WO1995019838A1 - Formation de produits de type engrais granules - Google Patents

Formation de produits de type engrais granules Download PDF

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Publication number
WO1995019838A1
WO1995019838A1 PCT/IE1995/000004 IE9500004W WO9519838A1 WO 1995019838 A1 WO1995019838 A1 WO 1995019838A1 IE 9500004 W IE9500004 W IE 9500004W WO 9519838 A1 WO9519838 A1 WO 9519838A1
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WO
WIPO (PCT)
Prior art keywords
pellets
zone
forward flow
unit
curtain
Prior art date
Application number
PCT/IE1995/000004
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English (en)
Inventor
Henry Browne
Original Assignee
Irish Fertilizer Industries Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Irish Fertilizer Industries Ltd. filed Critical Irish Fertilizer Industries Ltd.
Priority to AU14244/95A priority Critical patent/AU1424495A/en
Publication of WO1995019838A1 publication Critical patent/WO1995019838A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/006—Coating of the granules without description of the process or the device by which the granules are obtained

Definitions

  • This invention relates to pellet formation or granulation.
  • the invention relates to the formation of pellets or granules of a fertiliser product, such as urea.
  • the invention is especially directed to the formation of pellets or granules or particles by means of a layering process.
  • a diversity of processes or methods are known for the formation of granules or pellets of a fertiliser product such as urea.
  • a fertiliser product such as urea.
  • liquid urea in melt form is projected in droplet form through perforations from a bucket-type unit at the top of a tall tower.
  • the particles of liquid leaving the perforations of the bucket solidify during their fall through the prilling tower and are also cooled.
  • Formed and cooled pelletised product is removed immediately for storage from the bottom of the tower.
  • increased tower height is required, but cost and planning restrictions frequently constrain the possibility of providing such a taller structure.
  • a spray coating of liquid melt is applied to particles initially formed for example by prilling, to develop particles or pellets of larger diametral dimensions.
  • an initial seed product may also serve to initiate the process, and a proportion of the output material may then be drawn off for recycling to provide new raw material for continuous operation.
  • granulation or layering processes function by solidifying successive layers of solution or slurry or melt onto the surfaces of particles which are separately fed into the granulator and are made to grow during their passage through the granulator unit by continual spraying.
  • the achievement of particles of uniform size is a particular objective of such processes, but because growth is not uniform, this objective typically requires the adoption of further technical features, possibly involving the recycling of at least a proportion of the final product.
  • Layering is to be distinguished from accretion, which is growth by continuous projection of very small liquid droplets onto particles.
  • Accretion is a continuous process of growth and drying, as compared with the stepwise procedures of layering.
  • each granule is made up of a very large number of droplets, for example several thousand.
  • a particular arrangement uses a fluidised bed technique in which the input granules are fluidised by air distributed into the granule bed through an underlying perforated plate.
  • a urea solution is then atomised in air-assisted spray nozzles and sprayed within the bed onto the fluidised particles within the bed, typically in an upward direction through the bed from the base of the fluidised bed, and the particles then grow by accretion with simultaneous water evaporation.
  • the evaporation enables part of the released heat to be removed, and air and vapour extraction arrangements are thus a necessary part of the system.
  • US-A-4,237,814 (corresponding to GB-A-1,432,931) describes multi-cell fluidisation and atomisation apparatus for the continuous production and/or coating of granules, for example in the pharmaceutical and agricultural chemical industries.
  • a series of upright cylindrical cells are provided, through which an initially particulate material moves sequentially.
  • Inlet and outlet openings are provided at various heights in these cells, for movement of material from cell to cell.
  • the cells are provided with rotary agitators, of different configuration from cell to cell. Gas injection from beneath the cells brings about fluidisation of the material in the cells, and the fluidised material is contacted by an atomised liquid in at least some of the cells.
  • a rotating drum is provided with internal lifting flights or fins for raising, during rotation of the drum, granules introduced into the drum as feedstock to an elevated location within the drum, from where they fall onto inclined collecting pans or tables.
  • the granules then again fall from the edge of the pans or tables to form falling curtains, onto or into which a urea melt is continuously sprayed.
  • the granules may be cooled by evaporation of a fine water mist sprayed into the drum unit, or they may be cooled by air. Air cooling may be effected by air flow through the pans or tables.
  • An exemplary drum arrangement is described in US-A-4,842,790, according to which materials are granulated in an enclosed vessel by spraying molten material onto rapidly moving granules of substrate.
  • a horizontally rotating drum has lifting flights and deflector pans, and granules or prills cascade over the pans to form vertical curtains which are contacted with a molten spray of the same substance. Air is moved through the drum for cooling.
  • EP-A-0,278,246 describes a rotary granulation drum for the production of granulated bisphenols.
  • a bisphenol seed material is fed into the drum to fall in a curtain-like pattern. As it falls, it is sprayed with molten bisphenols, while an inert gas stream is simultaneously fed into the drum to cool the granulate produced.
  • FR-A-2,324,355 provides a method for the granulation of ammonium nitrate fertilisers, in which part of the material is prilled. Sieved prills of substantially uniform size are then used to form a moving bed of material which is sprayed with the remainder of the fertiliser, thus increasing the granule size.
  • the spraying may be effected in a rotating drum.
  • drum arrangement in particular presents problems in regard to product cooling, and air extraction with minimisation of dust.
  • a further problem in a drum arrangement is the progressive reduction in the proportion of product lifted with progressive advance of material through the drum. If all particles are lifted at the start or input end of the drum, and there is a doubling of the weight of the particles during their passage through the drum, then only 50% of the granules will be lifted at the downstream or output end of the drum. The result of this is that either particles are lifted less frequently or a residue of particles is never lifted at all. It is a particular object of the present invention to overcome this disadvantage of drum layering techniques.
  • drum throughput There is a reduction in the proportion of product lifted in volume terms at any location along the drum as compared with the input end of the drum. If all of the particles are lifted at the start of the drum, only 50% of the particles will be lifted by the end of the drum. Thus, at the output end, particles which have been sprayed with melt have a 50% chance of either being lifted onto the table for cooling or of not being lifted and remaining in the rolling bed, hot and uncooled and forming agglomerates.
