What is the principle of the SNCR process?

SNCR (Selective NonCatalytic Reduction) – a denitration technology based on selective non-catalytic reduction. Process principle: Within a high-temperature range (927–1093°C), without the use of a catalyst, reducing agents containing NH3 groups such as ammonia or urea are injected into the flue gas. These NH3-based reducing agents can selectively reduce NOx in the flue gas to N2 and H2O, with virtually no reaction occurring with the oxygen present in the flue gas.

Should ammonia gas or ammonia water be sprayed into the flue gas?

In the temperature range of 927–1093 °C, without the use of a catalyst, amino reducing agents such as ammonia or urea can selectively reduce NOx in flue gas to N2 and H2O, with virtually no reaction occurring with the oxygen present in the flue gas. The main reaction when ammonia (NH3) is used as the reducing agent is: 4NH3 + 6NO → 5N2 + 6H2O. This reaction primarily takes place at temperatures around 950 °C.  Experiments show that when the temperature exceeds 1093 °C, NH3 is oxidized to NO, thereby increasing the NOx emission levels. The reaction is: 4NH3 + 5O2 → 4NO + 6H2O. When the temperature is below 927 °C, the reaction is incomplete, resulting in a high rate of ammonia escape and thus new pollution. It can be seen that either too high or too low temperatures are not conducive to controlling pollutant emissions. Due to the narrow optimal reaction temperature range, the optimal temperature changes as the load varies. To accommodate these changes, a large number of nozzles must be installed in the furnace, with their positions and quantities adjusted as the load changes. Furthermore, the residence time of the reactants is very short, making it difficult for them to mix thoroughly with the flue gas, which results in low denitration efficiency.   The current trend is to use urea ((NH4)2CO) as a reducing agent to make the operating system safer and more reliable, without having to worry about ammonia leaks causing new pollution. At this point: (NH4)2CO → 2NH3 + CO; NH3 + NO → N2 + H2O; CO + NO → N2 + CO2 

Ammonia gas or ammonia solution? Either is fine. Ammonia can be sprayed directly; it’s better to have heating, and the ammonia solution should first evaporate