JP5878046B2 - Turbo refrigerator and control method thereof - Google Patents

Description

  The present invention relates to a turbo chiller including an economizer, and more particularly to a turbo chiller using a multistage compression economizer cycle and a control method thereof.

  Conventionally, a turbo refrigerator used in a refrigeration air conditioner or the like is configured by a closed system in which a refrigerant is enclosed, an evaporator that takes heat from cold water (fluid to be cooled) and evaporates the refrigerant to exert a refrigeration effect; A compressor that compresses the refrigerant gas evaporated in the evaporator to form a high-pressure refrigerant gas; a condenser that cools and condenses the high-pressure refrigerant gas with cooling water (cooling fluid); and depressurizes the condensed refrigerant. An expansion valve (expansion mechanism) that is expanded by being connected by a refrigerant pipe. When a multistage compressor that compresses refrigerant gas in multiple stages with a multistage impeller is used as the compressor, the refrigerant gas generated in the economizer that is an intermediate cooler installed in the refrigerant pipe between the condenser and the evaporator Is introduced into an intermediate stage of the compressor (an intermediate part of a multistage impeller) (for example, Patent Document 1).

JP 2009-236430 A

  In the above-described turbo refrigerator equipped with the economizer, the liquid refrigerant and the refrigerant gas are separated by the economizer, and the separated refrigerant gas is introduced into the intermediate stage of the multistage compressor (intermediate part of the multistage impeller). The refrigeration effect as a whole cycle is increased. When operating a centrifugal chiller equipped with an economizer, there is a sufficient pressure difference between the condenser and the evaporator near the rated operation, so the refrigerant returns from the condenser to the evaporator via the economizer, The liquid refrigerant does not stay in the gas, and the gas-liquid separation function of the economizer works effectively.

However, at the start of operation of the refrigerator, there is no pressure difference between the condenser and the evaporator, so the return of the refrigerant to the evaporator worsens and the liquid refrigerant stays in the economizer.
In recent years, there has been an increasing demand for downsizing the refrigerator to reduce the installation space, and the economizer tends to be miniaturized as much as possible. For this reason, the function of the demister may be impaired by the liquid refrigerant remaining in the economizer at the start of operation of the refrigerator, the gas-liquid separation function of the economizer cannot be fully exhibited, and the refrigerant droplets are in the middle of the multistage turbo compressor. It is sucked into the stage (the middle part of the multistage impeller). That is, the refrigerant droplets carry over from the economizer to the intermediate stage of the multi-stage turbo compressor, so that the refrigerant droplets hit the impeller rotating at high speed. If the frequency of starting and stopping becomes high and such a situation continues for a long period of time, the impeller is eroded, the compressor performance is deteriorated, and the compressor cannot be stably operated.

  The present invention has been made in view of the above circumstances, and a turbo chiller capable of preventing the refrigerant droplets from being sucked into the intermediate stage of the multistage compressor from the economizer when the operation of the refrigerator is started, and a control method therefor The purpose is to provide.

