Reduction of nitrogen oxide (NOx) emission from a kiln plant.

摘要

In a kiln plant for burning mineral raw materials, e.g. cement raw materials, by means of nitrogen containing, solid fuel, e.g. coal, and which plant comprises a kiln (1), a material cooler (2) coupled after the kiln and a multistring, multistage preheater (18-27 and 18 min -27 min ) mounted before the kiln, the one string, the kiln string (18-27), being in direct connection with the kiln riser pipe (8) and the second string, the calcining string (18 min -27 min ), being connected to a separate calcinator (4) to which combustion air is supplied in the form of spent cooler air through an inlet (7), a NOx-reducing zone is established in the kiln riser pipe (8) and a part of the kiln string from an inlet (13) for nitrogen containing solid fuel of a fuel duct (10) and an inlet (12) of a branch-off (14) for the supply of spent cooler air. The length of the NOx-reducing zone, the combustion in the zone of the supplied carbon containing fuel for reaction between nitrogen atoms (N) and the nitrogen oxide (NO) formed in the kiln for forming harmless nitrogen (N2) and the separation of non-combusted fuel with partially calcined raw materials from the kiln smoke gases in the cyclone stage (18), and the further treatment of said products in the calciner (4) where the combustion of the fuel supplied from the kiln riser pipe and having a reduced nitrogen content thus causing a reduction of the NOx-emission from the calciner string (18 min -27 min ), ensure a high degree of reduction in the total NOx-emission from the plant.