This invention relates to a separator and particularly, although not exclusively, relates to a compact separation system including new de-oiling cyclones and de-gassing filtration to meet the demanding requirements of offshore oil and gas production requirements whilst meeting ever more difficult environmental discharge limits, for example a separator for separating or partially separating oil, from a continuous water phase, from hydrocarbon production well fluids, having a wide effective flow range thereby capable of operating efficiently from low flow rates of liquids to high flow rates of liquids, without the need for separate pressure vessels, or automated valves to control flows, together with a low pressure drop cyclone liner followed by a degassing filter with minimal backwash waters required with all waste streams delivered to a centrifuge to achieve an integrated process system .

A search of prior art shows many related applications and granted letters of patent surrounding de-oiling hydrocyclones in particular reference can be made to

US005507955 and US005154826.

In practice it has been found that when preparing a oil field development plan the reservoir expected production profiles are of considerable importance when designing the required processing equipment to separated and stabilise the crude oil, and in particular the expected produced water cuts that will need to be treated for disposal to the environment or re-injected. Figure 1 is a simplified chart which ignores gas for this exercise but clearly shows the transition from continuous oil phase through phase inversion to continuous water phase.

It can be seen that with regards to produced water, a flow range of a few thousand barrels of water per day up to 50,000 barrels per day or more in this example oil field or Gas field in the case of shale gas fracture waters production life will need to be managed.

A typical flowrate per individual cyclone liner verses, the pressure drop through the cyclone liner from inlet to water outlet are given in Table 1 below. One important feature of de-oiling hydrocyclones is the individual cyclone liners flowrate turndown whilst maintaining efficient oil droplet separation. At the initial design phase of such a process the system designer will need to understand the following process variables: Oil reject maximum flowrate for the system as a percent of the inlet water to be treated, is normally today no more than 2% of the inlet flowrate, when the produced water to be treated has approximately 2,000 ppm or less of free oil droplets to be removed, depending on the droplet size distribution.

The pressure ratio between inlet pressure and outlet pressure, again it should be noted that several factors affect this ratio, such as the available inlet pressure to the system, either by natural pressure drive or pumped, the required oil reject pressure to allow the same to report to next process stage, typically the pressure ration for de-oiling hydrocyclones is in the range of 1.4 to 3.5 with 1 .8 being a popular ratio, it would be normal therefore to expect a process pressure and flowrate as shown below in Table 1

Table 1

It is evident therefore with the inlet pressure available in Table 1 above and the required pressure at the oil reject of 0.1 barg the pressure drop through an individual cyclone liner is 1 .73 barg at a maximum flowrate of 1 .35 m ³ /hr and a minimum flowrate will be circa 0.66 m ³ /hr. For example if the required total flowrate of produced water to be treated was 250 m ³ /hr, then dividing this flowrate by the maximum flowrate per liner at the given inlet pressure available would give a maximum of 185 cyclone liners for maximum flow and with a design minimum flowrate requirement of 25 m ³ /hr would require 38 cyclone liners. It is evident therefore that a single cyclone vessel with 185 cyclone liners installed would not meet the required minimum flowrate or turndown for the process. It is normal practice therefore to have multiple vessels with valve means each with different numbers of cyclones installed and to switch vessels on and off depending on the flowrate required to be treated, or to have complicated means to isolate individual inlets and rejects of a number of cyclone tubes inside the pressure vessel, or to have a minimum flow recycle pump to ensure the inlet flowrate to the smallest vessel containing cyclone tubes stays above its minimum efficient flowrate even when the produced water flowrate to be treated has dropped below its minimum flow for the vessel to be efficient.

Figure 2 shows a typical de-oiling hydrocyclone efficiency chart against flowrate.

The curve shown in Figure 2 is dependent on several factors such as:

Specific gravity differential between the water and oil

Oil droplet size distribution, typically the oil droplet should be over 10 microns diameter for maximum effective separation

The retention time in the cyclone liner, being measured between the units inlet to water underflow.

The operating temperature of the fluid to be treated, higher temperatures generally reduces viscosity of the fluids, and the inter-facial drag forces and boundary layer effects encountered within the system.

Figure 3 is a chart giving a typical migration probability curve for a given cyclone geometry, this graph indicates the probability of a given oil droplet size migrating to the cyclones central core during use and as such able to exit the cyclone through the oil rich overflow outlet. The curve is dependant on several factors including but not limited to, fluid temperature and hence viscosity, SG differential between the water and oil, interfacial drag forces, boundary layer effects and the apparent enhanced gravity force created in the cyclone tube. It can be seen that the variables described above are mostly a function of Stokes Law which describes floatation or settling of particles.

In the example in Figure 3 above it can be seen that there could be a 40% probability of removing the 5 micron oil drops, and a 99% probability or D99 of removing the 12 micron drops of oil. It is important therefore to have detailed knowledge of the oil droplet distribution in the produced water when designing systems for treatment of same. This is best achieved by digitising a video of the produced water at line temperature and pressures, and then applying suitable shape analysis software to determine the actual condition of the water and oil to be treated. Figure 4 is a chart indicating the selection of cyclone tubes or liners needed to manage a flow range from low flow to high flow over time without windows or gaps in operability at required oil removal efficiencies:

It can be seen from Figure 4 that a skid mounted valved system with a minimum of three cyclone vessels, either manually or automatically operated will be required to operate the process uninterrupted throughout the required flow range. This increases the space requirement footprint for the system which is particularly undesirable offshore or subsea, and increases the capital cost due to the controls and

instrumentation required, together with the maintenance and spares associated with the same.

