WO2009095241A1

WO2009095241A1 - Continuous porous bed centrifuge

Info

Publication number: WO2009095241A1
Application number: PCT/EP2009/000579
Authority: WO
Inventors: Martin Bartosek; Patrizia Broccia; Simona Biagi; Armando Marcotullio
Original assignee: Eni S.P.A.
Priority date: 2008-01-28
Filing date: 2009-01-26
Publication date: 2009-08-06
Also published as: ITMI20080125A1; GB2468252B; GB201010597D0; GB2468252A

Abstract

Continuous porous bed centrifuge for the continuous separation of immiscible liquids, for example water and mineral oil/petroleum, obtained by a modification to conventional disk centrifuges for increasing their efficiency, wherein the disks have been substituted by a filling with solid particles which act as filtrating and coalescent bed. The filtrating bed does not have mechanical containment elements.

Description

CONTINUOUS POROUS BED CENTRIFUGE

The present invention relates to a continuous porous bed centrifuge. More specifically, the present invention relates to a continuous porous bed centrifuge for the continuous separation of immiscible liquids, for example water and mineral oil/petroleum, obtained by a modification to conventional disk centrifuges for increasing their efficiency. The disks are substituted with a filling with solid particles which act as a filtrating and coalescent bed. Tests for the de-oiling of water associated with oil production have been successfully performed.

Disk centrifuges are apparatuses used for the continuous or semi-continuous separation of liquids, possibly containing solid particles, based on the action of centrifugal force on the fluid introduced into a rotor. For the modification, object of the present invention, centrifuges which allow the discharge of the heavy liquid phase (aqueous) are considered. In order to automate the process and make it continuous, however, the continuous discharge of the light phase (oil) and discharge of the solids must be envisaged. The interior of the rotor of conventional centrifuges generally contains cut-cone-shaped disks with spacers and holes for conveying the liquids. The heavy phase (liquid or solid) is concentrated in the outer part whereas the lighter phase tends to surface towards the rotation axis. The solids which accumulate in the rotor can be discharged at pre-established intervals. The complete discharge of the rotor is controlled by a washer activated by a hydraulic circuit which exploits the thrust generated by the centrifugal force.

In the upstream oil field, the large volumes involved and the cost are among the main factors that limit the use of centrifuges, however they are_. characterized by efficiency, with an encumbrance and flexibility in terms of feeding which can allow them to be advantageously used in certain cases, for example in platforms.

The Applicant has found that it is possible to provide improvements in the purification process of layer water (heavy phase) which substantially lower the concentrations of oil in the wastewater. It has been found, in fact, that it is possible to modify a conventional disk centrifuge by eliminating the disks and adapting the system to allow a filtrating filling, for example sand, to be charged and discharged during the rotation of the centrifuge. The modification introduced has the purpose of forming a filtrating and coalescent bed subjected to centrifugal force in order to favour the adhesion of the oil particles on the porous surface of the bed and separate them from the aqueous phase. This result is demonstrated in European patent application Nr. 1,809,423 which describes a centrifuge in which the plates have been substituted by a filtrating filling of solid particles arranged inside a first rotating conical mantle which forms an interspace with a second outer conical mantle, coaxial to the first. In order to prevent the filtrating filling, i.e. sand, from leaving the interspace, the device of European patent 1,809,423 envisages the use of a perforated separation element, situated at the base of the two mantles, and which keeps the interspace separated from the central body of the centrifuge. It has been surprisingly found that the presence of the separation element is not necessary as it has been experimentally verified that the operating mode of the centrifuge remains substantially unvaried also in the absence of said separation element, as there have been no losses of filtrating element due to entrainment on the part of the liquid through the interspace. By removing the perforated separation element, a potential blockage point is eliminated, improving the self-cleaning performances of the rotor following the discharge maneuver of the solids. An object of the present invention therefore relates to a continuous porous bed centrifuge, for the continuous separation of a fluid consisting of two immiscible liquids in dispersion, consisting of: a) a first outer compact rotating mantle having an essentially conical form; b) a second inner compact mantle having an essentially conical form, integral with the outer mantle and arranged so as to form an interspace with said outer mantle in free communication with the interior of the centrifuge; c) a closing base integral with the outer mantle through a sealing washer; d) a first duct integral and coaxial with the outer rotating mantle; e) a second tube coaxial and internal with respect to the first, and not rotating, for the feeding of the dispersion; f) a filling in the form of particles capable of filling from 40 to 95% of the internal volume of the centrifuge.

