RU2349682C2 - Electrolytic installation for obtaining sodium hypochlorite - Google Patents

Abstract

FIELD: chemistry, engines and pumps.

SUBSTANCE: installation for obtaining sodium hypochlorite contains not less than two flow-through electrolysis units, on whose case are placed several electrolytic cells, electrode module, composed of unipolar and bipolar electrode plates, unit for supplying water to dissolve table salt and container to dissolve the salt solution, which is connected to the pump - flow controller for supplying the salt solution into the first electrolysis unit, whose outlet is connected with the inlet of the second electrolysis unit. Outlet of the second electrolysis unit is connected with the inlet of the following electrolysis unit, and the outlet of the last electrolysis unit is connected to the reservoir for storing the sodium hypochlorite obtained, which is provided with a nozzle for releasing hydrogen emissions to the atmosphere and a nozzle for supplying sodium hypochlorite to the decontaminated water. Unit for supplying water for diluting is further connected with a pipe for supplying the initial salt solution to the first electrolysis unit and with the pipe, installed between the outlet for the electrolysis products from the first electrolysis unit and their entrance into the second electrolysis unit. Amount of unipolar and bipolar electrodes in the electrolysis unit are more than in the first one, and the distance between the electrodes is accordingly smaller.

EFFECT: increase in the reliability of the working of electrolysis unit, providing optimization of the electric regime in each of the electrolytic cells.

2 dwg

Description

The invention relates to electrochemistry, and in particular to electrolytic methods for producing hypochlorite solutions by electrolysis, and can be used to disinfect water and wastewater.

Among the known oxidative methods of water treatment, the leading place belonged to chlorination. The relative availability and low cost of liquid chlorine led to its widespread use in water treatment practice.

However, technological (rather complicated technology, special safety measures during transportation, storage and use, etc.), economic (maintenance of the reagent farm and additional staff of maintenance personnel), environmental (chlorine toxicity and the high probability of the formation of toxic, mutagenic during water treatment and carcinogenic halogen-containing organic compounds) aspects of the use of liquid chlorine stimulated the search for a more economical technical solution.

Currently, chlorine-containing reagents are used as a substitute for liquid chlorine, which are safer and less toxic than liquid chlorine.

In recent decades, a solution of sodium hypochlorite NaClO containing active chlorine, which is equivalent to pure chlorine in its disinfecting and sterilizing qualities, has been increasingly used all over the world. Its use practically removes all dangerous and harmful production factors inherent in the use of liquid and gaseous chlorine - a potent toxic substance.

In this case, the sodium hypochlorite solution obtained by the electrochemical method (grade E according to TU 6-01-29-93) is the cleanest and least toxic product (hazard class 4 according to GOST 12.1.007-76) and has the highest disinfection efficiency.

The advantages of electrolytic sodium hypochlorite as an effective bactericidal agent, the simplicity and reliability of electrolysis plants, as well as the interest of consumers in the application of a safe electrochemical method of water disinfection, have led to the creation of a large number of electrolyzers that are most diverse in design.

Technological schemes of electrolysis plants operating on sodium chloride solutions can be either flowing or periodic with a recirculation system.

The main difference between the operational parameters of flow electrolysers and the parameters of periodic electrolyzers is that in the first case, the electrolysis process can be considered stationary, time-independent. Moreover, if the flow rate of the brine supplied to the electrolysis, and the current load on the electrolyzer remain constant, then the concentration of the sodium hypochlorite solution withdrawn from the electrolyzer remains unchanged.

In batch cells, the concentration of sodium hypochlorite depends on the time elapsed since the start of the electrolysis.

In the case of the use of periodic electrolyzers, maintenance personnel should spend much more time on the organization of the process due to the fact that he is forced to fill the recirculation system with a solution several times a day and drain sodium hypochlorite from them.