  • a pellet treatment system comprising at least one plurality of forward flow units, each for advancing pellets from an input zone of the forward flow unit to a discharge zone of the forward flow unit, and a respective treatment zone associated with each said forward flow unit of said plurality through which treatment zone pellets pass from said discharge zone of the unit to either the input zone of a further forward flow unit or to a collection region, the treatment zone having means for directing a fluent material towards passing pellets.
  • the invention provides a pellet layering system comprising at least one plurality of forward flow units for advancing pellets from an input zone to a discharge zone together with pellet cooling, and a respective layering zone associated with each said forward flow unit of said plurality through which layering zone pellets pass from said discharge zone to either the input zone of a further forward flow unit or to a collection region, the layering zone having means for applying a melt, solution or slurry material to passing pellets.
  • the invention is also directed to a pellet layering system comprising at least one plurality of forward flow units, each for advancing pellets from an input zone of the forward flow unit to a discharge zone of the forward flow unit together with pellet cooling, and a respective layering zone associated with each said forward flow unit of said plurality through which layering zone pellets pass from said discharge zone of the unit to either the input zone of a further forward flow unit or to a collection region, the layering zone having means for applying a melt, solution or slurry material to passing pellets.
  • Said means for applying a melt, solution or slurry material to passing pellets may comprise a plurality of nozzles positioned downstream of said layering zone relative to the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit, while said means for directing a fluent material towards passing pellets may likewise comprise a plurality of nozzles positioned downstream of said treatment zone relative to the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit.
  • means are provided for enabling adjustment of the spacing of said plurality of nozzles from the discharge zone and for enabling adjustment of the spray axes of the nozzles.
  • spray conditions may be adjusted so that blow-through is substantially minimised, although in certain circumstances, it may also be advantageous to provide protecting air curtains, to prevent material from the product curtain being driven against and adhering to internal walls of the system of the invention.
  • said layering zone may be defined by a treatment zone and said means for applying a melt, solution or slurry material to passing pellets may be defined by means for directing a fluent material towards passing pellets.
  • the treatment zone of the system of the invention may serve for a variety of production purposes in the handling and processing of pelletised material, including, inter alia, layering or fattening.
  • the invention may also be applied to operations such as the cooling of product of large surface area by the application of a volatile substance or material to the pelletised material passing through the treatment zone. Such a process step may be effected in connection with the prevention of product from caking, by applying an evaporative coating to product in the treatment zone of the system of the invention.
  • a diversity of treatments may be effected in the treatment zone, including, inter alia, the application of a solid or liquid fluent material to the passing pellet product.
  • the solvent applied may be for immediate volatilisation, for cooling purposes, or the solvent material may partially evaporate while also partially adhering to the pellets and subsequently slowly volatilising.
  • a solvent material may be combined with a coating, the coating persisting and remaining on the pellets even after the solvent has volatilised.
  • a particular application of the present invention to which it is especially directed as identified in the foregoing further aspects is the application of a melt, solution or slurry material to pellets passing through the treatment zone, in order to increase the dimensions and weight of the pellets in a layering or fattening process.
  • the treatment zone therefore comprises a layering zone in which the fluent material in the form of a melt, solution or slurry material is directed towards and applied to the passing pellets.
  • the layering zone of these aspects of the invention is defined by the treatment zone of the invention in its first aspect, while the melt etc. application means is defined by the fluent material directing means of the invention in its broadest aspect.
  • each said forward flow unit of said plurality comprises fluidised bed means having an apertured surface over which the pellets pass, and means for directing a flow of gas through said apertured surface to establish a fluidised bed of said pellets.
  • Said means for directing a flow of gas through said apertured surface to establish a fluidised bed of said pellets suitably comprises a gas plenum underlying said apertured surface and means for regulating passage of gas from said plenum to said apertured surface.
  • Said means for regulating passage of gas from said plenum to said apertured surface preferably comprises a baffle structure defining a multiplicity of airways of relatively small transverse dimension between said plenum and said apertured surface so that gas flows from the plenum to and through the apertures of said apertured surface in a direction substantially at right angles to a plane defined by said apertured surface.
  • Gas is suitably supplied to said plenum in an axial direction corresponding to the direction of advance of pellets from said input zone of the unit to the discharge zone thereof.
  • the system may include means for drawing off gas from a gas collection region located above said apertured surface.
  • Gas is suitably drawn off from said gas collection region located above said apertured surface in a direction substantially transverse to the direction of advance of pellets from said input zone of the unit to the discharge zone thereof.
  • Said gas collection region preferably has dimensions in cross-section in a plane parallel to a plane defined by said apertured surface which are substantially greater than the corresponding dimensions of the apertured surface so that a disengagement chamber is defined in said gas collection region for separation of particulate material entrained in gas entering said gas collection region.
  • Each said forward flow unit of said plurality other than the first said unit is also suitably disposed downwardly of a preceding said unit, and pellets pass from one unit of said plurality to the next unit of said plurality in succession by falling under the influence of gravity through a region defining said treatment zone.
  • Said forward flow units of said plurality may be arranged in a tiered or stacked array, with reversal of the direction of pellet advance on the forward flow units of said plurality from tier to tier.
  • the system of the invention may comprise two said pluralities of forward flow units, each plurality defining a said stacked array, as well as means for transferring pellets from a collection region associated with the final forward flow unit of one of said stacked arrays to the input zone of the first forward flow unit of the other of said stacked arrays.
  • said forward flow units of said plurality are arranged in a stepped array, with the direction of pellet advance on the forward flow units of said plurality being the same for each step.
