US 3258849 A
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Description (OCR text may contain errors)
I' 'July 5, 1966 I J. s, RAI-r1' 3,258,849
ROTARY GRANULATOR AND DRYER Filed April 2. 1963 vk/vrai da/y Suma/Farr a y l f rrmwfys United States Patent O 3,258,849 RGTARY GRANULATOR AND DRYER John Stewart Raitt, Edinburgh, Scotland, assignor to Scottish Agricultural Industries Limited, Edinburgh, Scotland, a corporation of Great Britain Filed Apr. 2, 1963, Ser. No. 270,076 Claims priority, application Great Britain, Apr. 9, 1962, 13,538/ 62 8 Claims. (Cl. 34-102) The present invention is concerned with improvements in or relating to granulators.
The object of the invention is to provide a granulator of simplified construction which permits granules to be produced substantially by a layering process in a convenient and efficient manner.
According to the present invention a gr-anulator comprising a drum rotatable about a substantially horizontal axis is one wherein said drum contains therein lifting means -attached at one end portion of the drum for lifting therein and transferring therefrom solid material into a stationary receiving and transferring means connected to an external support and adapted to receive and transfer said solid material from said end portion to the other end portion of the drum, wherein one end of the drum has an opening at least sufficiently wide for at least connecting means to pass therethrough from the receiving and transferring means to said external support, and wherein the first mentioned end portion has at least an opening for discharge of solid material.
Preferably said lifting means comprises buckets or scoops fitted into the drum so that on rotation of the granulator they lift the solid material up and discharge it into said stationary receiving and transferring means. The stationary receiving and transferring means is preferably a stationary inclined chute. Preferably the opening for discharge of solid material in the first mentioned end portion is concentrically positioned at the end of this end portion so that its diameter controls the bed depth of the solid material, i.e. the granules, in the drum.
Alternatively, said first mentioned end portion has a closed end and a stationary plate adjacent to this closed end and said opening for discharge of solid mate-rial is an aperture near the perimeter of said closed end and said stationary plate has a corresponding aperture in its lower segment which is in periodic alignment with the drum aperture and bed of solid material during rotation of the drum to permit discharge of solid lmaterial through said apertures.
If stationary means is provided to permit removal of gases and vapours this means is preferably fitted to a stationary plate adjacent to said other end portion of the drum.
1f desired, external or internal means of heating or cooling are associated with the granulator of the invention.
If the apparatus of the invention is to be used in a layering process, it is essential for etiicient granulation that the recycle ratio, which is herein defined as the ratio of rate of recycle of material within the drum to the rate of addition of material to be granulated, is kept as large as possible. Under equilibrium conditions the rate of addition of material to be granulated will be equivalent to the rate of removal of material from the granulator, Therefore, for a given production rate the recycle ratio is proportional to the rate of recycle of material within the drum. This recycle rate is a function of the number and size of buckets and scoops and the peripheral speed of the drum. It is known that this peripheral speed is limited to that range in which the bed of material moves substantially with a rolling action, which is desirable for the said layering process. Preferably, it should be so arranged that the material discharged by the buckets or scoops forms a continuous stream in the said stationary transferring means. For example, if a 6 cWt./hr. production rate is desired at a 55:1 recycle ratio, then this can be achieved in a 4 ft. 3 in. internal diameter drum rotating at 13 r.p.m., thus having a peripheral speed of 173 ft./min., and fitted with 16 buckets, each discharging 3 lbs. of material down the stationary transferring means.
By way of example three embodiments of a granulator according to the invention will now be described with reference to the accompanying diagrammatic drawings. Each drawing is a diametrally sectional elevation through the respective embodiment of a granulator, and lin FIGS. 1 to 3 of the drawings similar parts of the grauulators are given the same reference numerals.
In FIG. 1 4a rotatable drum 1, of 4 ft. 3 in. internal diameter, open at both ends 2 and 3, is mounted substantially horizontally. 4 is a chute, inclined at `an angle of 45 to the horizontal, which -is attached to `one end of la connecting rod 5, the other end of which is att-ached to a wall 6. 7 are lifting cups, sixteen in number, fitted in the dnum 1 which, on rotation of drum 1, carry solid material 8 up until it drops into the chute 4. 'I'he opening at end 2 is wider than the opening at end 3, land is bounded by a lip 9 to retain the desired depth of circulating solid material -8 in drum 1. The two pipes 10 and 11 are for the addition of liquids or gases, and each is fixed to the connecting rod 5. Pipe 10 is directed to the chute 4, and pipe 11 enters under the bed 8 of solid material.
