Question 277Steam Plants - 1st Asst/Chief

The correct answer is D) Sodium phosphate. Sodium phosphate is a common chemical used in boiler water treatment to precipitate out calcium minerals that can cause scale buildup in boiler systems. Calcium and other minerals dissolved in the boiler water can form hard deposits on the boiler surfaces, which reduces heat transfer efficiency and can potentially damage the boiler. Adding sodium phosphate to the boiler water causes the calcium minerals to precipitate out of solution, preventing scale formation. The other answer choices are incorrect because they do not specifically address the precipitation of calcium minerals. Phenolphthalein is an indicator used to test pH, caustic soda (sodium hydroxide) is used to raise pH, but neither of these directly precipitates calcium from the water.