Some facts you should know about Phosphate Treatment for Boilers

What should you be doing? First ask your boiler what limits it can tolerate. If you find yourself trying to operate to specifications beyond these limits and/or you must continuously add disodium phosphate to keep within the chosen block on the control chart, you may be in trouble. Get away from that traditional congruent phosphate program quickly and switch to an Equilibrium Phosphate program that can be made fully compatible with your system. Stop trying to follow specifications derived from other plants or organizations. They may be industry standards, but they are also capable of damaging your plant. If you didn't know how to ask your boiler the right questions and listen to its answers, you also have a monitoring and control problem to address.

PO4 vs. pH Diagram. Click for full image.

The Phosphate vs. pH Diagram shows how the control ranges for Congruent Phosphate and Equilibrium Phosphate Treatments differ. The initial Coordinated Phosphate Treatment used the Na/Phosphate ratio of 3.0 as the control range. This corresponds to the ratio in pure trisodium phosphate and control was based upon keeping below this line. Congruent Phosphate Treatment or CPT went further and recommended keeping the ratio below 2.6 and at the same time keeping the pH high enough to maintain corrosion protection. The new concept of EPT adds only TSP and lets the system seek its own equilibrium. As the diagram shows, the CPT and EPT control ranges are incompatible. EPT was initially developed at Ontario Hydro by Jan Stodola.

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This page last updated 2003-June-09