SCR denitration | ammonia escape the causes and control measures
With the rapid development of social economy, environmental protection has attracted more and more attention. The emission standard of nitrogen oxide treatment (NOx) is becoming more and more strict. Ammonia escape is an important parameter affecting the operation of SCR system.
What factors influence the high ammonia escape?
1) Catalyst clogging will also affect ammonia escape. When the catalyst is blocked, the denitrification efficiency will decrease. Sometimes, in order to keep the environmental protection parameters below the standard, more ammonia will be sprayed, so that the catalyst will be easy to age, causing local blockage, and the performance will be affected, resulting in the increase of local ammonia escape.
2) Uneven distribution of ammonia spray flow of ammonia spray gun. The local distribution of ammonia in the flue gas is uneven, the flow rate of the flue gas is not uniform, the amount of ammonia sprayed at the outlet of different spray guns is different, and the ammonia escape will be higher where the concentration is high.
3) Different temperature influences. If the flue gas temperature and reaction temperature are too low, the reaction rate of NOx and ammonia will decrease, and a large number of NH3 will escape. If the reaction temperature is too high, ammonia will produce extra NO, so the temperature needs to be controlled. If the temperature is too high or too low, the reaction effect will be affected and escape will be increased.
4) Ammonia concentration. If the ammonia concentration is out of control, for the boiler, the higher the ammonia concentration, the higher the ammonia escape.
How to control the problem of ammonia escape?
1) The catalyst has a service life. In order to ensure qualified environmental protection, in the process of using the boiler, a large amount of ammonia spray will cause the ammonia escape to rise. Therefore, when the catalyst is aging, it needs to be replaced when the furnace is stopped for major and minor repairs at ordinary times.
2) The flue gas temperature affects the reaction effect of SCR and SNCR, and thus affects the ammonia escape. The general temperature of the selected catalyst is controlled in the range of 300-380℃, and the boiler temperature needs to be adjusted through the boiler.
3) In the denitrification reaction zone of coal-fired boilers, dust will accumulate when dust is removed, and the accumulation of dust will increase ammonia escape. Therefore, in the process of boiler operation, SCR reactor needs to be purged at least once a week to reduce the concentration of ammonia escape.
4) For the uneven distribution of ammonia injection flow, it is necessary to adjust the control ball valve of ammonia spray gun, regularly check the ammonia spray gun in operation of the boiler, dredging or replacing it in time to ensure the normal operation of ammonia spray gun.
Reasonable control of ammonia escape concentration at the SCR outlet of the boiler can effectively prevent the corrosion of the SCR denitration unit, control the ammonia escape rate of the SCR unit to about 3ppm or below, and reduce the influence of ammonia escape on the denitration efficiency of the SCR.