BE628406A - - Google Patents

Description

       

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  "Process for producing pellets of substantially uniform dimensions and products obtained".



   The present invention relates to a new process for forming tablets of water-soluble substances, normally solid, for example tablets of fertilizers, fertilizers, etc.



   An object of the invention is to provide a novel granulation process capable of producing fat pellets of more uniform size than the pellets formed.

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 by currently known methods.



   Another object of the invention is to provide a novel granulation process for producing uniform fertilizer pellets of a wider range of sizes than that presently produced by current granulation processes.



   Another object of the invention is to provide a novel granulation process for the production of fertilizer pellets, in which a high degree of control over the granulation conditions is maintained during the formation of the pellets. Yet another object of the invention is to provide a novel granulation process for the production of fertilizer pellets which is continuous and free from production stoppages and losses due to silt formation.



   Another object of the invention is to provide a new granulation process for the production of fertilizer pellets which is more efficient, economical and simpler than current processes.



   Yet another object of the invention is to provide a novel granulation process, in which a substantial portion of the solids to be granulated is supplied to the granulation apparatus in the form of a slurry or solution.



   In the processes currently used for the formation of fertilizer pellets, these pellets are obtained by "agglomeration" processes. In these agglomeration processes, a dry powdery material, usually having dimensions of less than 20 mesh, is moistened with a wetting fluid, and rolled, shaken or agitated, until the particles come together. of the plastic state, called "agglomeration point". At this stage, the particles start to agglomerate or adhere to form granules comprising several particles,

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The process described above gives rise to difficulties which prevent the formation of pellets of uniform dimensions.

   as well as other undesirable results. Firstly, the size of the pulverulent fertilizer material, the
20 meshes or less, hardly allows a uniform transfer of the wetting fluid, this transfer being often impossible. Drops of moisture falling into a mass of this dry pulverulent material tend to curl up into small beads of varying sizes, instead of dispersing throughout the bed of material. These difficulties in uniformly wetting a material of this size results in the formation of granules of a wide range of sizes, including oversized granules and undersized granules.

   In addition, there is a marked tendency, during wetting of this fine powdery material, for the material to adhere to solid surfaces, for example the floors of the granulator.



   Another disadvantage of the foregoing method of agglomeration is the difficulty of maintaining the proper moisture content during granule formation. If the moisture content is too low, so that the particles are insufficiently plasticized, inefficient agglomeration occurs.



  On the other hand, if the moisture content is too high, the particles approach a muddy state or undergo complete coalescence into a slime, causing production stoppages and losses. For example, an increase in humidity of about 1% over the moisture content required for agglomeration will turn the mixture into a slime.



   A main difficulty in the agglomeration process arises from the fact that many substances which one wishes to transform into pellets are initially made by a chemical reaction (or recovered from a material containing them).

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 under the volume of an aqueous solution or mud.

   Such a solution or slurry obviously cannot be made directly into pellets. On the other hand, a solid material in powder form is introduced into a granulating apparatus and, although the solid material can be moistened with the solution. or sludge, instead of being with water, to raise its moisture content to the point of agglomeration, the amount of sludge that can be so added is strictly limited, which is evident from what was pointed out above, The final pellets will be formed mainly from the subs. solid powdery tances. This requires an important diet. tance and continue finely divided solids.



   It is possible to dry a solution or slurry to recover the solids it contains, and then to grind these solids to about 20 mesh; is generally too expensive, however. In most agglomeration processes, the continuous feed of finely divided solids is ensured by recycling ground materials, previously transformed into pellets. The oversized and undersized material exiting the granulator is not sufficient to supply the feed, so large quantities of pellets will. otherwise sold must be crushed and returned to the granulator.

     Frequently, up to $ 10 to 10 pounds must be recycled for each pound of finished product, making the process slow and very expensive, and requiring an ins. large and costly installation.



   A fundamental object of the invention is to provide a relative by which to prepare pellets consisting mainly of solids derived from solution or slurry.



  In the description and in the claims, the term "sludge" will be used to denote a substance which can be pumped, to

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 aqueous vehicle, containing solids which must all be formed into pellets, whether these solids are dissolved or suspended, or both.



   The new methods of the present invention overcome the disadvantages of the prior art methods and permit the formation of uniform pellets of a relatively wide range of sizes, generally in the range of about 0.03 inch to. about 1.5 inch in diameter. Loan burr about 0.03 to 0.25 inch in diameter, the pellets preferred) having a diameter of between 0.063 and 0.185 inch.



