20 SOLENISANDRITZ


Pulp Paper & Logistics


Controlling boiler water chemistry from a knowledge base


Automated systems for treating boiler water offer much more reliable results in the control of contaminants such as acids, caustics and liquors. Anderson José Beber* describes the OnGuard iController from Solenis


in getting the boiler water chemistry under control. Congruent phosphate control is the boiler water internal treatment most widely in many industries, especially in the pulp and paper, due to its inherent contamination possibilities. The great benefit is the ability of this programme to absorb small quantities of contaminants, such as acid, caustic, liquors and others. The big challenge is to maintain the sodium phosphate (NaPO4) ratio inside established limits. If the boiler chemistry is controlled within these limits, the risks of deposition and many forms of corrosion are practically eliminated.


H


igh pressure boiler users such as pulp mills have always faced challenges


Due to contamination and


variations in steam production, manual systems produce irregular results of ‘in box time’ on control charts. The first generations of


automated systems brought excellent results, with a high percentage of in box time. OnGuard iController, the controller described here, has improved this control significantly, providing much more reliable results in the boiler water treatment.


This article describes the results of the knowledge-based control applied to the high pressure boilers at a pulp mill and show precise conclusions for this controller.


Sodium phosphate Congruent Phosphate Control is the only treatment programme


for markets such as pulp and is also widely used in other industries where the risk of water contamination is possible. Although it is not new, it is by far the best choice where there can be significant feed-water contamination. The contamination can occur


from the demineralisation systems (acid and caustic), condensate (iron, copper, process streams) and specific processes (oils, liquors, etc). Along with that, the process can tolerate larger quantities of solids such as iron (maximum 10 ppb in feedwater) when compared to an All Volatile Treatment (maximum 2 ppb iron in feedwater). Researchers Marcy and Halsted


first established the concepts and limits for Congruent Phosphate in 1964. After that, in 1975,


Rosemer and Dale optimised the recommendations based on the boiler operating pressure. Rosemer and Dale in fact defined the limits for each boiler pressure group, in which the higher the pressure, the lower will be the maximum allowable solids quantity. OnGuard iController not only


controls the phosphates blend and ratio dosed into the boiler. It also can foresee short- and medium-term variations on the boiler water chemistry and steam production based on a historical data registry and knowledge over many operating days.


Congruent phosphate programme Congruent Phosphate is one of the phosphate programme options for high-pressure boilers.


Figure 1 – Congruent phosphate control diagram January/February 2018


Figure 2 – Configuration screen for the steam system on the OnGuard iController


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