GB1572649A

GB1572649A - Process and apparatus for the manufacture of granules such as fertilizer granules

Info

Publication number: GB1572649A
Application number: GB10904/77A
Authority: GB
Original assignee: Unie Van Kunstmestfabrieken BV
Current assignee: Unie Van Kunstmestfabrieken BV
Priority date: 1976-03-20
Filing date: 1977-03-15
Publication date: 1980-07-30
Also published as: NO770976L; RO72706A; AR213518A1; PT66322B; TR19598A; ATA176477A; FI770823A; JPS52114569A; BG27729A3; AT354404B; HU174184B; ES456997A1; BE852617A; IT1086722B; PT66322A; DE2711761A1; PL106855B1; FR2344330A1; BR7701682A; NL7602953A

Description

(54) PROCESS AND APPARATUS FOR THE MANUFACTURE OF GRANULES, SUCH AS FERTILIZER GRANULES (71) We. UNIE VAN KUNSTMESTFABRIEKEN B.V., a Netherlands Limited Liability Company of Postbus 45, Utrecht, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed. to be particularly described in and by the following statement: This invention relates to a process and apparatus for the manufacture of granular material from a liquid phase comprising an aqueous solution, melt or suspension of such material, and particularly relates to such a manufacture wherein preformed granules together with a flow of gas are introduced into the lower end of a vertically disposed tube, and enlarged granules are separated from the said flow of gas at the upper end of the said tube.

A process for the production of granules has previously been proposed wherein the liquid phase to be granulated is atomized and is blown upward through a granulation zone into a bed of preformed granules. The gas flow causes a continuous circulation of the granules within the bed so that atomized liquid phase is repeatedly deposited on the existing granules as a thin coat. The bed is provided with an overflow by way of which part of the resulting granules is discharged continuously.

Such a process however has disadvantages. Thus as the granulation zone freely communicates circumferentially with the bed, it is possible that granules leave the granulation zone too soon, i.e. before the liquid phase coating has solidified sufficiently thereon. It is also possible that granules pass through the bed without encountering any liquid phase at all. In such a process moreover the granules circulate in the upper part of the bed for a longer period of time and so do not grow in size and have to be recycled after having been discharged and screened off, thus adversely affecting the capacity of the plant.

Also the other granules take up too large an amount of liquid phase, resulting in the risk of the liquid phase having not fully solidified when the granules leave the granulation zone.

These phenomena together result in too wide a spread of granule diameter.

By the practice of the invention a continuous process may be employed in which the granules being built up contact the liquid phase during each recycle operation, and wherein a much smaller range of sizes of final granules is obtainable.

The invention provides a process for the manufacture of granular material from a liquid phase comprising an aqueous solution, melt or suspension of such material, wherein preformed granules together with a flow of gas containing the said liquid phase in an atomized state are introduced upwardly into the lower end of a vertically disposed tube, whereby the said preformed granules become at least partly covered with liquid phase and are entrained by the rising flow of gas to the upper end of the said tube, said tube confining the granule-laden rising flow of gas so as to prevent granules from entering or leaving said rising flow of gas between said lower and upper ends thereof, and the said preformed granules covered with at least partly solidified liquid phase are separated from the said flow of gas at the upper end of the said tube.

Preferablv the process is a continuous process, particularly wherein granules of differing sizes are separated from the gas flow at the top of the said tube, and granules of size smaller than that required are subsequently separated from the said granules and recycled to the bottom of the said vertical tube.

In a particular embodiment of the invention the overhead gases obtained from the top of the said vertical tube after separation of granules therein are purified and dust separated off thereby is incorporated in the liquid phase.

The process of the invention is preferably effected whereby dependent on the amount of liquid phase, and its water content where applicable, the amount and the temperature of the gas introduced into the vertical tube and the time of contact between the solid particles and the gas, are so chosen that the heat released is sufficient to obtain a dry product, a separate drying treatment thereby being unnecessary. In this context a dry product means that the granules do not stick together to an inadmissible extent during the build-up of granulation. Thus the particles may include some water. A particular advantage of this preferred embodiment is that the heat content of the liquid phase is used economically.

