JPH0333983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a screw refrigerator whose refrigeration cycle is formed by an oil injection screw compressor.

[Conventional technology]

In conventional oil injection screw compressors,
Lubricating oil is injected into the rotor chamber to seal the gaps between the male and female rotors and between the rotor and the casing, thereby improving volumetric efficiency.
The refrigerant is cooled to remove overheating of the refrigerant due to compression.

[Problem to be solved by the invention]

However, in conventional screw refrigerators, when liquid mist of refrigerant from the evaporator is sucked into the compressor, a large amount of refrigerant dissolves into the lubricating oil, reducing the viscosity of the lubricating oil. If such lubricating oil is supplied to the bearing, damage to the bearing may occur. Furthermore, the oil separation efficiency in the oil separator connected to the compressor discharge side is reduced, and a large amount of oil contained in the refrigerant flows into the condenser and evaporator, resulting in a reduction in heat transfer. Furthermore, if this phenomenon continues for a long period of time, there will be a shortage of oil in the oil separator, which has the disadvantage of causing accidents due to insufficient lubrication.

In order to improve this drawback, the inventor conducted repeated research and focused on the fact that the discharge temperature decreases when a large amount of refrigerant mist is sucked into the compressor, leading to the present invention.

That is, on the Molière diagram in Figure 1, cycle a
-b-c-d indicates standard cycle. cycle
a'-b'-c-d show the case where frozen mist is inhaled. When the evaporation pressure Pe and the condensation pressure Pc are kept constant, a difference occurs in the degree of superheating of the discharged gas with respect to the condensation pressure saturation temperature Te. In normal operation, the discharge gas temperature Tb is about 60 to 80°C, and the temperature difference (degree of superheating) is ΔTb. However, when the liquid mist is inhaled, the discharge gas temperature Tb' drops to about 50°C or more, and the temperature difference decreases to ΔTb.

Based on these phenomena, the present invention sets the degree of superheating (temperature difference) △Ts corresponding to the practically allowable limit of refrigerant mist intake amount as the set temperature difference, and sets the temperature difference to be equal to or less than the set temperature difference △Ts. In this case, hot gas from the condenser is guided to the suction port of the compressor to increase the temperature of the discharged gas and suppress the amount of refrigerant that dissolves into the lubricating oil.

That is, as shown in FIG. 4, when suction gas containing a large amount of mist is sucked into the compressor from the evaporator, the discharge temperature (T ₂ ) decreases, and the degree of superheat (T ₂ - T ₃ ) decreases.
becomes smaller. Therefore, when the discharge gas (T ₅ ) from the condenser is bypassed to the suction section of the screw compressor, the gas containing mist from the evaporator at temperature T ₁ and the bypass gas at temperature T ₆ are mixed and the temperature increases.
The refrigerant is sucked into the compressor at T ₁ ' and the discharge temperature rises to T ₂ ', which suppresses the sudden temperature rise due to heating of the suction gas, prevents hunting of the on-off valve, and prevents refrigerant from dissolving in the lubricating oil. The purpose of this invention is to provide a screw refrigerator that enables stable control and eliminates the problems of conventional methods.

[Means to solve the problem]

The present invention provides a screw refrigerator equipped with a screw compressor, an oil separator, a condenser, an evaporator, and a refrigerant path connecting these devices. A gas bypass path with a switch is provided between the low-pressure refrigerant gas path and a part of the high-pressure refrigerant gas in the condenser is introduced under reduced pressure into the low-pressure refrigerant gas in the evaporator, and the low-pressure refrigerant gas is sucked into the compressor. A pressure sensor and a temperature sensor are provided in the discharge side path of the screw compressor to detect the discharge pressure of the screw compressor and the temperature of the discharge fluid discharged from the screw compressor, and both The sensor is connected to a computing unit that computes the relative relationship between the discharge pressure and the temperature of the discharged fluid, and the degree of superheat of the discharged gas is detected. This screw refrigerator is characterized in that the bypass amount of hot gas guided to the screw compressor suction port via the bypass path is controlled in substantially inverse proportion to the degree of superheat of the discharged gas.

