CN111397082B

CN111397082B - Refrigerant recovery system and control method

Info

Publication number: CN111397082B
Application number: CN202010248134.0A
Authority: CN
Inventors: 杨巨沁; 张新明; 周涯宸; 王成; 潘余彬
Original assignee: Ningbo Aux Electric Co Ltd
Current assignee: Ningbo Aux Electric Co Ltd
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2021-10-26
Anticipated expiration: 2040-04-01
Also published as: CN111397082A

Abstract

The invention provides a refrigerant recovery system and a control method, wherein the system comprises: the device comprises a recovered container, a compressor, a convergent-divergent nozzle, a mixing container, a condenser and a recovery container; a first pipeline which is communicated with a first outlet of a recovered container and a first inlet of the mixing container, and the compressor and the convergent-divergent nozzle are arranged on the first pipeline in series; the second pipeline is communicated with the mixing outlet of the mixing container and the recovery inlet of the recovery container, and the condenser is arranged on the second pipeline; and the liquid recovery pipeline is communicated with the second outlet of the recovered container and the second inlet of the mixing container. The invention realizes the simultaneous recovery of the gas-liquid two-phase refrigerant under the matching of the convergent-divergent nozzle and the mixing container, does not need to manually switch the recovery mode, simplifies the operation steps of the recovery system, effectively shortens the recovery time, and simultaneously can reduce the air suction and exhaust amount of the compressor and lighten the condensation load of the condenser.

Description

Refrigerant recovery system and control method

Technical Field

The invention relates to the technical field of refrigerant recovery, in particular to a refrigerant recovery system and a control method.

Background

The refrigerant is not directly discharged and needs to be recycled by special recycling equipment for recycling because of the toxicity, the combustion explosiveness and the corrosiveness to materials of the refrigerant and the reduction of the ozone amount in the atmospheric layer, thereby bringing global greenhouse effect. At present, a gas-liquid composite recovery method is mostly adopted to recover the refrigerant, however, in the operation process of the recovery equipment, the liquid refrigerant and the gaseous refrigerant are still recovered separately, and the switching time node of the two is randomly controlled by an operator according to experience, so that the most reasonable recovery efficiency and recovery rate cannot be achieved.

Disclosure of Invention

The invention solves the problems that: how to improve the recovery speed and the recovery efficiency of the refrigerant recovery system.

To solve the above problems, the present invention provides a refrigerant recovery system comprising: by recovery vessel, compressor, convergent-divergent nozzle, mixing vessel, condenser and recovery vessel, still include: a first pipeline which communicates a first outlet of the recovered container with a first inlet of the mixing container, and on which the compressor and the convergent-divergent nozzle are arranged in series; the second pipeline is communicated with the mixing outlet of the mixing container and the recovery inlet of the recovery container, and the condenser is arranged on the second pipeline; and the liquid recovery pipeline is communicated with the second outlet of the recovered container and the second inlet of the mixing container.

Therefore, the first pipeline and the liquid recovery pipeline realize simultaneous recovery of the gas-liquid two-phase refrigerant under the matching of the convergent-divergent nozzle and the mixing container, on one hand, the recovery mode does not need to be manually switched, the operation steps of the recovery system are simplified to a certain extent, the recovery time is effectively shortened, and the recovery efficiency is improved; on the other hand, the air suction and exhaust amount of the compressor can be reduced, and the condensation load of the condenser can be reduced; in addition, the mixing container can also be used as a buffer zone, so that the flow speed and the pressure of the refrigerant are effectively reduced, and the protection of the condenser is improved.

Optionally, the method further comprises: and the pressure sensor is arranged in the mixing container and is used for acquiring the pressure at the second inlet, and the acquired pressure is used for controlling the flow of the liquid recovery pipeline and/or the second pipeline.

From this, through setting up pressure sensor to the control parameter of the flow of the pressure that will acquire as control liquid recovery pipeline and second pipeline can avoid when the pressure differential is too little, and liquid recovery pipeline still communicates, leads to too much refrigerant to be detained in the pipeline, reduces the system recovery rate.

Optionally, a second control valve is arranged on the liquid recovery pipeline, the second control valve is electrically connected with the pressure sensor, and the second control valve is adapted to adjust the opening according to the obtained pressure so as to control the flow rate of the liquid recovery pipeline; and a first control valve is arranged on a pipeline between the condenser and the recovery container, the first control valve is electrically connected with the pressure sensor, and the first control valve is suitable for adjusting the opening according to the acquired pressure so as to control the flow of the second pipeline.

From this, through set up the second control valve on liquid recovery pipeline to associate the second control valve with pressure sensor, can control liquid recovery pipeline's flow more rapidly accurately, simultaneously, through the aperture according to the first control valve of second entry pressure control that obtains, can realize the control more accurate to the flow, improve the accuracy of refrigerant recovery system control.

Another object of the present invention is to provide a control method for a refrigerant recovery system as described above, so as to better improve the recovery speed and the recovery efficiency of the refrigerant recovery system.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a control method of a refrigerant recovery system based on the above refrigerant recovery system, comprising:

after the refrigerant recovery system enters a refrigerant recovery mode, the gaseous refrigerant compressed by the compressor is subjected to isentropic injection through a scaling spray pipe, and low pressure is formed in a mixing container of the refrigerant recovery system to obtain the pressure in the mixing container;

and controlling the flow of a liquid recovery pipeline of the refrigerant recovery system according to the acquired pressure.

Therefore, the second inlet pressure in the mixing container is used as a control parameter of the flow of the liquid recovery pipeline, on one hand, the gas-liquid two-phase refrigerant is recovered at the same time, and the recovery time is effectively shortened; on the other hand, the refrigerant directly entering the mixing container does not increase the condensation load, so that the condensation load is reduced; in addition, the gas-liquid recovery mode does not need to be switched, the operation steps are simplified, and the recovery rate of the refrigerant is improved.

Optionally, the refrigerant recovery system enters a refrigerant recovery mode comprising: after a starting signal of the refrigerant recovery system is received, controlling to start the compressor; compressing, with the compressor, a gaseous refrigerant drawn into the compressor through a first line; carrying out isentropic injection on the compressed gaseous refrigerant by using the scaling spray pipe; the liquid refrigerant or the gaseous refrigerant in the recovered container enters the mixing container through the liquid recovery pipeline under the action of pressure difference, and is mixed with the gaseous refrigerant sprayed out of the convergent-divergent nozzle in the mixing container; the mixed refrigerant is condensed by a condenser, and the condensed refrigerant is recovered in a recovery container.

Therefore, the flow rate of the liquid recovery pipeline can be controlled more quickly and accurately by specifying the operation state of each device in the refrigerant recovery system, so that the control precision of the refrigerant recovery system is improved.

