Subsea pressure booster

Abstract

Subsea turbomachine for boosting the pressure of petroleum fluid flow from subsea petroleum productions wells or systems, comprising an electric motor and a compressor or pump driven by the electric motor, a fluid inlet and a fluid outlet, distinctive that the turbomachine comprises a pressure housing common for the electric motor or stator, and compressor, pump or rotor; a magnetic gear inside the common pressure housing for operative connection between the motor or stator and compressor, pump or rotor; and a partition inside the common pressure housing, arranged so as to separate a motor or stator compartment from a compressor, pump or rotor compartment.

Claims

1. A subsea turbomachine for boosting a pressure of a petroleum fluid flow from subsea petroleum production wells or systems, the subsea turbomachine comprising: an electric motor comprising a rotor and a stator, the rotor and the stator being disposed in a motor compartment; a fluid inlet; a fluid outlet; a pressure housing common for the electric motor and at least one of a compressor and a pump; a magnetic gear inside the common pressure housing for operative connection between the electric motor and the at least one of the compressor and the pump; an electric motor shaft and a turbomachine shaft; wherein an outer ring of the magnetic gear is connected to the electric motor shaft and an inner ring of the magnetic gear is connected to the turbomachine shaft, or opposite; wherein the electric motor shaft and the turbomachine shaft are suspended in bearings; a partition inside the common pressure housing, arranged so as to separate the motor compartment hermetically from a pump or compressor compartment such that the subsea turbomachine has no external liquid lubrication system or supply; and a pressure balancing device independent from the fluid inlet and the fluid outlet comprising an arrangement between an inlet side of the pump or compressor compartment and the motor compartment, the pressure balancing device further comprising two control valves.

2. The subsea turbomachine according to claim 1, wherein a gearing ratio of the magnetic gear is 1:1.

3. The subsea turbomachine according to claim 1, comprising at least one of a planetary magnet gear and an inner cycloid magnet gear wherein an inner ring of the at least one of the planetary magnet gear and the inner cycloid magnet gear is connected to the compressor or pump.

4. The subsea turbomachine according to claim 1, wherein the magnetic gear comprises permanent magnets.

5. The subsea turbomachine according to claim 1, wherein the magnetic gear comprises electromagnets on at least one of a low speed side, a high speed side, or both sides of the magnetic gear.

6. The subsea turbomachine according to claim 5, wherein a rotational speed of a magnetic field on at least one of the low speed, the high speed, or both sides of the magnetic gear can be controlled to vary speed of the pump or compressor up and down compared to the speed of the electric motor shaft.

7. The subsea turbomachine according to claim 1, wherein the magnetic gear is arranged as a gearbox that makes the magnetic gear possible to change a step-up ratio standstill by use of an ROV or by a dedicated electric motor disposed at the gearbox.

8. The subsea turbomachine according to claim 1, comprising at least one penetrator connected for receiving electric power and signals to operate the turbomachine.

9. The subsea turbomachine according to claim 1, wherein the magnetic gear is a radial magnetic gear with the partition arranged between the inner and outer parts.

10. The subsea turbomachine according to claim 1, wherein the magnetic gear is a cycloid magnetic gear or any radial magnetic gear with the partition arranged between the inner and outer parts.

Description

FIGURES

(1) FIGS. 1 and 2 illustrate prior art solutions,

(2) FIGS. 3 to 6 illustrate embodiments and features of the present invention, and

(3) FIG. 7 gives examples of magnetic gears.

(4) FIG. 8 illustrates a preferable embodiment of the invention, and

(5) FIG. 9 illustrates in some more detail the magnetic gear of a subsea turbomachine of the invention.

DETAILED DESCRIPTION

(6) In the following the invention in several embodiments will be illustrated and explained by figures. Reference is made to Table 2 for understanding of FIG. 3-5. It shall be mentioned that only main components necessary for understanding of the invention are included in FIGS. 3-6.

