JP7246069B2 - Heat recovery system and heat recovery method - Google Patents

Description

The present disclosure relates to heat recovery systems and heat recovery methods.

Warm waste water is discharged from various factories in various processes. Warm waste water at around 90°C can often be reused as a heat source, but hot waste water at 60 to 80°C is often discarded. Therefore, if the heat contained in warm waste water of 60 to 80° C. can be utilized, low-temperature waste heat can be effectively utilized.
Patent Documents 1 and 2 disclose a heat recovery system that uses a heat pump having a heat absorption part (or evaporator) and a heat dissipation part (or condenser) to recover heat from warm wastewater discharged from a building or the like to obtain hot water. disclosed. In Patent Document 3, a heat pump in which heat pump cycle components such as a compressor, an evaporator, and a condenser are provided in a refrigerant circuit is used, and heat is recovered from warm wastewater discharged from a building or the like to obtain hot water. A system is disclosed.

JP-A-2-146463 JP-A-2005-127620 JP-A-2003-42539

The heat recovery systems disclosed in Patent Documents 1 to 3 use a plurality of indirect heat exchangers between warm waste water, a heat medium of a heat pump, and tap water to obtain hot water from warm waste water. Indirect heat exchange is performed twice. In indirect heat exchange, since there is a temperature difference between the heat mediums that perform heat exchange, the heat recovery efficiency is reduced by the temperature difference. In addition, there is a problem of high cost due to the use of a plurality of indirect heat exchangers.

One embodiment proposes a heat recovery system for obtaining a heat source at a reusable temperature from warm wastewater, which is low-temperature and difficult to use the stored heat, and which is low-cost and has high heat-recovery efficiency. aim.

(1) A heat recovery system according to one embodiment includes:
a flash tank for flashing the first warm waste water;
a compressor for compressing the low-pressure steam in the flash tank to generate compressed steam having a temperature higher than that of the first warm waste water;
Prepare.
In the configuration of (1) above, the first warm waste water is flashed in a flash tank to form low-pressure steam, and this low-pressure steam is compressed by a compressor to generate compressed steam having a higher temperature than the warm waste water. As a result, the first warm waste water, which has a relatively low temperature (for example, 50 to 80°C) and is difficult to utilize its own heat, can be used as a heat medium capable of utilizing heat around 90°C. In addition, since the heat medium that serves as a high-temperature heat source can be directly generated from the first warm waste water without indirect heat exchange in the process of generating the compressed steam, the thermal efficiency can be improved. Moreover, since an expensive indirect heat exchanger is not used, the cost is reduced.

(2) In one embodiment, in the configuration of (1),
A first stratification tank having an upper portion provided with an inlet and an outlet for the first warm water and a lower portion provided with an inlet and an outlet for the second warm water discharged from the flash tank is provided.
According to the above configuration (2), the first warm waste water and the second warm waste water, which has a lower temperature than the first warm waste water, are stored in the upper space of the first stratification tank due to the difference in specific gravity. Two-temperature waste water is separated and stored in the lower space of the first stratification tank. Therefore, the first warm waste water stored in the first stratification tank can be stably supplied to the flash tank by one tank, and the second warm waste water stored in the first stratification tank can be used for other purposes.

(3) In one embodiment, in the configuration of (1) or (2),
A liquefier is provided for liquefying the compressed steam discharged from the compressor to generate hot water.
According to the configuration (3) above, by converting the compressed steam discharged from the compressor into hot water, it is possible to obtain high-temperature water of around 90° C. for a wide range of applications.

(4) In one embodiment, in the configuration of (3),
The hot water is supplied to the first supply destination, and the used hot water after the hot water is used as a heat source at the first supply destination is returned to the liquefier.
According to the above configuration (4), when the compressed steam discharged from the compressor is changed to hot water, the hot water after use as a heat source at the first supply destination is used as a cooling medium, so that the compressed steam can be turned into hot water without overheating. That is, by adding the potential heat of the hot water after use to the potential heat of the compressed steam, it is possible to convert the compressed steam into high-temperature hot water. This makes it possible to obtain hot water with a wide range of applications.

(5) In one embodiment, in the configuration of (4),
A filling material capable of increasing the contact area between the compressed steam and the hot water after use is provided inside the liquefier.
According to the configuration of (5) above, since the filler is provided, it is possible to improve the heat exchange efficiency between the compressed steam and the hot water after use. Therefore, the hot water after use can be used to liquefy the compressed steam with a small temperature difference without requiring a separate cooling medium.