  • the system may comprise at least two said pluralities of forward flow units, each plurality defining a said stepped array, with reversal of the direction of pellet advance on the forward flow units from each stepped array to the following stepped array.
  • Pellets then preferably pass from the final forward flow unit of at least one of said pluralities of forward flow units to the first forward flow unit of a further said plurality of forward flow units by falling under the influence of gravity through a region defining a treatment zone.
  • the system suitably comprises means for establishing a falling curtain of pellets in each said treatment zone.
  • Said means may be adapted to vary the width of said falling curtain of pellets in said treatment zone.
  • Said means may comprise flow restraining members for maintaining a substantially predetermined flow density in the falling curtain of pellets for said treatment zone.
  • said flow restraining members comprise two pivotable gate members mounted on a support plate, the support plate having a free edge region from which the pellets fall to define said curtain.
  • said means for establishing a falling curtain of pellets in each said treatment zone comprises at least one structure positioned for engagement by the stream of pellets leaving the discharge zone of the respective forward flow unit.
  • Said at least one structure suitably comprises a multiplicity of teeth or tines.
  • Said at least one structure may be a primary curtain-forming structure and a secondary curtain-modifying structure may then be positioned for engaging the falling curtain of pellets at a level downstream of said primary curtain-forming structure.
  • Said secondary curtain-modifying structure suitably also comprises a multiplicity of teeth or tines.
  • the spacing of the teeth or tines of said secondary curtain-modifying structure is preferably the same as the spacing of the teeth or tines of said primary curtain-forming structure and said secondary curtain-modifying structure is displaced relative to said primary curtain-forming structure so that the teeth or tines of said secondary curtain-modifying structure underlie the gaps between the teeth or tines of the primary curtain-forming structure.
  • the or each said structure substantially defines a plane and is mounted for selective adjustable orientation of said plane relative to the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit.
  • the or each said structure may occupy a declining adjustable orientation in the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit relative to a plane substantially defined by said direction of advance of said stream of pellets, or alternatively, in an especially favoured construction, the or each said structure may occupy a rising adjustable orientation in the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit relative to a plane substantially defined by said direction of advance of said stream of pellets.
  • the rising structure orientation is especially advantageous in securing an optimum diffused curtain, especially in conjunction with - li ⁇ the toothed or comb-type arrangement identified above.
  • the particular further arrangement in which a two-stage structure is provided allows the second series of combs to be disposed in locations such as to further distribute any concentrations of material falling from the first structure, while also the staggered gap arrangement of the dual structure, in conjunction with the use of relatively wide spacings between the teeth of the combs, reduces and substantially eliminates the likelihood of any serious clogging or build-up of material on these curtain-forming structures.
  • the or each said structure suitably comprises a rotatably adjustable shaft provided with means for selectively varying the angular orientation of the structure.
  • said shaft suitably extends transversely to said direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit and is located at a spacing from said discharge zone, while said means for selectively varying the angular orientation of the structure suitably comprises at least one lever arm.
  • the system of the invention preferably also comprises means for varying the dimensions of said falling curtain of pellets in said treatment zone, such as an underflow weir for regulating the depth of flow of pellets leaving the forward flow unit at said discharge zone of the unit.
  • Said underflow weir suitably comprises a vertically displaceable plate member positionable to define a selectively variable gap between a lower edge region of the plate member and a plane substantially defined by the direction of advance of the stream of pellets leaving the discharge zone of the forward flow unit.
  • Said means for varying the dimensions of said falling curtain of pellets may also comprise at least one horizontally displaceable plate member positionable to define a selectively variable transverse discharge aperture at said discharge zone of the forward flow unit.
  • Two horizontally displaceable plate members may be provided, said selectively variable transverse discharge aperture being defined between opposed spaced apart edge regions of said plate members.
  • the system of the invention may also comprise means for regulating advance of pellets on each said unit from said input zone to said discharge zone, such as an underflow weir arrangement for regulating the depth of advancing pellets carried on a support surface of the unit.
  • Said underflow weir arrangement suitably comprises a pivotally mounted plate extending downwardly towards said support surface from a pivot axis towards said support surface, a flow gap being defined between a free edge region of the plate and said support surface, and the vertical dimension of said flow gap being varied by pivotal adjustment of the plate.
  • the invention also extends to a pellet layering system substantially as described herein with reference to and as shown in any one or more of the accompanying drawings, as well as to a method of layering pellets substantially as described herein with reference to any one or more of the accompanying drawings, and pellets layered using the system or method as above identified.
  • Figure 1 is a diagrammatic sectional side view of a structure incorporating the principles of the invention
  • Figure 2 is a part cutaway pictorial representation of the system of Figure 1,
  • Figure 3 is a reproduction of Figure 1 showing the flow of material through the system
  • Figure 4 is a schematic diagram of a staircase type embodiment of the system of the invention
  • Figure 5 is a schematic diagram of a staircase or stepped embodiment in which staircase portions are sequentially arranged in a stack structure
  • Figure 6 is a schematic diagram of an arrangement in which two half-height stacks are arranged side-by-side, with product transfer from the discharge end of the first stack to the input zone of the second stack,
  • Figure 7 is a diagrammatic, partially-sectioned side view of an alternative structure incorporating the principles of the invention.
  • Figure 8 is a diagrammatic sectional end view of one of the fluidising units of the arrangement of Figure 7,
  • Figure 9 is a part cutaway schematic pictorial representation of a unit of the structure of Figure 7,
  • Figure 10 is an end view of the intermediate weir arrangement of the unit of Figure 9,
  • Figure 11 is a diagrammatic end view of the vertical weir of a unit of the structure of Figure 7,
  • Figure 12 is a diagrammatic end view of the horizontal weir of a unit of the structure of Figure 7,
  • Figure 13 is a top or plan view of the comb-type deflector of a unit of the system of Figure 7,
  • Figure 14 is an enlarged end view of the comb deflector of Figure 13, showing the cross-sectional profile of the teeth or bars of the comb,
