Tratamiento de torres de enfriamiento: cambios y desafíos

Tratamiento de torres de enfriamiento: cambios y desafíos

The History of Cooling Tower Treatment

Oxidizing biocides offer the primary defense mechanism against microbiological fouling in cooling systems. Chlorine is the biocide most often associated with water treatment. Produced as an element by Carl Wilhelm Scheele in 1774 and confirmed by Humphrey Davy in 1810, chlorine has had an enormous impact on global health since its introduction as a sterilizing agent for drinking water in the early 1900s, and for other applications even earlier. 

For much of the 20th century, gaseous chlorine was the primary cooling water oxidizing biocide because of its effectiveness and low cost. However, safety issues and changes to cooling water scale/corrosion inhibitor chemistry have necessitated a change in biocide chemistry. 

Cooling Tower Treatment Chemistry

Blending chlorine and water initiates the following reaction:

Cl2 + H2O → HOCl + HCl

Hypochlorous acid (HOCl) kills microbes. But, as the water pH rises, especially above approximately 7,5, the following dissociation reaction occurs: 

HOCl  → H+ + OCl

El ion hipoclorito (OCl) es mucho menos efectivo que el ácido hipocloroso como agente biocida. 

Evolution of Cooling Treatment

This was largely not a problem in the middle of the last century, when cooling tower treatment commonly consisted of sulfuric acid for scale control and sodium dichromate for corrosion control. These programs offered straightforward control, with pH typically maintained within a 6,0–6,5 range. However, issues related to hexavalent chromium toxicity, emerged in the 1970s and 80s. They led to the abandonment of this treatment method for all open cooling water and most closed cooling water systems. In most cases, the replacement programs were based on a core chemistry of inorganic and organic phosphates (phosphonates) typically operating at a pH range of approximately 8,0–8,5. donde el cloro y la lejía de grado industrial se volvieron mucho menos efectivos en estas aguas más alcalinas.  

cooling tower treatment

Cooling Tower Treatment Solutions

Con lo que llegamos a la actualidad, donde los programas de fosfato y fosfonato para inhibición de incrustaciones y corrosión se están eliminando de modo gradual por las inquietudes ecológicas relacionadas con la descarga de fósforo, como puede evidenciarse en los numerosos brotes de algas tóxicas en los Estados Unidos. Also, much more effective phosphate-free scale/corrosion control methods, such as ChemTreat’s FlexPro® technology, are now available. However, these programs still operate at a moderately basic pH, which inhibits the effectiveness of chlorine and bleach.  

Bleach-activated bromine provides an alternative option by producing the analogous hypobromous acid (HOBr). HOBr dissociates at a higher pH than HOCl and can be more effective in alkaline waters. Compounds like monochloramine (NH2Cl) (such as ChemTreat proprietary SurfClean™ CL4515) and monobromamine (NH2Br) have also been developed. Although weaker than HOCl or HOBr, they penetrate the slime produced by microbiological colonies more efficiently, killing the underlying organisms.  

ChemTreat has also developed a new stabilized halogen chemistry that offers better contact properties of the biocide, improving killing efficiency. (A Midwestern utility presented a paper on this chemistry at the recent 39th Annual Electric Utility Chemistry Workshop.) These programs can also be supplemented with nonoxidizing biocides that help offer a “one-two” punch against cooling system microbiological fouling.   

Comuníquese con ChemTreat para obtener ayuda en el diseño de un programa de tratamiento personalizado para su aplicación. Al igual que con otras tecnologías, se requiere un análisis detallado para determinar la viabilidad de utilización de los métodos. Siempre consulte los manuales y las guías de su equipo.