Stable Chlorination & Easy Chemical Transport for Rooftop Cooling Towers with Sigura™ Cal Hypo


Sodium hypochlorite (liquid bleach/NaOCl) has long been the most widely used biocide for controlling microorganisms that promote algae and biofilm formation in cooling towers. But many cooling towers located on building rooftops don’t have easy access for transporting the heavy liquid solution.
Transporting liquid beach to these sites can be precarious, especially when there is a spill hazard associated with sodium hypochlorite. This is one of the reasons why third-party service providers are often retained to manage these cooling tower sites.

One third-party service provider serving parts of the West Coast, recently evaluated the use of Sigura™ calcium hypochlorite applied through Sigura™ feed systems. The purpose of the trial was to determine the suitability of the oxidizing halogen and feed system as a replacement to commercial bleach as a cooling tower’s primary biocide. The trial was run on two 50-ton rooftop cooling units serving a regional site.

The switch has brought more consistent chlorine residual and far easier bulk chemical handling.

Issues With Bleach

The site had long used 12.5 percent sodium hypochlorite, stored on the roof. Metering pumps (0.21 GPH) dosed the bleach on a timer at 32 seconds every 400 seconds. The target residual for the water in both towers (between 0.3 and 0.5 PPM) is based on a scheduled colorimetric test. Both towers typically run at two cycles and enter blow down based on total dissolved solids (TDS) sensor readings. Using sodium hypochlorite presented two major issues at the site. The first one was location. The two 50-ton cooling towers serving the facility are located on the rooftop of an ancillary building. Once a month, service techs had to pump sodium hypochlorite from the ground floor up to the two storage drums up on the roof.

The second issue at the site was the inherent instability of stored sodium hypochlorite. There were reported issues with maintaining the desired chlorine residual, primarily due to the relatively large quantity of stored bleach and low feed rates.

Pump output had to be adjusted frequently in order to maintain the desired level, because the sodium hypochlorite being stored was deteriorating and losing chemical activity. The solution strength of bleach is constantly changing, which often makes accurate chlorine feed control difficult. Dry calcium hypochlorite has much greater stability than liquid bleach, which brings more consistency in solution strength.

Performance Trial

The service provider installed two Sigura™ A300N-GF calcium hypochlorite feeders to treat the cooling towers at the site. For the trial, tower basin water was used for supply water. Once the units were placed on line, the desired chlorine output was dialed into the feeders. After a few adjustments based on residual testing, it was determined a consistent residual was achieved at a <0.5 GPM flow rate.

Streamlined Operation

The Sigura™ A300N-GF feeder is a compact gravity feed system capable of producing high feed rates (although feed rates used for this trial were low). The feeder works with Sigura™ calcium hypochlorite tablets. A scale inhibitor in the tablets helps prevent scale build-up in the feeder for a low-maintenance chlorination solution. The unit’s precise chlorine control and highly adjustable chlorine output meets a wide variety of application needs.

The Sigura™ calcium hypochlorite tablets have long shelf life with minimal degradation – ideal for remote locations. The A300N-GF feed system’s Wave Technology dissolves tablets from the bottom, keeping unused tablets dry for producing a predictable, uniform feed rate.


Positive Changes

At the cooling towers serving the site, the A300N-GF feeders provided a consistent chlorine concentration, eliminating the need for frequent pump adjustments for the two cooling towers. Unlike when they were using bleach, getting the biocide up onto the building rooftop was not an issue. Here, just 24 tablets, approximately 14 pounds of product, provide sufficient available chlorine to supply both cooling towers for about 30 days.

Based on the positive results of the performance trial, not only did this large service provider switch this customer over to cal hypo, it also acquired approximately 80 additional Sigura™ A300N-GF feeders, which they are currently installing at other customer sites.

The company’s end goal is to soon have most of its similar type accounts, about 200 in total, transitioned from bleach to Sigura™ calcium hypochlorite.

Reassessing Cal Hypo to Address System & Site Challenges

Like this service company’s hundreds of customer sites, there are many cooling tower operations where the long shelf life, high concentration, and compact storage of Sigura™ calcium hypochlorite chemistry provides a number of key advantages. By switching to cal hypo, which contains 65 percent chlorine equivalent, operators or their service providers are now handling only about one-fifth the weight of liquid bleach.

For use in cooling tower applications calcium hypochlorite is best suited to low-alkalinity, low- hardness water and systems with low cycles of concentration. Sigura™ calcium hypochlorite and the Sigura™ A300N-GF feed system offer cooling tower operators and their service providers a highly effective biocide designed for controlling microorganisms to maintain system cleanliness, achieve associated production efficiency gains, and help guard against Legionella.

No large storage tanks are required when using Sigura™ cal hypo, so significant savings can be realized in reduced capital and maintenance costs. Plus, there’s no liquid biocide sitting in storage tanks losing solution strength, consistency, and value. Sigura™ calcium hypochlorite and Sigura™ engineered feed systems reliably make readily available hypochlorite solution on demand.

The company’s end goal is to have similar accounts transitioned from bleach to Sigura™ calcium hypochlorite.