  • Figure 15 is a part cutaway schematic pictorial representation of a unit of the structure of Figure 7, similar to Figure 9, but showing an alternative deflector arrangement,
  • Figure 16 is a side view of the deflector and spray bar region of the arrangement of Figure 15,
  • Figure 17 is the top or plan view of the dual comb-type deflector of the arrangement of Figure 15, and
  • Figure 18 is an end view of the comb deflectors of Figures 15, 16 and 17, showing the circular cross-sectional profile of the teeth or tines of the combs.
  • the granule formation or pellet layering system of the invention provides a tiered stack of tables 1, of which a limited number are shown, but a considerably greater number of which may exist in a practical structure, each table 1 defining an air bed having a perforated surface 2 through which air flows upwardly.
  • the structure of the invention may be housed within an overall enclosure having side walls 3.
  • An air box or duct 4 of decreasing cross-sectional dimension underlies the table 1 and provides for conveyance of air to the underside of the perforated top structure 2.
  • the table 1 is rectangular, having an appropriate * length and transverse dimension, the table area optionally increasing as the need dictates at various stages from the top of the stack to the final or lowermost table 1 in a stack.
  • each table 1 may be level or gently declined, as shown in the drawings, from an input or feed end 5 of the table 1 at which granules are introduced by means not shown in the drawings, to a discharge or output end 6 of the table, from where granules move on to the next stage, or, in the case of the final table, to an output or collection stage.
  • the table in which the table is level or gently declined, it may also be walled at the upstream end and along its sides and provided with an underflow weir type arrangement at the downstream end, so that forward flow and granule advance take place by fluidisation of the material on the table induced by the upward air flow through the perforated surface of the table 1. Only side walls 7 are shown in Figures 1 and 2.
  • Air flowing up through the perforated surface 2 of the table 1 cools granules located on that table and maintains the onward progression of granules along the level or gently declining surface 2 of the table 1 from the input end 5 to the discharge end 6.
  • the granules flow onto a declining plate 11 set at an appropriate angle to extend in a downward direction away from the discharge end 6 of the table 1 to a free edge or lip 12 of the declining plate 11, over which the product stream flows to define a falling curtain of particles in a layering region of the system.
  • the declining plate 11 is equipped with a product stream width control mechanism 13, 14 which determines the product stream width and density presented for spraying in the layering zone, this zone being indicated by reference 15 in Figure 3.
  • the product stream falls from the free edge 12 of the declining plate 11 to form the required curtain, reference 16, Figure 3, in this layering zone 15, where urea melt material, reference 17, Figure 3, is blown onto the falling particles, so that they are layered during this freefall stage.
  • a particular arrangement is illustrated in the drawings, but this represents an exemplary configuration only, and a diversity of alternative arrangements may also be adopted for this stage of the operation.
  • An inlet air duct 21 typically of rectangular cross-section, conveys air to the air box or duct 4 underlying the perforated surface 2 of each table 1, for upward air flow through the perforated surface 2 and the establishment of a fluidised cooling bed of particles on the upper surface of the table 1.
  • Draw-off of air from the fluidised bed takes place above the table 1 by means of a cowl
  • a curtain deflector plate 24 projecting substantially vertically downwardly forward of the free edge or lip 12 of each declining plate 11 has a curved lower edge 25, this serving to deflect the falling curtain 16 of particles into the layering zone 15 and, in the construction shown in the drawings, also to secure a reversal of the direction of particle advance from table to table downwardly through the stack of tables.
  • a melt supply pipe or duct 26 serves for infeed of melt material, and discharge of melt from this supply line takes place by way of nozzles 27 to form the required urea melt spray 17 in the layering zone 15.
  • the discharge opening 18 is altered or regulated by pivoting the members or gates 13, 14 towards or away from each other as required, about their axes of pivoting 19, these being suitably located at the inner or upper edge of the plate 11, where it is juxtaposed against the discharge edge of table 1, and extending substantially vertically with respect to the plane of plate 11.
  • Effectively the outlet 18 from the declining plate 11 is throttled so as to maintain the required flow density in the curtain 16 at each level in the stacked array of tables of the system.
  • the same product flow rate per unit length of curtain may thus be achieved, if so required, for each level of the system.
  • the width of the spraying or layering area 15 is determined by the width of the curtain 16 resulting from the control operations carried out by means of the pivoting throttling members or "lock gates" 13, 14.
  • the gate or throttle opening 18 may be adapted at each level to achieve the required performance.
  • the length and width dimensions of the tables 1 may increase progressively from the top of the stack to the bottom. However, progressive increase for each tier may not be necessary and the same size of table may be suitable for a number of the tiers.
  • Each progressive table in the sequence may be sized to cater for a range of mass flows arising from various overall plant loads and also in a stepwise way to cater for the progressive increase in mass flow through the system.
  • Heat balance considerations may define the quantity of airflow through the fluidised layer on each table 1 for heat supply or removal.
  • the bed area is directly proportional to plant capacity, while bed thickness and temperature, air velocities, pressures and temperatures are substantially constant and independent of capacity.
  • Residence time on tables may be increased by the provision of the underflow or overflow weir arrangement already mentioned.
  • the hinge member or lock gate arrangement 13, 14 provides that the curtain density is the same per unit length and thus that the spraying rate per unit length of curtain may be maintained at the optimum required levels regardless of plant design capacity.
  • the body of granules falling from the lip of the table may be transformed into a more diffuse flow, as distinct from a single curtain.
  • the spray is then blown through a relatively deep falling mass of material, so as to achieve maximum adherence of sprayed material to the granules and minimum blow-through of non-adhering urea. Blow-through results in build-up of unused melt material on surfaces of the system, or alternatively the formation of unwanted dust and fines.
  • a diffuse spray region facilitates uniform layering and maximises the degree of adherence of spray material to the passing granules, while minimising the formation of agglomerates of the doublet or triplet etc. granule type.
  • Material falling through the spray zone 15 also undergoes a reversal of flow direction, so that it descends onto the next table 1 downwards for travel along that table in the opposite direction to the direction of flow on the first table 1.
  • a similar reversal of flow direction applies at each successive spray treatment zone.
  • Each passage through a spray zone 15 leads to a build-up of material on the granules, so that a staged layering process proceeds by virtue of the stage by stage passage of the granules through each successive segment or sector of the system.
