Disinfection Technology: New Vortex Feeder Reduces Chlorine Risks

The municipal water treatment industry continues to face pressure from all sides to provide safe, dependable water supplies while being challenged to reduce risks associated with chlorine gas, lower operating costs and use less labor for operations and maintenance. Solid chlorine in the form of calcium hypochlorite tablets has provided an excellent alternative.

Calcium hypochlorite tablets are stable with a shelf life of up to one year and are considered safe to handle and store, eliminating the capital expense of containment and bulk handling associated with bleach.

To Transform the solid tablets into a usable solution, water simply is passed over the tablets, and depending on the configuration of the feeder and characteristics of the particular brand of tablet, a consistent calcium hypochlorite solution is created. To change the amount of chemical being placed into solution, the amount of water passing over the tablets is varied resulting in more or less erosion of the solid tablet.

Until now, there have been two basic classes of non-powered tablet feeders. One immerses the entire charge of tablets, making control and intermittent operation difficult.

The other can be described as a gravity flow device, which takes a pressurized source of water and passes a metered amount over only a small portion of the tablets.

A disadvantage of such devices is that they typically require large volumes of water to complete the dissolution process. For example, a two-pound-per-hour feeder may take as much as 18 gallons of fresh water per minute to dissolve the tablets. To change the erosion rate, the flow rate must be varied through the system.

A new vortex gravity feeder changes all the rules for this type of device. The vortex technology, required a reduced volume of water to dissolve much larger quantities of chemical per hour. As an example, the company's Model 80G with a storage capacity of 80 pounds of tablets can delivery 10 pounds chlorine per hour with only 8 gpm of water flow. The rate of dissolution can be infinitely varied from zero to maximum delivery without changing the rate of flow through the feeder.

Manipulation of the vortex within the mixing chamber of the feeder re-circulates a portion of the total flow passing over the tablets, providing for precise control of the dissolution process without changing the overall total flow rate. Although this design will operate on less water, there is no reasonable limit to the amount of flow passing through the feeder, enabling the user to match solution concentration with water characteristics.

These new feeders require only 0.8 gpm per pound of chlorine delivered in one hour. Reduced water demand is easier to accommodate, and steady flow rates mean fewer external components, valves and controls.

These new feeders are designed around the latest version of Hammonds' proprietary vortex designs that have no moving parts. The company currently offers a variety of units, ranging from small units that deliver .013 pounds of chlorine per hour to large custom feeders that can deliver up to 350 pounds of chlorine per hour. This new family of feeders will perform in a wide range of applications including high volume potable water treatment and combined sewer overflow.