ELECTROLYTIC REACTORS

Abstract

The invention relates to an electrolytic reactor, in particular for separating phosphate from phosphate-containing liquids and/or recovering phosphate salts, comprising an inlet (16) for an electrolysis liquid and a flow channel (20) adjoining same, a magnesium metering unit (12) comprising two electrodes (22, 24) of different polarity being arranged in the flow channel (20), at least one of the two electrodes (22, 24) being a sacrificial electrode (20), wherein the magnesium metering unit (12) is designed as a free-level reactor and a mixing/sedimentation unit (14) being connected downstream of the magnesium metering unit (12) in the direction of flow, said mixing/sedimentation unit having a feed inlet (40) for the phosphate-containing liquids and an outlet (26) for the purified liquid for the obtained phosphate product.

Claims

1. An electrolytic reactor, in particular for separating phosphate from phosphate-containing liquids and/or recovering phosphate salts, comprising an inlet (16) for an electrolysis liquid and a flow channel (20) adjoining same, a magnesium metering unit (12) comprising two electrodes (22, 24) of different polarity being arranged in the flow channel (20), at least one of the two electrodes (22, 24) being a sacrificial electrode (22), wherein the magnesium metering unit (12) is designed as a free-level reactor and a mixing/sedimentation unit (14) being connected downstream of the magnesium metering unit (12) in the direction of flow, said mixing/sedimentation unit having a feed inlet (40) for the phosphate-containing liquids and an outlet (36) for the purified liquid and for the obtained phosphate product.

2. The reactor according to claim 1, wherein the sacrificial electrode (22) is only in contact with the electrolysis liquid in regions, a contact (28) of the sacrificial anode (22) being arranged above a liquid level.

3. The reactor according to claim 1, wherein the sacrificial anode (22) is formed from electrode bars (26), in particular from magnesium bars, which are arranged in a vertical chute (29) and are in particular held in a spring-loaded manner in the direction of the flow channel (20).

4. The reactor according to claim 1, wherein the sacrificial anode (22) is supported on a spacer so as to form the electrolysis gap, and the spacer is, in particular, formed from plastics ribs.

5. The reactor according to claim 1, wherein the length of the magnesium metering unit (12) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

6. The reactor according to claim 1, wherein the distance between the magnesium metering unit (12) and the mixing/sedimentation unit (14) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

7. The reactor according to claim 1, wherein the flow cross section in the magnesium metering unit (12) is much wider than it is high, in particular the ratio of height to width is at least 1:50, preferably at least 1:70 and more preferably at least 1:100.

8. The reactor according to claim 1, wherein the flow cross section of the magnesium metering unit (12) has a rectangular cross section in the direction of flow and a constant flow cross section over the entire region of the magnesium metering unit (28).

9. The reactor according to claim 1, wherein the upper electrode (22) in the operating state is movable and can be adjusted to the lower electrode (24) in order to maintain a constant height (S) of the electrolysis gap.

10. The reactor according to claim 1, wherein the inlet (16) for the electrolysis liquid has a circular cross section (17) and, in the flow channel (20) upstream of the magnesium metering unit (12), the cross section transitions into a rectangular cross section that is larger, in particular much larger, than the circular cross section.

11. The reactor according to claim 1, wherein the mixing and sedimentation unit (14) is funnel-shaped, in particular pyramid-shaped, or is designed as channels (46) that taper downward.

12. The reactor according to claim 2, wherein the sacrificial anode (22) is supported on a spacer so as to form the electrolysis gap, and the spacer is, in particular, formed from plastics ribs.

13. The reactor according to claim 12, wherein the length of the magnesium metering unit (12) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

14. The reactor according to claim 4, wherein the length of the magnesium metering unit (12) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

15. The reactor according to claim 3, wherein the length of the magnesium metering unit (12) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

16. The reactor according to claim 2, wherein the length of the magnesium metering unit (12) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

17. The reactor according to claim 13, wherein the distance between the magnesium metering unit (12) and the mixing/sedimentation unit (14) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

18. The reactor according to claim 14, wherein the distance between the magnesium metering unit (12) and the mixing/sedimentation unit (14) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

19. The reactor according to claim 15, wherein the distance between the magnesium metering unit (12) and the mixing/sedimentation unit (14) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

20. The reactor according to claim 16, wherein the distance between the magnesium metering unit (12) and the mixing/sedimentation unit (14) in the direction of flow is much shorter than the flow channel (20), in particular at most half as long, in particular at most one third as long and, more particularly, at most one quarter as long.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further advantages and advantageous embodiments of the invention are shown in the following drawing, in which:

[0040] FIG. 1a: is a sectional representation of a first embodiment;

[0041] FIG. 1b: is a plan view of the reactor according to FIG. 1a;

[0042] FIG. 2a-d: show an alternative embodiment of the reactor;

