing a compressed gas by means of an oil-free gas compressor 11; and a heat pump unit 20 having a refrigeration cycle 21 in which heat of the compressed gas discharged from the gas compressor unit 10 is used, directly or indirectly, for evaporation of a refrigerant. The refrigeration cycle 21 includes a hot water supply heat exchange part 26 that uses heat of the refrigerant to raise the temperature of water to obtain hot water.

Description

Exhaust heat recovery system and exhaust heat recovery method

[0001] The present disclosure relates to an exhaust heat recovery system and an exhaust heat recovery method.

[0002] Patent Document 1 discloses a technology for recovering heat from compressed air discharged from a two-stage compressor to heat water and produce hot water. Specifically, the compressed air discharged from the first-stage compressor body is subjected to heat recovery and cooling in an intermediate-stage heat exchanger for waste heat recovery and an intercooler, and the compressed air discharged from the second-stage compressor body is subjected to heat recovery and cooling in a discharge-stage heat exchanger for waste heat recovery and an aftercooler. The heat recovered in the intermediate-stage heat exchanger for waste heat recovery and the discharge-stage heat exchanger is used to heat the water and produce hot water.

[0003] International Publication No. 2017 / 111120

[0004] In Patent Document 1, two heat exchangers are provided downstream of the first-stage compressor body and upstream of the second-stage compressor body, and two heat exchangers are provided downstream of the second-stage compressor body. This results in a complex configuration requiring many heat exchangers. Because pressure loss occurs when compressed air passes through the heat exchangers, using many heat exchangers may reduce the operating efficiency of the compressor. Furthermore, because the only heat sources for producing hot water are the intermediate-stage waste heat recovery heat exchanger and the discharge-stage waste heat recovery heat exchanger, there is a risk that high-temperature hot water may not be obtained.

[0005] An object of the present disclosure is to supply high-temperature hot water using exhaust heat from a gas compressor with a simple configuration.

[0006] The present disclosure provides an exhaust heat recovery system comprising: a gas compressor unit that produces compressed gas using an oil-free gas compressor; and a heat pump unit having a refrigeration cycle that directly or indirectly utilizes the heat of the compressed gas discharged from the gas compressor to evaporate a refrigerant, wherein the refrigeration cycle includes a hot water supply heat exchange section that uses the heat of the refrigerant to heat water to produce hot water.

[0007] This configuration allows compressed gas to be supplied to a consumer, and allows the exhaust heat of the gas compressor (e.g., the heat of the compressed gas discharged from the gas compressor) to be effectively utilized to produce hot water. In particular, the exhaust heat of the gas compressor is utilized to drive the refrigeration cycle, and the refrigerant heated by the refrigeration cycle can be utilized to produce high-temperature hot water. Because the compressed gas can be effectively cooled by utilizing the refrigeration cycle, there is no need to install many heat exchangers in the gas compressor unit, allowing for a simple configuration. Furthermore, because the gas compressor is oil-free, the temperature of the compressed gas discharged is high, making exhaust heat recovery highly effective.

[0008] The heat pump unit may include a refrigerant compressor that compresses the refrigerant, an inverter that adjusts the rotation speed of the refrigerant compressor, and a control device that controls the rotation speed of the refrigerant compressor via the inverter.

[0009] According to this configuration, the rotation speed of the refrigerant compressor can be controlled by the control device via the inverter, so that the amount of cooling in the refrigeration cycle can be adjusted.

[0010] The heat pump unit may include a gas-water heat exchanger that exchanges heat between the compressed gas discharged from the gas compressor and cooling water, thereby cooling the compressed gas and heating the cooling water, and a water-refrigerant heat exchanger that exchanges heat between the cooling water heated in the gas-water heat exchanger and the refrigerant, thereby cooling the cooling water and heating the refrigerant.

[0011] According to this configuration, the gas-water heat exchanger recovers heat from the compressed gas to the cooling water, and the water-refrigerant heat exchanger recovers heat from the cooling water to the refrigerant. Therefore, a specific configuration for exhaust heat recovery can be realized.

[0012] The heat pump unit may have a cooling water temperature sensor that measures the temperature of the cooling water upstream of the gas-water heat exchanger, and the control device may control the rotation speed of the refrigerant compressor so that the detection value of the cooling water temperature sensor is within a predetermined range.

[0013] According to this configuration, the temperature of the cooling water supplied to the gas-water heat exchanger can be maintained within a predetermined range, and therefore the amount of cooling of the compressed gas in the gas-water heat exchanger can be maintained within a suitable range.

[0014] The gas compressor may be a two-stage compressor having a low-pressure stage compressor body and a high-pressure stage compressor body, and the gas-water exchange section may have a water-cooled intercooler that cools the compressed gas discharged from the low-pressure stage compressor body, and a water-cooled aftercooler that cools the compressed gas discharged from the high-pressure stage compressor body.

[0015] According to this configuration, it is possible to easily realize an exhaust heat recovery structure that utilizes cooling water when using a two-stage compressor.

[0016] The gas compressor unit may have a gas temperature sensor that measures the temperature of the compressed gas downstream of the water-cooled intercooler and upstream of the high-pressure stage compressor main body, and the control device may control the rotation speed of the refrigerant compressor so that the detection value of the gas temperature sensor falls within a predetermined range.

[0017] According to this configuration, the temperature of the compressed gas taken in by the high-pressure stage compressor main body can be maintained within a suitable range.

[0018] The gas compressor unit may include a drain separator that separates drain from the compressed gas downstream of the gas-water heat exchanger, and an adsorption dryer that dries the compressed gas downstream of the drain separator.

[0019] According to this configuration, moisture can be removed from the compressed gas by the drain separator and the adsorption dryer. Furthermore, the drain separator can improve the performance of the adsorption dryer.

[0020] The heat pump unit may include a gas-refrigerant heat exchanger that exchanges heat between the compressed gas discharged from the gas compressor and the refrigerant to cool the compressed gas and heat the refrigerant.

