WO2014058468A1

WO2014058468A1 - Electric field assisted centrifuge

Info

Publication number: WO2014058468A1
Application number: PCT/US2013/031843
Authority: WO
Inventors: Alp T. Findikoglu; Robert N. TROTTER
Original assignee: Los Alamos National Security LLC
Current assignee: Los Alamos National Security LLC
Priority date: 2012-10-08
Filing date: 2013-03-15
Publication date: 2014-04-17
Anticipated expiration: 2015-04-08

Description

ELECTRIC FIELD ASSISTED CENTRIFUGE

STATEMENT REGARDING FEDERAL RIGHTS

[0001] This invention was made with government support under Contract No. DE- AC52-06NA25396 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present application claims the benefit of United States Provisional Patent Application Numbers 61/710,945 for "Electric Field Assisted Centrifuge" and 61/710,910 for "Electric Field Induced Separation Of Components In An Emulsion," both of which applications were filed on October 08, 2012, and the entire content of both applications being hereby specifically incorporated by reference herein for all that they disclose and teach.

FIELD OF THE INVENTION

[0003] The present invention relates generally to the separation of oil from solid materials removed from oil wells and oil sands and, more particularly, to the use of a combination of electric fields at specific amplitudes, gradients and frequencies, with centrifugal forces in a single electrical/physical processing system to separate oil from solid particles.

BACKGROUND

[0004] There are many waste streams with unacceptably high concentrations of unwanted materials/impurities, such as oil in drill cuttings. Current environmental laws require oil content to be below 1% by weight in order for it to be lawfully disposable on drilling operation sites. The only commonly used technology that provides such oil separation is a hammer-mill, such devices being heavy and energy inefficient.

[0005] Industry standard centrifugal separations typically reduce the oil concentration to between about 2% and about 4% by weight. Other, more elaborate separations include chemical and thermal treatment of the solid/liquid mixture. [0006] Efficient removal of oil from oil sands and oil shale remains an important oil separation process, in this situation, the oil not being an unwanted impurity, but rather a valuable energy resource.

SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention overcome the disadvantages and limitations of the prior art by providing an apparatus and method for separating fluids from solid materials coated therewith.

[0008] Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

[0009] To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the apparatus for separating oil from solid materials coated therewith dispersed in a fluid hereof includes: a first circular electrically insulating support member having a first axis and a circumference; a plurality of equally spaced-apart elongated electrodes disposed parallel to the first axis within the circumference of the first support member and equally distant therefrom, and supported thereby, wherein alternate electrodes are grounded; a second circular electrically insulating support member, spaced-apart from the first support member having a second axis collinear with the first axis, and a second circumference equal to the first circumference for supporting the plurality of electrodes; a cylindrical electrically conducting grounded mesh structure effective for capturing the solid materials, having a second axis collinear with the first axis and a third circumference equal to the first circumference, and supported by the first support member and the second support member, the first support member, the second support member, the plurality of electrodes and the mesh structure forming a rotatable centrifuge cage, the fluid being in contact with the centrifuge cage; a first voltage source for generating a chosen voltage having a chosen frequency in electrical communication with those electrodes of the plurality of electrodes which are not grounded, whereby a chosen electric field distribution and a chosen electric field gradient distribution are established between adjacent electrodes in the plurality of electrodes and between those electrodes of the plurality of electrodes which are not grounded and the cage effective for producing dielectric breakdown of the fluid containing coated materials; and means for rotating said centrifuge basket about the first axis.

