EP3123030B1 - Method for pumping in a system of vacuum pumps and system of vacuum pumps - Google Patents

Description

Technical field of the invention

The present invention relates to a pumping method for improving flow and final vacuum performance in a vacuum pump system whose main pump is a screw-type dry vacuum pump, while reducing the output gas temperature and its electrical energy consumption. Also, the present invention relates to a vacuum pump system that can be used to perform the method of the present invention.

Prior art

General trends of increasing vacuum pump performance, reducing plant costs and energy consumption in industries such as chemicals, pharmaceuticals, vacuum depositions, semiconductors, etc. have brought significant evolutions in terms of performance, energy saving, congestion, training, etc.

The state of the art shows that to improve the final vacuum it is necessary to add additional stages in multi-stage Roots vacuum pumps or multi-stage Claws. For screw-type dry vacuum pumps, additional turns must be applied to the screws, and / or the internal compression ratio must be increased.

The speed of rotation of the pump plays a very important role which defines the operation of the pump in the different phases of emptying the speakers. With the internal compression ratios of the pumps available on the market (whose order of magnitude is for example between 2 and 20), the electrical power required in the pumping phases at suction pressures between atmospheric pressure and 100 mbar about or otherwise said to mass flow strong, would be very high. The trivial solution is to use a speed variator which allows the reduction or the increase of the speed and consequently of the power according to the different criteria of the pressure type, maximum current, limit torque, temperature, etc. But during the periods of operation in reduced speed of rotation there are drops of flow at high pressure, the flow rate being proportional to the speed of rotation. Frequency converter speed variation imposes additional cost and bulk. Another trivial solution is the use of bypass valves at certain stages in multi-stage Roots or Claws vacuum pumps, respectively at certain well defined positions along the screws in the dry vacuum pumps of the type. to screw. This solution requires many parts and has reliability problems.

The state of the art vacuum pump systems that aim at improving the final vacuum and increasing the flow rate shows Roots booster pumps arranged upstream of the dry primary pumps. This type of system is cumbersome, works either with by-pass valves having reliability problems, or by employing means of measurement, control, adjustment or control. However, these means of control, adjustment or control must be actively controlled, which necessarily results in an increase in the number of components of the system, its complexity and cost.

The document WO2014 / 012896A2 proposes to use downstream of a roots-type primary vacuum pump an ejector mounted in parallel with the outlet orifice of the primary pump to reduce the final vacuum achievable by this type of pump. In this document, the ejector is provided with motor fluid by an external gas line which may advantageously be the same as that used for purging the primary type pump roots. In addition, the document WO2011 / 061429A2 teaches that it is possible to lower the power consumption of a primary vacuum pump if means for controlling the external motor fluid supply of the aforementioned ejector are incorporated in the pumping system. These control means have for The purpose is to switch on and off the ejector at the most favorable moments for an optimal reduction of the electric power of the primary pump.

Finally, the document JP2007100562A proposes to replace the engine fluid source as a gas line with an external and isolated air compressor.

Summary of the invention

It is an object of the present invention to provide a pumping method in a vacuum pump system which provides a better vacuum than that which can be obtained by means of a dry vacuum pump of the screw-only type (from order of 0.0001 mbar) in a vacuum chamber.

Another object of the present invention is to propose a method of pumping in a vacuum pump system which makes it possible to obtain a higher flow rate at low pressure than that which can be obtained by means of a dry vacuum pump of the type shown in FIG. screw alone when pumping a vacuum chamber.

The present invention also aims to propose a method of pumping in a vacuum pump system to reduce the electrical energy required for the vacuum of a vacuum chamber and its maintenance, as well as the drop in temperature exhaust gases.

These objects of the present invention are achieved by means of a pumping method which is carried out in the context of a pumping system whose configuration consists essentially of a dry screw-type primary vacuum pump provided with a pumping orifice. a gas inlet connected to a vacuum chamber and a gas outlet opening in a conduit which is provided with a check valve before opening into the atmosphere or other devices. The suction of an ejector supplied with motor fluid by a compressor driven by at least one shaft of the primary vacuum pump is connected in parallel with the nonreturn valve, its outlet going to the atmosphere or joining the conduit of the primary pump after the check valve.