   In the U.S. patent, A. N 2,926,079 granted on February 23, 1960 (and in British patent N 894,773, as well as in French patent N 1,206,782, which correspond to this US patent, A.), A process has been described in which nuclei - aux of the substance to be transformed into pellets, having a moisture content below the point of agglomeration, are separated * by stirring in a chamber and mixed with hot drying gases passing through this chamber, While they are thus separated - Res (generally in a state of free fall), the cores are coated with fine droplets of a slurry usually introduced by spraying the slurry into the hot drying gases.



  Although the moisture content of the cores can in this way be temporarily elevated above the point of agglomeration, the action of the gases is to dry the deposited mud droplets almost instantaneously, so that the cores Coated have their moisture content which is again reduced to below the point of agglomeration, before they can join together or come into contact with uncoated cores under the conditions of agglomeration. Therefore, by covering and covering the cores, pellets consisting primarily of slurry-derived solids are produced, these pellets being round, smooth and remarkably uniform in size.

   An advance

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 The feature of this process is that, when desired, slurry droplets, spray dried in the chamber, without coming into contact with the separated cores, serve to provide, in part at least, a continuous supply of fresh kernels.



   The process of the present invention is based on the fact that, while for agglomeration, a mass or bed of cores must reach a critical moisture content, as hereinafter pointed out, effective agglomeration takes a certain time. The surfaces of the kernels must either be soft enough to allow them to adhere together, or the applied slurry must reach a sticky or tenacious quality, or devy, and these actions do not occur instantly.
It becomes possible, therefore, to apply a slurry to a portion of a mass or bed of cores, so as to moisten them up to or up to above the point of agglomeration, and, by the application of immediate agitation,

   separate the coated cores and mix them with hot drying gases which will dry them to below the agglomeration point before they come into contact again. This is because, until effective agglomeration begins, there is only minimal force holding the nuclei together. The amount of sludge added is not limited to the amount of critical agglomeration, but can significantly exceed this.



   The results are similar to the process claimed in the aforementioned US patent except the following: the separation of the cores may not be as perfect, so that a number of pellets may contain two cores or more. The pellets can thus be brought to size at a somewhat faster rate and their formation may require a somewhat greater percentage of initially solid material. Some of the lozenges may not present

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 the complete surface uniformity which generally characterizes cores which are coated in a totally separated state.

   However, the cores are still remarkably uniform in size, they are made mostly of mud-derived solids, and they are strong and robust. The process involves substantially the same expense and results in substantially the same commercial advantages as the cores. common agglomeration processes.



   In addition, the process of the invention can be combined with the process of the above USA patent, both with regard to the coating of the cores while they are in a separate state, and with regard to relates to the formation of nuclei by spray drying.



   The term "core" as used herein will be defined hereinafter in order that the present process will be understood. This term "core" refers to particles which are susceptible to being coated with additional material during formation of the desired pellets. Therefore, the term "core" as used herein refers to the particles which are the embryos of the final fertilizer pellets. It is not necessary, however, that the cores be of the same substance as the slurry solids, as it is easily possible in the present process to produce pellets consisting of: two or more substances . For example, it is possible to form ammonium nitrata pellets on a base formed from limestone cores.



   The dimensions of the cores are such that they tend to disseminate moisture before agglomeration occurs, the dimensions of the cores being larger than the dry powdery particles used in the common agglomeration process. Because of this, the cores are generally larger than 20 to 30 meshes and they are always larger than 40 meshes. Advantageously, a mass of the cores, when

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 when moistened with excess fluid, will rapidly transfer and disseminate additional moisture throughout a large volume, these nuclei only very loosely tending to hold together by surface tension fluid at the start.



   With smaller particles, such as those used in prior processes, humidification brings these fine particles into sufficiently close contact that the mass almost immediately tends to roll up into granules much larger than the constituent particles.



   It will be understood that a small percentage of particles having dimensions smaller than the cores may be present in the granulator, these particles usually being pulverized material recycled for further processing. These recycled fine particles are not in themselves cores, as defined above, but they can be employed in the formation of cores by humidifying these particles in a manner which will be described by after.



   The cores to be used according to the present process can be obtained by many different methods. If desired, particles of the desired chemical composition and size can be employed, produced independently of the process. Preferably, however, the cores are produced by using a portion of the slurry to be used later in the coating operation. Therefore, a portion of the slurry containing the solids can be sent to the granulator and dried therein, resulting in the formation of the desired nuclei by evaporation of the liquid or solvent.

