JPS5824634B2 - Reitou Souchi Nadoni Okeru Youryyousei Gountenhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling refrigeration capacity in a refrigeration system by operating a combination of a turbo compressor and a screw compressor.

In general, the economical operating costs of refrigerators used for air conditioning or for freezing parts to be cooled are extremely important factors in planning and designing refrigeration equipment, and when the refrigeration capacity is large, The quality of operation has a large effect on efficiency and running costs, and especially in large-capacity refrigeration systems, it is possible to combine turbo chillers and/or absorption chillers and operate multiple chillers in series or in parallel. However, when the load falls below a certain level, combined operation becomes impossible or the operation efficiency deteriorates extremely. There are few that can maximize the advantages of the driving method.

In other words, when conventionally using a large capacity of refrigerant on the low temperature (or low pressure) side, the high pressure side screw compressor may not be able to absorb the amount of gas discharged in the final compression process of the turbo compressor.
At this time, the number of screws was divided to cope with the problem, but this required complicated control and the configuration was complicated and expensive.

In addition, in the conventional combination method, the suction vane of the turbo compressor and the slide vane of the screw compressor are simultaneously controlled by a signal from a detector such as an automatic temperature controller installed on the outlet side of the evaporator tube of the turbo chiller. Since it is a combination of different models, it is difficult to match them because the characteristics of the individual units differ, and when the load falls below a certain level, combined operation becomes impossible, and the operating efficiency of the system also decreases.

In other words, during partial load, different types of compressors use the same signal to control their capacity at the same time.In the case of the compressor, the differential pressure is no longer constant and becomes smaller, resulting in operation outside the maximum efficiency point and the power increases. do.

In addition, this effect has the disadvantage that the smaller the capacity range, the greater the effect becomes.

The present invention aims to eliminate these conventional drawbacks, and provides a method that ensures highly efficient operation and enables economical operation even when there are many opportunities for partial load operation of the refrigeration equipment. It is intended to provide.

In order to achieve this objective, the inventors conducted extensive research and focused on the fact that while turbo compressors have a large degree of efficiency decline during partial load operation that deviates from the design point, screw compressors have only a small degree of efficiency decline. Then, a turbo compressor is installed on the low pressure side and a screw compressor is installed on the high pressure side to perform two-stage compression or binary compression.The turbo compressor is used at a constant compression ratio, that is, the maximum efficiency point, and the entire system is This invention was made with the idea of significantly improving the operating efficiency of the machine.

The present invention provides a turbo compressor on the low pressure side and a screw compressor on the high pressure side to perform a two-stage compression refrigeration cycle or a dual compression refrigeration cycle, and to provide a pressure PR signal after the suction vane of the turbo compressor. and a signal of the suction side pressure PT of the screw compressor to a pressure ratio adjustment mechanism,
When the pressure ratio PT/pR becomes a value different from the pressure ratio setting value that gives substantially the highest efficiency to the turbo compressor, capacity control of the screw compressor is performed to adjust the pressure ratio PT/PR of the turbo compressor. This is an operating method for controlling the refrigeration capacity of a refrigeration system, which is characterized by performing control to keep it substantially constant.

An embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a two-stage refrigeration cycle or a secondary A refrigeration cycle (these refrigeration cycles will be described later with examples shown in FIGS. 3 and 5) is performed, and the pressure PR in the suction vane 6 section of the turbo compressor 5 before the impeller 7 and the screw compressor Pressure P leading to the suction side of 10
T (i.e., the discharge pressure of the turbo compressor 5) and the pressure adjustment mechanism (
leading to the compression ratio switch 24 as a pressure ratio adjustment mechanism),
When the pressure ratio PT/PR reaches the royal power ratio set value that gives the turbo compressor 5 almost the maximum efficiency, the slide valve 9 serving as a capacity control mechanism is operated in the opening direction to increase the output of the screw compressor 10. By controlling the capacity to reduce the capacity, the compression ratio of the turbo compressor 5 is maintained at the set value,
To maintain the efficiency of a turbo compressor 5 to the highest level and to maintain good efficiency of the entire device.

The effect will be explained in detail below.

PE is the suction pressure of the turbo compressor 5, which is approximately equal to the evaporation pressure of the evaporator 1, Pc is the condensation pressure of the condenser 12, 21 is a temperature detector as a load detector on the low pressure side, and the suction vane 60 operating section Operate V1.

