EP1817261A1

EP1817261A1 - Method and device for treating a fluid by electrolysis

Info

Publication number: EP1817261A1
Application number: EP05799910A
Authority: EP
Inventors: Pascale Thery; Hélène FRANCY-CHAUSSON
Original assignee: Saint Gobain SEVA SA
Current assignee: Saint Gobain SEVA SA
Priority date: 2004-09-16
Filing date: 2005-09-15
Publication date: 2007-08-15
Also published as: WO2006030162A1

Abstract

The invention concerns a method for treating a fluid and in particular at least for carbonate removal from water in a reactor (1), said reactor (1) comprising at least one anode (A) capable of being connected to a positive terminal of a current generator (2) and at least one cathode (C) capable of being connected to a negative terminal of said current generator (2), characterized in that said fluid is subjected to intense mixing inside said reactor (1).

Description

METHOD AND DEVICE FOR TREATING A FLUID BY

ELECTROLYSIS

The present invention relates to a process for treating a fluid and especially at least decarbonation of water in a reactor, said reactor comprising at least one anode that can be connected to a positive terminal of a current generator and to the minus one cathode that can be connected to a negative terminal of said current generator. It relates more particularly to the major improvement of the performance of such a method and the associated device, both during the treatment of the fluid and during the cleaning of the electrodes used in the implementation of the electrolysis decarbonation process.

Calcium carbonate (CaCO ₃ ), commonly known as limestone, is naturally contained in water. Conditions of use of the water make it possible to precipitate, generating various types of problems which are expensive for the user and in particular at the industrial level, by scaling of the distribution, cooling circuits, or even by the degradation of the results in industrial manufacturing processes using water.

In order to provide at least a partial or total solution to this problem, calcium carbonate electro-reduction processes have been developed to extract the calcium carbonate in solid form.

The prior art thus knows the French patent application N ⁰ FR-A-2 552 420 according to which the decarbonation of water is carried out by electrolysis by means of a rectangular-shaped signal, producing a high current density. making it possible to obtain at the cathode an OH-ion concentration such that it causes the formation of calcium carbonate microcrystals, with subsequent precipitation of calcium carbonate and elimination in capacities that are ancillary to the electrolytic treatment capacity, these capacities being positioned downstream of the reactor hosting the electrodes. In a variant described in the French Patent Application FR-A- 2 731 ⁰

420, the immediate precipitation of the calcium carbonate is carried out in the electrolytic treatment chamber: the electrolysis is carried out between an anode and a cathode within the water to be treated which constitutes the electrolyte, by first constituting the cathode a thin and porous adhesive coating comprising calcium carbonate intended for to promote the growth by nucleation and the formation of germs which support the birth of calcium carbonate crystals. In an attempt to at least partially remove these deposits, a gas flow is produced only through the pores of the cathode (by gas blowing or by hydrogen generation in situ by electrolytic reduction of water) so that crystals that form on said porous coating are peeled off from it by the action of the gas flow. This method is implemented in a reactor comprising a vessel and two series of parallel plates forming anodes and cathodes, which the liquid to be treated runs upward.

The electrochemical reaction causes the precipitation of CaCO ₃ in the basic medium created in the vicinity of the cathode (s). This CaCO ₃ falls partly in the bottom of the reactor where it is discharged regularly, but another part remains on the cathodes.

It is then necessary to regularly perform a complete mechanical cleaning of the cathodes to avoid blocking the system by caking. This makes it necessary to stop the device and to reproduce the preliminary step of forming a porous thin coating comprising calcium carbonate before returning to service or to substitute the cathodes to be cleaned by cathodes already ready to use and provided that they are ready for use. then have a cathode stock ready for use.

In any case, it is necessary to very regularly stop this device for cleaning and during the shutdown, of course, no fluid can be treated.

The result of the electrolysis chemical reaction of water is a lowering of TH and TAC (softening and decarbonation): o TH (Hydrotimetric Title) is the indicator of total hardness of water and corresponds to the calcium and magnesium ion content according to the following relationship, in French ( ⁰ F): TH = ([Ca ²⁺ ] + [Mg ²⁺ ]) / 10 ^"4 mol.l ^{" 1} (knowing that TH = TH _ca + THM _g ); (Reminder: 1 ° F = 0.2 meq.F ¹ = 0.7 degree English = 0.56 degree German) o The TAC (Full Alkalimetric Title) is the content of a water in alkalis (hydroxides), in carbonates and alkali or alkaline earth bicarbonates (or hydrogen carbonates). In the current vocabulary, it gives the measure of total alkalinity. TAC = (2, [CO ₃ ² I + [HCO ₃ I + [OH]) / 10 ^"4 mol.l ⁴ in French degrees o When CaCO ₃ precipitation occurs, TH _ca and TAC drop simultaneously Precipitation depends on the calco-carbonic equilibrium and not only the calcium content of the water, each water has a specific precipitation potential according to its use. It should be determined to achieve adequate decarbonation.

Indeed, the most common scaling comes from a modification of the carbon chain of water, resulting in precipitation of calcium carbonate. The equilibrium is defined by the following reaction:

Ca (HCO ₃ ) ₂ <-> CaCO ₃ + CO ₂ + H ₂ O, for which a theoretical pH constant, pH _s , which is the saturation pH, can be defined.

Modification of certain parameters such as pH, dissolved CO ₂ concentration or temperature can cause a break in the calco-carbonic equilibrium and cause the scaling phenomenon. Thus, the water is scaling: o When pH _water > pH _s because the water is supersaturated with CaCO ₃ ; o When [CO ₂ ] <[CO ₂ ] _e , [CO ₂ ] _e represents the balancing CO ₂ concentration for which the calcium bicarbonate remains stable in solution; and o When the temperature of the water increases because under the effect of this increase, a degassing of CO ₂ occurs due to the decrease of its solubility in water and the calco-carbonic equilibrium will tend towards the formation free CO ₂ from the bicarbonates, which causes the precipitation of CaCO ₃ .