   Further, as mentioned earlier, a dry pulverized material, usually a recycled material, can be sent to the granulator and humidified to.

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 form the nuclei by incipient granulation.



   It is necessary in practicing the invention that the bed of cores in the granulation apparatus be generally maintained at the moisture content required for agglomeration, portions. located only in the bed being brought to a moisture content above the point of agglomeration. The granulator is preferably a cylindrical oven-like vessel mounted so that its axis is nearly horizontal and arranged to be moved about its axis of symmetry.



  It has longitudinal vanes inside so that, during its rotation, these vanes pick up masses of the cores, carry them upwards and let them fall to the bottom of the granulation apparatus, thus achieving an agitation of which the degree will depend on the speed of rotation. The term "bed" as used in this specification refers to masses of cores which are substantially in contact with one another in the bottom of the granulator and as carried. upwards by the vanes, until they release them so that they fall to the bottom of the granulation apparatus.

   It will be understood that other suitable apparatus can be used as granulation apparatus, for obtaining agitation of the bed and for contacting the cores with hot gases, for example the Rotolouvre drying apparatus. , the Multilouvre dryer and Fluo-solids reactors (i.e. fluidized bed reactors).



   If the bed were uniformly moistened to the point of agglomeration, it would be impossible to avoid the common agglomeration action, since it would not be possible to subject all parts of the bed simultaneously to the necessary agglomeration. required for the separation of coated cores. bias if the bed is generally maintained well below a level

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 of agglomeration moisture, it is easily possible to moisten a certain localized portion of this bed, for example a surface portion, and then immediately subject this portion to agitation to achieve the objects of the invention. .



   At the start of the operation of the granulation apparatus, it is advisable to place therein a material having good core dimensions in order to start the process. After that, however, the recycle material fed to the granulator generally does not have the core sizes as used herein. Generally, this material forms core particles by incipient agglomeration, although a small portion of the recycling material may be of sufficient size to act as cores.

   It is believed that this "incipient agglomeration" occurs because fines, by which is meant a solid material having dimensions substantially smaller than pits, tend to agglomerate more easily and more quickly than is the case. make larger particles. Therefore, if a localized portion of a cores mass containing fines is moistened with a slurry, the fines tend to stick to each other or to the cores almost immediately, and further a satisfactory degree of agitation. for separating coated cores has less tendency to individualize fines.

   The presence of a small percentage of fines is therefore a self-correcting condition and an advantage of the process of the invention is that a lesser amount of fines will be blown into the stack despite rapid passage of gases from the stack. hot drying through the chamber.



   The process will be described with reference to the formation of pellets of a fertilizer, but it should be understood that this description does not constitute a limitation of the invention.



  The bed of cores comprising particles of cores is subjected to

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 stirred and locally moistened with a slurry containing. ' a fertilizing material. This sludge preferably contains a significant portion of the solid fertilizer raw materials which subsequently coat the core particles.

   As a result, a significant portion of the raw fertilizer material and, preferably, most of this material is introduced into the slurry, while the remaining portion of the final fertilizer pellet is made up of the substance. In this way, the present process is different from previous processes, in which the fertilizer solids are granulated directly by the addition of a few percent moisture (5 to 15%). By incorporating a large amount of the raw fertilizer material in the form of a slurry and then covering the fertilizer cores with the raw material,

   it has been found that precise process control and product quality are advantageous enough to more than compensate for any increase in drying costs deriving from the transformation of the raw material into slurry.



   The sludge is preferably sprayed onto the bed cores so as to ensure uniform wetting of the particles. Any fertilizer composition which can be made into a pumpable slurry can be satisfactorily granulated in this process.

   The temperature of the sludge is not critical and it is only adjusted to give a slurry having satisfactory pumping characteristics,
It has been found that a very important factor in obtaining uniform pellets is that the moisture content of the granulation bed is generally or totally below the critical humidity at which agglomeration occurs. By "moisture content of the granulation bed" is meant the percentage of fluid phase present in the moist bed, whether or not this moisture comes from the sludge applied to the bed.

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 bed of nuclei, or whether it is moisture that can derive from the nuclei themselves. In other words, it is the liquid and the dissolved solids and not just the moisture present in the added sludge.

