CA1263095A

CA1263095A - Method and apparatus for disinfecting water by hypochlorite produced by electrochemically converting salt

Info

Publication number: CA1263095A
Application number: CA000477070A
Authority: CA
Inventors: Peter Rossler; Peter Fabian; Manfred Gundling
Original assignee: Heraeus Elektroden GmbH
Current assignee: De Nora Deutschland GmbH
Priority date: 1984-03-22
Filing date: 1985-03-21
Publication date: 1989-11-21
Also published as: DE3410489A1; ES8606207A1; ZA852090B; DE3410489C2; ES540968A0; DK128385D0; DK128385A; AU4018585A; EP0155479A2; EP0155479A3

Abstract

A B S T R A C T

In known processes and corresponding apparatus for water disinfection/sterilization, a hypochlorite solution is produced electrochemically by means of an electrolytic cell and dosed to the water to be disinfected. The invention is aimed at inexpensive production, under specific conditions, of a hypochlorite solution using such process and apparatus, and at the provision of a process and an apparatus particulary suitable for the production of small amounts of a hypochlorite solution in an intermittent operation. To this end, the method of this invention provides that water that is to be mixed with stocked-up brine is taken directly from a conduit in which a constant pressure is maintained, and the electrochemically produced hypochlorite solution is proportioned directly to the water being disinfected.
In an apparatus for carrying out the process, the electrolytic-cell supply line is connected to a conduit in which a constant pressure is maintained. In order to open or close the conduit, a shutoff device controlled by an electric auxiliary means is provided. The hypochlorite solution produced in the electrolytic cell is fed from the electrolytic cell through a dosing line directly to a dosing point in the conduit that is passed through by the medium to be disinfected.

Description

~_2~309~

METHOD AND APPARATUS FOR DISINFECTING OR STERILIZATIO~
OF WATER

This invention r~lates to a method for water disinfection/sterilization and to an apparatus for ~arrying out the method.
Weak aqueous solutions of hypochlorites are used for disinfection/sterilization of waters such as drinking water, municipal water (of genera~ use), bathing water, cooling water or wastewater. Such hypochlorite solutions also find the u-qe in medicine for sterilization of rubbers and plastic as well as in electroplating for decontamination of cyanide - containing liyuids.
Sodium hypochlorite solution is preferred in most I5 cases since sodium hypochlorite is not only a strong ~ut also an odorless oxidizing agent, harmless in concentrations required for disinfection purposes and moreover, it is marked by its immediate and long-lasting chemical action.
Such a sodium hypochlorite solution can b produced and proportioned using an electrolyzer sold by W.C. Heraeus GmbH. That apparatus comprises an electrolytic cell having a self-cleaning electrode set like the one described in UOS. Patent 4,422,919 (Fabian 25 et al.) issued December 27, 1983, entitled ELECTROLYTIC
CELL, and also other components, viz. stock containe~s for fresh water, brine and electrolyte hypochlorite, a number of dosing pumps, an energy supply unit, and an ~el ctronic control unit.
Two storage containers equipped with float valves are filled with water~ Neutral common salt is added to one of the two ~torage containers whereby a brine of predetermined concentration is produced. The brine and water are drawn from ~he two containers by a pump at a desired ratio. The actual salt concentration is measured at a measuring point and then the solution is fed to the .,~,, ~ > i., j, ., ~ ~

