Study On Viscosity Of Coal-oil Slurry In Direct Coal Liquefaction Conditions

It is an important technologic issue to direct coal liquefaction about the rheology of coal-oil slurry.In direct coal liquefaction process,the bridge bonds which connect coal configuration cells may be ruptured as temperature rising,and the free radicals come into being.The free radicals are unstable,if there is no high pressure hydrogen or enough solvent to stabilize it,it may combine into big molecules again,therefore,it would like to change the rheology of coal-oil slurry remarkably,even lead to saltation which make the resistance of system to increase,and if the temperature is overhigh partly,it also will coke and produce some solid sediments,all of which could affect the operation of the process.In this paper,the torque of slurry is measured with homemade experiment devices which could be operated in the condition of high pressure and high temperature,then the viscosities of slurry were calculated at temperature 220℃～450℃by two methods:Shearing force decomposition method and Power characteristic number method,which are developed based on equipment devices. Compared the two methods,the results of Power characteristic number method are better than that of Shearing force decomposition method.It is found that the logarithm of viscosity is lined up with the reciprocal of temperature.The affect of heating speeds,sheering speeds,the composition of liquefaction products and coal conversion ratios on the characteristic of viscosity is investigated.In experiment conditions, different sheering speeds do little influence on viscosity.When the heating speed is 5℃/min,the viscosity at temperature 220℃～250℃is almost constant.Above 250℃, it declines quickly,when temperature rises to 340℃,it declines slowly.While the heating speed is 10℃/min,it declines quickly at the beginning,then a small peak appears at temperature 340℃～390℃,and above 390℃,it begins to decline again.By swelling experiment and analyzing the composition of liquefaction products,it is found that when the temperature rise speed is 5℃/min,coal swelling restrains the decrease of viscosity at temperature 220℃～250℃.Above 340℃,the variation of viscosity could be related to mass preasphaltene.Besides,when the conversion ratio of coal is between 30%and 40%,the viscosity would increase.