  • the weight of material builds up, so that for example approximately twice the weight may emerge at the downstream end of the system as was put in as prills or granules at the start of the system, due to the layering of.the granules or particles by melt adhesion. However, essentially the same number of particles leave the system at the outlet as entered the system at the inlet.
  • the coating process is thus particularly uniform and efficient when the substrate is directed in the form of a falling curtain and the spray or melt material is directed onto this curtain.
  • a particular advantage of the flowing curtain process is reduced dust generation.
  • the provision of a dense curtain of granules allows the melt spray nozzles to be positioned relatively close to the falling mass of granules, while random atomisation into the airstream and formation of weak granule agglomerates are thereby also avoided.
  • the slope on the surfaces of the tables 1, where provided, keeps forward movement progressing on each level, but a relatively modest angle is sufficient.
  • substantially uniform air pressure prevails to give uniform distribution of air flow upwards through the table 1.
  • a single air supply manifold may distribute air to each of the ducts 4 at the different levels. Capacity may be enhanced by providing larger tables, for example of greater width, but without necessarily increasing the number of stages in the system.
  • the sprayed material (melt) to solids feed (prills) feed rate ratio determines the increase in particle or granule size achieved.
  • This sprayed material to solids feed ratio determines the number of spraying stages required to achieve the desired increase in particle or granule size.
  • the arrangement of the invention is not necessarily limited to urea pellets or particles only, and may also find application in the pelletisation or particle formation of other fertiliser products and products other than fertilisers.
  • each of the tables may be determined, inter alia, by the following considerations:
  • a similar size of table may be adequate for several tiers of the structure.
  • the flow rate of the curtain 16 is regulated and an optimum and constant curtain thickness can be maintained at each level.
  • the optimum spray density per unit length of curtain may be achieved for the curtain at each stage or level, with or without a diffusing arrangement to achieve enhanced voidage, as may be required.
  • a spray direction transverse to the curtain 16 or direction of particle or granule flow represents however only one possible manner of achieving a desirable spray arrangement, and, for example, the spray may alternatively be directed so as to extend or move in the same direction as the direction of curtain flow, in other words a with-flow spray arrangement may be provided rather than a transverse spray through the falling curtain or granule flow as described with respect to the drawings, Figure 3.
  • a diffused curtain in which enhanced voidage is present represents one manner of cutting down blow-through, but alternatively, a safety curtain may be defined by a downward flow of air to the rear and sides of the pellet curtain 16 relative to the spray nozzles 27, this safety curtain catching any blow-through and preventing it from adhering inappropriately to internal surfaces within the system and structure. Similar air curtains may be provided at each end of the falling curtain of granules or pellets, this preventing any blow-through or deviation of material along the side edges of the falling curtain which might adhere to the side walls of the units, leading to a build-up of deposited material.
  • the system of the invention may also be provided in a staircase type structure, rather than a stack, so that flow reversal between stages may be obviated and the granules flow forwardly from step to step of the staircase structure.
  • a combination of staircase and stack may be put in place, with a number of stages forming a staircase portion, followed by a flow reversal and a further subsequent number of stages forming a staircase portion on the next level down.
  • Figures 4 and 5 are schematic representations of staircase structures and combined step and staircase structures respectively.
  • the system comprises a series of stages 31a, b n, arranged in staircase manner, for a forward flow of granules from step to step of the staircase.
  • three stages 41a, 41b and 41c define the first staircase portion, with flow reversal following stage 41c, to bring the particles to be treated onto a further staircase portion 42a, 42b, 42c, on which the direction of flow is the opposite to that on staircase stages 41a, b and c, and so on for as many further staircase steps as are required.
  • the present invention enables the formation of large granules or pellets in a simple manner, avoiding the use of rotating structures.
  • the air table arrangements of the present invention provide for effective forward transport of the pellets with all necessary cooling, while a diversity of spray zone formation arrangements may be applied, offering effective coating and adherence of melt material, with minimisation of spray wastage and dust or coating formation.
  • the supply of air and spray material to a system in accordance with the present invention is also simplified, requiring no complex air spray arrangements while access to the individual segments of the structure of the invention for maintenance purposes is facilitated, compared with fluidised bed or rotary structures.
  • the structural layout of the system of the invention may be provided to achieve either a compact stacked structure, or a more extended staircase type arrangement, depending on the necessities of the site and process.
  • a structural layout may be achieved to allow for the re-elevation (by bucket elevator, for example) of the granules or particles to a next or following stage located at the same level as the first stage of the system.
  • An arrangement of this kind is shown in Figure 6.
  • a first stage or stack 51 six tables 1 are provided in a vertical array similar to the arrangement of Figure 1.
  • Particles fed to the first or uppermost table at infeed location 32 progress downwardly through stack 51 to a collection location 33 for stack 51, from which the partially treated particles are then raised by a bucket elevator 53 to the first table of the second stack 52. Further treatment in accordance with the principles of Figure 1 then takes place as the particles travel downwardly through the second stack, to the final system collection location 33, from which the finally layered treated particles are withdrawn for packaging or further handling as required, arrow 54.
  • a twelve-stage unit could be replaced by two six-stage units with a bucket elevator feeding the granules or particles from the final stage of the first unit to stage one of the second unit.
  • a granule formation or pellet layering system according to the invention in a modified construction again provides a tiered stack of units 101, five units 101a, 101b, 101c, lOld and lOle being shown in Figure 7.
  • Units 101a to lOld are substantially identical, while unit lOle is different in that it defines a collection region for layered granules treated by the system of the invention and does not include a spray feature.
  • the particular orientation shown for unit lOle namely that the table is arranged for material flow in the same direction as that of unit lOld, is an optional choice, and may vary depending upon the geometry of the installation.
  • unit lOle In an alternative arrangement, it would be possible for unit lOle to fully underlie unit lOld, thereby providing an especially compact configuration of stack.