15 is an evaporator that acts as an economizer, and its vapor is supplied to a pipe 8 connecting the turbo compressor 5 and the screw compressor 10 via a regulating valve v2;
2 is operated by a temperature detector 25 as a load detector on the high pressure side.

The diagram at the bottom of Fig. 1 shows the pressure at each part of the suction vane 6 at each opening degree. .3.
4 (gradual closing direction).

Those with PT indicate values for equal differential pressure, and those with PT' indicate values for equal compression ratio.

Although pT and PT' are slightly different as shown in FIG. 2, they are the same in FIG.

This will be explained in more detail with reference to FIG.

The horizontal axis shows the air volume Q, the vertical axis shows the pressure P, pc is the condensing pressure,
PF is the evaporation pressure, co, CI,...C4 is the performance curve of the turbo compressor 5 when the suction vane 6 is fully opened, ■...4, therefore, C6, C1・・・
...Screw compressor 10 is between C4 and pc
This will be shared by

The signal labeled P on each curve represents that point and represents the pressure at that point.

Note that pressure is expressed in absolute pressure.

The operating point of the turbo compressor 5 is assumed to be P'l''o, QTO.

A4 + A25...A4 is opening degree 1,...
..., resistance curve at 4, PRl, ...P
H1 is the pressure after the suction vane 6 at each opening degree, and if the value obtained by converting the air volume at this point into pressure PF: is Q1+...''+C4, then P□1.... ...The X coordinate value of the point PH1 is the vane opening degree, that is, the aperture degree A1.A2.A3.
Shows the maximum suction amount of the compressor (converted to PE pressure) at...

Therefore, C1, C2, C3... are the aperture degrees A1.
A2. P in A3...

This is a performance curve showing the air volume and pressure converted to pressure.

Even if you consider that the air volume converted to the pressure of Po is proportional to the refrigerating capacity, there is little error, so C8, C1, C2...... are the discharge pressures at the aperture degrees AO, AI, A2... , the refrigeration capacity will be displayed.

El, E2. E3 indicates the isoefficiency line, and each performance curve co,
C1...The point of highest efficiency on C4 is p'r
o, PT, j... PT4.

However, these PTo'...PT4 points,
The differential pressure with the corresponding PROI PRI j...PR4 is almost equal.

That is, in Figure 2 ΔTokiΔT1f:ΔT2f−ΔT3kiΔT4.

Therefore, the pressure PRo after the suction vane 6.

PRz・・・・・・For PR4, discharge pressure PTo + PTt at each opening degree, '・・・・・・PT4 as P
To-PRokiΔT.

PTt PRtf:ΔT.

ΔT during PT4-PR4.

If such a constant differential pressure control is performed, maximum efficiency operation can be performed at any opening degree.

However, in general, the mechanism for keeping the differential pressure constant is complicated, and the pressure ratio constant force type has a simpler mechanism, as shown in FIG. 4, for example.

Further, as shown in FIG. 2, the equidirectional lines are located above the geometrical curve M, and there is a possibility that the surging region will be entered in the low capacity region.

In such a case, it is preferable to use a constant compression ratio mechanism.

The geometric curve when the compression ratio is constant is indicated by M, and each point on it is indicated by PT'+ + PT'2...PT'4, which is approximated by the equidistant line. , there is no problem in practical use.

That is, by setting the following, the efficiency of the turbo compressor 5 can be almost the highest.

In the case of the turbo compressor 5, the efficiency decreases sharply as the compression ratio changes (on the contrary, in the screw compressor 10, the change in efficiency due to the change in the compression ratio is small, so the overall efficiency of the turbo compressor is maximized. The screw compressor operates at a constant efficiency, that is, a constant pressure ratio (according to the above formula for points PTo, PT2, PT3, etc. in Figure 2), and compression from that point to the final condensing pressure is performed by a screw compressor. If these people share their duties, the overall efficiency of the whole can be increased.

Here, the compression ratio shared by the screw compressor 10 is, for example, the pressure difference ΔSo, ΔS1, . . . in FIG.

The compression ratio corresponding to ΔS4 varies, but since the screw compressor is a positive displacement type, if the discharge pressure is high, it will expand, and if it is low, it will compress and match the condensing pressure, which is determined by the load. .

, thus providing a fixed compression ratio for each opening which results in the bag operating at maximum efficiency.

