Coalescer element with double-layer electrical insulator

Abstract

A coalescer element for an electrostatic coalescer device comprises an electrode surrounded by an electrical insulator, where the electrical insulator comprises i) an inner layer of epoxy material and ii) an outer layer of hydrophobic material.

Description

[0001] The present invention relates to a coalescer element for an electrostatic coalescer device, to an electrostatic coalescer device comprising such a coalescer element, and to a method for protecting the coalescer element of an electrostatic coalescer device from electrocorrosion and / or partial discharge during operation of the electrostatic coalescer device.

[0002] In a number of technical fields, such as in oil and gas production facilities, refineries, chemical plants, natural gas plants and supply / distribution installations, there is a need to separate water / oil mixtures or gas / water / oil mixtures. For example, crude oil deposits are often mixed with water and / or have to be obtained through water, such that the recovered raw resource is in fact an emulsion of small water droplets in a continuous crude oil phase, which may also contain more or less gas. The water droplets have to be separated from the oil phase in order to maximize the oil yield and ensure that the crude oil meets the product quality specifications. In principle, such separation can be achieved in a settling tank, which enables the separation of the oil phase and the water phase by gravity based on the different densities of the two phases. However, such separation techniques are very slow and do not result in an efficient separation, especially in the case where the water droplets dispersed in the oil phase are fine and small. Therefore, phase separation is usually achieved with a coalescer, which promotes the coalescence of the dispersed droplet phase of the emulsion, i.e., the increase in the size of the dispersed droplets caused by the merging of individual dispersed droplets, thereby facilitating phase separation by gravity.

[0003] One class of such coalescers is mechanical coalescers, which achieve the coalescence of the dispersed droplet phase of the emulsion by using a physical barrier to the flow of the emulsion. For example, plates are provided in the coalescer at an angle to the horizontal plane such that the water / oil mixture is guided around the horizontal plane, where the dispersed water phase, which is denser than the continuous oil phase, coalesces on the plates and subsequently drips down the inclined surface of the plates towards the outlet.

[0004] Another type of effective coalescer is the electrostatic coalescer, which generates a high-voltage electric field in the emulsion. Since water, especially salt water, is more polar and conductive electrically than oil, the salt water droplets dispersed in the continuous oil phase form dipoles that attract each other, resulting in the coalescence of the salt water droplets, thereby accelerating the phase separation by gravity. The electric field is generated by a plurality of high-voltage electrodes provided in the vessel of the electrostatic coalescer, where the electrodes are immersed in the emulsion during the operation of the electrostatic coalescer. Especially in the case of separating a water / oil mixture containing gas and / or a large amount of water compared to the amount of oil, it is necessary to electrically insulate any high-voltage electrodes, which is typically achieved by encapsulating each electrode with an electrically insulating material (e.g., with an electrically insulating organic compound, such as a fluorinated polymer). The enclosed electrodes are also referred to as coalescer elements. In the absence of such electrical insulators, the local formation of a water-continuous emulsion in the water / oil mixture will cause a short circuit between adjacent coalescer elements, especially in the case of separating a water / oil mixture including a large amount of water (e.g., up to 30 wt% water to an amount of water that causes the inversion of the water / oil mixture to become an oil-in-water emulsion). Thereby, the coalescer elements become non-functional within a certain amount of time, which greatly reduces the efficiency of the electrostatic coalescer device.