Optionally, controlling a liquid recovery line flow of the refrigerant recovery system according to the obtained pressure comprises: and comparing the obtained pressure with a preset pressure in the refrigerant recovery system, and adjusting the opening of a second control valve arranged on the liquid recovery pipeline according to the comparison result so as to control the flow of the liquid recovery pipeline.

Therefore, the acquired pressure is compared with the preset pressure, and the opening of the second control valve is controlled through the comparison result, so that the flow state of the liquid recovery pipeline is specified, the control precision of the refrigerant recovery system can be further improved, unnecessary communication is avoided, and the energy saving is facilitated.

Optionally, the adjusting an opening degree of a second control valve disposed on the liquid recovery pipeline according to the comparison result to control a flow rate of the liquid recovery pipeline includes:

if the acquired pressure is smaller than a first preset pressure, controlling the opening degree of the second control valve according to a first rule;

if the acquired pressure is greater than or equal to a first preset pressure and the acquired pressure is less than or equal to a third preset pressure, controlling the opening of the second control valve according to a second rule;

and if the acquired pressure is greater than the third preset pressure, controlling the opening of the second control valve according to a third rule.

Therefore, the acquired pressure is used as a control parameter and is compared with the first preset pressure and the third preset pressure, and then the opening rule met by the second control valve is judged, so that the control precision of the liquid recovery pipeline can be further improved, and the control stability of the system is improved.

Optionally, the first rule includes: controlling the second control valve to be 100% open;

the second rule includes: if the acquired pressure is greater than or equal to the first preset pressure and the acquired pressure is less than a second preset pressure, controlling the opening of the second control valve to reduce in an equal ratio within the range of 100-50% of the opening according to the acquired pressure; if the acquired pressure is equal to the second preset pressure, controlling the second control valve to be 50% in opening degree; if the acquired pressure is greater than the second preset pressure and the acquired pressure is less than or equal to the third preset pressure, controlling the opening of the second control valve to be reduced in an equal ratio within the range of 50% -0% of the opening according to the acquired pressure;

the third rule includes: controlling the opening degree of the second control valve to be 0;

the first preset pressure is smaller than the second preset pressure, and the second preset pressure is smaller than the third preset pressure.

Thus, by embodying the first rule, the second rule, and the third rule, the opening degree of the second control valve is further refined, and thus, the valve opening degree matching the obtained pressure is adaptively selected to sufficiently cope with the difference in the obtained pressure, and more accurate control of the refrigerant recovery system is realized.

Optionally, the first rule further includes: if the acquired pressure is smaller than a fourth preset pressure, controlling the compressor to stop running and sending a reminding signal; wherein the fourth preset pressure is less than the first preset pressure.

Therefore, the use safety of the system is improved, and potential safety hazards in the recovery process are avoided.

Optionally, the method further comprises: obtaining the rated filling amount of the recovered container; and adjusting the opening degree of a first control valve arranged on a second pipeline according to the acquired pressure and the rated charging amount so as to control the flow of the second pipeline.

Therefore, after the refrigerant recovery system enters the refrigerant recovery mode, the pressure in the mixing container and the rated charging amount of the recovered container are obtained in real time, and the obtained pressure and the rated charging amount are used as control parameters of the first control valve, so that the control precision of the refrigerant recovery system is further improved.

Optionally, the adjusting the opening degree of a first control valve disposed on a second pipeline according to the acquired pressure and the rated charging amount includes:

if the rated charging amount is larger than or equal to a preset charging value, adjusting the opening of the first control valve according to the acquired pressure;

and if the rated charging amount is smaller than a preset charging value, controlling the opening of the first control valve to be 100%.

Therefore, the acquired pressure and the rated charging amount are used as control parameters, and the opening degree of the first control valve is further judged, so that the control precision of the refrigerant recovery system can be further improved, and the operation stability of the system can be improved.

Optionally, the adjusting the opening degree of the first control valve according to the acquired pressure comprises:

if the acquired pressure is less than or equal to a second preset pressure, controlling the first control valve to be 100% in opening degree;

if the acquired pressure is greater than the second preset pressure and the acquired pressure is less than or equal to the third preset pressure, controlling the opening of the first control valve to be reduced in an equal ratio within the range of 100-50% of the opening according to the acquired pressure;

and if the acquired pressure is greater than the third preset pressure, controlling the opening of the first control valve to be 50%.

Thus, the opening degree of the first control valve is further refined, and the valve opening degree matched with the obtained pressure is adaptively selected according to the difference of the obtained pressure, so that more accurate control of the refrigerant recovery system is realized

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic diagram of a refrigerant recovery system according to an embodiment of the present invention;

fig. 2 is a schematic flow chart illustrating a control method of a refrigerant recovery system according to an embodiment of the present invention;

FIG. 3 is a schematic flow diagram illustrating a refrigerant recovery mode according to an embodiment of the present invention;

fig. 4 is a control flow chart of a second control valve according to an embodiment of the present invention;

fig. 5 is a control flow diagram of a first control valve according to an embodiment of the present invention;

fig. 6 is a schematic structural view of a conventional refrigerant recovery apparatus.

Description of reference numerals:

1-a recovered container, 1 a-a first outlet, 1 b-a second outlet, 2-a compressor, 3-a convergent-divergent nozzle, 4-a mixing container, 4 a-a first inlet, 4 b-a second inlet, 4 c-a mixed material outlet, 5-a condenser, 6-a recovery container, 6 a-a recovery inlet, 7-a first pipeline, 71-a first branch, 72-a second branch, 73-a third branch, 8-a liquid recovery pipeline, 9-a second pipeline, 91-a fourth branch, 92-a fifth branch, 10-a first control valve, 11-a second control valve, and 12-a pressure sensor;

1 '-recovered equipment, 2' -compressor unit, 3 '-four-way reversing valve, 4' -heat exchanger, 5 '-recovery tank and 6' -valve.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

Furthermore, the following description, if any, of "first," "second," etc. is used for descriptive purposes only and not for purposes of indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. Furthermore, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

In order to counteract the greenhouse effect caused by the dispersion of refrigerant gas used in an air conditioning system, laws and regulations set increasingly strict limits on the waste gas recovery process, however, the application and development of the current refrigerant recovery equipment are slow, besides the environmental awareness of workers is insufficient, in addition, various defects of slow recovery speed, low efficiency and the like exist in the practical application process of many current refrigerant recovery equipment, and the recovery equipment with relatively high recovery speed has the problems of large volume, inconvenience in carrying and the like.

