Papers by Keyword: Selective Non-Catalytic Reduction

Abstract: This paper is focused on the effect of treatment of fly ash after selective non-catalytic reduction (SNCR) with tannin on autoclaved aerated concrete (AAC) production in order to reduce or stop ammonia leakage from the fresh mixture due to its alkalinity. A pure form of tannin and a tannin-based product „Farmatan“ were used as a treatment in dosage ranging from 0,5 g – 3 g of agent per 1 kg of fly ash. Efficient dosage was determined at 2 wt.% of fly ash by the speed of an indicator change due to gaseous ammonia diluted in water. The rheological properties of fresh mixtures were observed by consistency test in Viskomat showing that Farmatan causes delay of hydration. The results of bulk density and compressive strength testing revealed that Farmatan causes an increase of bulk density and at higher amount decreases the compressive strength because of thermal crack formation due to combined effect of delayed hydration and thixotropy. Using x-ray diffraction (XRD) analysis there were no differences in phase composition observed.

Abstract: As the selective non-catalytic reduction denitration(SNCR denitration) was used in cement decomposition furnaces under the high concentration cement raw materials and complex flue gas composition , the denitration efficiency is poor and the reducing agent is largely consumed.In order to meet the more stricter requirements of environmental protection, there is an urgent need to improve the denitration efficiency of SNCR and reduce the escape of reducing agentsin order to prevent the unnecessary waste caused by excessive use of reducing agents and secondary atmospheric pollution.Therefore, studying the effect of cement raw materials and O₂ concentration on SNCR process is very important. In this paper, the initial concentration of NO and the ammonium to nitrogen ration (C_NH3/C_NO) was 800ppm and 1.5, respectively. The effects of cement raw material and oxygen concentration on the reaction process of NH₃+NO+O₂ in the temperature range of 750°C -1100°C were investigated by means of denitration rate, in Situ DRIFTS analysis.The results demonstrate when O₂ concentration was 5% and denitration temperature was 950°C, the deNOx rate reached a maximum of 89.64%, which due to O₂ promoted NH₃ and NO to react with O₂ to produce N₂ and H₂O. However,under the effect of cement raw material, O₂ can promote NH₃ which was adsorbed on the surface of cement raw material to react with O₂ and produce NO and H₂O, and the reaction of oxidation of NH₃ is dominant, therefore, the denitration reaction is inhibited. .When O₂ concentration was 5% and temperature was 850°C, the deNOx rate reached a minimum value of -109.09%. the high concentration cement raw material and flue gas composition reduce the denitration efficiency of cement kiln.

Abstract: _{Subscript text}The kinetic model for simulating the mechanism of the promoted effect of methanol on the NOxOUT process has been established and it mainly includes the optimal sub-mechanisms respectively for the NOxOUT process and the chemical reaction of methanol. The oxygen concentration does not obviously influence the maximum NO reduction efficiency in the range of 1-6 %, but the temperature window is overall shifted to lower temperature zone with oxygen concentration increased. Meanwhile, the mole ratio of urea to nitric oxide by a factor of 2 should be maintained between 1.5 and 2 from both the efficiency and running cost view. Also, ample residence time of 300/T-400/T s must be guaranteed for the reduction occurring thoroughly. Methanol does not compromise the maximum NO reduction efficiency and broadens the temperature window towards low temperature zone. The promoted mechanism of methanol on the NO_xOUT process is the abundant OH formation through the methanol regenerative reaction of CH₂OH/CH₃O+H2O=CH₃OH+OH and methanol should be maintained at 50-100 ppm for an obvious promoted effect. During the co-injection of methanol and urea, the “ammonia slip” is depressed, especially at 1173 K where the promoted effect on NO reduction is obvious, but emission of nitrous oxide is also markedly increased at this temperature.