HK1037561A - Wet granulation method for generating granules - Google Patents

Description

Wet granulation process for producing granules

Technical Field

The present invention relates to a shallow slot granulation process, and in particular to a wet granulation process for granulating fertilizers or other materials into industrially valuable granules.

Technical Field

The biggest disadvantage of the granulation technology is that the existing process requires a seed agent to form suitable conditions for granulation of the material. The use of seeds can seriously affect two important properties of the resulting granules, namely roundness and cross-sectional uniformity. Generally, the seed material is out of round, and as the primary particles, the raw material grows unevenly thereon to finally grow out of round particles, which also have the disadvantage of uneven particle density.

There is therefore a need for a process for synthesizing smooth, compact, uniform cross-section granules directly without the use of seed material and which eliminates the hazards associated with granulated fertilizer production.

The most recently granted Patent associated with the present invention is U.S. Patent No.5,460,765 to Derdall et al, 10/24/1995. This patent teaches a process for shallow slot granulation of a particular material, according to the method of Derdall et al, to give final granules having a particle size of about-5 mesh to +10 mesh. In the method of Derdall et al, it is necessary to add seed material of about-14 mesh to +28 mesh in order to initiate the process. Derdall et al teach that this not only controls the rate of particle growth, but also reduces agglomeration between particles, resulting in higher production efficiency. The Derdall et al patent also states that proper seed size is critical to the process in order to produce efficiencies in excess of 90%. This patent discloses that in order to obtain a stable state and maintain a uniform particle size distribution of-8 mesh to +6 mesh, a seed kernel of-14 mesh to +35 mesh is required.

The process of Derdall et al, while excellent, does not overcome the disadvantages of the prior granulation process, i.e. it requires a seed agent, requires dust control during the production to prevent the creation of unhealthy or potentially explosive environments, as is clearly seen at the beginning of column three, line 14 of the Derdall et al patent, which are described as follows: "if fine seeds of, for example, -35 mesh are used, it may be difficult to make the granulation process uniform and stable. "

The difficulties implied by the Derdall et al patent are due to the inherent problems of the shallow trench granulation process, namely cycling. If the seed particles are unstable, the process will be unstable and will also produce strong "cycles" as is well known to those skilled in the art. As a result, the large particles formed in the shallow grooves strongly break the small particles, which, of course, does not achieve the object of shallow groove granulation.

Also indicated in the third column, line 36: "Fine particles such as +35 mesh seeds can also be used, but this tends to produce over-seeding or over-granulation, reducing yield. "column three, line 45 also indicates: "use 20 mesh seed material to achieve the best control and uniform particle size distribution … …. "

It is well known that the larger the mesh number of the particles, the smaller the size thereof, the sizes of the corresponding mesh numbers being given below:

number of meshes	Approximate size, μm
		12	1680
16	1190
		20	840

30	590
		40	420
100	149
		200	74

According to the disclosure of Derdall et al, mesh numbers greater than +35 can lead to nucleation problems and reduced final yields. However, according to the present invention, high yields of good quality products, typically greater than 90%, can be achieved using fine powders of-35 mesh to +150 mesh, which successfully overcomes the difficulties encountered by Derdall et al, in contrast to those described in the preceding paragraph.

The particle size distribution of the nucleation material used in the invention is between-35 meshes and +150 meshes. Corresponding to less than 590 um and 105 um, respectively.

The prior art has not used the powdered nucleating agent to form uniform particles of-8 mesh to +4 mesh as in the present invention.

Some of the features of the invention have been described, the most significant advantage of which is that the granules formed by the invention have a high crushing strength and a clean cross-section. Experiments show that the crushing strength can reach 1-4 kg or higher.

At the beginning of column 33 line in the third column of the Derdall et al patent, this is written: "Large size seeds form low strength particles. "

From the nucleation agent size, the method described in the Derdall et al patent selects a seed agent of the size described in the patent. Derdall et al indicate that the ideal seed size is 20 mesh (+20 mesh); the powder used in the invention is 75-750% smaller than the required size of Derdall, but still achieves the ideal effect.

