JP2015194301A - turbo refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbo refrigerator which can avoid drop in controllability of an electric expansion valve and which avoids cost increase caused by installing a plurality of expansion valves.SOLUTION: A turbo refrigerator 1 includes: an evaporator 3 in which a refrigerant evaporates by depriving a fluid to be cooled of heat and refrigeration effect is exhibited; a multistage turbo compressor 1 which compresses the refrigerant by a multistage impeller 11; a condenser 2 which cools a compressed refrigerant gas by a cooling liquid and condenses it; and an economizer 4, which is an intermediate cooler, for supplying the refrigerant gas generated by evaporating a part of the condensed refrigerant liquid to an intermediate portion of multistage compression stages of the multistage turbo compressor 1. In a refrigerant pipeline 5 for leading the refrigerant from the condenser 2 to the economizer 4, an orifice 6 and an expansion valve 7 are installed in the order of the orifice 6, the expansion valve 7. In the refrigerant pipeline 5 for leading the refrigerant from the economizer 4 to the evaporator 3, an orifice 9 and an expansion valve 10 are installed in the order of the orifice 9, the expansion valve 10.

Description

  The present invention relates to a turbo refrigerator, and more particularly to an expansion mechanism of a turbo refrigerator.

  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 (intermediate part of a multistage impeller).

In the centrifugal chiller, a fixed orifice, a float valve, a motor operated valve, and the like are used for the expansion mechanism from the condenser to the economizer and from the economizer to the evaporator.
In the refrigeration cycle, when refrigerant gas that does not contribute to the refrigeration capacity is compressed by the compressor, excess power is consumed, leading to a reduction in efficiency of the refrigerator.
Conventionally, an electric valve has been adopted as an expansion mechanism, ensuring the liquid level of the primary body of the expansion valve (condenser, economizer), and avoiding gas bypass by liquid-sealing the primary side of the expansion mechanism Yes.

Although an electric valve is often used as the expansion valve, the flow rate Cv value (flow rate coefficient) and the control characteristics of the opening degree change depending on the type of the valve body.
Most of the expansion valves for turbo chillers are ball valves and butterfly valves.
In the low valve opening range, a change in the Cv value (flow coefficient) with respect to the valve operation amount is small, which is a so-called dead zone, which is not suitable for liquid level control requiring the above-described accuracy.
FIG. 6 is a graph showing the relationship between the valve opening degree of the ball valve and the butterfly valve and the Cv value (flow coefficient). As shown in FIG. 6, the low valve opening range is a non-controllability range where the change in the Cv value with respect to the valve operation amount is small. And in the area | region where a valve opening degree is comparatively high, it is a controllability favorable area | region where the change of Cv value with respect to valve operation amount becomes large.

In FIG. 6, if a small-diameter expansion valve is used on the premise that it is used in an area with good controllability, the return of the refrigerant to the evaporator becomes worse under low head conditions where the temperature difference between the cold water and the cooling water is small. There are cases where suction low pressure occurs and the operation of the refrigerator cannot be continued.
Therefore, a large-diameter expansion valve and a small-diameter expansion valve are juxtaposed in parallel, and expansion valve switching control is performed according to the temperature conditions of the refrigeration load or cold water / cooling water.

Japanese Patent No. 41099997

The conventional techniques described above have the following problems.
1) There is an unsuitable area for controllability of the electric expansion valve, and liquid level control with high accuracy is not possible.
2) In order to ensure controllability, when a plurality of large-diameter expansion valves and small-diameter expansion valves are installed in parallel, there is a problem that the cost increases.

  The present invention has been made in view of the above circumstances, and provides a turbo chiller that can avoid a decrease in controllability of an electric expansion valve and avoids an increase in cost due to the installation of a plurality of expansion valves. For the purpose.

  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 In the turbo chiller including an economizer that is an intermediate cooler, an orifice and an expansion valve are installed in the order of the orifice and the expansion valve in a refrigerant pipe that guides the refrigerant from the condenser to the economizer, and the evaporation from the economizer An orifice and an expansion valve are installed in the order of the orifice and the expansion valve in the refrigerant pipe for introducing the refrigerant to the vessel.

