🔍 Key Concepts

• Location and purpose of tube banks in a D‑type single furnace boiler • Difference between generating tubes (water/steam circulation) and superheater / desuperheater tubes (act on steam only) • Role of screening tubes placed between the furnace and the convection bank/superheater to protect them from radiant heat

💭 Think About

• Look closely at where item "F" is positioned relative to the burner, furnace, and the main bank of tubes—does it sit in the direct flame path or farther downstream in the gas flow? • Ask yourself whether the tubes at "F" are likely carrying water/steam mixture between drums, or whether they are mainly there to protect other tube banks from radiant heat. • Which of the listed tube types would logically be exposed directly to the furnace flame versus placed in a cooler gas path?

✅ Before You Answer

• Verify whether item "F" is located between the furnace and the main generating/superheater bank, acting like a shield. • Confirm if the tubes at "F" would normally carry steam only (superheater/desuperheater) or a water-steam mixture (generating/screening/waterwall). • Check standard D‑type boiler diagrams to see which tube set is usually placed right at the furnace exit to shield other tubes from excess radiant heat.