FR2597366A1 - Process for smoothing the surface of particles with nonuniform surface, especially of fertilisers and device for using this process - Google Patents

Abstract

This process for smoothing particles with a nonuniform surface, especially of fertilisers, consists in introducing these particles into a first smooth-walled part of a drum inside which these particles are set in relative motion by rotation of the drum while being sprayed with a slurry, in order to reduce the surface asperities of the particles and to coat them with the solid phase of the slurry, thus producing granules with a virtually smooth surface. The granules are then transferred into a second part of the drum, adjacent to the first, in which they are agitated and dried by air circulation. Application to the smoothing of particles originating from a compacting or a crushing operation.

Description

 The present invention relates to a method of smoothing the surface of irregular surface particles, especially a nitrogen or phosphorus salt, potassium hydroxide or a mixture thereof.

The invention also relates to a device for implementing such a method.

 The particulate products obtained by compaction have the disadvantage that the particles thus obtained have on their surfaces sharp and brittle edges which generate dust during handling.

 This disadvantage also relates to the particles obtained by compacting smaller particles as far as such particles from compaction. tend to crumble and thus produce dust.

 The object of the present invention is to overcome these drawbacks by providing a method and a device which are capable of producing granules with approximately smooth surface and thus producing little dust from particles with an irregular and friable surface. by friction during handling.

 The invention thus has for obJet a method of smoothing the surface of particles with an irregular surface, characterized in that in a first phase. the particles are at least superficially moistened and set relative to one another to reduce the roughness of their surface by mutual contact of these particles during their movement to obtain granules with approximately smooth surface and what in a second phase. the granules obtained are dried.

According to other characteristics
The particles are moistened with a slurry whose solid phase is intended to coat the particles.

 - During the drying phase. the granules are sprayed. a substance for coating them to increase their size.

 - The solid phase of the slurry and / or the sprayed substance. are of the same nature as the particles.

 The invention also relates to a device for carrying out the method as defined above, characterized in that it comprises a first stage comprising means for humidifying the particles and means for moving relative to these particles relative to each other. a second stage comprising means for drying the granules produced by the first stage.

means for introducing the particles into the first stage. means for transferring in the second stage the granules formed in the first stage and means for discharging the granules of the second stage.

According to other features of this device
the first stage comprises at least part of the length of a rotary drum. axis about horizontal. inside and in the vicinity of one end of which open the means for introducing the particles. the means for transferring the granules opening in the vicinity of the opposite end of this drum portion whose inner surface is approximately smooth and means for spraying a fluid on the particles being also provided inside said drum part.

 - The second stage comprises at least a portion of the length of a rotary drum, of approximately horizontal axis. inside and in the vicinity of one end of which. open means for transferring granules from the first stage. means for evacuating the granules. disposed at the opposite end of that drum portion and means for agitating the product and drying by a gaseous fluid, provided within said drum portion.

 - The two stages of the device may be formed in a drum or in two separate drums.

 According to a preferred embodiment. the drying means comprise a fluidized bed device disposed inside the drum forming part of the second stage.

The invention will be better understood on reading the following description of various embodiments given solely by way of example. and with reference to the accompanying drawings, in which
FIGS. 1 to 3 are schematic views of three embodiments of the device of the invention.

 In the definition given above. and in the following description. particles are the particulate crude product directly from crushing or compaction, and by granules, the particles obtained after smoothing the surface of the raw particles.

 The device illustrated in FIG. 1 comprises a drum 1 of approximately horizontal axis and rotatably mounted around this axis. This drum has at each of its ends. a ferrule 2 annular each delimiting a rim oriented radially inwardly of the drum around a corresponding central opening.

 This drum 1 is divided into two parts along its length by an annular ring 3 delimiting. an annular flange oriented radially inward and a central opening.

 A first portion of the drum extending between an end ferrule 2 and the ferrule 3 intermediate. defines a first stage A of the device of the invention. The second part of this drum between the other end shell 2 and the intermediate shell 3, defines the second stage of the device.

