System, Method and Apparatus

Field of Invention

The present invention relates to an apparatus for introducing a second flow into a first flow. The present invention further relates to a coupling assembly between an output shaft of a motor and an input shaft of a machine. It also relates to a seal assembly for sealing between a housing and a shaft rotatably mounted in the housing. The present invention further relates to a system for dispersing matter in a flow, as well as relating to a system for compression, preferably in-pipe compression of a flow. In particular, the invention relates to a system for compression in a confined space, preferably in the case of a mixed stream of gas, liquids and particulate solids. Advantageously, the invention relates to an In-pipe Gas Compression (IGC) system where the compression takes place in a small space and can handle three- phase (or multi-phase, or mixed) streams.

Summary of Invention

Re-integration

According to one aspect of the invention, there is provided an apparatus for introducing a second flow (usually of lower pressure) into a first flow, comprising a first conduit for carrying the first flow, the first conduit comprising means for generating a vortex in the first flow, and a second conduit for carrying the second flow, the second conduit having an outlet arranged to introduce the second flow into the vortex in the first flow. The apparatus is intended to integrate the first and second flows into one another. The vortex can effect mixing of the first and second flows and the increase in pressure of the second flow, in particular if the second flow has a higher density than the first flow. In this case the higher density second flow is subject to centrifugal forces acting to move the second flow away from the centre of the vortex. Preferably the outlet of the second conduit is located in a region of relatively lower pressure, preferably at or near the centre of the vortex, so as to effect suction of the second flow into the first flow. In addition, introduction at the centre of the vortex can optimise the mixing effect, in particular by acting to move the second flow outward with a more even angular distribution than otherwise. Entrainment can then increase the pressure of the second flow as it moves to a region of higher pressure as it migrates away from the low pressure central region of the vortex. Preferably the first and second conduits are substantially co-axial. This can further assist the mixing. In addition to the static pressure difference between the first and second conduit having the effect of causing the introduction of the second fluid into the first, the axial velocity of the second fluid can cause the entrainment of the second fluid into the first.

Preferably the second conduit comprises means for generating a further vortex in the second flow, the direction of rotation of the further vortex preferably being the same as the direction of rotation of the vortex. This can further assist the mixing. Preferably a suction conduit is arranged downstream of the outlet of the second conduit, the suction conduit being arranged to aspirate at least a portion of the flow. Preferably the suction conduit is arranged to be at a lower pressure than the outlet of the second conduit. This can enable entrainment of the second flow into the first flow even if the low pressure central region of the vortex alone does not provide a large enough pressure difference for entrainment. The suction conduit can effect suction of the second flow into the first flow. Preferably the inlet to the suction conduit is arranged at or near the centre of the vortex. The vortex can (in addition to effecting mixing of the first and second flows) also ensure that the second flow moves outward and away from the central region. Arranging the inlet of the suction conduit at or near the centre of the vortex can ensure that a substantial portion of the second flow may avoid suction into the suction conduit. The centrifugal effect in the vortex can prevent the second flow (e.g. a liquid) from entering the suction conduit.

Preferably the outlet of the suction conduit is in fluid communication with the first conduit upstream of the outlet of the second conduit. As the suction conduit aspirates a portion of the flow, this may ensure that the aspirated portion of the flow is returned to the first flow and not lost. Preferably the fluid connection to the first conduit is arranged at a position at relatively lower pressure, for example upstream of a compressor. This may ensure that the suction conduit is at a relatively lower pressure.

Preferably the second conduit and the suction conduit are substantially co-axial. This can assist in ensuring that a substantial portion of the second flow may avoid aspiration into the suction conduit. Preferably the average diameter of the first conduit downstream from the vortex generating vanes is smaller than at the outlet of the vaned region. This may cause the vortex generated in the first flow to become a free vortex which has a region of particularly high rotational velocity and hence low pressure at the centre. Preferably the cross-sectional area of the first conduit downstream from the outlet of the second conduit is larger (or alternatively smaller) than at the outlet of the second conduit. The smaller cross-sectional area may cause the vortex generated in the first flow to become a free vortex which has a region of particularly high rotational velocity and hence low pressure at the centre. A change in the average diameter of the first conduit may suffice to create the free vortex, in particular in the case of an annular flow path.

Preferably the cross-sectional area of the first conduit downstream from the outlet of the second conduit is larger (or alternatively smaller) than at the outlet of the second conduit, and larger (or alternatively smaller) than at the inlet to the suction conduit. The cross-sectional area being smallest between the second conduit and the suction conduit may cause the vortex generated in the first flow to become a free vortex which has a region of particularly high rotational velocity and hence low pressure at the centre, and further downstream again have lower rotational velocity. Again, a change in average diameter of the first conduit may suffice to create the free vortex, in particular in the case of an annular flow path. Preferably the average diameter of the first conduit downstream from the inlet of the second conduit is smaller than the average diameter of the first conduit at the mlet of the second conduit, in order to increase the speed of the vortex of flow.

Preferably the first conduit is arranged to carry predominantly a gas flow and the second conduit is arranged to carry predominantly liquids and solids. The apparatus is equally suitable for other combinations of flows, provided the second flow has a higher density than the first flow. For example, the first and second flows may both be predominantly liquid.

Preferably the means for generating a vortex in the first flow comprises a formation for imparting a rotational component to the flow. Preferably the means for generating a further vortex in the second flow comprises a formation for imparting a rotational component to the flow. Formations for imparting a rotational component include for example: vanes, ndges, baffles, channels and ducts.

Preferably the flow in the second conduit is at a (nominally) lower pressure than the flow in the first conduit.

Preferably there is further provided a formation for vortex stabilisation, preferably an elongate structure, preferably a cone or a needle. Preferably the formation is co-axial with the first and/or second conduit.

For efficient performance the formation may be rotatable, preferably in the same direction of rotation as the vortex.

Preferably the formation is attached to a rotatable shaft, preferably a compressor shaft, the compressor shaft preferably driving the first flow. Coupling

According to one aspect of the invention, there is provided a coupling assembly between an output shaft of a motor, and an input shaft of a machine, the motor being contained in a sealed housing, and the coupling comprising a magnetic coupling wherein a portion of the housing is shaped to fit between the output shaft of a motor and an input shaft of a machine. The coupling can permit hermetic sealing of the motor in the housing, while transferring torque from the motor to the machine. The sealed housing can prevent contaminants from entering into the motor and causing fouling and damage; it can also prevent matter from passing from the motor housing into the machine and the environment.

Preferably said portion comprises a ceramic component, preferably a single machined and fired (non- magnetic and non-electrically conductive) ceramic component. The ceramic component can provide a mono -magnetic, non-metallic sealing surface with favourable friction and thermal properties between the two parts being coupled.

Preferably one of the shafts has a female connecting part and the other of the shafts has a male connecting part, the magnetic coupling being provided between the male and female connecting parts. The female and male part may improve coupling, for example by providing a greater area over which the coupling may act. The portion of the housing shaped to fit between the output shaft of a motor and the input shaft of a machine is preferably shaped to fit between the female and male connecting parts.

Preferably there is a substantial tolerance in the fit in at least one of: axial, radial, and angular direction, between the input shaft of a machine and the portion of the housing shaped to fit between the output shaft of a motor and the input shaft of a machine. The magnetic coupling can be capable of functioning even with a misalignment; hence a substantial tolerance in the fit of the opposing coupling parts may be acceptable. This can be particularly beneficial for a modular construction where a motor module and a machine module are assembled independently, and mated together after the modules are assembled Modular construction can be especially convenient to minimise on-site assembly and facilitate convenient repair or change of compressor duty specification.

Preferably there is a substantial tolerance in the fit in radial direction between the input shaft of a machine and the portion of the housing shaped to fit between the output shaft of a motor and the input shaft of a machine, preferably between 0.1 and 2 millimetres, more preferably between 0.2 and 1 millimetres, yet more preferably between 0.3 and 0.7 millimetres.

Preferably there is a substantial tolerance in the fit in axial direction between the input shaft of a machine and the portion of the housing shaped to fit between the output shaft of a motor and the input shaft of a machine, preferably between 0.5 and 10 millimetres, more preferably between 1 and 7 millimetres, yet more preferably between 3 and 5 millimetres.

Preferably there is a substantial tolerance in the fit in angular direction between the input shaft of a machine and the portion of the housing shaped to fit between the output shaft of a motor and the input shaft of a machine, preferably between 0.5 and 5 degrees, more preferably between 1 and 3 degrees, yet more preferably between 1.5 and 2.5 degrees.

Preferably the female connecting part is provided on the input shaft of the machine. Alternatively the female connecting part is provided on the output shaft of the motor.

A lip part may be arranged between the housing and male or female connecting part on the input shaft of the machine, so as to prevent entry of matter between the housing and the connecting part on the input shaft as well as facilitate mounting and sealing. Preferably the machine is a compressor, preferably for location in a pipeline.

