CA1171800A - Low residence time solid-gas separation device and system - Google Patents
Low residence time solid-gas separation device and systemInfo
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- CA1171800A CA1171800A CA000421773A CA421773A CA1171800A CA 1171800 A CA1171800 A CA 1171800A CA 000421773 A CA000421773 A CA 000421773A CA 421773 A CA421773 A CA 421773A CA 1171800 A CA1171800 A CA 1171800A
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Abstract
ABSTRACT OF THE DISCLOSURE
This invention relates to an apparatus and method for rapidly separating particulate solids from a mixed phase solids-gas stream which may be at velocities up to 150 ft./sec. and at high temperature. Specifically, the device is designed for incorporation at the discharge of solid-gas reacting systems having low residence time requirements and carried out in tubular type reactors. Separation is effected by projecting solids by centrifugal force against a bed of solids as the gas phase makes a 180° directional change, said solids changing direction only 90° relative to the incoming stream.
This invention relates to an apparatus and method for rapidly separating particulate solids from a mixed phase solids-gas stream which may be at velocities up to 150 ft./sec. and at high temperature. Specifically, the device is designed for incorporation at the discharge of solid-gas reacting systems having low residence time requirements and carried out in tubular type reactors. Separation is effected by projecting solids by centrifugal force against a bed of solids as the gas phase makes a 180° directional change, said solids changing direction only 90° relative to the incoming stream.
Description
This is a divisional application of Application Serial No. 355,416 filed July ~th 1980 and entitled "Low Residence Tlme Solid-Gas Separation Device and System"
sAcKGRouND OF INVENTION
Chemical reaction systems utilizing solidsincontactwith 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 second 8 .
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 begins 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 li'7~0 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 phase 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 ~ ~'7~
product drawoffs on the inside surface of the conduit to separate solids from the gas phase by centrifugal 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 drawoffs which are spaced along the 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's 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. ~hile 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 , ..
:1.1'7~8~0 from the solid particles. 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 i5 the limitation on scale-up to commercial size. As conduit diameter increases the path traveled by the mixed phase stream increases proportionately so that large diameter units have separator residence times approach-ing 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 solid gas stream flow-ing 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 do not change direction while the gas phase changes direction relative to the 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 1.~718~0 separators of the prior art are illusory because of limitations in their efficiency, operable range, and scale-up potential.
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.
According to one broad aspect, the present invention relates to a solids-gas separator for effecting rapid reliable removal of particulate solids from a dilute mixed phase stream of solids and gas, said separator comprising an elongated chamber for disengaging solids from the incoming mixed phase stream, said elongated chamber including first and second opposed ends, and an elongated peripheral shell having opposed top and bottom portions, said chamber further comprising: a mixed phase inlet extending through the top portion of the peripheral shell of said chamber adjacent said first end of said chamber and perpendicular to the longitudinal axis thereof, said mixed phase inlet being of generally circular cross section with an inside diameter of Di; a solids phase outlet extending through the bottom portion of the peripheral shell of said chamber adjacent the second end of said chamber, said solids phase outlet being generally perpendicular to the longitudinal axis of said chamber and generally parallel to said mixed phase inlet, said solids phase outlet being aligned for down flow of discharged solids by gravity; a gas outlet extending through the top portion of the peripheral shell of said chamber and parallel to said mixed phase inlet said gas outlet being disposed intermediate said mixed phase inlet.and said solids outlet, and at a distance from said mixed phase inlet which is no greater than 4.0 Di as measured between their respective center lines; and a flow path extending 18~0 generally parallel to the longitudinal axis of said chamber between the first and second ends th reof, said flow path being in communication with said mixed phase inlet, said solids outlet and said gas outlet, said flow path being essentially rectangular in cross section and having a height equal to at least Di or 4 inches, whichever is greater, and a width between 0.75 Di and 1.25 Di, said flow path including a static bed accummulation area adjacent the bottom portion of said peripheral shell and extending from said first end of said chamber to said solids outlet such that when said mixed phase stream is directed through said mixed phase inlet the gas included therein will undergo a 180 change in direction to be removed from said chamber through said gas outlet and such that the solids in said mixed phase stream will form a generally arcuate static bed in said static bed accummulation area of said chamber, whereby the solids in said mixed phase stream will impinge upon said static bed as said solids are directed towards said solids phase outlet thereby minimizing erosion of said chamber by said solids .
