JP6654050B2 - Multi-stage variable gas recovery machine and multi-stage variable refrigerant recovery machine - Google Patents

Description

  The present invention relates to a multi-stage variable gas recovery machine and a multi-stage variable refrigerant recovery machine in which a plurality of compressors for recovering gas such as refrigerant from devices such as air conditioners, water heaters and refrigerators are arranged in series.

  Devices such as air conditioners, water heaters, and refrigerators use chlorofluorocarbon as a refrigerant, and when these devices are discarded, chlorofluorocarbon is collected by a fluorocarbon recovery machine. High-vapor-pressure refrigerants have been adopted as the chlorofluorocarbons used by these devices in accordance with recent energy savings and reductions in the global warming potential (GWP) of chlorofluorocarbons.

  The CFC recovery machine suctions and pressurizes CFC from the object to be collected by a compressor, liquefies it by a condenser, and collects it in a container. There are two types of chlorofluorocarbon recovery machines: a gas compression type that sucks the gas phase of the material to be recovered, and a liquid recovery type that sucks the liquid phase of the material to be recovered. , And the latent heat of vaporization is covered by the heat of adiabatic compression of the compressor to promote vaporization. Further, since the processing temperature of the refrigerating machine oil, which is collected along with the CFC, can be increased, the amount of CFC dissolved in the refrigerating machine oil can be reduced.

  Since the high vapor pressure CFC has a high pressure, the pressure fluctuation in the object to be recovered when the refrigerant or the like is recovered from the equipment (the object to be recovered) by the CFC recovery machine becomes large. The chlorofluorocarbon recovery machine operates in an unsteady process in which the operating pressure from the start of recovery of the refrigerant to the end of recovery is constantly fluctuating. In the case of high vapor pressure refrigerant, the pressure fluctuation is large, so high efficiency recovery is performed. Is making it difficult.

In order to obtain a high pressure (high compression ratio), a multistage compressor is generally used. If the ratio between the suction pressure and the outlet pressure of the final stage compressor is defined as full compression, and this value is Z, then in the case of n-stage compression, the ideal compression ratio for each stage is Z1 ^{/ n} . Here, ^{assuming that} the compression ratio of each stage is Z ^{1 / n} = z and the processing volume (volume) ratio of the former stage and the latter stage of the compressor is e, the relationship between the volume ratio and the compression ratio is e ^γ = z.
(V1 / V2) ^γ = P2 / P1 = z (here, adiabatic index: γ will be described later)
That is, when the compression ratio changes, the volume ratio of each stage of the compressor: V1 / V2 also changes.

  As the compression ratio of the compressor increases, the adiabatic compression temperature increases, and when air is mixed in, the dangerous explosion of air and refrigeration oil easily occurs. If the adiabatic (polytropic) index is CFC and air is 1.2 and 1.3, respectively, the suction temperature is 25 ° C (298.15K), and if the compression ratio is 5, the discharge temperature is 117 ° C and 159 ° C respectively. However, when the compression ratio is 20, the temperature reaches 218 ° C. and 322 ° C., respectively.

The following relations hold for the heat insulation (there is no heat flow into and out of the surroundings) and the change (compression and expansion) of the gas. Pb: pressure before change Pa: pressure after change Vb: volume before change Va: volume after change Tb: temperature pressure before change Ta: temperature after change When adiabatic index (specific heat ratio Cp / Cv): γ,
Ta / Tb = (Vb / Va) ^γ-1 = (Pa / Pb) ^{(γ-1) / γ} holds.
Here, the temperature and the pressure are an absolute temperature (K) and an absolute pressure. Further, the adiabatic index: γ is a value determined by the number of constituent elements, and is monoatomic gas: 1.6 diatomic gas: 1.4 triatomic gas or more: 1.3.
In an actual adiabatic change, the value becomes smaller than the above-mentioned theoretical adiabatic index due to the presence of the lubricating oil and a slight transfer of heat to and from the surroundings due to the temperature change. Although this is called a polytropic index, it is not necessary to properly use it in this specification.

  Patent Literature 1 discloses an example of a CFC recovery machine of a liquid phase recovery type.

Japanese Patent No. 3014820

As described above, when recovering the refrigerant or the like, the pressure in the object to be recovered fluctuates from the start of the recovery to the end of the recovery. However, there is a problem that the recovery rate cannot be increased.
That is, when recovering a low vapor pressure medium, the ratio of the suction pressure to the condensing pressure at the end of recovery is about 1/25, but when recovering a high vapor pressure refrigerant or the like, the pressure ratio (compression ratio) is 1. / 100.
It is difficult to cope with such a high compression ratio with a single-stage compressor, and it is difficult to increase the recovery rate of the refrigerant and the like.

In addition, the fluctuation of the compression ratio at the time of refrigerant recovery is large, and at the time of high vapor pressure refrigerant recovery, the compression ratio at the start of recovery and the compression ratio at the end of recovery vary greatly from 1 / 1.2 to 1/100. Efficient recovery is not possible with a multi-stage compressor with a fixed volume ratio.
Further, when recovering a high vapor pressure refrigerant or the like, the compression ratio of the recovery machine increases, and there is a danger of diesel explosion when the temperature of the refrigerant rises extremely greatly and air is mixed.

  In the liquid-phase recovery type refrigerant recovery machine, the refrigerant and the refrigerating machine oil can be separated, but at the time of recovery, the pressure fluctuates periodically every time the material to be recovered is exchanged, so that CFCs are redissolved in the refrigerating machine oil. The separation accuracy and recovery speed of CFCs and CFCs are contrary, and there is a limit to the separation accuracy.

  An object of the present invention is to provide a multi-stage variable gas recovery machine and a multi-stage variable refrigerant recovery machine that can efficiently and safely recover a high vapor pressure refrigerant or the like in a shorter time than before.