A pressure controller (such as for example a bladder-type passive regulator, or an automatic (e.g. passive) venting system, or other actively controlled pressure control systems) may be arranged to control the pressure in the sealed housing in dependence on the pressure difference between the interior and the exterior of the sealed housing. This can ensure that the pressure on the portion of the housing shaped to fit between the output shaft of a motor and an input shaft of a machine does not cause excessive loading or damage to said portion.

Preferably the pressure controller is arranged to control the pressure in the sealed housing by controlling flow at an inlet and/or outlet to the sealed housing, preferably a cooling flow, preferably a gas cooling flow.

Preferably a flow at an inlet and/or outlet to the sealed housing is arranged to cool the interior of the sealed housing, the flow preferably being a cooling flow, preferably a gas cooling flow. The flow may be directed between the output shaft of the motor and the sealed housing to cool the coupling assembly.

Preferably the coupling assembly further comprises said motor and optionally said machine.

According to one aspect of the invention there is provided a combination comprising a first and a second coupling assembly (each preferably according to any coupling assembly described above) wherein the first coupling is between an output shaft of a first motor, and a first end of an input shaft of a machine, the first motor being contained in a first sealed housing, and the second coupling is between an output shaft of a second motor, and a second end of the input shaft of the machine, the second motor being contained in a second sealed housing. The combination of two magnetic couplings at opposing ends of a machine input shaft can be particularly beneficial as it can provide the combined torque to the input shaft, without requiring the size of motor otherwise necessary for the combined torque. This may be useful for installation in narrow spaces. Further, the magnetic couplings can introduce losses during torque transients that tend to damp torsional oscillations between the motor and compressor sections. Further, if the machine is obstructed during operation (for example due to fouling or breakage), then magnetic couplings may slip and allow the motors to run down without damaging the shafts.

Seal

According to one aspect of the invention, there is provided a seal assembly for sealing between a housing and a shaft rotatably mounted in the housing, the assembly being suitable for use with a magnetic medium arranged between the shaft and the housing, and having at least one magnet arranged to position magnetic medium between the shaft and the housing. The seal can allow to hermetically seal the interior of the housing, while transferring torque via the shaft to the exterior of the housing. The sealed housing can prevent contaminants from entering into the housing and causing fouling and damage; it can also prevent matter from passing from the housing into the environment. Preferably the seal assembly further comprises the magnetic medium. Preferably the magnetic medium is solid at a first predetermined temperature, and arranged to seal without the use of the magnet; and preferably the magnetic medium is liquid at a second predetermined temperature and arranged to seal only with the use of the magnet. This may allow manufacture and assembly of the seal at the first (most likely lower) temperature. As the seal is solid, the interior of the housing can remain hermetically sealed for example during storage and transport. The second (most likely higher) temperature is preferably close to the operation temperature of the assembly. Hence under operational conditions the seal can be liquid and kept in place by the magnet.

Preferably the first predetermined temperature is between 0 and 50 °C; and the second predetermined temperature is between 50 and 250 °C, preferably above 75 °C.

Preferably the magnetic medium comprises a metal or amalgam, preferably beryllium or a beryllium amalgam, preferably containing a plurality of magnetic particles. The density of magnetic particles may be defined by conventional wisdom. Preferably the magnetic medium is immiscible with a mixed phase fluid flow.

Preferably the seal assembly further comprises heaters arranged to control the temperature of the magnetic medium. This can allow the assembly to become conditioned for operation at start-up. In a variant, the temperature of the ambient environment is sufficient to liquefy the metal seal.

In a variant, the magnetic medium comprises a ferrofluid or a hydrocarbon based liquid, preferably a magnetic liquid, preferably containing magnetic particles. Preferably the magnet is an annular shaft magnet and further comprising an annular housing magnet of complementary (or opposing) polarity mounted to the housmg. Preferably a chamber is arranged between the shaft and the housing for receiving the magnetic fluid between the shaft and the housing.

Preferably the seal assembly comprises at least one rare earth magnet and/or at least one electromagnet.

Preferably the seal assembly comprises a single stage seal.

Preferably the seal assembly comprises a pressure controller arranged to control the pressure in the housing in dependence on the pressure difference between the interior and the exterior of the housing. This may protect the seal from damage for example in case of pressure surges that could disrupt the liquid seal.

Preferably the seal assembly comprises the pressure controller arranged to control the pressure by controlling flow at an inlet and/or outlet to the housing, preferably a cooling flow, preferably a gas cooling flow.

According to one aspect of the invention, there is provided a seal assembly for sealing between a housing and a shaft rotatably mounted in the housing, comprising a chamber for receiving a magnetic fluid between the shaft and the housing, and having at least one shaft magnet mounted to the shaft arranged to position magnetic fluid between the shaft and the housing. Slug Abatement

According to one aspect of the invention, there is provided a system for dispersing matter in a flow comprising a detector for detecting a slug of matter in the flow, a disperser for dispersing the matter, and a compressor for compressing the flow, the detector and the disperser being arranged upstream from a compressor, the disperser operating in dependence on detection of the slug. Preferably the detector is adapted to re-direct at least some of the flow from the output of the compressor back to the disperser, upon detection of a slug of matter. Preferably the flow is substantially gaseous, and preferably the slug of matter is substantially liquid and/or solid. Preferably the slug of matter is a composite of gas, liquid and/or solid matter. Detection may include measuring a signal that relates to the (composite) density of the slug, or the (composite) mass of the flow.

Preferably the disperser channels re-direct (preferably gas) flow toward the slug of matter for reducing the density of the slug of matter and/or for breaking up the slug to occupy a lower composite density of mixed phase fluid. Preferably the slug is composite gas, liquid and solid matter, and preferably the density is the composite density of the slug.

Preferably the disperser comprises a plurality of nozzles. Preferably the plurality of nozzles are arranged to channel the re-directed flow orthogonal to the direction of the flow. Preferably the disperser is elongated, preferably elongate in the direction of the flow.

Preferably the detector is arranged upstream from the disperser.

Preferably the disperser is arranged upstream from a separator, the separator effecting separation of the matter from the flow, and the separator preferably being arranged upstream from the compressor.

Preferably the detector is adapted to switch the compressor to a surge, (full) recycle, or partial recycle (mode) to the (slug) disperser upon detection of a slug of matter.

Preferably the detector is adapted to re-direct a variable proportion of the flow from the output of the compressor back to the disperser. The variable proportion may be selected in dependence upon a signal that relates to the (composite) density of the slug, or the mass flow of the slug. This allows the system to re-direct a necessary flow portion toward a slug of measured density in order to reduce the density of the slug below a pre-determined density threshold. Preferably the system is suitable for use in a pipeline.

System— cooling unit and slug abatement

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising:

a compressor arranged to be driven by at least one motor;

a separator arranged upstream of the compressor for separating liquids and solids out of the flow; and a cooling device for cooling the motor, the device including a heat exchanger arranged upstream of the separator.

Preferably the system further comprises a system for dispersing matter in a flow, the system for dispersing matter in a flow preferably being arranged upstream of the separator and downstream of the heat exchanger. Alternatively, the system for dispersing matter in a flow may be arranged upstream of the separator and upstream of the heat exchanger. Preferably the system for dispersing matter in a flow is a system for dispersing matter in a flow as described above. Preferably the system further comprises a coupling assembly between the at least one motor and the compressor wherein the coolant pressure may be adjusted to prevent fracture (or damage) of the sealed housing. Preferably the cooling device is operable to adjust the pressure in the sealed housing. Preferably the coupling assembly is a coupling assembly as described above. Preferably the system further comprises a seal assembly between a housing of the at least one motor and a shaft of the compressor wherein the coolant provides the flow at the inlet and/or outlet to the sealed housing. Preferably the seal assembly is a seal assembly as described above.

Preferably the heat exchanger is connected to the inlet and/or outlet to the housing, preferably with a cooling flow, preferably with a gas cooling flow.

According to one aspect of the invention, there is provided a system for in-pipe compression of a flow comprising:

a compressor;

a system for dispersing matter in a flow, preferably as described above; and

a re-integrator, preferably an apparatus as described above;

wherein a latching non-return valve is arranged between the compressor and the re-integrator.

System— latching non-return valve

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising:

a compressor;

a separator arranged upstream of the compressor for separating liquids and solids out of the flow;

a re-integrator arranged downstream of the compressor for re-introducing said liquids and solids into the flow; and

a system for dispersing matter in a flow.

Preferably the system further comprises a latching non-return valve arranged between the compressor and the re-integrator.

Preferably the system for dispersing matter in a flow is a system for dispersing matter in a flow as described above.

Preferably the re-integrator is an apparatus for introducing a second flow into a first flow as described above.

