Abstract:
A bulk granular solids gravity flow curing vessel comprises an upper curing unit having a top opening for receiving particulate solids, a lower curing unit coupled to receive particulate solids from the upper curing unit, and at least one of the upper and lower curing units including a first intermediate section having substantially vertical sidewalls, a first hopper positioned to receive the particulate solids from the intermediate section, and a first velocity adjustment means positioned in the intermediate section and/or the first hopper. A bulk granular solids gravity flow curing vessel comprising a first section having substantially vertical sidewalls, a first hopper positioned to receive particulate solids from the first section, and a first velocity adjustment means positioned in the first section is also described. A bulk granular solids gravity flow curing vessels comprising a first section having substantially vertical sidewalls, a first velocity adjustment means positioned in the first section and having non-vertical sidewalls, a second section having non-vertical sidewalls, second velocity adjustment means positioned in the second section and having substantially vertical sidewalls is further described.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/329,898, filed Oct. 16, 2001. 
     
    
     
       BACKGROUND INFORMATION  
         [0002]    When bulk granular solids, such as aggregates, sugars, salts, chlorine compounds, polymers, or other materials that contain liquid soluble or reactive components are formed, they often tend to stick together. To prevent this sticking, the bulk solids are exposed to a curing atmosphere for several minutes or hours to condition the surface of the granules. This process usually requires storage in a confined space so as to control the curing conditions. A curing vessel is ideal for such curing provided that there is some slight inter-particle motion during the curing time to prevent sticking. A curing vessel is most efficient if the retention time of particles entering the vessel at the same time is about the same for all the particles. Inter-particle motion is difficult to maintain in a batch process, and the most efficient methods use a continuous moving bed process.  
           [0003]    Current methods for curing bulk granular solids include belt, vibratory, and screw conveyors, and various mixers such as tumble blenders, rotary cylinders, ribbon blenders, and plow blenders. All these tend to degrade the particles and produce fines. They also have limited low production rates. The most effective, most energy efficient, least particle degrading, high capacity curing vessel is one using continuous gravity flow of a contact bed. Current designs for contact bed gravity flow vessels neglect one or more of the following preferred conditions: (a) bulk solids contact pressure is preferably kept below the crushing pressure for the particles; (b) inter-particle motion between particles preferably occurs sufficiently to keep the particles from sticking; (c) retention time of the vessel is preferably about the same for all the particles; and (d) there are preferably no non-flowing regions in the vessel.  
           [0004]    There is a need for a bulk solids curing vessel that can be configured to address these preferred conditions.  
         SUMMARY OF THE INVENTION  
         [0005]    A bulk granular solids gravity flow curing vessel comprises an upper curing unit having a top opening for receiving particulate solids, a lower curing unit coupled to receive particulate solids from the upper curing unit, and at least one of the upper and lower curing units including a first intermediate section having substantially vertical sidewalls, a first hopper positioned to receive the particulate solids from the intermediate section, and a first velocity adjustment means positioned in the intermediate section and/or the first hopper.  
           [0006]    At least one of the upper and lower curing units can include a conical bin, wherein the first velocity adjustment means comprises a central insert positioned along a central axis of the bin. The central insert can comprise a rod positioned along the central axis of the bin, and a plurality of plates spaced along the rod and lying in planes that are perpendicular to the axis. The central insert can further comprise a plurality of cones and/or cylinders, each of the cones and/or cylinders having a base positioned adjacent to one of the plates.  
           [0007]    A second one of the upper and lower curing units can include a second intermediate section having substantially vertical sidewalls, a second hopper positioned to receive the particulate solids from the intermediate section, and a second velocity adjustment means positioned in the intermediate section and/or the first hopper. The second velocity adjustment insert can include a hollow cylinder that can be positioned to extend into the second hopper. The diameter of the hollow cylinder can be approximately one half of the diameter of the second intermediate section.  
           [0008]    The second velocity adjustment insert can alternatively comprise a horizontal flat plat. The second velocity adjustment insert can further comprise an upper extension and/or a lower extension.  