According to another broad aspect, the present invention relates to 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 p.hase 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 ~,..~
~ '7:l.8~0 inside width Di, a gas outlet, and a solids outlet, said inlet being at one end of the chamber disposed normal to the flow path whose height H is equal to at least Di or 4 inches, whichever is greater, and whose width W is no less than 0.75 Di but no more than 1.25 Di, said solids outlet being at the opposite end of the chamber and being aligned for downflow of discharged solids by gravity, said solids outlet including a first section which is collinear with the flow path and a second section normal to said first section and aligned for downflow of solids by gravity, said first section further being stepped away from a wall of the chamber opposite the mixed phase inlet, and said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet at a distance no greater than 4 Di 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 said wall of the chamber opposite to the inlet forming thereat and maintaining an essentially static bed of solids, the surface of the bed defining a curvilinear path extending through a generally circular arc of approximately 90 for the outflow of solids to the solids outlet, a secondary solids-gas separator in communication with said gas outlet, said secondary separator removing essentially all of the residual solids, a vessel in communication with said solids outlet and said secondary separator, said vessel receiving the discharg~ of solids from said chamber and said secondary separator, and pressure balance means to maintain a height of solids in said vessel to provide a positive seal between the chamber and the vessel.
i`"~.
~ 1'71BQ() 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 alternative geometic configuration of the separator shell.
FIGURE S 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.
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.
~i'7~0 FIGURE 7 iS a s]cetch oE 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.
DESCRIPTION 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 ll 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. Depend-ing upon the nature of the process 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. ~uench material should be introduced in line 15 in a way that precludes back flow of quench material to the separator. The residual solids are 18~0 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 down-stream 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 severely degraded by remaining in intimate contact with the solid phase. This is accomplished 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 sectional elevational view showing the preferred embodiment of solids-gas separation device 14 of the present invention. The separator 14 is provided witn a separator '' i ; ' ~ ' : ., ~71~3~0 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 maintenance 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 resistent linings 38, 39 and 41 respectively which may be required if solids at high velocities are encountered. Typical commercially available materials for erosion resistent 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 resistent linings when the separator is to be used in high temperature service.
Thus, process temperatures above 1500F. (870C.) are not inconsist-ent 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 as pipe 50, although otner 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 throuyh the separator is essentially rectangular in cross section having a height H and width W as shown in FIG~R~ 3. The embodiment shown in FIGURE 3 de-fines the geometry of the flow path by adjustment of the lining width *Trademarks ' 1 8~0 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 tne separation sbell 37 is fabricat-ed 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 resistence respectively.
Again referring to FIGURE 2, inlet 32 and outlets 33 and 34 are disposed normal to flow path 31A (shown in FIGURE 3) so that the incoming mixed phase stream from inlet 32 is required to under-go 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 aompleted a 180 change in direction.
Centrigugal 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 form in a surface configuration having a curvilinear arc 43. 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 o~ the arc 43 is detcrmined by thc geomctry of the particular separator and the inlet stream parameters such as velocity, mass flowrate, bulk density, and particle size. Because , . ... . .
~ ~'7~ ~ V
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 hign inlet velocities, up to 150 ft./sec., and the separator 14 is operable over a wide range of dilute phase densities, preferably between 0.1 and 10.0 lbs./ft3. The separ;ator 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, and more particularly, the flow path must be essentially rectangular, and there is an optimum relationship between the 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 Di of inlet 32, the preferred distance CL between the centerlines of inlet 32 and outlet 33 is not greater than 4.0 Di, while the most preferred distance between said centerlines isbetween 1.5 and 2.5 Di. Below 1.5 Di better separation is obtained but difficulty in fabrication makes this embodiment less attractive in most instances. Should this latter embodiment be desired, the , . . .