There have been long list of equipment used historically to manage produced water and reduced the free oil. The vast majority of them are based on the management or exploiting of apparent changes to gravity by applying centrifugal forces to aid and enhance the recovery of oil by using pressures available to rotate the fluids rather than rotating the machine as with centrifuges. As stated earlier this is due to a relationship that is often described by Stokes' Law for the terminal fall velocity as shown below:

It can be noted however that this relationship is valid only for 'laminar' flow (Laminar flow is defined as a condition where fluid particles move along in smooth paths or stratified layers gliding over one another; whereas 'turbulent' flow is characterized by fluid particles that move in random in irregular paths causing an exchange of momentum between particles). On this basis the relationship between droplet size and settling velocity can only be used with confidence for larger tank-type separators that have considerable retention times.

A large number of specialists have investigated the enhancement of the gravitational force acting on the particle to be separated to accelerate the movement of the particle or droplet. In terms of liquid/liquid hydrocyclones the initial work evolved from

Southampton University with work conducted by Colman and Thew. Since then there have been numerous designs and claims made, however, majority of these have focused on the same general arrangement for the hydrocyclone; a conical device.

Understanding the issues described above any improvement in the overall produced water systems available today will require: 1 . Smaller systems which minimise valves and instruments, particularly if the system is to be situated on the sea bed.

2. New generation of de-oiling cyclone tubes which are easier and cheaper to manufacture, which concentrates on higher flow-rates for less pressure drops. Also recognising the industry is lowering the amount of oil that can be discharged to the sea globally see www.ospar.org typically now 15ppm free oil in water is required for many fixed oil production platforms, and in the case of Shipping the International Martine Organisation see www.imo.org requires 15ppm oil in water for discharge to the sea, whilst focusing on microbe and bacteriological contaminates including planktons which are being transported around the world, by ballast and bilge waters.

3. To achieve both of the requirements in 1 and 2 above a better tertiary stage will be required to polish the outlet of the de-oiling cyclones, such as Filtration/Absorption capable of meeting 5ppm or less at the same time as removing fine solids or planktons. This is also a requirement if the water treated is to be re-injected into a disposal or production zone in the Oil and Gas production industry, which will also include the need to manage Sulphate Reducing Bacteria's SRB's, Volatile Organic Compounds VOC's Polychlorinated biphenyls PCB's. In the event that Membranes or Molecular sieves are used to achieve lower concentrations of contaminates the cleaner the water delivered to them the longer they will perform to specification between changing or cleaning procedures. In all cases the tertiary systems discussed above will require wash waters to be disposed of or transported somewhere.

It is also known to use cyclones to separate solids from liquids. Traditional solids removal cyclones require a tapered or conical section which reduces in diameter allowing the solid to concentrate in the bottom of the cone or spigot region, commonly referred to as roping. This creates a pressure drop across the unit which concentrates the solids prior to removal.

According to a first aspect of the present invention there is provided a cyclone separator comprising a housing defining a longitudinal vortex chamber, an inlet, a first phase outlet spaced from the inlet in the longitudinal direction of the vortex chamber, a second phase outlet disposed radially inwardly of the first phase outlet, a means for imparting a rotational flow within the vortex chamber, and a solid-walled core element arranged within the vortex chamber to define a flow passage between the core element and the housing, wherein the core element extends in the longitudinal direction of the vortex chamber and tapers to a tip in the direction from the first phase outlet towards the inlet such that the area of the flow passage defined between the core element and the housing decreases in the direction towards the first phase outlet, the second phase outlet comprising a port in the core element at a position at or adjacent the tip.

The diameter of the housing may be constant over the portion of the housing within which the core element extends.

The core element may be conical. The tip may be situated within the vortex chamber. The second phase outlet may be situated on the longitudinal axis of the vortex chamber.

The core element may comprise a passage which extends from the second phase outlet to the end of the core element which is away from the tip.

The means for imparting a rotational flow within the vortex chamber may comprise an array of vanes disposed within the vortex chamber.

The core element may comprise a helical formation at the surface of the core element. The core element may comprise an oleophilic material.

According to a second aspect of the present invention, there is provided a cyclone separator comprising a housing defining a longitudinal vortex chamber, an inlet, a first phase outlet comprising a first outlet port and a second outlet port which are spaced from the inlet in the longitudinal direction of the vortex chamber, a second phase outlet disposed radially inwardly of the first and second outlet ports, a first means for imparting rotational flow within the vortex chamber, a second means for imparting rotational flow within the vortex chamber, a solid-walled core element disposed within the vortex chamber to define a flow passage between the core element and the housing, the core element extending in the longitudinal direction of the vortex chamber, wherein the second phase outlet comprises a passage extending through the core element, the first outlet port is disposed between the first means for imparting rotational flow and the second means for imparting rotational flow, and the second outlet port is disposed such that the second means for imparting rotational flow is disposed between the first outlet port and the second outlet port. The second phase outlet may be disposed between the first means for imparting rotational flow and the second means for imparting rotational flow. The second means for imparting rotational flow may comprise an array of vanes disposed within the vortex chamber. The vanes may be arranged about the core element. A second phase flow passage may be defined between the vanes and the core element.

