WO1999003591A1

WO1999003591A1 - Installation for purifying electrically nonconductive liquids, in particular vegetable oils

Info

Publication number: WO1999003591A1
Application number: PCT/EP1998/004407
Authority: WO
Inventors: Gunter BÖRNER; Rainer Wetzel; Uwe Zimmerling; Burkhardt Nenn
Original assignee: ÖHMI FORSCHUNG UND INGENIEURTECHNIK GmbH; Siemens Aktiengesellschaft
Priority date: 1997-07-15
Filing date: 1998-07-15
Publication date: 1999-01-28
Also published as: DE19730331C1; AU8975698A

Abstract

The invention relates to installations having metallic reaction vessels for separating substances from electrically nonconductive liquids, in particular vegetable oils, by electrostatic separation. In accordance with the invention, an electric field is established between the vessel wall (10, 10') and a concentric inner electrode (20, 20'). In addition, the vessel (1-8 and 1') has an inflow (11) for the liquid that is to be filtered, an outflow (12) for the filtered liquid, and a conical discharge point (13) for the separated solid. The invention is characterized in that no filter media are used between the electrodes (10, 20), thus guaranteeing a continuous filtering process. During this process, the distance (s) between the surfaces of the inner electrode (20) and of the inside wall (10) is constant around the periphery of a horizontal cut. The interelectrode distance (s) depends, among other things, on the type of nonconductive liquid used, the suspended particles, the flow rate and the applicable tension.

Description

description

System for cleaning electrically non-conductive liquids, especially vegetable oils

The invention relates to a system for cleaning electrically non-conductive liquids, in particular vegetable oils, with reaction containers for the separation of substances from the electrically non-conductive liquids, in particular vegetable oils, according to the principle of electrostatic separation. The reaction in the container represents sedimentation of solid particles.

The electrofiltration of electrically non-conductive liquids is known. It is used in particular to separate unwanted substances from non-conductive liquids, for example vegetable oils, mineral oils, finishing oils, solvents, resins or glycerin. In particular for the use of vegetable oils, it should be considered that such oils are used in particular as food and are a renewable raw material. This results in a remarkable world raw production with an annual growth of approx. 5%.

For the refining of vegetable oils, a bleaching earth process is mainly carried out for the purpose of adsorbing unwanted accompanying substances. The so-called bleaching is an essential quality-determining process step in oil production. The bleaching earth after the adsorption step is conventionally separated by precoat filtration.

From DE 43 44 828 AI a method and an associated device for cleaning liquids containing solid particles is already known, in which the flowing Mixture of the liquids, such as the vegetable oils and solid particles, is exposed to one or more electrical fields. These homogeneous or inhomogeneous electrical fields of the same or alternating polarities cause the solid particles to migrate relative to the liquids, which themselves are only slightly or not at all conductive. In the previously known method the viscosity of the liquid is reduced in order to make the migration rate of the solid particles practically possible due to the fields. For example, the liquid is heated to such an extent that its viscosity is reduced to approximately 25% of the viscosity of the liquid at room temperature. The latter is particularly the case when heated to about 90 to 130 ° C.

In the prior art, the temperature field is used. To implement this method, a container with an inlet for the mixture and an outlet for the separate components is provided by arranging electrodes which are insulated from one another for generating the electric fields.

Starting from the latter device, it is the object of the invention to propose an improved system for cleaning non-conductive liquids, in particular for use with vegetable oils.

The object is achieved by the entirety of the features of claim 1. Further developments are preferably characterized by the subclaims. In particular, there is a relationship that describes the relationship between all relevant parameters of the system and the cleaning or filtration process that takes place therein. The invention realizes a container with which, on the one hand, the combination of the geometry of the apparatus, the flow behavior of the fluid and the application of an electric field between 5 and 50 kV / c, preferably between 8 and 30 kV / cm complete separation of the

Solid particles on at least one electrode and on the other a clarified fluid without using additional filter elements or filter aids. This makes it possible to achieve economic advantages over conventional pressure filtration methods. In particular, it is now possible to use fine-grain bleaching earth. This results in a further reduced cleaning effort and a reduced energy consumption.

