🔍 Key Concepts

• Boiler furnace construction – how refractory is used to protect tube walls and corners • Function of a corbel – what a supporting ledge or fillet usually does in masonry and furnace design • Location mentioned in the question – pay attention to furnace floor, walls, and corners vs. burner area or gas path

💭 Think About

• Think about what a small fillet or ledge of refractory at the junction of floor, wall, and corners would practically do during furnace operation • Ask yourself which choice best matches a "fillet" shape rather than a separate, large structural piece • Eliminate any options that describe components clearly located elsewhere in the boiler (e.g., gas path baffles, burner assemblies)

✅ Before You Answer

• Make sure you know what refractory is used for in boilers (insulation, protection from heat/slag, shaping gas flow) • Clarify in your mind what a fillet is (shape and purpose) and where it would be placed • Check which option directly relates to joints at the furnace floor, walls, and corners, since the question defines where the corbel is used