Investigation On Flow Characteristics In Disengager Vessels With Varied Coupling Configurations Between Two-stage Separators

Disengager vessel,miainly used to separate spent catalyst from oil-gas products generated in riser reactor and control the catalyst content in slurry,is an essentical part in FCC process.As petroleum feedstocks become heavier,oil-gas is much more easily to condensate and adhere on equipments' wall and then generate carbonaceous deposition.More seriously,the pipe will be choked and the process will be impacted.By means of FCD method,flow characteristics,residence time distribution and separation efficiency in disengager vessels with varied coupling configuration are investigated in this paper,to understand the conditions of coke's forming and then al eviate the coking problem.Simulated datas are in good agreement with actual flow rule,which increases the accuracy of the simulation.The results indicates that gas from rough cyclone in disengager vessel with “open” configuration is directly injected into inner space,and eventual y enters top cyclone after a long distance,which increases the residence time of oil gas from riser outlet.Oil gas from riser outlet is discharged fastly when the connecting height H is 562 mm,and the average residence time is 15.82 s.in addition,the first grade separation efficiency of the structure when H =562mm is relatively low,so that the coking problem of inner wall in vessel and outer wall of exhaust pipe in top cyclone will be alleviated with a higner concentration of catalyst particles.Oil gas from rough cyclone outlet in disengager vessel with “close-coupled” configuration enters into top cyclone inlet mostly,while little oil gas spreads into vessel.Many vortexes are formed near top cyclone inlet,which increases the coking possibility in this area.The average residence time of oil gas from riser outlet is less than 4s.However,residence time of oil gas from stripping section is huge and the average residence time is 147.11 s when L=180mm.As a result,coking substances is much more easily generated in equipments' wall with relatively lower temperature.Taking into account the stability of the operation of the device,this part of the oil and gas export method should be improved.Considering the influence of residence time and pressure drop fluctuation,the connection distance should not be too short.It is more appropriate to choose a structure with L=180 mm.And under the same operating conditions,the separation efficiency of “close-coupled” configuration is slightly lower than that of “open” configuration.Oil gas from stripping section is limited into the space below the sealing cover and is discharged through collecting pipe in ful-sealed vessel with “direct-coupled” configuration,a kind of anti-coking disengagers.The residence time of oil gas from stripping section is greatly reduced,meanwhile oil gas from riser outlet is discharged immediately.With the decrease of pipe's diameter ?,oil gas will be exhausted much more quickly.When ? equals to 780 mm,the average residence time of oil gas from riser outlet and stripping section are 2.51 s and 46.24 s.So this new type disengager could decrease the coking possibility while with a more sophisticated structure,larger pressure drop,and a little lower separation efficiency than that of the normal configurations.