JP3897751B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus using an oil-cooled two-stage screw compressor capable of adjusting capacity and a supercooler.

Conventionally, a refrigeration apparatus using an oil-cooled two-stage compressor and a supercooler is known (for example, see Patent Document 1).
JP-A-4-28975

  In Patent Document 1, an oil-cooled two-stage compressor, an oil recovery device, a hot gas defroster, a condenser, a supercooler, an expansion valve, an evaporator, and the hot gas defroster are returned to the compressor. A refrigeration apparatus is disclosed that includes a refrigerant circulation channel and an oil channel that guides oil in the oil recovery unit to an oil supply location in the compressor through an oil cooler. Further, this refrigeration apparatus branches from the portion between the condenser and the supercooler in the refrigerant circulation flow path, and then splits into two hands, one of which passes through the oil cooling on-off valve and the expansion valve, and the oil Passing through the cooler, reaching the intermediate pressure part of the compressor, the other passing through the supercooler via the supercooling on-off valve and expansion valve, the branch flow path to the intermediate pressure part of the compressor, Branching from a portion between the oil recovery unit and the hot gas defrosting device in the refrigerant circulation channel, and via a hot gas on / off valve, between the expansion valve and the evaporator in the refrigerant circulation channel A hot gas defrosting channel that joins the part is provided.

  In the refrigeration apparatus, the hot gas on-off valve is opened to control the intermediate pressure of the compressor at the time of hot gas defrosting for defrosting the evaporator, and the oil for a certain period of time. The cooling on-off valve and the supercooling on-off valve are closed, and the liquid refrigerant supplied to the oil cooling expansion valve and the supercooling expansion valve is stopped.

  The refrigeration apparatus described in Patent Document 1 is based on a self-lubricating system that supplies oil to a bearing in a compressor using a differential pressure (= discharge pressure-intermediate pressure) between a discharge pressure and an intermediate pressure. In the case of such a refrigeration apparatus, generally, when the load on the evaporator increases during operation, the suction pressure of the compressor increases, so that a state in which the differential pressure decreases occurs. If this decrease continues, the oil in the bearing will eventually run out due to insufficient lubrication, which may cause a damage accident in the bearing.

  Therefore, in the refrigeration apparatus described in Patent Document 1, the oil cooling on / off valve and the supercooling on / off valve are closed for a certain time immediately after the transition to the hot gas defrosting operation. However, what is determined based on this fixed time is not explicitly disclosed in Patent Document 1. However, the refrigeration apparatus described in Patent Document 1 sucks saturated wet gas into an intermediate casing portion of a compressor, mixes the saturated wet gas with low-stage discharge gas, and mixes the gas with the electric motor built in the compressor. After being used for cooling, it is sent to the higher stage. In order to avoid overheating of the electric motor, the gas supply cannot be stopped for a long time. That is, the oil cooling on-off valve and the over-cooling on-off valve are closed for a long time. Can not be set. However, on the other hand, there is a problem that the risk that the differential pressure is excessively reduced increases as the fixed time is shortened.

  Further, the state in which the differential pressure is excessively reduced occurs not only during hot gas defrosting but also when the load on the evaporator becomes excessive during normal refrigeration operation. Further, although not provided in the refrigeration apparatus described in Patent Document 1, there is also a refrigeration apparatus provided with a bypass flow path that directly connects the discharge side and the suction side of the compressor, and the discharge gas is sucked through the bypass flow path. Also in the hot gas bypass operation to return to the side, the above-described state of the differential pressure reduction occurs. Even if the oil cooling on-off valve and the supercooling on-off valve are closed for a certain period of time as described in Patent Document 1, the same problem as described above is caused against such a state in which the differential pressure is reduced. Arise.

  The present invention has been made with the object of eliminating the above-mentioned conventional problems, ensuring a differential pressure necessary for self-lubrication between discharge pressure and intermediate pressure, and preventing troubles due to insufficient lubrication in the compressor. It is an object of the present invention to provide a refrigeration apparatus that can do this.

