GRANULATOR FOR LIQUID SUBSTANCES, PARTICULARLY FOR UREA

Abstract

Granulator (1), in particular for urea, comprising an active system for removal of encrustations from at least one wall (4) with a surface (14) exposed to the granulation process, wherein said system operates by imparting a pulsed deformation to said wall.

Claims

1) A granulator for obtaining a solid product in the form of granules, starting from a supply of said product in liquid form, said granulator comprising walls which define a granulation chamber, wherein it comprises a system for removing encrustations or dust from at least one wall, said system comprising at least one shaking member which acts on said wall and which is configured to impart a pulsed deformation to said wall and said wall has a double structure, comprising a load-bearing wall and an internal wall facing the granulation chamber and said encrustation removal system is arranged to impart said pulsed deformation to said internal wall.

2) The granulator according to claim 1, wherein said at least one shaking member is a mechanical vibrator.

3) The granulator according to claim 1, wherein said internal wall bears against said load-bearing wall and is substantially in contact therewith.

4) The granulator according to claim 1, wherein said internal wall has its own support means and is spaced from said load-bearing wall.

5) The granulator according to claim 1, said internal wall being a thin membrane wall, preferably made of thin metal sheet or made of PTFE.

6) The granulator according to claim 1, said internal wall comprising a plurality of panels.

7) The granulator according to claim 1, wherein it comprises a plurality of shaking members acting in distributed manner on the surface of said wall.

8) The granulator according to claim 6, wherein said encrustation removal system comprises at least one shaking member for each panel or group of panels, of the internal wall.

9) The granulator according to claim 1, wherein said at least one shaking member is adapted to introduce a pressurized fluid means between the load-bearing wall and the internal wall so as to deform the internal wall.

10) The granulator according to claim 1, wherein the granulator comprises a plurality of nozzles for spraying the growth liquid and said internal wall has increased deformability in the vicinity of said nozzles.

11) The granulator according to claim 1, wherein said wall has a non-adhesive coating or lining directed towards the granulation chamber.

12) The granulator according to claim 1, wherein it operates in a fluid bed condition inside said granulation chamber.

13) The granulator according to claim 1, comprising a control system configured to activate said encrustation removal system manually or automatically at predefined intervals.

14) A method for removing encrustations from a wall of a granulator for obtaining a solid product in the form of granules, starting from a supply of said product in liquid form, in particular of a urea granulator, said wall having a double structure, comprising a load-bearing wall and an internal wall facing a granulation chamber, the method comprising the operation of imparting a pulsed deformation to said internal wall, through direct mechanical contact with at least one vibrating member and/or through a pressurized fluid means.

15) The method according to claim 14, wherein the pulsed deformation has a frequency of between 1 Hz and 20 Hz.

Description

DESCRIPTION OF THE FIGURES

[0055] FIG. 1 is a schematic representation of a granulator, for example a urea granulator.

[0056] FIG. 2 shows a side wall of the granulator according to FIG. 1, in a first embodiment of the invention.

[0057] FIG. 3 shows a variant of FIG. 2.

[0058] FIG. 4 shows a side wall of the granulator according to FIG. 1, in a second embodiment of the invention.

[0059] FIG. 5 shows in schematic form a control system for the pneumatic type activation.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] FIG. 1 shows in schematic form a urea granulator 1 which comprises a granulation chamber 2 defined by a bottom 3 and by side walls 4.

[0061] The granulator 1 has an essentially longitudinal crossing direction V from an inlet section 5 to an opposite outlet section 6. Inside the chamber 2, during operation, a fluid bed formed by the growing urea granules is created.

[0062] The granulator 1 comprises nozzles 7 which are distributed along the walls 2 and/or on the bottom 3. Said nozzles 7 spray liquid urea or highly concentrated urea solution (generally 96% or more) in order to feed the process.

[0063] Further details of the granulator 1 and the process are known to the person skilled in the art and do not need to be described for the purposes of understanding the invention.

[0064] FIG. 2 shows a schematic cross-section of a side wall 4 in a first embodiment of the invention.

[0065] Said wall 4 has a double structure comprising a load-bearing wall 10 and a membrane-type internal wall 11. The wall 11 is made for example of sheet metal with a small thickness (<1 mm) or of synthetic material and is sealed together with the load-bearing wall 10 along a peripheral edge 12. Sealing along the edge 12 may be performed with a weld if the materials so permit, for example if both the walls 10 and 11 are made of steel.

[0066] The internal wall 11 has a surface 14 (opposite to the load-bearing wall 10) which faces the granulation chamber 2. In some embodiments said surface 14 has undergone an anti-adhesion treatment. The wall 11 is therefore the wall which actually defines the granulation chamber 2, while the load-bearing wall 10 has the structural function of withstanding the mechanical stresses.

[0067] More specifically, FIG. 2 shows a preferred embodiment in which the wall 11 comprises a plurality of panels; in the figures two panels 11.sub.A and 11.sub.B can be seen. The load-bearing wall 10 is thus lined with a panelling which, as a whole, forms the internal wall 11 facing the granulation chamber 2. Each panel 11.sub.A, 11.sub.B, etc., has preferably its own sealed edge 12.

[0068] The internal wall 11, in the embodiment shown in FIG. 2, substantially bears against the load-bearing wall 10. Said embodiment may therefore be referred to as being of the coupled-wall type. Compressed air may nevertheless be introduced between the two walls 10 and 11.

[0069] It should be noted that the internal wall 11 acts an internal lining for the load-bearing wall 10. Owing to the sealed edge 12, the load-bearing wall 10 is not directly exposed to the environment of the granulation chamber 2 and therefore does not need to be designed for direct contact with the urea. The materials of the walls 10 and 11 may therefore be of a varying nature.

