AU682283B2

AU682283B2 - Electrolytic chlorination

Info

Publication number: AU682283B2
Application number: AU36002/95A
Authority: AU
Inventors: Lennie Franklin David; Michael Brian Roberts; Peter John Roberts
Original assignee: Clearwater Australia Pty Ltd
Current assignee: Clearwater Australia Pty Ltd
Priority date: 1994-10-07
Filing date: 1995-10-05
Publication date: 1997-09-25
Anticipated expiration: 2015-10-05
Also published as: AU3600295A

Description

Title

Electrolytic Chlorination

Field of the Invention

This invention relates to electrolytic chlorination and in particular relates to a method and apparatus for use in the cleaning of electrolytic chlorination cells used with the filtration of pool or spa water.

Background of the Invention A common means of chlorinating swimming pools is through the use of an electrolytic cell to produce chlorine by the electrolytic oxidation of chloride ions which are present in pool or spa water either, naturally, or by the addition of common salt. This chlorination technique is achieved by the use of an electrolytic chlorinator cell. The cell usually contains an anode and a cathode across which is applied a low DC voltage. The anode and cathode are usually housed in a single compartment and the water of the pool or spa flows through the cell. It is usual for the cell to be fed by a water pump via the pool filter usually referred to as the filter pump.

One of the biggest problems associated with this type of chlorination system concerns the need to periodically clean the calcium salt deposits which accumulate on the cathode. The frequency of cleaning varies from system to system but can be as regular as once a week or as irregularly as once every few months. There are a variety of cleaning methods such as mechanical scraping and brushing or removal through chemicals, particularly by immersion in an acid bath. Hydrochloric acid is the usual solvent that is used to clean the electrodes and the practice is to dismantle the cell and place the electrode assembly in the acid bath until the deposits have been removed. This process is time consuming and messy. There is also the problem that the life of the electrodes is reduced particularly when the acid bath has a pH value below 1.0. A further problem created by the calcium deposits on the electrodes concerns the fact that the coating deposits reduce the chlorine generating efficiency of the cell so that if the cleaning process is delayed, the efficiency of the cell drops off. If the process is delayed beyond the point where the deposits bridge the electrode gap as frequently happens when pools are neglected, then the anode life is substantially reduced because of the dramatic change in the chemical environment immediately adjacent to the anode.

It is these problems that have brought about the present invention.

Summary of the Invention According to one aspect of the present invention there is provided a method of operating an electrolytic chlorination cell for swimming pools or spas comprising adding, at periodic intervals, a discrete quantity of acid to the electrolyte in the cell. Preferably the acid is added to the cell when there is no flow through the cell. In another embodiment, the acid is added to the infeed line of the cell to thereby flow into the cell.

According to a further aspect of the present invention there is provided an electrolytic chlorination system for swimming pools and spas comprising an electrolytic cell fed by a water pump, a reservoir of acid coupled to the cell via a metering device wherein the metering device periodically dispenses a metered quantity of acid to the electrolytic cell.

Preferably the metering device is coupled to the water pump and operates to release a discrete quantity of acid when the pump stops. Alternatively, the metering device may be controlled by a timer. The metering device may be a conventional metering pump such as a peristaltic pump diaphragm or piston pump. In another option to reduce use of acid, a pressure switch or similar device may be included to prevent flow of acid when the water pump is operating.

According to a still further aspect of the present invention there is provided a metering device comprising a pressure chamber arranged to be connected to a source of pressure, a delivery chamber arranged to be coupled to a source of fluid and displaceable drive means to cause suction of the fluid into the delivery chamber and ejection of the fluid from the delivery chamber, the drive means being displaceable by variation in pressure in the pressure chamber.

