WO2023116070A1

WO2023116070A1 - Vpsa gas separation system and control method therefor

Info

Publication number: WO2023116070A1
Application number: PCT/CN2022/118192
Authority: WO
Inventors: 李伟华; 李传旭; 李波; 李卓; 邓光华; 隆勇; 蒲刚娆
Original assignee: 重庆冲能动力机械有限公司
Priority date: 2021-12-20
Filing date: 2022-09-09
Publication date: 2023-06-29
Also published as: CN114225633A

Abstract

Disclosed is a VPSA gas separation system, comprising a plurality of turbines arranged in parallel and a gas separation assembly. The plurality of turbines are used for conveying air to the gas separation assembly, or vacuumizing the gas separation assembly. Each turbine is connected to a drive motor and a variable frequency drive, all the variable frequency drives being in communication connection with a control apparatus, and the control apparatus being used for controlling the output of the variable frequency drives. The present invention solves the problems in the prior art of the high manufacturing costs of customized large-scale centrifuge units and the small high-efficiency operating range and small adjustable working condition range of large-scale centrifuge units, and has the effects of expanding the adjustable working condition range of the centrifuge unit and reducing the production cost and maintenance cost of the centrifuge unit.

Description

VPSA gas separation system and its control method

technical field

The invention relates to the technical field of VPSA vacuum pressure swing adsorption, in particular to a VPSA gas separation system and a control method thereof.

Background technique

In the existing VPSA gas separation system, the mainstream is based on the Roots machine, and a single or double Roots blower and Roots vacuum pump are used as the power equipment of the system. The advantages and disadvantages of the application of Roots blower as power equipment in VPSA gas separation system have been elaborated (such as CN108678973A). The characteristics of Roots blower such as low efficiency, large noise, and small capacity have seriously restricted the development of the VPSA industry.

The application of centrifugal blower and centrifugal vacuum pump in the VPSA gas separation system can bring many advantages, but also requires targeted improvement and design of the centrifuge. The application of the centrifuge further improves the efficiency of the VPSA gas separation system, and also solves the It solved the problem of exhaust volume and noise, and greatly promoted the development of VPSA industry.

However, the application of large-scale centrifugal units also has two disadvantages. One is the high cost of large-scale centrifugal units. The cost of centrifugal units with fluctuating speeds that meet the working conditions of VPSA gas separation systems is very high, which is 3 to 4 times that of traditional Roots machines. times, there are reasons for strong customization and small batches, as well as the difficulty in supporting and processing large-scale centrifugal units. The motors and frequency converters supporting centrifugal units also need to be customized, and the supporting costs are also very high. The second is the characteristics of the centrifuge unit, which has a small range of high-efficiency zones and a small adjustable range. The characteristics of the centrifuge cannot be as close to straight as the Roots machine. To meet the output requirements of the VPSA gas separation system, a large range of adjustment work is required. The application is subject to certain constraints.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a VPSA gas separation system and its control method, which solves the high manufacturing cost of customized large centrifugal units and the high efficiency working range of large centrifugal units existing in the prior art The problem of small size and small range of adjustable working conditions.

According to an embodiment of the present invention, a VPSA gas separation system includes several turbines and gas separation assemblies arranged in parallel, several turbines are used to deliver air to the gas separation assembly or vacuumize, and each turbine is connected to a The drive motor is connected to the frequency converter, and all the frequency converters are connected with a control device for controlling the output of the frequency converter.

Preferably, the turbines have the same structure and are equipped with the same frequency converter.

Preferably, the turbine is a double-head turbine.

Preferably, the turbine is provided with sensors for respectively detecting the winding temperature of the driving motor, the supporting bearing temperature and the rotor vibration of the turbine, and the gas inlet end of the turbine is provided with detection gas sensors. pressure and transmits a signal to the sensor of the control unit.

Preferably, the plurality of turbines include at least one set of centrifugal blowers and one set of centrifugal vacuum pumps, and the gas separation assembly includes several adsorption towers independently arranged for gas pressure swing adsorption, and the adsorption towers are all provided with product Gas pipeline and raw gas pipeline, a group of centrifugal blowers communicate with the raw gas pipeline through a pipeline with a program-controlled valve, a group of centrifugal vacuum pumps communicate with the raw gas pipeline through another pipeline with a program-controlled valve, and the product gas The pipeline is also provided with a program-controlled valve, which is remotely controlled by the control device, and an air pressure sensor is provided in the adsorption tower.