[0021] According to this configuration, the gas refrigerant exchange section can recover heat from the compressed gas to the refrigerant, thereby realizing a specific configuration for heat transport.

[0022] The heat pump unit may have a refrigerant temperature sensor that measures the temperature of the refrigerant upstream of the gas refrigerant heat exchanger, and the control device may control the rotation speed of the refrigerant compressor so that the detection value of the refrigerant temperature sensor is within a predetermined range.

[0023] According to this configuration, the temperature of the refrigerant supplied to the gas refrigerant exchanging section can be maintained within a predetermined range, and therefore the amount of cooling of the compressed gas in the gas refrigerant exchanging section can be maintained within a suitable range.

[0024] The gas compressor may be a two-stage compressor having a low-pressure stage compressor main body and a high-pressure stage compressor main body, and the gas refrigerant heat exchange unit may have a refrigerant intercooler that cools the compressed gas discharged from the low-pressure stage compressor main body, and a refrigerant aftercooler that cools the compressed gas discharged from the high-pressure stage compressor main body.

[0025] According to this configuration, it is possible to easily realize an exhaust heat recovery structure that utilizes a refrigerant when using a two-stage compressor.

[0026] The gas compressor unit may have a gas temperature sensor that measures the temperature of the compressed gas downstream of the refrigerant intercooler and upstream of the high-pressure stage compressor main body, and the control device may control the rotation speed of the refrigerant compressor so that the detection value of the gas temperature sensor falls within a predetermined range.

[0027] According to this configuration, the temperature of the compressed gas taken in by the high-pressure stage compressor main body can be maintained within a suitable range.

[0028] The gas compressor unit may include a drain separator that separates drain from the compressed gas downstream of the gas refrigerant heat exchange section, and an adsorption dryer that dries the compressed gas downstream of the drain separator.

[0029] According to this configuration, moisture can be removed from the compressed gas by the drain separator and the adsorption dryer. Furthermore, the drain separator can improve the performance of the adsorption dryer.

[0030] The exhaust heat recovery system may include a first housing in which the compressor unit is housed, a second housing in which the heat pump unit is housed, and a stand on which the first housing and the second housing are commonly arranged.

[0031] According to this configuration, since the first housing and the second housing are arranged on the same stand, it is easy to arrange the piping connecting the compressor unit and the heat pump unit.

[0032] A housing that commonly houses the compressor unit and the heat pump unit may be arranged on a stand.

[0033] According to this configuration, the compressor unit and the heat pump unit are housed in the same housing and are arranged on a stand, thereby realizing space saving.

[0034] The present disclosure also provides a method for recovering exhaust heat, including: producing compressed gas using an oil-free gas compressor; using the heat of the compressed gas discharged from the gas compressor directly or indirectly to evaporate a refrigerant in a refrigeration cycle; and heating water using the heat of the refrigerant heated in the refrigeration cycle to supply the water as hot water.

[0035] The refrigeration cycle may include a refrigerant compressor that compresses the refrigerant, an inverter that adjusts the rotation speed of the refrigerant compressor, and a control device that controls the rotation speed of the refrigerant compressor via the inverter, and the control device may output a control command to the inverter.

[0036] According to the present disclosure, high-temperature hot water can be supplied using a simple configuration by utilizing the exhaust heat of a gas compressor.

[0037] FIG. 5 is a schematic configuration diagram of an exhaust heat recovery system according to a first embodiment of the present disclosure. FIG. 6 is a first flowchart relating to temperature adjustment of coolant. FIG. 7 is a second flowchart relating to temperature adjustment of compressed air. FIG. 8 is a side view showing an example layout of the exhaust heat recovery system of FIG. 1. FIG. 9 is a schematic configuration diagram of an exhaust heat recovery system according to a second embodiment. FIG. 10 is a first flowchart relating to temperature adjustment of a refrigerant. FIG. 11 is a second flowchart relating to temperature adjustment of compressed air. FIG. 12 is a side view showing an example layout of the exhaust heat recovery system of FIG. 13. FIG. 14 is a schematic configuration diagram of an exhaust heat recovery system according to a modified example of the first embodiment. FIG. 15 is a schematic configuration diagram of an exhaust heat recovery system according to a modified example of the second embodiment.

[0038] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0039] First Embodiment Referring to FIG. 1 , an exhaust heat recovery system 1 according to a first embodiment of the present disclosure includes an air compressor unit 10 , a heat pump unit 20 , and a hot water supply unit 30 .

[0040] The air compressor unit 10 includes an oil-free air compressor 11. The air compressor 11 of this embodiment is a two-stage compressor including a low-pressure stage compressor body 12 and a high-pressure stage compressor body 13. However, the air compressor 11 is not limited to a two-stage compressor, and may be a one-stage or three or more-stage compressor. While the description here uses air as an example of the object to be compressed, the object to be compressed may be any gas other than air. Therefore, the air compressor unit 10 and the air compressor 11 are examples of a gas compressor unit and a gas compressor. In other words, the gas to be compressed by the gas compressor 11 may be either air or a gas other than air (e.g., a refrigerant gas).

[0041] In this embodiment, the low-pressure stage compressor body 12 is of a screw type and has a pair of male and female screw rotors inside. The pair of male and female screw rotors are mechanically connected to a motor 12a and are rotationally driven by the motor 12a. The motor 12a is electrically connected to an inverter 12b and has its rotation speed adjusted by the inverter 12b.

[0042] In this embodiment, the high-pressure stage compressor body 13 is of a screw type and has a pair of male and female screw rotors inside. The low-pressure stage compressor body 12 and the high-pressure stage compressor body 13 are driven via a drive device driven by a motor 12a. In detail, one pinion gear is attached to one axial end of the pair of screw rotors of the low-pressure stage compressor body 12 and one axial end of the pair of screw rotors of the high-pressure stage compressor body 13, and bull gears that drive the two pinion gears are driven by a single motor 12a.