(6) In one embodiment, in the configuration of (4) or (5),
a second stratification tank having an upper portion provided with an inlet and an outlet for the hot water liquefied by the liquefier and a lower portion provided with an inlet and an outlet for the used hot water;
a conduit returning the hot water after use from the outlet provided at the bottom of the second stratification tank to the liquefier;
Prepare.
According to the above configuration (6), high-temperature hot water obtained by liquefying the compressed steam in the liquefier is sent to the upper space of the second stratification tank, and the hot water is used as a heat source at the first supply destination, and the temperature is lower than that of the hot water. Since the hot water after use can be stored in the lower space of the second stratification tank, the stable supply of the hot water liquefied by the liquefier to the first supply destination and the stable supply of the hot water after use to the liquefier can be achieved in one tank. be possible.

(7) In one embodiment, in the configuration of (6),
A first stratification tank having an upper portion provided with an inlet and an outlet for the first warm water discharge and a lower portion provided with an inlet and an outlet for the second warm water discharged from the flash tank,
The second hot waste water stored in the lower part of the first stratification tank is supplied as a cooling medium to a second supply destination, and the used second warm waste water after being used as a cooling medium at the second supply destination is the It is configured to return to the top of the first stratification tank or the bottom of the second stratification tank.
According to the configuration of (7) above, it is possible to simultaneously supply the hot water as the heat source to the first supply destination and the second warm waste water as the cold heat source to the second supply destination.

(8) In one embodiment, in any one of the configurations (1) to (7),
The compressor is composed of a centrifugal compressor.
According to the configuration of (8) above, as the compressor, although the compression ratio is not as large as that of a positive displacement compressor, by using a centrifugal compressor with fewer sealing parts than a positive displacement compressor, Leakage and infiltration of compressed steam from outside or from the outside of the machine can be suppressed, thereby suppressing a decrease in thermal efficiency even when the temperature difference between warm waste water as a raw material and hot water to be produced is small.

(9) A heat recovery method according to one embodiment includes:
A flashing step of flashing hot waste water in a flash tank to produce low-pressure steam;
a generation step of compressing the low-pressure steam with a compressor to generate compressed steam having a temperature higher than that of the warm waste water;
including
The compressed steam is used as a heat source.
According to the above method (9), hot waste water is decompressed in a flash tank to form low-pressure steam, and this low-pressure steam is compressed in a compressor to generate high-temperature compressed steam from the warm waste water. As a result, the first warm waste water, which has a relatively low temperature (for example, 50 to 80°C) and is difficult to utilize its own heat, can be used as a heat medium capable of utilizing heat around 90°C. In addition, since the heat medium that serves as a high-temperature heat source can be directly generated from the first warm waste water without indirect heat exchange in the process of generating the compressed steam, the thermal efficiency can be improved. Moreover, since an expensive indirect heat exchanger is not used, the cost is reduced.

(10) In one embodiment, in the method of (9),
The temperature of the warm water is 70°C or higher and 90°C or lower, and the temperature of the compressed steam is 100°C or higher and 140°C or lower.
According to the method (10) above, hot waste water of 70 to 90° C. can be converted into compressed steam of 100 to 140° C. for a wide range of applications.

(11) In one embodiment, in the method of (9) or (10),
A liquefying step of liquefying the compressed steam discharged from the compressor to generate hot water is included.
According to the method (11), the liquefaction step makes it possible to obtain high-temperature water of around 90° C., which has a wide range of uses, from the compressed steam discharged from the compressor.

(12) In one embodiment, in the method of (11),
In the liquefying step,
The temperature of the compressed steam is 100° C. or higher and 140° C. or lower, and the temperature of the hot water in which the compressed steam is liquefied is 85° C. or higher and 100° C. or lower.
According to the method (12) above, high-temperature water of 85 to 100° C. for a wide range of applications can be obtained from the compressed steam discharged from the compressor.

According to some embodiments, low-temperature waste water, which is difficult to reuse, can be used as a heat medium capable of utilizing heat around 90°C. In addition, since a heat medium that serves as a high-temperature heat source can be generated directly from the first warm waste water without performing indirect heat exchange in the process of generating compressed steam, thermal efficiency can be improved, and an expensive indirect heat exchanger is not used. Low cost becomes possible.