  The minimum configuration of the present invention measures an intercooler (or an intermediate heat exchanger) disposed between a plurality of stages of compressors and the suction pressure of the first compressor and the discharge pressure of the last compressor. It is composed of two pressure gauges, an inverter-driven compressor or a variable-speed variable-DC motor-driven compressor such as a voltage control, which makes the rotation of the compressor variable, and an arithmetic control unit. In order for this configuration to function as a gas recovery unit, a condenser, a gas-liquid separator, and a rear cooler (or rear heat exchanger) disposed in the final stage compressor must be collected in a liquid state. In order to condense the refrigerant, a gas-liquid separator outlet valve for providing condensing pressure, AV5 or AV15 is installed. These gas-liquid separator outlet valves open when there is liquid and close when there is no liquid. All compressors are operated at an arbitrary number of revolutions, and two points of the suction pressure of the first compressor and the discharge pressure of the last compressor are measured, and the total compression ratio and the compression ratio of each stage to be controlled are calculated. Subsequently, the rotation ratio of the compressor is calculated and controlled based on the compression ratio and a preset adiabatic index. This series of measurements and calculations are performed instantaneously and repeatedly from the start of collection to the end of collection. In addition, it is necessary to display and output the collected filling amount of the collecting container and the like. The minimum configuration will be described with simple variable multi-stage compression described in a first embodiment described later.

Further, in addition to the above-described minimum configuration, the present invention measures the suction pressure and the discharge pressure of one compressor and four points of the suction temperature and the discharge temperature. An index is calculated, and a rotation ratio of the compressor is calculated and controlled from the adiabatic index and the compression ratio calculated above. This series of measurements and calculations are performed instantaneously and repeatedly from the start of collection to the end of collection. As a result, a change in the adiabatic index due to the incorporation of air can be measured, and accurate control can be performed in accordance with a change in the gas composition.
The configuration in which these four points are added corresponds to a multi-stage variable gas recovery machine described in a second embodiment described later. In this multi-stage variable gas recovery machine, in addition to the suction pressure and the condensing pressure, the suction temperature and suction pressure of each compressor, the discharge temperature and the discharge pressure are measured at four points, and the adiabatic index of the gas is calculated. The volume ratio (rotation ratio) of the compressor is calculated and controlled from the index and the calculated compression ratio. This series of measurements and calculations are performed instantaneously and repeatedly from the start of collection to the end of collection.

The present invention calculates the compression ratio from the two factors that fluctuate, the pressure of the material to be recovered, which is the suction pressure of the recovery machine, and the condensation pressure, which is the discharge pressure of the recovery machine, and changes the number of revolutions of each of the plurality of compressors. By operating at a reasonable compression ratio, an efficient recovery machine is realized.
The total compression ratio Z during operation is measured, and the compression ratio of each stage is z. From z = Z ^{1 / n} ,
Since Vb / Va = z1 ^{/ γ} , the volume ratio of each stage can be calculated and controlled. As described above, since the same control can be performed for n stages or two stages, the following description will be made using a two-stage compressor having the same capacity as the compressor.

The simple variable multi-stage compression as one of the embodiments of the present invention is performed only by measuring two pressures, that is, the pressure of the material to be recovered and the condensing pressure which is the discharge pressure of the recovery machine. When the recovery unit suction pressure P10, the condensing pressure and P13 all compression ratio: a Z = P13 / P10, in the case of two-stage compression Compression ratio: z is a Z ^1/2.
Here, when the adiabatic index: γ is a fixed value, the volume of the low-pressure compressor / the volume of the high-pressure compressor: e is
e = V1 / V2 = z1 ^{/ γ}
FIG. 3 shows an operation simulation when the adiabatic index γ set here is 1 and the adiabatic index of the actual gas is 1.15.
When Z = P13 / P10 = 2417 kPa / 100 kPa = 24.17,
z = e = 24.17 = 24.17 ^1/2 = 4.92, and when each compressor volume is represented by an operating frequency, the low-pressure compressor frequency is 111 Hz and the high-pressure compressor frequency is 22.6 Hz. At this time, since the adiabatic index of the actual gas is 1.15, the compression ratio of the low pressure stage is e ^1.15 = z1 = 6.248, and the compression ratio of the high pressure stage: z2 is
z2 = Z / z1 = 24.17 / 6.248 = 3.87. The intermediate stage pressure P12 is 642 kPa. As described above, by setting the adiabatic index: γ to a fixed value, the compression ratio of the low-pressure stage and the high-pressure stage is controlled slightly differently, but it is possible to perform the refrigerant recovery operation corresponding to the fluctuation of the total compression ratio. .

  Optimal control becomes possible if the adiabatic index can be measured even in a system in which the pressure fluctuates greatly and a foreign gas such as air is mixed like a recovery machine. In a pressure system that performs adiabatic change, the adiabatic index can be calculated if the pressure change and the temperature change can be measured. Calculates from the gas flowing into the recovery machine, so it can detect the optimal volume ratio of the multi-stage compressor and the mixing of air, preventing dangerous diesel explosions due to air and refrigeration oil, and preventing temperature rise, pressure rise, etc. An identification alarm that identifies the cause of a failure can be issued.

An example of variable multi-stage compression in a liquid phase recovery type CFC recovery machine will be described. Assuming that the suction pressure of the recovery unit is P1 and the condensing pressure is P3, the total compression ratio is Z = P3 / P1, and the compression ratio of each stage in the case of two-stage compression is Z ^1/2 . Here, the operation is performed at a temporary adiabatic index (any value from 1 to 1.6), and the suction temperature T1, the low-pressure discharge pressure P2, the low-pressure discharge temperature T2, the high-pressure suction temperature T3, the high-pressure discharge temperature T4, Then
The adiabatic index: γ = 1 / (1- (logt / logz)) can be calculated from {P2 / P1 = z, T2 / T1 = t} or {P3 / P2 = z, T4 / T3 = t}. Operation at an arbitrary compression ratio of the stage and control based on the outlet temperature of each stage can be performed as needed. At the same time, the incorporation of a different gas such as air can be detected as a “change in the measured adiabatic index γ”. An operation simulation is shown in FIG.

  In the present invention, since the refrigerant is compressed in at least two stages, the liquid-phase recovery-type CFC recovery device allows two oil units using adiabatic compression heat to be installed. The other is a "refrigeration oil refining unit" that minimizes the amount of chlorofluorocarbons dissolved in the refrigerating oil.

  Both the CFC vaporization unit and the refrigerating machine oil refining unit are connected to the lowest pressure at the head of the recovery machine and the suction side of the compressor via automatic valves. Each unit has a built-in heat exchanger for supplying adiabatic compression heat of the compressor as a heating source, and a pressure gauge is arranged in each unit, and a thermometer and a heater are arranged in the purification unit. Most of the refrigerating machine oil containing the refrigerant is vaporized and recovered in the vaporization unit, and moves to the purification unit. The purifying unit suction valve AV3 compares the pressures of the purifying unit and the vaporizing unit, and the purifying unit suction valve AV3 closes when the pressure of the purifying unit is lower than the pressure of the vaporizing unit. Liquefaction is prevented, and the re-low pressure area of the recovery machine can always be continued. Further, vaporization is promoted by the adiabatic compression heat of the high-pressure compressor, and high separation efficiency between the refrigerating machine oil and the refrigerant can be realized.