- ~'71~
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 or 4 inches in height, whic7never is greater. Practice teaches that if H is less than Di or 4 inches the incoming stream is apt to disturb the bed solids 42 thereby re-entraining solids in the gas product leaving through outlet 33.
Preferably H is on the order of twice Di 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 Di, most preferably between 0.9 and 1.10 Di.
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 heiyht 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 '~etween the stripping vessel 22 and the separator 14 is determined by the force required to move the solids in bul~ 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 , .
, t'718~0 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 checi~ or "flapper"
valve 29 at the outlet of line 16, or a pressure control valve 29a in vapor line 24. The pressure may be regulated by selecting 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 stripper 22.
While such gas 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, residence times as low as 0.1 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. More particularly, radii extending from opposed ends of the curvilinear arc 43 would be angularly separate~ from one another by 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. With-out the weir 44 an arc somewhat less than or equal to 90 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 strip-ping 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 the gas outlet 33 and the weir 44 is extended to establish a solids bed of greater length L is preferably less than or equal to 5 Di. Although the gas flow pattern 61 does not develop the preferred U-shape, a crescent shaped arc is obtained which limits erosion potential to area 64. Embodi-ments shown by FIGURES 5 and 6 are useful when the solids loading of the incoming stream is low. The emoodiment of FIGURE 5 also nas 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 possible to use a stepped solids outlet 65 having a section 66 collinear with the t~O
flow path as well as a gravity flow section 67. Wall 68 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 deaeration 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 plate, or an equivalent flow restriction device as shown in FIGURE 9. The venturi 69 having dimensions DV
(diameter at venturi inlet), DVt (diameter of venturi throat), and e (angle of cone formed by projection of convergent verturi walls) is placed in the collinear section 66 of the outlet 65 to greatly improved deaeration of solids. The embodiment of FIGURE 10 is a variation of the separator shown in FIGURE 9. Here, inlet 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. ~s before the gas portion of the feed follows the ~-shaped pattern of line 45.
However, an asymptotic bed will be formed unless there is a restric-tion in the solids outlet. A weir would be ineffective in establish-~,_~,.......
7~E~q~O
ing bed height, an~ 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 66 as shown in FIGURE 10 to improve the deaeration 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 in the various drawing figures and listed in the Nomenclature below:
CL Distance between inlet and gas outlet centerlines Di Inside diameter of inlet Dog Inside diameter of gas outlet Do6 Inside diameter of solids outlet Dv Diameter of venturi inlet Dvt Diameter of venturi throat H Height of flow path Hw Height of weir or step L Length from gas outlet to weir or step as indicated in Figure 6 W Width of flow path e Angle of cone formed by projection of convergent venturi walls, degrees . ~
-` ~ 1'7~0 Table I
Dimensions of Separators in Examples l to 10 inches*
Example Dimension 1 2 3 4 5 6 7 8 9 10 3.875 3.875 3.875 3.875- 5.875 5.875 - 11 3.5 3.5 Di 2 . 2 2 2 2 2 6 6 2 2 Dog 1.75 1.751.75 1.75 1.75 1.75 4 4 1 1 D L ~ 2 2 2 2 ~ 6 6 2 ~ ~
H 4 4 4 4 4 4 12 12 7.5 6.75 Hw 0 75 0.75 0.75 0.75 0.75 0.75 2.25 2.25 0 4.75 e, degress _ _ _ _ _ _ _ _ _ 2~.1 * except as noted 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 tne 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 stream density was 0.612 lbs./ft.3 and the operation was performed at ambient temper-ature 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 lnch 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 O.Q08 seconds. Efficiency is defined as the percent removal of solids from the inlet stream.
Example 2 The gas-solids mixture of Example 1 was processed 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 lon~er and turbulence was increased. Separation efficiency ~or 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 approxi-mately twice that of Example 2. Separation efficiency improved to 83.8%.
Example 4 The preferred separator of Example lwas tested at the inlet flow rate of Example 3. Efficiency increased slightly to '"'''' ' .
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~.~7~8~
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 Dl. Residence time increased to 0.01 seconds, while efficiency was 73.0~.