[0010] In another aspect of the present invention and in accordance with its objects and purposes the method for separating oil from solid materials coated therewith dispersed in a fluid hereof includes: applying a selected voltage having a chosen frequency to alternate electrodes in a plurality of equally spaced-apart, elongated parallel electrodes in contact with the fluid, and disposed in a circular pattern having a first axis and a first circumference, wherein the adjacent electrodes are grounded, the plurality of electrodes being surrounded by a cylindrical electrically conducting grounded mesh structure effective for capturing the solid materials having a second axis collinear with the first axis and a second circumference larger than the first circumference, the plurality of electrodes and the mesh structure forming a centrifuge cage having an axis collinear with the first axis; whereby a chosen electric field distribution and a chosen electric field gradient distribution are established between adjacent electrodes in the plurality of electrodes and between those electrodes of the plurality of electrodes which are not grounded and the cage effective for producing dielectric breakdown of the fluid containing the coated materials; and rotating the centrifuge cage about the first axis.

[0011] Benefits and advantages of embodiments of the present invention include, but are not limited to, providing an apparatus for separating fluids from solid materials coated therewith, wherein the degree of separation for the simultaneous application of physical forces and electrical forces is greater than that for either force by itself, or for the sequential application of these forces in either order.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

[0013] FIGURE 1 is a schematic representation of a perspective view of an embodiment of the present invention illustrating electric fields combined with a centrifuge (shown without a containment vessel); where FIG. 1A illustrates an array of parallel, alternate polarity electrodes circumferentially disposed on a nonconducting plate, FIG. 1 B illustrates a second nonconducting plate for supporting the electrodes, and a metallic screen mesh circumferentially disposed between the nonconducting plates, and FIG. 1C illustrates drill cuttings in a suspension of oil and water being poured through a hole in the second nonconducting plate into the rotating electrode/mesh apparatus shown in FIG. 1B, hereof, with solely DC or RF electric fields, or simultaneous RF and DC electric fields being applied to parallel electrodes as the drill cuttings migrate to and are trapped in the mesh.

[0014] FIGURE 2 is a schematic representation of the apparatus shown in FIG. 1 C hereof, illustrating an apparatus for supplying the electric fields, and a motor for rotating the centrifuge cage (again shown without a containment vessel), the drill cuttings being dried after the separated water and oil have been removed from the apparatus.

[0015] FIGURE 3 is a graph of the average oil content of the drill cuttings when processed using the centrifuge only, the centrifuge with DC, the centrifuge with RF, and the centrifuge with both DC and RF simultaneously, as a function of time.

[0016] FIGURE 4 is a graph of the average oil content of the drill cuttings when processed using the centrifuge with both RF and DC voltages applied, as a function of RF voltage, for 1 min. and 3 min.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The use of electric fields for separating water from water-in-oil emulsions is a complex process involving intercoupled electrodynamic, hydrodynamic, and electrokinetic effects, and non-equilibrium mechanisms. The determination of the optimal conditions for a given system requires detailed knowledge and control of the process. For successful implementation of electric fields for oil-water separation, electrical energy is coupled to the system in such a manner that emulsion coalescence is enhanced, the break-up of coalesced water droplets is significantly reduced, and the undesirable coupling of electrical energy either to enlarged water droplets or the separated water phase, and other components of the heterogeneous system is carefully managed.

[0018] Previous studies have shown that electric fields may enhance the emulsion coalescence and water droplet size increase through several mechanisms, including dipole-dipole attraction, migratory coalescence due to induced or contact charges, migratory coalescence due to induced or permanent dipoles in an electric field gradient, droplet chain formation and bridging, and dielectric breakdown. Electric fields can also efficiently couple energy to water-in-oil emulsions through bulk mode oscillations or interfacial polarization effects, in which case a frequency- dependent dielectric response is expected in the medium.