In order to achieve the above-described object, a turbo refrigerator of the present invention includes an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, and a multistage turbo compressor that compresses the refrigerant using a multistage impeller. A condenser that cools and condenses the compressed refrigerant gas with a cooling fluid, and evaporates a part of the condensed refrigerant liquid to supply the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor A turbo chiller including an economizer that is an intermediate cooler that is provided in a flow path that connects the economizer and an intermediate portion of a multistage compression stage of the multistage turbo compressor, and a control valve that opens and closes the flow path , A liquid level measuring means for measuring the level of the economizer, and a control device for controlling the opening and closing of the control valve based on the liquid level obtained by the liquid level measuring means . At the start of operation It is kept closed and the control valve performs control to open the control valve when the liquid level of the economizer from the start of operation after a predetermined period of time is equal to or less than the predetermined height, the control device, the start of the operation of the refrigerator Even if the liquid level of the economizer exceeds the predetermined height after a predetermined time has elapsed, the control valve is controlled to open if the pressure difference between the condenser and the evaporator is equal to or higher than a predetermined pressure. It is characterized by.
The economizer is configured by disposing a demister on the upper part of a container-like storage unit that stores liquid refrigerant. The demister separates droplets contained in the refrigerant, and the droplets are collected in the container-like storage unit. It is like that. However, since the liquid refrigerant stays in the economizer at the start of operation of the refrigerator, the liquid level of the liquid refrigerant reaches the lower end of the demister or near the lower end, and the gas-liquid separation function of the demister may be impaired. Since the level level of the economizer reaches a steady level after a predetermined time from the start of operation of the refrigerator, for example, 1-2 minutes, the liquid level is measured after a predetermined time, for example, 1-2 minutes after the start of operation. . If the distance from the liquid level of the economizer to the lower end of the demister is equal to or greater than a predetermined distance (for example, 100 mm), the refrigerant droplets do not carry over, so the control valve is opened and the use of the economizer cycle is started.
Here, the liquid level of the economizer is a predetermined height. The distance from the liquid level of the economizer to the lower end of the demister is sufficient (for example, 100 mm or more), and the refrigerant droplets carry from the economizer to the multistage turbo compressor. The liquid level that does not cause overflow. The distance (for example, 100 mm) from the liquid level of the economizer to the lower end of the demister is a numerical value obtained experimentally.
According to the present invention, the pressure difference (ΔP) between the condenser and the evaporator is not less than a predetermined pressure even when the liquid level of the economizer exceeds a predetermined height after a predetermined time has elapsed since the start of operation of the refrigerator. If there is, there is no fear that the refrigerant droplets are carried over to the multistage turbo compressor, so the control valve is opened and the use of the economizer cycle is started. The predetermined pressure is, for example, 0.2 MPa when R134a is used as the refrigerant.
According to a preferred aspect of the present invention, the liquid level measuring means comprises a liquid level gauge.
The turbo chiller control method of the present invention includes an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multistage turbo compressor that compresses the refrigerant with a multistage impeller, and a compressed A condenser that cools and condenses the refrigerant gas with a cooling fluid, and an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor. A turbo chiller control method comprising: an economizer; and a control valve that opens and closes the flow path provided in a flow path that connects the economizer and an intermediate portion of a multistage compression stage of the multistage turbo compressor, When the operation of the refrigerator is started, the control valve is closed, and when the economizer liquid level is equal to or lower than the predetermined height after a predetermined time has elapsed from the start of operation, the control valve is opened, and a predetermined time has elapsed since the start of the operation of the refrigerator. Even when the liquid level of the economizer after exceeds the predetermined height, the pressure difference between the evaporator and the condenser, characterized in that opening the control valve as long as or greater than a predetermined pressure.
According to a preferred aspect of the present invention, the liquid level of the economizer is measured by a liquid level gauge.

According to an embodiment of the present invention, an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multistage turbo compressor that compresses the refrigerant with a multistage impeller, and a compressed refrigerant gas A condenser that cools and condenses the refrigerant with a cooling fluid, and an economizer that is an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor And a control valve that opens and closes the flow path, the condenser, and the evaporation are provided in a flow path that communicates the economizer and an intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor. Differential pressure measuring means for measuring the pressure difference of the container, and a control device for controlling the opening and closing of the control valve based on the pressure difference obtained by the differential pressure measuring means, the control device starts the operation of the refrigerator Sometimes the control valve Closed advance, performs control to open the control valve when the pressure difference between the evaporator and the condenser after the start of operation exceeds a predetermined pressure.
According to the above embodiment , at the start of the operation of the refrigerator, the refrigerant droplets in the multistage compression stage of the multistage turbo compressor are closed by closing the control valve installed in the flow path connecting the economizer and the multistage turbo compressor. It is controlled so that it is not sucked (carry over) into the middle part. Then, control is performed to open the control valve when the pressure difference between the condenser and the evaporator becomes equal to or higher than a predetermined pressure after the operation is started. This is because the pressure difference between the condenser and the evaporator increases after the start of operation of the refrigerator, so that the liquid refrigerant returns to the evaporator without staying in the economizer, and the multistage compression of the multistage turbo compressor from the economizer This is because it is possible to prevent the refrigerant droplets from being carried over to the middle part of the stage.
Here, the pressure difference (ΔP) between the condenser and the evaporator is equal to or higher than a predetermined pressure. For example, when R134a is used as the refrigerant, the pressure difference (ΔP) between the condenser and the evaporator is 0.2 MPa or more. is there. The predetermined pressure varies depending on the type of refrigerant, but is based on the difference between the condensation pressure and the evaporation pressure determined from the physical properties of the refrigerant in a steady operation state (for example, an evaporation temperature of 6 ° C. and a condensation temperature of 38 ° C.). In view of this, the value is determined by obtaining the difference between the condensation pressure and the evaporation pressure determined from the physical properties of the refrigerant corresponding to the temperature difference between the evaporation temperature and the condensation temperature (for example, 13 ° C.).

According to an embodiment of the present invention, the differential pressure measuring means, ing from a pressure gauge provided in the evaporator and a pressure gauge provided in the condenser.