           [0009]    The first velocity adjustment means can comprise a central insert positioned along a central axis of the upper curing unit. The upper curing unit can comprise a frusto-conical bin. The central insert can comprise a rod positioned along the central axis of the bin, and a plurality of plates spaced along the rod and lying in planes that are perpendicular to the central axis. The central insert can further comprise a plurality of cones and/or cylinders, each of the cones and/or cylinders having a base positioned adjacent to one of the plates. The upper curing unit can alternatively comprise a plurality of frustum and cylindrical sections.  
           [0010]    A second velocity adjustment insert can be positioned in the lower curing unit. The second velocity adjustment insert can comprise a hollow cylinder or a horizontal flat plat. Upper and lower extensions can be connected to the plate.  
           [0011]    The upper curing unit can comprise one or more conical sections having a convergence angle of less than 10 degrees from vertical. The first hopper can comprise a one-dimensional converge racetrack hopper. A plurality of additional one-dimensional converge racetrack hoppers can be coupled to the first hopper. A vertically adjustable cylinder can coupled to the bottom of each of the one-dimensional converge racetrack hoppers.  
           [0012]    The invention also encompasses bulk granular solids gravity flow curing vessels comprising a first section having substantially vertical sidewalls, a first hopper positioned to receive particulate solids from the first section, and a first velocity adjustment means positioned in the first section.  
           [0013]    The invention further encompasses bulk granular solids gravity flow curing vessels comprising a first section having substantially vertical sidewalls, a first velocity adjustment means positioned in the first section and having non-vertical sidewalls, a second section having non-vertical sidewalls, second velocity adjustment means positioned in the second section and having substantially vertical sidewalls. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0014]    [0014]FIGS. 1A, 1B and  1 C are front, side and top views of a curing vessel constructed in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIGS. 2A, 2B,  2 C,  2 D and  2 E are various views of a conical shaped upper curing unit of the curing vessel;  
         [0016]    [0016]FIGS. 3A, 3B and  3 C are front, top and side views of an embodiment of the lower curing unit with multiple outlets;  
         [0017]    [0017]FIGS. 4A, 4B and  4 C are front, top and side views of the one-dimensional racetrack shaped cross-section curing unit hopper with a single outlet;  
         [0018]    [0018]FIGS. 5A, 5B and  5 C are front, top and side views of the upper portion of the one-dimensional convergence racetrack shaped hopper including a flow adjusting insert;  
         [0019]    [0019]FIGS. 6A, 6B and  6 C are front, top and side views of the upper portion of the hopper showing the insert extending upward;  
         [0020]    [0020]FIGS. 7A, 7B and  7 C are front, top and side views of the upper portion of the hopper showing the insert extending downward;  
         [0021]    [0021]FIGS. 8A, 8B and  8 C are front, top and side views of the upper portion of the hopper showing the insert extending both upward and upward;  
         [0022]    [0022]FIGS. 9A and 9B are top and side views of an alternative conical and cylindrical shaped curing unit and associated insert; and  
         [0023]    [0023]FIGS. 10A, 10B, and  10 C, are front, top and side views of a curing vessel including multiple features of the invention in combination. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    This invention provides a bulk solids vessel comprising an essentially vertical upper and converging lower section that limits solids contact pressure on bulk granular solids passing through it to less than the bulk crushing pressure of the granules and provides a means for introducing inter-particle motion sufficient to prevent particle sticking. The difference in retention time of any two particles introduced into the vessel is generally within plus or minus approximately 30% of the average retention time of all the particles in the vessel, and the vessel wall can be steep enough and of such a shape that there are no non-flowing regions in the vessel.  
