CLIAMS:1. A process for conversion of the Zinc Sulphate Monohydrate powdery material, in to spherical, hard, non- friable granules of desired size without change in the chemical composition of the material, its solubility properties in water and colour, wherein the process comprises :
a. arranging a pan granulator at an angle,
b. loading seed material having a size of -10 to +14 tyler mesh and occupying 20 to 25% of pan volume on the pan granulator,
c. feeding zinc sulphate monohydrate powdery material of size 90% minus 60 tyler mesh to the pan granulator,
d. spray feeding a low pressure steam as binder to the pan granulator enabling zinc sulphate monohydrate in the said pan granulator to layer onto the seed material to form granules with an enlarged particulate material of about 60% by weight having a particle size distribution of about -5 to +9 tyler mesh,
e. drying the green granules exiting from pan granulator in drying means for an appropriate time at an appropriate temperature,
f. screening the dried granules for segregating the product from oversize and fines fractions, and
g. cooling and coating the dried product size granules with an anti caking agent to make it non friable, characterized in that the said granules having a particle size distribution of about -5 to +9 tyler mesh.
2. The process as claimed in claim 1 wherein the pan angle shall be 50 – 60° from horizontal.
3. The process as claimed in claim 1 wherein the low pressure steam binder at a pressure of 2.0-3.0 kg/cm2g.
4. The process as claimed in claim 3 wherein the binder temperature is in the range of 130-140 deg C.
5. The process as claimed in claim 1 wherein the LP steam as binder is admitted on the zinc sulphate monohydrate bed on the pan in such a flow that the free moisture of the green granules coming out of the pan shall be within 9-13% w/w.
6. The process as claimed in Claim 1 wherein the operation speed of pan shall be in the range of 25-30 rpm.
7. The process as claimed in Claim 1 wherein the residence time of the material in the pan shall be in the range of 15-20 minutes.
8. The process as claimed in Claim 1 wherein the feed zinc sulphate monohydrate powder rate to pan of 400 mm diameter and 126 mm depth shall be in the range of 15-20 kg/hr for achieving desired product size in the range of -5+9 tyler mesh and also to achieve maximum conversion into the product size granules.
9. The process as claimed in claim 1 wherein the zinc sulphate monohydrate powder feed material shall be of size 90% passing through 60 tyler mesh.
10. The process as claimed in Claim 1 wherein the number of nozzles for steam sprays feeding shall be 3-4.
11. The process as claimed in Claim 1 wherein the steams spray nozzle spacing shall be 30-60 mm from one another.
12. The process as claimed in Claim 1 wherein the spray angles of the binder spray nozzles is in the range of 40° - 90°.
13. The process as claimed in claim 1 wherein the feeding of particulate material to pan should not be pulsating.
14. The process as claimed in claim 1 wherein exiting granules from pan granulator have a moisture percentage of 9 to 13% w/w.
15. The process as claimed in claim 14 wherein the granules exiting out of the pan granulator from will have particle size distribution of about 60% in the size range of 5 to +9 tyler mesh.
16. The process as claimed in claim 14 & 15 wherein the green granules exiting out of the pan granulator shall be dried in the drying means to reduce the moisture from 9- 13% to a range 1-2%.
17. The process claimed in claim 16 wherein the drying means is a drying chamber having a plurality of belt conveyors arranged in such a way that the first conveyor receives the green granules from the pan granulator discharge and discharges on the second conveyor and from there to subsequent conveyors to give sufficient residence time for drying.
18. The process claimed in claim 17 wherein the belt conveyors shall be provided with variable frequency drive motors to change the speed of the belt and thereby the residence time of the material in the drying chamber.
19. The process claimed in claim 17 wherein the required residence time for zinc sulphate monohydrate green granules on the drying means for drying from 9-13% moisture to 1-2% moisture is 5-8 minutes.
20. The process claimed in claim 17 wherein the air temperature in the drying means required for drying the green granules shall be in the range of 120-150°C.
21. The process claimed in claim 1 wherein material after drying is screened to segregate the product from oversize and undersize fractions.
22. The process claimed in claim 1 wherein product size fraction is further cooled and coated with an appropriate anti-caking agent.
23. The process claimed in claim 22 wherein the anti-caking agent shall be selected from the group comprising of Servo 60 gear oil, Coconut oil, Indocoat TQ-50 supply by M/s Indo amine and Acalf-50 supplied by M/s Filtra catalyst Pvt ltd in order to achieved desired characteristics of the product such as no colour change, no change in chemical composition, no change in solubility.
24. The process claimed in claim 22 where in the dosage of the anticaking agent shall be in the range of 0.4-0.6% of the final production rate of the granular zinc sulphate monohydrate.
25. The process as claimed in claim 1 can be operated in commercial scale using a pan of diameter in the range of 1.5-2.0 m and depth about 0.300 mm to produce final dried granular product athe rate of 0.5-0.6 tons/hr. .
26. The process as claimed in claim 25 where in the rate of feeding of zinc sulphate monohydrate powdery material to the said dimensioned pan shall be in the range of 800-1000 Kg/ hr. ,TagSPECI:FIELD OF THE INVENTION
The present invention relates to
A method of granulating Zinc Sulphate monohydrate powder in to spherical shaped uniformly sized granules without affecting the Zinc content & solubility of the material.
A method that produces hard granules with almost no friability for easy handling and application by the end users.
The usage of Pan granulator also called as pan pelletiser/Disc pelletiser for the above process which brings out spherical and uniformly sized granules falling in to the desired size range of -5+9 tyler mesh i.e -4+2 mm..
The selection of suitable drying equipment for drying the green granules that are soft and delicate while coming out of the above step for removal of excess moisture from them and to make them hard.
The coating of the dried Zinc Sulphate Monohydrate granules in a coating drum to reduce the friability, to control the presence of powdery fraction and to give shining appearance to the product while maintaining the original colour of the product i.e white..

BACKGROUND OF THE INVENTION
Fertilizers are widely used for supplying the required nutrients to the plants and thereby to give better yield. They are applied in different methods viz soil application also called as field application, foliar spray and fertigation i.e thro drip irrigation. Fertilizers that are applied through soil are to be supplied in granular form to keep them stable to weather conditions and easy for handling. There are some fertilizers which are produced in the form of dusts, powders, liquids and emulsions. Powders are preferred for foliar application and fertigation for ease of dissolving in water. Granular fertilizers are preferred for soil applications to ensure slow dissipation and absorption by plant. Zinc Sulphate monohydrate that is available in powder form, though found to be comfortable for foliar application and fertigation purposes, bears a lot of discomfort while applying through soil, thereby suffering disadvantages in its usage for soil application.