   For example, in the granulation of a fertilizer consisting of 40% ammonium nitrate) 23% potassium chloride and 37% limestone, the percentage of water is only 4% at the agglomeration point, while the percentage of fluid phase is 20%. This difference is due to the fact that the dissolution of soluble salts in water increases the weight of fluid, decreases the weight of solid, and thus increases the percentage of fluid phase in the mixture, which we call the humidity of the granulation bed.



   The addition of slurry to the bed of solids in the granulation apparatus and the simultaneous evaporation of the liquid sets a certain moisture content of the granulation bed. As mentioned above, there is a maximum humidity of the bed. , above which agglomeration occurs, giving particles of too large dimensions. Therefore, the moisture content should be low enough that an accumulation of the particles is formed not by agglomeration but by the formation of coatings on the wetted particles as a result of solvent evaporation from the applied slurry. to particles.



   Those skilled in the art will understand that the critical moisture content for different fertilizers and other substances will vary depending on their chemical composition. The moisture content required to produce agglomeration for any particular fertilizer can be carefully checked in the laboratory and is referred to as "agglomeration moisture".



   A method for determining the agglomeration point is described below.

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   Has 6 samples each contained in 100 ml Erlenmeyer flasks. and each consisting of 40 grams of the material for which the agglomeration point is to be determined, water is added with precision using a burette to form a series of samples having moisture contents near the point of agglomeration. agglomeration and not differing from each other by more than 0.5% humidity. The mouth of each vial was sealed with a tight fitting rubber stopper and shaken violently for 4 minutes, tapping the vials intermittently on a table to release adhering solids.



  The samples are poured into separate watch glasses and these glasses are arranged in increasing order of moisture content. If agglomeration moisture has been included in the samples, there will be a marked change in the appearance of the material with that moisture content. At this moisture content, the material will have coiled into solid round balls 10 mesh and larger in diameter and all samples with the higher moisture content will be muddy or contain larger, more plastic granules. . This experiment can be performed at any temperature desired so as to determine the agglomeration point of the material both at elevated temperatures and at room temperature.



   In applying the present invention to a particular fertilizer, therefore, the humidity of the granulation bed of that fertilizer should be lower than the agglomeration humidity thereof. It is only when the humidity of the bed approaches the point of agglomeration that it becomes critical. It follows that an important part of the process is the control of the moisture content of the bed. granulation so that this content does not approach the point of agglomeration.



   The operation according to the present invention will be

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       described below as it occurs in the drum or granulation chamber. As noted, the core bed is, as a whole, below the agglomeration moisture content and, therefore, is in a powdery state. The drum is rotated so as to produce the agitation which will be discussed later. Hot drying gases, which will also be more particularly discussed hereinafter, are caused to pass continuously through the drum.



   The sludge is introduced in appropriate quantities into the drum so as to be distributed over the bed in order to moisten the latter locally. This can be done by spraying the sludge onto the bed in the lower portion of the drum, but other distribution methods are possible. The sludge introduced need not be in the form of fine droplets. Any method of distribution or introduction can be adopted even providing for the supply of the sludge to the bed in the form of a stream. By "local bed wetting" is meant wetting not applying to the total bed volume at the sludge feed site.

   Generally, only a superficial portion of the bed is moistened, leaving between this moistened portion and the walls of the drum, a large layer of cores whose moisture content is below the point of aggregation,
Upon localized humidification of the bed, the portion thus humidified and the adjacent non-humidified portions of this bed are subjected to agitation and, in particular, they are lifted by the vanes of the drum and discharged at adjacent points from the top of this bed. drum, from which they fall up and down through the hot drying gases.

   The drying prevents any sticking of the moistened portions to the walls of the drum and,

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 as the action which is described occurs before the moment when agglomeration begins, the result of this action is a fall of the bed in the form of particles through the hot gases. The nuclei of the wetted portion, which are somehow held together under the action of a small force, tend to separate during this falling action, from ma. to be made distinct in the coated state or to be formed into groups not more than about dqux or three cores also in the coated state.



   During drying, as the material falls through the hot gases, the coated cores or groups of cores are immediately dry so that by the time they again reach the lower portion of the drum they no longer have a content. humidity greater than the point of agglomeration, i.e. they are in a non-agglomerated state. At the same time, the bed cores, which are not in the initially wetted portion, are further dried.

