Multiphase fluid treatment

An apparatus for the treatment of a multiphase fluid, comprising a rotatable shaft having a fluid flow path coaxial with the shaft. A fixed guide member surrounds the shaft and comprises annular plural helical channels for imparting centrifugal forces to the fluid to concentrate heavier fluid into an outer annular flow path around an inner flow path for lighter fluid. An impeller is supported on and driven by the shaft. The flow in the outer flow path is diverted, so as to divert the flow of the fluid of greater specific gravity into an annular channel member having an impeller. A stationary scoop extracts fluid from the channel member. The impeller comprises generally radially outwardly extending disks receiving fluid flowing on the inner flow path between them. Guide vanes are carried by the disks for guiding the fluid radially outwardly. A discharge chamber in the form of a volute is provided for the lighter fluid on the inner flow path issuing from between the disks.

FIELD OF THE INVENTION 
The invention relates to treatment of a multiphase fluid, for example, in a 
transport or separator system. 
BACKGROUND OF THE INVENTION 
The handling of a multiphase fluid, that is, a mixture of at least two 
fluids of different phases, presents problems arising for example from the 
different physical characteristics of liquids and gases, in particular, 
the virtual incompressibility of the former and the ready compressibility 
of the latter, and also from variations in the relative amounts of liquids 
and gases in the multiphase fluid. For example, in oil production, a well 
may produce a mixture of crude oil, crude gas, water and sand or like 
particulate material. It is desirable in many instances to place such a 
mixture under increased pressure, but this is difficult because pumps with 
impellets designed to pump liquid are unsuitable where the liquid contains 
a high gas content. Similarly, ordinary gas compressors are unsuitable for 
use where liquid is present in the gas in any substantial amount. 
SUMMARY OF THE INVENTION 
In accordance with the invention, there is provided apparatus for treatment 
of a multi-phase fluid, comprising an inlet stage leading to a treatment 
stage, the inlet stage comprising a cyclonic separator device in which the 
multiphase fluid is divided into separate flows consisting at least 
substantially of fluid of higher and lower specific gravities 
respectively, for at least one of further separation, pumping, and 
compression in the treatment stage. 
The invention is accordingly concerned in one aspect with the provision of 
a pump/compressor unit arranged for efficient pressurising of a multiphase 
fluid regardless of variations in the quantities of gas or liquid in the 
fluid. 
A pump/compressor apparatus in accordance with the invention is thus 
arranged for receiving an incoming multiphase fluid and directing the 
fluid cyclonically to effect separation of the phases, with a stream of 
fluid with the highest specific gravity as a layer at the outer surface of 
the cyclone and a stream of fluid with the lowest specific gravity in the 
centre of the cyclone. The incoming fluids with the highest specific 
gravity are then directed into a helical path at the outer periphery of 
the apparatus along which energy is added by means of rotating impeller 
guide vane passages increasing the rotational velocity of the fluid, and 
thus the pressure. The incoming fluids with the lowest specific gravity 
are similarly acted upon by a rotating impeller means, preferably 
providing for compression of the fluids which will typically comprise 
gaseous material. 
The invention thus provides a pump/compressor unit having an inlet for a 
multiphase fluid, means for separating the fluid into its components and 
for pressurising the components by respective impeller means. Preferably 
the two impeller means are parts of a single impeller assembly. 
The impeller assembly can thus provide an interior defining a first flow 
path along which the gaseous or lower specific gravity fluids are directed 
along the impeller assembly axis and then transported radially by blades 
or vanes. The cross-sectional area of the flow path preferably reduces 
progressively in the flow direction, so as to enhance compression of the 
fluid. The compressed fluid of the first stream can then be discharged 
from around the impeller assembly periphery. 
Radially adjacent of the first flow path, a second flow path is provided 
for the higher specific gravity or liquid stream, between the exterior of 
the assembly and a housing within which the assembly rotates. The second 
path again effects axial re-direction of the stream, into an annular 
trough or channel from which the liquid is accelerated by impeller means 
to an outlet by way of a fluid pick-up or scoop device. 