Apparatus according to the invention comprises a vertical tube means for introducing a gas flow at the lower end of the said vertical tube, atomizing means for introducing at the said lower end of the vertical tube a flow of atomized liquid phase, means for introducing in said flow of gas preformed granules, and means for separating granules from the gas at the upper end of said vertical tube.

The said means for introducing preformed granules in the said gas flow may for example comprise a feed box for the granules surrounding the said atomizing means.

In one embodiment of apparatus according to the invention a plurality of vertical tubes are connected to a joint feed box. In another embodiment of the invention, a plurality of vertical tubes communicate with a joint collecting chamber.

The invention is hereinafter particularly described and illustrated in the accompanying drawing, which is a schematic illustration of one embodiment of the invention, and in the following Examples.

Referring to the drawing, a vertical tube 1 is provided at the bottom with a downwardly diverging portion and is in open communication with a feed box 2 for solids. A spraying nozzle 3 is fitted in this feed box to atomize a liquid phase, which may be a melt or a solution of granular material, or a suspension of granules of less than the required size, over the cross-section of the tube. The discharge opening of the spraying nozzle is located at a short distance above the transition from the conical part of the feed box to the cylindrical part in order to prevent material from being deposited in the transitional zone which would interfere with and ultimately stop, the circulation. The wall of the influx end of the tube may diverge in a downward direction to reduce the risk of granular material being deposited against the inner wall of the tube. This liquid is supplied from a vessel 11 by way of line 12, pump 22, and line 4. The feed box is furthermore connected to a booster compressor 23 by pipe 5.

The upper end of the tube 1 is connected to a chamber 6 for collecting the granules developed during upward passage of gas and material in tube 1, and separating the air. The bottom of chamber 6 may be provided with means e.g. a porous or perforated intermediate bottom, through which air can be supplied to keep the granules collecting in the chamber in motion and thus prevent bridging. The conveying gas is passed through conduit 7 to a cyclone 8. where the dust contained in the gas is separated of. The purified gas is discharged through conduit 9. e.g. to a heat exchanger, to recover any heat still present.

The dust separated off is passed through line 10 to vessel 11 wherein it is taken up in fresh liquid supplied through line 21. Chamber 6 is also provided with a discharge 13 through which part of the resulting granules are recycled directly to feed box 2. A very simple construction is obtained if the chamber 6 and the feed box 2 form a unit and in connection with each other.

Part of the resulting granules is discharged from chamber 6 through 14 into a screening device 15.

The desired final product passes through conduit or chute 16 to a storage place, if so desired after having been cooled and/or powdered. The undersize product leaves screening device 15 through line or chute 17. The product that is too coarse is passed through a line or chute 18 to a crusher installation 19. The undersize product and the crushed product are recycled together to feed box 2 through conduit 20. Vertical tube 1 has, preferably, a circular cross-section. The spraying nozzle 3 is then fitted centrally and axially with respect thereto. However it is also possible to use a tube of oval section and it will then be desirable to use a plurality of spraying nozzles disposed side-by-side in order to effect uniform distribution of the liquid over the cross-section. Also if a circular tube is used, it is possible to apply more than one spraying nozzle.

The following Examples of the invention are provided.

Example 1 To prepare urea granules, 60 kg/hour of a urea solution is fed to a granulator of the type illustrated in the accompanying drawing having a vertical tube of 85 mm in diameter and 1.10 m length. This solution was art a temperature of 118"C and contained 10% of water. 66 kg/hour of granules were recycled.

The amount of air used for transport was 300 m3/hour (N.T.P.). The temperature of the air was 85"C.

120 kg/hour of granules with a temperature of 90"C were discharged to a screening installation having a 4 mm mesh width screen.

The undersized fraction was recycled at a rate of 66 kg of granules per hour. The remaining 54 kg of granules had the following composition: 1% < 3.0 mm 9% < 3.5 mm 18% < 3.75 mm 75% < 4.0 mm 95% < 4.5 mm The final moisture content was 0.1%, and the breaking strength was 40 kg/cm2.

After leaving the granulating zone. the air for transport was at a temperature of 75"C.

