IE44229B1 - Process and apparatus for producing granules by solidification of a product in the liquid phase - Google Patents

Abstract

1536849 Forming granules in fluidised beds CHARBONNAGES DE FRANCE 4 Aug 1976 [18 Aug 1975] 34285/75 Heading B1F [Also in Division B5] Granules, e.g. of pitch or bitumen, are formed by solidification of drops of liquid phase introduced onto a fluidised part of a cooled pulverulent solid e.g. silica, situated above a perforated grid 2, Fig. 2, there being a non-fluidised part situated above an imperforate metal plate 4, inclined vibrations being applied to the bed by vibrator 8 so that the forming granules are circulated e.g. as shown by arrow 11 in Fig. 1 so that they pass up screens 9, particulate material passing through the screens back to the bed, and granules being discharged at the end of the screens. Cooling may be effected by cooling tubes, by evaporation of water introduced into the fluidising gas or directly into the bed, or by recycling part of the cooled product.

Description

The present invention relates to a process/for producing granules by solidication of drops of a product in the liquid phase.

It is already known to granulate substances such as pitch, for example by introducing them in drops into a current of water. The granules of product obtained by this process nevertheless entrain a little water, which is inconvenient for certain applications, so that a drying treatment is required.

It is also known to granulate substances in the liquid state by forming them into drops which are introduced into a container containing a fluidised bed. British Patent No. 1,355,443 describes a process of this kind. Nevertheless, in processes of this type difficulties sometimes arise with certain materials due to the sticking together of the granules when they come into contact before being completely solidified; the discharge of the products from the granulator also gives rise to problems.

It is a main object of the invention to overcome* these difficulties and obtain very regular granules.

According to the invention there is provided a method for the manufacture of granules by solidification of drops of substances in liquid phase, such as herein described, comprising the step of employing a fluidisation container having a bottom and containing a bed of pulverulent solid material used as a processing phase, the bottom of said container comprising a grid and means for feeding a fluidisation agent upwards through the grid, the surface of said bottom being constituted partly of the grid and partly of at least one continuous masking element so that only a vertical columnar zone above the grid is fluidised by the fluidisation agent while above the remaining portion of the grid is one or more non-fluidised vertical zones which form one or more zones not subjected to the action of the fluidisation agent, said container further comprising vibrating means for vibrating said container by means of vibrations to the horizontal applied in a direction which is inclined/, wherein the drops are introduced into the vertical columnar fluidised zone of the container, the bed is kept at a suitable temperature for solidification of the substance and the obtained granules being circulated by motion of pulverulent solid material due to the combination of vibrations and fluidisation are extracted from the bed by using the circulation current.

The bed permits the solidification of the drops and, because of the circulation flow in the bed, enables the drops to be entrained immediately they arrive in the bed.

The circulation flow of the particulate material is preferably perpendicular to the direction of introduction of the drops. It may, however,have any other direction.

Inside the container, circulation currents are thus created in the non-fluidised zone, and these in turn give rise to circulation in the fluidised zone.

One end of the fluidised bed may be fed with particulate material and an equivalent amount of particulate material withdrawn at the other end of the bed. The speed of circulation must be sufficient to enable the drops to be separated from one another as soon as they arrive in the bed. However, experience shows that it is preferable for the rate of flow of the particulate material to be very great in comparison with that of the granulated product to obtain a sufficiently rapid entraining movement.

The utilisation of vibrations makes it possible for the speed of circulation of the products in the fluidised zone to be regulated in a very flexible manner. In particular, it is possible to achieve rapid circulation permitting a high rate of flow of drops per unit of surface of the fluidised layer. 44239 The circulation currents thus achieved 1» the noilfluidised. zone can he used to separate from the particulate material of the bed the granules obtained by the process as described in our Patent Specification ilo. 40509.

The product to be granulated is introduced into the bed in a molten state. The temperature of the particulate material in the fluidised zone is kept sufficiently low to effect sufficiently rapid solidification of the drops to prevent the particulate material from sticking to the surface of the drops.