Such a method of pumping is in particular the subject of independent claim 1. The various preferred embodiments of the invention are further the subject of the dependent claims.

The method essentially consists in supplying the ejector with fluid from a compressor driven by at least one shaft of the vacuum pump and operating the ejector continuously all the time that the primary vacuum pump dries with a screw pump the gases contained in the vacuum chamber by the gas inlet orifice, but also all the time that the screw-dried primary vacuum pump maintains a defined pressure (eg the final vacuum) in the chamber by pushing back the gases going up by its exit.

According to a first aspect, the invention resides in the fact that the coupling of the dry primary screw vacuum pump and the ejector does not require specific measurements and devices (eg pressure sensors, temperature sensors, current, etc.), servocontrols or data and calculation management. Therefore, the vacuum pump system adapted for carrying out the pumping method according to the present invention comprises a minimum number of components, is very simple and costs significantly less than existing systems.

According to a second aspect, the invention lies in the fact that, thanks to the new pumping method, the primary dry screw vacuum pump can operate at a single constant speed, that of the electrical network, or rotate at variable speeds according to its own mode of operation. Therefore, the complexity and cost of the vacuum pump system adapted for carrying out the pumping method according to the present invention can be further reduced.

By its nature, the ejector built into the vacuum pump system can still operate without damage according to this method of pumping. Its dimensioning is conditioned by a minimum motor fluid consumption for the operation of the device. It is normally single-storey. Its nominal flow rate is chosen as a function of the volume of the outlet duct of the dry primary vacuum pump with screw limited by the non-return valve. This flow rate may be 1/500 to 1/20 of the nominal flow rate of the dry primary screw vacuum pump, but may also be lower or higher than these values. The driving fluid for the ejector may be air, but also other gases, for example nitrogen.

The non-return valve, placed in the duct at the outlet of the dry primary screw vacuum pump, may be a standard item available commercially. It is dimensioned according to the nominal flow rate of the dry primary screw vacuum pump. In particular, it is expected that the check valve closes when the suction pressure of the primary dry screw vacuum pump is between 500 mbar absolute and the final vacuum (eg 100 mbar).

According to another variant, the ejector is multi-stage.

According to yet another variant, the ejector may be made of high chemical resistance material substances and gas commonly used in the semiconductor industry, both in the single-stage ejector variant as in that of the multi ejector -floor.

The ejector is preferably small.

According to another variant, the ejector is integrated in a cartridge which incorporates the non-return valve.

According to yet another variant, the ejector is integrated in a cartridge which incorporates the check valve and this cartridge itself is housed in an exhaust silencer, fixed to the gas outlet port of the vacuum pump. primary dry screw.

According to the method of operation of the vacuum pump system according to the invention, the ejector still pumps in the volume between the gas outlet of the dry primary vacuum pump screw and the check valve.

According to another variant of the present invention, the compressor can draw atmospheric air or gases into the gas outlet duct after the check valve. The presence of the compressor makes the screw pump system independent of a source of compressed gas, which may respond to certain industrial environments.

At the start of a drain cycle of the chamber, the pressure is high, for example equal to the atmospheric pressure. Due to the compression in the dry primary screw vacuum pump, the pressure of the gases discharged at its outlet is higher than the atmospheric pressure (if the gases at the outlet of the primary pump are discharged directly to the atmosphere) or higher. than the pressure at the input of another device connected downstream. This causes the non-return valve to open.

When this check valve is open, the action of the ejector is very weakly felt, as the pressure of its input is almost equal to that of its output. On the other hand, when the check valve closes at a certain pressure (because the pressure in the chamber has meanwhile dropped), the action of the ejector causes a gradual reduction of the pressure difference between the chamber and the duct after the valve. The pressure at the outlet of the primary dry screw vacuum pump becomes that at the inlet of the ejector, that of its outlet always being the pressure in the duct after the non-return valve. The more the ejector pumps, the more the pressure at the outlet of the primary vacuum pump dries, in the volume limited by the closed non-return valve, is reduced and consequently the pressure difference between the enclosure and the outlet of the dry primary vacuum pump with screw down. This small difference reduces internal leakage in the dry primary screw vacuum pump and lowers the pressure in the enclosure which improves the final vacuum. In addition, the screw-type primary vacuum pump consumes less and less energy for compression and produces less and less compression heat.