[0019] Briefly, embodiments of the present invention include apparatus and method for combining centrifugal forces with electric field and electric field gradient induced forces for improving the separation of oil from materials coated therewith. The technique is termed Electric Field Assisted Centrifuge (EFAC), and combines electric field induced forces with physical separation forces such as centrifugation in a single electrical/physical processing system. The simultaneous application of both types of forces achieves separations that are not possible by either one alone, or by both in series. As the electric field is applied to the mixture, it separates the fluid component (oil and/or water for oil well-related materials) from the solid components, the centrifuge, being operated with between 25 g and 3,000 g, removes the fluid component from the mixture resulting in a solid discharge from the centrifuge which has less fluid thereon than would derive from simple centrifugation for a similar time period. In the situation where the solid material has been exposed to an oil/water mixture, the same type of processing provides similar results. As the oil/water mixture is introduced into the centrifuge, the electric field is applied and separates the oil and water from the solid material. The oil component can then be separated from the oil and water mixture by further processing with electric fields or other separation techniques known in the industry, and cleaner water may be discharged from the centrifuge.

[0020] Base oil/drilling mud may be separated from drill cuttings, colloidal, low specific-gravity solids may be reduced in both aqueous and non-aqueous drilling fluids, produced sand may be separated from a crude oil production stream, and slop water (weak oil/water emulsions or mixtures) may be separated. The reduction in oil concentration in accordance with the teaching of embodiments of the present invention would allow oil companies to reduce drilling and completion wastes, reduce residual synthetic base oil on drill cuttings discharged overboard into receiving waters on offshore drilling operations, recover reusable non-aqueous base fluids, reduce the cost of reconditioning drilling fluids, specifically, non-aqueous fluids, reduce the processing and disposal cost of slop water, and reduce the cost of maintaining and conditioning drilling fluids during drilling operations.

[0021] The term "oil", as used herein, therefore, includes natural oil from wells, and natural and synthetic oils employed in drilling mud. The term "fluid", as used herein, includes liquids comprising oil or oil/water emulsions, and the term "solid materials", as used herein, includes drill cuttings and sand.

[0022] Although an actual reduction to practice has been achieved using RF and DC electric fields in cooperation with a centrifuge, any electrical force, such as electrostatic, DC, AC, dual frequency, pulsed DC, RF, microwave, EFIS, etc., in cooperation with any physical force, including centrifugal, cyclonic, high velocity air, pressure differential, etc., is expected by the present inventors to be effective.

[0023] Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the FIGURES, similar structure will be identified using identical reference characters. It will be understood that the FIGURES are presented for the purpose of describing particular embodiments of the invention and are not intended to limit the invention thereto. Turning now to FIGURE 1 , shown is a schematic representation of a perspective view of an embodiment, 10, of the present invention illustrating electric fields combined with a centrifuge. FIGURE 1A illustrates an array of parallel, alternately powered and grounded electrodes, 12, circumferentially disposed on nonconducting plate, 14, such as one constructed from polyether ether ketone (PEEK). FIGURE 1 B illustrates second nonconducting plate, 16, similar to plate 14 for supporting electrodes 12, the assembly being enclosed by metallic mesh or screen, 18, circumferentially disposed between the nonconducting plates, and forming thereby rigid, cylindrical centrifuge basket or cage, 20, having axis, 22. FIGURE 1 C illustrates drill cuttings in a suspension of oil and water, 24, being poured into hole, 26, in plate 16 for processing. RF and DC electric fields may simultaneously be applied to parallel electrodes 12 as the drill cuttings migrate to and are trapped in the mesh.

[0024] FIGURE 2 is a schematic representation of apparatus 10 shown in FIG. 1 C hereof, illustrating apparatus, 28, for supplying electric fields to apparatus 10. Electrical connections to rotating electrodes 12 may be accomplished using mercury- based, sliding electrical contacts, 29, in bottom plate 14. Shown also is motor, 30, for driving shaft or spindle, 31 , which passes through hole 26 collinearly with axis 22 and is attached to nonconducting plate 14, for rotating centrifuge cage 20. Centrifuge cage 20 may be rotated from below by employing a motor without a spindle also attached to plate 14 (not shown in FIG. 2). Drill cuttings are dried by centrifugation after the separated water and oil have been removed from the apparatus. Apparatus 28 may include tunable RF signal generator, 32, amplifier, 34, voltage step-up circuit, 36, RF transmission line, 38, DC bias, 40, voltage step-up circuit, 42, inductance matching circuit, 44, and diagnostic current and voltage probes, whereby electrical shorts can be detected, temperature probes, etc., 46. Containment vessel, 48, having fluid input pump, 50, and outlet port, 52, permit fluid to be flowed through cage 20 to increase the quantity of solid material collected on mesh 18. Mesh 18 is shown grounded in FIG. 2, but may be negatively biased in some situations.

