coal selection criteria for industrial pfbc firing project 3.2 - CCSD

“Coal Selection Criteria for Industrial PFBC Firing”
Tomatoh-Atsuma has to limit its SOx emission below 94 ppm, NOx emission below 98
ppm and dust emission below 28 mg/Nm 3 . It successfully operates under normal
conditions while producing 10 ppm SOx, 40 ppm NOx and less than 10 mg/Nm 3 dust. In
accomplishing this excellent result, coal with 0.9% sulfur and 1.6% nitrogen was fired
and a Ca:S ratio of 3-6 was used (Koshimizu 1998).
In Fukuoka, Japan, the emissions of SOx should be 76 ppm or less, NOx should be a
maximum of 60 ppm and the concentration of soot and dust at the stack outlet should not
exceed 30 mg/Nm 3 . To meet these requirements, Karita is firing coals which contain
1.0% or less sulfur and a maximum of 55% volatile matter.
The Osaki plant faces more stringent NOx and particulates emission regulations. The
maximum permissible emission limit for SOx is the same as Karita (76ppm), 19ppm for
NOx and 9 mg/Nm 3 for particulates. The harsh regulations were not a problem for Osaki
as its technology enabled operation at full load while producing only 7.0 ppm SOx, 17.8
ppm NOx and 3.5 mg/Nm 3 particulates.
A correlation was developed to predict the emission of NOx from bench and pilot scale
PFBC and it was found that pressure had no influence on the emission of NOx (Newby,
Keairns et al. 1989):
NOx = 12.25 exp(2827/T) [O2] 0.24 Xn 0.44 Y -0.1 (ppmv)
where T = bed temperature (K)
[O2] = volume percent oxygen in the combustion products
Xn = weight percent nitrogen in the coal
(Eq. 3)
Y = concentration of SO2 in the combustion products (ppmv)
In contrast, other researchers found that NO emissions decreased with increasing pressure
and increasing Ca:S ratio (Nagel, Spliethoff et al. 1999). At pressures above 4 bar and
with extra sorbent feed, NO emissions reduced with increased temperature. On the other
hand, N2O emissions were independent of pressure and sorbent added, but instead
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