| A large amount of SO2,NOx and particulate matter are produced during coal combustion while generating energy.To meet increasingly stringent environmental requirements,power plants upgrade a single technology to meet the "ultra-low" emission limits for SO2,NOx and PM.However,the lack of overall collaboration occurs among equipment unit and much room can be improved in energy efficiency.The national key research and development program proposed an integrated control route for coal-fired pollutants based on hot-gas filtration.And then,the simultaneous removal of SO2,NOx,and particulate matter were specifically investigated under a novel scrubber,and further validated the industrial feasibility using 5000 Nm3/h coal-fired flue gas.Besides,the adsorption between magnesium-based adsorbent and SO3 were simulated using density functional theory(DFT)in quantum chemistry,revealing the effect of flue gas components on the adsorption site and adsorption energy.The main content and conclusions are listed below:A new spray-and-scattered-bubble experimental setup based on preozonation was built for simultaneous removal of SO2 and NOx,which combines the advantages of the common spray tower and the jet bubble reactor.The results showed the removal of SO2 and NOx can be significantly improved as compared to a separate spray column or bubble reactor,by as much as 17%,for the spray column and 18%for the bubble reactor for NOx and 11%for the spray column,and 13%for the bubble reactor for SO2,forliquid/gas ratio of 4 L/m3 or immersion depth of 100 mm.The O3/NO molar ratio had little effect on the SO2 removal,but it strongly affected the removal efficiency of NOx especially when it was less than 1.0.Both the liquid/gas ratio and immersion depth demonstrated a positive correlation with the removal efficiency.However,a balance must be maintained between efficiency and economics.The increase of inlet SO2 concentration in the flue gas has little effect on the desulfurization efficiency,which proves that the spray-and-scattered-bubble has a wide range of fuel adaptability.The problem of a large amount of particulate matter generated during the ab-WGFD process has also attracted intense attention.Given the positive effects of jet bubble reactors as particulate matter traps,the emission characteristics of particulate matter in this new scrubber on the basis of ammonia solution was investigated.Compared with the conventional spray-only method,this new technology generates a lower particulate level based on the same desulfurization efficiency,and the particulate size has an effectively unimodal distribution with a main size range from 0.156 mm to 1.64 mm.The amount of particulate matter significantly increases in the presence of SO2 in the flue gas and was positively correlated w:ith the SO2 concentration.The liquid/gas ratio showed a positive correlation with the particulate matter emissions,while the immersion depth is closely tied to the inhibition effect.A larger adsorption energy between was found to exist between the sulfites and(NH4)2SO4 particles.The adsorption mechanism of SO3 on the surface of magnesium-based adsorbents was studied by using density functional theory in quantum chemistry due to the plume phenomenon caused by SO3 generated in the process of SCR and ozone oxidation.Different adsorption configurations were constructed through multi-directional adsorption angles and the action mechanism of SO3 adsorption on MgO(001)surface was finally optimized.Furthermore,the influence mechanism of coal-fired flue gas components on the adsorption of SO3 on MgO(001)surface was discussed,such as O2 and SO2,.The results showed that the adsorption activity of O top site was higher than that of Mg top site,and the similar sulfate structure formed by SO3 on the surface of MgO(001)was the key for the adsorption.The configuration parameters of each removal unit of the 5000 Nm3/h test platform for the integrated control of coal-fired pollutants were designed.Further,the experimental studies on NOx removal by SCR-high-temperature dust collector,the absorption of NOx and SO2 based on preoxidation,and the SO2,PM2.5 removal by spray-and-scattered-bubble method were carried out.The results showed that the PM concentration at the outlet of the high-temperature precipitator is around 8 mg/Nm3,and the ammonia escape maintained at 3 mg/Nm3,which greatly reduced the hazards of catalyst blockage and poisoning.When the O3/NO molar ratio is 1.0,the scrubber can increase the NOx removal efficiency by 28%and 37%,and the SO2 removal efficiency by 11%and 25%.During long-term operation,the average daily emission concentrations of PM,SO2,and NOx at the outlet of the absorption tower are about 5 mg/Nm3,20 mg/Nm3,and 25 mg/Nm3 respectively,reflecting excellent control levels of the three-level denitrification(low-nitrogen combustion,SCR and pre-oxidation technology),two-stage dust removal(high-gas filtration,spray-and-scattered-bubble scrubber)and two-stage desulfurization(spray,bubble).The energy efficiency plays a key role in the system evaluation,and the competition between alternatives can be evaluated by some kinds of energy efficiency indicators on a macro-level.However,the current assessment system usually was limited in ability to the single indicator such as environment and economy.Motived by this purpose,this study applies a fuzzy comprehensive evaluation method to construct a multi-criteria comprehensive energy efficiency assessment system including techniques,environmental protection,economy and social benefits.The most important asset is that it developed and implemented an analytic hierarchy process(AHP)to determine weights of indicators that gives an extra strength and credibility to the results.A case study involving this new route and two existing routes can be proven useful to the engineers and practitioners working on the decision-making processes ofadvanced post-treatment technologies for coal-fired units. |
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