According to the present invention, the filling of particles is contained inside the rotating system due to the centrifugal force and is not separated from the interspace between the two mantles by any separation element .

During the rotation of the centrifuge, the fluid fed is pushed towards the outside by centrifugal force and passes through the bed of particles, becoming separated. The heave phase therefore passes into the interspace between the outer mantle and inner mantle and is discharged into the outside environment, possibly by suction, using known methods. The light phase is concentrated upstream of the filtrating bed, in the centre of the centrifuge, and exits from above, also possibly by means of suction using known methods . The filtrating particles, also subjected to centrifugal force, do not rise or only slightly rise along the interspace . The filtrating and coalescent bed (filling) preferably consists of particles, for example sand, or tiny balls having different particle-sizes. The surfaces of the filling particles can be treated in order to have specific surface tension characteristics. In particular, according to the present invention, the filling particles are spherical to favour their charging and discharging but can also have any other form, for example they can be in the form of pellets or cubes, or other geometrical forms, balls of microfibres or shapeless sand.

The particles can be full or have cavities and the surfaces can be smooth or porous to increase their coalescence effect.

The density of the solid particles must be higher than that of the light liquid phase. It is preferable but not binding for them to be also denser than the heavy liquid phase.

The particles are rigid and can be treated on the surface to change the wettability and favour the coalescence process and facilitate the detachment between the grains in both the discharging and charging phase .

Silicon coatings and treatment with silanizing agents have been tested on silicate balls.

The particles can be made of glass, polymeric, ceramic, metallic materials, oxides, (for example silica, silicates, alumina) , ion exchange resins, zeolites, hollow glass microspheres, sands, infusorial earth, but also crystals of salts with a low solubility in the heavy liquid phase. The average dimensions of the filling particles can vary from 1 μm to 3 mm, determined by methods known to experts in the field (for example, the Coulter method) .

Spheres with a diameter of 500 μm are preferred. The distribution of the diameters can be well defined, distributed or bimodal . The larger particles can be charged followed by fine particles.

The charging phase of the particles can be effected under dry conditions or in the form of a slurry in the process liquid or in another liquid. The charging liquid, if necessary, can be viscosized to help the suspension of the solid.

The charging and discharging phases of the filling can be automated. During the discharge, the filtrated solids possibly contained in the dispersion to be separated, are also expelled with the filling particles. The discharging of the complete contents of the rotor reduces the necessity of frequent maintenance operations due to the fouling of the disks.

The continuous centrifuge, object of the present invention, is now described with reference to the drawing of the enclosed figure which represents an illustrative and non- limiting embodiment, assuming a water/oil dispersion as process fluid.

With reference to the drawing, (1) represents the outer rotating mantle, (2) the inner mantle, (4) the closing base, (5) the washer interposed between the closing base and the outer mantle, (6) the feeding tube of the dispersion, not rotating and coaxial to the tubular duct (7) which is a part of the rotor. The upper part of the rotor (8) is equipped with a regulation system of the light phase/heavy phase flow-rate ratio. The separated fluids leave the top part of the centrifuge .

The filling (9) in particle form, is indicated by the shadowed area which, in the functioning phase, can rise slightly (3) inside the interspace (10) .

The functioning of the continuous centrifuge, object of the present invention, appears evident on the basis of the enclosed figure and above description. In particular, the centrifuge is started by rotating the conical mantles and closing the washers by the feeding of water (11) . The centrifuge is charged with the filtrating particles (9) and with the fluid, or dispersion, (12) through the tube (6) and the tubular duct (7) . Due to the centrifugal effect, both the filling and fluid are thrust against the walls of the inner mantle, the fluid percolates through the filling and the oily component of the dispersion is withheld by the surfaces of the filling particles, it coagulates and tends to surface towards the centre of the rotor. The filtrated water is channeled in the interspace (10) , only partially occupied by the filtrating element

(9) , and passing from the flow-rate regulation system, it is sent into the outside (W) . The oil, or oily phase,

(12) accumulates in the central body (13) and is sent and discharged into the outside environment (0) , through the upper part of the rotor (8) . The arrows indicate the course of the fluid: the dark arrows represent the dispersion/concentrated oily phase, the light arrows the filtrated water. When the filtrating bed becomes blocked and must be substituted, the feeding of the dispersion is stopped and the centrifuge is possibly slowed down. The sealing washer (5) is then released, and the exhausted filtrating bed (S) can be discharged through the opening (14) which is formed between the conical mantle and the closing base.