Though zinc sulphate monohydrate is used widely for foliar application, there is requirement to supply through soil also for balanced supply of the nutrients. For application through soil, powders are not comfortable as they may fly away and also it dissolves very fast and leach away easily thereby imparting nutrient losses. Moreover the powders absorb moisture from the atmosphere faster than the granules due to high surface area. Hence granular form of zinc sulphate monohydrate is felt necessary due to its ease of handling and application through broadcasting or by a mechanical means for soil application. The advantage of Granular zinc sulphate is that it can be used for foliar application and fertigation purposes also as the solubility of the material does not get affected due to coversion into granular form. Hence there arose the necessity to find out a suitable method of granulating Zinc Sulphate Monohydrate.
The granular formulation is generally a dry composition that can be applied to soil and/or vegetation by spreading or broadcast application. Upon application and subsequent irrigation or rainfall the active chemical agent will associate with the water and allow the active chemical agent to spread to the surrounding locus. This association allows the active chemical agent to be transported with the passing water, thereby further increasing the coverage of the active chemical agent.
Ideally, the granules shall be spherical and have a smooth surface, which lead to desired flow characteristics in bulk form.

PRIOR ARTS
Zinc sulphate exists in three different forms viz., anhydrate, monohydrate, and heptahydrate. The monohydrate and heptahydrate forms are widely used as fertilizer grades which contain 33% & 21% zinc content respectively.
The manufacturing process of Zinc sulphate monohydrate powder is a well-known prior art by reaction of the reactants such as Zinc Oxide, Zinc dust, Metallic Zinc, Zinc Carbonate etc with Sulphuric acid. The zinc sulphate solution thus formed by reaction is dried in spray drier to evaporate the water and to obtain Zinc Sulphate Monohydrate in the form of crystalline powder. One of the prior arts using Zinc Oxide as one of the raw materials is represented by the reaction:
ZnO + H2SO4 -- > ZnSO4.H2O
All the prior arts from the above mentioned raw materials describe the manufacturing process for the production of zinc sulphate monohydrate in the crystalline powder form only,
There are no prior arts to manufacture Zinc Sulphate monohydrate in granular form.
The present invention takes the Zinc Sulphate Monohydrate powder produced by any one of the prior arts as feed material and coverts in to the granular form.
Some fertilizers like Urea are manufactured in the form of prills which is a well-known prior art for getting round shape. But the prill is different from the granule. A prill is formed by solidification of the molten liquor when exposed to cooling where as a granule is formed by accretion and agglomeration of few small particles together. Prills are inferior in strength than granules.
There are many prior arts for granulation of fertilisers one of them being the drum granulation process for production of granular fertilisers such as Di-ammonium phosphate (18-46-0 grade), Mono ammonium phosphate (11-52-0 grade), Ammonium phosphate sulphates such as 16-20-0, 20-20-0. 18-9-0, other NP fertilisers such as 14-28-0, 20-20-0, Nitro phosphates such as 20-20-0, 23-23-0, 24-24-0 , NPK fertilisers such as 15-15-15, 10-26-26, 12-32-16, 22-22-11, 14-35-14, 17-17-17, 14-28-14, 19-19-19 , Urea phosphates such as 28-28-0, 24-24-0, 20-20-0 etc.,
One of the greatest disadvantages known in the drum granulation process is the use of huge quantity of seed material to achieve the proper conditions for granulation to result in a pellet or granule shape. By making use of a seed, the resulting granule gets affected in its shape, roundness and cross sectional uniformity. Typically, if seeding material is not round, the result is an out-of-round particle formation.
The prior arts also use other granulation processes like fluid bed granulation, compacting granulation, Basket granulation etc for some of the fertilisers. But all these processes produce irregular or cylindrical shaped granules but not the round spherical granules.
This invention, which does not exist in the prior arts, brings out the art of granulating the Zinc Sulphate Monohydrate powder, a popular micronutrient fertilizer containing Zinc at 33%, by Pan Granulation technique.
US patent no 2,121,399 by Ivan L Haag published on 21st June, 1938 is related a process for production of zinc sulphate monohydrate having a basicity not more than 0.06%. and having lower ratio of Chlorine to zinc than the zinc containing crudes. Here the focus is to reduce the basicity and chloricne content of the product. It is not related to the present invention of production of zinc sulphate monohydrate in granular form.
US patent 3,408,169 A by JB Thompson et al published on 29th Oct, 1968, the author describes pan granulation method for the production of nitrogenous compounds and claimed the said nitrogenous compound as Urea or ammonium nitrate. It is not related to the Zinc Sulphate monohydrate granulation process.
US patent 3,905,796 Published on 16th Sept, 1975 to Ghelfi discloses a process for dehydrating and granulation of manure based fertilisers where a homogenous and durable pulp is granulated and dried. It is different from present invention of Zinc sulphate monohydrate granulation.
US patent 4,082,532 by Hugo Imhof published on 4th April, 1978 discloses a process for manufacturing extruded cattle manure pellets. The material is first converted to strands by extrusion process and then converted to pellets. It is different from the present invention of granulation of Zinc sulphate monohydrate powder.
US patent 4,157,371 by Daunton L Paulson et al published on 5th June, 1979 describes a method of agglomerating fine ore powders. The invention is used to agglomerate extremely fine dust particles in a collection bin and process them before sending the resultant agglomeration to storage or a further processing location. This method agglomerates the by product dust particles on a smooth circular horizontal disc with a raised outer edge comprising the steps of a) depositing said particles on the disc’s surface b) rotating the said disc at a substantially constant edge speed c) spraying a liquid binder on said particles and (d) conveying said formed agglomerate by centrifugal and tangential forces to move it over. This patent is on improved version of recovery of duct particles in a process over the other types of recovery. It is no way related to the present invention of Conversion of zinc sulphate monohydrate powder to granular form by using pan granulation and subsequent steps.
US patent 4,339,402 A by Richard K Henry published on 13th July 1982 describes a method comprising the steps of supplying particulate batch material which contains 10-20 percent by weight of Na2 O, to a slanted rotatable surface; supplying liquid to the slanted rotatable surface to render the batch particles with the ability to adhere to one another upon impaction; rotating the slanted rotatable surface in a given direction to cause the material on the surface to move up along the surface and then downwardly at least partially under the influence of gravity so as to move in generally elliptical paths, whereby individual particles are caused to impact against one another and adhere thereto to form pellets, the size of the substantially finished pellets being in the range of 3/8 inch to 5/8 inch in diameter i.e 9.5 to 15.9 mm dia. This patent is related to pelletizing particulate batch material for use in a glass melting furnace but not related to zinc sulphate monohydrate.
US patent 4,659,557 A by Lenz et al published on 21st April 1987, describes a process for producing pourable and storable ferrous sulphate consisting essentially of mixing ferrous sulphate heptahydrate and brown coal dust mixed together in a proportion of 6:1 to 1:6.6 by volume and wherein the brown coal dust has a moisture content of 8% to 10%. It is a process of coating ferrous sulphate heptahydrate with dehydrated brown coal but not related to the present invention of conversion of Zinc sulphate monohydrate powder in to granular form.
One prior art through US patent 5,108,481 by Thomas C Shutt et al published on 28th April, 1992 discusses the art of granulating Ferrous sulphate monohydrate in a disc pelletizer by spraying aqueous ammonium sulphate solution as binder. In this patent the focus is on pelletisation of ferrous sulphate monohydrate where as the present invention is regarding granulation of zinc sulphate monohydrate powder to produce spherical granules.
US patent 5,352,674 A by Cummings published on 4th Oct, 1994 describes chemically stable granular insecticidal compositions of phosphoroamidothioates and phosphoroamidodithioates comprising at least 75 weight percent of ammonium sulfate effective for granulating the insecticidal components.
Also disclosed in this patent the usage flowability agent, Lubricant and binder with the provison that the total weight percent of such additives in said granular composition ranges from at least 1 weight percent to less than about 6 weight percent. It is different from the present invention of Granulation of Zinc sulphate monohydrate powder.
US patent 5,443,764 by Lloyd published on 22nd Aug, 1995 describes the invention relates to a process for the preparation of water-dispersible granules which comprises mixing the desired ingredients of the granules to form an extrudable composition, extruding the mixture, and rolling the extrusions to break them down into granules. It is particularly suitable for the preparation of water-dispersible granules comprising agricultural chemicals (also known as dry flowables) as the process enables high production rates to be achieved and the products have high suspensibility and rapid dispersion. It is an extrusion method of granulation hence different from the present invention of Granulation Zinc sulphate monohydrate powder by pan granulation and the subsequent steps.
Another prior art vide the US patent 5,460,765 by Gary Derdall et al published on 24th Oct, 1995 describes the art of granulating industrial materials of particulate nature or powder form by grinding the material in to fine size such as 95% passing thro 150 mesh or 90% passing thro 200 mesh or much finer and feeding to a pan along with seed material and binder solution. Here the author claimed the said powder material is selected from the group consisting of Potassium sulphate, ammonium sulphate, potassium chloride, ammonium chloride, Sulphur, potash, magnesia, kaoline, and soda ash. The author also claimed that the binder solution as water. But the present invention is on granulating zinc sulphate monohydrate powder which is not mentioned in the above group. Moreover in the present invention the binder used is low pressure steam because the temperature of the material is also claimed as an important factor.
US patent 6,013,209 by Robin Phinney Published on 11th Jan, 2000 describes an apparatus and method for uniform granulation involving the use of an initial feedstock having 99.9% particle size of -150 mesh and 90% particle size of 200 mesh. The feedstock may be contacted in a pan granulator which includes a minor amount of nucleating material of about -35 mesh. The method is designed to be useful for forming granules of size distribution -8 mesh to +4 mesh having a plurality of layers of differing material. The binder in this patent includes lignosol, sugars, saturated salts and proteins, water, calcium sulfate, sodium sulfate, potassium chloride, dry gluttens, wheat grains, barley grains, rice grains and calcium phosphate. It is different from the present invention of conversion of zinc sulphate monohydrate powder in to granular form using Low Pressure steam as binder by the pan granulation and subsequent steps for drying and coating.
The prior art vide US patent 6,372,008 B1 by Marvin L Boote et al published on 16th April, 2002 describes a method to convert metallic heptahydrate salts such as iron and zinc sulphate heptahydrates into agricultural type materials such as fertilizer products which are highly effective to address iron chlorosis and other problems in the plants. The claims are the usage of metallic heptahydrate mixturesto address iron chlorosis and the humates as binding agent for granulating the mixture. It is different from the present invention of granulation of zinc sulphate monohydrate powder using low pressure steam as binder.
The US patent 6,582,637 B1 by Robin Phinney published on 24th June, 2003 relates to granulation of compost materials for fertilizer applications. The author describes that the invention is an improved method of granulating the compost powder in the absence of a nucleating material, seed material or other initiator. The binder mentioned in this patent includes a member selected from the group consisting of gluten, starch, neutral lignosulphonate of ammonia, neutral lignosulphonate of potassium lignosol or combination thereof. It is related to encapsulation of agricultural seeds with compost material granulated there around. It is different from the present invention of zinc sulphate monohydrate granulation by pan granulator and subsequent steps.
US patent 6,582,638 B1 by Edward John Key published on 24 th June, 2003 describes a granulator comprising a perforate screen located within a housing, a roller having a curved convex outer surface and located within the housing wherein the roller is adapted to pivot relative to the perforate screen so that in operation, plastic material is able to be forced through the perforate screen by the roller surface as the roller pivots. It is entirely different from the present invention of Conversion of Zinc sulphate monohydrate powder into granular form by pan granulation and subsequent steps.
US patent 6, 752, 943 B1 by Prakash Mahadev Jadav et al published on 22nd June, 2004 describes an apparatus and process for granulation of dry powder materials. The apparatus is an extruder consisting of a rotating spiral worm screw in a chamber, an apertured plate, holding frame, guiding slant, blunt edge, etc. It ia an extrusion method of granulating dry powders and is different from the present invention of Zinc sulphate monohydrate powder granulation by pan granulator and subsequent steps thereafter.
US patent 2006 0247149 by Poul Bach et al published on 2nd Nov, 2006 is related to a process of coating of a core unit comprising an active component with a liquid dispersion comprising a solvent, a dissolved salt and solid dispersed particles. It is related to the coating of a core unit comprising of proteins or enzymes as active components layered over an inert core particle and is different from the present invention of granulation of zinc sulphate monohydrate and the process thereafter to form hard spherical granules.

OBJECT OF THE INVENTION
Main object of the present invention is to bring out an improved version product for Zinc Sulphate monohydrate which does not have the drawbacks of the prior art zinc sulphate monohydrate product such as powders.
One object of the present invention is to granulate Zinc Sulphate monohydrate powder in to spherical shaped granules.
It is another object of the invention to identify a granulating equipment that can produce green granules of zinc sulphate monohydrate to achieve maximum conversion of zinc sulphate powder into granules of the size range -5+9 tyler mesh i.e -4+2 mm.
It is another object of the invention to produce uniformly sized granules of zinc sulphate monohydrate final product after passing thro the screen such that 90% falling in the size range of -5+9 tyler mesh i.e -4+2 mm.
It is another object of the present invention to produce hard granules of zinc sulphate monohydrate so that during handling and storage the granules will not get crushed due to impact.
It is further object of the invention to produce zinc sulphate monohydrate granules with almost no friability for easy handling and comfort in application by the end users.
It is still further object of the invention to identify suitable binder to produce zinc sulphate monohydrate granules while maintaining the Zinc content & solubility of the product same as that of the zinc sulphate monohydrate powder.
It is still further object of the invention to find out suitable paramters, by conducting experiments, for granulating the zinc sulphate monohydrate to bring out superiority to the product granules with respect to sphericiity while maintaining the Zinc content & solubility of the product same as that of the zinc sulphate monohydrate powder.