[0043] FIG. 3a-c: show another alternative embodiment of the reactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] FIGS. 1a and 1b show a first reactor according to the invention. The reactor is an electrolytic reactor and is provided as a whole with the reference sign 10. The reactor comprises two magnesium metering units 12 and a mixing/sedimentation unit 14. The two magnesium metering units 12 are arranged on opposite sides of the mixing/sedimentation unit 14. An inlet 16 is provided in each case, which transitions via a first flow portion 17 from a circular to a rectangular cross section. In another flow portion 18, the rectangular cross section changes in height and width in order to then transition into the magnesium metering unit 12 in the course of the flow channel 20. As a result, the flow is homogenized and the smallest possible height of the flow cross section relative to the width is achieved in order to be able to electrolytically meter in the largest possible amount of magnesium. Furthermore, two electrodes 22 and 24 are provided, which enclose between them the flow channel 20 at least in portions, the upper electrode 22 being designed as a sacrificial electrode and preferably consisting of trapezoidal magnesium bars 26, which complement one another with their oblique side surfaces. The electrode 22 is loaded in the direction of the flow channel 20 by means of a resilient element (not shown). The magnesium bars 26 are received in a chute 29 that can be filled from above. The electrical contacting of the electrode 22 takes place via a contact element 28 which engages and is contacted at the uppermost electrode bar designated here with 26a.

[0045] The magnesium metering unit 12 provides an electrolysis zone or an electrolysis gap and is open with respect to the environment, and therefore it is not a pressure reactor but rather a free-level reactor. The lowermost of the electrode bars 26b projects with its lower end into the flow channel 20 and is wetted there by the electrolysis liquid flowing through the flow channel 20, such that magnesium ions pass into the electrolysis liquid by means of the electrolysis and the electrode 22 is consumed. The electrode 22 is always adjusted in the direction of the flow channel 20 by means of spring loading (not shown here).

[0046] To keep the cross section of the flow channel 20 constant, a spacer (not shown) is provided, preferably made of plastics ribs, on which the lowermost electrode bar 26b is supported. In the exit of the flow channel 20 and in the entrance into the mixing/sedimentation unit 14, the magnesium is then reacted with the phosphorus and the ammonium of a phosphate-containing feed flow, the inlets for which are provided with the reference sign 40. The feed flow is metered in at all corners of the pyramid-shaped, downwardly tapering mixing and sedimentation unit 14. The mixing/sedimentation unit 14 comprises a mixing zone 32, in which a feed flow is fed, and a sedimentation zone 34. The mixing of the electrolysis liquid, in particular of a filtrate, with the feed flow results in a reaction taking place over the entire cross-sectional area D of the mixing/sedimentation device 14 and the product produced falls in the direction of the arrow 36 and can be collected. The product is filtered and the liquid is recirculated.

[0047] In particular, in this way, no electrical contact 28, 30 of the electrodes 22, 24 comes into contact with the liquid, thereby reducing the risk of corrosion. Furthermore, the actual zone in which magnesium ions are metered in is very short, and therefore no deposits are to be expected in this region. Indeed, a substantial part of the reaction only takes place in the mixing/sedimentation unit, and can then immediately reach the sedimentation zone 34 from the mixing zone 32 as a product. In this way, the operating time of the reactor can be significantly prolonged.

[0048] In order to prevent further deposits, brief polarity reversals of the electrodes 22, 24 may also be carried out, as a result of which deposits on the cathode are introduced with the liquid flow into the container of the mixing/sedimentation unit 14. It is particularly preferred if the region covered by the electrodes 22, 24 in the flow channel 20 for forming the magnesium metering unit 12 is much shorter in the direction of flow than the total length of the flow channel 20. In particular, this region may constitute less than ¼ of the length of the entire flow channel 20. Furthermore, the portion downstream of the metering unit 12 as far as the mixing/sedimentation unit 14 is also much shorter than the total length of the flow channel 20. In this way, it is ensured that the reaction and thus also the formation of struvite crystals only take place in the mixing/sedimentation unit 14. In the manner described, problems which have occurred in practice with corresponding reactors can be avoided.

[0049] The electrolysis gap between the two electrodes 22 and 24 is preferably designed such that the length of the electrolysis zone is much longer than the height of the gap S. In particular, the gap height S is also much smaller than the width B of the electrodes 22, 24. In particular, a height/length ratio of 1:150 and a height/width ratio of at least 1:100 are provided here. In this way, good electrolysis rates are achieved. In this case, the gap has a rectangular cross section which is in particular larger, in particular much larger, than the circular cross section of the inlet 16. This can be clearly seen in FIG. 1b.

[0050] If the flow flows with as uniform a flow cross section as possible and as simultaneously as possible into the electrolysis zone, particularly good rates can be achieved over the electrolysis zone.

[0051] Furthermore, the feed flow 40 is fed in via baffles 42, which ensure uniform input. The flow guide walls are used to produce an eddy, which is generated by the flow 16 exiting from the reaction space. The feed flow 40 is mixed therein.

[0052] Finally, an outlet 44 is provided, which serves in particular to adjust the fill level in the mixing and sedimentation unit 14.

[0053] FIGS. 2 and 3 show analogous designs, FIG. 2 differing in that the supply by means of the inlet 16 takes place only from one side. Otherwise, the reactor 10′ is constructed in an identical manner to the reactor according to FIG. 1.

[0054] The reactor 10″ comprises three reactors 10 according to FIG. 1, which are connected in parallel and each have two inlets 16. The mixing and sedimentation units 14 are formed continuously as a channel 46, as can be seen in FIG. 3b. Alternatively, these may also be designed separately and may each be funnel-shaped. The metering units 12 are each formed separately. In this way, the reactors 10 can be adapted to the respective requirements in terms of size.