🔍 Key Concepts

• regenerative air heater purpose and operation in a boiler system • what conditions inside the boiler or gas path make it unsafe or undesirable for full air flow through the heater • typical boiler operations that temporarily change gas flow, temperature, or cleanliness (like soot blowing or steaming rate changes)

💭 Think About

• Ask yourself during which listed operation you might get large amounts of soot, ash, or hot debris moving through the gas path that could damage or foul the air heater. • Consider which operations are normal steady‑state conditions versus short, disruptive maintenance or cleaning actions. • Think about when you would want to protect the air heater elements by routing some air around them instead of directly through them.

✅ Before You Answer

• Identify which option involves cleaning or disturbing soot/ash in the boiler or gas path. • Decide which option would most likely send particulate matter or very hot gas surges through the air heater. • Eliminate any options that describe normal routine operation where bypassing the air heater would defeat its efficiency purpose.