It is still further object of the invention to find out suitable drying equipment for drying the green granules that are soft and delicate, without causing breakage and attrition.
It is another object of the invention to identify suitable coating oil for the dried Zinc Sulphate Monohydrate granules in a coating drum to reduce the friability, to control the presence of powdery fraction and to give shining appearance to the product while maintaining the original colour of the product i.e white.
It is overall object of the invention is to develop a process consisting of suitable equipments, binder coating oil and the operating parameters etc for Conversion of Zinc sulphate powder in to spherical, hard, non-friable granules maintaining the composition, solubility and colour of the product granules same as that of the powder.
The above objects i.e a granular zinc sulphate monohydrate product having improved hardness, non-friable and anti-caking properties and which is useful for direct application to the soil or for foliar and fertigation purposes, can be achieved by pan granulation and subsequent process steps. That are being described in the coming section.
In the process of this invention, the pan acts as a device where growth of granule takes place by internal recycle based upon controlled seeding to the pan and the size segregating capacity of the pan. During the rotation of the pan small particles roll around the face of the pan and picks up the binder and moisture. These particles reside at the bottom of the granulation bed and get layered by the fresh feed until they rise vertically to the bed surface and then exit as product. By taking care of the critical parameters like angle of the pan to the horizontal, speed of the pan, zinc sulphate monohydrate powder feed rate, location of feeding, binder spray rate and location product characteristics can be varied. The discharged product is then dried in a dryer to a desired moisture percentage where the granule strength is in the acceptable level. Later the cooled product is coated with anti caking agents to make it non friable.
The friability and caking problems as well as other problems suffered in the storage, handling and distribution of the fertilizer products have been alleviated to a significant degree in this invention. The invention as disclosed imparts to the product satisfactory anti-caking and hardening characteristics and overcomes prior art disadvantages.
The present invention relates to an improved fertilizer particulate products and a method to prepare a novel granular products. The hardness, non-friability and anti-caking of a product is enhanced as per this invention.
The improved granulated product as obtained in this invention is useful for either direct application to the soil or for foliar and fertigation purposes. The improved hardness, non-friable and anti-caking characteristics render the product superior to other forms of zinc sulphate monohydrate available in the market.
Thus, in accordance with one aspect of the present invention, there is provided a granular product having improved hardness, non-friable and anti-caking properties, said product being transformed into granular form produced from pan granulator.
In accordance with another aspect of the present invention, there is provided a method for producing a granular product having improved hardness, non-friable, and anti-caking properties comprising the steps of size enlargement and conversion of zinc sulphate monohydrate into a granular form.
A method of pan granulation of zinc sulphate monohydrate powder material into granules has been disclosed substantially. The method involves formation of the granule directly on the pan from the feedstock without intermediate steps. The result is a product having a completely uniform cross section and sufficient granule strength. This method has the advantage of allowing granulation of material that is difficult to granulate in prior art in a safe and expedient manner.
The process involves the conversion of particulate into agglomeration using a pan granulator but under certain operating conditions.
It is to be noted that generally wet granulation is inherently complicated, since irregular particle crystallography is inherently difficult to control. Wet powders not uniform in size and this would lead to non-uniform accretion, over nucleation and eventual breakdown of the process. For these reasons among others, the prior art has not realized an effective and viable process for wet granulation. But this invention has disclosed a simple but successful method.

STATEMENT OF THE INVENTION
The novel feature of this invention is to manufacture zinc sulphate monohydrate granules in such a way that the granules are spherical, hard, non-friable from the zinc sulphate monohydrate powder by adopting the pan granulation and subsequent steps such as drying in a specifically selected dryer and coating with a selected coating agent. The additional important feature of this invention is maintaining the characteristics such as the content of zinc and other chemical components, solubility and whiteness of the product granules same as to that of the feed powdery material to the pan granulator.

A SUMMARY OF THE INVENTION
In accordance to the above said objects Zinc sulphate monohydrate granules and a method for the manufacture there of are disclosed. Specifically the focus in this invention is to manufacture hard, spherical and nonb friable zinc sulphate monohydrate granules adopting pan granulation and subsequent steps.
High friability is a significant restraint to the use of prilled and granular products. Upon physical impact, the prills or granules tend to break into smaller particles, and produce substantial dust while being handled, transported, and applied to the intended soil environment. Thereby the particle hardness and non-friability become important. Firstly, when fertilizers are used as generally bulk blend fertilizer products there needs to be a predetermined, closely-sized range of granules to avoid unwanted segregation of the component products. If the granulated product breaks into smaller particles, segregation of the fertilizer composition is likely to occur. Further particle hardness and non-friability are vital to prevent the break down of prilled or granular fertilizer products when introduced into a modern, power operated distribution gadgets commonly in agriculture industry. The breakdown of the granules or prills results in uneven distribution of the fertilizer from gadgets to the soil/air. These granulated products may be shattered to an extent that the smaller pieces fall in a shorter trajectory from the gadgets and thus form a more narrow and a more concentrated swath on the soil surface than is intended.
Commercial fertilizer distributors and farmers recognize the superior chemical properties of granular products and have accordingly made heightened demands for the hardness and non-friability of said particles. This greater emphasis on particle hardness and non-friability arises from the fact that the modern methods of handling and transportation result in more crushing of the granulated particles. In addition, those involved in the handling, transportation and distribution of the fertilizer products are making increased demands for a non-dusting product. Such demands are based in large part on health and safety considerations.
Granular size becomes crucial in many applications as many of the fertilizers require slow dissociation in the soil. Hence attention on high crushing strength and larger size granule is the demand of the market need though standardized products are achieved in prior art. Thus there is a need for improved method of granulation in the field of fertilizers.
Fertilizers can be manufactured as granules and many methods are known in prior art. Granules are larger, harder, and more resistant to moisture. As a result, granulated fertilizers have become a more suitable material for fertilizer blends. Commercial granulation of fertilizers is done by known processes such as Drum granulation, Fluidized Bed Granulation, Spouted Bed Granulation.
There are several granulation equipments and processes that are well described in the literature and in the prior arts mentioned in the previous sections. Though the drum granulation is used widely for many fertilisers, the applicability of the same to the present subject of zinc sulphate monohydrate is unsatisfactory because of reduced sphericity of the granules. Moreover it is not economical because of necessity of maintaining high recycle ratio in the range of 3:1 to 6:1. Conventional drum granulation uses higher quantity of recycle material hence the shape of the recycle material plays dominant role in obtaining the shape of the resultant product. The shape of recycle material would be generally irregular because it is obtained by crushing of the oversize material that is generated in the drum granulator. The drum granulator would generate only about 20-30% of its feed as product size granules and the rest in the form of either oversize or fines, both being irregular in shape. Also in the drum granulation it is a common phenomena that few smaller particles undergo agglomeration, i.e sticking together, to form a bigger particles resulting irregular shaped granules. This happens because of the impact, i.e gravitational force of material falling from height from the top of the drum to the bottom during tumbling action.
