Apparatuses and methods for gas-solid separations using cyclones
Cyclones for gas-solid separators are described, which are especially applicable for use in a downflowing third stage separator (TSS) for the removal of dust particles, such as solid catalyst fines, from the flue gas streams exiting the catalyst regenerator in fluid catalytic cracking (FCC) processes. A number of important flow characteristics result from the configuration of the cyclones, particularly with respect to the relative axial lengths over which swirl vanes and central hubs of the cyclones extend. These characteristics include a decrease in growth of turbulent eddies that conventionally result from a sudden expansion, in open cross-sectional area, of gas exiting swirl vanes.
1. A cyclone for a gas-solid separator, the cyclone comprising
(a) a barrel;
(b) a central hub disposed within the barrel to provide an annular section between the central hub and the barrel, wherein the central hub has a lower, tapered section in the form of a conical end cap; and
(c) swirl vanes extending radially into in the annular section over an axial length of at most about 75% of an axial length of the central hub.
2. The cyclone of claim 1 , wherein the axial length over which the swirl vanes extend into the annular section is at most about 50% of the axial length of the central hub.
3. The cyclone of claim 1 , wherein the axial length over which the swirl vanes extend is in an upper half of the axial length of the central hub.
4. The cyclone of claim 1 , wherein the central hub has an upper, non-tapered section.
5. The cyclone of claim 4 , wherein the upper, non-tapered section is cylindrical.
6. The cyclone of claim 5 , wherein the upper, non-tapered section of the central hub is disposed concentrically within the barrel.
7. The cyclone of claim 4 , wherein the swirl vanes extend over all or a portion of the axial length of the non-tapered section and not over any portion of the axial length of the tapered section.
8. The cyclone of claim 1 , wherein the swirl veins are helical.
9. A gas-solid separator comprising an upper tube sheet, a lower tube sheet, and at least one cyclone extending through the tube sheets, the cyclone comprising an impure gas inlet at an upper end of a barrel above the upper tube sheet, a solid particle outlet at a lower end of the barrel between the upper tube sheet and the lower tube sheet, and a purified gas outlet below the lower tube sheet, wherein the cyclone further comprises
(a) a barrel;
(b) a central hub disposed within the barrel to provide an annular section between the central hub and the barrel; and
(c) swirl vanes extending radially into in the annular section over an axial length of at most about 75% of an axial length of the central hub.
10. The gas-solid separator of claim 9 , wherein the solid particle outlet is at a radial periphery of the barrel.
11. The gas-solid separator of claim 10 , wherein the purified gas outlet is concentric with the barrel.
12. The gas-solid separator of claim 9 , comprising a plurality of cyclones, each comprising an impure gas inlet at an upper end of a barrel above the upper tube sheet, a solid particle outlet at a lower end of the barrel between the upper tube sheet and the lower tube sheet, and a purified gas outlet below the lower tube sheet, each cyclone further comprising
(a) a barrel;
(b) a central hub disposed within the barrel to provide an annular section between the central hub and the barrel; and
(c) swirl vanes extending radially into in the annular section over an axial length of at most about 75% of an axial length of the central hub.
13. The gas-solid separator of claim 12 , wherein the plurality of cyclones number from about 5 to about 300 cyclones.
14. The gas-solid separator of claim 12 , further comprising a process gas inlet in communication with the impure gas inlets of the plurality of cyclones.
15. The gas-solid separator of claim 14 , further comprising a particle-rich gas outlet in communication with the solid particle outlets of the plurality of cyclones.
16. The gas-solid separator of claim 15 , further comprising a particle-lean gas outlet in communication with the purified gas outlets of the plurality of cyclones.
17. A process for purifying a gas stream contaminated with solid particles, the process comprising:
(a) feeding the gas stream to a process gas inlet of the gas-solid separator of claim 13 , wherein the process gas inlet is in communication with the impure gas inlets of the plurality of cyclones;
(b) withdrawing an underflow gas stream from a particle-rich gas outlet in communication with the solid particle outlets of the plurality of cyclones; and
(c) withdrawing a clean gas stream from a particle-lean gas outlet in communication with the purified gas outlets of the plurality of cyclones.
18. The process of claim 17 , wherein the gas stream is an effluent from a catalytic reactor or a catalyst regenerator of a fluid catalytic cracking (FCC) process.
19. The process of claim 17 wherein the gas stream is an effluent from a catalytic reactor or a catalyst regenerator of a methanol to olefins (MTO) process.