How to Make Prills

Abstract

The method of making prills comprises the steps of: - providing a hollow body configured to rotate about a first axis of rotation, the hollow body comprising a wall configured rotationally symmetrically about the first axis, thereby enclosing an interior space, the wall comprising a plurality of through holes forming a nozzle; - providing a second body shaped to fit within the interior space of the hollow body, the second body being nested inside the hollow body such that a gap is obtained between the inner surface of the wall of the hollow body and the outer surface of the second body; - supplying a flow of liquid to the gap through a liquid inlet in liquid communication with the gap; - generating a jet of liquid from the nozzle at least radially outward relative to the first axis by driving rotational movement of at least one of the hollow body and the second body about the first axis of rotation using a rotary drive unit; The method includes the steps of: applying a reciprocating pressure excitation to the jet of liquid by moving one of the hollow body and the second body relative to the other of the hollow body and the second body along a first rotation axis using a reciprocating drive unit; and - separating the rotation of one of the hollow body and the second body and the reciprocating drive unit.

Description

[Technical field]

[0001] The present invention relates to a method for making prills. [Background technology]

[0002] Prilling is a known process for converting a quantity of liquid, particularly a quantity of molten material, into a plurality of reasonably uniform spherical particles. Prilling involves two operations: first, generating droplets from a quantity of liquid, and second, solidifying the droplets by cooling them individually as they fall through an ascending ambient air stream. Since no agglomerates are formed, the size distribution of the droplets determines the size distribution of the product. Plastic prills and detergent powders are examples of the resulting products.

[0003] By mounting the droplet generator on top of a prilling tower, which is essentially a large cooling tower, heat is transferred from the droplets to the air as they fall and solidify, and the tower needs to be tall enough so that the particles are strong enough not to break upon impact with the floor of the tower.

[0004] A distinction is usually made between two approaches to generate these droplets. The first approach uses a stationary prilling bucket, which in its simplest form can best be compared to a showerhead, where the liquid is forced through a stationary bucket with distributed nozzles, generating jets of liquid. These jets break up after a certain distance, thereby forming droplets. The second approach uses a rotating prilling bucket, which is equipped with distributed nozzles on the side walls and / or on the bottom. By rotating the bucket at a certain rotational speed, the centrifugal force pushes the liquid through the nozzles, thereby generating the jets. Prilling devices with rotating prilling buckets tend to have a larger production capacity than those with stationary buckets.

[0005] A key step in the prilling process is the generation of droplets from the liquid stream, and in particular the precise and accurate control of the size of the droplets and therefore of the resulting prills. The size distribution of the prills (also known as particle size distribution) produced using existing droplet delivery methods is usually quite broad. In particular, they usually produce "dust particles", which tend to reduce the process yield and contaminate the surroundings of the equipment. On the other hand, they also usually produce large droplets, which are not fully solidified at the end of the process, i.e., when they reach the floor of the tower. As a result, they can break up on impact and "stick" (i.e., agglomerate) together spherical particles that are collected at the bottom of the tower. This results in a further reduction in the process yield. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to alleviate at least some of the aforementioned problems, in particular to increase the prilling yield. [Means for solving the problem]

[0007] To this end, the present invention provides - providing a hollow body configured to rotate about a first axis of rotation, the hollow body comprising a wall arranged rotationally symmetrically about the first axis, thereby enclosing an interior space, the wall comprising a plurality of through holes forming the nozzle; - providing a second body shaped to fit within the interior space of the hollow body, the second body nesting inside the hollow body so that a gap is obtained between the inner surface of the wall of the hollow body and the outer surface of the second body; - supplying a flow of liquid, such as molten material, into the gap, preferably through a liquid inlet in liquid communication with the gap; - generating a jet of liquid from the nozzle in at least a radially outward direction relative to the first axis by driving a rotational movement of at least one of the hollow body and the second body, preferably with a rotational drive unit, about a first axis of rotation; - applying a reciprocating pressure excitation to the jet of liquid by moving one of the hollow body and the second body relative to the other of the hollow body and the second body along a first axis of rotation, preferably by means of a reciprocating drive unit; - decoupling one of the hollow body and the second body and the rotation of the reciprocating drive unit; The present invention provides a method for making prills, comprising:

[0008] A variable pressure is applied to the liquid present in the gap by driving one of the hollow body and the second body reciprocally along the axial direction of the first axis by the reciprocating drive unit. It should be noted that even in this case, the second body is suspended, i.e. nested, so that the gap is formed large enough so that the hollow body and the second body do not contact each other. These pressure pulses propagate to the jet of liquid generated through a nozzle in the wall of the hollow body, causing the jet to break up into equal droplets, resulting in droplets of substantially more uniform size. In order to improve the accuracy with which the pressure fluctuations applied to the liquid can be controlled, the rotation of one of the hollow body and the second body and the reciprocating drive unit about at least an axis parallel to the first axis is decoupled. Thereby, the reciprocating drive unit does not need to rotate with the hollow body, which also allows a simpler and more robust construction of the reciprocating drive unit, or to be able to counter any torsional forces, such as those propagated from one of the hollow body and the second body, that would otherwise be introduced into the reciprocating drive unit. For example, even if only the hollow body is driven, the liquid present in the gap will effectively act as a fluid coupling, thereby transmitting a torque to the second body. Therefore, to isolate the reciprocating drive unit from these rotations and the associated torque, it is possible to use piezoelectric elements superimposed in the reciprocating drive unit. These can generate vibrations at a large band of frequencies with sufficiently large force amplitudes and can be precisely controlled, so that strong vibrations of small amplitudes can be generated at a predetermined frequency and transmitted to one of the hollow body and the second body. This allows the excitation of the liquid present in the gap by a reciprocating pressure excitation with a predetermined frequency. However, piezoelectric elements are very sensitive to torsional loads and can therefore be easily damaged.