According to a third aspect of the present invention, there is provided a separator comprising a vessel defining a cyclone inlet chamber and a plurality of cyclone separators, each cyclone separator comprising a housing defining a longitudinal vortex chamber, an inlet, a first phase outlet and a second phase outlet, wherein the cyclone separators are arranged so that their inlets are in communication with the cyclone inlet chamber, the inlets of the cyclone separators being disposed within the cyclone inlet chamber in a manner such that the inlet of at least one of the cyclone separators is first exposed to fluid in the cyclone inlet chamber at a fluid level different from that at which at least one other of the cyclone separators is first so exposed.

The inlet of the said one cyclone separator may be enclosed by a weir which defines the fluid level at which that inlet is first exposed to fluid.

Multiple weirs may be disposed within the vessel to provide a plurality of fluid levels at which respective inlets of the cyclone separators are exposed to fluid.

A valve may be arranged at each of the second phase outlets of the respective cyclone separators to prevent flow through the second phase outlets into the respective vortex chambers.

According to a third aspect of the invention there is provided a system in which a cyclone separator in accordance with the first aspect of the invention and a separator in accordance with a second aspect of the invention are incorporated into a single modular package including a degassing filter and a centrifuge which is able to be arranged as a vertical column able to be cantilevered on the side of existing platforms such as manned or unmanned well head platforms. This is advantageous where no other space is available on the central processing platform or installation or it is a requirement to reduce the flow of fluids through the pipework that connect the producing wells to the central processing installation. The system may be used to treat produced water when there is a shortage of water to enable efficient system cleaning such as in desert locations and where it is not desirous to use evaporation ponds to treat wash waters which are considered not environmentally effective.

According to a fourth aspect of the invention there is provided a cyclone separator comprising: a longitudinal vortex chamber having an inlet for a mixture comprising a lighter phase, a heavier phase and solids (solids phase); a heavier phase outlet longitudinally spaced away from the inlet, a lighter phase outlet disposed between the inlet and the heavier phase outlet, and a solids outlet disposed radially outwardly with respect to the lighter phase outlet; wherein the cyclone separator is configured to promote rotational flow of the mixture within the vortex chamber such that, in use, solids are forced radially outwardly towards the solids outlet; and a flow rotation accelerator disposed within the vortex chamber, the flow rotation accelerator being arranged such that, in use, phases of the mixture which bypass the solids outlet are accelerated by the flow rotation accelerator.

The flow rotation accelerator may be disposed between the lighter phase outlet and the solids outlet. The flow rotation accelerator may comprise an array of vanes which extend radially outwardly from the longitudinal axis of the vortex chamber.

The vortex chamber may comprise a converging portion which extends between the flow rotation accelerator and the heavier phase outlet, wherein the converging portion is arranged to converge in the direction towards the heavier phase outlet.

The solids outlet may comprise an annular outlet which is arranged coaxially with the vortex chamber. For example, the solids outlet may comprise an annular slot which extends completely about the longitudinal axis of the vortex chamber, an array of arced slots or a substantially circular array of holes arranged about the longitudinal axis of the vortex chamber.

The cyclone separator may further comprise a solid-walled core element disposed within the vortex chamber adjacent the inlet, wherein the core element is arranged to promote vortex flow within the vortex chamber. The cyclone separator may further comprise a plenum arranged in fluid communication with the vortex chamber via the solids outlet. The plenum may comprise an annular chamber arranged coaxially with the vortex chamber. The plenum may act as a flow restrictor for restricting flow of the heavier and lighter phases through the solids outlet. It will be appreciated that the solids outlet may be provided with other suitable flow restrictors for restricting flow of the heavier and lighter phases through the solids outlet.

The lighter phase outlet may be disposed substantially at the longitudinal axis of the vortex chamber.

The cyclone separator may further comprise a duct which extends radially with respect to the vortex chamber, wherein the duct provides fluid communication between the lighter phase outlet and the exterior of the vessel. The end of the duct adjacent the lighter phase outlet may comprise a funnel arranged to funnel lighter phase from the lighter phase outlet through the duct.

The lighter phase outlet may be provided at the flow rotation accelerator, the flow rotation accelerator having a core through which the duct extends.

There may be provided a cyclone separator comprising: a longitudinal vortex chamber having: an inlet, a heavier phase outlet spaced away from the inlet in the longitudinal direction of the vortex chamber, a lighter phase outlet disposed between the inlet and the outlet with respect to the longitudinal direction of the vortex chamber, and a solids outlet disposed between the inlet and the lighter phase outlet with respect to the longitudinal direction of the vortex chamber, wherein the solids outlet is disposed radially outwardly of the lighter phase outlet; a means for imparting rotational flow which is arranged to impart a rotational flow in the region of the vortex chamber between the inlet and the solids outlet; and a means for accelerating the rotational flow, which is disposed between the solids outlet and the lighter phase outlet with respect to the longitudinal direction of the vortex chamber, wherein the means for accelerating the rotational flow is arranged to accelerate rotational flow in the region of the vortex chamber between the solids outlet and the heavier phase outlet.

In one embodiment, shown in Figures 9 to 12, there is provided a separator for separating oil droplets from continuous phase oily waste water into a first fluid, a second fluid which is denser than the first fluid, the separator comprising a de-oiling cyclone liner 102, that is easier and cheaper to manufacture whilst achieving higher flow-rates at less delivery pressure.