  In order to solve the above-mentioned problems, the present invention provides a refrigerant circulation flow in which at least an oil recovery unit, a condenser, a supercooler, a main expansion valve, and an evaporator are interposed after an oil-cooled two-stage screw compressor. And an oil passage for guiding oil in the oil recovery device to an oil supply location in the compressor via an oil cooler, and the supercooler includes the condenser and the main in the refrigerant circulation passage. Branch from the portion between the expansion valve and the supercooling on / off valve and the supercooling flow path via the supercooling expansion valve pass, and this branch flow path leads to the intermediate pressure part of the compressor. In the refrigeration apparatus provided, the capacity that operates by switching the flow path at the flow path switching section interposed in the branch section of the oil flow path to the oil flow path portion, and makes the compressor full load state or unload state An intermediate pressure signal indicating the detected pressure is detected by adjusting means and the pressure of the intermediate pressure portion. An intermediate pressure detector, a discharge pressure detector for detecting a discharge pressure of the compressor and outputting a discharge pressure signal indicating the detected pressure, and a pressure indicating a detected pressure from the intermediate pressure detector and the discharge pressure detector In response to the signal, the differential pressure between the discharge pressure and the intermediate pressure is calculated, and when this differential pressure is within the range necessary for self-lubricating in the compressor, the compressor is brought into a full load state and the supercooling is performed. When the on-off valve is opened and the differential pressure decreases from the range, when the differential pressure reaches the first set value, the compressor is unloaded and the differential pressure is further reduced. In addition, an arithmetic control unit is provided that performs control to close the overcooling on-off valve when the second set value smaller than the first set value is reached.

  Further, in the present invention, in addition to the above configuration, when the arithmetic control unit reaches a third set value larger than the second set value when the differential pressure increases from a state equal to or lower than the second set value. It was set as the structure which performs control which opens the said on-off valve for supercooling.

  Furthermore, in addition to the above-described configuration, the present invention may be configured such that the arithmetic control unit performs the first setting when the differential pressure increases from a state equal to or lower than the first set value while the overcooling on-off valve is open. When the fourth set value larger than the value is reached, the compressor is controlled to be in a full load state.

  According to the refrigeration apparatus of the present invention, the differential pressure necessary for oil lubrication can be ensured, and the operation range of the compressor can be expanded, and the occurrence of trouble due to insufficient lubrication can be prevented. .

  Further, when the third set value that is larger than the second set value is reached, there is an effect that the hunting at the supercooling on / off valve can be prevented by the control to open the supercooling on / off valve.

  Furthermore, when the fourth set value that is larger than the first set value is reached, there is an effect that hunting at the flow path switching unit can be prevented by controlling the compressor to be in a full load state.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a refrigeration apparatus 1 according to the present invention. This refrigeration apparatus 1 includes an oil-cooled two-stage screw compressor 11, an oil separation and recovery unit 12, a condenser 13, a supercooler 14, a main on-off valve 15, A refrigerant circulation channel I in which the main expansion valve 16 and the evaporator 17 are interposed is formed.
The oil-cooled two-stage screw compressor 11 includes a first-stage compressor 22 and a second-stage compressor 23 driven by a motor 21, and the discharge port of the first-stage compressor 22 and the second-stage compressor 23. The suction port is in communication with the intermediate flow path 24. The first stage compressor 22 will be described in more detail later with reference to FIGS.

  An oil separation element 25 is provided in the oil separation / recovery unit 12 located on the discharge side of the second stage compressor 23, and an oil reservoir 26 is provided below the oil separation element 25. An oil flow path II is connected to the oil reservoir 26, and the oil in the oil reservoir 26 passes through an oil cooler 27, a part of which passes through a flow path switching unit 28, and further passes through an oil flow path portion IIa. It can be guided to the space on the back side of the lift valve 47 in the first stage compressor 22. The remaining oil passes through the oil passage portion IIc, enters the gas compression space in the first stage compressor 22 and the bearing / shaft seal portion, and passes through the oil passage portion IId to the gas in the second stage compressor 23. It is led to the compression space, bearing and shaft seal. The configuration in which oil can be guided to the space on the back side of the lift valve 47 in the first stage compressor 22 through the flow path switching unit 28 and further through the oil flow path portion IIa will be described in more detail later. .

