WO1994014708A1

WO1994014708A1 - A device for separation of emulsions by electrochemical precipitation

Info

Publication number: WO1994014708A1
Application number: PCT/SE1993/001074
Authority: WO
Inventors: Mats Hållberg
Original assignee: Sp/Wm Dricksvatten Ab
Priority date: 1992-12-18
Filing date: 1993-12-15
Publication date: 1994-07-07
Also published as: SE470423B; SE9203831L; SE9203831D0

Abstract

The invention refers to a device for separation of emulsions by electrochemical precipitation in which metal ions for binding the emulsified compounds are supplied to the emulsion by electrolysis and which comprises a tubular sacrificial metal electrode (1), a counter-electrode (2) located in register with the end surface of the sacrificial electrode at a spacing (h) therefrom so as to form a gap (6), through which the emulsion is carried and which is maintained by means of spacers (5) mounted on said counter-electrode, the sacrificial electrode (1) engaging said spacers (5) with its end surface, current supply means (5, 9, 10) to the sacrificial electrode (1) and the counter-electrode (2) and a drive device (12, 13) for providing a mutual angular movement between said pair of electrodes (1, 2) around their axis of symmetry. In order to assure a really un-interrupted operation of the device while maintaining a structural simplicity thereof the invention suggests that the current supply means to the sacrificial electrode (1) comprise at least one metal member (5), isolatingly mounted and serving as spacer, said metal member simultaneously being adapted to provide a scraping action on oxides and contaminations on the active surface of said sacrificial electrode.

Description

A device for separation of emulsions by electrochemical precipitation

The present invention refers to a device for separa- tion of emulsions by electrochemical precipitation in which metal ions for binding the emulsified compounds are supplied to the emulsion by electrolysis and which comprises a tubu¬ lar sacrificial metal electrode, a counter-electrode located in register with the end surface of the sacrificial elec- trode at a spacing therefrom so as to form a gap, through which the emulsion is carried and which is maintained by means of spacers mounted on said counter-electrode, the sac¬ rificial electrode engaging said spacers with its end sur¬ face, current supply means to the sacrificial electrode and the counter-electrode and a drive device for providing a mutual angular movement between said pair of electrodes around their axis of symmetry. A device of this kind is known in principle from EP-0 341 614.

A number of different devices for separation of emulsions by electrochemical precipitation have been sugges¬ ted over the years. The common problem which all these sug¬ gestions have been intended to solve but failed to do to a full extent is to assure a continuous operation of the device. Often the emulsions which are to be separated con- tain a lot of different substances which are difficult from a separation point of view and have a tendency to cause de¬ posits on the surfaces of the electrodes and also oxidation of the sacrificial electrode. From AT-389 061 is known an electrode of a kind similar to the electrode according to the present invention in which it is suggested that the spa¬ cing means are constituted by roller bodies or simple scra¬ per means for removal of the impurities and oxidation pro¬ ducts from the surfaces of the electrodes. Thereby it is particularly intended that the roller bodies and the two co- operating electrode surfaces are to be shaped such that during operation it occurs not only a rolling motion but also a certain sliding movement in order to improve the wear of the electrode surfaces. From DE-C 3 723 745 is known a device for electro lotation in which the consumed anode layer and the electrolysis foam occurάng is uniformly scra¬ ped in the flow direction of the emulsion. The scraping action may be obtained by means of a brushing device.

In the above-stated EP-0 341 614 (= DE-A 3 816 226) it has been disclosed a construction in which the sacrifi¬ cial electrode or anode 100 is connected with a current source through a conduit 120 which is secured by the end thereof remote from the counter-electrode or cathode. This implies, however, that only a limited angular movement bet¬ ween the two electrodes is allowed in one direction before the rigidly secured conduit 120 forces a stopping and rever¬ sal of the angular movement. Of course this is a hindrance and complicates the construction but implies that there is no need to use sliding contacts in engagement with the sac¬ rificial electrode 100.

