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What is
Electrochlorination?
Electrochlorination
is an electrolysis process where natural seawater or
a salt solution is converted into a sodium
hypochlorite solution. The dissolved salt is sodium
chloride (NaCl), where one sodium atom (Na) is bound
to one chlorine atom (Cl). When direct current is
passed by titanium electrodes through a sodium
chloride solution in an undivided cell, an oxygen
atom is attached to the sodium chloride to produce
sodium hypochlorite (NaOCl).
- Oxidation of
chloride ions at the anode produces liberated
chlorine (Cl2).
- Reduction of
water at the cathode produces sodium hydroxide (NaOH).
- The liberated
chlorine Cl2
immediately reacts with the sodium hydroxide
NaOH to produce sodium hypochlorite (NaOCl).
The overall electro
chemical reaction is as follows:
2NaCl (salt) + H2O
(water) => NaOCl (sodium hypochlorite) + NaCl (salt)
+ H2
(hydrogen)
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An old chlorination system:
hazardous
buckets
of hypochlorite. |
A new flow-through
electrochlorination system:
automated continuous generation of hypochlorite. |
Sodium
Hypochlorite Applications
Sodium hypochlorite,
also known as “hypo”, “bleach” or "liquid chlorine,"
is a powerful oxidant. It is used worldwide for:
- Marine growth
anti-biofouling (e.g., to prevent slime, mussel,
barnacle growth, etc.)
- Disinfection
(e.g., for drinking water, general
anti-bacterial purposes, etc.)
- Chemical
treatment (e.g., bleaching, removal of iron,
manganese, etc.)
Typical uses and
applications:
- Marine Vessels
- Power Stations
- Oil & Gas
Installations
- Off-shore
platforms
- Desalination
Plants
- Wastewater
plants
- Potable water
plants
Advantages of Electrochlorination
Electrochlorination
is a 100% safe chlorine technology, which generates
Cl2
as needed in the form of a low-concentration hypo
solution. The process only uses seawater plus
electricity, or fresh water and salt plus
electricity. Advantages include:
- On-site,
on-demand generation.
- No need to
purchase expensive chemicals.
- No handling or
bulk storage of hazardous chemicals.
- Automatic
operation to minimize human error/
Electrochlorination
is the safe, economical alternative to hazardous,
high concentrations of commercial chlorine products,
e.g., gaseous chlorine, commercial hypo, or dry
chlorine. It is also safe for the environment, as
there are no heavy metal byproducts, such as copper
or lead, and the hypochlorite (NaOCl) reverts back
to common salt (NaCl) after giving up its oxygen
atom.
Electrochlorination to Avoid Bio-Fouling
Micro-fouling
refers to a layer of slime over surface. On heat
exchanger plates and tubes, micro-fouling can reduce
heat transfer efficiency by as much as 25% and also
accelerate corrosion. Periodic maintenance to clean
the surfaces is required, creating downtime and
increasing running costs.
Macro-fouling
refers to barnacle and mussel growth. Inside
seawater pipes and cooling systems, macro-fouling
can gradually restrict seawater flow and
consequently reduce flow and heat transfer
efficiencies. In extreme cases, pipes and valves can
become completely blocked, resulting in equipment
damage and major system shutdowns.
Hypochlorite
continuous and shock dosing are used to
effectively control micro and macro-fouling in
seawater applications. In continuous dosing, a low
level of chlorine is continually supplied. This
protects against the majority of bio-fouling, but
unfortunately certain macro organisms can become
resistant to low level dosing. These macro organisms
can be eliminated by shock dosing, where much higher
levels of chlorine are applied for a short time at
regular intervals.
Electrochlorination Systems Hardware
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Electrochlorination electrolizer flow-through electrode
systems. |
Electrolyzer Subsystem
The electrolyzer
consists of anodes and cathodes that are arranged to
form multiple cells in series. The number of cells
is determined by the application and the amount of
chlorine to be generated. The anodes and cathodes
are arranged in a concentric tubular assembly, where
seawater is passed in the annular space between the
outer and inner tubes. High-velocity seawater
reduces scaling and acts as a continuous self
-leaning mechanism.
Farwest anodes and
cathodes are made of titanium. The anodes are coated
with mixed metal oxides (MMO), which is essential
for the generation of chlorine and can last from 5
to 8 years. Farwest electrolyzers are guaranteed for
5 years continuous duty.
Electrolyzer Maintenance
All water contains
dissolved calcium and magnesium. During
electrolysis, calcium carbonate and magnesium
hydroxide will deposit on the cathode, a process
referred to as “scaling.” Scale is easily
removed by flushing the electrolyzer with 5% diluted
hydrochloric acid. This process takes about an hour
and should be done after 10 days continuous
electrochlorination. The consumption of hydrochloric
acid is very low .
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