Method of reducing NOx in a combustion flue gas

A method of decreasing the concentration of nitrogen oxides in a combustion flue gas, comprising the steps of:

• (a) forming a combustion flue gas in a combustion zone, the combustion flue gas comprising nitrogen oxides;
• (b) providing overfire air and droplets of an aqueous solution or powdered particles of a selective reducing agent in a burnout zone, the droplets or particles having an initial average size of about 50 μm to about 1000 μm;
• and
• (c) contacting the combustion flue gas with the overfire air and the selective reducing agent in the burnout zone to thereby decrease the concentration of nitrogen oxides therein.

A method of decreasing the concentration of nitrogen oxides in a combustion flue gas, comprising the steps of:

• (a) forming a combustion flue gas in a combustion zone, the combustion flue gas comprising nitrogen oxides;
• (b) injecting a reburn fuel into the combustion flue gas in a reburn zone downstream from the combustion zone and adapted to decrease the concentration of nitrogen oxides;
• (c) providing overfire air and droplets of an aqueous solution or powdered particles of a selective reducing agent in a burnout zone downstream from the reburn zone, the droplets or particles having an average size such that the average droplet or particle lifetime is greater than the overfire air mixing time with the combustion flue gas;
• and
• (d) contacting the combustion flue gas with the overfire air and the selective reducing agent in the burnout zone to thereby decrease the concentration of nitrogen oxides therein.