On the other hand, it is also obvious that the study of the mechanical concept seeks to reduce the volume between the gas outlet of the dry primary screw vacuum pump and the non-return valve for the purpose of go down the pressure faster.

Brief description of the drawings

• la figure 1 représente de manière schématique un premier système de pompes à vide pompage; et
• la figure 2 représente de manière schématique un deuxième système de pompes à vide.

The features and advantages of the present invention will appear in more detail in the following description with examples of vacuum pump systems given for illustrative and non-limiting with reference to the accompanying drawings which represent:

• the figure 1 schematically shows a first pump vacuum pump system; and
• the figure 2 schematically represents a second system of vacuum pumps.

Detailed description of the drawings

Figure 1 represents a first vacuum pump system SP adapted for implementing a pumping method.

This vacuum pump system SP comprises an enclosure 1, which is connected to the suction port 2 of a dry primary screw vacuum pump 3. The gas outlet orifice of the primary vacuum pump dries at 3 is connected to the duct 5. A discharge non-return valve 6 is placed in the duct 5, which after this non-return valve continues in gas outlet duct 8. The non-return valve 6, when it is closed, allows the formation of a volume 4, between the gas outlet port of the primary vacuum pump 3 and itself. The vacuum pump system SP also comprises an ejector 7, connected in parallel with the non-return valve 6. The suction orifice of the ejector is connected to the volume 4 of the duct 5 and its discharge orifice is connected to the duct 8. The supply duct 9 provides the driving fluid for the ejector 7.

Figure 2 represents a second vacuum pump system SP adapted for implementing a pumping method.

Compared to the system represented in figure 1 , the system represented in figure 2 further comprises a compressor 10 which supplies the gas flow rate at the pressure necessary for the operation of the ejector 7.

One embodiment of the invention provides that the compressor 10 is driven by at least one shaft of the primary dry screw pump 3. Its energy consumption so that it can provide the flow of gas at the pressure necessary to operate the ejector 7 is much smaller (eg of the order of 3% to 5%) compared to the gain on the energy consumption of the main pump 3. The compressor 10 can suck the atmospheric air or gases in the gas outlet duct 8 after the non-return valve 6. Its presence makes the vacuum pump system independent of a source of compressed gas, which can meet certain industrial environments.

As soon as the dry, screw-type primary vacuum pump 3 is started up, the driving fluid for the ejector 7 is fed by the compressor 10. The dry screw-type primary vacuum pump 3 draws the gases into the chamber 1 through the conduit 2 connected to its inlet and compresses them to discharge thereafter to its exit in the conduit 5 by the non-return valve 6. When the closing pressure of the non-return valve 6 is reached, it closes. From this moment the pumping of the ejector 7 gradually lowers the pressure in the volume 4 to the value of its limit pressure. In parallel, the power consumed by the primary dry screw pump 3 gradually decreases. This occurs in a short period of time, for example for a certain cycle in 5 to 10 seconds.

With a judicious adjustment of the flow of the ejector 7 and the closing pressure of the non-return valve 6 as a function of the flow rate of the dry primary screw vacuum pump 3 and the volume of the chamber 1, it is furthermore it is possible to reduce the time before closing the non-return valve 6 with respect to the duration of the emptying cycle and thus reduce the losses of engine fluid during this operating time of the ejector 7 without effect on the pumping. Moreover, these "losses" which are minute, are taken into account in the balance of energy consumption. On the other hand, the advantage of simplicity credits an excellent reliability of the system as well as a lower price of 10% to 20% in comparison with similar pumps equipped with PLC and or variator, controlled valves, sensors, etc.

Certainly, the present invention is subject to many variations as to its implementation. It is understandable that it is not conceivable to exhaustively identify all the possible modes. It is of course conceivable to replace a means described by equivalent means without departing from the scope of the present invention. All these modifications are part of the common knowledge of a person skilled in the field of vacuum technology.

