JP2015152220A - Waste heat recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste heat recovery system which recovers waste heat generated from a waste heat source with efficiency of a heat pump maintained at a high level by stabilizing a temperature of cooling water even when an ambient temperature or an operation load of the waste heat source fluctuates.SOLUTION: A waste heat recovery system has a temperature sensor 7 on first piping 3 connecting a waste heat source 1 and a heat pump 5. A control section 25 connected to the temperature sensor 7 stably maintains a temperature of cooling water, which is a heat source of the heat pump, at a high level by: performing variable speed operation of an inverter 15 for a cooling tower motor in accordance with a measurement result of the temperature sensor 7; and keeping a measurement value of the temperature sensor 7 within a preset range through adjustment of cooling performance of a cooling tower.

Description

  The present invention relates to an exhaust heat recovery system that uses exhaust heat generated in an exhaust heat source as a heat source of a heat pump via cooling water.

  In general, an apparatus that generates exhaust heat often includes a cooling tower and a cooling water circulation pipe for releasing the exhaust heat to the atmosphere.

  The exhaust heat source is cooled by the cooling water, that is, the cooling water is heated by the exhaust heat source, then cooled by the cooling tower, and again input to the exhaust heat source. Conventionally, the exhaust heat of the cooling water is only discharged to the atmosphere, that is, discarded. However, with the recent development of heat pump technology, the exhaust heat can be recovered and reused in many cases.

  Here, when exhaust heat is efficiently and stably recovered by a heat pump and is to be reused, it is desirable to keep the temperature of the cooling water as high and stable as possible.

  This is because when the exhaust heat is collected by the heat pump, the power required by the compressor provided in the heat pump can be reduced when the temperature of the cooling water as the heat source is higher. Accordingly, even when the same amount of heat is generated by the heat pump, the efficiency of the heat pump is improved when the temperature of the cooling water serving as the heat source is higher.

  Here, generally, the temperature of the cooling water at the exhaust heat source outlet is often set with an upper limit of about 45 ° C. This is because, when the temperature is higher than this temperature, chemicals such as a corrosion inhibitor that has been thrown into the cooling water are deposited, which may affect the entire apparatus.

  In most cases, a constant speed motor is used for the fan and cooling water circulation pump provided in the cooling tower, and the operation is constant regardless of fluctuations in the outside air temperature and the amount of exhaust heat. For this reason, the cooling water temperature constantly fluctuates due to fluctuations in the outside air temperature and the amount of exhaust heat.

  When the exhaust heat of the cooling water is recovered by a heat pump and reused, it is efficient if the cooling water temperature can be stably maintained at the upper limit temperature of about 45 ° C.

  Here, the upper limit set temperature of the cooling water of about 45 ° C. occurs during summer, particularly during midsummer. This is because the cooling capacity of the cooling tower decreases because the outdoor temperature is high in summer, and the cooling water temperature rises the most throughout the year.

  On the other hand, since the outside temperature of the cooling tower is low in winter, the cooling capacity of the cooling tower is relatively increased, and it is not uncommon for the cooling water temperature to decrease by about 10 ° C. compared to summer.

  Moreover, not only the temperature change of the cooling water due to seasonal fluctuations but also the fluctuation of the amount of exhaust heat caused by the fluctuation of the operating load of the exhaust heat source, it is not easy to keep the temperature of the cooling water stable.

  Therefore, as in Patent Document 1, the exhaust heat source load sensor and the temperature of the cooling water are measured by the sensor, and the exhaust heat utilization for adjusting the cooling water flow path and controlling the rotation speed of the cooling tower fan according to the measurement result. Devices etc. have been proposed.

JP-A-7-27413

  When utilizing the exhaust heat of cooling water in the heat pump, the temperature of the cooling water supplied to the heat pump affects the efficiency of the heat pump, so it is most important to maintain a high and stable cooling water temperature to the heat pump. It is.

  However, in the exhaust heat utilization device described in the cooling water temperature patent document 1, a load sensor for measuring the load on the electrical device, a plurality of temperature sensors, a three-way valve, and the like are required, which complicates the device and controls the control device. However, since the three-way valve is not prioritized, there is a problem that it is difficult to keep the cooling water temperature supplied to the heat pump high and stable.

