WO2013179252A1

WO2013179252A1 - Electrostatic coalescer and method of use thereof

Info

Publication number: WO2013179252A1
Application number: PCT/IB2013/054467
Authority: WO
Inventors: Fatiha AKROUR; Tony Cornelius ROEST; Donald R. Smuin
Original assignee: Aker Process Systems As
Priority date: 2012-05-30
Filing date: 2013-05-30
Publication date: 2013-12-05

Abstract

Multistage compact electrostatic coalescer (CEC) comprising at least a first fluid passage between two cylindrical electrodes, at least a second fluid passage between two cylindrical electrodes, and an at least partly cylindrical outer shell comprising a first end section defining an electrode free volume, wherein the outer shell comprises at least one fluid inlet and at least one fluid outlet, the first and second fluid passages are concentric, and wherein said inlet is in fluid communication with said first fluid passage, said first fluid passage is in communication with said second fluid passage at least mainly via said electrode free volume and said second fluid passage is in fluid communication with said outlet, such that the electrostatically imposed coalescing is interrupted in said volume while the flow pattern characteristics and overall flow direction of fluid is changed therein.

Description

Electrostatic coalescer and method of use thereof

The present invention relates to an electrostatic coalescer and a method of use. Especially the present invention relates to an electrostatic coalescer applicable for the treatment of fluids with high viscosity. Background

The use of electrostatic coalescer for coalescing droplets of a first fluid in a second fluid is well known in the art. The electrostatic field influences a conductive fluid differently that a non-conductive fluid and therefore a coalescer is used to treat mixtures of fluids with different conductivity, such as water in oil emulsions.

Known coalescers comprise different additional features for enhancing the separation efficiency, the economical feasibility, the structural efficiency or other benefits. One group of coalescers accordingly include arrangements to make use of a cyclone effect combined the electrostatic effect. These devices are referred to as electrostatic cyclone coalescers. Another group of coalescers are those which do not involve the use of a cyclone effect or similar swirling of the fluids, but are focused on providing compact coalescer with high efficiency compared to equipment volume and structure. This group is referred to as compact electrostatic coalescers or CEC's. The present invention relates especially to an alternative CEC, applicable also for treatment of fluids with high viscosity. Prior art

WO2007/085900 discloses a vertical CEC arrangement where the process fluid flows up through the centre of an electrode, where after the liquid flow changes direction and flows down the annulus between the centre electrode and an outer electrode. WO2004/007908 disclose a similar solution where the fluid to be treated is past through the internal of the coalescer before flowing through concentric electrically charged cylindrical plates. The fluid only passes one time through an electrostatic field. FR2924621 discloses a horizontal electrostatic coalescence device.

FR2663947 describes an electrostatic coalescer comprising vertical electrodes. The fluid flows from the top to the bottom passing the electrodes. In the coalescer section the cross section area is increased resulting in reduced flow velocity.

EPO 166479 discloses an electrostatic coalescer arrangement where the process fluid enters at a top corner of a horizontal vessel and then passes down through a first electrostatic arrangement in a first section of the vessel. Thereafter the fluid stream changes direction and passes up through a second section comprising an

electrostatic arrangement. A part of the fluid with highest density is separated of before the rest of the fluid passes into the second electrostatic arrangement. US Patent 6136174 describes a compact electrostatic coalescer which is a device for coalescing finely dispersed droplets of a conducting fluid emulsified in a stream of non conducting fluid. This device provides more effective coalescing by passing the emulsion through narrow annular flow channels in a non-laminar or turbulent flow regime as the emulsion is subjected the high intensity electrical field. In this CEC (Compact Electrostatic Coalescer) the coalescing takes place in a single pass (downward) flow configuration.

A person skilled in the art knows that turbulent flow of a water-in-oil emulsion is known to promote coalescence of smaller droplets, if the emulsion is relatively unstable, but also to cause rupture of larger droplets. In a more stable emulsion, typical crude oil, turbulent flow alone would not generally promote satisfactory coalescence because of the need for water droplets to be held in contact for a sufficient period of time for the interfacial film to be ruptured. However, the person skilled in the art knows that flow through intense electrostatic field causes the dispersed water droplets to be electric dipoles in an oil continuous emulsion and will be held in contact by dipole-dipole interaction.

Utilizing both above described mechanisms for coalescing, is the essential contribution of the Compact Electrostatic Coalescer system.

The flow regime of a fluid in relative motion to a surface is defined by the Reynolds number R_e.

For flow in a pipe or tube, the Reynolds number is generally defined as:

where:

p = density (kg/m³, lbm/ft³ )

V= velocity (m/s, ft/s)

μ = dynamic viscosity (Ns/m², lbm/s ft)

D_H = hydraulic diameter of the pipe (m,

v = kinematic viscosity (m²/s, ft²/s)

Q = volumetric flow (m³/s, ft³/s)

A = cross sectional area (m², ft²)

For an annular duct, such as the channels in the Compact Electrostatic Coalescer; (2) where

D₀ is the inside diameter of the outside pipe, and

Dj is the outside diameter of the inside pipe.