Alternatively the system further comprises a latching non-return valve arranged downstream of the re- integrator.

Preferably the re-integrator is an apparatus for introducing a second flow into a first flow as described above; and the system for dispersing matter in a flow is a system as described above; and the system for dispersing matter in a flow is adapted to re-direct all of the flow from the output of the compressor back to the disperser, upon detection of a slug of matter; and the latching non-return valve is adapted to be latched closed during re-direction of all of the flow from the output of the compressor back to the disperser; and the compressor outlet pressure is adapted to be maintained above the pressure downstream of the latching non-return valve; and a further conduit is adapted to conduct fluid from the re-integrator to a region downstream of the latching non-return valve during re-direction of all of the flow from the output of the compressor back to the disperser.

Preferably said further conduit is arranged to conduct fluid from a region of the re-integrator where predominantly liquid collects.

Alternatively the re-integrator may be an apparatus for introducing a second flow into a first flow as described above; and the system for dispersing matter in a flow is a system as described above; and the re-integrator is adapted to conduct the variable proportion of the flow from the output of the compressor back to the disperser.

Preferably the re-integrator is adapted to conduct the variable proportion of the flow from the output of the compressor back to the disperser from a region of the re-integrator where predominantly gas collects.

Preferably the latching non-return valve comprises a conventional non-return valve with a normally open condition that may be modified by electrical or mechanical intervention to remain closed until any ingested slug is removed from the gas stream. System— separation/re-integration

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising:

a compressor,

a separator arranged upstream of the compressor for separating liquids and solids out of the flow; and a re-integrator arranged downstream of the compressor for re-introducing said liquids and solids into the flow. Preferably re-introduction of liquids and solids into the flow is driven by the action of the compressor on the flow and/or occurs in the absence of a pump. Preferably the re-introduction occurs with minimal moving parts. Preferably the re-introduction is passive. Preferably the re-introduction is powered by the compression of production gas. Preferably the re-introduction occurs in the absence of a pump. Preferably the system comprises a single motor that powers compression, separation, and re- introduction.

Preferably the re-integrator is an apparatus as described above.

Preferably the separator is arranged to separate a fluid flow and direct a first part of the flow to the compressor, the outlet from the compressor communicating with the first conduit of the re-integrator, and to direct at least a second part of the flow to the second conduit of the re-integrator, bypassing the compressor, the re-integrator being arranged to re-integrate liquid from at least the second part into the first part at a position downstream from compressor.

Preferably the system further comprises at least one of:

a coupling assembly between a motor and a compressor, preferably as described above;

a seal assembly between a housing and a shaft, preferably as described above; and

a bearing assembly comprising at least one of: a magnetic bearing; and a gas bearing.

System— hermetic motor

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising a motor and a compressor and a coupling assembly between the motor and compressor (preferably as described above) wherein the motor is arranged to be sealed from the flow in the pipe.

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising a first motor, a compressor and a second motor,

wherein a first coupling assembly (preferably as described above) is arranged between the first motor and a first end of the compressor, and

wherein a second coupling assembly (preferably as described above) is arranged between the second motor and a second end of the compressor, and

wherein each motor is arranged to be sealed from the flow in the pipe.

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising:

a motor;

a compressor;

a shaft connecting the motor and the compressor;

a housing containing the motor arranged to seal the motor from a flow in the pipe; and a seal assembly for sealing between the housing and the shaft, preferably as described above. System— pump and common shaft

According to one aspect of the invention, there is provided a system for in pipe compression comprising a compressor;

a first separator arranged upstream of the compressor for separating liquids and solids out of a first flow to the compressor to form a second flow;

a second separator arranged to separate a gas and solid component out of the second flow, the second flow being directed to a pump downstream of the second separator; in which

downstream of the compressor and the pump the first and second flows are re-combined.

This arrangement allows the liquid component of the flow (the second flow) to be pumped so as to achieve higher pressure to facilitate recombination with the gas component of the flow (the first flow) downstream of the compressor. The gas and solid component separated out of the second flow by the second separator can be entrained in the liquid flow prior to reintegration with the gas flow.

The second separator may be arranged to separate the gas and solid component of the second flow into a gas stream and a solid stream.

Preferably the system comprises a re-integrator arranged to re-combine the second flow with the gas and/or solid component downstream of the pump. The re-integrator may for example comprise an ejector for entraining the solid/gas component into the high pressure liquid flow.

The gas stream may be combined with the first flow, optionally upstream of the first separator. Preferably the pump is arranged to be driven with the compressor by a common drive member. The system may comprise a motor arranged to drive the pump and the compressor via a common drive shaft of the motor. The pump may comprise a turbo pump.

The gas and solid component separated out of the second flow by the second separator may contain substantially liquids and solids, and may also contain a liquid component. For example, the gas and solid component separated out of the second flow by the second separator may be approximately tenfold concentrated in the liquid component with respect to the second flow upstream of the separator.

System— modular

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising:

a motor module;

a compressor module; and

a coupling assembly between the motor and compressor (preferably as described above). Preferably the motor module and the compressor module are connectable to one another. Preferably the coupling assembly accommodates a substantial tolerance in the fit between the motor module and the compressor module in at least one of: axial, radial, and angular direction. Preferably said radial tolerance is between 0.1 and 2 millimetres, more preferably between 0.2 and 1 millimetres, yet more preferably between 0.3 and 0.7 millimetres. Preferably said axial tolerance is between 0.5 and 10 millimetres, more preferably between 1 and 7 millimetres, yet more preferably between 3 and 5 millimetres. Preferably said angular tolerance is between 0.5 and 5 degrees, more preferably between 1 and 3 degrees, yet more preferably between 1.5 and 2.5 degrees. System— general

According to one aspect of the invention, there is provided a system, preferably for in-pipe compression of a flow, comprising at least one of:

a separator comprising at least one of: a centrifugal separator; a cyclonic separator; a static separator; and conventional powered or turbine separator;

a re-integrator preferably comprising an apparatus as described above;

a system for dispersing matter in a fluid flow preferably as described above;

at least one compressor;

at least one motor contained in a sealed housing;

a coupling assembly between at least one motor and a compressor preferably as described above;

a seal assembly between a housing and a shaft preferably as described above; and

a bearing assembly comprising at least one of: a magnetic bearing; and a gas bearing.

Preferably any of the above described systems is mounted at least partially; substantially; or completely in a pipe section. Preferably the pipe section is connectable, preferably at each end to a respective further pipe section, the further pipe sections preferably forming parts of a continuous pipework.

Preferably any of the above described systems is mounted in a pressure vessel.

Preferably any of the above described systems is for use with gas, preferably natural gas.

The system, method, and apparatus for compression may comprise one, some or all of the following features, in any appropriate combination:

• A liquid re-integration system post compressor stage

• A slug abatement system

· A hermetic motor with magnetic coupling on motor

• A hermetic motor with magnetic coupling on compressor module

• A single shaft system (no coupling), preferably with a seal comprising magnetic fluid.

• Two motors coupled via magnetic couplings to each end of a compressor module

• Gas bearings up to 2 0kW sizes or magnetic bearings for larger size compressors · Any of the above in an in-pipe gas compressor system • Any of the above in an in-pipe gas compressor system contained wholly within a sealed pressure vessel (i.e. truly 'in-pipe' apart from electronics control system

The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.

The invention also provides a computer program and a computer program product for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein.

The invention also provides a signal embodying a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein, a method of transmitting such a signal, and a computer product having an operating system which supports a computer program for carrying out any of the methods described herein and/or for embodying any of the apparatus features described herein.

Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently. Furthermore, features implemented in hardware may generally be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.

These and other aspects of the present invention will become apparent from the following exemplary embodiments that are described with reference to the following figures in which:

Figure 1 shows a block diagram of a first embodiment of a compression system;

Figure 2 shows a block diagram of a second embodiment of the compression system;

Figure 3 shows a block diagram of a third embodiment of a compression system;

Figure 4 shows a block diagram of a slug abatement system;

Figure 5 shows a schematic diagram of the slug abatement system with active re-integration; Figure 6 shows a schematic diagram of the slug abatement system with passive re-integration;

Figure 7 shows a schematic diagram of a fourth embodiment of the compression system;

Figure 8 shows a schematic diagram of a fifth embodiment of the compression system;

Figure 9 shows a partial cross-section of the fourth embodiment of the compression system;

Figure 10 shows a cross-section of a compressor with a single-motor configuration, coupled by a magnetic coupling;

Figure 11 shows a cross-section of a compressor module connected to a motor module;

Figure 12 shows the detail of a modular connection with a magnetic coupling;

Figure 13 shows a cross-section of a compressor with a two-motor configuration;

Figure 14 shows a connection between a motor and a compressor, with a magnetic coupling on the motor side;

Figure 15 shows a connection between a motor and a compressor, with a magnetic coupling on the compressor side;

Figure 16 shows a cross-section of a motor with a cooling circulation and a magnetic coupling;

Figure 17 shows a connection between a motor and a compressor, with a single unbroken shaft;

Figure 18 shows an illustration of a first embodiment of a (re-)integration component;

Figure 19 shows an illustration of a second embodiment of a (re-)integration component;

Figure 20 shows an illustration of a third embodiment of a (re-)integration component;

Figure 21 shows an illustration of a fourth embodiment of a (re-)integration component;

Figure 22 shows an illustration of a fifth embodiment of a (re-)integration component; and

Figure 23 shows a schematic diagram of a compression system according to another embodiment of the invention.