In a further embodiment, shown in Figures 17 to 20, there is provided a pressure vessel 202 having an inlet 204 for the flow which passes through its side wall and reports to an upper chamber 206 which has a plurality of weirs or tubes 208 at varying levels, each weir or tube 208 defines a cavity 210 within the chamber 206 that has a different number of cyclones 212 inside with means for causing the flow to rotate within the cyclone a first outlet in the vessel 202 in the upper chamber 206 for the first fluid, the first outlet comprising a conduit type passage individually plumbed into each bank of cyclones, in each cavity 210 in the upper chamber 206 a second outlet for the second fluid, the second outlet being situated towards the bottom wall of the vessel 202. The cyclones 212 are arranged within the upper chamber 206 such that the inlets to the cyclones 212 are at substantially the same level within the chamber 206. An advantage of this arrangement is that the vessel can be preassembled without the weirs 208. The weirs 208 can be subsequently added, or altered, to characterize the performance of the vessel 202. Preferably, and the central axis of the vessel 202 is substantially vertical. Preferably, the vessel 202 is substantially symmetrical about its central axis. Preferably, the vessel 202 is cylindrical. Preferably, the means for causing rotation comprises shaping or aligning the inlet to the cyclone so that inlet flow is directed away from the central axis of the cyclone preferably. The vessel 202 is operated at above atmospheric pressure, preferably a gas vent 214 and pressure control means is provided in an upper part of the vessel 202, preferably, the vessel 202 is a fluid tight pressure vessel, which can be operated in a hostile environment, such as on an offshore oil production facility or at the seabed. In practice, the first outlet from the vessel 202 the oil rich outlet is at a lower pressure than the separator vessel.

The inlet fluid may comprise a hydrocarbon fluid, such as crude oil and the more dense fluid comprises of water, such as produced water. A preferred embodiment of the present invention provides a separator able to be fitted at the commencement of the oil fields production, during which time only a small flowrate of water is expected to be produced, with the ability to manage increase's and slugs of multiphase flow

throughout the oil fields life. The total throughput of the compact separator is controlled by the interface (oil and water) level control system with the outlet control valve of the same situated downstream of the compact separator in its clean water outlet pipework. All other flow fluctuations will be managed in the compact separator without the need for the actuation or operation of valves or other means either inside the vessel or externally whilst treating the produced water up to the separators maximum design throughput. The system described will require fewer utilities, manpower, and maintenance together with removing the bulk of moving parts, control and

instrumentation from existing skid mounted de-oiling hydrocyclone systems available today. Preferably, the system is able to manage large variations in flow-rates without a process upset, hence affording the separator vessel a high turn down ratio.

A further embodiment comprises a degassing filter with a cyclonic inlet to remove free gas prior to filtration with the ability to have its media washed to recover the medial bed by means of a fluidising unit feeding the filtration media to a media cleaning cyclone with the media being returned to the filter and the wash water reporting to a multiphase pressurised centrifuge.

High Flow low Delta P Cyclone

Figure 9 shows a lower pressure high flow de-oiling cyclone 102 (DPS MK2.1 ) comprising a tubular section 104 having an inlet 105 with first inlet means vane system 106 or one or more tangential inlets to create a rotational or spinning flow regime within a swirl chamber 107 defined by the parallel tube section 104 which has a defined length to diameter ratio followed by a second spin generator 108 preferably designed to create a higher spin rate positioned on a central oil take off tube 1 10 which can be parallel or tapered towards an outlet 1 12. The purpose of the first spin inlet 106 is to remove the bulk of the oil by creating a stable vortex core of gas, oil and water having collected all or most of the larger oil droplets without excessive shear which creates smaller more difficult to remove oil drops. The second spin vane 108 then accelerates the fluid to move the smaller drops to the outer surface of the oil take off tube 1 10 which may have a spiral groove cut on its surface either clockwise or anticlockwise to the direction of fluid flow reporting to an outlet port 1 14 of the oil take off tube 1 10. The oil take off tube 1 10, if tapered, will create a coalescing effect which may cause the oil to migrate in a direction which is in reverse of the main water flow up the spiral groove to the outlet port 1 14. Outlet 1 16 positioned in a vortex tube section 1 18 of the tubular section 104 may be used to remove any solids in particular sands, ashpaltines or scale particles which may otherwise build up within the vortex tube section 1 18 which could cause the pressure drop through the unit to increase in use with the potential to cause blockages. In produced water with larger oil droplet size distributions it is advantageous to feed the smallest droplets only into a tertiary filter system in order to lengthen run times between washing the media and avoid the formation of mud balls (large collection of oil wetted media firmly adhering to each other to form a ball). The outlet 1 16 may also be used to remove water from the vortex tube section 1 18.

Detailed experimental work undertaken is given below to show the benefits of such a cyclone.

Further to the initial cyclone design, characteristic data for cyclone performance with varying temperature was determined. Temperatures of 20°C, 30°C and 40°C (these can be higher but this work is better conducted at site pilot plants) were used, with the flowrate and pressure drop through the cyclone recorded.

A feed water tank was heated using three immersion heaters, to the required temperatures. Once these temperatures were achieved, varying flow-rates and back pressures were applied to the cyclones to determine the effect of the changing temperature. Data was recorded utilising the Lab VIEW see www.ni.com/labview distributive control system and data collection, changes to the swirl inlets were created by use of a solid 3D printer using ABS plastic to create the required parts. Figure 5 shows the test set-up.

