DeNOx System |
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Catalyser |
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| Process Description |
DeNOx system cut |
| The reduction of NOx-emissions (fluegas denitrification)is carried out with primary and secondary measures. Primary measures are tasks at the point at which nitrogen oxides occur, e.g. within the firing point of a burner. Employing these measures, reductions of more than 30% can be attained. However, even these reductions are not enough to fullfill all legal requirements. For that reason, secondary measures are applied here. It is primarily the SCR process (Selective Catalytic Reduction process) which is applied. The heart of the plant is a catalyser which causes the chemical conversion of the nitrogen oxides without taking part in the chemical reaction itself. The fluegases occur in the reactor and are enriched by a mixture of ammoniac and air. The liquid ammoniac is taken from the ammoniac storage, vaporised and then injected in the DeNOx reactor. In this process, the ammoniac gas acts as reduction material; the nitrogen is removed from the oxygen. The result is molecular oxygen (N2) and water (N2O). The catalyser system is also called the DeNOx reactor. The individual catalyser elements are compounded in the reactor to larger elements and are distributed on several levels. The size of a DeNOx reactor may reach several cubic meters. There are several possibilities to configure a catalyser: * Alignment in front of the air heater - behind the electrofilter This is the socalled "high-dust" alignment. The advantage is the high temperature (c. 320°C against obstruction of the catalyser); disadvantage is the high dust content which damages the catalyser * Alignment behind the catalyser: This socalled "Low-Dust”- alignment limits the disadvantages, however it requries repeated heating of the fluegases which have cooled at this point. |
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