〔Example〕

An embodiment of the present invention will be described with reference to FIG. 4 and a low-pressure refrigerant gas path leading from the evaporator 5 to the suction port of the screw compressor 1. It is provided as a mechanism for introducing reduced pressure into the low-pressure refrigerant gas in the evaporator 5 and heating the low-pressure refrigerant gas sucked into the compressor. A pressure sensor 11 and a temperature sensor 12 are provided in the discharge side path of the screw compressor 1, and a computing unit 1 that uses these sensors 11 and 12 to calculate the relative relationship between the discharge pressure and the temperature of the discharged fluid.
3 to detect the degree of superheating of the discharged gas, and the computing unit 13 is connected to the switching device 8 to detect the hot gas that is led from the condenser 4 to the screw compressor suction port via the bypass path 7. The screw refrigerator is characterized in that the amount of bypass is controlled in substantially inverse proportion to the degree of superheating of discharged gas.

In this case, the degree of superheating (temperature difference) in a certain state
Various methods are used to detect this, but for example, a pressure sensor 11 that detects the condensation pressure and a temperature gas sensor 12 that detects the discharge gas temperature are provided,
The difference between the saturation temperature corresponding to the pressure detected by the pressure sensor 11 and the discharge gas temperature detected by the temperature sensor 12 is calculated by the calculator 13, and the opening/closing device 8 of the gas bypass path 7 is controlled based on the calculated value. It is something that performs operations.

The position of the pressure sensor is not limited to the oil separator, but may be provided in any high-pressure gas section from the discharge casing of the screw compressor 1 to the inside of the condenser. Further, the temperature sensor 12 may be provided at an appropriate location in the refrigerant flow path from the discharge casing of the screw compressor 1 to the inside of the condenser, and the oil flow path from the oil separator to the oil cooler.

The gas bypass passage 7 that guides the hot gas from the condenser 4 to the suction port of the screw compressor 1 is provided with an opening/closing device 8 (for example, an opening/closing valve) to adjust the temperature difference according to the amount of suction mist, that is, the temperature difference in the degree of superheating. In response to the,
Bypass flow should be controlled. That is, for example, if the temperature difference does not fall below the set temperature difference, the on-off valve is closed, and as the temperature difference falls below the set temperature difference, the opening of the on-off valve is opened in approximately inverse proportion to the degree of decrease. , it may be fully opened when the temperature difference is zero. Alternatively, it may be simply turned on and off.

Current, voltage, resistance, on/off contact signals, and other means are used for signals from the computing unit to the on-off valve.

Further, this on-off valve can also be used as a hot gas bypass device during low load. Even if the low load is detected by detecting the compressor suction amount (by slide valve stroke, etc.), the on-off valve is fully opened, giving priority to the on-off valve operation based on the temperature difference mentioned above. good.

Note that the screw compressor 1 is driven by a driving machine 2. 3 is an oil separator as an oil separation device, 4 is a condenser, 5 is an evaporator, and 6 is a pressure reducing valve, and a refrigerant path connects these devices. Further, the gas bypass path 7 connects the condenser 4 and a low-pressure refrigerant gas path connected to the suction port of the compressor 1, and is provided with an on-off valve as an on-off device 8 in the middle.

9 is an oil cooler, and 10 is an oil pump, which supplies separated and recovered lubricating oil to the bearing and rotor chamber of the screw compressor 1.

