Study Of The Coal Chars Made In Different Atmospheres On The Structure And Combustion Characteristics

Coal is the basic industry of our national economy, however, there are many problems in the process of exploitation and utilization. Coal combustion in a large scale leads to CO2 content increasing in the atmosphere, which causes the greenhouse effect and global warming. Oxy-fuel combustion technology can make the CO2 content in the flue gas significantly increase. In this condition, CO2 in the flue gas is captured according to carbon capture and storage(CCS) technology. The physicochemical properties of coal char under high CO2 concentrations directly influence its ignition and combustion efficiency. So it was necessary to study its structure characteristics under different pyrolysis atmosphere and its combustion characteristics.H-form lignite and bituminous coal were selected in this experiment in order to reduce the influence of alkali metal in raw coal. Firstly, coal char was obtained in the horizontal tube furnace with 900℃ and 7 min under N2 and CO2 atmosphere. The results showed that under different pyrolysis atmosphere, the content of fixed carbon, elemental carbon and the ratio of C/H and C/O in the CO2 char were all lower than that in the N2 char. For the same H-form coal, CO2 coal char surface gap was more developed, with traces of gasification reaction, while the microcrystalline structure of CO2 coal char was more irregular than N2 char.Secondly, pyrolysis experiment was carried out in the drop tube furnace with 900℃,1100℃ and 1300℃ under N2 and Ar/CO2 atmosphere, considering the dual effects of CO2 specific heat and gasification reaction. In the experiment, the specific heat of Ar/CO2 atmosphere was the same with N2 atmosphere. The results showed that under the same temperature, Ar/CO2 char yield was lower than the the N2 char, and the relative change of the char yield coal increased with the temperature rising. Ar/CO2 char yield was mainly influenced by pyrolysis, while the effects of gasification reaction on char yield was less than 1/5.Finally, the combustion characteristic differences of CO2 char and N2 char was researched through thermogravimetric experiment, of which the atmospheres were 21%O2/79%Ar, 21%O2/79%N2 and 21%O2/79%CO2. It shows that the ignition temperature of the bituminous coal char increased and its reactivity decreased both respectively in the above-mentioned atmosphere. There is no obvious change of lignite coal char. The surface pore of CO2 char was more developed. The reactivity was higher and its combustion temperature was lower under the same combustion atmosphere.