According to an embodiment of the present invention, the control device is configured such that, even when a pressure difference between the condenser and the evaporator does not become a predetermined pressure or more after the start of operation of the refrigerator, the control device It intends line control to open the control valve.
Usually, the pressure difference (ΔP) between the condenser and the evaporator becomes a predetermined pressure (for example, 0.2 MPa) or more in a short time (1 to several minutes) after the operation of the turbo refrigerator is started. However, under exceptional conditions such as when the temperature of the cooling water is too low, the pressure difference (ΔP) may not reach the predetermined pressure. In this case, even if the economizer cycle is used with the control valve opened, the refrigerant load, that is, the refrigerant circulation amount itself is small, so that the possibility that the refrigerant droplets carry over from the economizer to the multistage turbo compressor is extremely low. Therefore, in the present invention, when a predetermined time has elapsed (for example, 30 minutes have elapsed) since the start of operation of the refrigerator, the control valve is opened and the use of the economizer cycle is started.

According to an embodiment of the present invention, it is provided with a liquid level measuring means for measuring the level of the economizer, and the control device closes the control valve at the start of operation of the refrigerator, and after a predetermined time has elapsed from the start of operation. intends line control of liquid level in said economizer opens the control valve when it is below a predetermined height.
According to an embodiment of the present invention, the economizer comprises temperature measuring means for measuring the temperature of the refrigerant supplied to the intermediate part of the multistage compression stage of the multistage turbo compressor, and the control device is operating the refrigerator have opened the control valve, it intends row control to close the control valve when the measured value obtained by the temperature measuring means during operation occurs hunting repeated variations.

According to an embodiment of the present invention, an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multistage turbo compressor that compresses the refrigerant with a multistage impeller, and a compressed refrigerant gas A condenser that cools and condenses the refrigerant with a cooling fluid, and an economizer that is an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor And a control valve that opens and closes the flow path, and is provided in a flow path that communicates the economizer and an intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor, and from the economizer to the multi-stage turbo A temperature measuring means for measuring the temperature of the refrigerant supplied to an intermediate part of the multistage compression stage of the compressor, and a control device for performing opening / closing control of the control valve based on the measured value obtained by the temperature measuring means. , Wherein the control device, keep the control valve open during operation of the refrigerator, the line control to close the control valve when the measured value obtained by the temperature measuring means during operation occurs hunting repeating variation Yeah.

According to the above embodiment , when the refrigerant droplets carry over and the refrigerant droplets are sucked into the intermediate portion of the multistage compression stage of the multistage turbo compressor, the refrigerant droplets hit the temperature measuring means. Then, since the refrigerant droplets are immediately evaporated on the surface of the temperature measuring means, the detected temperature is lowered. Since the refrigerant droplet repeatedly hits the temperature measuring means, the temperature measurement value repeatedly fluctuates, so-called hunting occurs. Therefore, in the present invention, the control valve is closed when hunting occurs in the measured value of the temperature measuring means.

According to an embodiment of the present invention, the temperature measuring means, ing from a temperature sensor installed in the intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor.

According to an embodiment of the present invention, after the control valve is closed, the control device controls the control valve when a pressure difference between the condenser and the evaporator or a liquid level of the economizer satisfies a predetermined condition. It intends line control to open.
According to the above embodiment , after the control valve is closed, when the pressure difference between the condenser and the evaporator or the liquid level of the economizer satisfies a predetermined condition, there is no risk of carryover of refrigerant droplets. Open and start using the economizer cycle.
Here, when the pressure difference between the condenser and the evaporator or the level of the economizer satisfies a predetermined condition, the pressure difference (ΔP1) between the condenser and the evaporator is measured when the control valve is closed. In addition, the level of the economizer (H1) is measured, and then the pressure difference (ΔP2) between the condenser and the evaporator is higher than the pressure difference (ΔP1) when the control valve is closed by a predetermined pressure (for example, 0.05 MPa) or more. The economizer liquid level (H2) is lower than the economizer liquid level (H1) when the control valve is closed by a predetermined height (for example, 20 mm) or more. The predetermined pressure (for example, 0.05 MPa) and the predetermined height (for example, 20 mm) are numerical values obtained experimentally.

According to an embodiment of the present invention, an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multistage turbo compressor that compresses the refrigerant with a multistage impeller, and a compressed refrigerant gas A condenser that cools and condenses the refrigerant with a cooling fluid, and an economizer that is an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor And a control method of a centrifugal chiller comprising a control valve provided in a flow path communicating the economizer and an intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor, wherein the control valve opens and closes the flow path. at the start of the operation kept closed with the control valve, the control valve open when the pressure difference between the evaporator and the condenser after the start of operation exceeds a predetermined pressure.

