Question 20Steam Plants - 1st Asst/Chief

The correct answer is D. According to the illustration SG-0003, item number 7 represents the "insulating block" in the typical boiler furnace rear wall. Insulating blocks are used to line the interior of the furnace to provide thermal insulation and protect the outer walls from the high temperatures within the boiler. The other answer choices are incorrect because: A) Item 3 represents the "burner", which is a different component of the boiler furnace. B) Item 1 represents the "boiler shell", which is the outer casing of the boiler, not the insulating material. C) Item 2 represents the "refractory", which is a different type of insulating material used in the furnace.