It is significant in the invention that the inner wall of the metallic containers with the associated inner electrode are constructed in a specific construction. It can be a cylindrical or a rounded flat container. Advantageously, the inner wall of the container and the inner electrode are formed on all sides in the region of the separation zone without edges, so that a completely smooth surface of both electrodes is thus achieved. The efficiency can thus be increased.

In the overall system with several tanks, at least two reaction tanks are connected in a modular manner so that a continuous discharge of liquid is ensured. This enables continuous or at least quasi-continuous production operation of the system.

In the plant according to the invention, the reaction containers are connected on the solids side to a collecting container for re-sedimentation. The sedimentation process taking place in the plant according to the invention can be carried out with pressure filtration can be combined, which further increases the efficiency of the overall system and its range of applications.

Further details and advantages of the invention result from the following description of figures of exemplary embodiments with reference to the drawing in conjunction with further subclaims. They each show a schematic representation

1 shows the side view of a container, FIG. 2 shows the associated inner electrode,

3 shows an alternative arrangement of a container with a concentric inner electrode, FIG. 4 and FIG. 5 sections along the lines IV-IV and V-V in FIG. 3,

6 shows the top view and FIG. 7 shows the side view of an arrangement of a plurality of containers which are connected in series in a modular manner, and FIG. 8 shows a plurality of reaction containers connected together with a collecting container.

The same or equivalent parts are provided in the figures with the same or corresponding reference numerals. Some of the figures are described together.

In the figures, 1 to 8 mean reaction vessels for sedimentation of solid particles from a liquid through electrostatic fields, which are arranged next to one another in particular as a battery and are connected fluidically in parallel. The number of containers is arbitrary and is determined by the required throughput of the entire system.

FIG. 1 shows an example of a single container 1, which is constructed from metallic material with a solid container wall 10. Go from the container wall 10 an inlet 11 for the liquid to be filtered, an outlet 12 for the clarified liquid and a conical outlet 13 for the separated solid.

In FIGS. 1, 6 and 7, the reaction containers 1 to 8 are designed with their container walls as rounded flat containers. However, a container 1 'can also be cylindrical with its container wall according to FIGS. 3, 4 and 5.

In FIG. 2, the inner electrode designed for one of the containers 1 to 8 according to FIGS. 1, 6 or 7 is designated by 20. It consists in particular of at least one large-area and flat separating plate 21, which is combined with a round tubular frame 22. The electrode 20 with its separating plate 21 is adjusted to the geometry of the inner volume enclosed by the container wall 10.

It is essential in the construction of the container and the inner electrode according to FIGS. 1 and 2 and 3 to 5 that the container with its container wall and the inner electrode in the region of the separation zone are formed on all sides without edges. The distance s between the two electrodes formed in this way is constant all round and l.a. smaller than 50 mm. Overall, a completely smooth surface of all electrodes is achieved. Thus there can be no disturbing field inhomogeneities that would degrade the efficiency of a reaction vessel.

In the electrostatic sedimentation of solid particles from liquids in suitable containers, the geometric sizes of the container used, the material parameters of the liquids to be cleaned, the flow parameters and the electrical field sizes of the arrangement also play a role. According to the invention, it was found that the following relationship must be fulfilled:

, where the symbols used mean the following l _A : length of the separating electrode A _q : free flow cross section V: volume flow s: electrode spacing q: average particle charge

E: field strength η: viscosity of the fluid f: average particle radius m _p : average particle mass t: start-up time

K: apparatus constant

If the above relationship is taken into account, the necessary boundary conditions for the use of specific liquids, in particular with regard to the geometry of the containers and the electrical field sizes of the system, can be found. In particular, the viscosity of the liquid to be cleaned reflects the temperature dependence of the separation process.

An electrical high-voltage supply unit 30 is applied to the container according to FIGS. 1 or 6 to 7, with which an electrical field with a suitable electrical field size, in particular field strength E, is generated for the respective sedimentation problem. For example, field strengths of 8 to 30 kV / cm have proven to be suitable in standard systems. FIGS. 3 to 5 show an alternative arrangement to that of FIG. 1 and FIG. 2 consisting of a container and the associated inner electrode: it is essential here that the container wall 10 'enclose a round cylinder in which the inner electrode 20' is arranged concentrically. Liquid outlet 11, finished product outlet 12 and outlet 13 for the separated solid are essentially in the same form as in FIG. 1. Again, there are no edges between the inner container wall 10 'and the outer surface of the electrode 20'. Furthermore, it is particularly important in FIG. 3 that the inner electrode 20 'widens from a smaller to a larger cross section in the direction of flow of the fluid.