Preferably, the inlet pipes of the centrifugal blower are all connected to one pipeline, and the inlet end of the pipeline is provided with an inlet filter box, and the outlet pipes of the centrifugal vacuum pump are all connected to another pipeline, and The gas outlet end of the pipeline is provided with a muffler, and the product gas pipelines of the adsorption tower are all connected to another pipeline, and a buffer tank is provided at the gas outlet end of the pipeline.

A control method of a VPSA gas separation system, utilizing the aforesaid VPSA gas separation system,

When adjusting the output of the VPSA gas separation system, determine the quantity of the centrifugal blower and centrifugal vacuum pump put into production;

First, vacuumize one of the adsorption towers through a group of centrifugal vacuum pumps. When the detection value of the air pressure sensor in the adsorption tower reaches the set value, the program-controlled valve is controlled by the control device. remote control, so that the group of centrifugal vacuum pumps vacuumizes the next adsorption tower;

Then a group of centrifugal blowers are used to input raw material gas to the previous adsorption tower. When the air pressure sensor in the adsorption tower detects that the air pressure reaches the set value, it is switched to the other vacuumed adsorption tower through a program-controlled valve. The above-mentioned adsorption towers carry out raw material gas input, and carry out the vacuumizing and raw material gas input of all described adsorption towers in sequence;

Before vacuuming, it is the gas reaction in the adsorption tower and the discharge process of the product gas obtained by the reaction. By controlling the program-controlled valve on the product gas pipeline, the product gas is discharged through the product gas pipeline. During the product gas discharge process In the process, when the pressure value of the air pressure sensor in the adsorption tower drops to the set value, the product gas pipeline is closed and vacuumized. Due to the discharge of product gas, the time for vacuuming during the production process is shorter than the time for conveying gas. .

Preferably, the sum of the vacuuming time of the adsorption tower is equal to the sum of the reaction time of the adsorption tower and the output time of the product gas.

Preferably, according to the inlet air pressure detection values of the centrifugal blower and the centrifugal vacuum pump, the output of the corresponding frequency converter is controlled by the control device.

Compared with the prior art, the present invention has the following beneficial effects:

1. The centrifugal blower or centrifugal vacuum pump installed in parallel is used for gas compression or vacuuming, and by reducing the number of centrifuges invested, it can realize the improvement of the working condition range of the centrifugal unit without adding any additional equipment. Adjustment, expanding the range of adjustable working conditions of the centrifugal unit to meet the demand for output adjustment of the VPSA gas separation system; at the same time, it can ensure that each centrifugal blower or centrifugal vacuum pump invested is in a high-efficiency working range, so that the centrifugal unit can operate at a high efficiency. The whole flow rate of 0-110% working range is adjustable; at the same time, the centrifuge invested in non-customized production, the manufacturing cost of the unit is lower than that of the customized large-scale centrifuge unit, and it is easier to operate and will not cause a long time for equipment maintenance. Downtime can ensure the maintenance of production and reduce the manufacturing cost and maintenance cost of the centrifuge unit.

2. Use at least one set of centrifugal blowers and one set of centrifugal vacuum pumps to inflate and evacuate the adsorption towers in the VPSA gas separation system, and remotely control the program-controlled valves through the control device to achieve alternate inflation and vacuuming between multiple adsorption towers Vacuuming improves the production efficiency. The centrifugal blower and the centrifugal vacuum pump communicate with the raw material gas pipeline of the adsorption tower through a parallel main pipeline, and the main pipeline communicates with the raw gas pipeline of each adsorption tower through a pipeline equipped with a program-controlled valve. , which is convenient for control and reduces the total length of the pipeline, saving costs.

