GB2463274A

GB2463274A - Apparatus and methods for separating a multiphase fluid

Info

Publication number: GB2463274A
Application number: GB0816265A
Authority: GB
Inventors: Kenneth James Adams; Badrul Huda; Sam Kingman; Edward Henry Lester; John Peter Robinson
Original assignee: BP Exploration Operating Co Ltd
Current assignee: BP Exploration Operating Co Ltd
Priority date: 2008-09-05
Filing date: 2008-09-05
Publication date: 2010-03-10
Also published as: GB0816265D0

Abstract

Apparatus for separating a multiphase aqueous/liquid hydrocarbon solution comprises a separator vessel having an inlet 2, a plurality of outlets 4, 5, a microwave irradiation treatment zone and a waveguide 6 arranged to direct microwave radiation into the microwave irradiation treatment zone from either above or directly into the emulsion layer of the multiphase solution. The separator may contain a baffle 16 between the aqueous phase outlet 5 and the liquid hydrocarbon phase outlet 4, and an interior cavity for retaining the multiphase solution for treatment. The waveguide may be arranged to transmit radiation through a microwave transparent window. Also disclosed is an apparatus in which the microwave radiation is contained in the treatment zone by a Faraday cage (fig 2, 36). The end of the waveguide may extend into the cage. Methods for use of both sets of apparatus are also provided.

Description

I

AN APPARATUS AND METHOD FOR SEPARATING A MTJLTIPHASE FLUID

The present invention relates to an apparatus and method for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase, and optionally a gaseous phase, in particular, for separating an emulsion layer comprising an aqueous phase dispersed in a liquid hydrocarbon phase into its component phases within a separator vessel.

Oil/water separation is a fundamental process in upstream oil production. An oil/water emulsion is produced from wells and transported to a separator tank or vessel through a flowline. The emulsion is in the form of water droplets dispersed in an oil phase.

In practice, produced liquid hydrocarbons, in particular, crude oils, form three layers in a separation vessel, these being an upper liquid hydrocarbon layer, a lower aqueous layer and an intermediate emulsion layer (often referred to as a "rag layer"). It is necessary to separate the water from the oil and typically this is carried out in large separation tanks where, with sufficient residence time, the phases will separate due to density difference, with the water dropping out of the oil phase. The different layers may then be removed from the tank. The emulsion of the intermediate emulsion layer may be stabilized by naturally occurring surfactants in the produced fluid, however, the demulsification of the intermediate emulsion layer can be problematic.

In order to enhance the speed of separation and reduce the size of the separation tanks, the fluid may be heated, chemicals added or electrostatic coalescers used. The use of microwave radiation to aid demulsification of water-in-oil emulsions is known with the microwaves assisting the separation process. The water droplets in the emulsion absorb microwave energy to a much greater extent than the oil or any gas present with the result that the temperature of the water droplets increases to more than that of the surrounding oil. The water droplets drop through the oil, resulting in an increased coalescence of the droplets.

Conventional assemblies for treating emulsions with microwave energy are typically arranged along a flowline, that is, before the separating tank. The fluid is still in the form of an emulsion in the flowline as the flow through the flowline tends to prevent any separation of the water and oil.

US 4,582,629 describes a method for erthancing the separation of oil and water dispersions and emulsions by treating the same with microwave radiation in conjunction with conventional separating devices. The emulsion or dispersion is subjected to microwave radiation, only for a short period of time, and the emulsion or dispersion will be heated to separation temperature by conventional means. The method is said to be applicable to both oil external and water external systems, that is, water-in-oil and oil-in-water emulsions respectively. The emulsion or dispersion is treated at a power level of from about 1 Watt to about 500 Watts per gallon (264.2 to 132,086.4 Watts per m3) of emulsion or dispersion. It is said that this treatment is not sufficient to raise the temperature of the emulsion to levels normally used for separation, but will greatly enhance the resultant separation once heating is completed by conventional means.

The method of US 4,582,629 may be used in combination with conventional treatment vessels such as heat treaters, which are tanks modified to add heat and provide residence time in the system. Microwaves would either be used directly in the tank to generate heat and interfacial disruption, or in a section of a flowline just ahead of the tank.

Likewise, the method could be used in washtariks or gun barrel treaters, either in the tank or in the pipeline leading into the tank. However, it has now been found that microwave irradiation of the entire flow of multiphase fluid in a section of the flowline just ahead of the tank and also microwave irradiation of the entire contents of a tank is uneconomiè in terms of the power demands for the microwave generator.

US 4,810,375 relates to a method of and apparatus for enhancing the separation of oil and water emulsions and dispersions by treating the same with microwave radiation, whether alone or in conjunction with additional conventional separating devices. In the method of US 4,810,375, an oil-water emulsion or dispersion is conveyed via an inlet to an applicator where it is heated by microwave energy from a power source through a circulator and waveguide. The heated stream exits the applicator through an outlet to a separator vessel where the stream separates into an upper oil phase and a lower oily water phase. The separated phases are then recovered through outlets on the separator vessel.