An object of the invention is to propose a major improvement of the processes of the prior art by providing a reliable decarbonation process, whose instantaneous and overall yields can be increased by at least 40%, or even 50%, or even more .

Another object of the invention is to provide a water decarbonation process that is at least partially or completely automatic, including self-cleaning phases that require no or little human intervention.

It is thus possible to operate the reactor for very long periods, which may be of the order of several years, without complete stop, the cleaning being operated in masked time, for very short periods and while fluid coming out of the reactor is still used.

The present invention thus relates in its broadest sense to a process for treating a fluid and in particular at least decarbonation of water according to claim 1. This process is carried out in a reactor, this reactor comprising at least one anode connectable to a positive terminal of a current generator and at least one cathode connectable to a negative terminal of said current generator.

According to the invention, the fluid undergoes intensive stirring inside said reactor. For intensive stirring in the sense of the present invention is meant that the fluid is subjected to an additional mixing action, adding to the simple movement of the fluid under the action of the introduction of the fluid to be treated and the recovery of treated fluid.

Thus, all the fluid present inside the entire reactor is subjected to a mixing action, that is to say both in the vicinity of the (or) anode (s) and the (or) cathode (s).

Indeed, the present invention is based on a quite surprising observation: the inventors have found that additional stirring in the reactor has the consequence both of improving the instantaneous yield of the reactions, but also of facilitating the reaction. cleaning: They realized that, for a reason still unknown, the crystallization of the calcium carbonate takes place in a very particular form when the electrolyte is subjected to a mixing at the level of the

(Or) anode (s) than the (or) cathode (s) and that this very particular form has the important advantage of detaching itself extremely easily from the cathode, making the cleaning of the latter extremely easy.

The process according to the invention has several alternative or cumulative variants for carrying out intense stirring inside the reactor.

In a first variant, said stirring is performed by injecting gas into said fluid at a flow rate at least substantially equal to that of the fluid and preferably from 2 to 10 times that of the fluid.

For a parallelepipedic treatment tank (right parallelepiped), the air supply flow rate is preferably:

from 3 to 10 m ³ / h of air per m ² of floor area of the treatment tank, and preferably of the order of 7 m ³ / h of air per m ² of ground surface of the tank of treatment, and

from 5 to 20 m ³ / h of air per m ³ of treatment tank volume and preferably of the order of 12 m ³ / h of air per m ³ of volume of treatment tank. In a second variant, said stirring is performed by recirculation R carried out by suction of said fluid at at least one location in said reactor and discharge of said fluid to at least another location in said reactor.

For the implementation of this variant, a recirculation R is preferably operated between a buffer tank and a treatment tank of said reactor and in that the raw water is introduced not into the treatment tank, but into the tank. buffer and distributed treated water is taken not from the treatment tank, but from the buffer tank.

This recirculation flow R is preferably from 4 to 20 times greater, and more preferably of the order of 10 times greater, than the average flow rate of treated water delivered at the outlet of the buffer tank.

The recirculation flow rate R in liters per hour is, preferably at least 10 times, or even at least 50 times, greater than the volume in liters of the treatment tank from which the fluid is drawn and in which the fluid is discharged. In a third variant, said stirring is operated by at least one mechanical means such as an agitator or a propeller, driven by a movement inside said reactor.

In all these variants, said intense stirring is permanently proportional to the fluid flow, the proportion may preferably vary, especially during a cleaning phase.

According to a particularly advantageous characteristic of the invention, at least one and preferably all cathodes (s) present (s) a corrugated surface.

Preferably the depth p of a corrugation and preferably of all the corrugations (s) is at least 2 mm relative to the mean plane of said cathode. According to another particularly advantageous characteristic of the invention, the distance between the mean plane of a cathode (C) and the average plane of the adjacent anode (A) is between 10 and 60 mm and preferably between 20 and 30 mm.

According to another particularly advantageous characteristic of the invention, during a cleaning phase, said cathode at least to be cleaned is connected to a positive terminal of a current generator and is preferably subjected to a current intensity of the current. from 3 to 30 Am ² , especially from 5 to 20 Am ² and preferably of the order of 10 Am ^-2 .

According to another particularly advantageous characteristic of the invention, during a cleaning phase, said cathode at least to be cleaned is connected to a positive terminal of a current generator and is preferably subjected to a current intensity of the order of 1 to 3 times the current intensity used to perform said treatment.

During the cleaning phase, a current is applied across said current generator which is connected to said cathode at least to clean for a period, preferably of the order of one to several minutes.

In addition, during the cleaning phase, intense stirring is preferably caused inside said reactor, this stirring being carried out more preferably still according to at least one of the above variants. In addition, during the cleaning, the conductivity of the fluid can be increased, in particular to a value of between 800 and 8000 microns per centimeter.

To increase the conductivity of the fluid, one solution consists in adding at least one salt, preferably neutral, of the Na ₂ SO _{4 type} . Finally, said cleaning phase is preferably programmed to be performed automatically at regular intervals, for example every week to every month or every three months, or on instruction of a measuring system, that is, that is, without human intervention or with very light human intervention.

The present invention also relates to a reactor for treating a fluid and especially at least decarbonation of water for the implementation of the method according to the invention.

The treatment reactor comprises at least one anode that can be connected to a positive terminal of a current generator and at least one cathode that can be connected to a negative terminal of said current generator and is characterized in that it comprises means for intense stirring inside said reactor and more specifically inside the treatment tank.