For turbulent flow through a concentric annulus, D_eff = (D₀ - )/ζ.

ζ.= Dimensionless term used as correction factor for the hydraulic diameter.

The pressure loss in a pipe, tube or duct can be expressed with the D'Arcy- Weisbach equation:

Δρ λ (1 / ¾) (ρ V² 1 2) (3) where

Δρ = pressure loss (Pa, psi)

λ = D'Arcy-Weisbach friction coefficient

1 = length of duct or pipe (m, ft)

DH = hydraulic diameter (m, ft)

p = density (kg/m³, lb/ft³)

V = velocity (m/s, ft/s)

The D'Arcy-Weisbach friction coefficient λ is determined from the Moody diagram. This diagram plots the Darcy-Weisbach friction factor λ against Reynolds number Re and relative roughness ε / D.

In establishing the physical dimensions for the CEC the designer must ensure that there is sufficient transit time (Retention Time) with a corresponding Reynolds number to effectively coalesce the dispersed water particles at the same time working within the hydraulic constraints of process system to prevent any gas breaking out from the oil because of the pressure drop through the unit as this would reduce the coalescing effectiveness of the CEC.

The more viscous the fluid the more difficult this becomes such as when applying an existing CEC for the treatment of Heavy Oil emulsions.

Because of the high treatment viscosities associated with Heavy Oils compared to light or conventional oils, to reach a non-lamina flow regime the designer must process the Heavy Oil at high flow velocities or with wider annular spacing to increase the hydraulic diameter or a combination of both. The disadvantage of increasing the annular space is that the power supply has to be increased to maintain the same high intensity field as with the narrow annular channels. Moreover, as discussed in US Patent 6, 136, 174 the ratio of flow gap "a" to the radius of the inside grid should preferably not be greater than 0.3 to keep the electrical field uniform through the channel.

As seen from the D'Arcy-Weisbach pressure loss equation, pressure loss is proportional to velocity squared, and high pressure drop can prevent increasing the fluid velocity enough to reach a non-laminar flow regime. Thus the benefit of coalescing through mechanical contact of the dispersed water droplets diminishes. In addition, increasing the fluid velocity through the channels will lead to reducing the total residence time through the unit. The residence time inside the unit must be sufficient to reach a minimum required coalescing retention time to ensure that the maximum amount of water droplets are charged.

Using a Compact Electrostatic Coalescer according to US Patent 6, 136, 174 with single pass flow configuration with heavy viscous fluid, the above conditions i.e. sufficient residence time and non-laminar regime are difficult to meet without increasing the length of the unit to meet the coalescing performance and since it must be installed in a vertical orientation, it becomes impractical to integrate with other elements of the oil treating system. Objectives of the invention

An objective of the present invention is to overcome the above mentioned problems related to the known solution. The performance of existing application is limited to light emulsion with low viscosities. One object is to provide a compact electrostatic coalescer applicable also for handling water in heavy oil emulsions, where the heavy oil is oil with high viscosity.

A further goal is to provide a CEC applicable for use with different ranges of viscosity emulsions; high, medium and low.

It is also a goal to provide a compact solution where a number of coalescer efficiently may be arranged in series. A further objective is to provide a compact electrostatic coalescer that can be installed in direct connection to a gravity separator.

The present invention aims at providing a coalescer which is especially efficient in coalescing the smallest droplets within the process fluid into medium size droplets.

The present invention provides a multistage compact electrostatic coalescer (CEC) comprising at least a first fluid passage between two cylindrical electrodes, at least a second fluid passage between two cylindrical electrodes, and an at least partly cylindrical outer shell comprising a first end section defining an electrode free volume,

wherein the outer shell comprises at least one fluid inlet and at least one fluid outlet, the first and second fluid passages are concentric, and wherein said inlet is in fluid communication with said first fluid passage, said first fluid passage is in communication with said second fluid passage at least mainly via said electrode free volume and said second fluid passage is in fluid communication with said outlet, such that the electrostatically imposed coalescing is interrupted in said volume while the flow pattern characteristics and overall flow direction of fluid is changed therein.

An important aspect of thee invention is that preferably all the fluid from the first passage enters (i.e. is in fluid communication) into this volume, and preferably all of the fluid from the volume exits (i.e. is fluid communication) into the second fluid passage. The defined volume, at a particular size and shape, with a certain fluid flow, imposes a desirable flow pattern (preferably a toroidal flow with moving core) within the volume, different from the flow pattern formed in the passages, and at the same time the volume is not exposed directly to an electrostatic field from electrodes, hence enabling division of the larger water droplets, and at the same time the overall flow direction is turned from overall the flow direction of the upstream first fluid passage to the flow direction of the downstream second fluid passage, whereby all these elements improve the overall performance and size of the compact coalescer.