Example 6 Same conditions apply as for Example 5 except that the solids loading was increased to 102 lbs./min. to give a stream density of 1.18 lbs./ft.3. As observed previously in Examples 3 and 4, the separator efficiency increased with higher solids loading to 90.6~.
Example 7 The preferred separator configurtion 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 180F. 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 stabilized by a 2.25 inch weir, and gas loss was prevented by a positive seal of solids.
. ~ .
'718~0 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.3/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 ~ was tested in a unit having a
sAcKGRouND OF INVENTION
Chemical reaction systems utilizing solidsincontactwith 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 second 8 .
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 begins 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 li'7~0 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 phase 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 ~ ~'7~
product drawoffs on the inside surface of the conduit to separate solids from the gas phase by centrifugal 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 drawoffs which are spaced along the 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's 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. ~hile 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 , ..
:1.1'7~8~0 from the solid particles. 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 i5 the limitation on scale-up to commercial size. As conduit diameter increases the path traveled by the mixed phase stream increases proportionately so that large diameter units have separator residence times approach-ing 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 solid gas stream flow-ing 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 do not change direction while the gas phase changes direction relative to the 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 1.~718~0 separators of the prior art are illusory because of limitations in their efficiency, operable range, and scale-up potential.
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.
According to one broad aspect, the present invention relates to a solids-gas separator for effecting rapid reliable removal of particulate solids from a dilute mixed phase stream of solids and gas, said separator comprising an elongated chamber for disengaging solids from the incoming mixed phase stream, said elongated chamber including first and second opposed ends, and an elongated peripheral shell having opposed top and bottom portions, said chamber further comprising: a mixed phase inlet extending through the top portion of the peripheral shell of said chamber adjacent said first end of said chamber and perpendicular to the longitudinal axis thereof, said mixed phase inlet being of generally circular cross section with an inside diameter of Di; a solids phase outlet extending through the bottom portion of the peripheral shell of said chamber adjacent the second end of said chamber, said solids phase outlet being generally perpendicular to the longitudinal axis of said chamber and generally parallel to said mixed phase inlet, said solids phase outlet being aligned for down flow of discharged solids by gravity; a gas outlet extending through the top portion of the peripheral shell of said chamber and parallel to said mixed phase inlet said gas outlet being disposed intermediate said mixed phase inlet.and said solids outlet, and at a distance from said mixed phase inlet which is no greater than 4.0 Di as measured between their respective center lines; and a flow path extending 18~0 generally parallel to the longitudinal axis of said chamber between the first and second ends th reof, said flow path being in communication with said mixed phase inlet, said solids outlet and said gas outlet, said flow path being essentially rectangular in cross section and having a height equal to at least Di or 4 inches, whichever is greater, and a width between 0.75 Di and 1.25 Di, said flow path including a static bed accummulation area adjacent the bottom portion of said peripheral shell and extending from said first end of said chamber to said solids outlet such that when said mixed phase stream is directed through said mixed phase inlet the gas included therein will undergo a 180 change in direction to be removed from said chamber through said gas outlet and such that the solids in said mixed phase stream will form a generally arcuate static bed in said static bed accummulation area of said chamber, whereby the solids in said mixed phase stream will impinge upon said static bed as said solids are directed towards said solids phase outlet thereby minimizing erosion of said chamber by said solids .
According to another broad aspect, the present invention relates to 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 p.hase 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 ~,..~
~ '7:l.8~0 inside width Di, a gas outlet, and a solids outlet, said inlet being at one end of the chamber disposed normal to the flow path whose height H is equal to at least Di or 4 inches, whichever is greater, and whose width W is no less than 0.75 Di but no more than 1.25 Di, said solids outlet being at the opposite end of the chamber and being aligned for downflow of discharged solids by gravity, said solids outlet including a first section which is collinear with the flow path and a second section normal to said first section and aligned for downflow of solids by gravity, said first section further being stepped away from a wall of the chamber opposite the mixed phase inlet, and said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet at a distance no greater than 4 Di 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 said wall of the chamber opposite to the inlet forming thereat and maintaining an essentially static bed of solids, the surface of the bed defining a curvilinear path extending through a generally circular arc of approximately 90 for the outflow of solids to the solids outlet, a secondary solids-gas separator in communication with said gas outlet, said secondary separator removing essentially all of the residual solids, a vessel in communication with said solids outlet and said secondary separator, said vessel receiving the discharg~ of solids from said chamber and said secondary separator, and pressure balance means to maintain a height of solids in said vessel to provide a positive seal between the chamber and the vessel.
i`"~.
