What is Selective Catalytic Reduction?

The selective catalytic reduction is nothing but a means of converting nitrogen oxides, also known as NOx, into diatomic nitrogen (N2) and water with the help of a catalyst. These catalysts are made from a very porous ceramic material such as titanium oxide, and active catalytic components are usually either oxide of base metals or various precious metals. Therefore, each catalytic component has its advantages and disadvantages.

Why go for Dürr’s Cat. X CR?

Cat. X CR is majorly used when high nitrogen oxide conversion rates are needed. The air pollution control system uses selective catalytic reduction, which separates nitrogen oxide (NOx) from the flue gases and processes exhaust gases. This can be used for flue gas purification if installed in Oxi. X DF (direct-fired thermal oxidizer) system or can also be used as a stand-alone unit. And as the name suggests, this air pollution control system unit operates on the principle of Catalysis.

On which principle does Cat. X CR functions?

This system usually functions between the temperature range of 300 to 500 degrees Celsius. Therefore, the exhaust air entering the system must be of a specific temperature. If this is not the case, it must be pre-heated with the help of an air-to-air heat exchanger. Generally, the air is heated with a burner or another type of heater until it touches the temperature where the catalyst is operational.

With the help of the catalyst, the nitrogen monoxide (NO) is reduced to nitrogen dioxide (NO2). 

The primary function of the catalyst is to lower down the reaction temperature to the required operating temperature of 300 to 350 degrees Celsius, which in its absence would have been between 900 to 1000 degrees Celsius.

Once the catalyst startup temperature has been reached, an ammonia and water solution is injected into the system. The ammonia in the system is used as the reducing agent. It reacts with the nitrogen monoxide (NO) and nitrogen dioxide (NO2) present in the exhaust air, leaving behind nitrogen and water as the byproduct of the reaction. Thus, the chemical reaction which takes place in the catalyst is selective. This implies that the priority of this air pollution control system is to minimize the levels of nitrogen oxide while simultaneously reducing the unwanted reactions of other substances. Once the catalyst changes the nitrogen oxides, the energy extracted during the process is reused to pre-heat the untreated exhaust gas.

What does a Cat. X CR consists of?

The Cat. X CR air pollution control system includes a catalytic reactor with an upstream support burner or electric heating system, an ammonia injection station, and a heat exchanger. The heat exchanger helps in recovering the heat and helps in pre-heating the exhaust air. This supply of heat is only needed if the exhaust air is below the reaction temperature of the pollutants or the startup temperature of the catalyst.

In what all area can the Cat. X CR be used?

Dürr’s Cat. X CR air pollution control system is majorly used in the chemical and petrochemical industries. Such systems have also proved to be highly efficient when it comes to purifying the exhaust gases emitted during the glass manufacturing process.

Some other areas where selective catalytic reduction is also used are –

• Breaking down the pollutants that produce nitrogen oxide (NO)
• Cleaning the flue gases that are generated directly from the heated steam generators
• Separating the nitrogen oxide (NO) gas from the exhaust gases
• Treating the flue gases in the power stations

So, why go for a Cat. X CR air pollution control system?

• It can combine with the Oxi. X DF and the Oxi. X RTO
• It can also be used as a stand-alone system
• Up to 99.9% purification is possible with this system
• Reduced loss of pressure

The temperature required for its functionality is also very low