O ₂ / CO ₂ NO Coal Combustion Research And Hg Emission Characteristic Atmosphere

Coal is the most important primary energy in our country, and the CO2concentration in flue gas from coal combustion accounts for about15%, making the greenhouse effect become one of the major environmental problems. O2/CO2combustion technology has been paid more and more attentions in recent years. Through this new technology, the CO2concentration in exhaust can increase significantly, so that CO2in flue gas can be liquefied directly for utilization. But the study on O2/CO2combustion is still in a fresh field, and the characteristics of pollutant emission still need further investigation. In order to explore the potential advantages and to provide the theoretical basis for the simultaneous removal of multi-pollutants, the characteristic of the NO and Hg emission from the pulverized coal combustion under O2/CO2atmosphere was investigated and the influence of various operation factors on their emissions under the O2/CO2atmosphere was also analyzed in this paper.Xuzhou bituminous coal and Loudi anthracite coal was selected as samples. The combustion characteristic under O2/CO2atmosphere was researched by using the thermogravimetric Analyzer. The results show that compared with burning in O2/N2atmosphere, the ignition time and burnout time in O2/CO2atmosphere delayed, the kindling point increased, and the burning velocity slowed down. When the O2concentration increased, the ignition and burnout temperature reduced, and the burnout time advanced. Moreover, the general combustion parameter of O2/CO2atmosphere was elevated with the increasing O2concentration.The influence of various operation factors on NO emission in O2/CO2combustion was researched. It was observed that the NO release in O2/CO2atmosphere was similar to that in conventional combustion:both of them showed bimodal distribution, but the total emission of NO in O2/CO2atmosphere is less. With the temperature raise, the total emission of NO increased in both atmosphere, and this phenomenon was more significant in O2/CO2atmosphere. The emission of NO reduced gradually with the decrease of O2concentration. And after adding calcium-based additives into the pulverized coal, the emission of NO was inhibited, which was more obvious in O2/CO2atmosphere. The coal which contents more nitrogen released more NO, but the conversion rate was lower.Also, the Hg emission in O2/CO2atmosphere was studied. With the temperature raised from700℃to900℃, the elemental mercury emission increased slightly, but its ratio reduced. When the O2concentration rose from10%to40%, the emission of elemental mercury was inhibited, and the ratio of elemental mercury dropped gradually. In O2/CO2atmosphere, the emission of elemental mercury was elevated apparently by increasing CO2concentration, but the increment dropped with the reducing atmosphere strengthening. In addition, calcium-based additives can contribute to the reduction of elemental mercury emission, and it is more effective in O2/N2atmosphere. The emission of elemental mercury mainly depends on the mercury content in coal—the higher mercury content is, the more elemental mercury releases. Results also show that the chlorinity may have effect on the speciation of mercury.