The oily water is recirculated through a water load connected to the circulator and returned to the separator vessel. Thus, the entire feed stream to the separator vessel is subjected to 30. microwave irradiation resulting in the separation of the feed into two layers in the separator vessel. As discussed above, microwave irradiation of the entire feed stream to the separator vessel is uneconomic in terms of the power demands for the microwave generator.

US 4,889,639 discloses a similar apparatus to that disclosed in US 4,810,375 but differs therefrom in that the oily water is recirculated through the applicator rather than through a water load.

WO 01/46353 describes a method and apparatus in which a used oil sample having at least 1% (by weight) aqueous substances is heated to a temperature of from about 20°C to about 60°C in a heating section ahead of the separator tank, and the heated oil is extracted by adding super critical CO2 to a demulsification section, whereby a volume of water is removed from the heated used oil sample. The heating step can be accomplished by a microwave heating process or by conventional heating techniques. A microwave generator with a power output of 6kW at 2.45GHz is applied to an emulsion flowing at 8.51 liters per minute.

US 4,853,507 is directed to an apparatus for treating oil and water emulsions in which microwave energy is radiated into an applicator section having a waveguide with a tapered applicator element which separates the input and output sections of the waveguide.

Emulsion is passed through the waveguide ahead of a settling/separating tank and the emulsion is heated in the waveguide by the microwave radiation. The emulsion is subsequently separated into the constituent components in the settling/separating tank.

US 4,855,695 is directed to an apparatus for automatic tuning of microwave energy in a demulsifier system using a waveguide applicator. A microwave transparent window is placed across the waveguide and the fluid to be treated is passed into the waveguide beyond the window and a surfactant is injected into the waveguide. These fluids are then heated by microwave radiation and exit the waveguide into a separator vessel. The microwave transparent window is designed to inhibit fluid flowing back into the microwave source. The heating of the emulsion in this system is not symmetrical and the microwave transparent window may be subject to damage from inclusions in the emulsion such as sand, gravel or rocks which would affect the performance of the system. As discussed above, microwave irradiation of the entire feed stream to the separator vessel is uneconomic in terms of the power demands for the microwave generator.

EP 1,050,330 is directed to a microwave energy application apparatus to break oil and water emulsions. A stream of hydrocarbon and water emulsion is pumped into a microwave cavity. Dual opposing emulsion flow chambers with a centrally supplied microwave guide form a double-ended resonant chamber with multiple RF energy reflectors to treat the flowing emulsion. The emulsion feedstock enters into the bottom of both flow chambers and exits to a centrifuge or storage vessel for separation.

The present invention relates to an apparatus for separating a multiphase fluid comprising an aqueous phase, liquid hydrocarbon phase and optionally a gaseous phase into its component phases.

According to a first preferred embodiment there is provided an apparatus for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the apparatus comprising: a separator vessel for separating the multiphase fluid into an upper liquid hydrocarbon layer, a lower aqueous layer and an intermediate emulsion layer comprised of droplets of aqueous phase dispersed in the liquid hydrocarbon phase, the separator vessel having an inlet for receiving the multiphase fluid, a plurality of outlets for removing component phases of the multiphase fluid after separation and a microwave irradiation treatment zone for treating the emulsion layer as it flows through the separator vessel; and a waveguide arranged to direct microwave radiation into the microwave radiation treatment zone of the separator vessel either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases.

Upstream of the microwave radiation treatment zone of the separator vessel, the multiphase fluid separates, under gravity, into a lower aqueous layer, an upper liquid hydrocarbon layer and an intermediate emulsion layer comprising droplets of aqueous phase dispersed within a liquid hydrocarbon phase. The microwave radiation treatment zone of the separator vessel is arranged in the region of the separator vessel that contains the intermediate emulsion layer.

Preferably, the apparatus further comprises a baffle located in the separator vessel between an outlet for removal of the aqueous phase and an outlet for removal of the liquid hydrocarbon phase to inhibit the separated aqueous phase from passing through the outlet for the liquid hydrocarbon phase.

In a preferred embodiment, the apparatus further comprises a microwave transparent window located in a face of the separator vessel, the wave guide being further arranged to direct microwave radiation through the microwave transparent window into the separator vessel, an end of the waveguide being adjacent the microwave transparent window. Preferably, the microwave transparent window is located in the upper wall of the separator vessel such that the microwave radiation is directed through the headspace in the separator vessel and through the upper liquid hydrocarbon layer into the microwave radiation treatment zone. Alternatively, the waveguide may penetrate through the wall of the separator vessel with the end of the waveguide being terminated with a microwave transparent window to inhibit flow of the fluid from the separator vessel to the microwave source. The microwave transparent window may be formed from one or more of sapphire, quartz glass, or KevlarTM.

Accordingly, the waveguide may terminate in the head space of the separator vessel, in the liquid hydrocarbon layer or in the upper part of the intermediate emulsion layer.