Statistry inventory H1070, filed 7.1992 by Harrison et al, discloses a method of pelletizing potash fertilizers. The process involves the use of a conventional rotary drum granulator, shallow slot granulator or other conventional granulation device to convert the specific potassium sulfate or chloride by polymerization.

This document makes no specific mention of the elimination of seed agents, feedstock size, or other important process control parameters associated with producing quality commercial particles. In addition, the process is obviously a polymerization process, which, as is well known, generally involves the polymerization of particles suspended in a liquid into aggregates or chunks upon impact. These granules or macroparticles have varying degrees of internal spacing and are not tightly bonded (Hawley's Condensed Chemical Dictionary, 11 th edition, 1987).

A particular advantage of the present invention is that the proposed process allows sulphur to be granulated. According to air pollution regulations, it is now necessary to increase sulfur content for lean soils. The agricultural science shows that the sulfur fertilizer can increase the yield and the quality of crops, is beneficial to the nitrogen absorption process of the crops, and further has the promotion effect on protein synthesis, nitrogen fixation, photosynthesis and disease resistance.

Currently, sulphur granulation is a dry synthesis method, which is very hazardous due to the sulphur, especially sulphur dust, being explosive and difficult to handle, and there is a need for a safe and reliable sulphur granulation process in view of this disadvantage. The invention provides a harmless sulphur granulation method, which can prepare sulphur and additives into pesticides, herbicides and active bacteria capable of being released slowly.

Wet granulation is very complicated because of the irregular crystallographic characteristics of the particles which are difficult to control. The wet powder is not uniform, which can lead to non-uniform growth, over-nucleation and even interruption of the process. For these reasons, there is no effective and reliable wet granulation process in the art.

Boeglin et al, U.S. Patent No.3,853,490, disclose a granulation process for granulating potassium sulfate. The method uses 50% of large particle excitation material of-6 +65 mesh, 10% to 30% of particles of-200 mesh and a fraction of particles of-65 +200 mesh. The patent mentions that the granulation process is carried out on conventional equipment but does not discuss the control problems associated with shallow slot granulation, and it is known from the Derdall et al that there are difficulties in controlling the stability of the granulation process even with a seed material of +35 mesh. The greatest difficulty is controlling the "circulation" which causes large particles to break down small particles, and therefore, Boeglin et al may simply use the drum granulation process, since it does not encounter the complications characteristic of shallow slot granulation.

Mc Go wan et al, in patent U.S. patent No.3,711,254, disclose a method of granulating a potassium fertilizer. This method provides a rough description and includes both shallow trough or drum granulation methods in one process.

Kurtz, patent No.5,322,532, discloses a sodium bicarbonate blasting (blast) medium. The blasting media comprises an agglomerate of sodium bicarbonate and sodium carbonate. This patent does not have a detailed description of other forming processes, nor other materials, other than agglomeration.

Other patent documents that are of little relevance to the present invention include U.S. patent nos. 4,371,481, 4,264,543, 5,108,481, 3,206,508, 3,206,528, 4,344,747 and 5,124,104.

The prior art lacks clear guidelines for the preparation of fertilizers, shot-peening agents, odor eliminators or water softeners having the following advantages:

a) a uniform cross-section;

b) high density;

c) no seeds or crystal nuclei are required;

d) higher crushing strength compared with the prior art;

e) uniformity of material across the particle;

f) each particle has a greater amount of material.

There has been a long felt need for such high quality particles and methods of synthesizing such particles. The present invention perfectly meets the above-mentioned needs.

Industrial applications

The invention is applied to the fertilizer industry.

Disclosure of Invention

It is an object of the present invention to provide an improved process for the production of a wide variety of granules or particles for industrial use which overcomes the disadvantages of the prior art.

It is another object of an embodiment of the present invention to provide a wet granulation method for granulating a raw material, the method comprising the steps of:

providing a feedstock having a particle size of-150 mesh in an amount of about 99.9%, the feedstock having a particle size of-150 mesh comprising about 90% of particles of-200 mesh in 99.9% of the feedstock;

providing about 6 to 8 weight percent binder material;

contacting said binder material and said feedstock material in a shallow bottom granulation tank under humid conditions, said shallow tank having a moisture content of about 1.5% to about 11% by weight; and

in the shallow tank, the raw material is directly granulated without the presence of seeds or a nucleating material.

