Low NO.sub.x combustion process and system

In combination with a coal-fired fluidized bed boiler, the exhaust stream from said fluidized bed boiler being at a temperature of about 600.degree.-650.degree. F. and including from about 3 to 6 weight % oxygen, from about 50 to 500 ppmv of NO.sub.x, and from about 50 to 300 ppmv of N.sub.2 O;

• a system for reducing the quantities of oxides of nitrogen, including N.sub.2 O, that are present in said exhaust stream said system comprising:
• a thermal reaction zone at which fuel and air are burned, said zone being connected to receive said exhaust stream and provide a modified heated stream which includes small quantities of combustibles and of oxygen;
• a first catalyst bed for receiving and passing the modified heated stream, said bed operating under overall reducing conditions, the quantity of oxygen in said stream being in stoichiometric excess of the amount of N.sub.2 O and NO.sub.x, but less than the amount of said combustibles;
• whereby the N.sub.2 O and NO.sub.x are first oxidized to NO.sub.2, and then the NO.sub.2 is reduced by the excess combustibles;
• heat exchanger means for receiving, passing and cooling the stream from said first catalyst bed;
• means for adding air to the resulting stream from said heat exchanger to produce a further cooled stream having a stoichiometric excess of oxygen;
• and
• an oxidizing catalyst bed for receiving and passing said further cooled stream over an oxidizing catalyst to oxidize remaining excess combustibles, to thereby provide an effluent stream having environmentally safe characteristics.