Effect of pyrolysis temperature on dynamic combustion mechanism evolution of semi-coke from low-rank coal pyrolysis
The combustion characteristics and kinetic parameters of semi-cokes prepared at different pyrolysis temperatures were studied by a thermal analyzer via Flynn-Wall-Ozawa(FWO)and Kissinger-Akah-Sunose(KAS)methods.Furthermore,the Malek method was used to explore the mechanism functions corresponding to activation energy at different conversion stages.The results indicate that increasing pyrolysis temperature deteriorates the combustion performance of semi-coke and increases the energy consumption.When conversion α＞0.5,the second derivative of activation energy and conversion tends to stabilize.There are differences in combustion dynamic mechanisms at different conversion stages.When α＜0.5,the combustion dynamic mechanism of semi-cokes is mainly chemical reactions(G(α)=(1-a)-1-1).As the conversion increases,the combustion dynamic mechanism changes from a standard mechanism model of random nucleation and nuclei growth(G(α)=[-ln(1-α)]2/3)to a dynamic mechanism model with diffusion as the main restric-tive step.In addition,with the increase of pyrolysis temperature,semi-coke is more likely to be trans-formed into a restrictive step dominated by diffusion at lower conversions.
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