[0043] The types of the low-pressure stage compressor body 12 and the high-pressure stage compressor body 13 are not limited to screw types and may be any type. A motor and an inverter may be attached to each of the low-pressure stage compressor body 12 and the high-pressure stage compressor body 13. Furthermore, if the low-pressure stage compressor body 12 and the high-pressure stage compressor body 13 are not of a type that allows for adjustable rotation speeds, the inverters 12b, 13b may be omitted.

[0044] The air compressor unit 10 has an air-water heat exchanger 14 that cools the compressed air of the air compressor 11. The air-water heat exchanger 14 has a water-cooled intercooler 14a that cools the compressed air discharged from the low-pressure stage compressor body 12, and a water-cooled aftercooler 14b that cools the compressed air discharged from the high-pressure stage compressor body 13.

[0045] In this embodiment, the air compressor unit 10 has a drain separator 15 that separates drain from the compressed air downstream of the air-water heat exchange section 14, and an adsorption dryer 16 that dries the compressed air downstream of the drain separator 15.

[0046] The drain separator 15 is disposed downstream of the water-cooled aftercooler 14 b and removes drainage that may be generated by cooling in the water-cooled aftercooler 14 b. The drain separator 15 may be of a known type, such as a centrifugal separator.

[0047] The adsorption dryer 16 is disposed downstream of the condensate separator 15 and dries the compressed air. The adsorption dryer 16 may be of a known type, such as an adsorption filter.

[0048] The drain separator 15 and the adsorption dryer 16 are not essential components and may be omitted as necessary.

[0049] The heat pump unit 20 has a refrigeration cycle 21 that indirectly uses the heat of compressed air discharged from the air compressor 11 to evaporate a refrigerant. The type of refrigerant is not particularly limited, and may be any known type that is generally used in the refrigeration cycle 21.

[0050] In this embodiment, the heat pump unit 20 has an air-water heat exchanger 14 that exchanges heat between the compressed air discharged from the air compressor 11 and the coolant, thereby cooling the compressed air and heating the coolant. The air-water heat exchanger 14 is shared by the air compressor unit 10 and the heat pump unit 20. The heat pump unit 20 also has a water-refrigerant heat exchanger 22 that exchanges heat between the coolant heated in the air-water heat exchanger 14 and the refrigerant, thereby cooling the coolant and heating the refrigerant. The water-refrigerant heat exchanger 22 may be any known heat exchanger, such as a fin-type or tube-type heat exchanger.

[0051] In the water-cooled intercooler 14a of the air-water heat exchanger 14, heat exchange is performed so that the compressed air discharged from the low-pressure stage compressor body 12 is cooled and the cooling water is heated. Similarly, in the water-cooled aftercooler 14b of the air-water heat exchanger 14, heat exchange is performed so that the compressed air discharged from the high-pressure stage compressor body 13 is cooled and the cooling water is heated. The water-cooled intercooler 14a and the water-cooled aftercooler 14b may be any known heat exchanger, such as a fin type or a tube type.

[0052] The cooling water circulates through a cooling water flow path 24 so as to flow in this order through the water-cooled intercooler 14a, the water-cooled aftercooler 14b, the water-refrigerant heat exchanger 22, and the pump 23. The cooling water flow path 24 has a structure that allows the cooling water to circulate.

[0053] The refrigeration cycle 21 includes a refrigerant compressor 25 that compresses the refrigerant, a condenser 26 (also referred to as a hot water supply heat exchanger 26) that condenses the refrigerant, an expansion valve 27 that expands and cools the refrigerant after passing through the condenser 26, and an evaporator (water-refrigerant heat exchanger) 22 that recovers exhaust heat by heat exchange with the refrigerant. The refrigerant compressor 25, condenser 26, expansion valve 27, and evaporator 22 are arranged in this order to circulate the refrigerant.

[0054] The refrigerant compressor 25 is, for example, a screw type and has a pair of male and female screw rotors therein. The pair of male and female screw rotors are mechanically connected to and rotated by a motor 25a. The motor 25a is electrically connected to an inverter 25b, and its rotation speed is adjusted by the inverter 25b. The rotation speed of the refrigerant compressor 25 may be adjusted to follow the rotation speed of the air compressor 11, i.e., in accordance with the capacity adjustment of the air compressor 11. The capacity adjustment is intended to adjust the amount of discharge gas in accordance with the consumption amount of discharge gas at the consumption destination. Specifically, when the control device 28 increases the rotation speed of the air compressor 11, it outputs a control command to the inverter 25b of the refrigerant compressor 25 to increase the rotation speed of the refrigerant compressor 25. When the control device 28 decreases the rotation speed of the air compressor 11, it outputs a control command to the inverter 25b of the refrigerant compressor 25 to decrease the rotation speed of the refrigerant compressor 25. The rotation speed control based on the coolant temperature sensor 28a and the gas temperature sensor 28b described below is preferably performed after the rotation speed control of the refrigerant compressor 25 in accordance with the capacity adjustment of the air compressor 11. The capacity adjustment of the air compressor 11 is intended to control the rotor rotation speed in the air compressor 11 having the inverter 25b. The capacity adjustment of the air compressor 11 may be achieved by a slide valve capable of adjusting the capacity of the discharge gas of the air compressor 11, or, when multiple gas compressors 11 are provided, may be achieved by controlling the number of gas compressors 11.

[0055] The hot water supply unit 30 has a water supply section 31, a hot water supply heat exchange section (condenser) 26, and a hot water outlet 32. The hot water supply heat exchange section (condenser) 26 is shared by the heat pump unit 20 and the hot water supply unit 30.

[0056] The hot water supply unit 30 uses the heat of the refrigerant heated in the refrigeration cycle 21 to heat water and supply it as hot water. The term "water" here refers to the object to be heated and is not limited to the water temperature. "Hot water" refers to heated water. 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). Specifically, the hot water supply heat exchanger (condenser) 26 cools (condenses) the refrigerant in the refrigeration cycle 21 and heats the water supplied from the water supply unit 31, thereby producing hot water. That is, the hot water supply heat exchanger (condenser) 26 heats the water using the heat of the refrigerant to produce usable hot water. The hot water is extracted from the hot water outlet 32 ​​and supplied to any desired destination. The hot water taken out from the hot water outlet 32 ​​may be heat exchanged with a fluid or the like in a heat exchanger separate from the condenser 26, thereby utilizing the waste heat at the supply destination. The hot water supply heat exchange unit (condenser) 26 may be any known heat exchanger such as a fin type or a tube type.

