EP2419641A2

EP2419641A2 - Roughing pump method for a positive displacement pump

Info

Publication number: EP2419641A2
Application number: EP10714627A
Authority: EP
Inventors: Peter Birch
Original assignee: Oerlikon Leybold Vacuum GmbH
Current assignee: Leybold GmbH
Priority date: 2009-04-17
Filing date: 2010-04-16
Publication date: 2012-02-22
Also published as: TW201042152A; WO2010119121A3; US20120063917A1; JP2012524204A; KR20110136899A; WO2010119121A2; DE102009017887A1; CN102395792B; US9017040B2; CN102395792A

Abstract

The invention relates to a simple and energy efficient roughing pump method for a positive displacement pump (10), used to produce a maximum differential pressure (ΔP _max) between the inlet (18) and the outlet (20) of the positive displacement pump (10), in which the rotational speed (Ω) of the positive displacement pump (10) is adapted to the maximum differential pressure (ΔP _max) to be generated, such that the power consumption (3, 4) of the positive displacement pump (10) is close to the minimum power (2) required for gas compression for producing the maximum difference pressure (ΔP _max).

Description

Grobpumpyerfahren for a positive displacement pump

The invention relates to a coarse pumping method for a positive displacement pump and to a positive displacement pump device for producing a coarse pressure difference.

In the present case, a coarse pressure difference is understood as meaning a negative pressure difference in the sense of a rough vacuum or a positive pressure difference in the sense of a coarse pressure application. A typical rough vacuum is in the range of up to 500 mbar pressure difference and typically between 100 and 300 mbar pressure difference. For a great variety of applications, there is a great need for rough vacuum pumps, which are usually designed as single-shaft pumps. Centrifugal compressors or are designed as Seitenkanalverdϊchter. Side channel compressors have a fixed volume flow capacity and must always be operated at a continuously high speed. They work on the principle of torque transmission using the Euier energy equation for compressible fluids. Side channel compressors must be operated even at a large pressure difference between the input and the output of the compressor to produce a correspondingly low flow rate at its full volume flow capacity. The power required by the compressor is proportional to the volumetric flow capacity, the theoretically minimum required power for compressing and transporting a small gas flow being proportional to the actual volumetric flow capacity. Due to this difference between actual applied power and the power physically required to compress the gas flow, the use of such conventional rough vacuum compressors is inefficient.

Displacement pumps, such as a Roots pump, are particularly effective for maintaining low pressures where no large volume flow is to be conveyed, or for producing low pressure differences. To generate a rough vacuum with a large pressure difference, positive displacement pumps, such as Roots pumps, have not been used so far.

The invention has for its object to provide a simple and energy-efficient coarse pumping method and a corresponding coarse pumping device.

The coarse pumping method according to the invention is defined by the features of claim 1. The positive displacement pump device according to the invention is defined by the features of claim 9.

Claim 1 defines a coarse pumping method for a positive displacement pump, for establishing a differential pressure between the input and the output of the Displacement pump. In this case, the rotational speed of the positive displacement pump is adapted to the maximum differential pressure to be produced in such a way that the power consumption of the positive displacement pump approaches the physically minimal power required for the gas compression to produce the differential pressure. The advantage of a positive displacement pump over a conventional rough vacuum pump, such as a side channel compressor, is that the pump power is variable by varying the speed or piston stroke. By reducing the speed, the generated pressure and the power consumption of the positive displacement pump can be reduced. The positive displacement pump is in this case designed so that its maximum power consumption at maximum speed is greater than the theoretically minimum required power for compressing the gas to produce the desired pressure difference. In other words, that the pump is suitable for a larger pressure difference. In this case, by reducing the rotational speed of the positive displacement pump, the differential pressure generated by the pump can be reduced in such a way that the power consumption of the pump approaches the minimum required power for the gas compression. Adjusting the power consumption to the power required for gas compression is only possible with electronically controlled positive displacement pumps, but not with the conventional side channel compressors. A positive displacement pump makes it possible to deliver a closed volume of gas from the pump inlet to the pump outlet at an adjustable rate.