The object of a coalescer is to increase the droplet size of the non-continuous phase of an emulsion thereby increasing the efficiency of the downstream separation of the continuous phase and the non-continuous phase. However as the smallest droplets are the most difficult to separate out the efficiency and performance of a coalescer is especially related to its ability to "remove" the smallest droplets by creating larger droplets. When influenced by the electrostatic field in the first zone the small droplets coalesce to form medium size droplets. The medium size droplets continue to grow by absorbing small droplets or other medium size droplets as they pass through the first zone and the second zone. However for the coalescing to take place the droplets have to be in close proximity of each other. According to the present invention the volume is provided to allow for a change in flow direction without or with limited splitting of small droplets but allowing for the splitting of large droplets into medium size droplets thereby provide an increase in

concentration of medium size droplets and thereby increasing the probability of the remaining small droplets to coalesce with the medium size droplets in the second electrostatic coalescing zone.

The present invention also provides a compact electrostatic coalescer (CEC) comprising a first vertical fluid passage between two cylindrical electrodes where at least one of the cylindrical electrodes in said first fluid passage is fully insulated, a second vertical fluid passage between two cylindrical electrodes where at least one of the cylindrical electrodes in said second fluid passage is fully insulated, and a vertically arranged outer shell, wherein

the vertically arranged outer shell comprises at least one fluid inlet and at least one fluid outlet where both the fluid inlet and the fluid outlet are arranged below the electrodes, and

wherein said inlet is in fluid communication with said first vertical fluid passage, said first vertical fluid passage is in communication with said second vertical fluid passage and said outlet is in fluid communication with said second vertical fluid passage.

In one aspect of the multistage compact electrostatic coalescer according to the present invention the intended flow direction in the first fluid passage is opposite the intended flow direction in the second fluid passage and wherein the volume allows a change in flow pattern characteristics and change in overall flow direction which is beneficial for the overall efficiency of the coalescer.

In a further aspect of the multistage compact electrostatic coalescer the volume comprises one or more deflectors. In one embodiment of this aspect the deflector is an extension into the volume of the cylindrical electrode separating the first fluid passage and the second fluid passage.

In yet another aspect of the multistage compact electrostatic coalescer the distance X between the free end of the cylindrical electrode separating the first second fluid passage and the second fluid passage or the free end of the deflector and the outer shell forming the volume is larger than or equal to 1.1a, wherein a is the radial distance between the two cylindrical electrodes of the first fluid passage, preferably X≥∑a_n wherein n is the number of first fluid passages and n>2.

In an aspect of the present invention the free end of the deflector is bend towards the first fluid passage with a distance d, preferably

d > 0.05a where a is the radial distance between the two cylindrical electrodes in the first fluid passage.

In one aspect of the invention both the fluid inlet and the fluid outlet are arranged at or near a second end of the outer shell and said inlet is conical with an increasing cross sectional area in an intended flow direction, and said outlet is conical with a decreasing cross sectional area in the intended flow direction. In another aspect of the invention the intended flow direction is upwards in the first fluid passage, and downwards in the second fluid passage. Accordingly the fluid can enter through the bottom, flow up through the first passage and down through the second passage and leave trough the outlet at the bottom. In one aspect of the invention the distance between the two cylindrical electrodes in the first fluid passage is a, and the distance between the two cylindrical electrodes in the second fluid passage is b, and wherein a is equal to or lager than b.

In one embodiment b is approximately equal to a ±20 %. In another aspect of the invention the coalescer comprises a plurality of parallel first fluid passages in fluid communication with the inlet and the top section, and where the coalescer comprises a plurality of parallel second fluid passages in fluid communication with the volume and the outlet.

The coalescer may further in one embodiment of the invention comprise fluid distribution means and or baffles to direct the fluid through the coalescer, especially in the volume.

The compact electrostatic coalescer according to the present invention comprises in another aspect thereof a centre cylindrical electrode which is plugged to prevent inside flow, and wherein this centre cylindrical electrode is extending in height above the other electrodes. Here the centre electrode is adapted to efficient change the direction of flow of process fluid for further coalescing, preferably the extending of height is more than 1/10 of the inner diameter of the coalescer.

In a further aspect the compact electrostatic coalescer according to the present invention, the centre cylindrical electrode comprises a spindle at top carrying one or more of the remaining electrodes.

In another aspect the coalescer is adapted to apply a voltage and or frequency over the at least two electrodes of the first fluid passage which is different from a voltage and or frequency to be applied over the at least two electrodes of the second fluid passage. In yet another aspect of the multistage compact electrostatic coalescer according to the present invention, a deflector is arranged in the volume to also assist radially change in flow direction whereby the electrode forming a wall between the first and second passage is extended into the volume as a curved deflector, directing the fluid to the inner second electrostatic passage.

In a further aspect a deflector is arranged in the volume to also assist radially change in flow direction whereby the electrode forming the wall between the first and second passage is extended into the volume and is structured as an opening in the cylindrical electrode.

In one aspect of the multistage compact electrostatic coalescer at least one of the cylindrical electrodes of each fluid passage is fully insulated. In a further aspect all the cylindrical electrodes are fully insulated. The terms "at a bottom" and "at the bottom" of the vertical arranged outer shell refers to a position in the lower section of the vertical shell, below the electrodes.