In the following detailed description, an in-pipe gas compression system (IGC) is described and examples of operation environments given. A vanety of implementations are described in more detail. Specific sub-systems and components are further described in more detail.

In-pipe Gas Compression System

Referring to Figure 1 which shows an example of a compression system, in a sufficiently large pipe section 100 (or similar vessel) there is housed a compressor 102 in series with fluid flow through the pipe 100. A motor 104 drives the compressor. The motor is mounted in the pipe. The motor is an electric motor, for example a permanent magnet (brushless) two or four pole motor, with a 500 kW power output and operable at speeds between 20,000 rpm and 45,000 rpm, or greater Use of a permanent magnet motor is advantageous due to negligible maintenance requirements, higher power density and high efficiency over a broad range of operating conditions, but other types of motor could be used. In the illustrated example the motor's power supply unit 106 and control unit 108 are external to the pipe, but they could equally be housed within the pipe. The compressor 102 compresses the gas flowing through the pipe, either in a single compression stage or in a multistage compression configuration. The components are mounted in the pipe by attachment to the pipe, e.g. by fastening, welding, clamping, or an interference-fit, with or without additional frame or structural elements. The motor 104 is hermetically sealed from the flow in the pipe 100. To hermetically seal the motor 104 while enabling transmission of power to the compressor 102, different examples of couplings 103 and seals are described in more detail with reference to Figures 14 to 17. Hermetic sealing of the motor helps maintain reliability of the motor, especially for operation under harsh conditions regarding thermal and chemical environment. Alternative to hermetic sealing of the motor, a motor open to the compression medium can be implemented, if necessary with suitable coatings or canning to protect components such as wiring in the environmental conditions The passage of compression gas through the system cools the components housed inside the pipe. An additional cooling unit 136 can further assist cooling. For example, a cooling circuit to the motor, the compressor, the motor power supply, or the control unit is possible. A heat exchanger 134 may assist temperature control of components. Cooling using process fluids as the sole heat sink reduces the complexity of the system, as there is no need for e.g. an external cooling circuit (potentially requiring wet connections). The heat exchanger 134 is shown to be positioned in the pipe 100 but it could also be external to the pipe 100. If the heat exchanger 134 is positioned in the pipe, the passage of production gas (along with any liquid) cools the heat exchanger and hence coolant. A refrigeration cycle with active cooling (as opposed to passive cooling with the heat exchanger 134) may assist the cooling. Any refrigerant providing below ambient temperature may be used according to conventional wisdom.

Bearings are provided to accommodate rotation (journal bearing) and thrust (thrust bearing). Thrust bearings ensure that operation is robust to flow fluctuations and other effects that exercise an axial force in particular on the compressor. Gas bearings may be used, for example as described in EP1104504 or EP1104505. Alternatively, magnetic bearings may be used. Gas is used for lubrication of frictionless gas bearings. Gas and magnetic bearings require no additional lubrication and enable high speed operation with low losses. Bearings that require no additional lubrication minimise the potential for contamination of the gas stream, and are advantageous regarding low maintenance requirements and costs, and high reliability. Gas bearings are preferred for up to 250 kW compressors, and magnetic bearings are preferred for larger size compressors or when the shaft is otherwise too heavy, or too low speed, for sufficient operation of a gas bearing.

A separator unit 110 (for example a centrifugal separator), in series with the fluid flow and upstream of the compressor, separates liquids and solids including: gas/oil mixtures, liquids, water/condensate, foam, sand, debris or other material out of the gas stream. This allows the compressor to operate even if the incoming fluid stream contains matter that could otherwise damage or over-power and hence trip the compressor. Typical types of separator units 110 include centrifugal separators, cyclonic separators, and static separators such as filters or gravitation-assisted separators; or separators that by means of their rotational nature increase the pressure of the liquid stream above that of the gas stream to aid movement of the liquid portion. A liquid transport channel 112 carrying the liquids and solids is arranged to bypass the compressor. In the example shown in Figure 1, the liquid transport channel 112 is arranged externally to the pipe 100 carrying the gas stream to the compressor 102. In the illustrated example a reservoir 128 is connected to the liquid transport channel 112 to temporarily hold liquids and solids. One-way valves 132, 133 (also referred to as non-return valves, NRVs) prevent backflow. In the example illustrated in Figure 1, a pump 124 ensures transfer of the liquid and solid stream in the liquid transport channel 112. The pump 124 also generates some residual suction at the separator unit 110 to help aspirate liquids and solids post separation. The heat exchanger 134 is positioned upstream of the separator 110. This allows the presence of any liquid content in the production gas to help reduce the thermal loading on the production gas to be compressed, as this liquid (after absorbing heat from the heat exchanger) bypasses the compressor in the liquid transport channel. Figure 2 shows an alternative arrangement of the liquid transport channel 112. Instead of the liquid transport channel 112 being external to the pipe 100 carrying the gas stream to the compressor 102, the liquid transport channel 112 is contained within the pipe 100, arranged in a separate compartment or duct alongside or within the main gas conduit. Features affecting whether or not the liquid transport channel 112 is arranged within the pipe 100 include the required cross-sectional area of the liquid transport channel 112 and the pipe 100, as well as the required size of the liquid storage reservoir 128.

Separation and Re-integration

Separation of liquid and solid matter from the gas stream enables compression of the gas alone. Separation of a substantial proportion of the liquid and solid loading from the gas stream may also be satisfactory with a compressor able to accept a limited non-gas proportion, and this may be more easily achieved or achieved with a reduced pressure loss in the separator. It may however be necessary to reintroduce the separated liquid and solid matter back into the gas stream post-compression. In an active re-integration system with an active re-integration unit 115 as shown in Figure 1, a pump injects the liquid back into the compressed gas stream with a suitable method of diffusion to ensure adequate mixing of gas and liquid if this is desirable. In a passive re-integration system with a passive reintegration unit 114 as shown in Figure 3, passive re-integration is achieved with suction-assisted and vortex-assisted integration, as is described in more detail below.

With reference to the embodiments illustrated in Figures 1 to 3, a re-integration unit 113 (either a passive re-integration unit 114 or an active re-integration unit 115), in series with the liquid flow and downstream of the compressor, re-combines the liquid and solid matter from the liquid transport channel 112 with the compressed gas. Re-integration is desirable if the liquids and solids are not to be simply discarded, but are to be transported along in a mixed-phase production flow.

In an active re-integration system as shown in Figure 1, the pump 124 connected to the liquid transport channel 112 actively re-injects the liquid and solid stream into the gas stream.

In a passive re-integration system, as shown in Figure 3, the liquid and solid stream is passively reintegrated into the gas stream with suction assisted and/or vortex-assisted integration.

For suction-assisted re-integration the pressure differential between inlet gas flow and outlet compressed gas flow is used to power a passive gas-liquid re-integrator. A suction channel 126 connects the reintegration unit 114 to a low-pressure position, in the illustrated example upstream of the separator unit 110 The purpose of the suction channel 126 is to provide a lower pressure area 140 in proximity to the outlet 142 of the liquid transport channel 112. The effect of the low-pressure region is to aspirate liquid exiting (possibly with a passive vortex motion) from the outlet 142 of the liquid transport channel 112 into the gas stream. Any liquid that does enter the suction channel 126 is returned to a position upstream of the separator. In the illustrated example the suction channel 126 connects upstream of the separator unit 1 10, but it may alternatively connect to another position upstream of the compression, for example downstream of the separator unit 1 10. The suction channel 126 may incorporate one-way valves 132 to prevent backflow for example during start-up.

For vortex-assisted integration a vortex (or generally a rotational flow component) is imparted to the gas stream (creating a forced vortex, e.g. by means of vanes), and the outlet 142 from the liquid transport channel 112 is positioned at the centre of rotation. The lower pressure at the vortex centre assists suction of liquid from the outlet into the gas stream.

