On-site Electrochlorination Frequently Asked Questions
What is the difference between Brine and Seawater Electrochlorination?
Seawater electro chlorination systems utilize a very simple electrolysis process, combining two common consumables (seawater and electricity) to generate a disinfecting agent, Sodium Hypochlorite. However, brine is an artificial solution of Sodium Chloride salt with the perfect characteristics for the electrolysis process, which is the alternative to seawater in an electrochlorination system. Seawater Electrochlorination system produces sodium hypochlorite up to 0.2% concentration, while a Brine Electrochlorination system could achieve concentrations up to 0.8% of hypochlorite. Brine Electrochlorination systems are mostly used for chlorination of potable water, whereas Seawater Electrochlorination systems are favorable for industrial uses such as power plants, refineries, and petrochemical companies.
Are sodium chloride, sodium hypochlorite, and hydrogen gas, which are the products and by-products of the On-site Electrochlorination Process, health-hazardous?
Sodium chloride crystal used in On-site Electrochlorination processes is only considered hazardous to health when it is ingested in large quantities.
The concentration of sodium hypochlorite liquid produced by the On-site Electrochlorination unit is less than 1.0%wt which is significantly weaker than commercial bulk supply ones, which is approximately 12.5%wt. However, handling such material must be carefully done. The chemical itself is slightly alkaline and forms an oxidizing and bleaching agent which is corrosive and may cause damage to skin and clothing on contact. Additionally, mixing Sodium Hypochlorite with any form of acid will generate highly toxic chlorine gas, which is a health hazard.
Hydrogen gas is a flammable or explosive gas at certain concentrations, above 4%v/v, which poses a physical danger to the personnel in the area. Moreover, if hydrogen gas is present in occupied areas, it can be inhaled into the body, and although it is considered non-toxic, it could cause an oxygen-deficient environment at high concentrations. Individuals breathing in such an area may experience headaches, ringing ears, dizziness, drowsiness, unconsciousness, nausea, vomiting, and depression of the sense. In extreme circumstances, death may occur.
For additional information, one must refer to Material Safety Data Sheets.
Can we expand the capacity after installation?
The total plant capacity may be expanded by adding additional electrolyzer skids operating in parallel, but it must be taken into account that all the ancillary equipment and process inputs must be scaled up to handle the additional capacities.
It must be mentioned that the skid does not allow for additional electrolyzers. Notice that each system is optimized and tested to certify the nominal capacity.
Which material is preferred for a hypochlorite tank, and why?
Because sodium hypochlorite solutions are corrosive, they are typically stored in either Polyethylene (PE) or Fiberglass Reinforced Plastic (FRP) atmospheric storage tanks. The life expectancy of material and its cost is the basis of our material decision. FRP lasts longer than PE; on the other hand, it costs more.
What considerations must be taken into account for the hypochlorite tanks?
Hypochlorite tanks must be placed indoors to avoid extreme temperatures and direct sunlight exposure. However, if it is installed outdoors, heat tracing, insulation, and arrangements for sun shading must be considered to avoid degradation from UV and freezing at low temperatures. Other essential considerations for hypochlorite tanks are ventilation ductwork for tanks placed indoors, level sensors, the position of overflow nozzles, pressure transducers, and intrinsic safety barriers inside the tank that will prevent sparks in a hydrogen-rich environment.
What are the main characteristics of water for the Brine fed packages?
Concentration of calcium and magnesium dissolved in potable grade water is crucial because these solids deposit on the electrode surface, leading to lower overall efficiency. A water softener is often required to bring concentrations to less than 17 mg/L (ppm) hardness.
The water supply must have <1 mg/L chlorine residual and temperatures between 10-24°C.
Since electrolysis reactions generate heat, the inlet water temperature to cells must be maintained in a certain operating range. Consequently, an inline water heater or chiller may also be required.
What are the required properties of salt for Brine systems?
or optimum operation and efficiency the salt used in our electrochlorination package must contain a certain mass fraction of solids, such as arsenic, iron, mercury, etc.; additionally, the quantity of calcium and magnesium contaminated in salt must be as low as possible because of the formation of deposits on the electrodes. The Salt is better to be high quality with min 99.7 wt% sodium chloride purity having less than 0.14% w/w (dry basis) Ca/Mg, coarsely granular, or pelletized.