~ 1'71BQ() 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 alternative geometic configuration of the separator shell.
FIGURE S 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.
-7a-a"~ ~.
.
~i'7~0 FIGURE 7 iS a s]cetch oE 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.
DESCRIPTION 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 ll 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. Depend-ing upon the nature of the process 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. ~uench material should be introduced in line 15 in a way that precludes back flow of quench material to the separator. The residual solids are 18~0 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 down-stream 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 severely degraded by remaining in intimate contact with the solid phase. This is accomplished 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 sectional elevational view showing the preferred embodiment of solids-gas separation device 14 of the present invention. The separator 14 is provided witn a separator '' i ; ' ~ ' : ., ~71~3~0 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 maintenance 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 resistent linings 38, 39 and 41 respectively which may be required if solids at high velocities are encountered. Typical commercially available materials for erosion resistent 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 resistent linings when the separator is to be used in high temperature service.
Thus, process temperatures above 1500F. (870C.) are not inconsist-ent 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 as pipe 50, although otner 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 throuyh the separator is essentially rectangular in cross section having a height H and width W as shown in FIG~R~ 3. The embodiment shown in FIGURE 3 de-fines the geometry of the flow path by adjustment of the lining width *Trademarks ' 1 8~0 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 tne separation sbell 37 is fabricat-ed 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 resistence respectively.
Again referring to FIGURE 2, inlet 32 and outlets 33 and 34 are disposed normal to flow path 31A (shown in FIGURE 3) so that the incoming mixed phase stream from inlet 32 is required to under-go 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 aompleted a 180 change in direction.
Centrigugal 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 form in a surface configuration having a curvilinear arc 43. 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 o~ the arc 43 is detcrmined by thc geomctry of the particular separator and the inlet stream parameters such as velocity, mass flowrate, bulk density, and particle size. Because , . ... . .
~ ~'7~ ~ V
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 hign inlet velocities, up to 150 ft./sec., and the separator 14 is operable over a wide range of dilute phase densities, preferably between 0.1 and 10.0 lbs./ft3. The separ;ator 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, and more particularly, the flow path must be essentially rectangular, and there is an optimum relationship between the 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 Di of inlet 32, the preferred distance CL between the centerlines of inlet 32 and outlet 33 is not greater than 4.0 Di, while the most preferred distance between said centerlines isbetween 1.5 and 2.5 Di. Below 1.5 Di better separation is obtained but difficulty in fabrication makes this embodiment less attractive in most instances. Should this latter embodiment be desired, the , . . .
- ~'71~
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 or 4 inches in height, whic7never is greater. Practice teaches that if H is less than Di or 4 inches the incoming stream is apt to disturb the bed solids 42 thereby re-entraining solids in the gas product leaving through outlet 33.
Preferably H is on the order of twice Di 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 Di, most preferably between 0.9 and 1.10 Di.
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 heiyht 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 '~etween the stripping vessel 22 and the separator 14 is determined by the force required to move the solids in bul~ 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 , .
, t'718~0 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 checi~ or "flapper"
valve 29 at the outlet of line 16, or a pressure control valve 29a in vapor line 24. The pressure may be regulated by selecting 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 stripper 22.
