1 October 1997
these systems to meet past particulate emissions requirements without the addition of a particulate
control device, and the ability to easily adjust and maintain secondary combustor conditions. The
large field-erected units always operate in the excess-air mode.
4-2. PACKAGED INCINERATOR.
a. Retort-Type Incinerators.
(1) Most small, packaged incinerators in the 100-1000 lb/h (i.e., 1.2 to 12 tons/day)
capacity range are of the stationary hearth, retort-type. Gases are directed through a series of
connected "U"-shaped combustion chambers that share common walls and a common base (in lieu
of an "in-line" configuration). Figure 4-1 illustrates a typical "U"-shaped retort design.
(2) The "U"-shaped retort requires the gases to make right turns in both the horizontal and
vertical directions. This return flow of the gases permits the use of a common hot wall between the
various chambers. The compactness of a "U"-shaped retort incinerator saves space, yet it provides
a gas flow path that is long enough to keep the gases at the temperatures for the time required to
complete the oxidation process.
(a) Combustion air is introduced into each chamber at the rate required to achieve
complete burndown for the mode of operation (i.e., starved-air or excess-air).
(b) Solid waste is batch-fed through a sliding door onto a vented grate hearth. Each
batch pushes the previous batch along the hearth where it is ignited by the prior material. As the
material burns, the ash falls through the grate into the ash chamber.
(c) Primary chamber air, usually at substoichiometric ratios (i.e., starved-air mode) to
minimize fly ash, is introduced above and below the grate and controlled by dampers in the ducts
supplying air to each zone. Each succeeding chamber has provisions for adding more air and has
supplemental burner/heaters so that the desired temperature and stoichiometric ratios can be
adjusted and controlled in each chamber.
(3) The small, packaged, single units have wide application for the controlled destruction
of small quantities of municipal-type waste and are especially well suited for burning unique types of
waste that must be processed separately from general wastes.
(4) They are designed to be operated 8-16 h/day so that ash removal and certain
maintenance can be performed during the shutdown.
b. I n-line Retort Type Incinerator. The in-line packaged unit also has all chambers in one
housing, but the gases make 90o turns in the vertical direction only. Thus, the secondary chamber
is in-line, at the end of the primary chamber, rather than mounted alongside. The in-line unit is
therefore longer and less compact than the standard "U"-shaped retort design. All other aspects of
operation and performance are similar to the retort unit.
4-3. MODULAR INCINERATOR.
a. General Description.