Preferably, the drive means comprises a flexible diaphragm dividing a housing into the pressure chamber and delivery chamber. In an alternative embodiment, the device comprises a cylinder and the drive means is in the form of a piston displaceable within the cylinder, opposite sides of the piston defining the pressure and delivery chambers. In another embodiment, a double piston and cylinder arrangement is utilised whereby the two pistons are interconnected, one cylinder defining the pressure chamber and a second cylinder defining the delivery chamber.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a side elevational view of an electrolytic chlorination cell illustrating one position of an acid injection point, Figure 2 illustrates a modification of the pipework of the cell.

Figure 3 illustrates an electrolytic chlorination system in accordance with one embodiment of the invention, and Figures 4 and 5 illustrate the system with different metering devices. Description of Preferred -Bmbodiments

This invention results from a discovery that injecting a small quantity of acid, preferably hydrochlori acid, into an electrolytic cell at frequent intervals has the effect of ensuring that the electrodes can be kept fre of calcium deposits. It has been discovered that a preferred means of keeping the electrodes clean is to inject a discrete amount of hydrochloric acid into the top of the electrolytic cell when the filter pump is not operating. In other words, when there is no flow of electrolyte. This ensures a sufficiently concentrated acidic solution in the cell to remove or prevent formation of calcium deposits. It is however, also viewed as possible to inject the acid into the flow upstream of the electrolytic cell. The addition of the acid depresses the pH sufficiently to reduce or even halt the accumulation of deposits on the electrodes.

A conventional electrolytic cell 10 modified to include an acid injection point 30 is shown in Figures 1 and 2. The cell 10 comprises a cylindrical housing 11 closed at one end 12, and with a removable cover member 13 screw threadedly located on the other end. The cover member 13 supports a pair of spaced plates or grids 14, 15 that constitute the anode and cathode of the cell. The plates are coupled to a DC voltage of between 6 and 7 volts. The underside 17 of the cell housing 11 includes inlet and outlet ports 21, 20 spaced along the length of the housing. The acid injection point 30 is positioned at the top of the housing 11 so that the acid percolates through the cell from the top to the bottom. It should be noted that the specific gravity of hydrochloric acid is greater than water.

In the embodiment shown in Figure 2, the acid injection point 30 is shown, but it is understood that the acid could also be injected into the flow of the electrolyte or water prior to entry to the electrolytic cell. To ensure that the acid is not lost to the cell 10, a ϋ bend arrangement 25, 26 is configured which prevents the acid from disappearing down the pipe by diffusion. The 'U' bend arrangement 25, 26 can also be used with the cell of Figure 1. Figures 3, 4 and 5 illustrate three pool filtration and chlorination systems that embody the present invention.

In all three embodiments, water from the swimming pool or spa travels to the filtration unit along a delivery pipe 31 that is coupled to an electric pump 32 which in turn passes the water through a filter and sometimes, heater unit 33. The outlet 34 of the filter 33 is fed through the inlet 21 of the chlorinator cell 10 to leave the chlorinator cell from the outlet 20 to return to the pool along return pipe 35. In Figures 3 and 4, a metering device 50 is positioned between the inlet of the filter pump 32 and the chlorinator cell 10. In Figure 5, the device 50 is between the filter pump outlet and the chlorinator cell 10. In both cases, the device is coupled to a source of hydrochloric acid contained in a carboy 36. The acid is at usual commercial strength or less. As shown in Figure 3, the metering pump 50 comprises a dome shaped housing 51 with a transversely extending flexible diaphragm 52 that defines a pressure chamber 53 and a delivery chamber 54 on opposite sides of the diaphragm. The base of the housing 51 includes an aperture 55 sealed by a needle valve 56 and coupled to suction line 57 which goes to the acid carboy 36 via a one way valve 58. The base of the housing 51 also includes a delivery outlet 59 that is coupled to the injection point 30 of the chlorinator 10 via a line 60 and one way valve 61. The pressure side 53 of the metering device is coupled to the suction side of the pump 32 via a line 64. When the pump 32 is running, the suction created by the filter pump 32 causes a partial vacuum in the chamber 53 to lift the flexible diaphragm 52 against a compression spring 65 that acts between the diaphragm 52 and the interior of the dome shaped housing 51. The displacement of the diaphragm reduces the pressure in the compartment 54 which has the effect of causing acid from the carboy 36 to fill the compartment 54 via the suction line 57. When the filter pump stops, as it would do in a normal filtration system one or more times daily, the pressure in compartment 53 approaches atmospheric pressure and the spring 65 forces the diaphragm downward to reduce the size of the delivery chamber 54 to force the acid in that compartment into the chlorinator cell 10 via the delivery line 60. This is the delivery stroke of the metering device. The one way valve 58 prevents acid returning to the carboy during the delivery stroke and the one way valve 61 prevents pool water escaping from the chlorinator 10 to the delivery chamber 54 of the metering pump. The needle valve 56 is used to prevent siphoning of the acid contained in the carboy in situations where the equipment is above the level of the pool.