According to a second aspect of the present invention there is provided an apparatus for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous phase into its component phases, the apparatus comprising: a separator vessel for separating the multiphase fluid into an upper liquid hydrocarbon layer, a lower aqueous layer and an intermediate emulsion layer comprised of droplets of aqueous phase dispersed in the liquid hydrocarbon phase, the separator vessel having an inlet for receiving the multiphase fluid, a plurality of outlets for removing component phases of the multiphase fluid after separation and a microwave irradiation treatment zone for treating the emulsion layer as it flows through the separator vessel; and a waveguide arranged to direct microwave radiation into the microwave radiation * treatment zone of the separator vessel either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases, and * 30 a Faraday cage within the separator vessel arranged to contain the microwave radiation within the cage.

Preferably, the waveguide has a first end which extends into the Faraday cage in the separator vessel.

An advantage of the Faraday cage is that this mitigates the risk of microwave radiation being irradiated out of the separator vessel, for example, by being transmitted by piping. The Faraday cage also forms a multimode cavity.

In a preferred embodiment, the separator vessel has a longitudinal axis and an interior surface; and the cage comprises two wire meshes respectively forming a first wall of the cage and a second wall of the cage, the meshes being longitudinally separated along the longitudinal axis of the separator vessel and extending between an upper and a lower interior face of the separator vessel, the first wall being located upstream of the end of the waveguide positioned in the separator vessel and the second wall being located downstream thereof, the interior surface of the vessel forming additional walls of the cage.

In a further preferred embodiment, the cage comprises four mesh walls.

Preferably, the mesh walls each have a plurality of apertures defined by the separation of opposing sides of the apertures, the separation being less than the wavelength of the applied microwave radiation to contain the microwaves within the cage.

The cage is preferably attached to the interior wall of the separator vessel.

In a preferred embodiment, a microwave transparent window is positioned on an end of wave guide. The microwave transparent window may be formed from one or more of sapphire, quartz glass, or KevlarTM.

The apparatus may comprise a plurality of Faraday cages located within the separator vessel. One or more Faraday cages may be located in use in the multiphase fluid in the separator vessel. Preferably, the multipha.se fluid comprises a crude oil distillate fraction having an aqueous phase dispersed therein.

According to a third aspect of the present invention there is provided a method..for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases using the apparatus defined above.

According to a fourth aspect of the present invention there is providemetbod for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the method comprising: (a) passing the multiphase fluid through a microwave radiation treatment zone in a separator vessel; (b) heating the multiphase fluid by subjecting the multiphase fluid to microwave radiation in the separator vessel, the microwave radiation being directed into the multiphase fluid either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases; and (c) withdrawing a liquid hydrocarbon stream and an aqueous stream from the separator vessel.

According to a fifth aspect of the present invention there is provided a method method for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the method comprising: (a) passing the multiphase fluid through a microwave radiation treatment zone in a separator vessel; (b) heating the multiphase fluid by subjecting the multiphase fluid to microwave radiation in the separator vessel, the microwave radiation being directed into the multiphase fluid through a Faraday cage located in the multiphase fluid to focus the microwave radiation and to heat the aqueous phase dispersed in the multiphase fluid and assist in separation in the separator vessel of the multiphase fluid into component phases; and (c) withdrawing a liquid hydrocarbon stream and an aqueous stream from the separator vessel.

The multiphase fluid may be a produced fluid from a hydrocarbon production well andlor may comprise a crude oil distillate fraction having an aqueous phase dispersed therein.

The present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a schematic cross-section of a separator vessel according to a first preferred embodiment; Figure 2 is a schematic cross-section ofa separator vessel according to a second preferred embodiment; and Figure 3 is an end elevation of the separator vessel of Figure 2.

An apparatus according to a first preferred embodiment for separating a multiphase fluid comprising an aqueous phase, liquid hydrocarbon phase and optionally a gaseous phase is shown in Figure 1. The apparatus comprises a separator vessel 1 having a fluid inlet 2, a first outlet 3 for removing the separated gaseous phase, a second outlet 4 for removing the separated oil phase, and a third outlet 5 for removing the separated aqueous phase. A waveguide 6 extends through the upper wall of the separator vessel 1 at a location between the inlet 2 and the gas outlet 3 and into the interior of the separator vessel thereby directing microwave radiation into a microwave radiation treatment zone 7.

The multiphase fluid is introduced into the separator vessel I through the fluid inlet 2. In the separator vessel 1, the fluid separates under gravity into an upper oil layer 10, an intermediate emulsion layer 12 and a lower water layer 14, with greater separation of the oil and water phases being achieved as the fluid flows from the inlet to the outlets of the separator vessel. The end of the waveguide 6 which is within the interior of the separator vessel 1 preferably extends, in operation, above or into the oil layer 10 but not into the water layer 14. A baffle 16 extends into the interior of the separator vessel 1 from the bottom wall thereof, between the water outlet 5 and the oil outlet 4. The baffle 16 acts to inhibit the separated water from exiting the vessel 1 through the oil outlet 4.

The baffle 16 is located downstream of the microwave radiation treatment zone at a location along the longitudinal axis of the separator vessel 1 at which the multiphase fluid has either substantially separated into its component phases or the thickness of the intermediate emulsion layer 12 has been substantially reduced owing to coalescence of the droplets of aqueous phase under the influence of the microwave radiation. Typically, a baffle plate 16 is arranged across the separator vessel 1, perpendicular to the direction of flow of the multiphase fluid. The top of the baffle plate 16 is located within the liquid hydrocarbon layer 10 in the separator vessel 1 so that the aqueous phase is retained by the baffle plate 16 and the liquid hydrocarbon phase flows over the top of the baffle plate 16.