According to an embodiment of the present invention, the pressure difference between the evaporator and the condenser, measured by a pressure gauge provided in the evaporator and a pressure gauge provided in the condenser.
According to an embodiment of the present invention, even when the pressure difference between the evaporator and the condenser after the start operation of the refrigerator is not higher than a predetermined pressure, rather the control valve from the start of operation after a predetermined period of time to open .

According to an embodiment of the present invention, at the start operation of the refrigerator kept closed with the control valve, the control valve when the liquid level of the economizer from the start of operation after a predetermined period of time is equal to or less than the predetermined height Open .
According to an embodiment of the present invention, the control valve is opened during operation of the refrigerator, and the temperature measurement value of the refrigerant supplied from the economizer to the intermediate portion of the multistage compression stage of the multistage turbo compressor during operation. There it closes the control valve when the has occurred hunting repeated variations.

According to an embodiment of the present invention, an evaporator that takes heat from a fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multistage turbo compressor that compresses the refrigerant with a multistage impeller, and a compressed refrigerant gas A condenser that cools and condenses the refrigerant with a cooling fluid, and an economizer that is an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor And a control method of a centrifugal chiller comprising a control valve provided in a flow path communicating the economizer and an intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor, wherein the control valve opens and closes the flow path. When the control valve is opened during the operation, and during operation, hunting occurs in which the temperature measurement value of the refrigerant supplied from the economizer to the intermediate portion of the multistage compression stage of the multistage turbo compressor repeatedly fluctuates. It closes the serial control valve.

According to the embodiment of the present invention, the temperature of the refrigerant supplied from the economizer to the intermediate part of the multistage compression stage of the multistage turbo compressor is the temperature set in the intermediate part of the multistage compression stage of the multistage turbo compressor. that be measured by the sensor.
According to an embodiment of the present invention, after closing the control valve, the control valve Open when liquid level in the pressure difference or the economizer of the evaporator and the condenser satisfies a predetermined condition.

The present invention has the following effects.
(1) The refrigerant droplets are not carried over from the economizer to the intermediate portion of the multistage compression stage of the multistage turbo compressor at the start of operation of the refrigerator, and the impeller erosion caused by the refrigerant droplets can be avoided. it can. Therefore, it is possible to realize the operation of the refrigerator that is stable and reliable over a long period of time.
(2) When a refrigerant droplet carryover from the economizer to the multi-stage turbo compressor occurs during operation of the refrigerator, the refrigerant droplet is carried by closing the control valve between the economizer and the compressor. Over can be stopped quickly.

FIG. 1 is a schematic diagram showing an embodiment of a turbo refrigerator according to the present invention. FIGS. 2A, 2B, and 2C are flowcharts showing a control procedure performed by the control device based on the control method of the present invention at the start and during operation of the turbo chiller.

Hereinafter, an embodiment of a turbo refrigerator and a control method thereof according to the present invention will be described with reference to FIGS. 1 and 2. 1 and 2, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a schematic diagram showing an embodiment of a turbo refrigerator according to the present invention. In the embodiment shown in FIG. 1, a turbo refrigerator using a two-stage compression single-stage economizer cycle will be described. As shown in FIG. 1, the turbo refrigerator includes a multi-stage turbo compressor TC that compresses refrigerant, a condenser 4 that cools and condenses the compressed refrigerant gas with cooling water (cooling fluid), and cold water (cooled). Installed in front of and behind the economizer 6, an evaporator 5 that takes heat from the fluid) and evaporates the refrigerant to exert a refrigeration effect, an economizer 6 that is an intermediate cooler disposed between the condenser 4 and the evaporator 5 And an expansion mechanism 8 for depressurizing and expanding the condensed refrigerant, and these devices are connected by a refrigerant pipe 9 through which the refrigerant circulates.

  In the embodiment shown in FIG. 1, the multi-stage turbo compressor TC is a two-stage turbo compressor, and the first-stage compressor 1, the second-stage compressor 2, and the compression that drives these compressors 1 and 2. And a machine motor 3. The discharge side of the first stage compressor 1 and the suction side of the second stage compressor 2 are connected by a flow path 10. In the multistage turbo compressor TC, the refrigerant gas introduced from the evaporator 5 into the first stage compressor 1 is compressed by the first stage by the first stage compressor 1, and then the second stage compressor 2 by the flow path 10. The refrigerant gas introduced into is compressed in the second stage by the second stage compressor 2 and then sent to the condenser 4.