The Existing De-oiling cyclone liner's in the market today at 20°C provided a line of best fit that gave the equation;

ΔΡ = 9.7161 Q2 - 3.8768Q + 8.4954

At 30°C we achieved the following relationship;

ΔΡ = 9.4615Q2 - 1.9525Q + 7.9929

At 40°C the graphed results yielded;

ΔΡ = 9.3508Q2 - 0.5971 Q + 7.6047

For analytical purposes the equations will be considered to take the form of; ΔΡ = a.Q2 + b.Q + c

Where (a) and (b) are constants and (c) is the y-intercept. As the temperature increased the values of (a) have decreased slightly from equation 1 to equation 2 and 3. The values of (b) have increased and the (c) values have decreased. Figure 6 shows equations 1 -3 seen in graphical form.

Figure 6 shows the effect of temperature on pressure drop through the existing liner. The graph shows a close correlation between the three curves. The 40°C curve appears to achieve the highest pressure drops, with the 20°C curve showing the smallest. This can be attributed to a larger increase in values of b to the decreasing values of (a) and (c).

The cyclone shown in Figure 9 yielded the following equations as the temperature was increased;

At 20°C;

ΔΡ = 0.3679Q2 + 0.2097Q + 7.688 At 30°C;

ΔΡ = 0.3684Q2 + 0.2735Q + 9.4333

And at 40°C; Note different hoses used here

ΔΡ = 0.3725Q2 + 0.0632Q + 1 .8523

From these three equations we can see that the step from 20°C to 30°C has caused an increase in all of the constants, while the step from 30°C to 40°C has caused the (b) and (c) values to decrease. Figure 7 below shows a graph of equations 5-7.

Figure 7 shows the effect of temperature on the cyclone shown in Figure 9.

From the equations and graphs listed above it can be seen that the change in temperature plays a role in the pressure drop through the cyclone. However this difference is seen to generally be no more than about 10kPa between the three temperatures tested. The exact effect the temperature has on the pressure drop is harder to determine. In determining the pressure drop, the temperature has the most influence on the

Reynolds number, by affecting the values for density and viscosity of the fluid.

Reynolds number,

As temperature increases it tends to cause the density and the viscosity of the fluid to fall. While the density is inversely proportional to the temperature, the viscosity is exponentially dependent upon temperature.

Figure 8 shows an industrial standard cyclone and Hydropak (US005045218) results for flow against pressure drop. These show a steep increase in pressure used to maintain flow at the conditions needed to separate oil from water. If we consider burning pressure to do work then it simply equates to work done i.e. force times distance moved for a given weight, in our case we wish to migrate a given droplet size of oil to the vortex core where it can be collected and removed from the water, given that the de-oiling cyclones on the market today cannot meet discharge limits alone then a lower pressure drop at greater flow-rates is desirous, with the outlet water quality meeting the inlet conditions of a tertiary filter or enhanced compact floatation system then a cyclone capable of higher flow-rates at a lower pressure drop is needed in order to have sufficient pressure available to pass through the tertiary system. The curve for a variant of the cyclone (DPS MK1 ) shows high flow-rates with very low pressure drop but very low efficiencies for oil from water separation was recorded hence not suitable, whereas the embodiment shown in Figure 9 (DPS MK2.1 ) was capable of treating up to 1 1 m3/hr with a Delta P of 4 barg, whilst meeting efficiency levels suitable for filtration or tertiary systems.

Dimensional ratio of the embodiment shown in Figure 9: Inlet 1 (spin Vane)

Area of the Oily water inlet normal to flow was 189mm ² (based on 4 areas of 47.25mm) Internal diameter of the tube: 2 inch, equal to 50.4mm. The length of first vortex chamber between the first swirl unit 106 and the second swirl unit 108 in Figure 9 can be varied depending on the available pressure drop and work required to be done by the unit. This enables bespoke designs to be tailored to specific applications. In general the vortex chamber can be as short as 8mm and longer than 500mm. Mechanically as this is a straight tube it is a very economical way of varying the performance of the unit.

In practice a distance from 8mm to 300mm from the first swirl unit 106 to the second swirl unit 108 can be used for a 50.4mm inside diameter vortex tube. Generally it has been recorded that longer lengths establish a more stable vortex where pressure is available, this allows the vortex tubes to be tailored to actual conditions existing. The ratio above will change the distance based on the inside diameter of the larger or smaller vortex tubes.

Flow rate (Q) as a function of Pressure drop (ΔΡ):

AP=aQ ² +bQ+c a, b, c are constants

The cyclone described above is cheaper to manufacture as it is not required to have an accurate long cone where the internal surface is almost a perfect circle free from ridges, oval sections and abrupt diameter charges. Conventional methods of manufacture require swageing of the tail of the cyclones which is difficult and expensive to achieve when using the industry required duplex stainless steels.

The cyclone shown in Figure 9 can be manufactured from standard pipe sections with ceramic or cast internals.

Figure 9 is a cross-section through a de-oiling cyclone able to treat more produced water with less driving pressure whilst meeting in inlet requirements of a filtration or other tertiary systems.

It is the intention therefore to be able to separate two streams of differing densities while presenting a smaller footprint and volume envelope than existing devices; in addition to a lower pressure drop and acceptable separation efficiency. The hydrocyclone separates the streams by virtue of the difference in density between them. This shall be achieved by enhancing the apparent difference in density by increased gravitation force, thereby accelerating the separation. The device shall have no moving parts, other than those to control either the flow or the pressure associated within the separator; these shall most probably be in the form of control valves.

