At present, the main denitrification technologies applied in industry are: SCR and SNCR. The core of SCR denitrification technology is to use NH3 to undergo redox reactions with NOx under catalytic conditions at lower reaction temperatures (300-400 ℃); SNCR denitrification technology involves the oxidation-reduction reaction between NH3 and NOx at high temperatures (800-1000 ℃). The preparation of NH3 includes ammonia water, liquid ammonia, urea, and their ammonia containing raw materials.

SCR denitrification technology

SCR denitrification technology has the advantages of low reaction temperature and high denitrification efficiency, and has become the main method for controlling NOx. In SCR technology, the catalyst is the core, and its performance directly affects the removal efficiency of NOx. However, SCR technology has the following drawbacks:

Catalysts are prone to poisoning, which increases the instability of the system;

Catalysts are prone to clogging, which affects boiler output;

The construction cost of catalysts accounts for 30% to 50% of the entire SCR denitrification system, and their operation also accounts for 30-50% of the total operating cost.

SNCR denitrification mainly involves injecting amino reducing agent into the temperature window at the top of the furnace (850~1000 ℃), without the need for a catalyst, and using the NH3 released by the reducing agent to selectively reduce NOx in the flue gas into harmless N2 and water.

SNCR technology has a moderate denitrification rate, does not require catalysts, has low operating costs, and a short construction period, making it suitable for the transformation of small and medium-sized boilers and various kilns for denitrification.

There are the following problems in the SNCR process: spraying 10-20% ammonia or urea solution into the reaction zone can cause a sudden and significant drop in temperature, and the temperature in each area of the reaction zone is uneven, resulting in low denitrification efficiency. Currently, the general denitrification efficiency is only 30-50%, which affects the combustion efficiency in the furnace. Huaneng Laiwu Power Plant dismantled the SNCR denitrification device.

At present, cement plants generally use SNCR denitrification technology with purchased ammonia water for denitrification, which has the following disadvantages:

Ammonia water belongs to hazardous chemicals and requires registration for transportation and storage. Once leaked, causing harm and significant losses;

The ammonia content in industrial ammonia water is generally not more than 20%, which means that 80% of the transportation volume is water. This causes inconvenience in transportation and limited storage, thereby increasing the purchase cost;

When using ammonia water, not only does it lower the furnace temperature, but it also consumes a lot of energy. Adding one ton of ammonia water to the kiln requires an additional energy consumption of about 90 kilograms of standard coal (which can be easily estimated based on the latent heat of evaporation and heat capacity of water);

For some regions, the high price of ammonia water greatly increases the cost of denitrification. If the price of one ton of ammonia water (with a 20% content) is greater than 800 yuan, it is higher than the price of urea (which contains 50% ammonia and costs around 2000 yuan).

Suggest adopting the new technology of urea ammonia production: urea on-site ammonia production technology [authorization number CN 101555025B], which can generate a profit of 300-500 yuan per ton of urea processed.

5. During denitrification, a large amount of ammonia water is used, causing ammonia escape: Ammonia water has poor reaction efficiency with NOx at high temperatures in the decomposition furnace, and the NH3/NOx molar ratio is generally 1.5:1.

Guangxi SNCR denitration equipment Lanzhou SNCR denitration equipment