         [0025]    [0025]FIGS. 1A, 1B and  1 C are front, side and top views of a curing vessel constructed in accordance with the present invention. A chute  1  or other means for introducing the particulate solids  2  continuously into the curing vessel is positioned at the top of the vessel. In the embodiment of FIGS. 1A, 1B and  1 C, the upper curing unit includes four conical bins  3 , each having a short vertical section  4  and a slightly converging frusto-conical portion, or cone  5 . Alternatively, the curing vessel could be constructed using a single one of these bins. However, the use of multiple bins in parallel provides a greater curing capacity without using larger bins that might crush the particles. Central inserts  6  are positioned along a vertical axis of each bin. The addition of an insert  6  to each bin enhances the effectiveness of the vessel by slowing down the granular solids at the center of the bin so that the retention time in the vessel is more uniform. The insert  6  also provides inter-particle motion at the center whereas without the insert, the inter-particle motion may be insufficient to keep the particles from sticking. The outlet  7  of the bin provides the means for feeding the particulate solids to a larger diameter lower curing unit  8 . Since the solids  9  exiting the upper bins have been partially cured, they can withstand the higher pressures associated with the larger lower curing unit  8 . The lower curing unit  8  includes an intermediate section  10  and a hopper  11 . The intermediate section  10  of the lower curing unit  8  can be a vertical cylinder or a slightly converging cone. Preferably, the outer shell of the intermediate section is a conical frustum with a convergence angle from top to bottom of no more than approximately 10 degrees from the vertical and where such angle  0 , the top diameter D, and the flow rate Q are selected so that the slowest average volumetric strain rate VSR as given by:  
           VSR= 4 TAN(θ) Q /(π D   3 /4)  
         [0026]    exceeds that required as determined experimentally to prevent the particles from sticking to each other.  
         [0027]    The vertical section  4  of the upper curing unit has a height H that preferably does not exceed half of its diameter and the diameter times the bulk specific weight of the particulate solids does not exceed two times the bulk crush strength of the particulate solids. Preferably, the height H of the vertical section  4  or fill level in the vessel is such that γ H does not exceed the breaking strength of the granular particles, where γ is the bulk specific weight of the granular solid.  
         [0028]    One or more inserts can be used to impose strain between particles flowing in the central core of the conical frustum and to slow down the normally faster flow in the conical frustum region. The inserts may also extend upward or downward or both along the axis of the vessel so as to form a conical shape. Preferably, the area of the insert in a horizontal plane, perpendicular to the solids flow direction, is between approximately 1% and 20% of the cross-sectional area of the conical frustum in a plane perpendicular to the direction of solids flow at the level of the insert.  
         [0029]    A slight convergence is useful to limit crushing pressures on particles when the height of the upper portion exceeds half of its diameter. The curing vessel would need to be extremely high if a conical hopper were used. Instead of a cone, a much flatter one-dimensional converge race track cross-section hopper  11  is used to reduce the headroom. Multiple racetrack shaped one-dimensional convergent hoppers  12  are used to further reduce headroom. The multiple hoppers feed a receiving belt conveyor  13 . Adjustable cylinders  14  can be used to control the outflow of particulates to the belt  13  and add layers  15 ,  16 , and  17  upon each other. The cylinders also provide a quick adjustment for reversing the belt direction simply by changing the relative heights of the outside cylinders  15  and  17  so as to reverse the height of the layers  15  and  17 . The relative layered depths  15 ,  16 , and  17  can also be adjusted to fine tune the inter-particle motion in the vessel.  
         [0030]    In the vessel of FIGS. 1A, 1B and  1 C, the converging outer shell of the hopper can be comprised of racetrack shaped cross-sections arranged such that convergence occurs only in one direction at a time with the walls of the converging portion of the vessel steep being enough to produce flow adjacent to the walls and a nearly uniform flow velocity across the cross-section.  
         [0031]    The inter-particle motion in the converging sections of the hopper is generally provided by the convergence. The inter-particle motion of the particulates in the cylindrical or steep walled intermediate section  10  of the lower curing unit is provided by a flow adjusting insert in the form of an inner-hollow cylinder  18 .  
         [0032]    The lower curing unit and insert can be arranged so as to produce flow at the converging walls around the insert where such flow extends both above and below said insert. Preferably, the horizontal distance between the converging walls and the insert is approximately half the width of the insert in the horizontal direction perpendicular to the axis of the hopper.  
