US2414700A - Method for making granular superphosphate - Google Patents

Description

"Jan. 2l, 1947. M. sHoELD METHOD FOR MAKING GRANULAR SUPERPHOSPHATE Filed June l5, 1938 Patented Jan. 21, 1947 2,414,700 ICE METHOD Fon MAKING on ANULAR,

SUPERPHOSPHATE Mark Shoeld, Baltimore, Md.,l assignor to The glavison Chemical Corporation,

Baltimore,

Application June 15, 1938. Serial No. 213,925

(Cl. Z1-40) 21 Claims.

This invention relates to the manufacture of granular superphosphate.

In the manufacture of granular superphosphate, a preferred form of process is one in which the superphosphate, with sufficient water, is agitated to produce agglomerated particles. These agglomerated particles are then subjected to a drying step under further agitation to form hard, dry granules. Ordinarily, this type of process is carried out in apparatus which comprises a rotary drum in which the particles are agglomerated. Particles thus agglomerated are subjected to the drying step in another rotary heated drum.

Another form of process comprises agglomerating or conditioning and then drying in the same rotary drum in different sections of the drum. An aqueous medium may be added to produce the desired initial moisture content to assist in the agglomeration.

The granular superphosphate obtained comprises hard, dry, globoid, nodular, encrusted and indurated particles having several times the crushing strength of ordinary fully cured den superphosphate.

When fresh superphosphate directly from the den is charged into the conditioner of the granulating unit, there is in many instances sufficient variation as to physical condition of the den super to make this operation impractical. The diiiculty is that at times the agglomeration in the conditioner is excessive so that large lumps form, and occasionally a clayey mass is formed. This causes trouble due to sticking of the material in the conditioner and the dryer, and the final material is too large and non-uniform as to size and moisture content. When the material from the dryer is too large the amount of dust produced during the subsequent milling operation is excessive. Up to the time of this invention it was necessary to put the fresh super into preliminary storage or to rasp and aerate it, so as to allow proper control of particle size in the conditioner. This procedure entailed, of course, considerable extra cost due to the rehandling of the material and storage facilities required.

By means of this invention, fresh den super can be transferred directly from the den to the conditioner, and the particle size from the conditioner can be controlled within the accuracy that the commercial application of the process requires. This is accomplished by feeding in a determined amount of dry material to the feed end of the conditioner where it enters with the fresh den super.

The maximum capacity of the granulating unit is obtained by using super from a stationary den, unshaved and unrasped, because the den super is at the maximum possible temperature. It is therefore important, if maximum capacity is desired, to avoid storing or rasping the super prior t'o granulation. Using this invention it is possible to do so. In other words there is not only saving due to elimination of handling, rasping and storing charges, but the capacity of the granulating unit is also increased.

Any dry or reasonably dry material may be used as the additive, as for instance sand, if it is required to cut the concentration of P205 in the final product. Well cured den super may be used. 'Ihe most suitable material is, however, classifier dust, which is obtained in the following manner.

The granulated material from the unit goes to storage for a minimum of approximately 10 When shipping granular superphosphate, the material from storage is passed over a screen to eliminate any oversize. This oversize goes to a mill, is crushed, and is returned to the screen. The entire product from the screen is passed through a pneumatic classifying system where substantially all fines are removed. The dust free material is discharged into bags ready for shipment. The amount of classifier dust may vary from 10 to 20% of the total production.

Instead of using pneumatic classification, double screening may be used. 'Ihe net result Will however be approximately the same.

'I'he classiiier dust may be sold by itself or mixed with regular den super and sold as run of pile or cut to 16%. The advantage of using it back in the granulating system is however quite considerable as has been pointed out above. Moreover, the dust has a high percentage of available P205.

phosphate in territories where to add sand as iiller. An additional advantage is obtained when the ground phosphate rock the P205 in this becomes superphosphate, there obtained.

Among the objects of the invention are to reduce handling, save time and cost of production, and insure a more uniform product.

Other objects will be apparent from the description of the apparatus used and the process as set forth.

The single figure of the drawing is a diagrammatic illustration of a form of apparatus which I may employ, the apparatus being shown. in section.