  According to the present invention, on the high stage side between the condenser and the economizer, the orifice provided on the primary side of the expansion valve provides a pressure loss as a base to limit the amount of refrigerant circulation, and the expansion valve located downstream. Control the liquid level of the condenser. By providing the orifice on the primary side of the expansion valve in this way, the region in which the expansion valve opens and closes shifts to a good controllability region in which the Cv value (flow coefficient) changes sensitively with respect to the valve operation amount. The problem of a decrease in control responsiveness can be solved. By performing the liquid level control with high accuracy in the condenser by the orifice and the expansion valve, the gas bypass amount of the refrigeration cycle can be reduced, and the efficiency of the refrigerator can be avoided. Similarly, on the lower stage side between the economizer and the evaporator, similarly, the orifice provided on the primary side of the expansion valve gives a pressure loss as a base to limit the refrigerant circulation amount, and the economizer is connected with the downstream expansion valve. Control the liquid level. Thus, by performing liquid level control with high accuracy in the economizer by the orifice and the expansion valve, the gas bypass amount of the refrigeration cycle can be reduced, and a decrease in efficiency of the refrigerator can be avoided.

According to a preferred aspect of the present invention, the orifice is a fixed orifice, and the expansion valve is an electric expansion valve having a variable opening.
According to a preferred aspect of the present invention, the control device includes a liquid level sensor that is installed in each of the condenser and the economizer and measures a refrigerant liquid level height, and a control device that controls the opening degree of the expansion valve. The apparatus controls the opening degree of the expansion valve between the condenser and the economizer based on the measurement value of the liquid level sensor installed in the condenser, and uses the measurement value of the liquid level sensor installed in the economizer. Based on this, the opening degree of the expansion valve between the economizer and the evaporator is controlled.

  According to a preferred aspect of the present invention, a pressure sensor that is installed in each of the condenser and the evaporator and measures the pressure of the condenser and the pressure of the evaporator, and a control device that controls the opening degree of the expansion valve are provided. And the control device includes an opening degree of an expansion valve between the condenser and the economizer, the economizer and the economizer based on a pressure difference between the condenser pressure and the evaporator pressure measured by the pressure sensor. The opening degree of the expansion valve between the evaporators is controlled.

  According to a preferred aspect of the present invention, a relationship between the pressure difference between the condenser pressure and the evaporator pressure and the opening degree of the expansion valve is obtained in advance, and the previously obtained relationship is stored in the control device, The control device, based on the relationship obtained in advance from the pressure difference between the condenser pressure and the evaporator pressure measured by the pressure sensor, the opening of the expansion valve between the condenser and the economizer, and the The opening degree of the expansion valve between the economizer and the evaporator is determined.

The present invention has the following effects.
(1) By accurately controlling the liquid level of the condenser and the economizer, the gas bypass amount of the refrigeration cycle can be reduced, and the efficiency of the refrigerator can be avoided.
(2) It is possible to avoid an operation region where the control response of the electric expansion valve is poor and to make the operation region good in controllability.
(3) It is possible to control the liquid level of the condenser and the economizer with a single expansion valve by avoiding an increase in cost by installing a plurality of expansion valves in parallel to ensure control responsiveness. .

FIG. 1 is a schematic diagram showing a first embodiment of a turbo refrigerator according to the present invention. FIG. 2 is a Mollier diagram when an orifice and an expansion valve are connected in series. FIG. 3 is a schematic diagram showing an embodiment in which a liquid level sensor is provided in the turbo refrigerator shown in FIG. FIG. 4 is a schematic view showing an embodiment in which a pressure sensor is provided in the turbo refrigerator shown in FIG. FIG. 5 is a graph showing the relationship between the pressure difference between the condenser and the evaporator and the opening of the expansion valve. FIG. 6 is a graph showing the relationship between the valve opening degree of the ball valve and the butterfly valve and the Cv value (flow coefficient).

