Sodium Hypochlorite Generation units are currently installed in several applications to finitely obtain a Safe and economical disinfection / antifouling method for water. Sodium Hypochlorite water solution offer a powerful biocide and disinfecting agent in several applications and provides an efficient equipments protection against macro and micro organic fouling growth. In situ biocide generation avoid the undesirable side effects of commercial hypochlorite, such us: » transportation safety hazard » hard deposit alkalinity build up » handling and storage of gas chlorine. Sodium Hypochlorite production plants eliminates the heavy costs associated to the purchasing of commercial biocide products and the dependency upon outside Suppliers.

1. CDB Engineering S.P.A.
Experience
-
SODIUM HYPOCLORITE PLANT
PRESENTATION

2. Background
Sodium Hypochlorite Generation units are currently
installed in several applications to definitely obtain a
Safe and economical disinfection / antifouling method
for water.
Sodium Hypochlorite water solution offer a powerful
biocide and disinfecting agent in several applications
and provides an efficient equipments protection against
macro and micro organic fouling growth.

3. In situ biocide generation avoid the undesirable side
effects of commercial hypochlorite, such us:
- transportation safety hazard
- hard deposit alkalinity build up
- handling and storage of gas chlorine.
Sodium Hypochlorite production plants eliminates the
heavy costs associated to the purchasing of commercial
biocide products and the dependency upon outside
Suppliers.

4. Applications
Onsite and offsite Sodium Hypochlorite generator units are
mainly employed and installed for :
– Off shore platforms
– Large desalination plants
– Power stations
– Refrigeration plants
– Petro-chemical complex for the associated utilities water
treatments
– Sea water intakes
– Generally where a big mass of water need to be disinfected before
final using

5. Technology results
By electrolysis technologies of salty water it
is possible to obtain a reliable, low
maintenance, safety and CAPEX / OPEX
convenient units in lieu of the unsafe and
obsolete gas chlorine dosing

6. Range of supplies
CDB Generation units can be provided in a
wide range of production capacity:
- From 1 to 5 kg/h active Cl2 for off shore
small applications (single skidded units)
- Up to 100 / 200 kg/h active Cl2 for very
large industrial complexes or power stations
(composite skids packages)

7. Unit description 1/2
Equipments and materials can be
designed tailored to the specific needs of
the customer as well as designed in
accordance to the principal applicable
codes and norms such as
ASME, ANSI, BS, IEC.

8. Unit description 2/2
To minimise the customer activities at site and to limit
the erection time , units are delivered in complete
preassembled skidded parts, mainly (see flow diagram):
– booster station ( if required)
– strainers
– electrolysers
– Dosing / shock pumps
– air blowers
– HCl cleaning facilities
degassing tank, transformer rectifiers, LCP are
normally provided loose for large production units

9. Principle Flow Diagram

10. Materials:
Long electrodes warranty periods is
possible thanks to the strong resistant
used material (ASTM B265) for electrodes
and to the special stable coating for anodes
Parts subjected to corrosion, because of
aggressive raw water and Hypochlorite
solution, are
based on FRV and PVC

11. Supply Warranty:
• system free from defects in workmanship
and materials for a period of 12 months
from start up and 18 months from shipment
• generator cells for 5 years

12. Engineering and management services
• Units will be delivered complete of operation and maintenance
manuals as well as of the equipments dimensional drawings.
• During the design phase it will be produced the usual set of
documentation, according to the specific customer needs, and for his
design and review ( general arrangement, BL positions, civil works
and loads, ITP, electrical loads etc)
• After delivery, according to the customer request, CDB can send to
site skilled specialized personnel to supervise the erection and start up
activities and for the training of Owner’s operation personnel

13. Process description 1/3
Seawater (or brine water) provides the feedstock for the
electrolytic cells.
Though the seawater has been passed through
drum screens with a mesh size before entering the
SW pumps, it shall be passed through automatic, self-
cleaning fine mesh strainers to remove any debris
remaining before being allowed to enter the electrolytic
cells. Sodium hypochlorite solution output from each of
the cell assemblies is to be channelled to the degasifier for
hydrogen gas to be removed.

14. Process description 2/3
The generation of Sodium hypochlorite (NaClO) solution
from raw sea water (or brine) is performed by an electro-
chemical process doing partial electrolysis of NaCl
contained in sea water once it flow through anodic and cathodic
electrodes. Electrodes are energized by DC current make available by
an controlled diodes rectifier.
Raw water, filtered by mesh filters, is fed the NaClO generators. The
generator cells are usually connected electrically and hydraulically in
series such us that sea water flow form the first electrolyser and then
to the others before exiting the sodium hypochlorite degassing tank.

15. Process description 3/3
The hydrogen gas disengages from the liquid phase in the
upper part of the tank and is diluted with air generated
by dedicated fans to keep the hydrogen concentration well
under the explosion level .
NaClO produced solution is stable enough without
substantial loss in the storage / degassing tank during the
time between the shock treatments.
Finally sodium hypochlorite is pumped by centrifugal
pump up to the injector at the dosing points for the
continuous and shock treatments.

16. Involved electrochemical reactions :
Anode producing free chlorine
2 (Na+ Cl-) 2 Na+ + Cl2 + 2 e-
Cathode producing Hydrogen:
2 H2O + 2 e- 2 OH- + H2
Bulk reaction producing Sodium Hypochlorite
iones OH- migrate from cathode and react closed to the anode as:
2 NaOH + Cl2 NaClO + NaCl + H2O.
All the above gives the overall reaction in water :
NaCl + H2O NaClO + H2 .
Cations present in the raw water (mainly Magnesium and Calcium) form Carbonates
and Hydroxides coming out as suspended solid which are carried out during raw water
flowing. Nevertheless periodically (usually twice per year) deposits are removed by
electrodes by diluted acid cleaning.

17. Suplier references:
• CDB Engineering S.p.a. :
• Via L. Maggi snc, Loc. Zorlesco - 26841
Casalpusterlengo (LO) – Italy –
• Tel. +39 0377 912268 / 65,
• Fax. +39 0377 910668
• e.mail cdb@cdbengineering.com
• Website: www.cdbengineering.com