| O2/CO2 combustion is suggested as one of the possible, promising technologies for capturing and reducing the emission of carbon dioxide from power plants coal combustion. Earlier studies have provided some basic understanding about pollutant removal and flue gas purification behaviour of coal under the O2/CO2 combustion conditions. But under O2/CO2 atmosphere pulverized coal ignition mechanism haven't been recognized clearly. Therefore, it has great scientific and practical signigicances to investigate the coal ignition characteristics under O2/CO2 combustion.A wire-mesh reactor was used to study Datong bituminous coal and Loy Yang brown coal ignition characteristics under air and O2/CO2 atmosphere, the effect of coal characteristics and heat transfer process on coal ignition was studied. An increase in the average particle ignition temperature was observed for the coal when air (21%O2/79%N2) was replaced with a mixture of 21%02/79%C02. The Datong bituminous coal ignition temperature under 21%02/79%C02, increase about 35.7℃compared to air atmosphere, refered to Loy Yang brown coal that is about 23.8℃. It was found that ignition temperature decrease with the increase of oxygen concentration in both atmospheres. When oxygen concentration raised to 30%, pulverized coal ignition temperature was similar to those obtained under O2/N2 atmosphere, coal ignition temperature will be similar to that under air atmosphser if the oxygen concentration correctly choosed.The reaction kinetics of char samples under O2/N2 and O2/CO2 atmosphere were investigated by utilizing thermal gravimetric analysis. The apparent activation energy of char which was made from bituminous coal and brown coal under N2 and CO2 atmosphere showed a great difference. Under O2/CO2 atmosphere, the pulverized coal apparent activation energy was higher than that under O2/N2 conditions with the same oxygen concentration. The reaction characteristics between char and oxygen changed because of the difference of atmosphere, the combustion process was restrained by high concentration of CO2. In particular, the char reactivity was largely responsible for the observed difference in particle ignition temperature in air and in 21%02/79%C02. Sequential extractions have been performed to classify the chemical forms of sodium in coal. We found that water-solute and ammonium acetate-solute sodium are the main form in Loy Yang brown coal. Compared with raw coal, the BET surface area of water-washed coal increased, and the apparent activation energy of coal combustion decreased, the ignition temperature of coal samples both decrease in air and O2/CO2 atmosphere. Compared with raw coal, the BET surface area of ammonium acetate-washed and H-form coals decrease, the apparent activation energy of coal combustion increased, the ignition temperature of coal samples both increase in air and O2/CO2 atmosphere, an increase in the average particle ignition temperature of 50 and 100℃separately, acid wash showed a great effect on brown coal. It is concluded that the Na in coal as carboxylates (-COONa) and as NaCl can both improve ignition characteristics of coal samples. The presence of sodium resulted in a transfer of electrons to or form the carbon substrate causing a redistribution of electrons in the graphite structure, and an increase in the C-O bond strength during oxidation. The formation of intercalation compounds might have very substantial effects on the electronic properties of the graphite substrate, which could influence the reactivity of carbon atoms on the surface. Na added in coal as NaCl can increase the BET surface area, so the coal ignition temperature decreases. It is concluded that the Na in coal as carboxylates (-COONa) shows more significant catalytic effect on average particle ignition temperature than Na in coal as NaCl.An unsteady-state model of pulverized coal cloud was used to study the ignition characteristics of a Datong bituminous coal under the conditions of O2/N2 and O2/CO2 atmosphere. The ignition temperature of a Datong bituminous coal was also investigated in a small furnace, to validate the accuracy of the model. The ignition delay time under O2/CO2 atmosphere was similar to that under air atmosphere with the increase of coal concentration. The coal igniton temperature increase with the increase of ambient temperature; the experimental results carried out by small furnace agree with the simulation results. Homogeneous ignition and joint hetero-homogeneous ignition happened in this numerical study under O2/N2 atmosphere. But it appears a great difference in O2/CO2 atmosphere, pulverized coal calculated in this paper also ignite heterogeneously as well, because the diffusivity of volatile in CO2 is lower than in N2. The calculation was also carried out under microgratity where natural convection is very weak, the ignition temperature under microgravity is lower and the ignition delay time is longer than that under normal microgravity. It showed a great difference when the coal concentration is small, with the increase of coal concentration the results were very close between the two environments.A wire-mesh reactor was used to study Datong bituminous coal and Loy Yang brown coal combustion characteristics under air and O2/CO2 atmosphere, where the secondary reactions of the evolved volatiles were minimised. CO and CH4 emission characteristics were studied under air and O2/CO2 atmosphere. We found that CO emission concentration under O2/CO2 atmosphereis higher than that under air, and it's also slower than it under air. The direct oxidation of carbon and gasification reaction between carbon and CO2 are the main reasons for the increased amount of CO.The CH4 emission concentration under O2/CO2 atmosphereis higher than that under air.
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