For example, referring to fig. 6, fig. 6 is a schematic structural diagram of a conventional combined gas-liquid recovery system, which is a refrigerant recovery apparatus having the highest recovery efficiency, and the combined recovery method adopted by the system includes both a liquid recovery method and a gas recovery method. In the recovery process, firstly, the refrigerant in the recovered equipment 1 'is recovered in a liquid state (in the direction shown by the X line in fig. 4), the compressor unit 2' is used for exhausting gas to the recovered equipment 1 'for pressurization, the liquid refrigerant is pressurized to the recovery tank 5', and after about 90% of the refrigerant is recovered, the refrigerant cannot be recovered gradually when the recovery rate is reduced; by manually controlling the four-way reversing valve 3', the recovery system is switched to a gas compression recovery method (direction shown by Y line in fig. 4), and the gas refrigerant remaining in the recovery device 1' is sucked by the compressor unit 2', condensed by the heat exchanger 4', and recovered into the recovery tank 5 '. Meanwhile, the gas recovery pipeline and the liquid recovery pipeline are both provided with valves 6' to control the flow of each pipeline; however, in the controlled recovery process of this system, the switching time node between the liquid recovery and the gas recovery is controlled randomly by the operator by experience, and if the switching time is too early or too late, it is difficult to ensure the most reasonable recovery efficiency and recovery rate.

In order to solve the above problems, the present invention provides a refrigerant recovery system and a control method thereof, in which a convergent-divergent nozzle and a mixing container are provided on a conventional refrigerant recovery device, and a low pressure is generated when the convergent-divergent nozzle sprays, so that a gaseous refrigerant and a liquid refrigerant sprayed by the convergent-divergent nozzle converge into the mixing container and enter a condenser together for recovery. The refrigerant recovery system can simultaneously recover the gas-liquid two-phase refrigerant without manually switching the recovery mode, simplifies the operation steps of the recovery system to a certain extent, accelerates the recovery efficiency of the system and recovers as much refrigerant as possible; in addition, only a mixing container is required to be added to the traditional recovery equipment, so that the method is simple and convenient, devices such as a convergent-divergent nozzle and the like do not need to be modified, and the universality of a recovery system is improved.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

Referring to fig. 1, an embodiment of the present invention provides a refrigerant recovery system, including: the recovery container 1, the compressor 2, the convergent-divergent nozzle 3, the mixing container 4, the condenser 5, and the recovery container 6 further include: a first pipe 7 communicating the first outlet 1a of the recovered vessel 1 with the first inlet 4a of the mixing vessel 4, and the compressor 2 and the convergent-divergent nozzle 3 being provided in series on the first pipe 7; a second pipeline 9 for communicating the mixing outlet 4c of the mixing container 4 with the recovery port of the recovery container 6, and the condenser 5 is disposed on the second pipeline 9; and a liquid recovery line 8 for connecting the second outlet 1b of the recovered vessel 1 and the second inlet 4b of the mixing vessel 4.

Specifically, the first line 7 includes a first branch 71, a second branch 72 and a third branch 73 which are communicated in sequence, and the second line 9 includes a fourth branch 91 and a fifth branch 92 which are communicated in sequence, that is, the first branch 71, the second branch 72, the third branch 73, the fourth branch 91 and the fifth branch 92 are communicated to form a gaseous refrigerant recovery line. The recovered container 1 includes a first outlet 1a and a second outlet 1b, and the recovery container 6 includes a recovery inlet 6 a; the mixing vessel 4 comprises a first inlet 4a, a second inlet 4b and a mixing outlet 4 c. The first outlet 1a of the recovered container 1 is communicated with the inlet of the compressor 2 through a first branch 71, the outlet of the compressor 2 is communicated with the inlet of the convergent-divergent nozzle 3 through a second branch 72, the outlet of the convergent-divergent nozzle 3 is connected with the first inlet 4a of the mixing container 4 through a third branch 73, the mixed material outlet 4c of the mixing container 4 is connected with the inlet of the condenser 5 through a fourth branch 91, the outlet of the condenser 5 is communicated with the recovery inlet 6a of the recovery container 6 through a fifth branch 92, and the first outlet 1a of the recovered container 1 is communicated with the second inlet 4b of the mixing container 4 through the liquid recovery pipeline 8.

The compressor 2 sucks the gaseous refrigerant in the recovered container 1, carries out isentropic compression, discharges the high-temperature and high-pressure gaseous refrigerant to enter the nozzle of the inlet of the convergent-divergent nozzle 3, and has accelerated flow rate due to the smaller flow passage, a low pressure is generated at the outlet of the convergent-divergent nozzle 3, the injected gaseous refrigerant enters the mixing container 4, the pressure in the third branch 73 is reduced, a low pressure is generated in the mixing container 4 communicated with the third branch 73, that is, a pressure difference is generated between the mixing container 4 and the recovered container 1, and the liquid refrigerant in the recovered container 1 is subjected to the pressure difference, directly enter the mixing container 4 through the second pipeline 9, the liquid refrigerant is mixed with the high-temperature high-pressure gaseous refrigerant sprayed by the convergent-divergent nozzle 3 and then enters the condenser 5 for condensation, and the condensate enters the recovery container 6 through the fourth branch 91, so that the recovery process of the refrigerant is realized.

Therefore, in the refrigerant recovery system provided by the embodiment of the invention, under the coordination of the convergent-divergent nozzle 3 and the mixing container 4, the first pipeline 7 and the liquid recovery pipeline 8 realize simultaneous recovery of gas-liquid two-phase refrigerant, on one hand, the recovery mode does not need to be manually switched, the operation steps of the recovery system are simplified to a certain extent, the recovery time is effectively shortened, and the recovery efficiency is further improved; on the other hand, since the liquid refrigerant is not compressed by the compressor 2 through the gasification process, the suction and exhaust amount of the compressor 2 can be reduced, and the condensation load of the condenser 5 is reduced, so that the service life of the whole refrigerant recovery system is prolonged, and in addition, the mixing container 4 can also be used as a buffer area, so that the flow rate and the pressure of the refrigerant are effectively reduced, and the protection of the condenser 5 is improved.

In the embodiment of the invention, the convergent-divergent nozzle 3 is a laval nozzle, the front half part of the laval nozzle is contracted from big to small to a narrow throat from middle, and the narrow throat is expanded from small to big outwards, the structure can ensure that the speed of the gas flow is changed due to the change of the nozzle cross section area to play the role of a 'flow rate amplifier', if the gas speed is higher, the pressure is lower, the gas flow speed from the laval nozzle is very high (supersonic speed is possible, and the supersonic speed is generally not), therefore, the process of isentropic injection can cause the extremely low pressure (possibly lower than the atmospheric pressure) of the mixing container 4.