[0005] However, even though the electrical insulator protects the coalescer elements of the electrostatic coalescer device from short circuits between adjacent coalescer elements, such electrostatic coalescer devices are not entirely satisfactory. That is, in such electrostatic coalescer devices, water droplets or large contaminants such as sand or deposits from crude oil can create a conductive bridge perpendicular to the electrode surface that connects the electrically insulating surface of one electrode to the electrically insulating surface of the opposite electrode. The electrical insulator will prevent a large resistive current from being driven from one metal electrode to the other. However, in an environment, such as in a crude oil emulsion, saltwater droplets can coalesce onto the electrically insulating surface and form large water patches on the surface that contains a large amount of ions. In a high voltage electric field, these saltwater patches can be regarded as reservoirs of charge, enabling a corona discharge that typically passes through the crude oil, emulsion, or gas from one enclosed electrode surface and terminates at a water patch or ground on the opposite enclosed electrode. The damaging effects of these corona discharges on the material enclosing the electrodes depend on the discharge energy (i.e., ion content, voltage level, area of the water patch, etc.) and the volume of the deposited energy. Given the potential difference between the electrodes, the smaller the area of the water patch, the less energy is released in each discharge. The current peak in the corona discharge and thus the energy release are related to the conductivity of the saltwater patch, and the likelihood of having a corona discharge increases with an increase in the voltage difference and a decrease in the saltwater surface tension. The reason for this is that with a lower surface tension, the saltwater patch is more likely to form sharp tips under the influence of the electric field, which will subsequently cause a large field amplification near the tips. The sensitivity of the above-mentioned corona discharge to the surface tension can be related to the electrodes of the coalescer element as follows. If the electrically insulating material on the enclosed electrodes is hydrophilic, the enclosed electrodes will tend to be wetted by water, which means that when exposed to water in the emulsion, crude oil, or gas, they will form large water-wetted regions (patches) on the surface of the electrodes. The larger the area of such a water film / patch, the lower the surface energy stored in the water film / patch, thus enabling the formation of tips along the direction of the electric field perpendicular to the surface.

[0006] Another problem with high voltage electrical insulators is surface deposits. As long as the surface resistance remains high, the electric field distribution between the endpoints of the electrically insulating electrode is immaterial. However, problems arise if conductive contaminants are allowed to deposit on the surface of the electrical insulator. Water from a humid environment will interact with the accumulated deposits and form a conductive path along the surface of the insulating material from the endpoints to the endpoints of the associated electrically insulating (one or more) electrodes. This will result in a surface current being generated on the electrical insulator, causing a potential short circuit along the surface (i.e., in a plane) with the enclosed surface.

[0007] In view of this, the basic object of the present invention is to provide a coalescer element for an electrostatic coalescer device, which comprises an electrode surrounded by an electrical insulator, and the electrode is protected from electro-corrosion and partial discharge during the operation of the electrostatic coalescer device, that is, when used for separating a water / oil mixture or a gas / water / oil mixture, and in particular from corona discharge. However, even with a complex shape, the electrode can still be easily and cost-effectively produced, thereby increasing the service life of the coalescer element, and in particular its electrical insulator, and thus extending the length of the time interval between the need to replace the coalescer element with a new coalescer element without reducing the efficiency of the electrostatic coalescer device.

[0008] According to the present invention, this object is achieved by providing a coalescer element for an electrostatic coalescer device, which coalescer element comprises an electrode surrounded by an electrical insulator, wherein the electrical insulator comprises i) an inner layer of an epoxy material and ii) an outer layer of a hydrophobic material.

[0009] For the reason that the electrical insulator of the electrode of the coalescer element comprises an inner layer of an epoxy material and an outer layer of a hydrophobic material, not only can the electrical insulator even with a complex shape be easily and cost-effectively manufactured, but also a coalescer element is obtained which is well protected from electro-corrosion, against partial discharge and in particular against corona discharge during its operation in the electrostatic coalescer device, that is, when used for separating a water / oil mixture or a gas / water / oil mixture. More specifically, the inner layer made of an epoxy material is characterized not only by very good moldability on the one hand, but also by very high hardness and durability against discharge on the other hand, while the outer layer made of a hydrophobic material improves the wetting properties of the underlying inner layer of the epoxy material (i.e., is not wetted by water), thereby reliably avoiding the above-mentioned problems, that is, discharge and surface arcing under a given electric field due to the coalescence of salt water droplets and surface contamination by conductive contaminants such as dust. Since electro-corrosion is reduced for a given electric field, the service life of the coalescer element and in particular its electrical insulator is increased, thereby extending the length of the time interval between the need to replace the coalescer element with a new coalescer element without reducing the efficiency of the electrostatic coalescer device.

[0010] According to the present invention, the electrical insulator of the coalescer element comprises i) an inner layer of an epoxy material and ii) an outer layer of a hydrophobic material. According to the present invention, an epoxy material means any material comprising one or more epoxy resins (i.e., one or more crosslinked or non-crosslinked polyepoxides). The polyepoxide or epoxy resin can be a homopolymer or a copolymer respectively. In addition to the polyepoxide or epoxy resin, the epoxy material can respectively comprise one or more hardeners or other compounds, such as one or more fillers.