The heat released on the solidification of the molten piOducts and their subsequent cooling has to he dissipated. This can he achieved hy regulating the temperature of the gas used to effect the fluidisation of the particulate material, hut sufficient cooling of this gas to dissipate all the calories given up by the molten products, although technically possible, cannot he achieved economically. It is to he noted that a limit is set to the air flow since it cannot exceed, a certain value, for example 0.1 to 1 meter per second for solid particulate material.

The dissipation of the heat given up hy the molten products can he considerably accelerated hy providing heat exchange means in the bed. The heat exchange means may be a cooler in which a cooling fluid, circulates. For example,a water circulation type cooler may he located in the fluidised zone above the grid through which the fluidising agent flows.

It is also possible to utilise the heat absorption capacity of certain changes of state, for example, vaporisation. A vaporisable liquid may he injected into the fluidising agent.

In the cane of the vaporisation of water, the watei· is atomised into tho fluidisation •..•ir ..-nd tho evaporation of the microdrops in the fluidised zone will cool the latter.

Further, a vapori sable liquid may be injected into the ·' fluidised bed. For example water may be injected directly into the fluidised, zone itself. Another way to supply calories or : I extract hoot above the fluidisation grid, is by partly recycl- i ing (for example 10% of the internal, rate of flow) part of the : I pulverulent product which it is then necessary to discharge, and then t /heat or cool before reintroducing it.

It has been found, surprisingly that, when the cooling achieved in this manner was Sufficiently vigorous, spherical granules which contained practically no particuwere obtained late auxiliary treatment material sticking to their surfaces /. Conversely, the speed of cooling can be regulated so that a certain amount of the particulate material adheres to the surface of the granules if this material has particular properties, such as an anti-caking action, or a filler action. It should be noted that the auxiliary treatment material may be constituted by the actual product which is to be granulated, which is divided to the desired fineness to permit fluidisation.

In this case the entrainment of the particulate auxiliary material treatment / adi-ering to the surface of the granules is not trouble.'-; onio.

The method of the invention can be applied to the granulation of various molten products, for exair.(fle pitch, bitumen, thermoplastic resins, or glass. The method can also be used to granulate concentrated solutions - 5 44329 introduced into the bed, by solidifying by crystallisation, for example, solutions of urea or ammonium nitrate.

The invention also comprehends an apparatus for granulating a material in the form of drops, comprising a fluidisation container having a bottom and containing a bed of pulverulent solid material used as a processing phase, the bottom of said container comprising a grid and means for feeding a fluidisation agent upwards through the grid, the surface of said bottom being constituted partly of the grid and partly of at least one continuous masking element having a main direction so that only a vertical columnar zone above the grid is fluidised by the fluidisation agent while above the remaining portion of the grid is one or more non-fluidised vertical zones which form one or more zones not subjected to the action of the fluidisation agent, said apparatus further comprising vibrating means for vibrating said container by means of vibrations applied in a direction which is inclined and in vertical plan is parallel to the direction of said continuous masking element(s), heat exchange means provided in the bed, and means for introducing drops into the vertical zone subjected to the action of the fluidisation agent.

In a preferred embodiment the apparatus may comprise separating and discharging means consisting of at least an inclined discharging screen located at least partly in one of the said non-fluidised zones to discharge granules at an external overflow point.

It is an important advantage of the invention that large quantities of granules can be processed by allowing recycling of very small amounts of solid particulate material forming the fluidised bed while the speed of travel of ibe pariiculnte material is sufficiently high to move the granules away from the place where the product is dropped into the bed. Thus the formation of clusters is avoided, because the granules being formed has insufficient time to gather at their dropping place and they are rapidly entrained towards the separating and discharging means.

As is known, vibrations arc not transmitted through a fluidised bed; thus the granules are subjected to normal conditions of fluidisation. S/he vibrations, however, are transmitted to the non-fluidised zones of the bed of pulverulent material and tend to move it in the direction of application of the vibrations. High efficiency is obtained when the direction of the vibration is substantially coincident with a direction corresponding to the non-fluidised zones of the bed of pulverulent material. Uhder the effect of the vibrations in such a direction, it is observed that the particulate material, with the granules it contains, moves towards one end of the non-fluidised zone .