         [0033]    The insert extends upward or downward or both in a racetrack shaped cross-section with a continually decreasing cross-sectional area. Preferably, the top most extension of the insert exceeds the height of the upper hopper section and/or the extension downward protrudes into the lower hopper section. The extension of the insert upward or downward may have essentially vertical sides in regions where the hopper has essentially vertical or slightly diverging sides, and where the lower extension has a sloping section that is steeper than the upper hopper portion of the one-dimensional convergence hopper and less steep than the lower portion of the one-dimensional convergence hopper, and where both slopes are greater than the angle of repose of the particulates  
         [0034]    The insert  18  serves as means for introducing shear in the intermediate vertical section, and preferably extends above the juncture of the converging and vertical section and is adjustable vertically so as to allow the lower edge of the cylinder to extend below the junction of the upper cylinder and the converging sections. The cylinder can be adjusted to provide a somewhat faster but controlled flow in the center of the vessel as well as varying flow velocities in the annular region around the cylinder and between the converging vessel walls. The cylinder can be placed low enough to cause sufficient differential velocities in the flowing material so as to produce a blending of material.  
         [0035]    A lower converging section of the hopper  11  can comprise a multiple outlet one-dimensional racetrack cross-section formed at the top of a lower converging section, a single elongated race track divided into two or more hoppers that first transition to a less elongated race track and then to a circle, or an even less elongated race track less than that at the top.  
         [0036]    The required shear to prevent particle sticking can be accomplished by regulating the feed rate from the multiple outlets so as to produce the required shear strain between particles. Alternatively, the shear strain can be caused by a racetrack shaped insert in the upper converging racetrack section, with the insert lying essentially perpendicular to the axis of the upper converging section.  
         [0037]    [0037]FIGS. 2A, 2B,  2 C,  2 D and  2 E are various views of the conical shaped upper curing unit of the curing vessel. A basic insert shown in FIG. 2A comprises a plurality of flat plates  19  arranged on support rod  20 , held in place by a support  21 . The cross-sectional area of the plates must be sufficient to influence the solids flowing around it. This requires a cross-sectional area  22  (see FIG. 2B) that is between 1% and 20% of the total cross-sectional area  23  (see FIG. 2B) of the conical section in a plane perpendicular to the direction of solids flow at the level of the insert. FIG. 2C shows the addition of cones  24  to the insert, with the cones being oriented to point in a direction opposite the direction of flow of the solids. This prevents buildup of solids on the insert and more clearly defines the region of shear imposed by the insert. The cone also may extend the region of influence upward from a flat plate further than if solids were allowed to build up on the plates  19 . FIG. 2D shows the addition of cones  25  extending below the flat plates. This defines the flow channels and spheres of influence below the plates more precisely than the angle of repose of the particulate solids. FIG. 2E shows the inserts with cones  24  and  25  extending both upward and downward. The upper curing unit can have a retention time sufficient to cure the particulates to a breaking strength sufficient to withstand the larger pressures of the larger lower vessel.  
         [0038]    [0038]FIGS. 3A, 3B and  3 C are front, top and side views of the lower curing unit  8  with multiple outlets. A one-dimensional convergence racetrack shaped cross-section hopper  11 , includes end walls  26  making up the circular part of the racetrack that are vertical or slightly diverging downward with the flat sidewalls  27  converging downward. The hopper horizontal cross-section changes continually from a circular racetrack shape  28  at the top of hopper  11  to the combination of straight sides with circular end sections of a racetrack shape  29 . Multiple additional hoppers  12  have vertical or slightly diverging downward flat sidewalls  30  with the circular end walls  31  converging downward. The cross-section changes continuously from the straight-sided circular ended type racetrack  29  to a circular racetrack ×at the bottom. A transition piece  134  connects the elongated oval-shaped racetrack  29  of the first hopper  11  to the individual oval shaped racetrack sections of the upper parts of the lower hoppers  12 . The racetrack cross-sections of the transition pieces  134  have quarter circular racetrack sections connected to straight sections.  