Further the present invention provides a method for coalescing a process fluid wherein the method comprises passing the process fluid at a velocity providing non- laminar flow through a first fluid passage between at least two electrical charged electrodes into an end section comprising a volume,, and thereafter providing non- laminar flow from the volume in the opposite direction through a second fluid passage between at least two electrical charged electrodes all within one treatment unit. In one aspect of the present invention the volume is electrode free, such that no electrostatically imposed coalescing takes place within the volume.

In an aspect of the present method at least one of the at least two electrodes in each of the fluid passages is fully electrically insulated. In another aspect both electrodes of each passage are fully electrically insulated.

In another aspect of the method the one treatment unit is a multistage compact electrostatic coalescer according to the present invention.

The method according to the present invention can in one embodiment thereof be applied for coalescing a high viscosity oil and/or a high viscosity emulsion.

In one aspect of the present invention the flow pattern within the volume is toroidal with a moving core. In one aspect of the invention the process fluid has a Reynolds number of is equal to or above 2100 within anyone of the fluid passages.

In another aspect of the invention the process fluid has a Reynolds number of between 2100 and 8000 in the first fluid passage and wherein the process fluid has a Reynolds number of between 2100and 8000 in the second fluid passage.

The term "high viscosity" is used here to refer to fluids with a viscosity in the range of 35cP to 80cP. Accordingly the term "high viscosity oil" refers to the viscosity of the oil in an emulsion to be treated with a coalescer according to the present invention.

The term "process fluid" as used here refers to water-in-oil emulsion susceptible to coalescing in an electrostatic field.

To overcome the problems mentioned above a compact coalescer with a two pass flow configuration has been developed.

The described two pass flow configuration can be used with different ranges of viscosity emulsions; high, medium and low. The electrostatic field influences the water droplets in the fluid stream to coalesce and form larger droplets, which subsequently may be separated from the oil. The flow conditions within the first pass through the coalescer should be selected to during the passing form larger droplets that can be transported upwards by the fluid stream. The droplets will grow additionally through coalescing when passing down trough the second pass.

In one aspect of the present invention the outlet from the second pass and out of the coalescer unit is constructed to avoid or minimize the re-sharing of the water droplets after the coalescing of the fluid stream. The present invention It might seem implicit that the flow direction could be reversed, the learned individual will know that the high turbulences of the fluid in the outlet cone could re- shear the coalesced water droplets back into smaller sizes due to the contact between the fluid leaving the cone and the inner cone.

Brief description of the drawings

The present invention will be discussed in further detail with reference to the enclosed drawings, where:

Figure 1 schematically illustrates the cross section of an embodiment of the device according to the present invention; Figure 2 schematically illustrates the cross section of another embodiment of the device according to the present invention.

Figure 3 schematically illustrates an embodiment of the present invention.

Figures 4a, 4b and 4c illustrate schematically the dismounting of an embodiment of the present invention. Figure 5 schematically illustrates the changes in the size of the water droplets as the fluid passes the coalescer.

Figure 6 schematically illustrates a section of a further embodiment of a coalescer according to the present invention.

Figure 7a illustrates an embodiment of the present invention. Figure 7b and 7c illustrate two alternative configurations of the cross-section A-A of figure 7a.

Figure 7d illustrates the cross-section B-B of figure 7a.

Figure 8a illustrates another embodiment of the present invention. Figure 8b illustrates a cross-sectional view A-A of figure 8a.

Figures 9a to 9e illustrate the changes in number and size of the droplets as the fluid passes the first zone and the top volume.

Figure 9f and 9g illustrate the possible embodiments of the deflector.

Principal description of the invention

The present invention provides a compact electrostatic coalescer. Referring to the embodiment illustrated on figure 1 the vertically arranged coalescer comprises a coned inlet 2 arranged at the lower end (bottom) of the device. Process fluid 1 enters vertically into the inlet and as the fluid rises up it is distributed into the first electrostatic coalescing zone 5 of the electrostatic section 7 arranged in the annulus between the outer wall of the coalescer and a cylinder 4 arranged coaxially inside the coalescer. When the fluid reaches the upper part of the coalescer above the section 7 the direction of the fluid stream is turned 180 degrees and the fluid flows down through a second electrostatic coalescing zone 6 of the electrostatic section 7. The second zone is arranged inside the cylinder 4 between the inside wall of the cylinder 4 and a fluid restriction member 1 1 arranged at the centre of the coalescer. The first zone 5 upward flow section and the second zone 6 downward flow section are created by a grounded annular grid cylinder 4 serving as a partition between the two passes. At least one electrode 8 is arranged within each zone. The distance a across the flow part is adjusted so as to allow for the flow requirements to be met in the electrostatic section 7. The purpose of the fluid restriction member 1 1 is to secure that the flow requirements are met in the second zone 6. For illustrative purposes only one electrode 8 is arranged within each zone, however a number of electrodes may be arranged across the radial distance of each zone, and both the cylinder 4 and the outer wall of the coalescer may serve as grounded grids arranged with electrically chargeable electrodes in-between.

Because of the internals symmetry, a liquid distributor is not required for either of the two pass directions when only a few grids form the flow paths. However when a multitude of grids are used in each flow pass, then a liquid distribution device for multi-electrode flow paths could be used.