Example 2 Granules of calcium ammonium nitrate were prepared according to the invention in an apparatus of the type illustrated in the accompanying drawing, having a vertical tube of internal diameter of 110 mm and a length of 1260 mm and protruding with a lower end into a feed box with a cone angle of 40"C, an upper diameter of 440 mm and an air feed opening in the bottom of 55 mm diameter, to which an air supply pipe was connected. In this pipe a liquid supply pipe was mounted centrally and axially and at the exit end thereof a spray nozzle 3 was fitted in such a position that its discharge opening was at a distance of 30 mm above the air feed opening. To the upper end of the feed box 2 a cylindrical shell was connected having a height of 1120 mm and provided with an overflow discharge pipe for granules. The diameter of this pipe. which was connected to the shell at about 900 mm from the bottom. was 100 mm. At its top the shell was connected to a gas collecting chamber with a diameter of 1000 mm through a conical portion. The position of vertical pipe 1 was variable in the vertical direction and hence also the width of the annular passage between the lower edge of the pipe and the conical wall of the feed box.

The conditions and results of some typical experiments are presented in the accompanying Table. All experiments were carried out using initial preformed small granules which had been formed in a prilling tower and were fed into the granulating apparatus immediately after prilling to prevent them from cooling down. In the Table: d5(, indicates the diameter of the granules at which 50% by weight of the granules is smaller and 50% by weight is larger.

B is the breaking strength of the granules, which is defined as the force in kg required per square cm of cross-section of the granule for breaking the granule.

R is the roundness of the granules, which is determined by measuring the percentage by weight of the granules rolling down along a slanting disc rotating at a fixed speed that leaves the disc in an arbitrarily selected area at the lower side.

In the experiments d5() was increased by 0.45-0.70 mm and the fraction of particles between 2.0 and 4.0 mm was 78-809. The roundness of the product was better than that of the starting material.

TABLE Experiment No. 1 2 3 4 Diameter D of vertical pipe mm 110 110 110 110 Width S of annular passage mm 95 95 110 110 Feed kglh CAN suspension 60 60 60 82 Air 632 592 665 570 Prills 60 60 60 65 Flow rate in vertical pipe m. tons/h 11 11 13 11 Temperature "C CAN suspension 100 140 140 100 Air ~ 90 75 75 95 Prills 70 70 75 75 Circulating material 60 60 60 50 No H2O in CAN suspension 15 5 6 16 Fresh prills do mm 2.50 2.40 2.40 2.40 H2O % (wght) 1.95 2.25 2.25 2.05 B kg/cm- 43 53 42 42 kg/cm- R % (wght) 56 68 62 68 Product d5() mm 2.95 3.10 2.90 3.00 H2O % (wght) 0.80 0.70 1.15 1.35 B kg/cm- > 49 > 48 > 47 39 R % (wght) 64 73 73 78 Fraction 2.0-4.0 mm % (wght) 78 78 80 79 The process and apparatus according to the invention are suitable for granulatin sulphur, ammonium sulphate, urea, calcium ammonium nitrate, calcium nitrate, NP(K) fertilizer and fertilizers containing magnesium, and combinations of two or more thereof.

WHAT WE CLAIM IS: 1. A process for the manufacture of granular material from a liquid phase comprising an aqueous solution. melt or suspension of such material, wherein preformed granules together with a flow of gas containing the said liquid phase in an atomized state are introduced upwardly into the lower end of a vertically disposed tube, whereby the said preformed granules become at least partly covered with liquid phase and are entrained by the rising flow of gas to the upper end of the said tube, said tube confining the granule-laden rising flow of gas so as to prevent granules from entering or leaving said rising flow of gas between said lower and upper ends thereof, and the said preformed granules covered with at least partly solidified liquid phase are separated from the said flow of gas at the upper end of the said tube.

2. A process according to Claim 1. wherein, dependant on the amount of liquid phase, and its water content where applicable, the amount and temperature of the gas introduced into the said vertical tube and the time of contact between the solid particles and the gas are so chosen that the heat released in the process is sufficient to obtain a dry product, as hereinbefore defined.

3. A process according to Claim 1 or Claim 2, which is a continuous process.

4. A process according to Claim 3, wherein granules of differing sizes are separated from the gas flow at the top of the said tube, and granules of size smaller than that required are subsequently separated from the said granules and recycled to the bottom of the said vertical tube.

5. A process according to Claim 3 or Claim 4, wherein overhead gases obtained from the top of the said vertical tube after separation of granules therein are purified and dust separated off thereby is incorporated in the said liquid phase.

