The control of bio-fouling and sanitizing water systems by chlorination has been proven to be the most effective method for water treatment. Hypochlorination from salty water provides an effective anti-fouling method of water treatment that is safe for personnel and the environment.

The generation of sodium hypochlorite (bleach) from on-site hypochlorite generators is the safe anti-fouling and marine growth prevention alternative to chlorine gas chlorination systems as the chlorine generated in the generator is locked up as sodium hypochlorite at concentrations below the threshold of hazardous materials (1%) mandated by the EPA.

Electrichlor on-site hypochlorite generators provide sodium hypochlorite to control marine growth in industrial cooling water equipment, water/wastewater treatment in water supply systems and for refineries and offshore production platforms in Class 1, Division 1 & 2 hazardous locations. Electrichlor hypochlorite generators are suitable for indoor locations, or outdoors on a concrete foundation with a sunshade. However, in freeze conditions, indoor locations are recommended. Due to elements in seawater that can be affected by electrolysis, seawater is not recommended as the medium for producing hypochlorite for drinking water applications.

Seawater Systems
 
In industrial and off-shore marine seawater cooling water systems, hypochlorite derived from seawater is introduced into the cooling water system to prevent bio-fouling in piping and equipment.

In industrial plants such as power stations, chemical plants and refineries, seawater is usually drawn from a pit or sump through seawater supply pumps located close to a seawater inlet pipe or channel.

The seawater to the hypochlorite generator(s) is piped from the downstream side of the seawater supply pumps to provide the salty water from which the hypochlorite is derived.

Seawater passing through the generator is converted to sodium hypochlorite in a constant flow “once through” process providing a concentration of up to 1500 mg/l of sodium hypochlorite. The hypochlorite is collected in a degas/storage tank before being returned and diffused with the incoming seawater in the seawater supply pump(s) pit or sump. In most applications 0.1 to 0.3 mg/l of free available chlorine above the seawater chlorine demand is sufficient to control marine growth in cooling water systems. The chlorine demand of seawater can range from less than 0.5 mg/l in open ocean situations to 5 or 6 mg/l in coastal and harbor areas. In situations where the chlorine demand fluctuates, a shock treatment may be necessary from time to time. Should shock treatment be required, it should be accompanied with a suitable de-chlorination method located before the seawater return to ensure the local marine species are not affected by the release of over chlorinated seawater. The de-chlorination process can be controlled by measuring the free available chlorine with a chlorine analyzer at the outlet of the seawater return system, and then injecting the correct amount of de-chlorination chemical automatically.

Due to the high levels of Ca and Mg in seawater that build up on the negative (cathodes) electrodes, cleaning will be required from time to time. To facilitate this, Electrichlor seawater systems are equipped with a cleaning system based on the use of sulphamic acid. Sulphamic acid is an inert, dry crystalline powder, similar to sugar and is universally available in 25, 50 and 100 kg bags that can be stored in a dry environment for up to 5 years. Cell cleaning is achieved by circulating a 10% sulphamic solution through the hypochlorite generator for 40 minutes once weekly or after every 200 hours operation. As the powder is safe to handle when dry, a minimal amount of protective gear is required.

Brine Systems
 
The generation of hypochlorite from brine is replacing gaseous chlorination systems in water and wastewater treatment plants around the world.

In these systems food grade salt (NaCl) is loaded into a brine saturator and fed with softened water. A saturated (26%) brine solution from the saturator is mixed with softened water to produce a 3% brine concentration that is batch fed through the hypochlorite generator(s). The batch is recirculated several times to raise the concentration to 8000 mg/l and exhaust the NaCl in solution. The batch is then dumped into a degas/storage tank from where it is injected into the water supply or wastewater systems.

As softened water is used in brine systems, only minimal acid cleaning is necessary, if at all. However, Electrichlor provides an integral acid cleaning system as a standard product with brine systems, so that cleaning can be accomplished if/when required.

Materials
 
Electrichlor electrolytic cells are all titanium with DSA (dimensionally stable) anodes coated with MMO (mixed metal oxides). No other metals are used in the manufacture of Electrichlor hypochlorite cells.

Description
 
Electrichlor electrolytic cells are highly efficient due to the patented monopolar, multipass circular configuration that allows a progressively longer residence time for the adsorption of Cl- into the outgoing hypochlorite solution (see Fig. 1). Electrichlor electrodes have an even current density over all anode and cathode surfaces due to the unique physical and electrical design which further enhances the overall efficiency of the Electrichlor electrolytic cell, promoting long anode life. All wetted parts of the Electrichlor cell are MMO (Mixed Metal Oxide) on anode active surfaces.
Cells are manufactured such that the anode assembly can be removed easily without the use of special tools; only a wrench is necessary for the complete disassembly. Should anodes need inspection or replacement, they can be dismantled in place and the anode assembly returned for replating. Due to their long operational life, (10 years and beyond) spare anodes are not necessary to be held in inventory; however, should they need replating, they can be returned to Electrichlor.
Electrichlor electrolytic cells are guaranteed against defective parts for 12 months from startup and for 5 years for the MMO anode coating under normal operating conditions.

Hydrogen gas is a by-product of the sodium hypochlorite process. Hydrogen disassociates readily with water and can be completely disengaged by holding the gaseous hypochlorite in a degas tank for a minimum of 7 minutes. The degas tank is equipped with a blower to dilute the hydrogen with ambient air to below the threshold of the LEL (lower explosion level). The hydrogen/air mixture is then exhausted to atmosphere.