~_ 3 _ electrolytic cell where it is converted electroche~ically to sodium hypochlorite. The sodium hypochlorite solution t~us produced is stored in a container and is supplied therefrom by means of a dosing pump, in a re~uired amount, to the water to be disinfected. HDCS electrolyzers of that kind have proved very userul for water disinfection, particularly for disinfecting drink water at large construction sites, bathing water in open swimming pools, utility water for the food industry, cooling water for power stations, and wherever it is necessary to prepare a large quantity of sodiumhypochlori~e solution since the costs of such an electrolyzer are of minor importance in such a case. The situation looks entirely di~ferent, however, where only sMall amounts of -the hypochlorite solution are needed, especially when the demand is not continuous, that is, does not occur every day. This situation is common e.g. for small private swimming pools of or those located close to a water supply. Besides, the too high apparatus costs, also the space requirements grow relatively high due to a large number of storage containers and pumps involved. Moreover, hypochlorites are not particularly stable when exposed to light and decompose relatively quickly. Thus, it is impossible to store large quantities of those compounds for longer periods of time.
The object of the present invention is to provide a process and an apparatus for production of a hypochlorite solution, the process and the apparatus enabling the economical production of the solution without extensive expenditures, specific requirements being met, and expecially suitable for the production of small amounts of a hypochlorite solution in an intermittent operation.
~ccording to one aspect of the invention! a method is provided ~or disinfection/steriliæation of _ 4 - ~3~5 water, in which predetermined amounts oE salt containing brine and water are mixed at a desired ratio and wherein the thus obtained aqueous solution whos~ salt concentration is measured, is electrochemically transformed to a hypochlorite solution, which hypochlorite solution is then added in metered fashion to the processed water, the water to be mixed with the predetermi-ned amount of salt containing brine being drawn directly from a pipe line which is under a constant pressure, and the electrochemically produced hypochlorlte solution being added in metered fashion directly to the water to be disinfected, wherein the step of measuring the salt concentration of the solution passing through a shunt to the pipeline is effected in a salt concentration measuring cell after the passage of the aqueous solution through an adjustable flow metering device but before the electrochemical transferring of the aqueous solution.
According to another aspect of the invention, an apparatus is provided for the production of a hypochlorite solution from water containing small amount of salt, the apparatus being operable on a shunt of a conduit and comprising an electrolytic cell, a saLt solution container being in fluid communication therewith via a pump and an interconnected chloride concentration analyser wherein the electrolytic cell is at its outlet end in fluid communication with a dosage point, a supply means for supplying water to th~ salt solution conveyed from the solution container, and an electronic/electric control and energy supply unit, wherein the supply means is fed from a conduit in which a constant pressure is maintained, the conduit being open or closed by means of a shutoff device controlled by an electric supplementary control means, wherein the electrolytic cell is supplied to a dosage point of the conduit from the electrolytic cell through a direction dosing line.
The process does not comprise any expensive intermediate steps. In order to mix water with the stocked-up brine, the water is taken directly from a conduit in which a constant pressure is maintained. The hypochlorite solution produced electrochemically is proportioned directly to the water being disinfected. The ~2~

hypochlorite so]ution is produced only in such amount which is instantly needed and used. No intermediate storage of the solution is invo]ved. The apparatus can be used in all cases where it is possible to install a circuit in which a constant pressure is maintained. The capacity of the apparatus can be adjusted virtually steplessly, within its limits, to the demands of a receiving device. The amount of the hypochlorite solution produced in the electrolytic cell is merely such as to correspond to the flow rate through the conduitO The solution is supplied directly to the receiving point at a required delivery rate (per unit of time) without any other proportioning device. The basic operating parameters of the apparatus, like the amount of current, Amps, supplied to the electrolytic cell, the rate of flow through the cell, l/h, and salt cOnCentrAtiOn, g NaCl/l can be controlled and adjusted.
For system monitoring purposes, it is prudent to provide an adjustable flow measuring device in the supply line that lead~ to the electrolytic cell, the device being located before a chloride concentration analyser and after the inlet point of the brine (taken from the brine container) to the supply line. Such analyser can be installed at this place since the amount of water fed to the electrolytic cell corresponds to the dosage quantity supplied to the conduit.
Preferably, the regulated direct-current supply of the electrolytic cell, the electric shutoff device in the water feed iine as wel~ as the brine containar pump adapted to operate as a dosing pump, are switched on centrally by the auxiliary ~ontrol unit. Consequently, all the electrical components of the apparatus are energized only when a hypochlorite solution is to be proportioned to the water being disinfected.
In order to install the electrolytic apparatus to co-operate automatically with a receiving device, e~g. a ~2~i3~