Accordingly, the outlets 5, 4 for the aqueous and liquid hydrocarbon phases are located upstream and downstream of the baffle plate 16 respectively.

The waveguide 6 acts as a microwave applicator and is arranged to direct microwaves into the microwave radiation treatment zone 7 of the separator vessel 1. The microwaves are introduced into the top of the separator vessel 1 through the waveguide 6 and above or into the oil layer 10, above the emulsion layer 12. As oil is essentially transparent to microwaves, the microwave energy will be absorbed by the water droplets that are dispersed in the emulsion layer that is flowing through the microwave radiation treatment zone 7 causing heating of the water droplets and enhancing separation of the emulsion into its constituent components, the water separating into the lower water layer 14 and the oil separating into the upper oil layer 10. Any residual microwave energy will be absorbed by the water in the water layer 14, thereby inhibiting reflections of the microwave energy from, for example, the bottom of the separator vessel 1. The microwaves are preferably not introduced into the side of the vessel 1 or from below as the water within the vessel will absorb the microwave energy which would be a waste of energy as it is not necessary to heat the water layer 14.

The wave guide 6 may be sealed at one end with a microwave transparent window (not shown) to inhibit fluid from flowing to the microwave source. In preferred embodiments, the waveguide 6 is a hollow pipe waveguide which may be pressurized, for example, with dry process air, nitrogen or another inert gas The microwave transparent window may be formed, for example, from KevlarTM, sapphire, quartz glass, or any other suitable material that is transparent to microwave radiation. By "substantially transparent to microwave radiation" is meant that the upper hydrocarbon layer and the gaseous phase each absorb less than 1% of the microwave radiation. Furthermore, it has been found that by using a plurality of wave guides 6, at least 80% of the volume of the intermediate emulsion layer may be subjected to microwave irradiation.

In a further preferred embodiment (not shown), the waveguide 6 may be positioned outside the separator vessel 1 rather than having a portion which extends into the separator vessel 1. In this preferred embodiment, an end of the wave guide may be positioned adjacent a microwave transparent window in the top face of the separator vessel 1 such that the microwaves are directed from above the oil layer 10.

By directing the microwaves from above the emulsion and water layers 12, 14, very little energy is absorbed as it passes through the oil layer 10, meaning the majority of the energy can be absorbed in the emulsion layer 12. Directing the radiation from other directions or from multiple directions around the circumference of the separator vessel 1 may result in radiation being absorbed by the water layer 14 thereby reducing the amount of energy absorbed by the emulsion layer 12 and this is therefore undesirable as the efficiency of the separation apparatus would be reduced.

A reflector (not shown) may be provided in the hollow pipe wave guide 6 for reflecting the microwave radiation through the window(s) in the pipe wall so that the microwave radiation is transmitted directly into the intermediate emulsion layer 12, preferably, in a substantially horizontal direction thereby mitigating the risk of loss of microwave radiation into the lower aqueous layer 14. Suitable reflection means would be well known to the person skilled in the art. Where the longitudinal axis of the wave guide 6 is substantially vertical, the reflection means typically reflects the microwave radiation through anangle of approximately 90° (for example, through an angle of 70 to 1100, preferably 80 to 100°) such that the microwave radiation passes through the window(s) of the hollow pipe wave guide 6 and is transmitted directly into the intermediate emulsion layer 12 in a substantially horizontal direction.

Figures 2 and 3 show a separator vessel 20 according to a further preferred embodiment of the present invention. As in the embodiment of Figure 1, the multiphase fluid is introduced into the separator vessel 20 through a fluid inlet 22 and the fluid separates, under gravity, in the vessel 20 into an upper oil layer 23, an intermediate emulsion layer 24 and a lower water layer 25. A waveguide 26 which acts as a microwave applicator extends into the vessel 20 at a position between the fluid inlet 22 and a gas outlet 28 through which gas released from the fluid during treatment may be removed. An outlet 30 through which oil released from the fluid during treatment may be removed is located in a lower wall of the separator vessel 1 and a further outlet 32 for removing water released from the fluid during treatment is also located in the lower wall of the vessel 20.

The waveguide 26 extends through the upper wall of the separator vessel 20 at a location between the inlet 22 and the gas outlet 28 and into the interior of the separator vessel 20.

The end of the waveguide 26 which is within the interior of the separator vessel 20 preferably extends, in operation, above or into the oil layer 23 but not into the water layer 25 so that the microwave radiation is directed into emulsion layer as it flows through the microwave radiation treatment zone.

A baffle 34 extends into the interior cavity of the separator vessel 20 from the bottom face thereof, between the water outlet 32 and the oil outlet 30. The baffle 34 acts to inhibit the separated water from exiting the vessel 20 through the oil outlet 30.