(7) TABLE-US-00002 TABLE 2 Item # Explanation  1 Motor  2 Compressor or other turbomachine  3 Pressure housing  4 Shaft seal  4′ Partition  5 Compressor (or other turbomachine) inlet  6 Compressor (or other turbomachine) outlet  7 Compartment for motor and magnetic gear or low speed part of the magnetic gear  8 Compartment for compressor and high speed side of gear  9, 9′ Shafts 10 Shaft coupling either rigid or flexible or common shaft for compressor and motor 11, 11′, 11″, Radial bearings 11′″ 12, 12′ Axial bearings 13 Magnetic gear 14 Low speed side of magnetic gear 15 High speed side of magnetic gear 16 Partition, diaphragm or shroud hermetically separating low and high speed of gear 17 Pressure vessel or tank for nitrogen 18, 18′ Control valves 19 Pressure-Volume-Regulator (PVR) 20, 20′, 20″ Tubes

(8) Reference is made to FIG. 3 illustrating a pressure booster in the form of a compressor with magnetic gear and electric motor, and where the magnetic gear has a step-up ratio that steps up the speed from that of the motor shaft, which is low enough to be supplied with a low enough frequency to have stable cable transmission, to the necessary speed of the compressor. The motor can for instance rotate with a speed of 3000 rpm, i.e. the electric power has a frequency of 50 Hz for a 2-pole motor, and the gear can have a step up ratio of 2.5:1, meaning that the compressor has a speed of 7500 rpm. If the surface located power source has a VSD, the frequency can for instance be varied between 33 and 67 Hz. A partition 4′ is arranged between the magnetic gear 13 and the pressure housing and inside the magnetic gear, not shown, between the gear higher speed and lower speed sides.

(9) Reference is made to FIG. 4 illustrating that there is a partition 4′ with a shaft seal between the compressor 2 in compartment 8 and the motor and magnetic gear in compartment 7. Pressure vessel or tank 17 contains nitrogen reservoir at high pressure, e.g. 400 bar charging pressure, and nitrogen is supplied in a small but sufficient rate to the motor-gear compartment to keep its atmosphere harmless with respect to ingress harmful components of boosted gas which in principle will be kept our of the motor-gear compartment by flow of nitrogen from motor compartment and into the compressor. Some ingress of contaminants from the gas being boosted may sometimes happen, but these components will be diluted to harmless levels by the continuous supply of nitrogen. Alternatively the nitrogen can be supplied by tube in an umbilical.

(10) If the arrangement shown in FIG. 4 with supply of nitrogen from a pressure vessel is used, the flow regulation by valve 18 can be controlled by measurement of the pressure in the vessel 17. The decrease of the pressure is expression for the flow out of the vessel with sufficient accuracy because the temperature of the gas volume in the tank is close to constant, i.e. the seawater temperature, that at deep water is close to constant year around. Alternatively to setting a small flow of nitrogen through valve based on calculations and experience to keep the nitrogen atmosphere in compartment 7 harmless, the valve can be controlled by having sensors in the nitrogen atmosphere that measures the concentration of contaminants in the nitrogen; e.g. total hydrocarbons, selected hydrocarbons (e.g. heavy hydrocarbon molecules) water vapour, H.sub.2S, CO.sub.2, MEG vapour or other harmful components that indicates the degree of contamination of the atmosphere. The valve 18 can than based on these measurements regulate the supply of nitrogen to keep the degree of contamination below a harmful level. This level can be established by experience and knowledge about the tolerance of the various contaminants of the materials in compartment 7. The control of valve 18 can either be continuous or intermittent.

(11) In FIG. 5 is given an illustration of a compressor where the high speed motor side of the magnetic gear is hermetically separated from the low speed motor side by a partition or diaphragm also called shroud. In this way the motor with its part of the gear and magnetic bearings is hermetically separated (compartment 7) from the compressor with the high speed part of the gear and magnetic bearings (compartment 8). Some kind of pressure balancing of the pressure of the motor-gear atmosphere of compartment 7 compared to the suction pressure of the compressor in compartment 8 will be necessary to keep the requirements of the strength of the shroud reasonable. In FIG. 5 the pressure balancing is arranged by supply of nitrogen from tank 17 (or alternatively from tube in umbilical) through pressure transmitting tube 20 and by a Pressure-Volume-Regulator, PVR, which is a well known and verified device. A pressure transmitting tube is connected to the compressor compartment, and the PVR will continuously compare and control the pressure of the motor-gear atmosphere to be close to the compressor suction pressure. Pressure balancing can also be arranged with an arrangement of pressure regulating valves 18 and 18′ and pressure sensor or sensors that detects the pressure difference between the motor-gear compartment and the compressor suction pressure.

