NOx Emissions from Cement Mfg - US Environmental Protection ...

CHAPTER 5
NO CONTROL TECHNIQUES
x
As discussed in Chapter 4, nitrogen oxides (NO ) are formed
x
by the oxidation of nitrogen during the fuel combustion process.
The formation of thermal NO is a function of the flame
x
temperature and the amount of nitrogen and oxygen available for
the thermal reaction; and to reduce the amount of thermal NO x
formed, these variables need to be minimized. The formation of
fuel and feed NO is not as well understood as the thermal NO
x x
formation. In general, however, the greater the amount of fuel
and feed nitrogen, the greater the fuel NO emissions.
x
Therefore, reducing the amount of fuel and feed-bound nitrogen
will reduce the contribution of the fuel and feed NO .
x
The typical NO emissions from a cement plant depend upon
x
the type of the cement kiln as shown in Table 4-4. For any given
type of kiln, the amount of NO formed is directly related to the
x
amount of energy consumed in the cement-making process. Thus,
measures that improve the energy efficiency of this process
should reduce NO emissions in terms of lb of NO /ton of product.
x x
With the rising costs of energy and the very competitive cement
market, greater attention is being paid to reduce over-burning of
clinker, improving gas-solids heat transfer and increasing
overall energy efficiency. Continuous emissions monitoring of
CO, NO , and O provide an indication of clinker burning
x 2
conditions and also provide an input for process control. Newer
cement kiln designs are generally based on preheater/precalciner
systems which provide very efficient gas-solids contact and a
greater energy efficiency.
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