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150 HP firetube boiler operating at 110 PSIG. Steam is used for heating, pasteurization and the Clean-In-Place (CIP) system in the milk producing process.
Historically, the system was operated using 100% make-up, as there was no provision for condensate return. Further, there was no heating of the feedwater, which entered the boiler at approximately 75o F. The make-up was unsoftened; total feedwater hardness averaged 40 parts per million (ppm).
The low feedwater temperature necessitated high sulfite dosages to remove dissolved oxygen and maintain a boiler water sulfite residual. The elevated boiler water dissolved solids contributed by the excessive sulfite feed, along with heavy sludge loading from the high feedwater hardness resulted in high sludge conditioner feed and extreme blowdown rates. As chemical feed control was sometimes erratic, the boiler tubes were covered with scale ranging in thickness from 1/8" to 1/4". The high blowdown losses and decreased heat transfer both contributed to excessive boiler fuel usage.
The problems were exacerbated when a new CIP system was installed. The new system, which used 25% more steam than the one it replaced, increased the total steam demand to the point where the boiler could not keep up with steam demand under full production load.
Plant management called on International Chemtex Corporation to help solve the problem. The Chemtex representative recommended a comprehensive program that included the installation of a steam sparge to heat the feedwater and reduce sulfite consumption, softening the make-up water to decrease sludge loading and allow higher boiler water cycles of concentration, a return of condensate where possible to improve feedwater quality and further raise feedwater temperature, and insulating steam lines to reduce radiant losses. He proposed a chemical program consisting of B-289 catalyzed sulfite for removal of dissolved oxygen and B-290 sludge conditioner for on-line clean-up of boiler scale deposits.
Plant management implemented Chemtex's recommendations. Almost immediately, the boiler was able to supply all the plant's steam requirements, even under the heaviest load conditions. After one year's operation on the B-290 program, the internal inspection of the boiler waterside showed patchy areas of bare metal, and the remaining scale deposits had been softened and reduced to 1/16" to 1/8".
Not only was the boiler able to keep pace with steam demand, heat transfer was significantly improved as a result of scale removal, resulting in a reduction in stack temperature of 50 o F. The plant reported a net savings in fuel costs of over $175,000 per year.