THERMAL EXPANSION: Of necessity parts of any incinerator system are hot while other parts may be near ambient temperature. This temperature differential causes many problems.


Refractory Lining - Expansion Joints: A refractory lined metal vessel is constructed of several layers - steel plus one or more layers of brick or hard castable refractory. During operation the layer closest to the combustion area is hotter than the outer layer.  Expansion differences require that soft joints be built into the refractory layer to avoid pressure stresses, crushing and loss of refractory material.  Refractory linings constructed of ceramic fiber blanket or board don't usually have these problems, but might have others!

Source of problem: Poorly designed or installed refractory lining.


Steel Shell - Expansion Joints:  Metal vessel shells expand when hot.  Incinerator shells are often designed for operation as high as 400o F to guard against dewpoint problems.   A furnace or duct anchored at both ends can exert tremendous stresses when heated, causing deformation unless a bellows or other expansion joint is included. A cold waste gas plenum or relatively cool boiler shell expands less than the hot furnace shell it may be welded to, causing deformation or cracked welds. A hot flue gas tubesheet may expand more than the associated tubes or shell in a waste gas preheater, causing cracking at the welds.

Source of problem: Inadequate provision for unequal expansion.



Tie Down Points:  Horizontal vessels are normally supported by saddles.  Even if an expansion joint between the vessel and associated stack or boiler is installed, if the saddle at each end of the vessel is bolted securely to the concrete foundation, then the vessel is not free to expand and deformation will result. One saddle should be equipped with a slide plate to allow movement.

Source of problem: Improper saddle design.


Stacks: Incinerator exhaust stacks expand when heated. Stack length can increase substantially, depending on the shell temperature, which may range above 400o F. A stack supported by guy wires can exert enough force to deform or break the wires unless provision is made when the guys are tensioned during installation. A freestanding stack subject to rain or winter weather will experience uneven cooling - result: "bowing" of the stack as one side becomes cooler than the other. External insulation or a standoff "rainshield" with air gap will protect from uneven cooling.

Source of problem: Improper stack design.