TM 5-810-15
Table 3-6. Stoker Selection Factors.
Vibrating
Traveling
Traveling
Grate Stoker
Grate Stoker
Chain Grate
Stoker
Crossfeed
Spreader
Crossfeed
Spreader
Crossfeed
Feed
Feed
Applicable
100,000-
20,000-
100,000-
50,000-
20,000-
Boiler Size, pph
150,000
150,000
250,000
250,000
75,000
Maximum Grate
400,000
600,000
450,000
750,000
450,000
Heat Release,
Btu/ft2-hr
Maximum Furnace
25,000
25,000
25,000
25,000
25,000
Heat Release,
Btu/ft3-hr
Coal Parameters
0-10
0-10
2-15
0-10
2-15
Moisture %
Volatile
Matter %
30-40
30-40
30-45
30-40
30-45
Fixed Carbon %
40-50
40-50
40-55
40-50
40-55
Ash %
5-10
5-10
6
5-15
6
Btu/lb (Mm)
12,500
11,000
11,000
Free Swelling
5
Index (Max)
Ash Softening
2,300
2,300
2,200
2,300
1,900
Temp, F (Reducing
Stimulus)
Coal Size
1"x0"
1-1/4"x3/4"
1"x0"
1-1/4"x3/4"
1"x0"
Max Fines thru
1/4" Screen Max
40%
50%
60%
40%
60%
Stoker Turndown1
3:1
3:1
3:1
3:1
3:1
(Stable Fire)
Particulate
1.0-1.5
1.4-10
0.6-1.5
1.4-10
0.6-1.5
Emissions
106 Btu
1
To achieve this turndown rate, reference should be considered in the construction of the boiler for either membrane or welded
wall construction or tube and tile type construction. Note some loss in boiler thermal efficiency will occur at lower loads.
Note: Coal sizing and quality have a direct influence on the efficiency of stoker fire boilers. These selection factors do not apply
to those western fuels which have high moisture 25 percent or more content and have a lignite type ash characteristic.
air which controls the velocity of solids through the
3-14.
Overfire air.
combustor. Ash must be removed from the bottom
a. General. Overfire air is the ambient air sup-
of the combustor to control solids inventory, bed
plied by either the FD fan or a separate fan that
quality, and prevent agglomeration of solids.
may also be used for fly ash reinjection and is used
Arrangement of tuyeres or air distribution devices
on all types of stoker fired boilers. The purpose is
must direct ash flow toward bed drains. Figure 3-
to aid combustion and to insure the coal particles
13 shows the major ACFB boiler components.
are as completely burned as possible.
b. Upper combustor and transition zone. The
b. Port location. Overfire air ports are located on
upper combustor is waterwall design. Solids and
either or both the front and rear furnace walls.
gases leave the combustor through a transition
section which must account for three dimensional
3-15. Atmospheric circulating fluidized bed
thermal expansion between the major boiler com-
(ACFB) boiler components.
ponents.
a. Lower combustor. Fuel is fed into the refrac-
c. Solids separator. The transition section with
tory lined lower combustor section where fluidizing
expansion joint connects the combustor to a solids
air nozzles on the floor of the combustor introduce
separator. Two different separator designs include
3-19
Previous Page