Electrolytic Cells
 
As the water flow within the tubular electrolytic cell is tangential to any build up of Ca and Mg on the surface of the cathode tubes, the fluid flow will cause the build up to flake off and be washed out through the system. This promotes self cleaning in Electrichlor electrolytic cells.

Types
 
There are two types of electrolytic cell design; monopolar (multiple poles) and bi-polar (one pair). Monopolar cells have all cathode surfaces reacting with an equivalent matching anode surface, so that for each anode plate or tubular surface there is an equivalent cathode. In a bi-polar cell there is a single anode at one end of the cell and a single cathode at the other. A series of parallel titanium plates with one side MMO coated are placed between the anode and cathode. When operating, with seawater flowing between the plates the dc current passes from the anode to an uncoated titanium plate, through the titanium plate, and then exits from the surface of the MMO coating, across the seawater to the uncoated side of the next plate and so on until the current reaches the cathode. Because the internal current paths cannot be predicted, the MMO coatings in bi-polar cells may suffer excessive wear rates and be prone to premature failure.

All equipment installed in/on Electrichlor hypochlorite generators has been selected for 30 years service. Only quality equipment is installed to ensure the maximum life possible.

Materials
 
Electrichlor hypochlorite generators are equipped with materials to mitigate corrosion. Due to the nature of the process and the corrosive environment where this type of equipment is installed, Electrichlor hypochlorite generators have been manufactured from non-corrosive materials.

• Cell cubicles - weather resistant NEMA 4X (IP-54) 316L stainless steel
• Skids - 100 x 50 mm 316L stainless steel
• Degas Tank – FRP with a nexus veil
• Pipework – schedule 80 CPVC
• Valves – CPVC or PVC
• Pumps – either magnetic drive FRP or titanium
• Degas Blower – 316L stainless steel with non-sparking fan
• Motors – TEFC or explosion proof in hazardous areas
• Instruments – inert wetted parts or fitted with gauge isolator
• Control Cubicle – weather resistant NEMA 4X ( IP-54) 316L stainless steel

Control System
 
Each hypochlorite generator is manufactured for “Stand Alone” service and therefore is equipped with an individual control system. This means that in locations where multiple units are installed, each unit can be operated independently and individually from its control station or from a remote location over the customer’s DCS system.

The control cubicle is equipped with a PLC and a 12” color touch screen with graphic pages for operator interface and operation. Alarms are annunciated on an alarm page and operate a red strobe light on top of the control cubicle.

Hydrogen Dispersal
 
Hydrogen generated in the electrolytic process and entrained with the hypochlorite, is allowed to settle in the degas tank for a minimum of seven minutes. Ambient air is blown into the top of the degas tank to reduce the hydrogen/air concentration to below the lower explosion level of hydrogen. The mixture at a concentration of less than 1% hydrogen is then exhausted to atmosphere.

Acid Cleaning System
 
Each generator is equipped with a small acid tank and a recirculating acid pump. The acid tank is sized to allow the electrolytic cells to be cleaned. A sulphamic acid concentration of 10% is recirculated through the electrolytic cells for 40 minutes to remove Ca and Mg buildup on the negative electrodes. On the completion , soda ash is added to the liquid to neutralize the solution and recirculated for a further 3 minutes. The system can then be drained and flushed and returned to service. Cleaning is conducted from the operator’s touch screen once weekly, or after every 200 hours operation.

Electrichlor hypochlorite generators are suitable for installation in refineries and offshore production platforms in Class 1, Div. 1 & 2 hazardous locations. All electrical equipment that may cause a spark is installed in purged NEMA 4X enclosures that require instrument air or inert gas connected to a purge control panel. Flameproof motors and intrinsically safe instruments are provided on pumps and equipment where required.

The following information should be followed in selecting or specifying a sodium hypochlorite generator:

• Cell construction – tubular of monopolar design.
• All electrodes – titanium with DSA anode coating of MMO guaranteed for 5 years.
• Removable anodes – without the use of special tools.
• Hypochlorite output guarantee - >4.5kW/kg of equivalent chlorine with all auxiliaries operating.
• 12” color touch screen.
• Equipment to be skid mounted – on 100 x 50 mm 316L SS channel.
• Equipment housing materials to be weatherproof and non corrosive – FRP and 316L stainless steel.
• Degas and acid tanks to be FRP or PVC.
• Generator to be suitable for indoor or outdoor installation.
• Pipework and valves to be schedule 80 CPVC/PVC.
• Instruments to have either non-metallic wetted parts or be fitted with gauge isolators.
• Integral sulphamic acid cleaning.

Hypochlorite Generator Selection Chart

Selecting an Electrichlor hypochlorite generator can be achieved from the Selection Chart below or by forwarding the following information to Farwest:

Flow rate of water to be chlorinated Level of chlorination (normal) Level of chlorination (shock) Water analysis table (if possible)

m³/hour mg/liter mg/liter to include chlorine demand**

** Chlorine demand is the exact dosage of chlorine necessary (mg/liter) to kill all water-borne bacteria, pathogens and algae, and not leave any excess (free) chlorine in solution.

How to Order

Contact Farwest Corrosion Control at (310) 532-9524 for product information, configuration assistance and pricing. Or email marine@farwestcorrosion.com