🔍 Key Concepts

• Function of downcomers in a water-tube/package boiler and where they are located relative to the furnace gas path • How hot furnace gases are kept from directly impinging on parts that are not meant for high radiant heat • Typical furnace-side protection methods: waterwall tubes, screen tubes, refractory/insulation, baffles

💭 Think About

• Visualize a cutaway of a modern auxiliary package boiler: where would the downcomers be placed so they can carry relatively cooler water down without being overheated by flame radiation? • Which of the listed items is normally placed directly in the path of hot gases to absorb heat, and which are usually for casing protection or flow direction, not for shielding internal tubes? • Think about which component is specifically designed to form a cool water barrier around the furnace rather than just redirecting gas flow.

✅ Before You Answer

• Identify which option(s) are actually water-filled tubes exposed to furnace radiation versus solid materials. • Ask: which component in the list normally forms the furnace enclosure in a modern water-tube/package boiler design? • Confirm that the chosen option is something that would realistically be arranged between the flame/hot gas and the downcomer, not off on the casing or outer shell.