In Pan Granulation process tumbling agglomeration technique is employed in a pan granulator. Product with desired size range can be produced by playing with only few parameters like choice of binders, dosage rate of binders, rpm of pan, granulation time; angle of inclination feed position, binder spray position etc. A threshold quantity of binder is required for optimum granulation yield. Generally speed of the pan is inversely proportional to the rate of granulation. Granulation time is also inversely proportional to the granulation yield however it becomes critical at certain points. Angle of inclination of the pan also has significant effect on the granulation yield.
But the prior art, when read singly or collectively, is deficient of uniform cross section, tightly packed ness and granule strength of fertilizer granules.
There has been a long felt need for granules having these desirable properties and the present invention addresses these needs.
In the present invention, the maintenance of non pulsating pan and the moisture content in the pan, moisture content of product specifically by usage of liquid and solid route, more specifically through liquid route which substantially prevents dust formation during the process.
The important inventive concept of the present invention is the ability to granulate economically using seed material during the initial stage of pan granulation process. In this manner, the process can be loosely referred to as a pan accretion – nucleation process; the process proceeds generally as accretion i.e., a nucleation site accretes the surrounding material. The present technology, i.e. feeding of Zinc Sulphate monohydrate powder to the pan should not be pulsating and binder assist in the material accretion around the nucleation site to produce a tightly packed granule with high feedstock content.

DESCRIPTION OF THE DRAWINGS
Illustrative and presently preferred embodiments of the invention are shown in the accompanying drawings in which:

Fig. 1 is Process Flow Diagram for Zinc Sulphate Monohydrate granulation
Fig. 2 is Pan Granulator
Fig. 3 is Belt Conveyor dryer
Fig. 4 is a photograph of Zinc Sulphate monohydrate powder that is used as feed material .
Fig.5 is a photograph of Zinc Sulphate monohydrate granules produced in pan granulator.
With reference to the above said drawings the process of the invention is illustrated schematically in Fig 1 which is a Process flow diagram for zinc sulphate monohydrate granulation comprising of various steps viz granulation drying, screening, coating and packing. Recycling of the crushed oversize granules and the fines is also shown in the diagram.
Reference numeral 01 denotes feeding of fresh zinc sulphate monohydrate powder as raw material into a Raw material hopper 03. Numeral 02 denotes a mixture of crushed oversize & fines obtained from the process after screening. This is fed into the Raw material hopper 03 along with the raw material i.e fresh Zinc sulphate monohydrate powder. Numeral 03 is raw material hopper which receives fresh zinc sulphate monohydrate powder and the recycle material from the process to feed on to a conveyor/elevator 05.
Alternately, in order to ensure thorough mixing of the fresh zinc sulphate monohydrate with the recycle rushed oversize and fines, these materials can be fed into 04 which a blender, ribbon blender or paddle mixer, which discharges the mixed material after blending on to the conveyor/elevator 05.
Conveyor/elevator 05 receives the raw material and recycle powders discharging into raw material feed bin 06. The conveyor/elevator 05 can be a slant conveyor or high lift conveyor or bucket elevator based on the availability of the space in the plant lay out and general arrangement. Numeral 07 is a table feeder which receives the material from 06 and discharges in to pan granulator 08 at a controlled feed rate. Pan granulator 08 is an inclined rotating pan which is described in detail in fig 2.
The numeral 09 is binder spray on the material bed in the pan granulator 08 to help granules formation from the powder by layering and agglomeration techniques. Numeral 10 is a dryer which dries the green granules coming out of the pan granulator. Numeral 11 is hot air generator which supplies hot air to dryer 10 through electrical heating source 13. Numeral 12 is a forced draft fan which supplies air to dryer 10 through 13.
Numeral 14 denotes cyclone separator, arranged two nos in series to separate the dust particles from the exhaust air coming out the dryer. This arrangement is to minimize the loss of zinc sulphate monohydrate powder in to ambient air as suspended particulate matter.
Numeral 15 is an induced draft fan which draws the exhaust gases from the dryer through the dust separating cyclones and discharges to the atmosphere through the stack 16.
The dried granules are discharged by the dryer on to the conveyor/elevator 17 which can be a slant conveyor/high lift conveyor/bucket elevator based on the plant layout and space availability for the equipments. Numeral 18 is a double deck screen which separates the dried granules in to three size fractions namely product size, oversize and fines. The fines are collected in a trolley 19 and recycled back to RM hopper 03. The oversize granules from the screen 18 are crushed in the oversize mill 20 and the powder is collected as 21 i.e powder to recycle. It is recycled back into RM hopper 03.
The product size fraction from the screen 18 is sent into the coating drum 22 where it is coated with coating agent from the coating agent tank 26 by using dosing pumps and spray nozzles. The coated granules are discharged on to a product conveyor 23 and sent to packing thro the product bins 24. The numeral 25 is the bag conveyor for the bags of zinc sulphate monohydrate granular product.
Figure 2 is schematic drawing of the pan granulator which illustrates the important items in the pan granulation system which is heart of this invention for the conversion of zinc sulphate monohydrate powder in to granular form. Numeral 26 is the side scrapper which is fixed at 12 o’clock position of the pan. It scraps the material that is sticking to the rim and bottom plate of the pan. Numeral 27 is rotating central scrapper which avoids the scaling formation to the bottom plate of the pan in the central area. Numeral 28 is a rotating pan arranged in inclined position at 50- 60 deg from the horizontal position whose angle can be changed based on the specific characteristics of the material to be granulated and the size of the granules desired. The speed of the pan also can be varied based on the specific characteristics the speed regulator of the material to be granulated and the size of the granules desired. Numeral 29 is the Zinc sulphate monohydrate powder feed point on to the pan granulator from the table feeder (numeral 7 of figure 1) discharge hose.
Numeral 30 is the position of additive spray points. The additive material is also called as binder because it is the key substance that binds the individual particles of the feed material to agglomerate and to facilitate layer formation. Numeral 31 is the top weir of the rim of the pan through which zinc sulphate monohydrate, after size enlargement, comes out of the pan granulator as green granules i.e wet granules of zinc sulphate monohydrate.
Numeral 32 is the discharge chute thro which the green granules are discharged to the next operating step i.e drying.
