AU6223180A - Low residence time solid-gas separation device and system - Google Patents

Description

LOW RESIDENCE TIME SOLID-GAS SEPARATION DEVICE AND SYSTEM

This invention relates to a device and system for separating solids from a gas. More particularly, the invention relates to a device and system for separating solids from a mixed phase gas-solids stream.

Background of the Invention

Chemical reaction systems utilizing solids in contact with a gaseous or vaporized stream have long been employed. The solids may participate in the reaction as catalyst, provide heat required for an endothermic reaction, or both. Alternatively the solids may provide a heat sink in the case of an exothermic reaction. Fluidized bed reactors have substantial advantages, most notably an isothermal temperature profile. However, as residence time decreases the fluidized bed depth becomes shallower and increasingly unstable. For this reason tubular reactors employing solid-gas contact in pneumatic flow have been used and with great success, particularly in the catalytic cracking of hydrocarbons to produce gasolines where reaction residence times are between 2 and 5 seconds.

As residence times become lower, generally below 2 seconds and specifically below 1 second, the ability to separate the gaseous products from the solids is diminished because there is insufficient time to do so effectively. This occurs because the residence time requirements of separation means such as cyclones begin to represent a disproportionate fraction of the allowable reactor residence time. The problem is acute in reaction systems such as thermal cracking of hydrocarbons to produce olefins and catalytic cracking to produce gasoline using improved catalysts where the total reactor residence times between 0.2 and 1.0 seconds. In these reaction systems conventional separation devices may consume more than 35% of the allowable contact time between the two phases resulting in product degradation, coke formation, low yields and varying severity .

In non-catalytic, temperature dependent endothermic reactions, rather than separating the phases, it is possible to quench the entire product stream after the requisite reaction period. However, these solids are usually recycled and are regenerated by heating to high temperatures. A quench of the reactor effluent prior to separation would be thermally inefficient. However, it is economically viable to make a primary separation of the particulate solids before quench of the gaseous stream. The residual solids in the quenched stream may then be separated in a conventional separator inasmuch as solids gas contact is no longer a concern.

In some reaction systems, specifically catalytic reactions at low or moderate temperatures, quench of the product gas is undesireable from a process standpoint. In other cases the quench is ineffective in terminating the reaction. Thus, these reaction systems require immediate separation of the phases to remove catalyst from the gas phase. Once the catalyst has been removed, the mechanism for reaction is no longer present.

The prior art has attempted to separate the phases rapidly by use of centrifugal force or deflection means. Nicholson U.S. Patent 2,737,479 combines reaction and separation steps within a helically wound conduit containing a plurality of complete turns and having a plurality of gaseous product drawoffs on the inside surface of the conduit to separate solids from the gas phase by centrigugal force. Solids gravitate to the outer periphery of the conduit, while gases concentrate at the inner wall, and are removed at the drawoffs. Although the Nicholson reactor-separator separates the phases rapidly, it produces a series of gas product streams each at a different stage of feed conversion. This occurs because each product stream removed from the multiple product draw offs which are spaced along rhe conduit is exposed to the reaction conditions for a different time period in a reaction device which has inherently poor contact between solids and gases. Ross et al U.S. Patent 2,878,891 attempted to overcome this defect by appending to a standard riser reactor a modification of Nicholson's separator. Ross' separator is comprised of a curvilinear conduit making a separation through a 180° to 240° turn. Centrifugal force directs the heavier solids to the outside wall of the conduit allowing gases that accumulate at the inside wall to be withdrawn through a single drawoff. While the problem of product variation is decreased to some extent, other drawbacks of the Nicholson apparatus are not eliminated.

Both devices effect separation of gas from solids by changing the direction of the gas 90° at the withdraw point, while allowing solids to flow linearly to the separator outlet. Because solids do not undergo a directional change at the point of separation, substantial quantities of gas flow past the withdraw point to the solids outlet. For this reason both devices require a conventional separator at the solids outlet to remove excess gas from the solid particules. Unfortunately, product gas removed in the conventional separator has remained in intimate contact with the solids, has not been quenched, and is, therefore, severely degraded.

Another drawback of these devices is the limitation on scaleup to commercial size. As conduit diameter increases the path traveled by the mixed phase stream increases proprotionately so that large diameter units have separator residence times approaching those of conventional cyclones. Increasing velocity can reduce residence time, but as velocities exceed 60 to 75 ft./sec. erosion by particles impinging along the entire length of the curvilinear path becomes progressively worse. Reduction of the flow path length by decreasing the radius of curvature of the conduit also reduces residence time, but increases the angle of impact of solids against the wall thereby accelerating erosion.

