| With the increase of coal demand,in order to improve the efficiency of coal mining,the current mining technology leads to a lot of residual coal and serious air leakage in the goaf,which makes coal spontaneous combustion occur frequently.The spontaneous combustion of coal in goaf is uncertain in space and time,which leads to some problems in the conventional fire-fighting methods.Therefore,this paper puts forward the idea of microencapsulation.The high-efficiency inhibitor was microencapsulated with temperature responsive materials,so as to realize the release of core material inhibitor at fixed time and fixed point.This method can effectively overcome the adverse effects of the environment and the properties of the inhibitor on the resistance effect,and can improve the resistance life and efficiency.It is of great significance to the prevention and control of coal spontaneous combustion in goaf.With PEG6000 as the wall material and LDHs as the core material,the microcapsules were successfully prepared by melting dispersion condensation method.TG/DSC,FTIR and SEM-EDS were used to study the pyrolysis,coating,surface morphology and dispersion of microcapsules.The results showed that the microcapsules were smooth in appearance,cohesionless and dispersed evenly among particles,with a diameter of about 200 ?m.The effective elements of PEG6000 are C and O.the characteristic peaks of PEG6000 and LDHs are found after grinding.It has good thermal stability.The pyrolysis is mainly divided into three stages.The initial pyrolysis temperature is 232.47 ?,PEG6000 plays a role of resistance before pyrolysis,and LDHs plays a role of resistance during pyrolysis.Before the operating temperature of the wall material is 59.8 ?,the total heat release is 983J/g.TG/DSC experiments were carried out to study the effect of microcapsules with different core wall ratio on the spontaneous combustion characteristics of coal sample a,calculate its apparent activation energy,comprehensively select the best core wall ratio,and apply it to coal samples B and C.The results show that the resistance of microcapsules to coal spontaneous combustion is mainly reflected in the first and third stages of TG and DSCcurves,and the best effect is when the core wall ratio is 1:5.In the first stage,the mass residual rate increased from 92.4% to 94.4%,T1 from 91.4 ? to 100.2 ?,the heat flux decreased from 0.54 mW/mg to 0.13 mW/mg,and the heat release increased from-56.1 J/g to26.2 J/g.In stage three,T6 increased from 358.9 ? to 371.5 ?,T7 increased from 479.4 ?to 553.9 ?,heat flow decreased from 14.02 mW/mg to 8.82 mW/mg,and total heat release decreased from 2610.1 J/g to 2404.2 J/g.The activation energy of the first and third stages of TG and DSC curves was calculated.The activation energies of A1,A2,A3 and A4 are 40.33kJ/mol,53.55 kJ/mol,54.39 kJ/mol and 52.42 kJ/mol respectively in the stage of water evaporation and gas desorption.The activation energies of A2,A3 and A4 are relatively close,but the growth rate of A4 is the fastest,with the trend of increasing with the increase of temperature,so the effect of A4 in this stage is better.In the thermal decomposition stage,the activation energy was 141.82 kJ/mol,169.26 kJ/mol,154.24 kJ/mol,178.36 kJ/mol,and A4 was the largest and significantly higher than A1,A2 and A3.Kissinger method further verified the calculation results of FWO method.The microcapsules with optimal core to wall ratio also have excellent resistance effect on coal samples B and C,greatly reducing the heat release,heat release rate and mass loss of coal spontaneous combustion,and effectively delaying the characteristic temperature.The research results are of great significance to the theory and method of coal fire disaster prevention and control. |
PDF Full Text Request