In FIG. 2 a rotatable drum 12, open at both ends 13 and 14, is mounted substantially horizontally. At end 13 there is located a stationary plate 15, which is attached to one end of a connecting rod 16, the other end of which is attached to a Wall 17. This plate 15 -is fitted with a duct 18 for efiiuent gas removal, Vand with an outlet pipe 19, which -receives solid material from the bed 8 from lifting cups 20, four in number, fitted to the drum 12.` 21 is an endless transport belt. The dimensions of the dnum 12 are substantially the same as those of the drum 1, illustrated in FIG. 1.
In FIG. 3 a rotatable drum 22, open :at end 23 and closed at end 24, is mounted substantially horizontally. A stationary plate 25 is located at closed end 24. This plate 25 is fitted with a duct 26 for effluent gas removal passing through a centrally positioned opening 27 through the closed end 24. Plate 25 has also an orifice 28 in its lower segment. When these orifices 28 and 29, and the bed of solid material 8, are in periodic [alignment during rotation of the drum 22, discharge of solid material takes place through the orifice 28. The dimensions of the drum 22 are substantially the same as those of the drum 1, illustrated in FIG. 1.
An :alternative method of discharge is to have a Weir, fixed or adjustable, not shown in FIG. 3, over which the material is allowed to spill out through orifice 28.
The apparatus of the invention has been found to be particularly applicable for the production of granular `ammonium nitrate, granular ammonium sulphate, granular monoammonium phosphate and various metal metaphosphates and sulphates in granular form.
For example, granular monoammonium phosphate is conveniently produced from wet-process phosphoric acid and gaseous ammonia in the reactor illustrate in FIG. 2 under the following conditions:
Concentration of acid 46.6% P205. Rate of rotation of drum 13 r.p.m. Rate `of recycle of material within the drum 330 cwt./hr. Production rate 6.0 cwt./hr.
Percent of product size in solid discharge 72% Moisture content of material t discharged from granul-ator 0.31% H2O. Bed temperature 107 C. Moisture content of material at point of acid addition 0.51% H2O.`
What I claim is:
1. A granulator comprising: a drum rotatable about a substantiallyhorizontal axis and having a discharge opening in one end portion for discharging solid material from said drum; lifting means attached to the inner per-iphery of said drum at said one end portion for lifting material from the bottom of said drum and subsequently dropping the material during rotation of said drum; means for internally recycling material from said one end portion to said other end portion, said recycle means including lifting means attached to the inner periphery of said dr-um at said one end portion for lifting material from the bottom of said drum and subsequently dropping the material during rotation of said drum, said recycle means further including stationary receiving and transferring means disposed within said drum for receiving material dropped by said lifting means and for returning the dropped material to said other end portion of said drum; a stationary support exterior of said drum; and connecting means interconnecting said support, and said receiving and transferring means for positioning the latter in said drum. Y
2. A granulator as claimed in claim 1 including stationary duct means for removing gases from said one end portion, said duct means being supported by a stationary plate.
3. A graniilator as claimed in claim 1 including heat exchanger means for said drum.
4. A granulator as claimed in claim 1 wherein said lifting means comprises scoops.
5. A granulator as claimed in claim 1 wherein the stationary -receiving and transferring means isa stationary inclined chute.
6. A granulator as claimed in claim 1 wherein the opening for discharge of solid materi-al is concentrically positioned at the end of said one end portion.
7. A granulator as claimed in claim 1 wherein said one end portion has a closed end and a stationary plate adjacent to this closed end, said opening for discharge of solid material being an aperture near the perimeter of s-aid closed end and said stationary plate having a corresponding aperture in its lower segment which is in periodic alignment with the drum aperture during rotation of the drum.
8. A granulator comprising: a drum mounted for rotation about a substantially horizontal axis, said drum having a discharge opening lat one end for discharging solid material from said drum and -an inlet opening at the other end, s-aid inlet opening being coaxial with said drum; two stationary inlet conduits extending into said other end through Said inlet open-ing; and means for internally recycling material from said one end to said other end, s-aid recycle means including lifting means attached to the inner periphery of said drum near said one end for lifting solid material from the bottom of said drum and subsequently dropping the material during rotation of said drum and a stationary inclined chute wholly within said drum extending downwardly from said one end to said other end for receiving solid material dropped by said lifting means and for transferring the material to said other end.
References Cited by the Examiner UNITED STATES PATENTS 534,491 2/1895 Atwood 34-136 X 582,587 5/1897 Hay 263-33 2,122,170 6/1938 Zotos 263--33 2,443,462: 6/1948 Kimberlin et al. 34-135 X 3,021,081 2/1962 Leader 241-91 FOREIGN PATENTS 18,299 11/ 1904 Austria. 571,115 2/1933 Germany. 814,182 6/1959 Great Britain.
FREDERICK L. MATTESON, JR., Primary Examiner.
WILLIAM F. ODEA, JOHN J. CAMBY, Examiners.
D. A. TAMBURRO, Assistant Examiner.