The speed is vorzu in flowless state, being

V _{5 is} the volume flow pump capacity of the positive displacement pump,

C _/ leakage volume return flow within the pump, P _out the output side pressure of the positive displacement pump,

Pin, _m i _n the minimum input side pressure of the positive displacement pump with ΔP _mgx - P _ou t - Pin, min and

Ω _m a _x the maximum speed! the positive displacement pump and Ω <Ω _max

are, set. The coarse pressure difference ΔP _{max to} be set may be in a range of up to -500 mbar or up to +500 mbar. In particular, a typical coarse pressure difference is given in a range between ± 200 to ± 400 mbar.

Preferably, the torque T of the pump drive is reduced with increasing pressure difference ZiP between output-side pressure P _out and input-side pressure P _1n and with increasing pump speed. The reduction of the torque occurs above a speed limit Ω _{v /} r, up to which preferably constant torque prevails. The speed limit Ω _{v / r} should be> 0 and preferably below 30 Hz. The course of the torque above the speed limit value Ω _v / _f over the pressure difference is preferably linearly decreasing. Such a torque reduction can be carried out in an electric motor using an electronic inverter, wherein the value of the limit speed Ω _{v / r} should be chosen as low as possible. With an electronic inverter, a limiting speed Ω _{v / f} of 10 Hz can be achieved. The reduction of the torque with increasing pressure difference is advantageous because the torque 7 according to the formula

T = v _v - (^ - Pj / 36,

Ω "max

in which ~ O ^~

Vs the volume flow capacity,

Ω _mgχ the maximum speed of the positive displacement pump,

P _ou t the output side pressure and P _in the input side pressure

are dependent on the input-side pressure. In other words, only a certain torque is needed to reach a certain input pressure P _{! N.} Since the power P is the product of the torque T and the speed Ω, so the power depends on the pump speed. The minimal input-side pressure P _mιm j _π sol! to minimize the pump power to be achieved at the lowest possible speed Ω can be achieved.

The Verdrängerpumpenvorrchtung invention according to claim 9, in addition to the positive displacement pump, a pump drive and a control device for reducing the speed of the positive displacement pump according to the method of claim 1. In this case, the positive displacement pump device preferably has a reservoir for the pressure difference ΔP _{max to be produced} as part of the control device. In particular, the memory has a program for setting the rotational speed Ω according to the relationship mentioned in claim 1.

The pump drive is preferably an electric motor and the control device may be an electronic inverter. The electric motor may be an induction motor, a reluctance motor or a brushless DC motor. The positive displacement pump is preferably a Roots pump or alternatively a claw screw pump or a dry rotary vane pump. The positive displacement pump may be formed in one or more stages, wherein the plurality of stages may have different displacement capacities. The positive displacement pump may be air-cooled or liquid-cooled, for example by water or oil. In the following an embodiment of the invention will be explained in more detail with reference to FIGS.

Show it:

Figure 1 is a block diagram of a Verdrängerpumpenvorrichtung according to the first Ausführungsbeispiei and

FIG. 2 shows a performance diagram for the positive-displacement pump device according to FIG. 1.

The positive displacement pump device 16 according to FIG. 1 consists of a positive displacement pump 10, a pump drive 12 for the positive displacement pump 10 and a control device 14 connected to the pump drive 12. The positive displacement pump 10 is a Roots pump and the pump drive 12 is an electric motor. The control device 14 is an electronic inverter, with which the rotational speed of the pump drive 12 and the positive displacement pump 10 are adjustable.

At the suction-side inlet 18 of the positive-displacement pump 10, an inlet-side pressure P _in is present in the intake channel of the pump. At the pressure-side outlet 20 of the positive-displacement pump 10, an outlet-side pressure P _out is present in the outflow channel of the positive-displacement pump 10. As will be described below with reference to FIG. 2, the positive-displacement pump 10 is oversized for the prevailing pressures P _in and P _out and for the resulting pressure difference ΔP _max -P _o u _t ~ Pi _n , so that the power consumption of the pump 3,4 by reducing the speed of the pump drive 12 and the positive displacement pump 10 by means of the control device 14 to the minimum power required for gas compression 2 for producing the differential pressure ΔP _max approximates. Oversized means that the pump is designed for a larger pressure difference. _ -j

In Figure 2, the input side pressure P _1n in millibars are plotted on the horizontal axis, the volume flow V in cubic meters per hour on the right vertical axis and the resulting power Pwr in watts on the left vertical axis. In the illustrated embodiment, the positive displacement pump 10 is used in coarse pumping operation for generating a rough vacuum (English: rough vacuum). In this case, approximately atmospheric pressure prevails at the pump outlet 20, that is, P _out is 1000 mbar. The pressure P _{m, mm} to be produced by the pump at the pump inlet 18 is 700 mbar, that is to say the differential pressure ΔP _max = P _ou t -Pm, mm to be produced is 300 mbar. Of course, the pump can also be used for generating an input-side pressure P _1n of 1300 mbar, in which case the amount of the pressure difference ΔP _{max to be produced is} 300 mbar.

