The electrochlorination system is normally used where the coolant agent of the condenser, into a steam generation plant, is by sea water. The salty water needs to be chlorinated to avoid growth of mainly blue mussels and algae on the generation plant parts. The system’s task is to produce Sodium Hypochlorite by electrolysis of part of incoming salty cooling water and then to dose the Sodium Hypochlorite to the cooling circuit. This process is called Electrochlorination system. Dosage creates unfavorable conditions for fouling mussel larvae that may occur in the cooling water during summer and autumn periods preventing from settling them into plant parts where they could grow.
The equipment for the salty water electrolysis consists mainly in feed water pumps, taking salt water from generation unit, electrolyzers, degassing tank, set of valves, pressure boosting pumps and an automation system that will grant the automatic Sodium Hypochlorite production and dosage into the cooling water flow. Additional equipment are also foreseen for periodically washing and cleaning of electrolyzers from deposits and scaling as well as for Hydrogen removal from the Sodium Hypochlorite storage tank.
ELECTROLYSIS OF SALT WATER
In electrolyzers the Sodium Hypochlorite is produced by electrolysis of salt (sea) water. Electrolyzers consist of a number of electrodes (cells) fed with DC voltage and high current.
Below figure gives the reaction base scheme to produce Sodium Hypochlorite and relevant chemical reaction formula:
- Anodic reaction: 2NaCl (seawater, brine) => 2Na+ + Cl2 + 2e-
- Cathodic reaction: 2H2O + 2e- => H2+ 2OH-
- Bulk reaction: 2 NaOH + Cl2 => NaClO + NaCl +H2O
- Overall reaction : NaCl + H2O => NaClO + H2
Below figure gives the plant process concept flow diagram: