TM 5-815-1/AFR 19-6
(3) NOx. Control by specifying furnace and com-
when ponding is not viable. The dry ash
bustion air controls designed to maintain lim-
should be cooled and conditioned with
ited flame temperatures under operating con-
water before being transported for land
(4) Opacity. Control by particulate removal and
g. Coal fired fluidized bed boilers. NSPS cover lim-
itation for particulates; SO2; NOx; and opacity. Meth-
can be the more stringent requirement for
ods of modifying or controlling emissions are discussed
in the following.
f. Wood waste and bark fired boilers. NSPS cover
(1) Particulates. Control by use of fabric filter or
limitation for particulates and opacity. Methods of
an electrostatic precipitator. Most units will
modifying or controlling emissions are discussed in the
not require a mechanical collector in series
with the baghouse or electrostatic
precipitator. However, if high dust loadings
(a) Control by use of a mechanical collector
are anticipated an in-line mechanical collector
followed by either a scrubber or an elec-
in series with the baghouse or electrostatic
precipitator may be justified.
(b) Control by use of wet scrubber.
(2) SO2. Controlled by the metering (feeding) of
(c) Control by use of electrostatic
lime stone into the fluidized fuel bed.
(3) NOx. The comparatively low furnace tem-
(d) Control by use of gravel bed filter.
peratures experienced in fluidized bed boilers
(2) Opacity. Opacity is controlled by particulate
limits the heat generated NOx formation. No
special devices or controls are required for
controls. The "as-fired" condition of wood
NOx control on fluidized bed units.
(4) Opacity. Controlled by particulate removal
waste fuel will impact the choice of
particulate control equipment.
and properly adjusted and designed
(a) Hogged bark and wood chips with 45%
(5) Ash handling and removal systems. Can be
to 55% moisture usually require a
mechanical collector followed by a
dry or wet and may be automated cycles or
scrubber or an E SP. Material collected in
continuous ash removal utilizing equipment
the mechanical collector is a combination
and methods previously discussed.
of char, ash, and sand. The material is
Municipal solid waste-fired boilers
classified to separate the char from the
(MSW) and boilers using refuse
ash/sand mixture so the char can be
reinjected into the furnace combustion
zone. The ash/sand mixture is discharged
a. Municipal solid waste fired boilers fall
in the same
by gravity or conveyor to a holding tank
emission regulation category as an incinerator. Com-
which can be either wet or dry. All ash-
pliance is only required for particulate emission regula-
hopper discharge openings must be pro-
tected from air infiltration by rotary-seal
b. Boilers using refuse derived fuels must meet the
discharge valves or an air-lock damper
incinerator regulations and are also required to meet
arrangement, to prevent ignition of hot
emission standards for any other fuels fired in the
boiler. In most states the allowable emissions are
(b) Dry wood wastes that are chipped to less
calculated on the ratio of fuels fired and which cover
than 1" x " size may not require the
control of particulate, SO2, NOx, and opacity.
mechanical collector and reinjection
(1) Particulats Use mechanical collectors as a
equipment. Gas clean-up equipment of
primary device followed by either a fabric
choice may then be either the scrubber or
filter or an electrostatic precipitator. The ESP
electrostatic precipitator. Ash discharge
is favored when there is co-firing with coal in
hoppers need to be protected by seal
the MSW boiler. Without coal co-firing,
valves or air locks in all cases.
(c) Fabric filters are avoided because of the
high. Wet scrubbers should be avoided
potential for burning the fabric with hot
because of possible odor pick up.
char carry over.
(2) SO2. SO2 formation is a function of the sulfur
(d) Ash handling is usually accomplished
content in the refuse and fuel. In most cases
using a hydraulic conveying system
no SO2 removal devices are necessary.
However, when required a dry scrubber
(e) Screw conveyors or drag-chain conveyors
system followed by either a baghouse or an
are acceptable alternatives for dry
electrostatic precipitator is preferred.
handling of ash from wood-fired boilers