1 October 1997
(c) The height of the furnace at the inlet is reduced in order to force the burning away
from the charging door. The chamber increases to its full height where partial combustion and
pyrolysis occur in order to accommodate the large flow of gases released.
(d) A large opening strategically located in the roof of the furnace discharges the
partially oxidized vapors, gases, and particulates into the secondary combustion chamber. Some
manufacturers attach two primaries to a common secondary chamber and manifold more than one
secondary chamber to a heat-recovery boiler.
(2) Secondary Combustion Chamber. Irrespective of the configuration, the secondary
combustion chamber is essentially a solid-walled, solid-floored, horizontal, refractory-lined cylinder.
(a) Length and diameter are determined by the volume of gas that leaves the primary
chamber, the amount of gas generated by the secondary burner and the necessary retention times
for completion of the required reactions. The size of the chamber is such that it takes from 1.5 to
2.5 s from the time the gases enter the chamber until they leave.
(b) The burner flame and secondary combustion air are introduced just above the
secondary chamber gas inlet opening. Gases entering the chamber are injected in such a manner
as to induce a swirling action to enhance the agitation needed to improve mixing and uniform
(c) Normally, the gases leaving the secondary chamber are vented to a heat-recovery
boiler to produce steam or hot water. However, an alternate discharge path, via a "dump valve" in
the secondary chamber discharge duct, is required to allow direct discharge to the atmosphere in
the event of an upset condition (i.e., a case where the boiler is forced to shut down because of
equipment failure). The hot gases generally cannot be sent to the gas-cleanup system if their
temperature is above 500F, so they must be "dumped" to the atmosphere. In such a case, the
waste feeding operation is stopped, but the waste in the incinerator continues to burn.
e. Excess-Air Modular Incinerator.
(1) Primary Combustion Chamber. The primary combustion chamber of the EAU modular
incinerator usually uses a porous grate that allows larger volumes of air to be introduced to the
bottom of the bed and in a more uniform manner than that provided on the SAU.
(a) The grate is usually a manufacturer's patented design that provides unique means
for introducing underfire air and for moving the waste along the length of the furnace. The plane of
the floor is inclined, and the mechanism for moving the waste also imparts a slow tumbling action to
the bed of waste as it is moved and burns along the length of the combustion chamber.
(b) Because of the larger amounts of air required (i.e., S.R.= 1.1 vs. S.R.= 0.6-0.9 for
the SAU), and the consequent larger volume of combustion gases, the primary chamber volume for
an EAU will be larger than a comparable-capacity SAU. The primary chamber length and the
residence time for burndown will be shorter than those for an SAU. Overfire air inlets direct air to
the full length of the bed. Exterior ducting and valving controls the amount of air directed to each
stage (zone) of combustion.