Pappas U.S. Patent 3,074,878 devised a low residence time separator using deflection means wherein the sol id gas stream flowing in a tubular conduit impinges upon a deflector plate causing the solids, which, have greater inertia, to be projected away from a laterally disposed gas withdrawal conduit located beneath said deflector plate. Again, solids so not change direction while the gas phase changes direction relative to th inlet stream by only 90° resulting in inherently high entrainment of solids in the effluent gas. While baffles placed across the withdrawal conduit reduce entrainment, these baffles as well as the deflector plate are subject to very rapid erosion in severe operating conditions of high temperature and high velocity. Thus, many of the benefits of separators of the prior art are illusory because of limitations in their efficiency, operable range, and scale-up potential.

SUMMARY OF INVENTION

It is an object of the separator of this invention to obtain a primary separation of particulate solids from a mixed phase gas-solid stream.

It is also an object of the separator to effect the separation rapidly and with a minimum of erosion.

An additional object object of this invention is to provide a separation system that obtains essentially complete separation of gas from the solids phase, although a controlled flow of gas with the solids phase is consistent with the operation of the device.

Another object of this invention is to provide a separation system to provide essentially complete separation of the solids from the mixed phase stream.

A further object is to effect a separation at high temperature and/or high velocity conditions with a minimum of gas product degradation.

Another object of this invention is to provide a method for rapidly attaining a primary separation of solids from a mixed phase gas-solid stream.

These and other objects of this invention will be apparent from an inspection of the specification and figures and claims.

The separation device and system of the present invention rapidly disengages particulate solids from a mixed phase gas-solids stream with a minimum of erosion. The separator consists of a chamber having an inlet at one end and a solids outlet at the other with the gas outlet therebetween. Each inlet and outlet is normal to the basic flow pattern within the separator. The gas outlet is oriented so that the gas portion of the feed undergoes a 180° change in direction, while the solids outlet is preferably aligned for downflow. Solids are projected by centrifugal force to a wall of the separator normal to and opposite to the inlet as the gas changes direction 180° forming thereat a bed of solids having an arcuate surface configuration of approximately 90° upon which subsequent solids impinge. The curve of the bed extends to the solids outlet and forms a path along which solids flow. Erosion of the wall opposite the inlet of the separator is diminished or eliminated by formation of the bed, which also aids in establishing a U-shaped 180° flow pattern of the gas stream.

The separation system is comprised of the primary separator, a secondary separator, and a stripping vessel. The gas .outlet of the primary separator is connected to the secondary separator via a conduit, while the stripping vessel is similarly connnected to the solids outlet. Pressure regulating means are used to control the flow of gas to the stripping vessel.

In the preferred separator embodiment a weir is used to establish a more stable bed, although a weirless separator may be used. Alternatively, the solids outlet flow path may be restricted by other means which aid in the deaeration of solids. However, in all embodiments of the separator of the present invention the loss of gas entrained with the solids phase is small because of the directional changes imposed on both gas and solid phases.

In the preferred embodiment the separator is designed within several geometric constrainst in order to maximize the separation efficiency. It is essential that the flow path have a rectangular cross section in order to obtain good efficiency. To obtain high efficiencies a separator with an inlet inside diameter D_i should preferably have a flow path height of at least D_i or 4 inches, whichever is greater. Similarly, the width of the flow path should be between 0.75 and 1.25 D_i while the distance between inlet and gas outlet centerlines should be no great er than 4 times D_i. DESCRIPTION OF FIGURES

FIGURE 1 is a schematic flow diagram of the separation system of the present invention as appended to a typical tubular reactor. FIGURE 2 is a cross sectional elevational view of the preferred embodiment of the separator.

FIGURE 3 is a cutaway view through section 3-3 of FIGURE 2.

FIGURE 4 is a cutaway view through section 3-3 of FIGURE 2 showing an alternate geometric configuration of the separator shell.

FIGURE 5 is a sketch of the separation device of the present invention indicating gas and solids phase flow patterns in a separator- not having a weir.

FIGURE 6 is a sketch of an alternate embodiment of the separation device having a weir and an extended separation chamber.

FIGURE 7 is a sketch of an alternate embodiment of the separation device wherein a stepped solids outlet is employed, said outlet having a section collinear with the flow path as well as a gravity flow section.

