Page 304 - Wastewater Solids Incineration Systems

Incinerator Maintenance 265

original (either special-shaped or standard-sized bricks). The bricks must be
mortared to the remaining inner row and to each other. Once a row is started, it
must be completed without interruption before the mortar sets up.
When a hearth has flattened out enough to require replacement, it must be
removed very carefully. Plywood and wooden shoring must support the hearth
immediately below the flat hearth to take the additional load of bricks. The hearth is
removed one row of bricks at a time, starting at the row closest to the central shaft.
Typically, bricks are bonded ceramically to the adjacent row and will not release
the entire row when the first brick is knocked out. After all bricks are removed back
to the skew-back row, the skew-back bricks should be examined for soundness and
cracks and repaired as necessary. The inner surface should be ground smooth to
receive the new bricks.
Reconstruction of the new hearth begins with installation of support forms under
the hearth, which establish the correct arch. The load of the new hearth is carried to
the hearth below temporarily. Installation of the new bricks starts at the outer skew-
back row and proceeds toward the center. Mortar is applied to the outer row of bricks
and between the new bricks. Once a row is started, work must continue uninter-
rupted until that row is completed, before the mortar sets up.
After all bricks are in a row, they must be “tightened up” to take up any air space
between bricks. A hearth that is constructed loosely will settle quickly and fail. The
temporary support system can be removed as soon as the last (inner) row of bricks is
completed. If special-shaped bricks are used, an adequate supply for future repairs
should be stocked. Otherwise, there can be a long downtime waiting for supplies.
1.8.4 Drop Holes
Drop holes being plugged with soft slag is one of the most prevalent problems with
incinerator operation. The typical drop-hole configuration of a 7-m (23-ft) diameter
incinerator has 30 equally spaced rectangular holes with a cross-sectional area of
2
0.11 m (1.14 sq ft) each. Typically, plugging starts at the four corners of a drop hole
and then progresses throughout the remaining opening. By increasing the drop-
2
hole size to 0.34 m (3.7 sq ft) and using an arch construction to eliminate two cor-
ners, plugging can be reduced dramatically.
The modified larger hole actually uses the space of the two original holes and
the special-shaped bricks between them. The arch can be constructed with 100%
castable and standard-sized arch bricks (see Figure 11.3). “Poke” holes for cleaning
out plugged holes while the incinerator remains online can be added above each
drop hole.