[0009] The method can generate a substantially uniform pressure distribution in the liquid over substantially the entire circumference of the inner space. It can control the size of the droplets more precisely and accurately, thereby improving the performance of the prilling process in terms of particle / droplet size distribution. Furthermore, it can distribute the droplets more uniformly over the width of the prilling tower, thereby further improving the yield of the prilling process. The method thus makes it possible to create droplets with less dimensional variation when compared to prilling methods according to the prior art. A liquid stream, such as a molten material, is transformed in the prilling process into droplets, which solidify over time, thereby making it possible to obtain prills. It is noted that the method, i.e. the method of supplying droplets, can also be applied to other processes, where it is advantageous to supply droplets with small dimensional variations.

[0010] In a preferred embodiment, the step of decoupling rotation includes providing a coupling mechanism between the reciprocating drive unit and one of the hollow body and the second body, and enabling relative rotation between the one of the hollow body and the second body and the reciprocating drive unit by the coupling mechanism about at least an axis parallel to the first axis. The coupling mechanism or coupling unit is configured to enable relative rotation between the one of the hollow body and the second body and the reciprocating drive unit in a reliable manner.

[0011] In a preferred embodiment, the coupling mechanism comprises a first rotary bearing unit and a second rotary shaft, and the step of providing the coupling mechanism comprises the steps of coupling a lower end of the reciprocating drive unit to a first portion of the first rotary bearing unit and coupling one of the hollow body and the second body to the second portion of the first rotary bearing unit, and during the step of applying a reciprocating pressure excitation, the lower end of the reciprocating drive unit moves in a direction substantially parallel to the second axis between a first position and a second position, and the step of enabling relative rotation comprises rotating the second portion of the rotary bearing unit relative to the first portion of the first rotary bearing unit about the second rotary shaft. The reciprocating drive unit and one of the hollow body and the second body are thereby effectively coupled via rotary bearings, such that substantially no damaging torsional loads are transmitted to the reciprocating drive unit.

[0012] In a preferred embodiment, the hollow body provided is at least partially substantially cylindrical and / or conical in shape, the internal space is at least partially substantially cylindrical or conical in shape, and the second body provided is substantially similar in shape to the internal space of the hollow body, such that the width of the resulting gap is substantially constant along the entire circumference of the second body. In such a hollow body, a substantially uniform pressure distribution can be generated in the liquid substantially over the entire circumference of the internal space, which in turn improves the performance in terms of droplets of uniform size and can further distribute them more uniformly over the width of the prilling tower, thereby increasing the yield of the prilling process.

[0013] The method then further preferably further comprises the step of coaxially configuring the hollow body, the second body and the first rotary bearing unit, so that the first and second rotation axes coincide and the hollow body, the second body and the first rotary bearing unit rotate about the same rotation axis, whereby during use substantially only axial forces act on the first rotary bearing unit, and therefore no other reaction forces need to be transmitted, for example to a support frame of the device, achieving a robust and simple configuration.

[0014] According to a preferred embodiment, the method further includes controlling, with the controller, the reciprocating drive unit to move one of the hollow body and the second body relative to the other of the hollow body and the second body at a predetermined motion frequency and amplitude. The controlled action of the controller allows for customization of the frequency and / or amplitude with which to drive the reciprocating drive unit to further improve yield. For example, it has been found that the operating frequency and / or operating amplitude for driving the reciprocating drive unit can be determined, for example, based on the viscosity of the liquid, such that the jet breaks up into droplets that are substantially more uniform in size, thereby improving yield.

[0015] In a preferred embodiment, the method includes the steps of coupling the reciprocating drive unit to the frame assembly and axially suspending the coupling mechanism from the reciprocating drive unit. This allows the use of reciprocating drive units that require a certain amount of pretension to operate accurately and reliably. It is further preferred that the method further includes the step of arranging a second rotating bearing unit, the second rotating bearing unit configured to rotate between the reciprocating drive unit and the frame about a third rotation axis, the third rotation axis being substantially parallel to and preferably coinciding with the second rotation axis. The reciprocating drive unit is thereby disposed between the two bearing units and freely rotates about its axis. Even if the first bearing unit (partially) fails, the second bearing unit can still prevent the reciprocating drive unit from having to bear excessive torque arising from one of the hollow body and the second body.

[0016] In a preferred embodiment, the method includes the step of blocking substantially any rotation of the reciprocating drive unit about the second axis of rotation by means of a rotating blocking mechanism. The coupling mechanism preferably includes a rotating blocking mechanism. Due to, for example, a small amount of friction in the coupling mechanism, a relatively small torque may still be able to pass through the coupling mechanism. By blocking the rotation with the provided blocking mechanism, this torque is received by the blocking mechanism and is thereby bypassed by the reciprocating drive mechanism. To block the rotation (relative to the frame), a blocking pin is preferably provided in the blocking mechanism, which allows for a simple and reliable way of blocking the rotation.