FIGURE 8 is a variation of the embodiment of FIGURE 7 in which the solids outlet of FIGURE 7 is used, but is not stepped.

FIGURE 9 is a sketch of a variation of the separation device of FIGURE 7 wherein a venturi restriction is incorporated in the collinear section of the solids outlet.

FIGURE 10 is a variation of the embodiment of FIGURE 9 oriented for use with a riser type reactor. DES CRIPTION OF INVENTION

FIGURE 1 is a schematic flow diagram showing the installation of the separator system of the present invention in a typical tubular reactor system handling dilute phase solid-gas mixtures. Solids and gas enter tubular reactor 13 through lines 11 and 12 respectively. The reactor effluent flows directly to separator 14 where a separation into a gas phase and a solids phase stream is effected. The gas phase is removed via line 15, while the solid. phase is sent to stripping vessel 22 via line 16. Depending upon the nature of the preocess and the degree of separation, an inline quench of the gas leaving the separator via line 15 may be made by injecting quench material from line 17. Usually, the product gas contains residual solids and is sent to a secondary separator 18, preferably a conventional cyclone. Quench material should be introduced in line 15 in a way that precludes black flow of quench material to the separator. The residual solids are removed from separator 18 via line 21, while essentially solids free product gas is removed overhead through line 19. Solids from lines 16 and 21 are stripped of gas impurities in fluidized bed stripping vessel 22 using steam or other inert fluidizing gas admitted via line 23. Vapors are removed from the stripping vessel through line 24 and, if economical or if need be, sent to downstream purification units. Stripped solids removed from the vessel 22 through line 25 are sent to regeneration vessel 27 using pneumatic transport gas from line 26. Off gases are removed from the regenerator through line 28. After regeneration the solids are then recycled to reactor 13 via line 11.

The separator 14 should disengage solids rapidly from the reactor effluent in order to prevent product degradation and ensure optimal yield and selectivity of the desired products. Further, the separator 14 operates in a manner that eliminates or at least significantly reduces the amount of gas entering the stripping vessel 22 inasmuch as this portion of the gas product would be severly degraded by remaining in intimate contact with the solid phase. This is accomplisehd with a positive seal which has been provided between the separator 14 and the stripping vessel 22. Finally, the separator 14 operates so that erosion is minimized despite high temperature and high velocity conditions that are inherent in many of these processes. The separator system of the present invention is designed to meet each one of these criteria as is described below-. FIGURE 2 is a cross sentional elevational view showing the preferred embodiment of solids-gas separation device 14 of the present invention. The separator 14 is provided with a separator shell 37 and is comprised of a solids-gas disengaging chamber 31 having an inlet 32 for the mixed phase stream, a gas phase outlet 33, and a solids phase outlet 34. The inlet 32 and the solids outlet 34 are preferably located at opposite ends of the chamber 31, while the gas outlet 33 lies at a point therebetween. Clean-out and mainenance. manways 35 and 36 may be provided at either end of the chamber 31. The separator shell 37 and manways 35 and 36 preferably are lined with erosion resistant linings 38, 39 and 41 respectively which may be required if solids at high velocities are encountered. Typical commercially available materials for erosion resistant lining include Carborundum Precast Carbofrax D, Carborundum Precast Alfrax 201 or their equivalent, A thermal insulation lining 40 may be placed between shell 37 and lining 38 and between the manways and their respective erosion resistant linings when the separator is to be used in bigh temperature service. Thus, process temperatures above 1500°F. (870°C.) are not inconsistent with the utilization of this device.

FIGURE 3 shows a cutaway view of the separator along section 3-3. For greater strength and ease of construction the separator 14 shell is preferably fabricated from cylindrical sections such a,s. pipe. 50, although other materials may, of course, be used. It is. essential that longitudinal side walls 51 and 52 should be rectilinear, or slightly arcuate as indicated by the dotted lines 51a and 52a. Thus, flow path 31A through the separator is essentially rectangular in cross section having a height H and width W as shown in FIGURE 3. The embodiment shown in FIGURE 3 defines the geometry of the flow path by adjustmentof the lingin width for walls 51 and 52, Alternatively, baffles, inserts, weirs or other means may be used, In like fashion the configuration of walls 53 and 54 transverse to the flow path may be similarly shaped, although, this is not essential. FIGURE 4 is a cutaway view along Section 3-3 of FIGURE 2 wherein the separation shell 37 is fabricated from a rectangular conduit. Because the shell 37 has rectilinear walls 51 and 52 it is not necessary to adjust the width of the flow path with a thickness of lining. Linings 38 and 40 could be added for erosion and thermal resistance respectively.

