🔍 Key Concepts

• Heat transfer and soot: Soot on heating surfaces acts as an insulator, changing how heat moves from the gas to the water/steam. • Stack (exhaust) temperature: What happens to gas temperature leaving the boiler if less heat is transferred into the water/steam? • Superheater vs desuperheater behavior: Understand how temperatures change when heat transfer in the boiler is impaired.

💭 Think About

• If the heating surfaces are coated with soot, does more or less heat get into the steam/water? Where does that ‘missing’ heat go? • Think about how exhaust gas temperature and steam temperatures are related: if the boiler absorbs less heat, what happens to the gas leaving the boiler? • Compare what each answer choice implies physically: which effect is the most direct symptom of poor heat transfer on heating surfaces?

✅ Before You Answer

• Be clear on what an uncontrolled interdeck superheater is (takes whatever heat the gas gives it; no active control). • Ask yourself whether fuel oil and air requirements would realistically go up or down if the boiler becomes less efficient. • Decide which temperature (stack, desuperheated steam, or superheater outlet) would show the earliest and most obvious sign of heavy soot acting as insulation.