Steam Generator Chemical Cleaning Process

Written by chris passas
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The chemical cleaning process for a steam generator removes pollutants and impurities that impede the transfer of heat within the generator that may result in system failure. The specific type of chemical cleaning process depends on such factors as the steam generator's design, flow rate, operating temperature and pressure, and the type of metal used in its construction. The process of chemical cleaning a steam generator often involves a water flush of condensate and feedwater systems, followed by an alkaline boil-out and concluded with a steam blowing of the generator.

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Flushing With Water

Residual pollutants and impurities from the fabrication of the steam generator include metal scales, welding slag, oil and dirt. Chemical cleaning removes metal scales and corrosives, but flushing the steam generator with water can remove simpler debris such as dirt and sand.

Hot Alkaline Chemical Cleaning

Hot alkaline chemical cleaning removes oil, grease and other protective coatings that were necessary during the fabrication of the steam generator, but will act as pollutants and impurities during operation. All brass and bronze components of the steam generator are replaced with steel or steel alloy components for the duration of the chemical cleaning process to avoid further pollution from the corrosion of the metals.

Steam Blowing

Steam blowing involves blowing out the main steam piping, superheater and reheater. This process can involve either continuous steam blowing or intermittent periods of steam blowing, depending on what is considered more effective for the type of steam generator. The steam blowing continues until solid particle erosion is no longer present on the plating of the main steam line.

Acid and Chelant

Steam generators that require a more thorough cleansing are treated with an acid or chelant chemical cleaning procedure. A chelant is a chemical that inhibits metal ions from reacting with other ions to create metallic scales or precipitants. Mineral acids, organic acids and chelants remove most deposits from within the steam generator.

Acid and Chelant Cleaning Methods

The circulation method of acid or chelant chemical cleaning applies to steam generators with positive liquid flow paths, and involves circulating the chemical cleaning solution through the steam generator until the chemical content of both the chemical cleaning solution and the iron and copper content of the steam generator reach a constant value. This indicates the end of the chemical reaction between the chemical cleaning solution and the iron and copper content within the steam generator. The static method of acid or chelant chemical cleaning applies to steam generators that do not allow for positive circulation of the chemical cleaning solution, and involves allowing the chemical cleaning solution to soak within the steam generator for a stipulated amount of time before flushing it out.

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