Study Of Promotion Of Electron Emission By NO-Corona Cathode On Performance Of Denitration By SNCR

Technique of electron emission by no-corona cathode is based on the theory that alloy material of Barium and Tungsten could emit thermion at the high temperature, so a certain amount of self-excitation electron could be emitted in the high-temperature (800℃-1100’C) flue gas of the industrial furnace, and the electron density is 2-3 orders of magnitude as much as technique of electron emission by corona cathode at a low voltage (6kV). Denitration by Selective Non-Catalytic Reduction (SNCR) method is a very suitable technique for denitration in coal-fired boiler at China, also has the benefits of low capital cost and simple operation, but the defects of low denitration efficiency and amount of escaping NH3 limit its application. In this thesis, technique of electron emission by no-corona cathode is combined with the process of denitration by SNCR, the high-energy electron will be added to the mixed flue gas, which is hoped to chance the reaction process, and improve the deficiency of denitration.Firstly, the test bed of reactor of electron emission by no-corona cathode is built, the former CFB boiler is transformed for the test of denitration by SNCR, in which, the ammonia injection system, on-line detecting system and flue gas control system are added. The related reaction mechanisms are also introduced.Secoundly, the dynamic and static tests are performed with respect to the electron emission of no-corona cathode material, in which, the chance of electron emission density is detected under several operating conditions, and the functional relationship between the density and temperature or voltage is deduced. The dynamic and static tests, as the emission characteristics shows a general similar trend as to the temperature and voltage increase, and the electron emission density goes up with a exponential function curve. With the operating condition of 12kV and 1000℃, the electron emission density could reach 0.995 mA/cm2.Thirdly, the test of denitration by SNCR is performed in the reactor of electron emission by no-corona cathode, the operating conditions (temperature T, voltage U, density of electron emission J, NSR and residence time T) are changed so as to investigate the variation of NO removal efficiency. When the voltage and temperature change, the energy of electron in the cathode material would increase, and the possibility of electron breaking through launch barriers would aggrandize, the quantity and energy of emitted electron would also aggrandize. As a consequence, the quantity of radical (NH2, NH, OH and O) increases, and the reaction between NH3 and NO is enhanced, then the NO removal efficiency is enhanced and the quantity of NH3 escaping is reduced. With the operating condition (U=12kV, T=1000℃, NSR=1.5, t=1.5s), the denitration efficiency, energy consumption and quantity of NH3 escaping achieve the optimal state, the NO removal efficiency could reach 70.8%, which prove the feasibility and industrial application value of denitration by combining of electron emission by no-corona cathode and SNCR.