In the portion of the refrigerant circulation flow path I between the supercooler 14 and the main on-off valve 15, after passing through the supercooling on-off valve 31 and the supercooling expansion valve 32, it passes through the supercooler 14 and passes through the intermediate flow path. The subcooling flow path III reaching 24 is branched.
An intermediate pressure detector 33 is provided in the intermediate flow path 24 so that the intermediate pressure can be detected, and a discharge pressure detector 34 is provided on the discharge side of the second stage compressor 23 so that the discharge pressure can be detected. Each of the intermediate pressure signal indicating the detected pressure by the intermediate pressure detector 33 and the discharge pressure signal indicating the detected pressure by the discharge pressure detector 34 is input to the arithmetic control unit 35, and the differential pressure ΔP between the two pressures by the arithmetic control unit 35. Based on (= discharge pressure Pd−intermediate pressure Pm), control of opening / closing of the supercooling on / off valve 31 and channel switching in the channel switching unit 28 is performed as described later.

  As shown in FIGS. 2 to 4, in the first stage compressor 22, the suction port 41 into which the refrigerant gas from the evaporator 17 flows is formed on one side, and the discharge port 42 following the intermediate flow path 24 is formed on the other side. And a pair of male and female screw rotors, ie, a female rotor 44 and a male rotor 45, which are rotatably accommodated in a casing 43. Further, a bottomed hole 46 is formed on the discharge side of the casing 43, and a lift valve 47 is fitted therein so as to be able to advance and retreat. The end of the bottomed hole 46 on the screw rotor side is the end face of the female rotor 44. And a through hole 48 that communicates with the suction port 41 and the bottomed hole 46 is also opened. Furthermore, the oil flow path II is bifurcated by a flow path switching unit 28 using a three-way switching valve as an example, and one of the oil flow path portions IIa is a lift valve facing the bottom of the bottomed hole 46. 47 communicates with the space in the bottomed hole 46 on the back side, and the other oil passage portion IIb communicates with the suction port 41. Then, by switching the flow path in the flow path switching unit 28, the portion of the oil flow path II before branching communicates with the oil flow path portion IIa and is disconnected from the oil flow path portion IIb, or the oil flow The path portion IIb is cut off from the portion of the oil flow path II before branching, and is in a state of communicating with the oil flow path portion IIa.

  FIG. 2 shows a state in which the portion of the oil passage II before branching communicates with the oil passage portion IIa and is blocked from the oil passage portion IIb. In this case, high-pressure oil fills the space on the back side of the lift valve 47, and the lift valve 47 moves forward to close the end face of the female rotor 44 and the right end face of the through hole 48. Therefore, the compressed refrigerant gas does not leak from the right end surface of the female rotor 44 and return to the suction port 41 through the through hole 48, and the first stage compressor 22 is in a full load state. Accordingly, the oil-cooled two-stage screw compressor 11 itself is also in a full load state.

On the other hand, FIG. 4 shows a state in which the oil passage portion IIb is disconnected from the portion of the oil passage II before branching and communicates with the oil passage portion IIa. In this case, the pressure of the refrigerant gas compressed in the tooth groove portion of the female rotor 44 acts on the front surface of the lift valve 47, and the oil on the back surface side of the lift valve 47 is sucked through the oil passage portions IIa and IIb. 41, the lift valve 47 moves backward,
The right end surface of the female rotor 44 and the through hole 48 communicate with each other. Accordingly, the compressed refrigerant gas is released from the right end surface of the female rotor 44 to the suction port 41 through the opening of the bottomed hole 46 and the through hole 48 as indicated by the arrow X, and is compressed in the first stage. The machine 22 is in an unloaded state. Accordingly, the oil-cooled two-stage screw compressor 11 itself is also unloaded.
2 and 4, the black portion of the three-way switching valve that is the flow path switching unit 28 indicates that the flow path is closed, and the white portion indicates that the flow path is open. Yes.