  Further, the economizer 6 and the flow path 10 are connected by a flow path 11, and the refrigerant gas separated by the economizer 6 is an intermediate portion of the multistage compression stage (two stages in this example) of the multistage turbo compressor TC ( In this example, it is introduced into a portion between the first stage and the second stage). An electric control valve 7 is provided in a flow path 11 connecting the economizer 6 and the multistage turbo compressor TC, and supply and stop of supply of refrigerant gas from the economizer 6 to the compression stage of the multistage turbo compressor TC. Can be controlled.

  In the refrigeration cycle of the turbo chiller configured as shown in FIG. 1, the refrigerant circulates through the multistage turbo compressor TC, the condenser 4, the evaporator 5, and the economizer 6, and chilled water is generated by the cold heat source obtained by the evaporator 5. Is manufactured, corresponds to the load, and the amount of heat from the evaporator 5 taken into the refrigeration cycle and the amount of heat corresponding to the work of the multistage turbo compressor TC supplied from the compressor motor 3 are supplied to the condenser 4. Released into cooling water. On the other hand, the refrigerant gas separated by the economizer 6 is introduced into an intermediate portion of the multistage compression stage of the multistage turbo compressor TC, merged with the refrigerant gas from the first stage compressor 1 and compressed by the second stage compressor 2. The According to the two-stage compression single-stage economizer cycle, since the refrigeration effect portion by the economizer 6 is added, the refrigeration effect is increased by that amount, and the efficiency of the refrigeration effect is improved as compared with the case where the economizer 6 is not installed. Can do.

  As described above, the turbo chiller provided with the economizer 6 can construct a highly efficient refrigeration cycle, but no pressure difference between the condenser 4 and the evaporator 5 occurs at the start of the operation of the refrigerator. For this reason, the return of the refrigerant to the evaporator 5 becomes worse and the liquid refrigerant stays in the economizer 6. For this reason, the function of the demister may be impaired by the liquid refrigerant staying in the economizer 6, the gas-liquid separation function of the economizer 6 cannot be sufficiently exhibited, and the refrigerant droplets are intermediate between the multistage compression stages of the multistage turbo compressor TC. There is a problem of being sucked into the part.

  Therefore, in the present invention, when the operation of the refrigerator is started, the control valve 7 installed in the flow path 11 connecting the economizer 6 and the multistage turbo compressor TC is closed, so that the refrigerant droplets are generated in the multistage turbo compressor TC. Is controlled so as not to be sucked into (carry over) the intermediate portion of the multi-stage compression stage.

Next, a configuration for controlling opening and closing of the control valve 7 will be described.
As shown in FIG. 1, the condenser 4 and the evaporator 5 are provided with a pressure sensor P1 and a pressure sensor P2, respectively. A temperature sensor T1 that measures the inlet refrigerant temperature of the second stage compressor is installed at the inlet of the second stage compressor 2 of the multistage turbo compressor TC. The economizer 6 is provided with a liquid level gauge LV. The pressure sensor P1, the pressure sensor P2, the temperature sensor T1, and the liquid level gauge LV are each connected to the control device 20. The control valve 7 is connected to the control device 20.

With the above-described configuration, the pressure signal S1 from the pressure sensor P1, the pressure signal S2 from the pressure sensor P2, and the liquid level signal S3 from the liquid level gauge LV are input to the control device 20, respectively, from the pressure signals S1 and S2. The pressure difference (ΔP) between the condenser 4 and the evaporator 5 is detected, and the liquid level (L _H ) of the liquid refrigerant in the economizer 6 is detected from the liquid level signal S3. Further, the temperature signal S4 from the temperature sensor T1 is input to the control device 20, and the inlet refrigerant temperature of the second stage compressor 2 is detected.

  In the present invention, at the start of the operation of the refrigerator, by closing the control valve 7 installed in the flow path 11 connecting the economizer 6 and the multistage turbo compressor TC, the refrigerant droplets become multistage of the multistage turbo compressor TC. The control valve is controlled so that it is not sucked into (carryed over) into the middle part of the compression stage, but the condition that the refrigerant droplets do not carry over to the multistage turbo compressor TC side after the start of operation is satisfied. 7 is controlled to make the best use of the economizer cycle.