  The vapor pressure of chlorofluorocarbon used differs for each type of chlorofluorocarbon, and when air, which is a non-condensable component, is mixed, it only exists in the gas phase of chlorofluorocarbon in the condenser. Troubles such as different types of chlorofluorocarbon, air mixing, influence of outside temperature, and contamination of the condenser cannot be specified. The adiabatic index calculated from the compression process accurately represents the incorporation of air, so it is possible to operate in advance such as an alarm or to move and remove the air to the container, thereby preventing the explosion of the diesel, safely and without interruption. Efficient collection work is possible.

It is a lineblock diagram showing the 1st example of an embodiment of the present invention by a gas compression type refrigerant recovery machine. FIG. 4 is a characteristic diagram illustrating an example of a pressure change during refrigerant recovery according to the first embodiment of the present invention. It is explanatory drawing which shows the simple variable multistage compression example (example which made adiabatic index (gamma) fixed value) of the refrigerant | coolant recovery machine to which the 1st Embodiment of this invention was applied. It is a lineblock diagram showing a liquid phase recovery type refrigerant recovery machine of a 2nd embodiment of the present invention. It is a flowchart which shows the example of the collection | recovery process by the 2nd Example of this invention. FIG. 9 is a characteristic diagram illustrating an example of a pressure change during refrigerant recovery according to a second embodiment of the present invention. It is explanatory drawing which shows the example of the variable multi-stage compression by the example of 2nd Embodiment of this invention (the example which calculates | requires the true adiabatic index γ after starting operation with the adiabatic index γ at an initial value, and the example at the time of air mixing).

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The first embodiment is an example of a gas compression type refrigerant recovery machine, and the second embodiment is an example of a liquid phase recovery type refrigerant recovery machine. The gas compression type refrigerant recovery machine of the first embodiment is an example of a simple variable multistage compression in which only pressure is measured and control is performed.

<1. First Embodiment>
[1-1. Configuration of gas compression type CFC recovery machine]
FIG. 1 shows a configuration example of a gas compression type CFC recovery device 200. The refrigerant recovered by the gas compression type Freon recovery machine 200 is high vapor pressure Freon.
The object to be recovered 10 is a device such as an air conditioner or a water heater, and includes a CFC filling unit 11. The inside of the Freon filling portion 11 is in a state where Freon of different phases are stacked. That is, there is a dissolving phase 11a of refrigerator oil and liquid Freon on the lower side, and a gaseous Freon 11b above it. Note that FIG. 1 shows one recovered object 10, but a plurality of recovered objects 10 may be connected to the liquid-phase recovery type refrigerant recovery machine 100 to simultaneously recover Freon from a plurality of objects to be recovered 10.

  The gas compression type chlorofluorocarbon recovery machine 200 is for extracting the chlorofluorocarbon 11b from the material to be recovered 10. A pipe 13 for taking out the chlorofluorocarbon from the object to be recovered 10 is connected to the upper side of the chlorofluorocarbon filling section 11, and the chlorofluorocarbon 11 b is taken out of the pipe 13 by this pipe 13. The pipe 13 is connected to the to-be-collected object connection part 251 of the gas compression type refrigerant recovery machine 200. The to-be-collected connection part 251 is connected to the low-pressure compressor 211 via a pipe 252. A recovery machine inlet valve V11 and an automatic valve AV11 are arranged in the middle of the pipe 152. The opening and closing of the automatic valve AV11 is controlled by the control unit 243. Further, a pressure sensor P10 is disposed in the pipe 252. The pressure in the pipe 252 detected by the pressure sensor P10 corresponds to the pressure in the Freon filling portion 11 of the object 10 to be recovered.

  The gaseous Freon 11 b in the Freon filling portion 11 of the object 10 is supplied to the low-pressure compressor 211 via the pipe 252. The CFC supplied is compressed according to the ratio of the processing volumes of the low-pressure compressor 211 and the high-pressure compressor 212. In the low-pressure compressor 211 and the high-pressure compressor 212, the compression ratio of the low-pressure stage is variably set by changing the power supply frequency by an inverter. The necessary compression ratio is calculated from the pressure sensor P11 and a measured value of a sensor P13 described later. It is one example that the low-pressure compressor 211 and the high-pressure compressor 212 are inverter-type variable compressors. For example, a compressor whose compression ratio can be variably set by a voltage applied to a DC motor may be used. . Alternatively, the processing volume ratio between the low-pressure compressor 211 and the high-pressure compressor 212, which may be fixed or multi-stage transmission, is controlled by the control unit 243. A pressure sensor P11 is arranged on the suction side of the low-pressure compressor 211, and a pressure sensor P13 is arranged on the discharge side of the high-pressure compressor 212. Then, the CFCs compressed by the low-pressure compressor 211 are supplied to the intercooler 221 via the pipe 253.

  In the intercooler 221, the heated Freon is cooled using the fan 222, and the cooled Freon is supplied to the high-pressure compressor 212 via the pipe 254. The high-pressure compressor 212 compresses the supplied Freon by closing the automatic valve AV15. The high-pressure compressor 212 compresses to a pressure corresponding to the condensation temperature of the condenser 232 if no air is mixed. When non-condensable components such as air are mixed, the pressure increases. This pressure is measured by a pressure sensor P13 arranged on the discharge side of the high-pressure compressor 212. Then, the CFCs compressed by the high-pressure compressor 212 are supplied to the rear cooler 231 via the pipe 255. In the rear cooler 231, the Freon is cooled using the fan 232, and the cooled Freon is supplied to the gas-liquid separator 241 via the pipe 256. A relief valve SV11 is provided in the middle of the pipe 256.

  The compressed Freon supplied to the gas-liquid separator 241 is liquefied by being cooled by the condenser 232. This liquefied Freon accumulates in the gas-liquid separator 241. The liquid fluorocarbon stored in the gas-liquid separator 241 is supplied to the recovery container 242 via the automatic valve AV15 and the pipe 257. An automatic valve AV15 and a valve V12 are attached to the pipe 257. The automatic valve AV15 is opened when a predetermined amount of Freon has accumulated in the gas-liquid separator 241 and supplies Freon to the collection container 242. After supplying Freon to the collection container 242, the automatic valve AV15 is closed. The opening and closing of the automatic valve AV15 is controlled by the control unit 243.

