Selective Non-Catalytic Reaction (SNCR)
This process converts nitrogen oxides to environmentally neutral nitrogen and water by addition of ammonia water. In contrast to the SCR process, no catalyst is required in this process.
Aqueous ammonia is fed through lances with nozzles all over the surface of several levels situated above the furnace chamber. Each feed level is supplied with a solution adapted to the temperature level, appropriately mixed beforehand in several mixing containers. Steam or compressed air are used as cooling and nebulizing medium.
The denitrogenation process takes place within a relatively narrow temperature range between 850°C and 1050°C, with the residence time of the nozzle-fed solutions also playing a significant role. This is why the flue gas temperature in the first boiler pass is measured by means of sound waves. If the gas temperature is too high, the undesirable nitrogen oxide resulting from the combustion of ammonia may be produced. A uniform temperature profile across the nozzle feed levels as well as an adequate reaction path within this narrow temperature range is therefore important.
This process is computer-assisted in EEW Energy from Waste plants. On the basis of the readings from three alternative nozzle feed levels, the computer selects the one with the right temperature window.
In order to achieve a maximum separation efficiency, more ammonia solution is fed through the nozzles than is consumed. Excess quantities are removed again in the subsequent flue gas cleaning procedure.