Again referring to FIGURE 2, inlet 32 and outlets 33 are disposed normal to flow path 31A (shown in FIGURE 3) so that the incoming mixed phase stream from inlet 32 is required to undergo a 90° change in direction upon entering the chamber. As a further requirement, however, the gas phase outlet 33 is also oriented so that the gas phase upon leaving the separator has completed a 180° change, in direction.

Centrifugal force propels the solid particles to the wall 54 opposite inlet 32 of the chamber 31, while the gas portion, having less momentum, flows through the vapor space. of the chamber 31. Initially, solids impinge on the wall 54, but subsequently accumulate to form a static bed of solids 42 which ultimately f orm in a surface configuration having a curvilinear arc 43 of approximately 90°. Solids impinging upon the bed are moved along the curvilinear arc 43 to the solids outlet 34, which is preferably oriented for downflow of solids by gravity. The exact shape of the arc 43 is determined by the geometry of the particular separator and the inlet stream parameters such, as velocity, mass flowrate, bulk density, and particle size. Because the force imparted to the incoming solids is directed against the static bed 42 rather than the separator 14 itself, erosion is minimal. Separator efficiency, defined as the removal of solids from the gas phase leaving through outlet

33, is, therefore, not affected adversely by high inlet velocities, up to 150 ft./sec., and the separator 14 is operable over a wide range of dilute phase densities, pre.ferably between 0.1 and 10.0 lbs./ft³, The separator 14 of the present invention achieves efficiencies of about 80%, although the preferred embodiment, discussed below, can obtain over 90% removal of solids. It has been found that separator efficiency is dependent upon separator geometry inasmuch, as the flow path, must be essentially rectangular and the relationship between height H, and the sharpness of the U-bend in the gas flow. Referring to FIGURES 2 and 3 we have found that for a given height H of chamber 31, efficiency increases as the 180° U-bend between inlet 32 and outlet 33 becomes progressively sharper; that is, as outlet 33 is brought progressively closer to inlet 32. Thus, for a given H the efficiency of the separator increases as the flow path and, hence; residence time decreases. Assuming an inside, diameter D_i of inlet 32, the preferred distance CL between the centerlines of inlet 32 and outlet 33 is less than 4.0 D_i, while the most preferred distance between said centerlines is between 1.5 and 2.5 D_i. Below 1.5 D_i better separation is obtained but difficulty in fabrication makes this embodiment less attractive in most instances. Should this latter embodiment be desired, the separator 14 would probably require a unitary casting design because inlet 32 and outlet 33 would be too close to one another to allow welded fabrication.

It has been found that the height of flow path H should be at least equal to the value of D_i or 4 inches in height, whichever is greater. Practice teaches that if H is less than D_i or 4 inches the incoming stream is apt to disturb the bed solids 42 thereby re-entraining solids inthe gas product leaving through outlet 33. Preferably H is on the order of twice D_i to obtain even greater separation efficiency. While not otherwise limited, it is apparent that too large an H eventually merely increases residence time without substantive increases in efficiency. The width W of the flow path is preferably between 0.75 and

1.25 times D_i, most preferably. between 0.9 and 1.10 D_i.

Outlet 33 may be of any inside diameter. However, velocities greater than 75 ft./sec. can cause erosion because of residual solids entrained in the gas, The inside diameter of outlet 34 should be sized so that a pressure differential between the stripping vessel 22 shown in FIGURE 1 and the separator 14 exist such that a static height of solids is formed in solids outlet line 16, The static height of solids in line 16 forms a positive seal which prevents gases from entering the stripping vessel 22. The magnitude of the pressure differential between the stripping vessel 22 and the separator 14 is determined by the force required to move the solids in bulk flow to the solids outlet 34 as well as the height of solids in line 16. As the differential increases the net flow of gas to the stripping vessel 22 decreases. Solids, having gravitational momentum, overcome the differential, while gas preferentially leaves through the gas outlet 33.