[0011] For example, the epoxy material forming the inner layer of the coalescer element's electrical insulator comprises one or more self-crosslinking epoxy resins, i.e., one or more epoxy resins, each of which is self-crosslinking, for example due to the open epoxy groups of the epoxy resin molecules and the open epoxy groups covalently bonding different epoxy resin molecules. Such opening of the epoxy groups or ring-opening of ethylene oxide can be carried out respectively in the presence of a very strong acid such as hexafluorophosphoric acid. In this embodiment, the epoxy material forming the inner layer of the coalescer element's electrical insulator can consist of one or more self-crosslinking epoxy resins, or can additionally contain other compounds, such as one or more fillers.

[0012] According to an alternative embodiment of the present invention, the epoxy material forming the inner layer of the coalescer element's electrical insulator comprises one or more epoxy resins cured with a hardener. In this embodiment, the epoxy material forming the inner layer of the coalescer element's electrical insulator can consist of one or more epoxy resins cured with a hardener, or can additionally contain other compounds, such as one or more fillers.

[0013] According to an alternative and particularly preferred embodiment of the present invention, the epoxy material forming the inner layer of the coalescer element's electrical insulator is a composite comprising one or more epoxy resins and fillers dispersed in the one or more epoxy resins. Such composites are characterized on the one hand by very good moldability, and on the other hand by very high hardness and durability against discharge. According to the present invention, a composite refers to any kind of mixture of one or more epoxy resins and fillers, regardless of whether there are at least to some extent physical or chemical bonds between the one or more epoxy resins and the fillers. In addition, the fillers enable shrinkage to be reduced in order to adjust the thermal expansion of the epoxy material to that of the material of the electrode and to obtain high dielectric strength. For example, the composite can be a physical mixture of one or more epoxy resins with one or more fillers dispersed therein, without any chemical bonds between the molecules of the one or more epoxy resins and the fillers. However, it is also possible that there are non-covalent bonds, such as ionic bonds and hydrogen bonds, or even covalent bonds between a single epoxy resin molecule and filler molecules, atoms, ions, etc.

[0014] One or more of the epoxy resins included in the composites of the foregoing embodiments can be non-crosslinked, self-crosslinked or cured with a hardener.

[0015] The present invention has no particular limitation regarding the chemical nature of the fillers. However, particularly good results are obtained when the fillers included in the composite forming the inner layer of the coalescer element's electrical insulator are inorganic fillers and / or ceramic fillers.

[0016] In a further development of the concept of the present invention, it is proposed that the filler is made of a material comprising a compound containing one or more compounds selected from zirconium dioxide, zinc oxide, titanium carbide, silicon carbide, silicon nitride, silicon dioxide, barium titanate and any combination of two or more of the foregoing compounds. In particular, the filler may consist of any of the foregoing compounds, i.e., the filler may not contain any additional compounds other than these.

[0017] Good results are particularly obtained when the filler is silicon dioxide, surface-modified silicon dioxide, coated silicon dioxide or surface-modified and coated silicon dioxide.

[0018] In principle, the present invention has no particular limitation on the form and size of the filler included in the composite of the inner layer of the electrical insulator of the electrostatic coalescer device. Preferably, the filler is present in the form of powder, granules, pellets, etc. When the filler has a d 50 particle size of 1 to 1,000 μm, good results are particularly achieved. More preferably, the d 50 particle size of the filler in the inner layer of the electrical insulator of the coalescer element is 10 to 50 μm, and most preferably the d 50 particle size of the filler is 15 to 35 μm.

[0019] In a further development of the concept of the present invention, it is proposed that the composite of the inner layer of the electrical insulator of the coalescer element comprises 30 to 60% by weight of an epoxy material and 70 to 40% by weight of a filler.

[0020] Regardless of whether the epoxy material forming the inner layer of the electrical insulator of the coalescer element contains or consists of one or more self-crosslinking epoxy resins, or contains or consists of one or more epoxy resins cured with a hardener, or contains or consists of a composite containing one or more epoxy resins and a filler dispersed in the one or more epoxy resins, the present invention has no particular limitation on the chemical properties of the one or more epoxy resins included in the inner layer of the electrical insulator of the electrostatic coalescer device. Preferably, the one or more epoxy resins included in the inner layer of the electrical insulator of the coalescer element are selected from glycidylamine-type epoxy resins, glycidyl ether-type epoxy resins, diglycidyl ether-type epoxy resins, epoxy resins having a naphthalene skeleton, biphenyl-type epoxy resins, dicyclopentadiene-type epoxy resins, phenol aralkyl-type epoxy resins, diphenylfluorene-type epoxy resins and any combination of two or more of the foregoing compounds.