Using this compression ratio as a set value, the compression ratio switch 24 compares the compression ratio at the time of detection obtained from the input pR and PT with the set value, and if it is less than the set value, opens the slide valve 9 to reduce the capacity. Operate it so that it does.

Now, when the low pressure side refrigeration load decreases, the brine outlet temperature drops, so the temperature detector 21 such as an automatic temperature controller is activated, the suction bay 76 is closed via the operating part v1, and the air volume is reduced.

Therefore, if the opening degree of the slide valve 9 remains unchanged, the capacity of the screw compressor 10 will not change, so the discharge pressure pT of the turbo compressor 5 will drop significantly and the compression ratio PT/PR will decrease.

As a result, the compression ratio switch 24 is activated and the slide valve 9 is opened, so the capacity of the screw compressor 10 decreases, and as it matches the discharge air volume of the turbo compressor 5, the discharge pressure pT recovers and returns to the predetermined compression ratio. The valve will recover and operate at its maximum efficiency at that opening.

Furthermore, when the load on the high pressure side decreases, the brine outlet temperature decreases, so the automatic temperature controller detector 25 operates and the valve V2
closes and the amount of gas passing through the screw compressor 10 decreases.

If the opening degree of the slide valve 9 remains unchanged, the capacity of the screw compressor 10 will not change.
0, that is, the discharge pressure pT of the turbo compressor 5 decreases significantly.

The compression ratio switch 24 is operated in the same manner as above, the slide valve 9 is opened, and the compression ratio is restored in the same manner as above, allowing maximum efficiency operation.

Moreover, this compression ratio switch 24 has an effective effect at the time of startup.

In other words, at startup, since pE=pR=pT, the compression ratio P
Since T/PR=1, which is smaller than the predetermined value, the open circuit of the compression ratio switch 24 (the circuit that gives the signal to move the slide valve 9 in the opening direction) is closed, so the slide valve 9 is always closed before startup. It must be fully open and ready to start.

To further explain the embodiment of the present invention with reference to the drawings, in FIG. The refrigerant gas is sucked into the turbo compressor 5 via the suction bay 76, and the sucked refrigerant gas is compressed by the impellers T at each stage of the turbo compressor 5 and discharged, and then passed through the slide valve 9 in the piping 8 to the screw. After being fed into the compressor 10, it is further compressed and discharged through the conduit 11 to the condenser 12, so that both the compressors 5 and 10 are combined in series to enable a two-stage compression refrigeration cycle operation.

In this condenser 12, cooling water is passed through a condenser tube 13 to liquefy the refrigerant gas, and a piping 1 having a control valve v6
4 to return to the evaporator 15, and further circulate to the evaporator 1 through a pipe 16 having a regulating valve v5.

The evaporator 15 also includes an evaporator tube 17 through which cold water passes, and the refrigerant gas evaporated in the evaporator passes through an eliminator 19.
The liquid droplets are removed at , and connected to the screw compressor 10 through a pipe 18 having a regulating valve v2.

Note that a bypass pipe 20 having a control valve v3 is provided between the conduit 3 and the pipe 8, and a temperature detector 21 such as an automatic temperature controller provided on the outlet side of the evaporator tube 4 is used to detect the minimum air volume to prevent surging. In addition, in order to control the air volume from the minimum air volume to the rated volume, the operating part V1 of the suction bay 76 is also controlled by the temperature sensor 21 to adjust the opening and closing of the vane. It is set so that the amount of suction gas can be adjusted.

Furthermore, the suction bay 76 and impeller 7 of the turbo compressor 5
The pressure pR1 of the portion between the two and the pressure PT of the circuit leading to the discharge side, that is, the suction side of the screw compressor 10 are detected.

Pressure detectors 22 and 23 such as automatic pressure regulators are provided respectively, and their outputs are input to the compression ratio switch 24, and the outputs actuate the slide valve 90 operating section V4 to adjust the compression ratio P.
The slide valve 9 is operated to open when T/PR becomes less than a predetermined set value at which maximum efficiency can be obtained.

For example, as shown in FIG. 4, the compression ratio switch 24 includes a lever R having a fulcrum O between contacts a (slide valve 9 closing direction) and b (slide valve 9 opening direction). P at intervals of r, , r2, respectively.
A bellows operating rod operated by RIPT is connected.