By regulating the pressure in the stripping vessel 22 it is possible to control the amount of gas going to the stripper. The pressure regulating means may include a check or ''flapper" valve 29 at the outlet of line 16, or a pressure control 29a device on vessel 22. Alternatively, as suggested above, the pressure may be regulated by select ing the size of the outlet 34 and conduit 16. to obtain hydraulic forces acting on the system that set the flow of gas to the sttipper 32, While such gaa is degraded, we have found that an increase in separation efficiency occurs with a bleed of gas to the stripper of less than 10%, preferably between 2 and 7%. Economic and process considerations would dictate whether this mode of operation should be used. It is also possible to design the system to obtain a net backflow of gas from the stripping vessel. This gas flow should be less than 10% of the total feed gas rate. By establishing a minimal flow path, consistent with the above recommendations, residences times as low as0.1 seconds or less may be obtained, even in separators having inlets over 3 feet in diameter. Scale-up to 6 feet in diameter is possible in many systems where, residence. times approaching 0.5 seconds are allowable.

In the preferred embodiment of FIGURE 2 a weir 44 is placed across the flow path at a point at or just beyond the gas outlet to establish a positive height of solids prior to solids outlet 34. By installing a weir (or an equivalent restriction) at this point a more stable bed is established thereby reducing turbulence and erosion. Moreover, the weir 44 establishes a bed which, has a crescent shaped curvilinear arc 43 of slightly more than 90°. An arc of this shape diverts gas towards the gas outlet and creates the U-shaped gas flow pattern illustrated diagramatically by line 45 in FIGURE 2. Without the weir 44 an arc somewhat less than or equal to 90º would be formed, and which would extend asymptotically toward outlet 34 as shown by dotted line 60 in the schematic diagram of the. separator of FIGURE 5. While neither efficiency nor gas loss (to the stripping vessel) is affected adversely, the flow pattern of line 61 increases residence time, and more importantly, creates greater potential for erosion at areas 62, 63 and 64. The separator of FIGURE 6 is a schematic diagram of another embodiment of the separator 14, said separator 14 having an extended separation chamber in the longitudinal dimension. Here, the horizontal distance L between th.e gas outlet 34 and the weir 44 is extended to establish a soli.ds bed of greater length, L is preferably less than or equal to 5 D_i, Although the gas flow pattern 61 does develop the preferred U-shape, a crescent shaped arc is obtained which limits erosion potential to area 64, Embodiments- shown by FIGURES 5 and 6 are useful when the solids loading of the incoming stream is low. The embodiment of FIGURE 5 also has the minimum pressure loss and may be used when the velocity of the incoming stream is low.

As- shown in FIGURE 7 it is equally pssible to use a stepped solids outlet 65 having a section 66 collinear with the flow path as well as a gravity flow section 67. Wall 6.8 replaces weir 44, and arc 43 and flow pattern 45 are similar to the preferred embodiment of FIGURE 2. Because solids accumulate in the restricted collinear section 66, pressure losses are greater. This embodiment, then, is not preferred where the incoming stream is at low velocity and cannot supply sufficient force to expel the solids through outlet 65. However, because of the restricted solids flow path, better dearation is obtained and gas losses are minimal,

FIGURE 8 illustrates another embodiment of the separator 14 of FIGURE 7 wherein the solids outlet is not stepped, Although a weir is not used, the outlet restricts solids flow which helps form the bed 42. As in FIGURE 6, an extended L distance between the gas outlet and solids outlet may be used. The separator of FIGURE 7 or 8 may be used in conjunction with a venturi, an orifice, or an equivalent flow restriction device as shown in FIGURE 9. The venturi

69 having dimensions D_v (diameter at venturi inlet), D_vt

(diameter of venturi throat), and θ (angle of cone formed by projection of convergent venturi walls) is placed in the collinear .section 66 of the outlet 65 to greatly improve dearation of solids. The embodiment of FIGURE 10 is a variation of the separator shown in FIGURE. 9, Here, in-let 32 and outlet 33 are oriented for use in a riser type reactor. Solids are propelled to the wall 71 and the bed thus formed is kept in place by the force of the incoming stream. As before the gas portion of the feed follows the U-shaped pattern of line 45. However, an asymptotic bed will be formed unless there is a restriction in the solids outlet. A weir would be ineffective in establishing bed height, and would deflect solids into the gas outlet. For this reason the solids outlet of FIGURE 9 is preferred, Most preferably, the venturi 69 is placed in collinear section 6.6 as shown in FIGURE 10 to improve the dearation of the solids. Of course, each of these alternate embodiments may have one or more of the optional design features of the basic separator discussed in relation to FIGURES., 2, 3 and 4.