3. By evacuating and inflating each adsorption tower in turn, the time for vacuuming and inflating all adsorption towers is a cycle. After one adsorption tower is vacuumed and inflated, the whole set of centrifugal vacuum pumps and centrifugal blowers will The subsequent adsorption tower is vacuumed and inflated. During this process, the inflated adsorption tower starts to react, and the molecular sieve absorbs part of the gas. After the reaction reaches the time, the product gas starts to be discharged. The vacuuming process and the inflation process are based on the required time. By increasing or reducing the number of centrifugal blowers and centrifugal vacuum pumps, it can not only ensure the accuracy of the process time, but also ensure that each invested centrifugal blower and centrifugal vacuum pump is in a high-efficiency working range.

Description of drawings

Figure 1 is a process flow diagram of an embodiment of the present invention.

Fig. 2 is an efficiency curve diagram of an embodiment of the present invention.

Figure 3 is a graph of pressure P versus time t for a typical VPSA gas separation system.

Fig. 4 is a control operation diagram of a single centrifugal vacuum pump in the embodiment of the present invention.

In the above drawings: 1. Air intake filter box; 2. Centrifugal blower; 3. Frequency converter; 4. Centrifugal vacuum pump; 5. Program-controlled valve; 6. Adsorption tower; 7. Buffer tank; 8. Muffler; 9 1. Raw material gas pipeline; 10. Product gas pipeline.

Detailed ways

The technical solutions in the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1-2, in order to expand the range of adjustable working conditions of the turbine unit in the VPSA gas separation system and reduce the manufacturing cost of the turbine unit, the embodiment of the present invention proposes a VPSA gas separation system, including Several turbines and gas separation components, several turbines are used to deliver air to the gas separation components or vacuumize, each turbine is connected with a drive motor and a frequency converter 3, and all frequency converters 3 are connected with a control device for communication. The device is used to control the output of the frequency converter 3 .

The turbine unit includes two main pipelines and the centrifugal blower 2 or the centrifugal vacuum pump 4 fixedly connected to the two main pipelines, the air inlet pipe and the air outlet pipe respectively. The efficiency curves are known or obtained through measurement. When in use, after the pressure ratio is required for inflation or vacuuming, the number of centrifugal blowers 2 or centrifugal vacuum pumps 4 to be put into use is selected according to the required volume flow rate, that is, to achieve a large The adjustment of the working conditions of the turbine unit within the range; at the same time, when the centrifugal blower 2 or centrifugal vacuum pump 4 fails, the original centrifugal blower 2 or centrifugal vacuum pump 4 is replaced by an unstarted centrifugal blower 2 or centrifugal vacuum pump 4, The faulty centrifugal blower 2 or centrifugal vacuum pump 4 can be repaired, and the VPSA gas separation system continues to run during the maintenance process, which ensures production efficiency and reduces maintenance costs; the centrifugal blower 2 or Existing equipment can be used for the centrifugal vacuum pump 4, and the production requirements of the VPSA gas separation system are met by selecting different centrifugal blowers 2 or centrifugal vacuum pump 4 quantities, further reducing maintenance costs and manufacturing costs. The frequency converter 3 corresponding to the centrifugal blower 2 or the centrifugal vacuum pump 4 is controlled by the control device, and the variable-speed rotation of the rotor of the centrifugal blower 2 or the centrifugal vacuum pump 4 is controlled through the frequency conversion output of the frequency converter 3 to the high-speed motor, so that the centrifugal The type blower 2 or the centrifugal vacuum pump 4 runs along its corresponding efficiency curve to improve the energy efficiency of the turbine unit.

As another embodiment of the present invention, in order to further reduce the production and maintenance costs of the turbine sets, the turbines have the same structure and are equipped with the same frequency converter 3 . By manufacturing the centrifugal blower 2 or the centrifugal vacuum pump 4 as general-purpose equipment, mass production can be carried out in production, and supporting costs can be reduced. 2 or centrifugal vacuum pump 4 has less impact on the VPSA gas separation system; using the same centrifugal blower 2 or centrifugal vacuum pump 4, the overall efficiency curve of the turbine unit is more accurate, and the working condition adjustment of the turbine unit is more accurate precise.

As another embodiment of the present invention, in order to improve the energy efficiency of the centrifugal blower 2 or the centrifugal vacuum pump 4, the turbine is a double-head turbine. By setting the existing low-inertia rotor, that is, the two ends of the motor rotor are coaxially fixedly connected to the impeller of the turbine to realize the form of double heads and reduce the moment of inertia of the rotor. During the process of variable speed rotation of the high-speed motor controlled by the frequency converter , The moment of inertia of the rotor is small, and the centrifugal blower 2 or the centrifugal vacuum pump 4 has a small workmanship to overcome the moment of inertia, thereby improving the energy efficiency of the centrifugal blower 2 or the centrifugal vacuum pump 4 .

