A new chemical cleaning method for power plants, especially for plants with once-through boilers, is described. In this method chemical cleaning of the loop is accomplished by utilizing temperatures of over 100 C and pH values down to about 4.0. The acid dosing—HCl or H2SO4—takes place in the feedwater discharge piping after the boiler feed pump. Before the latter, hydrazine is added to raise the pH value to over five in order to protect the pump. This serves simultaneously as a “transport medium” for the acid through the loop. In addition, hydrofluoric acid can be added to the cleaning solution for the removal of silica, and citric acid for complexing of the dissolved iron. The latter measure will prevent the reprecipitation of dissolved iron. At the time of writing 14 Benson boilers, two Sulzer monotube boilers, and one drum boiler with the associated power-station equipment have been chemically cleaned by the method developed. The cleanings actually carried out are described in part and the information derived from them explained in more detail.

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