Method and apparatus for reducing nitrogen oxides using spatially selective cooling

摘要

A method and apparatus are described for reducing NOx in a combustion zone such as a boiler by spatially selectively injecting a cooling fluid into the combustion zone so that the fluid is entrained to intersect an identifiable NOx producing zone. The cooling fluid can be water or a gas or mixture of them and whose temperature is sufficiently low or whose combined mass flow and temperature are sufficiently low so that the cooling fluid can reach the NOx producing zone and cool it to a temperature where the NOx production is significantly reduced. In one embodiment of the invention a cyclone boiler has a number of identifiable NOx producing zones. Several of these are targeted by spatially distinct cooling fluid streams placed at strategic locations. At one location the cooling fluid such as a water spray is placed in a duct in the path of the secondary air to deliver a cooling secondary air stream or a combination thereof with a hot flue gas and which is shaped to correspond in cross-section to that of the NOx producing zone targeted by the cooling fluid. Significant NOx reduction is achieved.