   As a result, the moisture content of the bed as a whole is kept below the point of agglomeration and there is no tendency for cores which are not directly moistened by the sludge to repair. tie accumulate moisture by absorption from the humidified areas so as to eventually achieve an agglomerated moisture content.



   The action described is continuous and repetitive, so that the cores and the groups of coated cores are re-coated repeatedly until they reach the desired pellet sizes. In this connection, it may be noted that, as some particles may contain two or more nuclei, the tendency of these particles to separate from the others by the falling action is greater the larger these particles are. Therefore, the product of the process is characterized by a remarkable uniformity of

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 dimensions of the pellets,
The action is at all times under the control of the operator, as he can modify the speed of rotation of the drum and the resulting degree of agitation and he can modify the quantity of sludge introduced.

   This enables continuous operation under non-caking conditions and the production of pellets in which most of the solids drift / slurry, the pellets having the characteristics of pellets formed primarily by coating and not by agglomeration.



   It is also within the scope of the invention to provide for spraying additional quantities of sludge into the hot drying gases so as to cover or cover the cores, provided that these cores are dried by the gases before they are dried. cannot come into contact under conditions which would otherwise allow them to form an agglomeration. Further, as the hot drying gases pass through the drum, the slurry can be sprayed therein to produce spray-dried droplets capable of acting as cores.



   These various actions can be made to occur in the same section or in different sections of the drum. By way of example, the pellets can be formed as set forth herein and subsequently given a coating, while they are in a separate state, as described in the aforementioned US patent, in order to. increase their uniformity and surface gloss.



   Generally speaking, the temperatures of the hot gases are those which would be used in the normal operation of a rotary dryer for drying a fertilizer material which has been made into pellets by agglomeration. Obviously, the particular temperature of an or.

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 The drying gas will vary depending on the temperature necessary to maintain the moisture content of the core bed below the agglomeration point, and it should not be so high as to produce decomposition of the material. It has been found that the temperature of the gases should generally be; in the range of 250 to 1000 * F.



   The core bed temperature is a function of the wetness or percentage of fluid phase present in the bed. For satisfactory operation of the granulator, this temperature should be between the wet bulb temperature of the outlet gases and approximately.



    50 degrees above the maximum boiling point of liquid i in the sludge. Generally, the temperature of the bed material in the granulator will vary from 150 to 260 F. As this temperature is a function of wetness or percentage of pre-fluid phase. - feels in the bed, it is useful because it indicates when the percentage of fluid phase reaches its critical moisture content or agglomeration. Operation at bed temperatures below about 140 F. results in excessive mass wetting and loss of control. It is not the low temperature that causes this difficulty but the excess moisture in the bed, which is measured by the temperature of this bed.



   It has been found that the range of moisture content of the slurry can vary as far as pelletization is involved. It is necessary that the slurry contains sufficient moisture to exhibit a suitable pumping characteristic. Amounts greater than sufficient value may be used but would result in higher drying costs, since, upon adding the slurry to the solids bed in the granulator, heat.

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 sufficient must be produced by the hot drying gases so that there is simultaneous evaporation of a sufficient quantity of moisture from the sludge so that the moisture content * of the bed does not reach the point of agglomeration.



   It should be further noted that the quality of the granules produced varies depending on conditions such as the variation of the rate of addition of the sludge to each section of the granulation apparatus, the variation of the temperature of the inlet gases. , variation in inlet gas flow, variation in recycle rate, spray drying of the slurry in the granulator, and control of the initial humidification process.



   Pellets produced according to the present invention vary from 1.5 to 0.03 inches. Pellets having even larger dimensions can be produced if desired because there is no problem in producing pellets having more than 1.5 inches in diameter. In the case of pellets smaller than 0.03 inch in diameter, on the other hand, there is a problem due to the small size of the cores used in the formation of the pellets and due, in particular, to the uniform humidification. of these cores, for reasons already described in detail previously.



   The present process can be used in the production of fertilizer pellets of any desired chemical composition. As those skilled in the art know, a fertilizer is commonly referred to by a three number system, such as 3-9. -6, these figures representing respectively the percentage of nitrogen, phosphorus as% phosphoric anhydride, and potassium as!. potassium carbonate, which is found in fertilizer. Therefore, a 3-9-6 fertilizer represents a fertilizer containing 3% nitrogen, 9% phosphorus pentoxide (generally called phosphate) and 6% potassium carbonate.

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   Examples of typical fertilizer compositions of interest in the present process are given below, together with parts by weight of the ingredients used in the production of the fertilizer.