  Hereinafter, an embodiment of a turbo refrigerator according to the present invention will be described with reference to FIGS. 1 to 5. 1 to 5, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic diagram showing a first embodiment of a turbo refrigerator according to the present invention. As shown in FIG. 1, a turbo refrigerator includes a turbo compressor 1 that compresses refrigerant, a condenser 2 that cools and compresses the compressed refrigerant gas with cooling water (cooling fluid), and cold water (cooled fluid). ), An evaporator 3 that evaporates the refrigerant and exerts a refrigeration effect, and an economizer 4 that is an intermediate cooler disposed between the condenser 2 and the evaporator 3. Are connected by a refrigerant pipe 5 that circulates.

  In the embodiment shown in FIG. 1, the turbo compressor 1 is composed of a multi-stage turbo compressor, and the multi-stage turbo compressor is composed of a two-stage turbo compressor, and a first-stage impeller 11 and a second-stage impeller 12. And a compressor motor 13 that rotates these impellers 11 and 12. On the suction side of the first stage impeller 11, a suction vane 14 for adjusting the suction flow rate of the refrigerant gas to the impellers 11 and 12 is provided. The turbo compressor 1 is connected to the economizer 4 by a flow path 8, and the refrigerant gas separated by the economizer 4 is an intermediate portion (in this example, two stages) of the multi-stage compression stage (two stages in this example) of the turbo compressor 1. A portion between the first stage impeller 11 and the second stage impeller 12) is introduced.

  In the refrigeration cycle of the turbo chiller configured as shown in FIG. 1, the refrigerant circulates through the turbo compressor 1, the condenser 2, the evaporator 3, and the economizer 4, and chilled water is generated by the cold heat source obtained by the evaporator 3. The amount of heat from the evaporator 3 that is manufactured and corresponds to the load and taken into the refrigeration cycle and the amount of heat corresponding to the work of the turbo compressor 1 supplied from the motor 13 are released to the cooling water supplied to the condenser 2. Is done. On the other hand, the refrigerant gas separated by the economizer 4 is introduced into an intermediate portion of the multistage compression stage of the turbo compressor 1, merged with the refrigerant gas from the first stage compressor, and compressed by the second stage compressor. According to the two-stage compression single-stage economizer cycle, since the refrigeration effect portion by the economizer 4 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 4 is not installed. Can do.

  As shown in FIG. 1, a refrigerant pipe 5 connecting the condenser 2 and the economizer 4 is provided with a high stage orifice 6 and an electric high stage expansion valve 7. The refrigerant pipe 5 connecting the economizer 4 and the evaporator 3 is provided with a low stage orifice 9 and an electric low stage expansion valve 10. The orifices 6 and 9 are fixed orifices, and the expansion valves 7 and 10 are motorized valves with variable valve openings. The reason why the orifices 6 and 9 and the expansion valves 7 and 10 are referred to as “high stage” and “low stage” is that the pressure between the condenser 2 and the economizer 4 is higher than that between the economizer 4 and the evaporator 3. The high pressure side is the “high stage” and the low pressure side is the “low stage”.

  By configuring as shown in FIG. 1, on the high-stage side, the high-stage orifice 6 provided on the primary side of the high-stage expansion valve 7 gives a pressure loss as a base to limit the refrigerant circulation amount, and downstream The liquid level of the condenser 2 is controlled by the high stage expansion valve 7 located at the center. By providing the high stage orifice 6 on the primary side of the high stage expansion valve 7 in this way, the Cv value (flow coefficient) changes sensitively to the valve operation amount in the region where the high stage expansion valve 7 opens and closes. Shift to a good controllability range, and the problem of a decrease in control responsiveness can be solved. By performing high-precision liquid level control in the condenser 2 by the high-stage orifice 6 and the high-stage expansion valve 7, the gas bypass amount of the refrigeration cycle can be reduced, and a decrease in the efficiency of the refrigerator can be avoided.