In FIG. 2, the volume flow V, which is established in the positive-displacement pump 10 during operation for producing the input-side pressure P, _{n> mm} , is designated by the reference numeral 1. When the pump starts, there is still atmospheric pressure on the input side, ie P _1n - P _out . In this case, the resulting pressure difference ΔP = P _out _{-P 1n} -0. The volume flow V in the pump is then aiso equal to the volume flow capacity V _{5 of} the positive displacement pump 10. With decreasing pressure P _{1n on the} input side, the delivered volume flow V linearly decreases until the input-side pressure P _{ιπ, mιπ} = 700 mbar is reached. The produced maximum pressure difference .DELTA.P _m ax = Pout - Pιn, mm = 300 mbar is reached and delivered by the positive displacement pump 10 volume flow V = O.

The pump capacity of the positive displacement pump 10 is proportional to the pressure difference .DELTA.P and provided in Figure 2 with the reference numeral 3. At input-side pressure P, _n = P _out and resulting pressure difference ΔP = 0, the pump power 3 is equal to zero. It increases linearly up to its maximum with the input-side pressure P _1n = P _{mιmm achieved} and the resulting pressure difference

Δr max ~ 'out ~' in, min - The power required physically to compress the gas to produce the pressure difference ΔP _{max is} calculated by the relationship

Pwr = V - AP = V • (P _out - P _1n).

This results in the physically required for the gas compression input power of the positive displacement pump 10 to produce the pressure difference .DELTA.P _max . This physical minimum output power is designated by the reference numeral 2 in FIG. It is in the case of minimal pressure difference AP = O and in the case of minimal volumetric flow V = O is always zero and runs hyperbolic with a maximum for P, _n , mm <Pm <P _0U f

By comparing the maximum capacity 3 of the positive displacement pump 10 with the physical Mimmal input power 2, it becomes clear that the difference between these two powers increases with decreasing input pressure P _1n and is particularly significant for large pressure differences in the vicinity of ΔP _max . For small pressure differences in the vicinity of AP = O, however, the pump performance 3 is only slightly above the physically required minimum power 2. At low pressure differences AP, the positive displacement pump 10 thus works most effectively and is always ineffective with increasing pressure differences. For this reason, positive displacement pumps 10 have hitherto been used only for producing or maintaining only slight pressure differences. For large pressure differences, which typically occur during coarse pumping, positive displacement pumps have been avoided so far due to the low efficiency. Instead, side channel blowers are typically used in the coarse pumping area, but they have the drawback that they always have to be operated at constant speed in order to obtain their pumping speed. A speed control to improve the efficiency of pumps therefore differed completely in the rough pumping. The invention is based on the principle that positive displacement pumps promote a firmly umschiossenes volume, wherein the speed of the positive displacement pump has no influence on the respectively funded enclosed volume. With positive displacement pumps, the speed only affects the throughput of the pumped enclosed volume. This advantage is used according to the invention in order not to operate a per se oversized positive displacement pump 10 with its oversized performance 3, but by reducing the speed of the positive displacement pump 10, the pump power 3.4 of the physical minima! approach required input power 2. With the previous rough vacuum pumps, such as side channel blowers, this is not possible so far.

The pump speed is thereby reduced by reducing the speed of the electric motor 12 by means of the inverter 14. Here, the pump speed is Ω on the relationship

set. P _in is the prevailing suction pressure on the input side 18 of the positive displacement pump 10. At the start of the pump, P _1n = P _outl so that ΔP = 0. With decreasing input side pressure P _in the backflow caused by leaks within the pump increases. Here C _{1 is} the associated backflow (English: back leakage conductance) in cubic meters per hour. The return flow Q is calculated according to

C ₇ = (P _1n "V ₅ -Q) / (P ₀ Ut-P _1n ),

where Q is the mass flow in millibars times cubic meters per hour. The mass flow rate Q is calculated according to Q = Pm * V ₅ - C ₁ * (Pout - Pm).