A pressure sensor 11 is provided in the gas phase of the oil separator 3 to detect the pressure of the discharged gas, and a temperature sensor 12 is provided in the liquid phase to detect the temperature of the separated oil (i.e., the temperature of the discharged gas). approximately equal).
Reference numeral 13 denotes a calculation unit, which calculates the saturation temperature corresponding to the discharge gas pressure measured by the pressure sensor 11, calculates the temperature difference between the temperature of the discharge gas detected by the temperature sensor 12, and controls the opening/closing operation so that this temperature difference does not become less than the set temperature difference. A close signal is given to the device 8, and when the temperature difference falls below the set temperature difference, an open signal is given that gives an opening degree inversely proportional to the amount of decrease from the set temperature difference to open the opening/closing device 8.

Regarding the operation, during normal operation, the amount of mist sucked into the screw compressor 1 is below the allowable value.
Based on the discharge gas pressure determined by the pressure sensor 11 and the discharge gas temperature determined by the temperature sensor 12, the calculation unit 13
Since the temperature difference determined by is larger than the set temperature difference, the switching device 8 remains closed. When the intake mist amount exceeds the allowable value, the temperature difference becomes less than the set temperature difference, and the opening degree of the switching device 8 is selected according to the amount of decrease from the set temperature difference by a signal from the calculator 13, and the hot gas in the condenser 4 is is drawn into the compressor 1, the temperature of the discharged gas is increased, and the amount of refrigerant trapped in the oil can be minimized.

Therefore, the oil separated from the discharged gas has a low refrigerant content, has almost no decrease in viscosity, and can perform a good lubricating effect. In addition, the separation efficiency in the oil separator is improved, the amount of oil adhering to the condenser 4 and evaporator 5 is reduced, and the heat transfer effect is prevented from being impaired, and the oil amount in the oil tank is prevented from decreasing. Since the amount of oil that reaches the temperature of This eliminates the need for additional equipment.

Pressure sensor 11 and temperature sensor 1 in Fig. 2
2, a temperature and pressure switch may be used to detect the temperature and pressure, and a solenoid valve may be used as the opening/closing device 8, and the solenoid valve may be opened and closed by an on/off contact signal.

Note that the opening/closing device 8 can also be used as a hot gas bypass device during low load.
That is, the load detection mechanism generates a signal when the load is smaller than a predetermined set load, is unloaded, or is a low load close to it, and the switchgear 8 is opened with priority over the signal due to the temperature difference described above, and the hot gas is released. will be introduced. This dual use simplifies the device.

That is, the temperature sensor 12 detects the temperature of the discharged gas, and the pressure sensor 11 simultaneously detects the pressure of the discharged gas, converts the discharged gas pressure into a saturated gas temperature, and calculates the relative value of the discharged gas temperature in the calculator 13. For example, the relationship is calculated as (discharge gas temperature - saturated gas temperature = degree of superheat), the output section outputs a control amount corresponding to this degree of superheat, and the gas bypass path 7 is opened or closed according to the control amount output value. The device 8 is maintained at a predetermined opening degree, that is, the valve opening degree is closed when the degree of superheating is high, and the valve opening degree is open when the degree of superheating is small.

The example in FIG. 3 shows an embodiment of the load detection mechanism. The load detection mechanism may detect the intake gas amount of the compressor 1, but in this example, the intake gas amount is detected by the stroke of the slide valve 14. That is, a rod 15 is provided on the slide valve 14, a limit switch 17 is actuated by a striker 16 at the end of the rod 15, and the suction amount is detected by detecting when the slide valve 14 has reached the stroke end, that is, near the unloading position. and detect the load. 18 is a suction port, 19 is a discharge port, and 20 is a rotor.

〔Effect of the invention〕

According to the present invention, the drawbacks of the conventional technology can be accurately eliminated.
It prevents the viscosity of the lubricating oil from decreasing to provide good lubrication, prevents a decrease in heat transfer in the condenser and evaporator, and prevents a decrease in the amount of oil in the oil tank, allowing screw refrigerators to operate at high performance. It is possible to achieve extremely great practical effects.