Fig 3 is a schematic diagram of Belt conveyor dryer that is proposed fro drying of the green granules coming out of pan granulator to remove the moisture from 9-13%in the green granules to 1-2% after drying. Numeral 33 of this figure is the drying chamber where multiple conveyors are arranged such that the first conveyor receives green granules from Pan Granulator out let. One conveyor discharges the material to the subsequent feed end and finally the dried material is discharged at the outlet of the bottom most conveyor. Numeral 34 is the endless belts of the conveyor which carries the green granules and the belt of which will be able withstand the temperature of hot air that is blown through the drying chamber. The belt shall have appropriate porosity for movement of air through the belt bottom and through the material on the belt. Numeral 35 is the driving drum of the belt conveyor which is connected to a motor of preferably variable frequency type. Numeral 36 is the driven drum. Numeral 37 is the Heater which consists of multiple heating coils to vary the temperature of the air in the dryer. Numeral 38 is feeder for green granules coming out of the pan granulator to feed into the drying chamber i.e on feed end of the first belt conveyor in the chamber.
Fig 4 is a photograph of zinc sulphate monohydrate powder that is aimed to be granulated and the fresh feed material for this invention.
Fig 5 is the photograph of zinc sulphate monohydrate granules, the final product of this invention which are round in shape, hard and non friable and whose chemical composition and solubility do not vary from the fedd zinc sulphate monohydrate powder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In this invention, art of granulating the Zinc Sulphate monohydrate powder in a very high yield process in conjunction with a specially designed pan granulation system is disclosed. Accordingly, this invention provides a process for pan granulating the Zinc Sulphate monohydrate powder and subsequent steps, wherein the process comprises:
a. Providing Zinc Sulphate monohydrate powder feed material having a size of about 90% minus 60 tyler mesh with the free moisture content not exceeding 3% into the pan granulator.
b. initial feeding of the Zinc Sulphate Monohydrate seed material having a size of -10 to +14 mesh occupying 20-25% of pan volume,
c. Feeding the Zinc Sulphate Monohydrate powder to a pan granulator containing seed material, feeding a binder steam to the pan granulator at required flow rate sufficient to create wetness and provide heat to the material in the pan for imparting the granulating phenomena.
d. drying the green granules in a conveyor dryer at 120-150 degrees C for 5-8 minutes, and
e. Cooling the dried product using any of the conventional coolers
f. Coating the cooled product by anti caking agents with a dosage in the range of 0.4-0.6% for making the product non friable.
Hence the first preferred embodiment of the present invention is applying Pan Granulation technique for the granulation of Zinc sulphate monohydrate powder as this technique can granulate the material to obtain higher sphericity than by the other granulation methods described in earlier sections.
The second preferred embodiment of the present invention is the positioning of the pan at an angle of 50-60 deg from its horizontal. In the pan granulation, which is one of the steps in the present invention as shown in the numeral 8 of fig 1, as the pan is inclined at 50-60 deg from the horizontal, gravitational impact is low and agglomeration i.e particle sticking together and formation of an irregular bigger size granule doe not happen. The inclination helps to roll down the smaller size granules from top to bottom due to gravitational force and from bottom to top due to centrifugal action on the material. This rolling phenomena helps the powdery material to make a layer on the smaller size granules that already exist in the pan. By this layering process the powdery material will build on the seed granules that are smaller insize to a desired size range say -5+9 tyler mesh, like onion skin manner.
The third preferred embodiment of the present invention is choosing the steam as suitable binder for the process of granulation of zinc sulphate monohydrate powder. In many of the granulation processes the usage of foreign substances as binding agent is more common for imparting cohesive nature to the individual particles and thereby helping the granulation.. Usage of foreign substances as biding agents changes the chemical composition of the material that is subjected to the granulation and also may affect the solubility of the granulated product. The additive/binder that can be used in any granulation process is generally a solution of suitable binding substance compatible to the feed material that is to be granulated. It may be even just water in some of the cases of the granulation. But in this invention Low Pressure Steam is choose as the binder for granulation of Zinc sulphate monohydrate powder. The choice of steam as binder is arrived by carrying out several experiments by different binders and by studying the conversion% to the desired size fraction. Usage of other chemical substances/additives as binder changes the chemical composition of the material due to the addition of foreign matter and there by there is definite possibility of reduction of zinc content from its content in the feed powdery material to its content in the product granular material. Usage of Low pressure steam does not create such problem because steam addition is nothing but moisture addition with heat. Moisture already exists in the material and hence it is not a foreign matter, it is present in feed material at 2-3% and continues to be present at an acceptable level of around 1% in the product granules also. Whereas the spraying of steam imparts increase of moisture to the granules that are formed in the pan granulator the excessive moisture than the desired value can be removed by drying in the next equipment of the process flow diagram i.e numeral 10 of fig 1,
Another reason of the third embodiment of the invention i.e choosing addition of steam as binder is that it does not affect the solubility of the material. Usage of any foreign substance that affects the solubility of the Zinc sulphate monohydrate in water, is not acceptable to the end users of the granulated zinc sulphate because when they use it for foliar spray or for drip irrigation the insoluble material will choke the nozzles and causes lot of inconvenience by the way of stopping the flow of the dissolved zinc sulphate solution thro nozzles.
By the experimental observations it is found that the usage of Low Pressure steam as binder is no way inferior to the usage of other chemical substances, because Low Pressure Steam is creating favorable environment for layering process of powdery material on the smaller granules like onion skinning manner and thus able to increase the size of the granule imparting sufficient strength to the granule.
With respect to the conversion% also Low Pressure steam is no way inferior to other binding substances because usage of Low Pressure steam as binder is able to give 50-60% conversion from feed to product size granules whereas the other substances are also able to give more or less the range.
With respect to the strength of the granules that are formed, the usage of Low Pressure saturated steam at the pressure of 2-3 kg/cm2 g i.e in the temperature range of 130-140 degC as binder gave more strength than the usage of other substances as binders hence the usage of the steam is one of the preferred embodiment of the present invention. The reason behind obtaining the higher strength by usage of Low Pressure Steam as binder over the usage of other chemical substances/additives as binder is that the Low Pressure Steam is having temperature and latent heat in it which is sufficient to raise the temperature of the rolling bed to an extent that is sufficient to favour the granulation. Even though it cannot be described as a phenomena of melt granulation or /fused granulation due to the temperature that is caused by steam the zinc sulphate monohydrate particles will reach a tendency to attach to one another due to the increased vanderwall forces. Usage of steam of higher pressure than the above said value makes the material to spill and splash and hence disturbs the material bed that is to be granulated.
The addition of steam as binder does not change the color of the zinc sulphate monohydrate material that is to be granulated. It maintains the same color to the product granules as that of feed zinc sulphate monohydrate powder. Usage of any foreign substance that imparts different color to the Zinc sulphate monohydrate is not acceptable to the end users because they are used to it and identify the whiteness of the product as the specific attribute of the zinc sulphate monohydrate. Hence maintaining the same original white color of the powdery material to the product granules also is an important factor that is considered in this invention.
Usage of Low Pressure steam as binder also inhibits the dust formation during the process while improving the handling quality of the granular Zinc Sulphate mono hydrate product. The pan granulation is a simple mechanical configuration and by selective operation of the pan. Granulation can be done to produce narrowly desired size granules of reasonable strength with good efficiency and economic performance.