[0017] A preferred embodiment further includes providing the stacked piezoelectric elements to a reciprocating drive unit and contracting and / or expanding the stacked piezoelectric elements in a direction substantially parallel to the first axis to move one of the hollow body and the second body relative to the other of the hollow body and the second body. The stacked piezoelectric elements can deliver the force required to propagate pressure fluctuations, or pressure pulses, to the jet, so that they break up into more equally sized droplets. Furthermore, even at the required force levels, the stacked piezoelectric elements can be precisely driven in terms of frequency and amplitude.

[0018] A step of applying a preload to the reciprocating drive unit using a biasing mechanism is further included in a preferred embodiment of the method. Some types of actuators require a certain amount of preload to function properly. In a non-limiting example, stacked piezoelectric elements are available that require a minimum predetermined amount of tension preload to function reliably. For example, the step of preloading the reciprocating drive unit using a biasing mechanism includes suspending the coupling mechanism and one of the hollow body and the second body from the reciprocating drive unit to apply a tension preload to the reciprocating drive unit. Thereby, gravity itself acts as a preload applied to the reciprocating drive unit, thus obtaining a simple and robust biasing mechanism.

[0019] Preferably, the method provides a shaft assembly comprising a first shaft and a second shaft, and further comprises the steps of arranging the second shaft between the coupling mechanism and one of the hollow body and the second body, and arranging the first shaft between the rotation drive unit and the other of the hollow body and the second body. Since the second body is arranged in the interior space of the hollow body and the bodies need to be driven in different ways, the shaft assembly is arranged such that the second shaft is arranged between the coupling mechanism and one of the hollow body and the second body and can drive one of the hollow body and the second body in a reciprocating motion, and the first shaft is arranged between the rotation drive unit and the other of the hollow body and the second body and can rotate at least the other of the hollow body and the second body, thereby applying a centrifugal force to the liquid in the gap. Preferably, the method further comprises the step of arranging the first shaft and the second shaft coaxially, thereby resulting in a compact shaft assembly suitable for the stated purpose. Alternatively or additionally, the method preferably comprises the step of arranging the first shaft at least partially radially surrounding the second shaft, or arranging the second shaft at least partially radially surrounding the first shaft, whereby also a compact shaft assembly can be obtained, in which case the inner shaft is also protected by the outer shaft.

[0020] Alternatively or additionally, the step of providing a shaft assembly preferably further includes providing a third bearing system and disposing the third bearing system between the first shaft and the second shaft, the third bearing system comprising at least a linear bearing member, and the method further includes using a reciprocating drive unit to move one of the hollow body and the second body relative to the other of the hollow body and the second body along the first axis of rotation while moving the second shaft axially relative to the first shaft, preferably these being the only relative movements that the third bearing system is capable of. The third bearing system thereby allows for smooth operation with reduced friction. Furthermore, by coupling the first shaft and the second shaft via the third bearing system, forces applied to the second shaft are transferred to the first shaft instead of the coupling mechanism, independent of torque and axial forces around the shaft.

[0021] In a preferred embodiment, the method further comprises the steps of arranging a rotational transmission mechanism between the hollow body and the second body and coupling the rotational movement of the hollow body and the second body around the first axis by means of the rotational transmission mechanism. The rotational movement transmitted from the rotational drive to the hollow body is thereby transmitted to the second body as well. Both bodies thereby rotate at the same rotational speed, thus reducing shear effects in the liquid, but these shear effects, which may be present, for example, due to the speed difference of the hollow body and the second body, have a speed-slowing effect on the liquid. Thus, by coupling the rotational movements of the hollow body and the second body, the centrifugal force acting on the liquid in the gap, and thus the pressure of the liquid acting on the inner surface of the wall of the hollow body, can therefore be more precisely controlled.

[0022] Preferably, the rotational transmission mechanism provided comprises a male connector disposed at a non-zero radial distance from the first axis to one of the hollow body and the second body, and a female connector disposed on the other of the hollow body and the second body, the female connector being configured to slidably receive the male connector for coupling the rotational movement of the hollow body and the second body, but allowing relative movement between the hollow body and the second body in the axial direction, thereby providing a simple and robust coupling of rotation.

[0023] In a preferred embodiment, the method comprises the step of supplying a flow of liquid to the gap, which step comprises supplying the liquid through a liquid inlet opening in the second body and subsequently through at least one through hole of the second body forming a liquid connection between the gap and the liquid inlet. In use, the liquid is thereby supplied to the gap located between the hollow body and the second body. In that case, the method preferably further comprises the steps of arranging a primary through hole extending substantially parallel to the first axis and opening in the lower section of the hollow body, and supplying the liquid through the primary through hole to the lower section of the hollow body. The supply of liquid to the gap is thereby substantially uniform around the gap in the radial direction, which is also preferred when the first through hole is arranged substantially centrally in the second body. Alternatively or additionally, the method may further comprise the steps of configuring secondary through holes at the periphery of the second body, extending at least radially outwardly from the first axis, and feeding liquid to the gap through the secondary through holes. The liquid feed can thereby be dispersed over the gap, thus resulting in a more uniform distribution over the periphery of the gap in the axial direction. The step of configuring the secondary through holes then preferably comprises the step of arranging the secondary through holes of the second body at a non-zero distance of the nozzles of the hollow body, as viewed along the radial direction. By arranging the holes and the outlets such that they do not substantially overlap, a more uniform pressure distribution can be obtained over the inner wall of the hollow body. A more uniform pressure distribution at the wall results in more uniform (liquid) conditions at the nozzles arranged at the wall. The jet conditions are thereby more uniform, and therefore the droplets are formed more uniformly over the various nozzles.

