Electro - chlorination plant aims to prevent the deposition of marine organism such as barnacle, sea mussel and other shellfishes in the cooling water system, by directly electrolyzing seawater, without using any chemicals. The cooling water system is used to cool the some equipment in main or other process.
The following is the simplified Electro-Chlorination System:
Figure 1. electro-chlorination system
The basic reaction that happen in Electro- Chlorination System is electrolysis. The electrolysis is ia technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential.
figure 2. electrolysis process
Where as the reaction that happen in Electro-Chlorination System are the following:
- Anode (+ pole) is happen oxidation which negative ion (Anion or Cl-) will be oxydized (Anion will go to Anoda)
- Cathode (-pole) is happen reduction which positive ion (cation) will be reduction (cation will go to cathode). Due to the Na+ is strong metal as 1 A group in Periodical Table of the Elements, H2O or water will be reduced in Cathode.
The reaction is below:
The injection of chlorine ( NaOCl ) is in two place, one is in intake pit, second is in sea water. Keep the chlorine product concentration and flow are enough so the free residual chlorine is 1 ppm ( during continues dosing) and 3 ppm ( during shock dosing). The chlorine injection point is in the following place:
figure 3. chlorine injection point
To calculate the Chlorine Production Efficiency, can be used the following formula:
If the efficiency is low (less than 75%), it's mean the Calcium and Magnesium deposits accumulated on the cathode of electrolyzer. It shall result in decreased efficiency and increase power consumption so need periodically acid cleaning (al least once a month base on actual fouling degree).Use HCl 10% as chemical cleaning agent because can dissolve Mg(OH)2 and CaCO3.
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