Experimental Study And Numerical Simulation Of Pressured High Temperature Entrained Flow Coal Gasification With High Ash Fusion Tmeperature Coal

With the rapid development of our national economy, the energy and environment are increasingly become the limitation of our national economy development. Considering our characteristics of energy structure with rich coal, short of petroleum and natural gas, the entrained flow coal gasification technology with high pressure and large scale has become one of the important means and directions in clean coal and coal conversion technology in the future. For the purpose of developing new entrained flow coal gasification with dry ash out to fit our high ash fusion temperature coal, the coal char gasification reaction characteristics at high temperature, coal gasification characteristics in 25kg/h lab-scale coal gasification experimental system, one dimensional mathematical model simulation and coal ash fusion characteristics under coal gasification condition was researched and paper has been researched to supply necessary basic data and theory guidance.Firstly, based on the extensive investigation of coal ash fusion characteristics of main coal mining area in China, the coal char-O2/CO2/H2O gasification reaction characteristics of selected coal samples were studied with isothermal thermogravimetry method by using TGA-51H. The results were shown that the coal char gasification reaction characteristics at high temperature were different from the condition of at low temperature, the reaction control step is transferred from chemical reaction control zone to pore diffusion control zone at around 1200℃～1300℃. When the temperature was higher than coal ash fusion temperature, the coal ash fusion behaviour, mainly the distribution form changed, is caused to the differences above. The coal char which was produced with high heating rate has much higher gasification reactivity than those that with low heating rate because high voidage in coal char surface which is produced in the stage of fast coal pyrolysis. The gasification reaction velocity of coal char with high heating rate is above 1~2 order of magnitude than those that with low heating rate. The inherent gasification reactivity of coal type is much related to the contents of volatile, hydrogen and fix carbon in coal and is linear with the value of parameterβwhich represent the coal rank. The effect of pressure on gasification reaction rate at low temperature is much higher than that at high temperature. The transition temperature from chemical reaction control to pure diffusion control decreases with the increasing of pressure. The reaction rate increases evidently with the increasing pressure when the pressure is lower than 1.6MPa while when the pressure is above 1.6MPa the effect of pressure is become smaller and smaller.The gaification characteristics of coal with high ash fusion temperature were studied by using 25kg/h lab-scale entrained flow gasification experimental system at temperature range below 1400℃which was suitable for dry ash out. The results were shown that the gasification temperature increases with the increasing of O/C molar ratio. The high temperature is favourable to the gasification reaction to move for the direction of absorption but higher content of oxygen can get higher content of CO2 and lower content of CO and H2. The cold gas efficiency will decrease when the O/C molar is too high. Under the experimental conditions the optimal gasification temperature range is from 1300℃to 1350℃, corresponding higher the cold gas efficiency and carbon to gas conversion. Under this condition, the ash in the bottom of gasifier and cyclone is existed as solid in the view of overall except some little parts are melted in the size of severalμm. And the ash in the bag filter has not melted. Due to the melted part is accounted for very little percentage within the whole ash. The tendency of slagging is small and will not meet slagging and jam problems on the discharging of coal ash.Based on the research of kinetic of coal char gasification reaction and coal gasification characteristics, one dimensional mathematic simulation of 25kg/h pressured entrained flow gasifier had been set up. The model can truly reflect the process in the entrained flow gasifier. The simulation of entrained flow coal gasification was indicated success by comparison between model value and experimental value.The ash melting characteristics at different stages of coal char-H2O gasification reaction process was studied by using SEM-EDX. The results were shown that quite different the ash melting process under combustion condition, under gasification condition the coal ash melting is mainly started at the middle and latter process of coal gasification. Under coal gasification condition, the starting melting part is mainly caused by minerals which contain Fe element and after that the minerals which contain Ca element are begin to melt. The staring melt temperature is usually 100～150℃lower than initial deformation temperature(IDT) which is got by ASTM test. Under both reducing conditions, the starting belting temperature of coal ash under coal char-H2O reaction condition is higher than that under coal char-CO2 reaction condition, the reason is concerned of the content of CO.