Overview
Low-temperature SCR denitrification is an advanced air pollution control technology designed to reduce nitrogen oxides (NOx) in industrial exhaust gases at temperatures between 150–300°C. Unlike conventional SCR systems requiring 300–400°C, it suits applications where heat recovery is prioritized or flue gas temperatures are inherently low (e.g., cement kilns, biomass boilers). The system integrates a catalytic reactor, ammonia/urea injection grid, and control unit. It meets stringent environmental regulations (e.g., China's Ultra-Low Emission standards) and is increasingly adopted in coal-fired plants, chemical processing, and waste-to-energy facilities.
Structure and Working Principle
A typical low-temperature SCR system consists of a reactor housing filled with honeycomb or plate-type catalysts, an ammonia injection grid (AIG), and ductwork for flue gas distribution. The catalyst—often vanadium-tungsten-titanium (V2O5-WO3/TiO2) or novel manganese-based formulations—activates the reaction between NOx and reductants (NH3 or urea). Flue gas enters the reactor at 150–300°C, where injected ammonia/urea reacts with NOx to form harmless nitrogen (N2) and water (H2O). Key design challenges include uniform gas flow distribution and minimizing ammonia slip (unreacted NH3). Bypass dampers and hybrid systems (e.g., combining with SNCR) enhance flexibility.
Key Features
1. **Temperature Adaptability**: Operates efficiently at lower temperatures than traditional SCRs, reducing reheating energy costs. 2. **High Efficiency**: Achieves >90% NOx removal with optimized catalysts. 3. **Modularity**: Prefabricated units simplify installation in space-limited retrofits. Advanced systems incorporate SO2-resistant catalysts and automated control for varying load conditions. Some use dual-layer catalysts (e.g., MnOx-CeO2 for low temps + V2O5/TiO2 for backup) to handle flue gas fluctuations. Dust filters upstream prevent catalyst clogging.
Application Areas
Primary users include coal-fired power plants (especially those with wet flue gas desulfurization, which cools exhaust), glass manufacturing, and chemical industries (e.g., nitric acid plants). Municipal waste incinerators also adopt low-temperature SCR to comply with EU 2010/75/EU directives. In China, retrofit projects dominate due to 2025 emission targets. Overseas, it’s favored in biomass energy facilities where exhaust temperatures rarely exceed 200°C. Shipping and decentralized industrial boilers are emerging markets.
Maintenance and Precautions
Routine maintenance includes catalyst layer inspections (every 6–12 months) for fouling or sulfation, and AIG nozzle cleaning. Catalyst life spans 3–5 years but may shorten with high sulfur/ash content. Online SO2 monitoring is critical to prevent poisoning. During shutdowns, protect catalysts from humidity and particulate deposition. Use sootblowers cautiously to avoid physical damage. Spare catalyst modules should be stored dry, below 40°C. Unexpected activity drops may indicate alkali metal (e.g., K, Na) contamination from fuel impurities.
B2B Procurement Guide
1. **Specifications**: Define NOx inlet concentration, flow rate, and space constraints. 2. **Catalyst Type**: Choose between standard V2O5 (cost-effective) or novel metals (Mn, Ce) for sulfur-rich gases. 3. **Vendor Evaluation**: Prioritize suppliers with retrofit experience and local service teams. Total costs include catalysts (30–50% of CAPEX), reactor steelwork, and installation. For reference, a 300MW power plant system may cost $2–4 million. Leasing models (e.g., pay-per-ton NOx removed) are gaining traction. Verify compliance with ISO 11042 (performance testing) and request case studies from similar industries.
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