EP0834018A1

EP0834018A1 - Multistage, screw-spindle compressor

Info

Publication number: EP0834018A1
Application number: EP96922831A
Authority: EP
Inventors: Christian Dahmlos; Dietmar Rook; Ralf Steffens
Original assignee: SIHI INDUSTRY CONSULT GmbH; SIHI Ind Consult GmbH
Current assignee: Sterling Industry Consult GmbH
Priority date: 1995-06-21
Filing date: 1996-06-18
Publication date: 1998-04-08
Anticipated expiration: 2016-06-18
Also published as: US5924855A; ATE187528T1; JPH11508015A; ES2141515T5; WO1997001038A1; EP0834018B2; ES2141515T3; KR100424386B1; DE59603870D1; TW377384B; JP3965507B2; DK0834018T4; GR3032683T3; PT834018E; KR20000000512A; DK0834018T3; EP0834018B1

Abstract

PCT No. PCT/EP96/02631 Sec. 371 Date Dec. 15, 1997 Sec. 102(e) Date Dec. 15, 1997 PCT Filed Jun. 18, 1996 PCT Pub. No. WO97/01038 PCT Pub. Date Jan. 9, 1997The invention provides a two-rotors screw compressor having active cooling means on the pressure side of the motive rotor.

Description

Multi-stage screw compressor

In screw-type compressors, as are known from EP-A 472933, the achievable pressure difference depends to a large extent on the leakage losses between the circumferential surfaces of the rotors, which are moved relatively to one another, and the pump chamber housing. In view of this, the aim is to keep the play between these surfaces as small as possible. However, operational safety requires greater scope with regard to the temperature-related thermal expansion of the rotors.

It is known to cool rotors of twin-shaft compressors directly (EP-A 290664) by providing a heat transfer medium (lubricating oil) in a bearing cavity of the rotor, which is cooled by a stationary cooling coil protruding into the bearing cavity. This has the disadvantage that the bearing cavity of the rotor has to be sealed. However, the seals required for this are susceptible to malfunction, particularly at high speeds. High losses also occur in the heat transfer medium which is swirled between the rotating rotor and the stationary cooling coil, which lead to heat generation and question the cooling effect.

It is customary to cool the conveyed medium, for example by injecting liquid coolant (US-A4,515,540) or by returning part of the conveyed medium after cooling (DE-A 25 44 082). Such cooling can also be provided in combination with the invention; however, this is aimed at cooling the rotor, so that it can assume a temperature, in particular in the area of the sensitive bearings, which is below the pressure-side temperature of the conveyed medium.

The invention is therefore based on the object, a screw compressor in To provide the preamble of claim 1 type, in which the rotors are cooled independently of the conveyed medium in such a way that good conditions are created for a small game between the rotors among themselves and between the rotors and the pump chamber housing, without it from susceptible to failure ¬ seals required.

The solution according to the invention consists in the features of claim 1 and preferably in those of the subclaims.

The solution according to claim 1 is composed of two components, namely firstly the feature that the displacement rotors are cooled more on the pressure side than on the suction side, and secondly a cooling technology using the special design of the rotor bearing.

The idea of cooling the rotors more on the pressure side than on the suction side is based on the fact that, in these machines, the greater part of the compression heat is generated in the chambers located closer to the pressure side and enclosed by the rotors and the pump chamber housing, since they informe the leakage losses and possibly contain a larger gas mass than the chambers closer to the suction side, even if the volume is the same. If you prefer to remove the heat from the area of the rotors close to the pressure side, you will be able to achieve constant diameter ratios of the rotors over their entire length, rather than if the rotors are cooled over their entire length. Multi-stage rotors are to be understood as those whose screw threads forming the compression chambers revolve the rotor several times, so that a plurality of compression chambers are formed over the rotor length, in each case on the suction and pressure sides. In a three-stage arrangement, the screw turns revolve three times around the associated rotor. The number of stages can be determined in accordance with the respective printing area. At least five stages are preferably used.

