a. combusting coal in a primary combustion zone of the combustion unit under conditions of low or no excess oxygen during combustion in the zone wherein the excess oxygen in the combustion zone is no greater than two percent (2%);

b. as a result of step (a), generating substantial amounts of carbon rich fly ash during combustion and entraining the fly ash into flue gas generated by the combustion;

c. entraining the carbon rich fly ash in the flue gas flowing through a flue gas passage in the combustion unit;

d. releasing mercury during the combustion into the flue gas in the flue gas passage;

e. staging combustion air by injecting combustion air in a post-combustion zone downstream of the combustion zone in the flue gas passage of the combustion unit;

f. adsorbing the released mercury with the carbon rich fly ash generated during combustion, wherein the adsorption occurs in the flue gas passage;

g. directing the flue gas with the carbon rich fly ash and adsorbed mercury through the flue gas passage to a fly ash waste treatment system;

h. collecting the fly ash with the adsorbed mercury in the fly ash waste treatment system, wherein the fly ash remains in the flue gas and in the flue gas passage from combustion to collection and is removed from the flue gas after collection; and

i. exhausting the flue gases after adsorbing the released mercury to reduce mercury in the flue gases to be exhausted.