Determining of kinetic characteristics of chemical cleaning from scale deposits in steam boiler generating tubes

Abstract

Reliable operation of steam boilers is maintained by periodic in-service cleanings of the internal surfaces of the steam-water path. Such cleanings can be made with traditional and new acid cleaning agents. The nec-essary condition for developing an effective chemical cleaning program is predicting its required duration taking into account the properties of the detergent used and the contamination of the metal surface. Insufficient duration of this operation leads to increased residual contamination, while excessive duration – to metal dissolution. Traditionally, the required time for chemical cleaning is evaluated according to the results of laboratory experiments. The aim of this study is to obtain analytical dependencies and characteristics describing the kinetics of the acid stage of steam boiler chemical cleaning. The laboratory studies of the acid stage of chemical cleaning of samples of high-pressure steam boiler generating tubes were performed by the chemical etching method. The rates and completeness of the removal of lumpy and uniform deposits by acid reagents were also determined. The method of mathematical modeling was used to obtain the kinetic equation. The conditional purification rate constants for this equation were found by the methods of statistical processing of laboratory results. A description of the scale removal rate from the inner surface of the steam generating tubes is proposed as a first-order kinetic equation depending on their specific contamination and reagent washing solution acidity. The equation allows calculating the required duration of chemical cleaning for providing a given value of specific residual contamination of the metal surface. According to the results of the laboratory studies, the conditional rate constants of purification were determined using proven detergent reagents and types of scale. The adequacy of the obtained results is ensured by their consistency with real-life data. The results of the study can be used to select the technology of acid stages of chemical cleaning of lumpy and uniform deposits and justify their duration for providing standard values of specific residual contamination of the surface of steam generating tubes of drum boilers.