[0024] In a preferred embodiment, the method comprises the steps of arranging a substantially fin-shaped member in the through hole of the second body and rotating the liquid flow with the rotation of the second body by means of the fin-shaped member. The fin-shaped member can be used to impart a rotational movement of the hollow body and / or the second body to the liquid flow entering the liquid inlet. The fin-shaped member preferably projects inwards from a peripheral wall that defines the through hole. It is further preferred that the fin-shaped members project substantially radially inwards and / or that they extend over substantially the entire height of the through hole, at least at the location of the peripheral wall. Thereby, the liquid flow can be effectively forced into a rotational movement by the rotation, thereby forming a stable vortex of liquid inside the hollow body or the second body.

[0025] In a preferred embodiment, the hollow body and the second body are hollow truncated cones, and the step of applying a reciprocating pressure excitation comprises a step of reciprocatingly varying the width of the gap between the hollow body and the second body. The bucket-shaped body may be shaped on the outside, for example, as a truncated cone, i.e. a truncated cone of a cone. The hollow body and / or the second body preferably comprise an interior space of substantially similar shape. Due to the bucket shape (i.e. a truncated cone or a truncated cone), the body is substantially symmetrical, and therefore, by configuring the body substantially coaxially, a uniform gap is obtained between the outer surface of the second body and the inner surface of the wall of the hollow body. By driving one of the hollow body and the second body reciprocally, the width of the gap is reciprocally varied, and thus a pressure pulse can be introduced into the liquid that may be present in the gap.

[0026] In a preferred embodiment, where the jet of liquid breaks up into droplets, the method further comprises the steps of generating a flow of cooling fluid and at least partially solidifying the dispensed droplets by cooling them as they move through the generated flow of cooling fluid. Thereby, the droplets of liquid, preferably molten material, are solidified by the flow of cooling fluid. The cooling fluid can be, for example, either a cooling liquid or a cooling gas, depending on the properties of the liquid. In addition, the direction of the flow of cooling fluid can be substantially along the direction of the falling droplets (e.g., substantially vertically downwards in the direction of gravity), but can also be substantially opposite to the direction of the falling droplets (e.g., substantially vertically upwards in the direction of gravity). By varying these parameters of the flow of cooling fluid, the time (and / or distance) at which the droplets at least partially solidify can be adjusted to a desired specification. For example, even for very small prills, it can be ensured that the prills will fall to the bottom of a suitable cooling tower, and that when they reach the bottom of the cooling tower, they will at least be solidified to an extent that agglomeration of the prills is significantly reduced, or even substantially prevented.

[0027] The invention is further illustrated by the following figures, which show preferred embodiments of the method, in which a droplet supplying device is used to generate prills from a liquid stream, and which are not intended to limit the scope of the invention in any way. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 is a schematic 3D perspective view of a droplet dispensing apparatus for creating prills used to carry out an embodiment of the method according to the invention. [Diagram 2] 2 is a schematic cross-sectional view of the droplet dispensing apparatus of FIG. 1 in a first plane; [Diagram 3] FIG. 2 is a schematic cross-sectional view of a droplet dispensing device in a first plane, enlarged at a top section of the device. [Figure 4]FIG. 2 is a schematic cross-sectional view of a droplet dispensing device in a first plane, enlarged at a bottom section of the device. [Diagram 5] 2 is a schematic cross-sectional view of the droplet dispensing apparatus of FIG. 1 in a second plane; [Figure 6] FIG. 2 is a schematic cross-sectional view of a droplet dispensing device in a second plane, enlarged at the top section of the device. [Figure 7] FIG. 2 is a schematic cross-sectional view of a droplet dispensing device in a second plane, enlarged at the bottom section of the device. [Figure 8] FIG. 2 shows a schematic diagram of a preferred embodiment of a reciprocating drive mechanism and coupling mechanism for use in a droplet dispensing apparatus; [Figure 9] 1 is a photograph of an experimental result of a conventional droplet dispensing device. [Figure 10] 4 is a photograph of experimental results of a droplet dispensing apparatus according to an embodiment of the present invention. [Figure 11] FIG. 2 shows a schematic diagram of two different types of nozzles arranged in the peripheral wall of a hollow body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] FIG. 1 shows a schematic 3D perspective view of a droplet feeder used to implement an embodiment of the method according to the invention. The droplet feeder 1 comprises a lower rotating assembly 2 comprising a hollow body 21 and a second body 22. A rotational drive unit 3 is configured to drive the rotation of the lower rotating assembly 2, a reciprocating drive unit 4 is configured to reciprocate the second body 22 along a rotation axis I, and a coupling mechanism 8 is configured to decouple the rotation from the reciprocating drive unit 4. The apparatus may further comprise a stationary frame assembly 5 comprising a mounting bracket 51 for mounting the apparatus in, for example, a suitable cooling tower, i.e., a prilling tower (not shown). Furthermore, the cylinder 52 is similar in size to the opening that needs to be inserted to mount the apparatus, typically in a prilling tower. An inlet piping system 6 is provided for supplying liquid to the lower rotating assembly 2 of the apparatus 1 and is described in more detail below. The operation of an embodiment of the apparatus 1 is described in more detail below with reference to FIGS. 1 to 8 and 11.

