TM 5-815-1/AFR 19-6
c. Startup burners. Startup burners are supplied in
and changing of the primary to secondary air
the bed or air ducts to heat the bed up to coal ignition
ratio
temperature. The startup burner can be used for low
(3) Only fuel bound nitrogen converted to NOx
loads. Usually it is capable of carrying about 20 percent
(thermally formed NOx is negligible)
or more of boiler capacity.
(4) High combustion efficiency, (as high as 99
d. Fluidized bed heat exchanger. The fluid bed heat
plus percent)
exchanger is used to cool the ash to about 750 degrees
(5) High turn-down and load following ability
Fahrenheit. The coolant can be feedwater or any pro-
(6) Uses a variety of fuels including:
cess fluid which requires heating. The metallurgy of the
-- high sulfur
heat exchanger must be compatible with the fluids it is
-- low BTU
handling.
-- high ash
e. Flue gas clean-up for particulate. Either an elec-
-- low cost
trostatic precipitator or a baghouse may be used for
-- waste materials
particulate control. Basic guidelines established for
(7) High boiler efficiency (85 to 90 plus percent)
determining which type unit to use on a conventional
(8) Load changes greater than 5% per minute
coal fired unit may be used to select the particulate
(9) No
retractable
sootblowers.
Rotary
control device for a fluidized bed boiler. Electrostatic
sootblower may be used
precipitators can encounter resistivity problems
(10) No slagging of coal ash
because of the low sulfur content in the particulate to
(11) Low maintenance
be collected.
(12) Dry ash
f. Ash-handling systems.
(13) Broad tolerance to changes in coal quality
(1) The ash-handling systems are similar to ash-
(14) Sulfur removal w/o need for scrubbers
b. Disadvantages:
handling systems for conventional boilers.
The bottom ash does have to be cooled prior
(1) Bed turn-down capability not clear
to disposal. Most of the ash-handling systems
` (2) Startup procedures more complex
are dry, and the ash can be sold for use in
(3) Control response almost instantaneous
other products.
(4) Use of partial bed slumping as load control
(2) Some potential uses of the ash are: aggregate
mechanism for bubbling bed
in concrete; road base ingredients; stabiliza-
(5) Requirement of a free-board for combustion
tion of soil embankments; pozzolan in
efficiency for bubbling bed
masonry units and mortar; agriculture and
(6) Corrosion susceptibility in bubbling bed
livestock feeds extender; and neutralization of
(7) Calcium-to-sulfur ratio greater than 2.5
spent acid wastes.
causes degradation of boiler efficiency
(8) Fluidized bed is a newer technology than con-
13-7.
Advantages and disadvantages
ventional boilers
(9) Complex under-bed fuel-feed system required
a. Advantage:
for some bubbling beds
(1) Low SO2 emissions
13-10
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