The separator of the present invention is more clearly illustrated and explained by the examples which follow. In these examples, which are based on data obtained during experimental testing of the separator design, the separator has critical dimensions specified in Table I, These dimensions (in inches except as noted) are indicated inthe various drawing figures and listed in the Nomenclature below: CL Distance between inlet and gas outlet centerlines D_i Inside diameter of inlet

D_og Inside diameter of gas outlet

D_os Inside diameter of solids outlet D_v Diameter of venturi inlet D_vt Diameter of venturi throat

H Height of flow path

H_w Height of weir or step

L Length from gas outlet to weir or step as indicated in FIGURE 6 Width of flow path

Angle of cone formed by projection of convergent venturi walls, degrees

Example 1 In this example a separator of the preferred embodiment of FIGURE 2 was tested on a feed mixture of air and silica alumina. The dimensions of the apparatus are specified in Table I. Note that the distance L from the gas outlet to the weir was zero. The inlet stream was comprised of 85 ft. ³/min. of air and 52 lbs./min. of silica alumina having a bulk density of 70 lbs./ft.³ and an average particle size of 100 microns. The steam density was 0.612 lbs./ft.³ and the operation: was performed at ambient temperature and atmospheric pressure. The velocity of the incoming stream through the 2 inch inlet was 65.5 ft./sec, while the outlet gas velocity was 85.6 ft./sec. through a 1.75 inch diameter outlet. A positive seal of solids in the solids outlet prevented gas from being entrained in the solids leaving the separator. Bed solids were stabilized by placing a 0.75 inch weir across the flow path.

The observed separation efficiency was 89.1%, and was accomplished in a gas phase residence time of approximately 0.008 seconds. Efficiency is defined as the percent removal of solids from the inlet stream.

Example 2 The gas-solids mixture of Example 1 was process in a separator having a configuration illustrated by FIGURE 6. In the example the L dimension is 2 inches; all other dimensions are the same as Example 1, By extending the separation chamber along its longitudinal dimension, the flow pattern of the gas began to deviate from the U-shaped discussed above. As a result residence time was longer and turbulence was increased. Separation efficiency for this example was 70.8%. Example 3

The separator of Example 2 was tested with an inlet stream comprised of 85 ft.³/min. of air and 102 lbs./min. of silica alumina which gave a stream density of 1.18 lbs./ ft.³, or approximately twice that of Example 2. Separation efficiency improved to 83.8%.

Example 4 The preferred separator of Example 1 was tested at the inlet flow rate of Example 3. Efficiency increased slightly to 91.3%.

Example 5 The separator of FIGURE 2 was tested at the conditions of Example 1. Although the separation dimensions are specified in Table I note that the distance CL between inlet and gas outlet centerlines was 5.875 inches, or about three times the diameter of the inlet. This dimension is outside the most preferred range for CL which is between 1.50 and 2.50 D_i. Residence time increased to

0.01 seconds, while efficiency was 73.0%.

Example 6

The preferred separator configuration of FIGURE 2 was tested in this Example. However, in this example the apparatus was increased in size over the previous examples by a factor of nine based on flow area. A 6 inch inlet and 4 inch outlet were used to process 472 ft.³/min. of air and 661 lbs./min. of silica alumina at 180°F. and 12 psig.

The respective velocities were 40 and 90 ft./sec. The solids had a bulk density of 70 lbs./ft.³ and the stream density was 1.37 lbs./ft.³. Distance CL between inlet and gas outlet centerlines was 11 inches, or 1.83 times the inlet diameter; distance L was zero. The bed was stabilize by a 2.25 inch weir, and gas loss was prevented by a positive seal of solids. However, the solids were collected in a closed vessel, and the pressure differential was such that a positive flow of displaced gas from the collection vessel to the separator was observed. This volume was approximately 9.4 ft. /min. Observed separator efficiency was 90.0%, and the gas phase residence time approximately

0.02 seconds.

Example 8

The separator used in Example 7 was tested with an identical feed of gas and solids. However, the solids collection vessel was vented to the atmosphere and the pressure differential adjusted such that 9% of the feed gas, or 42.5 ft.³/min., exited through the solids outlet at a velocity of 3.6 ft./sec. Separator efficiency increased with this positive bleed through the solids outlet to 98.1%.

