In the beginning, there was gaseous chlorine, and what a miracle it was. Gaseous chlorine came in a neat pressurized bottle, was easy to transport and store, and could be administered into every phase of the water treatment process. It was an operator’s dream come true. It would kill just about anything found in a municipal environment, required very little attention during the process and best of all, it was cheap. Then came the Occupational Safety and Health Administration, the U.S. Environmental Protection Agency and liability lawyers. Accidents do happen, and when they did, people were either killed or injured, and what was once a wonderful disinfection tool turned into a horse of a different color.
The Industry Responds
It wasn’t long until the chlorine industry answered the call. Scrubber systems and all sorts of leak-detection devices were developed to protect against accidental discharges. At the regulator’s insistence, the industry devised exhaustive plans for personnel safety, emergency response and the identification of “kill zones.” Gas was still cheap to buy, but the process and the protective boilerplate quickly drove the price up to an all-time high.
Bleach was the natural alternative because it was cheap and available. Unfortunately, onsite bleach generation promised all the benefits without the storage issues, but required substantial capital outlays for complex, often difficult-to-maintain systems that could produce bleach as required.
Solid Chlorine Tablets
Moving further down the chlorine chain, the chlorine industry discovered the solid chlorine tablets. Introduced first into swimming pools, they gained immediate acceptance as a potent disinfectant, were easy and safe to handle, and although more expensive, answered a real need in the recreational market.
The tablet manufacturers were quick to explore other markets for this new alternative. In the early days, swimming pool feeders were used to turn the solid tablet into a solution for injection into water. Those early feeders were anything but consistent, earning tablet chlorination a reputation for being hard to control and pricy when compared to the alternatives of gas and bleach.
Hammonds Technical Services, Inc. was among the first to introduce a factory engineered and manufactured tablet system. Initially, pool tablet feeders were utilized, but it was obvious that potable disinfection demanded more sophistication—and so a family of Vortex feeders was developed in conjunction with positive displacement metering pumps that would provide the foundation for Hammonds’ tablet chlorinators. There are several other systems marketed today using similar technology, but all, including Hammonds equipment, share one overriding problem: the high cost of chemicals. Tablets are the most expensive form of chlorine. Their relatively high cost has kept them from the vast majority of municipal and industrial water treatment applications.
Granulated Calcium Hypochlorite
Soon after the introduction of those first tablet feeders, Hammonds visualized a much larger potential for solid chlorine disinfection through the use of various forms of granulated chlorine (granulated calcium hypochlorite). Although considerably cheaper, granulated calcium hypochlorite has two difficult physical characteristics: It is hydroscopic and cannot be stored in large volume containers such as super sacks for extended periods of time. Being hydroscopic, it quickly absorbs moisture from the atmosphere and becomes difficult to feed with consistency. On the storage and handling side, large containers build exothermic heat and cannot be stored for extended periods, especially in hot weather. What is very safe and stable in tablet form can become unstable and present a fire hazard if special precautions are not taken with large-volume containers of the product.
Seeking to address these two issues, Hammonds designed a closed environment granulated feeder that utilizes a blending chamber having a negative pressure that draws product from a sealed container of granulated calcium hypochlorite. Because the chemical is packaged in a sealed container, moisture from the environment is not introduced during the solution mixing process, making it possible to achieve consistent feed rates as vacuum draws product into the Vortex mixing chamber. Granulated material is mixed thoroughly into the solution through high energy mixing and is placed into a solution tank ready for metering into a process. Granulated calcium hypochlorite may be packaged in a simple, proprietary polybag suitable for the application that holds 5 to 400 lbs of product. The bags are easy to handle and dispose of when empty. Smaller cubic volumes eliminate the exothermic heat issue. A typical high volume potable or wastewater system might utilize bags in the range of 50 lbs with automated handling systems requiring very little onsite attention from operators.
These systems are ideal for applications where higher chemical demand rules out tablets as an alternative due to their higher cost. A sealed product package and blending system all but eliminate hazards to people, other equipment and the environment. Granulated chlorine offers our industry some exciting new options at a time when users would be well served by another alternative.
RSS: WQP Articles