The main object of the present invention now is to provide a device of the afore-mentioned kind, in which the drawback of the prior constructions has been eliminated while maintaining a structural simplicity of the device. This is now achieved according to the invention substan¬ tially in that the current supply means to the sacrificial electrode comprise at least one metal member, isolatingly mounted and serving as spacer, said metal member simulta¬ neously being adapted to provide a scraping action on oxides and contaminations on the active surface of said sacrificial electrode.

With the invention it is now possible to assure a reliable continuous operation of the device which further¬ more is structurally simple and does not require any repea¬ ted reversal of the angular movement between the two elec¬ trodes. The invention is particularly well suited for being used in local water purification of qualified kind such as cleaning of waste water from automobile maintenance estab¬ lishments and the like where the waste water contains large quantities of environmentally dangerous and/or otherwise harmful compounds and where electrochemical precipitation therefore is particularly advantageous to use. Such waste water is mixed up with clay, diesel , and lubricating oil, hydraulic oil, rubber particles, diesel carbon deposits etc. By way of example the invention will be further des¬ cribed below with reference to the accompanying drawing in which Fig. 1 is a longitudinal section of a device according to the invention while Fig. 2 illustrates a partially broken and partially sectioned perspective view of the same device, the metal bodies serving as spacing means, however, having another shape than in Fig. 1.

As is evident from the drawing a device according to the invention comprises a tubular sacrificial electrode 1 of metal which in this case is placed vertically above a coun- ter-electrode 2. The latter is supported by a stand 3 from a suitable support and carries centrally a guide shaft 4 which extends through the central cavity of the sacrificial elec¬ trode 1 in order to guide the same during rotation. Prefe¬ rably the guide shaft 4 is made of a material with low fric- tion such as polyamide.

For supplying current to the sacrificial electrode 1, which preferably is connected as anode, is according to the invention in the side of the counter-electrode or cathode 2 facing the sacrificial electrode arranged one or more metal bodies 5 serving as spacing means and lying with their end surface at a desired distance h from the surface of the counter-electrode 2 in order to leave between said surface and the end surface of the sacrificial electrode 1 a distance or gap 6 of a size suitable for the electrolysis. In this connection it is to be pointed out particularly that in Fig. 1 the sacrificial electrode 1 only for the sake of clearness has been illustrated as raised a substantial dis¬ tance from the metal bodies 5 serving as spacing means. The liquid from which the emulsion is to be removed is introdu- ced through an inlet conduit 7 from below through a channel in the guide shaft 4 and emerges from suitable openings 8 distributed around the periphery of said shaft immediately above the surface of the counter-electrode 2 such that the liquid is distributed in the gap 6. Through conventional cable clips, suitable current conductors 9 are connected to the metal bodies 5 serving as spacers and for the rest they are surrounded by a suitable electrical isolator 11 in the counter-electrode 2. In Fig. 1 of the drawing the two sec¬ tioned metal bodies 5 have been illustrated located at various radiuses from the axis of symmetry of the device in order to show that in the case a plurality of current supply and spacing means 5 is arranged on the surface of the coun¬ ter-electrode 2 the same are radially distributed over said electrode surface in order to secure that the same in its entirety in total is scraped at each revolution of mutual rotation between the electrodes. A mutual angular movement is to be maintained in operation between the sacrificial electrode 1 and the coun¬ ter-electrode 2 and in the present case the counter-elec¬ trode 2 is stationary while the sacrifical electrode 1 is rotatably driven by means of a drive motor 12 which on its shaft carries a driving roller 13 which engages the outer periphery of the sacrificial electrode 1 and which prefe¬ rably is electrically driven. Also other drive mechanisms may be used such as a V-belt which is driven by a pulley mounted on the shaft of an electric motor. In its turn, the counter-electrode 2 is connected with the current source through a conduit 10 and a cable clip of known type.