In the discharge phase, the water fed by (11) is washed away causing the release of the washer which causes the formation of the opening (14) . After the closing of the washer by re-establishing the water feeding (11) , the centrifuge can be charged again for subsequent functioning. All the discharges expelled by centrifugation are collected in the channels situated around the rotor and integral with the outer body of the centrifuge (15) . Some experimental deoiling tests of process water contaminated by mineral oil and gasoline in dispersion, are described hereunder for illustrative and non-limiting purposes . The tests effected were of the comparative type between a traditional disk centrifuge and a modified centrifuge .

A first prototype described in European patent application 1,809,423 (containing the perforated separation element at the base of the interspace) with a nominal flow-rate of 500 1/h was successfully tested on process water obtaining deoiling yields three times higher than the disk separator.

An industrial prototype was constructed with a nominal flow-rate of 5000 1/h. The tests were effected with a disk and filling rotor with and without the separation element at the base of the interspace according to the object of the present invention. EXAMPLE 1 The equipment consisted of a skid containing a modified industrial centrifuge with a nominal flow-rate of 5000 1/h, expansion feeding and discharge tanks, service pumps, inertization and control system. The plant is suitable for continuous separations of heavy phase (water) , light phase (oil) and solids and allows the regulation of the flow-rates between the phases by means of integrated centripetal pumps in the upper part of the centrifuge and external regulation valves.

The tests were effected using, as filling particles, silicate balls having an average diameter of 0.5 mm otherwise used for gravel packs in wells. The feeding consisted of an emulsion decanted for 1-2 days in large- dimensioned tanks of water containing mineral oil and gas oil in dispersion. A first series of tests was effected, comparing the performances of the disk rotor with the modified rotor. The tests were compared after a running of two hours of stabilization at constant regime.

The concentration of hydrocarbons in feeding water varied within a range of 30-500 ppm, the reference flow- rates were 1000 1/h, the removal flow-rates of the light phase (concentrated oil in water) were about 50 1/h (with recycling) . The residual oil proved to be approximately 35% of the initial quantity for the disk centrifuge and 4-25% of the initial quantity for the filling centrifuge. EXAMPLE 2

At the end of the functioning test, the filling centrifuge was emptied and the rotor dismantled to verify its state which proved to be substantially unaltered. In a second functioning test, the perforated separation element was removed as it is a critical point for the high pressure drops. The functioning tests showed that the filling does not rise into the interspace and that it remains confined in the central chamber. The internal mantle was subsequently improved by eliminating the step, initially present, for supporting the separation element. Once the running had been restarted, the centrifuge functioned regularly with an unchanged efficiency, without the entrainment of filling particles, also allowing a better regulation of the flow- rates.

Claims

1. A continuous porous bed centrifuge, for the continuous separation of a fluid consisting of two immiscible liquids in dispersion, consisting of: a) a first outer compact rotating mantle having an essentially conical form; b) a second inner compact mantle having an essentially conical form, integral with the outer mantle and arranged so as to form an interspace with said outer mantle in free communication with the interior of the centrifuge; c) a closing base integral with the outer mantle through a sealing washer; d) a first duct integral and coaxial with the outer rotating mantle; e) a second tube coaxial and internal with respect to the first, and not rotating, for the feeding of the dispersion; f) a filling in the form of particles capable of filling from 40 to 95% of the internal volume of the centrifuge .

2. The centrifuge according to claim 1, wherein the filling preferably consists of particles or tiny balls having different particle-sizes, possibly treated so as to have specific surface tension characteristics.

3. The centrifuge according to claim 1 or 2, wherein the filling particles are spherical.

4. The centrifuge according to claim 1 or 2, wherein the filling particles are in the form of pellets, cubes, balls of microfibres.

5. The centrifuge according to claim 1 or 2, wherein the filling particles consist of shapeless sand.

6. The centrifuge according to claim 1 or 2, wherein the filling particles are full or have cavities and the surfaces are smooth or porous.

7. The centrifuge according to claim 1 or 2, wherein the filling particles have a density higher than that of the light liquid phase.

8. The centrifuge according to claim 1 or 2, wherein the filling particles are made of glass, polymeric, metallic materials, oxides, ion exchange resins, zeolites, hollow glass microspheres, sands, infusorial earth, crystals of salts with a low solubility in the heavy liquid phase.

9. The centrifuge according to claim 1 or 2, wherein the filling particles have average dimensions ranging from 1 μm to 3 mm.