It will be appreciated that although the first conduit 7 may be considered a gaseous recovery conduit, the first outlet 1a of the recovered vessel 1 may be considered a gaseous outlet, the second outlet 1b may be considered a liquid outlet, the first inlet 4a of the mixing vessel 4 may be considered a gaseous inlet, and the second inlet 4b may be considered a liquid inlet. However, the definitions herein as the gaseous outlet and the liquid outlet are only for the sake of clarity of description, and are not a limitation on the state of the refrigerant flowing out, that is, the liquid refrigerant or the gaseous refrigerant may flow out from the first outlet 1a or the second outlet 1 b. The recycling container 6 commercially available at present comprises a high inlet pipe and a low inlet pipe, in the embodiment of the present invention, the first inlet 4a of the mixing container 4 is a high inlet, the second inlet 4b thereof is a low inlet, correspondingly, the first pipeline 7 is a high inlet pipe, and the liquid recycling pipeline 8 is a low inlet pipe, thereby reducing the flow resistance of the refrigerant to some extent and increasing the recycling speed.

In addition, because the liquid refrigerant directly enters the mixing container 4 under the action of pressure difference, the liquid refrigerant is continuously evaporated in the recovered container 1 so as to keep the recovery pressure of the system unchanged, and the recovery time of the liquid refrigerant is shorter than that of the gaseous refrigerant, therefore, along with the recovery process, the liquid refrigerant is recovered first, and only pure gaseous refrigerant is left in the recovered container 1 finally. In this state, since the recovery vessel 1 is always in a relatively high pressure environment with respect to the mixing vessel 4, the gaseous refrigerant enters the mixing vessel 4 through the liquid recovery line 8, and is finally condensed by the condenser 5 to be supplied to the recovery vessel 6.

It will be appreciated that the pressure in the mixing vessel 4 will vary depending on the amount of gaseous or liquid refrigerant entering as the recovery process progresses, and that the refrigerant recovery system further comprises a pressure sensor 12, the pressure sensor 12 being arranged in the mixing vessel 4 for obtaining the pressure at the second inlet 4b and controlling the flow in the liquid recovery line 8, and/or in the second line 9, depending on the obtained pressure, in order to facilitate better control of the recovery process.

Therefore, the pressure sensor 12 is arranged in the mixing container 4, and the acquired pressure at the second inlet 4b is used as a control parameter for controlling the flow of the liquid recovery pipeline 8 and the flow of the second pipeline 9, so that the control precision of the refrigerant recovery system can be further improved, the situation that when the pressure difference is too small, the liquid recovery pipeline 8 is still communicated, excessive refrigerant is retained in the pipeline, and the recovery rate of the system is reduced.

The above-mentioned controlling the flow rate of the liquid recovery pipeline 8 and/or the second pipeline 9 according to the obtained pressure may be an automatic or manual controlling of the flow rate of the liquid recovery pipeline 8 or the second pipeline 9 according to the detected pressure.

Preferably, in the embodiment of the present invention, a second control valve 11 is disposed on the liquid recovery pipeline 8, the second control valve 11 is electrically connected to the pressure sensor 12, and the second control valve 11 is adapted to adjust an opening degree according to the acquired pressure so as to control the flow rate of the liquid recovery pipeline 8.

Therefore, by providing the second control valve 11 on the liquid recovery line 8 and associating the second control valve 11 with the pressure sensor 12, the flow rate of the liquid recovery line 8 can be controlled more quickly and accurately, thereby improving the control accuracy of the refrigerant recovery system.

Further, a first control valve 10 is arranged on a pipeline between the condenser 5 and the recovery container 6, the first control valve 10 is electrically connected with a pressure sensor 12, and the first control valve 10 is suitable for adjusting the opening degree according to the acquired pressure so as to control the flow rate of the second pipeline 9.

Thus, by controlling the opening degree of the first control valve 10 based on the acquired pressure of the second inlet 4b, it is possible to achieve more accurate control of the flow rate and improve the accuracy of control of the refrigerant recovery system.

Furthermore, by controlling the closing of the first and

second control valves

10 and 11 after the refrigerant has been recovered in the recovery tank 6, the amount of refrigerant remaining in the liquid line, the first line 7, and the second line 9 that is discharged to the outside environment can also be reduced when the recovery tank 6 is removed from the recovery system.

In the refrigerant recovery system provided in the above embodiment, the first branch 71 and the first outlet 1a of the recovered container 1, and the liquid recovery pipeline 8 and the second outlet 1b of the recovered container 1 are detachably connected by flanges. Correspondingly, the third branch 73 and the first inlet 4a of the mixing vessel 4, the liquid recovery pipeline 8 and the second inlet 4b of the mixing vessel 4, the fourth branch 91 and the mixing outlet 4c of the mixing vessel 4, and the fifth branch 92 and the recovery inlet 6a of the recovery vessel 6 are also detachably connected through flanges. Of course, the detachable connection can be realized by screw thread fit or other structures, and is not limited to the flange connection. The arrangement is beneficial to the replacement of the recovered container 1, the mixing container 4 and the recovery container 6, and the use scene of the refrigerant recovery system is enlarged.

The refrigerant recovery system provided by the embodiment of the invention can be used for recovering the refrigerant in a motor vehicle air conditioner or a household air conditioning unit or an industrial refrigeration air conditioning system.

To further explain the recovery rate of the refrigerant recovery system according to the embodiment of the present invention, the recovery rate of the refrigerant recovery system (referred to as the recovery system 1) according to the embodiment of the present invention is compared with the recovery rate of the conventional gas-liquid composite recovery system (referred to as the recovery system 2), and the recovery container 1 is an air conditioner unit.

At present, the refrigerant recovery (about the rated charge of the unit) is selected according to the rated power of the compressor 2 and the corresponding recovery speed, as shown in table 1:

TABLE 1 recovery speed and rated charge corresponding table

Meanwhile, for the low-pressure sucked liquid refrigerant in the mixing container 4, the gas injection ratios (i.e., the liquid amounts injected by one gas) of the convergent-divergent nozzle corresponding to the equipment pressures with different rated charge amounts or different refrigerants are also different, and the corresponding relationship between the rated charge amount and the gas injection ratio is shown in table 2, wherein the recovered container 1 is an air conditioner unit, and the refrigerant is R22:

TABLE 2 corresponding table of rated charge and gaseous injection ratio

Rated charge/(kg)	Gaseous injection ratio
		≤200kg	1.2
200kg < rated charge < 500kg	1.0
		Rated charging amount is more than or equal to 500kg and less than or equal to 1000kg	0.9
＞1000kg	0.75

It will be appreciated that the ratio of the simultaneous recovery of liquid and vapor refrigerant to the overall recovery process (which is approximately equal to the liquid refrigerant ratio of the original system) determines the overall recovery efficiency, regardless of the effect of the evaporation of liquid refrigerant on the vapor-liquid ratio of the recovered vessel.

Assuming that the original liquid refrigerant accounts for 60 percent, the approximate rated charge of the unit needing to be recovered is 400kg, and the gaseous injection ratio is 1.0 by combining the corresponding relations of the tables 1 and 2.

