JP6001997B2 - Turbo refrigerator - Google Patents

Description

  The present invention relates to a turbo chiller, and more particularly to a turbo chiller in which a plurality of control valves connected in parallel are installed in a pipe that guides a refrigerant from a condenser side toward an evaporator.

  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. And an expansion mechanism that is expanded by being connected by a refrigerant pipe.

Conventionally, as the expansion mechanism of the condensed refrigerant in the turbo refrigerator, an orifice with a fixed opening is often used. However, when an orifice with a fixed opening is used, a condenser is used in an intermediate period when the cooling water temperature is low. And the pressure difference between the evaporator and the refrigerant liquid becomes difficult to return from the condenser to the evaporator. As a result, the refrigerant tends to stay in the condenser, and the amount of refrigerant in the evaporator may be insufficient to lower the liquid level.
Therefore, a motor-operated valve alone, a fixed orifice and a motor-operated valve, a temperature expansion valve, a plurality of solenoid valves, and the like are installed in a refrigerant pipe that guides the refrigerant from the condenser side toward the evaporator. These control valves are often used for controlling the liquid level of the evaporator.

However, the refrigerant liquid level control of the evaporator is affected by the type of the evaporator heat transfer tube of the individual turbo chiller, the shape of the evaporator, etc., and the refrigerant liquid level control of the evaporator does not necessarily improve the heat exchange efficiency of the evaporator. It does not mean that
The motor-operated valve alone, the fixed orifice and motor-operated valve, the temperature-type expansion valve and the plurality of solenoid valves are insufficient for fine refrigerant flow rate control as control valves, and there is still room for improvement.

Japanese Patent No. 3360362

  The present invention has been made in view of the above-described circumstances. A plurality of control valves are connected in parallel to a pipe for introducing a refrigerant from the condenser side to the evaporator, and a differential pressure between the condenser and the evaporator (or an economizer and an evaporator) is provided. It is an object of the present invention to provide a turbo chiller capable of finely controlling the flow rate of refrigerant supplied to an evaporator by switching and using the plurality of control valves in accordance with the differential pressure of the evaporator.

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, a multistage turbo compressor that compresses the refrigerant with an impeller, A turbo chiller comprising: a condenser that cools and condenses compressed refrigerant gas with a cooling fluid; and an economizer that supplies refrigerant gas to an intermediate portion of a multistage compression stage of the multistage turbo compressor , wherein the economizer side wherein a plurality of valves of the installed connected in parallel to the refrigerant pipe for guiding the refrigerant towards the evaporator is disposed a plurality of control valves Cv value is different, the upper portion of the economizer from the droplets contained in the refrigerant The demister is separated from the economizer and the liquid level of the economizer reaches the upper limit liquid level where the distance from the refrigerant liquid level to the lower end of the demister is a predetermined distance. A liquid level upper limit level detector, and a controller for controlling the plurality of control valves, the control device, condenser side and the Cv value based on the differential pressure between the evaporator is different from the plurality of control valves There line control switching of the control device, when the refrigerant liquid level of the economizer by the liquid surface upper level detector is detected to have reached the upper limit liquid level, operating among said plurality of control valves The opening of the control valve is operated in the opening direction .
According to the present invention, a plurality of control valves are connected in parallel to a pipe that guides the refrigerant from the economizer side to the evaporator, and the pressure is controlled according to the pressure difference between the condenser and the evaporator (or the pressure difference between the economizer and the evaporator). By switching and using a plurality of control valves, it is possible to finely control the flow rate of the refrigerant supplied to the evaporator.

According to the present invention, since the refrigerant gas separated by the economizer is introduced into the middle part of the multistage compression stage of the multistage turbo compressor, the refrigeration effect portion by the economizer is added, so that the refrigeration effect increases by that amount. Thus, high efficiency can be achieved.
According to the present invention, when the level of the economizer reaches the upper limit, among the plurality of control valves connected in parallel, by operating the opening of the operating control valve in the opening direction, the economizer liquid The position can be lowered. Therefore, the liquid level of the economizer can be maintained below the upper limit liquid level, and the carryover of the refrigerant droplets from the economizer to the intermediate portion of the multistage compression stage of the multistage turbo compressor can be prevented.