A known installation for producing sodium hypochlorite, in which mineralized groundwater containing sodium chloride, is supplied from a well 1 through a pipe 2 to a distribution tank 3. From a tank 3, mineralized water flows by gravity to a flowing electrolyzer 4. A predetermined flow rate of mineralized water supplied to the flowing electrolyzer 4, is installed by valves 5 and is controlled by a flowmeter 6. Flowing electrolyzer 4 contains a tank 10 with inlet and outlet pipes located on its opposite walls Kami 11 and 12, respectively. Electrode cassettes 13, perpendicular to the sodium chloride stream and parallel to each other, are installed in the container 10, each of which consists of a group of vertical plate electrodes 14. The plate electrodes 14 are connected in a bipolar circuit with current supply to the end electrodes 14 of each electrode cassette 13. The electrode cassettes 13 are connected in parallel to a common stabilized power supply 15.

In the cell 4, electrolytic decomposition of an aqueous solution of sodium chloride occurs, the result of which is the formation of sodium hypochlorite and the evolution of hydrogen. A solution of sodium hypochlorite of a predetermined concentration from a flowing electrolyzer 4 by gravity enters the buffer tank 7, from where it is pumped to a storage tank 9. From a reservoir 9, a solution of sodium hypochlorite by gravity enters the entry points for water disinfection. (RF patent No. 2100483).

The main disadvantage of this electrolysis plant is its limited use, as it is intended for the production of sodium hypochlorite from weakly concentrated solutions containing 1.5-8.0 g / l sodium chloride; therefore, it cannot be used for the electrolysis of concentrated sodium chloride solutions.

In the case of a solution from an aqueous solution of sodium chloride, the initial solution should contain at least 30-40 g / l sodium chloride, and, to increase the yield of chlorine, cascade inclusion of electrolyzers is used.

Known electrolysis installation "Sea clor" company "De Nora" for the production of sodium hypochlorite from sodium chloride. A concentrated brine is prepared in the salt dissolving tank, which is then diluted to a predetermined concentration of 25-30 g / l in the intermediate tank. The solution is pumped by a metering pump through a mesh filter into the electrolyzer or sequentially into a series of electrolyzers. The sodium hypochlorite obtained by electrolysis is collected in a storage tank. Electrolysis gases are removed after each electrolysis cell into a gas separator, and then into the atmosphere. Sodium hypochlorite in the treated water is supplied by a metering pump.

Power supply of electrolyzers is carried out from the rectifying unit.

The installation is equipped with automation elements that turn off the rectifier unit in violation of the technological mode of operation of the installation. Periodically, as the cathodes are overgrown with deposits of hardness salts, the electrolyzer is washed with a closed acid loop. (G.L. Medrish et al. Disinfection of natural and wastewater using electrolysis. M: Stroyizdat. 1982, p.31).

The content of active chlorine in the finished product is 5-6 g / l. Higher chlorine concentrations (up to 8 g / l) can be achieved by partial recirculation of the solution, which increases energy consumption.

To increase the yield of the liquid-phase target solution obtained by electrolysis of the initial salt solution, after the first stage of electrolysis of the initial highly concentrated salt solution, include the subsequent electrolysis of the solution obtained in the previous stage when diluted with water (RF patent No. 2151120).

The implementation of this method is given in the patent of the Russian Federation No. 2134733.

The essence of the device lies in the fact that it contains a housing with parallel electrodes installed in it, placed between two partitions located along a series of parallel electrodes, the last of which are connected to current leads and are monopolar, and intermediate ones are bipolar. The electrodes divide the casing into a primary chamber in series with each other, an electrolysis chamber and a finished product collection chamber, as well as a device for supplying an initial electrolyte solution to the casing and an opening in the casing for draining the finished product, with a partition separating the primary chamber from the electrolysis chamber, made in the lower part of the perforated, the partition separating the electrolysis chamber from the collection chamber of the finished product is made with an overflow hole in the lower part to which ene drain pipe installed vertically in the finished product collection chamber and made open at its upper end, to electrolyte supply device installed at the top of the electrolysis chamber and the primary chamber is provided disposed in its upper part a device for the water supply.

