Separation of fluidized solids suspended in a gaseous phase

Abstract: Apparatus for separating fluidized solids (e.g. catalytic particles) suspended in a gaseous phase comprises a riser (20) which is generally vertically positioned within a catalyst disengaging zone and which has a plurality of openings (22) around the circumference of the riser (20) at its discharge end. The openings (22) in the riser (20) have a vertical stub portion that extends tangentially outwardly from the riser and communicates with a first end of an upwardly sloping curvilinear (50) tunnel that terminates at a second end. The second end of the tunnel (50) opens into a tangential opening in the primary cyclone (30). The area of the opening of the first end of the tunnel is larger than the area of the opening of the second end of the tunnel (50).

Description: The present invention is concerned with the separation of fluidized solids from a fluidizing gaseous phase. More particularly though not exclusively, the present invention is concerned with the separation of fluidized catalytic particles from the gas suspension phase in a fluidized catalytic cracking unit. There are wide varieties of chemical processes which are conducted using particles of fluidized particle size suspended in a gaseous phase. Of particular importance in the petroleum industry is the well known fluidized catalytic cracking process (FCC) in which the particles that are fluidized and suspended in a gaseous phase are catalyst particles. In this typical hydroconversion process, it ultimately becomes necessary to separate the particulate material from the fluidizing gas and this is generally achieved in a catalyst separation zone equipped with cyclones. Recent trends of fluidized catalytic cracking have tended toward operation of the process at higher temperatures with extremely active catalysts. The concomitant result is that there has been an ever-increasing necessity to be able to efficiently separate the catalyst from the fluidizing media in an extremely rapid and efficient manner in order to minimize undesirable side reactions. Consequently, there has been a plethora of methods and apparatuses developed to achieve the separation of fluidized catalyst particles from the fluidizing gas. The following U.S. Patents illustrate the number of apparatuses and methods employed: U.S. Patent 4,070,159; U.S. Patent 4,176,083; U.S. Patent 4,572,780; U.S. Patent 4,606,814; U.S. Patent 4,629,552; U.S. Patent 4,778,660; U.S. Patent 4,792,437; U.S. Patent 4,869,880 and U.S. Patent 4,909,993. The foregoing patents show various riser termination devices with internal vanes and the like used in an attempt to bring about satisfactory separation of fluidized particles from the entraining gas. EP-A-0 168 916 discloses apparatus for the fluidized catalytic cracking of a hydrocarbon feed. In the embodiment shown in Figs. 6 and 7 of the document, the upstream portion of a riser conduit is configured as a pipe extending into a larger diameter downstream portion. The annulus so formed is covered by a metal ring having orifices in open connection with the main reactor vessel to permit stripping gas to pass through into the said downstream portion. The present invention relates to an improved method and an apparatus for removing fluidizable particles from a fluidizing gaseous stream. It addresses the problem of providing apparatus which will permit the fluidized solid fluid gas mixture to travel directly from a riser into a primary cyclone. In particular, the natural movement of the fluidized solids needs to be channelled into the cyclone in such a way as to avoid abrupt diversion of the gas stream and changing of its essential flow pattern as it exits the riser and enters a primary cyclone. If according to the invention from one aspect there is provided an apparatus for separation of fluidized solids suspended in a gaseous phase, comprising: (a) a vessel having a disengaging zone; (b) a vertical tubular riser positioned in the vessel, the riser having an axially-closed discharge end located in the disengaging zone, the riser having at its discharge end a plurality of openings in the periphery; (c) a pair of vertical projections for each peripheral opening in the riser, the projections extending outwardly and substantially tangentially to the tubular riser; (d) a cyclone for each opening and riser, the cyclone having an inlet for receiving entrained solids discharged from the respective opening in the riser, the cyclone inlet having an area less than the area of the respective opening of the riser. (e) an arcuately shaped tunnel communicating between each riser opening and the respective cyclone inlet, the tunnel having an inlet end which fits around but is spaced apart from vertical projections extending outwardly from the tubular riser; whereby entrained solids discharged from the riser are introduced into