deNOx

DeNOx refers to technologies and strategies used to reduce nitrogen oxide (NOx) emissions from combustion sources such as power plants, industrial boilers, cement kilns, and marine engines. NOx forms mainly as thermal NOx in high-temperature flames and as fuel NOx from nitrogen in the fuel. Reducing NOx is important for air quality, human health, and to comply with environmental regulations.

Primary DeNOx methods modify the combustion process to limit NOx formation. Techniques include low-NOx burners, staged combustion (air or fuel staging), and flue gas recirculation, which lower flame temperatures and control combustion conditions to minimize NOx formation at the source. These approaches are often implemented during boiler design or during retrofit projects.

Secondary or post-combustion DeNOx technologies remove NOx from flue gas after it forms. The two main families are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). SCR injects a reducing agent (usually ammonia or urea) into the flue gas before a catalyst, converting NOx to nitrogen and water; typical reductions range from 70% to 95% within a specific temperature window (roughly 250–400 C). SNCR also uses ammonia or urea without a catalyst and achieves roughly 30% to 60% NOx removal, generally at higher temperatures around 850–1100 C and with less precision.

Operational considerations include ammonia slip and catalyst poisoning by sulfur oxides or ash, as well as reagent handling, storage, and dosing control. DeNOx systems are widely applied in fossil-fuel power plants, cement and kiln operations, refining, and marine propulsion, and are guided by regulatory frameworks such as national air quality standards and regional directives.