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The Evolution Characteristic of the Char’s Pore Structure and Surface Functional Groups During the Reaction Process under O2/CO2 Atmosphere

Author: ChenQiaoQiao
Tutor: HuSong;SunLuShi
School: Huazhong University of Science and Technology
Course: Thermal Power Engineering
Keywords: coalchar O2/CO2 reactivity functionalgroup BET XRD
CLC: TK16
Type: Master's thesis
Year: 2009
Downloads: 26
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Abstract


Attention on the greenhouse effect is mainly paid to how to control the discharge ofCO2 efficiently in the world. As an effective controlling method, O2/CO2 coal combustiontechnology becomes a present research focus. The reaction mechanisms of coal char underO2/CO2atmosphere are different from that under traditional atmosphere. The evolution lawof coal char’s physical and chemical structure duringthe reaction process changes which iscausedbythesedifferences,andconverselythechangescanaffectthereactionprocess.Theevolutioncharacteristicofthechar’sporestructureandsurfacefunctional groupsduringthereaction process under O2/CO2atmosphere is mainly studied in the paper. It is detailed asfollows.First of all, the reactivity test of imperforate pure carbon particles under O2/CO2,CO2/Ar,O2/Aratmospherehavebeencarriedout onthermal gravimetricanalysis. Dynamicanalysis is made due to the results. It shows that the existing of CO2 has influence on thereaction;CarbonparticlescanreactwithCO2onlyathightemperature;Theorderofcarbonreactionrateunderdifferentatmosphereislistedfromlowtohigh:CO2/Ar,O2/CO2,O2/Ar.Secondly, the combustion experiments of three kinds of typical coals under O2/CO2,CO2/Ar, O2/Ar atmosphere have been carried out on thermal gravimetric analysis. Due tothe results, the reaction characteristics are studied and dynamic analysis is made. It showsthat different kinds of coals at various temperatures behavedifferentlyevenunder thesameO2/CO2 atmosphere. O2/CO2 atmosphere can promote the combustion process of the coalwithhigh-volatile.Finally, char samples of typical coals at different conversion rates are prepared underO2/CO2 atmosphere and isothermal condition. Then the samples are tested on FourierTransformInfraredSpectra,NitrogenIsothermalAdsorption/DesorptionandXRDanalyzer.The evolution characteristics of char are compared such as surface functional group,specific surface area, adsorption/desorption curves, BJH pore distribution and particlemicrocrystalline structure. The analysis indicates that functional groups decrease asconversion rate increases, and hydroxyl group changes rapidly while ether group changes slowly under high temperature. In 1000℃reaction temperature, the variation curves aboutcharparticlespecificsurfaceareaofthethreecoals present likean“M”whilethosepresentlike an inverse“V”in 1200℃reaction temperature; As the reaction carries on, theporeadsorption of the three char particles increases at the beginning of the reaction, anddecreases when the conversion rate reaches to some range. The internal mesopores of threechar particles change drasticallybefore the conversion rate reaches a fixed value. The ratioof mesopores occupied in pore structure begins to decrease while that of macroporesincreases correspondinglywhentheconversionrateis abovethefixedvalue.Bycomparingthe XRD spectra, it’s found that the microcrystalline compositions of raw coal particles aredifferent, and the evolution law of microcrystalline structure is also different, and the coalchar’smicrocrystallinestructurechangesmoreintenselyatthehighertemperature.

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CLC: > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Fuel and combustion
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