Next, the refrigeration apparatus 1 in operation will be described.
In the refrigerant circulation flow path I, the refrigerant gas sucked from the suction port 41 of the first stage compressor 22 is compressed, passes through the intermediate flow path 24 from the discharge port 42, and is second with oil from the oil flow path II. The air is sucked in from a suction port (not shown) of the stage compressor 23, further compressed by the second stage compressor 23, and discharged from the discharge port (not shown) together with oil toward the oil separator / collector 12. In addition to the oil described above, the intermediate channel 24 also joins the refrigerant from the supercooling channel III that has passed through the supercooler 14.

  In the oil separator / collector 12, the compressed refrigerant gas and oil are separated, and the refrigerant gas flows through the oil separation element 25 and flows to the condenser 13, while the separated oil drops, and the oil Collected in the reservoir 26. The refrigerant gas flowing into the condenser 13 releases heat and condenses into a refrigerant liquid, exits the condenser 13, and passes through the subcooler 14. A part of this refrigerant liquid is diverted to the supercooling flow path III and is expanded through the supercooling on-off valve 31 and the supercooling expansion valve 32 to reduce the temperature. After the refrigerant liquid in the circulation channel I is supercooled, it changes to the refrigerant gas and merges with the refrigerant gas in the intermediate channel 24 as described above. Then, the refrigerant liquid in the supercooled refrigerant circulation flow path I is throttled and expanded through the main on-off valve 15 and the main expansion valve 16 except for the above-described part of the refrigerant liquid that is divided into the supercooling flow path III. After the temperature is lowered, the evaporator 17 takes heat from the outside, evaporates and becomes refrigerant gas, and returns to the suction port 41 of the first stage compressor 22. Thereafter, the same circulation as described above is repeated.

  On the other hand, the oil in the oil reservoir 26 flows into the oil flow path II and is cooled by the oil cooler 27, and a part of the oil is diverted to the gas compression space in the first stage compressor 22, the bearing / shaft seal. And the gas compression space in the second stage compressor 23 and the bearing / shaft seal are respectively supplied with oil. Further, the remaining oil excluding the diverted oil is guided to the flow path switching unit 28 and supplied into the first stage compressor 22 by the flow path switching unit 28 controlled as follows. The lift valve 47 that puts the compressor 22 in a full load state or an unload state serves to adjust the capacity of the first stage compressor 22.

Next, with reference to FIG. 5 (horizontal axis: differential pressure ΔP, vertical axis: (upper stage) state of flow path switching unit, (lower stage) state of on / off valve for supercooling), flow by arithmetic control unit 35 during operation Control for the path switching unit 28 and the supercooling on-off valve 31 will be described.
In the oil-cooled two-stage screw compressor 11, particularly the second-stage compressor 23, the bearing / shaft seal is self-lubricated by the differential pressure ΔP between the discharge pressure and the intermediate pressure, and is in operation. In addition, it is necessary to keep the differential pressure ΔP larger than a value within a range in which the differential pressure ΔP can be self-lubricated, for example, the first set value P1. For this reason, the differential pressure ΔP is greater than the first set value P1 during the operation in the full load state where the lift valve 47 is in the forward position and the refrigerant is also flowing through the supercooling flow path III. When it gradually decreases and reaches the first set value P1, the flow path switching unit 28 first switches the flow path according to the control signal from the arithmetic control unit 35, and the oil-cooled two-stage screw compressor 11 has the capacity. After the adjustment, the lift valve 47 moves back to the unloaded state. As a result, even when the suction pressure of the first stage compressor 22 is high, the discharge of the compressed refrigerant gas from the first stage compressor 22 is suppressed, and the oil-cooled two-stage screw compressor 11 has a reduced intermediate pressure. It will be easy to do. Note that “FL” on the vertical axis in FIG. 5 means the state of the flow path switching unit 28 that brings the oil-cooled two-stage screw compressor 11 into a full load state, and “UL” means the oil-cooled two-stage screw compressor. 11 represents the state of the flow path switching unit 28 that puts 11 into the unloaded state.