For the implementation of the first variant of the method, said intense stirring means are preferably constituted by at least one porous pipe or pierced with micro-holes, said pipe being fed by a pump or a pressure reducer, for formation of bubbles in the fluid, especially air bubbles or nitrogen.

In this variant, said micro-holes preferably have a diameter less than or equal to 2 mm and preferably less than or equal to 1 mm. For the implementation of the second variant of the method, said intense stirring means are preferably constituted by at least one fluid extraction mouth, at least one fluid discharge mouth and at least one a pump positioned between said extraction mouth and said discharge mouth. For the implementation of the third variant of the method, said intense stirring means are preferably constituted by at least one mechanical means such as an agitator or a propeller, as well as a drive system capable of driving said moving mechanical means within said reactor.

The depth (p, p ') of a corrugation and preferably of all the corrugations (s) is at least preferably 2 mm.

According to another particularly advantageous characteristic of the invention, the distance between the mean plane of a cathode and the mean plane of the adjacent anode is between 10 and 60 mm and preferably between 20 and 30 mm.

In all the variants of the invention, the current generator used is preferably capable of generating a current density of the order of 3 to 30 Am ^-2 , especially 5 to 20 Am ^-2, and preferably of the order of 10 Am- ² in said cathode (s) Finally, in all the variants of the invention, the reactor preferably comprises automatic control means for automatically cleaning said cathode. less to clean at regular intervals or on instruction of a measuring system.

Said cathodes are preferably positioned on supports facilitating their extraction.

For the implementation in particular of this possibility, the reactor may comprise means for guiding the electrodes, preferably positioned outside a treatment tank.

Advantageously, the present invention thus makes it possible to implement a method of electrolysis treatment, and particularly of decarbonation of water, which is particularly efficient and which may comprise a phase of cleaning the electrodes and which may be at least partially or totally automated. . In addition, these phases being very short and very effective, it is possible to achieve them in masked time, without interrupting the extraction of fluid from the reactor.

The present invention will be better understood on reading the following detailed description of nonlimiting exemplary embodiments and the attached figures:

FIG. 1 illustrates an exemplary schematic diagram of a decarbonation reactor according to the invention;

FIG. 2 illustrates the diagram of the decarbonation reactor of FIG. 1 during decarbonation; FIG. 3 illustrates a perspective view of a decarbonation reactor according to the invention;

FIG. 4 illustrates an exploded view of the decarbonation reactor of FIG. 3;

FIG. 5 illustrates the cathode extraction step of the decarbonation reactor of FIG. 3;

• Figures 6, 7 and 9 illustrate three different ways to achieve intense brewing means by bubbling;

• Table 8 illustrates the variation of abatement and voltage during a 60-day test period of a reactor such as that illustrated in Figure 7; FIG. 10 illustrates a first exemplary embodiment of the intense stirring means by fluid recirculation;

FIG. 11 illustrates a second exemplary embodiment of the intense stirring means by fluid recirculation;

• Table 12 illustrates the variation of abatement as a function of the average contact time in minutes for a reactor such as that illustrated in FIG. 11;

FIG. 13 illustrates an exemplary embodiment of the intense stirring means by setting in motion a mechanical means;

FIG. 14 illustrates a vertical sectional view of a baffled reactor, the baffles being formed with cathodes and solid anodes and the fluid passing through the top and bottom of the electrodes;

FIG. 15 illustrates a top view of a baffled reactor, the baffles being formed with cathodes and solid anodes and the fluid passing through the right and the left of the electrodes; FIG. 16 illustrates a vertical sectional view of a baffled reactor, the baffles being formed with cathodes and deployed anodes and the fluid passing through the top and bottom of the cathodes and through the anodes;

FIG. 17 illustrates an exemplary schematic diagram of the decarbonation reactor of FIG. 1 during a cleaning according to a first solution, by polarity inversion;

FIG. 18 illustrates a corrugated anode according to the invention;

FIG. 19 illustrates a partial view of an exemplary embodiment of the corrugations of the anode of FIG. 18; FIG. 20 illustrates a partial view of another embodiment of the corrugations of the anode of FIG. 18; and

• Figure 21 illustrates the evolution of the abatement with respect to the current density, firstly for a corrugated cathode and secondly for a flat cathode under identical experimental conditions.

It is specified that the proportions between the various elements represented are not rigorously respected in these figures in order to facilitate their reading.

FIG. 1 illustrates the schematic diagram of a known type of decarbonation treatment device or reactor (1) consisting of a current generator (2), a tank (3) and at least one anode ( A) and a cathode (C) positioned inside the vessel (3) and electrically connectable to said generator (2). Each anode (A) and each cathode (C) consists of a plate positioned substantially vertically and illustrated here in plan view. The fluid to be treated, in this case water, circulates inside the hollow right parallelepiped treatment vessel (3), between the anodes and the cathodes.

The cathodes consist for example of a flat plate made of 316L stainless steel and the anodes are of the "non-consumable" type DSA (Dimensionally Stable Anode), for example made of titanium coated with noble metals (IrO ₂ , Ir, Ta, Ru,. ..). In the case where several anodes and several cathodes are positioned in the tank (3), the anodes are electrically connected to each other by means of a bus-bar (BA) and the cathodes are electrically connected to each other using a bus-bar (BC). For the decarbonation of water, electrolysis of the water is carried out between the cathodes connected to the negative pole of the generator (2) via the bus-bar (BC) and the anodes connected to the positive pole of the generator ( 2) via the busbar (BA), as can be seen in Figure 2. The realization of this decarbonation of water generates both a deposit of calcium carbonate in the bottom of the tank (3), as well as on the cathodes (C).