   Example 1
Type 14-014
452 pounds of potassium chloride
800 pounds of ammonium nitrate
748 pounds of dolomitic lime
Example2
Type 14-0-14.



   452 pounds of potassium chloride
1287 pounds of ammonium sulfate
261 pounds of dolomitic lime
Example 3
Type 20-0-20
645 pounds of potassium chloride
1143 pounds of ammonium nitrate. '
212 pounds of dolomitic lime
Example 4
Type 10-10-10
323 pounds of potassium chloride
1010 pounds of superphosphate
67 pounds of ammonia
143 pounds of ammonium nitrate
437 pounds of ammonium sulfate
20 pounds of dolomitic lime
Example 5
Type 5-10-5.



   162 pounds of potassium chloride
1010 pounds of superphosphate
33 pounds of ammonia
72 pounds of nitrate, ammonium
218 pounds of ammonium sulfate
505 pounds of dolomitic lime
As shown by the preceding examples, a fertilizer of a particular grade or type can be prepared starting from different formulas, as illustrated by type 14-0-14 of Examples 1 and 2, each of the formulas of these examples being of a different chemical composition.

   Agglomeration points

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 for each of these formulas will also be different,
In the following table, the points of agglomeration are given for a certain number of the fertilizers of the preceding examples, these points of agglomeration having been determined by the method described in detail previously.



   Board
 EMI20.1
 
<tb> Formula, <SEP> N <SEP> Type <SEP> of input <SEP> in <SEP>% <SEP> of water
<tb>
<tb> 5 <SEP> 5-10-5 <SEP> 11.3% <SEP> to <SEP> 70 F.
<tb>



  10-10-10 <SEP> 9.2% <SEP> to <SEP> 70 F.
<tb>



  3 <SEP> 20-0- <SEP> 20 <SEP> 5.2% <SEP> to <SEP> 60 F.
<tb>
 



   The process of the invention will be described below with reference to the accompanying drawings.



   Figure 1 shows a schematic view of an arrangement for implementing the method described here,
Figure 2 is a longitudinal sectional view of the granulation apparatus of Figure 1,
Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2.



   Referring to the drawings, the solid feed consisting of recycled solids and other solids is sent from a feed system 1 to a granulator 2 to form a bed of cores therein. A sludge 3 containing raw fertilizing materials which are to be placed in coatings on the cores is mixed in the mixing and storage tank 4 by means of a stirring device 5, the sludge being heated up to the desired temperature by a Heating apparatus 6. The sludge may however be the product of a direct manufacturing process for the material to be pelletized.



   The sludge is then pumped by means of a pump 7 through line 8 from where it is sprayed onto the bed of cores through nozzles 9 and 10. The moisture content of the bed of cores is adjusted by passing a hot gas or a mixture of gases

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 hot through the granulation apparatus,. counter-current or in the same direction as that of the circulation of other materials.



  In the particular embodiment referred to herein, the hot gas enters through the inlet end 2a and exits at the opposite conical end 2b of the granulation apparatus, the wetted bed of cores being caused to fall to. through hot drying gases. Suction is caused at the wizarding end of the gases from the granulator by a fan 11 to aid in the extraction of gases from the granulator. The blower 11 is preferably connected to a cyclone separator 12 for the removal of fine particles present in the outlet gases passing from the granulator to the blower 11 via the duct 13. A valve 14 is provided to control the flow of the outlet gases.



   The material coated cores obtained in the granulation apparatus are collected in the product receptacle 15 by falling through the discharge hopper 16. The coarse elements are crushed and they are transferred to the recycling receptacle. 17 with the elements of too small dimensions, to be sent again to the hopper or feeding system 1.



   If desired, a drying apparatus 18 is provided to condition the formed granules which are fed to it by a feed apparatus 19. This drying apparatus may be of the rotary type of small size, driven by a belt by means of with a motor 20 and a belt 21. This drying apparatus is supported in rotation on rollers 22 by means of circles 23 supported by this drying apparatus and being in contact with the rollers Hot gases similar to those blown in through the granulation apparatus pass through this drying apparatus.



   The granulation apparatus 2, as shown, is of a common rotary type, driven by a motor 24 and a belt 25. This granulation apparatus is rotatably supported.

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 on rollers 26 by means of rings 27 provided on the device and being in contact with these rollers,
As shown in Figure 2, the granulating apparatus 2 comprises a cylindrical shell 28 arranged so that its axis of symmetry is approximately horizontal.



