Selective Non-Catalytic Reduction (SNCR) Technology Overview Selective Non-Catalytic Reduction (SNCR) is a widely used post-combustion technology designed to reduce nitrogen oxide (NOx) emissions from industrial processes, particularly in power plants, waste incinerators, and large-scale boilers. Unlike catalytic methods, SNCR operates without a catalyst, relying instead on precise temperature control and chemical reactions to break down NOx into harmless nitrogen (N₂) and water (H₂O). Process Mechanism The SNCR process involves injecting a nitrogen-based reducing agent—typically ammonia (NH₃) or urea (CO(NH₂)₂)—into the flue gas stream within a specific temperature window, usually between 900°C and 1,100°C. At these high temperatures, the reagent decomposes and reacts with NOx to form N₂ and H₂O. The key reactions are: - For ammonia: \[ 4NH₃ + 4NO + O₂ → 4N₂ + 6H₂O \] - For urea (which first decomposes into ammonia): \[ CO(NH₂)₂ → NH₃ + HNCO \] Advantages 1. Cost-Effectiveness: SNCR systems are simpler and less expensive than catalytic alternatives (e.g., SCR) since they require no catalyst beds or complex infrastructure. 2. Flexibility: Suitable for retrofitting existing facilities due to minimal space requirements. 3. Low Maintenance: No catalyst replacement or fouling concerns, reducing operational costs. Challenges 1. Temperature Sensitivity: Efficiency drops outside the optimal range, requiring precise control. 2. Ammonia Slip: Excess reagent can escape unreacted, leading to secondary pollution. 3. Lower Efficiency: Typically achieves 30–70% NOx reduction, less effective than SCR. Applications SNCR is favored in industries with moderate NOx reduction needs, such as coal-fired boilers, cement kilns, and biomass plants. Its simplicity makes it attractive for facilities seeking a balance between performance and cost. Conclusion While SNCR has limitations, its affordability and ease of implementation ensure its continued use in emission control strategies, particularly where high-efficiency systems are not economically justified. Advances in injection techniques and reagent optimization continue to enhance its performance. (Word count: 500)