For the recovery system 2, the liquid refrigerant is recovered first, and then the gaseous refrigerant is recovered, when the recovery speed of the pure liquid refrigerant is 200kg/h, and the recovery speed of the pure gaseous refrigerant is 50kg/h, the total recovery time of the recovery system 2 can be calculated to be 240/200+ 160/50-4.4 h; when the recovery rate of the pure liquid refrigerant is 300kg/h and the recovery rate of the pure gaseous refrigerant is 70kg/h, the total recovery time of the recovery system 2 can be calculated to be 240/300+ 160/70-3.086 h, that is, the refrigerant recovery time of the recovery system 2 is 3.086-4.4h h.

With the recovery system 1, the gas-liquid refrigerant is recovered at the same time, and the liquid refrigerant is recovered first. With reference to table 1, when the recovery rate of pure liquid refrigerant is 200kg/h and the recovery rate of pure gaseous refrigerant is 50kg/h, the total recovery time of refrigerant in the recovery system 1 can be calculated to be 240/200+ {160- (240/200) × 50}/50 ═ 3.2 h; when the recovery rate of pure liquid refrigerant is 300kg/h and the recovery rate of pure gaseous refrigerant is 70kg/h, the recovery time of the recovery system 1 can be calculated to be 240/300+ {160- (240/300) × 70}/70 ═ 2.28h, that is, the refrigerant recovery time of the recovery system 1 is 2.28 to 3.2 h.

As can be seen from the comparison, the recovery speed of the refrigerant recovery system for simultaneously recovering the gas phase and the liquid phase provided by the embodiment of the invention is higher than that of the existing gas-liquid composite recovery system, and the recovery efficiency is improved by about 26.12% -27.27%. The calculation process is as follows: 0.806/3.086 is 26.12%, 1.2/4.4 is 27.27%.

Referring to fig. 2, another embodiment of the present invention further provides a control method of the refrigerant recovery system, including the steps of:

s1, after the refrigerant recovery system enters a refrigerant recovery mode, the gaseous refrigerant compressed by the compressor 2 is subjected to isentropic injection through the convergent-divergent nozzle 3, and low pressure is formed in the mixing container 4 of the refrigerant recovery system to obtain the pressure in the mixing container 4;

s2, controlling the flow rate of the liquid recovery line 8 of the refrigerant recovery system according to the acquired pressure.

Therefore, after the refrigerant recovery system enters a refrigerant recovery mode, the pressure in the mixing container 4 is obtained in real time, and the pressure of the second inlet 4b in the mixing container 4 is used as a control parameter of the refrigerant flow in the liquid recovery pipeline 8, on one hand, through the matching of the convergent-divergent nozzle 3 and the mixing container 4, the liquid refrigerant can directly enter the mixing container 4 through the liquid recovery pipeline 8 and is mixed with the high-temperature and high-pressure gaseous refrigerant in the mixing container 4, so that the simultaneous recovery of the gas-liquid two-phase refrigerant is realized, the recovery time is effectively shortened, and the recovery efficiency is improved; on the other hand, since the refrigerant (liquid refrigerant) which is not compressed is mixed with the refrigerant compressed in the mixing container 4 by the compressor 2, the temperature and pressure of the refrigerant entering the condenser 5 are reduced to some extent, and it is not necessary to condense all the refrigerant in the recovered container 1, and the refrigerant directly entering the mixing container 4 does not increase the condensation load, so that the condensation load is reduced, thereby prolonging the service life of the whole refrigerant recovery system.

Since the recovery rate of the liquid refrigerant is higher than that of the gaseous refrigerant, the refrigerant recovered through the liquid recovery pipeline 8 may include the liquid refrigerant and the gaseous refrigerant in the recovered container 1, and thus, switching between gas-liquid recovery modes is not required, the operation steps are simplified, and the refrigerant recovery rate is improved.

Specifically, as shown in fig. 3, the refrigerant recovery mode of step S1 includes:

s11, after receiving the starting signal of the refrigerant recovery system, controlling to start the compressor 2;

s12, the compressor 2 compresses the gaseous refrigerant sucked into the compressor 2 through the first pipe 7;

in this step, the gaseous refrigerant in the recovery tank 1 is sucked into the compressor 2; while the liquid refrigerant continues to evaporate in the recovered vessel 1 to maintain the recovery pressure of the apparatus constant.

S13, performing isentropic injection on the gaseous refrigerant compressed by the compressor 2 through the convergent-divergent nozzle 3;

after the isentropic spraying process of the convergent-divergent nozzle 3, a pipeline (namely, the third branch 73) connected with the outlet of the convergent-divergent nozzle 3 forms a low-pressure environment, the third branch 73 is communicated with the pressurized pipeline mixing container 4, the pressure in the mixing container 4 is reduced, a pressure difference is generated between the mixing container 4 and the recovered container 1, and under the action of the pressure difference, the liquid refrigerant below the recovered container 1 directly enters the mixing container 4 through the liquid recovery pipeline 8.

S14, the liquid refrigerant or the gaseous refrigerant in the recovered container 1 enters the mixing container 4 through the liquid recovery line 8 under the action of the pressure difference, and is mixed with the gaseous refrigerant sprayed from the convergent-divergent nozzle 3 in the mixing container 4.

A pressure difference is generated between the mixing container 4 and the recovered container 1, under the action of the pressure difference, the liquid refrigerant below the recovered container 1 directly enters the mixing container 4 through the liquid recovery pipeline 8, meanwhile, when the uncompressed refrigerant is mixed with the refrigerant compressed by the compressor 2, the pressure in the mixing container 4 is not completely the same, that is, the pressure at the first inlet 4a is much lower than that at the second inlet 4b, therefore, preferably, a pressure sensor 12 can be arranged at the second inlet 4b of the mixing container 4, and the liquid refrigerant can be sucked into the mixing container 4 only when the pressure at the second inlet 4b and the recovered container 1 generate a sufficient pressure difference. The performance of low pressure generated when the convergent-divergent nozzle 3 sprays can be utilized, and the pressure at the second inlet 4b of the mixing container 4 is used as a control parameter to control the operation state of the liquid recovery pipeline 8 in the refrigerant recovery process.

S15, the injected refrigerant is condensed by the condenser 5, and the condensed liquid refrigerant is recovered in the recovery tank 6.

Thus, by specifying the operation state of each device in the refrigerant recovery system, the flow rate of the liquid recovery line 8 can be controlled more quickly and accurately, and the control accuracy of the refrigerant recovery system can be improved.

Referring to fig. 4, in step S2, the method for controlling the flow rate of the liquid recovery line 8 of the refrigerant recovery system according to the obtained pressure P includes:

s21, comparing the obtained pressure P with a preset pressure in the refrigerant recovery system;

s22, adjusting the opening of the second control valve 11 disposed on the liquid recovery line 8 according to the comparison result to control the flow rate of the liquid recovery line 8.