     Preferably, however, a slight downward slope, for example 1 / 8th of an inch per foot of length is provided towards the gas inlet end 2a to accelerate the exit of the solid granules to the discharge hopper 16. The The granulator has a series of vanes 29 of sufficient capacity to lift the material from the core bed, for example twice on average per revolution. The outlet end 2b of the granulator is preferably tapered to provide a better sealed connection with the outlet system. The vanes
29 are cut a short distance from the ends of the granulator to prevent effects affecting the rate of discharge of the granulator.



   In operation, the sludge is fed continuously into the granulation apparatus through nozzles 9 and 10.



  By way of example only, one of these nozzles has been shown to face downward on the bed. The granulator is rotated at a suitable speed, for example 16 revolutions per minute, in order to drop the solid cores from the bed through the slurry spray and through the hot gases containing the combustion products of the bed. Fuel oil and air, continuously blown through the granulator to distillate the solvent from the slurry, leaving the desired cores covered with fertilizer pellets.



   It is advisable to carry out at predetermined intervals, for example every fifteen minutes, a sieve analysis of the effluent from the granulation apparatus. The amount of recycling is calculated on the basis of this analysis and the

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 weight of the flow obtained. This calculated weight of the recycle material is subjected to crushing and continuously returned to the granulator from the recycle receptacle.
17 towards the hopper 1, This method of introducing the material. re-recycling, as provided by sieve analysis, is called the natural reclycling rate.



   A number of fertilizer pellets were prepared according to the foregoing method, as shown by the following examples.



   Example 6
This example illustrates the preparation of fertilizer pellets starting from the fertilizer composition of Example 1, type 14-0-14.



   A bed of cores (from recycling material and dried pulverization) of type 14-0-14 and showing a sieve analysis giving 9% retained on a 10 mesh sieve, 89.7 % passing through a 10 mesh screen and held on a 30 mesh screen, 1.3% passing through a 30 mesh screen, is sprayed with a slurry at a temperature of 95 F., this slurry comprising 79% fertilizer 14-0-14 and 21% water (all the suspended matter was less than 10 mesh and no wetting or dispersing agents were added), under the following operating conditions Bed humidity: 0.75% Bed temperature 182 F.



   Inlet gas temperature: 360 F.



   Outlet gas temperature: 204 F.



   At the end of a 3-3 / 4 hour treatment period, the following results were obtained!
Production rate (effluent from the granulation device - recycled material):
32 lbs / hour of dried and sized product passing through a 4 to 16 mesh screen
Feeding weight! 72 lbs

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Granulation Apparatus Effluent Rate: 40.8 lbs per hour
Composition analysis
99.6% t 14-0-14 0.4%: humidity
Analysis on a sieve: retained on a 4 mesh sieve: 15.8% passing through a 4 mesh sieve and retained on a 5 mesh sieve: 12.6% passing through a 5 mesh sieve and. retained on a 10 mesh sieve:

     70.3% passing through a 10 mesh sieve: 1.3%
Recycled material:
Rate: 8.8 pounds per hour; roughly equivalent to one material (+ 4 stitches and - 10 stitches)
Composition Analysis 99.6% of 14-0-14
0.4% moisture
Analysis on a sieve; all 100% ground material passing through a 10 mesh screen.



   The operating conditions and the results of two additional treatments are given in Examples 7 and 8 below,
Example 7
Granulated materials: 14-0-14 from example 1
Production rate: 41.5 lbs / hour of dried and sized product (-4 mesh, -16 mesh)
Duration of treatment 6- 1/4 hours
Feeding weight: 68 pounds
Slurry feed; Sprayed through an air spray nozzle and directed to the third fifth and fourth fifth of the granulation bed
Mud: Composition analysis
81% of 14-0-14
19% water
All the suspended matter passes through a sieve of
12 stitches.



     Temperature of 85 F.



   Granulator effluent: Rate t 41.5 pounds per hour.

 <Desc / Clms Page number 25>

 



   Composition analysis: the same as for tr @@@ ment 6
Analysis on sieve: retained on 4 mesh sieve: 0.7% passing through 4 mesh sieve and retained on 5 mesh sieve 1.6% passing through 5 mesh sieve and retained on 10 mesh sieve: 8918% passing through 10 mesh sieve mesh and retained on 16 mesh sieve: 7.7% passing through 16 mesh sieve: 0.2% Recycled material: None Core material: Arrow spray of the same composition as the product or effluent from the granulation apparatus.



