• Pristine Water

Sea Water Electrochlorination System

Why is Chlorination is required in seawater treatment plants

The purpose of the Seawater Hypo Chlorination System is to generate and Inject Hypochlorite solution into Sea Water Intake Structures to inhibit the growth of the biological organisms and to prevent slime deposits on the wall of circulating cooling water pipes.

The seawater from the sea will be delivered to the Hypochlorination System. If the pressure is not sufficient, it will be boosted by means of Seawater Booster Pumps (which shall be located within the Hypochlorination Building). Seawater Booster Pumps will feed seawater to automatic backwash strainers to ensure that the seawater is rid of large debris. Seawater will then pass through Hypochlorite Generators where the sodium hypochlorite solution will be generated from seawater by the electrolysis process. The generated sodium hypochlorite solution will be stored in the downstream Hypochlorite Solution Storage Tanks.

Hypochlorite solution from storage tanks will then be dosed continuously as well as intermittently (shock dosing) to the intake structure. The continuous Hypochlorite dosing rate shall be controlled manually in order to maintain a level of 0.2 mg/l free residual chlorine at the cooling water discharge at the seal pit. Shock chlorination has been envisaged at 5 mg/l with a frequency of once every 8 hours for a duration of 20-30 minutes.

Main equipment in the Seawater Hypochlorination System

Seawater Booster Pump

These pumps are required if inlet seawater is not provided at a pressure of at least 2 kg/cm3. These pumps are normally made up of Duplex Stainless Steel. Working and stand by pumps are provided with inlet and outlet valves, check valves, and required instruments.

Auto Backwash Strainers

The mechanical cleaning of the circulating water is performed by Automatic Backwash Strainers. The strainers can remove suspended solids of a particle size larger than 0.5 mm and be automatically self-cleaning. The strainers are complete with interconnecting pipework, isolating valves, pressure gauges, and automatic backwash equipment. The operation
of the strainers will be controlled by a differential pressure switch. One strainer will
be on stand-by.

Hypochlorite Generators

The main equipment of the system is the Sodium Hypochlorite Generator, otherwise known as an Electrolyzer. The generators are used to produce the hypochlorite solution and will be
installed indoor. These can be of Horizontal type or Vertical type depending on the space available, capacity, and configuration. Most of the time, two or three Electrolyzer cells are connected together to achieve the desired capacity. The hydraulic connections are either parallel or in series.

Transformer/Rectifiers

The Transformer Rectifier controlled power supply will be self-cooling. These can either be Air-cooled, Seawater cooled or Oil cooled and fitted with rectifiers of either Thyristors or Diodes. The output of the hypochlorite from each generator is directly proportional to the direct current (D.C.) output of the power supply. The Transformer/Rectifiers are provided with control panels for local and/or remote control and monitoring.

Acid Cleaning Unit

The acid Cleaning system is provided with an Acid tank that will hold diluted Hydrochloric Acid. HCl dosing pump pumps the diluted acid through the Electrolyzer to remove the deposits of Calcium and Magnesium salts. The tank is designed to hold enough acid for one complete operation.

Hypochlorite Degassing cum Storage Tanks

The hypochlorite solution flows to the sodium hypochlorite degassing cum storage tank. The tanks are made of fiberglass. The storage capacity shall be sufficient to cover the shock dosing requirement. The necessary level switches are provided, for high-level alarm, level switch for switching on/off the hypochlorite generator, low-level switch which will, in case of being triggered, interrupt the continuous hypochlorite injection and will stop the shock dosing pumps.
Two sets of (100%) fresh air blowers are installed next to the tank to blow air into the tank to blow out the entrapped Hydrogen. As an added safety precaution, the Auto switchover of the Blower occurs in the event of the operating blower tripping. Open Top Tanks do not need Blowers.

Dosing System for Continuous Chlorination and Shock Chlorination

Normally, two continuous dosing pumps are provided, for continuous flow of hypochlorite solution to the dosing point. Most of the time a set of Shock Dosing pumps are provided to meet the demand of biofouling control. While the continuous pumps dose hypo solution at a lower rate, the shock dosing pumps dose a higher rate of the solution but for a shorter time.

Instrumentation and Control

Pressure Gauges, Pressure Switches, Flow Meters, Temperature Controllers, Level Switches, Level Controllers, Hydrogen Detectors, etc., are provided in the system to monitor the operation of the chlorine production. The output from all the instruments are connected to a Control Panel to properly control and monitor the operation. These Control Panels are either Relay based or PLC based. PLC based system has an interface with the plant DCS through SCADA.

Piping and Valves

Normally PVC or CPVC pipes are used in Sodium Hypochlorite Generation Systems, with PVC or CPVC Valves and fittings. These items are not only resistant to corrosion but easy to fabricate and erect.