1 is a system diagram of a heat recovery system according to one embodiment; FIG. 1 is a system diagram of a heat recovery system according to one embodiment; FIG. 1 is a system diagram of a heat recovery system according to one embodiment; FIG. 1 is a system diagram of a heat recovery system according to one embodiment; FIG. It is process drawing of the heat recovery method which concerns on one Embodiment. 4 is a table showing calculated COP values for heat recovery systems according to some embodiments. 4 is a table showing calculated COP values of a conventional closed-cycle heat pump as a comparative example.

Several embodiments of the present invention will now be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as the embodiment or shown in the drawings are not meant to limit the scope of the present invention, but merely illustrative examples.
For example, expressions denoting relative or absolute arrangements such as "in a direction", "along a direction", "parallel", "perpendicular", "center", "concentric" or "coaxial" are strictly not only represents such an arrangement, but also represents a state of relative displacement with a tolerance or an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "identical", "equal", and "homogeneous", which express that things are in the same state, not only express the state of being strictly equal, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state.
For example, expressions that express shapes such as squares and cylinders do not only represent shapes such as squares and cylinders in a geometrically strict sense, but also include irregularities and chamfers to the extent that the same effect can be obtained. The shape including the part etc. shall also be represented.
On the other hand, the expressions "comprising", "comprising", "having", "including", or "having" one component are not exclusive expressions excluding the presence of other components.

1-4 are system diagrams showing heat recovery systems 10 (10A, 10B, 10C, 10D) according to some embodiments. As shown in FIGS. 1 to 4, the heat recovery system 10 (10A to 10D) depressurizes the relatively low temperature (eg, 60 to 80° C.) warm waste water a (first warm waste water) discharged from a factory or the like. and a compressor 14 for compressing the generated low-pressure steam b in the flash tank 12 to generate compressed steam c having a higher temperature than the warm water a. .
In the above configuration, the hot waste water a is depressurized in the flash tank 12 to form the low-pressure steam b. The low-pressure steam b is compressed by the compressor 14 to generate compressed steam c having a higher temperature than the hot waste water a. As a result, the warm wastewater a, which has a relatively low temperature (for example, 50 to 80° C.) and is difficult to utilize its own heat, can be used as a heat medium capable of utilizing heat around 90° C. Further, since the compressed steam c, which serves as a high-temperature heat source, can be directly generated from the hot waste water a without performing indirect heat exchange in the process of generating the compressed steam c, so that the thermal efficiency can be improved. Moreover, since an expensive indirect heat exchanger is not used, the cost is reduced.

In one embodiment, as shown in FIGS. 1-4, hot water a is supplied to flash tank 12 via line 22 . The flash tank 12 is composed of a vertically erected hollow cylindrical container, and is configured such that the inside can be decompressed. By decompressing the inside of the flash tank 12, part of the supplied hot waste water a is vaporized into low-pressure steam b. The low-pressure steam b is supplied to the compressor 14 through a line 25 connected to the top of the flash tank 12 .
In one embodiment, the interior of the flash tank 12 is provided with a gas-liquid separation material 24 across the entire cross-section of the flash tank 12 . The gas-liquid separating material 24 has a structure similar to that of the filler 48 described later, and is made of a material capable of increasing the contact area with the moisture contained in the vaporized steam. When the moisture adheres to the gas-liquid separating material 24, the liquid can be efficiently separated from the vapor.

In one embodiment, the inlet of the conduit 22 in the flash tank 12 is provided above the gas-liquid separator 24 . The liquid adhering to the gas-liquid separation material 24 flows down by gravity and accumulates in the lower part of the flash tank 12 . Since the low-pressure steam b vaporized in the flash tank 12 takes the latent heat of vaporization, both the gas and the liquid in the flash tank 12 are cooled and have a lower temperature than the warm waste water a supplied to the flash tank 12 . Vaporized low-pressure steam b is sent to the compressor 14 via a pipe line 25 connected to the upper portion of the flash tank 12, and non-vaporized hot waste water d (second warm waste water) is sent to a pipe connected to the lower portion of the flash tank 12. Channel 26 is evacuated by pump 28 . Warm waste water a is supplied to the flash tank 12 from a heat recovery device (not shown) or the like, and warm waste water d is discharged to a heat recovery device (not shown) or the like.