the cyclone inlet. According to the invention from another aspect there is provided a process of separating entrained solids from a gaseous phase, comprising: guiding a mixture thereof from a generally vertically disposed riser within a vessel to at least one cyclone separator; increasing the acceleration of the mixture by guiding it along an arcuate flow path which decreases in cross-section from an exit in the riser to an inlet of the cyclone so that the mixture enters the cyclone at a velocity resulting in improved separation of solids from the gaseous phase. The invention will be better understood by referring by way of example to the accompanying drawings, wherein:- Figure 1 is a fragmentary elevational view of an FCC unit showing, in part, a riser, one primary and one secondary cyclone and the unique tunnel structure in accordance with a preferred embodiment of the present invention. Figure 2 is a simplified plan view showing the upper section of a typical fluidized cat cracking unit, incorporating the structure of Figure 1. Figure 3 is a side view of a riser terminating in a separation zone and equipped with arcuately shaped stubs. Figure 4 is a diagrammatic side view of the tunnel communicating with the riser and a cyclone. The apparatus to be described below is particularly suitable for use in operation of a typical fluidized catalytic cracking unit and, consequently, the description of the invention will be made with particular reference to such a unit. Nonetheless, it should be readily appreciated that the apparatus will be equally suitable for separating fluidized solids from gases in other processes requiring such separation. In fluid catalytic cracking processes, a catalyst of fluidized particle size that has been heated to an elevated temperature, for example, in the range of about 1150°F (621°C) to about 1350°F (732°C), is introduced with a petroleum feedstock into the bottom of a riser tube, with the result that there is a large volume of gaseous hydrocarbons generated therein, which are at temperatures of from about 950°F (510°C) to about 1000°F (538°C). This results in the concurrent flow of the catalyst particles and the vapor hydrocarbons through the riser tube, where they are introduced into a disengaging zone for the purpose of separating the catalyst from the vapor phase. For separating the catalyst particles from the vapor phase exiting from the riser, the gas is passed outwardly from the discharge end of the riser in substantially a tangential direction and then arcuately into and through an upwardly curvilinear conduit or tunnel for tangential entry into the inlet of a primary cyclone. Referring now to Figures 1 and 2, there is shown a solids gaseous separation system located within a vessel 10. The system includes a riser 20, which is generally vertically disposed within vessel 10. Riser 20 has an upstream end (not shown) in which fluidized solid particles, such as fluidized catalyst particles, enter and progress upwardly through to the downstream end 24 of the riser 20. The riser tube 20 at the downstream end 24 is closed at its top by plate 21. A plurality of ports 22 are spaced preferably uniformly around the periphery of the riser tube 20 at the downstream end 24. Each of the openings in ports 22 are further defined by a pair of vertical walls or projections 25 that are substantially tangential to the periphery of the riser 20. These stub-like projections 25 provide a primary means for guiding the flow of entrained solids from the downstream end of the riser outwardly in a substantially tangential direction. Optionally and preferably, (see Figure 3) each pair of stub-like projections 25 is provided with a top projection 26 and a bottom projection 27 connecting the side walls 25 and defining there between a substantially rectangular opening or short stub-like conduit. As can be seen in Figure 3, in the preferred embodiment of the present invention, the bottom wall 27 is sloped in an upward direction. In the vessel 10, as can be seen, particularly in Figure 2, are provided a plurality of primary cyclones 30, which will correspond in number to the number of openings 22 in riser 20. Optionally and preferably, there will be provided a plurality of secondary cyclones 40 corresponding in number to the primary cyclones 30. The gas outlet 31 of a primary cyclone 30 will be connected through a conduit 32 to the respective inlet of the secondary cyclone 40. It is important that the ports 22 in the downstream end 24 of riser 20 be substantially larger than the respective openings 33 into the primary cyclones 30. Indeed, it is particularly preferred, in the practice of the present invention, that the openings or ports 22 be from about 90% to about 100% greater than the openings 33 in the primary cyclones 30. As shown in Figures 1 and 2, a tunnel 50 is provided for each of the ports 22 to guide the flow of