What is Selective Catalytic Reduction (SCR)?
Selective Catalytic Reduction (SCR) is a technology used to reduce the emission of nitrogen oxides (NOx) from the exhaust gases of industrial processes and internal combustion engines. By using a reductant, usually ammonia (NH3) or urea, in the presence of a catalyst, NOx is converted into nitrogen (N2) and water (H2O).
How Does SCR Technology Work?
In SCR systems, the reductant is injected into the exhaust stream where it mixes with the NOx. The mixture then passes over a catalyst, typically composed of materials like titanium dioxide (TiO2), vanadium pentoxide (V2O5), and tungsten trioxide (WO3). The catalyst facilitates the chemical reaction that converts NOx into N2 and H2O, thereby reducing harmful emissions.
Vanadium-based catalysts: These are the most common and widely used due to their high activity and sulfur resistance.
Zeolite-based catalysts: Known for their thermal stability and high NOx conversion rates, especially in mobile applications like automotive exhaust systems.
Iron and copper-exchanged zeolites: These are typically used in low-temperature applications and offer excellent NOx reduction performance.
High Efficiency: SCR can achieve NOx reduction efficiencies of over 90%.
Versatility: It can be used in a variety of applications, from power plants to diesel engines.
Reduced Emissions: By converting NOx to N2 and H2O, SCR helps in meeting stringent environmental regulations.
Cost-Effectiveness: Over the long term, the reduction in NOx emissions can lead to lower compliance costs and potential tax incentives.
Ammonia Slip: Excess ammonia can slip through the system unreacted, leading to secondary pollution.
Catalyst Deactivation: Over time, catalysts can lose their activity due to fouling, poisoning, or thermal degradation.
Operating Costs: The need for continuous supply of reductants like ammonia or urea can add to operational costs.
Space Requirements: SCR systems can be bulky, making them challenging to implement in space-constrained applications.
