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Installations of flue gas denitrification by selective catalytic reduction
Emissions of NOx are created in the boilers and furnaces at high temperatures during the homogeneous reaction in the gaseous phase of oxygen and nitrogen which is present in the flue gas. Such a "thermal oxides of nitrogen" is essentially any form of NO with very low contents of NO2. Another contribution to the overall value of NOx results from presence of nitrates or any other nitrogen containing compound between the treated product or burned at high temperature.
Uncontrolled emissions of NOx depend primarily on various process parameters, such as the speed of fuel combustion, geometry of the oven, amount of fuel consumed and its quality. NOx emissions can vary significantly depending on location and from the boiler. Catalytic SCR system is certainly the most common and most effective technology for reducing emissions of nitrogen oxides. Process provides reaction of ammonia (NH3) with NOx to produce nitrogen (N) and steam (H2O).
Two basic reactions that occur in the catalyst:
4NH3 + 4NO + O2 -> 4N2 + 6H2O
4NH3 + 2NO + O2 -> 3N2 + 6H2O
Such reactions occur in the reactive sites of the catalyst, placed inside the DeNOx reactor, therefore it is very important that exhaust gas stream coming into this element is the most homogeneous. For this reason, it is important run simulations and analysis of flow dynamics in order to properly design a reactor that will work in the conditions of a process. The choice of performance requirements for the SCR system determines the overall design of the SCR system.
Required for reaching reduction of NOx emissions is usually the first parameter determined when considering the possibility of implementing the SCR system. In theory, reduction of NOx level of 100 percent is possible, but in the practical application of this technology achieves of results over 90 percent is complicated. Both the technical and economic limitations determine the maximum NOx reduction that can be achieved for a given installation. In addition to the NOx reduction performance, the second determinant of the catalyst project will be a maximum injection of ammonia that has been adopted for the system. The size of the catalyst is very largely dependent on the maximum specified ammonia injection.