For cooling, the invention uses a special technology adapted to the type. This type of construction presupposes that each displacement rotor is mounted in a floating manner on a stationary bearing tube which surrounds the rotor shaft and at least one rotor-side bearing and projects into the rotor. Only this is cooled directly, while the cooling of the rotor takes place indirectly by the mutually opposing peripheral surfaces of the rotor and the bearing body being heat exchangeable to one another. are ordered. The bearings and the rotor shaft are particularly well cooled because they are located within the bearing tube.

In order to improve the heat transport between the opposing surfaces of the rotor and the bearing body, these can be equipped with properties which improve the heat exchange. In order for the convective heat exchange to be intensified by mediating the air layer between the surfaces, the intermediate space should not be connected to the suction side but to the pressure side. The surfaces can also be provided with elevations and depressions which improve the heat transfer coefficient to the medium located therebetween. The mutual distance between the two surfaces should be as small as possible. To improve the radiation exchange, such a treatment of the surfaces can be provided that they have a high absorption number in the area of thermal radiation.

The heat transfer to the opposing surfaces of the rotor and the bearing body can also be improved in that the gas located between them is caused to flow. For this purpose, the intermediate space can be connected to a gas source. The gas flow can also be used for heat dissipation if the gas temperature is selected accordingly (cooling if necessary). In addition, he can, if necessary, exercise a blocking function to protect the bearing and drive area from the access of the conveying medium or of substances contained in the conveying medium.

The gas used is expediently fed to the pressure side of the machine. The interacting surfaces of the rotor and bearing body can be equipped with conveying elements to convey the gas. This can make it unnecessary to provide an external source of pressurized gas. This also applies if the gas supplied is primarily intended to serve as a blocking and not for cooling purposes. The conveying effect of the surfaces can be brought about in particular by equipping them with a conveying thread on one or both sides. Instead of or in addition, they can also be conical, so that the centrifugal force is used for the promotion. Such means promoting the movement of the gas in the intermediate space are also useful for improving the heat transfer when no additional gas supply is provided.

The part of the bearing body protruding into the rotor cavity is expediently equipped with channels through which cooling liquid flows, which are preferably arranged close to the circumferential surface of the bearing body opposite the rotor.

Since the thermal expansion of the rotor is limited thanks to the cooling according to the invention, the housing may be intensively cooled or at least kept at a predetermined temperature without the risk of the rotor starting up on the housing due to thermal play. The efficiency of the pump can be increased by the cooling effect exerted on the pumped medium in this way.

It is known in particular in the case of vacuum pumps to allow gas under higher pressure to flow into the compression cells of the machine in order to cool the conveying medium and / or to reduce noise. This technique, referred to as pre-admission, is also advantageously used in connection with the invention. For example, chilled gas from a suitable source can be used. An external heat exchanger can be avoided by leading the pre-inlet gas through a heat exchanger located in the cooling chamber on the housing side. Instead of gas, liquid can also be added in the scooping chamber, which evaporates there and thereby extracts heat from the medium being conveyed.

The cooling of the bearing body, at least in the area in which it is located in the heat influence of the rotor, has the great advantage that rolling bearings can be used which are permanently lubricated with grease and are therefore particularly low-maintenance and do not pose a risk of contamination for the delivery space .

The above-mentioned possibility of equipping the interacting surfaces of the rotor and bearing body with conveying elements can be used to protect the bearing area from foreign substances that could come from the scooping area. For this purpose, the cooperating conveying members are designed with the conveying direction leading out of the rotor cavity.

As a result, foreign matter, in particular also heavier substances than the medium to be conveyed, and with the supply of barrier medium also the medium itself is prevented from penetrating into the rotor cavity against the direction of conveyance and penetrating into the bearing and drive area. This effect is supported by gravity.