To further promote the creation of a lower pressure at the vortex centre, the channel can have a constriction (or waist) downstream of where the forced vortex is generated. In this case the forced vortex is subsequently directed into an annular or circular cross-section region with an average diameter that is reducing in the direction of the flow, and which is devoid of vanes or flow directing devices, a free vortex is created which has a region of particularly high rotational velocity and hence low pressure at the centre, especially if this is coaxial with the axis of rotation. By combining vortex-assisted and suction-assisted integration, complete re-introduction of the liquid and solid matter can be achieved, thus avoiding the need for a pump. The combination is especially beneficial as the vortex further acts to centrifuge liquid droplets and solids out of the centre of rotation. When liquids and solids move into the gas stream, they are forced radially outward in the vortex, and introduction of the liquids and solids into the suction channel 126 is minimised. A further advantage associated with use of a suction channel is that the suction provided accentuates the free vortex at its centre, reducing the necessary intensity of the forced vortex generation and the pressure drop which is associated with its generation. Passive re-integration is described in more detail with reference to Figures 18 to 20. The suction channel 126 can, instead of being external to the pipe 100 as illustrated in Figure 3, be contained within the pipe 100. Slug Abatement System

Separator units 110 are known to occasionally pass undesirable amounts of liquid into the predominantly gaseous stream in the event of particularly large masses of liquid entering the separator system. Such a large mass or globule of liquid (such as water condensate or hydrocarbons, possibly with inclusion of solid matter such as sand or debris) in the gas stream is known as a slug. Slugs, especially if of larger size, are difficult for separators (especially centrifugal separators) to deal with effectively, and they may potentially overwhelm the separator 110 and pass on into the compressor 102. This could cause fouling, disruption, or damage to the compressor 102, or even the separator 110 Therefore a slug abatement system may assist the separator unit 110 that collects the liquid that returns to the gas stream via the re-integration unit 113. The slug abatement system compnses a slug abatement unit 138 upstream of the separator 110 and a recycle channel 146 with a valve 148 that carries compressed gas from downstream of the compressor 102 to the slug abatement unit 138. Figure 4 shows the slug abatement system in more detail. A slug detector 1502 is located upstream of the separator 110 and the compressor 102. Slug detection can for example be by an optical (visible or infrared light), ultrasound, or other mass detection device (such as electric field perturbation). When the detector has identified a slug upstream of the separator 1504 the compressor is controlled to enter a recycle (or surge) mode wherein compressed gas is recycled (or bled or partially recycled) back into the input side of the compressor system. The compressed gas is recycled via a tube to a slug abatement unit 138 within the production pipeline. In the slug abatement unit 138 nozzles feed the compressed gas into the pipe to inject gas into the liquid slug, thus reducing its density. The slug may partially disrupt and break apart. The now diluted slug is easier for the separator 110 to deal with as the gas-liquid ratio is controlled to that which can be successfully dealt with by the separator and hence separation and compression can operate normally. The compressor is returned to normal compression operation when the large slug has dissipated and moved past the compressor to the outlet stream. The slug abatement system operates by diluting the slug (and reducing the slug density), not by macerating it, although further maceration may assist the slug abatement system. The slug abatement operates by recycling fluids; it is not necessary to reduce the compressor speed. On the contrary, the compressor speed may even be increased.

Figures 5 and 6 illustrate the slug abatement system in more detail. A compressor surge/recirculation valve 1600 is opened and the compressor enters into a recycle mode so that gas is returned back to the inlet from the compressor plenum. The recycled gas is fed back into the stream at the slug abatement unit 138, upstream of the separator 110. In the slug abatement unit 138 the recycled gas is dispersed along a reasonably long section of pipe, for example by a tube with holes in it. The incoming compressed (recycled) gas stream has the effect of breaking up and dispersing the slug and the material is delivered in a more distributed (over time and space) manner to the separator 110. As a result the separator 110 maintains its design function and the liquid is removed from the stream.

The incoming liquid from the slug acts to cool the (recycled) gas entering the stream from the slug abatement unit 138, thus potentially preventing overheating. If the system includes a cooling unit 136 with a heat exchanger 134, then the heat exchanger 134 is optimally located upstream of the separator 110, either upstream or downstream of the slug abatement unit. Positioning the heat exchanger 134 upstream of the slug abatement unit 138 allows the heat exchanger to take advantage of the cooling effects of the slug, and it prevents the heat exchanger 134 being subjected to the relatively higher temperature (recycled) gas entering the stream from the slug abatement unit 138; this is preferable in particular if the slug abatement system operates in partial recycle mode. If however the slug abatement system operates at full recycle mode, or with a high recycle rate, then there is likely to be only little flow upstream of the slug abatement unit 138, and the gas velocity over the outside of the heat exchanger 134 may become too low. In this case the optimum position of the heat exchanger 134 is therefore between the slug abatement unit 138 and the separator 110.

Once all liquid has been separated from the gas flow, compression can be resumed in the normal mode. The slug abatement system is suitable for use with any type of compressor system (including any rotodynamic system such as turbine impeller systems and screw compression systems).

A gas flow powered macerator can be incorporated downstream of the gas nozzles to help to further break up the diffused (but still possibly relatively globular) slug and hence assist ingestion by the liquid separator.

The downstream non-return valve 144 (NRV) closes when the system goes into recycle mode, dependent upon the actual recycle rate. When the compressor needs to go back on line, the NRV 144 is unlatched and can open, the surge valve is then closed and the compression system resumes normal operation.

Three variants of the slug abatement system are described with different means for dealing with the separated liquid prior to it being recombined with the compressed gas flow. The first variant described here is a system with active re-integration with an electric pump (as illustrated in Figures 1 and 5). On detection of a slug the compressor is controlled to enter recycle mode where gas from the output of the compressor is recycled to the slug abatement feed pipe. By the time the valves have operated to achieve this, the slug is adjacent to the slug abatement unit 138. Gas from the compressor recycle dilutes the slug and the resultant two-phase flow in the liquid separator input has a reduced liquid to gas ratio such that the separator can easily cope with the lower density flow. The separated liquid is removed from the gas flow and pumped to the system outlet (via a liquid reservoir) as normal.

If the recycle rate is high enough to close the NRV 144, then only the part of the slug next to the slug abatement unit 138 is affected. In order to ingest an especially large slug the system the machine may have to go in and out of recycle mode and provide a series of blasts to the slug and mgest the whole slug in sections. If a partial recycle is used, then the machine can continue to compress and deliver gas along the pipeline (with the NRV 144 remaining open) and the slug is continuously ingested and diluted. A variable recycle valve 1604 (e.g. in place of or in addition to the surge valve 1600) can also be used to optimise the flow. This would also allow the compressor to be used at mass flows lower than its surge margin.

A combination of slug abatement and a two phase mass flow measurement system in place of the slug detector may also be used to allow the optimum gas recycle rate operating on a given slug. Recycling the gas to a position upstream of the separator is particularly important for low flow operation mode (for instance below surge limits) as this operation mode heats up the gas. The liquid contents of the mixed phase flow cool hot incoming gas charge to the compressor and allow higher recycle rates to be used.

The second variant of the slug abatement system described here is a system with passive re-integration (as illustrated in Figures 3 and 6). Two different implementations are described:

a) In the case of a complete recycle of gas with the NRV 144 (here located downstream of the reintegration unit) closed, all liquids are reintroduced post-compression and are recycled with the gas to the compressor inlet and none exit to the production tubing downstream of the NRV 144. A possible approach is to latch the NRV closed and take steps (such as partially close the surge/recycle valve and/or increase the compressor speed) to maintain the compressor outlet pressure at a level above the pressure downstream of the NRV. Another valve then opens, venting a region of the re-mtroducer which was predominantly liquid to the region downstream of the NRV. When exiting the recycle mode, after the slug has been fully ingested, the NRV is unlatched.

b) In the case of a variable recycle of gas by means of a variable recycle valve (in which case the NRV 144 remains open), recycle gas is drawn from a region 150 of the re-introducer 114 that is predominantly gas-filled, away from where liquid collects in the re-introducer. An example of a suitable re-introducer is illustrated in Figure 20.

The third variant of the slug abatement system described here is a system with an expander in the recycle pipe (impeller driven energy recovery). The power from the gas is used to drive a pump (not illustrated) in the recycle channel 146 (with the NRV 144 closed, this time no latching is necessary). The passive re-introducer continues to be used and the recycle channel 146 ingests from a region of the passive re-introducer which has predominantly liquid content. The pump pressure rise is low if the recycle channel 146 is sized to an optimum configuration. If the pump ingests liquid from the separator outlet, it would tend to suck in gas from the liquid inlet pipe to the passive re-introducer. Therefore a valve (active or NRV) is required to prevent this happening.

