Research On Particle Deposition Mechanism In Flue Gas Turbine Of Fluid Catalytic Cracking Unit

As the core equipment of the energy recovery system of catalytic cracking unit,the flue gas turbine can recover the heat and pressure energy in the high temperature flue gas and drive the operation of the main fan,steam turbine or generator,thereby significantly reducing the energy consumption of the catalytic cracking unit.However,the catalyst particles in the high-temperature flue gas are easy to deposit and foul in the internal flow channel of the flue gas turbine,affecting the normal operation of the flue gas turbine and even causing frequent downtimes,seriously affecting the economic benefits of the device.At present,there is still a lack of sufficient knowledge about the deposition and fouling of catalyst particles in the flue gas turbine.Most of the conclusions come from the field experience and there is no systematic study on the deposition mechanism of the particles.In this paper,aiming at the deposition of catalyst particles in flue gas turbine from the high temperature flue gas,the mechanism of catalyst particle deposition in flue gas turbine was systematically studied by means of theoretical analysis,experimental research and mathematical modeling.Firstly,the gas-solid two-phase flow in the flue gas turbine is studied.Taking the actual flue gas turbine of catalytic cracking unit as a benchmark,the model flue gas turbine was designed by the similarity criterion.The gas-solid two-phase flow field in the model flue gas turbine was measured by particle image velocimetry.Particle motion inside the model flue gas turbine is captured using the high-speed camera.The gas-solid two-phase flow characteristics at different gas-phase flow rates are studied.The movement law of gas-phase flow field and solid-phase particles are summarized.Secondly,the particle deposition process in the flue gas turbine was studied by a specially designed experimental apparatus for the dynamic deposition of flue gas turbines.The deposition morphological images,the mass of the deposited particles and the particle size analysis of the deposited particles were used to study the influence of different parameters such as inlet air volume,feed concentration and inlet particle size on the particle deposition on the rotor blades of flue gas turbine.Thirdly,through the experimental apparatus on the operation platform of the refinery,experiments were carried out on the high-temperature particle deposition in the field.The effects of different operating parameters on the deposition and fouling were studied,such as flue gas temperature,water vapor content and catalyst particle concentration in flue gas.Finally,on the basis of experimental study,the calculation model for the deposition of high-temperature flue gas catalyst particles on the surface of the flue gas turbine blade was established.By writing a user-defined function(UDF),the new particle deposition model was used to replace the original particle deposition boundary conditions to calculate the particle deposition at the wall numerically.The results show that the model can accurately predict the deposition site and deposition mass distribution trends.The research results provide a theoretical foundation and basis for further improving and optimizing the operation of flue gas turbines,and have a significant impact on long-term safe operation of catalytic cracking units.Therefore,it has remarkable scientific research significance and engineering application value.