Design Of Internal Components And Flow And Backmixing Characteristics In An Up-flow Reactor

The up-flow reactor is a new type of hydrogenation reactor for residual oil,in which gas and liquid flow concurrently upwards through the catalytic bed,which shows "slight expansion".It has some advantages over the fixed-bed(such as trickle bed)reactor commonly used in the residual oil hydrogenation operation,such as wide range of feed residual oils,slowdown of bed pressure drop increase and prolonged operation cycle.However,there are still some operating problems,such as local temperature jump,hot spots,coking,etc.to be resolved.The most direct and effective way is to install proper internals inside the reactor.Therefore,in this work,novel internals are designed to solve the above problems and evaluated based on the measurements of characteristics of flow and back-mixing in the up-flow reactor.Such exploration is thought significant for both academic research and industrial application.In this thesis,an up-flow reactor with diameter of 300 mm was built up for cold model tests.Air and water are used to simulating gas and residue oil.Packed particles are the spherical alumina catalyst particles of three different sizes and two densities.The superficial gas velocity ranges from 1.24×10-2 m·s-1 to 3.63×10-1 m s-1,the superficial liquid velocity is in the range of 9.48×10-4 m s-1 to 5.96×10-3 m s-1,the height-to-diameter ratio(H/D)of the bed is between 1.5 and 4.0,and the bed expansion rate is less than 5.0%.The effects of these factors,especially the internal components,on the bed pressure drop,gas holdup,liquid holdup and axial backmixing were explored.The main conclusions are as follows:(1)The total pressure drop of the bed packed by 3.0 mm,4.5 mm or 6.0 mm particles increases with the increase of superficial gas and liquid velocity,particle density and liquid viscosity,while the total pressure drop decreases with the increase of the size of packing particles.The total pressure drop of the bed with a new designed internal is lower than that of the reactor without an internal.The correlation of the total pressure drop of an up-flow reactor with an internal is obtained:(2)The gas holdup increases with the increase of superficial gas velocity and liquid velocity.The larger the size of packing particles is,the larger the gas holdup.The correlation of the gas holdup is:(3)The liquid holdup decreases with the increase of superficial gas velocity and increases with the increase of superficial liquid velocity.The larger the size of packing particles,the smaller the liquid holdup.The correlation of the liquid volume is established:(4)The Peclet number decreases with the increase of the superficial gas velocity,particle density and the height-to-diameter ratio,so the bed axial backmixing is intensified.On the contrary,the Peclet number increases when the superficial liquid velocity and particle size become larger.The Peclet number in the reactor with an internal is smaller than that of the reactor without the internal,which means that the internal can strengthen the axial backmixing in the bed.The Peclet number with an internal is obtained based on the measurements:(5)Based on the comprehensive comparison of three evaluation criteria:bed pressure drop,average residence time and Peclet number,the best opening percentage of the internal is 0.125,and its most suitable installation height is 450 mm.Internal V is the best choice among five internals tested.