         [0039]    The vessel of FIGS. 3A, 3B and  3 C includes multiple outlets wherein the means for removing material includes multiple adjustable vertical cylinders ending at various heights above a belt feeder. The cylinder heights increase in the direction of belt movement so as to place one layer of particulates on top of another. The cylinders can be adjustable vertically so as to allow reversal of the belt direction and still provide flow from each of the multiple outlets. Also, the vertical cylinders may be adjusted so as to regulate the particulate flow velocity in the hopper above it and thus control the inter-particle motion between particulates and/or control the relative retention time in the vessel so as to cause blending of the particulates.  
         [0040]    A screw feeder  39  can serve as means for removing particulates from the vessel. A screw feeder with varying shaft diameters can define the removal rate from each of the outlets. Preferably, the pitch of the screw is constant and uniformity of flow velocity at the outlets of the hopper is achieved by a vertical section between the screw inlet and the hopper outlet.  
         [0041]    A hollow cylinder  18  with support rods  34  supported by the top  35  of the vessel can be adjusted so that the lower edge  36  of the cylinder  18  lies below the circular racetrack  28  of the first racetrack shaped hopper  11 . This produces a faster moving central flow channel with somewhat slower flow near the vertical end walls  26  of the hopper  11  and an even slower flow between the hollow cylinder  18  and upper vessel side walls  26  of the hopper  11 . This causes the inter-particle motion necessary to prevent sticking of the particulates. If more inter-particle motion is required to prevent sticking of the particulates or if some degree of blending in time is desired, the cylinder  18  can be adjusted downward by support rods  34 . A screw feeder with varying capacities under each hopper outlet is used to extract the solids from the hoppers. Varying shaft diameters  37 ,  38 , and  39 , which decrease toward the outlet  40 , can provide the required change of screw capacity. The vertical sections  41  between the screw and the hopper outlet  33  provide a uniform velocity at the hopper outlet  33 .  
         [0042]    [0042]FIGS. 4A, 4B and  4 C show a single outlet one-dimensional convergence racetrack shaped cross-sectional hopper  8 ′. FIGS. 4A, 4B and  4 C are the front, top and side views, respectively, of this hopper. This configuration has the advantage of using a single outlet and a much smaller feeder. In the case shown, a single inlet chute  1 ′ is used to place particulates  52  into the vessel  8 ′. The height of the vertical section  10 ′ must be such that it does not cause the granules to crush. If this section  10 ′ is a slightly downward converging cone (0.5 degrees is sufficient in many cases), the bulk crushing strength of the particulates must exceed γD/2 by the time the particulates reach the top  28 ′ of the one-dimensional convergent hopper  11 ′. γ is the bulk density of the particulates and D is the top diameter of the upper section  10 ′. If the vertical section  10 ′ is a cylinder or a slightly diverging cone, the bulk crushing strength of the granules must exceed γ times the average height of the material in section  10 ′ by the time the material reaches the top  28 ′ of hopper  11 ′. The end walls  26 ′ of the hopper  11 ′ are vertical or diverging slightly downward while the sidewalls  27 ′ converge to the racetrack shape  29 ′. The lower hopper  12 ′ has side walls  30 ′ vertical or diverging slightly downward, while end walls  31 ′ converge to a circular cross-section  33 ′. In some cases where minimizing headroom is of the essence, the lower portion of hopper  12 ′ can be cut off at a level with an oval cross-section and a larger feeder can be used at this position to remove the particulates.  
         [0043]    The bottom  36  of hollow cylinder  18  is shown significantly lower than in FIG. 3. This lower position of the cylinder will provide blending with time, thus causing an homogenizing of upstream process variations.  