In the context of the present invention, that is to say when an intense mixing by intense bubbling (according to the first variant), by intense recirculation (according to the second variant) or by intense mechanical stirring (according to the third variant) is operated, it has been found that, surprisingly and contrary to the teaching of the French patent application N ⁰ FR-A-2 731 420, it was not necessary to operate a prior step of constitution on the cathodes of a porous thin coating comprising calcium carbonate before use, which simplifies the implementation of the treatment process.

Specific reactors have been designed to test the implementation of the invention. These reactors are of the type shown in Figures 3 to 5.

In the decarbonation reactor (1) according to the invention, illustrated in FIGS. 3 to 5, the tank (3) is mounted on a frame (4) comprising a hopper forming the bottom of said tank (3).

The anodes (A) are fixedly positioned inside the tank (3) but the cathodes (C) are extractable because they are all supported by longitudinal supports (5, 5 '), themselves supported by a trolley ( 6).

Thus, simply lift the carriage (6), as can be seen in Figure 5, to extract in one operation all the cathodes (C).

To prevent any contact between the anodes and the adjacent cathodes, guide means (10) are provided. These guide means consist, on the illustrated version, of at least one vertical cylinder, and preferably two vertical cylinders, connected (s) rigidly to the carriage (6) and each cooperating with a vertical cylindrical tube, by sliding to inside said tube or tubes. Centering devices are also provided. All these means are provided outside the tank (3), to protect them from the action of the treatment. The extraction of the cathodes is made easier thanks to a removable electrical connector of the socket-lug type. This system makes it possible to connect and disconnect the connections easily manually and facilitates the extraction of the electrodes.

During the decarbonation treatment, the fluid is introduced through the orifice (9) located in the upper part of the hopper (4) and flows overflow by an evacuation located in the upper part of the tank (3).

The mouth (8) located at the lower end of the hopper allows the evacuation of calcium carbonate removed from the water and unhooked cathodes, this mouth also allows the emptying of the tank. During the decarbonation treatment, the fluid undergoes intensive mixing inside the reactor (1) and more precisely inside the tank (3).

FIGS. 6 to 8 illustrate different alternative or cumulative versions of the first variant embodiment of the intense stirring according to which said intense stirring means consist of at least one porous pipe (11, 11 ', 11 ", 11'") or pierced with micro-holes (illustrated by dots), said pipe being fed by a pump or a pressure reducer (not shown), for the formation of bubbles in the fluid, in particular air or nitrogen bubbles.

Air or nitrogen is introduced into the pipe via a bubbling orifice (12, 12 ', 12 ", 12'").

In the version shown in Figure 6, the hose (11) is wound around the water inlet pipe located longitudinally substantially horizontally, in the top of the hopper, perpendicular to the electrodes, about 15 cm from them.

The hose (11) is wound so that it forms at least one loop on itself per meter of water inlet hose. This pipe is of the type used for automatic watering of gardens.

In the version shown in Figure 7, the pipe (H ') is rigid and positioned on the entire inner periphery of the hopper, in its upper part, by welding a pipe inside the frame.

This version was tested using a compressed air source connected to a regulator set to deliver 0.5 bar with the following parameters:

Δ TH obtained without bubbling is 12 ° F, while Δ TH obtained with bubbling using an air flow of 25 L / Min, 10 times higher than the water flow, is 16.6 ⁰ F A gain of 4.6 ⁰ F was thus obtained, which represents nearly 40%.

This version was tested on a reactor equipped with a tank of 150 Liters of reaction volume with the following parameters and the following results were obtained at 30 days:

Table 1

The reduction thus goes from 10.8 ⁰ F without bubbling to 15 ⁰ F with bubbling. It is therefore increased by about 40% with bubbling.

Thus for the same abatement desired, the volume of the equipment can be reduced by about 30%. The pH is increased by bubbling and becomes identical to the initial value.

The evolution of the layer was followed over 2 months. At startup, the cathode plates are free of limescale. The voltage is 8.2V and the reduction 15 ⁰ F.

FIG. 8 illustrates the evolution of the voltage (V in Volts) and of the reduction (in ⁰ F) over a period of 60 days (on the abscissa) during which the bubbling test was carried out.

For about 30 days the voltage gradually increases until it reaches

11V. The reduction remains stable at 15 ^° F. Visually the thickness of the layer deposited on the electrodes increases and the layer becomes denser throughout this period. This increase in tension is usual. It is caused by the electrical resistance of the layer of limestone deposited.

From 30 days the voltage stabilizes at 11V and the abatement remains constant at 15 ⁰ F. Visually the layer of limestone continues to grow. The test was stopped after 60 days, the tension and depression no longer evolving.

Another test was carried out on a water of different characteristics (water N ⁰ 2). The results are in all respects similar. This effect is not related to the quality of a particular water:

Table 2 The gain in reduction is also 40%.

The following table gives the dimensions of the tank used for these two examples, as well as the values of the parameters of air flow with respect to the surface and the volume of the tank:

Table 3

In the version shown in FIG. 9, at least one rigid pipe (H ") is positioned substantially transversely in the top of the hopper, that is to say parallel to the electrodes, and / or at least one pipe (H '") rigid is positioned substantially longitudinally in the top of the hopper, that is to say perpendicular to the electrodes.

In the illustrated version, two rigid transverse pipes (H ") and two rigid longitudinal pipes (H '") are used. These pipes can communicate with each other at their intersection to facilitate the distribution of air or injected gas.