water intake, it i8 advantageou~ to provide 2 flow monitor with an impulse transmitter, which component, can set the electrolytic cell in operation via the electric/electronic control system to start the production of required amount of hypochlorite solution in an impulse-dependent mode.
When the apparatus is connected into a circulation line, it can be controlled by the already existing control device of the circulating pump and no separate, extra components are necessary.
A direct control of the electrolytic cell, depending on the instantaneous value of chloride concentration in the supply line, is possible through a direct electric connection of the chloride concentration analyser with the transformer/rectifier unit.
In order to facilitate the maintenance of the apparatus on one hand and also to keep space requirements for installation of the apparatus on the site to a minimum, it is helpful to arrange the components of the apparatus, viz. electrolytic cell, chloride concentration analyser~ shutoff device, flow measuring and controlling device and energy supply control unit, on a vertical mounting plate, for instance one installed on a wall near the receiving device. Thus, little space, especially little horizontal surface will be taken by the apparatus.
Moreover, not only are all the components rsadily accessible for control and regulation purposes but they can also be easily maintained and their operation supervised.
The invention is explained in more detail by the following description of on~ oE its embodiments in conjunction with a drawing which shows schematically an electrolytic apparatus with electric and hydraulic connections, the apparatus being installed and operated on a shunt of a conduit.

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The electrolytic apparatus is of a co~pact design. Its essential components, i.e. the electrolytic cell 1, an energy supply unit embodied by a transformer/
rectifier 2, a supplementary control unit 3 as well as measuring and control components installed on the supply line 4 of the electrolytic cell, e.g. a reducing valve S, a solenoid valve 6, an overflow valve 7, a flow measuring and oontrolling device 8 and a salt concentration mea ~ ~ cell or analyser 9 are visibly arranged on a mounting plate 10 which is indicated in the drawing on an enlarged scale as c~mpared to the cell 1. The plate 10 can be mounted vertically, e.g. on a wall, using boreholes 11. The supply line 4 is connected to a tapping 12 of a pipe line 13 through which the medium to be disinfecte~ lS pumped in the flow direction indicated by an arrow 14. A flexible pipe may be utilized as the supply line 4 between the reducing valve 5 and the tapping point 12, while the part of the supply line 4 between the reducing valve 5 and the inlet end 15 of the electrolytic cell 1 consists, preferably, of rigid chlorine-resistant plastic pipes that can be joined using commercial PVC adhesives. The liquid taken from the line 13 is fed through the reducing valve 5 tnat lS ~et on a f~ ed pressure, and through the solenoid valve 6 adaped to open and close the su,vply line 4, to the flow measuring and control device 8. Moreover, a part of the liquid branches off between the solenoid valve 6 and the flow control device 8 and is led to a brine container _ that is automatically filled with water through a float valve lB~ 5alt tablets 19, for instance sodium chloride tablets are dissolved in water that fills the container 17. The brine 20 that is thus stocked up in the brine container 17 can be proportioned by means of a pump 21 mounted on the container 17, in this case a dosing pump, through a delivery conduit 22 to the supply line 4 before the inlet to the flow measuring and controlling device 8.

The outlet end 23 of the electrolytic cell 1 is connected through a flexible dosing line 24 to a dosage point 25 on the circulating line 13, the point 25 located behind the tapping point 12 as viewed in the direction of flow.
Between the tapping point 12 and the dosage point 25 is provided an orifice plate 2~ in the circulating line 13 in order to create a pressure difference between the tappin~
point 12 and the dosage point 25. The supply line 4 may also be connected to a fresh-water line 27 through a shutoff/check valve 28 instead of being connected to the tapping point 12. The fresh-waterline 27 indicated by a broken line in the drawing.
The entire apparatus is centrally energi~ed and controlled by the transformer/rectifier unit 2 and the supplementary control unit 3. The supplementary control unit 3 compriseq a mains connection 29 through which the dosage pump 21 is energized simult~neously. The supplementary control unit 3 is connected to the dosing pump 21 via an impulse line 30, to the solenoid valve 6 via a power-and-control line 31, and to the transformer/
rectifier through a supply line 32. The transformer/
rectifier unit 2 may be provided with a separate power line 33, but its mains supply may also be effected through the central mains connection 29. The elèctrolytic cell 1 is energized from the transformer/rectifier unit through the leads 34 indicated by dash-dotted lines in the drawing.
In operation, the saturated salt solution from the brine container 17 is proportioned to the water that is fed through the supply line 4. The water stream loaded with a predetermined amount of the concentrated salt solution flows then through the salt concentration analyser 9 to the electrolytic cell 1 in which the salt is partly converted to hypochlorite. The thus produced hypochlorite solution is then fed directly to the circulating line 13, i.e. to the water being treated or , . .