It can be seen from FIGS. 6 to 8 that, for example, there are eight containers in a complete system, which in turn are designated 1 to 8 in detail. Two containers 1/2, 3/4, 5/6 and 7/8 are connected in such a way that they can work alternately. This ensures that a quasi-continuous production operation for the cleaning or filtration of non-conductive liquids, such as vegetable oils in particular, is ensured. In particular, the individual reaction vessels are connected in parallel in a modular manner, so that the cleaned product can be discharged continuously.

It is shown specifically in FIG. 8 that a plurality of containers 1 to 8 for sedimentation of solid particles from a liquid are connected to a single collecting container 50 with a subsequent valve 51. This means that the separated substances are re-sedimented, which is equivalent to an increase in the concentration of these substances.

The arrangement as a flat container according to FIGS. 6 and 7 results in a space-saving battery with a corresponding Reaction vessels 1 to 8. Overall, a compact block is thus formed, which is integrated into an overall system for alternating operation of the individual reaction vessels 1 to 8 and optionally with a unit for pressure filtration. Such a unit is not shown in the figures since it is known from the prior art. The efficiency of the system can thus be improved.

Claims

claims

1. Plant for cleaning electrically non-conductive liquids, in particular vegetable oils, with at least one metallic reaction container for the separation of substances from the electrically non-conductive liquid, in particular vegetable oil, according to the principle of electrostatic separation, with the following features:

- An electric field is between a container wall (10) as an outer electrode and a concentric

Built up internal electrode (20),

- The container (1 - 8 and 1 ') has an inlet (11) for the liquid to be cleaned, an outlet (12) for the clarified liquid and a conical outlet (13) for the separated solid,

no filter medium is used between the electrodes (10, 20), which ensures continuous filtration operation,

- The distance (s) between the surface (20,20 ') and the inner wall of the container (10,10') in the horizontal section is constant all round, the electrode distance (s) depending on the type of non-conductive liquid, the suspended particles, the throughput and depends on the applicable voltage.

2. Plant according to claim 1, characterized in that the geometric sizes of the container (1 - 8 and 1 '), material parameters of the liquid and the fluidic parameters and dielectric field sizes meet the following relationship:

, where the symbols have the following meaning: l _A length of the separating electrode A _q free flow cross-section V volume flow s electrode spacing q _p average particle charge

E Field strength η Fluid viscosity f Average particle radius m Average particle mass t Start-up time

K apparatus constant

3. Plant according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the electrode spacing (s) is less than 50 mm.

4. System according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the electric field (E) is between 5 and 50 kV / cm, preferably between 8 and 30 kV / cm.

5. Plant according to claim 1, d a d u r c h g e k e n n - z e i c h n e t that the container (1 - 8) is a cylindrical container (1 ').

6. Plant according to claim 1, characterized in that the container (1 - 8) is a rounded flat container (1).

7. Plant according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the inner wall

(10, 10 ') of the container (1-8) and the inner electrode (20) in the region of the separation zone are formed on all sides without edges and thus a completely smooth surface of the electrodes (10, 20) is achieved.

8. System according to claim 7, so that the inner electrode (20) widens from a smaller to a larger cross section in the flow direction of the fluid.

9. Plant according to one of claims 1 to 8, d a d u r c h g e k e n n e e c h n e t that at least two reaction vessels (1 - 8) are modularly interconnected so that a largely continuous liquid entry and discharge is guaranteed.

10. Plant according to claim 9, d a d u r c h g e k e n n - z e i c h n e t that the reaction containers (1 - 8) are connected to a collecting container (50), with which the separated substances are re-sedimented, which corresponds to their increase in concentration.

11. Plant according to claim 10, characterized in that the reaction vessels (1-8) are combined with a unit for pressure filtration, the solids flow from the reaction vessels (1-8) or from the collecting vessel (50) of an additional, simplified filtration for solids de-oiling is subjected.