In a preferred aspect of the present invention, the plurality of control valves are an electric ball valve or an electric butterfly valve whose inherent flow rate characteristic is equal percent from a low opening to a medium opening.
The plurality of control valves in the present invention must be motor-operated valves for automatic control, and the type of valves becomes a problem for fine refrigerant flow rate control. Gate valves and ball valves have poor controllability, and ball valves and butterfly valves are ideal for refrigerant flow rate control because the inherent flow characteristics of the valves are equal percent. In the present invention, by using an electric ball valve and an electric butterfly valve having different Cv values in parallel connection, extremely fine refrigerant flow control can be performed.

A preferred embodiment of the present invention is provided with means for measuring the outlet temperature of the cooling fluid exchanges heat with the refrigerant in the evaporator, and means for measuring the refrigerant temperature in the evaporator, the control device, the fluid to be cooled The flow rate of the refrigerant supplied to the evaporator is controlled by the plurality of control valves so that the evaporator LTD defined as a temperature difference between the outlet temperature and the evaporator refrigerant temperature approaches the target LTD.
According to the present invention, the outlet temperature of the fluid to be cooled that exchanges heat with the refrigerant in the evaporator is measured and the refrigerant temperature in the evaporator is measured. From these measured values, the outlet temperature of the cooled fluid and the evaporator refrigerant temperature are measured. Obtain an evaporator LTD, defined as the temperature difference. Then, the obtained evaporator LTD is compared with a preset target LTD, and the flow rate of refrigerant supplied to the evaporator is controlled by a plurality of control valves so as to bring the obtained evaporator LTD closer to the target LTD. At this time, by switching and controlling a plurality of control valves based on the pressure difference between the condenser side and the evaporator, fine refrigerant flow control to the evaporator can be performed, and more accurate LTD control is possible. become.

In a preferred aspect of the present invention, the evaporator refrigerant temperature is obtained from the pressure in the evaporator.
Since there is a correlation between the refrigerant temperature of the evaporator and the pressure in the evaporator, the evaporator refrigerant temperature can be obtained by measuring the pressure in the evaporator.

In a preferred aspect of the present invention, the economizer is provided with a liquid level lower limit level detector, and when the refrigerant liquid level of the economizer reaches the lower limit liquid level , the opening degree of the control valve that is operating among the plurality of control valves. Is operated in the closing direction.
According to the present invention, when the level of the economizer reaches the lower limit, the economizer liquid is operated by closing the opening of the operating control valve among the plurality of parallel-connected control valves in the closing direction. The rank can be raised. Therefore, the liquid level of the economizer can be maintained at a desired liquid level.

According to the present invention, the flow rate of the refrigerant supplied to the evaporator is controlled very finely by using a plurality of control valves having different Cv values in parallel connection in a pipe for guiding the refrigerant from the condenser side toward the evaporator. Can do.
Further, according to the present invention, since the flow rate of the refrigerant supplied to the evaporator can be controlled very finely, the evaporator LTD can be accurately controlled to the target LTD, and the heat transfer performance of the evaporator can be controlled. Can be improved.

FIG. 1 is a schematic diagram showing an embodiment of a turbo refrigerator according to the present invention. FIG. 2 is a diagram showing a case in which a plurality of electric control valves are switched and used in accordance with the differential pressure (ΔP) between the economizer 4 and the evaporator 3 and the differential pressure (ΔP). FIG. 3 is a diagram showing a relationship between the refrigeration load factor (%) obtained by the experiment and the target LTD (° C.).

Hereinafter, embodiments of a turbo refrigerator according to the present invention will be described with reference to FIGS. 1 to 3. 1 to 3, 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. As shown in FIG. 1, a turbo refrigerator includes a multi-stage 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). An evaporator 3 that takes away heat from the fluid) and evaporates the refrigerant to exert a refrigeration effect, and an economizer 4 that is an intermediate cooler disposed between the condenser 2 and the evaporator 3. The refrigerant is connected by a refrigerant pipe 5 through which the refrigerant circulates.

  In the embodiment shown in FIG. 1, the multistage turbo compressor 1 is composed of a two-stage turbo compressor. The multistage 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 of the multistage compression stage (two stages in this example) of the multistage turbo compressor 1 (this In the example, it is introduced in the part between the first stage and the second stage).

