Experimental Study Of The Performance Of Cyanuric Acid/Melamine Based Selective Non-catalytic Reduction

Although our country has taken measures to adjust the structure of traditional energy consumption, coal will still plays an important role in energye cnsumption for a long time in the future.Coal plays an important role in energye cnsumption and electricity generated by coal-fired power plants keeps the dominant in the electrieity frame, this situation caused serious environmental pollution problems.With the improvement of the environmental protecting consciousness, the control of industrial emissions has become more stringent, the nitrogen oxides emissions has decreased, but still at a high level. Large amounts of nitrogen oxides emissions can cause respiratory diseases, cardiovascular and cerebrovascular diseases, acid rain, acid mist, ozone depletion. At present, the main NOx control technologies is SNCR in the coal-fired plants. SNCR has some advantages of none catalysts, simple equipment, low cost, high effieieney and combined with other NOx control technologies which may become one of the optional NOx control technologies adapted to the situation of coal-fired plants.The performances of cyanuric acid and melamine based on SNCR were investigated in a drop tube furnace system.The research covered the effects of temperature, residence time, initial oxygen concentration, molar ratio of cyanuric acid to NO, initial NO concentration, additives(ammonium dihydrogen phosphate, CO, H2O, sodium carbonate, sodium acetate trihydrate, ferrocene, ferric sulfate) on the efficiency of the RAPRE NOx process and the effects of temperature, residence time, molar ratio of melamine to NO, initial NO concentration on the SNCR of NOx by melamine.The NOx reduction performances of SNCR process was carred out with cyanuric acid as reducing agent.The results suggest that the maximum denitrification efficiency is 83.07％at 900℃ and corresponding maximum efficiency is 83.46%, the temperature window is 875℃～1150℃, the appropriate residence time is 1.1～1.2 s, the appropriate O2 concentration is 2％～3％and the appropriate molar ratio is 0.5. Prolonging the residence time, increasing the molar ratio and keeping higher initial NO concentration can increase the NO removal efficiency respectively. Small amounts of O2 can increase the efficiency but excessive oxygen concentration will decrease the efficiency. Experiments were conducted using ammonium dihydrogen phosphate, CO, H2O, sodium carbonate, sodium acetate trihydrate, ferrocene and ferric sulfate as additives respectively to investigate the effect on Selective Non-Catalytic Reduction proeess. The addition of ammonium dihydrogen phosphate can improve the maximum denitrification efficiency and the optimum reaction temperature which is good to widen the temperature window and the temperature window will moves to the lower temperatures. Little ammonium dihydrogen phosphate additive can promote NO removal, while higher concentration of ammonium dihydrogen phosphate will decrease the SNCR process. The addition of CO or H2O can promote the maximum denitrification efficiency at lower temperatures which can extend the temperature window and the temperature window will moves to the lower temperatures. At the same time adding CO and H2O can achieve better results especially at higher temperatures. The addition of sodium salts(sodium carbonate, sodium acetate trihydrate)and iron-containing compounds(ferrocene, ferric sulfate) can decrease the efficiency and increase the optimum reaction temperature which can narrow the temperature window and shift the temperature window towards the higher temperatures. These additives can decrease the SNCR process.The NOx reduction performances of SNCR process was carred out with melamine as reducing agent.The results suggest that the maximum denitrification efficiency is 96.27％at 750℃, the temperature window is 535℃～1150 ℃, the appropriate residence time is 1.1～1.3 s and the appropriate molar ratio is 0.8. Extend the residence time, increasing the molar ratio and keeping higher initial NO concentration can increase the NO removal efficiency respectively.