| The maturation of flue gas pollutant control technologies is highly pertinent given the current energy demand and production methods. The complexity of the flue gas environment, including both physical conditions and chemical composition, often necessitates equivalently complex treatment systems which are large, have high principal and operating costs, and affect the normal operation of boilers, among other detractions.In China, pollutant emission from coal-fired sources is related to the large energy requirement. Furthermore, the intensity of the localized pollution due to the concentration of economic activity means that for China to achieve fundamental improvement in air quality, coal-fired enterprises must implement more stringent plant emission standards than equivalent coal-fired enterprises in other countries. Achieving ultra-low emissions of pollutants in flue gas is an important direction for future survival and development. The focus of current research is the development of new technology to simultaneously reduce multiple contaminants in flue gas to ultra-low emission levels, which is very important for improving pollutant mitigation efficiency and reducing the size and cost of pollutant control devices.The method, ozone oxidation combined wet scrubbing to achieve synergistic removal of the various pollutants in flue gas, has many advantages, including low reaction temperature, low energy consumption, and the reaction product of ozone is oxygen introducing no other pollution in flue gas treatment process, etc. Relatively speaking, this method has broad application prospects on synergistic governance of various pollutants in the flue gas.For traditional wet spray scrubbing, the removal efficiency of NO2 is low. This paper first identifies I" from among several chemically active substances as a promising candidate additive for the promotion of NO2 removal, according to chemical reaction electrode potential theory. Next, comprehensive studies of I- as additive, including the I" concentration, oxygen concentration in simulated flue gas, the initial concentration of SO2 and NO2 in the simulated flue gas and the volume concentration ratio of SO2/NO2, pH value of the circulating slurry, etc. The results show that the removal efficiency of NO2 gradually increases with the increase of the concentration of I-. When [I’]= 2 mol/L, the removal efficiency of NO2 can be up to 98.7%. Oxygen in the flue gas has no effect in the removal of NO2 by I-. The presence of SO2 in the flue gas could make I-achieve circulation and lossless. Experimental results collaborate the use of electrode potential theory for additive selection, and the proposed removal mechanism for NO2.Increased understanding of the reaction between NOx and O3 was attained by assessing the reaction kinetics under various conditions. A reaction mechanism was proposed and applied in Chemkin where a sensitivity analysis highlighted the most pertinent reaction steps. It was found that the reaction temperature, O3/NOx molar ratio and reaction time are the major factors in the generation of N2O5.Lower temperature (≤90℃),O3/NOx molar ratio> 1 and longer reaction time (> 2s) are favorable for the generation of N2O5. The models showed that for a reaction temperature of 70℃, O3/NOx molar ratio=2.0 and reaction time=4s, the production rate of N2O5 can be above 80%. The calculations also suggest that when O3/NOx molar ratio>1, the SO2 oxidation rate increases, a trend which increases with the increased reaction temperature. When the reaction temperature=90℃, the SO2 oxidation rate can be up to 5%.Targeted experimental studies are carried out on the basis of the simulation results. Small pilot studies on the reaction conditions between O3 and NOx, including reaction temperature, O3/NOx molar ratio, reaction time, and the concentration of SO2, support what was projected by the reaction mechanism and simulation results regarding the reaction between O3 and NOx. Next, a test was conducted using wet scrubbing to remove the N2O5. The test results indicate that by this method was capable of more than 90% denitration efficiency.A 5000 Nm3/h pilot test platform was built, based around the critical parameters indicated by the reaction mechanism, to carry out pilot test. The results show that when the temperature of flue gas before spray scrubbing tower=90℃,O3/NOx molar ratio=2.0, the pilot test platform was able to achieve more than 90% denitration efficiency and 98% desulfurization efficiency.Based on the preceding theoretical and experimental research, a technology demonstration project was successfully carried out on carbon black drying furnace flue gas at a flow rate of 60,000 Nm3/h. During commissioning tests on the demonstration project, in addition to achieving denitration efficiency in line with the levels reached in the pilot scale tests, it was also shown that:pH value of the circulating slurry has a minor impact on the denitration efficiency and forced oxidation of the slurry increased the denitration efficiency of the system to some extent. After optimization of the operating parameters, the concentration of SO2 and NOx can be reduced from an initial concentration of 800～1000 mg/Nm3 and 600～ 900 mg/Nm3 to<35 mg/Nm3 and 10～20 mg/Nm3. The operation results in an actual industrial installation show that ozone oxidation of NO to N2O5 can be effectively combined with traditional limestone-gypsum wet desulphurization to achieve ultra-low emissions of both SO2 and NOx in flue gas, simultaneously.Comparing the technical characteristics and costs of using ozone to oxide NOx to N2O5, against the current mainstream technologies, including SCR and SNCR coupling SCR, to achieve ultra-low emissions of NOx in flue gas; oxidizing additive denitration is higher in cost, while the main equipment layout is simple. Oxidizing additive treatment is suitable for low temperature flue gas (<120℃) and has prospective application in removal of other pollutants, including the efficient removal of Hg. |
PDF Full Text Request