Claims (16)

1. Pumping method in a system of vacuum pumps (SP) comprising:

   - a primary dry screw-type vacuum pump (3) with a gas entry orifice (2) connected to a vacuum chamber (1) and a gas exit orifice (4) leading into a conduit (5) before coming out into the gas outlet (8) of the system of vacuum pumps (SP),

   - a non-return valve (6) positioned in the conduit (5) between the gas exit orifice (4) and the gas outlet (8), and

   - an ejector (7) connected in parallel to the non-return valve (6),

   - a compressor (10),

   the method being characterized in that
   the compressor (10) is driven by at least one of the shafts of the primary dry screw-type vacuum pump (3);
   the primary dry screw-type vacuum pump (3) is put in operation in order to pump the gases contained in the vacuum chamber (1) through the gas exit orifice (4);
   in a simultaneous way, the ejector (7) is fed with working fluid by the compressor (10); and
   the ejector (7) continues to be fed with working fluid all the time that the primary dry screw-type vacuum pump (3) is fed by a source of energy and evacuates the vacuum chamber (1).
2. Pumping method according to claim 1, characterized in that it uses an ejector (7) whose outlet rejoins the conduit (5) after the non-return valve (6).
3. Pumping method according to any one of the claims 1 to 2, characterized in that the nominal flow rate of the ejector (7) is selected as a function of the volume of the exit conduit (5) of the primary dry screw-type vacuum pump (3) which is limited by the non-return valve (6).
4. Pumping method according to any one of the claims 1 to 3, characterized in that the working fluid of the ejector (7) is compressed air and/or nitrogen.
5. Pumping method according to any one of the claims 1 to 4, characterized in that the non-return valve (6) closes when the pressure at the suction end of the primary dry screw-type vacuum pump (3) is between 500 mbar absolute and the final vacuum.
6. Pumping method according to any one of the claims 1 to 5, characterized in that it uses an ejector (7) made of material having increased chemical resistance to substances and gases commonly used in the semiconductor industry.
7. Pumping method according to any one of the claims 1 to 6, characterized in that it uses the ejector (7) integrated in a cartridge incorporating the non-return valve (6).
8. Pumping method according to claim 7, characterized in that it uses the cartridge accommodated in an exhaust muffler fixed to the gas exit orifice (5) of the primary dry screw-type vacuum pump (3).
9. System of vacuum pumps (SP) comprising:

   - a primary dry screw-type vacuum pump (3) with a gas entry orifice (2) connected to a vacuum chamber (1) and a gas exit orifice (4) leading into a conduit (5) before coming out into the gas outlet (8) of the system of vacuum pumps (SP),

   - a non-return valve (6) positioned in the conduit (5) between the gas exit orifice (4) and the gas outlet (8), and

   - an ejector (7) connected in parallel to the non-return valve (6),

   - a compressor (10)

   the system of vacuum pumps (SP) being characterized in that
   the compressor(10) is driven by at least one of the shafts of the primary dry screw-type vacuum pump (3);
   the ejector (7) is designed to be able to be fed with working fluid by the compressor (10) all the time that the primary dry screw-type vacuum pump (3) is fed by a source of energy and evacuates the vacuum chamber (1).
10. System of vacuum pumps according to claim 9, characterized in that outlet of the ejector (7) rejoins the conduit (5) after the non-return valve (6).
11. System of vacuum pumps according to any one of the claims 9 to 10, characterized in that the nominal flow rate of the ejector (7) is selected as a function of the volume of the exit conduit (5) of the primary dry screw-type vacuum pump (3) which is limited by the non-return valve (6).
12. System of vacuum pumps according to any one of the claims 9 to 11, characterized in that it is designed to use as working fluid of the ejector (7) compressed air and/or nitrogen.
13. System of vacuum pumps according to any one of the claims 9 to 12, characterized in that the non-return valve (6) is designed to close when the pressure at the suction end of the primary dry screw-type vacuum pump (3) is between 500 mbar absolute and the final vacuum.
14. System of vacuum pumps according to any one of the claims 9 to 13, characterized in that the ejector (7) is made of material having increased chemical resistance to substances and gases commonly used in the semiconductor industry.
15. System of vacuum pumps according to any one of the claims 9 to 14, characterized in that the ejector (7) is integrated in a cartridge which incorporates the non-return valve (6).
16. System of vacuum pumps according to claim 15, characterized in that the cartridge is accommodated in an exhaust muffler fixed to the gas exit orifice (5) of the primary dry screw-type vacuum pump (3).

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