  In view of such problems, the present invention stably maintains the temperature at the heat pump inlet of the cooling water even if the outside air temperature of the cooling tower or the operating condition of the exhaust heat source varies, and the exhaust heat of the cooling water is reduced. An object is to provide an exhaust heat recovery system that can be efficiently utilized by a heat pump.

  (1) An exhaust heat recovery system according to the present invention includes an exhaust heat source, a heat pump connected to the exhaust heat source and a first pipe, a temperature sensor installed on the first pipe, and a downstream of the heat pump. A cooling tower connected to the side by a second pipe, a cooling tower motor for driving a fan installed in the cooling tower, a circulation pump connected to the cooling tower by a third pipe, and the circulation In an exhaust heat recovery system comprising a circulation pump motor that drives a pump and a fourth pipe that connects the circulation pump and the exhaust heat source, a value of the temperature sensor connected to the temperature sensor and the cooling tower motor And a control unit for controlling the cooling tower motor so as to be within a preset range.

  The exhaust heat recovery system according to the present invention measures the temperature near the heat pump inlet of the cooling water with a temperature sensor, operates the cooling tower motor with ON-OFF control based on the measured result, and increases the cooling capacity of the cooling tower. By adjusting the temperature, the temperature of the cooling water is controlled to be within a preset range.

  (2) The exhaust heat recovery system according to the present invention is the exhaust heat recovery system according to (1), wherein the cooling tower motor includes an inverter for a cooling tower motor that performs variable speed operation, and the control unit includes the cooling tower. The cooling tower motor inverter is controlled in place of the motor.

  (3) The exhaust heat recovery system according to the present invention is the exhaust heat recovery system according to (2), wherein the circulation pump motor includes an inverter for circulation pump that performs variable speed operation, and the control unit includes the cooling motor. In addition to controlling the inverter for the operation, the circulation pump inverter is controlled.

  The exhaust heat recovery system according to the present invention further includes a circulation pump inverter in addition to the cooling tower motor inverter, and controls the circulation pump inverter when the temperature of the cooling water is likely to decrease in midwinter, for example. By reducing the circulation rate, the temperature of the cooling water is prevented from lowering. This makes it possible to maintain the cooling water temperature in the vicinity of the heat pump inlet.

  (4) Further, in the exhaust heat recovery system according to (3), the control unit controls the cooling tower motor inverter in preference to the circulation pump inverter. Features.

  In the exhaust heat recovery system according to the present invention, when the temperature of the cooling water supplied to the heat pump decreases, the cooling capacity in the cooling tower is first suppressed, and cooling is performed only when the cooling water temperature cannot be prevented from decreasing. Reduce water circulation. This is to secure as much heat as possible by the heat pump.

  According to the exhaust heat recovery system described in (1), the temperature of the cooling water supplied to the heat pump can be stably kept within a certain range by adjusting the cooling capacity of the cooling tower even if the outside air temperature fluctuates. It is possible to keep. It is also possible to reduce the amount of cooling water and the use of chemicals such as corrosion inhibitors that are put into the cooling water.

  According to the exhaust heat recovery system described in (2), it is possible to finely adjust the cooling capacity of the cooling tower by controlling the cooling tower motor with the inverter at a variable speed, and the cooling water temperature is more stably controlled. It becomes possible to keep in a certain range. Further, the amount of chemicals such as cooling water and corrosion inhibitors can be reduced.

  According to the exhaust heat recovery system described in (3), in addition to the effect of the invention of the exhaust heat recovery system described in (2), the temperature of the cooling water to be introduced into the heat pump by adjusting the amount of the circulating cooling water Can be kept more stable.

  According to the exhaust heat recovery system as described in (4), in addition to the effect of the invention of the exhaust heat recovery system as described in (3), the temperature of the cooling water supplied to the heat pump can be controlled even in severe cold periods such as midwinter. It becomes possible to keep it as high and stable as possible.