According to the author of the invention, due to the oncoming liquid flow, the speed of movement of gas bubbles relative to the surface of the electrodes is reduced, which contributes to a more uniform flow of electrolysis in the volume of the electrolyte, the preservation of electrode electrode layers, and also provides the contact time of the gas bubbles with each other, sufficient for their enlargement. As a result, the shielding of the electrodes by gas bubbles is reduced. These factors contribute to increasing the efficiency of electrolysis and increasing the yield of the finished product.

However, given that the water entering the first chamber to dilute the electrolyte plays the role of a water trap, gas bubbles entering it are problematic. The design of the installation to maintain the operation mode of each chamber requires a certain ratio of flows: water for dilution and electrolyte, the mass of electrolyte and the mass of the solution in the drain pipe, etc. All these factors affect the yield of sodium hypochlorite and the concentration of active chlorine in it, which complicates the operation of the installation.

The closest technical solution to the proposed one is the OSEC installation for the production of sodium hypochlorite by WALLACE & TIERNAN.

The electrolysis plant is protected by UK patent No. 2068016A with a priority of July 1, 1980 (by the date of the convention patent application in England), but the invention itself was created in the USA, protected by US patent No. 4248690 with priority June 28, 1980, published February 03, 1981 g.

The electrolysis installation includes four series-connected electrolysers consisting of several electrode cells (presumably three).

An initial salt solution is introduced into the first cell, and water in equal volumes is introduced into the second and third chambers through the nozzles, and the electrolysis process in the last cell is completed by ten-fold dilution of the initial salt solution, which contains 26.4 wt.% Sodium chloride (approximately 300 g / l), i.e. dilution with water in the last electrolyzer is 1:10 (30 g / l sodium chloride). Water is supplied to dilute the concentrated brine of sodium chloride and electrolysis products through a water softener. After the concentrated brine is dissolved to the initial concentration in the saturator, the solution is fed through the brine metering pump to the first electrolytic cell of the first electrolyzer. The obtained sodium hypochlorite from the outlet of the last (fourth) electrolyzer enters the storage tank, which is equipped with a pipe for the release of hydrogen by means of a blower into the atmosphere and a pipe for supplying sodium hypochlorite through a metering pump for disinfection of water.

The removal of hydrogen from each cell is carried out separately and through the hydrogen collector is introduced into the finished sodium hypochlorite line.

The power supply of each cell is carried out from the rectifier. The installation is controlled by an automation system.

Salt consumption per 1 kg of chlorine equivalent is 3.0-3.9 kg, depending on dilution with water, salt quality and temperature.

The disadvantages of the known technical solutions include:

- the difficulty of ensuring the tightness of electrolyzers due to the presence in the body of fittings for supplying water for dilution and removal of gaseous products of electrolysis;

- increased energy consumption, because as the electrolyte concentration decreases, it is necessary to change the electric mode or the design of the electrode assembly of the electrolytic cells, and this is not carried out in this invention.

The technical problem solved by the invention is the elimination of the above disadvantages in order to increase the reliability of the electrolytic cells and to keep the potential value of the electrolytic cells constant during all stages of electrolysis.

The technical result is achieved due to the fact that in the known electrolysis installation for the production of sodium hypochlorite, comprising several, at least two flow-through electrolyzers, in the housing of which are placed several electrolytic cells with an electrode module consisting of monopolar, connected to a power source, and bipolar plate electrodes mounted in parallel at a certain distance from each other, a water supply unit for diluting sodium chloride in the tank, and for dilution electrolysis products in the process of its implementation, the capacity for preparing a solution of sodium chloride is connected to a metering pump for supplying a solution of sodium chloride to the first cell, the output of which is connected to the input of the second cell, the output of the second cell is connected to the input of the subsequent cell, and the output of the last cell to the reservoir for storing the obtained sodium hypochlorite, and the tank is equipped with a pipe for the release of hydrogen into the atmosphere and a pipe for supplying sodium hypochlorite for disinfection during Changes and additions have been made, namely:

- the water supply for dilution is additionally connected to the pipeline for supplying the initial solution of sodium chloride to the first electrolyzer;

- and with a pipeline between the outlet of the electrolysis products from the first electrolyzer and their entry into the second electrolyzer;

- the number of monopolar and bipolar electrodes in the second cell is greater than in the first;

- the distance between the monopolar and bipolar electrodes in the second cell is correspondingly smaller than in the first cell;

- the design of the electrolytic cells included in the installation, starting from the second electrolyzer, is similar.

