NOx reduction with SNCR and SCR systems using urea as a reducing agent

Yara is a leading urea producer in the world and has supplied its customers with urea for many years, including for the reduction of NOx emissions:

• With SNCR systems, urea is often the reducing agent chosen for safety reasons. However, it is less effective than ammonia as urea needs to be converted into ammonia before the process of reducing NOx can take place.
• We provide either solid urea, typically for dilution on site or urea in solutions with various concentrations

Why choose urea as a reagent to control NOx emissions:

• You may wish to choose urea for safety reasons. It has less risk in the workplace and requires no special training, unlike ammonia
• Urea is not dangerous. It is stable, non-volatile, non-flammable and non-explosive

Urea can be safely transported, stored and handled without the need for specific training.
However, there are disadvantages in using urea as a reducing agent in the control of NOx:
Urea may lead to additional emissions of nitrogen oxides or of carbon moNOxide which are both harmful gases
Urea is less effective than ammonia for NOx reduction
There is an increased likelihood of contamination and corrosion in equipment downstream from the point of injection
Leaks of urea solution cause the formation of a white precipitate salt which makes your equipment seem aged
When mixed with hard water, urea and flakes can clog your NOx control system
Solid urea is to be delivered and maintained at a temperature sufficient to prevent it from crystallizing. The crystallization point depends on the level of urea concentration. For example, 40% urea solution of crystallizes at 0°C.