 A chute 4 for introducing particles with an irregular surface. opens out inside the drum near its end in the first stage and a nozzle 5 for spraying a fluid.

such as water or an aqueous bead. is provided inside the portion of the drum 1 of the first stage 1. This nozzle 5 is oriented downwards to spray a mass of particles P present at the bottom of the drum and is connected to fluid supply means of sprinkling outside the drum through the interior of a pipe 6. The inner cylindrical wall of this first part of the drum 1 of the first stage A. is approximately smooth so that by rotation of the drum, the particles of the mass P are set relative to each other as will be explained later.

 The second part of the drum 1 of the second stage B. is similar to the granulation drum described in the patent application No. 85 12 082 of the application resse and comprises on the whole of its inner cylindrical wall longitudinal fins 7, circumferentially distributed on this cylindrical wall, these fins projecting radially towards the inside of the drum.

 The second stage B also comprises a fixed fluidized bed device 8. connected to a fan (not shown) at the outside of the drum via a conduit line 9. As described in the above-mentioned patent, the grid of the fluidized bed device 8 extends approximately over the entire length of the second floor B being oriented upwards while being also inclined upwards in the direction of rotation of the drum so that the granules from the first floor A and raised by the fins 7, fall on this fluidized bed device 8 or they are dried and / or cooled before falling into the drum.

 Optionally, a spray boom of a fluid containing a substance capable of coating the granules, for example a molten salt, a slurry or a suspension, can be provided under the fluidized bed device 8 in such a way that the nozzles 11 of this ramp are oriented in a suitable direction to spray on the curtain granules which fall from the fluidized bed device 8. This spray bar 10 is connected to supply means provided outside the drum by lntermedialre of a pipe 12.

 The operation of the device according to this first embodiment is as follows: particles with a surface area, resulting from crushing or compaction, are introduced into the first stage A of the drum 1 via the chute 4; the particles thus introduced are set relative to each other by rotation of the drum 1 and are sprayed with a fluid, preferably water or an aqueous product via the nozzle 5 to humidify at In the course of their relative movements, the particles come into contact with each other so that their asperities previously softened by humidification, are reduced. the formation of dust being prevented by the humidification of the medium.

 By overflow above the rim formed by the shell 3, the granules formed by smoothing the surface of the particles are transferred to the second stage B or they are taken up by the lifting fins 7 which lift these granules and drop them on the surface. fluidized bed device 8 where they are dried and / or cooled before falling back to the bottom of the drum curtain being, if necessary, coated during their fall by the substance sprayed by the nozzles 11. The pellets repeat a number this cycle is repeated by the lifting fins 7, cooling and / or drying on the fluidized bed device 8, before emerging from the drum 1 by overflow over the rim formed by the ferrule 2 fixed at the outlet end drum.

 The fluid sprayed by the nozzle 5 in the first stage A may simply be water to humidify at least superficially the mass P of particles whose surface is being smoothed by mutual contact of these particles with each other or an aqueous slurry of which the solid phase is of a nature identical to or different from that of the particles in order to humidify them at least superficially while coating them with the solid phase to contribute to their smoothing by covering the residual asperities and filling in the depressions between these asperities.

 The coating substance sprayed, if appropriate, by the ramp 10 may be of the same or different nature as the original particles and may be in the form of a slurry or molten salt. In the case where this coating substance of the second stage 8 is in the form of a molten salt, the air diffused by the fluidized bed device 8 has not only a drying function of the granules from the first stage A but also a cooling function of the molten salt coating sprayed by the nozzles 11 of the ramp 10.

 The changes made to the embodiment illustrated in FIG. 2 with respect to the previously described embodiment consist in modifying the drying means of this device.

 The fluidized bed device 8 is replaced by a conventional arrangement in which the drum is swept by a stream of hot gases introduced by the outlet end of the product and extracted in an intermediate zone 13 of the drum located at the end of the second neighboring stage B first floor A.