Similarly, on the low-stage side, similarly, the low-stage orifice 9 provided on the primary side of the low-stage expansion valve 10 gives a pressure loss as a base to limit the refrigerant circulation amount, and the low-stage expansion valve on the downstream side 10, the liquid level of the economizer 4 is controlled. By providing the low stage orifice 9 on the primary side of the low stage expansion valve 10 in this way, the Cv value (flow coefficient) changes sensitively to the valve operation amount in the region where the low stage expansion valve 10 opens and closes. Shift to a good controllability range, and the problem of a decrease in control response can be solved. By performing highly accurate liquid level control in the economizer 4 using the low stage orifice 9 and the low stage expansion valve 10, the amount of gas bypass in the refrigeration cycle can be reduced, and a decrease in efficiency of the refrigerator can be avoided.
Further, as shown in FIG. 1, an expansion valve having a different diameter is installed in parallel by installing an orifice and an expansion valve in series between the condenser 2 and the economizer 4 and between the economizer 4 and the evaporator 3. Can be avoided, and the problem of increased cost of the refrigerator can be solved.

  FIG. 2 is a Mollier diagram when an orifice and an expansion valve are connected in series. As shown in FIG. 2, the expansion process from the condensing pressure to the economizer pressure is performed in two stages of the high stage orifice 6 and the high stage expansion valve 7, and the expansion process from the economizer pressure to the evaporating pressure is performed in the low stage orifice 9 and the low stage. This is performed in two stages of the expansion valve 10.

Next, a specific control method for the expansion mechanism of the turbo refrigerator configured as described above will be described.
FIG. 3 is a schematic diagram showing an embodiment in which a liquid level sensor is provided in the turbo refrigerator shown in FIG. As shown in FIG. 3, in the present embodiment, liquid level sensors 17 and 18 are provided in the condenser 2 and the economizer 4, respectively. The liquid level sensors 17 and 18 are each connected to the control device 20. The high stage expansion valve 7 and the low stage expansion valve 10 are also connected to the control device 20.

  In the turbo chiller configured as shown in FIG. 3, the liquid level sensor 17 measures the liquid level of the condenser 2 and inputs the measured value to the control device 20. The control device 20 controls the opening and closing of the high stage expansion valve 7 so that the liquid level of the condenser 2 becomes a predetermined height. Here, the predetermined height in the condenser 2 refers to a height at which the lowermost heat transfer tube is not immersed in the refrigerant liquid, and the opening degree of the high stage expansion valve 7 is controlled so as to be the liquid level. Do. Further, the liquid level sensor 18 measures the liquid level height of the economizer 4 and inputs the measured value to the control device 20. The control device 20 controls the opening and closing of the low stage expansion valve 10 so that the liquid level of the economizer 4 becomes a predetermined height. Here, in the economizer 4, the predetermined height refers to a height at which the gas-liquid separation demister provided in the economizer 4 is not immersed in the refrigerant liquid, and the opening of the low-stage expansion valve 10 is set to this liquid level. Control.

  Thus, by performing the liquid level control with high accuracy in the condenser 2 by the high stage orifice 6 and the high stage expansion valve 7, it is possible to reduce the gas bypass amount of the refrigeration cycle and to avoid the efficiency reduction of the refrigerator. Further, by performing highly accurate liquid level control in the economizer 4 by the low stage orifice 9 and the low stage expansion valve 10, it is possible to reduce the gas bypass amount of the refrigeration cycle and avoid a decrease in efficiency of the refrigerator.

Since the liquid level sensor that continuously outputs the liquid level is expensive, a method of simply controlling the opening degree of the expansion valve by the pressure difference between the condenser and the evaporator may be used.
FIG. 4 is a schematic view showing an embodiment in which a pressure sensor is provided in the turbo refrigerator shown in FIG. As shown in FIG. 4, pressure sensors 21 and 22 for detecting the pressures of the condenser 2 and the evaporator 3 are provided. The pressure sensors 21 and 22 are each connected to the control device 20. The high stage expansion valve 7 and the low stage expansion valve 10 are also connected to the control device 20.

