3. For definitions of stoker grate burning rates, furnace volume and radiant heating
surface, see the section.
4. For smokeless condition, the minimum burning rate for tangent tube or membrane
furnace wall construction is 250,000 Btu/ft2/hr active stoker grate area which equates to
2/3 - 1 maximum boiler turndown, with a tube and tile (spaced tubes backed by
refractory) or refractory furnace. This release rate can be reduced to 200,000
Btu/ft2/hr which equates to 3.5 - 1 maximum boiler turndown
5. All grate heat release rates are based on maximum continuous rating (MCR) with
allowance for 110% rating for 2 hour emergency peak per 24 hours.
6. Coal with volatile content less than indicated should not be applied, as loss of
ignition could result.
Some chain grate designs are applicable for anthracite coal firing.
8. Further turndown beyond that indicated under Note 4 may be obtainable dependent upon
allowable emission requirements and/or pollution abatement equipment applied.
9. For excess air requirements at the boiler outlet over the boiler/stoker limits
operating range, see MIL-HDBK-1003/6. Consult boiler and stoker manufacturers for
predicted excess air requirements at various loads.
10. In cases where coal quality is less than in above tables, consult NAVFAC
headquarters Code 04 for direction.
Pulverizers. Pulverizers are used to reduce crushed coal to a powder-like
fineness usually in the order of 70 percent passing through a 200 mesh screen. To
facilitate the pulverizing and pneumatic circulation of the coal fuel within the
pulverizer, hot air (up to 650 degrees F (343 degrees C)) is introduced into the
pulverizer for the purpose of drying the coal. A pulverizer fan is used either as a
blower or exhauster which either forces or draws hot primary air through the pulverizer
and through the discharge
coal-air piping to the burners. If a blower is used, one
pulverizer will usually furnish coal directly to several burners. If an exhauster is
used, a distributor located beyond the fan discharge is used to distribute the
air mixture to several burners.
Types of Pulverizers.
The principal types of pulverizers are as
Ball and race