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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to 80 percent. Using a mol ratio of 0.5 will give <strong>NOx</strong> reductions<br />
of approximately 40 percent.23 The reagent consumptions can be<br />
significantly higher with greater ammonia slip in SNCR systems as<br />
compared to SCR systems. Operating experience has identified<br />
several concerns with both ammonia and urea-based SNCR processes.<br />
The most frequently reported is the buildup of ammonium bisulfite<br />
scale which is significant for sulfur-containing fuels. SNCR<br />
processes also appear to convert some NO to N2O.33 The rate of<br />
N2O formation is a weak function of both the reactant and the NO<br />
concentration. However, N2O formation seems to be inherently<br />
more prevalent in systems using urea than those using ammonia.34<br />
The <strong>NOx</strong> destruction efficiency also depends upon the flue<br />
gas residence time in the appropriate temperature window. Unlike<br />
an SCR system where the reaction temperature is controlled in a<br />
dedicated reactor, an SNCR system relies on the existing gas<br />
temperature profile to provide an adequate residence time for a<br />
desired <strong>NOx</strong> destruction. Maximum achievable <strong>NOx</strong> reduction in a<br />
cement kiln may thus depend upon the gas temperature profile.<br />
5.3 SUMMARY OF APPLICABLE <strong>NOx</strong> CONTROL TECHNOLOGIES<br />
Combustion zone control approaches discussed in Section<br />
5.1.1 are based upon providing optimum kiln operating conditions<br />
which will increase the energy efficiency and productivity of the<br />
cement-making process while minimizing <strong>NOx</strong> emissions. Such<br />
measures will provide a baseline of <strong>NOx</strong> emissions in cement kilns<br />
without any specific <strong>NOx</strong> control equipment. Although these<br />
simple process control approaches will reduce <strong>NOx</strong> emissions in<br />
poorly operated kilns; for the purposes of this ACT document,<br />
such approaches are considered to be needed for proper kiln<br />
operation and not specifically considered as <strong>NOx</strong> control tech-<br />
niques.<br />
Information obtained during this study indicated that some<br />
plants indeed relied on process monitoring and control and<br />
process modifications as a means to maintain <strong>NOx</strong> emissions within<br />
their respective permit limits.<br />
The <strong>NOx</strong> reduction effect of process modifications discussed<br />
5-25