Next, conditions for opening the control valve 7 and using the economizer cycle after starting the operation of the refrigerator will be described. This condition was obtained by experiment.
1) Open the control valve 7 when the pressure difference between the condenser 4 and the evaporator 5 exceeds a predetermined pressure.
Assuming a standard operating state (steady operating state), when R134a is used as the refrigerant, if the evaporation temperature in the evaporator is 6 ° C. and the condensation temperature in the condenser is 38 ° C., the evaporation pressure is 0 due to the physical properties of the refrigerant. .362 MPa and the condensation pressure is 0.963 MPa. Therefore, the pressure difference (ΔP) between the condenser and the evaporator in the standard operation state (steady operation state) ≈0.6 MPa.

  On the other hand, considering that it is at the start of operation, if the temperature difference between the evaporation temperature and the condensation temperature is 13 ° C, the evaporation temperature in the evaporator is 7 ° C and the condensation temperature in the condenser is 20 ° C. From the physical properties of the refrigerant, the evaporation pressure is 0.375 MPa and the condensation pressure is 0.572 MPa. Therefore, it is possible to derive a pressure difference (ΔP) ≈0.2 MPa between the condenser and the evaporator at the start of operation of the refrigerator. That is, if the pressure difference (ΔP) between the condenser and the evaporator is 0.2 MPa or more, it is considered that the liquid refrigerant returns to the evaporator without staying in the economizer.

  Therefore, the present inventors repeatedly performed start / stop experiments while confirming the pressure difference (ΔP) between the condenser and the evaporator using a turbo refrigerator configured as shown in FIG. At this time, the temperature sensor T1 installed in the second stage compressor 2 of the multistage turbo compressor TC measures the refrigerant temperature at the inlet of the compressor, and is provided in the flow path 11 connecting the economizer 6 and the multistage turbo compressor TC. The presence or absence of carryover of refrigerant droplets was observed from the observation window. In this case, when the refrigerant droplet carryover occurs and the refrigerant droplet is sucked into the second stage compressor 2, the refrigerant droplet hits the temperature sensor T <b> 1 installed at the inlet of the second stage compressor 2. Become. Then, since the refrigerant droplets are immediately evaporated on the surface of the temperature sensor T1, the detected temperature is lowered. Since the refrigerant droplet repeatedly hits the temperature sensor T1, the temperature measurement value repeatedly fluctuates, so-called hunting occurs. This hunting is to repeat a temperature change above a predetermined temperature (for example, ± 0.5 ° C. or more) in a short time (for example, 5 minutes). That is, the carryover of the refrigerant droplet can be detected from the measured value of the temperature sensor T1.

  Thus, the pressure difference (ΔP) between the condenser 4 and the evaporator 5 is measured by measuring the refrigerant temperature at the inlet of the compressor by the temperature sensor T1 and observing whether or not the refrigerant droplets carry over from the viewing window. Was 0.2 MPa or more, it was confirmed that there was no carryover of refrigerant droplets. That is, when the refrigerant is R134a, the control valve 7 is controlled to open when the pressure difference (ΔP) between the condenser 4 and the evaporator 5 becomes 0.2 MPa or more after the operation of the refrigerator is started. The carryover of the refrigerant droplets from the economizer 6 to the intermediate portion of the multistage compression stage of the multistage turbo compressor TC can be prevented.

2) Open the control valve 7 when the level of the economizer 6 is below a predetermined height.
The economizer 6 is configured by disposing a demister 12 (see FIG. 1) on an upper part of a container-like storage unit that stores liquid refrigerant. The demister separates droplets contained in the refrigerant, and the droplets are in a container shape. It is collected in the storage part.
However, since the liquid refrigerant stays in the economizer 6 at the start of operation of the refrigerator, the liquid level of the liquid refrigerant reaches the lower end or near the lower end of the demister, and the gas-liquid separation function of the demister may be impaired.

  Therefore, the present inventors have repeatedly performed start / stop experiments while measuring the liquid level of the economizer 6 with a liquid level gauge LV using a turbo refrigerator configured as shown in FIG. At this time, the temperature sensor T1 installed in the second stage compressor 2 of the multistage turbo compressor TC measures the refrigerant temperature at the inlet of the compressor, and is provided in the flow path 11 connecting the economizer 6 and the multistage turbo compressor TC. The presence or absence of carryover of refrigerant droplets was observed from the observation window. The liquid level of the economizer 6 reaches a steady level after a predetermined time from the start of operation of the refrigerator, for example, 1 to 2 minutes. Therefore, measurement of the liquid level starts 1 to 2 minutes after the start of operation.

