MIL-HDBK-1003/7
Table 4
Maximum Velocities (ft/sec) in Convection Sections
for Coal, Wood, or Solid Waste Boilers
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*
*
Single Pass
Multi-Pass
* Stoker Type
*
Water Tube
Water Tube
*
*
*
*
Solid
*
*
Coal
Wood
Waste
Coal
*
*
* Underfeed stoker
*
75
60
*
*
* Spreader stoker
*
60
50
50
*
* Traveling grate
* (with reinjection)
*
*
*
*
* Spreader stoker
60
50
50
* Traveling grate
*
* (without reinjection)
*
*
*
* Traveling grate
*
75
60
* (front gravity feed)
*
*
*
* Solid waste
*
30
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b) Extended surface (metal and metallic surfaces extending from the tubes
or headers): sixty percent of the flat projected area, except that metal blocks not
integral with tubes or headers, extended surfaces less than 1/4 inch (6.35 mm) thick or
more than 1-1/4 inches (31.75 mm) in length, and the part of the extended surface which
is more than one tube or header radius from the tube of header from which it extends are
not included.
c)
Furnace exit tubes: the projected areas of those portions of the
first two rows of exit tubes receiving radiant heat from the fire.
4.5.2
Types of Stokers Used in Power Plants
4.5.2.1
Front Gravity Feed Traveling Grate Stoker. For plant capacities in the 25,000
pounds of steam per hour (pph) (11400 kg/hr) to 160,000 pph (7260 Kg/hr) range, the
traveling grate stoker method of firing can be used for moderately changing wide load
swings. It will handle fuels that have widely varying characteristics, from low
volatile anthracite, coke breeze to high and medium volatile bituminous. It is
particularly efficient with free-burning type coals in the Mid-West producing areas and
can handle lignite and subbituminous coals. The type of furnace configuration,
including long rear arches, are important when using the traveling grate stoker to burn
very low volatile fuels, such as anthracite or coke breeze. Front arches are used with
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