[0025] Chosen frequency may be between approximately 100 Hz and approximately 1 GHz, chosen electric field distributions may be between about 0.01 kV/cm and about 100 kV/cm, and chosen electric field gradient distributions may be between approximately 0.01 kV/cm² and approximately 10³ kV/cm².

[0026] Having generally described the present invention, the following EXAMPLES provide additional details.

EXAMPLE 1

[0027] The combined effect of centrifugal and electric-field-induced forces on the separation of oil from a synthetic drilling mud system with ceramic proppant (beads) was measured. Mesh screen 18 may be electrically grounded, floating or charged, and the 1.6 mm diameter x 1 10 mm long electrodes 12, spaced-apart by 3 mm (surface-to-surface) were located about 3 mm therefrom (surface-to-surface). Drum 20 had an inner diameter of 61 mm.

1. Centrifuge-Only Measurements:

[0028] Approximately 100 mL (-200 g) of ceramic beads were loaded into the centrifuge; after centrifugation -80 g was used for the Retort oil content determination. It was found that when less than -25 g (or, -800 rpm) the contents of the centrifuge are not uniformly pushed out towards the wall, making the determination of the average g-force difficult. Above 25 g and below 50 g, the centrifuge was stable and measurements demonstrated a clear trend for oil content, while between 50 g and 100 g, keeping the centrifuge rotationally stable became progressively more difficult; further, measurement of oil content below 2%w is not straightforward because of the potential for contamination from the remaining oil on the walls of the assembly and the mesh. Using 37.5 g, the measured oil content was observed to drop precipitously within a few minutes, saturating at 2.2-2.6 wt.% of oil after 12 min.

2. Centrifuge + DC Bias Measurements:

[0029] The electrodes have alternating polarities leading to largely circumferential electric fields in the basket; however, the mesh allows radial electric fields/forces (i.e., parallel to the g-Force) to be applied in the centrifuge. When a positive (+) bias is applied to the mesh screen, i.e., the electric field is radial, oil content drops, whereas a negative (-) bias to the mesh screen leads to increased oil content with respect to centrifuge only results. Additionally, the oil content does not saturate within 12 min. (as is the situation for the centrifuge only), but continues to change with applied bias beyond 12 min.

3. Centrifuge + RF Bias Measurements:

[0030] The oil content was observed to drop with increasing RF bias, saturating at ~2wt.% (as was observed for the centrifuge only, and negative dc bias to the mesh screen). The largest drop in oil content was observed at 2 MHz, whereas at 100 kHz the drop was the smallest. At 30 MHz, the drop similar to that for 2 MHz, however an appreciable temperature rise was observed, without additional drop in oil content.

4. Centrifuge + DC + RF Bias Measurements:

[0031] In this case, the application of both DC and RF bias during centrifuging was not observed to yield additional oil content drop when compared to the centrifuge plus RF bias only. Additionally, at high DC and RF bias (1 kVdc and 172 Vrms) the electrode system created a short that led to excessive current flow without enhanced oil removal.

[0032] The results are summarized as follows:

a. DC bias with the electric field parallel to the g-force field has been found to enhance oil separation in the synthetic mud system with ceramic proppants; however, at high dc bias, shorting of electrodes may occur.

b. RF bias has also been found to enhance oil separation; an approximately megahertz frequency range is the most promising range because of a combination of limited heating effects and increased separation efficiency.

c. RF + DC bias does not yield further enhanced separation; rather, RF + DC bias may lead to processing difficulties because of electrode shorting.

