Pumps – Motor driven – Motor rotor intermediate coaxial pump rotors
Reexamination Certificate
2000-12-15
2003-09-09
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Motor rotor intermediate coaxial pump rotors
C417S356000, C417S423700, C310S154010
Reexamination Certificate
active
06616421
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compressor assembly, in particular to a compressor assembly comprising a compressor having a rotatable impeller and a motor driving the compressor, the impeller and the motor being linked by a direct drive.
BACKGROUND OF THE INVENTION
Compressors having an impeller rotatable within a compressor casing are well known in the art. Such compressors include both centrifugal compressors or radial flow compressors and axial flow compressors. In centrifugal or radial flow compressors, the fluid being compressed is caused by the rotating impeller to flow along a passageway in which the cross sectional area normal to the flow gradually decreases in the direction of flow. Axial compressors operate by causing the fluid to be compressed to flow along a passage of constant or substantially constant cross sectional area. An example of such a compressor is disclosed in U.S. Pat. No. 4,428,715.
Compressors of the aforementioned types may be driven by a range of motors, such as internal combustion engines, and turbines. However, in many applications it is both preferable and desirable to drive centrifugal and axial flow compressors using electric motors. Typically, induction or synchronous electric motors have been employed to drive compressors. To date, a major drawback associated with the use of electric motors to drive rotating impeller compressors has been the linkage between the electric motor and the compressor impeller. A given compressor will have a specific speed of rotation of the impeller in order to achieve the compression duty required of it. At the same time, an induction electric motor will have an optimum speed of rotation, at which the torque output is at a maximum. Heretofore, in order to link the compressor with a suitable electric drive motor, it has been necessary to employ an arrangement of one or more gears. In this way the different optimum speeds of rotation of the compressor and the electric motor can be accommodated. A particular problem arises in the case of high speed centrifugal compressors, having power requirements of the order of 200 horsepower or less. Such compressors are often required to operate at high speeds, which can be in excess of 50,000 rpm. The optimum speed of rotation of an induction electric motor suitable for this duty is far lower than the speed of rotation required of the high speed compressor, requiring a gear assembly to be employed in the drive assembly of the compressor. However, for such compressors, the high costs of incorporating an arrangement of gears in the drive assembly results in a significant economical disadvantage. This in turn has led to other forms of compressors, such as screw compressors, being favored for such duties.
Accordingly, there is a need for a compressor assembly in which the requirement for a gear assembly in the drive is dispensed with and in which the compressor and the electric motor are directly linked. There is an especial need for a direct drive compressor and electric motor assembly capable of operating at the high speeds of rotation specified above.
A rotordynamic machine is disclosed in U.S. Pat. No. 6,043,580, for use in the pumping of a fluid. The machine comprises an electrical assembly in combination with a turbomachine or centrifugal pump. The electrical assembly acts as a combined electric motor and bearing assembly, having a rotor supported and rotated by magnetic fields generated in a stator. In this way, the motor is bearing-free. The rotor of the motor is formed as part of the shaft connecting the electrical assembly with the turbomachine or pump. U.S. Pat. No. 6,043,580 discloses that the combined electric motor and bearing assembly may be arranged on the principles of an induction motor, an asynchronous motor, a reluctance motor, or a synchronous motor. Specific designs mentioned in U.S. Pat. No. 6,043,580 include assemblies having a rotor with one or more permanent magnets and a rotor designed as a cage rotor with a short circuited cage. In the specific embodiment disclosed and described in detail in U.S. Pat. No. 6,043,580, the combined motor and bearing assembly comprises a stator having two sets of current windings, one set for generating the magnetic fields to rotate the rotor, the second set for generating the magnetic journaling for supporting the rotor shaft in position. The rotor is designed as a cage rotor, having the same number of poles as the stator windings generating the drive, but a different number of poles to the stator windings providing the support for the shaft.
U.S. Pat. No. 6,043,580 is concerned specifically with overcoming the problems associated with magnetic bearings and their limited bearing capacity. The solution proposed, as discussed above, is to arrange an electric motor, which may be one of a wide variety of arrangements of electric motor, such that the rotor is both supported and rotated by a magnetic field. U.S. Pat. No. 6,043,580 does not disclose or suggest an assembly for use at the high speeds of rotation specified above.
U.S. Pat. No. 6,056,518 discloses a fluid pump for use in the coolant system for an automobile. The fluid pump disclosed comprises a switched reluctance electric motor, in which the impellor of the pump is the rotor of the electric motor. The operating speeds for the fluid pump disclosed in U.S. Pat. No. 6,056,518 are low, being stated to be from 0 to 5000 rpm. U.S. Pat. No. 6,056,518 specifically teaches that the advantage of using the switched reluctance motor is that it does not rely for operation upon the use of magnets, which are stated to be heavy, costly and to degrade quickly over time.
SUMMARY OF THE INVENTION
According to the present invention there is provided a compressor assembly comprising
a compressor having a compressor casing comprising a fluid inlet and a fluid outlet;
an impeller rotatable within the compressor casing;
an electric motor;
a rotatable drive shaft assembly extending from the electric motor into the compressor casing;
the impeller being mounted on the drive shaft assembly and rotatable therewith within the compressor casing; and
the electric motor comprising a stator and a rotor, the rotor being mounted on the drive shaft assembly and rotatable therewith; wherein the compressor assembly operates at a speed of 25,000 rpm or higher.
A range of electric motors may be employed in the compressor assembly of the present invention. Such motors include induction motors, synchronous motors and asynchronous motors.
Surprisingly, contrary to the suggestions in the prior art, it has been found that the use of a permanent magnet electric motor allows a direct drive compressor assembly to be constructed which is particularly suitable for operation at high speeds. Accordingly, a permanent magnet motor is the preferred motor for use in the assembly of the present invention.
It has been found that a permanent magnet motor may be employed to drive a rotating impeller compressor using a direct drive configuration, that is one in which the impeller of the compressor and the rotor of the motor are directly connected and rotate at the same speed. It has been found that a permanent magnet motor may be used to drive the rotatable impeller of a compressor, allowing the gear assembly or gear box to be dispensed with and a direct drive assembly to be employed.
The compressor assembly of the present invention is operated at high speeds. In this respect, high speed operation is considered to be when the compressor and motor operate at speeds of 25,000 rpm and higher. The compressor assembly of the present invention may be operated at speeds of 50,000 rpm, with speeds of 75,000 rpm and higher being possible. With such high speeds of operation, it has been found that the efficiency of the motor design plays an important role. Induction motors, require a magnetic field to be induced in the rotor, which is typically comprised of a plurality of iron laminations. At the high speeds of rotation required of the compressor assembly of the present invention, the need to induce
Czechowski Edward S.
Mruk Gerald K.
Weber Peter J.
Bielinski Peter A.
Cooper Cameron Corporation
Freay Charles G.
Hartmann Michael P.
Liu Han L.
LandOfFree
Direct drive compressor assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Direct drive compressor assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct drive compressor assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3036544