  The control unit 243 calculates the working volume ratio between the low-pressure compressor 211 and the high-pressure compressor 212 based on the pressure values detected by the pressure sensors P11 and P13. Then, the control unit 243 controls the operation states of the low-pressure compressor 211 and the high-pressure compressor 212 so as to achieve the calculated compression ratio.

  In the following description, the pressure values detected by the pressure sensors P10 to P14 are indicated by the reference numerals assigned to the sensors. For example, let P11 be the pressure detected by the pressure sensor P11.

[1-2. Example of pressure change during refrigerant recovery]
FIG. 2 shows changes in the pressure of each part from the start to the end of the recovery of the gas compression type CFC recovery device 200 and changes in the compression operation state of the two compressors 211 and 212. The vertical axis in FIG. 2 indicates pressure, and the horizontal axis indicates time.
In FIG. 2, changes in the pressure P11 on the suction side of the low-pressure compressor 211, the pressure P12 on the discharge side of the low-pressure compressor 211 (= the suction side of the high-pressure compressor 212), and the pressure P13 on the discharge side of the high-pressure compressor 212 are shown. Is shown. FIG. 2 shows changes in the total compression ratio Z of the two compressors 211 and 212 and the compression ratio z of each stage. The pressure P12 on the discharge side of the low-pressure compressor 211 is also the pressure on the suction side of the high-pressure compressor 212, and the pressure P13 on the discharge side of the high-pressure compressor 212 is also the pressure of the gas-liquid separator 241.

  The pressure at the initial stage of recovery (the room temperature pressure in FIG. 2) is determined by the type of chlorofluorocarbon, and is in the range of several hundreds to 2,000 kPa. Here, an example of recovering Freon having a vapor pressure of about 1650 kPa will be described. Then, when the pressure P11 on the suction side of the low-pressure compressor 211 decreases to a predetermined pressure, the collection of CFCs is completed.

Explaining the pressure change shown in FIG. 2, when the refrigerant having the actual adiabatic index of 1.15 is recovered at the fixed adiabatic index of 1.0, the pressure P13 on the discharge side of the high-pressure compressor 212 increases to 2208 kPa at the timing t21. . When the pressure P11 on the suction side of the low-pressure compressor 211 at this time is 680 kPa, the total compression ratio Z is 3.25, so that the volume ratio of the compressors 211 and 212 at each stage = compression ratio z1 (∵ The fixed adiabatic index (1.0) is 1.80, and the low-pressure compressor 211 operates at an inverter frequency of 67.12 Hz and the high-pressure compressor 212 operates at an inverter frequency of 37.2 Hz. At this time, the compression ratio z1 of the low pressure stage is 1.80 ^1.15 = 1.97 from the actual adiabatic index of 1.15, and the compression ratio z2 = Z / z1 of the high pressure stage is 1.65. In this state, the pressure P12 on the discharge side of the low-pressure compressor 211 becomes 1338 kPa.

At the timing t22, the pressure P13 on the discharge side of the high-pressure compressor 212 increases to 2417 kPa, and the pressure P11 on the suction side of the low-pressure compressor 211 decreases to 210 kPa. At this time, the total compression ratio Z is 11.51, and the compression ratio z1 of each of the compressors 211 and 212 is 3.39. In this state, the inverter frequency of the low-pressure compressor 211 becomes 92.09 Hz, and the inverter frequency of the high-pressure compressor 212 becomes 27.15 Hz.
At this time, the pressure P12 in the intermediate stage becomes 856 kPa.

At the timing t23, the pressure P13 on the discharge side of the high-pressure compressor 212 is 2417 kPa, and the pressure P11 on the suction side of the low-pressure compressor 131 is 170 kPa. In this state, the inverter frequency of the low-pressure compressor 211 becomes 97.1 Hz, and the inverter frequency of the high-pressure compressor 212 becomes 25.75 HzHz.
At this time, the pressure P12 in the intermediate stage becomes 782 kPa.

  Further, at timing t24, the pressure P13 on the discharge side of the high-pressure compressor 212 is 2417 kPa, and the pressure P11 on the suction side of the low-pressure compressor 211 becomes 100 kPa. At this time, the total compression ratio Z is 20.14, and the volume ratio of the compressors 211 and 212 at each stage is 4.49. Therefore, the inverter frequency of the low-pressure compressor 211 is 110.9 Hz, and the high-pressure compressor 212 Becomes 22.6 Hz. The pressure P12 on the discharge side of the low-pressure compressor 211 becomes 624 kPa. Then, in this way, the controller 243 varies the rotation speeds of the two compressors 211 and 212 until the pressure P11 on the suction side of the low-pressure compressor 211 reaches the predetermined pressure of 10 kPa until the pressure reaches the predetermined pressure. The operation of collecting CFCs is performed.

[1-3. Pressure change example]
FIG. 3 is a simulation showing a gas having an actual adiabatic index γ: 1.15 based on the rotation speed (frequency) set value based on the fixed adiabatic index γ: 1.0 and the operation in the change of FIG.

  As described above, the compressors 211 and 212 to which the two variable rotation mechanisms are added, the pressure sensors P11 and P12, and the control unit having an advanced arithmetic function can realize a high recovery rate even with a high vapor pressure refrigerant. . Even in the case of the gas-compression type CFC recovery device 200, the temperature may be measured and controlled by the pressure and the temperature in the same manner as the liquid-phase recovery CFC recovery device 100 described below.

The variable rotation mechanism of the two compressors 211 and 212 has been described by stepless frequency control using an inverter, but three or more compressors and the variable rotation mechanism are variable control using a DC motor and multi-step frequency control using an inverter. , And control with one unit at a fixed rotation speed is also possible.

<2. Second Embodiment>
[2-1. Configuration of refrigerant recovery machine]
FIG. 4 shows a configuration example of the liquid phase recovery type refrigerant recovery machine 100.
The refrigerant recovered by the liquid-phase recovery type refrigerant recovery machine 100 is a high vapor pressure refrigerant (CFC).
The object to be recovered 10 is a device such as an air conditioner or a water heater, and includes a CFC filling unit 11. A CFC filling section 11 is provided. The inside of the Freon filling portion 11 is in a state where Freon of different phases are stacked. That is, there is a dissolved phase 11a of the refrigerating machine oil and liquid Freon on the lower side, and a gaseous Freon 11b thereon.
Since 95% of the Freon charged in the object to be recovered 10 in which the refrigerant Freon has not been lost is present in the liquid dissolved phase, separation and recovery from the dissolved phase is important.
Also in the case of the liquid-phase recovery type refrigerant recovery machine 100, a plurality of objects to be recovered 10 are connected to the liquid-phase recovery type refrigerant recovery machine 100, and Freon is simultaneously recovered from the plurality of objects to be recovered 10 Is also good.

