Research And Application On Flue Gas Desulfurization And Denitrification

The emission of sulfur dioxide(SO2)and nitrogen oxides(NOx)are the binding targets of China's economic development.The construction of flue gas desulphurization and flue gas denitrification facilities is an important technical means of reducing emissions.In the recent twenty years,a lot of basic researches and engineering practices in our country have been carried out which drastically promoted the development of purification technology of the flue gas.The latest near-zero emissions standard of NOx:50 mg/m3,SO2:35 mg/m3,dust:5 mg/m3 could be achieved under the current purification technology.However,the technique of flue gas desulfurization and denitrification have some general drawbacks such as the tough operation of denitrification unitun under low-load condition,the low utilization rate of desulfurization wastewater treatment system,the high investment and operating cost.To address these issues,this paper mainly conducted investigations on the following three aspects:the exploitation of low temperature SCR catalyst,zero discharge technology of desulfurization waste water and a new technology of simultaneous desulfurization and denitrification by biological methods.The main contents of this paper are as follows:A series of WO3 modified MnOx/TiO2 and SixCe1-xO2/ATS catalysts were developed due to the poor efficiency of V2O5-WO3/MoO3-TiO2 at lower temperature.The relationship between TiO2 crystal phases and calcination temperatures,the effect of TiO2 crystal phases on MnOx/TiO2,the effect of WO3 loadings on the properties of MnOx/TiO2 as well as the catalytic activity and poisoning resistance(K2O?CaO?SO2?vapor)of modified catalysts,catalytic mechanism and activity of CeO2/SiO2 were systematically studied.Particularly,the 15%MnOx/5%WO3/TiO2 exhibits excellent low-temperature catalytic performance(above 85%)in a wide temperature range of 80-320 ?.Based on the above results of the powdered catalyst,studies on honeycomb SCR catalyst and industrial applications were carried out.To achieve the best preparation methods of honeycomb catalyst,air speed,oxygen content,and molar ratio of NH3/NO,wear ability,compressive strength and thermal stability as evaluation indicator and chief influences including roasting temperature,roasting time,kinds and addition amount of addition in the preparation process of laboratory size honeycomb catalyst were optimized.Industry size of 15%MnOx/5%WO3/TiO2 honeycomb catalysts were prepared and the denitrification performance and industrial application performance in Guohua Taicang Power Plant for honeycomb catalyst were also studies.The results shows that the honeycomb catalyst synthesized in the paper has excellent purification performance for power plant flue gas with over 90 NOx conversion at average.In view of the problems,like complex equipment,high cost,poor operating environment and poor purification effect of Cl-for desulfurization wastewater purification process,a new type of wastewater flue gas evaporation process was developed.The influence of this technological on load,structure and performance of dust collector,comprehensive utilization of fly ash and material balance of system were systemically studied.Single axis acoustic levitation experimental platform was built to explore wastewater droplet pyrolysis process and optimum particle size and pace times of evaporation process.Results indicate that the increase of precipitator load caused by product that were brought by wastewater evaporates are negligible and has no impact on dust removal.Because after wastewater humidifying the flue gas temperature was higher than that of the flue gas acid dew point,so zero discharge of desulfurization wastewater device are not corrosive to precipitator and downstream equipment.Operating systems could be simplified by means of omitted hardening and tempering.The product quality after desulfurization wastewater vaporized was too small to cause any impact on comprehensive utilization of fly ash,only about 1%of the total.Zero discharge of desulfurization wastewater technological by reduction flue gas temperature of FGD inlet to decreased water consumption of FGD system.After desulphurization wastewater droplets evaporate were captured by electrical precipitator and could not cause harmful ion concentration in the desulfurization serous.Then the feasibility of the desulfurization wastewater zero discharge technology was verified by pilot experiment on a 300 MW generator.We could conclude that flue gas heat could meet the waste water evaporation and had no influence on ESP and downstream equipment by calculating.The wastewater capacity was determined.Wastewater treatment process scheme and selection of atomized spray gun were designed.The experimental results indicate that flue gas evaporation process could realize the zero emission of desulfurization wastewater without affecting downstream process.Aiming at the problems,like high-cost,secondary pollution for maturely technology of desulfurization and denitrification,systematical study of bio trickling filter tower simultaneous desulfurization and denitrification process was carried out.Biological drop tower test rig was set up.Simultaneous desulfurization and denitrification could be realized by means of activated sludge and water from a certain sewage treatment plant in turn by screening,domestication,directional cultivating and biofilm colonization for 25 days.The by-product was the mixture of H2SO4 and HNO3 which could be used as hydrometallurgy leach liquor or compound fertilizer.So the process were feasible and economicalTo improve the purification efficiency of the bio-trickling filter tower,the means of adding chemicals or metal ions catalysis and screening of packing were also discussed.One element experiments and orthogonal design experiments were carried out to achieve the optimal recipe of chemical enhancers.On the base of the theory of adsorption-biofilm and the experimental data of purification process,dynamic models were established for bio-trickling filter before and after enhancement in dealing with SO2 and NOx,and the model equations were solved numerically according to experiential data consisting of three aspects:pollutant concentration of exit,purification efficiency and biochemical degradation property.The results show that the dynamic models provided here are quite suitable for bio-trickling filter simultaneous desulfurization and denitrification process and after strengthened the correlation increases notably.The flue gas of 1000 Nm3/h thermal power plant were employed in pilot test of simultaneous desulfurization and denitrification to investigate the purification performance.The results show that bio trickling filter after enhancement has high purification performance of the flue gas.The measured efficiency for SO2 and NOx reaches 95%and 40%,respectively.According to the contrast of the experimental data and theoretical data,the dynamic model was modified,which laid foundation for industrial application.