Therefore, the acquired pressure is compared with the preset pressure, and the opening degree of the second control valve 11 is controlled according to the comparison result, so that the flow change state in the liquid recovery pipeline 8 is specified, the control precision of the refrigerant recovery system can be further improved, unnecessary communication is avoided, and the energy consumption is saved.

In step S22, the adjusting the opening degree of the second control valve 11 disposed on the liquid recovery line 8 according to the comparison result to control the flow rate of the liquid recovery line 8 includes:

s221, if the acquired pressure P is smaller than a first preset pressure P1(P is smaller than P1), controlling the opening degree of the second control valve 11 according to a first rule;

s222, if the acquired pressure P is greater than or equal to a first preset pressure P1 and the acquired pressure is less than or equal to a third preset pressure (P1 is greater than or equal to P3), controlling the opening of the second control valve 11 according to a second rule;

and S223, if the acquired pressure P is greater than the third preset pressure P3(P is greater than P3), controlling the opening degree of the second control valve 11 according to a third rule.

It will be appreciated that the amount of refrigerant in the recovered vessel 1 will affect the gaseous injection ratio of the convergent-divergent nozzle 3 and thus the pressure in the mixing vessel 4, and that the recovery rate will be affected with great possibility if the opening of the second control valve 11 is kept constant for different refrigerant recovery conditions.

Therefore, in the embodiment, the acquired inlet pressure P is used as a control parameter and is compared with the first preset pressure P1 and the third preset pressure P3, and then the opening rule met by the second control valve 11 is judged, so that the control precision of the liquid recovery pipeline 8 can be further improved, and the control stability of the system is improved.

Preferably, the first rule comprises: controlling the second control valve 11 to be 100% open, that is, when P < P1, indicates that the pressure difference between the mixing container 4 and the recovered container 1 is large, which is favorable for the suction of the liquid refrigerant, and therefore, the second control valve 11 is maintained in a fully open state, so that the maximum amount of liquid refrigerant enters the mixing container 4, thereby increasing the recovery rate of the refrigerant.

Further, the first rule further includes:

if the obtained pressure P is less than the fourth preset pressure P4, controlling the compressor 2 to stop running and sending a reminding signal; wherein the fourth preset pressure P4 is less than the first preset pressure P1.

When P < P4, it means that the pressure in the mixing vessel 4 is extremely low and may affect the overall stability of the system, and it means that the refrigerant in the recovery vessel 1 is not suitable for recovery using the recovery system provided by the present invention. At this time, the compressor 2 is controlled to stop running, and after the running is stopped, the sound control module in the refrigerant recovery system gives out a prompt: by means of the arrangement, the use safety of the system can be improved, and potential safety hazards in the recycling process are avoided.

Wherein the second rule comprises:

if the acquired pressure P is greater than or equal to the first preset pressure P1 and the acquired pressure P is less than the second preset pressure P2(P1 is greater than or equal to P < P2), controlling the opening of the second control valve 11 to be reduced in an equal ratio within the range of 100-50% of the opening according to the acquired pressure;

if the acquired pressure P is equal to the second preset pressure P2(P — P2), the second control valve 11 is controlled to 50% open;

if the acquired pressure P is greater than the second preset pressure P2 and the acquired pressure P is less than or equal to a third preset pressure P3(P2 is greater than P and less than or equal to P3), controlling the opening of the second control valve 11 to be reduced in an equal ratio within the range of 50-0% of the opening according to the acquired pressure;

the first preset pressure P1 is less than the second preset pressure P2, and the second preset pressure P2 is less than the third preset pressure P3, i.e. P4 < P1 < P2 < P3.

The opening degrees of the second control valve 11 corresponding to the pressures acquired by the devices with different amounts of the recovered refrigerant or different refrigerants are different, and according to the experience data of the inventor, the opening degree of the second control valve 11 is further refined by comparing the acquired pressure P with the first preset pressure P1, the second preset pressure P2 and the third preset pressure P3, so that the valve opening degree matched with the acquired pressure P is adaptively selected according to the difference of the acquired pressure, and the refrigerant recovery system is more accurately controlled.

In addition, the values of the first preset pressure P1, the second preset pressure P2, the third preset pressure P3 and the fourth preset pressure are all in positive correlation with the refrigerant rated charge of the recovered container 1.

The lower limit of the low pressure formed after the isentropic injection of the convergent-divergent nozzle 3 is increased as the rated refrigerant charge is increased, and therefore, the preset parameters P1, P2, P3 and P4 in the judgment of the opening degree of the second control valve 11 are increased accordingly, thereby further improving the regulation accuracy of the liquid recovery line 8.

Wherein the third rule comprises: the opening degree of the second control valve 11 is controlled to 0. That is, when P ≧ P3, it means that the pressure difference between the mixing container 4 and the recovered container 1 is small, and the liquid refrigerant cannot be sucked into the mixing container 4 under this pressure, so the second control valve 11 is kept in the closed state, and it is avoided that when the pressure difference is too small, the liquid recovery pipeline 8 still has refrigerant flowing, and excessive refrigerant remains in the pipeline, which reduces the system recovery rate.

In addition, as shown in fig. 5, in order to further improve the control accuracy of the refrigerant recovery system, the fifth branch 92 is provided with a second control valve 11, and the method for controlling the refrigerant recovery system further includes:

s3, acquiring the rated charging amount of the recovered container 1;

s4, adjusting the opening degree of the first control valve 10 provided on the second line 9 according to the acquired pressure and the rated charge amount to control the flow rate of the second line 9.

It is to be understood that, although the invention has described the steps in the preparation in forms of S1, S2, S3, S4, etc., this description is only for ease of understanding, and the forms of S1, S2, S3, S4, etc. do not represent a limitation on the order of the steps. That is, step S3 of the present invention may be performed after step S1, or simultaneously with steps S1 and S3, and simultaneously with steps S2 and S4.

The rated charging amount determines the power of the compressor of the selected recovery system, so that the pressure of the compressed gas reaching the mixing container 4 is different, therefore, after the refrigerant recovery system enters the refrigerant recovery mode, the rated charging amount of the recovered container 1 is obtained in addition to the pressure in the mixing container 4 in real time, and the obtained pressure and the rated charging amount are used as control parameters of the first control valve 10, so that the control precision of the refrigerant recovery system is further improved.

In step S4, adjusting the opening degree of the first control valve 10 disposed on the second pipeline 9 according to the acquired pressure and the rated charge amount to control the flow rate of the second pipeline 9 includes:

s41, comparing the rated filling amount of the recovered container 1 with a preset filling value;

s42, if the rated charging amount is larger than or equal to the preset charging value, adjusting the opening of the first control valve 10 according to the acquired pressure;

s43, if the rated charge is smaller than the preset charge, the first control valve 10 is controlled to be 100% open.

