In a method to decrease emission of mercury, a factor is selected to
control a combustion process to generate a flue gas comprising fly ash
with enhanced unburned carbon; the combustion process is controlled
according to a factor selected from reburning fuel, flue gas temperature,
OFA injection, coal particle size, LNB flow, LNB design, combustion zone
air, stoichiometric ratio of fuel, fuel/air mixing in a primary combustion
zone and fuel/air mixing in a secondary combustion zone to produce the
flue gas comprising fly ash with enhanced unburned carbon and to vaporize
mercury; and the flue gas is allowed to cool to collect fly ash with
enhanced unburned carbon with absorbed mercury. A system to decrease
emission of mercury; comprises a combustion zone that is controlled to
generate a flue gas comprising fly ash with enhanced unburned carbon and
that produces vaporized mercury; and a post combustion zone to cool the
flue gas to collect fly ash with enhanced unburned carbon with absorbed
mercury.