The introduction of preliminary dilution of sodium chloride solution to 100-120 g / l NaCl in the pipeline eliminates the intermediate capacity and allows you to optimize the electrical mode of the first electrolyzer without additional dilution of the initial sodium chloride solution inside the first electrolyzer.

Additional dilution of the electrolyte containing electrolysis products after the first electrolysis cell reduces the concentration of the solution to the optimum (30-40 g / l), therefore, dilution of the electrolyte after the second electrolysis cell is not required.

Improving the reliability of the electrolytic cells is achieved by eliminating the fittings for water supply and removal of gaseous products of electrolysis, which together with the electrolyte in transit enter the storage tank for sodium hypochlorite.

The inversely proportional dependence of the total area of the electrodes and the current density of the first and subsequent electrolyzers makes it possible to maintain a constant potential on all electrolytic cells of the electrolysis cells and reduce energy consumption, increasing the efficiency of the installation by ~ 15%.

The identity of the design of the second and subsequent electrolyzers facilitates their manufacture and replacement, and also allows you to reserve the number of electrolyzers in the installation, because on the basis of experimental data, it was found that the best results in the yield of active chlorine are achieved with 4-6 electrolyzers.

Figure 1 shows a flow chart of the treatment of water with sodium hypochlorite; figure 2 - flowing electrolyzer to obtain sodium hypochlorite from a solution of sodium chloride.

Figure 1 shows the node 1 of the water supply for diluting concentrated brine of salt located in the tank 2, filter 3, metering pump 4, controlled valves 5 installed on additional pipelines 6 and 7, electrolyzers 8, 9, and all subsequent electrodes have the designation 9, because their design is the same. The electrolytic cells are powered from the rectifier 10. The output of the last cell is connected by a pipe 11 to a buffer tank 12 for storing the finished sodium hypochlorite. The buffer tank is equipped with a pipe 13 for discharging gaseous products of electrolysis (hydrogen) and a pipe 14 for supplying sodium hypochlorite to disinfect water.

From figure 2 it can be seen that the flow electrode consists of a housing 15 having nozzles 16, 17 for introducing an initial solution of sodium chloride and outputting electrolysis products, respectively. Electrolytic cells 18 are placed inside the housing (four are shown in FIG. 2, but may be more), an electrode module 19 formed by plate-shaped, parallel-mounted monopolar electrodes 20 and bipolar electrodes 21, wherein the monopolar electrodes are connected to the corresponding pole of the rectifier 10, forming an anode and cathode. Between the electrodes are insulating gaskets 22, and the electrodes of each electrolytic cell are fastened with ties 23.

The installation works as follows.

Water from the unit 1 of its supply to the dissolution of table salt enters the tank 2, in which there is a concentrated brine of table salt. Salt solution through a filter 2 is pumped by a metering pump 3 to the supply line to the first electrolyzer 1. Water is supplied to dilution unit 1 via line 6 to the same line to dilute the initial sodium chloride solution to 100-120 g / l. The water flow is regulated by valve 5 and is controlled by a flow meter (not shown in Fig. 1). In the first electrolytic cell 8 and subsequent electrolytic cells 9, electrolysis of a solution of sodium chloride or products of the previous electrolysis takes place. All electrolytic cells are flowing and consist of a housing 15 having an inlet pipe 16 through which sodium chloride solution is supplied with a given concentration, and in the electrolytic cells 9 are products of the previous electrolysis. Four electrolytic cells 18 and an electrode assembly 19, including monopolar 20 and bipolar 21 plate electrodes located in parallel at a certain distance, are placed in the housing 15.

Monopolar 20 electrodes are connected to the rectifier 10, forming an anode (+) and a cathode (-). On the bipolar 21 electrodes, due to the flow of electrolyte between them, anodes and cathodes are also formed. When electric current is passed through electrolyte solutions, redox reactions occur.