[0021] Good results are particularly obtained when the epoxy resin included in the inner layer of the electrical insulator of the coalescer element is selected from tetraglycidyl diaminodiphenylmethane, triglycidyl p-aminophenol, triglycidyl aminocresol, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, resorcinol type epoxy resin, and any combination of two or more of the foregoing compounds.

[0022] As described above, one or more epoxy resins included in the inner layer of the electrical insulator of the coalescer element or forming the inner layer of the electrical insulator of the coalescer element may be non-crosslinked, self-crosslinking, or cured with a hardener. Preferably, the inner layer of the electrical insulator of the coalescer element contains one or more epoxy resins cured with a hardener. In addition, it is preferred that the hardener is a compound having one or more amino groups, one or more acid anhydride groups, one or more azide groups, one or more phenolic groups, one or more alcoholic groups, one or more thiol groups, or any combination of two or more of the foregoing groups.

[0023] More specifically, the hardener is preferably selected from diamines, aminobenzoates, acid anhydrides, imidazole derivatives, aliphatic amines, tetramethylguanidine, thiourea adduct amines, carboxamides, polythiols, and any combination of two or more of the foregoing compounds.

[0024] Good results are particularly obtained when the hardener is selected from dialkyl toluene diamine, dicyandiamide, diaminodiphenylmethane, diaminodiphenyl sulfone, and any combination of two or more of the foregoing compounds.

[0025] According to a very particularly preferred embodiment of the present invention, the inner layer of the electrical insulator surrounding the electrode of the coalescer element for an electrostatic coalescer device according to the present invention comprises or preferably consists of a composite comprising 30 to 60% by weight of an epoxy material and 70 to 40% by weight of a filler, wherein the epoxy material is a diglycidyl ether type epoxy resin cured with a hardener, and wherein the filler is silica, surface-modified silica, coated silica, or surface-modified or coated silica.

[0026] In a further development of the concept of the present invention, it is proposed that the inner layer of the electrical insulator of the coalescer element of the present invention has a thickness of 1 to 40 mm.

[0027] According to the present invention, the electrical insulator of the coalescer element comprises i) an inner layer of an epoxy material and ii) an outer layer of a hydrophobic material. Particularly good results are obtained when the outer layer - i.e., the hydrophobic material forming the outer layer - has a contact angle of at least 90° and preferably at least 110° measured between air and brine at 23 °C according to ASTM D5946 (2017).

[0028] Suitable examples of hydrophobic materials for forming the outer layer of the electrical insulator of the coalescer element of the present invention are hydrophobic materials selected from polysilanes, fluoropolymers, acrylates, polyepoxides, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polydimethylsiloxane, polysiloxanes, polyesters, polyurethanes, hybrid polymers, and any combination of two or more of the foregoing compounds. Preferred examples thereof are fluoropolymers such as polytetrafluoroethylene, and hybrid polymers such as inorganic-organic hybrid polymers.

[0029] According to a particularly preferred embodiment of the present invention, the outer layer of the electrical insulator of the coalescer element is made of an inorganic-organic hybrid polymer. Preferably, the inorganic-organic hybrid polymer comprises i) glass and / or ceramic units and ii) organic units. In this regard, the term "organic unit" of the inorganic-organic hybrid polymer refers to a segment of a polymer chain having a substituted or unsubstituted hydrocarbon backbone. Of course, the hydrocarbon backbone may contain heteroatoms such as -O- in the case of a polyether segment, -N- in the case of a polyamine segment, -S- in the case of a polythiol segment, and so on. In addition, the term hydrocarbon backbone includes polymer segments of aromatic units bonded to each other and polymer segments of alicyclic units bonded to each other. The inorganic-organic hybrid polymer may consist of several glass and / or ceramic units, the glass and / or ceramic units being connected to each other via organic units, the organic units being chemically bonded to the glass and / or ceramic units. Chemical bonding in this regard refers to covalent bonding, ionic bonding, bonding through hydrogen bonds, or bonding through van der Waals bonds. Preferred is covalent bonding.

