Claims:WE CLAIM:

1) A process for preparing the granular composition of urea based NPK fertiliser containing Nitrogen (N), phosphorous (P) and Potassium (K) using a pipe reactor and a granulator with urea and potash as solid raw materials, the process comprising of:
a) injecting Phosphoric acid and liquid ammonia as first liquid reactant into a pipe reactor to form Ammonium phosphate and generate high quantity of exothermic reaction heat,
b) injecting Sulphuric acid into the pipe reactor as another liquid reactant for reaction with ammonia to form ammonium sulphate and generate high quantity of exothermic reaction heat,
c) maintaining the pipe reactor skin temperature at 142 -145 deg C,
d) melting of Urea prills placed as solid particles within a granulator bed of a granulator using the heat generated in the granulator by spraying the hot slurry from pipe reactor into the granulator and allowing formation of eutectic solution of Urea and Potash in Ammonium Phosphate and Ammonium Sulphate in the rolling granulator bed of the granulator maintained at a temperature in the range of 85-900C, more specifically 87 deg C, due to spray of hot slurry from the pipe reactor on the rolling bed of Urea, Potash and Recycle material (check) in the granulator with the exothermic reactions and heat generation,
e) allowing accretion and agglomeration by fusion of the solid raw materials and melt granulation to occur with the liquid phase bridging among the solid particles in the granulator, the solid particles being Urea, potash and the recycle fines (check) in the granulator bed
f) forming of Urea Phosphates and Urea Sulphates due to interaction of urea with free acids thus forming integrated granules with uniform composition.
g) forming two portions of Ammoniacal Nitrogen source with the said generated Ammonium Sulphate in the pipe reactor contributing to a first portion of Ammoniacal Nitrogen in the prepared granulator composition of the fertiliser and that the said generated Ammonium Phosphate in the granulator contributing to another second portion of Ammoniacal Nitrogen in the prepared granulator composition of the fertilizer, and
h) drying the prepared granulator composition of the fertilizer from the granulator in a rotary dryer for reducing the moisture content and thereafter cooling granules in a rotary cooler such that final moisture content of the granulator composition of the fertilizer is in the range of 1.0-1.5%, more specifically in the range 1.0 to 1.2%.

2) The process for preparing the granular Urea based NPK fertiliser as claimed in claim 1, wherein the injection of sulphuric acid in to the pipe reactor at 1.42 lpm per ton of final product of granulator composition of the fertilizer along with the other liquid raw materials viz., phosphoric acid and liquid ammonia, generates more exothermic heat and there by pipe reactor skin temperature reaching as high as 142-145 degC and this high temperature favoring melt granulation phenomena in the granulator bed materials viz urea, potash & recycle powder material (Check).

3) The process for preparing the granular Urea based NPK fertiliser as claimed in claim 1, wherein the final product of granulator composition of the fertilizer has atleast 8.4-8.5% Ammoniacal Nitrogen and 8.4-8.5% Urea Nitrogen which is favoring for melt granulation phenomena and thereby it favors the achievement of strength granules in the final product with the crushing strength of 1.8-2.0 kg.

4) The process for preparing the granular Urea based NPK fertiliser as claimed in claim 1, wherein the process further includes maintaining low moisture content in the granulator bed in the range of 2-3%.

5) The process for preparing the granular Urea based NPK fertiliser as claimed in claim 1, wherein the process includes using potash having a size in the range of 1.7 mm or higher.

6) The process for preparing the granular Urea based NPK fertiliser as claimed in claim 1, wherein the process further includes a low recycle rate of 3:1 such that recycle rate is 3.0 tons per hour for obtaining the product at the rate of 1.0 ton per hour.

7) A granular composition of Urea based NPK fertilizer prepared as per process as claimed in claims 1-6.

8) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizer are typically spherical with the spherity being in the range of 56-58.

9) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizers are uniform with uniformity index being above 33%.

10) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizers are hard with crushing strength in the range of 1.8 to 2.0 kg.

11) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizers contain -4+2 mm fraction more than 80%, the obtained fraction is 84.9%.

12) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizers possess low hygroscopic behavior, when tested in a cylindrical jar as per the standard test procedure laid down by IFDC under the conditions, 80% relative humidity and 30 deg C temperature, in a humidity chamber, and proved with the moisture absorption of 140 mg/cm2 area.

13) The granular Urea based NPK fertiliser as claimed in claim 7, wherein the produced granules of the fertilizers possess low hygroscopic behavior, when tested in a cylindrical jar as per the standard test procedure laid down by IFDC under the conditions, 80% relative humidity and 30 deg C temperature, in a humidity chamber, and proved with the moisture penetration of 2.1 cm.
, Description:FIELD OF THE INVENTION

The present invention relates to a process for the manufacture of Urea based high grade NPK fertilisers such as 17-17-17 with good sphericity, crushing strength, uniform size and durability nature while using Urea and Muriate of potash as constituents of the product using the pipe reactor technology and sulphuric acid injection in to the pipe reactor in order to achieve sufficient temperature in granulator bed so as to get melt granulation or fused granulation instead of moisture granulation.