[0030] 2-4 show schematic cross-sectional views of the droplet feeder 1 for producing the prills of FIG. 1 in a first plane. FIGS. 5-7 show schematic cross-sectional views of the droplet feeder of FIG. 1 in a second plane substantially perpendicular to the first plane. The lower rotating assembly 2 comprises a rotating hollow body 21 in which a rotating second body 22 is arranged. The hollow body 21 and the second body 22 are shaped such that the second body 22 fits into the internal space 211 of the hollow body 21 and is shaped (at least on its outside) such that the second body 22 is substantially shaped to match the internal space 211, thereby forming a gap 23 between the outer surface of the second body 22 and the inner surface of the peripheral wall of the hollow body 21. The hollow body 21 and the second body 22 are preferably substantially bucket-shaped (i.e., formed as a hollow truncated cone) and are configured such that, when mounted in the prilling tower, the upper sections of the bodies 21, 22 have a larger dimension (e.g., diameter) than the bottom sections of the bodies 21, 22. This helps to distribute the droplets more evenly throughout the prilling tower.

[0031] The second body 22 may comprise an opening 221 at its bottom, in addition to a number of small through-holes 222 which may be arranged over several rows of through-holes 222 which may be located at different (angular) positions in the peripheral wall of the second body 22 as seen around the axis of rotation I. These rows of through-holes 222 may extend over substantially the entire height of the second body 22.

[0032] In use, the central inlet 24 directs a flow of liquid into the interior space of the second body 22. The central inlet 24 may comprise a number of flow directing elements 241, 242 that help direct the flow towards the interior space of the second member 22 and / or in the direction of rotation. The flow then flows through the opening 221 and / or through the number of through holes 222 into the gap 23. The number of through holes, also called nozzles 91, 92, are arranged in the peripheral wall 212 of the hollow body 21. In use, the hollow body 21 rotates about the axis of rotation I, and thus any liquid held in the gap 23 is subjected to centrifugal forces resulting from this rotation, thereby generating pressure on the liquid, which is forced out of the number of nozzles 91, 92, thus forming jets 901, 911 of liquid (see Figures 9 and 10), which are at least partially directed radially outward with respect to the axis of rotation I. The width of the gap 23 can be varied reciprocally by driving the reciprocating drive unit so that pressure pulsations can be introduced into the liquid present in the gap 23, as described in more detail below. These pulsations will be propagated to the jets issuing from the nozzles 91, 92. By adjusting the frequency and amplitude with which the width of the gap 23 is varied, pressure pulsations can be obtained that cause the jets to break up rapidly into droplets, resulting in droplets of substantially equal size, with the spread in droplet size being greatly reduced.

[0033] The nozzles 91, 92 (see FIG. 11) can be configured in different ways in the peripheral wall 212. For example, a first nozzle 91, a second nozzle 92, or any combination of these and other types of nozzles can be arranged in the peripheral wall 212. The first nozzle 91 is configured as a through hole that is substantially perpendicular to the outer and / or inner surface of the peripheral wall 212. The second nozzle 92 is configured as a through hole that extends substantially horizontally, i.e. substantially perpendicular to the axis of rotation I, after the droplet feeder is mounted on the prilling tower. Alternatively, a recess 93 is arranged in the outer surface of the peripheral wall 212 of the hollow body 21, so that the through hole of the second nozzle 92 can open in the recess 93, the surface of the recess 93 being substantially perpendicular to the through hole of the second nozzle 92.

[0034] The second body 22 may further comprise several fin-shaped members 223 extending from the central shaft connection body 224 in a substantially radial direction towards the peripheral wall 225 of the second body 22. These fin-shaped members 223 rotate the liquid entering the interior space of the second body 22 together with the second body 22. Furthermore, further flow directing elements 226 may be arranged in the upper section of the fin-shaped members 223 to help disperse the liquid throughout the second body 22. Thereby, a stable and substantially constant vortex of the rotating liquid can be obtained in the second body and in the hollow body, which creates more constant process conditions in the nozzles 91, 92 and thus a better control of the process. In this embodiment, the second body 22 is connected at its upper section 226 to the upper section 213 of the hollow body 21. The hollow body 21 itself is driven by the rotary drive unit 3. An outer shaft 71 is provided connected at a first end 711 to the rotary drive unit and at a second end 712 to the upper section 213 of the hollow body. The outer shaft 71 may be connected by a rotary bearing 74 to a stationary frame assembly 5. The stationary frame assembly comprises a frame mounting bracket 51 for mounting or positioning the droplet generation device 1 to a prilling tower.

[0035] The second body 22 is connected to the inner shaft 72 by means of a central shaft connection body 224 configured to receive and couple to the lower part 721 of the inner shaft 72. The inner shaft 71 is mostly surrounded by the outer shaft 72 and supported by several plain bearings 73, so that the inner shaft 71 is movable relative to the outer shaft 72 in a direction along and a rotational direction about the rotational axis I, preferably only in a direction along and a rotational direction about the rotational axis I. To protect the plain bearings 73 and the space between the inner and outer shafts 71, 72 from dust and / or liquid contamination, a flexible shaft cover 75 is arranged between the bottom section 712 of the outer shaft 71 and the central shaft connection body 224.