As another embodiment of the present invention, in order to understand the working conditions of the centrifugal blower 2 and the centrifugal vacuum pump 4 more accurately, the turbine is provided with a device for detecting the winding temperature of the driving motor, the supporting bearing temperature and the The sensor for the vibration of the rotor of the turbine, the inlet end of the turbine is provided with a sensor for detecting the gas pressure and transmitting the signal to the control device. The motor winding temperature, bearing temperature, and rotor vibration are detected by the sensor on the casing to avoid damage to the motor and bearing due to overheating during use. By detecting the rotor vibration, it can be detected whether the rotor is in a balanced state during operation; When the sensor detects that the centrifugal blower 2 or the centrifugal vacuum pump 4 is in an abnormal state, it can be stopped and replaced by an unstarted unit to ensure the safety of the production process. By detecting the inlet air pressure change of the centrifugal blower 2 or the centrifugal vacuum pump 4, the detected result is transmitted vertically to the control device, and the control device obtains the inlet air pressure change curve, and controls the output fluctuating voltage of the frequency converter 3 according to the inlet air pressure change curve , and then control the rotor of the centrifugal blower 2 or the centrifugal vacuum pump 4 to run along the set speed curve under the changing inlet pressure, so as to realize the high energy efficiency of the centrifugal blower 2 or the centrifugal vacuum pump 4 .

As shown in Figures 1-2, in order to reduce the manufacturing cost of the VPSA gas separation system, the several turbines include at least one group of centrifugal blowers 2 and one group of centrifugal vacuum pumps 4, and the gas separation assembly includes several independently arranged The adsorption tower 6 used for gas pressure swing adsorption, the adsorption tower 6 is provided with a product gas pipeline 10 and a raw gas pipeline 9, and a group of centrifugal blowers 2 communicate with the raw material gas pipeline 9 through a pipeline equipped with a program-controlled valve 5 A group of centrifugal vacuum pumps 4 communicate with the raw gas pipeline 9 through another pipeline provided with a program-controlled valve 5, and the product gas pipeline 10 is also provided with a program-controlled valve 5, which is remotely controlled by the control device, and the adsorption tower 6 is provided with an air pressure sensor.

The switch of the pipeline is controlled by the program-controlled valve 5, the centrifugal blower 2 of the whole group carries out the output of raw material gas through a pipeline, and the centrifugal vacuum pump 4 of the whole group is vacuumized through a pipeline, and three Adsorption tower 6, the end of the general pipeline of described centrifugal blower 2 of whole group and the described centrifugal vacuum pump 4 of whole group all is provided with the shunt pipeline of band program control valve 5 and the feed gas pipeline of three adsorption towers 6 respectively. connected, the three adsorption towers 6 can be alternately inflated and vacuumed to improve production efficiency, reduce the total length of pipelines, and reduce the manufacturing cost of the VPSA gas separation system.

As shown in Figure 1, when using the VPSA gas separation system to produce oxygen, the inlet pipes of the centrifugal blower 2 are all connected to a pipeline, and the inlet end of the pipeline is provided with an inlet filter box 1, the said The gas outlet pipes of the centrifugal vacuum pump 4 are all connected to another pipeline, and the gas outlet end of the pipeline is provided with a silencer 8, and the product gas pipeline 10 of the adsorption tower 6 is connected to another pipeline, and the pipeline A buffer tank 7 is provided at the gas outlet end. Improve the quality of the intake air through the intake filter box 1, reduce the noise of the exhaust process of the VPSA gas separation system through the muffler 8, buffer the product gas through the buffer tank 7, and install an oxygen concentration detection device in the buffer tank 7, The concentration of the product gas is detected, and then the use method of the product gas is felt.

