Research on the Explosion Suppression Characteristics and Mechanism of Composite Powder Explosion Suppressant for Coal Dust Explosion

Author:Wang Xiang

Supervisor:zhang yan song


Degree Year:2019





Based on the analysis of different coal dust dynamics,the mathematical model of suppressing coal dust explosion by inert dust was established.On the basis of the fully understanding of the rule of inert suppressant,a new simple process,low cost and efficient compound powder suppressant was achieved,which solved the key problem in the development of suppressant and revealed the suppressive mechanism of compound powder suppressant.For the intrinsic properties of coal,the suppressive mechanism of coal dust,with different volatile contents and different particle sizes,was proposed,which provides a valuable reference for the development of compound powder suppressant,as well as for the targeted selection of adopting suppression means.The main tasks and conclusions of this study are as follows:1.A mathematical model for the suppression of coal dust explosion by inert dust was established based on the theory of solid-gas-solid three-phase heat transfer in spherical confined space,the volatile devolatilization DAEM model and the combustion reaction of the main volatile components(H2,CO,CnH2n+2,CnH2n,CnH2n-6,CnH2n-i2)and the fixed carbon-involved.Both the value of Pmax and(dP/dt)max determined by the prediction model are higher than the corresponding experimental values,and the relative errors of them are less than 0.15,which can realize the main prediction of suppression experimental results.The suppressive effect of fly ash cenosphere to bituminous coal(sampled at Shenmu,Shaanxi)is better than that to brown coal(sampled at Zhaotong Yun ’ nan).2.Carbamide/fly ash cenosphere compound suppressant of double layer reticulated shells was made by taking the modified fly ash cenospheres as the inner spherical shell carrier and using the equal volume impregnation method.Through the explosion flame propagation experiment,the explosion characteristic inhibition experiment,and the tests of SEM,FTIR,and TG-DSC etc.,the researcher achieved the nano-load of carbamide on the surface of the fly ash cenosphere and improved the surface tension of it.During the 0~τ1 stage,the nano-carbamide particles rapidly participated in the volatile gas phase combustion reaction,which mainly contributed to the reduction of(dP/dt)max.The fly ash cenosphere mainly(but not only)act on the τ1~T2 stage resulting in a char incomplete reaction,which in turn reduces Pmax.The effects of micro-nano scale complementary and deceleration-depressurization coupling effect to suppress explosion by stages are proposed.3.Adopted the reproducible shell powder as the main component,the S-S compound suppressant was made by one-step jet milling method,which realized the mechanical dry coating of NaHCO3 onto shell powder and tackled the contradiction between dispersibility and suspension force.When the additive amount of S-S compound suppressant was 40wt%,the suppression would be largely achieved.Based on the mechanism of deceleration-depressurization coupling effect to suppress explosion by stages,and synthesizing the comprehensive combustion characteristic index and the characteristics of explosion suppression tests,the explosion suppression characteristics of coal dust with different volatile contents were further investigated,which revealed that the suppression efficiency of active suppressant on coal dust with high volatiles was better,so was the inert suppressant on coal dust with low volatiles.4.Studies in terms of explosion suppression characteristics,minimum ignition energy and flame propagation dynamics of coal dust with different particle sizes were carried out from the perspectives of explosion lethality and explosion possibility.For the coal dust with larger particle size,the heat capacity was higher,the speed-time curve of flame propagation presented an obvious pulsating trend,and the dust cloud flame presented a glomerate feature.The combustion duration of the solid phase material of large-particle coal dust was long,which made the inert powder with long-term blocking effect had a better inhibitory effect.However,coal dust with small particle size had large specific surface area and high heat transfer eficiency,so the velocity effect of explosion needed to be offset from the two aspects of reducing combustion environment temperature and consuming free radicals.Combined with different particle sizes of coal dust combustion dynamics analysis and introducing the Kohler number,the differences in the variaty particle size on coal dust explosion suppression was explained from the perspective of coal dust combustion mechanism.The results show that the surface heating rate of large coal is less than its overall pyrolysis rate.Large coal underwent devolatilization-volatile combustion-fixed carbon combustion process,while heterogeneous and gas-phase reactions on the small coal surface occurred almost simultaneously.Then the suppression mechanism of "overall small scale and local large scale" was put forward on explosion suppression with different particle sizes.