  Furthermore, when the differential pressure ΔP does not stop decreasing and the differential pressure ΔP reaches the second set value P2 (<P1) that is smaller than the first set value P1, the control signal from the arithmetic control unit 35 causes an excess. The cooling on-off valve 31 is closed, and the supply of refrigerant from the subcooling channel III to the intermediate channel 24 is also stopped. As a result, the oil-cooled two-stage screw compressor 11 is in a state in which the intermediate pressure is more likely to decrease, and the differential pressure ΔP necessary for self-lubricating is ensured, and the operating range of the oil-cooled two-stage screw compressor 11 is expanded. And troubles due to insufficient oil lubrication of the bearings are prevented.

  The first set value P1 is a lower limit value of the differential pressure that can realize the lubrication necessary for sufficiently exhibiting the shaft seal effect of the shaft seal portion even when the bearing is sufficiently lubricated. The set value P2 is desirably set based on empirically derived lower limit values of the differential pressure that can be self-lubricated and based on these lower limit values.

As a result of the above-described control, when the differential pressure ΔP starts to increase and first reaches a third set value P3 (P2 <P3 ≦ P1) that is greater than the second set value P2 and equal to or less than the first set value P1, supercooling The on-off valve 31 is opened, and the supply of refrigerant from the subcooling channel III to the intermediate channel 24 is started. In this way, by making a difference between the second set value P2 and the third set value P3, hunting at the supercooling on-off valve 31 is prevented. Further, when the differential pressure ΔP continues to increase and reaches a fourth set value P4 (> P1) that is larger than the first set value P1, the channel switching is performed in the channel switching unit 28, and an oil-cooled two-stage screw is performed. The capacity of the compressor 11 is adjusted, and the compressor 11 shifts to a full load state in which the lift valve 47 advances. Thus, hunting in the flow path switching unit 28 is prevented by making a difference between the first set value P1 and the fourth set value P4.
In other words, the third set value P3 and the fourth set value P4 are related to the second set value P2 for the former, and the first set value P1 for the latter. In addition, the flow path switching unit 28 is determined so as not to cause humming, and hysteresis control is performed.

  The present invention does not limit the flow path switching unit 28 to the one using the above-described three-way switching valve. In addition to the three-way switching valve, for example, as shown in FIGS. A flow path switching unit 28 </ b> A including the valve 51 and the second opening / closing valve 52 is also included. 6 and 7 differ from FIGS. 2 and 4 only in that the flow path switching unit 28A is applied instead of the flow path switching unit 28, and there is no functional change, and the other configurations are substantially the same. 6 and 7 that are common to FIGS. 2 and 4 are assigned the same reference numerals and description thereof is omitted.

In the first stage compressor 22, a first on-off valve 51 is provided in the oil passage II before branching, and a second on-off valve 52 is provided in the oil passage portion IIb branched therefrom. As shown in FIG. 6, only the second on-off valve 52 is closed so that the first stage compressor 22A is in a full load state, and only the first on-off valve 51 is closed as shown in FIG. 22A enters an unload state.
The first on-off valve 51 and the second on-off valve 52 shown in FIGS. 6 and 7 are shown in black when they are closed, and are shown in white when they are open, as described above.

Further, the present invention also includes a refrigerating apparatus that employs the configuration shown in FIG. 8 instead of the configuration in the frame indicated by the two-dot chain line in FIG.
In the refrigerant supercooling section shown in FIG. 8, the branch point from the refrigerant circulation flow path I of the supercooling flow path III is the primary side of the supercooler 14. The configuration in the frame indicated by the two-dot chain line is substantially the same. And about this same part, the same number as the structure in the said frame is attached | subjected in FIG.

Further, the present invention does not limit the capacity adjusting means to the lift valve 47 described above, but also includes a refrigeration apparatus using a known slide valve or piston valve as the capacity adjusting means.
Incidentally, the slide valve forms a part of the curved wall portion of the rotor chamber in the casing housing the screw rotor at the meshing portion of the male and female screw rotors, and advances and retreats in the direction parallel to the axis of the screw rotor. The capacity of the screw compressor is adjusted by increasing or decreasing the return amount of the gas confined in the tooth gap portion to the suction port.
The piston valve forms a part of the curved wall portion of the rotor chamber in the casing that houses the screw rotor, and advances and retreats in the radial direction of the screw rotor to the gas suction port confined in the tooth groove portion of the screw rotor. The screw compressor capacity is adjusted by increasing / decreasing the return amount.

