Application of flue gas denitrification technology in the metallurgical industry: comparison of SCR and SNCR technologies
2024-07-25
The iron and steel industry is an important part of the national economy, providing an indispensable material basis for the life of the country and its people. However, with the constant increase in iron and steel production, the problem of waste gas emissions is becoming more and more serious. The waste gases generated during the steel production process pollute the atmosphere to a certain extent. Among them, nitrogen oxides (NOx) are one of the main pollutants that harm human health and the environment. Therefore, waste gas purification in the metallurgical industry is especially important. Flue gas denitrification technology is one of the effective means of controlling NOx in the waste gases of the metallurgical industry, selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) technology is currently the main one of the two denitrification technologies, which play a key role in the metallurgical industry in the treatment of flue gases.
Overview of flue gas denitrification technology
Flue gas denitrification technology is the process of converting nitrogen oxides in flue gases into harmless substances using chemical reactions or physical methods. According to different processing principles, flue gas denitrification technologies can be divided into three categories: dry, semi-dry and wet. Among them, dry denitrification mainly uses catalysts to promote the reaction between NOx and reducing agents (such as ammonia, urea, etc.); semi-dry denitrification adds the appropriate amount of water based on the dry method to improve the reaction efficiency; and wet denitrification involves converting NOx into harmless substances through a liquid phase reaction.
Selective Catalytic Reduction (SCR) Technology
l Principle
SCR technology uses reducing agents such as ammonia (NH3) to selectively react chemically with NOx under the influence of a catalyst to produce harmless nitrogen (N2) and water (H2O). The presence of a catalyst lowers the reaction temperature and increases the reaction rate, resulting in a significant increase in denitrification efficiency.
lApplication
In the metallurgical industry, SCR technology is typically used to treat high temperature, high dust, high sulfur exhaust gases. Since the catalyst has certain temperature and dust requirements, pre-treatment of the exhaust gases, such as cooling and dust removal, is necessary. In addition, SCR technology can be combined with desulfurization technology to achieve comprehensive desulfurization and denitrification.
l Features
(1) High denitrification efficiency: Under suitable reaction conditions, the denitrification efficiency of SCR technology can reach more than 90%.
(2) Strict requirements for exhaust gas conditions: The activity and service life of the catalyst are affected by temperature, dust content and other factors, so strict exhaust gas pre-treatment is required.
(3) Higher investment and operating costs: the need to use catalysts and reducing agents, as well as the complexity of equipment design, which leads to relatively high investment and operating costs.
Selective Non-Catalytic Reduction (SNCR) Technology
Principle
SNCR technology uses reducing agents such as urea or ammonia to selectively react chemically with NOx to produce harmless nitrogen and water without a catalyst. The reaction usually occurs under high temperature conditions, so it is also called high temperature denitrification technology.
lApplication
In the metallurgical industry, SNCR technology is suitable for treating low and medium temperature waste gases. Since no catalyst is required, the temperature and dust content of the exhaust gases are relatively low. SNCR technology is usually combined with the exhaust system of boilers, heaters and other equipment to realize denitrification treatment of exhaust gases.
lFeatures
(1) Moderate denitrification efficiency: Under suitable reaction conditions, the denitrification efficiency of SNCR technology can reach 60-80%.
(2) Lower exhaust gas condition requirements: Due to the absence of a catalyst, the temperature and dust content of the exhaust gas are relatively low.
(3) Lower investment and operating costs: Since there is no need for a catalyst and complex equipment design, this results in relatively low investment and operating costs.
Comparison of SCR and SNCR technologies
l Denitrification efficiency: The denitrification efficiency of SCR technology is higher than that of SNCR technology, the former can reach more than 90%, the latter 60%-80%.
l according to the requirements for exhaust gas conditions: SCR technology has higher requirements for exhaust gas temperature and dust content, and requires strict pre-treatment; and SNCR technology requires less in terms of exhaust gases.
l Investment and operating costs: The investment and operating costs of SCR technology are higher than those of SNCR technology, mainly due to the use of catalysts and reductants and the complex structure of the equipment.
Scope of application: SCR technology is suitable for treating high temperature, high dust and high sulfur exhaust gases; while SNCR technology is suitable for treating low and medium temperature exhaust gases.
SCR technology has the characteristics of mature technology, high denitrification efficiency, stable operation, no secondary pollution, etc. SCR technology is usually selected when the denitrification efficiency must be greater than 70%. The efficiency of denitrification using SCR technology can be more than 90%.
The denitrification efficiency of SNCR in pulverized coal combustion is usually 40~50%, and the denitrification efficiency in circulating fluidized bed is usually 50~70%.
