CURRENT STATE OF NOX ABATEMENT IN THE CEMENT INDUSTRY

Oxides of nitrogen are produced in rotary kiln plants in the cement in dustry because of the nature of the process. In Germany the cement wor ks are governed by the NOx limits set by TA Luft (German Clean. Air St andards), which have been updated progressively during the past years. This specifies NOx emissions of 0.50 g/m(3) for new plants and 0.80 g /m(3) for existing plants. For the majority of plants these limits can , only be met if appropriate abatement measures are taken. Primary mea sures for NOx abatement deal mainly with smoothing the kiln, operation . and the use of low primary air burners for the rotary kilns. These m easures have already been successfully implemented in many cement work s, and have led to significant reductions in the average NOx emissions from rotary kiln plants. Another possible abate ment procedure is sta ged combustion for the precalciner system. Investigations on existing plants and the experience acquired during a demonstration project prom oted by the Federal Environmental Office, Berlin, have shown that NO f rom the main. firing system is decomposed and NOx emissions can be eff ectively reduced. However, the level of reduction rate is limited, and this applies in, particular to the reduction of NOx peak values. The SNCR (selective non-catalytic reduction) process was tested on two rot ary kiln plants in long-term tests as part of the demonstration projec t. The original level in, these plants was 1.2 to 1.5 g/m(3) NOx. By u sing SNCR technology it is possible to meet the limit of 0.80 g/m(3) e ven under the evaluation conditions specified in Section 2.1.5 of TA L uft. It will be possible to utilize the experience gained from the dem onstration project also in, other cement kilns. Selective catalytic re duction (SCR) of nitrogen oxides, which is widely used in large power stations, is not straightforward to use in, cement works and has not y et been tested on an industrial scale.