[0030] Furthermore, it is preferred that the inorganic-organic hybrid polymer comprises silica units as glass and / or ceramic units and siloxane units and / or substituted or unsubstituted hydrocarbon-based polymer units as organic units. For example, the inorganic-organic hybrid polymer comprises an organic part different from polysiloxane, a polysiloxane part, and an optional inorganic part, wherein the organic part preferably comprises polyfunctional i) urethane and ii) ether (meth)acrylate groups or thioether (meth)acrylate groups, and wherein the polysiloxane part is preferably formed from an alkoxysilane, such as an alkoxysilane having the formula R n Si(OR) (4-n) , where R is an alkyl group, such as a C1-C4-alkyl group. The optional inorganic part may contain silica units.

[0031] In a further development of the concept of the present invention, it is proposed that the outer layer of the electrical insulator of the coalescer element has a thickness of from 10 to 1,000 μm.

[0032] The inner layer of the electrical insulator of the coalescer element for the electrostatic coalescer device according to the present invention is preferably directly connected to the outer layer of the hydrophobic material, i.e. preferably there is no intermediate layer between the inner layer and the outer layer. The inner layer and the outer layer may or may not be connected by physical and / or chemical bonds. Even if not preferred, it is possible to provide an intermediate layer between the inner layer and the outer layer, for example an intermediate layer acting as an adhesion promoter between the inner layer and the outer layer.

[0033] The electrostatic coalescer device and more particularly the coalescer element may further comprise a transformer, wherein the electrode and the transformer are completely surrounded by the electrical insulator. Preferably, the transformer is a high voltage transformer for converting a low voltage from a power source into a high voltage. Thus, it is preferred that the transformer comprises a primary low voltage winding and a secondary high voltage winding, the latter preferably being connected to the electrode, while the low voltage winding is preferably connected to the power source or a frequency converter which in turn is connected to the power source.

[0034] The coalescer element according to the present invention can be manufactured easily and economically using a moulding step.

[0035] More particularly, the coalescer element can be manufactured by a method comprising the following steps:

[0036] i) placing a metal electrode into a mould,

[0037] ii) filling the mould with one or more epoxy resins, which preferably comprise the aforementioned fillers dispersed in one or more epoxy resins,

[0038] iii) heating the mould (for example in a heating furnace) to a temperature of from 120 °C to 190 °C and preferably from 150 °C to 160 °C in order to harden the one or more epoxy resins,

[0039] iv) after the hardening of the one or more epoxy resins is complete, demoulding the part and optionally trimming excess epoxy resin so that the coalescer element obtains the desired shape,

[0040] v) coating the coalescer element obtained in step iv) with a layer of hydrophobic material, and

[0041] vi) hardening the hydrophobic material at a temperature of from 120 to 180 °C and preferably from 140 to 160 °C and thereby bonding the hydrophobic material to the epoxy resin (for example in a heating furnace).

[0042] In a preferred embodiment, where the coalescer element comprises a transformer, the method for manufacturing the coalescer element preferably comprises the following steps:

[0043] i) Before placing the thus obtained assembly into a mold preferably comprising a wire guide, providing a transformer comprising a primary low-voltage winding and a secondary high-voltage winding and connecting it to a metal electrode, where preferably the primary wires of the transformer are placed so as to be led out of the mold,

[0044] ii) Filling the mold with one or more epoxy resins, which preferably comprise the aforementioned fillers dispersed in the one or more epoxy resins,

[0045] iii) Heating the mold (e.g., in a heating furnace) to a temperature of 120 °C to 190 °C and preferably 150 °C to 160 °C in order to harden the one or more epoxy resins,

[0046] iv) After the hardening of the one or more epoxy resins is completed, demolding the part and optionally trimming excess epoxy resin so that the coalescer element obtains the desired shape,

[0047] v) Coating the coalescer element obtained in step iv) with a layer of hydrophobic material, and

[0048] vi) Hardening the hydrophobic material at a temperature of 120 to 180 °C and preferably 140 to 160 °C and thereby bonding the hydrophobic material to the epoxy resin (e.g., in a heating furnace).

[0049] Another aspect of the present invention is an electrostatic coalescer device, which comprises:

[0050] i) A container containing at least two of the aforementioned coalescer elements, and

[0051] ii) An AC power supply for supplying an AC voltage to the electrodes of at least two coalescer elements.

