Research On Some Key Issues In The Preheating Process Of A Pyrolysis Furnace

Staged coal conversion,with pyrolysis as its foundation,is one of the clean and effective coal utilization technologies.Pyrolysis furnace is one of the key equipment in the system since the coal pyrolysis process takes place in it.In order to reduce the energy needed in the pyrolysis furnace and to improve the system efficiency,a preheating process prior to the coal being sent to the furnace is essential.The higher the temperature that the coal is preheated to,the less the energy needed in the furnace.However,as the preheating temperature increases,coal pyrolysis reactions start to take place with changes in the characteristics of the particles and the production of tar,which may lead to the cohesion of coal particles.And the process of the preheated coal being sent to the furnace could be therefore interfered.Some experiments were conducted to investigate this problem.Four pulverized coals were pyrolyzed from 300? to 700??using a fixed-bed reactor.Sieve analysis was used to investigate changes in char particle size.SEM,FTIR and N2 adsorption were employed to investigate changes in surface morphology,chemical structure and pore structure of the char particles,and the mechanisms of particle changes were discussed.Results suggest that the char particles tend to become finer with increasing pyrolysis temperature.When the pyrolysis temperature is below 400?,active pyrolysis reactions do not occur and pore structures altered a little caused by removal of moisture and a limited release of volatile matter.In this stage,the particle size slightly decreases and the particle size changes mainly occur to those with larger particle size.When the pyrolysis temperature increases beyond 500?,the decrease in particle size is significantly sharper than those below 500?as a result of greater extent of condensation reactions at high temperatures.Pore structure changes significantly at this stage and contraction of the particles form more fractures and cracks on char surfaces,which can further reduce particle size by generating small particle fragments.Investigations on the yields and the condensation of coal tar and the possible cohesion that could be caused by tar were conducted.The pulverized Shenhua and Ximeng coals were pyrolyzed from 300? to 700?using a fixed-bed reactor.The overall yields and the condensation characteristics in different condensation temperatures were investigated.GC-MS was employed to characterize the compounds of tar samples.Then some experiments were designed to study the cohesion of coal caused by the condensation of tars.The possible preheating methods were proposed according to the experimental results.