WO2001012289A1

WO2001012289A1 - Method for separating an emulsion by using microwave radiation

Info

Publication number: WO2001012289A1
Application number: PCT/NO2000/000265
Authority: WO
Inventors: Pål J. NILSEN; Anna Kornfeldt; Tomas Nygren; Rebei Bel Fdhila
Original assignee: Abb Research Ltd.
Priority date: 1999-08-17
Filing date: 2000-08-17
Publication date: 2001-02-22
Also published as: AU6740600A; NO993968D0; BR0012990A; NO993968L; OA12152A; CN1370089A; ZA200200710B

Abstract

A method for treating an emulsion comprising droplets (1) of water in an organic liquid (2) in order to separate the water and the organic liquid, wherein the emulsion is subjected to microwave radiation, where the emulsion is subjected to electromagnetic radiation with a frequency in the range from 300 MHz to 100 GHz, that the droplets are selectively heated, and that, within the given frequency range, the frequency is chosen to be within a region in which the water has an elevated tendency of transforming electromagnetic radiation into heat.

Description

METHOD FOR SEPARATING AN EMULSION BY USING MICROWAVE RADIATION

5 The present invention is related to a method for treating an emulsion comprising droplets of water in an organic liquid in order to separate the water and the organic liquid, wherein the emulsion is subjected to microwave radiation. The invention is in particular related to separation of an emulsion comprising water and oil. In the oil production industry, most of the crude oil produced is mixed with water. o It is, therefore, necessary to separate the water and the oil for subsequent transport of the oil to a refinery and recycling of the water.

A method for enhancing a separation of hydrocarbon and water from an emulsion thereof by subjecting said emulsion to microwave radiation is known from U.S. pat. No. 4,582,629. Microwave radiation is here defined to extend from 1 to 300 s GHz. It is stated that microwave frequencies between 2 and 3 GHz are preferred. The effect on the emulsion by said microwave treating is mentioned possibly to result from a combination of two mechanisms. The first mechanism is said to be heating as in a conventional system. The second mechanism is said to be connected with the excitation of bound water molecules, which disrupt surfactant molecules present in an o interfacial film between each water droplet and the oil.

However, there is a need for a more detailed evaluation of the effect of microwaves on an emulsion comprising water and oil in order to find an optimum frequency range for said radiation. This is necessary to minimise the power consumption and thus make the processes economically feasible for separation of ₅ large quantities of emulsions.

The object of the present invention is to devise ways to design a method so as to achieve a more effective separation of water and an organic liquid from an emulsion thereof. It should thereby be possible to separate the water and the oil faster and/or to a lower power consumption than what is possible today. o The object is achieved in that the emulsion is subjected to electromagnetic radiation with a frequency in the range from 300 MHz to 100 GHz, that the droplets are selectively heated, and that, within the given frequency range, the frequency is chosen to be within a region in which the water has an elevated tendency of transforming electromagnetic radiation into heat, The/ total energy needed for the separation is decreased and the following gravitational separation rate Is increased.

The equipment could thereby be made smaller, the weight of the equipment be reduced, etc., which is of special importance for offshore applications. It is also possible to reduce the amount of demulsifiers added to destabilise the interfacial layer, which results in a more cost-efficient and environmentally advantageous method.

The inventive idea is to heat the water droplets by subjecting the emulsion to microwaves at a frequency where water has an elevated ability to transform electromagnetic energy into heat. Due to the fact/that the oil has a much lower ability to transform electromagnetic energy into heat than water in said range, substantially only the water droplets will be heated. The interfacial layer between each water droplet and the oil will in turn be heated by heat conduction from the heated droplets.

This heating of the interfacial layer will cause the stabilising constituents of said layer s to disrupt in the oil and it is thereby possible for the droplets to coalesce. Therefore, the power consumption can be reduced and the process become more economically feasible.

The efficiency to convert electromagnetic energy into heat for a specific material is determined by its dielectric loss factor. The loss factor of materials o containing water is due to different effects at different frequencies. It is known that the dielectric loss factor of water has a peak value for a frequency of about 20 GHz due to free water relaxation. At lower frequencies, e.g. be- low 4 GHz, the effects of

DC conductivity on the loss factor becomes of increasing importance. This is especially of importance for water containing salt. The optimum dielectric loss factor 5 may, thus, be located at different frequencies for various conditions. The optimum frequency for obtaining said optimum energy transformation for the emulsion in question is determined by, for example, salt content, temperature, and water droplet size. The frequency used is preferably within a region where it results in such a water peak value. o A further object of the invention is to devise ways to design a method so as to achieve a more effective separation of salt water and an organic liquid from an emulsion thereof, wherein the emulsion is subjected to electromagnetic radiation. This object is achieved in that the emulsion is subjected to electromagnetic radiation with a frequency in the range from 300 MHz to 1.9 GHz. Salt water has an increasingly better ability to transform electromagnetic energy into heat with lower frequencies from about 3 GHz. This ability for the salt water increases especially rapidly from a frequency of 2 GHz and downwards. For example, the salt water has a distinctly higher ability to transform electromagnetic energy into heat when it is subjected to electromagnetic waves with a frequency of 1.5 GHz than 2 GHz.

