Study On Shear Resistance Of Slag Body During Combustion Of High-alkali Coal

Zhundong coal is high quality power coal,but its Na content is high which often cause serious slagging problem.Slagging greatly reduces the heat transfer coefficient of the heat exchange tube,which affects the normal operation of the boiler.Nowadays,controlling slagging has become a hot issue.Therefore,the study of fracture at high temperature by the mechanical properties of the slag body is of certain guiding significance to solve the slagging problem.Firstly,in order to understand the microstructure of the slag body,Nano-CT scanning method was adopted for the massive slag body in this paper.Meawhile,the 3D reconstruction was carried out with CTvox and Avizo software,and the pore structure and particle size distribution of the local slag body were analyzed.Secondly,in order to obtain the shear characteristics of slag body at high temperature,the direct shear tests at200 ?,400 ?,600 ? and 800 ? were carried out on the basis of the modification of the normal temperature direct shear instrument by means of reshaping fly ash,and the stress-strain relationship of slag body at high temperature was obtained.Finally,in order to study the contact force and force chain distribution in particles at high temperature,the direct shear test at 800 ? was simulated by changing the mesoscopic parameters of discrete element software PFC,and the contact force and force chain distribution at different shearing stages were obtained.The following conclusions are obtained:(1)The slagging body is stratified and mainly formed by ash particles with small particle.The channels and particle systems in the slag body are distributed in parallel.Most of the particle systems have no regular shape,and most of the channels are distributed in the shape of tubes and rods.(2)At the same temperature,with the increase of the normal compressive stress,the shear strength and residual strength increase significantly;Under the same normal phase pressure,with the increase of temperature,the shearing displacement increases obviously,and the time to reach the shearing becomes longer.(3)At each temperature,the slope at the initial shearing stage is small,which may be due to the existence of pores between particles during the initial shearing,and the initial shearing process is the process of compacting samples.(4)With the increase of temperature,the angle of internal friction decreases and the cohesion increases,probably,because the cementation between particles is enhanced by high temperature.(5)Different normal compressive stresses correspond to different shear conditions,but the areas with greater contact force after shearing are all in the diagonal region caused by the motion of the straight shear box and the area where particles still contact after shearing.(6)The weak chain is always distributed around the strong chain,forming a coronal structure.The strong chain acts as a "skeleton" to support the whole particle system.