- SCR denitration technology;
Gas DENITRATION technologies, also known as selective catalytic reduction (SCR) denitration technology, is a process that converts nitrogen oxides (NOx) into nitrogen (N2) and water (H2O) with the help of a catalyst. This is achieved by adding a reductant, such as anhydrous ammonia (NH3), aqueous ammonia (NH4OH), or a urea (CO(NH2)2) solution, to a stream of flue or exhaust gas and reacting it onto a catalyst. The reaction produces nitrogen (N2) and carbon dioxide (CO2) in the case of urea use.
SCR technology is widely used in various industries, such as coal-fired boilers, incinerators, furnaces, and kilns plants. It is a mature and reliable technology, with a high efficiency that can reduce NOx by 70-95%. Additionally, SCR technology offers other benefits including:
- High efficiency (more than 98%)
- Low ammonia escape rate (≤4ppm)
- Reliable with low operating costs.
the reactions involved in SCR denitration technology:
NO + NH3 → N2 + H2O
NO + NH4+ → N2 + 2H2O
NO + 1/2(NH2)2CO → 1/2(N2) + CO2 + 2H2O
- SNCR denitration technology
Selective Non-Catalytic Reduction (SNCR) is another denitration technology that reduces nitrogen oxide (NOx) emissions in the flue or exhaust gases. It is a chemical reaction process that uses ammonia or urea as a reducing agent to break down NOx into nitrogen (N2) and water (H2O) without the aid of a catalyst.
SNCR technology injects ammonia or urea solution into a high-temperature flue gas zone, where the reducing agent reacts with NOx to form N2 and H2O. This process is optimized by controlling the temperature and amount of reducing agent added to the flue gas. SNCR is typically used in boilers, furnaces, and other high-temperature combustion systems.
SNCR technology has the following features:
- Lower capital and operating costs compared to SCR technology
- High adaptability to different fuel types and combustion systems
- Can reduce NOx emissions by up to 70%
- Easy to retrofit into existing power plants or industrial facilities
- However, SNCR may have lower removal efficiencies than SCR and can produce ammonia slip, which is the unreacted ammonia that escapes the process and can contribute to air pollution.
The general reaction for SNCR is the reduction of NOx with ammonia:
2NO + 2NH3 + O2 → 2N2 + 3H2O
Alternatively, a modified SNCR process called “Advanced SNCR” (ASNCR) can also occur, which involves the reduction of NOx with urea:
2NO + CO(NH2)2 + O2 → 2N2 + 2CO2 + 2H2O
In both reactions, the ammonia or urea is added to the flue gas at a temperature range of 800°C to 1100°C. The ammonia or urea reacts with the NOx in the flue gas, forming nitrogen, water vapour, and carbon dioxide. The reaction is highly exothermic, meaning it releases heat, and the high temperatures involved ensure that the reaction occurs quickly and efficiently.