Example 9

The separator of FIGURE 8 was tested in a unit having a 2 inch inlet and a 1 Inch gas outlet. The solids outlet was 2 inches in diameter and was located 10 inches away from the gas outlet (dimension L). A weir was not used. The feed was comprised of 85 ft.³/min. of air and

105 lbs. /min. of spent fluid catalytic cracker catalyst having a bulk density of 45 lbs./ft³ and an average particle size of 50 microns. This gave a stream density of

1.20 lbs./ft.³. Gas inlet velocity was 65 ft./sec, while the gas outlet velocity was 262 ft./sec. As in Example 7 there was a positive counter-current flow of displaced gas from the collection vellel to the separator. This flow was approximately 1.7 ft.³/min. at a velocity of 1.3 ft./sec

Operation was at ambient temperature and atmospheric pressure. Separator efficiency was 95.0%. Example 10

The separator of FIGURE 9 was tested on a feed comprised of 85 ft.³/min. of air and 78 lbs./min. of spent

Fluid Catalytic Cracking catalyst. The inlet was 2 inches in diameter which resulted in a velocity of 65 ft. /sec, the gas outlet was 1 inch in diameter which resulted in an outlet velocity of 262 ft./sec This separator had a stepped solids outlet with a venturi in the collinear section of the outlet. The venturi mouth was 2 inches in diameter, while the throat was 1 inch. A cone of 28.1 was formed by projection of the convergent walls of the venturi. An observed efficiency of 92.6% was measuued, and the solids leaving the separator were completely dearated except for interstitial gas remaining in the solids' voids.

Claims (37)

1. A solids-gas separator designed to effect rapid removal of particulate solids from a dilute mixed phase stream of solids and gas, the separator comprising a chamber for disengaging solids from the incoming mixed phase stream, said chamber having rectilinear or slightly arcuate longitudinal walls to form a flow path essentially rectangular in cross section, said chamber also having a mixed phase inlet , a gas phase outlet , and a solids phase outlet, with the inlet at one end of the chamber disposed normal to the flow path, the solids outlet at the other end of the chamber, said solids outlet suitable for downflow of discharged solids by gravity, and the gas outlet therebetween oriented to effect a 180° change in direction of the gas.

2. The separator of claim 1 having a mixed phase inlet of inside diameter D_i and which is further characterized by a flow path with a preferred height H equal to at least D_i or 4 inches, whichever is greater and with a preferred width W between 0.75 and 1.25 D_i, and having a gas outlet located between the mixed phase inlet and solids outlet at a preferred distance from the inlet which is no greater than 4.0 D_i as measured between their respective centerlines.

3. The separator of claim 2 wherein the most preferred distance between inlet and gas outlet centerlines is no less than 1.5 D_i but no greater than 2.5 D_i.

4. The separators of claims 2 or 3 wherein the most preferred height H of the flow path is twice D_i.

5. The separators of claims 2 or 3 wherein about 80% of solids contained in the inlet stream is removed.

6. The separators of claim 4 wherein the most preferred width W of the flow path is no less than 0.9 D_i but no greater than 1.10 D_i.

7. The separators of claim 5 wherein about 90% of solids contained in the inlet stream is removed.

8. The separator of claim 2 having a solids removal outlet the first section of which is collinear with the flow path and the second section normal to the first section, and aligned for downflow of solids by gravity.

9. The separators of claim 8 further comprised of a flow restriction placed within the collinear section of the solids removal outlet.

10. The separators of claim 9 wherein the f low res triction i s an or if ice .

11. The separators of claim 9 wherein the preferred flow restriction is a venturi.

12. The separators of claims 1 or 2 further comprising a weir placed across the flow path beyond or at the gas outlet but before the solids outlet.

13. The separators of claims 1 or 2 having a chamber fabricated of circular cross section, said separator further comprised of flow path shaping means whereby the flow path geometry is made essentially rectangular.

14. The separators of claim 13 wherein the shaping means is a lining of a ceramic material placed upon the chamber walls.

15. The separators of claim 13 wherein the shaping means are baffles inserted into the separator chamber.

16. The separators of claims 1 or 2 whose chamber walls are lined with an erosion resistant lining.

17. The separators of claims 1, 2, 6 or 8 whose chamber walls are lined with a thermal insulation lining.

18. The separators of claim 16 further comprised of a thermal insulation lining placed between the chamber walls and the erosion resistant lining.

19. The separators of claims 1, 2, 8 or 9 having a chamber whose longitudinal dimension is extended beyond the gas outlet by a length L.

20. The separation of claim 19 whose preferred length L of the chamber extension is less than or equal to 5 D_i.

21. The separators of claims 1, 2 or 8 further comprised of a clean-out manway on one or both ends of the separator chamber.