With reference to the enclosed drawings a more close description of embodiment examples of the invention follows hereunder.

In the drawings figure 1 is a cross-sectional schematic drawing of two water droplets in a continuous oil phase before and after having been subjected to microwave radiation and figure 2 is a diagram of temperature and frequency effects on the dielectric properties of pure water and aqueous NaCI.

Crude mineral oil consists of a mixture of hydrocarbons with different structures, i.e. paraffinics, iso-paraffϊnics, naphtenics, aromatics, and poly-aromatics. Minor quantities of hydrocarbon molecules containing heteroatoms are also present. The heteroatoms are sulphur, nitrogen, and oxygen. The presence of these molecules containing heteroatoms both regarding quantity and type, is of 1 great importance for the oil-water phase separation. These compounds which have a more polar nature than the pure hydrocarbons are grouped in different classes: resins, asphaltenics, and maltenes. The stabilisation mechanism of water droplets in crude oil is regarded as a steric and particle stabilisation. Schematically, stable emulsions are formed if the heteroatoms no longer are dissolved in the oil phase but form hydrogen bondings at the oil-water interface. Figure 1 illustrates two water droplets 1 in a continuous oil phase 2. Each droplet 1 is covered by an interfacial layer 3 comprising the above-mentioned resins, asphaltenics, and maltenes. Asphaltenic particles are indicated with the reference numeral 4. The coalescence of the water droplets will be hindered due to the fact that they, or in more detail the interfacial layers, have a rigid layer of large molecules, with a partly polar nature. Thus, it is needed to disrupt the interfacial layer or dissolve the constituents thereof in the oil in order to achieve coalescence of the water droplets. It is in figure 1 also illustrated how two water droplets, which are set free from the interfacial layers, collide. The droplets will coalesce when they collide, larger droplets are obtained, and finally phase separation is promoted.

Figure 2 is based on data from the book Industrial Microwave Heating" by A.C. Metaxas and R.J. Meredith, page 60, 1983. The graph shows t a effective loss factor ε"_eff as a function of frequency for pure water and salt water. The dielectric loss factor is a measure of the efficiency of water to convert electromagnetic energy into heat. It is noted that there is a peak value in the effective loss factor for water at 250C at about 20 GHz. This is due to free water relaxation. The peak value for the effective loss factor reaches about 35 at 20 GHz. The dielectric loss factor for oil is considerably lower at 20 GHz and has a peak value below 1 GHz. This implies that it is possible to selectively heat the water by subjecting the emulsion to high frequencies, such as 20 GHz. Thus, the oil will substantially not be effected by radiation at such a high frequency. The interfacial layers will in turn be heated by heat conduction from the water droplets. Furthermore, the interfacial layers have a more polar character/ compared to the oil and will thus also directly be effected by the radiation.

Depending on, for example, the structure of the water and the volume fraction water in relation to the oil, the characteristic optimum frequency at which it will absorb energy most efficiently, differs. It is, of course, also possible to change the properties of the water and thereby also change the characteristic frequency by adding additives.

According to the invention, particularly for water droplets that are generally free from sail or has a fairly low salt content, the emulsion is subjected to microwave radiation with a frequency in the range from 3.1 to 100 GHz, suitably at least 3.5 GHz, especially at least 4.0 GHz, preferably at least 6.0 GHz, and in particular at least 10.0 GHz. It is further preferable to use a frequency of at least 14 GHz, particularly at least 18 GHz, and especially approximately 20 GHz. The emulsion is further preferably subjected to a microwave radiation with a frequency lower than 30 GHz and particularly lower than 25 GHz. According to a preferred embodiment, within the given frequency range, the frequency is chosen to be within a region in which the water has an elevated tendency of transforming electromagnetic radiation into heat, Preferably, the utilised frequency is approximately the frequency for which the transformation tendency of the water has a peak value, or at least 75% of said peak value. By using that frequency, the power consumption for realising J he separation will be minimised. However, the term elevated should be understood in a broad sense. Elevated is referred to as a value 25% above the lowest dielectric loss factor value in each given range, preferably 50% above said lowest value, and even more preferred 100% above said value. For the range from 3.1 GHz to 100 GHz, a frequency which results in a loss factor of more than 25, preferably more than 30, and most preferably more than 40, should be chosen.