[Brief explanation of the drawing]

Fig. 1 is a Molière diagram showing the influence of inhalation mist, Fig. 2 is a flow diagram of an embodiment of the present invention, and Fig. 3 is a Molière diagram showing the influence of inhalation mist.
The figure is a longitudinal sectional view of a screw compressor according to an embodiment of the present invention, and FIG. 4 is a Molière diagram showing the characteristics of the present invention. DESCRIPTION OF SYMBOLS 1... Compressor, 2... Drive machine, 3... Oil separator, 4... Condenser, 5... Evaporator, 6... Pressure reducing valve, 7... Bypass path, 8... Switching device, 9 ……
Oil cooler, 10... Oil pump, 11... Pressure sensor, 12... Temperature sensor, 13... Arithmetic unit, 14
...Slide valve, 15... Rod, 16...
Striker, 17... Limit switch, 18...
...Suction port, 19...Discharge port, 20...Rotor.

Claims (1)

[Scope of Claims] 1 In a screw refrigerator equipped with a screw compressor 1, an oil separation device 3, a condenser 4, an evaporator 5, and a refrigerant path connecting these devices, the condenser 4 and the evaporator 5 A gas bypass passage 7 with a switching device 8 is provided between the condenser 4 and the low-pressure refrigerant gas passage leading to the suction port of the screw compressor 1.
A part of the high-pressure refrigerant gas in the evaporator 5 is introduced under reduced pressure into the low-pressure refrigerant gas in the evaporator 5 to heat the low-pressure refrigerant gas sucked into the compressor. A pressure sensor 1 that detects the temperature of the fluid discharged from the machine 1
1 and a temperature sensor 12 are provided in the discharge side path of the screw compressor 1, and both sensors 11 and 12 are connected to a computing unit 13 that calculates the relative relationship between the discharge pressure and the temperature of the discharged fluid, and calculates the overheating of the discharged gas. The calculation unit 13 is connected to the switching device 8 and the bypass amount of the hot gas guided from the condenser 4 to the screw compressor suction port via the bypass path 7 is determined based on the superheat degree of the discharged gas. A screw refrigerating machine characterized by having a configuration in which control is performed almost inversely proportionally. 2 In a screw refrigerator equipped with a screw compressor 1, an oil separator 3, a condenser 4, an evaporator 5, and a refrigerant path connecting these devices, the screw compressor 1 is A gas bypass passage 7 with a switching device 8 is provided between the low-pressure refrigerant gas passage connected to the suction port, and the condenser 4
A part of the high-pressure refrigerant gas in the evaporator 5 is introduced under reduced pressure into the low-pressure refrigerant gas in the evaporator 5 to heat the low-pressure refrigerant gas sucked into the compressor. A pressure sensor 1 that detects the temperature of the fluid discharged from the machine 1
1 and a temperature sensor 12 are provided in the discharge side path of the screw compressor 1, and both sensors 11 and 12 are connected to a computing unit 13 that calculates the relative relationship between the discharge pressure and the temperature of the discharged fluid, and calculates the overheating of the discharged gas. At the same time, the computing unit 13 is connected to the switching device 8 and the bypass amount of the hot gas guided from the condenser 4 to the screw compressor suction port via the bypass path 7 is determined based on the superheat degree of the discharged gas. The screw compressor 1 is configured to control the amount of compressed gas in substantially inverse proportion to the amount of compressed gas, and further includes a detection section that detects the amount of compressed gas of the screw compressor 1, and when the detected value becomes smaller than a predetermined amount of compressed gas, the detection section detects the amount of compressed gas. A screw-through refrigerator characterized in that the screw-through refrigerator is connected to the opening/closing device 8 so that opening/closing operations of the opening/closing device are given priority to operations based on temperature differences. 3. The screw refrigeration according to claim 2, wherein the compressed gas detection unit for screw compression is a screw compressor equipped with a variable capacity slide valve, and is equipped with a limit switch that is detected by the stroke of the slide valve. Machine.