Study On Measuring Viscosity Of Coal Slurry At High Temperature And High Pressures

The viscosity of coal slurry under high temperature and high pressure is very important for designing coal slurry preheaters and reactors of coal direct liquefaction. Measuring coal slurry viscosity under high pressure and high temperature was very difficult ,heating and high hydrogen pressure also be needed to ensure hydrogenation and prevent coking , deepness of hydrogenation and sedimentation of coal particles in the slurry are prevented by the stirring impeller to disturb the flow for overcoming the resistance of transfer quality. Enough hydrogen should be guaranteed also. Normal viscometers can not measure viscosities at coal hydrogenation liquefaction conditions. An apparatus for measuring coal slurry at coal liquefaction conditions is developed by Beijing Research Institute of Coal Chemistry. Two calculation methods-Power number method and Shearing force decomposition method were developed. In this paper relationships of Shengli coal slurry viscosities against temperature and dynamics of swelling behavior also be studied,swelling dynamics equations and activation energy E were acquired.Using Power number method for measuring viscosity of fluids should follow those behind. Power number Po is obtained by dimensional analysis , Po=2 2ρnN 3 D 5 = K( Dμnρ) x ( n gD)y. Viscosities of fluids can be calculated by the relationship between power number and viscosity found on power curve. The power number method can be used when Re < 300. Glycerin etc whose viscosity and density were known were taken as standard reagent to check the reliability of the apparatus. Torque M of the slurry at some rotating speed were measured to calculate the power number Po , get corresponding Re from the power curve,and then viscosities of fluids can be calculated by the relationship :η=ρnd. In this paper, viscosities of Shengli coal slurry were obtained by using the method. In the heating stage of 20℃to 220℃, the curve of apparent viscosity of Shengli coal slurry against temperature is related to Vogel equation very well. it can be written asη= 6.89×exp[783.61/(T + 136.5)].In the range of the temperature, no liquefaction happened during this temperature range. The curves of viscosity versus temperature were obtained and the influence of heating rate on the changes of apparent viscosity of coal slurries to temperature was studied. At low heating rate (2℃/min),a viscosity peak was presented in the curves of apparent viscosity versus temperature at 225℃(115mPa·s); At high heating rate(>2℃/min) there was no viscosity peak in the curves . The power number method get a good result for measuring viscosities of coal slurries when Re<300.We also developed a method for measuring lower viscosities fluids at coal liquefaction conditions which we called shearing force decomposition method. The force decomposition method is based on Newton glutinosity law and Prandtl momentum transfer theory. The method suggest that the fluid shearing force in container consists of laminar flow shearing force and turbulence flow shearing force multiply each area rate and then plus together. The formula is written as follow:Tetralin,octanol,diesel oil,zinc chloride,water,glycerin etc whose viscosity and density were known were taken as standard reagents to check the reliability of the apparatus. Measuring torque M of fluids at different n , coefficient k2 was get by regressing of n and M,and then regress of viscosities and k2 , the relationship between k2 andμshows a very good linear one: k 2 = 2.3914×10 5μ+ 3.7317×103. For unknown fluids, first regressing of k 2 through measuring torque M at different n ,and then viscosities can be calculated by the equation: k 2 = 2.3914×10 5μ+ 3.7317×103.The viscosity of the heavy Shenhua coal liquefaction stream from hot separator bottom of bench scale test unit was measured and calculated by shearing force decomposition method. Dynamics of swelling behavior for Shengli coal particles in recycle solvent were studied during 20-80℃. Fluence of temperature on swelling rate was small, the balance swelling rate was 1.9. For Shengli coal particles, the swelling rate became bigger when temperature rose up. Two methods were studied on swelling behaviors for Shengli coal particles. Adsorption swelling method is based on swelling mechanism and the dynamics equation was ddqt = k ( Vl 0 VVs 0q)(Q s q). It can describe the swelling behavior of coal particles very well, the activation energy E is 1.59 kJ/mol. Suuberg method was from literature, the dynamics equation was m/m∞=(Q-1)/(Q∞-1)=ktn, the activation energy E is 1.36 kJ/mol. The first method is better than the second for its dynamics equation and experiment results.