  • the system of the invention is especially versatile in regard to the location and interrelationship between the successive units in the various tiers of the stack, and can readily be adapted to any product situation and any dimensional limitations.
  • the upper end of unit 101a is also different, in that it includes an infeed location 132, where granules are initially entered into the system.
  • Units 101b, c and d are substantially identical, save only that the hand of operation is reversed from unit to unit.
  • Each unit 101 has an airbed region defined by a perforated surface 102 through which air flows upwardly from a supply plenum or chamber 104 underlying the surface 102.
  • Each unit has outer side walls 103 defining an exterior region of the structure, as seen more clearly in Figure 8. These side walls 103 terminate at lower flanges 181 along their bottom edges and at upper flanges 182 along their top edges. The lower flanges 181 of each unit in the structure engage either the upper flanges of an underlying unit or the case of the lowermost units, support members.
  • the underlying air plenum 104 has a decreasing cross-sectional dimension from its point of connection to an inlet air duct 121.
  • the granule carrying region defined by the perforated surface 102 is generally rectangular, having length and transverse dimensions appropriate to the required performance of the system.
  • the surface 102 of each unit 101 is gently declined, as shown in the drawings, from an input or feed end 105 of the surface 102 at which the granules are introduced onto the surface either at the infeed end 132 of the system, for the first unit 101a, or by a falling motion from a preceding unit, for units 101b to lOle.
  • the granules move on to the next stage in the cascade manner already described, or, in the case of the final unit lOle, to a collection location 133.
  • Side walls 107 are provided along the sides of the surfaces 102 of each stage, having a lower parallel sided side wall region 107a extending upward from the perforated surface, and then widening out by means of outwardly tapering wall portions 107b towards the upper flanges 182 of the outer side walls 103.
  • a generally hopper-shaped space is thus defined above the surface 102, underlying the air collection region 122, the base of which is defined by the perforated surface 102.
  • the surface 102 may suitably be defined by a top layer of expanded metal underlaid by an arrangement 119 for providing directional control of the air flow reaching the apertures of the plate, through which the air percolates from the underlying plenum 104. In the arrangement shown, the air is fed into the plenum chamber in the direction of product flow.
  • the air flow directional control feature 119 By providing an air flow directional control feature 119 on the underside of the apertured plate or sheet 102 of expanded metal, the air flow is constrained to move in a substantially vertical manner substantially perpendicular to the plane defined by the apertured surface 102 through these apertures and into the pelleted or granular material.
  • the air flow directional control feature 119 is thus arranged to minimise or substantially eliminate any angular component in the air flow which would tend to direct the material either to the side of the surface 102 or to retard or accelerate its flow.
  • the air flow directional feature 119 suitably consists of a structure limiting the possibility for transverse air movement on the underside of the apertured plate.
  • Such an arrangement may consist of a multiplicity of baffles or similar structures defining adjacent but transversely separated flow regions of small dimensions to cut down flow components of motion other than vertical or perpendicular to the apertured plate or surface 102.
  • the air flowing up through the perforated surface 102 of the unit 101 also cools granules located on the surface and maintains the onward progression of the granules along the gently declining surface 102 of unit 101 from the input end 105 to the discharge end 106 of the unit.
  • Control of flow along the surface 102 may be further regulated by means of a pivoting underflow weir 109 located approximately midway along the length of the surface 102, the further operation of which will be subsequently described in more detail.
  • each unit of units 101a to lOld granules flow over a declining comb plate 111 set at an appropriate and adjustable angle to extend in a downward direction away from the discharge end 106 of the unit 101.
  • the product stream from the surface 102 flows over the comb plate 111 to define a thick falling curtain 116 of particles in the layering region 115 of the system.
  • the discharge end region 106 of each unit is equipped with a product stream width control mechanism consisting of an adjustable vertical weir 112 and a likewise adjustable horizontal weir defined by members 113 and 114 which determines the product stream width and density presented for spraying in the layering zone 115.
  • the product stream falls from the comb plate 111 to form the required curtain, and melt material 117 from nozzles 127 is blown onto the falling particles, so that they are layered during this freefall stage.
  • Figures 7 to 9 include arrangements for drawing off air from the fluidised bed by means of the air collection region 122 defined above the perforated surface 102, from which air is extracted by means of a side-exit exhaust duct or passage 123.
  • the air collection region 122 is defined between the side walls 103 of the next unit 101 up in the structure, or an equivalent arrangement for the uppermost unit 101a, and because of the diverging side wall arrangement 107b above the perfo ' rated surface, the air collection region 122 has considerably greater volume and cross-sectional area in the generally horizontal plane as compared with the perforated surface or table 102. In this manner, advantageous performance may be achieved in a system according to the invention in terms of airflow and minimisation of material carry-over.
  • This region thus provides a dis-entrainment or disengagement chamber in which larger particles carried along in the air flow may become disengaged for return to the fluidised bed, by virtue of the tapering-in upper wall portions 107a which define a generally hopper-shaped lower portion to the disengagement region or chamber portion 122 above the bed.
  • the air flow speed is thus reduced in this region, so that small dust particles and aerosols may be extracted, but useful material is returned to the main product stream.
  • a deflector plate 124 is located above the layering zone 115 and a further deflector 125 is located at the input end 105 of the next unit 101 down in the stacked structure.
  • a melt supply duct 126 serves for infeed of melt material, discharge of melt from this supply line 126 taking place by way of the nozzles 127 to form the required melt spray 117 in the layering zone 115.
  • the spray angle is adjustable by virtue of duct 126 being rotatably mounted and connected to a melt supply source through a rotary joint arrangement.
  • the intermediate weir is defined by a pivotally mounted plate 141, depending from a transverse pivot axis or bar 142 extending along its upper edge.
  • This pivot axis is mounted for pivotal displacement in the side walls 107a and 103 and a pivot handle 143 enables the angle of pivoting to be adjusted.
  • the gap 144 between the lower edge of the plate 141 and the upper surface of the table portion 102 may be varied.
  • the dimensions of the plate are however such that even in the vertical condition of the plate 141, a minimum gap 144 is always defined between the lower edge of the intermediate weir 111 and the underlying table surface 102.