10 It is further not necessary to utilise said optimum frequency, but instead achieve good separation results by utilising a frequency lower than the optimum frequency and still within the claimed range, due to the fact that the curve illustrating the dielectπc loss factor as a function of frequency slopes upwards from the beginning of said range to the peak value of the dielectric loss factor.

It is known that the penetration depth of the microwaves in the water is smaller for higher frequencies and has a minimum for about 20 GHz. The penetration depth is approximately 3 mm for the frequency 20 GHz. On the contrary, the penetration depth is approximately 40 mm for a frequency of 5 GHz. The size of water droplets in emulsions needing enhanced separation is well below the penetration depth, typically

20 below 20 lam. However, lower frequencies are preferably chosen for emulsions with a comparatively higher water content in order to obtain the desired separation.

The above discussed method is, of course, applicable to both water and salt water.

The invention is also related to a method for treating an emulsion comprising 2.5 droplets of salt water in an organic liquid in order to separate the water and the organic liquid, wherein the emulsion is subjected to electromagnetic radiation with a frequency less than 1.9 GHz. The dashed lines in figure 2, which are indicated with 0.3 molal and 0.1 molal, indicates that the salt water has an elevated tendency of transforming electromagnetic radiation into heat at frequencies less than about 3 GHz.

30 Said tendency is, however, extremely good for frequencies less than 2 GHz. As an example, the effective loss factor reaches 100 at 900 MHz for a 0.3 molal solution. The oil has a maximum tendency of transforming electromagnetic radiation into heat at low frequencies. The optimum dielectric loss factor for heptane is, for example, less than 1 GHz. This implies that the oil will be heated to a larger extent with lower frequencies. As has been discussed above, the inventive idea is to selectively heat the water by applying microwaves effecting the water but substantially leaving the oil unaffected. Due to the radically increasing dielectric loss factor for the salt water at frequencies below 2 MHz, there should be an optimum frequency lower than 2 GHz, for which the water is still heated to a substantially larger extent than the oil. For frequencies lower than this optimum frequency, the oil will be heated to v a large extent, which is disadvantageous in that heating the oil takes a longer time, requires higher power and thereby also comparatively extensive arrangements.

The emulsion is, according to the last mentioned method, subjected to electromagnetic radiation with a frequency in the range from 3 MHz to 1.9 GHz, suitably lower than 1.8 GHz especially lower than 1.5 GHz, and in particular lower than 1.1 GHz. Further, the frequency is preferably at least 30 MHz, especially at least 0.3 GHz, particularly at least 0.6 GHz, and in a preferred example, at least 0.8 GHz.

The larger penetration depth of the microwaves at the given lower frequency interval is advantageous in that emulsions with a larger water content may be irradiated and in that larger emulsion amounts per unit time may be treated.

The emulsion is preferably effected in such a way that the heated water droplets collide. This can be accomplished by, for example, stirring the emulsion or selectively affect the droplets, by means of, for example, an electric field or acoustic field. Ac- cording to a preferred embodiment, the emulsion is brought to flow with a 5 turbulent flow during said radiation.

Thereby, the emulsion is flowing in a pipeline system and not a stationary batch system. In such a pipeline system, the dwell time during which each specific amount of the emulsion is subjected to the treatment is less than five seconds, preferably less than three seconds, more preferably even less than one second. The o treatment time and the power of the electromagnetic radiation are chosen such that the temperature increase of the bulk emulsion is less than 10 °C. The emulsion including the water part thereof remains in a liquid state. The pipeline system is preferably a pipeline system from an oil reservoir to a gravity separator tank system in which the treated emulsion is to separate into water and oil under the influence of gravity. The microwave treatment system may also be located between individual separator tanks in such a separator tank. Thanks to the invention, the time needed for the separation in the separator tank system can be reduced.

Accordingly, the invention includes the use of amicrowave applicator or the like arranged for the purpose of performing the inventive treatment method on an emulsion flowing through such a pipeline system. In some cases, the turbulence from transportation in the pipe system will be enough.

As a complement to subjecting said emulsion to said radiation, the emulsion is, according to an alternative, also heated by supplying heat energy from, for example, conventional heating apparatuses, In some applications, especially as a function of different or changing processing parameters, such as emulsion temperature, oil/water content, and salt content in the water, the frequency of the microwave radiation is periodically changed within the chosen frequency range. Thus, the frequency for which the water shows an elevated tendency of transforming the microwave energy, into heat can be used in spite of changing parameters during the process.