With the two pass configuration, the residence time and fluid regime requirements will be met. After having past down through the second zone 6 the treated process fluid 15 recombines in an outlet cone 3 connected to the lower end of the cylinder 4 and then exits the vessel by and elbowed pipe nozzle 9.

The grid length or coalescing section 7 length governs the retention time in each path. Further the embodiment of the coalescer comprises a top volume 10 above section 7. This volume allows for change in flow direction, and any gas that may be released from the process fluid during the treatment may be collected in the upper part of this volume and can be removed through a normally closed outlet (not shown). The size of the top volume 10 is in an embodiment of the present invention elected to provide lower fluid velocity than through the electrostatic section thereby securing lower fluid velocity when the direction of flow is changed/reversed. The flow path of figure 1 is preferred as this flow arrangement minimises the re-sharing of the coalesced water droplets when the coalesced stream leaves the outlet cone of the coalescer.

The general mechanical construction of the Compact Electrostatic Coalescer, such as the support and isolation of the positive and ground annular grids, inner mandrel, connections for venting any gas from the top of the unit, low level shut down switch etc., are known from exciting Compact Electrostatic Coalescers and are for instance described within US Patent 6, 136, 174. This publication also provides a description of a multi-annular configuration. A person skilled in the art is considered familiar with these and similar possible construction details and these are not repeated here.

Generally the process fluid is a liquid emulsion but during handling variations in composition, temperature or pressure may unintended result in dissolved gas being released from the liquid phase. Such gas will due to the vertical orientation gather in the top section 10. A normally closed gas outlet 12 is arranged in the top part of the top section for occasional removal of gas through outlet 12, if necessary as per US Patent 6, 136, 174.

Figure 1 further illustrates the distance between two electrodes in each passage. In the first passage the distance between two adjacent electrodes is "a", and in the second passage the distance between to adjacent electrodes is "b".

The coned inlet 2 does not allow for any areas with lower velocity that could result in settlement of water, heavier components or particles. However, also other inlet structures could be applied, such as a curved tank bottom. The fluid inlet arranged in the centre of the curved bottom combined with the velocity of the fluid will result in a conical flow pattern. In the circumferential area surrounding the fluid inlet opening the velocity will be lower, but due to the curvature of the bottom only a limited volume of settlements would arise as higher amount would slide towards the opening and be transported up through the coalescing section by the fluid velocity. The centre cylindrical electrode or flow restriction member 1 1 is preferably plugged to prevent inside flow, and has a large enough diameter to achieve narrow gaps in between the electrodes to achieve non-laminar flow for the given flow rates. In addition in one embodiment this centre cylindrical electrode is extending in height above the other electrodes adapted to an efficient change of the flow direction of process fluid in further coalescing. Preferably this center cylindrical electrode extends with a height of more than approx 1/10 of the inner diameter of the coalescer.

In the upward passage of the fluid the characteristics of the fluid will change, e.g water droplets would be more coalesced, hence in one preferred embodiment the frequency pattern of the voltage used on the insulated electrodes for the first fluid passage are different from on the insulated electrodes second fluid passage, this to optimize the overall coalescing effect. The term "frequency pattern" means that the voltage is around one particular frequency, but it can also mean so-called dual or multiple frequency voltages.

Different voltage patterns for each passage would mean that one needs one power source for the insulated electrodes of each flow pattern direction, so for some processes which not requires so optimized power supply, a common frequency pattern for both flow passage directions can be used. Referring to figure 2 where an alternative embodiment of the present invention is disclosed. Here the streams through the vertical coalescer are reversed and the process fluid/emulsion 101 to be treated enters through and inlet 102 and up inside an inner conical inlet. The process fluid passes first trough a first inner electrostatic coalescing zone 105 arranged between a centrally located fluid restriction member 1 1 1 and cylindrical prolongation 104 of the inner inlet. After having past the first zone the arrives at a top zone 1 10 where the direction of flow is turned 180 degrees and the process fluid flows down through a second coalescing zone 106 arranged radially outside the first zone between the outside of the cylindrical prolongation 104 and the outer wall of the coalescer. Thereafter the coalesced fluid flows out of the coalescer through the conical outlet 109. The conical shape of the outlet provides a smooth transition of the stream. Accordingly the fluid passes twice through the coalescing section 107. Within the coalescing section 107 electrodes 108 are arranged at a radial distance a/b to coalesce water droplets in the oil. With the configuration as illustrated on figure 2 the cross sectional area of the second zone 106 is larger than the first zone 105 resulting in lower flow rate in the second zone. Whereas in the embodiment illustrated on figure 1 the situation is the opposite when the distance between the electrodes a is equal b. Accordingly the present invention provides a coalescer with a two pass configuration where the velocity of the fluid trough the two zones can be increased or decreased with out installing any moving parts between the two zones.

Generally the process fluid is a liquid emulsion but during handling variations in composition, temperature or pressure may unintended result in dissolved gas being released from the liquid phase. Such gas will due to the vertical orientation gather in the top section 1 10. A normally closed gas outlet 1 12 is arranged in the top part of the top section for occasional removal of gas through outlet 12, if necessary.