         [0044]    [0044]FIGS. 5A, 5B and  5 C shows a curing vessel  8 ″ with a single outlet one-dimensional racetrack cross-section hopper  11 ″ with a single outlet lower hopper  12 ″ that is equipped with an insert  37  which allows a much flatter angles in the hopper and thus saves headroom and associated costs. Except for the angles, the features of the hopper sections  11 ″ and  12 ″ are the same as in FIGS. 4A, 4B and  4 C. The insert  37  is supported on rods  34  the same as the hollow cylinder  12 ″ in FIGS. 1A, 1B and  1 C and FIGS. 3A, 3B and  3 C. In this case, the insert is a flat plate  37  and does not allow material to pass through it. The insert  37  is racetrack shaped. The width of the racetrack, as evident in FIG. 5C, is approximately half the horizontal distance between the slopping walls  27 ″ of hopper  11 ″ at the elevation of the insert. The distance between the oval ends  40  of the insert  37  and the slightly diverging end wall  26 ″ of hopper  11 ″ is approximately equal to half the width of the oval  29 ″ between hopper sections  11 ″ and  12 ″. This distance is the same as the distance between flat plates  30 ″ in FIG. 5C. The insert  37  provides a slowing of the particulate flow in the center of vessel  8 ″ as well as provides the necessary interparticle motion between the particulates in vessel  8 ″. The insert can be moved up and down on support rods  34  to optimize both the interparticle motion and the uniformity of retention time in vessel  8 ″.  
         [0045]    [0045]FIGS. 6A, 6B and  6 C show the same vessel and insert as in FIGS. 5A, 5B and  5 C except the insert  37  includes an upward extension  38  comprising a series of racetrack shapes stacked to a top line  43 . The top line  43  generally lies above the intersection  28 ″ of the upper cylinder or cone  10 ″ and the hopper  11 ″. The end walls  41  of the insert are essentially vertical while the side plates  42  form a converging channel with the side plates  27 ″ of hopper  11 ″. In this way, the flow channel formed by the insert approximates a one-dimensional convergence. The advantage of the insert extension upward is that the flow channel formed is positively defined by the insert as opposed to the particulate defined shape that is free to form on the flat plate. This assures that interparticle motion of the particulates extends upward into the cylinder  10 ″, and assures flow at the walls of hopper  11 ″.  
         [0046]    [0046]FIGS. 7A, 7B and  7 C shows a similar insert to that of FIGS. 5A, 5B and  5 C with a downward extension  44  comprising a plurality of racetrack shapes that compliment the shape of the hopper. The end walls  45  of the extension  44  are essentially vertical while the side walls  46  form an angle somewhat steeper than the hopper walls  27 ″ of hopper  11 ″. This one-dimensional convergence shape compliments the shape of hopper  11 ″. As the extension continues downward, the insert shape changes so as to complement the shape of hopper  12 ″. The transition  47  between these two shapes is generally at or above the transition  29 ″ of hoppers  11 ″ and  12 ″. The racetrack configuration continues below the transition  47  with essentially vertical flat plates  48  and curved end walls  49  that extend to a lower line  50 . Walls  49  are generally less steep than the converging walls  31 ″ of the hopper  12 ″ but steeper than the angle of repose of the particulates. By extending the insert downward, the insert walls influence the flow of the particulates at the walls of hoppers  11 ″ and  12 ″. Without the insert extension, the flow is determined only by the angle of repose of the particulates below the flat insert.  
         [0047]    [0047]FIGS. 8A, 8B and  8 C show the same hopper and insert as FIGS. 5A, 5B and  5 C with the insert extending both upward and downward. This achieves the advantages of both the upward and downward extensions of the insert as described in FIGS. 6A, 6B and  6 C and FIG. 7B.  
         [0048]    The headroom required for the upper conical curing vessel can be minimized by using various combinations of cones  52 ,  54 ,  56  and cylinders  58 ,  60 ,  62  in both the outer vessel  5 ′ and the associated insert  6 ′ as shown in FIGS.  9 A, and  9 B. The vertical section can be more extensive than in FIG. 2 by using the convergence produced by the conical portions of the insert  6 ′ to produce the necessary volumetric strain rate VSR.  