Such a pump/compressor device would be self-regulating, and also 
self-priming because gas would not have to be drained out before pumping 
could commence. The device would itself act as a fluid lock, because it 
would never empty completely, so preventing gas from blowing back from the 
gas outlet in the absence of incoming liquid. Also, gas lock is prevented, 
so non-functioning cannot result from intolerance of an essentially 
gaseous input. 
Alternatively, the invention can be embodied in a centrifugal separator 
apparatus for separating the components of a multiphase fluid, the 
apparatus having an inlet stage similar to that described above for 
providing the separate flows. The fluid flows at the outlet of the helical 
path are directed into a rotating separator. The or each fluid flow with 
the highest specific gravity is directed into an impeller stage with 
passages defined by guide vanes with or without an inner wall. The liquid 
layers then proceed axially along the inner surface of the separator 
cylinder or drum and are discharged therefrom in any suitable way as by 
reception in a discharge chamber into which a discharge scoop extends. The 
gaseous component of the multiphase fluid is also brought into rotation by 
the guide vanes and proceeds axially through the separator drum. Any 
liquid drops remaining will be separated from the gas by centrifugal force 
and the dry gas can be withdrawn from the separator without further 
pressure increase. 
In operation, the incoming fluid is efficiently brought to full rotational 
speed, without turbulence in the outlet, and with improved separation. By 
selecting appropriate average outlet cross-sectional areas from the 
impeller, improved separation efficiency can be obtained because the 
average momentum of the fluid in the outlet can be made equal to the 
average momentum of fluid in the separator phase.

The pump/compressor unit illustrated in FIG. 1 comprises a stationary 
casing 10 having axially opposed open ends closed by end plates 11 through 
apertures in which respective drive shafts 12 and 14 extend along a common 
axis from respective electric drive motors 15 and 16. At the lefthand end 
(as shown) an inlet chamber 17 in the form of a volute is provided within 
the casing around its axis and into which a multiphase fluid is introduced 
in use from outside by means of an inlet fitting 19. 
The incoming mixture has a rotational movement imposed on it by the shape 
of the inlet chamber 17 and this movement is enhanced in the next stage by 
a fixed guide member 20, shown in FIG. 2, received in an annular chamber 
communicating with the inlet chamber and into which the fluid moves in the 
axial direction. The guide member 20 comprises an inner sleeve 24 with 
external fins 25 defining with the inner wall 26 of the casing 10 plural 
helical channels for the multiphase fluid. The centrifugal force generated 
by the rotary movement of the fluid causes the heavier fluid or fluids, 
that is, the liquid component of the mixture, to concentrate into an 
annular flow path A against the casing wall 26 whilst the less dense 
gaseous component occupies a flow path B at the inner region of the 
channels. The multiphase fluid is thus cyclonically separated into 
concentric layers of increasing density in the radially outward direction. 
Continuing in the axial flow direction, the interior of the casing 10 next 
has a radially enlarged portion 30 constituting a pump/compressor stage. 
Carried on the free end of the shaft 12 is a first part of an impeller 
assembly comprising concentric inner and outer sleeves 31 and 32 providing 
between them an annular passage continuing the annular space between the 
sleeve 24 and the inner wall 26. Axially adjacent the inner sleeve 31 is a 
member 34 which flares radially outwardly in the flow direction, so as to 
redirect the primarily gaseous fluid stream adjacent the inner sleeve 31 
along a radially outward direction. The impeller assembly part on the 
shaft 12 also comprises an annular disc 35, extending generally radially 
outwardly from a position near to, but spaced from, the downstream end of 
the outer sleeve 32, so as to form therewith an annular passage 36 through 
which can flow the outer layer of the fluid, comprising the denser, 
liquid, phase. The inner edge of the disc 35 thus separates the inner and 
outer layers, typically of gaseous and liquid components respectively, 
formed in the multiphase fluid by the centrifugal force generated 
upstream. 