It is a block diagram of the freezing apparatus which concerns on this invention. It is sectional drawing which shows the outline of a 1st stage compressor with the flow-path switching part in the freezing apparatus shown in FIG. It is the III-III sectional view taken on the line of FIG. 2 in a full load state. FIG. 3 is a cross-sectional view corresponding to FIG. 2 in an unloaded state. It is a figure which shows the relationship between the differential pressure | voltage in the refrigeration apparatus shown in FIG. 1, and the operation state of a flow-path switching part and the overcooling on-off valve. It is sectional drawing corresponding to FIG. 2 which applied the other flow-path switching part. It is sectional drawing corresponding to FIG. 4 to which the flow-path switching part shown in FIG. 6 is applied. It is a block diagram which shows the other structure of the supercooling part in the freezing apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refrigeration apparatus 11 Oil-cooled two-stage screw compressor 12 Oil separation and recovery machine 13 Condenser 14 Supercooler 15 Main on-off valve 16 Main expansion valve 17 Evaporator 21 Motor 22 First stage compressor 23 Second stage compressor 24 Intermediate flow path 25 Oil separation element 26 Oil pool part 27 Oil cooler 28, 28A Flow path switching part 31 Supercooling on-off valve 32 Supercooling expansion valve 33 Intermediate pressure detector 34 Discharge pressure detector 35 Operation control part 41 Suction Port 42 Discharge port 43 Casing 44 Female rotor 45 Male rotor 46 Bottomed hole 47 Lift valve 48 Through hole 51 First on-off valve 52 Second on-off valve I Refrigerant circulation flow path
II Oil channel IIa, IIb, IIc, IId Oil channel part
III Supercooling flow path X Arrow

Claims (3)

Following the oil-cooled two-stage screw compressor, at least the oil recovery unit, the condenser, the supercooler, the main expansion valve, and the refrigerant circulation passage in which the evaporator is interposed and the oil in the oil recovery unit are oil-cooled. An oil flow path that leads to an oil supply point in the compressor through a vessel,
The supercooler has a supercooling flow path that branches from a portion between the condenser and the main expansion valve in the refrigerant circulation flow path and that passes through a supercooling on-off valve and a supercooling expansion valve. Pass through
In the refrigeration apparatus provided so that this branch flow path leads to the intermediate pressure part of the compressor,
A capacity adjusting means that operates by switching a flow path at a flow path switching section interposed in a branch section of the oil flow path to an oil flow path portion, and sets the compressor to a full load state or an unload state;
An intermediate pressure detector that detects the pressure of the intermediate pressure section and outputs an intermediate pressure signal indicating the detected pressure;
A discharge pressure detector that detects a discharge pressure of the compressor and outputs a discharge pressure signal indicating the detected pressure;
When the pressure signal indicating the detected pressure is received from the intermediate pressure detector and the discharge pressure detector, the differential pressure between the discharge pressure and the intermediate pressure is calculated, and this differential pressure is within the range necessary for self-lubrication in the compressor When the compressor is in a full load state and the on / off valve for supercooling is opened, and the differential pressure decreases from the range, the differential pressure first reaches the first set value. An arithmetic control unit that controls the supercooling on-off valve to be closed when the compressor is unloaded, and the differential pressure decreases and reaches a second set value that is smaller than the first set value. A refrigeration apparatus comprising:   When the differential pressure increases from the state equal to or lower than the second set value, the arithmetic control unit performs control to open the overcooling on / off valve when the third set value larger than the second set value is reached. The refrigeration apparatus according to claim 1, wherein the refrigeration apparatus is performed. When the arithmetic control unit reaches a fourth set value larger than the first set value when the differential pressure increases from a state equal to or lower than the first set value under the open state of the overcooling on-off valve, The refrigeration apparatus according to claim 1 or 2, wherein the compressor is controlled to be in a full load state.

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