1 October 1997
(2) Secondary Combustion Chamber. The design of the secondary chamber for the
modular EAU attempts to produce the same mixing, chamber temperatures, and retention times as
for the SAU. However, since the EAU secondary chamber inlet gas temperature tends to be 400-
500F higher, less additional secondary combustion air is required (see table 3-12). The final
combustion of unburned gases, vapors, and particulates (i.e., 25-50% of that discharged to the
SAU secondary chamber) will require less time and less supplemental heat. Like the modular SAU,
the EAU must have a hot gas "dump valve" to bypass the heat exchanger and/or flue gas treatment
system when either system is not operating.
f. Controlled-Air Modular Incinerator. Some incinerator designs, referred to as "controlled-air"
incinerators, use a modified single chamber and a grate system similar to that of the excess-air
units. By careful control of underfire and overfire air, they achieve performance similar to a starved-
air unit, even though they have the physical appearance of an excess-air unit..
4-4. FIELD-ERECTED INCINERATOR.
a. General Description. When the capacity of a waste incineration system exceeds the
nominal 200-250-t/day capacity of modular incinerator systems, field-erected incinerators are
usually used because of their higher operating efficiency and more dependable operation. Their
design is comparable with the design used for coal-fired boilers; however, the design contains a
number of significant, unique features required for the efficient destruction of municipal-type waste.
Figure 4-1 illustrates a typical field-erected mass-burn incinerator.
b. System Configuration. Because of the large stream of waste serviced by these facilities, it
is important the facility have redundant destruction capability so that outage of one furnace will not
result in a large accumulation of waste.
(1) Field-erected furnaces with their integrated boilers also require time for maintenance
and repair, as well as allowances for forced outages due to failure of any major component in the
unit. If three units are used, it is common to size each unit to handle one-half of the facility's total
capacity. Similarily, if four units are used, each is sized to handle one-third total capacity.
(2) In general, an 80% availability is projected for field-erected units.
c. Design Description for In-Line Grate Systems.
(1) Primary Combustion. The basic design uses an excess air grate of patented design,
which may be a traveling grate, a rocking grate, a reciprocating grate, or some combination thereof.
(a) The grate meters waste delivered by the feeding system, which includes a crane
and a long chute. The waste then flows by gravity down onto the grate.
(b) The grate then moves the bed of waste through the primary combustion section
until the residues are dumped off the grate into a water--filled ash-quench system, where the ash is
cooled and removed by conveyor.
(c) Air is metered to locations along the length of the grate system to control the rate of
drying, volatization, and burndown of the nonvolatiles and char. The primary combustion air is