NO331484B1 - Method and apparatus for node braking of a compressor - Google Patents

Abstract

When magnetic bearings in a compressor for the propulsion of hydrocarbons in pipelines fail, or in the event of a power failure, spare bearings of the mechanical type must take over. These spare bearings wear out. In order to reduce the wear on the spare bearings and thereby increase the time between maintenance operations, which is particularly important for a compressor on the sea cage, it is proposed that the compressor be equipped with a vortex brake based on a permanent magnet (1) which can be quickly brought to a starting position with a brake disc the rotary shaft of the compressor by means of a mechanically prestressed spring system (2, 3, 4, 8, 9).

Description

Method and device for emergency braking of a compressor

The present invention relates to compressors for "boosting" hydrocarbon transport in pipelines, preferably in a seabed environment. More specifically, the invention relates to emergency braking to stop such compressors, in the event of a power failure or in situations with failure of magnetic bearings.

Subsea compressors with magnetic bearings are usually equipped with spare bearings of the ball bearing, roller bearing or plain bearing type. These spare bearings come into operation in the event of an emergency stop, i.e. if the magnetic bearings fail, or in the event of a power cut. The emergency bearings are designed for a certain number of such emergency stops, for example 3-5 emergency stops, before the compressor has to be taken up for maintenance. Such maintenance is costly, and can also result in production losses.

The number of emergency stops before overhaul can be increased if the emergency bearings are subjected to less stress during each emergency stop. One way to achieve this is to brake the compressor at each emergency stop. The brake that is then used should be very reliable, and should not cause increased wear or create wear products.

One type of brake that will be able to solve the problem is a contactless magnetic brake, i.e. a so-called eddy current brake.

Since these brakes must work when the magnetic bearings fail or in the event of a power cut, they must use permanent magnets, and be designed so that they come into operation in the event of a power cut or an emergency stop signal.

An eddy current brake based on permanent magnets is known from US patent no. 5,712,520. However, the construction is not suitable for compressors, but is intended to brake rotors in a drive system.

There thus remains a need to provide a method and a device for emergency braking of a compressor in situations such as described above.

According to the present invention, there is therefore provided a method as defined precisely in the attached patent claim 1. Advantageous embodiments of the method according to the invention appear from the associated non-independent patent claims 2-4.

Furthermore, according to the invention, an emergency braking device is provided as defined precisely in the attached independent patent claim 5. Favorable embodiments of the emergency braking device according to the invention appear from the associated non-independent patent claims 6-9.

Another aspect of the present invention is presented in the attached independent application claim 10.

In the following, the invention will be elucidated in more detail by reviewing a preferred embodiment and variants thereof, and at the same time reference will be made to the attached

fig.1 which schematically shows the preferred embodiment of an emergency braking device according to the invention.

In a compressor of the type indicated at the outset, one or more brake discs 5 must be arranged around the compressor's rotation shaft (which is not shown in Fig. 1). Only part of the brake disc 5 is shown in fig. 1, as the compressor's axis of rotation can be assumed to be perpendicular to the disk 5 shown, in the plane of the paper. Disc 5 thus rotates in and out of the paper plane.

The brake disc 5 must at least have a ring area 7 which is made of conductive material, preferably a metal. The ring area can have any width, preferably from the disc's periphery all the way to the axis of rotation. Thereby, the entire brake disc 5 can preferably be made of compact metal or another electrically conductive material.

Otherwise, an already installed disc for bearing or axial bearings in the compressor can be used as such brake disc 5, especially when it concerns a compressor on the seabed.

The braking effect is provided by inducing current paths (eddy currents) in the disk 5 by moving a permanent magnet 1 above and below a part of the brake disk 5, or at least to a position where interaction is achieved with such a conductive ring area 7 as mentioned above. An electromotive force will act on these current paths which will try to counteract rotations, thereby slowing down the compressor.

The permanent magnet 1 is shown as a horseshoe magnet with an air gap 6 arranged so that when shifted to the left in the figure, the air gap 6 will mainly be filled by the thickness of the brake disc 5, but there must of course be a small clearance on both the top and bottom so that one avoids mechanical contact. One also sees that an arrangement of two separate magnets with different poles facing each other, i.e. with the same air gap in between, can replace the horseshoe magnet.

The position shown with solid lines for the permanent magnet 1 is braked as the rest position for the brake, while the position shown with dashed lines is referred to as the brake position. When an abnormal situation occurs, i.e. a power cut or a failure of at least one magnetic bearing in the compressor, it is important that the shift from rest position to braking position occurs quickly, so that wear on the previously mentioned spare bearings in the compressor takes place in as short a time as possible. On the right in fig. 1 shows an example of a simple mechanism which can provide a quick shift from the rest position to the brake position, and without the need for electrical power for the shift operation itself.

The function of an electric motor 3 is to tension a spring 2 (here a spiral spring) between the magnet 1 and a stop 8. The tensioning takes place by a gear rotating in engagement with grooves on a piston rod 9. In the example, the spring 2 is laid around same piston rod 9. The motor 3 thus drives the piston rod 9, and thus the permanent magnet 1, to the right while the spring 2 is tensioned, until the referred rest position is reached, where the permanent magnet 1 does not interact with the brake disc 5. Here a locking device 4 snaps in and holds the system in the rest position, with tensioned spring 2. In the case shown, the locking device is a simple locking pin, but can have other designs, such as a hook, claw or other.