Starting from the capacity 3 of the positive displacement pump 10

the reduced speed Ω for approaching the minimum physical input power 2 is determined as follows:

The volume flow capacity V _{5 of} the positive displacement pump is predetermined and is in the Roots pump of the embodiment 42Qm ³ / hr. Typically, rough vacuum pumps have a volumetric flow capacity in the range between 1 and 2000 m ³ / hr. The output-side pressure P _ou t is specified as the atmospheric pressure of 1000 mbar, so that the pump power 3 increases with decreasing input pressure P _1n . As the input side pressure P _1n decreases, the influence of the backflow Q within the pump increases. The volume flow capacity V ₅ = 420m ³ / hr. is reached at maximum speed Ω _max = 100 Hz. By reducing the speed can be a reduced

F., - Ω volume flow capacity of - be obtained. Max

The pump torque T (English: torque) is calculated according to

T = Pwr / Ω

and considering

Pw T = V ₅ ® Δ P / 36

for the reduced torque too niax

It can be seen that the input-side pressure Pj _n depends on the applied torque T. This relationship can be exploited by utilizing the inherent current control of an electronic inverter 14 to control torque T via control of the current in an electric motor 12. With the inverter 14, the torque T of the pump drive 12 with increasing differential pressure AP and with increasing pump speed above a Grenzdrehzahi Ω _{v / f} of 10 Hz is continuously reduced. The torque curve of the inverter is up to the limit speed! Ω _{v / f} constant and falls above the limit speed Ω _{v / f} linearly to 0 from. This is advantageous because the torque according to the above equation depends on the input pressure P _iπ , so that in order to reach a certain input pressure P _in only a certain torque is needed.

Since the power P as a product of torque T and speed Ω also depends on the pump speed, the rotational speed Ω of the positive displacement pump 10 is initially set in such a way that the minimum input pressure P 1 _m i _n to be produced is attained at the lowest possible rotational speed Ω in order to achieve the required torque Pump power 3.4 to minimize. When operating the positive displacement pump 10 with this reduced speed Ω, the torque curve with continuously decreasing torque described above is then used to approximate the power consumption 4 of the positive displacement pump 10 to the physically minimum required power 2.

At minimum inlet pressure Pm, mm, when the volumetric flow V = O, is the input side pressure

p. = p. _^ P ^{36 T Ω} ^ in in, min out - \ τ

^V S Taking into account the volume of return flow C ₁ , in the event that the volume flow V = O,

From this it is possible to determine the speed Ω for which the pump power, taking into account the volume return flow C _1, is approximated by leakages within the pump to the minimum physical input power 2. Here, P _{! N is} the approximate pump input power 4, which differs from the minimum physical input power 2 by the volume backflow Q within the pump. The approximated pump input power is provided with the reference numeral 4 in FIG. The approximate pump input power 4 becomes at the speed

reached. As FIG. 2 shows, the reduced pump input power 4 compared to the pump power 3 at maximum speed Ω _{max of} the positive displacement pump 10 is clearly approximated to the minimum physical input power 2. In other words, that means that the positive displacement pump 10 operates much more effectively at the reduced speed Ω than at the maximum speed Ω _max . A correspondingly oversized positive displacement pump 10 operating at reduced speed Ω according to the above relationship operates more effectively than a conventional roughing pump, such as a side channel compressor.

Claims

claims

1. Coarse pumping method for a positive displacement pump (10), for establishing a maximum differential pressure (ΔP _max ) between the input (18) and the output (20) of the positive displacement pump (10), wherein the rotational speed (Ω) of the positive displacement pump (10) in such a way is adapted to the maximum pressure to be produced {.DELTA.P _max ) that the power consumption (3,4) of the positive displacement pump (10) to the minimum power required for the gas compression (2) for the production of the maximum differential pressure {.DELTA.P _max ) approaches.

2. rough pumping method according to claim 1, characterized in that the speed (Ω) to reach the maximum differential pressure {.DELTA.P _max ) via

the relation 3 O, ^I where

V _{5 is} the volume flow pump capacity of the positive displacement pump,

C ₁ leakage leakage volume flow within the pump,

P _out the output side pressure of the positive displacement pump,

Pi _{n, m} i _n the minimum input side pressure of the positive displacement pump with ΔP _max = P _out - P _in , _m in and

Ω _{max is} the maximum speed of the positive displacement pump with Ω <Ω _max

are, is set.