EXAMPLE 2

[0033] With a 30.7 mm radius, rotation of mesh 18 at 1710 rpm generates an approximately 100-g force on the mesh wall. The mesh opening was 0.0180 in. (#20 mesh size). A sample of drill cuttings (Retort Analysis: -12% oil, -2% water, -86% solids) was diluted with 9 wt.% Saraline base oil, and metal shavings were removed from the oil mud using a permanent magnet. Results using the apparatus described in FIG. 2, hereof are shown in TABLES 1 and 2 and in FIGS. 3 and 4, hereinbelow. In TABLE 1 , the centrifuge only measurements were performed using -100 g force on the mesh wall for 1 min. and 3 min. and form the measurement baseline. That is, centrifuge measurements form the baselines to which the combined centrifuge/electric field measurements are compared. The measurements include: baseline centrifuge only, centrifuge + RF (at 2MHz), centrifuge + DC, and centrifuge + RF (at 2MHz) + DC for 1 min. and 3 min.

TABLE 1

Notes for TABLE 1 :

1. For Cmod 2, the reference baseline was centrifuge only for 1 min.

2. *Temperature measured remotely using a hand-held IR Thermometer.

3. For Cmod4-Cmod9, the reference baseline was centrifuge only for 3 min.

4. For Cmod4: *For a fixed input power level, the measured voltage started at 300 Vrms, dropped to 260 Vrms, then increased to 400 Vrms at the end of the process.

5. For Cmod5: *For a fixed input dc voltage, the current dropped from -8 mA at the beginning to -5 mA at the end of the process.

6. For Cmod6: *Current dropped from -6 mA at the beginning to -4 mA at the end.

7. For Cmod7: *RF voltage started at 370, dropped to 260, then increased to 430 Vrms while DC bias shorted after -15 s.

8. For Cmod8: *RF voltage started at 360, dropped to 250, then increased to 440 Vrms while DC bias shorted after 15 s.

[0034] TABLE 2 provides retort analyses for the drill cuttings.

TABLE 2

[0035] FIGURE 3 is a graph of the average oil content of the drill cuttings when processed using the centrifuge only, the centrifuge with DC, the centrifuge with RF, and the centrifuge with both DC and RF simultaneously, as a function of time. [0036] FIGURE 4 is a graph of the average oil content of the drill cuttings when processed using the centrifuge with both RF and DC voltages applied, as a function of RF voltage, for 1 min. and 3 min.

[0037] As may be observed from the TABLES 1 and 2 and the FIGS. 3 and 4, in this case, the best results were derived from the centrifuge + RF field + DC field measurements (Cmod7); for 3 min. at 370 V_rms and 1 kV dc bias, the average oil concentration in the mesh was reduced from 10.6 wt.% of oil to 7.4 wt.% using the centrifuge only measurement as a baseline if the full contents of mesh basket 20 was analyzed. However, the cuttings closest to the electrodes had an oil concentration of 3.4 wt.%, which was determined by separate chemical analysis. Thus, the oil content was reduced from 10.6 wt.% to 3.4 wt.% in the zone where the electric field and the electric field gradient levels were the highest.

[0038] The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims

[0039] WHAT IS CLAIMED IS:

1. Apparatus for separating oil from solid materials coated therewith dispersed in a fluid, comprising: a first circular electrically insulating support member having a first axis and a circumference; a plurality of equally spaced-apart elongated electrodes disposed parallel to the first axis within the circumference of said first support member and equally distant therefrom, and supported by said first support member, wherein alternate electrodes are grounded; a second circular electrically insulating support member, spaced-apart from said first support member having a second axis collinear with the first axis, and a second circumference equal to the first circumference for supporting said plurality of electrodes; a cylindrical electrically conducting grounded mesh structure effective for capturing said solid materials, having an axis collinear with the first axis and a third circumference equal to the first circumference, and supported by said first support member and said second support member, said first support member, said second support member, said plurality of electrodes and said mesh structure forming a rotatable centrifuge cage, said fluid being in contact with said cage; a first voltage source for generating a selected voltage having a chosen frequency in electrical communication with those electrodes of said plurality of electrodes that are not grounded, whereby a chosen electric field distribution and a chosen electric field gradient distribution are established between adjacent electrodes in said plurality of electrodes and between those electrodes of said plurality of electrodes which are not grounded and said cage effective for producing dielectric breakdown of said fluid containing coated materials; and means for rotating said centrifuge cage about the first axis.