  In the refrigeration cycle of the turbo chiller configured as shown in FIG. 1, the refrigerant circulates through the multistage 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. Is produced, and corresponds to the load, and the amount of heat from the evaporator 3 taken into the refrigeration cycle and the amount of heat corresponding to the work of the multistage turbo compressor 1 supplied from the compressor motor are supplied to the condenser 2 Released into water. 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 multistage 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, the refrigerant pipe 5 that connects the economizer 4 and the evaporator 3 is provided with a plurality of electric control valves 6A, 6B,... Connected in parallel, from the economizer 4 to the evaporator. The flow rate of the refrigerant returned to 3 can be controlled. FIG. 1 shows an example in which two electric control valves 6A and 6B are installed. In the type of centrifugal chiller that does not include the economizer 4, the plurality of electric control valves 6 </ b> A and 6 </ b> B connected in parallel are provided in a refrigerant pipe that connects the condenser 2 and the evaporator 3. The flow rate of the refrigerant returned to the evaporator 3 can be controlled.

  The electric control valves 6A and 6B shown in FIG. 1 are composed of an electric ball valve or an electric butterfly valve whose inherent flow rate characteristic is equal percent from a low opening to a medium opening. One control valve 6A is a ball valve or butterfly valve having a small (low) Cv value (flow coefficient), and the other control valve 6B is a ball valve or butterfly valve having a large (high) Cv value. Here, the Cv value is small (low) means that the Cv value is in the range of 5 to 100, and the Cv value is large (high) means that the Cv value is in the range of 100 to 1000. . Further, it is sufficient that there are two or more electric control valves, and a ball valve and a butterfly valve may be mixed as the types of valves.

  As shown in FIG. 1, the economizer 4 is provided with a pressure sensor P <b> 1 that measures the pressure in the economizer 4, and the evaporator 3 is provided with a pressure sensor P <b> 2 that measures the pressure in the evaporator 3. Yes. The pressure sensor P1 and the pressure sensor P2 are connected to the control device 10, respectively. In addition, the electric control valves 6 </ b> A and 6 </ b> B are connected to the control device 10. Thereby, the control apparatus 10 can detect the differential pressure between the economizer 4 and the evaporator 3. Further, the economizer 4 is provided with a liquid level upper limit level detector LVH that detects when the refrigerant liquid level reaches the upper limit and a liquid level lower limit level detector LVL that detects when the refrigerant liquid level reaches the lower limit. Has been.

  As shown in FIG. 1, the evaporator 3 is provided with a temperature sensor Tbo for measuring the cold water outlet temperature and a temperature sensor Te for measuring the evaporator refrigerant temperature. That is, the outlet temperature of the cold water that exchanges heat with the refrigerant in the evaporator 3 is measured by the temperature sensor Tbo, and the refrigerant temperature in the evaporator 3 is measured by the temperature sensor Te. The temperature sensor Tbo and the temperature sensor Te are each connected to the control device 10. Thereby, in the control apparatus 10, the temperature difference of the cold water exit temperature and the evaporator refrigerant temperature, that is, the evaporator LTD can be calculated.

Next, the operation of the turbo refrigerator configured as shown in FIG. 1 will be described.
In the present invention, a plurality of electric control valves 6A and 6B connected in parallel are installed in the refrigerant pipe 5 connecting the economizer 4 and the evaporator 3, and the plurality of electric control valves 6A and 6B are connected to the economizer. 4 and the evaporator 3 are used by switching them according to the differential pressure.
FIG. 2 is a diagram showing a case in which a plurality of electric control valves are switched and used in accordance with the differential pressure (ΔP) between the economizer 4 and the evaporator 3 and the differential pressure (ΔP). That is, the pressure in the economizer 4 is measured by the pressure sensor P1, and the pressure in the evaporator 3 is measured by the pressure sensor P2. These measurement signals are sequentially sent to the control device 10, and the control device 10 detects the differential pressure (ΔP) between the economizer 4 and the evaporator 3. Then, a plurality of electric control valves 6A and 6B are switched and used by the control device 10 in accordance with the differential pressure (ΔP) between the economizer 4 and the evaporator 3. That is, as shown in FIG. 2, when the differential pressure (ΔP) between the economizer 4 and the evaporator 3 is small, a high Cv value valve, that is, an electric control valve 6B is used, and the differential pressure between the economizer 4 and the evaporator 3 is used. When (ΔP) is large, a low Cv value valve, that is, an electric control valve 6A is used. When the differential pressure (ΔP) between the economizer 4 and the evaporator 3 is an intermediate value, both a high Cv value valve and a low Cv value valve are used. As described above, by switching and using the plurality of electric control valves 6A and 6B having different Cv values according to the differential pressure (ΔP) between the economizer 4 and the evaporator 3, it is possible to perform extremely fine refrigerant flow rate control. it can.