When the rated charging amount is smaller than the preset charging value, the influence of the total amount of the refrigerant in the recovered container 1 on the second pipeline 9 is not large, and at the moment, the first control valve 10 is kept in a full-open state, so that the speed of the refrigerant flowing to the recovery container 6 is kept to the maximum extent, and the recovery speed of the refrigerant is improved. Whereas when the nominal charge is greater than or equal to the preset charge value, the amount of refrigerant in the recovered container 1 is correlated with the opening degree of the first control valve 10, if the opening degree of the first control valve 10 is kept constant for different refrigerant recovery conditions, the recovery rate is greatly affected. Accordingly, the control accuracy of the refrigerant recovery system can be further improved and the operation stability of the system can be improved by determining the opening degree of the first control valve 10 using the acquired pressure P and the rated charge amount as control parameters.

Wherein the step S41 of adjusting the opening degree of the first control valve 10 according to the acquired pressure includes:

if the acquired pressure P is less than or equal to a second preset pressure P2(P is less than or equal to P2), controlling the first control valve 10 to be 100% open;

if the acquired pressure P is greater than the second preset pressure P2 and the acquired pressure P is less than or equal to a third preset pressure P3(P2 < P ≦ P3), controlling the opening of the first control valve 10 to decrease proportionally within the range of 100% -50% opening according to the acquired pressure P;

if the acquired pressure P is greater than the third preset pressure P3(P > P3), the first control valve 10 is controlled to 50% open.

It can be understood that when the acquired pressure P is less than or equal to the second preset pressure P2, the inlet pressure in the mixing container 4 is relatively low, the injection liquid amount is relatively large, and the opening degree of the first control valve is controlled at 100% to meet the recovery rate and the buffering requirement. When the obtained pressure P is higher than the third preset pressure P3, the inlet pressure in the mixing container 4 is relatively not very small, the injection liquid amount is not large, but injection is still performed, and in order to meet the requirements of recovery speed and buffering, the opening degree of the first control valve still needs to be controlled at 50%.

Therefore, the opening degrees of the first control valve 10 corresponding to the pressures acquired by the devices with different amounts of the recovered refrigerants or different refrigerants are different, and according to the experience data of the inventor, when the rated charge amount is larger than or equal to the preset charge value, the acquired pressure P is compared with the second preset pressure P2 and the third preset pressure P3, so that the opening degree of the first control valve 10 is further refined, and therefore, the valve opening degree matched with the acquired pressure P is adaptively selected according to the difference of the acquired pressure, and the refrigerant recovery system is controlled more accurately.

TABLE 3 nominal charge, acquired pressure, first control valve opening, second control valve opening correspondence table

To better explain the relationship between the rated refrigerant charge amount, the acquired pressure in the mixing container 4, and the opening degrees of the first control valve 10 and the second control valve 11 in the control method of the refrigerant recovery system according to the above embodiment, the inventors have made a description based on research and development experience with an air conditioning unit as the recovered container 1 and with R22 refrigerant as an example, as shown in table 3:

as can be seen from table 3, in the case where the bank rated charge is greater than or equal to 800kg, the first preset pressure P1 is set to 0.3atm (0.8 atm), the second preset pressure P2 is set to 0.6atm, the third preset pressure P3 is set to 0.9atm, and the fourth preset pressure P4 is set to-0.1 atm.

When the pressure sensor detects that the pressure of the second inlet 4b in the mixing container is less than 0.3atm, the second control valve 11 is fully opened, and the first control valve 10 is fully opened; when the acquired pressure is 0.6atm, the opening degree of the second control valve 11 is 50%, and the opening degree of the first control valve 10 is 100%; when the acquired pressure is greater than 0.9atm, the opening degree of the second control valve 11 is 0%, and the opening degree of the first control valve 10 is 50%; when the acquired pressure is in the range of 0.3-0.6atm, the opening degree of the second control valve 11 corresponds to the acquired pressure in equal proportion, the opening degree of the first control valve 10 is maintained at 100%, namely the opening degree of the second control valve 11 is in the range of 100-50%, and is reduced in equal proportion with the increase of the acquired pressure; when the acquired pressure is in the range of 0.6-0.9atm, the opening degree of the second control valve 11 and the opening degree of the first control valve 10 both correspond to the acquired pressure in equal proportion, namely the opening degree of the second control valve 11 is in the range of 50% -0%, and is reduced in equal proportion along with the increase of the acquired pressure; the opening degree of the first control valve 10 is in the range of 100% -50%, and decreases in equal proportion to the increase in the acquired pressure.

When the pressure sensor 12 detects that the pressure at the second inlet 4b in the mixing container 4 is less than-0.1 atm, although the opening degrees of the first control valve 10 and the second control valve 11 are both 100%, the operation of the compressor 2 of the refrigerant recovery system needs to be controlled to stop at the time of safety and stability, and furthermore, a warning sound "please recover with a proper recovery machine" can be emitted.

In the case where the battery set rated charge is less than 800kg, the first preset pressure P1 is set to 0.2atm, the second preset pressure P2 is set to 0.4atm, the third preset pressure P3 is set to 0.8atm, and the fourth preset pressure P4 is set to 0 atm. At this time, the first control valve 10 is always kept in the non-fully opened state, and when the pressure sensor 12 detects that the pressure of the second inlet 4b in the mixing container 4 is less than 0atm, although the opening degree of the first control valve 10 is also 100%, it is necessary to control the compressor 2 of the refrigerant recovery system to stop operation at this time for safety and stability, and further, an alarm "please recover with an appropriate recovery machine" may be issued.

When the pressure sensor 12 detects that the pressure at the second inlet 4b in the mixing container 4 is less than 0.2atm, the second control valve 11 is fully opened; when the acquired pressure is at 0.4atm, the opening degree of the second control valve 11 is 50%; when the acquired pressure is greater than 0.8atm, the opening degree of the second control valve 11 is 0%; when the acquired pressure is in the range of 0.2-0.4atm, the opening degree of the second control valve 11 corresponds to the acquired pressure in equal proportion, namely the opening degree of the second control valve 11 is in the range of 100-50%, and decreases in equal proportion with the increase of the acquired pressure; and when the acquired pressure is in the range of 0.4-0.8atm, the opening degree of the second control valve 11 is in the range of 50% -0%, and decreases in equal proportion to the increase of the acquired pressure.

