? The denitration efficiency of SNCR flue gas denitration technology is generally 3% ~ 8%, which is greatly influenced by the boiler structure size. Using SNCR technology, the current trend is to use urea instead of ammonia as reducing agent.
? Technical principle:
In the range of 85 ~ 11℃, the main reaction of NOx reduction by NH3 or urea is:?
NH3 as reducing agent? 4? NH3? +? 4NO? +O2? →? 4N2? +? 6H2O
urea as reducing agent? NO+CO(NH2)2+1/2O2? →? 2N2? +? CO2? +? H2O
? System composition:
The flue gas denitrification process of SNCR system is completed by the following four basic processes:?
receiving and storing reducing agent; Inject diluted reducing agent into a proper position of the boiler; ?
metering output of reducing agent, mixing and diluting with water; Reducing agent is mixed with flue gas for denitration reaction.
? Technical features:
? Mature and reliable technology, high effective utilization rate of reducing agent and stable system operation? The equipment is modularized, occupies a small area, and has no by-products and secondary pollution.
? Composition of flue gas denitrification system
?
basic process of denitration system and additive effect:
? Solutions based on pure ammonia, ammonia water and urea (such as satamin and carbamin secondary additives) are popular to a great extent at present.
? Through selective NOn-catalytic reduction, no from amino group generates nitrogen and water vapor at 8℃-15℃.
? NH2+NO? < => ? H2O+N2
? When an aqueous solution containing ammonia compounds is used, the decomposition of the compounds will release ammonia gas. In other words, ammonia can only be volatilized from ammonia-containing compounds after the atomized fluid is evaporated.
? The selectivity of reaction between free radicals is not very strong. Therefore, sufficient removal of additives is still necessary. Fig. 1 shows the relationship between the stoichiometric factor NSR and NOx removal when the flue gas temperature is 95℃.
? Process design and device description:?
? Fuel additive storage and feeding device?
? Satamin additive is a patented product. According to the boiler size and annual fuel consumption, Satamin additives are generally supplied in barrels of 2,5 and 1, liters per barrel. ? For large-scale devices, a large storage tank and feeding controller are generally set, and Satamin and Carbamin are low ammonia water solutions. Therefore, during the filling process of the storage box, or in case the storage box is damaged, no toxic gas will escape near the storage location. A mezzanine box or storage box is enough in the storage tank. If the equipment is placed outdoors, the storage box should be considered for heat tracing or insulation, and the drainage area should be waterproof. The rainwater drain valve must be closed during the filling process. Tank cars use compressed gas to unload liquid. Magnetic coupling pump and submersible pump are needed when transporting additives to NOx removal workshop.
? Mixing and distribution system:
? The reducing agent is diluted with water. Tap water or well water can be used to dilute Satamin and Carbamin reducing agents. ?
? If there is no additive to prevent high and low temperature corrosion in the fuel, the feeding system of reducing agent after dilution can be added to the injection system through the mixing and distribution system depends on the geometry size of the combustion chamber. Water-cooled spray gun with single-phase nozzle is very successful in boiler application. The spray gun with compressed air for two-phase nozzle is suitable for layered combustion boiler.
? Secondary emission:
? Burning sulfur-rich fuel (>: .5% s), when the temperature is less than 35℃, high NH3 concentration in flue gas can form ammonia sulfate. Unlike ammonium bisulfate, ammonium sulfate is a pollution-free by-product. When the temperature is less than 16℃, the formation of ammonium bisulfate is related to the amount of SO3 and NH3 in the flue gas. Ammonium bisulfate is easy to cause scaling and corrosion on the surface of heat exchanger. However, the formation of ammonium bisulfate can be avoided by using reasonable removal additives (Satamin and Carbamin products). ? The allowable ammonia emission value of the improved SNCR device depends on the size of the boiler, which is 5-3 mg/m3. ? The design of NOx removal device is based on the use of additives satamin and carbamin, and the system does not affect the boiler efficiency. The reaction heat is equivalent to the evaporation heat of dilution water.
attachment: what is the difference between SNCR and SCR?