While such gas 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, residence times as low as 0.1 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. More particularly, radii extending from opposed ends of the curvilinear arc 43 would be angularly separate~ from one another by 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. With-out the weir 44 an arc somewhat less than or equal to 90 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 strip-ping 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 the gas outlet 33 and the weir 44 is extended to establish a solids bed of greater length L is preferably less than or equal to 5 Di. Although the gas flow pattern 61 does not develop the preferred U-shape, a crescent shaped arc is obtained which limits erosion potential to area 64. Embodi-ments shown by FIGURES 5 and 6 are useful when the solids loading of the incoming stream is low. The emoodiment of FIGURE 5 also nas 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 possible to use a stepped solids outlet 65 having a section 66 collinear with the t~O
flow path as well as a gravity flow section 67. Wall 68 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 deaeration 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 plate, or an equivalent flow restriction device as shown in FIGURE 9. The venturi 69 having dimensions DV
(diameter at venturi inlet), DVt (diameter of venturi throat), and e (angle of cone formed by projection of convergent verturi walls) is placed in the collinear section 66 of the outlet 65 to greatly improved deaeration of solids. The embodiment of FIGURE 10 is a variation of the separator shown in FIGURE 9. Here, inlet 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. ~s before the gas portion of the feed follows the ~-shaped pattern of line 45.
However, an asymptotic bed will be formed unless there is a restric-tion in the solids outlet. A weir would be ineffective in establish-~,_~,.......
7~E~q~O
ing bed height, an~ 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 66 as shown in FIGURE 10 to improve the deaeration 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 in the various drawing figures and listed in the Nomenclature below:
CL Distance between inlet and gas outlet centerlines Di Inside diameter of inlet Dog Inside diameter of gas outlet Do6 Inside diameter of solids outlet Dv Diameter of venturi inlet Dvt Diameter of venturi throat H Height of flow path Hw Height of weir or step L Length from gas outlet to weir or step as indicated in Figure 6 W Width of flow path e Angle of cone formed by projection of convergent venturi walls, degrees . ~
-` ~ 1'7~0 Table I
Dimensions of Separators in Examples l to 10 inches*
Example Dimension 1 2 3 4 5 6 7 8 9 10 3.875 3.875 3.875 3.875- 5.875 5.875 - 11 3.5 3.5 Di 2 . 2 2 2 2 2 6 6 2 2 Dog 1.75 1.751.75 1.75 1.75 1.75 4 4 1 1 D L ~ 2 2 2 2 ~ 6 6 2 ~ ~
H 4 4 4 4 4 4 12 12 7.5 6.75 Hw 0 75 0.75 0.75 0.75 0.75 0.75 2.25 2.25 0 4.75 e, degress _ _ _ _ _ _ _ _ _ 2~.1 * except as noted 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 tne 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 stream density was 0.612 lbs./ft.3 and the operation was performed at ambient temper-ature 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 lnch 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 O.Q08 seconds. Efficiency is defined as the percent removal of solids from the inlet stream.
Example 2 The gas-solids mixture of Example 1 was processed 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 lon~er and turbulence was increased. Separation efficiency ~or 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 approxi-mately twice that of Example 2. Separation efficiency improved to 83.8%.
Example 4 The preferred separator of Example lwas tested at the inlet flow rate of Example 3. Efficiency increased slightly to '"'''' ' .
' ~
~.~7~8~
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 Dl. Residence time increased to 0.01 seconds, while efficiency was 73.0~.
Example 6 Same conditions apply as for Example 5 except that the solids loading was increased to 102 lbs./min. to give a stream density of 1.18 lbs./ft.3. As observed previously in Examples 3 and 4, the separator efficiency increased with higher solids loading to 90.6~.
Example 7 The preferred separator configurtion 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 180F. 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 stabilized by a 2.25 inch weir, and gas loss was prevented by a positive seal of solids.
. ~ .
'718~0 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.3/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 ~ 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 ~S ft.3/min. of air and 105 lbs./min. of spent fluid catalytic cracker catalyst having a bulk density of 45 lbs./ft.3 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 vessel to the separator. Thi5 flow was approximately 1.7 ft.3/min.
at a velocity of 1.3 ft./sec. Operation was at ambient temperature :
., ' .
O
and atmospheric pressure. Separator efficiency was 95.0%.
Example lO
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 l 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 measured, and the solids leaving the separator were completely deaerated except for interstitial gas remaining in the solids' voids.
at a velocity of 1.3 ft./sec. Operation was at ambient temperature :
., ' .
O
and atmospheric pressure. Separator efficiency was 95.0%.