  A pipe 12 for taking out the chlorofluorocarbon from the material to be recovered 10 is connected to a lower side of the chlorofluorocarbon filling section 11, and the chlorofluorocarbon 11 a of the dissolved phase is sent through the pipe 12. The pipe 12 is connected to the to-be-collected object connection part 151 of the liquid-phase recovery type refrigerant recovery machine 100. The connection section 151 is connected to the vaporization unit 110 via a pipe 152. A recovery machine inlet valve V1 and an automatic valve AV1 are arranged in the middle of the pipe 152. The automatic valve AV1 is controlled by the control unit 145. Further, a pressure sensor P0 is disposed in the pipe 152. The pressure in the pipe 12 detected by the pressure sensor P0 corresponds to the pressure in the Freon filling portion 11 of the object 10 to be recovered.

  The dissolved phase Freon 11a accumulated in the Freon filling portion 11 of the object to be recovered 10 is taken out to the vaporization unit 110 via the pipe 152. An intercooler 111, which is a heat exchanger, is arranged in the vaporization unit 110, and the heat generated when cooling the fluorocarbon passing through the intercooler 111 promotes the vaporization of the dissolved phase fluorocarbon 110a in the vaporization unit 110. You. The vaporization unit 110 is provided with a pressure sensor P1 for detecting an internal pressure and a temperature sensor T1 for detecting an internal temperature.

Further, a purification unit 120 is connected to the lower side of the vaporization unit 110 via a pipe 161. The pressure in the purification unit 120 is detected by a pressure sensor P1 '. The temperature in the purification unit 120 is detected by the temperature sensor T0. An automatic valve AV4 is arranged in the middle of the pipe 161. The opening and closing of the automatic valve AV4 is controlled by the control unit 145.
A rear cooler 121, which is a heat exchanger, is disposed in the purification unit 120, and the heat generated when cooling the fluorocarbon passing through the rear cooler 121 promotes the vaporization of the fluorocarbon in the dissolved phase 120a in the purification unit 120. Is done. Further, a heater 122 is provided in the purification unit 120, and the vaporization of the chlorofluorocarbon in the purification unit 120 is also promoted by the heating by the heater 122.
A pipe 162 having an automatic valve AV6 is attached to a lower side of the purification unit 120. When the automatic valve AV6 is opened, the oil in the refining unit 120 is discharged to the outside. The opening and closing of the automatic valve AV6 is controlled by the control unit 145.

The CFC vaporized in the vaporization unit 110 is supplied to the low-pressure compressor 131 via a pipe 153. Further, the chlorofluorocarbon vaporized in the purification unit 120 is supplied to the low-pressure compressor 131 via the pipe 163. Note that a pressure sensor P2 and a temperature sensor T2 are disposed on the discharge side of the low-pressure compressor 131.
An automatic valve AV2 is arranged in the middle of the pipe 153, and an automatic valve AV3 is arranged in the middle of the pipe 163. Opening and closing of these automatic valves AV2 and AV3 are controlled by the control unit 145.

The low-pressure compressor 131 compresses Freon supplied from the vaporization unit 110 and the purification unit 120 via the pipes 153 and 163. The processing volume of the low-pressure compressor 131 is variably set by changing the power supply frequency by an inverter. One example in which the low-pressure compressor 131 is an inverter-type variable compressor, for example, a compressor whose compression ratio can be variably set by a voltage applied to a DC motor may be used.
The CFCs compressed by the low-pressure compressor 131 are supplied to the intercooler 111 via a pipe 154. In the intercooler 111 arranged in the vaporization unit 110, the Freon that has become hot due to the compression by the low-pressure compressor 131 is cooled.

  Then, the CFC cooled by the intercooler 111 is supplied to the high-pressure compressor 132 and further compressed. A temperature sensor T3 is disposed on the suction side of the high-pressure compressor 132, and a temperature sensor T4 and a pressure sensor P3 are disposed on the discharge side of the high-pressure compressor 132. The processing volume of the high-pressure compressor 132 is also variably set by changing the power supply frequency by the inverter. Also in the case of the high-pressure compressor 132, an inverter-type variable compressor is one example, and another type of compressor such as a compressor using a DC motor may be used. The compression rates of the low-pressure compressor 131 and the high-pressure compressor 132 are controlled by the control unit 145.

The Freon compressed by the high-pressure compressor 132 is supplied to a rear cooler 121 disposed in the purification unit 120 via a pipe 156. In the rear cooler 121, the Freon heated to a high temperature by the compression in the high-pressure compressor 132 heats the refrigerating machine oil in the refining unit and cools the Freon. The pipe 156 between the high-pressure compressor 132 and the rear cooler 121 is branched on the way and connected to the inside of the purification unit 120 via the automatic valve AV7. The automatic valve AV7 is a pressure valve that is closed during the collection of CFCs and opened when the refrigerating machine oil of the refining unit 120 is discharged.
The Freon cooled by the rear cooler 121 is supplied to the condenser 141 via the pipe 157. A temperature sensor T5 is disposed on a pipe 157 at the inlet of the condenser 141. Further, a relief valve SV1 is disposed in the pipe 157.

  A fan 142 is attached to the condenser 141, and the refrigerant in the condenser 141 is liquefied by cooling by the fan 142 and closing the automatic valve AV5, and the liquefied chlorofluorocarbon is supplied to the gas-liquid separator 143 via the pipe 158. Is done. The gas-liquid separator 143 is a device that can store a predetermined amount of liquid fluorocarbon. The temperature sensor T5 is attached to the gas-liquid separator 143.

The liquefied chlorofluorocarbon stored in the gas-liquid separator 143 is supplied to the collection container 144 via the pipe 159. An automatic valve AV5 and a valve V2 are attached to the pipe 159. The automatic valve AV5 is opened when a predetermined amount of Freon accumulates in the gas-liquid separator 143, and supplies Freon to the collection container 144. After supplying Freon to the recovery container 144, the automatic valve AV5 is closed. The opening and closing of the automatic valve AV5 is also controlled by the control unit 145.
Further, inside the refrigerant recovery machine 100, an outside air temperature sensor RT is installed.

