B. Buecker
May 1, 1992
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Journal
Power Engineering
Abstract
This paper discusses sodium phosphate compounds, notably trisodium and disodium phosphate which have been used for years at many fossil-fired power plants for boiler water treatment. The principal purpose is to buffer the boiler water at a suitable pH while adding a compound, PO{sub 4}, which reacts with contaminants to form a non-adherent sludge. Utility chemists usually try to maintain sodium to phosphate ratios within a narrow range 2.3/2.6 to 1. This range provides the best buffering capabilities without exposing the boiler tube metal to acidic or caustic corrosion. In November 1986, a POWER ENGINEERING article by Thaler and Sinha outlined a list of practical calculations which allowed utility engineers and chemists to determine the sodium to phosphate ratios in boiler water. The article discussed the triprotic nature of phosphate in aqueous solutions (H{sub 3}PO{sub 4}H{sub 2}PO{sub 4}, HPO{sub 4} and PO{sub 4}). It showed how the various dissociation constants of these species can be used to determine the concentrations of trisodium, disodium, and monosodium phosphate in solution, and from that the sodium to phosphate ratio. Utilizing the information in that article, this author wrote the calculations into a BASIC program. The program has been used to track the sodiummore » to phosphate ratios of coal-fired boilers at a midwestern utility.« less