MIL-HDBK-1003/7
Section 10.
ASH HANDLING
Ash Handling Systems. See MIL-HDBK-1003/6 Section 4, Paragraph titled "Ash
10.1
Handling", for requirements. Ash handling systems are required for removal of bottom
ash and fly ash from coal fired boilers. Ash production rates can be determined using
the known ash content (from proximate or ultimate analysis) and firing rates of the
coal. The typical distribution of ash from combustion of coal is shown in Table 21.
Table 21
Typical Distribution of Boiler Ash
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*
*
Eastern
Western
*
*
Bituminous
Sub-Bituminous
*
*
Percent
Percent
*
*
* Stoker Coal Boiler:
*
*
*
Bottom ash
35
35
*
*
Fly ash
60
60
*
*
Last pass or economizer hoppers
5
5
*
*
* Pulverized Coal Boiler:
*
*
*
Bottom ash
20
30
*
*
Fly ash
75
65
*
*
Last pass or economizer hoppers
5
5
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Bottom ash is collected in the boiler bottom ash hopper. For a stoker coal
fired boiler, bottom ash also includes ash which falls through the grate into the
siftings hopper. Fly ash is collected in the boiler, last pass hoppers or hoppers below
an economizer, hoppers below an air heater, mechanical dust collector hoppers,
electrostatic precipitator hoppers, or bag house filter hoppers. The removal and
handling of bottom ash and fly ash from collection hoppers is accomplished by the use of
one of several systems which are described as follows. Also see ash handling equipment
manufacturers' reference manuals for detailed descriptions of arrangement, operation,
and control of ash handling components and systems.
Pneumatic. Pneumatic ash handling systems are available as a complete vacuum
10.1.1
system, complete pressure system or a combination vacuum-pressure system.
10.1.1.1 Vacuum System. Vacuum for conveying bottom ash or fly ash is produced
hydraulically by the use of a water jet pump, thermally by the use of a steam jet pump,
or mechanically by the use of motor driven rotary exhausters. Air is admitted into the
end of the conveyor pipe and ash is admitted at intermediate points through ash intake
fittings or automatic valves. The ash is then conveyed to a storage silo through
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