  • FIGS 11 and 12 show details of the vertical and horizontal weirs 112 and 113, 114 located at the discharge end of the unit 101.
  • the vertical weir is defined by a plate 151, which is movable in an upward and downward direction and is held in place by suitable guide means.
  • Lugs 152 extending from each end of the plate 151 at its lower corners carry spigots 154 which engage in vertically extending guide slots 153 for movement of this weir plate 151.
  • An underflow weir arrangement is thus defined by the gap between the lower edge of the plate 151 and the surface 102 of the table of the unit. Flow may be completely shut-off by lowering weir 151 to its lowermost position.
  • Flow control is further regulated by the horizontal weir members 113, 114, defined by respective left and right plate portions 161a and 161b. Lateral displacement of these units is again controlled by guide lugs 162 carrying spigots 164 engaging in horizontally aligned guide slots 163.
  • the plates may be moved inwards to define a minimum flow control opening between their inner edges, and withdrawn outwards to allow full flow over substantially the entire width of the fluidising table structure, this maximum flow condition being indicated in ghost outline by reference 113', 114'. Any required intermediate gap may also be selected and maintained.
  • the comb-type deflector plate 111 is shown in Figures 13 and 14.
  • the comb structure has teeth 171 extending from a base bar or pivot axis 172, and the angle of the declining nominal surface defined by the teeth 171 may be varied relative to surface 102 by adjusting pivot arms 173 fixedly extending radially from pivot axis 172 at each end.
  • the cross-section of the teeth 171 of the comb 111 as shown in Figure 14 is also arranged to narrow in a downward direction from their upper surface 174, so that according as granules fall through the gaps 175 between the combs, they are encountering an increasing transverse dimension between the teeth 111, so as to substantially minimise the risk of particles becoming jammed between the teeth.
  • An advantage of the comb-type deflector arrangement is that the body of granules falling from the discharge end 106 of the table 102 are transformed into a more diffuse flow, so that the spray 117 is blown through a relatively deep mass of falling material so as to achieve maximum adherence of sprayed material to the granules and minimum blow-through of non-adhering melt.
  • Other features of the system as described in connection with Figures 7 to 14 inclusive are essentially identical with those already discussed in regard to Figures 1 to 3, and 4, 5 and 6 of the drawings.
  • FIG. 15 and 16 An alternative comb plate structure is shown in Figures 15 and 16 in pictorial and side view respectively and in more detail in Figures 17 and 18.
  • two comb plates or curtain-forming structures 211 and 218 are provided.
  • the first or main comb plate 211 is reversed in disposition as compared with the comb plate Ul of Figure 9 to define a primary curtain-forming structure.
  • the pivot axis 272a of comb plate 211 is located immediately at the leading or discharge end of the perforated or apertured surface 102, this axis is located forward of, above and at a spacing from the discharge end of table 102.
  • the teeth or tines 271a of the comb plate 211 extend forwardly from this pivot axis 272a towards the discharge end of the table 102.
  • the material leaving the table impacts against the upwardly inclined nominal surface or plane defined by the comb structure 211 to fall through the tines 271a and also slide to some extent back towards the discharge end, during formation of the fall ng curtain.
  • a wider tine spacing is used than in the arrangement of Figures 9, 13 and 14, the tine spacing being approximately double that of the previous arrangement.
  • a second comb plate 218 is located at a spacing below the first comb structure 211 to define a secondary or curtain-modifying structure.
  • Comb structure 218 has tines 271b similar to those of structure 211, and is similarly arranged to be angularly adjustable about a respective pivot axis 272b. Tines 271b of structure 218 are however approximately one-half the length of tines 271a of comb structure 211.
  • Tine spacing for structure 218 is the same as that of structure 211, but the tines of comb plate 218 are staggered as compared with those of comb structure 211, so that tines 271b of unit 218 underlie the gaps 275 between the tines 271a of plate 211. In this way, material which has passed through the gaps 275 of the upper plate 211 strikes the tines 271b of the lower plate 218, thereby inducing further diffusing action in the falling curtain.
  • the tines 271a, 271b are preferably also circular in cross-section, as shown in Figure 18.
  • FIG. 15 and 16 Also shown in Figures 15 and 16 is the location of the spray nozzles, which may be two, three, or more in number, distributed along the length of the falling curtain. Nozzle angle, spray direction and spacing from the curtain are also suitably selectively variable within a nozzle adjustment region indicated by reference 228 in Figures 15 and 16.
  • the nozzles 227 and the nozzle feedline 226 may be located anywhere within this region 228, by virtue of a melt supply duct being carried peripherally around this region and the nozzle line 226 being mounted on a rotatable nozzle adjustment plate 229, itself positionable at any location within the region 228.
  • This high level of adjustability is achieved by the melt supply being effected by way of a number of rotational joints in the feed lines. Thus the required high degree of adjustability noted above may readily be achieved.
  • the shape and spray pattern of the jet issuing from the nozzle may also be varied by alignment of the nozzle head or by selection of nozzles of alternative spray configurations.
  • An important advantage of the present system is that individual measurement and control of temperature are possible at each stage of the system of the invention. This is an important advance over drum technology, in which the scope for temperature control within the rotating unit is relatively limited. If the level of air circulation in the drum is high, short-circuiting of pellet flow may take place, while the speed of the exhaust airflow may lead to curtain distortion within the drum.
  • airflow is adjustable, and in addition, because withdrawal of air takes place above the table or fluidised bed means of the system of the invention, impingement of airflow patterns on curtain formation and maintenance is substantially minimised. There is a relatively low rate of draw-off of air at each level. Thus the likelihood of major airflow turbulences being created is reduced.
  • the amount of air passing through the system, while substantial in aggregate, is relatively modest at any one level, so that the volume flow of air at any one level is again modest.
  • a further advantage of the invention arising from the essentially random motion of particulate solids is substantial homogeneity of the moving mass with respect to particle size.
  • Optimisation of the effect of spray distance i.e. the distance between the spray nozzle and the particles, may be accomplished by placement of the spray nozzles at an optimum distance from the falling curtain of particles. Close control over spray distance, in the manner described above, enables significant reduction in the possible degree of superheat of the molten coating medium.
  • the spray nozzles may be aimed at any portion of the curtain without affecting the coating uniformity on individual particles. The location of the spray nozzles avoids their being subjected to bombardment by falling particles, thereby eliminating agglomeration by molten substrate.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

