Experimental Research On Coal Pyrolysis With A Pressurized Drop Tube Furnace

In this paper,the pyrolysis and gasification character of NM sub-bituminous coal has been studied on a high pressure drop-tube furnace(PDTF).The object of this thesis was to get the effect of different pressures,temperatures and atmospheres on high heating rate pyrolysis,and to get the properties of pyrolysis product,char and gasification rates,to provide the basic data for gasifier modeling.The main results are presented as follows:1.The effect of pyrolysis condition on pyrolysis products.Increasing the temperature would promote the degree of pyrolysis,increase the weight loss rate of pyrolysis char;when pyrolysis at 900℃,the weight loss rate of coal was higher than the industrial analysis Vdaf.For those product of same pyrolysis temperature,pyrolysis under higher pressure would decrese the weight loss,and the char had higher Vdaf.Compared to the nitrogen conditions,the effect of pyrolysis temperature was lesser on hydrogen conditions.The gas product of pyrolysis had characters as follows:when pyrolysis temperature went higher,CO2 and CO production ratio increases,the yield of CH4 increased at 500～800℃,and reached the peak at 900℃.The yield of C2H4 reached the peak at 800℃.The comparison between the results show that pyrolysis under nitrogen atmosphere,the pressure increase will decrease yield of all gases;When total pressure went up,the hydrogen pressure went up increases CH4 yield greater than the total pressure decreases the yield.The yield of CH4 increased obviously,while the partial pressure of hydrogen increased with the increase of the volume fraction of hydrogen.The hydrogen partial pressure increased the yield of CH4 and decreased the yield of other gases.As for liquid product,aromatics compounds were the main components of tar,except for the tar under nitrogen conditions which contains a certain amount of aliphatic compounds.Most of the compounds were fused ring compounds.For the nitrogen atmosphere conditions,the pressure increase would make the tar component in the number of carbon ring more than the proportion of fused ring aromatic products.Differences between hydrogen atmosphere tar composition and nitrogen atmosphere composition were found,when the partial pressure of hydrogen was higher,the inhibition of hydrogen radicals for polycondensation is significant.2.CO2 gasification kinetics of char.Gasification properties was measured with isothermal thermogravimetric methods,The effects of pyrolysis conditions in the range of 500～1000℃ and pressure atmospheric～1MPa on the gasification activity were summarized.High temperature pyrolysis char had lower gasification reactivities than low temperature char,high pressure pyrolysis char had lower gasification reactivities than ambient pressure char,but the effect of pressure were lesser than temperature.For the conditions at atmospheric pressure,gasification activity of the pyrolysis char prepared with hydrogen were higher than that of the nitrogen pyrolysis char,but for the pressurized conditions,the effect of hydrogen on the gasification activity was not significant.The reaction with coal is mainly methanization,which has little effect on the chemical structure of coal char.Coal-CaO mixture had very high reaction rate at beginning of gasification,and decreased significantly after a certain time.