[0052] Preferably, the electrostatic coalescer device further comprises one or more power supplies and one or more frequency converters, which are arranged outside the container, where each of the coalescer elements is connected to a frequency converter, and each frequency converter is connected to a power supply, where each coalescer element comprises an electrode and a transformer, where the transformer is electrically connected to the frequency converter, and the transformer is electrically connected to the electrode of the coalescer element. Also, preferably the transformer is a high-voltage transformer for converting the low voltage from the power supply into a high voltage, and comprises a primary low-voltage winding and a secondary high-voltage winding.

[0053] According to another aspect, the present invention relates to a method for protecting a coalescer element of an electrostatic coalescer device from electro-corrosion and / or partial discharge, in particular corona discharge, during operation of the electrostatic coalescer device, wherein the method comprises the following steps:

[0054] a) providing the aforementioned electrostatic coalescer device,

[0055] b) feeding a water / oil mixture or a gas / water / oil mixture into the container, and

[0056] c) supplying an AC voltage to the electrodes of the at least two coalescer elements, thereby separating the water / oil mixture into an oil phase and a water phase, or separating the gas / water / oil mixture into a gas phase, an oil phase and a water phase.

[0057] Preferably, in step b), the water / oil mixture or the gas / water / oil mixture is fed into the container so that all the coalescer elements are immersed in the water / oil mixture or the gas / water / oil mixture.

[0058] Subsequently, the present invention is described by way of illustrative but non-limiting drawings, wherein:

[0059] Figure 1 shows a schematic view of an electrostatic coalescer device comprising coalescer elements according to an embodiment of the present invention.

[0060] Figure 2 shows an electrical schematic sketch of the electrostatic coalescer device shown in the examples as viewed from the low voltage side and described therein Figure 1 of the electrostatic coalescer device shown in

[0061] Figure 1 The electrostatic coalescer device 10 shown in

[0062] in Figure 2 comprises a container 12 which contains a plurality of coalescer elements 14, wherein each coalescer element 14 comprises an electrode surrounded by an electrical insulator. In addition, the electrostatic coalescer device 10 comprises an AC power supply 16 and a frequency converter 18 outside the container 10, wherein each coalescer element 14 is connected to the frequency converter 18, and each frequency converter 18 is connected to the power supply 16. A low voltage line 20 leads from each frequency converter 18 to the electrode in order to connect the electrode to the corresponding frequency converter 18. In addition, the electrostatic coalescer device 10 comprises a controller (not shown) which is implemented, for example, such that it determines the impedance of each electrode of the coalescer element 14 in a time-resolved manner during operation of the electrostatic coalescer device 10, whereby the voltage of each electrode of each coalescer element 14 can be controlled individually and in a time-resolved manner.

[0062] In Figure 2 shows as viewed from the low voltage side Figure 1An electrical schematic sketch of the electrostatic coalescer device shown in []. It includes a voltage source on the left side, and high-voltage coalescer elements in the middle and on the right side. The high-voltage coalescer elements include a transformer and an electrode, both of which are enclosed in an electrical insulator. The transformer has an inductance L, and the electrode has a variable resistance R and a variable capacitance C. The capacitor and resistor vary with time, while the inductor is constant. The inductor represents the inductance in the transformer and is thus constant over time. During the operation of the electrostatic coalescer device, the capacitor and resistor will change. They will depend on the amount of water in the water-oil emulsion, the temperature of the emulsion, the water droplet drainage of the emulsion, etc. All these time variations will have a time scale from several seconds to several minutes.

[0063] Subsequently, the present invention is described by way of illustrative but non-limiting examples. Examples

[0064] Before placing the thus obtained assembly into a mold including a threading frame, the high-voltage side of a transformer including a primary low-voltage winding and a secondary high-voltage winding is connected to an electrode made of stainless steel with a length of 1 m, a width of 4 mm, and a height of 50 cm. Before filling the mold with a mixture of 50 wt% glycidyl ether type epoxy resin and 50 wt% zinc oxide filler, the primary wire of the transformer is placed so as to lead out from the mold. Subsequently, the mold is placed into a heating furnace and heated therein to a temperature of about 160 °C to cure the epoxy resin. Then, the mold is removed from the furnace, the coalescer element is demolded, and the excess epoxy resin is cut off so that the coalescer element obtains the desired shape. Subsequently, the coalescer element is coated with an FEP (fluorinated ethylene propylene) layer.