  In the following description, the pressure values detected by each of the pressure sensors P0 to P4 and the temperature values detected by each of the temperature sensors T1 to T5 and RT are indicated by reference numerals attached to the sensors. For example, let P1 be the pressure detected by the pressure sensor P1, and let T1 be the temperature detected by the temperature sensor T1.

  The control unit 145 performs identification, determination, and calculation based on the pressure values detected by the pressure sensors P0 to P4 and the temperature values detected by the temperature sensors T1 to T5 and RT, and controls the entire recovery machine. I do. Regarding the second embodiment, the adiabatic index is calculated from “the compression ratio of P2 / P1 and the temperature ratio of T2 / T1” or “the compression ratio of P3 / P2 and the temperature ratio of T4 / T3”. From P3 / P1, the processing volume ratio of the low-pressure compressor 131 and the high-pressure compressor 132 according to the purpose is calculated and controlled. A specific example of the operating state of the low-pressure compressor 131 and the high-pressure compressor 132 under the control of the control unit 145 will be described later.

[2-2. Flow of operation of liquid phase recovery type refrigerant recovery machine]
The flowchart of FIG. 5 shows a flow of an operation of recovering the refrigerant and the refrigerating machine oil in the refrigerant recovery machine 100.
In the flowchart of FIG. 5, the processing from step S11 to step S19 shows a flow from the recovery of the refrigerating machine oil containing Freon from the object to be recovered 10 to the vaporizing unit 110 to the discharge of the refrigerating machine oil from the refining unit 120. . The processing from step S21 to step S29 shows the flow of the operation of refrigerant recovery and the operation control of the compressors 131 and 132. The process of collecting and generating and discharging the refrigerating machine oil and the operation control process of the CFC recovery are performed in parallel. Also, generally used collection containers are 20L, 23L, and 100L containers, and if a room air conditioner is used, 20 to 120 CFCs can be collected.

  When chlorofluorocarbon is collected by the chlorofluorocarbon collection machine 100, the collection container 144 and the object to be collected 10 are connected to the chlorofluorocarbon collection machine 100, and the collection mode button is pressed. AV1 opens and starts the low-pressure compressor 131 and the high-pressure compressor 132.

First, a process of collecting and discharging the refrigerating machine oil will be described.
The dissolved phase Freon 11a in the Freon filling portion 11 of the object 10 is sucked into the vaporization unit 110 (Step S11). The chlorofluorocarbon vaporized in the vaporization unit is compressed by the low-pressure compressor 131 and the adiabatic compression heat vaporizes the chlorofluorocarbon in the vaporization unit 110 (step S12). It accumulates and increases in the vaporization unit. If the refrigerating machine oil has accumulated above a certain level (step S13) and the refining unit is empty (step S14), AV4 is opened and the refrigerating machine oil in the vaporizing unit 110 is moved to the refining unit 120. (Step S15)

  The refrigerating machine oil transferred from the vaporizing unit promotes vaporization of the dissolved chlorofluorocarbon by adiabatic compression heat of the compressor 132 and heating by the heater 122. (Step S16) (Step S17). During this time, the recovery unit repeats the recovery and gradually accumulates the refrigerating machine oil.

The control unit 145 monitors the pressure P1 'of the purification unit 120 and the pressure P1 of the vaporization unit 110 in order to prevent re-dissolution of CFCs in the refrigerating machine oil in the purification unit. Is [AV2: closed, AV3: open], the opposite is [AV2: open, AV3: closed] when [P1 '> P1]. (Step S18)
During this time, the suction pressure of the low-pressure compressor 131 repeats from 1616 kPa to the recovery end pressure (about 20 kPa) in the example of FIG. On the other hand, in the refining unit 120, since the vaporization of CFCs is slow due to the refrigerating machine oil that has been treated in the vaporization unit, the pressure P1 'of the purification unit 120 is maintained at a recovery end pressure around 20 kPa, so that a large amount of CFCs are removed from the refrigerator. Recovery can be realized.

  During the execution of the refining process in the refining unit, the refrigerating machine oil of the vaporizing unit 110 gradually increases and reaches a specified value (step S14), and the completion of the refining is confirmed (step S19). In the embodiment, when the temperature and the pressure are maintained for a certain time, the liquid is drained (step S20), and then the liquid is moved. (Step S15) The trigger of the completion of purification is not limited to the embodiment, and a large number of timers, level sensors, and a series of operations can be employed.

Next, the flow of operation control of the recovery machine 100 in FIG. 4 from step S21 to step S29 will be described.
When P0 is higher than the set value (when the recovery mode is in the standby state), AV1 opens and the low-pressure compressor 131 and the high-pressure compressor 132 start. The pressure P1 of the vaporizing unit 110 and the pressure P3 on the discharge side of the high-pressure compressor 132 are measured, and the volume ratio e of each compressor is calculated from the overall compression ratio Z, z and the adiabatic index initial value: γ to operate. Further, during the operation of both compressors 131 and 132, the compression ratios Z and z are always obtained, the adiabatic index of the gas is calculated and calculated from the pressure ratios of P3 / P2 and T4 / T3, and the temperature ratio, and the optimal operation is continued ( Steps S21 and S22).

  When the collection of CFCs proceeds and the value of the gas adiabatic index γ is within the specified range in step S23, the control unit 145 proceeds to the determination in step S24. When a predetermined amount of liquefied Freon is accumulated in the gas-liquid separator 143 in step S24, the automatic valve AV5 is opened, and the Freon in the gas-liquid separator 143 is sent to the recovery container 144 (step S25). Then, when the pressure P0, which is the pressure on the side of the object to be recovered 10, falls below the specified value, if this pressure is maintained for the set holding time, the collection of CFCs is completed (step S26). Change the object to be collected and start the next collection.