According to an advantageous embodiment, the cooperation kenden surfaces as funding bodies in that at least one of them is provided with a conveyor thread. Both can also be provided with conveyor threads. The direction of the thread or threads is chosen so that the desired conveying direction results. According to another embodiment of the invention, the opposing circumferential surfaces of the rotor and the bearing body are conical with a diameter increasing in the direction of conveyance, so that the centrifugal force penetrates any substances in the direction of the increasing diameter, i.e. towards the scoop space. It is also possible to combine several of these types of funding (e.g. conveyor thread and taper).

This effect is increased by connecting the rotor cavity to a flushing or sealing gas source. Thanks to the promotional effect, this source need not be under pressure; however, this is not out of the question. The gas can also serve cooling purposes.

A particularly important consequence of the invention is the security against the penetration of liquid into the bearing and drive area. As a result, the pump is not only insensitive to the surge of liquid with regard to the sealing effect, but it can also be rinsed specifically, especially for cleaning. For this purpose, special devices can be provided for the admission of a washing liquid, which serves, for example, to loosen and flush out impurities deposited on the rotor or housing surfaces. If the operating speed cannot be maintained during this time, the rotors should be driven at an appropriately reduced speed. Corresponding control or regulating devices can be provided for this. It is particularly simple and advantageous to regulate the speed as a function of torque, because the speed reduction then results automatically. The speed reduction can be small if only relatively small amounts of liquid are sprayed into the gas flow. The greater the proportion of liquid in the filling of the delivery spaces, the lower the speed will be with a torque-dependent drive. Complete flooding of the scooping space can even be provided as long as the then possible low speed and the conveying effect still present in the space between the rotor and bearing body in connection with the geodetic height of the bearing body within the rotor are sufficient for this Prevent the rinsing liquid from entering the storage area.

The invention allows security against the passage of liquid both in the loading drive state as well as in the idle state. In both states, gravity and the pressure difference act, in the operating state, the conveying elements.

The invention is explained in more detail below with reference to the drawing, which illustrates a longitudinal section through an advantageous embodiment.

The motor housing 2 rests on the foot part 1, which is possibly integrally connected at the top to the flange-like base plate 3 on which the pump chamber housing 4 is built. This is closed at the top by a cover 5 which contains a suction opening 6.

On the base plate 3, the flange plates 50 of the bearing bodies 7 are fastened in a manner to be explained later, each of which is used for mounting a rotor 8, the circumference of which preferably has two-helical displacement projections 9, which engage in a manner of a tooth engagement in the conveying cavities 10 engage between the displacer projections 9 of the adjacent rotor. In addition, the displacer projections 9 cooperate on the circumference with the inner surface of the pump chamber housing part 4. The rotors 8 are connected to the suction chamber 11 at the top and to the pressure chamber 12 at the bottom.

The pressure chamber 12 is connected to a pressure outlet, not shown. These parts are provided at the lower end of the vertically positioned scoop chamber.

Each rotor 8 is connected in a rotationally fixed manner to a shaft 20 which is supported at the bottom in the bearing body 7 by a permanently lubricated roller bearing 21. A second, also permanently lubricated rolling bearing 22 is located at the upper end of a tubular part 23 of the bearing body 7, which projects into a concentric bore 24 of the rotor 8 which is open downwards, that is to say on the pressure side. This bearing 22 is preferably located above the center of the rotor 8. The tubular part 23 of the bearing body preferably extends through the greater part of the length of the rotor 8. The end of the tubular part 23 is substantially higher than the pressure outlet 17 when the pump is arranged vertically This is helpful for protecting the bearing and drive region from the ingress of liquid or other heavy contaminants from the scooping area.

