🔍 Key Concepts

• Screen tubes are water-cooled tubes placed in front of other tube banks to "screen" them from the direct radiant heat of the furnace. • In a typical marine D‑type boiler, the screen tubes are located between the furnace and the main generating/superheater bank, usually sloping up toward the steam drum. • Screen tubes usually appear as a relatively small bank of closely spaced parallel tubes directly in the flame path, not against the outer casing.

💭 Think About

• Look at the flame path from the burner opening and trace where the hot gases first travel— which labeled tube bank is positioned to shield the larger tube bank behind it? • Compare the tube banks indicated by the letters in the choices: which one is clearly acting as a protective "curtain" in front of another bank rather than forming the outer furnace wall or the main generating bank? • Ask yourself which marked tubes are not against the furnace wall and are not deep inside the convection bank, but instead sit in between, right where you would want extra protection for the superheater/generating tubes.

✅ Before You Answer

• Verify that the tubes you pick are not the main generating bank deep in the back pass of the boiler. • Verify that the tubes are between the furnace space and another tube bank (superheater or generating bank), acting as a shield. • Confirm that the tubes you select slope toward and connect into the upper drum, consistent with screen tube construction.