Prevention of vapor phase corrosion by halogens in brewery pasteurizers.

Meier, D.A.

Abstract
Microbial contamination of the spray water used in pasteurisers can block and/or corrode parts of the equipment. For this reason, water intended for such use is normally treated with a biocide, of which the halogens chlorine and bromine are among the commonest. However, both of them (especially chlorine) are volatile, corrosive and toxic to humans as well as microorganisms, thus presenting employee safety problems. The most serious damage from an economic viewpoint is caused by water and chlorine vapours condensing together on metal surfaces, producing a film of an extremely corrosive solution of chlorine. This can occur whether pure chlorine gas is used or any of a variety of liquid and solid chlorine compounds. (All of the compounds used give off chlorine rich vapours on contact with water). Bromine and those of its compounds used for this purpose behave in a similar way. Achieving a high standard of accuracy in monitoring and controlling halogen dosage systems is difficult and laborious. It may be preferable to use halogens only in the cooler parts of the pasteuriser, and treat the hot zone with a different type of biocide. The effects of a "chlorine stabiliser", a manufactured chemical product of unspecified composition which when added to chlorinating compounds serves to reduce the volatility of the chlorine contained therein (thereby both reducing corrosion levels and economising on the biocide by reducing evaporation losses) are described. Trials in a brewery produced a reduction in corrosion levels, when the stabiliser was used with chlorine, of between 50 and 80%, and when used with other halogens (e.g. bromine) of between 25 and 50%. In addition, the task of controlling chlorine levels was made easier by using the stabiliser.
Keywords : bromine chlorination chlorine corrosion pasteuriser stabiliser water