In certain circumstances, by use of a very elastic diaphragm 52, there is no need for the coil spring 65. The elasticity of the diaphragm on return effects the delivery stroke.

In the embodiment shown in Figure 4, the metering device 70 is in the form of a piston 71 and cylinder 72. The piston 71 slides in the cylinder 72 against a spring 73 and effectively replaces the flexible diaphragm of the embodiment of Figure 3. In all other respects, this embodiment is the same as the one illustrated in Figure 3.

In the embodiment shown in Figure 5, the metering device 100 is in the form of a double piston and cylinder arrangement. A first pressure cylinder 101 contains a piston 102 that acts against a spring 103 within a chamber vented to atmosphere via a bleed hole 110. The piston 102 is connected through a connecting rod 108 via sealed passageway 104 to a delivery cylinder 105 which contains a delivery piston 106. The delivery cylinder 105 includes the delivery aperture 59, the needle valve 56 and acid entry aperture 55 that is in turn coupled to the acid

SUBSTITUTESHEET(RULE 2S) carboy 36. The pressure piston cylinder assembly 101 is connected to the pressure side of the filter pump 32 via the line 64. In this embodiment, the pressure from the filter pump acts on the upper piston 102 to force the piston upwardly against the spring 103 to in turn pull up the delivery piston 106 thereby causing acid to be drawn into the delivery cylinder 105. When the pump stops, the spring 103 pushes the pistons 102 and 106 down thereby ejecting acid from the cylinder 105 into the chlorinator cell 10 via the line 60.

It is understood that the shape and configuration of the metering pumps described with reference to Figures 3 to 5 would vary to suit particular requirements. The quantity of acid that is delivered during each delivery stroke can be correlated with the size of the metering device and the timing of the delivery stroke which is in turn coupled to the frequency of operation of the filter pump in any 24 hour period.

The embodiments shown in Figures 3 to 5 constitute a simple and cost effective means of delivering discrete amounts of acid to the chlorination cell and depends on the operation of the filter pump. It is envisaged that the user of the system would vary the operation of the filter pump i.e. the number of cycles to ensure that the desired quantity of acid reaches the chlorination cell. Most of the time switches used with conventional filter pumps provide a capacity to vary the frequency of the filtering cycles.

It is also envisaged that the systems described above could incorporate a form of feed back control by way of electrically operated solenoid valves positioned in one or more of the feed lines. In a situation where sufficient acid had been added or it is desired that no further acid should be added to the chlorination cell, a suitable signal will be sent to the solenoid valves to ensure that the system shuts down.

To prevent the likelihood of calcium carbonate build up on the electrodes in the chlorinator cell only a very small volume of acid needs to be injected into the cell at any one time. Dnlike the conventional acid cleaning methods in use, it is only necessary to reduce the pH value a little to ensure adequate cleaning action when using this novel approach. It is a simple matter to ensure that the pH is not depressed beyond the point at which damage to the electrodes could occur. It is usually considered that a pH level of less than 1 would be harmful. This should be contrasted with the conventional method of periodic washing of the electrodes to remove weeks of accumulation when it is necessary to start with a very low pH value because as the dissolution proceeds the pH value rises quickly due to the neutralisation of the acid. It is therefore quite impractical to start with a pH value of much above 1 as the acid bath would very quickly become depleted and ineffective in removing the deposits. The system described herein has the advantage that the pH level is always kept above 1 thereby reducing the likelihood of the harmful effects that are caused by acidic attack on the componentry of the system. Example

