| The utilization of coal has played an important role in the development of my country’s economy and industry,and the energy structure dominated by coal will not change substantially in the short term.With the full implementation of ultra-low emission technology,the emission of conventional pollutants such as nitrogen oxides,particulate matter and sulfur dioxide in the flue gas of coal-fired power plants has been effectively controlled.The emission of organic pollutants from coal combustion is one of the main anthropogenic emission sources and has received more and more attention.At present,there are few studies on the emission data and control methods of organic pollutants in coal-fired power plants,especially after ultra-low emission,the emission level of organic pollutants and the synergistic effect and mechanism of various pollutant control equipment on organic pollutants Still unclear.This study firstly sampled organic pollutants in coal,fly ash,slag and flue gas of ultra-low emission power plants,obtained the concentration of organic pollutants at the inlet and outlet of each pollutant control equipment through quantitative analysis,and explored the synergistic removal performance and mechanism of each equipment.Data on organic pollutant emissions from ultra-low emission power plants.Secondly,based on the fly ash injection mercury removal system of coal-fired power plants,a mechano-chemical coupling metal oxide modification method was proposed to improve the removal performance of fly ash for organic pollutants,and the modification mechanism and removal mechanism,affecting the modification.And the present work is devoted to solving some of these scientific problems related to the key parameters of fly ash removal efficiency of organic pollutants,the influence mechanism of complex flue gas components,the tolerance analysis of modified fly ash for water vapor and SO2,and the feasibility analysis of modified fly ash jet synergistic removal of organic pollutants.In this paper,field tests of non-methane total hydrocarbons,volatile organic compounds and polycyclic aromatic hydrocarbons(PAHs)were carried out on a 300 MW ultra-low emission unit and 50 000 m3/h flue gas pilot plant using the technology of "selective catalytic reduction denitration+low temperature electrostatic precipitator+wet desulfurization".The results showed that the collaborative removal efficiency of VOCs could reach over 80%using the APCD system with ultra-low emission technologies.Boiler load would affect not only the concentration and distribution of VOCs but also the removal efficiency of the APCD system.The major products for 100%and 50%loads were aromatic and halogenated organic compounds,respectively.Besides,higher load also received more VOCs reduction benefits.The reduction of aromatics and alkane/alkene compounds could reach 93%and 94%,respectively.However,the reduction of polycyclic aromatic hydrocarbons in fly ash was 57%,and the reduction of halogenated organic compounds and oxygen-containing VOCs could only reach less than 45%.The major mechanisms for the removal of VOCs are oxidation and condensation through a selective catalytic reduction system(SCR)and the air preheater system.The types and reaction conditions of catalysts in the SCR system play an important role in promoting the removal of organic pollutants.At present,activated carbon injection technology has been proved in engineering application can effectively control the emission of mercury,dioxins and other flue gas pollutants.However,the high cost of activated carbon limits the wide application.In comparison,modified fly ash has lower price and integration characteristics,avoiding offline modification,long-distance transportation and other links,simplifying the process.Therefore,the fly ash was modified by ball milling with mechanochemical coupling MnO2 to improve its oxidation activity to VOCs.This modification dramatically increased the toluene conversion to over 90%compared with less than 5%from unmodified samples.In addition,the carbon balance efficiency in the whole reaction process reached 94.3-97.5%with the content of by-products below 1%.Microscopic characterization and analysis further revealed that the ball milling modification could not only break the fly ash into amorphous structure particles,but also lead to the uniform dispersion of MnO2 in fly ash particles.Both XPS and TPR results confirmed that these two effects improve the performance of toluene oxidation.We also proposed a two-step mechanism for the toluene conversion by the modified fly ash sample,involving the oxidation of MnO2 in stage I and the redox activity of Mn2O3 in stage II.In addition,the outlet of the SCR system with a suitable temperature(about 300℃)proved to be the best place to spray modified fly ash.The feasibility and efficiency of removing VOCs from actual coal flue gas by jet modified fly ash were evaluated by using droplet furnace combined with carrying bed reactor.The results showed that the concentration of VOCs in flue gas decreased significantly after spraying modified fly ash,and the conversion rates of toluene and 12 detected VOCs were 89.5%and 82.3%,respectively,which were slightly lower than those in the fixed-bed reactor.This may be due to the competitive removal relationship between complex flue gas components and organic pollutants.In order to further investigate the removal mechanism and key influencing factors of organic pollutants from modified fly ash in complex coal-burning flue gas environment,the results showed that NO,NH3,H2O and SO2 all inhibited the removal of p-toluene,and the removal efficiency decreased by 8%.3%,30%and 80%after 30 minutes of reaction,respectively.This is mainly because the active sites on modified fly ash surface are occupied or consumed by competition.In order to improve the removal performance of modified fly ash in complex flue gas environment,Ce-Mn modified fly ash was synthesized by mechanochemistry in the presence of organic acid ligands.The results of fixed-bed evaluation test bed showed that ce-Mn modified fly ash exhibited stronger oxidation activity to benzene,toluene,m-xylene,ethylene and mixed VOCs,corresponding to 90%conversion at 283℃,237℃,216℃,264℃ and 224℃,respectively.Under the condition of 300℃,the removal efficiency of various organic pollutants was close to 100%.In addition,the inhibition of NO,NH3,H2O and other flue gas components was almost eliminated,showing good tolerance.By observing the surface morphological characteristics and surface chemical properties of the modified fly ash,it can be seen that the organic acid ligands make the samples have a larger surface area and rich micromesoporous structure,enhance the Ce doping into the MnO2 lattice,induce more surface oxygen vacancies,and promote the lattice oxygen migration to oxidize VOCs.And the samples showed the formation of more acidic sites to enhance their tolerance to SO2 and H2O.The total concentration of 12 volatile organic compounds decreased from 1347.3 μg/m3 to 131.2 μg/m3 by spraying Ce-Mn modified fly ash in a drogue furnace combined with a carrying bed reactor,and the removal efficiency was 90.3%.If the fly ash injection technology is combined with ultra-low emission technology of coal-fired power plants,98.3%of organic pollutants can be effectively controlled.In addition,the injection technology also provides synergistic control of pollutants such as SO2 and mercury at the lowest cost. |
PDF Full Text Request