In the tubular part 23 of the bearing body, cooling channels 25 are provided, which are connected to a cooling water source via channels 26 and via corresponding channels, which do not appear in the drawing, to a cooling water drain. The cooling channels 25 are preferably formed by helical recesses, which are covered tightly by a sleeve. The cooling of the rotor bearings extends the lifespan or the maintenance intervals of these bearings if they are permanently lubricated with grease. Furthermore, the cooling also keeps the peripheral surface of the tubular part 23 of the bearing body at a low temperature. This circumferential surface faces the inner circumferential surface of the cavity 24 of the rotor with a small distance. These surfaces are designed in such a way that they are capable of good heat exchange and heat can therefore be dissipated indirectly from the rotor via the tubular part 23 of the bearing body and its cooling devices 25. To improve the heat exchange between the mutually opposite surfaces of the tubular part 23 of the bearing body and the rotor cavity 24, these can be designed in a suitable manner. For example, they can be treated or burnished in such a way that the radiation exchange is favored by high absorption coefficients. The convective heat exchange by means of the gas layer located in between can be improved by a small surface distance and a suitable surface structure which leads to an increase in the heat transfer coefficient. For this purpose, one surface or both can be rough or with heat exchange fins or threads or the like. It is also possible to supply a sealing gas to the rotor cavity 24 through the bearing body or the shaft 20, which is discharged from the pressure chamber 12 with the pumped medium. In addition to shutting off the bearing region, it can also be used for additional cooling of the bearing, the bearing body and the rotor, but it is expedient not to pass it through the bearing or bearings so as not to contaminate them, but via a channel 28 forming a bypass.

Suitable sealing and / or locking devices are provided to protect the bearing and drive area from influences penetrating from the suction chamber. It is particularly advantageous to equip the opposing surfaces of the bearing body 23 and the inner surfaces of the rotor cavity 24 on one side or on both sides with a conveying thread, not shown, which exerts a conveying effect from the rotor cavity 24 to the pressure chamber 12. Because of their higher density, this conveying effect primarily affects solid or liquid particles and thereby prevents them from penetrating into the bearing and drive area. The conveying thread is expediently designed such that this effect is still effective even at a considerably reduced speed.

The conveying effect can also be brought about by the gap between the rotor and bearing body widens conically towards the pressure chamber. The gap width (distance of the surface of the bearing body from the surface of the rotor) remains essentially constant. In addition, in this case too, the opposing surfaces can be provided with a conveying thread on one side or on both sides; However, this is not necessary.

Since fitting the gap between the rotor and the bearing body with a delivery thread or a conicity which acts as a conveyor seals very effectively against the ingress of liquid or solid particles, additional sealing devices can often be dispensed with; however, they can be provided, preferably in a non-contact or low-contact type, e.g. Labyrinth seals or piston ring type seals.

Due to the sealing effect of the delivery thread or the taper of the gap, the pump according to the invention is insensitive to the presence of liquid in the pumping chamber as long as the rotors are rotating. This insensitivity also exists in the stationary state thanks to the high bearing arrangement in the rotor, as long as the liquid in the scooping chamber does not reach the storage level. It is not only important if the pumped medium carries a liquid surge, but can also be used for cleaning and / or cooling the pump by liquid injection. For example, cleaning or cooling liquid can be sprayed through nozzles, one of which is indicated at 27. The same or separate nozzles 27 can be used for spraying in the cleaning liquid and the cooling liquid.

If very heavy contamination is to be expected, there is the option of spraying cleaning fluid continuously during operation. When operating a vacuum pump, the cleaning liquid should, as far as it can get into the suction chamber, have a vapor pressure below the suction pressure. If the pump is multi-stage and the contamination (for example, depending on the pressure) is mainly reflected in the second and / or subsequent stages, there is the possibility of limiting the injection of the cleaning liquid to the second or subsequent stage and thereby to separate the suction side.

In most cases, however, the cleaning operation does not take place continuously, but periodically when cleaning needs are determined (for example as a result of an increase in the drive torque). Thanks to the pump's insensitivity to liquids, relatively large amounts of liquid can be used. If Due to the amount or type of cleaning fluid used, the operating speed cannot be maintained, the speed can be reduced accordingly. Suitable control devices are provided for this. For example, the speed can be controlled as a function of the drive torque, which automatically leads to a corresponding reduction in the speed compared to the operating speed when the power requirement is increased. The continuous rotation of the rotors during the cleaning phase not only serves to seal the rotor bearing, but also promotes the action of the cleaning liquid on the soiled surfaces.