[0057] The exhaust heat recovery system 1 also has a control device 28 that controls the rotation speeds of the low-pressure stage compressor body 12, the high-pressure stage compressor body 13, and the refrigerant compressor 25 via the inverters 12b, 13b, and 25b, respectively. The control device 28 is composed of hardware such as a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory), and software implemented therein.

[0058] In this embodiment, the heat pump unit 20 has a coolant temperature sensor 28a that measures a temperature t1 of the coolant upstream of the air-water heat exchanger 14. The air compressor unit 10 also has an air temperature sensor (an example of a gas temperature sensor) 28b that measures a temperature t2 of the compressed air downstream of the water-cooled intercooler 14a and upstream of the high-pressure stage compressor body 13.

[0059] The control device 28 controls the rotation speed of the refrigerant compressor 25 so that the detection value t1 of the coolant temperature sensor 28a falls within a predetermined range. Specifically, the control flow chart of the control device 28 will be described with reference to FIG.

[0060] When the refrigerant compressor 25 is operated (step S2-1), the coolant temperature sensor 28a measures the coolant temperature t1 (step S2-2). The control device 28 then determines whether the coolant temperature t1 is within a predetermined temperature range and whether it deviates from that range (step S2-3). If the coolant temperature t1 is lower than the predetermined temperature range, the control device 28 reduces the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S2-4) and returns to measuring the coolant temperature t1 (step S2-2). If the coolant temperature t1 is higher than the predetermined temperature range, the control device 28 increases the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S2-5) and returns to measuring the coolant temperature t1 (step S2-2). If the coolant temperature t1 is within the predetermined temperature range, the control device 28 maintains the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S2-6), and the air compressor 11 is operated (step S2-7). The flow relating to the temperature adjustment of the cooling water (i.e., the control from steps S2-2 to before S2-7) may be executed at all times while the air compressor 11 is in operation.

[0061] Alternatively or additionally, the control device 28 controls the rotation speed of the refrigerant compressor 25 so that the detected value t2 of the air temperature sensor 28b is within a predetermined range. Specifically, the control flow of the control device 28 will be described with reference to Figure 3. The flow related to the temperature adjustment of the compressed air (i.e., the control from steps S3-2 to before S3-7) may be executed continuously while the air compressor 11 is operating.

[0062] When the refrigerant compressor 25 is operated (step S3-1), the air temperature sensor 28b measures the compressed air temperature t2 (step S3-2). The control device 28 then determines whether the compressed air temperature t2 is within a predetermined temperature range and whether it deviates from that range (step S3-3). If the compressed air temperature t2 is lower than the predetermined temperature range, the control device 28 reduces the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S3-4) and returns to measuring the compressed air temperature t2 (step S3-2). If the compressed air temperature t2 is higher than the predetermined temperature range, the control device 28 increases the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S3-5) and returns to measuring the compressed air temperature t2 (step S3-2). If the compressed air temperature t2 is within the predetermined temperature range, the control device 28 maintains the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S3-6), and the air compressor 11 is operated (step S3-7).

[0063] The predetermined ranges of temperatures t1 and t2 are ranges that can realize an intake air temperature at which the high-pressure stage compressor body 13 can be efficiently operated. Note that, when the rotation speed of the refrigerant compressor 25 increases, the amount of cooling of the cooling water in the evaporator (water-refrigerant heat exchanger) 22 increases, the temperature t1 of the cooling water decreases, and the temperature t2 of the air taken in by the high-pressure stage compressor body 13 decreases. Conversely, when the rotation speed of the refrigerant compressor 25 decreases, the amount of cooling of the cooling water in the evaporator (water-refrigerant heat exchanger) 22 decreases, the temperature t1 of the cooling water increases, and the temperature t2 of the air taken in by the high-pressure stage compressor body 13 increases.

[0064] Referring to Fig. 4, in the exhaust heat recovery system 1 of this embodiment, the heat pump unit 20 and the condenser 26 are integrated and housed in a housing 2. A water supply unit 31 and a hot water outlet 32 ​​are provided on the side of the housing 2. The air compressor unit 10 is housed separately from these in a housing 3. These housings 2 and 3 are placed on the same stand 4 and are fluidly connected by a pipe 5 through which cooling water flows. In addition, a pump 23 for circulating the cooling water is attached to the pipe 5 outside these housings 2 and 3. However, the arrangement of the units 10, 20, and 30 is not limited to that shown in the figure and may be arbitrary.

[0065] This embodiment can also be said to be an exhaust heat recovery method for recovering exhaust heat from an oil-free air compressor 11, which includes an evaporation process in which exhaust heat from the air compressor 11 is supplied to the primary side of an evaporator 22 provided in a refrigeration cycle 21, thereby evaporating a refrigerant on the secondary side of the evaporator 22; a compression process in which the refrigerant flowing out from the evaporator 22 is supplied to a refrigerant compressor 25, thereby circulating the refrigerant in the refrigeration cycle 21 and compressing the refrigerant; a hot water generation process in which the refrigerant compressed by the refrigerant compressor 25 is supplied to the primary side of a condenser 26, thereby generating hot water on the secondary side of the condenser 26; and a decompression process in which the refrigerant flowing out from the condenser 26 is expanded and cooled by being decompressed (by an expansion valve 27).

[0066] The exhaust heat recovery system 1 of this embodiment provides the following advantageous effects.