The end of the waveguide 26 within the interior cavity of the separator vessel 20 is located in one or more Faraday cages 36 which are positioned inside the separator vessel to contain the microwaves applied through the waveguide 26. The cages 36 may be formed of two wire meshes which are longitudinally separated along the longitudinal axis of the separator vessel 20 and extend between the upper and lower interior faces of the vessel 20. The meshes 36 work with the interior wall of the vessel 20 to contain the microwave radiation. The separation of the wires in the mesh must be less than the wavelength of the applied microwave radiation to ensure the microwaves are contained within the cage 36, whilst permitting free movement of the emulsion in the separator vessel through the mesh, and the separated oil.and water through the mesh.

The one or more cages 36 may be supported by attachment to the interior wall of the vessel 1, as shown in Figure 3.

As mentioned above, the Faraday cage(s) 36 may comprise two mesh walls, the first wall being located upstream of the end of the waveguide 26 positioned in the separator vessel 20 and the second wall being located downstream of this end of the waveguide 26.

The cylindrical wall of the vessel 20 connected the two mesh sheets effectively completes the cage 36 by acting as the side walls of the cage.

In an alternative embodiment, the cage(s) 36 may be formed of four mesh walls arranged to form a self-contained cage within the vessel 20 and such an arrangement may have power density advantages in that microwave energy having a higher power density may be contained in the cage. The cages 36 enable standing waves to be established in each cage which enhances the focusing of the microwaves.

In a preferred embodiment, the separator vessel 20 has a longitudinal axis and an interior surface (inner wall), typically a cylindrical inner wall; and the Faraday cage 36 comprises two wire meshes respectively forming a first side wall of the Faraday cage 36 and a second side wall of the Faraday cage 36. There is no requirement to provide a bottom wall for the Faraday cage 36 as the aqueous layer 25 will contain the microwave radiation owing to its high dielectric constant. Where the wave guide 26 penetrates through the wall of the separator vessel 20 and into the Faraday cage 36, an upper mesh may be provided to form an upper wall for the Faraday cage 36. However, this upper mesh may be eliminated.

Typically, the two wire meshes that form the side walls of the Faraday cage 36 are located close to the side walls of the separator vessel 20 50 as to maximize the volume of the microwave irradiation treatment zone, for example, are the side walls of the Faraday cage 36 may be arranged within 0.25 metres of the side walls of the separator vessel 20. It is envisaged that the meshes that form the side walls of the Faraday cage 36 may be flat or where the separator vessel 20 has a cylindrical inner wall may be arcuate. In a further preferred embodiment, the cage 36 comprises four mesh walls. The two additional mesh walls are arranged transversely across the separator vessel 20 (perpendicular to the direction of flow). The side walls and transverse walls of the Faraday cage 36 may extend between the upper and lower walls of the separator vessel 20. However, it is preferred that the side walls and transverse walls of the Faraday cage 36 extend from a position at or near the level of the liquid hydrocarbon layer 23 in the separator vessel 20 to a position below the interface between the intermediate emulsion layer 24 and the aqueous layer 25.

Typically, the side walls of the Faraday cage 36 have a longitudinal length of at least 0.5 metres, preferably, 1 metre.

In a preferred embodiment, the microwaves may be introduced into one or more Faraday Cages 36 that are arranged to contain the microwaves in a multimode cavity.

It is advantageous to locate the Faraday cage(s) 36 within the emulsion layer 24 to maximise separation efficiency and minimize energy consumption.

As shown in Figures 1 to 3, the microwave radiation may be transmitted into the emulsion layer that is flowing through the microwave radiation treatment zone using a waveguide 6, 26 that penetrates through the wall of the section of the separator vessel 1, 20. In the event that the separator vessel 1, 20 is at an elevated pressure, a pressure seal (not shown) may be provided between the waveguide 6, 26 and the wall of the separator vessel 1, 20, for example, a flange connector.

The hollow pipe waveguide 6, 26 may be formed from a conductor such as silver, copper, aluminium or brass and filled with nitrogen or another inert gas of high dielectric strength. If necessary, the hollow pipe waveguide 6, 26 may be provided with an outer housing that is capable of withstanding the elevated pressure prevailing in the separator vessel 1, 20.

Although the apparatus of the present invention has been illustrated by reference to a horizontal separator vessel 1, 20, it is also envisaged that the apparatus may be in the fonn of a vertical separator vessel where the vertical separator vessel is the final separator vessel of a multistage separator system. Thus, the microwave separation zone(s) maybe used to replace the electrostatic coalescers of the final vertical separation stage.

The dielectric heating of a water-in-oil emulsion in the microwave radiation treatment zone of an apparatus according to one or more preferred embodiments greatly increases the separation efficiency compared to gravity settling alone. The mechanism, application time and optimum frequencies for the dielectric heating carried out by the application of microwave radiation to the emulsion are set out below.

