Boiler-Water Treatment

For industrial water cooled by recirculation through a spray or tray-type tower, chromates are the most reliable from the standpoint of efficient inhibition. However, the critical concentration is high and as the sulfate and chloride concentrations increase through evaporation of the water, chromates tend to cause pitting or may cause increased galvanic effects at dissimilar metal couples. Windage losses (loss of spray by wind) must be carefully avoided because chromates are toxic. Toxicity also makes it difficult to dispose of chromate solutions whenever it becomes necessary to reduce the concentration of accumulated chlorides and sulfates. 

Because of pollution problems that can be caused by chromates, numerous inhibitor systems have been developed as alternatives— for example, organic phosphonic acids, which are effective in alkaline waters and are biodegradable [8]. Nontoxic inhibitor formulations containing mixtures of azoles and water-soluble phosphates (e.g., disodium phosphate and sodium tripolyphosphate) have been developed [9]. Sodium molybdate, which is less toxic than sodium chromate, has also been reported to be a useful component of inhibitor formulations for use in recirculating aqueous systems [9,10]. Other nontoxic, chromate-free inhibitor formulations are based on mixtures of sorbitol, benzotriazole or tolytriazole, and water-soluble phosphates [9]. 

Sodium polyphosphate is often used in a concentration of about lO-lOOppm, sometimes with added zinc salts to improve inhibition. The pH value is adjusted to 5-6 in order to minimize pitting and tubercle formation, as well as scale deposition. Polyphosphates decompose slowly into orthophosphates, which, in the presence of calcium or magnesium ions, precipitate insoluble calcium or magnesium orthophosphate, causing scale formation on the warmer parts of the system. Unlike chromates, they favor algae growth, which necessitates the addition of algaecides to the water. Corrosion inhibition with polyphosphates is less effective than that by chromates, but polyphosphates in low concentration are not toxic, and the required optimum amount of inhibitor is less than that for chromates. 

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Uses. The principal use of monosodium phosphate is as a water-soluble soHd acid and pH buffer, primarily in acid-type cleaners. The double salt, NaH2P04 H PO, referred to as hemisodium orthophosphate or sodium hemiphosphate, is often generated in situ from monosodium phosphate and phosphoric acid in these types of formulations. Mixtures of mono- and disodium phosphates are used in textile processing, food manufacture, and other industries to control pH at 4—9. Monosodium phosphate is also used in boiler-water treatment, as a precipitant for polyvalent metal ions, and as an animal-feed supplement. 

Boiler Water Treatment. Alkanolamines, in general, provide excellent corrosion protection to steel in many appHcations. When used in boiler water treatment, AMP provides excellent protection to steel and copper in steam lines through efficient absorption of CO2, effectual distribution ratio for... 

The selection of boiler-water treatment is also dependent on the type of cooling water. When cooling water reaches the boiler, various compounds precipitate before others. For instance, seawater contains considerable magnesium chloride. When the magnesium precipitates as the hydroxide, hydrochloric acid remains. In some lake waters, calcium carbonate is a significant impurity. When it reaches the boiler, carbon dioxide is driven off in the... 

The quahty of feed water required depends on boiler operating pressure, design, heat transfer rates, and steam use. Most boiler systems have sodium zeohte softened or demineralized makeup water. Feed-water hardness usually ranges from 0.01 to 2.0 ppm, but even water of this purity does not provide deposit-free operation. Therefore, good internal boiler water treatment programs are necessary. 

Chelant Control. Chelants are the prime additives in a solubilizing boiler water treatment program. Chelants have the abihty to complex many cations (hardness and heavy metals under boiler water conditions). They accomplish this by locking metals into a soluble organic ring stmcture. The chelated cations do not deposit in the boiler. When apphed with a dispersant, chelants produce clean waterside surfaces. 

High Pressure Boiler Water Treatment. High pressure boilers usually have feed water composed of demineralized makeup water and a high percentage of condensate returns. Because of these conditions, high pressure boilers are prone to caustic and acid attack. Low pressure boilers that use dernineralized water and condensate as feed water are also susceptible to caustic and acid attack. 

Barium chloride finds use in the production of barium colors, such as the diazo dyes barium hthol ted [50867-36-2] and barium salt of Red Lake C [5160-02-1], a mordant for acid dyes and dying of textiles. Other uses include aluminum refining and boiler water treatment. 

In a turbine that is running, erosion-corrosion is pretty much confined to units that are operating on saturated steam with inadequate boiler-water treatment. This type of erosion takes place behind the nozzle ring and around the diaphragms where they fit in the casing. 

Hardness Calcium, magnesium, barium and strontium salts expressed as CaCOa Chief source of scale in heat exchange equipment, boilers, pipe lines, etc. forms curds with soap interferes wKh dyeing, etc. Softening, distillation, internal boiler water treatment, surface active agents, reverse osmosis, electrodialysis... 

The major commercial applications of hydrazine solutions are as blowing agents ( 40%), agricultural chemicals ( 25%), medicinals ( 5%), and — increasingly — in boiler water treatment now as much as 20%. The detailed pattern of usage, of course, depends to some extent on the country concerned. 

This is primarily engaged in analysis of boiler water treatment matters and involves on-site studies of various problems and the chemical examination of corrosion products, boiler scales, etc. It can also carry out certain types of metallurgical, fuel and inorganic analysis. Normal wet methods of analysis coupled with a visible ultraviolet and atomic absorption spectrophotometer are used for a wide range of analytical applications. Equipment in use by the engineering insurers providing these services can include an ion chromatograph, spectrometer equipment, atomic... 

Boiler water treatment Base exchange Dealkylization Demineralization Demin, water tank Demin, water pump Bulk acid and alkali storage Neutralizing... 

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