In order to improve the output of the VPSA gas separation system, the embodiment of the present invention proposes a control method for the VPSA gas separation system. When adjusting the output of the VPSA gas separation system, the input of the centrifugal blower 2 and the centrifugal vacuum pump 4 is determined. the quantity produced;

First, vacuumize one of the adsorption towers 6 through a set of centrifugal vacuum pumps 4. When the detection value of the air pressure sensor in the adsorption tower 6 reaches the set value, the control device will control the vacuum. The program-controlled valve 5 is remotely controlled so that the group of centrifugal vacuum pumps 4 vacuumizes the next adsorption tower 6;

Then a group of centrifugal blowers 2 are used to input the raw material gas to the last adsorption tower 6. When the air pressure sensor in the adsorption tower 6 detects that the air pressure reaches the set value, the program control valve 5 is switched to the other adsorption tower 6. The vacuumized adsorption tower 6 carries out raw material gas input, and carries out the vacuumization and raw material gas input of all described adsorption towers 6 in sequence;

Before vacuumizing, it is the gas reaction in the adsorption tower 6 and the discharge process of the product gas obtained by the reaction. By controlling the program-controlled valve 5 on the product gas pipeline 10, the product gas is discharged through the product gas pipeline 10. During the product gas discharge process, when the pressure value of the air pressure sensor in the adsorption tower 6 drops to the set value, the product gas pipeline 10 is closed to vacuumize. Due to the discharge of product gas, the time for vacuuming during the production process is Shorter than the delivery time of the gas.

By continuously vacuuming and inflating the adsorption tower 6 in the system, while ensuring sufficient gas output, the continuous work of the centrifugal blower 2 and the centrifugal vacuum pump 4 is maintained, and the process of stopping, waiting and starting up during the production process is avoided , because the switching on and off of the centrifugal blower 2 and the centrifugal vacuum pump 4 causes a lot of energy waste, thereby improving the utilization rate of energy.

As another embodiment of the present invention, in order to further improve the energy utilization rate of the VPSA gas separation system, the sum of the vacuuming time of the adsorption tower 6 is equal to the sum of the reaction time of the adsorption tower 6 and the product gas output time . While ensuring the continuous operation of the turbine unit, the oxygen in the adsorption tower 6 is fully separated and discharged through the product gas pipeline 10 to maintain a high oxygen production rate.

As another embodiment of the present invention, in order to keep the turbine unit running in a high-efficiency range, according to the inlet air pressure detection values of the centrifugal blower 2 and the centrifugal vacuum pump 4, the corresponding frequency converter is controlled by the control device 3 outputs are controlled. Real-time detection of the inlet air pressure of the centrifugal blower 2 and the centrifugal vacuum pump 4 by the gas detection device, and the detected value is transmitted to the control device, and the control device controls the output of the frequency converter 3 through the received signal value, and then controls the centrifugal blower 2 and the centrifugal vacuum pump 4. The rotor speed of the centrifugal vacuum pump 4 is controlled in real time. Compared with the fixed setting, it operates with the high efficiency curve of the centrifugal blower 2 or the centrifugal vacuum pump 4, which can keep the turbine unit at a high efficiency in case of abnormal intake air. Interval operation. The control modes of all the centrifugal vacuum pumps 4 equipped in the VPSA gas separation system are exactly the same. In the VPSA gas separation system, the pressure changes periodically with time as shown in Figure 3. In the process of this periodic change , if the centrifugal vacuum pump 4 does not adjust the speed, the centrifugal vacuum pump 4 has been running at 100% speed, and will be in an inefficient state in most working conditions. The controller collects the pressure value P in the adsorption tower 6. In the PLC program, through The characteristic diagram of the built-in centrifugal vacuum pump 4 is as shown in Fig. 4, and the highest efficiency line searches for the corresponding speed n under the pressure P, and then outputs the frequency corresponding to the speed n to the frequency converter 3 of the centrifugal vacuum pump 4, and the frequency converter 3 will centrifugally The operating speed of the centrifugal vacuum pump 4 is adjusted to the rotational speed n, so that the centrifugal vacuum pump 4 always operates in a high-efficiency state and runs along the highest efficiency curve. Multiple centrifugal vacuum pumps 4 adopt the same mode, so that the flow is superimposed and the pressure is kept consistent. By increasing or reducing the number of centrifugal vacuum pumps 4, the total working conditions meet the output requirements of the VPSA system. The same control mode is adopted for the centrifugal blower 2 .