However, the locking device 4 must be easily released, for example so that it is released in the event of a power failure, or by means of an emergency stop signal when a failing magnetic bearing is detected. When, for example, the locking pin 4 is released, the tensioned spring 2 will immediately drive the piston rod 9 and the permanent magnet 1 to the left, until a stop detail on the far right of the piston rod 9 hits the stop 8. The system has then arrived at the braking position shown by dashed lines. (The motor 3 is then either de-energized, or it was disengaged from engagement with the piston rod 9 when the tension was done - so that the motor does not prevent the movement to the left in the figure.)

Several of the elements shown in fig. 1, can be replaced by corresponding elements. As mentioned, these may be special brake discs 5 or discs that already have the function of bearing bearings. Furthermore, we have mentioned different types of permanent magnets. The mechanism itself which brings the permanent magnet 1 into engagement with the disc can have different designs, for example the magnet can be swung into place in a swinging movement in the same plane as the brake disc's plane, instead of such a linear, possibly radial, movement that the piston rod 9 provides. Then the spring will have an adapted design, and likewise the locking device 4.

The invention not only concerns compressors that are located on the seabed, but can also be used in offshore compressors or in land-based compressors with magnetic bearings and reserve bearings, and especially where it is a matter of having a long operating time between each maintenance stop.

It should also be noted that the brake device does not only need to comprise a single brake disc 5, it may be two or more. The mechanism for displacing one or more permanent magnets 1 can be a common mechanism, or several mechanisms can be arranged, one for each brake disc.

Finally, it should be noted that the two main aspects of the invention are an emergency braking device in a compressor, and a compressor with an emergency braking device. In addition, the subsequent patent claims specify an aspect with a method for emergency braking of a compressor, and an aspect with an application of an eddy current brake for emergency braking of a compressor.

Claims (10)

1. Procedure for emergency braking of a compressor with magnetic bearings and reserve bearings, which compressor has a rotation shaft on which at least one brake disc (5) with electrically conductive material at least in an annular area (7) is attached and rotates together with the rotation shaft, characterized in that at least one permanent magnet (1) with an air gap (6) is quickly brought from a rest position to a braking position where at least some of the ring area of the rotating brake disc (5) remains in the air gap (6), whereby eddy currents are generated in the conductive material and slows down the brake disc (5) and the rotation of the shaft, and that at least one permanent magnet (1) is brought to the brake position to reduce wear on the spare bearings that come into operation when the magnetic bearings fail or in the event of a power failure. 2. Method according to claim 1, characterized in that the permanent magnet(s) (1) are caused to emergency brake a disc (5) for bearing or axial bearings in the compressor, which disc (5) then also constitutes the brake disc (5). 3. Method according to claim 1, characterized in that the at least one permanent magnet (1) is brought to the braking position from a rest position by means of a mechanism (2, 3, 4) with a spring (2), an electric motor (3) for tensioning the spring (2) and a quick-releasable locking device (4). 4. Method according to claim 3, characterized in that the locking device, which consists of a locking pin (4), is triggered by withdrawal in the event of a power failure or by an emergency stop signal, whereby the spring (2), which is tensioned by the motor (3) to its rest position, releases and pushes at least one the permanent magnet (1) quickly to the braking position. 5. Emergency braking device for a compressor with magnetic bearings and spare bearings, which compressor has a rotation shaft on which at least one round brake disk (5) with electrically conductive material at least in an annular area (7) is fixed for rotation together with the rotation shaft, characterized in that at least one permanent magnet (1) with an air gap (6) is arranged to be brought quickly from a rest position to a braking position where at least some of the ring area (7) of the brake disc (5) remains in the air gap (6), for generation of eddy currents in the conductive material with a resulting braking effect for the brake disc (5) and the rotation of the shaft, and that the emergency braking device is designed to operate to reduce wear on the reserve bearings when the magnetic bearings fail or in the event of a power failure. 6. Emergency braking device according to claim 5, characterized in that the brake disc (5) consists of a disc (5) for bearing or axial bearings in the compressor. 7. Emergency braking device according to claim 5, characterized by the mechanism (2, 3, 4) for bringing the at least one permanent magnet (1) from the rest position to the braking position, comprising a spring (2), an electric motor (3) for tensioning the spring (2) as well as a quick-releasable locking device (4). 8. Emergency braking device according to claim 7, characterized in that the locking device consists of a locking pin (4) which is triggered by withdrawal in the event of a power failure or by an emergency stop signal, that the spring (2) is designed to be tensioned up to the rest position for the permanent magnet (1), and to release when the locking pin ( 4) is pulled back and push the permanent magnet (1) quickly to the brake position. 9. Emergency braking device according to claim 5, characterized by the fact that it is part of a compressor located on the seabed. 10. Application of a permanent magnet-based eddy current braking device for emergency braking of a compressor in the event of a power failure or failure of at least one magnetic bearing in the compressor.