fluidized solids from the riser 20 into the inlet 33 of the primary cyclone 30. In plan view, such as shown in Figure 2, the tunnels 50 have side walls 53 that are generally arcuately shaped, thereby providing for a substantially smooth transition of the flow of solids from the riser 20 into the primary cyclones 30. As indicated previously, however, the opening 22 of the riser is significantly larger than the opening 33 of the primary cyclone and, consequently, as can be seen in Figure 4, the bottom wall 52 of the tunnel 50 has a generally upwardly sloping direction that is generally curvilinear in shape. The top wall 51 of the tunnel 50 is generally horizontally disposed. Indeed, in one embodiment of the invention, the tunnel 50 can be positioned with respect to an internal baffle 70, shown in Figure 1, so that the baffle 70 can also serve as the top wall 51 for tunnel 50. In the practice of the present invention, the tunnel 50 has an opening at its inlet end that is sufficiently large to fit around the stub projecting walls 25 of riser 20, so as to permit movement of the tunnel 50 with respect to the riser 20 during thermal cycling of the vessel without creating any mechanical strains. This arrangement will also permit the entry of gases into the tunnel 50 from the reactor plenum. Because of the upward curvilinear design of the tunnel 50, tunnel 50 can be cleared of solids when conditions necessitate. Thus, it is particularly preferred that a space be provided between at least the bottom wall 52 of the tunnel and stub 27, so as to permit automatic draining of any particles that may possibly accumulate within the tunnel in the event of adverse operating conditions. As should be readily appreciated, by providing an arcuately shaped tunnel that has an inlet opening substantially larger than its outlet opening into the cyclone, a centrifugal force is created that aids the transitional flow from the riser to the primary cyclone. Once the entrained solids have entered into the tunnel from the riser, they accelerate and travel into the primary cyclone at the proper cyclone inlet velocity, thereby enhancing the separation efficiency of the primary cyclones.

Claims: An apparatus for separation of fluidized solids suspended in a gaseous phase, comprising: (a) a vessel (10) having a disengaging zone; (b) a vertical tubular riser (20) positioned in the vessel, the riser having an axially-closed discharge end (24) located in the disengaging zone, the riser having at its discharge end a plurality of openings (22) in the periphery; (c) a pair of vertical projections (25) for each peripheral opening in the riser, the projections extending outwardly and substantially tangentially to the tubular riser (20); (d) a cyclone (30) for each opening (22) in the riser (20), the cyclone having an inlet (33) for receiving entrained solids discharged from the respective opening (22) in the riser (20), the cyclone inlet (33) having an area less than the area of the respective opening (22) of the riser (20); and (e) an arcuately shaped tunnel (50) communicating between each riser opening (22) and the respective cyclone inlet (33), the tunnel (50) having an inlet end which fits around but is spaced apart from vertical projections (25) extending outwardly from the tubular riser (20); whereby entrained solids discharged from the riser (20) are introduced into the cyclone inlet (33). An apparatus according to claim 1, wherein the riser opening area is 90 to 100% greater than the cyclone inlet area. An apparatus according to claim 1 or 2, wherein the tunnel (50) includes an upwardly curvilinear bottom wall (52). An apparatus according to claim 1, 2 or 3, wherein the vertical projections (25) extending from the riser (20) are connected by top and bottom projections (26,27) defining a conduit. An apparatus according to claim 4, wherein the bottom projection (27) slopes upwardly. A process of separating entrained solids from a gaseous phase, comprising: guiding a mixture thereof from a generally vertically disposed riser (20) within a vessel (10) to at least one cyclone separator (30); increasing the acceleration of the mixture by guiding it along an arcuate flow path which decreases in cross-section from an exit (22) in the riser (20) to an inlet (33) of the cyclone (30) so that the mixture enters the cyclone at a velocity resulting in improved separation of solids from the gaseous phase. A process as claimed in claim 6, wherein the mixture is guided substantially tangentially outward from the riser (20) and upwardly and arcuately toward the cyclone separator (30).

Inventors: MELFI GEORGE, REINMAN KENNETH JOSEPH, SHAW DONALD FRANCIS, TAMMERA ROBERT FRANK, MELFI, GEORGE, REINMAN, KENNETH JOSEPH, SHAW, DONALD FRANCIS, TAMMERA, ROBERT FRANK
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1992
Main classification: C10G11
IPC codes: B01J8, B01D45, C10G11, B04C5