In one embodiment, as shown in FIGS. 3 and 4, a cold stratification tank 18 (first stratification tank) is provided. The low-temperature stratification tank 18 is provided with an inlet 30 and an outlet 32 for entering and exiting the warm waste water a at its upper portion, and an inlet 34 and an outlet 36 for entering and exiting the warm waste water d discharged from the flash tank 12 at its lower portion. The hot waste water a is supplied from the inlet 30 to the upper space of the low-temperature stratification tank 18 and from the outlet 32 to the flash tank 12 through the pipeline 22 . Hot waste water d is supplied to the lower space of the low-temperature stratification tank 18 from line 26 and inlet 34 and is discharged from outlet 36 via line 40 . The warm waste water a and the warm waste water d do not mix in the flash tank 12 .
According to this embodiment, the warm waste water a and the warm waste water d, which has a lower temperature than the warm waste water a, are stored in the upper space of the low temperature stratification tank 18 due to the difference in specific gravity, and the warm waste water d is stored in the low temperature stratification tank 18. It separates and stores in the lower space. Therefore, the warm waste water a stored in the low-temperature stratification tank 18 can be stably supplied to the flash tank 12 by a single tank, and the warm waste water d stored in the low-temperature stratification tank 18 can be appropriately used for other purposes.

In one embodiment, as shown in FIGS. 1 and 3, a liquefier 16 is provided downstream of the compressor 14 . The liquefier 16 liquefies the compressed steam c discharged from the compressor 14 to generate hot water. By converting the compressed steam c discharged from the compressor 14 into hot water, it is possible to obtain high-temperature water e of around 90° C., which has a wide range of uses.
In one embodiment, the liquefier 16 comprises a hollow cylindrical vessel that stands vertically. A pipe line 42 for discharging the high-temperature water e is connected to the lower part of the container, and the high-temperature water e is sent to a supply destination (utilization destination) 45 (first supply destination) by a pump 44 provided in the pipe line 42. .

In one embodiment, as shown in FIGS. 1 and 3, high temperature water e is supplied to the supply destination 45, and after-use hot water f after the high temperature water e is used as a heat source at the supply destination 45 is transferred to the liquefier 16. configured to return to According to this embodiment, when the compressed steam c discharged from the compressor 14 is converted into hot water inside the liquefier 16, the used hot water f after being used as a heat source at the supply destination 45 is used as a cooling medium. Thus, the compressed steam c can be changed to hot water without being heated more than necessary. That is, by adding the inherent heat of the hot water f after use to the compressed steam c, the compressed steam c can be changed to high-temperature hot water. As a result, it is possible to obtain high-temperature water e that has a wide range of uses.

In one embodiment, compressed steam c discharged from compressor 14 is connected via line 50 to the lower portion of liquefier 16 (located below filler 48). The compressed steam c supplied below the filler 48 rises, adheres to the surface of the filler 48, and is liquefied. After-use hot water f is supplied from the top of the liquefier 16 through a pipe line 46 (or 64) connected to the top of the liquefier 16, and comes into contact with the liquefied liquid of the compressed steam c adhering to the filler 48.

In one embodiment, the inside of the liquefier 16 is provided with a filler 48 capable of increasing the contact area between the compressed steam c and the hot water after use f. The filler 48 can improve the heat exchange efficiency between the compressed steam c and the hot water after use f. Therefore, the hot water f after use can be used to liquefy the compressed steam with a small temperature difference without requiring a separate cooling medium.
In one embodiment, the packing material 48 is provided on the entire cross section of the liquefier 16, thereby greatly increasing the contact area between the gas and the liquid, so that the compressed water vapor c can be liquefied with a low temperature difference.

In one embodiment, as shown in FIG. 3, a hot stratification tank 20 (second stratification tank) is provided downstream of the liquefier 16 . The high-temperature stratification tank 20 has an inlet 52 and an outlet 54 through which the high-temperature water e liquefied by the liquefier 16 enters and exits. The high temperature water e is supplied from the inlet 52 to the high temperature stratification tank 20 through the pipeline 60 by the pump 62 provided in the pipeline 60 , and is supplied from the high temperature stratification tank 20 to the supply destination 45 through the pipeline 66 . Also provided is a conduit 64 for returning hot water f after use to the liquefier 16 from the outlet 58 . After-use hot water f flows into the lower part of the high-temperature stratification tank 20 from the supply destination 45 through the pipe line 68 . The used hot water f in the hot stratification tank is returned to the liquefier 16 via line 64 from the outlet 58 .

