A method and apparatus for reducing air pollutants associated with dry
process, precalciner cement manufacturing is shown. Raw feed meal used in
cement production is heated in a special heating chamber to drive off
volatile compounds, such as organic materials and salts of ammonia.
Preferably, the feed meal is heated to a temperature of at least
350.degree. F. The gases that are driven off flow to the precalciner
where they are combusted and rendered harmless. Heat is provided by
diverting at least a portion of the exhaust gases from the cement
pyroprocessing kiln to the special heater. The raw feed meal is
indirectly heated using a heat exchange wall between the feed meal and
the kiln exhaust gas flow. In addition, a base-containing material such
as lime or precalcined feed meal, may be added to the raw feed before
treatment meal to promote the breakdown of inorganic ammonium compounds,
thereby releasing gaseous ammonia which is also destroyed upon subsequent
combustion. Hot precalcined meal may also be used to provide some of the
heat required to heat the raw feed meal in the special heating chamber.