           VSR =( dA/dX ) Q/A   2    
         [0049]    where A is the cross-sectional area between the insert and the outer vessel, X is the vertical direction and Q is the volumetric flow rate. Specifically, in the configuration of FIGS. 9A and 9B,  
           VSR= 16( D (tanθ 0 )− d (tanθ i )) Q /(π( D   2   −d   2 )( D   2   −d   2 ))  
         [0050]    where D is the inside diameter of the outer vessel, d is the outside diameter of the insert, θ 0  is the angle of the outer vessel wall measured from the vertical with positive inclined toward the insert, θ i  is the angle of the insert surface measured from the vertical with positive inclined toward the vessel.  
         [0051]    In the upper portion of the vessel in FIGS. 9A and 9B, the angle θ 0  is zero and the VSR is zero unless d is positive. Since VSR of zero is not acceptable it is necessary that d be non-zero at the top of the material in the vessel. Since VSR must occur throughout the vessel it is necessary for the vessel walls to converge in the region where the insert is a cylinder. In the lowest extremity of the vessel, the vessel walls are vertical and the VSR is achieved by the decrease of the insert diameter d. This divergence of the area ‘A’ causes an increased solids contact pressure on the particles. This is acceptable since the particles are partially cured at this position and can withstand the greater pressure.  
         [0052]    In the upper vessel, the headroom can be optimized by arranging the vessel and insert walls in a series of cones and cylinders so as to maximize the volume in a given height while still providing the required VSR and limiting the solids contact pressure to the granular breaking pressure at the particular stage of curing. This means a low pressure and high VSR in the initial stages with an allowable decrease in VSR and allowable increase in the solids contact pressure as the curing progresses lower in the vessel. This is illustrated by the different upper and lower vessel designs and in the choice of vessel and insert shape in the alternate upper vessel in FIGS. 9A and 9B.  
         [0053]    The lower vessel  8 ′″ as shown in the FIGS. 10A, 10B, and  10 C is comprised of multiple racetrack configurations  64 ,  66 ,  68 , racetrack interior inserts  70 ,  72 ,  74  and multiple outlets  76 ,  78 ,  80  so as to minimize the required headroom, while still maintaining the required VSR to keep the particles from sticking and maintaining the pressures below the crushing strength of the particles.  
         [0054]    The invention provides a bulk solids vessel comprising an essentially vertical upper and converging lower section that limits solids contact pressure on the bulk granular solid passing through it to less than the bulk crushing pressure of the granules and provides a means for introducing inter-particle motion sufficient to prevent the granules from sticking to each another.  
         [0055]    The invention can further provide a vessel as described above further comprising an outer shell, wherein the outer shell is a conical frustum with a convergence angle from top to bottom of no more than approximately 10 degrees from the vertical and where such angle θ, the top diameter D, and the flow rate Q are selected so that the slowest average volumetric strain rate VSR as given by VSR=4 TAN (θ)Q/(πD 3 /4) exceeds that required as determined experimentally to prevent the granules from sticking to each other.  
         [0056]    The invention can also provide a vessel and insert each comprised of conical frustum and cylindrical sections such that the vessel inside diameter D, the angle of the vessel θ 0 , the outside diameter of the insert d, the angle of the insert θ i  and the volumetric flow rate Q at any level are arranged such the average volumetric strain rate VSR as given by:  
           VSR= 16( D (tanθ 0 )− d (tanθ i )) Q /(π( D   2   −d   2 )( D   2   −d   2 ))  
         [0057]    exceeds that required to keep the particles from sticking.  
         [0058]    The present invention can further provide a vessel and insert each comprising racetrack shaped cross-sections such that the vessel forms a series of vertical and converging sections that converge in one dimension only such that the average volumetric strain rate VSR necessary to keep particles from sticking is given by  
           VSR =( dA/dX ) Q/A   2    
         [0059]    While particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the described embodiments may be made without departing from the scope of the invention as defined by the following claims.