Reaction Characteristics And Kinetics Of Light Burning Of Magnesite In A Mini-fluidized Bed

Magnesite is mainly composed of magnesium carbonate,MgCO3.The active magnesium oxide produced from light calcination of magnesite is mainly used in material of refractories,and also widely used in building materials,chemicals,paper,aerospace,automotive and environmental protection.For decades,industrialized magnesium oxide has been always produced by reverberatory furnace,which have many disadvantages,for example,low product activity,poor material adaptability(only for bulk magnesite),high energy consumption,and long calcination time(up to 12 hours),et al.Therefore,a representative technology of the transport bed flash-calcination(TBFC)of magnesite powder is developed by Shenyang University of Chemical Technology(SYUCT)In order to realize the industrial application of magnesite powder TBFC,it is of great significance to study the characteristics and kinetics of light calcination of magnesite.In this dissertation,the effect of particle size on the characteristics and kinetic parameters of magnesite powder calcination reaction was studied using the so-called micro fluidized bed reaction analyzer(MFBRA)and thermogravimetric analyzer(TGA).Then,we tried to use the so-called micro fluidized bed reaction analyzer(MFBRA)and thermogravimetric analyzer(TGA)to obtain the calcination reaction characteristics and kinetic parameters of magnesite powder in nitrogen and air atmosphere.Both activation energy and pre-exponential factor are significantly lower in MFBRA than in TGA.The gas product CO2 produced by magnesite decomposition is difficult to fully flow out from the crucible of TGA and thus inhibits the decomposition reaction of magnesite.For MFBRA,it can effectively reduce the inhibition effect from the formed CO2 that easily flows into the main gas flow surrounding the particles.To explain this phenomenon,we studied the effect of different atmosphere containing CO2 on the characteristics and kinetic parameters of magnesite powder calcination reaction.Overall,this dissertation verifies that MFBRA provides a reliable secure of the reaction rate and kinetic parameters for the gas-formation calcination or decomposition reactions like tested light calcination of magnesite.The results are as follows:1.The apparent activation energy(124.67kJ/mol)and pre-exponential factor(105 s-1)of magnesite calcination with a particle size of 75-50 u m was higher than those with a particle size of 45-75 ? m(113.92kJ/mol,105 s-1)in the MFBRA.In the TGA,the same conclusion can be obtained..It is also found that the magnesite decomposition reaction follows the nucleation and growth control model G(x)=-ln(1-x)in both MFBRA and TGA,indicating that the decomposition temperature and the apparent activation energy of magnesite powder calcination increased with the particle size increasing.The reason is that,the internal diffusion resistance of CO2 produced by magnesite decomposition increased as the particle size increasing.2.the activation energy of magnesite calcination measured in nitrogen and air is quite similar,indicating that the oxygen in the air has little effect on the calcination of magnesite.The time for complete decomposition of magnesite in MFBRA was short as a few seconds in MFBRA at temperatures above 800?,showing its reaction rate much quicker than in TGA.The apparent activation energy(?125kJ/mol)and pre-exponential factor(105 s-1)of magnesite decomposition measured by MFBRA were significantly lower than those obtained by TGA(?200kJ/mol,1015 s-1).However,It is also found that the magnesite decomposition reaction follows the nucleation and growth control model G(x)=-ln(1-x)in both MFBRA and TGA.3.The activation energy of magnesite calcination measured in 30%CO2+70%N2 and 30%CO2+60%N2+10%O2 is quite similar,about 400kJ/mol,1017s-1,further indicating that the oxygen in the air has little effect on the calcination of magnesite.The apparent activation energy and pre-exponential factor of magnesite calcination in CO2 are 474.44kJ/mol and 1020 s-1,respectively.It was shown that the kinetic data obtained in the atmosphere CO2 containing were much higher than those in air and nitrogen(-200kJ/mol,1015 s-1),indicating that CO2 severely inhibited the magnesite calcination,and the higher the CO2 concentration,the higher the apparent activation energy and the pre-exponential factor,the longer the complete decomposition time of the magnesite powder.