In accordance with the above statement, it might be preferred to repeatedly or continuously measure a property, such as droplet size, dielectric properties, water content, conductivity or temperature of the emulsion and to base the choice of frequency upon said measurement. It should be noted that the description presented above only should be considered as exemplifying for the inventive idea, on which the invention is built.

Thus, it is obvious for a man skilled in the art that detailed modifications may be made without leaving the scope of the invention.

Although the description above is focused on heating the water droplets and subsequently the interfacial layers by heat conduction so as to disrupt the layers by subjecting the emulsion to a microwave radiation, the destabilisation of the interfacial layers is regarded as a combination of a plurality of mechanisms, such as breaking hydrogen bonds between the surfactant molecules and the water molecules.

Claims

P a t e n t C l a i m s

1. A method for treating an emulsion comprising droplets (1) of water in an organic liquid (2) in order to separate the water and the organic liquid, wherein the emulsion is subjected to microwave radiation, characterised in that the emulsion is subjected to electromagnetic radiation with a frequency in the range from 300 MHz to 100 GHz, that the droplets are selectively heated, and that, within the given frequency range, the frequency is chosen to be within a region in which the water has an elevated tendency of transforming electromagnetic radiation into heat.

2. A method according to claim 1, characterised in that the effect of the radiation and the period of time, during which the emulsion is subjected to the radiation, are chosen such that it is the interfacial layer of the droplet which is in contact with the organic liquid that is selectively heated through the action of the radiation.

3. A method according to claim 2, characterised in that the effect and period of time are chosen such that the interfacial layers of at least a major part of the droplets in the emulsion are heated.

4. A method according to any one of claims 1-3, characterised in that the heating of the droplets is of such a magnitude that it causes a coalescence of heated droplets in the emulsion.

5. A method according to any one of claims 1-4, characterised in that the 5 emulsion is subjected to microwave radiation with a frequency of at least 3.1 GHz, suitably at least 3.5 GHz, specially 4.1 GHz, preferably at least 6.1 GHz, and in particular at least 10.0 GHz.

6. A method according to any one of claims 1-5, characterised in that the emulsion is subjected to electromagnetic radiation with a frequency of lower than 60 o GHz, suitably lower than 30 GHz, and preferably lower than 25 GHz.

7. A method according to any one of claims 1-6, characterised in that the emulsion is subjected to microwave radiation with a frequency of approximately 20 GHz.

8. A method for treating an emulsion comprising droplets (1) of salt water in an organic liquid (2) in order to separate the water and the organic liquid, wherein the emulsion is subjected to electromagnetic radiation, characterised in that the emulsion is subjected to electromagnetic, radiation with a frequency in the range from 300 MHz to 1.9 GHz.

9. A method according to claim 8, characterised in that an electromagnetic radiation with a frequency lower than 1.8 GHz, suitably lower than 1.5 GHz, and preferably lower than 1. 1 GHz is chosen.

10. A method according to claim 8 or 9, characterised in that an electromagnetic radiation with a frequency of at least 0.6 GHz, and preferably 0.8 GHz is chosen.

11. A method according to the preceding claims, characterised in that the emulsion is being effected in such a way that the heated water droplets collide.

12. A method according to the preceding claims, characterised in that the emulsion is brought to flow with a turbulent flow in order to make the heated water droplets collide.

13. A method according to the preceding claims, characterised in that the emulsion is heated by supplying heat energy.

14. A method according to claims 1-7, characterised in that the frequency is approximately the frequency for which the transformation tendency of the water has a peak value.

15. A method according to any one of the preceding claims, characterised in that the frequency is periodically changed within said frequency/range.

16. A method according to any one of claims 1-15, characterised in that a property of the emulsion is repeatedly or continuously measured, and that the choice of frequency is based upon said measurement.

17. A method according to any one of claims 1-16, characterised in that the emulsion is flowing in a pipe system when being subjected to the treatment, and that the dwell time during which each specific amount of the emulsion is subjected to the treatment is less than five seconds, preferably less than three seconds, and more preferably less than one second.

18. A method according to any one of claims 1-17, characterised in that the treatment time and the poser of the electromagnetic radiation are chosen such that the temperature increase of the bulk emulsion is less than 10 °C.

19. Use of a microwave applicator for the purpose of performing the method according to any one of claims 1-18 on a water- in-oil emulsion flowing through a pipeline system.