Nitrogen oxides (NOx) are one of the main pollutants in industrial production and cause significant harm to the atmospheric environment. With increasingly stringent environmental protection standards, various industries such as electricity, steel, and chemicals are facing pressure to reduce NOx emissions. Next, let us understand how denitrification catalysts achieve efficient treatment of nitrogen oxides?

 

1. Selective catalytic reduction (SCR) technology: core reaction mechanism
Selective catalytic reduction (SCR) technology is currently the most widely used and mature denitrification technology. Its core principle is to introduce a reducing agent (such as ammonia) into the flue gas, and under the action of the catalyst, NOx is selectively reduced to harmless nitrogen (N₂) and water (H₂O), thereby achieving denitrification.

 

The basic reaction equation of SCR reaction is:

4NO+4NH3+O2→4N2+6H2O4NO + 4NH_3 + O_2 \rightarrow 4N_2 + 6H_2O4NO+4NH3+O2​→4N2​+6H2​O6NO2+8NH3→7N2+12H2O6NO_2 + 8NH_3 \rightarrow 7N_2 + 12H_2O6NO2​+8NH3​→7N2​+12H2​O

The catalyst plays a role in promoting the reaction in this process, while controlling the reaction temperature so that the reductant reacts mainly with NOx and avoids oxidizing ammonia. The denitration efficiency of SCR technology can usually reach more than 90%, with a wide range of applications. It is the preferred technology for thermal power plants, steel mills and other industries.

 

2. Catalyst composition and structure: the key to affecting denitration efficiency
The catalyst is the core component of SCR technology, and its material composition and microstructure directly determine the reaction efficiency. Common catalyst materials include vanadium-titanium, vanadium-tungsten, manganese, iron-based and molecular sieve catalysts. Each material has its specific applicable temperature range and working condition requirements.

 

Vanadium-titanium catalyst: the most commonly used, suitable for a temperature range of 300-400℃, with a high cost-effectiveness.
Vanadium-tungsten catalyst: tungsten is added to vanadium-titanium to enhance the anti-sulfurization ability, suitable for high-sulfur flue gas.

Molecular sieve catalyst: the molecular sieve structure increases the specific surface area of ​​the catalyst, which helps to improve the catalytic effect in low and high temperature environments.

The structural design of the catalyst, especially the surface area and porosity, directly affects the contact efficiency of the reaction. The larger the specific surface area, the more opportunities for the reductant to contact NOx, and the higher the reaction efficiency. At the same time, the channel design needs to take into account the reaction rate and airflow resistance to ensure that the flue gas flow rate is not affected.

 

3. Optimization of active components: Improve anti-poisoning and durability
In actual working conditions, flue gas often contains impurities such as SO₂ and dust, which may poison the catalyst and reduce its denitrification efficiency. Therefore, the anti-poisoning performance of the catalyst is crucial. In response to this problem, researchers continue to improve the active components of the catalyst to enhance the catalyst's anti-poisoning and durability.

 

Anti-sulfurization: By adding tungsten elements or using molecular sieve structures, the catalyst's anti-sulfurization ability can be effectively improved to prevent SO₂ from being converted into sulfate and poisoning the catalyst surface.

Water resistance: In a low-temperature denitrification environment, water vapor may react with the catalyst surface, resulting in a decrease in catalytic activity. Adding water-resistant components can effectively improve the catalyst's water resistance and ensure its stability in a humid environment.

Alkali metal poisoning resistance: Under certain working conditions, flue gas contains alkali metals such as sodium and potassium, which will cause the catalytic activity to decrease after reacting with the catalyst. In response to this situation, a protective layer can be coated on the catalyst surface to reduce the contact of alkali metals with active components.

Through the improvement of active components, the anti-poisoning and service life of denitrification catalysts under complex working conditions can be significantly improved, ensuring that enterprises achieve long-term and stable denitrification effects.

 

4. Temperature control technology: the key to optimizing reaction efficiency
The efficiency of the SCR reaction is very sensitive to temperature, and too high or too low temperature will affect the catalytic effect. Different catalysts have their own optimal temperature ranges. For example, the optimal reaction temperature of vanadium-titanium catalysts is 300-400°C, while manganese catalysts are suitable for low temperature (180-250°C) conditions.

 

High temperature conditions: Under high temperature conditions, molecular sieve catalysts and vanadium-tungsten catalysts are more stable and less prone to deactivation. By rationally selecting catalyst materials, the denitrification efficiency under high temperature environments can be improved.

Low temperature conditions: For low temperature conditions such as cement plants or waste incineration plants, low temperature catalysts (such as manganese catalysts) can be selected or flue gas heating technology can be used to increase the temperature to ensure reaction activity.

In addition, temperature fluctuations will affect the life of the catalyst and the denitrification efficiency. Therefore, some manufacturers have introduced intelligent temperature control systems to monitor and adjust the reaction temperature in real time to ensure that the SCR reaction is carried out under optimal conditions.

 

5. Fluid mechanics optimization: Improve the uniformity of flue gas distribution
In order to achieve the best denitrification efficiency, the flue gas should be distributed as evenly as possible on the catalyst surface. This requires optimizing fluid mechanics when designing the reaction device, reducing airflow deviation and dead corners through reasonable flue gas drainage and distributor design, and maximizing the contact rate between the reducing agent and NOx.

 

Flue gas uniformizer: A flue gas uniformizer is set at the inlet of the SCR reactor to evenly distribute the flue gas to the catalyst surface to ensure the adequacy of the reaction.

Flow field simulation: Use flow field simulation technology to optimize the flue gas flow path and reduce the airflow deviation of the catalyst bed. Especially in large-scale industrial equipment, flow field simulation can effectively predict the flue gas distribution and provide a scientific basis for the structural optimization of the catalyst device.

The application of fluid mechanics optimization technology can further improve the overall denitrification efficiency of the SCR system and reduce the problem of unstable denitrification effect caused by uneven airflow distribution.

 

6. Catalyst regeneration technology: Extend service life
The activity of the catalyst will decrease during long-term use due to the accumulation of impurities and pollutants. The catalyst regeneration technology can partially restore the activity of the failed catalyst, thereby extending its service life.

Chemical cleaning: Use a solution to clean the impurities such as ash and sulfate on the surface of the catalyst to restore its activity.
Thermal regeneration: Through high-temperature treatment, pollutants adsorbed on the catalyst surface are decomposed and the catalytic performance of active components is restored.

The mature application of regeneration technology can not only reduce the cost of catalyst replacement for enterprises, but also reduce the amount of industrial waste to be processed and realize the recycling of resources.

 

خاتمة
The core technology of denitrification catalyst covers many aspects from material composition to structural design, from temperature control to fluid mechanics optimization. When selecting and using denitrification catalysts, enterprises need to make comprehensive considerations based on factors such as operating temperature, flue gas composition, and denitrification efficiency requirements. With the continuous improvement of environmental protection standards, catalyst technology in the future will pay more attention to the development of high efficiency, stability and durability to meet more stringent NOx emission control requirements.

 

Efficient denitrification catalysts can not only help enterprises meet environmental protection compliance requirements, but also effectively reduce the negative impact of production on the environment, and help achieve sustainable development environmental protection goals.