According to this embodiment, the high-temperature water e obtained by liquefying the compressed steam c in the liquefier 16 and the used hot water f can be stored in one high-temperature stratification tank 20 . The high-temperature water e and the used hot water f whose temperature is lowered by using the retained heat are stored in the upper space of the high-temperature stratification tank 20 due to the difference in specific gravity, and the used hot water f is stored in the lower space of the high-temperature stratification tank 20. and both are stored separately. This enables stable supply of hot water e to the supply destination 45 and stable supply of used hot water f to the liquefier 16 with one tank.

In one embodiment, line 64 is connected to the top of liquefier 16 . Therefore, the hot water f after use is returned to the space above the filling material 48 inside the liquefier 16 and flows down to the filling material 48 by gravity. As a result, the contact with the compressed steam c rising from below to the filler 48 is promoted, so the liquefying efficiency of the compressed steam c is increased.

In one embodiment, in the heat recovery system 10 (10C) shown in FIG. 2 supply destination). The hot waste water d is used as a cooling medium at the supply destination 72, and the temperature is lowered. After that, the hot water f after use is returned to the upper space of the low-temperature stratification tank 18 or the lower space of the high-temperature stratification tank 20 in which the hot waste water d having a similar temperature is stored via the pipe line 74 .
In the heat recovery system 10 (10C), it is possible to simultaneously supply hot water e as a heat source to the supply destination 45 and hot waste water d as a cold heat source to the supply destination 72 .

In one embodiment, compressor 14 comprises a centrifugal compressor. A centrifugal compressor does not have a large compression ratio as compared with positive displacement compressors such as screw compressors and reciprocating compressors, but it has fewer seals than positive displacement compressors. Therefore, it is possible to suppress the leakage of the compressed steam to or from the outside of the machine, thereby suppressing the deterioration of the thermal efficiency.

The heat recovery method according to one embodiment includes, as essential steps, a flash step S10 and a generation step S12, as shown in FIG. In the flash tank 12, the hot waste water a is depressurized and flashed (vaporized) to form low-pressure steam b. In the generating step S12, the low-pressure steam b is compressed by the compressor 14 to generate compressed steam c having a temperature higher than that of the hot waste water a. The generated compressed steam c is sent to the supply destination 45 and used as a heat source.
According to the above method, the warm waste water a, which is relatively low temperature (for example, 50 to 80°C) and difficult to utilize the potential heat, can be used as a heat medium capable of using the potential heat around 90°C. In addition, as in Patent Documents 1 to 3, indirect heat exchange is not performed in the process of generating compressed steam c, and compressed steam c, which serves as a high-temperature heat source, can be generated directly from hot waste water a, so thermal efficiency can be improved. Moreover, since an expensive indirect heat exchanger is not used, the cost is reduced.

In one embodiment, when the temperature of the hot waste water a is 70-90° C., compressed steam c of 100-140° C. can be obtained from the hot waste water a at this temperature. Therefore, it is possible to convert warm wastewater a, which is difficult to reuse, into compressed steam c, which has a wide range of uses.

In one embodiment, as shown in FIG. 5, after the generating step S12, a liquefying step S14 of liquefying the compressed steam c to generate hot water e is included. According to this embodiment, high-temperature water e with a wide range of applications can be obtained from compressed steam c.
In one embodiment, in the liquefaction step S14, high-temperature water e of 85-100° C. for a wide range of applications can be obtained from the compressed steam c of 100-140° C.

Table 1 shown in FIG. 6 shows calculated values of COP (coefficient of performance) obtained in the heat recovery system 10 (10A to 10D) according to some embodiments, and Table 2 shown in FIG. 3, a calculated COP obtained with a conventional closed-cycle heat pump using an indirect heat exchanger is shown as a comparative example. In Table 1, "Embodiment 1" refers to the heat recovery system 10 (10A, 10C) for obtaining high-temperature water e, as shown in FIGS. 2 and FIG. 4 refer to the heat recovery system 10 (10B, 10D) for obtaining compressed steam c.

In Tables 1 and 2, "low temperature side heat source hot water" means "warm water a" in FIGS. 1 to 4, "high temperature side" means "high temperature water e", ” means “temperature of low-pressure steam b”, and “discharge steam temperature” means “temperature of compressed steam c”. For the sake of understanding, they are given corresponding reference numerals. In addition, since the "high temperature side" in "Embodiment 2" in Table 1 means the compressed steam c, its temperature is the same as the "discharge steam temperature".
In addition, the "Carnot COP" is the value of COP calculated assuming that both the embodiment and the comparative example constitute the Carnot cycle, and the "estimated COP" is 70% of the actual COP of the "Carnot COP". It is a calculated value calculated by estimating that
Also, in Table 2, it is assumed that the temperature difference between the two heat mediums heat-exchanging in the indirect heat exchanger is 3.0°C.