In this case, when sodium chloride solution is used as the electrolyte, the essence of the process is as follows.

At the anode there is a discharge of chlorine ions (oxidation process): 2Cl- = Cl ₂ + 2-.

The released chlorine dissolves in the electrolyte (NaCl) with the formation of hypochlorous and hydrochloric acids: Cl ₂ + H ₂ O = HClO + HCl.

At the cathode, a discharge of water molecules occurs (reduction process): H ₂ O + e- = OH- + H +.

After recombination, hydrogen atoms are released from the solution in the form of a gas, while OH– ions remaining in the solution form alkali near the cathode with Na + ions.

Due to the mixing of the anolyte with catholyte, hypochlorous acid reacts with alkali to form sodium hypochlorite: HClO + NaOH = NaClO + H ₂ O.

If the entire amount of alkali formed at the cathode will flow to the anode, then the electrolysis process proceeds only with the formation of a solution of sodium hypochlorite.

The resulting sodium hypochlorite substantially dissociates with the formation of ClO- ions, which are capable of further anodic oxidation with the formation of the chlorate ion ClO ₃ -:

6ClO- + 6OH- -6- = 6Н ₂ O + 4Cl- + 2ClO ₃ - + 1,5O ₂ .

The concentration of ClO- ions significantly affects the further course of electrolysis. ClO– ions are discharged at much lower anode potentials than Cl– ions; therefore, even at low concentrations of sodium hypochlorite at the anode, a joint discharge of Cl– and ClO– ions begins.

The resulting sodium hypochlorite solution is sufficiently stable and can be stored for a long time without significant decomposition under certain conditions.

Obtained in the first electrolyzer 8, the electrolysis products through the outlet pipe 17 enters the pipeline 7 connected to the dilution unit 1. In it, the products of the previous electrolysis are diluted about three times, so that the concentration of chlorides in them is at a level of 30 g / l and enters the second the cell 9, and from it the reaction products enter the third cell, etc.

Accordingly, the current density in the first electrolytic cell 8 can be maintained in the range of 500-900 A / m ² , and in subsequent electrolytic cells 9, approximately two times less, i.e. 300-500 A / m ² . This is achieved by changing the number of monopolar and bipolar electrodes in such a way that the total area of the electrodes is proportional to the current density in them, i.e.

Sodium hypochlorite together with gaseous products through line 11 enter the buffer tank 12 for storing sodium hypochlorite. Using a blower (not shown in FIG. 1), hydrogen is separated from the sodium hypochlorite through a nozzle 13 and released into the atmosphere.

Sodium hypochlorite through the pipe 14 is sent to disinfect water.

The advantages of the invention are:

- to increase the reliability of the cells due to the exclusion of their depressurization;

- the voltage remains constant on all electrolytic cells of the electrolytic cell;

- optimization of electric mode;

- increase the extraction of chlorides of their initial solution of sodium chloride.

At present, individual elements of the electrolysis plant are being manufactured and at the end of this or the beginning of next year it will be commissioned.

Claims (1)

An electrolysis installation for the production of sodium hypochlorite, including at least two flow-through electrolyzers, in the housing of which several electrolytic cells are placed, an electrode module consisting of monopolar connected to a power source and bipolar plate electrodes mounted in parallel at a certain distance from each other, node water supply for the dilution of sodium chloride, which is in the container for preparing a solution of sodium chloride, which is connected to a metering pump solution salt in the first cell, the output of which is connected to the input of the second cell, the output of the second cell is connected to the input of the subsequent cell, and the output of the last cell is connected to the storage tank for the obtained sodium hypochlorite, which is equipped with a pipe for the release of hydrogen into the atmosphere and a pipe for supplying sodium hypochlorite to disinfection of water, characterized in that the site of supplying water for dilution is additionally connected to the pipe supplying the initial solution of sodium chloride in the first an electrolyzer and with a pipe installed between the outlet of the electrolysis products from the first electrolyzer and their entry into the second electrolyzer, the number of monopolar and bipolar electrodes in the second electrolyzer is greater than in the first one, and the distance between the electrodes is correspondingly smaller.

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