[0065] A plurality of these coalescer elements are placed in a container in several rows and connected to a frequency converter and an AC power supply so as to form an electrostatic coalescing device as schematically shown in []. Figure 1 as schematically shown in [].

[0066] Subsequently, the electrostatic coalescer device is operated by feeding it with a water / oil mixture and is operated at a temperature of 90 °C and a voltage of 10 kV for 365 days.

[0067] Subsequently, the coalescer elements are inspected. No cracks or other damages are seen on the coalescer elements. There is no sign of dielectric breakdown on any of the coalescer elements.

[0068] In addition, a methane depressurization test is performed on five of the coalescer elements. More specifically, at a temperature of 120 °C and a pressure of 75 bar, the coalescer elements are saturated with methane in a tank for 60 days. Subsequently, the heating is turned off and the tank is depressurized. The plates are visually controlled weekly for 15 weeks. There is no sign of any damage.

[0069] Comparative Example

[0070] In the prior art, coalescer elements are manufactured using Teflon as a single insulating and coating material with a thickness of 3 mm. More specifically, for each coalescer element, a high-voltage transformer and an electrode insulated with Teflon are made into two separate entities. The electrode is connected to the high-voltage side of the transformer through a high-voltage bushing. Due to the required Teflon thickness and high coating temperature, the only viable option is to use an oil-filled transformer enclosure. The transformer is fixed in a stainless-steel enclosure, and the enclosure is filled with evacuated oil to avoid voids and short circuits in the transformer. The electrodes are made of the same stainless steel as used in the foregoing embodiments and have the same dimensions. However, different from the embodiments, the electrodes in the comparative example are coated with a single layer of Teflon. Subsequently, the transformer connector and the Teflon-coated metal electrodes are connected to form a single coalescer element.

[0071] Then, a plurality of these coalescer elements are placed in a container in several rows, connected to a frequency converter and an AC power supply as in the foregoing embodiments, and operated by feeding a water / oil mixture therein, and the coalescer elements are operated at a temperature of 90 °C and a voltage of 6 kV.

[0072] The combination of high temperature and high voltage increases the growth rate of water trees in the insulator. The water trees eventually lead to a short circuit between the inner electrode and the grounded part inside the container. The insulator breaks down after 2 months.

[0073] In addition, a similar decompression test is performed on the coalescer elements as in the foregoing embodiments. During the subsequent decompression of the container, some delamination is shown in the insulator.

[0074] Reference Signs

[0075] 10 Electrostatic coalescer device

[0076] 12 Container

[0077] 14 Coalescer element

[0078] 16 AC power supply

[0079] 18 Frequency converter

[0080] 20 Low-voltage line

Claims

1. A coalescer element (14) for an electrostatic coalescer device (10), comprising an electrode surrounded by an electrical insulator, wherein the electrical insulator comprises i) an inner layer of an epoxy material and ii) an outer layer of a hydrophobic material.

2. The coalescer element (14) according to claim 1, wherein the epoxy material comprises or consists of one or more self-crosslinking epoxy resins.

3. The coalescer element (14) according to claim 1 or 2, wherein the epoxy material comprises or consists of a composite containing one or more epoxy resins and a filler dispersed in the one or more epoxy resins, wherein preferably the filler is made of a material comprising or consisting of a compound selected from zirconium dioxide, zinc oxide, titanium carbide, silicon carbide, silicon nitride, silica, barium titanate, and any combination of two or more of the foregoing compounds.

4. The coalescer element (14) according to claim 3, wherein the composite comprises 30 wt% to 60 wt% of the epoxy material and 70 wt% to 40 wt% of the filler.

5. The coalescer element (14) according to any one of the preceding claims, wherein the one or more epoxy resins comprise an epoxy resin selected from glycidylamine-type epoxy resins, glycidyl ether-type epoxy resins, diglycidyl ether-type epoxy resins, epoxy resins having a naphthalene skeleton, biphenyl-type epoxy resins, dicyclopentadiene-type epoxy resins, phenol aralkyl-type epoxy resins, diphenylfluorene-type epoxy resins, and any combination of two or more of the foregoing compounds.

6. The coalescer element (14) according to any one of the preceding claims, wherein the epoxy material comprises an epoxy resin cured with a curing agent, the curing agent preferably being a compound having one or more amino groups, one or more acid anhydride groups, one or more azide groups, one or more phenol groups, one or more alcohol groups, one or more thiol groups, or any combination of two or more of the foregoing groups, wherein preferably the curing agent is selected from diamines, aminobenzoates, acid anhydrides, imidazole derivatives, aliphatic amines, tetramethylguanidine, thiourea adduct amines, carboxamides, polythiols, and any combination of two or more of the foregoing compounds.