6. A process according to Claim 1, substantially as hereinbefore described and illustrated in the accompanying drawing, or in the Examples herein.

7. Granules obtained by a process according to any of Claims 1 to 6.

8. Apparatus for carrying out the process according to Claim 1, comprising a vertical tube. means for introducing a gas flow at the said lower end of the vertical tube. atomizing

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

TABLE Experiment No. 1 2 3 4 Diameter D of vertical pipe mm 110 110 110 110 Width S of annular passage mm 95 95 110 110 Feed kglh CAN suspension 60 60 60 82 Air 632 592 665 570 Prills 60 60 60 65 Flow rate in vertical pipe m. tons/h 11 11 13 11 Temperature "C CAN suspension 100 140 140 100 Air ~ 90 75 75 95 Prills 70 70 75 75 Circulating material 60 60 60 50 No H2O in CAN suspension 15 5 6 16 Fresh prills do mm 2.50 2.40 2.40 2.40 H2O % (wght) 1.95 2.25 2.25 2.05 B kg/cm- 43 53 42 42 kg/cm- R % (wght) 56 68 62 68 Product d5() mm 2.95 3.10 2.90 3.00 H2O % (wght) 0.80 0.70 1.15 1.35 B kg/cm- > 49 > 48 > 47 39 R % (wght) 64 73 73 78 Fraction 2.0-4.0 mm % (wght)

78 78 80 79 The process and apparatus according to the invention are suitable for granulatin sulphur, ammonium sulphate, urea, calcium ammonium nitrate, calcium nitrate, NP(K) fertilizer and fertilizers containing magnesium, and combinations of two or more thereof.

WHAT WE CLAIM IS: 1. A process for the manufacture of granular material from a liquid phase comprising an aqueous solution. melt or suspension of such material, wherein preformed granules together with a flow of gas containing the said liquid phase in an atomized state are introduced upwardly into the lower end of a vertically disposed tube, whereby the said preformed granules become at least partly covered with liquid phase and are entrained by the rising flow of gas to the upper end of the said tube, said tube confining the granule-laden rising flow of gas so as to prevent granules from entering or leaving said rising flow of gas between said lower and upper ends thereof, and the said preformed granules covered with at least partly solidified liquid phase are separated from the said flow of gas at the upper end of the said tube.
2. A process according to Claim 1. wherein, dependant on the amount of liquid phase, and its water content where applicable, the amount and temperature of the gas introduced into the said vertical tube and the time of contact between the solid particles and the gas are so chosen that the heat released in the process is sufficient to obtain a dry product, as hereinbefore defined.
3. A process according to Claim 1 or Claim 2, which is a continuous process.
4. A process according to Claim 3, wherein granules of differing sizes are separated from the gas flow at the top of the said tube, and granules of size smaller than that required are subsequently separated from the said granules and recycled to the bottom of the said vertical tube.
5. A process according to Claim 3 or Claim 4, wherein overhead gases obtained from the top of the said vertical tube after separation of granules therein are purified and dust separated off thereby is incorporated in the said liquid phase.
6. A process according to Claim 1, substantially as hereinbefore described and illustrated in the accompanying drawing, or in the Examples herein.
7. Granules obtained by a process according to any of Claims 1 to 6.
8. Apparatus for carrying out the process according to Claim 1, comprising a vertical tube. means for introducing a gas flow at the said lower end of the vertical tube. atomizing

means for introducing at the lower end of the said vertical tube a flow of atomized liquid phase, means for introducing in the said flow of gas preformed granules, and means for separating granules from the gas at the upper end of said vertical tube.
9. Apparatus according to Claim 8, wherein said means for introducing granules into the said flow of gas comprises a feed box for granules, surrounding said atomizer.
10. Apparatus according to Claim 9, comprising a plurality of said vertical tubes sharing a single said feed box.
11. Apparatus according to any of Claims 8 to 10, comprising a plurality of said vertical tubes connected to a joint collecting chamber.
12. Apparatus according to any of Claims 8 to 10, comprising means for separating granules within a given size range from the granules separated from the gas flow at the upper end of the said tube, and means for recycling to the lower end of the said tube granules of size below the lower limit of said size range.
13. Apparatus for the manufacture of granules, substantially as hereinbefore described and illustrated in the accompanying drawing.