The region of the separator vessel 1, 20 into which the wave guide directed the microwave radiation acts as an microwave radiation treatment zone wherein the aqueous phase of the multiphase fluid is selectively heated by subjecting the multiphase fluid to microwave radiation having a frequency of around between 1 MHz to 10GHz for an exposure time of less than 5 seconds, with a power density in the aqueous phase of at least i07 Wm3. Subjecting the multiphase fluid to microwave radiation with a power density of at least 1x107Wm3 in the aqueous phase for a short period of time has been found to result in particularly fast separation times. The high power density causes selective heating of the aqueous phase of the emulsion which is thought to result in two mechanisms arising within the emulsion layer. Firstly, the rapid heating of the aqueous droplets causes localized heating of the oil boundary layer around the droplets. As oil viscosity is highly sensitive to changes in temperature, the viscosity of the oil surrounding the droplets falls considerably, resulting in an increase in droplet settling velocity. Secondly, the rapid heating of the aqueous droplets causes the internal pressure of the droplets to increase, resulting in the expansion of the droplets. This also results in an increase in the droplet settling velocity. These mechanisms ensure that the droplets are more likely to collide and therefore more likely to coalesce with other droplets.

The aqueous phase being "dispersed" in the liquid hydrocarbon phase is intended to be interpreted to mean emulsified droplets of aqueous phase and optionally macroscopic aqueous domains that are contained within the liquid hydrocarbon phase of the emulsion that is passing through the microwave radiation treatment zone in the separator vessel.

Preferably, the multiphase fluid is a produced fluid from a hydrocarbon production well. The liquid hydrocarbon phase of the produced multiphase fluid may be selected from crude oils, crude oil blends, and gascondensates. The aqueous phase of the produced multiphase fluid may be selected from connate water, injection water and condensed water.

Crude oils often contain naturally occurring surfactants. Accordingly, emulsified droplets of aqueous phase may arise spontaneously when a mixture of crude oil and water is subjected to shearing, for example, in a production well, choke, or a flow line that is arranged upstream of the separator vessel (thereby imparting the energy required to form the emulsified droplets).

It is envisaged that the multiphase fluid that enters the separator vessel may adopt a laminar (stratified), churn, or annular flow regime.

Optionally, the produced fluid comprises a gaseous hydrocarbon phase, in particular, natural gas. At least part of the optional gaseous hydrocarbon phase may separate into a headspace of the separator vessel.

Where the produced fluid comprises a gaseous hydrocarbon phase, the gaseOus hydrocarbon phase may be separated from the multiphase fluid in a gaseous hydrocarbon-liquid hydrocarbon-water separator. Accordingly, a gaseous hydrocarbon stream is withdrawn from the separator vessel.

It is also envisaged that the multiphase fluid may arise in a refinery operation and may therefore comprise a crude oil distillate fraction having an aqueous phase dispersed therein. Examples of crude oil distillate fractions include gasoline, gas oil, diesel, jet fuel, kerosene, heating oil and mixtures thereof.

The amount of thermal energy deposited into a material due to electromagnetic irradiation of the material is dependent upon the electric field of the electromagnetic radiation within the material to be irradiated, the frequency of the electromagnetic radiation, and the dielectric properties of the material.

The liquid hydrocarbon phase and any gaseous hydrocarbon phase of the multiphase fluid are substantially transparent to the electromagnetic radiation, while the aqueous phase has a high dielectric constant and loss. The aqueous phase therefore strongly absorbs the electromagnetic radiation subsequently dissipating the. resulting stored energy as heat. Accordingly, the electromagnetic radiation selectively heats the droplets of aqueous phase and any macroscopic domains that are dispersed in the emulsion layer that separates from the multiphase fluid in the separator vessel thereby facilitating coalescence of the emulsified droplets of the aqueous phase and of any macroscopic domains of aqueous phase that are dispersed in the liquid hydrocarbon phase of the emulsion layer. In a preferred embodiment, at least 90%, and preferably at least 95%, of the electromagnetic radiation is absorbed by the dispersed aqueous phase of the emulsion layer thereby selectively heating the aqueous phase.

The electromagnetic radiation selectively heats the dispersed aqueous phase of the emulsion layer to a preferred temperature of at least 50°C, and preferably, to a temperature in the range 60 to 100°C. The temperature differential that develops between the selectively heated aqueous phase and the liquid hydrocarbon phase of the emulsion layer is preferably at least 20°C, and more preferably, at least 50°C.

The electric field portion of the electromagnetic radiation and the exposure time of the multiphase fluid to the electromagnetic radiation are related. Accordingly, for a given emulsion layer, the higher the electric field, the shorter the exposure time required to selectively heat the dispersed aqueous phase of the emulsion layer. The power input required to selectively heat the dispersed aqueous phase also increases with increasing amounts of dispersed aqueous phase. Thus, the power density andlor the exposure time required to selectively heat the dispersed aqueous phase increases with increasing amounts of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion layer. The amount of aqueous phase that is dispersed in the liquid hydrocarbon phase of the multiphase fluid is preferably in the range of 0.5 to 50% by weight (based on the total weight of the aqueous phase and the liquid hydrocarbon phase).

The aqueous phase of the emulsion layer may have salts dissolved therein. This is advantageous owing to the ionic mobility of the dissolved salts enhancing the selective heating of the dispersed aqueous phase. Preferably, the aqueous phase has a total salinity of at least 1,000 ppm, for example, at least 5,000 ppm. Examples of dissolved salts include sodium chloride.

