Biomedical Engineering Reference
In-Depth Information
Coal biomass
Steam
(A)
Coal
Steam
Biomass
Gasifier
(B)
Coal
Steam
Biomass
Auxiliary
steam
Biomass
boiler
(C)
FIGURE 10.3 Three options for cofiring biomass in a coal-fired boiler. (A) Direct cofiring—
biomass fed directly into the coal pulverizing mill. (B) Indirect cofiring—biomass is gasified
and gas is burnt in the boiler. (C) Parallel cofiring—biomass is fired in a separate boiler and
steam is fed into the steam header.
types and to very low biomass to coal cofiring ratios that is typically less than
5% by mass (Tillman, 2000). The volumetric ratio of the cofiring would, how-
ever, be much higher. For example, 5% by mass switchgrass (80 kg/m 3 )when
mixed with coal (881 kg/m 3 ) could give a volume percentage of about 37%.
The second option involves separate handling, metering, and pulverizing
the biomass in dedicated mills, and injecting it into the furnace through
existing pulverized fuel pipework upstream of the burners. This option
increases the pipeworks around the boiler, which may already be congested.
It may also be difficult to control and to maintain the burner-operating char-
acteristics over the normal boiler load curve.
The third option involves separate handling and pulverization of the
biomass
fuel. Here, pulverized biomass
is
injected through dedicated
 
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