Introduction #
Electrochlorination is essentially the electrolysis of a brine electrolyte, the electrolyte either seawater or an artificially produced brine solution. The chlorine related product of this electrolysis is sodium hypochlorite expressed as an equivalent in weight to chlorine.
In the absence of known reference works the emphasis herein is provide a subject information level from which personnel of all disciplines can make an informed judgement regarding both identifying their electrochlorination requirements and assessment of a suppliers technical proposal. A basic electrochlorination demand calculator (excel) is available on the website as a free download which is hoped to be of assistance to readers.
Chlorine is widely known for its properties for disinfection of potable water supplies and the control of marine fouling in seawater systems by virtue of being dosed at levels measured in ppm into those systems.
It can be practically supplied in many forms and herein the main sources are identified with the emphasis retained on once through Electrochlorination.
The basic electrochemical reaction is shown below where the electrolyte, a solution of sodium chloride in water, is subject to electrolysis by a DC electrical current.
Amongst the many technical requirements for safe and efficient operation the engineering technology applied to electrochlorination systems has to address the following process criteria.
- The liquid media product is corrosive to most metallic materials and plastic is extensively used.
- The product is typically generated in low concentration solutions of <=2000mg/l carrier stream.
- The Electrochlorination package will generally permit only one variable product concentration with which typically multiple dosing points will be treated, the flow to each point modified to suit any change in the cumulative weight demand.
- The hydrogen by-product has to be safely managed.
- In the case of seawater systems process by-products include the formation of insoluble hydroxides and their appropriate management is essential to avoid precipitation within the piping systems and tanks.
The main alternative sources of chlorine for water treatment are indicated below however it is assumed that the relative advantages and disadvantages of each system have been evaluated and electrochlorination has been selected.
Liquid Chlorine #
Delivered to and stored on site, administered through evaporation and control equipment to the water system. Many installations that have demonstrated historical reliable operation have been replaced with Electrochlorination systems due to liquid chlorines hazardous nature.
Bulk Sodium Hypochlorite. #
Delivered to and stored on site, administered through pumping systems and control equipment to the water system. Subject to rapid decay during storage at the concentrations logistics demand.
Chlorine Dioxide #
Manufactured on site from a bulk chemical supply of Sodium Chlorite and Hydrochloric acid. An effective biocide however again subject to the logistics from which electrochlorination offers freedom.
