1, SCR (selective catalytic reduction and denitrification) technology;
SCR (Selective Catalytic Reduction Denitrification) Technology in Boiler Denitrification Technology
SCR is the most mature flue gas denitrification technology at present. This is a denitration method after furnace. It was first put into commercial operation in Japan in the late 1960s and 1970s. It is called "selectivity" because reducing agents (NH3 and urea) selectively react with nitrogen oxides under the action of metal catalysts to generate N2 and H2O instead of being oxidized by O2.
Selective non-catalytic reduction is a method for reducing nitrogen oxides at 850 ~ 1 100℃ without using a catalyst. The most commonly used drugs are ammonia and urea. Ammonia gas is injected into the high-temperature flue gas denitration device as a denitration agent, and nitrogen oxides in the flue gas are decomposed into N2 and H2O under the action of a catalyst, and the reaction formula is as follows: 4NO+4NH3+O2 → 4N2+6H2O; NO+NO2+2 NH3→2 N2+3H2O； Generally, the above reaction can be effectively carried out in the temperature range of 200℃ ~ 450℃, and the denitrification efficiency can reach 80 ~ 90% under the condition of NH3 /NO = 1. The concentration of nitrogen oxides in flue gas is usually low, but the amount of flue gas is relatively large, so the catalyst used in SCR device must have high performance. Therefore, the catalyst used under this condition must meet the requirements of high reliability operation of coal-fired boilers. Generally speaking, the SNCR denitrification efficiency of large coal-fired units can reach 25% ~ 40%, and that of small units can reach 80%. Because this method is greatly influenced by the boiler structure size, it is often used as a supplementary treatment means of low nitrogen combustion technology. Its engineering cost is low, the layout is simple, and the floor space is small, which is suitable for the transformation of the old plant, and the new plant can be used according to the boiler design.
2.SNCR (selective non-catalytic reduction Denitrification) technology.
SNCR (selective non-catalytic reduction Denitrification) Technology Boiler Denitrification Technology
The principle of SNCR denitration technology SNCR process takes the furnace as the reactor, which is the main denitration technology used in the transformation of old units at present.
Generally, the removal rate of nitrogen oxides can reach 30%~50%, and the reducing agents used are generally ammonia, ammonia water and urea. Because the distribution performance of urea in boiler is better than that of ammonia, and urea is a general chemical, which is simple and safe to transport and store, and easy to obtain, while ammonia is a dangerous chemical, SNCR generally uses urea as reducing agent. The technology of selective non-catalytic reduction (SNCR) to remove nitrogen oxides is to inject a reducing agent containing NHx group into the furnace, which is quickly decomposed into NH3 and selectively reacts with nitrogen oxides in flue gas to generate harmless gases such as N2, CO2 and H2O. SNCR denitration process: The urea solid particles that meet the requirements are discharged into the urea storage bin, and then enter the liquid preparation tank by the metering and feeding device. Under the heating condition, urea solid particles and process water are prepared into urea solution, which is pumped to the solution storage tank by batching. The urea solution in the storage tank is sent to the spray system in front of the furnace through the booster pump and the delivery pipeline, and then sprayed into the furnace at 900~ 1 100℃ through the spray nozzles arranged around the boiler. The urea solution output from the storage tank can be mixed with process water to prepare urea solutions with different concentrations to meet the needs of different loads of boilers; The nozzles can be arranged in multiple layers to meet the requirements of different temperature zones. Scope of application: newly built, expanded and rebuilt units or old units in service, as well as units with low denitrification efficiency due to space constraints. SNCR process features: furnace as reactor, no catalyst, low investment and operation cost; The denitrification efficiency is moderate, generally 30%-50%, and the combination with low nitrogen combustion technology is better, and the denitrification rate can reach 70%; The blockage and corrosion of air preheater and electrostatic precipitator are lower than SCR.