A VIBRATING PRILLING BUCKET PARTICULARLY FOR PRILLING OF UREA

Abstract

A prilling bucket for prilling of a liquid, particularly for urea, comprising a rotating assembly, a vibrating assembly, a magnetostrictive actuator disposed to impart vibration to said vibrating assembly, wherein said magnetostrictive actuator is part of the rotating assembly and is firmly connected with said vibrating assembly and the bucket comprises a slip connector arranged to transfer electrical power to said actuator.

Claims

1) A prilling bucket for prilling of a liquid, comprising: a static part; a rotating assembly which is arranged to rotate relative to the static part and around a main axis of the bucket, a vibrating assembly which includes part or all of the rotating assembly, and is arranged to oscillate relative to the static part along the direction of said main axis; a magnetostrictive actuator disposed to impart vibration to said vibrating assembly; wherein the rotating assembly includes said magnetostrictive actuator and the magnetostrictive actuator is rigidly connected with said vibrating assembly; the bucket further comprising a slip connector arranged to transfer electrical power to said magnetostrictive actuator.

2) The bucket according to claim 1, wherein said slip connector is a slip ring.

3) The bucket according to claim 2, wherein said slip ring includes an outer cylinder element and an inner cylinder element, the outer element being coaxial around the inner element, the outer element being static and the inner element being rigidly fixed to the magnetostrictive actuator, the outer element comprising brushes or wires and the inner element comprising conductive rings in a slip contact with said brushes or wires.

4) The prilling bucket according to claim 1, wherein the magnetostrictive actuator is firmly connected to the vibrating assembly via a rigid element.

5) The bucket according to claim 4, wherein the rigid element has an elongate shape and preferably has the shape of a rod or a tube.

6) The bucket according to claim 4, wherein the rigid element has a first end rigidly connected to the magnetostrictive actuator and a second end, opposite to the first end, rigidly connected to a component of the vibrating assembly.

7) The prilling bucket according to claim 1, wherein the static part includes a hollow tube which is also a feed tube of the liquid to be prilled.

8) The prilling bucket according to claim 1, wherein the rotating assembly includes a perforated side wall of the bucket, and said perforated side wall is also part of the vibrating assembly.

9) The bucket according to claim 8, wherein the bucket includes a frame defining a chamber for containing the liquid to be prilled and the perforated wall is connected to said frame via suspension means adapted to act as a vibration isolator and to vibrationally decouple the perforated wall from the frame.

10) The bucket according to claim 9, wherein the magnetostrictive actuator is firmly connected to the rotating and vibrating assembly via a rigid rod; one end of the rod is secured to the actuator; the opposite end of the rod is secured to a bottom plate of the prilling bucket; said bottom plate is integral with the perforated said wall of the bucket, so that the bottom plate and the perforated side wall vibrates together; the perforated side wall is connected to a frame of the bucket via a deformable seal which acts as said vibration isolator so that the vibration is not transmitted from the side wall to the frame.

11) The bucket according to claim 1, wherein the vibrating assembly includes a rotating sub-assembly and optionally a non-rotating sub-assembly, the magnetostrictive actuator being part of the rotating sub-assembly of the vibrating assembly.

12) The prilling bucket according to claim 1, for the prilling of a urea melt.

13) Use of a prilling bucket according to claim 12 for the prilling of urea melt and the production of solid prills of urea.

Description

[0034] The invention is now elucidated with the help of the figures, wherein:

[0035] FIG. 1 is a sketch of a prilling bucket according to a preferred embodiment.

[0036] FIG. 1 illustrates the following items. [0037] 1 Prilling bucket [0038] 2 Static feed pipe [0039] 3 Rotating shaft [0040] 4 Liquid chamber [0041] 5 Perforated side wall [0042] 6 Bottom of the bucket [0043] 7 Magnetostrictive actuator [0044] 8 Transmission rod [0045] 9 Slip ring [0046] 10 Lower seal of the side wall [0047] 11 Upper seal of the side wall [0048] 12 Inlet pipe [0049] 13 Bearing [0050] 14 Frame [0051] 15 Inner cylinder [0052] 16 Rotation axis [0053] 17 Lower flange [0054] 18 Cover of the bucket [0055] 19 Upper section of shaft

[0056] The prilling bucket 1 is mounted for example vertically at top of a prilling tower.

[0057] The bucket 1 includes a shaft 3, which is configured to rotate around the axis 16 supported by bearings 13 relative to the frame part 14. The shaft 3 is connected to a suitable motor, not illustrated.

[0058] The shaft 3 passes through the static feed pipe 2, which does not rotate in operation. Said feed pipe 2 has an inlet pipe 12 for introduction of a liquid, for example urea melt U. From a bottom opening of the feed pipe 2, the urea melt U enters the liquid chamber 4.

[0059] The bottom end of the shaft 3 is fixed to the lower flange 17. The lower flange 17 in turn is connected to the perforated side wall 5 and to the bottom 6 via the lower seal 10. Said lower seal 10 is able to transmit a torque and, therefore, the perforated side wall 5 is put into rotation when the shaft 3 rotates. However the seal 10 is highly deformable in the vertical direction of the axis 16, being thus unable to transfer a vertical force, particularly if the force alternates with a high frequency. The upper seal 11 is similar, being flexible in the direction of the axis 16.

[0060] The magnetostrictive actuator 7 is fixed to an upper section 19 of the rotating shaft 3. The magnetostrictive actuator 7 rotates together with the shaft 3 and all other rotating parts of the bucket 1.

[0061] The magnetostrictive actuator 7, in addition, is rigidly connected to the bottom 6 via the rod 8. The drive shaft 3 is hollow and the rod 8 is mounted coaxial with said shaft 3. The bottom end of the rod 8 is fixed to the bottom plate 6 and the bottom plate 6 is fixed to the perforated side wall 5. The assembly of the bottom plate 6 and perforated side wall 5 is connected to the lower flange 17 and to the cover 18 by means of the seals 10, 11.

[0062] The magnetostrictive actuator 7 is powered by a slip ring 9. The slip ring is connected to a suitable electrical power source and comprises a static outer ring and a rotating inner ring 15. A suitable electric contact is established between the outer ring and the inner ring, for example with brushes or wires in contact with conductive rings.

[0063] When energized, the magnetostrictive actuator 7 oscillates according to the direction of the axis 16 with a frequency and amplitude depending on the excitation signal. This vibration is transmitted to the perforated side wall 5 via the rigid connection of the rod 8 and the bottom 6. The vibration is however filtered by the seals 10 and 11, so that it not transmitted to the flange 17 and cover 18.

[0064] In operation, the shaft 3 rotates the lower flange 17, the perforated side wall 5 and the cover 18. The magnetostrictive actuator 7 rotates as well, being fixed to the bottom 6 and the upper part 19 of the shaft 3. The perforated side wall is also vibrated along the axis 16. The liquid urea melt U contained in the liquid chamber 4 is ejected from the perforated side wall 5 due to centrifugal force; the vibration of the side wall 5 helps break the liquid jets into drops of a regular size and shape.