These pipes (H ", 11"') are fed by a rigid pipe not pierced or non-porous running along the inner periphery of the hopper, in its upper part. A particularly interesting effect of intense bubbling is that it allows degassing the CO ₂ dissolved in water. This CO ₂ is partly formed at the anode by the reaction HCO ^{3 "} - e- => ¹ AO ₂ + CO ₂ The dissolved CO ₂ acidifies the water, the intense bubbling thus makes it possible to raise the pH and therefore re-equilibrate the water in its calco-carbonic equilibrium.

The intense bubbling makes it possible to raise the pH from 0 to 2 points. By the same mechanism the intense bubbling allows the degassing of free chlorine from water. A certain concentration of free chlorine is profitable because it makes it possible to disinfect the water. The treatment favors the formation of free chlorine by oxidation of a part of the chloride ions present in the water following the reaction Cl ^" - e- => ¹ A CYl An excess of free chlorine is however harmful since it greatly accelerates the corrosion metals in the water The intense bubbling thus allows degassing and evacuating the free chlorine in the atmosphere so that the corrosivity of the water is acceptable The intense bubbling makes it possible to reduce the concentration of free chlorine from a factor of 5 to 20 to zero values.

In the absence of bubbling gas, the layer of limestone formed on the cathodes is porous, friable and powdery. Its density is 1.3 and a portion of the limestone formed falls to the bottom of the treatment tank. The most surprising effect of gas bubbling is that the layer of limestone formed on the cathodes is very dense, very hard and very compact. Its density is 1.9. It covers the entire cathode. Beads cover the edge edges of the cathode plates. Moreover, all the limestone extracted from the water remains attached to this layer. There is no deposit of limestone to evacuate from the bottom of the treatment tank. It is therefore all the more surprising to note that the adhesion of the limestone layer formed in the presence of gas bubbling on the cathode plates is very low, or almost zero. The holding of the limestone layer is in fact achieved by the total recovery of the cathode plates. These are taken in a limestone shell. If the edge beads are broken by hand, the limestone layer falls into heavy plates that can make the entire surface of the cathode. It is also possible to perform this stall by exerting a bending on the cathodes so as to break in a few pieces this limestone plate. Large slabs of limestone stand out then. Calcium carbonate does not adhere to the cathode at all. Once the shell is broken the plates of the cathodes are bare, with large shiny surfaces.

This behavior is very different from that observed during a treatment without bubbling gas or bubbling that is not intense inside the entire treatment tank because in both cases the layer of limestone formed on the cathodes adheres to the surface of the cathodes and the complete cleaning of the cathodes is very difficult to achieve.

These particular properties of the limestone obtained by intense gas bubbling can advantageously be used to ensure extremely simple and effective mechanical maintenance:

1. Extraction of the cathodes from the treatment tank;

2. Displacement of cathodes on a cleaning area; This cleaning area can be a simple waste bin; 3. Bending cathodes or breaking the edges of limescale shells by hand or with a small tool (small hammer, pliers); The limestone then falls into plates in the cleaning area where it can easily be recovered;

4. Refitting the cathodes in the treatment tank. The cleaning of the cathodes can also be carried out above the treatment tank. The limestone plates after cleaning the cathodes then fall into the treatment tank. They can then be evacuated at the bottom of the tank by the hopper.

The air supply flow rate is measured and adjustable (flow meter, pressure gauge, control valve).

This compressor or booster is connected to a pipe (11, 11 ', 11 ", 11'") serving as a gas nanny and placed at the bottom of the treatment tank, under the electrodes. The feeding of this nurse may be flexible or rigid. It can pass through the top of the tank or through the wall of the tank.

The nurse is located in the tank, under the electrodes at a distance of 50mm to 2000mm of the latter. It is composed of at least one flexible or preferably rigid tube. If this tube is rigid it ensures the positioning and the mechanical maintenance of the diffusers at the bottom of the tank. The nurse may also be composed of a network of tubes connected together.

Preferably, a single tube is positioned parallel to the length of the treatment tank. It can be positioned on a tank edge or preferably in the center to keep the symmetry of the installation.

Bubble diffusers are connected to this nurse. They can be circular or tubular. They can be pierced with slits 0.5 mm to 4 mm long or holes 0.3 mm to 3 mm in diameter.

Preferably, the "fine bubble" type diffusers used for the oxygenation of the purification basins will be used. These membrane diffusers will preferably be tubular so as to allow deposits to fall to the bottom of the tank without clogging the pores of the diffusers. The bubble diffusers are made of an EPDM elastomeric membrane pierced with slots 1.1 mm long and 0.3 to 3 mm wide. The air is blown through these diffusers and gives bubbles of 3 mm diameter on average (0.5 to 5 mm). The number of orifices per unit area is between 7 and 20 per cm ² .

These tubular "thin bubble" diffusers will preferably be arranged perpendicularly to a rigid and central nurse, on a horizontal plane, over the entire width of the treatment tank. The spacing between two diffusers can be between 200 mm and 800 mm.

Their number and exact location depend on the shape of the treatment tank to ensure maximum mixing for minimum airflow. FIG. 10 illustrates a first exemplary embodiment of the second intense stirring variant according to which said intense stirring means consist of two independent suction / discharge systems. Each system has a fluid extraction port (13), a fluid delivery port (14) and a pump (15) positioned between said exhaust port and said delivery port, pipes (16, 16 '). connecting each mouth to the pump.

It is of course possible to provide only one suction / discharge system comprising a single pump but several fluid extraction mouths and / or several fluid discharge mouths.

It is also possible to carry out a suction at the top of the tank and a discharge at the bottom of the tank.

The fluid extraction and fluid discharge mouths are located opposite, substantially at the same height in the top of the hopper, in the longitudinal end faces, about 15 cm below the electrodes.