Relating to the third variant, the expander can be used all the time to avoid the use of an electrically driven pump. Further the recycle gas potentially has a great deal of power and therefore a vortex can pressurise the liquid portion to above the gas portion pressure such that it is passed past the NRV. If a passive reintroduction system (as previously described) is implemented, then an NRV 132 between the liquid reservoir 128 and the re-integration unit 114 can prevent the pressure in the production pipe from forcing liquid from the reservoir 128 back into the separator 110 and pipe 100. In the recycle mode a higher pressure ratio can be achieved (by throttling or slightly increasing speed, or both), giving a compressor outlet pressure which is higher than the pressure downstream of the one-way valve 132. In this event the re-introduction of liquids may continue.

As mentioned above, the non-return valve is in some configurations a latching non-return valve. The latching non-return valve is controllable; in particular the condition of the valve is dictated by the flow of gas. The latching non-return valve can change the default state when the gas flow has stopped or reaches a threshold. A controller can be used to control the operation of the latching non-return valve in dependence on input from suitable sensors.

Modular In-pipe Gas Compression System

In the example illustrated in Figure 1 the compressor 102 and motor 104 are fully contained in a section of pipe 100, in-line and in series with fluid flow through the pipe 100 with no external rotating seals. The pipe is selected to enable operation in the intended environment, the pipe being for example able to withstand high internal or external pressure or exposure to corrosive liquids or gasses. In other examples, the compression system is contained wholly or partially within a section of pipe 100. In other examples, the compression system is contained wholly or partially within a vessel that can be sealed, and may for example be a vessel designed to withstand high pressure. The compression system being contained in a pressure vessel or pipe section is particularly important for sub-sea applications and for applications handling hazardous gasses. Since the compression system is contained in a vessel that is suitable for handling high pressures or hazardous gasses, compliance with safety requirements relating to leakage risks merely necessitates selection of a suitable vessel, and not adaptation of the entire compression system. Further, containment of components in the vessel or pipe section prevents or hinders tampering and access of unauthorised parties to the compression system and components, and improves overall security of operation. Containment of most or all of the components in a pipe section also provides ease of installation, especially where installation space is limited such as on off-shore platforms. The components can be mounted and interconnected in the pipe section at a production location, and the pipe section can then be installed on-site with minimal further connections necessary. The components being mounted in-pipe also eliminates the additional pipes otherwise necessary to connect in- and outlet to the compressor, reducing installation costs, space requirements, footprint, and weight.

The pipe section containing the compression system's components is designed to be modular, in particular being able to take the place of a regular section of pipe. To this ends in the examples illustrated in Figures 1 to 3 the pipe section 100 with the compression system has a flange 118 at either end that is connectable to a corresponding flange 120 on inlet 116 or outlet 122. The pipe section being modular enables re-allocation and re-use of a pipe section containing the compression system's components.

For certain requirements for example two pipe sections containing the compression system are arranged within a larger pipe. In other examples each pipe section contains one, two or more motors and one, two or more compressors. The selection of motor, compressor, pipe length and diameter, and other components in the compression system can be adapted to a desired compression performance, throughput, and environment. The design of this system may incorporate elements of design that allow a modular approach to the compressor train, such as sealed motor modules, compressor modules, etc. The application of field-swappable modules via magnetic couplings is possible and described later in this text.

The compression system can be positioned at suitable locations along a pipeline and serve as a compression booster. Remote monitoring and control of the compression system is possible. In another example the compression system is positioned in a vertical pipe at a wellhead and/or serving the production of gas. The gas compression system can operate at a wellhead, or within production and transport pipeline, and applications include gas compression in-pipe, at wellhead or downhole, at surface or subsea, or offshore. Figures 7 and 8 show schematic diagrams of compression systems in the absence of a slug abatement system and with active re-mtegration. Like reference numerals refer to like components to those shown in Figure 1. In Figure 7, the compression system has two compression stages 102-1, 102-2 in series. In Figure 8 the heat exchanger 134 has a motor cooling loop as well as two compressor bearing cooling loops (inlet bearing cooling loop and outlet bearing cooling loop).

In the embodiment illustrated in Figure 9, the compression system is based on configurations where more than one compressor is utilised in the IGC system, with seal-less wet gas compressors that are less than 3m in length and of a diameter small enough to be packaged in a 20 inch pressure casing. The compressors use an electric motor with multi stage compression to produce a pressure ratio between 1.3: 1 and 3 : 1 at flow rates in the range 5 to 25 million standard cubic feet dry gas per day.

The compression system illustrated in Figure 9 comprises a system sub-assembly of two compressor/motor modules (102-1/104-1 and 102-2/102-4) mounted in series with each other. A control module, comprising motor inverters and control hardware, is connected by an electric connection 500-1 and 500-2 to each compressor module. A single compressor/motor module comprises a sealed 500kW electric motor 104 driving a pair of compressor stages 102 via a magnetic coupling.

In another preferred embodiment, illustrated in Figure 10, the compression system is based on a compressor system designed to fit in a 20 inch diameter pipe 800. An electric motor 104 drives a compressor 102. Two shafts 804 and associated bearings 806 are included. Motor and bearings are gas cooled. Between 4 and 10 centrifugal compressor stages 812 are included. The bearings are magnetic. The shafts are coupled by a high speed, high torque magnetic coupling 810. The electric motor 104 (here a permanent magnet motor) is hermetically sealed in a motor housing 814. Hermetic connectors are provided. A heat exchanger is mounted where gas enters the system (at the back of the compression system in flow direction 816). Motor connections 818 in this example pass a flange connection 820 between pipe sections. A fluid flow path 822 is indicated.

To further enhance the modularity, sub-components of the compression system are contained in individual sections of pipe that are suitably connected. Figure 11 shows an example with the motor 104 mounted in a first pipe section and the compressor 102 mounted in a second pipe section. The first and second pipe sections are attached to one another with attachment flanges 830. For connection of the two sections magnetic coupling of the shaft between the motor and the compressor is particularly favourable, as the coupling offers advantages regarding tolerance in the fit between the two sections. The modules interface to each other for example as shown in more detail in Figure 12 with pins 834 and corresponding bores 834. In Figure 11 a magnetic coupling 810 connects the motor output shaft with the compressor input shaft. In Figure 12 the magnetic coupling is shown in more detail. A male magnetic coupling part 1006 and a female magnetic coupling part 1004 are fitted into one another, with the motor housing 1010 in between.

In Figure 12 the motor module and the compressor module are of differing lengths. The module length can be standardised, or selected in any manner that is suitable, for example with evenly spaced flange connection. The module arrangement can also provide the option of adding for example a second motor module or a second compressor module. For example if the motor module is 1/3 the pipe section length, and the basic compressor module is 2/3 the pipe section length, then the basic compressor module can be replaced with a short compressor module of 1/3 the pipe section length and a second motor module of 1/3 the pipe section length.

As previously mentioned, the use of magnetic couplings allows the implementation of field-swappable modules. The use of a sealed configuration for the motor is facilitated by a magnetic coupling 810 (the detailed configuration of which is described later in this text). The magnetic coupling allows the successful operation of the modular system in that this system is capable of tolerating axial and lateral misalignments in the module integration that would not be possible with conventional mechanical coupling techniques. The combination of magnetic coupling and magnetic bearings allows operation of the modular system with a tolerance of magnetic coupling to misalignment in both the radial and axial direction which is at least 10 times greater than that of mechanical couplings at rotational speeds and powers commensurate with the compressors described in this text. The angular displacement tolerance is equally beneficial being between 10 and 100 times as great as mechanical couplings. For example, misalignment in the radial direction in the order of magnitude of 0.2 to 1 millimetre, preferably up to approximately 0.5 millimetres, can be accommodated in the magnetic coupling. Tolerance to axial misalignment is significantly greater than to radial misalignment, in the order of magnitude of 0.5 to 10 millimetres, preferably up to approximately 4 millimetres. Tolerance to angular is in the order of magnitude of 0.5 to 5 degrees, preferably up to approximately 2 degrees. While conventional couplings make field replacement of a compressor shaft very impractical, a magnetic coupling allows more ease with field replacement.

In another preferred embodiment, illustrated in Figure 13, the compression has a two motor configuration. Instead of using one motor (as illustrated above), the use of two motors 900, 902 allows greater compression power, for example up to 1 Megawatt. Two smaller motors combined can be smaller (in particular in diameter) and less heavy than a single larger (and more impractical) motor, allowing installation in narrow spaces.