In one example, utilising the method and apparatus of the subject application, a 70,000 litre pebble-mix rendered domestic pool using a conventional electrolytic chlorination cell was coupled to a metering pump of the kind described above so that 20 ml hydrochloric acid of commercial grade was fed into the top of the chlorination cell every day during the period that the filter pump was not running. The metering device fed 20 ml of acid into the chlorinator and the pH in the cell was depressed to a value of 2.7 each time. This resulted in the maintenance of the electrodes in deposit free condition after five weeks of operation. This particular pool was chosen for this test because it was one where the electrodes would otherwise accumulate so much deposit in a two week running period that the electrode gap would be totally filled. This is a situation which causes significant reduction in both cell life and chlorine production. It was noted that the amount of acid that was used in this test per day, namely between 20 and 25 ml, was not sufficient to lower the pH of the main body of the pool water below 8.05.

A further advantage that emanates from the method described above is that the automatic injection of acid can be used to prevent the pH of the pool water in general from rising to values at which the chlorine becomes ineffective as can often happen in domestic swimming pools with surface finishes that involve plaster or cement. Thus, if it were desired to use this method as a pH control method for the pool, the frequency of acid dosing and/or the size of the dose can be increased as necessary. Alternatively, the acid dosing could be continued throughout the filter cycle during both the pump-on periods and the pump-off periods.

Since this invention in its broadest aspect relates to the periodic dosing of the chlorinator cell with acid, it is understood that a variety of dosing mechanisms may be used to supply the acid. In a preferred embodiment, these mechanisms are coupled to the filter and operate in reliance on the filter pump pressures so that when the pump is switched off the dose of acid is delivered. It is however understood that other timing devices can be used to control the delivery of the acid quite independently of the filter pump. It is further understood that devices such as pressure operated switches or flow switches can be used to activate a dosing pump.

Claims

1. A method of operating an electrolytic chlorination cell for swimming pools or spas comprising adding, at periodic intervals, a discrete quantity of acid to the electrolyte in the cell.

2. The method according to claim 1 wherein the acid is added to the cell when there is no flow through the cell.

3. The method according to claim 1 wherein the acid is added to the infeed line of the cell to thereby flow into the cell.

4. An electrolytic chlorination system for swimming pools and spas comprising an electrolytic cell fed by a water pump, a reservoir of acid coupled to the cell via a metering device wherein the metering device periodically dispenses a metered quantity of acid to the electrolytic cell.

5. The system according to claim 4 wherein the metering device is coupled to the filter pump and operates to release a discrete quantity of acid when the pump stops.

6. The system according to claim 4 wherein the metering device is controlled by a timer.

7. The system according to any of claims 4 to 6 wherein the metering device is a conventional metering pump such as a peristaltic pump, diaphragm or piston pump.

8. A metering device comprising a pressure chamber arranged to be connected to a source of pressure, a delivery chamber arranged to be coupled to a source of fluid and a displaceable drive means to cause suction of the fluid into the delivery chamber and ejection of the fluid from the delivery chamber, the drive means being displaceable by variation in pressure in the pressure chamber.

9. The pump according to claim 8 wherein the drive means comprises a flexible diaphragm dividing a housing into the pressure chamber and delivery chamber.

10. The pump according to claim 8 wherein the device comprises a cylinder and the drive means is in the form of a piston displaceable within the cylinder, opposite sides of the piston defining the pressure and delivery chambers.

11. The pump according to either claim 9 or claim 10 wherein a double piston and cylinder arrangement is utilised whereby the two pistons are interconnected, one cylinder defining the pressure chamber and a second cylinder defining the delivery chamber.