In this way a current is established in the non-fluidised zone so that the pulverulent material io entrained from the fluidised bed to the non-fluidised portion of the bed. Since fluidised beds have the property of flow like a liquid, rapid natural flow is formed in the fluidised bed which carries away the granules towards the non-fluidised zone, in which, because of tlio vibrations they are directed towards the means for separating and discharging by vibrations. 44339 It is easy to control the rate of circulation of the products by adjusting the width of the non-fluidised zones, or the frequency and amplitude of the vibrations, or by inserting flow regulating flaps separating the non-fluidised zone or zones from the fluidised zone to regulate the flow of the solid particulate material in the non-fluidised zone or zones.

The invention also comprehends products in granular form produced by the process of the invention.

In order that the invention may be more clearly understood 10 some embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:Figure 1 is a top view of an apparatus for carrying out the process of the invention, shown diagrammatically.

Figure 2 is a diagrammatical section on the line AA 15 of the apparatus shown in Figure 1, and Figures 3 and 4 show the apparatus of Figures 1 and 2 in simplified form and in particular show how a water circulation cooler can be fitted to the apparatus.

Referring to Figures 1 and 2, the apparatus comprises 20 a rectangular vessel 1, in which a grid 2 supports a fluidised bed of a solid particulate material and distributes the fluidising agent, such as a fluidising gas. At the base of the vessel there is a pipe 3 for supply of the fluidising gas. Around the periphery of the grid an unperforated metal plate 4 enables a 25 peripheral non-fluidised zone 5 to be formed all around the fluidised bed. Partitions 6 partly separate this zone from the fluidised zone. Flaps 15 are also provided to regulate the flow of the solid particulate material in the nonfluidised zone.

The apparatus also contains a vibration generator 7 connected to the vessel by lateral arms 8. The direction of the vibrations is inclined and in vertical plan is parallel to or masking element the direction of the longitudinal plate/ 4f. Screens 9 placed in the non-fluidised zone enable the granules formed to be discharged to the outside. A drop generator 10, shown diagrammatically in Figure 2, enables drops to be introduced into the fluidised zone and at the greatest distance from the vibrator. Through the action of the vibrations, circulation currents, represented by arrows 11 in Figure 1, are formed in the vessel, and through the action of these currents the granules formed are discharged through the screens 9, while the particulate material of the fluidised bed which passes through the screens remains in the vessel.

Figures 2 and 4 show a water circulation heat exchanger for cooling the fluidised bed. This cooler consists of a nest of tubes 12 placed above the grid 2. At their end the tubes 2q are connected in common to a water inlet pipe 12 and to a water outlet pipe 14, EXAMPLE 1 The apparatus shown in the accompanying drawings has been used for granulating an electrode pitch having a Kramer and Sarnow melting point KS 70-80°C.

The molten pitch is kept at 170°C in a vessel the bottom of which is pierced with round holes of 2 mm diameter. When it flows through these apertures the pitch is divided into 4.4 2 2 9 drops, which fall into a fluidised bed of silica sand whose granulometry is under 0.2 mm. The layer of sand is fluidised by blowing air at 20°C upwardly through the grid 2 and through the water circulation heat exchanger disposed inside the layer.

Under these operating conditions quasi-spherical balls or granules of pitch of a diameter 3 mm to 5 mm are obtained which have very little of the material of the bed adhering to their surface (less than 0.2%). If this small amount of silica could not be tolerated for the purposes for which the pitch is to be used, the silica of the fluidised bed could easily be replaced by a less troublesome material, such as alumina or coke dust.

The vessel containing the molten pitch is subjected to vibrations which makes it possible to increase the flow of drops through each aperture or to lower the temperature of the molten pitch, for example to use pitch at 155°C instead of 17O°C.

EXAMPLE 2 The process is carried out as in Example 1 but using, instead of pitch, a bitumen distillation fraction of KS 100 (Escorez resins - Trade Mark).