2. The apparatus of claim 1 , further comprising a second voltage source for providing a dc bias to those electrodes of said plurality of electrodes that are not grounded.

3. The apparatus of claim 1 , wherein said first voltage source comprises a tunable, broadband frequency voltage source.

4. The apparatus of claim 3, wherein the chosen frequency is between approximately 100 Hz and approximately 1 GHz.

5. The apparatus of claim 1 , further comprising electronic measurement apparatus for measuring voitage on those electrodes of said plurality of electrodes to which the selected voltage having a chosen frequency is applied, and for measuring current flowing between adjacent electrodes and between those electrodes of said plurality of electrodes to which the selected voltage having a chosen frequency is applicant and said conducting grounded mesh, whereby an electrical short therebetween is detected.

6. The apparatus of claim 1 , further comprising electronic apparatus for measuring temperature of said emulsion.

7. The apparatus of claim 1 , further comprising means for flowing said fluid through said cage.

8. The apparatus of claim 1 , wherein the chosen electric field distribution is between about 0.01 kV/cm and about 100 kV/cm, and the chosen electric field gradient distribution is between approximately 0.01 kV/cm² and approximately 10³ kV/cm².

9. The apparatus of claim 1 , wherein said fluid is chosen from oil and oil/water emulsion.

10. Method for separating oil from solid materials coated therewith dispersed in a fluid, comprising: applying a selected voltage having a chosen frequency to alternate electrodes in a plurality of equally spaced-apart, elongated parallel electrodes in contact with the fluid and disposed in a circular pattern having a first axis and a first circumference, wherein adjacent electrodes are grounded, the plurality of electrodes being surrounded by a cylindrical electrically conducting grounded mesh structure effective for capturing the solid materials having a second axis collinear with the first axis, and a second circumference larger than the first circumference, the plurality of electrodes and the mesh structure forming a centrifuge cage having an axis collinear with the first axis; whereby a chosen electric field distribution and a chosen electric field gradient distribution are established between adjacent electrodes in the plurality of electrodes and between those electrodes of the plurality of electrodes which are not grounded and the cage, effective for producing dielectric breakdown of the fluid containing dispersed materials; and rotating the centrifuge cage about the first axis.

11. The method of claim 10, further comprising the step of applying a dc bias to those electrodes to which the selected voltage having a chosen frequency is applied.

12. The method of claim 10, wherein said step of applying a selected voltage at a chosen frequency to alternate electrodes, further comprises applying a tunable, broadband frequency voltage thereto.

13. The method of claim 12, wherein the chosen frequency is between approximately 100 Hz and approximately 1 GHz.

14. The method of claim 10, further comprising the steps of measuring the voltage on alternate electrodes to which the selected voltage is supplied; and measuring the current flowing between adjacent electrodes, and between alternate electrodes to which the selected voltage has been applied and the grounded mesh, whereby an electrical short therebetween is detected.

15. The method of claim 10, further comprising the step of measuring the temperature of the fluid.

16. The method of claim 10, further comprising the step of flowing the fluid through the cage.

17. The method of claim 10, wherein the chosen electric field distribution is between about 0.01 kV/cm and about 100 kV/cm, and the chosen electric field gradient distribution is between approximately 0.01 kV/cm² and approximately 10³ kV/cm².

18. The method of claim 10, wherein the fluid is chosen from oil and oil/water emulsion.