 Alternatively, this arrangement can be reversed, the hot gases then being introduced at the intermediate zone 13 while they are extracted by the outlet end of the second stage B.

With this arrangement, the drying air penetrating according to the arrows F in the second stage
B, dehydrates the granules which are stirred by raising with the fins 7.

 In the third embodiment illustrated in FIG. the device comprises two separate drums and lb and provided at each of their ends with a ferrule 2 similar to that described above.

 The drum 1a is included in the first stage A and the drum 1b is included in the second stage B. The drum 1b is arranged at a level slightly lower than the drum 1 and a chute 16 is disposed at the outlet of this drum 1a. and opens at its lower end inside the drum lb in the vicinity of the inlet end thereof.

 With this arrangement, the particles are introduced into the first stage A via the chute 4. The granules obtained at the exit of the first stage A by smoothing the surface of the particles overflow into the hopper 16 from which they are introduced into the drum lb of the second stage B via the chute 17.

 In this embodiment, stirring is performed by means of the lifting fins 7 and drying by the fluidized bed device 8, the latter can of course be replaced by any other known drying means.

 The transfer means provided here in the form of a hopper and chute are exemplary since the relative arrangement of the drums 1a and 1b may be different from that illustrated in FIG. in this case, these transfer means may take any form known in the art, for example a conveyor belt or bucket.

 Any suitable particulate materials, and particularly fertilizers, that is, a material based on a nitrogen salt and / or a phosphate salt and / or potassium hydroxide can be treated by this process.

 When spraying a slurry in the first stage A, the interest is of course to concentrate this slurry to the maximum to have the least water possible to eliminate in the second stage B.

For potash slag particles, that is to say a mixture of slag from steel mills
THOMAS and potash, including nitrogen OX, 10 to 14 t. of phosphorus evaluated in P 205 and 14 to 15% of potassium evaluated in K20, the concentration of the slurry is approximately 40 to 50%.

 For a superphosphate (NP) type fertilizer comprising 14% nitrogen, N 2 O, 36% phosphorus evaluated as P 205 and 0% potassium, a slurry concentration of about 65% was reached.

 The mass flow rate of the slurry can be from about 10 to about 15% of the amount of particles entering the first stage.

 Without a spray coating in the second stage B, the mass increase of the particles between the inlet and the outlet of the device of the invention is not negligible, this increase being approximately 5 to 10% of the mass of particles. initial.

 In order to illustrate the effect of the process of the invention on the evolution in particle size and on the abrasion resistance of the granules obtained from these particles, an example of particle size distribution and indication is given below. on the abrasion resistance of irregular surface particles called incoming particles and granules obtained according to the process of the invention from these incoming particles, so-called outgoing granules.

 In this example, the particles are potassium slag with nitrogen oxidation, 14% phosphorus evaluated at 205 P and 14% potassium estimated at K20, the incoming particles being sprayed at the level of the first stage A with a slurry whose solid phase is of the same nature as that of the particles themselves.

Incoming particles: granulometry: 29.3 ?. > 4.00 mm
4.00 mm>22.2Z> 3.00 mm
3.00 mm>26.7Z> 2.00 mm
2.00 mm>16.8Z> 1.00 mm
1.00 mm>2.3Z> 500 /, 2.7Z <500t
- Abrasion test: 90.8 Z
Outbound granules: granulometry: 45,5Z> 4,00 mm
4.00 mm>29.1Z> 3.00 mm
3.00 mm>24.9Z> 2.00 mm
0.57. > 1.00 mm
0 Z <1.00 mm
- Abrasion test: 98.1 X
The abrasion test consists of measuring the resistance of the particles or granules after passing through a slow rotation ball mill. This mill comprises a jar of 5 1 in which 2 kg of hard porcelain balls 20 mm in diameter are placed. .