Referring to figure 3, this figure illustrates another embodiment of the present invention especially adapted for serial connection of more than one coalescer when the residence time and Reynolds number criteria can not be met using one unit. The figure illustrates two coalescers in series. In this embodiment the process fluid inlets 202, 202' are arranged horizontally for horizontal connection to another coalescer or other equipment. After the initial horizontal inlet the process fluid is directed upwards through a conical inlet similar to the embodiment illustrated on figure 1. The coalesced process fluid leaves the first coalescer through the outlet 209 and enters the second coalescer through inlet 202' .

Excessive shearing can re-emulsify water droplets therefore, the outlet from the coalescing zone is conical and the pipeline connecting the vertical conical outlet with the horizontal outlet 209 provides a smooth transition to avoid unnecessary stirring of the coalesced fluid. The gentle transition in this as well as in the other embodiments can be obtained by selecting a curvature and diameter of the bend adapted for this purpose.

The coalescer illustrated on figure 3 includes optional baffles/ fluid distribution units 20 and 22. These baffles are arranged in the top zone between the first and the second coalescing zone. The function of the baffles is to assist the change in flow direction from upwards to downwards and thereby also improve fluid distribution. The baffles are optional and the construction thereof can be selected freely from all known configurations of fluid directing baffles or fluid distribution means.

Figures 4a, 4b and 4c illustrates an embodiment of the coalescer according to the present invention and the possible mounting/demounting thereof. The centre electrode 31 1 can in one of the preferred embodiments be structurally integrated for a spindle 320 carrying the insulated electrodes from the top side, as a lateral bottom spindle would clash with the dividing electrode 323 of the passages. This structurally integrated design enables assembly and maintenance of the coalescer, bearing in mind that it is very important not to cause any damage to the insulation, as this will potentially short cut the electrostatic field under while the equipment shall operate. In operation a lid 321 closes the upper part of the coalescer. The electrical field is supplied to the some or all of the electrodes connected to the spindle via a cable 322, in the present embodiment passed through a separate inlet. Figure 4b illustrates the situation where the operation is stopped, the lid 321 is opened the cable 322 disconnected and the spindle 320 including the connected electrodes has been lifted out through the top opening. In the illustrated

embodiment the flow restriction member/centre electrode 31 1 comprises a connection element 332 for gripping the spindle/electrode arrangement when removing it from the rest of the coalescer. Also illustrated on figure 4b is the increased height 331 of the central electrode 31 1. Figure 4c illustrates a top view of the spindle 320.

Figure 5 illustrates the changes in droplet size of the water droplets 40 as the fluid passes through the first zone 5 and second zone 6 of the coalescer. When influenced by the electrostatic field in the first zone the small water droplets coalesce to form medium size droplets. The medium size droplets continue to grow by absorbing small droplets or other medium size droplets as they pass through the first zone 5 and the second zone 6. However for the coalescing to take place the droplets have to be in close proximity of each other. The treatment performed within the coalescer according to the present invention does not in it self result in separation of water from oil, but the coalescing increases the efficiency of the downstream separation in that the number of small droplets of the non-continues phase (normally water) has been significantly reduced. It is well known that gravity based separation of small droplets is at least time consuming and limited by the viscosity of the continues fluid.

This effect as well as a further effect obtained by the present invention is disclosed in further detail on figures 9a to 9g. Figures 9a to 9c illustrate the changes in droplet size as the fluid passes the passage al of the first electrostatic zone of the coalescer. The small droplets (black spots) of figure 9a collide in figure 9b and form some medium sized droplets (large black spots) and one large droplet (chequered) in figure 9c. The fluid leaves the passage al in figure 9d and enters the volume 710. Arranged within the volume 710 is a deflector 730 influencing the fluid stream as it changes the flow direction. The deflector in the illustrated embodiment is an extension of the electrode separating the first and the second electrostatic zone, which is angled towards the fluid stream coming from first electrostatic zone. The deflector imparts a toroidal flow pattern with a moving core. This is illustrated with the fat arrow marking the direction of movement of the center of the rotational flow. Figure 9e is a schematic illustration of this movement of the core. The old position of the toroidal movement is marked with the broken arrow and the new position with the full line. This movement of the fluid in the volume 710 has resulted in the splitting of the large droplet into two medium size droplets and small droplets have collided with both the formed medium sized droplets as well as the other droplets. The fluid thereafter continues into the passages such as bl of the second

electrostatic zone.

The figures 9f and 9g illustrate alternative embodiments of the deflector 730. On figure 9f the deflector is straight and angled with the angle Θ towards the inlet to the volume from the first zone, providing the end of the deflector 730 being removed a distance d from the prolongation of the electrode to which it is connected. On figure 9g the deflector 730 is curved with a radius r, and the distance between the end of the deflector and the prolongation of the electrode to which it is connected is d.

The shape of the deflector can be curved, straight or any combination thereof and adapted to the fluids to be treated. In one embodiment of the distance d is larger than 0.05 times the distance between adjacent electrodes: d > 0.05 a

With this configuration of the deflector an improved mixing with a toroidal flow pattern with moving core is obtained.