It is a figure showing a schematic structure of an exhaust heat recovery system concerning a 1st embodiment. It is a figure which shows schematic structure of the waste heat recovery system concerning 2nd Embodiment. It is a figure which shows schematic structure of the waste heat recovery system concerning 3rd Embodiment.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Such an embodiment is merely an example for facilitating understanding of the invention, and does not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  (First embodiment)

  First, the configuration of the first embodiment of the present invention will be described with reference to FIG.

  An exhaust heat recovery system 100 in FIG. 1 includes a first pipe 3 having one end connected to the exhaust heat source 1, and the other end of the first pipe 3 is connected to a heat pump 5.

  A temperature sensor 7 is installed on the first pipe 3. One end of the second pipe 9 is connected to the heat pump 5, and the other end of the second pipe 9 is connected to the cooling tower 11.

  The cooling tower 11 is provided with a cooling tower motor 13 for driving a fan installed in the cooling tower 11.

  One end of the third pipe 17 is connected to the lower part of the cooling tower 11, and the other end is connected to the suction side of the circulation pump 19. A circulation pump motor 21 is provided to drive the circulation pump 19.

  One end of the fourth pipe 23 is connected to the discharge side of the circulation pump 19, and the other end is connected to the exhaust heat source 1.

  Further, a control unit 25 that controls the cooling tower motor 13 based on the measurement result of the temperature sensor 7 is provided.

  Next, the operation of the first embodiment will be described.

  The exhaust heat discharged from the exhaust heat source 1 heats the cooling water, and the heated cooling water is sent to the heat pump 5 through the first pipe 3. The heat pump 5 collects heat using this cooling water as a heat source (that is, cools the cooling water), and inputs the heat to other uses. The cooling water cooled by the heat pump 5 is sent to the cooling tower 11 through the second pipe 9 and further cooled.

  The temperature sensor 7 installed on the first pipe 3 measures the temperature of the cooling water, and the control unit 25 controls the cooling tower motor 13 to be turned on and off so that the measurement result falls within a preset temperature range. Thus, the cooling capacity of the cooling tower 11 is adjusted.

  The cooling water cooled by the cooling tower 11 is sent to the suction side of the circulation pump 19 driven by the circulation pump motor 21 through the third pipe 17 and discharged from the discharge side of the circulation pump 19 through the fourth pipe 23. The heat source 1 is charged again.

  The effect of the first embodiment will be described.

  Since the efficiency of the heat pump 5 greatly depends on the cooling water temperature as the heat source, it is desirable that the cooling water temperature be as high and stable as possible. However, the cooling water temperature is generally set at an upper limit of about 45 ° C. in order to prevent precipitation of corrosion inhibitors and the like. That is, in order to effectively use as a heat source of the heat pump 5, it is necessary to maintain the temperature of the cooling water at about 45 ° C. as much as possible.

  In many cases, the fan of the cooling tower 11 is operated by a constant speed motor, and the cooling capacity of the cooling tower is relatively large in the winter season when the outside temperature is low compared to the summer time when the outside temperature is high. In addition, the cooling capacity of the cooling tower 11 is often designed on the basis of the daytime in the most severe midsummer, so that the capacity of the cooling tower is excessive in winter when the outside temperature is low, and the temperature of the cooling water is also higher than that in the summer. It is not uncommon for the temperature to drop by about 10 ° C.

  When the amount of exhaust heat from the exhaust heat source 1 decreases due to fluctuations in the operating load, the cooling water temperature decreases as in the case of a decrease in the outside air temperature.

  However, in the present embodiment, the cooling tower motor 13 that drives the fan of the cooling tower 11 is controlled by the control unit 25.

  As a result of the measurement by the temperature sensor 7, when the cooling water temperature decreases from about 45 ° C., the control unit 25 controls the cooling tower motor 13 to be turned on and off in order to reduce the cooling capacity of the cooling tower 11. Suppresses the cooling capacity.

  This makes it possible to supply cooling water as a stable heat source to the heat pump 5 without affecting the cooling of the exhaust heat source 1.