  In the turbo refrigerator configured as shown in FIG. 4, the pressure sensor 21 measures the pressure Pc of the condenser 2 and inputs the measured value to the control device 20. The pressure sensor 22 measures the pressure Pe of the evaporator 3 and inputs the measured value to the control device 20. The control device 20 calculates the pressure difference (Pc−Pe) between the condenser 2 and the evaporator 3 and performs control so that the expansion valve opening degree is extrapolated from a previously given table.

FIG. 5 is a graph showing the relationship between the pressure difference (Pc−Pe) between the condenser 2 and the evaporator 3 and the opening of the expansion valve. The relationship between the pressure difference (Pc−Pe) and the opening degree of the expansion valve shown in FIG. 5 applies to both the high stage expansion valve 7 and the low stage expansion valve 10. The relationship between the pressure difference (Pc−Pe) and the expansion valve opening as shown in FIG. 5 is obtained in advance and stored in a table. During the operation of the turbo refrigerator, the pressure sensors 21 and 22 measure the pressure of the condenser 2 and the pressure of the evaporator 3, respectively, and input the measured values to the control device 20. The control device 20 calculates the pressure difference (Pc−Pe) between the condenser 2 and the evaporator 3, and based on the relationship of FIG. 5 stored as a table, the expansion valve (that is, the high stage expansion valve 7 and the low stage expansion valve 7). The opening degree of the expansion valve 10) is controlled.
The relationship between the pressure difference obtained in advance and the opening of the expansion valve based on the electrical signal of the pressure difference between the pressure Pc of the pressure sensor 21 and the pressure Pe of the pressure sensor 22 without storing a table in the control device. Can be configured by an analog electronic circuit to control the opening degree of the expansion valve.

  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 Turbo compressor 2 Condenser 3 Evaporator 4 Economizer 5 Refrigerant piping 6 High stage orifice 7 High stage expansion valve 8 Flow path 9 Low stage orifice 10 Low stage expansion valve 11 First stage impeller 12 Second stage impeller 13 Compressor Motor 14 Suction vane 16 Oil tank 17 Liquid level sensor 18 Liquid level sensor 20 Control device 21 Pressure sensor 22 Pressure sensor

Claims (5)

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,
An orifice and an expansion valve are installed in the order of the orifice and the expansion valve in the refrigerant pipe for introducing the refrigerant from the condenser to the economizer,
A turbo chiller, wherein an orifice and an expansion valve are installed in the order of an orifice and an expansion valve in a refrigerant pipe for introducing a refrigerant from the economizer to the evaporator.   The turbo chiller according to claim 1, wherein the orifice is a fixed orifice, and the expansion valve is an electric expansion valve having a variable opening. A liquid level sensor that is installed in each of the condenser and the economizer and measures a refrigerant liquid level,
A control device for controlling the opening of the expansion valve;
The control device controls an opening degree of an expansion valve between the condenser and the economizer based on a measurement value of a liquid level sensor installed in the condenser, and measures a liquid level sensor installed in the economizer. The turbo refrigerator according to claim 1 or 2, wherein an opening degree of an expansion valve between the economizer and the evaporator is controlled based on a value. A pressure sensor installed in the condenser and the evaporator, respectively, for measuring the pressure of the condenser and the pressure of the evaporator;
A control device for controlling the opening of the expansion valve;
The controller is configured to determine an opening degree of an expansion valve between the condenser and the economizer and the economizer and the evaporator based on a pressure difference between the condenser pressure and the evaporator pressure measured by the pressure sensor. The turbo chiller according to claim 1 or 2, wherein the opening degree of the expansion valve is controlled. Predetermining the relationship between the pressure difference between the condenser pressure and the evaporator pressure and the opening of the expansion valve, and storing this preliminarily determined relationship in the control device,
The control device, based on the relationship obtained in advance from the pressure difference between the condenser pressure and the evaporator pressure measured by the pressure sensor, the opening of the expansion valve between the condenser and the economizer, and the The turbo refrigerator according to claim 4, wherein an opening degree of an expansion valve between an economizer and the evaporator is determined.

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