Method and apparatus for reducing nitrogen oxides using spatially selective cooling

A method for reducing NO.sub.x produced in a boiler fed with a fuel with primary air flow and preheated secondary air flow with the gases inside the boiler having a flow pattern resulting in at least one identifiable zone which tends to be a NO.sub.x producing zone embedded inside the combustion zone in the boiler, comprising the steps of:

• injecting a distinct stream of cooling liquid at a predetermined location in a portion of the preheated secondary air flow so as to produce a spatially distinctive cooled air mass flow within said secondary air flow;
• and with said location selected so that the cooled air mass flow is entrained by the secondary air flow to intersect said embedded identifiable NO.sub.x producing zone inside the boiler;
• and
• applying a sufficient amount of said stream of liquid to said predetermined location so as to significantly reduce the NO.sub.x generated from said identifiable NO.sub.x producing zone without significantly affecting temperatures of gases in the combustion zone outside said identifiable NOx producing zone.

An apparatus for reducing the production of NO.sub.x from a combustion zone fed with a fuel and combustion air causing a flow pattern inside the combustion zone with at least one identifiable zone which tends to be a NO.sub.x producing zone, comprising:

• means for producing a stream of cooling fluid at a predetermined location in a portion of the combustion air flow;
• with said location selected so that the stream of cooling fluid is entrained by said combustion air flow to intersect said identifiable zone;
• and
• means for controlling said stream of cooling fluid so as to produce a spatially distinct cooled mass flow in said combustion air flow to sufficiently lower the temperature of the identifiable zone to significantly reduce NO.sub.x produced therein without significantly affecting temperatures of gases in the combustion zone outside said identifiable zone.