Another intense recirculation stirring configuration R is illustrated in FIG. 11. In this configuration, the stirring is effected by recirculation on an intermediate storage tank called a buffer tank (30). The operation of this configuration is as follows:

The raw water (28) is discharged into the buffer tank (30). Recirculation R consists of pumping the water to be treated from this buffer tank (30) into the tank (3) and discharging into the same buffer tank (30) the treated water leaving the tank (3). ). The finally distributed water (32) not being taken from the tank (3), but from the buffer tank (30).

In order to improve the processing performance by intensive mixing, it is necessary that the recirculation flow rate R is 4 to 20 times greater than the average flow rate of treated treated water (32) at the outlet of the buffer tank (30). . The contact time for recirculating the water in the reactor, defined as the reactor volume divided by the recirculation flow rate, is then from 2s to 60s.

FIG. 12 illustrates the reduction measured as a function of the contact time with two different recirculation flow rates R, one at 5000 1 / h and the other at 2000 1 / h and without recirculation (SR). These measurements were made with a treatment tank of 26 liters, a buffer tank of 860 liters and a flow of raw water (28) from 0 to 138 1 / h.

In Fig. 12 the average contact time TCM is defined as the treatment volume divided by the raw water flow rate. The TCM without recirculation then represents the average contact time for the raw water that flows directly into the treatment tank and not into the buffer tank.

The following table presents the TCM gains needed to obtain a low or high abatement in case of recirculation (R) of low or high flow compared to the case without recirculation (SR):

Table 4 Thus:

- for small reductions (of the order of 20%) with high recirculation flows (192 times the volume of the reactor): gain of 60%;

- for small reductions (of the order of 20%) with low recirculation flows (77 times the volume of the reactor): gain of 29%;

- for high abatements (of the order of 36%) with high recirculation flows (192 times the volume of the reactor): gain of 23%;

- for high abatements (of the order of 36%) with low recirculation flow rates (77 times the volume of the reactor): gain of 0%.

As a result, the higher the recirculation flow rate, the higher the gain. The operation of the treatment is operated according to the quality of the water in the buffer. This quality is not constant as a function of the volume of the raw water supply and the design of the treatment tank and the buffer tank.

This operation is particularly recommended when a buffer tank is necessary, for example in case of need of very important but very punctual treated water or on semi-open cooling towers where the water can be treated as and when it is needed. concentrates.

The operation is safer because even in case of failure on the water treatment, there is no risk of water supply failure. If it is necessary to have a constant quality of treated water, it suffices to block the raw water supply flow at a constant value and to make sure that the water is perfectly mixed in the buffer. This operation is then indicated in all conditions.

FIG. 13 illustrates an exemplary embodiment of the third intense stirring variant according to which said intense stirring means consist of at least one mechanical means (17), in this case a propeller, driven in rotational movement inside the reactor (1) by a drive system (18) consisting of a reduction housing, a substantially vertical drive shaft and an electric motor, this motor being positioned under the hopper, outside the reactor.

The propeller here comprises four blades and has a diameter of about 25 cm. It is also possible to provide several propellers, driven, preferably each by the same engine, to reduce costs.

It is furthermore possible to use a stirrer, of the magnetic stirring-type consisting of a capsule of magnetic material, situated inside the tank (3), under the electrodes, and rotated by a magnetic plate loaded inversely. .

FIGS. 14 to 16 illustrate other exemplary embodiments of the third intense stirring variant according to which said intense stirring means are formed by forcing the circulation of the fluid inside the treatment tank (3) to follow a path having a plurality of baffles.

In the version illustrated in FIGS. 1 to 5, each anode / cathode pair can be considered as a mini-reactor. All these mini-tankers are assembled in the tank side by side, in parallel, which divides all the speed of the water between the plates. To ensure intense mixing, it is then possible to put the reactors in series so that the water passes successively and at high speed in the vicinity of all the cathodes. This can be achieved by circulating the water through a network of baffles preferably formed by all the electrodes. The electrode planes are preferably placed vertically to allow the deposition of limestone in the lower part.

In the example illustrated in FIG. 14, the fluid passes successively from above and below the electrodes during the treatment.

In the example illustrated in FIG. 15, the fluid passes successively through the right and left ends of the electrodes during the treatment.

In the example illustrated in FIG. 16, the fluid passes successively from above and below the cathodes and through the anodes during the treatment.

These three devices require water-tight cathodes, CP full cathodes. The first two devices require solid anodes AP which may consist for example of a titanium plate coated with noble metal oxide (DSA type anodes). The third device requires an expanded metal anode AD coated with noble metal oxide to which is added a porous membrane allowing the electric current to pass but a loss of charge when the water passes sufficient to force the passage of the water through the baffles.

FIG. 17 illustrates a cathode cleaning solution according to which electrolysis is operated for a few moments by inverting the polarities of the generator (2). As can be seen in this figure 17, during this cleaning phase the "cathodes" in stainless steel are connected to the positive pole of the generator (2) via the bus-bar (BC) and titanium "anodes" are connected to the negative pole of the generator (2) via the bus-bar (BA).

This first solution is of the type "anode-reversed cathode electrolysis", also called "anode-cathode reversal cleaning".

Tests have shown the effectiveness of polarity reversal for a limited time and at a given current density to clean all cathodes at once.

In particular, tests were carried out by first producing a limestone deposit on a stainless steel cathode forming a compact and smooth electrolysis layer in a tank of approximately 32 liters of tap water from the city of Paris (approximately 22 ⁰ F) under an electrolysis current of 4 amperes (ie J = 10 Am ^-2 ) and by permanent recirculation of this water for about 2 days.

In a first experiment, the generator being under controlled current of 4 A (ie J = 10 Am ^"2 ), the supply terminals were reversed a few moments (of the order of a few tens of seconds), which caused rapid detachment of large limestone slabs that have fallen to the bottom of the unit.