Example lO
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 l 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 measured, and the solids leaving the separator were completely deaerated except for interstitial gas remaining in the solids' voids.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A solids-gas separator for effecting rapid reliable removal of particulate solids from a dilute mixed phase stream of solids and gas, said separator comprising an elongated chamber for disengaging solids from the incoming mixed phase stream, said elongated chamber including first and second opposed ends, and an elongated peripheral shell having opposed top and bottom portions, said chamber further comprising:
a mixed phase inlet extending through the top portion of the peripheral shell of said chamber adjacent said first end of said chamber and perpendicular to the longitudinal axis thereof, said mixed phase inlet being of generally circular cross section with an inside diameter of Di;
a solids phase outlet extending through the bottom portion of the peripheral shell of said chamber adjacent the second end of said chamber, said solids phase outlet being generally perpendicular to the longitudinal axis of said chamber and generally parallel to said mixed phase inlet, said solids phase outlet being aligned for down flow of discharged solids by gravity;
a gas outlet extending through the top portion of the peripheral shell of said chamber and parallel to said mixed phase inlet said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet, and at a distance from said mixed phase inlet which is no greater than 4.0 Di as measured between their respective center lines; and a flow path extending generally parallel to the longitudinal axis of said chamber between the first and second ends thereof, said flow path being in communication with said mixed phase inlet, said solids outlet and said gas outlet, said flow path being essentially rectangular in cross section and having a height equal to at least Di or 4 inches, whichever is greater, and a width between 0.75 Di and 1.25 Di, said flow path including a static bed accummulation area adjacent the bottom portion of said peripheral shell and extending from said first end of: said chamber to said solids outlet such that when said mixed phase stream is directed through said mixed phase inlet the gas included therein will undergo a 180° change in direction to be removed from said chamber through said gas outlet and such that the solids in said mixed phase stream will form a generally arcuate static bed in said static bed accummulation area of said chamber, whereby the solids in said mixed phase stream will impinge upon said static bed as said solids are directed towards said solids phase outlet thereby minimizing erosion of said chamber by said solids.
a mixed phase inlet extending through the top portion of the peripheral shell of said chamber adjacent said first end of said chamber and perpendicular to the longitudinal axis thereof, said mixed phase inlet being of generally circular cross section with an inside diameter of Di;
a solids phase outlet extending through the bottom portion of the peripheral shell of said chamber adjacent the second end of said chamber, said solids phase outlet being generally perpendicular to the longitudinal axis of said chamber and generally parallel to said mixed phase inlet, said solids phase outlet being aligned for down flow of discharged solids by gravity;
a gas outlet extending through the top portion of the peripheral shell of said chamber and parallel to said mixed phase inlet said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet, and at a distance from said mixed phase inlet which is no greater than 4.0 Di as measured between their respective center lines; and a flow path extending generally parallel to the longitudinal axis of said chamber between the first and second ends thereof, said flow path being in communication with said mixed phase inlet, said solids outlet and said gas outlet, said flow path being essentially rectangular in cross section and having a height equal to at least Di or 4 inches, whichever is greater, and a width between 0.75 Di and 1.25 Di, said flow path including a static bed accummulation area adjacent the bottom portion of said peripheral shell and extending from said first end of: said chamber to said solids outlet such that when said mixed phase stream is directed through said mixed phase inlet the gas included therein will undergo a 180° change in direction to be removed from said chamber through said gas outlet and such that the solids in said mixed phase stream will form a generally arcuate static bed in said static bed accummulation area of said chamber, whereby the solids in said mixed phase stream will impinge upon said static bed as said solids are directed towards said solids phase outlet thereby minimizing erosion of said chamber by said solids.
2. A separator as in claim 1 wherein said elongated peripheral shell is generally cylindrical, and wherein the essentially rectangular cross section of said flow path is provided by structural means fixedly mounted in said chamber.
3. A separator as in claim 2 wherein said structural means comprises an erosion resistant lining.
4. A separator as in claim 3, wherein said structural means further comprises a weir mounted adjacent said solids outlet and intermediate said solids outlet and said gas outlet.
5. A separator as in claim 3 wherein said structural means further comprises at least one generally planar member fixedly mounted to said peripheral shell and aligned generally perpendicular to the longitudinal axis of said chamber.