In the invention, the maintenance of water in the shallow groove and in the product can effectively prevent dust from forming in the granulation process. This effect can also be enhanced by adding oils such as mineral oils, vegetable oils, seed oils, synthetic oils, etc. to the final product. Another feature of the present invention is that the granules produced may contain plant nutrients, production regulators, minerals, slow release ingredients and beneficial fungus. As nutrients, nitrogen, phosphorus, potassium are good examples; growth regulators include herbicides, insecticides, hormones, etc.; minerals will vary depending on soil and environmental conditions and may include copper, boron and other metals; the slow release agent may be selected from materials that release sulfur at a particular time during the growing period of the plant or crop; the bacteria can be selected within a wide range according to the specific requirements of the user. Finally, sulfur oxidizing bacteria and disease-resistant bacteria can be selected to improve the disease resistance of crops and the like.

Another feature of the invention is that the method can be easily and consistently applied to other areas of pelleting technology than agriculture. One of these is the technique of peening (blasting), in which sodium bicarbonate is known to be a very useful peening medium, but the rate of surface removal of such crystals is too high to be of practical use at all. The invention granulates sodium bicarbonate by doping other materials to enhance the abrasive resistance of the particles.

An important idea of the invention is that no seeding agent is required for granulation, in which respect the method can be simply referred to as a shallow trench nucleation method; the method is usually a crystallization process, i.e. a process in which the nuclei grow towards the surrounding material, in which the shallow groove rotation and the addition of binder help the nuclei grow towards the surroundings and increase the particle density and the raw material content.

As already described in the invention, the preferred embodiments are described below with reference to the accompanying drawings.

Brief Description of Drawings

Figure 1 shows a schematic diagram of a method according to an embodiment of the invention.

Figure 2 is a photograph of a cross-section of a prior art produced particle.

Fig. 3 is a photograph of the particles of fig. 2.

FIG. 4 is a photograph of a cross-section of a particle produced according to one embodiment of the present invention.

Fig. 5 is a photograph of the particles of fig. 4.

Fig. 6 is a photograph of a cross-section of potassium chloride granules produced by the prior art.

Fig. 7 is a photograph of a cross-section of red potassium chloride granules produced by the prior art.

Fig. 8 is a photograph of a cross-section of potassium chloride granules produced according to one embodiment of the present invention.

Fig. 9 is a photograph of the potassium chloride granules of fig. 8.

FIG. 10 is a photograph of a cross-section of a potassium chloride-containing pellet produced in accordance with one embodiment of the present invention.

In this document, like numbers refer to like elements.

Models for practicing the invention

Before explaining the process of the invention, a list is given of some general properties of compounds and materials which may be granulated.

TABLE 1 general Properties

Compound (I)	Crystal	Solubility in water	Melting Point C	Boiling point of	Harmfulness of
						Ammonium nitrate NH4NO3	Colorless and colorless	Dissolving in water, alcohol and alkali	169.6	210 decomposition	Pressurization or exposure to high temperatures may cause explosions
Ammonium sulfate (NH4)2SO4	Light brown to gray	Is soluble in water	513		Is free of
						KCL (potassium chloride)	Colorless or white	Is slightly soluble in water and alcohol	772	1500 sublimation	Is free of

Potassium nitrate KNO3	Transparent, colorless or white; crystals orPowder of	Soluble in water or glycerol, slightly soluble in alcohol	337	400 decomposition	The danger of combustion/explosion due to shock, heat or contact with organic substances
						Potassium sulfate K2SO4	Colorless or white hard crystals or powders	Is soluble in water	1072		Is free of
Sulfur S	An alpha-form orthorhombic, decahedral yellow crystal; beta-type monoclinic orthorhombic pale yellow crystal	Slightly soluble in alcohol and ether, soluble in carbon disulfide	alpha-S about 94.5 beta-S about 119		Too fine and flammable to pose a fire and explosion hazard
						Urea CO (NH2)2	White crystals or powders	Dissolved in water, alcohol or benzene	132.7	Decomposition of	Is free of
Sodium bicarbonate NaHCO3	White powder or crystal	Is soluble in water	270 begin to lose CO2		Is free of

Referring to fig. 1, a diagram generally illustrating a method formed in accordance with one embodiment of the present invention is shown.

