Tuesday, November 30, 2010

Ballymore Eustace Changes to On-Site Electro-Chlorination (OSEC)

Ballymore Eustace Water Treatment Plant supplies 70% of Dublin’s water and is currently being expanded from 250 Ml/d to 318 Ml/d, with a planned peak capacity of 400 Ml/d. Siemens Water Technologies have provided two OSEC systems each be capable of producing 1,000 kg/d of chlorine to replace the use of chlorine gas for chlorination. Both units will operate in tandem producing 24 hours’ worth of chemical during the 8 hour low-tariff energy period.
Siemens electrolyzer unit where brine is
turned into sodium hypochlorite

Water softened to <17 mg/L hardness is used to produce a 2.8% w/w brine solution from stored salt. The brine solution is passed through an electrolyzer (image right) where a current is passed between two electrodes resulting in chlorine gas being produced at the positive electrode (anode) and sodium hydroxide and hydrogen gas at the negative electrode (cathode). The chlorine then reacts with the sodium hydroxide to produce a 0.8% sodium hypochlorite  solution which is stored before added to the finished water for disinfection. Salt usage equates to 3.0-3.5 kg per kg chlorine equivalent. Fifty-seven liters of 0.8% sodium hypochlorite is equivalent to 0.45 kgs of chlorine gas or 3.79 liters of commercial sodium hypochlorite (12%). This results in a much safer and cost effective chlorination system.  Further information on Siemens OSEC technology.

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