The power density in the dispersed aqueous phase of the emulsion layer in the microwave radiation treatment zone is the energy absorbed per unit volume of the aqueous phase and can be approximated from the following Equation: Pd = 2ir.f.ac".E,2.

Pd is the power density (watts/rn3) f is the frequency of the applied energy (Hertz) a. is the permittivity of free space (8.854x10'12 F/rn) c" is the dielectric loss factor of the aqueous phase E. is the magnitude of the electric field inside the aqueous phase (volts/rn) The power density in the aqueous phase of the emulsion that is flowing through the microwave radiation treatment zone may be at least 1x107 Wm3, preferably, at least 1x108 Wrn3 and optionally at least lOx 10 Wm3.

The power density in the aqueous phase of the emulsion that is flowing through the microwave radiation treatment zone may be selected depending on the droplet size. This assessment of droplet size may be important as it has been found that the size of the droplets in the aqueous phase has a significant effect on the speed of separation following irradiation. Increasing the power density in the aqueous phase has been found to be advantageous for smaller droplet sizes, such as droplets having a diameter less than 2Omicrons. Droplets having a diameter of less than 2Omicrons have a high surface area to volume ratio. This has been found to result in a high rate of heat loss to the surrounding oil phase. This rapid cooling of the aqueous phase relative to the oil phase in turn reduces the ability of the droplet to coalesce with nearby droplets. However, subjecting smaller droplets to a greater power density in the aqueous phase can ensure advantageous separation times following irradiation. This assessment can be conducted using a microscope, for example to analyse a slide dosed with a sample of the multiphase fluid, though other suitable techniques may be apparent to the skilled reader.

The emulsion may be exposed to the electromagnetic radiation in the microwave radiation treatment zone of the separator vessel for less than 5 seconds, preferably, less than 3 seconds, more preferably, less than 1 second. The exposure time may be achieved by selecting a flow rate of the emulsion through the microwave radiation treatment zone that achieves the desired exposure time. Generally, the exposure time will be fixed by the flow rate of the emulsion. Accordingly, the electric field strength may be varied to produce the desired treatment regime.

It is believed that the relatively high power density of the electromagnetic radiation together with the relatively short exposure time results in rapid and selective heating of the dispersed aqueous phase of the emulsion thereby enhancing separation of the aqueous and liquid hydrocarbon phases in the separator vessel 1, 20 of the present invention.

In the context of the present invention, microwave frequency radiation is defined herein as electromagnetic radiation in the frequency range of around 300 MHz to 10 GHz.

Preferably, the desired power density is produced by developing a distribution of electric field such that the maxima in the electric field are sufficiently high to enhance the rate of separation of the emulsion layer into its component phases. The microwave radiation may be produced using at least one microwave generator such as a single mode or a multimode microwave cavity. In a preferred embodiment, a plurality of microwave generators are provided. The number of microwave generators will be dependent upon the power of each generator and the total power input required for selectively heating the dispersed aqueous phase of the multiphase fluid.

The emulsion may be subjected to microwave irradiation in the microwave radiation treatment zone in the presence of an additional heating source, an electrostatic field, an acoustic field, or combinations thereof in order to enhance coalescence of the emulsified droplets of the aqueous phase andlor of the macroscopic domains of the aqueous phase.

One or more embodiments of the present invention are particularly advantageous as the configurations permit the microwaves to target the water content in the emulsion rather than the oil, enabling targeted heating which raises the temperature of the dispersed aqueous phase of the emulsion layer in the separator vessel 1, 20 allowing faster and more complete separation than conventional separation techniques using, for example, fired heating with exchangers.

Furthermore, the microwaves may be generated adjacent to the equipment and applied through the waveguide 6, 26 to the separator vessel 1, 20 and the application of the microwaves may be made non-intrusive. In addition, the heating process is volumetric and does not rely on a temperature differential and the heat input is highly controllable thereby enabling the separation process to be highly controllable. Also, the energy may be efficiently transferred over distances in environmentally sensitive areas and the heat application process is less intrusive than conventional processes (as there are, for example, fewer flanges and seals) with lower environmental risks.

In summary, one or more preferred embodiments of the present invention therefore provide apparatus.with enhanced separator performance, enabling the heating of heavy oil in remote, environmentally sensitive locations. Various modifications to the embodiments of the present invention described above may be made. For example, other components and method steps may be added or substituted for those described above. Thus, although the invention has been described using particular preferred embodiments, many variations are possible, as will be clear to the skilled reader, without departing from the invention.