This example shows a 10 tonne per hour production line. Reference numeral 10 designates a feed stock which may be any suitable material, many examples of which have been given previously. The techniques presented herein may allow for the production of a number of products, including various sulfates, soda, sulfur, potash, kaolin, magnesium oxide, potassium, sodium, and ammonium chlorides, and the like.

The starting material may be present in an amount of 9.8 tons per hour (9.8 thr)^-1) Is introduced together with a suitable binding material as described previously. The feedstock and binder may then be introduced into a pulverizer 12 to pulverize the feedstock into a product containing particles of 99.9% -150 mesh, wherein 90% or more of the particles of-200 mesh are present. The pulverizer 12 may be a separate pulverizer or an air swept pulverizer or any suitable pulverizer known in the art. Upon comminution, stream 14 is introduced into a closed collection hopper 16, which collection hopper 16 includes a baglike chamber 18 leading to a dust collector. Collection hopper 16 also includes a suitable valve 20 for measuring dust entering collection bin 22. The bin 22 is mounted above two feeders 24 and 26 which split the material received from the bin 22 into two streams, the first of which is fed by the feeder 26 to a moistening mixer (not shown) and then 7.6 tons per hour (7.6 thr)^-1) Into a first shallow bottom granulation tank 28. As an example, the second feeder 24 feeds a second strand into a tundish or barrel mixer (not shown) and then at a rate less than that described above, such as 2.8 tons per hour (2.8 thr)^-1) Into a second shallow bottom granulation tank 30 to make up the balance of the 10 tonnes per hour line. Each mixer contains a mixture of binder and raw materials with a water content of 4 to 8% by weight.In this way, the material fed from the mixer into the pan is a wet material, thereby avoiding the formation of dust during the process. The water content in the binder is a variable parameter which depends on the nature (solid/water ratio) of the binder. Clearly, a high moisture content binder requires less water addition than a low moisture content binder.

A receiver 32 is mounted on the shallow trough 30 for holding-35 purpose dried stock (not shown). A variable speed measuring device (not shown) is mounted on the receiver 32. The feeder removes material from the receiver 32 and feeds the dry material into the trough 30. as will be appreciated by those skilled in the art, the troughs 28 and 30 include upper and lower scrapers 34, 36 and 38, 40, respectively, and the material from the receiver 32 is likewise fed into the trough 30 behind the upper scraper 38. In this example, the shallow grooves 30 are produced at an efficiency of 3 tons per hour, with 80% of the product being between-8 mesh and +20 mesh. The above results were obtained by controlling the ratio of raw material to dust to be between 1: 20 and 1: 100. It has been found that it is very effective to atomize the hot adhesive solution from any position between the 12 o 'clock position and the 5 o' clock position. The first shallow groove reaches a steady state when the correct free moisture content is reached, typically 1.5% to about 11%. In this way, particles can be formed directly on shallow grooves 30 in the absence of a seeding agent.

As noted above, the product formed on the shallow grooves 30 typically has 50% to 80% of the particles being-8 mesh. The product is discharged and dried by a dryer 38 (. The dryer may be a carry-on dryer, a trough dryer, or a rotary-vane dryer. The product formed on the shallow trough 28 is also fed to a dryer 38 by a suitable conveyor 40.

The product from the dryer 38 is passed through line 42 to a screen 44 which discharges at 4, 8 and 20 mesh. With fractions of +4 and 4 mesh and-20 mesh being sent to the shredder 12 for re-entry into the system, and the recycle stream being represented by 46. The fraction of 4 to +8 mesh is the final product, leaving the sifter 44, represented by numeral 48, as the final boutique. The-8 mesh to +20 mesh fraction is fed via line 50 to a hopper 52 equipped with a weighing belt feeder. From the weigh belt feeder 52, the material proceeds further into the shallow trough 28 and is further processed with incoming binder and added dust particles to produce the desired particles. This is an optional step depending on whether further raw materials are added.