Referring to the drawing I have shown a conditioner I and a. drier 2.

mounted on supports 5'. There are a plurality of rollers at each ring 4. The metallic cylinder 31s is adapted to be driven from some rotated by means of a gear rotated by means of a ring gear 6 driven by a pinion 6' mounted on the shaft of a motor 1. It

is to be understood that reduction gearing may be employed between the motor and the pinion 6', but for purposes of illustration no such reduction gearing is shown. The metallic cylinder is provided with a. partially closed end 9 having an aperture 9 therein into which sticks a. spout I0 of a hopper I I.v A slat conveyor or belt I2, which source of power, not shown, conveys fresh den superphosphate I3 from a superphosphate hopper I4. The superphoshate is delivered to the hoper I4 by means of a clam shell bucket which takes the material directly from the den, or some other means of transportation may be employed.

There is a sliding door I5 provided in one side of the hopper I4 adjacent an aperture I6. The door I5 is provided with a handle I1. By raising or lowering the door I5, the amount of fresh den super'phosphate I3 which is conveyed by the slat conveyor I2 can be determined.

Fed also into the hopper II is a dry, finely divided material I8 which may be sand, fully cured superphosphate, classifier dust, ground phosphate rock, or some other similar material. This material I8 is fed by means of a screw conveyor I9 operating in a conveyor box 20 located at the bottom of a hopper 2I. The screw I9 is 22 meshing with a pinion 23 driven by a variable speed motor 24.

Adapted to discharge an aqueous medium into the conditioner I are pipes 25 having nozzles 26.

Valves 21, which may be manually operated by an operator, control the amount of aqueous me'- dium discharged into the interior of the conditioner I.

Mounted on an instrument panel 28 are meters 29 and 30. The meter 29 is connected electrically to a pyrometer 3I located in a refractory lined combustion furnace 32, heated by a gas burner 33. The meter 30 is electrically connected to a thermometer 34 which is located in a discharge breeching 35 which covers the end of a. rotary cylinder 36 which forms the drier 2. The temperature of the hot gases entering the drier 2 and leaving the drier 2 are readable on the meter faces 29 and 30 respectively.

Mounted on the instrument panel 28 is a flood light 31 which is directed into the conditioner I. A supporting platform 38 is located adjacent the open end of the conditioner I. "I'he conditioner I is slanted downward from the end into which the fresh den superphosphate is discharged. An operator standing on the platform 38 at all times can visuallyinspect, by means of the floodlight 31, the interior of the conditioner I, and regulate by means of valves 21 the condition of the material in the conditioner I. The operator must be present on the platform at all times and by adjustment of the regulating valves 21, he maintains a constant physical condition of the material leaving the conditioner and entering the drier.

In the operating floor is a trap door 40 which is on hinges and provides easy access to a cleanout door 4I in a water-jacketed chute 42. A wall 43 forming the vertical upper section of chute 42 prevents the conditioned agglomerated particles from falling out of the upper end of the chute.

The water-jacketed chute 42 is provided with a water jacket 44 in which cooling fluid is circulated to prevent overheating of the chute. The connections for sending the uid through the water jacket are not shown. The lower end of the open end of v 4. the chute discharges into the upper end of the drier 2, which has an aperture 45 into which the lower end of the chute projects.

The rotary cylinder 36 which comprises the drier is slanted from the horizontal and is provided with rings 46 adapted to be supported by rollers 41 mounted on supports 48. As is the case with the construction of the conditioner I, there are a, plurality of rollers 41 at each station to rotatably support the rotary cylinder 36. To rotate the cylinder 36 of the drier 2 I have shown a ring gear 49 driven by a pinion 56 mounted on the shaft of'a motor 5I. Here again reduction 'gearing may be used if desired, but such a construction is not shown in order to simplify the illustration of the apparatus.

The discharge breeching 35 is connected to a pipe 52 which leads to the suction side of a blower 53 which is adapted to suck the gases through the pipe 52 and discharge them through a pipe 54. The blower 53 is mounted on a platform 55 upon which are mounted the supports 5' for the rollers 5 in which the conditioner unit is adapted to be rotatably supported.

