SELECTIVE CATALYTIC REDUCTION TO MEET DEMANDING LEVELS OF NOx CONTROL IN FLUE GASES
SCR (Selective Catalytic Reduction) systems are catalytic DeNOx solutions designed to reduce nitrogen oxides (NOx) in flue gas by injecting ammonia or urea and reacting on a catalyst. Compared to SNCR, the SCR is selected when the project requires higher conversion efficiency, more restrictive emission limits and stable operation within a compatible temperature window.
In PREMATECNICA we supply SCR systems adapted to each installation, considering gas composition, available temperature, NOx load, reactor space, integration with the smoke train and requirements for operation, maintenance and environmental compliance.
WHEN TO CHOOSE AN SCR SYSTEM
An SCR is appropriate when the installation needs to achieve a high NOx reduction and meet more demanding emission limits than those normally covered by a non-catalytic solution. The catalyst increases the reaction efficiency and allows to work with greater reducing capacity, provided that the gas is kept within a suitable temperature and is compatible with the catalytic medium.
In practice, SCR is often the logical choice when the goal is to minimise NOx with a high level of assurance, and the project can assume a catalytic reactor, reagent control, and more elaborate integration into the smoke train.
OPERATION AND REACTION PRINCIPLE
The SCR works by injecting ammonia, aqueous ammonia or urea into the smoke stream before it passes through a catalyst reactor. In the presence of the catalyst, the reagent favours the conversion of NOx to nitrogen (N2) and water (H2O), significantly reducing the charge of NOx to chimneys.
Efficiency depends on the distribution of the reagent, mixing with process gases, temperature, NOx load, catalyst state and control strategy. Therefore, the performance of SCR depends on the complete engineering of the system, not just the catalyst.
MAIN COMPONENTS OF THE SYSTEM
An SCR solution usually includes storage and preparation of the reagent, dosing system, injection grid or spears, catalytic reactor, instrumentation and operation control. In more complete projects, emissions monitoring and auxiliary equipment can be incorporated to improve reagent distribution or flow homogeneity.
The homogeneous distribution of the reagent at the catalyst inlet is critical to maximize NOx reduction and minimise ammonia slip.
TEMPERATURE AND LIMITATIONS WINDOW
The SCR operates within a specific temperature window, which depends on the catalyst and gas composition. If the temperature deviates from the proper range, efficiency decreases and operational problems may appear. In addition, certain substances can contaminate, deactivate or deteriorate the catalyst, so it is necessary to study closely the composition of the fumes.
The ammonia slip, i.e. the unreacted reagent that is released downstream, must also be checked.
INTEGRATION AND PREMATECNICA DESIGN
Each SCR system requires a specific design basis. In PREMATECNICA we analyse NOx load, gas flow, temperature, gas composition, available space, emissions target and coordination with upstream and downstream teams. From that basis, we help define the reactor location, injection scheme, dosing and integration with the smoke train.
Our approach combines combustion, emissions control and process integration to implement a reliable, operable SCR solution consistent with the project’s environmental requirement level.