From the COP values shown in Tables 1 and 2, it can be seen that the COP values according to the embodiment are greater than those of the comparative example. In Embodiments 1 and 2, there is no step of performing indirect heat exchange in all steps S10 to S14, and even in the liquefaction step S14, the compressed steam c and the used hot water f are directly heat-exchanged. There is no temperature difference between the two heat transfer mediums. Therefore, the COP is improved more than the comparative example.

According to some embodiments, it is possible to use low-temperature waste water, which is difficult to reuse, as a heat medium capable of utilizing heat at around 90° C., reduce the cost of the device, and improve the heat recovery efficiency. Therefore, it is possible to effectively use the energy discharged from the factory or the like.

10 (10A, 10B, 10C, 10D) heat recovery system 12 flash tank 14 compressor 16 liquefier 18 low temperature stratification tank (first stratification tank)
20 high temperature stratification tank (second stratification tank)
22, 25, 26, 38, 40, 42, 46, 50, 60, 64, 66, 68, 70, 74 pipeline 24 gas-liquid separation material 28, 44, 62 pump 30, 34, 52, 56 inlet 32, 36, 54, 58 outlet 45 supply destination (first supply destination)
48 filler 72 supply destination (second supply destination)
a Warm water discharge (1st warm water discharge)
b Low-pressure steam c Compressed steam d Warm water discharge (second warm water discharge)
e High temperature water f Hot water after use

Claims (9)

a flash tank for flashing the first warm waste water;
a compressor for compressing the low-pressure steam in the flash tank to generate compressed steam having a temperature higher than that of the first warm waste water;
a liquefier that liquefies the compressed steam discharged from the compressor to generate hot water;
with
The hot water is supplied to the first supply destination, and the hot water is returned to the liquefier as a cooling medium after the hot water has been used as a heat source at the first supply destination. collection system. The upper portion is provided with an inlet for the first hot water discharge, the lower portion is provided with an inlet for the second hot water discharged from the flash tank, and the upper and lower portions are provided with outlets for the stored warm water. 2. The heat recovery system of claim 1, comprising a stratification tank. 3. The heat recovery system according to claim 1, wherein the liquefier is provided with a filler capable of increasing a contact area between the compressed steam and the hot water after use. a second stratification tank having an upper portion provided with an inlet for the hot water liquefied by the liquefier, a lower portion provided with an inlet for the used hot water, and an upper and lower portion provided with outlets for the stored hot water;
a conduit returning the hot water after use from the outlet provided at the bottom of the second stratification tank to the liquefier;
The heat recovery system according to any one of claims 1 to 3, comprising: The upper portion is provided with an inlet for the first hot water discharge, the lower portion is provided with an inlet for the second hot water discharged from the flash tank, and the upper and lower portions are provided with outlets for the stored warm water. Equipped with a stratification tank,
The second hot waste water stored in the lower part of the first stratification tank is supplied as a cooling medium to a second supply destination, and the used second warm waste water after being used as a cooling medium at the second supply destination is the 5. The heat recovery system according to claim 4 , wherein the heat recovery system is configured to return to the upper part of the first stratification tank or the lower part of the second stratification tank. 6. The heat recovery system according to any one of claims 1 to 5, wherein the compressor is a centrifugal compressor. A flashing step of flashing hot waste water in a flash tank to produce low-pressure steam;
a generation step of compressing the low-pressure steam with a compressor to generate compressed steam having a temperature higher than that of the warm waste water;
a liquefying step of liquefying the compressed steam discharged from the compressor with a liquefier to generate hot water;
a return step of supplying the hot water to the first supply destination and returning the used hot water after the hot water has been used as a heat source at the first supply destination to the liquefier as a cooling medium;
including
A heat recovery method, wherein the compressed steam is used as a heat source. 8. The heat recovery method according to claim 7 , wherein the temperature of the hot water discharge is 70° C. or higher and 90° C. or lower, and the temperature of the compressed steam is 100° C. or higher and 140° C. or lower. In the liquefying step,
The heat recovery method according to claim 7 or 8 , wherein the temperature of the compressed steam is 100°C or higher and 140°C or lower, and the temperature of the hot water obtained by liquefying the compressed steam is 85°C or higher and 100°C or lower. .

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