Combustion Phenomena of High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 123

FIGURE 2.88 Comparison of in-furnace heat flux distributions by types of fuel and com-
bustion methods. (In-furnace temperature (TIC) = 1255 ~ 1265˚C, heat input = 1.28 MW
(1.1 Gcal/h)). (TIC represents Temperature Indicator Controller.)

1000 ~
1700 ° C

Volatile matter

Air

Flame

End of emission
of volatile matter

Combustion of char
(mainly carbon)

Ignition

Fly ash (unburned part)

Beginning of heat
dissolution by radiation
heat-transfer and conduction
heat-transfer

Rapid elevation of particles temperature
by radiation heat-transfer and conduction
heat-transfer

Air
+

Heating of particles by radiation
and heat-conductance from flame

Pulverized coal

Pre-heating zone
of coal particle

Flame zone
(combustion region of volatile matter)

After flame zone (combustion region of char)

Burner nozzle

Distance from burner

FIGURE 2.89 Combustion phenomena of pulverized coal particles.

2.5.2 C OMBUSTION P ROCESS OF C OAL
The combustion phenomena of coal are shown in Figure 2.89 37 in the case of
pulverized coal. Combustion phenomena proceed in the order of the following stages.
First, pulverized coal is preheated. Then, its volatile matter is emitted and ignited.
Next, both volatile matter and fixed carbon burn after reaching the maximum tem-
perature of particles. Finally, the coal turns to ash through complete combustion. To
understand these phenomena clearly and to investigate them more precisely, we take
each stage of combustion separately such as the initial properties of coal, the ignition