[0070] FIG. 3 shows a variant with spaced walls. In this variant of the invention, the internal wall 11 is supported by a structure of beams or sections 16, so as to space from each other the external wall 10 and the internal wall 11, defining a cavity 13.

[0071] The panels of the internal wall 11 are welded to the load-bearing structure formed by the beams 16. In this way inflation of the internal wall is simultaneous for all the panels.

[0072] The internal wall 11, both in a coupled-wall embodiment as shown in FIG. 2 and in a spaced-wall embodiment as shown in FIG. 3, may have a greater deformability in the region of the nozzles 7 in order to compensate for the constraining effect of the nozzles themselves. Preferably, the wall 11 has a smaller thickness in a region around said nozzles 7 or is made of a more flexible material. For example, the wall 11 is made of PTFE in the zones around the nozzles 7, while the remaining parts of the same wall 11 are made of sheet metal.

[0073] The granulator comprises one or more shaking devices 15 which may be mechanical vibrators acting directly on the internal wall 11 (for example cam vibrators), or spouts arranged so as to introduce compressed air into the space between the load-bearing wall 10 and the internal wall 11.

[0074] The internal wall 11, under the action of the shaking members 15, is deformed and behaves substantially as a membrane. The dotted line 11* in FIG. 3 indicates the deformation of the internal wall 11, while the reference f in the same figure indicates the maximum deformation of said wall 11.

[0075] The deformation of the wall 11 follows the pulsed progression of the stress transmitted by the devices 15, with a shaking effect of the surface 14 which removes possible solid deposits (crusts) or urea dust.

[0076] One advantage of the division into panels 11.sub.A, 11.sub.B, . . . , as shown in FIG. 2, where each of said panels has its own seal along the respective edge 12, consists in the fact that each panel has a small surface area and, consequently, ensures better control of the abovementioned deformation and swelling effect.

[0077] Preferably, a plurality of shaking panels 15 is provided, and even more preferably, at least one shaking device 15 is provided for each panel 11.sub.A, 11.sub.B, etc., of the internal wall 11.

[0078] FIG. 4 shows an embodiment in which the wall 4 has a single structure formed by the load-bearing wall 10 and the surface 14 consequently is formed by the inner side of said wall 10, directed towards the granulation chamber 2.

[0079] The pulsed deformation, in this single-wall embodiment, is imparted by means of direct contact, by one or more vibrators 20 which comprise at least one vibrating element 21 acting on the wall 10.

[0080] In the mechanical type embodiments (i.e. which use mechanical vibrators), the shaking members 15 are preferably components known per se. For example vibrators comprising a vibrating member, such as a piston, in direct contact with the wall of the granulator, or vibrators of the cam type, may be used. The latter comprise a casing which contains, mounted therein, a fast-rotating cam which, owing to its eccentricity, transmits vibrations to the casing. The casing of the cam vibrator, therefore, may be fixed directly to the wall of the granulator (for example the wall 11 of FIGS. 2, 3 or the wall 10 of FIG. 4) or may be fixed to a plate provided with lugs (of the feeler type) which bear against the wall of the granulator.

[0081] In some embodiments of the invention, both the pneumatic and the mechanical systems acting on the same internal wall 11 are provided. Said two pneumatic and mechanical systems may be used, simultaneously or alternately, for example for periodic cleaning and for extraordinary cleaning, respectively.

[0082] FIG. 5 shows in a simplified manner a system for introducing compressed air into the cavity 13 of FIG. 3, for embodiments of the pneumatic type. Said system essentially comprises an air inlet line 30, an air inlet valve 31, an air discharge line 32 with respective discharge valve 33, a PLC 34 which controls the valves 31 and 33.

[0083] In the rest condition, the system has the discharge valve 33 open and the inlet valve 31 closed. The control system 34 operates with a cleaning sequence which comprises the following steps:

[0084] the discharge valve 33 closes and the inlet valve 31 opens, allowing the compressed air supplied in the line 30 to flow into the cavity 13;

[0085] the pressure inside said cavity 13 consequently gradually increases, deforming the internal wall 11;

[0086] once a set pressure is reached, such as to produce a desired deformation of the internal wall, the PLC 34 closes the inlet valve 31 and opens the discharge valve 33.

[0087] Said sequence continues for the set operating time of the cleaning system, for example 5 seconds.

[0088] A system such as that shown in FIG. 5 may be used also to supply compressed air between the walls 10 and 11, in an coupled-wall system of the type shown in FIG. 2.

[0089] Pneumatically (and/or mechanically) imparted shaking of the wall of the granulator removes the encrustations or the dust (which, increasing, would form the crusts) from the surface 14 directly in contact with the fluid bed. The process for removing encrustations is performed with a suitable periodicity and may be manually or automatically controlled by a control system.

[0090] Based on the operating data, depending on the extent to which the crusts tend to form and depending on their consistency (more or less plastic or fragile), the activation interval of the cleaning sequence may be decided.

[0091] Frequent activation (e.g. every 5 minutes) may eliminate the dust as it is deposited, substantially avoiding the formation of crusts.

[0092] Less frequent activation may allow the formation of crusts and in this case the activation frequency is advantageously determined so that the crusts cannot reach the size and mass which would prevent their expulsion from the bed. In this way, the solid material which separates from the surface 14 may be transported by the fluid bed and expelled from the granulator 1, through the outlet section 6, instead of accumulating on the bottom 3.

[0093] The invention thus achieves the objects mentioned above, increasing the possibilities and prospects for using granulation for the production of solid urea, increasing the profitability owing to stoppages which are fewer and of shorter duration.