TM 5-810-15
Figures 3-7 and 3-8 illustrate the two more
has to be stabilized should be investigated in the
commonly used pulverizer types.
design stage so that suitable auxiliary fuel
b. Capacity. Pulverizer capacity is a function of
provisions can be designed into the plant. If oil
coal type, based on a grindability index, moisture
ignitors are used, either compressed air or steam
content, and fineness of the product. At least two
atomizers are used. Pressure on mechanical atomi-
pulverizers should be provided, and with one pul-
zation should not be considered due to safety
verizer off line for maintenance the remaining
factors.
b. Cost. The cost of these ignitors and the labor
pulverizers should be capable of supplying coal to
the boiler at the desired load with worst case coal.
required for their installation plus the fuel system
Figures 3-9, 3-10 and 3-11 show the influence of
required should be included in the LCCA. Ignitors
grindability and moisture content of coal on pul-
will be lit by high energy spark plug type lighters.
verizer operation.
3-9. Burners and NOx control.
3-8. Coal burner ignitors.
a. Burner design. State-of-the-art burner design
a. Types. Natural gas or No. 2 fuel oil ignitors
calls for low excess air operation to improve the
are required for firing pulverized coal. These igni-
boiler thermal efficiency (reduced exit gas temper-
tors will be capable of preheating the boiler prior to
ature and dry gas loss) as well as to reduce NOx
starting the pulverizer and firing coal. The ignitors
emissions. Coal burners will be specifically de-
should be able to carry about 10 percent of
signed for pulverized coal and compatible with the
maximum continuous rating (MCR) and are also
gas or oil ignitors to be supplied and produced by
used to stabilize the coal flame when the burner
a qualified manufacturer. Note, in the case of gas,
load is less than approximately 40 to 50 percent or
oil and pulverized coal fired units, a flame safety
other adverse fuel conditions such as high moisture.
system is also required.
The steam load at which the pulverized coal flame
3-12
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