  Thus, the distance from the liquid level of the economizer 6 to the lower end of the demister is measured by measuring the refrigerant temperature at the inlet of the compressor by the temperature sensor T1 and observing the presence or absence of carryover of refrigerant droplets from the viewing window. It was confirmed that there was no carryover of the refrigerant droplets when the thickness was 100 mm or more. That is, if the liquid level of the economizer 6 when the distance from the liquid level of the economizer 6 to the lower end of the demister is 100 mm is defined as the upper limit liquid level, the control is performed if the liquid level of the economizer 6 is equal to or lower than the upper limit liquid level. By performing control to open the valve 7, it is possible to prevent carryover of refrigerant droplets from the economizer 6 to the intermediate portion of the multistage compression stage of the multistage turbo compressor TC.

3) The control valve 7 is opened after the start of operation of the refrigerator, and the control valve 7 is closed when the measured value of the temperature sensor T1 causes hunting during steady operation using the two-stage compression single-stage economizer cycle.
Even when the conditions of 1) or 2) are met after the start of the operation of the refrigerator and the control valve 7 is opened and the steady operation is performed by utilizing the economizer cycle, the gas-liquid separation function in the economizer 6 is caused by a malfunction of the demister. In some cases, the refrigerant droplets cannot be sufficiently exhibited and carry over to the intermediate stage of the multistage turbo compressor TC. In that case, since the measured value of the temperature sensor T1 installed at the inlet of the second stage compressor 2 causes hunting, the control valve 7 is quickly closed.

FIGS. 2A, 2B, and 2C are flowcharts showing a control procedure performed by the control device 20 based on the control methods 1) to 3) when the turbo chiller is started and during operation. It is.
FIG. 2A is a flowchart showing a control procedure at the start of operation of the centrifugal chiller using the control method of 1). As shown in FIG. 2A, the operation of the turbo chiller is started, and then it is determined whether or not the pressure difference (ΔP) between the condenser 4 and the evaporator 5 has become equal to or higher than a predetermined pressure. When the pressure difference (ΔP) is equal to or higher than the predetermined pressure, the control valve 7 is opened and the use of the economizer cycle is started. In this case, the predetermined pressure differs depending on the type of refrigerant, but in the case of R134a, it is 0.2 MPa. When the pressure difference (ΔP) is less than the predetermined pressure, it is determined whether or not a predetermined time has elapsed since the start of operation. When a predetermined time has elapsed from the start of operation, the control valve 7 is opened and the use of the economizer cycle is started. Here, the predetermined time is, for example, 30 minutes and is a time obtained by experiment. If the predetermined time has not elapsed since the start of operation, the process returns to the pressure difference (ΔP) determination step.

  Usually, the pressure difference (ΔP) becomes a predetermined pressure (0.2 MPa) or more in a short time (1 to several minutes) after the operation of the turbo refrigerator is started. However, under exceptional conditions such as when the temperature of the cooling water is too low, the pressure difference (ΔP) may not reach the predetermined pressure. In this case, since the refrigeration load, that is, the refrigerant circulation amount itself is small, even when the control valve 7 is opened and the economizer cycle is used, the possibility that refrigerant droplets carry over from the economizer 6 to the multistage turbo compressor TC is extremely low. . Therefore, when a predetermined time has elapsed (for example, 30 minutes have elapsed) since the start of operation of the refrigerator, the control valve 7 is opened and the use of the economizer cycle is started.

  FIG. 2B is a flowchart showing a control procedure at the start of operation of the centrifugal chiller using the control method of 2). As shown in FIG. 2 (b), when a predetermined time has elapsed since the operation of the turbo refrigerator was started, it is determined whether or not the liquid level of the economizer 6 is equal to or lower than the upper limit liquid level. When the level of the economizer 6 is equal to or lower than the upper limit level, the control valve 7 is opened and the use of the economizer cycle is started. When the liquid level of the economizer 6 exceeds the upper limit liquid level, it is determined whether or not the pressure difference (ΔP) between the condenser 4 and the evaporator 5 exceeds a predetermined pressure. When the pressure difference (ΔP) is equal to or higher than the predetermined pressure, the control valve 7 is opened and the use of the economizer cycle is started. In this case, the predetermined pressure differs depending on the type of refrigerant, but in the case of R134a, it is 0.2 MPa. This is because even if the level of the economizer 6 is high, if there is a sufficient pressure difference between the condenser 4 and the evaporator 5, there is no possibility that the refrigerant droplets are carried over to the multistage turbo compressor TC. On the other hand, when the pressure difference (ΔP) is less than the predetermined pressure, the process returns to the level determination step of the economizer 6.

