Study On Flow Pattern Characteristics Of Particle Transportation In Stand Pipe Of Fluid Catalytic Cracking Unit

Stand pipe is an important equipment to realize the downward transportation of particles in catalytic cracking process(FCC).The gas-solid two-phase flow in the stand pipe belongs to the flow along gravity and reverse pressure gradient,and its flow pattern has the characteristics of complex diversity and transformation.During the operation of FCC unit,the failure of poor catalyst transportation from stand pipe often occurs,resulting in insufficient catalyst circulation,fluctuation of agent oil ratio,reactor temperature fluctuation and pipeline vibration,and even unplanned shutdown of FCC unit.Therefore,the research on the characteristics of gas-solid two-phase flow in stand pipe has important academic significance and practical value.Therefore,in this paper,a set of stand pipe experimental device composed of vertical pipe and inclined pipe in series(vertical pipe size Φ 150 mm × 5mm,length1800mm;Inclined pipe size Φ 150 mm × 5mm,3400 mm in length,45 ° to the horizontal,with catalyst particles(average particle size of 67 μ m.The particle density(1561 kg /m3)is a solid material and the compressed air is the aeration air.Under the conditions of different particle mass flow rate and aeration air volume,the pressure pulsation,particle velocity and concentration parameters under different flow states in the stand pipe are measured by pressure sensor and pv-6 optical fiber measuring instrument,and the gas-solid two-phase hydrodynamics characteristics in the stand pipe are investigated in detail.Experimental research shows that:1.There are different flow patterns in vertical and inclined pipes: dense phase fluidization flow,dilute phase fluidization flow and packed bed flow in vertical pipes;Creeping flow,fluctuating flow,stratified flow and fluidized flow appear in the inclined pipe.At least two flow patterns coexist in vertical and inclined tubes under the same operating conditions.2.The aeration air can promote the movement of gas-solid two-phase in the pipe system.The research shows that the opening of the corresponding valve when the fluidization flow occurs after the aeration air is introduced is earlier than that when the aeration air is not introduced,but there is still an uncontrollable area for the regulation of the pipeline by the butterfly valve,and a new flow state appears in the stand pipe:filling flow.3.The parameters of particle size material sealing capacity in stand pipe under different flow states are obtained,4.The pressure drop gradient variation diagram along the length of the stand pipe is established.The results show that there are gas holding section and degassing section in the movement of particles in the vertical pipe and inclined pipe without aeration air,while the particles in the vertical pipe are in the degassing section and the particles in the inclined pipe are in the gas holding section after aeration air is introduced into the elbow.