By raising the intensity to 10 amperes (ie J = 25 Am ^"2 ), an abundant gas evolution appeared and caused the detachment of the rest of the limestone.The cathode then appeared smooth and shiny.It was estimated, by weighing, at least about 90% the amount of limestone that could be recovered.

In a second experiment, the generator being under controlled current of 4A (ie J = 10 Am- ² ), the power supply terminals were inverted for 1 minute and the current was increased to 8 amps, which caused the detachment of a dense cloud of limestone powder which has slowly fallen to the bottom of the tank in the form of fine powder.

It is generally accepted that polarity inversion is detrimental to the life of the electrodes (in particular abrasion effect by release of H ₂ ); However, this can be tolerated for short periods. For example, a weekly inversion lasting less than fifteen minutes, at a current double that usually used, will lead to a negligible decrease in service life.

Life tests on cathodes and especially anodes having undergone up to 1400 cycles of inversion were also conducted and the surface state of the electrodes was observed after a different number of cycles. These tests showed that no degradation of properties was actually observed before 500 cycles. Due to one inversion per week, the electrodes can be stored for at least 10 years in the reactor before their replacement becomes necessary.

Another cleaning solution consists, for example, particularly for reactors without a large number of cathodes, to specifically introduce an electrode or two electrodes reported (E, E ') in stainless steel during the cleaning operation in the reactor (1), close to a cathode to clean and perform for a few moments (of the order of minutes) electrolysis between this (or these) electrode (s) reported (s) and the (or) cathode (s) to be cleaned, transforming this (or these) cathode (s) to be cleaned in anode time cleaning. A third cleaning solution called "cathode-cathode electrolysis cleaning" or "cathode-cathode inversion cleaning" consists of connecting one stainless cathode on two to the + pole and the other stainless cathodes to the pole - in order to clean the polarized electrodes positively; then reverse the current to clean the second half of the stainless steel electrodes. In this configuration the iridium oxide-coated titanium grids (the decarbonation anodes) are not electrically connected during cleaning and thus are not likely to be damaged during cleaning.

For the cleaning of even cathodes it is sufficient to make the cathodes pairs anodes by connecting them to a positive terminal of the generator and putting back cathodes odd cathodes, that is to say by connecting them to a negative terminal of the generator.

The cleaning of the cathodes is possible by electrolysis between two cathodes. It was performed on a weakly scaled cathode with a current density 1 to 3 times higher than the nominal density (8 A.nf ² ). The electrolysis between 2 cathodes requires a voltage approximately 2 times higher at current density identical to the standard conditions due to a doubled electrolyte thickness.

Whatever the cleaning solution inside the tank (3) chosen, during cleaning, the circulation of the fluid is preferably interrupted because during this phase the fluid is not effectively treated; however, during the polarity inversion the intensive stirring means are implemented to further accelerate the stall effect by inversion.

Experiments have shown that it is possible to halve the time required for stalling by using brewing means with identical current density.

Moreover, the circulation of the fluid is not necessarily interrupted during the cleaning because there are applications for which it is essential that the flow of water used is not interrupted, but for which it accepted that for short periods the water is not effectively treated.

In order to increase the cathode surface with respect to the anode surface, corrugated (C, C ") cathodes were made.

These cathodes have longitudinal waves over their entire surface, as can be seen in Figure 18, whose depth (p, p ') is at least 2 mm the the

and preferably at least 5 mm, whose distance (1,) from one wave to the other is at least 2 mm and preferably at least 5 mm and whose thickness (e, e ') is at least 0.5 mm.

The gain in cathode surface can thus be 50% to 75% and even up to 100%, even 120%.

The corrugations may, in cross-section, be U-shaped, as shown in FIG. 19, or V-shaped, as shown in FIG. 20, these shapes being reversible with respect to the following, or all in the same direction .

They can also be V-shaped with a cut bottom.

Tests were carried out with different current densities, for a surface increase of approximately 25% with U-shaped corrugations, inverted with respect to each other, of the type illustrated in FIG. is 10 mm, and the distance from one wave to another is 9.5 mm, for a thickness e 'of 0.5 mm. The results are summarized in the table below:

Table 5

As can be seen, at identical current intensity, that is to say for the same current consumption, the induced current density decreases with a corrugated cathode since the surface increases and the reduction increases.

FIG. 21 thus illustrates, for an identical contact time of 37 min, the evolution of the reduction ( ⁰ F) in ordinate with respect to the current density (in A / m ² ) on the abscissa, on the one hand for a corrugated cathode (solid line) and secondly for a flat cathode (dotted line) under the same experimental conditions. In addition, using lower current densities allows for lower power consumption.

Thus, as can be seen, to obtain a reduction of 12.5 ⁰ F, it suffices a current density of 6.5 A / m ² with a corrugated cathode, while it takes a current density of 7 A / m ² with a flat cathode to obtain the same reduction under the same conditions.

Experiments also show that a maximum reduction is obtained when an anode is centered between two cathodes, that is to say that the distance between the mean plane of an anode and an adjacent cathode is the same as the distance between this cathode and the next anode.

The present invention is described in the foregoing by way of example. It is understood that the skilled person is able to achieve different variants of the invention without departing from the scope of the patent as defined by the claims.

Claims

1. A method for treating a fluid and especially at least decarbonation of water in a reactor (1), said reactor (1) having at least one anode (A) connectable to a positive terminal of a generator of current (2) and at least one cathode (C) connectable to a negative terminal of said current generator (2), characterized in that said fluid undergoes intensive stirring inside said reactor (1).