If the value of the gas adiabatic index γ is not within the specified range in step S23, it is determined in step S27 whether the pressure P3 on the discharge side of the high-pressure compressor 132 is equal to or lower than a specified value. If the value is equal to or less than the value, the control unit 145 issues an air mixing alarm and opens the automatic valve AV5 to remove air (step S28). If the entry of air into the object cannot be removed and the pressure of P3 continues to rise and becomes equal to or higher than the specified value, the collecting operation is stopped (step S29).
Further, when the liquefied Freon is not accumulated in the gas-liquid separator 143 in the predetermined amount in step S24, it is determined in step S30 whether or not the pressure P3 on the discharge side of the high-pressure compressor 132 is equal to or less than a specified value. If P3 is equal to or smaller than the specified value, the process returns to the determination in step S24. When the pressure P3 on the discharge side of the high-pressure compressor 132 is equal to or higher than the specified value in step S30, the refrigerant taken out of the object to be recovered is a high vapor pressure refrigerant, and the liquid-phase recovery type refrigerant recovery device 100 recovers the refrigerant. Therefore, the collection operation ends (step S31). In this case, the recovery operation is performed using another recovery machine corresponding to the high vapor pressure refrigerant.

[2-3. Example of pressure change during refrigerant recovery]
FIG. 6 shows a change in pressure of each part from the start of recovery of the liquid-phase recovery type refrigerant recovery machine 100 to the vicinity of the end of recovery, and a change in a compression operation state of the two compressors 131 and 132. The vertical axis in FIG. 6 indicates pressure, and the horizontal axis indicates time.
In FIG. 6, changes in the pressure P1 on the suction side of the low-pressure compressor 131, the pressure P2 on the discharge side of the low-pressure compressor 131 (= the suction side of the high-pressure compressor 132), and the pressure P3 on the discharge side of the high-pressure compressor 132 are shown. Is shown. FIG. 6 shows the changes in the total compression ratio Z of the low-pressure compressor 131 and the high-pressure compressor 132, the compression ratio z of each stage, and the frequency (proportional to the rotation speed) of each stage. Note that t24 shows an example in which air is mixed and the adiabatic index γ of the gas changes to 1.2.

Referring to FIG. 6, the pressure P1 on the suction side of the low-pressure compressor 131 decreases as the recovery progresses.
In the liquid phase recovery, since the liquid phase of the material to be recovered decreases and the gas phase increases due to an increase in the gas phase, a part of the fluorocarbon vaporizes inside, and the pressure P1 on the suction side of the low-pressure compressor 131 gradually decreases due to a slight temperature decrease. . As the recovery proceeds further, the liquid phase disappears and only the gas phase remains, so that the pressure P1 drops rapidly.

  In FIG. 6, the discharge pressure P3 of the high-pressure compressor 132 is changed based on the overall heat transfer coefficient of the condenser and the liquefied amount of chlorofluorocarbon, based on the chlorofluorocarbon vapor pressure corresponding to the different condensation temperature for each chlorofluorocarbon. And the difference between the temperature and the room temperature. Accordingly, contamination of the condenser and deterioration of the cooling fan cause an increase in the discharge pressure P3 of the high-pressure compressor 132 and an increase in the discharge gas temperature of the high-pressure compressor 132. However, since the adiabatic index does not change, the cause can be identified.

  A large number of CFCs are collected at the same time, and a collection end pressure is collected up to a negative pressure region. Due to the pores and the object to be recovered that has been opened to the atmosphere, and the connection pipe between the object and the recovery machine is defective, air entrapment occurs on a daily basis. Removal of defective objects by alarm and inspection of equipment can identify and remove the cause without interrupting work. You can also avoid the worst diesel explosion.

  FIG. 6 is described in time series. The frequency change and the ratio of the high-voltage stage of the low-voltage stage from t31 to t34 are t31: about {52 and 54 Hz e: 1.06}, and t32: about {54 and 46 Hz e: 1. 18｝, t33: about {70 and 36Hz e: 1.98}, t34: about {111 and 23Hz e: 4.64}.

The timing t34 in FIG. 6 is an example in which air is mixed and the adiabatic index becomes 1.2.
Since the air does not condense, it accumulates in the gas phase of the gas-liquid separator and in the upper part of the condenser, and increases the pressure of the discharge pressure P3 of the high-pressure compressor 132 by the pressure corresponding to the partial pressure of the air.

According to the measured adiabatic index, when the suction temperature difference is large and the discharge temperature needs to be limited, it is possible to operate at each compression ratio of the low pressure stage and the high pressure stage depending on the situation, so the discharge temperature of each stage can be kept within a certain range Can control. [Example] P1, P2, P3, T1, T2, T3, and T4 are as shown in FIG.
T2 = T1 × (P2 / P1) ^{(γ-1) / γ}
T4 = T3 × (P3 / P2) ^{(γ-1) / γ}
In this equation, when T2 = T4, control can be performed so that the discharge temperature of each stage becomes the same.

FIG. 7 shows an example of temperature measurement → adiabatic index calculation.
The adiabatic index can be calculated by any combination of {P2 / P1, T2 / T1} or {P3 / P2, T4 / T3}, but in the embodiment, {P3 / P2, T4 / T3} is calculated from the mounting position of the thermometer. Calculated in combination. If the mounting position of the compressor and the thermometer is far from each other, the rise of the suction temperature cannot be measured due to recompression, which is a malfunction of the compressor, and the temperature is unfavorably affected by the outside air temperature.

As described above, according to the liquid-phase recovery type chlorofluorocarbon recovery machine 100 of the present embodiment, by providing the two compressors 131 and 132, even if the compression ratio Z of the entire chlorofluorocarbon recovery machine is designed to be large, each of them is not required. The compression ratio z in the compressors 131 and 132 can be reduced. Therefore, even in the case of recovering high vapor pressure Freon requiring a large pressure fluctuation as shown in FIG. 6 at the time of recovering the refrigerant or the like, good recovery in which the fluctuation of the compression ratio in the compressors 131 and 132 is suppressed is achieved. become able to.
As for the unit for treating oil, two units, ie, a vaporizing unit 110 and a refining unit 120 are arranged, and the two units 110 and 120 take out CFCs in two stages. From the oil discharged from the tank, most of the chlorofluorocarbon is removed, and this also enables efficient collection of chlorofluorocarbon.
In the case of the liquid-phase recovery type refrigerant recovery unit 100 of the example of FIG. 6, similarly to the case of the gas compression type CFC recovery unit 200 of FIG. 1, the temperature is not measured, and the adiabatic index γ is fixed in advance. As the value, the rotation speed of each compressor may be calculated and controlled.