If the two motors are identical, they can be connected in parallel and hence can be driven from a single inverter drive. Each motor drives the compressor shaft through its own magnetic coupling which has a degree of torsional compliance. The provision of equal torque from each motor results in equal angular displacement in relation to the common compressor shaft. If the motors are permanent magnet type motors, it is important to ensure that both motors are closely synchronized in rotational position. This can be achieved by using a position sensor. Alternatively in a sensorless scheme the motor voltage and current waveforms can be sensed and analysed in the drive control system to extract the motor counter electromotive force or inductance, from which the rotor position can be estimated. This ensures both motors operate harmoniously at commanded speed and torque, which matches the load demand. In a two drives, two motors system, optimum operation can be achieved by incorporating a control scheme where one drive is Master (leader) and the other is Slave (follower) with both configured for running torque control mode. Interconnection of the two drives is necessary in order to compare the speed reference signals. The torque reference from the Master drive operating at specific load is fed to the Slave drive to generate the torque set point. The Slave drive compares its own speed reference signal with the master and generates an error values that regulates the torque of the Slave motor. The system is torsionally balanced in that one motor leading the other has the tendency to both provide specific torque to meet demand. This ensures a common degree of angular displacement in each magnetic coupling to ensure that the shafts are synchronized. This effectively ensures that the motor drive is self-equalising in torque and rotational position. Any number of rotor poles of permanent magnet motor configurations is possible with this arrangement. A further advantage of the described arrangement is that magnetic couplings introduce losses during torque transients that tend to damp torsional oscillations between the motor and compressor sections. In the embodiment illustrated in Figure 13 two electric motors 900, 902, each for example 500 kW, are coupled to a compressor shaft 904 at each end of the shaft with magnetic couplings 906, 908. The combined motors provide the total power, and are controlled and synchronised from a single inverter/controller. In this scenario, the rotors of the two motors are effectively linked physically and electrically, and thus act like a single permanent magnet motor. The use of a single inverter/controller reduces the complexity of the system, and the likelihood of errors. By using magnetic couplings (as described in more detail below) the system can be arranged to provide a 'torque fuse', whereby if the compressor stops for any reason (e.g. fouling or breakage), then the motors may slip past the poles of the magnetic couplings to allow the motors to run down without breakage. This torque fuse arrangement can apply equally to single or double ended permanent magnet motor drive systems.

In all the embodiments described above, the gas is intended to flow along the motor housing to the compressor. The surface of the motor housing may be designed to incorporate cooling features such as heatsink vanes to maintain optimal cooling, for example by maintaining gas flow over the housing wherever possible.

Magnetic coupling

Figures 14 and 15 illustrate different configurations for the coupling between a motor shaft 1000 and a compressor shaft 1002. In all illustrated configurations the coupling allows the motor to be sealed, and is suitable for operation without requiring additional lubrication.

In Figures 14 and 15 the motor 104 is hermetically sealed from the gas stream by a housing 1010 that encloses the motor 104. Hermetic connectors may provide access to the motor 104, for example for electronic connections or coolant connections. The hermetically sealed motor shaft 1000 is connected to the compressor shaft 1002 by a magnetic coupling. A female part at one shaft end couples into a male part at the other shaft end. The male and female parts are of complementary magnetic configurations. The female part may comprise a plurality of regions of different magnetic polarity facing the male part. The coupling may for example incorporate rare earth permanent magnets, or electromagnets.

In Figure 14, the female part 1004 is attached to the motor shaft 1000 and the male part 1006 is attached to the compressor shaft 1002. In Figure 15, the female part 1004 is attached to the compressor shaft 1002 and the male part 1006 is attached to the motor shaft 1000. A lip part can be provided in the housing 1010 to protect the coupling interface.

In the illustrations the housing 1010 is shaped to accommodate the female part 1004 and the male part 1006 by providing a cup-shaped structure that ensures that the housing is sealed. Figure 16 shows the sealing cup 1700 in greater detail. The sealing cup 1700 is a single machined and fired non-magnetic ceramic component, providing a mono-magnetic, non-metallic sealing surface between the two parts being coupled. The sealing cup 1700 being ceramic offers advantages for the operation of the magnetic coupling, in particular with respect to friction and thermal properties.

Unlike conventional magnetic coupling arrangements, the air gaps between coupling elements and sealing cup 1700 are ventilated by circulating gas. Figure 16 shows a cooling circulation in the motor housing 1010. The cooling circulation of gas into the air gaps in the magnetic coupling assists cooling of the void between the coupling parts and the housing. The circulating gas allows cooling of the system that provides the ability to utilise this form of coupling in enclosed, high temperature systems where they are previously unutilised. Where the motor is hermetically sealed, then a separate recirculating system of coolant gas such as Helium or other non-reactive gas may be used. In this case, the cooling gas is circulated to a heat exchanger 134, still located within the production pipe, upstream of the separator 110. Here, the passage of production gas (along with any liquid) cools the heat exchanger and hence coolant gas ready to circulate back to the sealed motor housing. As described above, the heat exchanger 134 being positioned upstream of the separator 110 helps to reduce the thermal loading on the production gas to be compressed, as the liquid (after absorbing heat from the heat exchanger) bypasses the compressor in the liquid transport channel described above.

The cooling circulation can be controlled to maintain the pressure difference across the sealing cap below a pre-determined threshold, to prevent damage to the sealing cap. To do this, sensors measure the pressure external to the motor housing, and other sensors measure the pressure within the motor housing. A control unit monitors the pressure difference, and if it exceeds a threshold value, the pressure in the motor housing is adjusted by adapting the in- and outflow of cooling gas. Other means for maintaining the pressure difference across the sealing cap below a pre-determined threshold can be implemented (for example in the absence of the cooling circulation, or independent of the cooling circulation). An automatic (e.g. passive) venting system is suitable for example.

Magnetic Seal

Figure 17 illustrates a system with a single, common shaft 1200 and no couplings. This configuration is illustrated here to demonstrate a similar concept in sealing but utilising a more compact compressor solution. Misalignment in this design is of no consideration, and a single shaft 1200 is used. However, the motor compartment 104 must be kept free of debris and potentially harmful liquids. This is achieved by a novel configuration of metal amalgams to provide a magnetic liquid type seal. In Figure 17 a single shaft 1200 (or a shaft with a conventional coupling) connects the motor 104 and the compressor 102. To provide sealing of the motor 104 from the gas stream, a magnetic liquid seal is provided between the motor housing 1202 and the shaft 1200. A conventional mechanical seal could also be used instead of the described magnetic liquid seal. For the magnetic liquid seal, magnetic liquid 1204 is arranged between the shaft 1200 and the motor housing 1202 by means of magnets. In particular, a shaft magnet 1208 and a housing magnet 1206 of complementary polarity serve to position magnetic liquid between the shaft and the housing. The liquid allows the shaft to rotate freely, while sealing the gas stream from the motor. For example, an annular rare earth shaft magnet and an annular rare earth housing magnet of opposing polarity arranged to face one another contain the magnetic liquid between the magnets. Suitable magnetic liquids include ferrofluids; hydrocarbon based liquids; beryllium or beryllium amalgams (for example with ferroparticles); or other metals or amalgams that are liquid at the operational temperature of the seal assembly. Preferably the magnetic seal is a single stage seal, as opposed to a multiple stage seals at different pressure levels. Magnetic liquid seals are normally made utilising multiple stages of seal. In this application, a single seal is maintained by utilising more powerful retention magnets and a greater width of liquid seal. This is particularly relevant for low melting temperature beryllium-based liquids, where at room temperature they are solid and hold the shaft in place and protect the interior of the housing against contamination (e.g. during transport). At production gas temperatures, for example around 70 to 120 °C, the beryllium-based liquids melt and form a viscous magnetic liquid seal. Where production gas temperatures cannot be reached, the housing area may include heaters to locally control the temperature of the magnetic liquid. In this manner, the compressor system may be manufactured with the motor hermetically sealed (the seal being solid at room temperature), and remain so sealed during transport until installed in operational configuration, where the seal is melted for production compression.

Balancing the pressure across the seal helps to maintain seal integrity at all times. In the case of a magnetic seal, in particular a single stage magnetic seal, it may be necessary to control the pressure difference across the seal and maintain it below a pre-determined threshold. Otherwise damage to the magnetic seal may occur, for example in surge operation. This can be achieved akin to the pressure control described with respect to the magnetic coupling above. Sensors measure the pressure external to the motor housing, and other sensors measure the pressure within the motor housing. A control unit monitors the pressure difference, and, if it exceeds a threshold value, the pressure in the motor housing is adjusted by adapting the in- and outflow of gas, such as cooling gas of a cooling circulation. Other means for maintaining the pressure difference across the seal below a pre-determined threshold can be implemented (for example in the absence of the cooling circulation, or independent of the cooling circulation). In situations where an automatic (e.g. passive) venting system is unsuitable, bladder type arrangements can be used. Bladder type arrangements are particularly useful in combination with incompressible fluids.

The magnetic seal is equally suitable for use where the interior and/or exterior of the housing are filled with fluids other than gases (in particular liquids).

