DNT Selective Catalytic Reduction

Selective Catalytic Reduction (SCR)

Selective Catalytic Reduction (SCR) is the most effective method of controlling nitrogen oxide emissions (NOx) from combustion sources. It is a commercially proven flue gas treatment technology that has been demonstrated to remove over 90 percent of the NOx contained in combustion or process exhaust gas.

Selective Catalytic Reduction System reduces NOx emissions

Elimination of NOx creates a healthier environment and meets stringent new EPA and EU reduction requirements. SCR technology is widely used on different types of combustion systems such as coal fired boilers, simple and combined cycle gas turbines, process boilers, hydrogen reformers, etc. Virtually any hot flue gas containing NOx can be treated effectively with the SCR process as a retrofit or as new equipment.

NOx Reduction is performed through the Catalyst

The catalyst is at the heart of the SCR process. It creates a surface for reacting the NOx and ammonia, and allows for the reaction to occur within typical flue gas temperature ranges. The active ingredient in most NOx catalyst is Vanadium Pentoxide (V₂O₅) of various concentrations. For higher temperatures zeolites, tungsten or titanium matrices may be utilized as well. Catalyst configurations can be homogenous honeycomb, coated honeycomb or plate type catalyst.

The catalyst opening, composition and volume of catalyst are determined by components of flue gas chemistry, treatment temperature and amount of flue gas to be treated.

The Ammonia reducing agent is injected upstream of the catalyst. It is crucial that ammonia be evenly distributed along the face of the catalyst. Usually, it is necessary to ensure that the flue gas flow is even with flow chevrons and mixing devices. Then, an Ammonia Injection Grid is used to ensure that the ammonia is evenly distributed across the flue gas. As an alternative, urea solutions can be used as a source of ammonia - converted to ammonia either externally or in-situ.

NOx Reduction through the catalyst forms N2 and H2O

The reaction occurs in the pores of the catalyst bank. The catalyst bank may consist of one or more layers of catalyst for treatment. On the surface of the catalyst, the NOx will be selectively reduced by reacting with ammonia in the presence of oxygen to form harmless byproducts, water and nitrogen (H₂O & N₂).

Typically the range of temperature for this reaction is 500-850°F (260-454°C). In clean gas applications, specialty high-temperature formulations are able to achieve high NOx reduction at temperatures as high as 1100°F (593°C). This wide temperature range allows for flexibility in a retrofit situation and choices for multi-pollutant optimization in new equipment.

Selective Catalytic Reduction may be used in any industry with effluent gas at sufficient temperature containing nitrogen oxides such as Power, Petrochemical, Steel, Metal production, Pulp and Paper, Cement, Waste to Energy, Glass, Nitrous Acid Production etc. It is ideal to meet the EPA's stringent requirements for NOx reduction in any combustion application.