~6;3~
_9_ disinfected. Normally the supplementary control unit 3 of the electrolytic apparatus is coupled with the control unit of the circulating pump (not shown) of the line 13. The supplementary control uni~ 3, as explained above, energizes and controls the adjustable transformer/rectifier 2, the solenoid valve 6 and the dosing pump 21, whereas the transformer/rectifier 2 energizes the electrolytic cell 1 only and i~, on its part, controlled directly by the salt concentration analyzer 9. A power divider 35 in the transformer/rectifier 2 is coupled with the frequency-controlled electromagnetic dosing pump 21 through the supplementary control 3 via a frequency converter, so that the amount of concentrated brine supplied by the pump 21 through the pumping (delivery) line 22 is proportional to the supply current for electrolysis.
lS The txansformer/rectifier 2 may be controlled by a commercial redox- or C12- measuring and controlling device ~5.
~o this end, the apparatus shall be shifted to automatic operation with a hand/auto selector switch 37. In suah automatic operation mode, the apparatus works at its parameters fixed at 100% and will be switQhed on and off by the redox- or Cl2 measuring and controlling device 36.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Method for disinfecting/sterilization of water, in which predetermined amounts of salt containing brine and water are mixed at a desired ratio and wherein the salt concentration of the resulting aqueous solution is measured, in a salt concentration analyzer and the solution is electrochemically transformed to a hypochlorite solution, which hypochlorite solution is then added in metered fashion to the processed water, the water to be mixed with the predetermined amount of salt containing brine being drawn directly from a pipe line which is under a constant pressure, the electrochemically produced hypochlorite solution being added in metered fashion directly to the water to be disinfected, wherein the step of measuring the salt concentration of the solution passing through a shunt to the pipeline is effected in a salt concentration measuring cell after the passage of the aqueous solution through an adjustable flow metering device but before the electrochemical transformation of the aqueous solution in an electrolytic cell energized by a transformer/rectifier, said transformer/rectifier being controlled directly by said salt concentration analyzer.

2. An apparatus for disinfecting water which comprises an electrolytic cell making a hypochlorite solution by the electrolysis of a solution which is prepared by admixing a small stream of water from water under pressure in a conduit and salt containing brine from a stored supply of brine, which apparatus can be operated in the shunt of a circulating line, through which the water to be disinfected is pumped, said apparatus comprising a salt dissolving tank which is connected in terms of flow via a metering pump and a pipe with an inflow for the admission of water from the circulating line to the brine conveyed out of the salt dissolving tank, wherein said pipe is connected via a flow measuring device and an interposed salt concentration measuring cell with the inlet of the electrolytic cell, said electrolytic cell communicating on the exit-side end in terms of flow with a metering point in the circulating line, and with an electronic/electric control energy supply unit, wherein the inlet to the electrolytic cell is fed by one or more conduits under constant pressure which are each opened or closed by a shutoff element, controlled by an electric supplementary control and hypochlorite solution produced in the electrolytic cell is supplied to the metering point of the flow-carrying conduit via a direct metering line from the electrolytic cell.

3. The apparatus of claim 2, wherein the shutoff element is a solenoid valve.

4. The apparatus of claim 2, wherein an adjustable flow measuring device is provided before the salt concentration measuring cell.

5. The apparatus of claim 2, wherein a regulated direct current supply of the electrolytic cell with transformer/
rectifier, the shutoff element in the inflow, and the metering pump of the salt dissolving tank are turned on centrally by the supplementary control.

6. The apparatus of claim 5, wherein there is provided in the conduit traversed by the water to be disinfected a flow monitor with a pulse generator which, if there is flow, actuates the supplementary control, which then in turn switches on the transformer/rectifier, the electrical shutoff element, and the metering pump.

7. The apparatus of claim 5, wherein the supplementary control is coupled with a control of a circulating pump of the conduit configured as a circulating line for the water to be disinfected and is actuated by said circulating pump, which then in turn switches on and regulates the transformer/rectifier, the electrical shutoff element, and the metering pump.

8. The apparatus of claim 5, wherein the transformer/
rectifier is electrically connected with the salt concentration measuring cell.

9. The apparatus of claim 2, wherein all structural parts, with the exception of the salt dissolving tank with the metering pump and structural parts inserted directly into the conduit, are arranged on a mounting plate capable of being mounted vertically.