Abstract

Système de formation de granulés par enrobage discontinu dans la fabrication notamment d'engrais, dans lequel une succession de plateaux (1) destinés à porter les granulés à enrober sont superposés ou disposés l'un au-dessus de l'autre. Les granulés sont déplacés sur les plateaux (1) par fluidisation au moyen de l'air injecté dans le lit de granulés sur le plateau (1) à partir d'un conduit d'air (4) et à travers la surface perforée du plateau. Au niveau de l'extrémité de décharge (6) du plateau (1), les granulés s'écoulent vers le bas sur un élément de plateau (11) et atteignent un rebord ou bec (12) d'où ils tombent dans une zone d'enrobage voisine de l'extrémité d'entrée (5) du plateau sous-jacent. Les granulés traversent la zone d'enrobage en chute libre sous l'action de la pesanteur. Au cours de leur passage dans la zone d'enrobage (15), les granulés sont enrobés par pulvérisation d'une matière en fusion, en solution ou en suspension épaisse provenant d'une canalisation d'alimentation (26), d'où elle est expulsée par des buses (27). A mesure que les granulés traversent en descendant les zones d'enrobage (15) successives, dont chacune est associée à l'un des étages du système de plateaux superposés, leurs dimensions augmentent jusqu'à obtention des dimensions finales voulues dans l'étage final du système.
PCT/IE1995/000004 1994-01-22 1995-01-18 Formation de produits de type engrais granules WO1995019838A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU14244/95A AU1424495A (en) 1994-01-22 1995-01-18 Formation of pelleted fertiliser products

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9401211.9 1994-01-22
GB9401211A GB9401211D0 (en) 1994-01-22 1994-01-22 Formation of pelleted fertiliser products

Publications (1)

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WO1995019838A1 true WO1995019838A1 (fr) 1995-07-27

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AU (1) AU1424495A (fr)
GB (1) GB9401211D0 (fr)
WO (1) WO1995019838A1 (fr)
ZA (1) ZA95477B (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016146141A1 (fr) * 2015-03-19 2016-09-22 Pharma Technology S.A. Dispositif d'enrobage de matériau particulaire
CN110090598A (zh) * 2018-01-30 2019-08-06 徐州市禾协肥业有限公司 一种肥料料浆液滴固化成型的板式设备

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2594469A (en) * 1947-05-10 1952-04-29 Colgate Palmolive Peet Co Method of spraying freely falling particles
DE2024439A1 (de) * 1969-05-21 1970-11-26 Stauffer Chemical Company, New York, N.Y. (V.St.A.) Verfahren zur Herstellung von Agglomeraten aus kondensierten Alkaliphosphaten
US3666523A (en) * 1971-06-02 1972-05-30 American Cyanamid Co Process for coating particulate material with finely divided solids
FR2627404A1 (fr) * 1988-02-24 1989-08-25 Total France Procede et dispositif pour enrober des particules solides d'un film continu d'une matiere protectrice
EP0385901A1 (fr) * 1989-03-03 1990-09-05 Societe Anonyme Dite Mg Entreprise Dispositif d'impregnation en continu par pulverisation de produits granulaires et produit ainsi obtenu

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2594469A (en) * 1947-05-10 1952-04-29 Colgate Palmolive Peet Co Method of spraying freely falling particles
DE2024439A1 (de) * 1969-05-21 1970-11-26 Stauffer Chemical Company, New York, N.Y. (V.St.A.) Verfahren zur Herstellung von Agglomeraten aus kondensierten Alkaliphosphaten
US3666523A (en) * 1971-06-02 1972-05-30 American Cyanamid Co Process for coating particulate material with finely divided solids
FR2627404A1 (fr) * 1988-02-24 1989-08-25 Total France Procede et dispositif pour enrober des particules solides d'un film continu d'une matiere protectrice
EP0385901A1 (fr) * 1989-03-03 1990-09-05 Societe Anonyme Dite Mg Entreprise Dispositif d'impregnation en continu par pulverisation de produits granulaires et produit ainsi obtenu

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016146141A1 (fr) * 2015-03-19 2016-09-22 Pharma Technology S.A. Dispositif d'enrobage de matériau particulaire
CN107530665A (zh) * 2015-03-19 2018-01-02 制药技术股份公司 用于涂布颗粒材料的设备
US10357432B2 (en) 2015-03-19 2019-07-23 Pharma Technology S.A. Device for coating particulate material
CN110090598A (zh) * 2018-01-30 2019-08-06 徐州市禾协肥业有限公司 一种肥料料浆液滴固化成型的板式设备

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GB9401211D0 (en) 1994-03-16
ZA95477B (en) 1995-09-28
AU1424495A (en) 1995-08-08

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