[0067] The exhaust heat of the gas compressor 11 (heat of the compressed gas discharged from the gas compressor 11) can be effectively used to produce hot water. In particular, the exhaust heat of the gas compressor 11 is used to drive the refrigeration cycle 21, and the refrigerant heated by the refrigeration cycle 21 is used to produce high-temperature hot water. This allows hot water to be produced at a higher temperature than when hot water is produced using only the exhaust heat of the gas compressor 11. Because the compressed gas can be effectively cooled by using the refrigeration cycle 21, there is no need to provide many heat exchangers in the gas compressor unit 10, allowing for a simple configuration. Furthermore, because the gas compressor 11 is oil-free, the temperature of the compressed gas discharged is high, making exhaust heat recovery highly effective.

[0068] Furthermore, the rotation speed of the refrigerant compressor 25 can be controlled by the control device 28 via the inverter 25b, so that the amount of cooling of the refrigeration cycle 21 can be adjusted.

[0069] Furthermore, heat can be recovered from the compressed gas to the cooling water by the gas-water heat exchanger 14, and from the cooling water to the refrigerant by the water-refrigerant heat exchanger 22. Therefore, a specific configuration for exhaust heat recovery can be realized.

[0070] Furthermore, the control device 28 can maintain the temperature of the cooling water supplied to the gas-water heat exchanger 14 within a predetermined range, so that the amount of cooling of the compressed gas in the gas-water heat exchanger 14 can be maintained within a suitable range.

[0071] Furthermore, when a two-stage gas compressor 11 is used, a waste heat recovery structure using cooling water can be easily realized.

[0072] Furthermore, the control device 28 can maintain the temperature of the compressed gas taken in by the high-pressure stage compressor body 13 within a suitable range.

[0073] Furthermore, moisture can be removed from the compressed gas by the drain separator 15 and the adsorption dryer 16. Furthermore, the drain separator 15 can improve the performance of the adsorption dryer 16.

[0074] Furthermore, since the housings 2 and 3 are arranged on the same stand 4, it is easy to route the piping 5 connecting the compressor unit 10 and the heat pump unit 20. Note that, although the present embodiment shows an example in which the housings 2 and 3 are arranged on the same stand 4, the present disclosure is not limited to this and a stand may be provided for each of the housings 2 and 3.

[0075] Second Embodiment The exhaust heat recovery system 1 of the second embodiment shown in Fig. 5 recovers heat directly from compressed air using a refrigerant, unlike the first embodiment. Other than this, the system is substantially the same as the first embodiment. Therefore, the description of the parts shown in the first embodiment may be omitted.

[0076] In this embodiment, the air compressor unit 10 has an air-refrigerant heat exchanger 17 that cools the compressed air of the air compressor 11. The air-refrigerant heat exchanger 17 has a refrigerant intercooler 17a that cools the compressed air discharged from the low-pressure stage compressor body 12, and a refrigerant aftercooler 17b that cools the compressed air discharged from the high-pressure stage compressor body 13.

[0077] The heat pump unit 20 has a refrigeration cycle 21 that directly utilizes the heat of compressed air discharged from the air compressor 11 to evaporate refrigerant.

[0078] In this embodiment, the heat pump unit 20 has an air-refrigerant heat exchanger 17 that exchanges heat between the compressed air discharged from the air compressor 11 and the refrigerant, thereby cooling the compressed air and heating the refrigerant. The air-refrigerant heat exchanger 17 is shared by the air compressor unit 10 and the heat pump unit 20.

[0079] In the refrigerant intercooler 17a of the air-refrigerant heat exchange unit 17, heat exchange is performed so that the compressed air discharged from the low-pressure stage compressor body 12 is cooled and the refrigerant is heated. Similarly, in the refrigerant aftercooler 17b of the air-refrigerant heat exchange unit 17, heat exchange is performed so that the compressed air discharged from the high-pressure stage compressor body 13 is cooled and the refrigerant is heated. The refrigerant intercooler 17a and the refrigerant aftercooler 17b may be any known heat exchanger, such as a fin type or a tube type.

[0080] The refrigeration cycle 21 is configured so that the refrigerant flows in circulation through the air-refrigerant heat exchange section (evaporator) 17 (refrigerant intercooler 17a, refrigerant aftercooler 17b), the refrigerant compressor 25, the hot water supply heat exchange section (condenser) 26, and the expansion valve 27 in that order.

[0081] In this embodiment, the heat pump unit 20 has a refrigerant temperature sensor 28c that measures a temperature t3 of the refrigerant upstream of the air-refrigerant heat exchanger 17. The air compressor unit 10 also has an air temperature sensor (an example of a gas temperature sensor) 28d that measures a temperature t4 of the compressed air downstream of the refrigerant intercooler 17a and upstream of the high-pressure stage compressor body 13.

[0082] The control device 28 controls the rotation speed of the refrigerant compressor 25 so that the detected value t3 of the refrigerant temperature sensor 28c is within a predetermined range. Specifically, the control flow chart of the control device 28 will be described with reference to FIG.

[0083] When the refrigerant compressor 25 is operated (step S6-1), the refrigerant temperature sensor 28c measures the refrigerant temperature t3 (step S6-2). The control device 28 then determines whether the refrigerant temperature t3 is within a predetermined temperature range and whether it deviates from that range (step S6-3). If the refrigerant temperature t3 is lower than the predetermined temperature range, the control device 28 reduces the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S6-4) and returns to measuring the refrigerant temperature t3 (step S6-2). If the refrigerant temperature t3 is higher than the predetermined temperature range, the control device 28 increases the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S6-5) and returns to measuring the refrigerant temperature t3 (step S6-2). If the refrigerant temperature t3 is within the predetermined temperature range, the control device 28 maintains the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S6-6), and the air compressor 11 is operated (step S6-7). The flow relating to the refrigerant temperature adjustment (i.e., the control from steps S6-2 to before S6-7) may be executed at all times while the air compressor 11 is operating.

[0084] Alternatively or additionally, the control device 28 controls the rotation speed of the refrigerant compressor 25 so that the detected value t4 of the air temperature sensor 28d is within a predetermined range. Specifically, the control flow chart of the control device 28 will be described with reference to FIG. 7.