22. The separator of claims 1 or 2 wherein the inlet stream has a dilute phase density between 0.1 and

10. 0 lb s . /ft.³ and a velocity between 20 and 150 ft./ sec

23. A solids-gas separation system to separate a dilute mixed phase stream of gas and particulate solids into an essentially solids free gas stream, the separation system comprising: a chamber, for rapidly disengaging about 80% of the particulate solids from the incoming dilute mixed phase stream, said chamber having approximately rectilinear or slightly arcuate longitudinal side walls to form a flow path of height H and width W approximately rectangular in cross section, said chamber also, having a mixed phase inlet of inside width D_i, a gas outlet, and a solidis outlet, said inlet at one end of the chamber disposed normal to the flow path whose height H is equal to at least D_i or 4 inches, whichever is greater and whose width W is no less than 0.75 D_i but no more than 1.25 D_i, said solids outlet at the opposite end of the chamber and being suitable for downflow of discharged solids by gravity, and said gas outlet therebetween at a distance no greater than 4 D_i from the inlet as measured between respective centerlines and oriented to effect a 180° change in direction of the gas whereby resultant centrifugal forces direct the solid particles in the incoming stream toward a wall of the chamber opposite to the inlet forming threat and maintaining an essentially static bed of solids, the surface of the bed defining a curvilinear path of approximately 90° for the outflow of solids to the solids outlet,

a secondary solids-gag separator, said secondary separator removing essentially all of the residual solids, a first conduit connecting the gas outlet from the chamber to the secondary separator,

a vessel for the discharge of solids,

a second conduit connecting said vessel and the chamber, and,

pressure balance means to maintain a height of solids in said second conduit to provide a positive seal between the chamber and vessel.

24. The separation system of claim 23 further comprising quench means located in the first conduit.

25. The separation system of claim 24 wherein the preferred quench means is a spray nozzle for injection of quench fluid.

26, The separation system of claim 23 wherein the chamber has a solids removal outlet the first section of which is collinear with the flow path and the second section normal to the first section, and aligned for downflow of solids by gravity, said first section being stepped away from the wall of the chamber opposite the inlet.

27. The separation system of claim 23 wherein the solids discharge vessel strips residual gas from the solids using an inert gas or steam.

28. The separation system of claim 23 wherein the preferred secondary separation is a cyclone.

29. The separation system of claim 23 wherein the pressure balance means is the hydraulic forces acting on the chamber, second conduit and vessel, the second conduit being sized for sufficient pressure loss to provide the height of solids.

30. The separation system of claim 23 wherein the pressure balance is a check valve at the outlet end of the second conduit.

31. The separation system of claim 23 wherein the pressure balance means is a pressure control valve on the solids discharge vessel.

32. The separation systems of claims 23, 29, 30 or 31 wherein the pressure balcne means regulates the amount of residual gas to the solids discharge vessel, said gas flow being positive or negative, but having a flowrate in absolute numbers no greater than 10% of the inlet gas flow to the system.

33. A method for separating by centrifugal force particulate solids from a dilute mixed phase stream of gas and solids, the method comprising the steps of: adding the mixed phase stream to a chamber having a flow path of essentially rectangular cross section from an inlet of inside diameter D_i disposed normal to the flow path, said flow path having a height H equal to D_i or 4 inches, whichever is greater, and a width W greater than or equal to 0.75 D_i but less than or equal to

1.25 D_i,

disengaging solids from gas by centrifugal force within said chamber along a bed of solids found at a wall opposite to the inlet as the gas flows through said flow path, the gas changing direction 180°, and the solids bein projected 90° toward a solids outlet,

withdrawing the gaseous portion of the inlet stream from a gas outlet disposed 180° from the inlet , the gas portion containing about 20% residual solids, said gas outlet located between the solids outlet and inlet, the gas outlet being at a distance no greater than 4 D_i from the inlet as measured between respective centerlines, and

withdrawing the solids by gravity through the solids outlet.

34. The method of claim 33 further comprising the step of surther separating residual solids from the gaseous portion of the inlet stream removed via the gas outlet in a secondary separator.

35. The method of claim 34 wherein the preferred secondary operator is a cyclone.

36. The method of claims 33, 34, or 35 further comprising the step of stipping solids withdrawn from the solids outlet with inert gas or steam.

37. The method of claim 36 further comprising the step of withdrawing bleed gas with the solids, said bleed gas amounting to no more than 10% of the inlet gas.