Thus the current supply and spacing means 5 are made of a metal such as titanium, zirconium, tantalum or vanadium or an electrically conducting material covered by one of said metals. Said metals namely have the character to form immediately, when operating as anode in an electrolyte, an electrically isolating oxide film, which thus prevents fur¬ ther current flow in the non-intended direction, i.e. out- wardly into the gap 6 such that current only is led into the sacrificial electrode 1. A particular advantage of the design embodiment of the device illustrated in the drawing with the sacrificial electrode 1 resting through its own .weight on the current supply and spacing means while being guided by means of the shaft 4 is that when a piece l of tube is coming to an end and within short is consumed, a new piece of tube easily may be placed on top of the former on the shaft 4 without the need of any connecting measures.

In Fig. l of the drawing the current supply and spa- cing means 5 have been illustrated as made in two portions having preferably cylindrical shape, namely in order to facilitate the exchange of the portion of each spacing means

5 which with its end surface engages the sacrificial elec¬ trode 1 without requiring that the cable clip of the conduc- tor 9 first has to be removed from the rest of the spacing means.

In operation, liquid from which an emulsion is to be separated, thus flows out of the openings 8 and into the gap

6 and further outwardly beyond the periphery of the prefe- rably circular peripheral edge of the counter-electrode 2, where in the prefered embodiment having aluminium as sacri¬ ficial electrode 1, the aluminium hydroxide formed is floc¬ culated and flotated by means of the hydrogen bubbles formed on the surface of the counter-electrode or cathode 2 and en- train the emulsion components outwardly into a separation chamber 15 for finally passing over an overflow to an outlet conduit 16, preferably equipped with a coarse filter 17. From the separating device 15 clean water is discharged at 18. The water accompanying the flotated aluminium hyd¬ roxide sludge through the conduit 16 may be mixed, after the coarse filtration, with entering non-treated liquid for being repeatedly treated. This has the advantage that the sludge does not need to be finally filtered and that the process might be controlled in such a way that the liquid is treated in a circulation loop, i.e. several times. The puri¬ fied liquid in its turn only might need a final filtration. Although the sacrificial electrode 1 in the above- stated description only has been described as being tubular or hollow-cylindrical, the same also may be constituted of a plurality of rods having round or other contour around the inner side of an electrically isolating cylinder which is brought to rotate around the shaft 4.

In Fig. 2 is illustrated a partially sectioned per¬ spective view of the device according to the invention in which the current supply and spacing means 5 do not have circular cross sectional shape as in the embodiment accor¬ ding to Fig. 1 but wedge or circular-sector shape.

Claims

C l a i m s

1. A device for separation of emulsions by electroche- mical precipitation in which metal ions for binding the emulsified compounds are supplied to the emulsion by elect¬ rolysis and which comprises a tubular sacrificial metal electrode (1) , a counter-electrode (2) located in register with the end surface of the sacrificial electrode at a spa- cing (h) therefrom so as to form a gap (6) , through which the emulsion is carried and which is maintained by means of spacers (5) mounted on said counter-electrode, the sacrifi¬ cial electrode (1) engaging said spacers (5) with its end surface, current supply means (5, 9, 10) to the sacrificial electrode (1) and the counter-electrode (2) and a drive device (12, 13) for providing a mutual angular movement bet¬ ween said pair of electrodes (1, 2) around their axis of symmetry, c h a r a c t e r i z e d i n that the current supply means to the sacrificial electrode (1) comprise at least one metal member (5) , isolatingly mounted and serving as spacer, said metal member simultaneously being adapted to provide a scraping action on oxides and contaminations on the active surface of said sacrificial electrode.

2. A device according claim 1 and comprising a plura- lity of current supply means (5) circumferentially distribu¬ ted over the surface of the counter-electrode (2) , c h a ¬ r a c t e r i z e d i n that the current supply means (5) also are so distributed radially over the electrode surface that for each revolution of the rotation between the elec- trodes (1, 2) the whole end surface of the sacrifical elec¬ trode (1) is scraped.