 One kg of particles or granules previously sieved between 2 and 4 mm are introduced into the jar. After 15 minutes of rotation at 40 rpm. the balls are removed and the contents of the jar is passed over a large mesh sieve. The screened product is retried on a 2 mm sieve and the fraction refused by this sieve is weighed to the nearest gram.

 The result of the abrasion test is expressed as a percentage as follows.

Let P be the weight of the fraction refused to the sieve of 2 mm, the percentage of abrasion is then equal to P x 100
1000
The higher the percentage result of the abrasion test, the more granules or particles have a high mechanical strength, i.e. they have a lower ability to form dust.

 It can therefore be seen by referring to the numerical values given above that the granules obtained by the process of the invention from particles having an irregular surface have a much lower ability to form dust than particles from which these particles are obtained. granules were formed.

 Many variations are of course conceivable without departing from the scope of the lnventlon.

Thus, although the first stage of the device of the invention has been described using a drum or a smooth-walled drum portion, the first stage may comprise a granulation plate or a kneading screw. Similarly, any kind of conventional drying devices are conceivable to be implemented in the second stage B of the device of the invention.

Claims (11)

 1. A method of smoothing the surface of particles with an irregular surface, in particular particles of a nitrogen or phosphorus salt. potash or a mixture of these. characterized in that in a first phase. the particles are at least superficially moistened and set relative to one another to reduce the roughness of their surface by mutual contact of these particles during their movement to obtain granules with a roughly smooth surface and in a second phase, the granules obtained are dried.  2. Process according to claim 1, characterized in that the particles are moistened with a slurry whose solid phase is intended to coat the particles.  3. Process according to claim 1 or 2, characterized in that during the drying phase, the granules are sprayed with a substance intended to coat them to increase their size.  4. Process according to claim 2 or 3, characterized in that the solid phase of the slurry and / or the pulverized substance. are of the same nature as the particles.  5. Device for carrying out the following method according to any one of the preceding claims, characterized in that it comprises a first stage (A) comprising means (5.6) for moistening the granules and means (1). relative movement of these particles relative to one another, and a second stage (B) comprising means 18, 9, 13, 14, 15) for drying the granules produced by the first stage, means (4) for introducing the particles into the first stage, means (3; 16.17) for transferring into the second stage. the granules formed in the first stage and means (2) for discharging the granules of the second stage being further provided.  6. Device according to claim 5, characterized in that the first stage (A) comprises at least a portion of the length of a drum (2) rotatable. of approximately horizontal axis, inside and in the vicinity of one end of which, open the means (4) for introducing the particles, the means (3) for transferring the granules opening in the vicinity of the end opposed to this drum portion whose inner surface is approximately smooth and means (5,6) for spraying a fluid on the particles being also provided within said drum portion.  7. Apparatus according to claim 5 or 6, characterized in that the second stage (B) comprises at least a part of the length of a drum (1) rotating, of approximately horizontal axis, in the inte- close to one end of which. open means (3) for transferring granules from the first stage, means for discharging (2) the granules opening at the opposite end of this drum part, stirring means (7) and drying means (8.9 13,14,15) by a gaseous fluid of the granules also being provided inside said drum part.  8. Device according to claims 6 and 7, characterized in that the portions of drum length of the first and second stages, are defined by a same drum (1) the granule transfer means comprising a ferrule (3) arranged transversely a the inside of the drum at an intermediate location along the length thereof, thus delimiting two parts in the drum, associated for one with the first stage (A) and for the other with the second stage (B), the granules passing from one part to the other by overflow at the central opening of the ferrule.  9. Device according to claims 6 and 7, characterized in that the first and second stages each comprise a drum (la, lb) between which are arranged the means (16,17) for transferring granules.  10. Device according to any one of claims 5 to 9, characterized in that the drying means (8) are of the fluidized bed type.  11. Device according to any one of claims 7 to 9, characterized in that the drying means are of the hot gas scanning type flowing in the same direction as the product or in the opposite direction.