The hydrocyclone can be described in a number of sections, namely an inlet 105; swirl chamber 107; centre obstruction 1 10 and second swirl unit 108 and outlet 1 12. The outlet 1 12 may provide communication between the swirl chamber 107 and a second chamber 120 for collecting water removed from the swirl chamber 107. The second chamber 120 may comprise a second outlet 122 through which water can be removed from the second chamber 120.

The mixture of fluids to be separated shall enter into the hydrocyclone via the inlet 105 where a spin will be imparted to the fluids by a fin pack 106 that offers the required open area, or by a rectilinear, circular or tubular tangential inlet, or other suitable orifice.

The rotating mixture will impart an increased gravitational effect or centrifugal force on the objects entrained, where the lighter fraction will migrate to the centre, while the heavier objects will be thrown to the outer wall of the vortex tube where if required solids such as sand may be removed via outlet 1 16.

The lighter fraction, which has migrated to the centre of the hydrocyclone, shall be allowed to exit the device through an orifice 1 14 located at the top the obstruction or oil take off tube 1 10 which may have a taper on its outer diameter with smaller diameter at the inlet end of the cyclone 102 and larger diameter at the outlet end. This orifice 1 14 will be of a suitable size to allow the desired flow rate through without offering an undue flow or pressure drop.

The oil outlet tubes orifice location has been considered to be in a number of locations, the locations can be used depending on each application of the hydrocyclone. The orifice is located within the top of the oil take off tube 1 10; this may be in the centre, or off-set but within this area. Additional light phase outlets can be provided at the base of the oil take off tube 1 10. Following the bulk separation of the light phase, the heavier phase shall be accelerated by virtue of the second swirl unit 108 or reduction in the annulus created by the tapered oil take off tube 1 10, this acceleration shall increase the separation potential due to increased gravitational effect. This shall result in the yet to be separated, and therefore the smaller objects/oil drops, migrating in their respective direction depending on their density or being coalesced. Furthermore, the distance that these objects have to travel is progressively reduced given that the radius of open area between the hydrocyclone wall and oil take off tube 1 10 getting progressively smaller when the same is tapered.

The lighter phase that impacts on the obstruction (i.e. oil take off tube) 1 10 shall initially form a surface coating. To aid this, the material of the obstruction 1 10 shall be chosen to aid the separation and attract the lighter phase: for example in an oil and water separation system the obstruction 1 10 could be an oleophilic material, for example polypropylene or cast stainless steel. Once the lighter phase has impacted on the obstruction 1 10, the fluid shall be encouraged to reverse flow and 'climb' back up towards the location of the orifice coalescing as it goes to eject the lighter phase via 1 14. This may be achieved by using a simple smooth profiled obstruction, or by the inclusion of a surface that is conducive to this; for example, the inclusion of rifling which would therefore provide a section within the film of the lighter phase where the thickness of the film is thicker. In some instances the obstruction may have further outlets at its larger end connecting to the port within the obstruction which is defined by 1 14.

The heavier phase would then exit the hydrocyclone liner via the outlet 1 12 at the base of the obstruction 1 10.

Figures 17 to 20 are various cross-sections through a separator able to manage the required turndown in flows with a single vessel, containing no moving parts internally to the vessel.

The cyclone has simple pipework with the separation created by internals. This can be deployed in a riser from the sea bed or in the well casing itself. Multiple cyclones can also be inserted into pressure vessels or short versions can be placed at the water outlets of three separators or electrostatic dehydrators. The cone or tapered tube shown in isolation in Figures 13 and 14 can be parallel or tapered and is primarily a coalescing section, as described earlier it can have a spiral grove cut on its outer surface to further deliver oil at the surface of the tube to report to the oil outlet portals.

Figures 10 and 1 1 show sections of the cyclone shown in Figure 9 in the regions of the swirl inlets.

The separator shown in Figure 17 comprises a turndown cyclone vessel 202 which may incorporate vortex valves, gamma ray densitometers or other means to detect liquid levels within the vessel if required. It can be seen that the water or bottom outlet of each cyclone 212 has an inbuilt non return ball valve 216, shown in Figure 18, to inhibit clean water passing back through the cyclone when it is not in operation. The number of cyclones on line is dependent on the height of the liquid level in the vessel. Simplified schematic cross-sectional views of the turndown cyclone vessel are shown in Figures 19 and 20.

The process schematic shown in Figure 21 operates in the following manner. The produced water exits the horizontal three phase separator 302 under interface level control and reports to the a cyclone vessel 202, which removes treated water to a cyclonic degassing filter 402, the oil passes from its base to report to a centrifuge 502 which is able to operate at multiple phases up to 5 including sub-micron solids at atmospheric or elevated pressures with no need to change internals to operate correctly, for further treatment prior to returning the oil to the production system at a suitable pressure. Once the degassing filter media is contaminated with oil and solids the fluidiser 602 in its base (CyFlo) receives treated water and transports the filter media to a sand washing cyclone 702, the oily water from this stage reports to the centrifuge 502 and the media returns to the filter.

In certain cases the produced sands may be suitable to act as filter media once they have been removed from the process flow and cleaned, hence removing the need to ship out new media in the case of offshore or subsea installations in the event of loss of media as a result of media break up (attrition) for example.

Figures 22 and 23 show an alternative embodiment of a cyclone separator 802. The cyclone separator 802 comprises a longitudinal vortex chamber 804 having an inlet 806 at one end of the chamber 804 and a heavier phase outlet 808 at the other end of the chamber 804. The vortex chamber 804 is also provided with a lighter phase outlet 810, disposed between the inlet 804 and the heavier phase outlet 808, and a solids outlet 812, disposed between the lighter phase outlet 810 and the inlet 806.