<Modification>
In the above-described embodiment, an example of a recovery machine that recovers CFCs has been described. However, a similar configuration may be applied to a recovery facility that handles gases other than CFCs.
For example, the present invention may be applied to a gas recovery machine that recovers an insulating gas from a gas-insulated high-voltage transformer.
In the above-described embodiment, the recovery machine includes two compressors, that is, a low-pressure compressor (first compressor) and a high-pressure compressor (second compressor). On the other hand, three or more compressors may be provided to sequentially compress the gas.
In this case, the intercooler cools the gas compressed by the first stage or the intermediate stage compressor of the plurality of compressors, and the rear cooler cools the last stage compression of the multistage compressor. The machine compresses the compressed gas. Then, the pressure sensor detects the suction side pressure of the first stage compressor and the discharge side pressure of the last stage compressor, and uses the adiabatic index as a fixed value, following the pressure fluctuation of the system detected by the pressure sensor, The control unit changes the rotation speed of all the compressors or the compressors other than one compressor continuously or stepwise.

  In the above-described embodiment, an example has been described in which the number of revolutions is continuously varied using an inverter as the compressor. On the other hand, the number of rotations may be changed in a plurality of stages (multiple stages). Further, each compressor is configured to vary the rotation speed using an inverter, but a compressor that varies the rotation speed by another method may be applied. For example, a compressor using a variable-speed DC motor may be applied to vary the number of rotations. Regarding the process of varying the number of revolutions by the compressor, the number of revolutions may be varied stepwise in a plurality of stages, instead of continuously varying the number of revolutions. For example, in the case of an inverter-type compressor, the power supply frequency is changed in a plurality of stages. In the case of a compressor using a DC motor, the voltage can be changed in a plurality of stages, and three or more compressors can be used, or one of the plurality of compressors can have a fixed rotation speed. .

Further, in the first embodiment, the example in which the simple variable multistage compression is applied to the gas compression type recovery machine has been described, but the liquid phase recovery type refrigerant recovery machine has been described in the first embodiment. Simple variable multi-stage compression may be applied. That is, in the liquid-phase recovery type refrigerant recovery machine, the adiabatic index is a fixed value, and the rotation speed of all the compressors or the compressors other than one is continuously changed according to the pressure fluctuation of the system detected by the pressure sensor. A simple variable multi-stage compression that fluctuates dynamically or stepwise may be performed.
Further, the processing in the liquid phase recovery type refrigerant recovery machine described in the second embodiment may be applied to a gas compression type recovery machine. That is, in the gas compression type recovery machine, the adiabatic index of the gas is calculated from the pressure detected by the pressure sensor and the temperature detected by the temperature sensor, and the optimum rotational speed of each of the multi-stage compressors is calculated. You may. Further, in the gas compression type recovery machine, the entry of air may be detected based on the principle described in the second embodiment.

DESCRIPTION OF SYMBOLS 10 ... thing to collect, 11 ... Freon filling part, 11a ... Dissolved chlorofluorocarbon, 11b ... Gas phase chlorofluorocarbon, 12 ... Piping, 100 ... Liquid phase recovery type refrigerant recovery machine, 110 ... Vaporization unit, 110a ... Dissolved phase CFC, 111: Intercooler, 120: Refining unit, 120a: CFC in liquid phase, 121: Rear cooler, 122: Heater, 131: Low pressure compressor, 132: High pressure compressor, 141: Condenser, 142: Fan , 143: gas-liquid separator, 144, collection container, 145, control unit, 151, connection part of the object to be recovered, 152 to 159, 161, 162, piping, 200, gas compression type refrigerant recovery unit, 211, low pressure compressor , 212 high-pressure compressor, 221 intermediate cooler, 222 fan, 231 rear cooler, 232 fan, 241 gas-liquid separator, 242 recovery container, 243 control unit, P0 to P , P10~P14 ... pressure sensor, RT ... the outside air temperature sensor, T1~T5, T11~T16 ... temperature sensor, V1~V4, V11~V14 ... valve, AV1~AV6, AV11~AV15 ... automatic valve

Claims (4)

In a multi-stage gas recovery machine that recovers gas from collected objects,
A multi-stage compressor in which the rotation speed is variably set and compresses the recovered gas in order;
An intercooler that cools the gas compressed by the first stage or intermediate stage compressor of the plurality of stages of compressors,
A rear cooler for cooling the gas compressed by the last one of the plurality of compressors;
A pressure sensor that detects at least the suction side pressure of the first stage compressor and the discharge side pressure of the last stage compressor,
A control unit that controls the number of rotations of the plurality of compressors in accordance with the pressure detected by the pressure sensor,
The control unit, with the adiabatic index as a fixed value, following the pressure fluctuation of the system detected by the pressure sensor, continuously or stepwise the rotation speed of all the compressors or other compressors except one. A multi-stage variable gas recovery machine that fluctuates following. The suction-side pressure and temperature and the discharge-side pressure and temperature of at least one of the plurality of compressors are measured, and the adiabatic index is calculated by the control unit. The multi-stage variable gas recovery machine according to claim 1, wherein an optimum rotation speed is calculated, and air mixing is detected. In a multi-stage variable refrigerant recovery machine that recovers a refrigerant dissolved phase from a collected object filled with a refrigerant dissolved in a refrigerator oil,
A plurality of compressors, each of which has a variably set rotation speed and sequentially compresses the collected refrigerant,
An intermediate cooler for cooling the refrigerant compressed by the first or intermediate stage compressor of the plurality of stages of compressors, and a melt phase first received from the material to be recovered and a refrigerant compressed by the compressor And a heat exchange unit in the intercooler,
Said plurality of stages final stage refrigerant compressed by the compressor of the compressor to have a rear cooler for cooling, the rear cooler and the compressed refrigerant in the dissolved phase and the compressor for receiving from the vaporizing unit A purification unit for exchanging heat with
Each of the vaporizing unit and the refining unit, provided on a pipe connecting the first stage compressor of the plurality of compressors, comprising a compressor suction valve that is operated independently,
A multi-stage variable refrigerant recovery device that controls each of the compressor suction valves such that the pressure of the purification unit is maintained near the recovery end pressure of the suction pressure of the first stage compressor . A pressure sensor for detecting both the suction-side pressure and the discharge-side pressure of at least one of the plurality of compressors;
A temperature sensor that detects a suction side temperature and a discharge side temperature of the compressor that detects a suction side pressure and a discharge side pressure with the pressure sensor;
A control unit that calculates an adiabatic index of gas from the pressure detected by the pressure sensor and the temperature detected by the temperature sensor, and calculates an optimal rotation speed of the multi-stage compressor.
The multistage variable refrigerant recovery machine according to claim 3.

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