[0085] When the refrigerant compressor 25 is operated (step S7-1), the air temperature sensor 28d measures the compressed air temperature t4 (step S7-2). The control device 28 then determines whether the compressed air temperature t4 is within a predetermined temperature range and whether it deviates from that range (step S7-3). If the compressed air temperature t4 is lower than the predetermined temperature range, the control device 28 reduces the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S7-4) and returns to measuring the compressed air temperature t4 (step S7-2). If the compressed air temperature t4 is higher than the predetermined temperature range, the control device 28 increases the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S7-5) and returns to measuring the compressed air temperature t4 (step S7-2). If the compressed air temperature t4 is within the predetermined temperature range, the control device 28 maintains the rotation speed of the refrigerant compressor 25 via the inverter 25b (step S7-6), and the air compressor 11 is operated (step S7-7). The flow relating to the temperature adjustment of the compressed air (i.e., the control from steps S7-2 to before S7-7) may be executed at all times while the air compressor 11 is in operation.

[0086] The predetermined ranges of temperatures t3 and t4 are ranges that can realize an intake air temperature that allows efficient operation of the high-pressure stage compressor body 13. Note that, when the rotation speed of the refrigerant compressor 25 increases, the amount of refrigerant cooling in the evaporator (air-refrigerant heat exchanger) 17 increases, the refrigerant temperature t3 decreases, and the temperature t4 of the air taken in by the high-pressure stage compressor body 13 decreases. Conversely, when the rotation speed of the refrigerant compressor 25 decreases, the amount of refrigerant cooling in the evaporator (air-refrigerant heat exchanger) 17 decreases, the refrigerant temperature t3 increases, and the temperature t4 of the air taken in by the high-pressure stage compressor body 13 increases.

[0087] 8, in the exhaust heat recovery system 1 of the present embodiment, the air compressor unit 10, the heat pump unit 20, and the condenser 26 are integrated and housed in the same housing 6. The housing 6 is placed on a stand 4. A water supply unit 31 and a hot water outlet 32 ​​are provided on a side surface of the housing 6.

[0088] This embodiment can also be said to be an exhaust heat recovery method for recovering exhaust heat from an oil-free air compressor 11, which includes an evaporation process in which exhaust heat from the air compressor 11 is supplied to the primary side of an evaporator 17 provided in a refrigeration cycle 21, thereby evaporating a refrigerant on the secondary side of the evaporator 17; a compression process in which the refrigerant flowing out from the evaporator 17 is supplied to a refrigerant compressor 25, thereby circulating the refrigerant in the refrigeration cycle 21 and compressing the refrigerant; a hot water generation process in which the refrigerant compressed by the refrigerant compressor 25 is supplied to the primary side of a condenser 26, thereby generating hot water on the secondary side of the condenser 26; and a decompression process in which the refrigerant flowing out from the condenser 26 is decompressed to expand and cool it.

[0089] The exhaust heat recovery system 1 of this embodiment provides the following advantageous effects.

[0090] Heat can be recovered from the compressed gas to the refrigerant by the gas refrigerant heat exchanger 17. Therefore, a specific configuration for heat transport can be realized.

[0091] Furthermore, the control device 28 can maintain the temperature of the refrigerant supplied to the gas refrigerant heat exchanger 17 within a predetermined range, so that the amount of cooling of the compressed gas in the gas refrigerant heat exchanger 17 can be maintained within a suitable range.

[0092] Furthermore, when a two-stage gas compressor 11 is used, an exhaust heat recovery structure using a refrigerant can be easily realized.

[0093] Furthermore, the control device 28 can maintain the temperature of the compressed gas taken in by the high-pressure stage compressor body within a suitable range.

[0094] Furthermore, moisture can be removed from the compressed gas by the drain separator 15 and the adsorption dryer 16. Furthermore, the drain separator 15 can improve the performance of the adsorption dryer 16.

[0095] Furthermore, since the compressor unit 10 and the heat pump unit 20 are housed in the same housing 6 and are arranged on the stand 4, space saving can be achieved.

[0096] While specific embodiments of the present disclosure and their modifications have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented with various modifications within the scope of the present invention. For example, an appropriate combination of the contents of the individual embodiments may be an embodiment of the present invention.

[0097] The modification of the first embodiment shown in FIG. 9 differs from the first embodiment in the cooling water flow path 24. The cooling water flow path 24 includes a low-pressure stage cooling jacket 12c provided in the low-pressure stage compressor body 12 and configured to allow cooling water to flow therethrough, a high-pressure stage cooling jacket 13c provided in the high-pressure stage compressor body 13 and configured to allow cooling water to flow therethrough, and an oil cooler 18 that cools oil supplied to bearings and the like of the low-pressure stage compressor body 12 and the high-pressure stage compressor body 13. The cooling water flow path 24 branches into a flow path that flows to the water-cooled intercooler 14a and a flow path that flows to the water-cooled aftercooler 14b so that the cooling waters flowing through the water-cooled intercooler 14a and the water-cooled aftercooler 14b do not interfere with each other. The cooling water flow path 24 further branches into a flow path that flows to the low-pressure stage cooling jacket 12c and the high-pressure stage cooling jacket 13c, and a flow path that flows to the oil cooler 18. The order in which each component is provided in the cooling water flow path 24 is not particularly important.

[0098] The modified example of the second embodiment shown in FIG. 10 differs from the second embodiment in the refrigeration cycle 21. The refrigeration cycle 21 includes a low-pressure stage cooling jacket 12c provided in the low-pressure stage compressor body 12 and configured to allow a refrigerant to flow therethrough, a high-pressure stage cooling jacket 13c provided in the high-pressure stage compressor body 13 and configured to allow a refrigerant to flow therethrough, and an oil cooler 18 for cooling oil supplied to bearings of the low-pressure stage compressor body 12 and the high-pressure stage compressor body 13. The refrigeration cycle 21 may be branched into a flow path leading to the refrigerant intercooler 17a and a flow path leading to the refrigerant aftercooler 17b so that the cooling water flowing through the refrigerant intercooler 17a and the refrigerant aftercooler 17b does not interfere with each other. The cooling water flow path 24 further branches into a flow path leading to the low-pressure stage cooling jacket 12c and the high-pressure stage cooling jacket 13c, and a flow path leading to the oil cooler 18. The order in which each component is provided in the refrigeration cycle 21 is not particularly important.

