Operation and Maintenance Costs for Chlorination

Chlorine is commonly available in three different forms: gaseous chlorine, calcium hypochlorite, and sodium hypochlorite, which are all used in chlorination.

Gas chlorine is typically packaged in 150 lb cylinders and 1-ton containers. This is 100% elemental chlorine stored as a liquified gas under pressure. The chlorine is fed to the process using a pressure feed system which applies the chlorine gas directly to the process or a vacuum operated - solution feed system which uses a water operated ejector to create a chlorine solution which is applied to the process.

Calcium hypochlorite is typically packaged as a solid tablet containing 60% active chlorine. The chlorine is fed to the process using a simple tablet feeder that passes the process water through a tube of tablets, causing the tablets to dissolve into the water. More sophisticated tablet systems dissolve the tablets in water making a solution of controlled chlorine concentration, which is then fed to the process using a chemical dosing pump.

Sodium hypochlorite is a liquid containing 12-15% active chlorine when fresh. Sodium hypochlorite is typically delivered to plant storage tanks by truck and applied to the process using chemical dosing pumps. With this form of chlorine, the concentration decays over time.

On average, chlorine gas costs about 1/3 the cost of sodium hypochlorite and 1/5 the cost of calcium hypochlorite. So users of chlorine gas see significant savings in chemical costs. Also, sodium hypochlorite concentration decays over time, which represents an additional cost because more must be fed to achieve the same chlorine dosage.

Maintenance Frequency

Maintenance should be carried out on all chemical feed equipment, with the frequency being determined by the quality and quantity of the chemical used. Specific equipment and application conditions can also affect maintenance frequency. In the case of a gas chlorinator, this would include the total system capacity. High capacity gas chlorine systems using liquid vaporizers require more maintenance than systems using gas only.

For sodium hypochlorite installations , chemical dosing pumps are typically used. These can vary in type from small solenoid driven pumps to large peristaltic pumps, which would require more frequent and costly maintenance.

Simple tablet feeders using calcium hypochlorite tablets require very little maintenance. Tablet feeders that dissolve the tablets into a controlled concentration solution before feeding to the process are more complex and require more frequent maintenance.