Here, the geometric decrease means that the opening degree of the second control valve/the first control valve is gradually decreased as the acquired inlet pressure increases, and the ratio of the decreased opening degree value to the increased value of the inlet pressure is the same. For example, when the refrigerant R22 is charged with 900kg and the obtained pressure is 0.1atm, the opening degrees of the first control valve and the second control valve are both 100%; when the acquired pressure is 0.4atm, the opening degree of the second control valve is 83.3%, and the opening degree of the first control valve is 100%; when the acquired pressure is 0.7atm, the opening degree of the second control valve is 33.3%, and the opening degree of the first control valve is 83.3%.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method of controlling a refrigerant recovery system, comprising:

the device comprises a compressor (2), a convergent-divergent nozzle (3), a mixing container (4) and a liquid recovery pipeline (8); the compressor (2) and the convergent-divergent nozzle (3) are arranged in series; the convergent-divergent nozzle (3) is communicated with a first inlet (4 a) of the mixing container (4) through a branch; the liquid recovery line (8) is in communication with a second inlet (4 b) of the mixing vessel (4);

after the refrigerant recovery system enters a refrigerant recovery mode, the gaseous refrigerant compressed by the compressor (2) is subjected to isentropic injection through the convergent-divergent nozzle (3), and low pressure is formed in a mixing container (4) of the refrigerant recovery system to obtain the pressure in the mixing container (4);

controlling the flow of a liquid recovery line (8) of the refrigerant recovery system according to the obtained pressure;

and comparing the obtained pressure with a preset pressure in the refrigerant recovery system, and adjusting the opening degree of a second control valve (11) arranged on the liquid recovery pipeline (8) according to the comparison result so as to control the flow rate of the liquid recovery pipeline (8).

2. The refrigerant recovery system control method according to claim 1, wherein the refrigerant recovery system enters a refrigerant recovery mode including:

after a starting signal of the refrigerant recovery system is received, controlling to start the compressor (2);

-said compressor (2) compresses a gaseous refrigerant drawn into said compressor (2) through a first line (7);

the compressed gaseous refrigerant is subjected to isentropic injection by using the convergent-divergent nozzle (3);

liquid refrigerant or gaseous refrigerant in the recovered container (1) enters the mixing container (4) through the liquid recovery pipeline (8) under the action of pressure difference, and is mixed with the gaseous refrigerant sprayed out of the convergent-divergent nozzle (3) in the mixing container (4);

the mixed refrigerant is condensed by a condenser (5), and the condensed refrigerant is recovered in a recovery vessel (6).

3. A control method of a refrigerant recovery system according to claim 1, wherein the adjusting an opening degree of a second control valve (11) provided on the liquid recovery line (8) according to the comparison result to control a flow rate of the liquid recovery line (8) comprises:

if the acquired pressure is smaller than a first preset pressure, controlling the opening degree of the second control valve (11) according to a first rule;

if the acquired pressure is greater than or equal to a first preset pressure and the acquired pressure is less than or equal to a third preset pressure, controlling the opening of the second control valve (11) according to a second rule;

and if the acquired pressure is greater than the third preset pressure, controlling the opening degree of the second control valve (11) according to a third rule.

4. A control method of a refrigerant recovery system according to claim 3, wherein the first rule includes: controlling the second control valve (11) to be 100% open;

the second rule includes:

if the acquired pressure is greater than or equal to the first preset pressure and the acquired pressure is less than a second preset pressure, controlling the opening of the second control valve (11) to reduce in an equal ratio within the range of 100-50% of the opening according to the acquired pressure;

if the acquired pressure is equal to the second preset pressure, controlling the second control valve (11) to be 50% in opening degree;

if the acquired pressure is greater than the second preset pressure and the acquired pressure is less than or equal to the third preset pressure, controlling the opening of the second control valve (11) to be reduced in an equal ratio within the range of 50% -0% of the opening according to the acquired pressure;

the third rule includes: controlling the opening degree of the second control valve (11) to be 0;

5. The refrigerant recovery system control method according to claim 3, wherein the first rule further includes:

if the acquired pressure is smaller than a fourth preset pressure, controlling the compressor (2) to stop running and sending out a reminding signal; wherein the fourth preset pressure is less than the first preset pressure.

6. The refrigerant recovery system control method according to claim 2, further comprising:

obtaining the rated filling amount of the recovered container (1);

and adjusting the opening degree of a first control valve (10) arranged on a second pipeline (9) according to the acquired pressure and the rated charging amount so as to control the flow rate of the second pipeline (9).

7. The refrigerant recovery system control method according to claim 6, wherein said adjusting the opening degree of a first control valve (10) provided on a second line (9) in accordance with the acquired pressure and the rated charge amount includes:

if the rated charging amount is larger than or equal to a preset charging value, adjusting the opening degree of the first control valve (10) according to the acquired pressure;

and if the rated charging amount is smaller than a preset charging value, controlling the first control valve (10) to be 100% in opening degree.

8. The control method of a refrigerant recovery system according to claim 7, wherein said adjusting the opening degree of the first control valve (10) according to the acquired pressure comprises:

if the acquired pressure is less than or equal to a second preset pressure, controlling the first control valve (10) to be 100% in opening degree;

if the acquired pressure is greater than the second preset pressure and the acquired pressure is less than or equal to a third preset pressure, controlling the opening of the first control valve (10) to reduce in an equal ratio within the range of 100-50% of the opening according to the acquired pressure;

and if the acquired pressure is greater than the third preset pressure, controlling the first control valve (10) to be 50% in opening degree.

9. A refrigerant recovery system for implementing the control method of claims 1 to 8, the refrigerant recovery system comprising a recovered vessel (1), a compressor (2), a convergent-divergent nozzle (3), a mixing vessel (4), a condenser (5) and a recovery vessel (6),

the refrigerant recovery system further includes:

a first line (7) communicating the first outlet (1 a) of the recovered vessel (1) with the first inlet (4 a) of the mixing vessel (4), and the compressor (2) and the convergent-divergent nozzle (3) being arranged in series on the first line (7);

a second line (9) communicating the mixing outlet (4 c) of the mixing vessel (4) with the recovery inlet (6 a) of the recovery vessel (6), and the condenser (5) being arranged on the second line (9);

a liquid recovery line (8) communicating the second outlet (1 b) of the recovered container (1) with the second inlet (4 b) of the mixing container (4).

10. The refrigerant recovery system according to claim 9, further comprising:

a pressure sensor (12) arranged within the mixing vessel (4) for obtaining a pressure at the second inlet (4 b) for controlling the flow of the liquid recovery line (8) and/or the second line (9).

11. The refrigerant recovery system according to claim 10, wherein a second control valve (11) is provided on the liquid recovery line (8), said second control valve (11) being electrically connected to the pressure sensor (12), said second control valve (11) being adapted to adjust the opening degree according to the acquired pressure to control the flow rate of the liquid recovery line (8);

the condenser (5) and a pipeline between the recovery containers (6) are provided with a first control valve (10), the first control valve (10) is electrically connected with the pressure sensor (12), and the first control valve (10) is suitable for adjusting the opening degree according to the acquired pressure so as to control the flow of the second pipeline (9).