[0036] 3 shows a schematic cross-sectional view of the droplet feeder in a first plane, enlarged at the upper section of the device 1. A rotary drive unit 3 is provided to drive the outer shaft 71 by means of a second pulley 34, which in the present embodiment can be directly connected to the first end 711 of the outer shaft 71. The rotary drive unit 3 can comprise an (electronic) motor 31 driving a first pulley 32, the first pulley 32 and the second pulley 34 being coupled by a drive belt 33 transmitting the rotary motion from the motor 31 to the outer shaft 71. However, it should be noted that for this purpose any other suitable rotary transmission mechanism or gear mechanism can be used. The outer shaft 71 is coupled via a rotary bearing 74 to a shaft holding frame 54, which is formed by a tubular member connecting and holding the rotary bearing 74, and the shaft holding frame 54 is in turn connected to a frame base member 53, which also comprises a mounting bracket 51.

[0037] The inner shaft 72, the largest part of which is surrounded by the outer shaft 71, extends at its upper end 721 from the outer shaft first end 711. The upper end 721 is received by the outer shaft 81 of the coupling mechanism 8. The coupling mechanism 8 with a rotation bearing 82 receives the rotational movement of the inner shaft 72 and thereby protects the reciprocating drive unit 4 from any torsional forces that may damage the vibration element 41, which is preferably a superimposed piezoelectric element. The superimposed piezoelectric element can generate vibrations of a wide frequency band with a sufficiently large force amplitude and can be precisely controlled to obtain small vibration amplitudes.

[0038] Thus, to fix the vibration element 41, the element 41 is held between a lower connecting member 42 and an upper connecting member 43. The vibration element 41 is directly connected to and held by the upper connecting member 43. The lower connecting member 42 is directly connected to the upper section 83 of the coupling mechanism 8. The upper connecting member 43 is held by a second coupling mechanism 84, which also comprises a rotation bearing 85. Thereby, the reciprocating drive unit 4 is not restricted in its rotation about the rotation axis I, and therefore, even in the case where a slight torsional force is transmitted through the coupling mechanism 8, the vibration element 41 is substantially isolated from any potentially damaging torsional forces that may be transmitted from the inner shaft 72. To further assist in this, the coupling mechanism 8 comprises a block pin 86 that transmits the resulting torsional force to the frame suspension member 55.

[0039] The second coupling mechanism 84 is directly connected to the suspension member 55 via its upper stationary section 86. The reciprocating drive unit 4, the coupling mechanism 8, the inner shaft 72 and the second body 22 are thereby all suspended from the suspension member 55. Axial forces from these parts are thus transferred via the vibration element 41, thereby having a preload applied to the vibration element 41. These suspended parts 8, 72, 22 thus effectively form a biasing mechanism for the vibration element 41. The suspension member 55 is part of the stationary frame assembly 5.

[0040] 5, which shows a cross-section taken in a plane substantially perpendicular to the plane of Figures 2 to 4, shows the liquid inlet section 6, which comprises an assembly of tubular members and is configured at its first end 61 to connect to a liquid supply system and at its second end 62 the liquid inlet section 6 exits into the central inlet 24. Via the stationary first section 244 of the central inlet 24 the liquid is configured to flow to the second section 242 of the central inlet 24, which rotates together with the hollow body 21.

[0041] In use, the hollow body 21 is driven by the rotary drive unit 3 to rotate along the rotation axis I, as described above. Liquid is fed to the second body 22 through the liquid inlet section 6, so that it reaches the gap 23 through the second body 21, which is provided with several openings 221, 222. The reciprocating drive unit 4 is then used to vary the width of the gap 23. In the present embodiment, this is achieved by driving the vibration element 41, which transmits a reciprocating motion along the rotation axis I to the second body 22, via the coupling mechanism 8 and the inner shaft 72. By controlling the vibration element 41 according to a predetermined frequency and amplitude, pressure pulsations are directed to the liquid held in the hollow body 21. The combination of centrifugal forces due to the rotation and pressure pulsations induced in the liquid can form a jet through the nozzles 91, 92 that breaks into individual droplets, the individual droplets having only minor dimensional variations (when compared to conventional rotating droplet generators) and therefore which can be considered to be of substantially uniform size.

[0042] Results from an experimental setup with such a device are shown in FIG. 10, and results from an experimental setup with a conventional rotating droplet generator are shown in FIG. 9. The picture shows a hollow body 121 equipped with both a first nozzle 91 and a second nozzle 92. The second nozzle 92 is configured to open in a recess 93 arranged on the outer surface of the hollow body 121. In FIG. 9, it can be seen that an actual jet of liquid 901 leaves the nozzles 91, 92, which breaks up after a certain distance into a series of droplets 902 of different sizes. The droplets 902 have a large distribution in size, the jet breaks up into large first droplets, small second ones or into associated droplets. Further downstream, several different droplets may recombine to form even larger droplets, resulting in a large range in droplet sizes.