2. Method according to claim 1, characterized in that said stirring is operated by injecting gas into said fluid at a flow rate at least substantially equal to that of the fluid and preferably from 2 to 10 times that of the fluid.

3. Method according to the preceding claim, characterized in that for a parallelepiped processing tank, the air supply rate is 3 to 10 m ³ / h of air per m ² of floor surface treatment tank, and from 5 to 20 m ³ / h of air per m ³ of volume of treatment tank.

4. Method according to the preceding claim, characterized in that the air supply flow rate is of the order of 7 m ³ / h of air per m ² of floor area treatment tank and the order of 12 m ³ / h of air per m ³ of volume of treatment tank.

5. Method according to any one of the preceding claims, characterized in that said stirring is operated by recirculation R performed by suction of said fluid at at least one location in said reactor (1) and discharge of said fluid to at least one other place in said reactor (1).

6. Method according to the preceding claim, characterized in that a recirculation R is operated between a buffer tank (30) and a treatment vessel (3) of said reactor and in that the raw water (28) is introduced into the buffer tank (30) and the treated treated water (32) is removed from the buffer tank (30).

7. Method according to the preceding claim, characterized in that the recirculation flow R is from 4 to 20 times greater, and preferably of the order of 10 times greater, than the average flow of treated treated water (32). ) at the outlet of the buffer tank (30).

8. Method according to any one of claims 5 to 7, characterized in that the recirculation flow rate R in liters per hour is at least 10 times, or even at least 50 times greater than the volume in liters of the treatment tank (3) from which is drawn the fluid and in which the fluid is discharged.

9. Method according to any one of the preceding claims, characterized in that said stirring is operated by at least one mechanical means such as an agitator or a propeller, driven by a movement inside said reactor (1).

10. Method according to any one of the preceding claims, characterized in that said intense mixing is permanently proportional to the fluid flow rate, the proportion may preferably vary, especially during a cleaning phase.

11. Method according to any one of the preceding claims, characterized in that at least one and preferably all cathodes (s) (C, C ") has (s) a corrugated surface.

12. Method according to the preceding claim, characterized in that the depth p of a corrugation and preferably of all the corrugations (s) is at least 2 mm relative to the mean plane of said cathode.

13. Method according to any one of the preceding claims, characterized in that the distance between the mean plane of a cathode (C) and the average plane of the adjacent anode (A) is between 10 and 60 mm and preferably between 20 and 30 mm.

14. Method according to any one of the preceding claims, characterized in that during a cleaning phase, said cathode (C) at least is connected to a positive terminal of a current generator and is subjected to a current intensity of in the range of 3 to 30 Am ² , in particular from 5 to 20 Am ² and preferably of the order of 10 Am ^-2 .

15. Method according to any one of the preceding claims, characterized in that during a cleaning phase, said cathode (C) at least is connected to a positive terminal of a current generator and is subjected to a current intensity of the order of 1 to 3 times the current intensity used to perform said treatment.

16. The method of claim 9 or claim 10, characterized in that during the cleaning phase a current is applied across said current generator which is connected to said cathode at least to be cleaned for a duration of the order of one to several minutes.

17. Method according to any one of claims 9 to 11, characterized in that intense stirring is caused inside said reactor (1) during cleaning.

18. A method according to any one of claims 9 to 12, characterized in that said cleaning phase is programmed to be performed automatically at regular intervals or on instruction of a measuring system.

19. Reactor (1) for treating a fluid and in particular at least decarbonating water, in particular for carrying out the process according to any one of the preceding claims, said reactor (1) comprising at least one anode (A) connectable to a positive terminal of a current generator (2) and at least one cathode (C) connectable to a negative terminal of said current generator (2), characterized in that it comprises intense stirring means inside said reactor (1).

20. Reactor (1) according to the preceding claim, characterized in that said intense stirring means consist of at least one pipe (11, 11 ', 11 ", 11'") porous or pierced with micro-holes, said pipe being fed by a pump or a pressure reducer, for the formation of bubbles in the fluid, in particular air bubbles or nitrogen.

21. Reactor (1) according to the preceding claim, characterized in that said micro-holes have a diameter less than or equal to 2 mm and preferably less than or equal to 1 mm.

22. Reactor (1) according to any one of claims 14 to 16, characterized in that said intense stirring means consist of at least one fluid extraction mouth (13), at least one mouth of fluid delivery (14) and at least one pump (15) positioned between said extraction mouth and said discharge mouth.

23. Reactor (1) according to any one of claims 14 to 17, characterized in that said intense stirring means consist of at least one mechanical means (17) such as an agitator or a propeller, and d a drive system (18) capable of driving said moving mechanical means within said reactor (1).

24. Reactor (1) according to any one of claims 14 to 18, characterized in that the current generator is capable of generating a current intensity of the order of 3 to 30 Am ² , in particular 5 to 20 Am ² and preferably of the order of 10 Am ^"2 in said (or said) cathode (s) (C).

25. Reactor (1) according to any one of claims 14 to 19, characterized in that at least one and preferably all the cathode (s) (C, C ") has (s) a corrugated surface.

26. Reactor (1) according to the preceding claim, characterized in that the depth (p, p ') of a corrugation and preferably of all the corrugation (s) is at least 2 mm.

27. Reactor (1) according to any one of claims 14 to 21, characterized in that the distance between the mean plane of a cathode (C) and the mean plane of the adjacent anode (A) is between 10 and 60 mm and preferably between 20 and 30 mm.

28. Reactor (1) according to any one of claims 14 to 22, characterized in that said cathodes (C) are positioned on supports (5, 5 ') facilitating their extraction.

29. Reactor (1) according to any one of claims 14 to 23, characterized in that it comprises means for guiding the electrodes (10), preferably positioned outside a tank (3). treatment.