The discharge breeching 35 is provided with a discharge chute 56. Mounted on the discharge chute 56 is a swinging door 51 which prevents the blower 53 from sucking too much fresh air into the discharge breeching 35. By this construction of the swinging door a suction is created in the interior of the drier 2 and the gases from the interior of the drier 2 are discharged through the pipe 54. The dried granular particles are delivered into a receiving pit 58 from which they may be taken by means of a clam sheli bucket,

Y or some other conveying mechanism.`

l Fresh unrasped super-I3 direct from the den is charged in to hopper I4. The den super may as an example have the following average composition:

Per cent Moisture 10.56 Total P205 20.03 IIlSOl. P205 3.04 Avail. P205 16.99

This is a truly representative average and there may be slight variation in the composition especially as to moisture content between the top Per cent Moisture 1.7 Total P205 21.3 Insol. P205 1.2 Avail. P205 20.1

Conveyor feeder I2 and screw feeder I9 are so adjusted that the classifier dust represents 10% of the total feed. In other words, the ratio of fresh super to classier dust is 9 to 1 by weight.

The amount of water added to the material in the conditioner through sprays I0 averages approximately 1.2%. This does not mean that there is a uniform addition, because the operator on the platform givesconstant attention to the physical condition of the material in the conditioner and regulates the amount of water by means of valves 21, so that every minute of the day visual observation governs the proper physical condition of the material going to the dryer. The instant water additions may vary water, that is chemically from practically nothing to 2% or more. The range is generally from about l/.% to 2%.

water addition is so critical for proper operating conditions that a percent will produce a major change of physical condition of the material.

The granulated super from the dryer has the following composition:

' Per cent Moisture 5.15 Total P205 21.08 InSOl. P205- 2.75 Avail. P205 18.33 This material is allowed to stand in storage for a minimum of approximately days. After passing through the shipping unit the nal material in the bags analyzes as follows:

y Per cent Moisture a 1.67 Total- P205"` s 21.44 Insol. P205 L18 Avail. P205 20.26

It will be noted that the acidulation is established for granular superphosphate.

In connection with the moisture changesv in the material during the process, the following is of interest. The fresh den super has a moisture content of The material from the conditioner to the dryer .has the same average moisture content of 101/%. The granulated super from the unit shows about 5% moisture. The moisture eliminationin the dryer There is therefore an apparent dierence of 31/2% moisture between the material from the granulating unit and the matei-iai asI shipped. Careful investigation has shown. that the true and transfer through the shipping unit. The balance of 2% is changed from free water to xed bound water that` does C. by the standard method of moisture determination; l

The remarkable eilciency of the process from the standpoint of accelerated curing is seen from the above given example.

small fraction of a moisture loss between these. two points is only 11/2% andis due to handlinga substantially uniform agglomerated material is delivered from the conditioning step to the drying step. `A nal granulated product is obing o1' the prior art.

I claim: 1. A method of phosphate `comprising adding 1,0% by weight of glomeration, drying the agglomerated' 2. A method of manufacturing granular supermaterial by tumbling in ing the agglomerated particles while tumbling in a rotary drum. i

6. In the manufacture of grammar superphosthe mixture to a moisture content about the same as the freshsuperphosphate, agglomerating the material by tumbling in a. rotary drum, and drying the aggiomerated particles while tumbling in a rotary drum.

7. A method of agglomerating fresh superphosphate, comprising adding dry-finely divided materia] to the fresh den superphosphate and passing the fresh den superphosphate Vthrough a rotary drum, inspecting the mixture in the drum while adding an aqueous medium to obtain a mixture having a moisture content about the same as the moisture content of the fresh superphosphate, and regulating the aqueous medium to conform vwith the requirements as determined by the inspection.

8. A method of agglomerating fresh superphosphate comprising adding dry sand to the fresh den superphosphate and passing the fresh den superphosphate through arotary drum, inspecting the mixture in the drum while adding an aqueous medium to obtain a mixture having a moisturecontent about to the same as the fresh superphosphate, and regulating the aqueous medium to conform with the requirements as determined by the inspection.