  (Second Embodiment)

  Next, a difference between the second embodiment of the present invention and the first embodiment will be described with reference to the exhaust heat recovery system 105 shown in FIG.

  The configuration of the second embodiment is different from that of the first embodiment in that a cooling tower motor inverter 15 is connected to the cooling tower motor 13 so that variable speed operation is possible, and the cooling tower motor inverter 15 is controlled. This is a point controlled by the unit 25.

  In the operation of the second embodiment, the control unit 25 controls the cooling tower motor inverter 15 according to the measurement result of the temperature sensor 7.

  As a result, the cooling capacity of the cooling tower 11 can be adjusted more finely than in the case where the fans in the cooling tower 11 are controlled to be turned on and off, and the cooling water temperature can be kept stable. At the same time, the amount of cooling water and chemicals such as corrosion inhibitors can be reduced.

  (Third embodiment)

  Next, differences of the third embodiment according to the present invention from the second embodiment will be described with reference to the exhaust heat recovery system 110 shown in FIG.

  The configuration of the third embodiment is different from that of the second embodiment in that the circulation pump motor 21 is connected to a circulation pump inverter 27 so that variable speed operation is possible. This is a point controlled at 25.

  Although the operation of the third embodiment is basically the same as that of the second embodiment, the control unit 25 controls the circulation pump inverter 27 in addition to the cooling tower motor inverter 15 according to the measurement result of the temperature sensor 7. .

  Especially in the case of an open type cooling tower, there is a case where the cooling capacity becomes excessive due to a decrease in the outside air temperature in winter. In some cases, even if the cooling tower motor 13 that drives the cooling tower fan is stopped, This is to cope with a case where the temperature of the cooling water decreases.

  In such a case, since the temperature of the cooling water cannot be maintained at about 45 ° C. only by controlling the cooling tower motor inverter 15, the circulation amount of the cooling water is reduced by suppressing the rotation speed of the circulation pump 19. Thereby, for example, the cooling water temperature can be maintained at about 45 ° C. even in the severe winter season.

  In the third embodiment, the control unit 25 controls the two inverters, the cooling tower motor inverter 15 and the circulation pump inverter 27, but the cooling water temperature cannot be maintained by the control of the cooling tower motor inverter 15. It is preferable to control the circulation pump inverter 27 only in the case. This is to secure the amount of heat recovered by the heat pump 5 as much as possible.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings.

  It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used as an exhaust heat recovery system that efficiently recovers exhaust heat generated from an exhaust heat source with a heat pump.

100: Waste heat recovery system, 105: Waste heat recovery system, 110: Waste heat recovery system, 1: Waste heat source, 3: First pipe, 5: Heat pump, 7: Temperature sensor, 9: Second pipe, 11 : Cooling tower, 13: cooling tower motor, 15: inverter for cooling tower motor, 17: third piping, 19: circulation pump, 21: circulation pump motor, 23: fourth piping, 25: control unit, 27: Inverter for circulation pump

Claims (4)

An exhaust heat source,
A heat pump connected to the exhaust heat source by a first pipe;
A temperature sensor installed on the first pipe;
A cooling tower connected by a second pipe downstream of the heat pump;
A cooling tower motor for driving a fan installed in the cooling tower;
A circulation pump connected to the cooling tower by a third pipe;
A circulation pump motor for driving the circulation pump;
A fourth pipe connecting the circulation pump and the exhaust heat source;
In an exhaust heat recovery system comprising:
A controller that is connected to the temperature sensor and the cooling tower motor and controls the cooling tower motor so that the value of the temperature sensor is within a preset range;
An exhaust heat recovery system comprising: The cooling tower motor includes a cooling tower motor inverter for variable speed operation,
The exhaust heat recovery system according to claim 1, wherein the control unit controls the cooling tower motor inverter instead of the cooling tower motor. The circulation pump motor includes a circulation pump inverter that performs variable speed operation,
The exhaust heat recovery system according to claim 2, wherein the control unit controls the circulation pump inverter in addition to the control of the cooling motor inverter.   The exhaust heat recovery system according to claim 3, wherein the control unit controls the cooling tower motor inverter in preference to the circulation pump inverter.

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