Granules similar to those of Example 1 containing practically no material of the fluidised bed are obtained, EXAMPLE 3 25 Novolaks (phenol-formol resins) melted at 100°C to achieve correct fluidity are granulated as in Example 1 in a fluidised bedof silica sand whose particles pass through a 0.2 mm screen, the bed being kept at a temperature of 20°C.

Very hard granules, with low fragility, of a diameter of from 0 2 mm to 5 mm and entraining only very little sand, are obtained.

Claims (3)

1. A method for the manufacture of granules by solidification of drops of substances in liquid phase, comprising the step of employing a fluidisation container having a bottom and containing a bed of pulverulent solid material used as a processing phase, the bottom of said container comprising a grid and means for feeding a fluidisation agent upwards through the grid, the surface of said bottom being constituted partly of the grid and partly of at least one continuous masking element so that only a vertical columnar zone above the grid is fluidised by the fluidisation agent while above the remaining portion of the grid is one or more non-fluidised vertical zones which form one or more zones not subjected to the action of the fluidisation agent, said container further comprising vibrating means for vibrating said container by means of vibrations applied in to the horizontal a direction which is inclined/, wherein the drops are introduced into the vertical columnar fluidised zone of the container, the bed is kept at a suitable temperature for solidification of the substance and the obtained granules being circulated by motion of pulverulent solid material due to the combination of vibrations and fluidisation are extracted from the bed by psi ng the circulation current.

2. A method according to Claim 1, wherein the circulation current is used in the non-fluidised zone in order to separate the granules from the particulate material of the bed in this zone. 3. A method according to Claim 1 or Claim 2, wherein heat exchange means is provided in the bed. 4. A method according to Claim 3, wherein the heat exchange means is a cooler in which a cooling fluid circulates. 5. A method according to any one of Claims 1 to 4, wherein a vaporisable liquid is injected into the fluidising agent. 6. A method according to any one of Claims 1 to 5, wherein a vaporisable liquid is injected into the fluidised bed. 44829 7. A method according to any one of Claims 1 to 6, the product to be granulated is introduced into the bed state. wherein in the molten 8. A method according to any one of Claims 1 to 6, wherein the product to be granulated is introduced into the bed in the state of a concentrated solution capable of solidifying by crystallisation. 9. An apparatus for granulating a material in the form of drops, comprising a fluidisation container having a bottom and containing a bed of pulverulent solid material used as a processing phase, the bottom of said container comprising a grid and means for feeding a fluidisation agent upwards through the grid, the surface of said bottom being constituted partly of the grid and partly of at least one continuous longitudinal masking element arranged so that only a vertical columnar zone above the grid is fluidised by· the fluidisation agent while above the remaining are portion of the grid / one or more non-fluidised vertical zones which form one or more zones not subjected to the action of the fluidisation agent, said apparatus further comprising vibrating means for vibrating said container by means of vibrations applied in a to the horizontal direction which is inclined /and in vertical plan is parallel to the longitudinal /direction of said continuous masking element(s), heat exchange means provided in the bed, and means for introducing drops into the vertical zone subjected to the action of the fluidisation agent. 10. An apparatus according to Claim 9, including separating and discharging means consisting of at least an inclined vibrating discharging screen located at least partly in one of the said granules non-fluidised zones to discharge /at an external overflow point. Π. An apparatus according to Claim 9, comprising flow regulating flaps separating the non-fluidised zone or zones from the fluidised zone to regulate the flow of the solid particulate material in the non-fluidised zone or 5 zones. 12. A method for producing granules by solidification of drops of a product in the liquid phase, substantially as herein described with reference to Figures 1 and 2 or Figures 1 and 2 modified as in Figures 3 and 4 of the 10 accompanying drawings. 13. A product in granular form produced by a method according to any one of Claims 1 to 8 or Claim 12. 14. An apparatus for granulating a material in the form of drops, substantially as herein described with reference to 15 Figures 1 and 2 or Figures 1 and 2 modified as in Figures

3. And 4 of the accompanying drawings.