Page 303 - Wastewater Solids Incineration Systems

264 Wastewater Solids Incineration Systems

• Delivery time of standard-sized bricks is considerably less than for special-
shaped bricks.
• Cost of standard-sized bricks is approximately one-fifth that of special-shaped
bricks. The labor costs for building a complete hearth are nearly the same,
though there are more standard-sized bricks to handle. The overall cost of a
hearth with standard-sized bricks is approximately 40% that of a special-
shaped hearth.

1.8.2 Refractory Materials
The significant properties of a refractory, including high-temperature strength,
depend on its mineral makeup and the way these materials react to high tempera-
tures and incinerator environments. After refractory material (bricks or castable) has
been fired, fine and coarse materials form a ceramic bond.
The most significant properties of refractories are those that allow them to with-
stand conditions found in an operating incinerator. Refractories must withstand the
maximum service temperature in the incinerator at the combustion hearths and in
the vicinity of the burners.
Chemical reactions within an incinerator can contribute to ultimate destruction
of refractory materials. An experienced refractory supplier must know the chemicals
and gases that will be released in an incinerator before recommending the correct
refractory. The experiences of past incinerator operators are invaluable in deter-
mining the long-range history of a particular refractory material.

1.8.3 Hearth Repair and Replacement
A hearth should be replaced only when there is danger of collapse. As long as the
hearth has the proper arch, it can remain in use even if there is some localized
damage (loose or missing bricks or erosion from burner flame impingement).
A section of loose or missing bricks or even a melt-through by a burner flame can
be patched using castable refractory with stainless steel needle reinforcing. This is
accomplished by placing plywood supports against the underside of the damaged
hearth to carry the load to the next lower hearth. Loose and damaged bricks must be
removed before filling the void with the castable-stainless steel needle mix.
An in-hearth may lose one or more rows of bricks, even though the remainder
of the hearth has sufficient arch. To replace missing rows, workers need to install
temporary supports under the hearth and carry the load to the hearth below. The
exposed surface of the remaining inner row of bricks then needs to be cleaned.
Finally, each missing row needs to be reconstructed using bricks that match the