The pumping effect in the gap between the rotor and bearing body can also be used to pump sealing gas independently of an external compressed gas source. In general, however, the effect of such a compressed gas source will be preferred to convey the sealing gas in order to be independent of the rotor speed in the sealing gas supply.

The baffle housing 4 may include a chamber 30 which rotates over or over a large part of the circumference and circulates through the cooling water in order to keep the housing at a predetermined temperature. Cooling of the housing jacket is not necessary in all cases. However, it is advantageously possible in the context of the invention because the rotors 8 are also cooled and their thermal expansion is therefore limited. There is no need to fear that the rotors only start on the housing because they stretch while the housing is kept at a lower temperature.

The pump according to the invention can be equipped with pre-inlet. This means that in the areas of high, possibly even medium compression, channels 31 are provided in the housing, through which gas of higher pressure than the compression stage in this area of the scooping area is admitted into the scoop chamber, according to known Principles to effect cooling and / or noise reduction. According to an advantageous feature of the invention, the pre-inlet gas can be removed directly from the pressure side of the pump by being cooled in the cooling pockets 30 of the pump chamber shell 4. For this purpose, it can be passed through heat exchanger tubes 32.

The roller bearings 21, 22 in the example shown are angular contact ball bearings which are set against one another by a spring 29. Each shaft 20 preferably carries the rotor directly below the bearing 21, ie without an intermediate clutch. fer 35 of the drive motor, the stator 36 is arranged in the motor housing 2. The motor housing can be equipped with cooling channels 38.

The flange plates 50, which in the example shown consist of one piece with the bearing bodies 7, are placed on the top of the base plate 3 with their outer edges 51, which essentially follow the circumference of the suction chamber housing 4, and their abutting inner edges 52. The flange plates 50 are sealed with respect to the base plate 3. The end faces 53 following in radial section of a secant, on which they abut one another, are also equipped with a sealing insert.

Underneath the flange plates 50, between the edges 51, 52, there is a recess which, with the top of the base plate 3, encloses a space 39 which serves to accommodate synchronization gearwheels 40 which are rotatably fixed on the shafts by known means 20 are arranged between the bearings 21 and the motor rotors. So that they can mesh with each other in the area of the inner edges 52 of the flange plates 50, the inner edges have a cutout at a corresponding point through which the gearwheels pass. Below this section, a web remains on each side, to which the reference line in FIG. 1 refers to the reference number 52 which generally designates the inner edge. This web is advantageous not only for reasons of stability, but also because it enables a circumferential seal on the one hand with respect to the base plate 3 and on the other hand between the flattened secant surfaces of the flange plates 50.

The recesses 39 in the flange plates 50 have a diameter that is larger than the diameter of the synchronization gears 40. They are arranged a little eccentrically in relation to the inner edges 52, so that the synchronization gears 40 despite the assembly of the rotor units the presence of the sealing web at 52 can be used.

Since the space 39 containing the synchronization gears 40 is completely separated from the scooping space, there is no risk of contamination for the synchronization gears. They are only used for emergency synchronization of the rotors. Your teeth do not normally come into contact with each other. Lubrication is therefore generally not necessary. Although it can be used if desired, the dry running of the synchronization gearwheels simplifies the construction because a seal between the space 39 and the drive motors is not required. The synchronization gearwheels 40 can also serve as pulse encoder disks or can be supplemented by additional pulse encoder disks which are sensed by sensors 42, one of which is shown in FIG. These sensors 42 are connected to a control device which monitors the respective rotational position of the rotors with respect to a target value and corrects them via the drive. It is a matter of electronic synchronization of the rotors, which is known as such and therefore does not require any further explanation here. The play between the teeth of the synchronization gears 40 is slightly less than the backlash between the displacement projections 9 of the rotors 8. However, it is greater than the synchronization tolerance of the electronic synchronization device. If the latter function properly, neither the flanks of the displacement projections 9 nor the teeth of the synchronization gears 40 come into contact with one another. In the event that the latter should come into contact with one another, they are provided with a wear-resistant and possibly low-friction coating.