7. The coalescer element (14) according to any one of the preceding claims, wherein the inner layer has a thickness of 1 to 40 mm.

8. The coalescer element (14) according to any one of the preceding claims, wherein the outer layer has a contact angle measured between air and brine at 23 °C of at least 90°, preferably at least 120°, and more preferably at least 150°.

9. The coalescer element (14) according to any one of the preceding claims, wherein the outer layer is made of a hydrophobic material selected from polysilanes, fluoropolymers, acrylates, polyepoxides, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polydimethylsiloxane, polysiloxanes, polyesters, polyurethanes, hybrid polymers, and any combination of two or more of the foregoing compounds.

10. The coalescer element (14) according to claim 9, wherein the outer layer is made of an inorganic-organic hybrid polymer, which preferably comprises glass and / or ceramic units and organic units.

11. The coalescer element (14) according to claim 10, wherein the inorganic-organic hybrid polymer comprises an organic part different from the polysiloxane part and optionally an inorganic part, wherein the organic part preferably comprises polyfunctional i) carbamate and ii) ether (meth)acrylate groups or thioether (meth)acrylate groups, and wherein the polysiloxane part is preferably formed from an alkoxysilane, such as an alkoxysilane having the formula R n Si(OR) (4-n) , where R is an alkyl group, such as a C1-C4-alkyl group.

12. The coalescer element (14) according to any one of the preceding claims, wherein the outer layer has a thickness of 10 to 1,000 μm.

13. The coalescer element (14) according to any one of the preceding claims, further comprising a transformer, wherein the electrode and the transformer are completely surrounded by the electrical insulator.

14. A method for manufacturing the coalescer element (14) according to any one of the preceding claims, comprising the following steps: i) placing a metal electrode into a mold, ii) filling the mold with one or more epoxy resins, which preferably comprise fillers dispersed in the one or more epoxy resins, iii) heating the mold to a temperature of 120 °C to 190 °C and preferably 150 °C to 160 °C in order to harden the one or more epoxy resins, iv) after the hardening of the one or more epoxy resins is completed, demolding the part and optionally cutting away excess epoxy resin so that the coalescer element obtains a desired shape, v) coating the coalescer element obtained in step iv) with a layer of hydrophobic material, and vi) hardening the hydrophobic material at a temperature of 120 °C to 180 °C and preferably 140 °C to 160 °C and thereby bonding the hydrophobic material to the epoxy resin.

15. The method according to claim 14, wherein step i) comprises providing a transformer comprising a primary low-voltage winding and a secondary high-voltage winding and connecting it to the metal electrode before placing the assembly thus obtained into a mold which preferably comprises a threading frame, wherein the primary wire of the transformer is preferably placed so as to be led out of the mold.

16. An electrostatic coalescer device (10), comprising: i) a container (12) containing at least two coalescer elements (14) according to any one of claims 1 to 13, and ii) an AC power supply (16) for supplying an AC voltage to the electrodes of the at least two coalescer elements (14).

17. The electrostatic coalescer device (10) according to claim 16, wherein the electrostatic coalescer device (10) further comprises one or more power supplies (16) and one or more frequency converters (18), which are arranged outside the container (12), wherein each of the coalescer elements (14) is connected to a frequency converter (18), and each frequency converter (18) is connected to a power supply (16), wherein each coalescer element (14) comprises an electrode and a transformer, wherein the transformer is electrically connected to the frequency converter (18), and the transformer is electrically connected to the electrode of the coalescer element (14).

18. A method for protecting the coalescer elements (14) of an electrostatic coalescer device (10) from electrocorrosion and / or partial discharge during the operation of the electrostatic coalescer device (10), the method comprising the following steps: a) Provide the electrostatic coalescer device (10) according to claim 16 or 17, b) Feed a water / oil mixture or a gas / water / oil mixture into the container (12), and c) Supply an AC voltage to the electrodes of the at least two coalescer elements (14), thereby separating the water / oil mixture into an oil phase and a water phase, or separating the gas / water / oil mixture into a gas phase, an oil phase, and a water phase.

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