Automated Chemical Feed and Control System for Coordinated Phosphate pH Boiler Water Treatment Programs, 1996 Engineering Conference Proceedings

Loraine A. Huchler, P. E. & Randy Stein

Betz Water Management Group

A variety of phosphate-buffered water treatment programs including coordinated phosphate pH, congruent, and equilibrium phosphate are applied to minimize corrosion and maximize boiler reliability in industrial boilers using high purity feedwater. These treatment programs require that the ratio of two interde-pendent variables be controlled: pH (hydroxide concentration) and phosphate concentration. Manual adjustment of the chemi-cal feedrate to maintain the boiler water sodium (hydroxide) or pH to phosphate ratio in the correct control range can be difficult and manpower intensive. An innovative, automated chemical feed and control system has been developed specifically for congruent, coordinated phosphate pH and equilibrium phosphate treatment programs which maintains the boiler chemistry within tight control limits. This paper describes this chemical feed and control strategy as well as results from one of the field trials for a coordinated phosphate pH program. The data from the field trial on a 6.21 MPa (900 psig) boiler show excellent results, with a greater than three-fold improvement in conformance to the control ranges for pH and phosphate and a total elimination of manual adjustments following installation of the chemical feed and control system.