The cyclone separator 802 comprises a housing 814. The housing 814 comprises a first tubular section 816 and a second tubular section 818 connected by a collar arrangement 820.

The first tubular section 816 has an internal diameter which is greater than the external diameter of the second tubular section 818. The second tubular section 818 is partially inserted into one end of the first tubular section 816 such that the first and second tubular sections 816, 818 define an annular flow passage 822 between them. The end of the flow passage 822 adjacent the end of the second tubular section 818 defines the solids outlet 812. The tubular sections 816, 818 are held in position by the collar arrangement 820. The collar arrangement 820 defines an annular chamber 824 which is coaxial with the vortex chamber 804 and extends about the second tubular section 818. The annular chamber 824 defines a plenum into which the end of the annular flow passage 822 opposite the solids outlet 812 opens. The internal diameter of the annular chamber 824 is greater than the internal diameter of the portion of the first tubular section 816 which defines the flow passage. An outlet port 826 is provided through the end of the collar arrangement 820 opposite the flow passage 822, through which solids can be discharged. The outlet port 826 is provided at the lower region of the annular chamber 824.

The first tubular section 816 defines an inlet region 828 of the vortex chamber 804. A cap 830 encloses the end of the first tubular section 816 opposite the solids outlet 812. A solid-walled core element 832 extends inwardly from the cap 830 along the longitudinal axis of the vortex chamber 804. The solid-walled core element 830 comprises a cylindrical portion 834 adjacent the cap 830 and a frusto-conical portion 836 which extends from the cylindrical portion 834 towards the opposite end of the first tubular portion 816.

The inlet 806 comprises a port which is offset from the longitudinal axis of the vortex chamber 804 and opens through the wall of the first tubular section 816 and the cap 830. An inlet tube 838 extends outwardly from the inlet 806 in a generally tangential direction with respect to the vortex chamber 804. A sleeve 840 is disposed within the second tubular section 818. The sleeve 840 extends coaxially with the second tubular section 818. The sleeve 840 defines an outlet region 842 of the vortex chamber 804. The sleeve 840 tapers in the direction of the heavier phase outlet 808. The outlet region 842 of the vortex chamber 804 converges in the direction of the heavier phase outlet 808. The end of the sleeve 840 adjacent the solids outlet 812 flares outwardly and is sealed against the inner wall of the second tubular section 818.

The sleeve 840 is a modular arrangement comprising a plurality of tapered sleeve sections 844 which connect end-to-end to form the sleeve 840. A brace 846 is provided towards the end of the sleeve 840, which secures the sleeve 840 to the second tubular section 818.

A flow rotation accelerator 848 is disposed at the end of the second tubular section 818 adjacent the solids outlet 812. In the embodiment shown, the flow rotation accelerator 848 comprises a circular array of swirl vanes arranged about an axial core, similar to the arrangement shown in Figure 16. The flow rotation accelerator 848 forms a plug which fits in the end of the second tubular section 818 such that flow from the inlet region 828 into the outlet region 842 must pass through flow rotation accelerator 848. It will be appreciated that other means for accelerating the rotational speed of the rotational flow may be used, for example directional nozzles, propulsion means or other suitable arrangement.

The lighter phase outlet 810 is arranged within the outlet region 842 of the vortex chamber 804 adjacent the flow rotation accelerator 848. In the embodiment shown, the lighter phase outlet 810 is provided at the axial core of the flow rotation accelerator 848. The lighter phase outlet 810 opens into the outlet region 842 of the vortex chamber 804. A duct 850 extends from the lighter phase outlet 810 through the axial core of the flow rotation accelerator 848. The duct 850 comprises a funnel section 852 which defines the lighter phase outlet 810. The funnel section 852 is connected to a pipe 854 which extends from the funnel section 852 in the axial direction before turning through 90 degrees and exiting the cyclone separator 802 through the walls of the second tubular section 818, the first tubular section 816 and the collar 820 in a radial direction. The duct 850 may be provided in fluid communication with processing equipment for processing the lighter phase. In use, a pressurised mixture comprising a lighter phase, such as oil, a heavier phase, such as water, and solids, such as sand or grit, is fed along the inlet tube 838 through the inlet 806 into the inlet region 828 of the vortex chamber 804. The tangential arrangement of the inlet tube 838 with respect to the vortex chamber 804 ensures that a rotational/rotary flow is initiated within the vortex chamber 804. The solid-walled core element 832 obstructs flow in the radially inward direction and so assists in the formation of a vortex within the vortex chamber 804.

The rotational flow within the vortex chamber 804 causes the sand to be flung outwardly towards the wall of the vortex chamber 804 as the mixture flows along the vortex chamber 804 away from the inlet 806. At the same time, the rotational flow causes the water and the oil to begin to separate. The water, which is the heavier phase, accumulates radially outwardly of the oil, which is the lighter phase. The oil and water are expected to form at least partially separated layers within the inlet region 828 of the vortex chamber 804. The sand which collects along the inner surface of the first tubular section 816 is conveyed through the solids outlet 812, along the flow passage 822 and into the annular chamber 824. The annular chamber 824 provides a quiescent region of flow within which the sand settles before being discharged from the annular chamber 824 through the outlet port 826 for subsequent processing.