Figure 6 illustrate schematically a coalescer according to the present invention with a tangential inlet 401 , and four electrostatic zones. For illustrative purposes each zone is illustrated with only two passages, but normally there will be a larger number of narrow passages providing non-laminar flow trough the passages of each zone at acceptable velocities. The intended fluid flow is through inlet 401 , first zone al or a2, first volume 410, second zone bl or b2, second volume 410', third zone cl or c2, third volume 410", fourth zone dl or d2 and trough the outlet 415. As illustrated the direction of flow is reversed in each of the three volumes 410, 410' and 410". According to the present invention the volume is provided to allow for the change in flow direction without or with limited splitting of droplets, especially without reforming small droplets. Deflectors 30, 30' and 30" are arranged in each of the volumes as prolongations of the electrodes arranged between the different zones. The first deflector 30 is straight whereas the second 30' and third deflector 30" are angled towards the incoming fluid. The volumes can be further described by reference to the free height between the free end of the deflector and or the zone separating electrode and the wall defining the volume. The height of the first volume 410 is X, the height of the second volume 410' is Y and the height of the third volume 410" is Z. Preferably the heights X, Y or Z are equal to or larger than the distance a, b, c, and d between two adjacent electrodes. More preferably the height is at least 10% larger than the distance between the adjacent electrodes, which can be described as:

X > 1.1a Y > 1.1b Z > 1.1 c

More preferably the height/ distance X is equal to or larger than the sum of the width of the fluid passages in the first electrostatic zone, which can be described as follows if the distances between the electrodes in each zone are equal:

X > n-a Y > m-b Z > p c

Alternatively if the widths between electrodes within the same zone vary:

X >∑a -_]n Y >∑b 'm Z≥∑Cp where

n=number of fluid passages in the first zone,

m=number of fluid passages in the second electrostatic zone

p=number of fluid passages in the third electrostatic zone. Figure 7a illustrates another embodiment of the present invention with a tangential inlet 502 imparting a helical movement of the fluid from the right to the left into the volume 510 where the flow direction changes and the fluid is past on from the left to the right and through the outlet 515. After the last coalescing zone before entering the outlet the electrostatic treated fluid is past through baffles 60 arranged to straighten the flow transforming any helical flow to a straight flow. Preferably the baffles 60 are arranged upstream any reduction of the cross-section of the outlet pipe such as the reducer 535 with convex shape. The coalescer comprises cylindrical electrodes 508, 508', also illustrated on figure 7d showing the cross- sectional view along the line B-B. A deflector 530 is arranged in the volume 510 to also assist radially change in flow direction. The figures 7b and 7c illustrate two alternative configurations of the section comprising the volume 510 arranged to allow for the also radial change of the flow direction, showing cross-sectional views along the line A-A of figure 7a. On figure 7b the electrode 508 ' forming the wall between the first and second zone is extended into the volume 510 as deflector 530 with a curved deflector, directing the fluid to the inner second electrostatic zone. In the alternative illustrated on figure 7c the extended electrode 508' provides a deflector 530 structured as an opening in the cylindrical electrode.

Figures 8a and 8b illustrate an embodiment of the present invention with a tangential inlet 602, a first electrostatic zone 605 and a second electrostatic zone 606. Figure 8b illustrates the cross-section along the line A-A of figure 8a. The cylindrical electrode separating the first and second zones comprises an end section 630 reaching into the volume 610. The end section 630 functions as a deflector, improving the mixing and splitting large droplets into two or more medium sized droplets without splitting the small and medium sized droplets. Further illustrated on figure 8a is the possibility to connect the coalescer to a downstream gravity separator 690 via outlet 609. The coalescer in figure 8a is here illustrated in a horizontal orientation, but it could also be used in a vertical orientation (not shown), but then the outlet 609 connection to the gravitation separator 690 would then need a pipe bend (not shown) into the gravitation separator 690. As the inner passage 606 has a smaller diameter than the previous 605 passage, a continuation part 612 of the inner passage part 61 1 may be connected directly by a nozzle 613 to the gravity separator 690 without significantly need for further reduction (cone), hence the coalesced state is preserved better from when it exits the last electrical coalescing stage to when it enters the gravity separator, hence even better overall efficiency could be achieved. Due to the optimization of the droplets size distribution by the passage through the coalescer, providing fewer small droplets and more medium and large droplets the gravity separation will be less time demanding and the size of the separator could possibly be reduced. This feature of the present invention can be realised with any of the illustrated or discussed embodiments thereof. According to this feature the coalescer is an integrated reducer to a downstream gravity separator, thereby maintaining the coalesced state from the electrostatic coalescing into the

downstream separator.

