Gas/solid separation system for the regenerators of fluid catalytic cracking units
A gas/solid separation system that can be applied to any type of FCC unit regenerators, consists of a device for separating solid particles contained in a gas stream coming from the regeneration zone of a fluid catalytic cracking (FCC) unit bounded by an inner envelope ( 3 ) of cylindrical shape centered about the vertical axis of the regeneration zone, and an outer envelope ( 1 ) that has one approximately horizontal wall ( 15 ), followed by one curvilinear wall ( 16 ), and one approximately vertical wall ( 17 ), the set of said walls ( 15, 16, 17 ) covering the inner envelope ( 3 ) and forming a set of separation chambers ( 2 ) radially distributed around the inner envelope ( 3 ) in which the gas/solid suspension to be separated circulates. This system makes it possible to obtain, at the same time, very good separation efficiency while minimizing the pressure drop and only requiring a single downstream cyclone stage.
1. Device for separating solid particles contained in a gas stream coming from the regeneration zone of a fluid catalytic cracking (FCC) unit bounded by an inner envelope ( 3 ) of cylindrical shape centred about the vertical axis ( 11 ) of the regeneration zone ( 25 ), and an outer envelope ( 1 ) that has one approximately horizontal wall ( 15 ), one curvilinear wall ( 16 ), and one approximately vertical wall ( 17 ), the set of said walls ( 15 , 16 , 17 ) covering the inner envelope ( 3 ) and forming a set of separation chambers ( 2 ) radially distributed around the inner envelope ( 3 ) in which the gas/solid suspension to be separated circulates, each separation chamber ( 2 ) communicating, via inlet sections ( 4 ) with the inner cylindrical envelope ( 3 ) and, via outlet sections ( 5 ) with the lower part of the regeneration zone ( 25 ) and having at least one side outlet ( 6 ) located in the upper part of the side wall ( 22 ) of the separation chamber ( 2 ), said side outlet ( 6 ) being defined by the space between the portion of the vertical wall of the inner envelope ( 3 ) located immediately below the inlet section ( 4 ) and intrados ( 26 ) corresponding to the curvilinear wall ( 16 ) of the outer envelope ( 1 ), said device comprises, in addition, baffles ( 7 ) located between two successive separation chambers ( 2 ), each baffle ( 7 ) being fixed to the wall of the inner cylindrical envelope ( 3 ), and return legs ( 8 ) of cyclones ( 21 ) forming the secondary separation stage, are inserted between the separation chambers ( 2 ), and are aligned in a circle having a diameter between the diameter of the inner cylindrical envelope ( 3 ) and the larger diameter of the outer envelope ( 1 ).
2. Device according to claim 1 , in which each baffle ( 7 ) has an upwardly pointing wing shape, the upper end of the wing being located at a level below the upper level of a side opening ( 16 ).
3. Device according to claim 1 , in which each baffle ( 7 ) has a lower inclined part fixed to the wall of the inner cylindrical envelope ( 3 ), the angle of inclination being between 15 and 30 degrees relative to the vertical.
4. Device according to claim 1 , in which each baffle ( 7 ) has an upper, approximately vertical part located at least 150 mm with respect to the vertical wall of the inner cylindrical envelope ( 3 ).
5. Device according to claim 1 , in which there are 2 or 4 separation chambers ( 2 ), baffles ( 7 ) and return legs ( 8 ) of the cyclones and they form an assembly that respects the symmetry about the vertical axis ( 11 ) of the regeneration zone ( 25 ).
6. Device according to claim 1 , in which the level of a dense fluidized bed located in the lower part of the regeneration zone ( 25 ) is at least one meter lower than the level of the outlet sections ( 5 ).
7. Process for separating solid particles contained in a gas/solid suspension using the device according to claim 1 , in which the circulation rate of the gas/solid suspension in the inlet sections ( 4 ) is between 5 m/s and 30 m/s.
8. Process for separating solid particles contained in a gas/solid suspension using the device according to claim 1 , in which the mass flow rate ratio of the solid to the gas at the inlet sections ( 4 ) is between 2 and 40.
9. Process for separating solid particles contained in a gas/solid suspension using the device according to claim 1 , in which the gas outlet rate at the side openings ( 6 ) is between 5 and 30 m/s.
10. Process for separating solid particles contained in a gas/solid suspension using the device according to claim 1 , in which the gas/solid suspension is introduced into a vertical pipe ( 18 ) where it flows with vertical ascending flow, then enters into a centrifuging zone ( 19 ) via a flow area ( 4 ) where it rotates around 180° so as to enable the disengagement of the gas, which is mainly discharged via an opening ( 6 ), the solid particles moving vertical downwards through a vertical descending zone ( 20 ) and being discharged towards the lower part of the regeneration chamber ( 25 ) via the outlet section ( 5 ).
11. Process for separating solid catalyst particles contained in a gas/solid suspension comprising separating said suspension in the device according to claim 1 , in which the catalyst flow rate through the outlet section ( 5 ) is between 50 and 1500 kg/(m 2 ·s).
12. A process according to claim 11 , wherein the catalyst flow rate is between 100 kg/(m 2 ·s) and 500 kg/(m 2 ·s).
13. A process according to claim 7 , wherein circulation rate is between 8 m/s and 20 m/s.
14. A process according to claim 8 , wherein said mass flow rate ratio is between 4 and 25.
15. A process according to claim 9 , wherein the gas outlet rate is between 5 m/s and 12 m/s.