SNCR - Selective Non-Catalytic Reduction NOx Removal System


The Selective Non-Catalytic Reduction (SNCR) system is a technology developed by MDSJ AIR that converts NOx (nitrogen oxides) to N2 and H2O at high temperatures by injecting reactants without the need for a catalyst. The system can achieve high acceptable reduction rates without the use of additional catalysts, provided that the appropriate temperature range is maintained.

In the SNCR DeNOx system by MDSJ AIR ENGINEERING, the reactants, typically aqueous ammonia or urea, are directly injected into the combustion chamber or flue gas using carriers such as water for high efficiency within the correct temperature range as determined by MDSJ.

The SNCR DeNOx System

by MDSJ AIR ENGINEERING is designed for the simplest and most effective NOx reduction applications, typically for urea at temperatures between 900°C and 1100°C, and for aqueous ammonia at temperatures between 850°C and 900°C. SNCR also poses a high risk of ammonia vapor escaping from the stack due to improper dosing systems.

In the case of using ammonia or urea, the following general reactions occur according to the SNCR system by MDSJ AIR ENGINEERING:

Using Urea


Urea + 2 NO + ½ O2 → 2 N2 + 3 H2O

Using Aqueous Ammonia:

2NH3 + 2NO + 1/2O2 → 2N2 + 3H2O

Spray nozzles inject the NH3-water solution into the flue gas. Water will evaporate, and gaseous NH3 will react with NOx to form nitrogen gas (N2) and water vapor (H2O) in the SNCR. Aqueous ammonia or urea is injected into the combustion gases emitted from the combustion process to reduce NOx nitrogen gases (N2) within the temperature range of 870°C to 1150°C. The basic chemical principle is the reaction of ammonia or urea with NOx in the combustion gases at high temperatures to produce nitrogen gas (N2) and water vapor (H2O). SNCR systems provide the ability to reduce NOx by approximately 40-75%.

The MDSJ AIR ENGINEERING SNCR system evaluates pollutant levels in flue gas, adjusts dosing rates accordingly, and prevents unnecessary chemical consumption.


Selective Non-Catalytic Reduction (SNCR) is commonly used in traditional combustion plants that burn coal, biomass, and waste to reduce nitrogen oxide (NOx) emissions from industrial facilities.

Businesses seeking to meet national or local emission standards will often choose SNCR as an effective and cost-efficient NOx reduction system in the following cases:

Advantages of SNCR

Selective Non-Catalytic Reduction offers significantly lower investment costs compared to SCR technology, as it does not require an additional catalyst.

MDSJ SNCR systems are fully automated and designed to operate in challenging industrial environments. Our robust systems operate as specified with minimal downtime.