Re-integration

In Figure 18 a re-integration unit 114 is shown with vortex-assisted integration. The liquid transport channel 112 has its outlet 142 at the centre of the gas pipe 100 with the flow of compressed gas 1306. A vortex 1308 is generated in the gas flow by suitable flow vanes 1310 in the channel. At the centre of the gas vortex, the pressure is lowest, thereby assisting the liquid in the liquid transport channel 112 to enter the gas flow. The outlet of the liquid transport channel 112 also has vanes 1312 to impart a rotational component to the liquid flow. Once the liquid has entered the gas vortex, centrifugal action moves droplets away from the axis of the system, toward the pipe 100 wall.

In Figure 19 a re-integration unit 114 is shown with suction-assisted and vortex-assisted integration. The suction channel 126 is connected to a low-pressure drain. The suction channel 126 may be connected to the gas stream upstream of the compression, for example either up- or downstream of the separator unit 110. The difference in gas pressure pre-compression and post-compression powers passive re- integration. As the outflow of the suction channel 126 can contain liquids and solids, connection upstream of the separator unit 110 is advantageous, as it ensures that the flow to the compressor 102 is suitably conditioned. Liquid from the liquid transport channel 112 is drawn into the gas flow by the effect of the low-pressure inlet to the suction channel 126. Gas and liquid 1406 move along into the main gas outlet 1402. In the illustration the outlet channels 1402, 126 are shown to split and diverge for ease of illustration, but an implementation can have a single low-pressure outlet and a single main gas outlet.

By causing the liquid and compressed gas to rotate via an arrangement of vanes 1310, 1312, centrifugal action causes the droplets of liquid 1314 to move radially into the compressed gas vortex 1308. Whilst some liquid is likely to remain in the gas that is recirculated to the (lower pressure) inlet plenum of the compressor, the majority of liquid is centrifugally dispersed and follows the compressed gas outflow into the output plenum that discharges to the compressed gas production pipeline. In Figure 19 the gas pipe 100 is narrowest between the liquid transport channel outlet 142 and the suction channel inlet 140. The resulting vortex (in the absence of vanes or other structures forcing the vortex) increases the rotational velocity of gas in the constriction and transports the introduced liquid quickly away from the in- and outlet 142 140. The re-integration unit is suitable for use in other applications other than in-pipe compression. Operation can be adjusted by selection of the ratio of diameter of the outlet 142 from the feed channel and the inlet 140 of the suction channel 126, and gap length between inlet 140 to outlet 142. These dimensions affect liquid being centrifuged and hence the amount of liquid recycled to the compressor inlet.

In Figure 20 a re-integration unit 114 is shown with the recycle channel 146 for the slug abatement system downstream from the suction channel 126. The recycle channel 146 in this configuration draws fluid from a region 150 of the re-introducer that is predominantly gas-filled, away from where liquid collects in the re-introducer.

In Figure 21 an embodiment of the re-integration unit 114 is shown with a needle 1800 at the liquid transport channel outlet 142. The needle 1800 serves to stabilise the vortex formed between the outlet 142 of the feed channel 112 and the inlet 140 of the suction channel 140. The needle 1800 can prevent precession of the vortex within the pipe, which could cause disruption to the functioning of the re- integration unit 114. Alternative structures to the needle 1800 may be used, such as a spur, a barb or a cone, provided they are arranged central to the axis of the feed channel 112; this ensures that the vortex is stabilised at the optimum position that is co-axial to the feed channel, with the outlet 142 at the vortex centre. In Figure 22 an embodiment of the re-integration unit 114 is shown with a needle 1802 extending from the compressor shaft 1002 and out of the liquid transport channel outlet 142. The needle 1802 may extend to a position close to the inlet 140 of the suction channel. In operation the needle 1802 rotates with the compressor shaft 1002 so as to avoid excessive pressure drop across the needle due to friction effects at the needle surface. If such friction effects are great enough the pressure might not be sufficient for the re-integration unit 114 to function efficiently. The needle 1802 (similar to the needle 1800 described above) serves to stabilise the vortex formed between the outlet 142 of the feed channel 112 and the inlet 140 of the suction channel 140. The needle 1802 can prevent precession of the vortex within the pipe, which could cause disruption to the functioning of the re-integration unit 114, and direct the vortex to be aligned with the axis of the inlet 140 of the suction channel. The above description usually refers to applications relating to gas compression, but it is equally applicable to applications relating to other fluids, for example liquids, or solids that display fluid-like behaviour. For example, the re-integration unit is equally suitable for liquid/liquid applications, where a heavier liquid phase is integrated into a lighter liquid phase. Liquid pump and common shaft

Referring to Figure 23, another example of a compression system is shown for handling a flow which may have solid, liquid and gas phases. The system includes a first separator 200 (for example for compactness a vortex separator such as the I-SEP (TM) product supplied by Caltec Limited, or a rotating separator), and a motor 202 driving a compressor 204, which may function in a similar manner to those shown in Figure 1, and are housed within a pipe section 206. As before, the first separator 200 outputs a first predominantly gas phase 208 of the incoming fluid flow 210 to the compressor 204 past the motor 202 which is sealed from the flow 208. An output shaft 212 of the motor 202 drives the compressor 204. The first separator 200 also outputs a second flow 214 which remains after separating the gas flow, which is predominantly liquids and solids although it also likely contains a gas component, and which as before needs to be reintegrated with the gas flow 208 downstream of the compressor. Pumping of such a flow presents problems. Whilst it is possible to use a positive displacement pump, the solid component tends to cause wear to the pump. A turbo pump is not suitable for use with a flow containing more than a very small amount of gas, and cannot be used for example where the volume of gas is up to around 10%. A turbo pump is also advantageous because it can be designed smaller than other pumps for the same performance level.

In this embodiment, the second flow 214 is directed to a second separator 216 which may be a 3-phase separator (for example a gravity separator or a baffled tank design), and is arranged to separate out the gas and solid component of the second flow 214. The gas and solid component may then be combined in to a solid/gas flow 220, leaving a predominantly liquid flow 218 downstream of the second separator. Producing a predominantly liquid flow 218 is especially favourable for use with a turbo pump, because residual gas can cause variance on the pump head pressure, and can even make repriming of the turbo pump necessary. For example, each of the three phases may be separated by the second separator 216, and (as illustrated in Figure 23) the gas and solid flows may be subsequently combined. The gas and solid flows may still contain a liquid component, for example approximately 10% of the liquid content of the second flow 214. The liquid flow 218 may then be directed to a pump 222. By separating the solid/gas flow 220 from the liquid flow 218 before directing to the flow to the pump, fouling, damage and wear to the pump can be avoided. Because the second flow 218 is now predominantly liquid, a small high pressure pump such as a turbo pump may be used. The pump 222 may also be driven by output shaft 212 of the motor 202, with the gas flow 208 being directed around the pump 222. In the example illustrated in Figure 23 the pump 222 is on the same common shaft 212 as the compressors 204. This can provide design simplicity and avoid use of more bulky arrangements. The pump 222 may be coupled to the output shaft 212 of the motor 202 by a magnetic coupling such as is described above. A magnetic seal such as is described above may seal the pump 222 from the gas flow 208 being directed around the pump 222. An ejector 224 is provided for the purpose of recombining the high pressure liquid flow 226 exiting the pump 222 with the combined solid/gas component flow 220. In the ejector 224, the high pressure liquid flow 226 serves to entrain the solid/gas component flow 220 in a known manner. The ejectors 224, in addition to combining the liquid flow 226 and the solid/gas flow 220, can also protect the pump 222 from cavitation, backflow, and vibration. The combination of the second flow 226 with the solid/gas flow 220 at the ejector 224 results in a recombined solid/gas/liquid flow 228, which has the same components as the second flow 214 upon exit from the first separator 200, but is at higher pressure.

Alternatively to the example illustrated in Figure 23 the gas flow exiting the second separator 216 may be redirected back to the first predominantly gas flow 208. In this case the gas component in the flow 220 directed to the ejector 224 is low or negligible, and the flow 220 is predominantly solids.

The recombined solid/gas/liquid flow 228 is then recombined with the high pressure gas flow 230 exiting the compressor 204. The recombined resultant flow 232 thus exits the system at higher pressure. The recombination of the solid/gas/liquid flow 228 and the first flow 208 does not require the passive re-integration described above, as the pumping action of the pump 222 can provide suitable active reintegration.

By using the first separator 200 and second separator 216 as described above, the first separator 200 can be chosen to provide a low pressure loss separation such as is necessary for a high rate of incoming fluid flow 210. On the other hand, the second separator 216 can have a higher pressure drop, as the liquid portion requires significantly lower energy to pressurize over the same pressure difference per unit mass flow, thus the energy penalty associated with higher pressure drop in this stream is of significantly lower consequence. The liquid stream also has a relatively small volumetric flow in comparison with the gas stream, allowing other separation options For example, a gravity separator requiring a certain residence time can be chosen for the second separator 216. Therefore the arrangement with two separators addresses the requirements without unnecessary complexity or cost.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made withm the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.