6. A separator as in claim 1 wherein said solids outlet further includes a section aligned generally parallel to the longitudinal axis of said chamber and collinear with said flow path.
7. The separator of claim 1 wherein the longitudinal distance between said gas and solids outlets is less than or equal to 5 Di.
8. The separator of claim 6 further comprised of a flow restriction placed within the collinear section of the solids removal outlet
9. The separator of claim 8 wherein the flow restriction is an orifice of smaller cross sectional area than said flow path.
10. The separator of claim 8 wherein the flow restriction is a venturi.
11. The separator of claim 1 further comprised of a clean-out manway on one or both ends of the separator chamber.
12. 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 Di, a gas outlet, and a solids outlet, said inlet being at one end of the chamber disposed normal to the flow path whose height H is equal to at least Di or 4 inches, whichever is greater, and whose width W is no less than 0.75 Di but no more than 1.25 Di, said solids outlet being at the opposite end of the chamber and being aligned for downflow of discharged solids by gravity, said solids outlet including a first section which is collinear with the flow path and a second section normal to said first section and aligned for downflow of solids by gravity, said first section further being stepped away from a wall of the chamber opposite the mixed phase inlet, and said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet at a distance no greater than 4 Di 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 said wall of the chamber opposite to the inlet forming thereat and maintaining an essentially static bed of solids, the surface of the bed defining a curvilinear path extending through a generally circular arc of approximately 90° for the outflow of solids to the solids outlet, a secondary solids-gas separator in communication with said gas outlet, said secondary separator removing essentially all of the residual solids, a vessel in communication with said solids outlet and said secondary separator, said vessel receiving the discharge of solids from said chamber and said secondary separator, and pressure balance means to maintain a height of solids in said vessel to provide a positive seal between the chamber and the vessel.
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 Di, a gas outlet, and a solids outlet, said inlet being at one end of the chamber disposed normal to the flow path whose height H is equal to at least Di or 4 inches, whichever is greater, and whose width W is no less than 0.75 Di but no more than 1.25 Di, said solids outlet being at the opposite end of the chamber and being aligned for downflow of discharged solids by gravity, said solids outlet including a first section which is collinear with the flow path and a second section normal to said first section and aligned for downflow of solids by gravity, said first section further being stepped away from a wall of the chamber opposite the mixed phase inlet, and said gas outlet being disposed intermediate said mixed phase inlet and said solids outlet at a distance no greater than 4 Di 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 said wall of the chamber opposite to the inlet forming thereat and maintaining an essentially static bed of solids, the surface of the bed defining a curvilinear path extending through a generally circular arc of approximately 90° for the outflow of solids to the solids outlet, a secondary solids-gas separator in communication with said gas outlet, said secondary separator removing essentially all of the residual solids, a vessel in communication with said solids outlet and said secondary separator, said vessel receiving the discharge of solids from said chamber and said secondary separator, and pressure balance means to maintain a height of solids in said vessel to provide a positive seal between the chamber and the vessel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000421773A CA1171800A (en) | 1979-07-06 | 1983-02-16 | Low residence time solid-gas separation device and system |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55,148 | 1979-07-06 | ||
| US06/055,148 US4288235A (en) | 1979-07-06 | 1979-07-06 | Low residence time solid-gas separation device and system |
| CA000355416A CA1151084A (en) | 1979-07-06 | 1980-07-04 | Low residence time solid-gas separation device and system |
| CA000421773A CA1171800A (en) | 1979-07-06 | 1983-02-16 | Low residence time solid-gas separation device and system |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000355416A Division CA1151084A (en) | 1979-07-06 | 1980-07-04 | Low residence time solid-gas separation device and system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1171800A true CA1171800A (en) | 1984-07-31 |
Family
ID=27166733
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000421773A Expired CA1171800A (en) | 1979-07-06 | 1983-02-16 | Low residence time solid-gas separation device and system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1171800A (en) |
-
1983
- 1983-02-16 CA CA000421773A patent/CA1171800A/en not_active Expired
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| MKEX | Expiry |