3. Coarse pumping method according to claim 1 or 2, characterized in that the torque (T) of the pump drive (12) with increasing differential pressure and with increasing pump speed above a limit speed (Ω _{v / f} ) is continuously reduced, where O ≤ Ω _{v / f} ≤ 30 Hz.

4. rough pumping method according to one of claims 1-3, characterized in that the ratio of Ausgangsseititϊgem pressure (P _ou t) to input-side pressure (P _1n ) of the positive displacement pump at maximum possible speed (Ω _maχ ) of the positive displacement pump is greater than 3, and in particular is less than 10.

5. rough pumping method according to one of claims 1 - 4, characterized in that the amount of the differential pressure to be produced (.DELTA.P _max ) is in the range of up to 1000 mbar.

6. Coarse pumping method according to claim 5, characterized in that the amount of the differential pressure to be produced (ΔP _max ) is in the range of up to 500 mbar and in particular in a range between 200 and 400 mbar.

7. Coarse pumping method according to one of claims 1-6, characterized in that the rotational speed (Ω) is reduced by using an electronic inverter in an electric motor as a pump drive.

8. Coarse pumping method according to claim 7, characterized in that the electric motor is an induction motor, a reluctance motor or a brushless DC motor.

9. rough pumping method according to one of claims 1-8, characterized in that the positive displacement pump is a roots pump, a claw screw pump or a dry rotary vane pump.

10. rough pumping method according to one of claims 1-9, characterized in that the positive displacement pump is a Mehrstufenverdrängerpumpe with at least two pumping stages.

11. positive displacement pump device (16) for establishing a coarse pressure difference (ΔP _max ) between the input (18) and the output (20) of a positive displacement pump (10), with a pump drive (12) and with a control device (14) for adjusting the rotational speed ( Ω) of the positive displacement pump to the maximum differential pressure to be produced (ΔP _max ), such that the power consumption (3,4) of the pump (10) to the minima for the gas compression! required power (2) to produce the maximum differential pressure {ΔP _max ) approximates.

12. positive displacement pump device (16) according to claim 11, characterized in that the control device (14) has a memory for the differential pressure to be produced (.DELTA.P _max ).

13. Verdrängerpumpenvorrichtung (16) according to claim 12, characterized in that the memory is a program for determining the

reduced speed (Ω) over the relationship where

V _{5 is} the volume flow pump capacity of the positive displacement pump,

Q is the leakage volume return flow within the pump,

P _out the output side pressure of the positive displacement pump, Pi _n , _m i _n to be produced minimum input side pressure of the positive displacement pump with ΔP _max = P _out - Pm _, mm and

are, has.

14. Verdrängerpumpenvorrichtung (16) according to any one of claims 11-13, characterized in that the control device (14) has a torque reducing means for continuously reducing the torque (T) of the pump drive (12) with increasing differential pressure (.DELTA.P) and with increasing pump speed above a Grenzdrehzah! (Ω _{v / f} ).

15. positive displacement pump device (16) according to any one of claims 11-14, characterized in that the positive displacement pump (10) at its maximum speed (Ω _max ) a ratio of output pressure (P _o u _t ) to input-side pressure (P _1n ) of has at least 3 and in particular of at most 10.

16. positive displacement pump device (16) according to any one of claims 11 - 15, characterized in that the amount of coarse pressure difference to be produced (.DELTA.P _max ) is in the range of up to 1000 mbar.

17. Verdrängerpumpenvorrichtung (16) according to any one of claims 11-16, characterized in that the amount of coarse pressure difference to be produced (.DELTA.P _max ) in the range of up to 500 mbar and in particular in a range between 200 and 400 mbar.

18. positive displacement pump device (16) according to any one of claims 11-17, characterized in that the pump drive (12) is an electric motor and the speed reduction means (14) is an electronic inverter.

19. Verdrängerpumpenvorrichtung (16) according to claim 18, characterized in that the electric motor is a Induktionsrnotor, a reluctance motor or a brushless DC motor.

20. positive displacement pump device (16) according to any one of claims 11 - 19, characterized in that the positive displacement pump is a Roots pump, a claw screw pump or a dry rotary vane pump.

21. positive displacement pump device (16) according to any one of claims 11 - 20, characterized in that the positive displacement pump is a Mehrstufenverdrängerpurnpe with at least two pumping stages.