The free end of the shaft 14 carries a second part of the impeller assembly 
comprising an annular disc 40 extending generally radially outwardly to 
oppose the disc 35. Each disc carries impeller vanes or blades 41 
extending towards the other disc. The shafts 12 and 14 are driven by the 
motors 15,16 so as to rotate in opposite directions and the blades 41 are 
shaped to urge the gaseous stream directed to them by the member 34 to 
flow radially outwardly. The opposed faces of the discs 35 and 40 slightly 
converge in the radially outward direction so as to restrict the flow 
passage between them. The gaseous stream is thus compressed in its passage 
between the discs 35 and 36 and it flows outwardly from between them into 
a discharge chamber 45 in the form of a volute provided in the casing 10 
around the outer edges of the discs. A discharge fitting 46 communicates 
with the chamber 45 to conduct the compressed gaseous flow outwardly of 
the unit. 
The more dense, primarily liquid, stream flowing radially outwardly through 
the passage 36 between the sleeve 32 and the disc 35, at the side of the 
disc remote from the disc 40, is received in an annular channel formed by 
a member 50 secured to the disc 35 and comprising a concentric sleeve 
portion having at its free end an annular rim portion directed inwardly 
towards the shaft 12. Within the channel, impeller vanes or blades 51 on 
the disc 35 and the rim portion effect acceleration of the liquid. The 
liquid is extracted from this channel by a stationary scoop 52 comprising 
spaced disc portions extending outwardly into the channel of the member 50 
and providing passages for radially inward flow of the liquid from the 
channel. This discharge flow continues axially through a support portion 
projecting from an adjacent wall portion of the casing 10, and to a 
discharge outlet 55 by way of a passage 56 in the wall portion. 
The pump/compressor unit described and illustrated thus provides for the 
separation, and separate treatment, of the gas and liquid components of 
the incoming multiphase fluid, so that each can be pressurised by impeller 
means appropriate to the characteristics of the component which it 
handles. 
The separation of the gas and liquid stream can of course be maintained 
downstream of the unit if appropriate, but if the function of the unit is 
simply to effect transport of the multiphase fluid, the separate gas and 
liquid outputs can be combined for flow for example along a pipeline to 
equipment in which the fluid is subsequently treated. 
The centrifugal separator apparatus of FIGS. 3 and 4 has a stationary inlet 
stage largely corresponding in design and function to that of the 
pump/compressor unit of FIGS. 1 and 2. The inlet stage thus includes a 
stationary guide member 60 as shown in FIG. 3 which may be closely similar 
to the guide member 20 of FIG. 2 and which again serves to cause an 
incoming multiphase fluid to form into an axially flowing stream of 
material of higher specific gravity, typically one or more liquid layers, 
confined by a housing wall 61, and an inner stream of material of lower 
specific gravity, typically of a gaseous nature. 
From the stationary inlet stage of the apparatus, the concentric fluid 
streams enter a rotary impeller/separator stage, of which the inlet end 
only is shown in FIG. 4. This part of the apparatus comprises a drum 65 
which is rotated in use by a motor (not shown) about its axis 66. The drum 
wall at its inlet end has a short portion 69, with a diameter matched to 
that of the guide member 60, followed downstream by a frusto-conical 
portion 70 leading to a separator drum portion 72 of constant larger 
diameter. The inlet and frusto-conical wall portions mount a series of 
impeller vanes 75 extending inwardly preferably but not necessarily, to a 
concentric inner sleeve 76 of a diameter equal to that of the sleeve of 
the guide member 60. 
The impeller vanes 75 receive the fluids flowing concentrically in the 
helical paths imposed by the guide member 60 and act to increase the 
rotational speed of the fluids in the frusto-conical portion 70. The fluid 
layers then flow from the passages defined by the drum portion 70, the 
vanes 75 and the sleeve 76, to flow along the drum portion 72 where 
further separation occurs by conventional centrifugal separator action. 
Any liquid in the central gaseous flow joins the outer liquid layer (or 
layers where there are two liquids of different specific gravities). The 
liquid or liquids can be removed from the drum by conventional means or 
the centrifuge can be designed to be self-regulating as described in 
Application GB 91 26 415.0, the contents of which are incorporated herein 
by reference. The gas can be discharged from the drum through 
appropriately located apertures (not shown). 
The invention can of course be carried into effect in a variety of ways 
other than as specifically described and illustrated.