SELECTIVE NON-CATALYTIC REDUCTION TO CONTROL NOx WHEN THE PROCESS HAS ADEQUATE TEMPERATURE
Selective Non-Catalytic Reduction (SNCR) systems are non-catalytic DeNOx solutions designed to reduce nitrogen oxides (NOx) in flue gas by injecting urea or ammonia into a high temperature area of the process. Unlike SCR, they do not use catalyst, so their viability depends mainly on the available thermal profile, injection point and actual residence time before gases leave the reaction zone.
In PREMATECNICA we supply SNCR systems adapted to each installation, considering NOx load, household or duct geometry, gas flow, turbulence, injection strategy, reagent control and emission reduction objective.
WHEN TO CHOOSE AN SNCR SYSTEM
An SNCR is suitable when the installation needs to reduce NOx with a simpler and more economical solution than SCR, and the process has a sufficient thermal window for the reaction to take place without catalyst. Their natural setting is combustion equipment where the reduction target is compatible with a non-catalytic technology and where the injection point can be defined with discretion.
It is also an interesting option when seeking to improve the environmental performance of the process without incorporating a catalytic reactor, provided that the thermal regime is sufficiently stable and there is accessibility for placing spears or injection nozzles.
OPERATION AND REACTION PRINCIPLE
The SNCR works by injecting urea or ammonia directly into the stream of gases at high temperature. Under these conditions, the reagent favours the chemical conversion of NOx to nitrogen (N2) and water (H2O). The efficacy depends on temperature, mixture of reagent and gas, time available for reaction and type of reagent.
Therefore, the value of the system is not only in dosing the reagent, but in correctly selecting the injection point, distributing it homogeneously and adapting the control to the actual load changes of the equipment.
MAIN COMPONENTS OF THE SYSTEM
An SNCR solution usually includes storage and preparation of the reagent, dosing system, injection nozzles or spears, instrumentation and operation control. Depending on the process, it can incorporate several levels or injection zones to better suit the thermal profile of the home or duct.
The distribution of the reagent is one of the most sensitive points: a misplaced injection or poor mixing reduces performance and makes it difficult to achieve the planned reduction target.
TEMPERATURE AND LIMITATIONS WINDOW
The SNCR is heavily conditioned by the available temperature window, typically between 850 and 1050ºC. If the temperature is too low, the reaction loses effectiveness; if it is too high, unwanted reactions or inefficient reagent consumption may occur. In addition, load variability can displace that heat window and affect performance.
Therefore, the system must be designed with real operation criteria, not only with nominal process data.
INTEGRATION AND PREMATECNICA DESIGN
Each SNCR system requires a specific design basis. In PREMATECNICA we analyse NOx load, temperature profile, gas flow, equipment geometry, accessibility, reagent consumption and interaction with the gas train. From this basis, we help define the injection point, the spear configuration and the control strategy.
Our approach combines combustion, emissions control and process integration to implement a viable, stable SNCR solution consistent with the actual operation of the facility.