Calcium hypochlorite is a low-cost, solid biocide option for treating cooling towers. It has a number of advantages over the other options listed in Table 1.
Transportation, Storage and Handling
Treatment of cooling towers with chlorine gas is becoming increasingly rare. Solid halogen sources have the advantage of no potential for gas leaks or liquid spills.
Chlorine dioxide is an explosive gas at concentrations greater than 10% in air.2
Calcium hypochlorite is a highly concentrated form of chlorine and so minimizes shipping costs compared to sodium hypochlorite.
In NFPA 400, the National Fire Protection Association recommends secondary containment that is sufficient to contain a spill from the largest vessel plus 20 minutes of fire water.3 Fire water volumes will vary, but the following table shows the storage volume of NaOCl vs cal hypo.
Pounds of AvCl
NaOCl (12% AvCl, 10 lb/gal (75 lb/ft3), 9 lb AvCl /ft3)
Ca(OCl)2 (65% AvCl, 50 lb/ft3, 32 lb AvCl /ft3)