In case of a selective catalytic reduction (SCR), ammonia reacts with the harmful nitrogen monoxide (NO) and nitrogen dioxide (NO2) from the flue gas into harmless nitrogen (N2) and water. The reaction temperature is 200 to 450 °C.
In practice, urea-based ammonia-releasing reduction agents, such as the proven carbamin 5722 from ERC Technik, are the most suitable option available. SCR plants of ERC Technik essentially consist of metering and mixing sections, the atomisation equipment and the catalytic reactor, beeing equipped with up to four catalytic layers. In individual cases the catalytic converter can also be directly positioned in the flue gas channel. These systems can be arranged either downstream from the boiler (high-dust set-up) or after the flue gas cleaning (low-dust set-up). Re-heating of the flue gas prior to entry into the catalytic converter is usually necessary in case of the low-dust set-up.