Residual dust in the dryer 38 may be passed through a discharge line 54 of the dryer 38 to a hopper 56, and aggregate in the hopper 56 may be passed through both a line 58 to the bin 18 and a line 60 to the raw materials. The fines or dust entering the chamber 18 may also be removed through a secondary operation, such as wet scrubbing, as indicated by numeral 60 in fig. 1. It is obvious that a person skilled in the art can also cite further examples.

For the above system, the ratio of-8 mesh to +20 mesh required for stable operation of the shallow grooves 28 is between 1: 10 and 2: 5, with an optimum ratio of 1: 5. The shallow trough 28 is stable to operate quickly and is capable of producing +8 mesh to-4 mesh particles in yields above 95%. The yield of the whole production line exceeds 90 percent. As mentioned above, 10% by weight of the-20 mesh and +4 mesh particles and dry dust can be recycled to increase the yield and efficiency of the process, thereby ensuring that the highest output is achieved at low cost.

In addition, the angle and rate of rotation of the shallow grooves 28 and 30 can be adjusted to produce only +8 mesh to-4 mesh particles. It has also been found that varying the horizontal position of the shallow grooves, inclining their sides, is beneficial to improving the efficiency of the granulation process. The specific size of the inclination and horizontal angles depends on the rotation rate and the particles to be produced. As an alternative. Shallow slot tilt angles and or rotational speeds may be adjusted to produce particles of-10 mesh to about 100 mesh.

Obviously, the above-described operating method can be operated either alone or in combination with other operations, depending on the specific requirements of the application.

Obviously, it is also possible to fit a plurality of shallow grooves in the system for continuous growth of the particles. On the other hand, the process can also be decomposed, designed or able to produce a wide variety of valuable particles with multi-layered materials. Those skilled in the art will appreciate that the process can produce fertilizer in a variety of forms and in the form of pellets for specific uses, such as high-grade fertilizers for golf courses, slow release pellets, and the like.

Suitable options for binders include wood pulp, sucrose, saturated salts and proteins, water, calcium sulfate, sodium sulfate, potassium chloride, dried gums, wheat, corn, cereal, and calcium phosphates, among others. The choice of binder depends on the desired characteristics of the particles. The above examples are (therefore) only examples. For granulation of materials that are hazardous or whose dust has a potential for explosion. Binders with high moisture content, typically 30% to 60% or higher, may be selected, as may mixtures of binder materials.

In the case of raw materials and binders, it is not necessary to add moisture to the shallow grooves 28 and/or 30 with a sprayer when the binder has a high moisture content. In a further variation, the binder and the feedstock may be added simultaneously to the shallow trough, and these processes may vary depending on the nature of the material to be granulated.

Referring to fig. 2, fig. 2 shows ammonium sulfate-cored sulfur granules produced in accordance with the method set forth in the Derdall patent. It is clear that the particle comprises a core of larger size which occupies a larger volume of the particle. The particles are not uniform in cross-section and some local areas are hollow. In addition, the particles are not spherical. Both of these factors will reduce the quality and industrial value of the granules.

Figure 3 shows the overall sulfur granules formed by the method of Derdall et al. As is clear from this figure, the outer surface of the particles is loose, having a sand-grained outer surface structure. Such defects of non-compact surface are liable to generate dust, which brings about the handling problems previously described, in particular an increased risk of explosion.

In contrast, fig. 4 and 5 show high quality particles formed by the method of the present invention. Most importantly, the particles are completely without cores or seeds, and are uniform, continuous and compact as a whole. Fig. 5 shows the entire particle. Obviously, such particles have an external surface that is totally different from the particles produced by the previous process, which also eliminates dust or grit around the periphery of the particles. Such particles are denser, harder, more closed and contain more material (at least 95%) than particles produced by previous processes. In this way, the advantages listed above can be understood.

The potassium chloride granules produced according to the technique of Derdall et al are shown in FIGS. 6 and 7, which show two different compounds, demonstrating the presence of seeds critical for granulation.

Fig. 8 and 10 show potassium chloride granules produced by the method according to one embodiment of the invention. As shown, the particles are rounded, eliminating the inner core and the surface grit of fig. 6, which also includes a sulfur compound.