In the present invention, in parallel with the switching control of the plurality of electric control valves 6A and 6B according to the differential pressure (ΔP) between the economizer 4 and the evaporator 3, the evaporator LTD (the cold water outlet temperature and the evaporator refrigerant temperature Temperature difference) is measured, the opening degree of the electric control valves 6A and 6B is controlled to bring the evaporator LTD close to the target LTD, and the flow rate of the refrigerant returned from the economizer 4 to the evaporator 3 is controlled.
FIG. 3 is a diagram showing a relationship between the refrigeration load factor (%) obtained by the experiment and the target LTD (° C.).
The target LTD refers to LTD (= cold water outlet temperature−evaporator refrigerant temperature) when ideal heat transfer is performed in the actual evaporator. The target LTD changes according to each refrigeration load. Normally, as the refrigeration load decreases, the target LTD also decreases. The reason is that the evaporator is usually designed with a 100% refrigeration load. When the partial refrigeration load is used, the evaporator has a larger heat transfer area than the required heat transfer area. Heat transfer efficiency is relatively improved. Accordingly, the target LTD is smaller at the partial refrigeration load than at the 100% refrigeration load. The smaller the partial refrigeration load, the higher the heat transfer efficiency in the evaporator and the smaller the target LTD.
As shown in FIG. 3, when the refrigeration load factor is 20%, the target LTD is 0.6 ° C., and when the refrigeration load factor is 100%, the target LTD is 1.0 ° C. In the example shown in FIG. 3, the refrigeration load factor and the target LTD have a substantially linear relationship, but there may be a curved relationship depending on the model.

  The control device 10 stores in advance the relationship between the refrigeration load factor and the target LTD as shown in FIG. During the operation of the turbo refrigerator, the temperature sensor Tbo measures the chilled water outlet temperature and the temperature sensor Te measures the evaporator refrigerant temperature. These measurement signals are sequentially sent to the control device 10, and the evaporator LTD is calculated in the control device 10. The control device 10 grasps the refrigeration load factor at this time. The control device 10 compares the evaporator LTD obtained in this way with the target LTD (obtained from the refrigeration load factor at that time), and the electric control valve 6A and / or 6 in order to bring the obtained evaporator LTD closer to the target LTD. Or the opening degree of 6B is controlled and the flow volume of the refrigerant | coolant returned to the evaporator 3 from the economizer 4 is controlled. Specifically, if the obtained evaporator LTD is larger than the target LTD, the opening of the electric control valve 6A and / or 6B is increased to increase the flow rate of the refrigerant returned from the economizer 4 to the evaporator 3, If the obtained evaporator LTD is substantially equal to the target LTD, the flow rate of the refrigerant returned from the economizer 4 to the evaporator 3 is maintained without changing the opening degree of the electric control valves 6A and / or 6B. Thereby, the heat transfer performance of the evaporator can be optimized.

The economizer 4 is configured by disposing a demister 11 on an upper part of a container-like storage unit that stores liquid refrigerant. The demister 11 separates droplets contained in the refrigerant, and the droplets are stored in a container-like storage unit. It has come to be collected.
However, since the liquid refrigerant stays in the economizer 4 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.

  Therefore, the present inventors have repeatedly performed start / stop experiments while measuring the liquid level of the economizer 4 with a liquid level gauge using a turbo refrigerator configured as shown in FIG. At this time, the presence or absence of carryover of refrigerant droplets was observed from a viewing window provided in the flow path 8 connecting the economizer 4 and the multistage turbo compressor 1.

  In this way, by performing the observation of the presence or absence of carryover of the refrigerant droplet from the viewing window, if the distance from the liquid level of the economizer 4 to the lower end of the demister is a predetermined distance or more (for example, 100 mm or more), It was confirmed that there was no carryover of refrigerant droplets. That is, if the liquid level of the economizer 4 when the distance from the liquid level of the economizer 4 to the lower end of the demister 11 is a predetermined distance (for example, 100 mm) is defined as the upper limit liquid level, the liquid level of the economizer 4 is the upper limit liquid. If it is less than or equal to, the carryover of refrigerant droplets from the economizer 4 to the intermediate part of the multistage compression stage of the multistage turbo compressor 1 can be prevented.