Claims

Claims: 1. An apparatus for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the apparatus comprising: a separator vessel for separating the multiphase fluid into an upper liquid hydrocarbon layer, a lower aqueous layer and an intermediate emulsion layer comprised of droplets of aqueous phase dispersed in the liquid hydrocarbon phase, the separator vessel having an inlet for receiving the multiphase fluid, a plurality of outlets for removing component phases of the multiphase fluid after separation and a microwave irradiation treatment zone for treating the emulsion layer as it flows through the separator vessel; and a waveguide arranged to direct microwave radiation into the microwave radiation treatment zone of the separator vessel either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases.
2. An apparatus according to claim 1, further comprising a baffle located in the separator vessel between an outlet for removal of the aqueous phase and an outlet for removal of the liquid hydrocarbon phase to inhibit the separated aqueous phase from passing through the outlet for the liquid hydrocarbon phase.
3. An apparatus according to any one of the preceding claims wherein the separator vessel has an interior cavity for retaining the multiphase fluid for treatment, the waveguide extending into the cavity of the separator vessel.
4. An apparatus according to any one of the preceding claims, further comprising a microwave transparent window located in a wall of the separator vessel, the waveguide being further arranged to direct microwave radiation through the microwave transparent window into the separator vessel, an end of the waveguide being adjacent the microwave transparent window.
5. An apparatus according to any one of the preceding claims wherein an end of the waveguide is terminated with a microwave transparent window.
6. An apparatus according to any one of claims 4 or 5, wherein the microwave transparent window is comprised from one or more of sapphire, quartz glass, or KevlarTM.
7. An apparatus for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous phase into its component phases, the apparatus comprising: a separator vessel for separating the multiphase fluid into an upper liquid hydrocarbon layer, a lower aqueous layer and an intermediate emulsion layer comprised of droplets of aqueous phase dispersed in the liquid hydrocarbon phase, the separator vessel having an inlet for receiving the multiphase fluid, a plurality of outlets for removing component phases of the multiphase fluid after separation and a microwave irradiation treatment zone for treating the emulsion layer as it flows through the separator vessel; and a waveguide arranged to direct microwave radiation into the microwave radiation treatment zone of the separator vessel either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases, and a Faraday cage within the separator vessel arranged to contain the microwave radiation within the cage.
8. An apparatus according to claim 7, wherein the waveguide has a first end which extends into the Faraday cage in the separator vessel.
9. An apparatus according to claim 8, wherein: the separator vessel has a longitudinal axis and an interior surface; and the cage comprises two wire meshes respectively forming a first wall of the cage and a second wall of the cage, the meshes being longitudinally separated along the longitudinal axis of the separator vessel and extending between an upper and a lower interior face of the separator vessel, the first wall being located upstream of the end of the waveguide positioned in the separator vessel and the second wall being located downstream thereof, the interior surface of the vessel forming additional walls of the cage.
10. An apparatus according to any one of claims 7 or 8, wherein the cage comprises four mesh walls.
11. An apparatus according to any one of claims 9 or 10, wherein the mesh walls each have a plurality of apertures defined by the separation of opposing sides of the apertures, the separation being less than the wavelength of the applied microwave radiation to contain the microwaves within the cage.
12. An apparatus according to any one of claims 7 to 11, wherein the cage is attached to the interior wall of the separator vessel.
13. An apparatus according to any one of claims 7 to 12, further comprising a microwave transparent window on an end of waveguide.
14. An apparatus according to claim 13, wherein the microwave transparent window is comprised from one or more of sapphire, quartz glass, or KevlarTM.
15. An apparatus according to any one of claims 7 to 14 further comprising a plurality of Faraday cages located within the separator vessel.
16. An apparatus according to any one of claims 7 to 15, wherein the one or more Faraday cages are located in use in the multiphase fluid in the separator vessel.
17. Apparatus according to any one of claims 1 to 16, wherein the multiphase fluid comprises a crude oil distillate fraction having an aqueous phase dispersed therein.
18. A methOd for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, using the apparatus claimed in any one of the preceding claims.
19. A method for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the method comprising: (a) passing the multiphase fluid through a microwave radiation treatment zone in a separator vessel; (b) heating the multiphase fluid by subjecting the multiphase fluid to microwave radiation in the separator vessel, the microwave radiation being directed into the multiphase fluid either from above the emulsion layer or directly into the emulsion layer to heat the droplets of aqueous phase dispersed in the liquid hydrocarbon phase of the emulsion to assist in separation in the separator vessel of the multiphase fluid into its component phases; and (c) withdrawing a liquid hydrocarbon stream and an aqueous stream from the separator vessel.
20. A method for separating a multiphase fluid comprising an aqueous phase, a liquid hydrocarbon phase and optionally a gaseous hydrocarbon phase into its component phases, the method comprising: (a) passing the multiphase fluid through a microwave radiation treatment zone in a separator vessel; (b) heating the multiphase fluid by subjecting the multiphase fluid to microwave radiation in the separator vessel, the microwave radiation being directed into the multiphase fluid through a Faraday cage located in the multiphase fluid to focus the microwave radiation and to heat the aqueous phase dispersed in the multiphase fluid and assist in separation in the separator vessel of the multiphase fluid into component phases; and (c) withdrawing a liquid hydrocarbon stream and an aqueous stream from the separator vessel.
21. A method as claimed in any one of claims 18 to 20, wherein the multiphase fluid is a produced fluid from a hydrocarbon production well.
22. A method as claimed in any one of claims 18 to 20, wherein the multiphase fluid comprises a crude oil distillate fraction having an aqueous phase dispersed therein.