It is expected that at least some water will be discharge with the sand through the solids outlet 812 into the annular chamber 824. However, accumulation of water within the annular chamber 824 inhibits excessive flow of water through the solids outlet 812, but does not significantly inhibit the passage of sand through the solids outlet 812. Consequently, sand is removed from the influent mixture without removing excessive amounts of water with the sand.

The relatively large diameter of the inlet region 828 of the vortex chamber 804

(compared with the diameter of the outlet region 842 described below) means that the speed of rotation of the flow is relatively low. Consequently, the shear forces exerted on droplets of oil and water in the flow are relatively small and so are less likely to break-up the droplets into smaller droplets. This is advantageous since larger droplets can be separated using lower centrifugal forces, and hence rotational speeds, and so effective separation of a significant proportion of the oil and water within the inlet region 828 is achieved. Oil and water from which the sand has been removed flows from the inlet region 828 of the vortex chamber 804, through the vanes of the flow rotation accelerator 848 and into the outlet region 843 of the vortex chamber 804. The vanes accelerate the rotational flow to a greater rotational speed. This increases the centrifugal forces acting on the oil and water, which enhances separation. In particular, the increased centrifugal forces are more effective at separating smaller particles of water from the oil or vice versa. This second stage of separation ensures that oil droplets suspended in the water, and water droplets suspended in the oil, which are too small to be separated by the centrifugal forces generated in the inlet region 828 of the vortex chamber 804 are effectively separated in the outlet region 842 of the vortex chamber 804. Furthermore, since large droplets of oil and water were separated in the inlet region 828 of the vortex chamber 804, and so have collected as continuous phases radially inwardly and outwardly of the vortex chamber 804, they are unaffected by larger shear forces generated by the increase in the rotational speed. Consequently, as the oil and water flow along the outlet portion 842 of the vortex chamber 804, they form layers with the oil collecting along the longitudinal axis of the vortex chamber 804 and the water collecting at the inner surface of the sleeve 840.

As the water flows towards the heavier phase outlet 808, the convergence of the vortex chamber 804 causes the water to occlude the heavier phase outlet 808. Oil which has collected along the vortex chamber axis is forced back along the vortex chamber 804 towards the lighter phase outlet 810.

Therefore, in normal operation an oil core is formed in the outlet region 842 of the vortex chamber 804. The oil occludes the lighter phase outlet 810 and so prevents water from being discharged through the lighter phase outlet 810. The water occludes the heavier phase outlet 808 and so prevents oil from being discharged through the heavier phase outlet 808. Oil is discharged through the lighter phase outlet 810 and water is discharged through the heavier phase outlet. Consequently, effective separation of the oil and water is achieved.

Figure 28 shows performance characteristics of a particular embodiment of the cyclone separator 802. Figure 28 is a plot of particle/droplet size vs. percentage separation. The plot shows that the cyclone separator can achieve 90% separation of oil and water when configured to separate oil droplets having a nominal diameter (known as cut size) of 20 microns or above. Furthermore, this is achieved with significantly less pressure drop through the vortex chamber 804 than conventional cyclones. The cyclone separator 802 enables a target separation efficiency to be achieved at a greater flow rate and a lower pressure drop through the cyclone separator 802 than conventional cyclones.

Figure 24 is a schematic representation of an embodiment of the cyclone separator 802 shown in Figures 22 and 23. In this embodiment, the annular chamber 824 is disposed about the inlet region 828 of the vortex chamber 804. A baffle 817 is provided between the solids outlet 812 and the annular chamber 824.

Figure 25 is a schematic representation of a variant of the cyclone separator in which the inlet 806 is arranged coaxially with the vortex chamber 804. An array of swirl vanes 856 is disposed adjacent the inlet. The swirl vanes promote rotational flow of the mixture within the inlet region 828 of the vortex chamber 804.

Figure 26 is a schematic representation of a single pressure vessel 902 which accommodates a plurality of cyclone separators such as those described above, for example the cyclone separator 802 shown in Figure 23. Such an arrangement is compact. Furthermore, incorporating multiple cyclone separators within a single pressure vessel reduces the cost of a multiple cyclone arrangement.

Figure 27 is a cross-sectional view of the pressure vessel shown in Figure 26 in which multiple cyclone separators 802 are shown arranged within the vessel 902. The cyclone separators 802 extend longitudinally within the vessel 902. The inlets 806 may be connected to a common inlet 904 entering the vessel 902. Similarly, the heavier phase outlets, lighter phase outlets and solids outlets may be respectively connected to a common heavier phase outlet 906 and a common lighter phase outlet 908 and a common solids boot 910, for collecting the solids. Alternatively, the solids outlets may be connected directly to a common solids outlet.

During use, solids accumulate in the solids boot 910. The solids can be removed with the aid of a fluidiser, which then reports the solids at the correct concentration to a solids cleaning cyclone unit. It has been found that with the larger and heavier solids such as silicon sands above 30 microns the solids can settle into the boot without any control of a counter-current flow of water reporting back to the de-oiling inlet of the cyclone in a closed system, if smaller or lighter solids are being removed then a control of the counter-current flow from the solids boot 910 can be used such as a flow restriction or valve on a by-pass port back to the de-oiler inlet.

It will be appreciated that aspects of the other embodiments could be incorporated into the embodiments shown in Figures 22 to 25, for example a tapered core arrangement such as that shown in Figures 9 and 12 to 14 could be used.

The separator may be used to separate other types of mixture comprising a heavier phase, lighter phase and solids.