Furnace Firebox - Continued.

Refractory bricks are generally classified as the following:

a. Firebrick (primary duty to withstand high furnace temperatures and the wear and tear associated with combustion)

b. Insulating Brick (primary duty to insulate the firebox from the external ambiance.)

There are many ratings associated with refractory bricks. The highest rated bricks can withstand temperatures as high as 3300 deg F.

In a furnace, the firebox wall is constructed with many layers of materials. In most cases, the following arrangement of layers is used:

a. Firebrick (innermost layer – directly facing the radiant heat).

b. Supporting structural steel layer. The purpose this layer is to provide a support mechanism for the refractory bricks and the insulation.

c. Insulation. Usually 4 to 6 inches thick slabs of ceramic fiber material.

d. External metallic cladding (outer most layer) to protect the inner layers.