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims

A VPSA gas separation system is characterized in that: it includes several turbines and gas separation components arranged in parallel, several turbines are used to deliver air to the gas separation components or vacuumize, each turbine is connected with a drive motor and The frequency converters (3), all the frequency converters (3) are connected to a control device for communication, and the control device is used to control the output of the frequency converters (3).
A VPSA gas separation system according to claim 1, characterized in that: said turbines have the same structure and are equipped with the same frequency converter (3).
A VPSA gas separation system as claimed in claim 2, characterized in that: said turbine is a double-head turbine.
A kind of VPSA gas separation system as claimed in claim 3, is characterized in that: described turbine is provided with the sensor that is respectively used for detecting described drive motor winding temperature, supporting bearing temperature and the rotor vibration of described turbine , the inlet ends of the turbines are all provided with sensors for detecting gas pressure and transmitting signals to the control device.
A kind of VPSA gas separation system as claimed in claim 1, is characterized in that: described several turbines comprise at least one group of centrifugal blowers (2) and one group of centrifugal vacuum pumps (4), and described gas separation assembly comprises Several adsorption towers (6) are independently arranged for gas pressure swing adsorption. The adsorption towers (6) are all provided with product gas pipelines (10) and raw gas pipelines (9), and a group of centrifugal blowers (2) pass through a The pipeline provided with the program-controlled valve (5) communicates with the raw material gas pipeline (9), and a group of centrifugal vacuum pumps (4) communicates with the raw material gas pipeline (9) through another pipeline provided with the program-controlled valve (5). The gas pipeline (10) is also provided with a program-controlled valve (5), which is remotely controlled by the control device, and an air pressure sensor is provided in the adsorption tower (6).
A kind of VPSA gas separation system as claimed in claim 5, is characterized in that: the inlet pipe of described centrifugal blower (2) is all connected on the pipeline, and the inlet end of this pipeline is provided with inlet filter box (1), the gas outlet pipe of the centrifugal vacuum pump (4) is all connected on another pipeline, and the gas outlet end of the pipeline is provided with a silencer (8), and the product gas pipeline of the adsorption tower (6) ( 10) are all connected to another pipeline, and the gas outlet end of the pipeline is provided with a buffer tank (7).
A kind of control method of VPSA gas separation system, utilizes a kind of VPSA gas separation system described in claim 5, it is characterized in that:

When the output of VPSA gas separation system is adjusted, determine the quantity that described centrifugal blower (2) and centrifugal vacuum pump (4) put into production;

First, a described adsorption tower (6) is vacuumized, carried out by a group of described centrifugal vacuum pumps (4), when the detected value of the air pressure sensor in the described adsorption tower (6) reaches the set value, through the described adsorption tower (6) The control device remotely controls the program-controlled valve (5), so that the group of centrifugal vacuum pumps (4) vacuumizes the next adsorption tower (6);

Carry out raw material gas input to last described adsorption tower (6) by a group of described centrifugal blowers (2), after the air pressure sensor in this adsorption tower (6) detects that the air pressure reaches the set value, through the program-controlled valve ( 5) switch to another vacuumized adsorption tower (6) for raw gas input, and carry out the vacuuming and raw gas input of all the adsorption towers (6) in sequence;

Before vacuuming, it is the gas reaction in the adsorption tower (6) and the discharge process of the product gas obtained by the reaction. By controlling the program-controlled valve (5) on the product gas pipeline (10), the product gas passes through the product gas. The gas pipeline (10) is discharged. During the product gas discharge process, when the pressure value of the air pressure sensor in the adsorption tower (6) is reduced to the set value, the product gas pipeline (10) is closed and vacuumized. The discharge of product gas, the time of vacuuming during the production process is shorter than the time of conveying gas.
The control method of a kind of VPSA gas separation system as claimed in claim 7, is characterized in that: the sum of the vacuuming time of described adsorption tower (6) is equal to the reaction time and product gas output of one described adsorption tower (6) sum of time.
The control method of a kind of VPSA gas separation system as claimed in claim 7, is characterized in that: according to the inlet air pressure detection value of described centrifugal blower (2) and centrifugal vacuum pump (4), through described control device to corresponding The output of the frequency converter (3) is controlled.