Method for reducing nitrogen oxide on the primary side in a two-stage combustion process

A method for reducing a formation of nitrogen oxide on a primary side of a furnace and reducing or avoiding nitrous oxide and ammonia slip in an offgas of the furnace in which a fuel is burned in a combustion process having at least two stages, the method comprising:

• passing a fuel consecutively through each of a plurality of bed areas of a combustion bed of the furnace;
• feeding, individually to each of the bed areas, a primary gas including oxygen so as to burn the fuel in the combustion chamber of the furnace;
• introducing, into a downstream offgas burn-out zone, a secondary gas including oxygen so as to after-burn incompletely burned offgas components formed during the burning of the fuel;
• and
• axially mixing partial offgas streams from the combustion bed areas by injecting a water-gas mixture as at least one free jet above a surface of the combustion bed upstream from the downstream offgas burn-out zone so that the at least one free jet penetrates the partial offgas streams of the combustion bed areas so as to reduce a heating value of the offgas between the surface of the combustion bed and the downstream offgas burn-out zone.

An apparatus for reducing the formation of nitrogen oxide on a primary side of a furnace and reduce or avoid nitrous oxide and ammonia slip in an offgas of the furnace, the furnace being configured to burn a fuel in a combustion process having at least two stages, the apparatus comprising:

• a combustion chamber including a grate disposed therein;
• a combustion bed configured to receive a primary gas including oxygen so as to burn the fuel on the grate, the combustion bed including a plurality of combustion bed areas, each of the combustion bed areas having a respective feed of the primary gas and a partial offgas stream;
• an offgas burn-out zone downstream from the combustion chamber configured for after-burning of incompletely burned offgas components;
• a secondary gas introduction device configured to introduce a secondary gas including oxygen into the offgas burn-out zone;
• and
• an injection device configured to inject a water-gas mixture as at least one free jet above a surface of the combustion bed upstream from the offgas burn-out zone so that the at least one free jet axially penetrates the partial offgas streams of the combustion bed areas.