Abstract:
Prill heads having prilling assemblies that include adjustable openings. Prilling methods using the prilling assemblies can allow for the size of the openings to be varied during processing to alter the size of the prills as desired, or for clogged openings to be cleared, while maintaining operation of the prilling process. The prilling assemblies and prilling methods can be used to produce fertilizer products, including fertilizers comprising ammonium sulfate nitrate.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/360,082, filed Jun. 30, 2010, currently pending, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present technology relates to prilling processes, and in particular to a prilling apparatus and method utilizing an adjustable prill plate that provides openings of variable size. 
     DESCRIPTION OF RELATED ART 
     Prilling is a process by which solid particles are formed in an open tower via solidification as droplets fall from a prill head. Prilling is distinguished from spray drying by its near-complete or complete lack of volatile solvent. A prill head is the apparatus at the top of a prill tower which divides the molten material into the streams from which the prills form. 
     Current prilling operations utilize prilling plates that have only one size of opening in the prill head through which the molten material passes from the prill head into the prilling tower. If it is desired to change the size of the opening, the prilling operation is generally shut down so that prill plates having openings of a different size can be installed onto the prill head. Likewise, if openings in the prill plate become clogged by the molten material, operations generally have to be shut down to allow the prill plates to be cleaned and unclogged. 
     SUMMARY OF THE INVENTION 
     The present technology provides prilling assemblies and prilling methods that include a movable prill plate that allows adjustment of the size of the pathways through which a molten material passes to exit a prill head. 
     In one aspect, a prilling assembly is provided that includes a stationary prill plate having a plurality of orifices, and a movable prill plate adjacent to the stationary prill plate, the movable prill plate having a plurality of orifices that align with the orifices of the stationary prill plate to form pathways through the prilling assembly when the movable prill plate is in an open position. 
     In another aspect, a prilling method is provided that includes providing a prill head comprising a prilling assembly having a stationary prill plate and a movable prill plate adjacent to the stationary prill plate, the movable prill plate and the stationary prill plate each having a plurality of orifices that align to form pathways having a cross-sectional size; operating the prill head by passing a molten material through the pathways of the prilling assembly; and moving the movable prill plate with respect to the stationary prill plate to change the cross-sectional size of the pathways. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific examples have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification. 
         FIG. 1  illustrates one example of a prill head of the present technology. 
         FIG. 2  illustrates one example of a prilling assembly of the present technology. 
         FIG. 3  illustrates a second example of a prilling assembly of the present technology. 
         FIG. 4  illustrates a third example of a prilling assembly of the present technology. 
         FIG. 5  illustrates a side view of a fourth example of a prilling assembly of the present technology. 
         FIG. 6  illustrates a bottom view of the prilling assembly of  FIG. 5 . 
         FIG. 7  illustrates a side view of a fifth example of a prilling assembly of the present technology. 
         FIG. 8  illustrates a bottom view of the prilling assembly  FIG. 7 . 
         FIG. 9  illustrates a sixth example of a prilling assembly of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     The prilling assemblies and methods of the present technology can be used in any suitable prilling application, including but not limited to the production of fertilizer products, such as fertilizer products that comprise ammonium sulfate nitrate. 
       FIG. 1  shows a vertical cross section through the center of an open-topped, prill head  100 . The prill head  100  includes a sidewall  102  and a prilling assembly  104 . The sidewall  102  can form any suitable shape, such as a cylinder, oval, ellipse, triangle, square, rectangle, or a polygon. The prilling assembly  104  can be connected to the bottom end of the sidewall  102 , and can include a first prill plate  106  and a second prill plate  108 . 
       FIG. 2  shows one example of a prilling assembly  104  that can be used in a prill head  100  of  FIG. 1 . One of the prill plates of the prilling assembly  104  can be a stationary prill plate, while the other can be a movable prill plate. As illustrated in  FIG. 1 , the first prill plate  106  is a stationary prill plate, and the second prill plate  108  is a movable prill plate. The stationary prill plate  106  and the movable prill plate  108  can be immediately adjacent to each other, having a space between the prill plates  106  and  108  that is zero or as close to zero as reasonable practicable. The movable prill plate  108  can be operatively connected to a driving mechanism (not shown), such as a piston or a servo motor, that can control the movement and position of the movable prill plate  108 . 
     A stationary prill plate and a movable prill plate of the present technology can each have a plurality of orifices that pass through the prill plate from a top surface to a bottom surface of the prill plate. For example, referring to  FIGS. 1 and 2 , the stationary prill plate  106  and the movable prill plate  108  can each have a plurality of orifices  110 . The orifices  110  can be laid out in any suitable pattern having the plurality of orifices  110  spaced apart along the length and width of the prill plate. The orifices  110  of the stationary prill plate  106  and the movable prill plate  108  are preferably identical, or at least substantially identical, in shape and pattern, and are preferably in alignment to create fully open pathways through the prill plates  106  and  108  when the movable prill plate  108  is in an open position relative to the stationary prill plate  106 . The size of the pathways can be reduced, or the pathways can be closed completely, by moving the movable prill plate  108  to bring the orifices  110  of the movable prill plate  108  out of alignment with the orifices  110  of the stationary prill plate  106 , thus reducing the effective diameter and cross sectional area of the orifice. The orifices  110  can have any suitable shape, but preferably have a shape, such as a square, where the cross sectional shape remains constant as the effective diameter is reduced. Alternative examples of prilling assemblies having a stationary prill plate and a movable prill plate that operate in this manner are described below with reference to  FIGS. 3 through 9 . 
