Inferred Boiler pH from Conductivities in Solutions Containing Sodium Phosphate, Alkalizing Amines, and Amine Decomposition Products

ABSTRACT

Accurate knowledge of the pH in boiler water is an important and central chemical parameter for the monitoring and control of the boiler chemical conditions and is critical to minimizing the corrosion processes. pH measurements, however, are not always easily or accurately measured, so alternative means of correctly estimating the boiler pH can be useful for achieving these goals. In certain situations, the conditions are even quite complex and challenging since the impurities which negatively affect the chemical parameters arise from the treatment chemicals themselves, such as, for example, the products of the thermal decomposition of organic alkalizing amines used for pH control. Thus, it is the purpose of the present study to show an alternative way by means of the calculation of the inferred pH from the specific conductivity and the conductivity after cation exchange and to describe its application, together with these conductivities, to the monitoring and control of the boiler water in relatively complex solutions in which sodium phosphates, alkalizing amines, and amine decomposition products are present. The methodology described in the paper is applied in a cogeneration plant with a dual pressure heat recovery steam generator equipped with an air-cooled condenser, where, as demonstrated, very good results were achieved. The study also emphasizes the main concerns and disadvantages regarding the use of organic alkalizing amines in water/steam cycle water treatment.

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