2.2. Staging
Staging is used in various forms to control NO-xemissions.
Thereby a primary combustion zone with
nonstochiometric conditions is followed by cooling
the combustion products and a secondary combustion
zone. Often, air staging is used. That means, the
primary combustion takes place under rich conditions
and secondary air is injected for the secondary
combustion. The cooling of combustion products
can be achieved by direct cooling through radiation
and convection (see Fig. 3(a)) or by cooling through
mixing with recirculated combustion products from
further downstream (see Fig. 3(b)).