FIG.2 (c) is a flowchart which shows the control procedure in the driving | operation of the turbo refrigerator using the control method of said 3). Even when the conditions shown in FIG. 2 (a) or FIG. 2 (b) are satisfied after the start of the operation of the refrigerator and the control valve 7 is opened and the steady operation is performed by utilizing the economizer cycle, the economizer is caused by a malfunction of the demister. 6 may not sufficiently exhibit the gas-liquid separation function, and refrigerant droplets may be carried over to the intermediate stage of the multi-stage turbo compressor TC. Therefore, as shown in FIG. 2 (c), during the operation of the centrifugal chiller, it is determined whether the measured value of the temperature sensor T1 installed at the inlet of the multi-stage turbo compressor TC has caused hunting. When it occurs, the control valve 7 is closed, and the carryover of the refrigerant droplet is quickly stopped. When the control valve 7 is closed, the pressure difference (ΔP1) between the condenser 4 and the evaporator 5 is measured and the liquid level (H1) of the economizer 6 is measured. Thereafter, whether the pressure difference (ΔP2) between the condenser 4 and the evaporator 5 is higher than a pressure difference (ΔP1) when the control valve 7 is closed by a predetermined pressure (for example, 0.05 MPa) or not, or whether the economizer 6 It is determined whether or not the liquid level (H2) is lower than the liquid level (H1) of the economizer 6 when the control valve 7 is closed by a predetermined height (for example, 20 mm) or more. That is, the following equation is determined.
ΔP2 ≧ ΔP1 + 0.05 MPa (1)
H2 ≦ H1-20mm (2)
When the expression (1) or (2) is satisfied, the control valve 7 is opened because there is no risk of carryover of refrigerant droplets from the economizer 6 to the multistage turbo compressor TC. If neither the expression (1) nor the expression (2) is satisfied, the control valve is kept closed.

  Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention may be implemented in various different forms within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 1st stage compressor 2 2nd stage compressor 3 Compressor motor 4 Condenser 5 Evaporator 6 Economizer 7 Control valve 8 Expansion mechanism 10,11 Flow path 20 Control apparatus LV Level gauge P1, P2 Pressure sensor T1 Temperature sensor TC Multistage turbo compressor

Claims (4)

An evaporator that draws heat from the fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multi-stage turbo compressor that compresses the refrigerant with a multi-stage impeller, and cools and compresses the compressed refrigerant gas with the cooling fluid In a turbo chiller comprising a condenser and an economizer that is an intermediate cooler that evaporates a part of the condensed refrigerant liquid and supplies the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor,
A control valve provided in a flow path communicating the economizer and an intermediate portion of the multi-stage compression stage of the multi-stage turbo compressor, and opening and closing the flow path;
A liquid level measuring means for measuring the level of the economizer;
A control device that performs opening and closing control of the control valve based on the liquid level obtained by the liquid level measuring means,
Wherein the control device, leave at the beginning operation of the refrigerator closing the control valve, have row control to open the control valve when the liquid level of the economizer from the start of operation after a predetermined period of time is equal to or less than a predetermined height,
The control device is configured such that the pressure difference between the condenser and the evaporator is not less than a predetermined pressure even when the liquid level of the economizer exceeds the predetermined height after a predetermined time has elapsed since the start of operation of the refrigerator. turbo refrigerator according to claim row Ukoto control to open the control valve, if any. The liquid level measuring means, a turbo refrigerator according to claim 1, characterized in that it consists of the liquid level gauge. An evaporator that draws heat from the fluid to be cooled and evaporates the refrigerant to exert a refrigeration effect, a multi-stage turbo compressor that compresses the refrigerant with a multi-stage impeller, and cools and compresses the compressed refrigerant gas with the cooling fluid A condenser, an economizer as an intermediate cooler for evaporating a part of the condensed refrigerant liquid and supplying the evaporated refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor, the economizer and the multistage turbo compression A turbo chiller control method comprising a control valve provided in a flow path communicating with an intermediate portion of a multi-stage compression stage of a machine and a control valve for opening and closing the flow path,
At the start operation of the refrigerator kept closed with the control valve,-out said control valve when the liquid level of the economizer from the start of operation after a predetermined period of time is equal to or less than the predetermined height open,
Even if the liquid level of the economizer exceeds the predetermined height after the elapse of a predetermined time since the start of operation of the refrigerator, the control valve if the pressure difference between the condenser and the evaporator is equal to or higher than a predetermined pressure. the method of the turbo chiller, wherein the open Kukoto. The turbo refrigerator control method according to claim 3 , wherein the level of the economizer is measured by a liquid level gauge.

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