The fourth preferred embodiment of the invention is to put the Low Pressure steam on the rolling bed of zinc sulphate monohydrate in such a flow rate that is appropriate to raise the moisture content of the feed zinc sulphate powder to the level of 9-13% where it granulates faster and does not break into smaller granules. At this level of moisture content the cohesive forces among particles are sufficient to keep the material in granular form even though the centrifugal and gravitational forces act upon it. Higher flow rate of LP steam such that the zinc sulphate material in the pan reaches more moisture content than mentioned above would lead to oversize formation and reduces conversion to product size granules..
The fifth preferred embodiment of the invention is rotating speed of the pan. The pan revolves at a certain angle with the horizontal plane. The powder will tend to rise along with the revolving pan under the friction between the powder and the pan. But, the powder will also tend to fall down under the function of its gravity. Simultaneously, the powder moves to the pan edge because of the centrifugal force. The powder material rolls within the pan in a certain trace under the combined function of these three forces. It gradually attains the required size. Product may be withdrawn and segregated with standard sieves and oversized may be sent to crusher and undersized is generally recycled. Bulk density of the product of required size can be determined. Standard deviation of whole product and granulation yield can also be calculated.
Effect of rpm has a very pronounced effect on the amount of Zinc Sulphate monohydrate powder granulated. As the speed of the pan increases, the amount of granules formed decreases significantly. During the course of granulation, collision occurs between granules themselves and also with the wall of the pan. At high speed collision becomes higher and it breaks the granules. At low speed of pan most granules loose contact with the wall of the pan depending on the balance between gravitational and centrifugal forces and cause breakage of themselves and other granules as well. Both bulk density and granulation yield show increasing trend upto certain rpm and then decrease. Thus granulation yield is maximum at 25-30 rpm. So, there exists a specified speed of pan which is favorable for the granulation of Zinc Sulphate monohydrate powder. Thus the product obtained falls in a narrower range of size and more product of required size is obtained for that specified speed which is detailed above. Consequently the optimum speed of pan granulator emerges out to be within 25-30 rpm.
The sixth preferred embodiment of the present invention is residence time of the material in the pan. Effect of time of granulation on yield (%) and bulk density is also studied. Bulk density first decreases and beyond certain duration of granulation time, it shows ascendancy in trend. An increase in the bulk density with increase in granulation time supports the fact that more desirable product is formed. Thus quality of the product is increased with time. Meanwhile the granulation yield (%) also goes on increasing. Thus both quality and well as volume of yield are improved with time. But there is optimum time because after certain increased time the effect of granulation is reversed.
By increasing the time of granulation, mean diameter of the product (granules) may increase but at the same instant, the standard deviation is much less which indicates optimum granulation time is necessary for each process. The preferred granulation time in the range of 15-20 minutes. A definite proportion of binder steam and Zinc Sulphate monohydrate powder is needed for granulation. Because when ratio increases it yields very soft granules that break during the process. The preferred range to operate at 10 – 13 % moisture content w/w of the material in the pan.
Experimental results indicate that granulation rate depends closely on the slant angles of the disc, the revolving rate, the methods of adding admixtures, and granulation time. All of these parameters have been exploited intelligently to arrive at a novel method to achieve a better yield.
The seventh preferred embodiment of the present invention is the flow rate of the feed zinc sulphate monohydrate powder on to the pan. The Zinc Sulphate Monohydrate is first metered by a table feeder and fed onto the pan kept at about the desired position so that there is minimum vertical drop. The feed flow rates are to be maintained at a uniform rate. It has been observed from the experimental trials for a certain size of the pan there lies an optimum rate of feed material for achieving maximum conversion. The uniqueness of this granulation system is the conversion of the material into product of the size distribution in the range of -5 to +9 Tyler mesh is more than 60% which can not be achieved in any other granulation methods. In the experiments, a pan of 400 mm diameter & 126 mm depth was used and maximum conversion was achieved at the feed flow rate of 15-20 kg/hr. One of the essential conditions of the method of pan granulation is that the feeding of particulate material to pan should not be pulsating.
The eighth embodiment of the present invention is the usage of seed material during in fresh start of the process to speed up the initial granulation. The process concept used in this invention of granulating the zinc sulpate monohydrate powder is an accretion method i.e. layering of zinc sulphate monohydrate powder over the seed material. This will enable the use of pan granulator in an economic way. Keeping a narrow size range for the seed will minimize the tendency for the product distribution to broaden. Based on the results of the experimental trials, seed in the size range of -10+14 tyler mesh and to the volume of 20-25% are found to be best conditions for better results. The more uniform the seed size, the more uniform is the product size.
The nineth preferred embodiment of the invention is feeding of the binder steam by spray through multiple nozzles, the spray angle of the nozzle and the spray nozzle spacing. The number of nozzles shall be more specifically in the range of 3-4. Because of the possibility of oversize formation with single spray, multiple nozzles are preferred as they help proper distribution of binder on the feed material. Spray angle of the binder spray shall be more specifically in the range of 40° - 90 and the spray nozzle spacing shall be more specifically in the range of 30-60 mm in order to obtain better results of the granulation.
The tenth embodiment of the invention is the selection of suitable dryer for the drying of the green granules from the pan granulator. As the green granules from the pan granulator are soft and delicate due to high moisture content i.e 9-13% moisture, they are prone to breakage due to any minor impacts. So selection of suitable drying equipment is an important criteria for achieving the objects mentioned above. In the industrial processes where continuous production facilities are adopted for all the process steps, drying also shall be carried in a continuous process and continuous drying equipment to be choose. Out of the various continuous drying equipments such as rotary drum dryer, fluidized bed dryer, vibrating fluidized bed dryer, screen dryer, Conveyor Belt dryer, Rotary vacuum dryer etc the best option for this material is found to be the Conveyor belt dryer due to impact on the material during the travel of the material during the drying. In rotary drum dryer when the green granules fall from the top position of the dryer shell they may break into pieces. In the fluidized bed, vibrating fluidized bed dryer and screen dryers also the impact of vibration & fluidization forces may cause breakage of green granules. Hence the best suggested option is usage of conveyor dryer with multiple conveyors arranged in sequentially with the total length sufficient fro providing the required residence for drying. The residence time required for the drying of zinc sulphate monohydrate green granules from the pan granulator containing 9-13% moisture is found to be 5-8 min at the inlet drying air temp of 120-150 degC. The multiple conveyors shall be provided with the variable Frequency drive motor so as the increase/reduce the residence time of the material in the dryer.
The eleventh embodiment of the invention is to cool the dried product nearer to the ambient temperature by any of the conventional cooling processes.