9. A process for producing granular superphosphate from superphosphate fresh from the den comprising feeding the fresh superphosphate to a rotating drum that is slanted to the horizontal, together with a finely divided material, throwing a beam of light on the interior `of the drum so that the consistency of the mixture can be constantly inspected, introducing into the drum a yquantity of an aqueous medium to obtain a mixture having a moisture content about the same as the fresh superphosphate, passing the agglomerated particles from the conditioning step in this drum to a second drum where the particles are subjected to a drying step and elevated temperatures to form hard, dry, encrusted and indurated globule particles of several times the crushing strength of fully cured den superphosphate. s

10. A method of manufacturing granular superphosphate comprising adding fully cured den superphosphate to fresh superphosphate, then adding an aqueous medium to bring the mixture to a moisture content about the same as the fresh superphosphate, agglomerating the mixture, and

then drying the agglomerated particles.

11. In the manufacture of granular superphosphate, controlling the consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size by mixing by Wegiht of fully cured den superphosphate with the fresh superphosphate, then adding an aqueous medium, then agglomerating by agitating, and then drying while agltating. 12. In the manufacture of granular superphosphate, controlling the consistency of superphosphate fresh from the' den to enable the agglomeration of particles of substantially uniform size by mixing fully cured den superphosphate with the fresh superphosphate, then adding an aqueous medium to obtain 'a mixture having a, moisture content about the same as the fresh superphosphate, agglomerating the material by turnbling in a rotary drum, and drying the agglomerated particles while tumbling in a rotary drum. l 13. A method of agglomerating fresh superphosphate comprising adding about 10% by Weight of fully cured den superphosphate to the fresh den superphosphate, and passing the fresh den superphosphate through a rotary drum, inspecting the mixture in the drum while adding an aqueous medium to obtain a mixture having a moisture content about the same as the moisture content of the fresh superphosphate, and regulating the aqueous medium to conform with the requirements as determined by the inspection.

14. A method of manufacturing granular superphosphate comprising adding ground phosbring the mixture glomerated particles,

finely divided matreial superphosphate, then adding of an aqueous' medium to to the desiredlconsistency for agglomeration, agglomerating the mixture, and then drying the4 agglomerated particles.

15. In the manufacture of granular superphosphate, controlling the consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size by mixing ground phosphate rock with the fresh superphosphate, then adding about 2% of an aqueous medium to bring the mixture to a moisture content" about the same as the fresh superphosphate, then agglomerating by agitating, and then drying while agitating. A

16. In the manufacture of granular superphosphate, controlling thev consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size phate rock to fresh approximately 2% by mixing approximately 10% by weight of ground phosphate rock with the fresh superphosphate, the mixture to a ,moisture content about the same as the fresh superphosphate, agglomerating the material by tumbling in a rotary drum, and

drying the agglomerated particles `while tumbling in a rotary drum. y i

17. A method of agglomerating fresh superphosphate comprising addingground phosphate rock to the fresh den superphosphate, and passing the fresh den superphosphate through a. ro-

tary drum, inspecting the mixture in the drum While adding an aqueous medium to obtain a mixture having a moisture content about the same as the fresh superphosphate, and regulating the aqueous medium to conform with the requirements as determined by the inspection.

18. A method of agglomerating superphosphate containing material comprising adding dry finely divided material thereto, while adding an aqueous medium to bring the mixture to a moisture content about the same as the superphosphate, agglomerating the agglomerated particles.

19. A method of treating den superphosphate to manufacture a granular superphosphate fertilizer comprising adding 10% finely divided material to the den superphosphate, adjusting the moisture content of the mixture to lOl/2%, forming the mixture into agtumbling the agglomerated particles in a zone of hot gases until the moisture content 'of the particles is reduced to about 5% and discharging the particles from the drying zone.

20. A method of treating den superphosphate to manufacture a granular superphosphate fertllizer comprising adding 10% by weight of dry to the den superphosphate, adding about 2% of water to the mixture thereby raising the moisture content to around lOl/2%, forming the mixture into agglomerated particles, tumbling the particles in a zone of hot l gases until the moisture content of the particles is reduced to approximately 5%, and discharging the particles from the drying zone.

2l. A method of preparing granular superphosphate which comprises mixing with fresh den superphosphate a minor proportion of well cured den superphosphate, adding water thereto in amount to give the mass the proper consistency for agglomeration, and tumbling the mixture in a rotary drum until granules are formed.

' MARK SHOELD.

then adding an aqueous medium to bring 'v mixture and then drying the' by weight of dry`

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