If the compression ratio PT/PR at which the efficiency is maximized is N, then rl
If the ratio of and r2 is set as The contact point is closed and the slide valve 9 is opened.

Further, the control valve v2 is the evaporator tube 17 of the medium pressure evaporator 15.
The control valve V5 is automatically operated by a temperature detector 25 of the outlet temperature of
It is an association so that it can be operated automatically.

The screw compressor 10 has a capacity adjustment device using a slide valve 9, and the refrigerating capacity can be continuously and steplessly adjusted from 100 to 15%.

For example, during 100% operation with the slide valve 9 fully closed, the entire amount of gas in the rotor tooth space is sent out.

When reducing the capacity, open the slide valve 9, that is, move it to the discharge side and create a gap between the fixed part and the end of the slide valve 9. The teeth will not close until the rotor meshing point reaches the end of the slide valve 9. The gas in the groove returns to the suction side without being compressed, and compression begins only after the engagement point of the rotor reaches the end of the slide valve 9, which shortens the effective length of the rotor and reduces the stroke volume. Capacity adjustments are made.

The slide valve 9 can be operated electrically, hydraulically, or manually, and automatic operation is also possible in relation to the evaporation pressure and temperature.

In the illustrated example, a compression ratio switch 24 opens and closes the capacity control slide valve 9 of the screw compressor 10 when the compression ratio PT/PR of the compressor 5 fluctuates from a predetermined value (the value that provides the highest efficiency). That's how it is.

In the figure, 21 and 28 are compressor drive devices, and 29 and 30 are register bars.

FIG. 5 shows an example of a dual compression refrigeration cycle that employs a combination of two types of refrigerants in the cycle of FIG. 3.

The evaporator 15 is used as an economizer and the turbo compressor 5
The side cycle functions as a condenser, and the screw compressor 10 side functions as an evaporator, making it possible to operate a dual compression refrigeration cycle.

In this case, it is important to keep the compression ratio of the turbo compressor constant, so if the pressure ratio of the pressure detectors 22 and 230 is kept constant, the compression ratio of the turbo compressor can also be kept constant.

Note that it is also possible to combine independent cycles such as a turbo chiller cycle and a screw chiller cycle by connecting them via a bypass pipe, or to combine both independent cycles in a type that uses a single condenser.

At this time, the pressure of the pressure detector 23 has a substantially fixed relationship with the pressure of the pipe 8, so the pressure of the pressure detector 23 and PR
By keeping the pressure ratio constant, the compression ratio of the turbo compressor 5 can be kept constant.

According to the present invention, high operating efficiency can be ensured even during partial load operation, the overall operation can be carried out economically, the functions of both compressors can be utilized to the maximum, effective work can be carried out, and equipment can be saved. It is simple, inexpensive, and has the advantage of simplifying operational maintenance and additional handling.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic explanatory diagram, FIG. 2 is a Q-P characteristic diagram, FIG. 3 is a flow diagram, and FIG. 4 is an explanatory diagram of an embodiment of a compression ratio switch. FIG. 5 is a flow diagram of another embodiment. 1... Evaporator, 3... Conduit, 4...
... Evaporator tube, 5 ... Turbo compressor,
6...-suction vane, 7... impeller, 8... piping, 9... slide valve,
10... Screw compressor, 11...
Conduit, 12... Condenser, 13... Condenser tube, 14... Piping, 15...
Evaporator, 16...Piping, 17...Evaporator tube, 18...Piping, 20...
Bypass pipe, 21... Temperature detector, 22, 23
......Pressure detector, 24...Compression ratio switch, 25...Temperature detector, 26...
Liquid level detector, 27, 28... Compressor, drive device, V, , V4... Operating section, V2°V3.
V5. V, ... control valve.

Claims (1)

[Claims] 1 A turbo compressor is provided on the low pressure side and a screw compressor is provided on the high pressure side to perform a two-stage compression refrigeration cycle or a dual compression refrigeration cycle, and the pressure PR signal after the suction vane of the turbo compressor and the A signal of the suction side pressure PT of the screw compressor is guided to the pressure ratio adjustment mechanism, and when the pressure ratio PT/PR becomes a value different from the pressure ratio setting value that gives almost the maximum efficiency to the turbo compressor, the 1. An operating method for controlling the refrigeration capacity of a refrigeration system, comprising controlling the capacity of a screw compressor to keep the pressure ratio PT/PR of the turbo compressor substantially constant.