(12) In FIG. 6 is an illustrated pressure balancing device by use of two control valves being controlled by measurement of pressure differential between compartments 7 and 8. Nitrogen is supplied by control valve 18 while overpressure in compartment 7 compared to compressor suction pressure is released by control valve 18′

(13) In FIG. 7 is illustrated following types of magnetic gears: Spur (parallel, radial), planet and cycloid gear.

(14) FIG. 8 illustrates a preferable embodiment of the invention wherein a stator 21 is arranged in a stator compartment 22, separated by a partition 16 from a rotor compartment 28, the rotor compartment comprises a compressor 2 or pump arranged directly on the rotor shaft or coupled to the rotor 23. Preferably, pump or compressor impellers, or both, are arranged directly on the rotor shaft. Preferably the partition 16 seals the stator compartment hermetically from the rotor compartment. The partition preferably includes pole pieces 24, electromagnets or both, for enhanced magnetic coupling, arranged between the gear sides, for a set or controllable gear ratio. The gear ratio can be controlled by controlling optional electromagnets in the partition, the rotor position can be inferred from the impedance of the stator, by using an algorithm or a look up table. The rotor shaft may preferably comprise bearings on either end, and also on the shaft between rotor and impellers if required.

(15) FIG. 9 illustrates a preferable subsea turbomachine or a general purpose turbomachine or pressure booster according to the invention, wherein the magnetic gear is a radial magnetic gear with the partition 16 arranged between the inner part 25 and outer parts 26. Increasing the length of the gear allows better magnetic coupling and transfer of higher effect, which is preferable, but may require extra bearings on the gear end of the shaft. The partition comprises magnetic pole pieces 25 or electromagnets or both in the partition between the lower speed and higher speed sides of the gear. The number of pole pieces and/or electromagnets are related to the gear ratio, preferably the number of rotor elements and the number of pole pieces or electromagnets are multiples or fractions of the number of stator elements, the multiple or fraction ratios relate to the gear ratio. The gear ratio can be controlled by energizing or not energizing electromagnets in the partition, said electromagnets are preferably connected electrically to the stator power source or side, avoiding any slip rings or other rotatable electric connections. This figure illustrates in more detail the magnetic gear, the partition 16 and pole pieces 24 or similar, and the common pressure housing 3, whilst the motor with stators 21 and rotor 23, and the compressor 2 are illustrated out of scale and not to detail, for clarity. Bearings and some other features are for clarity not illustrated or only indicated in order to show more clearly how the magnetic gear coupling can be configured and arranged. With a radial gear of the type illustrated, which side is the inner or outer side or faster or slower side can be subject to a choice of design, however, in many cases the faster side should be the inner side since this will in most cases result in lower stress levels.

(16) Some of the advantages of the invention are as follows:

(17) Non-contact elements—no friction between the elements.

(18) High torque transfer due to multiple pole interaction.

(19) Utilization of peak torque.

(20) Input and output shafts can be isolated.

(21) Increased temperature range, no elastomeric seals.

(22) Inherent overload protection.

(23) Increased tolerance of misalignment.

(24) Several options for arranging shift of gear ratio, several mechanical and several electronic options.

(25) The liquid lubrication system and supply can be eliminated.

(26) The pressure boosters or turbomachines of the invention may include any features as described or illustrated in this document, in any operative combination, each such combination is an embodiment of the present invention. The invention also provides use of the turbomachine and pressure booster of the invention, for pressure boosting fluids subsea and topsides, particularly gas and oil subsea.