Electrode Anode / Cathode Sizing

Electrochlorination OEM’s will choose an Anode coating most suitable and cost effective for the electrolyte salinity and temperature. Titanium will rapidly corrode in anodic conditions unless suitably coated, it is however suitable for cathodic operation uncoated. Anode coatings range from electroplated Platinum to MMO (Mixed metal oxides).

Primarily Titanium will be used for anode substrate material with more commonly plain Titanium cathodes however possibly Hastelloy C cathodes.

In the selection of the electrolyser the anode coating thickness will be determined by the DC current density for the design. The DC current density will be in the region of 1100A/m² to 1500 A/m² increasing to 2500 A/m² in concentric tube technology electrolysers.

For the worked example herein the anode area for each electrolyser cell based on 1500 A/m² would be:-

550.4 ÷ 1500  =  0.367m²/Cell (3.67 m² / Electrolyser)

Electrolyser Voltage Requirement

The voltage (Potential Difference) necessary to drive the amperage required through the 10 Cells within the Electrolyser, and latterly through the electrolysers in series, is determined by a number of factors. The supplier needs to ensure that there is adequate voltage output from the transformer rectifier to ensure the DC current can pass through the seawater electrolyte in all seawater conditions.

Therefore a complete seawater analysis, encompassing all seasonal and tidal variations of salinity and temperature ranges, should accompany an enquiry for an electrochlorination system

Salinity of seawater can be expressed as either %, ppt (parts per thousand) ‰, or more generally as Chloride level g/l.

The usual representation of seawater is in ppt and this can be calculated from the Chloride level.

S (ppt) = 1.80655 x Chlorides g/l

Temperature also affects the resistivity of seawater and consequently the voltage requirement to ensure the required DC current can be passed through the electrolyser assemblies.

For a given anode coating there is a potential (Voltage) required before any current can be passed, no one figure can be quoted however 3 – 4VDC per cell would be reasonable to assume. 

Each OEM will have their own more complex methods of determining the voltage their system will require to comply with the seawater data specified and anode coating employed. For those interested there are calculations to determine the resistivity ratio of various seawater conditions that can be found in the Practical Salinity Scale.