CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/IB2018/056924, filed Sep. 11, 2018, claiming priority based on Belgian Patent Application No. BE 2017/5672 filed on Sep. 21, 2017, the contents of all of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cylindrical symmetric volumetric machine.

Background

A volumetric machine is also known under the name “positive displacement machine”.

In particular, the invention is intended for machines such as expanders, compressors and pumps with a cylindrical symmetry with two rotors, namely an inner rotor mounted rotatably in an outer rotor.

Such machines are already known and are described in U.S. Pat. No. 1,892,217 among others. It is also known that the rotors can have a cylindrical or conical shape.

It is known that such machines can be driven with an electric motor.

From Belgian patent application no. BE 2017/5459 it is already known that the electric motor can be mounted around the outer rotor, whereby the motor stator directly drives the outer rotor.

Such machine has many advantages in relation to the known machines whereby the motor shaft is connected by means of a transmission with the rotor shaft of the outer or inner rotor.

Thus, the machine will not only be a lot more compact, such that the footprint is smaller, it also means less shaft seals and bearings are required.

In known machines and the machine of BE 2017/5459, the rotors, bearings and other components need to be lubricated and cooled. An injection circuit is provided for this which will inject a liquid, such as oil or water, for example, in the machine, for lubrication, sealing and cooling. This injection circuit also comprises a system to pressurise the liquid and to be able to inject it in the machine.

There is also an injection of liquid between the inner rotor and the outer rotor, whereby this injection necessarily takes place at the inlet, which results in an increase of the inlet temperature.

There can also be an injection of liquid on the level of the motor, whereby the motor stator is provided with slots to let the liquid pass through. The motor may also be air-cooled.

As the liquid is also injected between the inner rotor and outer rotor, the gas will contain an amount of liquid at the outlet of the machine. That is why it is necessary that downstream from the machine a liquid separation takes place, whereby the injected liquid is separated from the gas.

Consequently, not only a separate liquid separator needs to be provided. Furthermore, in the case of a compressor, this also means a pressure loss.

The purpose of the present invention is to improve the lubrication and cooling for a machine as specified in BE 2017/5459.

SUMMARY OF THE INVENTION

To this end, the invention relates to a cylindrical symmetric volumetric machine, whereby the machine comprises a housing with an inlet opening and an outlet opening, with two co-operating rotors in the housing, namely an outer rotor which is mounted rotatably in the housing and an inner rotor which is mounted rotatably in the outer rotor, whereby liquid is injected in the machine, characterised in that at the outlet opening on the level of the inner rotor and outer rotor, a liquid separation takes place, whereby the separated liquid flows back into the machine, and in that the outer rotor has an axial extension on the level of the outlet opening which extends around this outlet opening almost up against the housing such that between the axial extension and the housing there is a space.

As both the inner rotor and the outer rotor will rotate at high speed at the outlet opening, the liquid particles will be flung outward by the centrifugal forces, i.e. toward the inside of the outer rotor. In this way they will be removed from the compressed air.

This provides the advantage that no separate liquid separator needs to be included, but that the separation happens in the machine itself.

Not only will this make the machine more compact, it will also ensure that, in the case the machine is a compressor, the pressure loss in the liquid separator can be avoided.

Preferably at least a part of the separated liquid ends up back into the machine via the liquid channels in the outer rotor.

‘Liquid channels in the outer rotor’ means that the liquid channels effectively run through the outer rotor. In other words, the outer rotor is provided with hollow channels in which or through which liquid can flow.

By providing liquid channels in the outer rotor, these particles can be collected and drained via the liquid channels.

The outer rotor has an axial extension on the level of the outlet opening, which extends around this outlet opening almost up against the housing such that between the axial extension and the housing there is a space.

Due to the centrifugal forces and the movement of the gas toward the outlet opening, the liquid particles will end up in said space between the housing and the axial extension of the outer rotor. The liquid can then be drained via this space.

Preferably a liquid channel extends in the axial extension which ends in the space between the housing and the axial extension.

Because the liquid ends up in the space, a kind of axial bearing will form between the housing and the outer rotor. As a result of this the forces that work on the ball bearing which supports the outer rotor, will become smaller. Consequently, a smaller ball bearing can be applied.

In a practical embodiment, the liquid channels in the outer rotor lead to one or more of the following locations:one or more injection points to the space between the inner rotor and the outer rotor;one or more injection points to one or more bearings of the machine.

The liquid channels allow the liquid to be led to the desired locations that need lubrication and/or cooling.

This provides the advantage that the injection between the inner rotor and the outer rotor does not have to be at the inlet side as the liquid channels can be made to end downstream from the inlet side to the space between the inner rotor and the outer rotor. This avoids an increase of the inlet temperature following injection at the inlet opening.

According to a preferred characteristic of the invention, the outer rotor has an open structure with passages for the sucked in gas, such that gas that is sucked in via the inlet opening must pass via the passages of the open structure before it ends up between the inner rotor and the outer rotor.

This has the advantage that a kind of air cooling of the machine is obtained, whereby the outer rotor can be cooled by the sucked in air.

This principle will also allow cooling of the liquid in the liquid channels.

Moreover, if the machine relates to a machine of BE2017/5459, it means the magnets embedded in the outer rotor can be actively cooled as well.