[0099] This application claims priority from Japanese Patent Application No. 2024-073571, filed April 30, 2024. Japanese Patent Application No. 2024-073571 is incorporated herein by reference.

[0100] The present disclosure may include the following aspects. (Aspect 1) An exhaust heat recovery system comprising: a gas compressor unit that produces compressed gas using an oil-free gas compressor; and a heat pump unit having a refrigeration cycle that directly or indirectly utilizes the heat of the compressed gas discharged from the gas compressor to evaporate a refrigerant, wherein the refrigeration cycle includes a hot water supply heat exchanger that uses the heat of the refrigerant to raise the temperature of water to produce hot water. (Aspect 2) The exhaust heat recovery system according to Aspect 1, wherein the heat pump unit has: a refrigerant compressor that compresses the refrigerant, an inverter that adjusts the rotation speed of the refrigerant compressor, and a control device that controls the rotation speed of the refrigerant compressor via the inverter. a gas-water heat exchanger configured to exchange heat between the compressed gas discharged from the gas compressor and cooling water to cool the compressed gas and heat the cooling water, and a water-refrigerant heat exchanger configured to exchange heat between the cooling water heated in the gas-water heat exchanger and the refrigerant to cool the cooling water and heat the refrigerant. (Aspect 4) The exhaust heat recovery system according to Aspect 3, wherein the heat pump unit has a cooling water temperature sensor configured to measure a temperature of the cooling water upstream of the gas-water heat exchanger, and the control device controls a rotation speed of the refrigerant compressor so that a detection value of the cooling water temperature sensor is within a predetermined range. (Aspect 5) The exhaust heat recovery system according to Aspect 3 or 4, wherein the gas compressor is a two-stage compressor having a low-pressure stage compressor main body and a high-pressure stage compressor main body, and the gas-water exchanger has a water-cooled intercooler that cools the compressed gas discharged from the low-pressure stage compressor main body and a water-cooled aftercooler that cools the compressed gas discharged from the high-pressure stage compressor main body. (Aspect 6) The exhaust heat recovery system according to Aspect 5, wherein the gas compressor unit has a gas temperature sensor that measures a temperature of the compressed gas downstream of the water-cooled intercooler and upstream of the high-pressure stage compressor main body, and the control device controls the rotation speed of the refrigerant compressor so that a detection value of the gas temperature sensor is within a predetermined range.(Aspect 7) The exhaust heat recovery system according to any one of Aspects 3 to 6, wherein the gas compressor unit includes: a drain separator that separates drain from the compressed gas downstream of the gas-water heat exchanger; and an adsorption dryer that dries the compressed gas downstream of the drain separator. (Aspect 8) The exhaust heat recovery system according to Aspect 2, wherein the heat pump unit includes a gas-refrigerant heat exchanger that exchanges heat between the compressed gas discharged from the gas compressor and the refrigerant, cooling the compressed gas and heating the refrigerant. (Aspect 9) The exhaust heat recovery system according to Aspect 8, wherein the heat pump unit includes a refrigerant temperature sensor that measures the temperature of the refrigerant upstream of the gas-refrigerant heat exchanger, and the control device controls the rotation speed of the refrigerant compressor so that a detection value of the refrigerant temperature sensor is within a predetermined range. (Aspect 10) The exhaust heat recovery system according to Aspect 8 or 9, wherein the gas compressor is a two-stage compressor having a low-pressure stage compressor main body and a high-pressure stage compressor main body, and the gas refrigerant heat exchanger has a refrigerant intercooler that cools the compressed gas discharged from the low-pressure stage compressor main body and a refrigerant aftercooler that cools the compressed gas discharged from the high-pressure stage compressor main body. (Aspect 11) The exhaust heat recovery system according to Aspect 10, wherein the gas compressor unit has a gas temperature sensor that measures a temperature of the compressed gas downstream of the refrigerant intercooler and upstream of the high-pressure stage compressor main body, and the control device controls the rotation speed of the refrigerant compressor so that a detection value of the gas temperature sensor is within a predetermined range. (Aspect 12) The exhaust heat recovery system according to any of Aspects 8 to 11, wherein the gas compressor unit has: a condensate separator that separates condensate from the compressed gas downstream of the gas refrigerant heat exchanger; and an adsorption dryer that dries the compressed gas downstream of the condensate separator. (Aspect 13) The exhaust heat recovery system according to aspect 3 or 8, comprising: a first housing in which the gas compressor unit is housed; a second housing in which the heat pump unit is housed; and a stand on which the first housing and the second housing are commonly arranged.(Aspect 14) The exhaust heat recovery system according to Aspect 3 or 8, wherein a housing that commonly houses the gas compressor unit and the heat pump unit is disposed on a stand. (Aspect 15) A method of recovering exhaust heat, comprising: producing compressed gas by an oil-free gas compressor; directly or indirectly utilizing heat of the compressed gas discharged from the gas compressor to evaporate a refrigerant in a refrigeration cycle; and heating water by the heat of the refrigerant heated in the refrigeration cycle to supply the water as hot water. (Aspect 16) The exhaust heat recovery system according to Aspect 15, wherein the refrigeration cycle includes: a refrigerant compressor that compresses the refrigerant; an inverter that adjusts the rotation speed of the refrigerant compressor; and a control device that controls the rotation speed of the refrigerant compressor via the inverter, and the control device outputs a control command to the inverter.