The twelfth embodiment of the invention is to coat the cooled product with suitable anticaking agent for making the granule non-friable, for giving anticaking properties and also for giving shining appearance, While coating with the anticaking agent the selection of the anticaking agent Shall be such that the zinc sulphate monohydrate granules composition, solubility and color shall not get effected significantly. Trials with various anticaking agents indicated that the best option is to select one among the group that consists of Servo 60 gear oil, Coconut oil, Indocoat TQ-50 supply by Indo amine and Acalf-50 supplied by Filtra catalyst Pvt ltd, The dosage of the anticaking agent shall be in the range of 0.4-0.6% of the final production rate of the granular zinc sulphate monohydrate.
The thirteenth embodiment of the present invention is to scale up the process for commercial production. Commercial scale production in the range of 0.5-0.6 tons/hr requires a pan of in the range of 1.5-2.0 m diameter and 0.3 m depth.
Although the invention has been described above in detail, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art.

EXAMPLE 1
The following operating parameters were used in the example 1.
1) Pan rpm: 26
2) Pan angle: 60 deg from horizontal
3) Zinc sulphate Monohydrate powder Feed rate: 20 kg/hr
4) Particle size of the feed material: 90% passing through 60 tyler mesh
5) Binder : Water
6) Operating hours : 2.0 hrs, Zinc Sulphate Monohydrate powder Feed material used : 39 kg
7) Moisture% in the Feed material: 3.2%
8) Zn% in the feed: 32.4%
The results obtained with the above parameters are as below:
a) Quantity of -5+9 tyler mesh Granular Product obtained after drying = 24.0 kg
b) % conversion into desired size granules: 24/39*100=61.5%
c) Moisture% in the green granules at the out let of the pan: 14.0%
d) Sphericity of the granules: Moderate
e) Hardness after drying to 1% moisture : 0.3 kg
f) Zn% in the product : 33.1%

EXAMPLE 2
The following operating parameters were used in the example 2, changing the binder.
1) Pan rpm: 28
2) Pan angle: 55 deg from horizontal
3) Zinc sulphate Monohydrate powder Feed rate: 20 kg/hr
4) Particle size of the feed material: 90% passing through 60 tyler mesh
5) Binder : Sudaband solution of 60% concentration, at the dosage of 110 g/kg of feed
6) Operating hours : 0.5 hrs, Zinc Sulphate Monohydrate powder Feed material used : 10 kg
7) Moisture% in the Feed material: 3.1%
8) Zn% in the feed: 32.0%
The results obtained with the above parameters are as below:
a) Quantity of -5+9 tyler mesh Granular Product obtained after drying = 6.3 kg
b) % conversion into desired size granules: 6.3/10*100=63.0%
c) Moisture% in the green granules at the out let of the pan: 9.2%
d) Sphericity of the granules: Good
e) Hardness after drying to 1% moisture : 0.3 kg
f) Zn% in the product : 33.1%

EXAMPLE 3
The following operating parameters were used in the example 3, introducing LP steam as binder.
1) Pan rpm: 30
2) Pan angle: 60 deg from horizontal
3) Zinc sulphate Monohydrate powder Feed rate: 20 kg/hr
4) Particle size of the feed material: 90% passing thro 60 tyler mesh
5) Binder : LP steam at pressure 2.5 kg/cm2g,
6) Operating hours : 5.5 hrs, Zinc Sulphate Monohydrate powder Feed material used : 112 kg
7) Moisture% in the Feed material: 3.0%
8) Zn% in the feed: 33.0%
The results obtained with the above parameters are as below:
a) Quantity of -5+9 tyler mesh Granular Product obtained after drying = 72 kg
b) % conversion into desired size granules: 72/112*100=64.3%
c) Moisture% in the green granules at the out let of the pan: 9.8%
d) Sphericity of the granules: Good
e) Hardness after drying to 1% moisture : 1.2 kg
f) Zn% in the product : 33.3%

EXAMPLE 4
The following operating parameters were used in the example 4.
1) Pan rpm: 27
2) Pan angle: 55 deg from horizontal
3) Zinc sulphate Monohydrate powder Feed rate: 20 kg/hr
4) Particle size of the feed material: 90% passing through 60 tyler mesh
5) Binder LP steam at pressure 2.0 kg/cm2g
6) Operating hours : 2.5 hrs, Zinc Sulphate Monohydrate powder Feed material used : 50 kg
7) Moisture% in the Feed material: 3.0%
8) Zn% in the feed: 32.5%
The results obtained with the above parameters are as below:
a) Quantity of -5+9 tyler mesh Granular Product obtained after drying = 31 kg
b) % conversion into desired size granules: 31/50*100=62.0%
c) Moisture% in the green granules at the out let of the pan: 9.1%
d) Sphericity of the granules: Good
e) Hardness after drying to 1% moisture : 1.2 kg
f) Zn% in the product : 33.1%

Example 1 involved a ‘control’ test which utilized water as binder. The granulation was good when the dosage of water was such that the green granules reach the moisture content of 13-14%. The conversion was satisfactory at 61.4% but the strength of the granules after drying to 1% moisture content was very poor at 0.3 kg. Also the friability of the uncoated granules was extremely high.

Example 2 involved usage of an adhesive solution procured from M/s Sudarsan Organics and named as Sudabond. The selection of this additive is due to its whiteness matching with the colour zinc sulphate powder. For meeting objects of the invention other additives which impart colour to the zinc sulphate granules is not suitable. At the parameters mentioned in this example, though the conversions and colour are good, the crushing strength of the dried granules s is poor at 0.3 kg. Few more trials were conducted varying the dosage of this additive but there was no improvement in the strength.
The best results were achieved in Example 3 in which LP steam of 2.5 kg pressure was used as binder. It produced granules with conversion of 64.3% and the crushing strength of the dried granules at 1.2 kg with very little friability. Example 4 is again with the usage LP steam but at a lower pressure i.e at 2.0 kg. There was no much change in the desired parameters of the granules. By this it is confirmed that LP steam at 2-2.5 kg pressure is giving the desired results. There was no change in colour, solubility and composition of the granules while using the LP steam as binder.
Several experiments were conducted using different granulating equipments such as drum granulation, basket granulator, Die pellet mill, and single screw extruder with different additives and varying their dosages but none of them gave better than the Example 3 & 4.
For drying of the green granules for removal of moisture several experiments were conducted to draw drying curve and there by arrived the time required to achieve the desired moisture conditions. Impact tests were conducted for the green granules to find out suitable dryer to handle them. On studying the various options of drying, it has been arrived that the Conveyor dryer is the best suitable equipment for this case.
For coating of the product granules after drying and cooling, in order to reduce the friability, various anticaking agents were tried and the best suitable ones are mentioned in the claims.
Having described the preferred embodiments of the present invention, it is anticipated that suitable modifications or variations of the parameters within the scope of this invention may give further improvement in results. Hence, the embodiments of the invention that have been described above are not limited thereto and it will be apparent to those skilled in the art that numerous modifications from part of the present invention in so far as they do not depart from the spirit, nature and scope of the claimed and described invention.
Thus, the present invention shall only be constructed in accordance with the following claims.