[0043] In Fig. 10, the liquid in the hollow body 22 is excited by pressure pulsations with a given frequency and amplitude. It is clear that the jet 911 starts to break up practically immediately after it leaves the nozzles 91, 92, and that the resulting droplets 912 are much more similar in size when compared to the droplets 911. In addition, the individual droplets 912 are seen to spread at more regular intervals, so that little coalescence of the droplets occurs. In the experimental setup, water / glycerin mixtures with different viscosities have been tested. In a first test, water with a viscosity of 1 mPa*s was used, and it was found that excellent results (in terms of narrow distribution of droplet sizes) could be obtained by introducing pressure pulsations caused by rotating the bucket so that the velocity of the water in the resulting jet is 1.5 m / s, and by introducing vibrations of about 280 Hz and with an amplitude of 20 μm. When using a somewhat more viscous mixture of 4 mPa*s, a set of substantially ideal conditions was found by introducing pressure pulsations, which for example occur by introducing vibrations with an amplitude of 35 μm at about 240 Hz when the liquid jet velocity is 1.3 m / s. With a more extreme mixture with a viscosity of 35 mPa*s, excellent results were obtained by introducing vibrations with an amplitude of 35 μm at about 190 Hz, for example for a velocity of 1.15 m / s.

[0044] FIG. 8 further shows an alternative embodiment of the coupling mechanism 108 and an alternative embodiment of the second coupling mechanism 1084, all other components being equal to the embodiment shown in FIGS. 1 to 7. The coupling mechanism 108 comprises two rotational bearings 1082, in particular thrust spherical roller bearings, which are preferably substantially equal. The bearings 1082 are configured such that the first ends 1086 are arranged adjacent to each other, such that the bearings only provide a rotational movement of the output shaft 82 relative to the housing unit 187 of the coupling mechanism 108, so that a reliable coupling mechanism 108 with minimal play in the axial direction is obtained. Axial play in the coupling mechanism 108 would affect the vibration transmission from the vibration element 41 to the second body 22 and thus have a negative effect on the performance of the droplet generation device 1. Furthermore, thrust spherical roller bearings are well suited to transmit high axial (i.e. thrust) loads, so that a reliable coupling mechanism 108 is obtained for transmitting axial forces from the reciprocating drive unit 4 to the second body. The second coupling mechanism 1084 also comprises a similar arrangement of two rotation bearings 1085, in particular thrust spherical roller bearings.

[0045] The invention is not limited to the embodiments shown, but extends to other embodiments falling within the scope of the appended claims. [Explanation of symbols]

[0046] 1 Droplet supply device 2 Lower rotating assembly 3 Rotation drive unit 4 Reciprocating Drive Unit 5 Stationary Frame Assembly 6 Inlet piping system, fluid inlet section 8 Coupling mechanism 21 Hollow body 22 Second Body 23 Gap 24 Center entrance 31 Motor 32 First pulley 33 Drive belt 34 Second pulley 41 Vibration Element 42 Lower connecting member 43 Upper connecting member 51 Frame mounting bracket 52 cylinders 53 Frame base member 54 Shaft holding frame 55 Suspension members 61 First end 62 Second End 71 Outer Shaft 72 Inner Shaft 73 Plain bearings 74 Rotary Bearing 75 Flexible shaft cover 81 Outer Shaft 82 Rotating bearing, output shaft 83 Upper Section 84 Secondary coupling mechanism 85 Rotary Bearing 86 Block pin, upper stationary section 91 Nozzle 92 Nozzle 93 Recess 108 Coupling mechanism 121 Hollow body 187 Housing Unit 211 Interior Space 212 Perimeter Wall 213 Upper Section 221 Opening 222 Through hole 223 Fin-shaped components 224 Central shaft connection body 225 Perimeter Wall 226 Flow Director, Upper Section 241 Flow-directing elements 242 Flow Directing Element, Second Section 244 Stationary First Section 711 First end 712 Second End 721 Lower part, upper end 901 Jet 902 Droplet 911 Jets, droplets 912 droplet 1082 Rotary bearing 1084 Second coupling mechanism 1085 Rotary Bearing 1086 First End I Rotation axis

Claims

1. 1. A method of making prills comprising the steps of: providing a hollow body configured to rotate about a first axis of rotation, said hollow body comprising a wall configured rotationally symmetrically about said first axis of rotation thereby enclosing an interior space, said wall comprising a plurality of through holes forming nozzles; providing a second body shaped to fit within the interior space of the hollow body, the second body nesting inside the hollow body such that a gap is provided between an inner surface of the wall of the hollow body and an outer surface of the second body; providing a flow of liquid to the gap through a liquid inlet in fluid communication with the gap; generating a jet of liquid from the nozzle in at least a radially outward direction relative to the first axis of rotation by driving a rotational movement of at least one of the hollow body and the second body about the first axis of rotation with a rotational drive unit; applying a reciprocating pressure excitation to the jet of liquid by moving one of the hollow body and the second body relative to the other of the hollow body and the second body along the first axis of rotation using a reciprocating drive unit; decoupling one of the hollow body and the second body and the reciprocating drive unit from rotation; Including, The step of isolating the rotation comprises: providing a coupling mechanism between the reciprocating drive unit and the one of the hollow body and the second body; allowing relative rotation between the one of the hollow body and the second body and the reciprocating drive unit via the coupling mechanism; Including, How to make prills.

2. the coupling mechanism comprises a first rotary bearing unit and a second rotary shaft, and the step of providing the coupling mechanism includes the steps of coupling a lower end of the reciprocating drive unit to a first portion of the first rotary bearing unit and coupling the one of the hollow body and the second body to a second portion of the first rotary bearing unit; During the step of applying a reciprocating pressure excitation, a lower end of the reciprocating drive unit moves in a direction parallel to the second axis of rotation between a first position and a second position; and 2. The method of making a prill as described in claim 1, wherein the step of enabling relative rotation includes the step of rotating the second portion of the first rotary bearing unit relative to the first portion of the first rotary bearing unit about the second axis of rotation.