[0101] REFRIGERATION CYCLE 1 Exhaust heat recovery system 2, 3 Housing 4 Frame 5 Piping 6 Housing 10 Air compressor unit (gas compressor unit) 11 Air compressor (gas compressor) 12 Low-pressure stage compressor body 12a Motor 12b Inverter 12c Low-pressure stage cooling jacket 13 High-pressure stage compressor body 13c High-pressure stage cooling jacket 14 Gas-water heat exchange section 14a Water-cooled intercooler 14b Water-cooled aftercooler 15 Drain separator 16 Adsorption dryer 17 Gas refrigerant heat exchange section (evaporator) 17a Refrigerant intercooler 17b Refrigerant aftercooler 18 Oil cooler 20 Heat pump unit 21 Refrigeration cycle 22 Water-refrigerant heat exchange section (evaporator) 23 Pump 24 Cooling water flow path 25 Refrigerant compressor 25a Motor 25b Inverter 26 Hot water supply heat exchange section (condenser) 27 Expansion valve 28 Control device 28a Cooling water temperature sensor 28b Air temperature sensor (gas temperature sensor) 28c Refrigerant temperature sensor 28d Air temperature sensor (gas temperature sensor) 30 Hot water supply unit 31 Water supply section 32 Hot water outlet

Claims

1. A waste heat recovery system comprising: a gas compressor unit that produces compressed gas using an oil-free gas compressor; and a heat pump unit having a refrigeration cycle that directly or indirectly uses the heat of the compressed gas discharged from the gas compressor to evaporate a refrigerant, wherein the refrigeration cycle includes a hot water supply heat exchange section that uses the heat of the refrigerant to heat water and turn it into hot water.

2. The exhaust heat recovery system of claim 1, wherein the heat pump unit comprises: a refrigerant compressor that compresses the refrigerant; an inverter that adjusts the rotation speed of the refrigerant compressor; and a control device that controls the rotation speed of the refrigerant compressor via the inverter.

3. The exhaust heat recovery system according to claim 2, wherein the heat pump unit has: a gas-water heat exchange section that exchanges heat between the compressed gas discharged from the gas compressor and cooling water, thereby cooling the compressed gas and heating the cooling water; and a water-refrigerant heat exchange section that exchanges heat between the cooling water heated in the gas-water heat exchange section and the refrigerant, thereby cooling the cooling water and heating the refrigerant.

4. The exhaust heat recovery system described in claim 3, wherein the heat pump unit has a cooling water temperature sensor that measures the temperature of the cooling water upstream of the gas-water heat exchange section, and the control device controls the rotation speed of the refrigerant compressor so that the detection value of the cooling water temperature sensor falls within a predetermined range.

5. The exhaust heat recovery system according to claim 3, wherein the gas compressor is a two-stage compressor having a low-pressure stage compressor body and a high-pressure stage compressor body, and the gas-water heat exchange section has a water-cooled intercooler that cools the compressed gas discharged from the low-pressure stage compressor body, and a water-cooled aftercooler that cools the compressed gas discharged from the high-pressure stage compressor body.

6. The exhaust heat recovery system described in claim 5, wherein the gas compressor unit has a gas temperature sensor that measures the temperature of the compressed gas downstream of the water-cooled intercooler and upstream of the high-pressure stage compressor main body, and the control device controls the rotation speed of the refrigerant compressor so that the detection value of the gas temperature sensor falls within a predetermined range.

7. An exhaust heat recovery system as described in any one of claims 3 to 6, wherein the gas compressor unit has: a drain separator that separates drain from the compressed gas downstream of the gas-water heat exchange section; and an adsorption dryer that dries the compressed gas downstream of the drain separator.

8. The exhaust heat recovery system of claim 2, wherein the heat pump unit has a gas-refrigerant heat exchange section that exchanges heat between the compressed gas discharged from the gas compressor and the refrigerant, cooling the compressed gas and heating the refrigerant.

9. The exhaust heat recovery system described in claim 8, wherein the heat pump unit has a refrigerant temperature sensor that measures the temperature of the refrigerant upstream of the gas refrigerant heat exchange section, and the control device controls the rotation speed of the refrigerant compressor so that the detection value of the refrigerant temperature sensor falls within a predetermined range.

10. The exhaust heat recovery system described in claim 8, wherein the gas compressor is a two-stage compressor having a low-pressure stage compressor body and a high-pressure stage compressor body, and the gas refrigerant heat exchange section has a refrigerant intercooler that cools the compressed gas discharged from the low-pressure stage compressor body, and a refrigerant aftercooler that cools the compressed gas discharged from the high-pressure stage compressor body.

11. The exhaust heat recovery system described in claim 10, wherein the gas compressor unit has a gas temperature sensor that measures the temperature of the compressed gas downstream of the refrigerant intercooler and upstream of the high-pressure stage compressor main body, and the control device controls the rotation speed of the refrigerant compressor so that the detection value of the gas temperature sensor falls within a predetermined range.

12. An exhaust heat recovery system as described in any one of claims 8 to 11, wherein the gas compressor unit has: a drain separator that separates drain from the compressed gas downstream of the gas refrigerant heat exchange section; and an adsorption dryer that dries the compressed gas downstream of the drain separator.

13. The exhaust heat recovery system described in claim 3 or 8, comprising: a first housing in which the gas compressor unit is housed; a second housing in which the heat pump unit is housed; and a stand on which the first housing and the second housing are commonly arranged.

14. The exhaust heat recovery system according to claim 3 or 8, wherein a housing that commonly houses the gas compressor unit and the heat pump unit is mounted on a stand.

15. A method for recovering exhaust heat, comprising: producing compressed gas by an oil-free gas compressor; directly or indirectly utilizing the heat of the compressed gas discharged from the gas compressor to evaporate a refrigerant in a refrigeration cycle; and heating water to produce hot water using the heat of the refrigerant heated in the refrigeration cycle.

16. The exhaust heat recovery method described in claim 15, wherein the refrigeration cycle comprises a refrigerant compressor that compresses the refrigerant, an inverter that adjusts the rotation speed of the refrigerant compressor, and a control device that controls the rotation speed of the refrigerant compressor via the inverter, and the control device outputs a control command to the inverter.

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