Figure 9 shows sodium bicarbonate particles formed in accordance with the present invention. Of note are the spherical appearance and compactness of the particles.

The present invention has commercial value and great industrial significance in granulation technology, and can endow various characteristics to the customized granules.

Although the present invention has been described by the above embodiments. The invention is not limited thereto. Various modifications may be made by those skilled in the art without departing from the spirit, nature and scope of the invention.

Claims (25)

1. A wet granulation process for granulating a feedstock into granules, the process comprising the steps of:

providing a feedstock containing about 99.9% particles having a size of-150 mesh, said 99.9% of particles having a size of-150 mesh comprising about 90% of particles having a size of-200 mesh;

providing about 6 to 8 weight percent binder material;

contacting said binder material and said feedstock material in a shallow bottom granulation tank under humid conditions, said shallow tank having a moisture content of about 1.5% to about 11% by weight; and

in the shallow tank, the raw material is directly granulated without the presence of seeds or a nucleating material.

2. The method of claim 1 wherein said moisture content is between about 1.5% and about 10.5%.

3. The method of claim 2, wherein said moisture content is about 8%.

4. The method of claim 1, wherein the particles are from-10 mesh to 100 mesh in size.

5. The method of claim 4, wherein said method is characterized by a production efficiency of at least 90%.

6. The method of claim 1, further comprising the step of transferring said pellets to a second shallow bottom granulation tank.

7. The method of claim 1, wherein the feedstock is selected from the group consisting of sodium bicarbonate, potassium sulfate, potassium chloride, potassium nitrate, ammonium sulfate, and sulfur.

8. The method of claim 1 wherein the binder material comprises about 60% moisture and 40% solids.

9. The method of claim 8 wherein about 7% to about 9% by weight of the bond material is added to the shallow groove.

10. The method of claim 1 wherein the adhesive material is dry and the moisture comprises water added to the shallow grooves.

11. The method of claim 6 wherein the feedstock for the second pan comprises between about 20% and 35% of product having a particle size in the range of-10 mesh to about 100 mesh.

12. The method of claim 11 wherein the product of said second pan comprises particles having a particle size of from about-4 mesh to about-8 mesh.

13. The method of claim 1 further comprising the step of adding an oil to the formed particles to facilitate dust control prior to further processing.

14. The method of claim 13, wherein said oil comprises an oil selected from the group consisting of canola oil, vegetable oil, and mineral oil.

15. A wet granulation process for granulating a feedstock into granules, comprising the steps of:

providing a feedstock comprising about 99.9% of particles having a size of-150 mesh, said 99.9% of particles having a size of-150 mesh comprising about 90% of particles having a size of-200 mesh;

a binder is provided having a moisture content of about 60% by weight and a solids content of about 40%.

Contacting said binder material and said feedstock material in a shallow bottom granulation tank under humid conditions, said shallow tank having a moisture content of about 1.5% to about 11% by weight; and

in the absence of seeds or nucleation material, particles of-10 mesh to about 100 mesh are formed directly from the feedstock in the shallow trough.

16. A fertilizer granule formed according to the method of claim 1.

17. The fertilizer granule as set forth in claim 16, characterized in that said fertilizer granule comprises ammonium sulfate.

18. The fertilizer granule as set forth in claim 16, characterized in that said fertilizer granule comprises ammonium nitrate.

19. The fertilizer granule as set forth in claim 16, characterized in that said fertilizer granule comprises potassium sulfate.

20. The fertilizer granule as set forth in claim 16, characterized in that said fertilizer granule comprises potassium chloride.

21. The fertilizer granule as set forth in claim 16, characterized in that said fertilizer granule comprises sulfur.

22. The fertilizer granule as set forth in claim 16, characterized in that said granule has a uniform and uniform cross-section.

23. The fertilizer granule as set forth in claim 18, characterized in that said granule has a uniform and uniform cross-section.

24. The fertilizer granule as set forth in claim 19, characterized in that said granule has a uniform and uniform cross-section.

25. The fertilizer granule as set forth in claim 20, characterized in that said granule has a uniform and uniform cross-section.