NOx Emissions from Cement Mfg - US Environmental Protection ...
NOx Emissions from Cement Mfg - US Environmental Protection ...
NOx Emissions from Cement Mfg - US Environmental Protection ...
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The concept of external flue gas recirculation for NO x<br />
reduction has not been demonstrated in cement kilns. Similarly,<br />
the potential of secondary combustion of fuel in conventional<br />
kilns (by "mid-kiln" firing) as an NO control technique has been<br />
x<br />
evaluated for whole tire burning only. This technique can be<br />
potentially applied with other waste-derived fuels as well and<br />
needs further demonstration. Secondary combustion of fuel is<br />
inherently present in all precalciner kilns and preheater kilns<br />
with riser duct firing and such kilns produce less NO emissions<br />
x<br />
compared to long dry kilns.<br />
Selective catalytic reduction (SCR) uses ammonia in the<br />
presence of a catalyst to selectively reduce NO emissions.<br />
x<br />
There have been limited pilot test programs of SCR. Selective<br />
noncatalytic reduction (SNCR) technology appears to be applicable<br />
to preheater/precalciner type kilns with limited data indicating<br />
its effectiveness. SNCR reduces NO with ammonia or urea without<br />
x<br />
a catalyst. SNCR is not considered applicable to long wet and<br />
dry kilns due to difficulties involved in continuous injection of<br />
reducing agents. There have been a few demonstrations of SNCR at<br />
preheater/precalciner kilns. Molar reagent ratio, temperature,<br />
and gas residence time in the appropriate temperature window are<br />
primary factors affecting NO x reduction efficiency. Table 2-2<br />
presents the potential NO x<br />
reductions with these techniques.<br />
2-4