🔍 Key Concepts

• Effect of soot deposits on heat transfer surfaces in boilers and economizers • Relationship between insulation/fouling and gas-side temperature leaving the boiler (stack temperature) • How soot buildup affects heat transfer efficiency from hot gases to water/steam

💭 Think About

• If soot acts like extra insulation on the tubes, what happens to the heat transfer from the hot gases to the water? More efficient or less efficient? • If less heat is transferred to the water because of soot, what would you expect to happen to the temperature of the gases that finally leave through the stack? • Look at each choice: which one is the most direct and typical indicator that the flue gas is not giving up its heat effectively?

✅ Before You Answer

• Compare what clean tubes vs soot-covered tubes do to overall boiler efficiency and exhaust temperature • Ask: in normal operation, would more soot make the stack gases hotter or cooler by the time they leave? • Eliminate options that are more related to feedwater system issues than to gas-side fouling/soot accumulation