How do we manage salt delivery and storage?
Salt is most often pneumatically conveyed to large storage and saturation tanks where it is stored ready for use and without harm or hazard to operations personnel. Salt is used for the preparation of brine solution as the feed to the electrolyzers in the on-site electrochlorination process. Brine is produced in a brine saturator tank that has a salt bed and by potable water being passed through it, the desired concentration of brine solution is obtained, which is 26.4%. Brine tanks are also used to store the prepared brine solution.
For bulk deliveries, saturator tanks are normally sized to hold 15-30 days’ inventory. Lower capacity packages may only require open-top, indoor, manually salt-loaded brine tanks; whereas larger capacity plants may install bulk loaded tanks outdoors. Outdoor installations may also require heat tracing and/or insulation in colder climates to prevent brine freezing. Features of these tanks can be designed by the needs of the user: ladder/cage, brine level monitoring, tank location, material construction, size, etc.
What will be the consequences of out-of-range water temperature?
Product temperature is an important parameter because the degradation of sodium hypochlorite depends on temperature.
Temperatures above 40°C drive rapid hypochlorite degradation, while temperatures less than 10°C may result in loss of anode coating as well as a conspicuous escalation of oxygen production.
How the safety of the packages is guaranteed?
As a result of a safe design, process controls, conservative hydrogen management philosophy, and advanced airflow measurement techniques, on-site electrochlorination is proved to be a safe option with no significant records of incidents.
Why the hydrogen gas generation in the process is worrisome?
Hydrogen mixed with air can form a highly flammable and dangerous mixture which can cause ignition and, in most cases, explosion if reached a certain concentration (4% in air) coupled with an ignition source. Hydrogen is present in the package in three different places: inside the electrolyzer, in the pipeline connecting the electrolyzer to the hypochlorite tank, and in the hypochlorite tank itself. Several measures must be considered at each of these three including the elimination of ignition sources and/or reduction of the hydrogen concentration significantly below its Lower Explosion Limit (LEL).
How the hydrogen gas is removed from the system?
To prevent and reduce the hydrogen gas accumulation in any section of our process, we manage to remove diluted hydrogen at the initial states of generation in our electrochlorination package. Hypochlorite solution and hydrogen gas mixture will be separated after leaving the electrolyzer cells in degassing tanks. Then hydrogen gas is diluted by air blowers. When its concentration walks into the safe range, it will be released from the tanks into the atmosphere.
What is the total plant safety?
Hydrogen gas detectors are included for monitoring possible gas leaks as hydrogen is generated as a byproduct in electrolyzers. Recommended installation is near the top of the hydrogen vent piping on the hypochlorite degassing tank.
Emergency shower and eyewash must be available nearby at all times. Also, a mist separator may be provided to guarantee that no acid vapors will disperse in the environment.
Total plant safety ensures that these types of detection and monitoring systems are interlocked with the plant operations center to notify of emergency chemical releases or equipment failure.
What is the evaluated and expected life of equipment?
The heart of any electrochlorination package is the Electrolyzer which has a life span dependent on the operating and site conditions in addition to proper maintenance. In ideal conditions, the Anodes may last for 7 years or longer.
The overall life of the package depends on the hours of operation, environmental factors, and maintenance periods.
The package is made up of ancillary equipment such as tanks, pumps, etc., that will be impaired at different rates depending upon water/salt quality and environment. Packages should last over 10 years with proper maintenance and electrolyzer replacement.
How much does the Transformer/Rectifier matter?
Consistent, steady flow of direct current (DC) to the electrolyzer is required to drive the process, and therefore a Transformer/Rectifier is always provided with the on-site electrochlorination package to turn available AC power to DC.
Transformer/Rectifier units are either placed near the electrolyzer or inside a nearby electrical room.
What is the philosophy of product hypochlorite injection?
In electrochlorination packages working in batch mode, a brine solution is cycled through the cell until it generates the scope capacity of hypochlorite. Then it is sent to degassing tank/tanks, and finally, the injection pumps will send the generated product to the point of use.
On the other hand, in continuous processes hypochlorite injection is carried out through continuous and shock dosing. Shock dosing is typically operated 3-4 times a day, with the chlorine concentration of 2-4 times more than the one in continuous dosing, to guarantee disinfection of biological particles in water.