     Referring to the specific example illustrated in  FIGS. 1 and 2 , the stationary prill plate  106  can be square or rectangular in shape, and the movable prill plate  108  can also be square or rectangular in shape. Preferably, each of the orifices  110  of both prill plates can be square in shape, and can be laid out in any suitable pattern having the plurality of orifices  110  spaced apart along the length and width of the prill plate such that the diagonals of all of the square orifices are aligned parallel to a common direction. For example, the pattern can preferably include the square orifices  110  being spaced equally and arranged in lines collinear to the diagonals of the square orifices  110 , with the lines of orifices  110  alternating such that every other line of orifices is offset parallel to the line by some distance, preferably half the distance between adjacent orifices  110  along the lines. When the movable prill plate is aligned with the stationary prill plate in an open position as shown in  FIG. 2 , the orifices  110  on each prill plate are in alignment to create fully open pathways through the prilling assembly. The pathways have a square cross-section that have an initial size equal to that of the orifices  110 . The effective diameter, and thus also the cross-sectional size, of the pathways can be reduced, while still maintaining a square shape, by moving the movable prill plate  108  in a direction A that is parallel to the diagonals of the orifices  110 . 
     During operation of a prill head  100  in a prill tower, the movable prill plate can be placed in its first position, in which the cross-sectional size of the pathways is the largest because the orifices of the movable prill plate are aligned with those of the stationary prill plate. Alternatively, the movable prill plate can be moved to an operating position that is not its first position, in order to create pathways of a desired cross-sectional size. A molten material, such as fertilizer material, can then be passed from the prill head into the prilling tower by providing the molten material to the prill head and passing the molten material through the pathways in the prilling assembly. The movable prill plate  108  can be moved to change the cross-sectional size of the pathways, and thus adjust the particle size of the resulting prills without shutting down, or to maintain a constant particle size by adjusting the prill plate openings to compensate for changes in the material being prilled, such as temperature. 
     Additionally, the material being prilled can sometimes clog one or more pathways in a prilling assembly, creating a plug and reducing the efficiency of the prilling head. In such instances, the clogs can be cleared without shutting down operations by moving the movable plate  108  from an operating position to a closed position in which the pathways are closed, waiting a desired period of time to allow pressure to build-up in the prill head  100 , and then moving the movable prill plate rapidly to its first position in which the orifices in the stationary plate  106  and movable plate  108  are in complete alignment to reopen the pathways. The movable prill plate  108  can then be moved back to an operating position. Preferably, the amount of pressure allowed to build-up is sufficient to push the clogs out of the reopened pathways, and the movement of the movable plate  108  can also facilitate loosening or breaking-up of clogs within the pathways. 
       FIGS. 3 through 9  illustrate alternative configurations of prilling assemblies that include a stationary plate and a movable plate. 
       FIG. 3  shows a prilling assembly  200  that includes a stationary prill plate  202  and a movable prill plate  204  that have a circular cross-section and can be convex with respect to the sidewall  102  of the prill head  100 . The stationary prill plate  202  has a plurality of orifices  206 . The movable prill plate  204  has a plurality of orifices  208  that can align with the orifices  206  of the stationary prill plate  202  to form pathways  210 . The orifices can be any suitable shape, such as the circular orifices in the illustrated example. In a preferred example, the orifices can be square, such as the orifices illustrated in  FIG. 1 . The orifices  208  can be laid out in any suitable pattern, such as having the plurality of orifices  208  spaced apart along concentric circles centered on the axis of rotation of the movable prill plate  204 , such that the midpoints of the diagonals of the orifices  208  are tangent to one of the concentric circles. The movable prill plate  204  can be rotated clock-wise or counter-clockwise in the direction B to change the cross-sectional size of the pathways  210 . 
       FIG. 4  shows a prilling assembly  300  that includes a stationary prill plate  302  and a movable prill plate  304 . The stationary prill plate  302  and the movable prill plate  304  can each have a bottom  306 , a first sidewall  308  and a second sidewall  310 . The bottoms  306 , first sidewalls  308  and second sidewalls  310  of the prill plates  302  and  304  can each include a plurality of orifices  314  that can align to form pathways through the prilling assembly  300 . The stationary prill plate  302  can also include two end walls  312 , which can be vertical, or a least substantially vertical. The movable prill plate  304  can be moved horizontally in the direction C to change the cross-sectional size of the pathways formed by the orifices  314 . 
       FIGS. 5 and 6  show a side view and bottom view, respectively, of a prilling assembly  400  that forms the shape of a truncated pyramid. 
       FIGS. 7 and 8  show a side view and bottom view, respectively, of a prilling assembly  500  that forms the shape of a circular cone. The prilling assembly  500  includes a stationary prill plate  502  and a movable prill plate  504 . The stationary prill plate  502  has a plurality of orifices  506 . The movable prill plate  504  has a plurality of orifices  508  that can align with the orifices  506  of the stationary prill plate  502  to form pathways  510 . The movable prill plate  504  can be rotated clock-wise or counter-clockwise in the direction D to change the cross-sectional size of the pathways  510 . 
       FIG. 9  shows a side view through the center of a prilling assembly  600  that forms a cylinder. The prilling assembly  600  includes a stationary prill plate  602  and a movable prill plate  604 . The stationary prill plate  602  has a plurality of orifices  606 . The movable prill plate  604  has a plurality of orifices  608  that can align with the orifices  606  of the stationary prill plate  602  to form pathways  610 . The movable prill plate  604  can be rotated clock-wise or counter-clockwise in the direction E to change the cross-sectional size of the pathways  610 . 
     From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.