  Operating conditions Bed humidity t 0.40% Bed temperature 220 F.



   Inlet gas temperature 420 F.



   Outlet gas temperature 220 F.



   Gas circulation rate 460 lbs / hour.



   EXAMPLE 8 Granulated material: 20-0-20 of Example 3 Production rate! 40 lbs / hour of a dried and sized product (-4 mesh, + 10 mesh) Treatment time: 6-1 / 4 hours Weight feed weight 65 lbs. Feed of slurry sprayed through an air atomizing nozzle on the second third of the granulator bed.



    Mud: Composition analysis: 83% of 20-0-20
17% water
All suspended material passes through a 12 mesh sieve.



   Mud temperature: 85-90 F.



  Effluent from the granulation apparatus:
Rate: 56 pounds per hour Composition: 99.7% 20-0-20 0.3% water
Analysis on sieve: retained on 4 mesh sieve 5.9% passing through 4 mesh sieve and retained on 5 mesh sieve: 13.2% passing through 5 mesh sieve and retained on 10 mesh sieve: 76.8% passing through sieve of 10 stitches 4.1%

 <Desc / Clms Page number 26>

 Recycled material: 16 lbs / hour (all material being +5 = wings or -10 mesh) Product: composition identical to the effluent from the granulation apparatus.



   Analysis on sieve: 100% of material passing through a 5 mesh sieve and retained on a 10 mesh sieve Core material: composition: identical to the effluent from the granulation apparatus Dimensions on sieve: 100% (-10 meshes +30 mail- the 'Operating conditions;
Bed humidity: approx, 0.2%
 EMI26.1
 Bed tempuratuïc 195 * Fi
Inlet gas temperature 195 F.



   Outlet gas temperature: 193 F.



   Gas circulation: 405 lbs / hour.

** ATTENTION ** end of DESC field can contain start of CLMS **.


    

Claims (1)

CLAIMS 1. A method for the continuous formation of rounded pellets of substantially uniform size, comprising providing a bed of cores of a substance to be pelletized, wherein said cores are in contact with each other. with the others, these cores having a particle size of at least about 40 meshes, this bed being arranged in a chamber comprising means for raising portions of this bed from the bottom of this chamber to a more point. raised therein and to release these raised portions so that they fall freely towards the bottom of the chamber, the humidification of localized portions only of this bed, in the lower portion of the chamber by an applica- direct spraying, of a substance to be pelletized and the immediate elevation and subsequent release of these bed portions before any agglomerating action occurs to any significant degree between the nuclei of the moistened portions, while hot drying gases are passed through the chamber, the local portions <Desc / Clms Page number 27> slightly moistened from this bed separating into separate coated cores and small groups of smaller cores than the desired pellets, due to the agitation provided during the elevation and release of the aforementioned portions of the bed, and the fall of the released portions of the bed from top to bottom through the hot drying gases, so that the coated cores and groups of cores are dried to a non-caking moisture content as they descend through the hot drying gases, and before they reach the bed at the bottom of the chamber, and also so that the uncoated cores have their moisture content reduced so as to keep the general moisture content of that bed below the agglomeration point. 2. The method of claim 1, wherein the sludge is applied to the bed so as to wet only surface portions of that bed. 3. The process of claims 1 or 2, wherein the cores and groups of cores are repeatedly coated with the solids of the slurry to the point of forming pellets of at least about 0.03 to 1, 5 inches, these pellets being comprised primarily of solids derived from this slurry. 4. The process according to any one of claims 1 to 3, comprising the step of purifying an additional quantity of sludge in the hot drying gases in the form of very small droplets, so as to coat them. coated cores and clusters of coated cores, while in a free-falling separate state in these hot drying gases, the action of these being such that they almost instantaneously dry the fine cups additional mud before the nuclei and snow groups reach the bed at the back of the chamber: <Desc / Clms Page number 28> 5. The process according to any one of Claims 1 to 4; comprising the step of spraying an additional quantity of slurry into the hot lick gases inside the chamber; so as to form spray-dried particles acting as superconnects EMI28.1 additional. 6. A method of continuously forming rounded pellets having substantially uniform dimensions as described above with reference to the accompanying drawings. 7. The products obtained by the process of any one of the preceding claims.