Method of reducing NO.sub.x component of flue gas in heating coking ovens, and an arrangement of coking oven for carrying out the method

A method of reducing NO.sub.x component of flue gas produced in the flame of a coking oven of the type having a plurality of vertical heating flues cooperating in pairs of flamed and non-flamed flues, the flamed heating flues including inlets for rich gas, primary air and lean gas arranged at the bottom region of the flues to provide a low level combustion stage, and further including inlets for secondary air and secondary lean gas arranged above said low level combustion stage to provide a high level combustion stage, partitions separating the flamed and non-flamed heating flues in respective pairs having a top opening for recirculating flue gas from the flamed flue to the non-flamed one, and a bottom opening for mixing a branch current of the recirculated flue gas with the supplied primary air and rich and lean gases in the flamed flue, comprising the steps of:

• a. adjusting the recirculation current rate, namely the volume ratio of the recirculated flue gas branch current to the flue gas current without recirculation, to amount between 20% and 50%;
• b. adjusting the combustion stage ratio, namely the volume ratio of the supplied primary air in the low level combustion stage to the supplied secondary air in the high level combustion stage to an amount between 40% and 70%;
• and
• c. arranging the high level combustion stage between 35% and 55% of the height of the heating flues.