Experimental Research On Coke Adhesion Characteristics In Pulverized Coal Combustion

An experimental system for on-line measurement of particle adhesion weight is designed and developed,which can be combined with the experimental platform for high temperature combustion of pulverized coal in sedimentation furnace.The device can overcome the interference of human factors in the process of particle deposition measurement,on-line measure the weight change of in-situ particle adhesion,and use the experimental system to explore the adhesion characteristics of coke in pulverized coal combustion.The on-line measurement system can be used to establish and validate the model of particle adhesion such as coke adhesion.Firstly,conventional combustion experiments were carried out at 1100-1400℃ with excess air coefficient of 1.2(oxidation atmosphere).Gas products,conversion and particle size distribution were quantitatively described.Then,the on-line measurement system of particle adhesion weight is calibrated to ensure the accuracy of temperature in the adhesion area and the stability of the measurement system.Subsequently,the influence of flue gas velocity on particle adhesion characteristics was investigated.It was found that when the flue gas velocity was lower than the critical value,the impact energy dissipated through particles and particles deposited.When the flue gas velocity was higher than the critical value,the adhesion rate of soft particles increased and that of hard particles decreased.Subsequently,the influence of temperature on the adhesion characteristics of coke was investigated.It was found that the adhesion rate increased with the increase of temperature,and the adhesion rate increased significantly between softening temperature and flow temperature.Finally,by changing the content of N2 in secondary air,and then changing the oxygen content,the influence of unburned carbon on the adhesion characteristics of coke is explored.The influence of oxygen concentration on ash deposition and slagging is divided into two stages.In the initial stage,some particles with better conversion rate adhere to the slagging surface,and then continue to capture other particles,resulting in a rapid increase in weight;in the second stage,with the increase of carbon particles on the surface.The slagging surface hardens,the probability of particle rebound increases,and the slagging rate decreases.At the same time,it is found that the adhesion characteristics of coke can be divided into three regions: the unburned carbon content of coke is lower than the minimum critical unburned carbon content,and the adhesion rate is mainly controlled by temperature;the unburned carbon content of coke is higher than the minimum critical unburned carbon content,and lower than the maximum critical unburned carbon content,which is controlled jointly;the unburned carbon content of coke is higher than the maximum critical unburned carbon content.With carbon content,the adhesion rate of coke particles tends to zero.SEM characterization of different ash and slagging sampling heads shows that from low temperature to high temperature,porous layer composed of loosely bound particles is transformed into slag layer.