Therefore, in the present invention, the electric control valve 6A for switching the plurality of electric control valves 6A and 6B connected in parallel according to the differential pressure between the economizer 4 and the evaporator 3 and for bringing the evaporator LTD close to the target LTD. 6B, when the liquid level of the economizer 4 reaches the upper limit or the lower limit, the opening degree of the electric control valves 6A, 6B is closed more or less so as to avoid the liquid level. Open or temporarily move. Thereby, the liquid level of the economizer 4 can be controlled to a preferable liquid level. That is, when the liquid level of the economizer 4 reaches the upper limit, the opening degree of the operating control valve among the plurality of control valves 6A and 6B connected in parallel is operated in the opening direction. Further, when the level of the economizer 4 reaches the lower limit, the opening degree of the operating control valve among the plurality of control valves 6A and 6B connected in parallel is operated in the closing direction.

  In the embodiment shown in FIG. 1 to FIG. 3, the turbo chiller using the economizer cycle has been described. However, in a turbo chiller of a type not provided with an economizer, a plurality of parallel-connected electric control valves 6A, 6B is provided in the refrigerant pipe connecting the condenser 2 and the evaporator 3, and the pressure sensor P1 is provided in the condenser 2, whereby a plurality of electric control valves 6A corresponding to the differential pressure between the condenser 2 and the evaporator 3 are provided. , 6B can be controlled so that the flow rate of the refrigerant supplied to the evaporator 3 can be finely controlled. In parallel with this, the opening degree of the electric control valve 6A and / or 6B is controlled to bring the evaporator LTD close to the target LTD, and the flow rate of the refrigerant supplied from the condenser 2 to the evaporator 3 is controlled.

  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 Multistage turbo compressor 2 Condenser 3 Evaporator 4 Economizer 5 Refrigerant piping 6, 6A, 6B Electric control valve 10 Controller 11 Demister P1, P2 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 multistage turbo compressor that compresses the refrigerant with an impeller, and a condenser that cools and compresses the compressed refrigerant gas with a cooling fluid And an economizer that supplies refrigerant gas to an intermediate portion of the multistage compression stage of the multistage turbo compressor ,
A plurality of valves of the installed parallel connection from said economizer side refrigerant pipe for guiding the refrigerant towards the evaporator, and a plurality of control valves Cv value is different,
A demister that is installed on top of the economizer and separates droplets contained in the refrigerant;
A liquid level upper limit level detector that is installed in the economizer and detects when the refrigerant liquid level of the economizer reaches an upper limit liquid level at which the distance from the refrigerant liquid level to the lower end of the demister is a predetermined distance;
A control device for controlling the plurality of control valves,
Wherein the controller, have the line switching control of the Cv value different control valve based on the differential pressure between the condenser side and the evaporator,
The control device detects the opening of the control valve that is operating among the plurality of control valves when the liquid level upper limit level detector detects that the coolant level of the economizer has reached the upper limit liquid level. A turbo refrigerator that is operated in an opening direction . 2. The turbo chiller according to claim 1, wherein the plurality of control valves are an electric ball valve or an electric butterfly valve whose characteristic flow rate characteristic is equal percent from a low opening to a medium opening. Means for measuring the outlet temperature of the cooled fluid that exchanges heat with the refrigerant in the evaporator;
Means for measuring the refrigerant temperature in the evaporator,
The control device controls the flow rate of the refrigerant supplied to the evaporator by the plurality of control valves so that the evaporator LTD, which is defined as a temperature difference between the cooled fluid outlet temperature and the evaporator refrigerant temperature, approaches the target LTD. The turbo refrigerator according to claim 1 or 2 , wherein The turbo refrigerator according to claim 3 , wherein the evaporator refrigerant temperature is obtained from the pressure in the evaporator. The economizer is provided with a liquid level lower limit level detector, and when the refrigerant liquid level of the economizer reaches the lower limit liquid level , the opening degree of the operating control valve among the plurality of control valves is operated in the closing direction. The turbo refrigerator as described in any one of Claims 1 thru | or 4 characterized by these.

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