Power Plant Engineering

Fig. 7.7(a)
of pulverized coal or fineness requirements vary, though not too greatly, from coal to coal (the higher the
fixed carbon, the finer the coal). For example, pulverized coal with 80 percent passing a 200 mesh
screen and 99.5 percent passing a 50-mesh screen possesses a surface area of approximately 1500 cm
2
/g
with more than 97 percent of that surface area passing the 200-mesh screen.
The fuel burners may be arranged in one of two configurations. In the first. individual burners,
usually arranged horizontally from one or opposite walls, are independent of each other and provide
separate flame envelopes. In the second, the burners are arranged so that the fuel and air injected by
them interact and produce a single flame envelope. In this configuration the burners are such that fuel
and air are injected from the four corners of the furnace along lines that are tangents to an imaginary
horizontal circle within the furnace, thus causing a rotative motion and intensive mixing and a flame
envelope that fills the furnace area. Vertical firing is also used but is more complex and used only for
hard-to-ignite fuels.
The burners themselves can be used to burn pulverized coal only (Fig. 7.8) or all three primary
fuels, i.e. pulverized coal, oil, or gas (Fig. 7.9). In Fig. 7.8, the coal impeller promotes the mixing of fuel
with the primary air and the tangential door built into the wind box provide turbulence of the main
combustion, or secondary, air to help mix it with the fuel-primary-air mixture leaving the impeller.
Regulating
Rod
Coal Nozzle
Air Register Door
(Secondary Air)
(Oil) Lighter
Windbox
Refractory Throat
With studded Tubes
Coal Impelier
Water Cooled
Furnace Wall
Fig. 7.8

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230
POWER PLANT ENGINEERING
Multi Purpose
Oil Lighter
Spin Vanes
Water
Cooled
Throat
Windbox
Inner Air
Register Outer Air
Register