Those skilled in the art will appreciate that various adaptations and modifications of the described preferred embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

Multistage compact electrostatic coalescer (CEC) comprising at least a first fluid passage between two cylindrical electrodes, at least a second fluid passage between two cylindrical electrodes, and an at least partly cylindrical outer shell comprising a first end section defining an electrode free volume,

wherein the outer shell comprises at least one fluid inlet and at least one fluid outlet, the first and second fluid passages are concentric, and wherein said inlet is in fluid communication with said first fluid passage, said first fluid passage is in communication with said second fluid passage at least mainly via said electrode free volume and said second fluid passage is in fluid communication with said outlet,

such that the electrostatically imposed coalescing is interrupted in said volume while the flow pattern characteristics and overall flow direction of fluid is changed therein.

Multistage compact electrostatic coalescer according to claim 1 , wherein the intended flow direction in the first fluid passage is opposite the intended flow direction in the second fluid passage and wherein the volume allows a change in flow pattern characteristics and change in overall flow direction which is beneficial for the overall efficiency of the coalescer.

Multistage compact electrostatic coalescer according to claim 1 or 2, wherein the volume comprises one or more deflectors.

Multistage compact electrostatic coalescer according to claim 3, wherein the deflector is an extension into the volume of the cylindrical electrode separating the first fluid passage and the second fluid passage.

Multistage compact electrostatic coalescer according to claim 3-4, wherein the distance X between the free end of the cylindrical electrode separating the first second fluid passage and the second fluid passage or the free end of the deflector and the outer shell forming the volume is larger than or equal to 1.1a, wherein a is the radial distance between the two cylindrical electrodes of the first fluid passage, preferably

X≥∑a_n wherein n is the number of first fluid passages and n>2.

Multistage compact electrostatic coalescer according to claim 4 or 5, wherein the free end of the deflector is bend towards the first fluid passage with a distance d, preferably

7. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein at least one of the cylindrical electrodes of each fluid passage is fully insulated.

8. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein both the fluid inlet and the fluid outlet are arranged at or near a second end of the outer shell and said inlet is conical with an increasing cross sectional area in an intended flow direction, and said outlet is conical with a decreasing cross sectional area in the intended flow direction.

9. Multistage compact electrostatic coalescer according to any of the previous claims wherein the coalescer is arranged vertically and

the intended flow direction is upwards in the first fluid passage, and downwards in the second fluid passage.

10. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein the distance between the two cylindrical electrodes of the first fluid passage is a, and the distance between two cylindrical electrodes of the second fluid passage is b, and a is equal to or lager than b.

1 1. Multistage compact electrostatic coalescer according to claim 10, wherein b is approximately equal to a ±20 %.

12. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein the coalescer comprises a plurality of parallel vertical first fluid passages in fluid communication with the inlet and the volume, and where the coalescer comprises a plurality of parallel vertical second fluid passages in fluid communication with the volume and the outlet.

13. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein the coalescer further comprises fluid distribution means and or baffles to direct the fluid through the coalescer, especially in the volume.

14. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein the coalescer comprises a centre cylindrical electrode which is plugged to prevent inside flow, and wherein this centre cylindrical electrode is extending in height above the other electrodes, preferably the extending of height is more than 1/10 of the inner diameter of the coalescer.

15. Multistage compact electrostatic coalescer according to claims 14, wherein the centre cylindrical electrode comprises a spindle at top carrying one or more of the remaining electrodes.

16. Multistage compact electrostatic coalescer according to any one of the previous claims, wherein the coalescer is adapted to apply a voltage and or frequency over the at least two electrodes of the first fluid passage which is different from a voltage and or frequency to be applied over the at least two electrodes of the second fluid passage.

17. Multistage compact electrostatic coalescer according to any of the previous claims, wherein a deflector is arranged in the volume to also assist radially change in flow direction whereby the electrode forming the wall between the first and second passage is extended into the volume as a curved deflector, directing the fluid to the inner second electrostatic passage.

18. Multistage compact electrostatic coalescer according to any of the previous claims wherein a deflector is arranged in the volume to also assist radially change in flow direction whereby the electrode forming the wall between the first and second passage is extended into the volume and is structured as an opening in the cylindrical electrode.

19. Method for coalescing a process fluid characterized in that the method

comprises passing the process fluid at a velocity providing non-laminar flow through a first fluid passage between at least two electrical charged electrodes into an end section comprising a volume, and thereafter providing non- laminar flow from the volume in the opposite direction through a second fluid passage between at least two electrical charged electrodes all within one treatment unit.

20. Method according to claim 19, wherein at least one of the at least two electrodes in each of the fluid passages is fully electrically insulated.

21. Method according to claim 19 or 20, wherein the one treatment unit is a

multistage compact electrostatic coalescer according to any one of the claims 1- 18.

22. Method according to claim 19, 20 or 21 , wherein the process fluid is oil or a water in oil emulsion, especially a high viscosity oil or high viscosity emulsion.

23. Method according to any one of the claims 19-22, wherein the flow pattern

within the volume is toroidal with a moving core.

24. Method according to any one of the claims 19-23, wherein the process fluid has a Reynolds number of equal to or above 2100 within the fluid passages.

25. Method according to any one of the claims 19-24, wherein the process fluid has a Reynolds number of between 2100 and 8000 in the first fluid passage and wherein the process fluid has a Reynolds number of between 2100 and 8000 in the second fluid passage.