In addition to the drive power and speed, the performance data of the pump are determined by the displacement or delivery volume formed on the rotors and thus by the length of the rotors. The delivery data can therefore be changed by changing the length of the pump part containing the rotors. A series of pumps with different performance data is therefore preferably characterized in that the individual pumps of this series differ in the gradation of the length of these parts, to which the pump chamber housing, the rotors and, if applicable, the tubular parts of the projecting into the rotors Bearing body belong.

It can be seen that each rotor with the associated bearing and drive devices forms an independently mountable structural unit which, in addition to the rotor, comprises the bearings 21, 22, the bearing body 7, the cooling devices provided therein, the shaft 20, the synchronization gear 40, the associated sensor 42 and the motor rotor 35. These units are completely pre-assembled in the pump. They can be easily removed or inserted from the base plate 3 after the removal of the pumping chamber housing. Their replacement can therefore be left to the user, while the manufacturer takes care of the maintenance of the sensitive units as such.

The pump is preferably of an isochoric design in order to be able to convey larger quantities of liquid without damage.

Claims

claims

1. Multi-stage screw compressor, the positive displacement rotors (8) are overhung on the pressure side on a stationary bearing tube (23) including the rotor shaft (20) and at least one rotor-side bearing (22), each projecting into the rotor (8), characterized in that the rotors (8) are cooled more on the pressure side than on the suction side, in that the part of the bearing tube (23) projecting into a rotor is cooled and the circumferential surfaces opposite one another

. the rotor (8) and the bearing tube (23) are heat exchangeable to each other.

2. Compressor according to claim 1, characterized in that the space between the opposing surfaces of the rotor (8) and the bearing tube (23) is connected to the pressure side (12).

3. Compressor according to claim 1 or 2, characterized in that at least one of said peripheral surfaces with the heat exchange with the medium between be¬ improving elevations and depressions are provided.

4. Compressor according to one of claims 1 to 3, characterized in that the said ge peripheral surfaces are aus¬ permitted with a high absorption number for heat radiation.

5. Compressor according to one of claims 1 to 4, characterized in that at least the part of the bearing tube (23) projecting into the rotor (8) contains coolant flow-through channels (25).

6. Compressor according to claim 5, characterized in that the cooling channels (25) na¬ he the rotor (8) opposite the circumferential surface of the bearing tube (23) are arranged an¬.

7. Compressor according to one of claims 1 to 6, characterized in that the circumferential surfaces of the rotor (8) and the bearing tube (23), which face each other with little play, are designed as non-contact cooperating conveying elements with a conveying direction leading out of the rotor (8).

8. Compressor according to claim 7, characterized in that it is arranged substantially vertically with a geodetically deep outlet opening.

9. Compressor according to claim 7, characterized in that at least one of the two opposite circumferential surfaces is provided with a conveying thread (28).

10. A compressor according to claim 7, characterized in that the mutually opposite peripheral surfaces are conical with a diameter increasing in the conveying direction.

11. Compressor according to one of claims 1 to 10, characterized in that the rotor cavity (24) is connected to a sealing gas source.

12. Compressor according to one of claims 7 to 11, characterized in that devices for torque-dependent control / regulation of the rotor drive are provided.

13. A compressor according to claim 12, characterized in that means (27) are provided for the inlet of a washing liquid into the scooping space.

14. A method for cleaning a compressor according to one of claims 1 to 13, characterized in that washing liquid is added to the scooping space and the rotors are driven in a torque-dependent manner.