3. 3. The method of making a prill according to claim 1 or 2, wherein the provided hollow body is at least partially cylindrical and / or conical in shape, and the interior space and the provided second body are at least partially cylindrical or conical in shape, such that the width of the resulting gap is constant along the entire circumference of the second body.

4. 4. The method of making a prill as described in claim 3, wherein the method includes a step of configuring the hollow body, the second body, and the first rotary bearing unit coaxially, such that the first rotation axis and the second rotation axis coincide, and the hollow body, the second body, and the first rotary bearing unit rotate about the same rotation axis.

5. 5. The method of making a prill according to any one of claims 1 to 4, further comprising the step of controlling, with a controller, the reciprocating drive unit to move the one of the hollow body and the second body relative to the other of the hollow body and the second body at a predetermined frequency and amplitude of motion.

6. A method of making a prill as claimed in any one of claims 1 to 5, comprising the steps of coupling the reciprocating drive unit to a frame assembly and axially suspending the coupling mechanism from the reciprocating drive unit.

7. 7. The method of making a prill as described in claim 6, further comprising the step of disposing a second rotational bearing unit between the reciprocating drive unit and the frame assembly, the second rotational bearing unit being configured to rotate about a third axis of rotation, the third axis of rotation being parallel to the second axis of rotation.

8. 8. A method of making prills as claimed in any one of claims 1 to 7, comprising the step of blocking any rotation of the reciprocating drive unit about the second axis of rotation with a rotation blocking mechanism.

9. 9. The method of making a prill as claimed in claim 8, including the step of providing said rotation blocking mechanism with a blocking pin for blocking said rotation.

10. 10. The method of making a prill according to any one of claims 1 to 9, further comprising the step of providing the reciprocating drive unit with stacked piezoelectric elements and contracting and / or expanding the stacked piezoelectric elements in a direction parallel to the first axis of rotation to move the one of the hollow body and the second body relative to the other of the hollow body and the second body.

11. The method of making prills according to any one of claims 1 to 10, further comprising the step of applying a preload to the reciprocating drive unit with a biasing mechanism.

12. The step of applying a preload to the reciprocating drive unit using a biasing mechanism comprises: suspending the coupling mechanism and the one of the hollow body and the second body from the reciprocating drive unit to apply a tension preload to the reciprocating drive unit.

12. A method for making the prills of claim 11 comprising:

13. 13. The method of making a prill according to any one of claims 1 to 12, further comprising the steps of providing a shaft assembly comprising a first shaft and a second shaft, disposing the second shaft between the coupling mechanism and the one of the hollow body and the second body, and disposing the first shaft between the rotational drive unit and the other of the hollow body and the second body.

14. 14. The method of making a prill as recited in claim 13, further comprising the step of coaxially disposing said first shaft and said second shaft.

15. 15. A method of making a prill as described in claim 13 or 14, comprising the step of positioning the first shaft to at least partially surround the second shaft in the radial direction, or the step of positioning the second shaft to at least partially surround the first shaft in the radial direction.

16. The step of providing a shaft assembly further includes providing a third bearing system and disposing the third bearing system between the first shaft and the second shaft, the third bearing system comprising at least a linear bearing member; 16. The method of making a prill according to any one of claims 13 to 15, further comprising the step of moving the second shaft relative to the first shaft in the axial direction while moving one of the hollow body and the second body relative to the other of the hollow body and the second body along the first axis of rotation using a reciprocating drive unit.

17. disposing a rotation transmission mechanism between the hollow body and the second body; coupling rotational motion of the hollow body and the second body about the first axis of rotation by a rotation transmission mechanism; 17. A method for making the prills of any one of claims 1 to 16, further comprising:

18. 18. A method for making a prill as claimed in any one of claims 1 to 17, wherein the step of supplying a flow of liquid to the gap comprises supplying the liquid through the liquid inlet opening in the second body and through at least one through hole in the second body which subsequently forms a liquid connection between the gap and the liquid inlet.

19. configuring a primary through hole extending parallel to the first axis of rotation and opening in a lower section of the hollow body; supplying the liquid through the primary through hole and into the lower section of the hollow body; 20. The method of making the prills of claim 18, further comprising:

20. defining a secondary through hole around the second body, the secondary through hole extending at least radially outward from the first axis of rotation; supplying the liquid to the gap through the secondary through hole; 20. A method for making the prills of claim 18 or 19, further comprising:

21. and configuring the secondary through hole includes disposing the secondary through hole of the second body at a non-zero radial distance of a nozzle of the hollow body.

21. A method for making the prills of claim 20.

22. disposing a fin-shaped member in the through hole of the second body; causing the flow of liquid to rotate with rotation of the second body by the fin-shaped members; 22. A method for making the prills of any one of claims 18 to 21, comprising:

23. 23. A method of making a prill as claimed in any one of claims 1 to 22, wherein the hollow body and the second body are hollow truncated cones and the step of applying a reciprocating pressure excitation includes the step of reciprocally varying the width of the gap between the hollow body and the second body.

24. The jet of liquid breaks up into droplets, and the method comprises: generating a flow of cooling fluid; at least partially solidifying the dispensed droplets by cooling the droplets as they travel through the generated flow of cooling fluid; 24. A method of making the prills of any one of claims 1 to 23, further comprising:

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