BACKGROUND OF THE INVENTION
The process universally followed for the manufacturing NP/NPK complex fertilisers, is reaction through Pre-Neutralizer/Pipe reactor route and granulation on rotary drum granulator. Here the mechanism responsible for initial granule formation and subsequent growth are agglomeration and accretion. In the granulation process Urea, potash and other appropriate filler materials are fed as solid particles whereas Ammonia and Acids are fed to the Pre-neutralizer /Pipe reactor. These solids and slurry both contact in the granulator and size enlargement of particle occurs either by accretion or by agglomeration. For some products to increase the liquid phase in granulator bed and to maintain the granulation bed temperature at appropriate levels, calculated quantities of steam is sprayed on to the granulator bed there by granulation is improved.

Most of the conventional wet granulation processes thro Pre-Neutralizer route involves in spray of slurry with limited reaction temperatures i.e. 116-121 Deg.C and with very high moisture content i.e., 18-20% in to granulator. This can be categorised as slurry granulation or moisture granulation where sufficient moisture i.e. 3-4% is required in granulator bed and moderate temperature at 60-70 Deg.C will be sufficient for good granulation.

The existing conventional wet granulation method is found not suitable for the production of NPK fertilisers more precisely Urea based NPK fertilisers such as 17-17-17 because the Urea based NPK formulation gives low crushing strength to the granule while granulated at low temperatures and also due to poor compatibility of Urea with potash it exhibits high hygroscopicity for such granules. Many people tried to improve the crushing strength of granules by increasing the granulator bed temperature by putting additional steam to the granulator. Due to this NPK products are becoming more hygroscopic and granulation and drying operations are becoming tough and expensive tasks, as we are putting additional moisture in the form of steam to the granulator.

During the drying, granules that pass through the dryer are so soft and wet, even granulator discharge chute sometimes gets plugged with this material. By the time this material enters the dryer, it picks up the temperature and becomes more softer and more delicate, so to retain the integrity of the granules at the dryer outlet, dryer drums are designed to be very lengthy even some processes suggest addition of anther rotary drum called “process cooler”, where the soft granules come out from dryer cools in the process cooler and gains the strength required to maintain integrity. So overall process is becoming complicated, expensive and hence led to uneconomical.

DESCRIPTION OF THE PRIOR ART
Since long period it is known that some improvements came in production of Urea based NPK fertilisers such as usage of molten urea, usage of fine potash, addition of process cooler, split of Urea feed in to Pre-neutralizer and granulator, split of liquid raw materials in to Granulator PR and Dryer PR, but all are having their own difficulties and dis-advantages.
US Patent No. 2618547 describes a continuous process for production of mixed fertilisers by forming reaction mixture by reacting ammonium source with Sulphuric acid or Phosphoric acid and then delivered to an inclined rotary tubular mixer equipped with knockers where solid material i.e., single super phosphate, triple supper phosphate and potassium source mixes with liquid phase and forms granules, here the author mentioned only low nutrient grades say NPK 6-9-6,4-12-4 and basically through SSP, TSP blends where scope for increasing Nutrient values is difficult and most of the grades contain filler material, Our invented process does not use Super phosphates and use phosphoric acid as P2O5 source, so we can give higher nutrient grades such as Urea based NPK 17-17-17 fertiliser.
US Patent No.3985538 discloses the process for the production of mixed fertilisers through pipe reactor route by Preheating the Phosphoric acid and neutralizing the acid with anhydrous gaseous ammonia in Pre-neutralizer and then fed by pump to second stage ammoniator a standard pipe reactor where it reacts rapidly with another stream of gaseous ammonia then introduces this ammonium phosphate melt is sprayed into the granulator where it gets coated on the recycle solid material then this coated material gets cooled in the cooler. Here drying step is avoided as the process involving the pressurised reaction of ammonium phosphate in the secondary reactor generates more heat. This patent focussed on pre-heating the phosphoric acid and usage of gaseous ammonia in Pre-neutralizer and pipe reactor to raise the reaction temperature. It has not mentioned sulphuric acid injection to pipe reactor and crushing strength of product granules. The process parameters also vary widely from the present invention. Hence the present invention is different from the above patent.
Chinese Patent No. 1891678A discloses a method for preparing NPK compound fertiliser with ammonium nitrate as the raw material consisting of the following steps: a) 99% concentration liquid ammonium nitrate and ammonium phosphate are mixed and heated to prepare a nitrate AP slurry, the weight ratio of the former one and the latter one is 1-10:1, the temperature of the mixed slurry is 145-165 deg. C. b). Sylvite, a potassium salt and an additive are preheated to 80-140 Deg.C. The nitrate AP slurry and the sylvite and the additive are mixed to form the fertiliser slurry, and the volumes of sylvite and additive are respectively 0~35% and 0-15% of the total weight. d). The NPK fertiliser slurry is sprayed from the top of cylindrical prilling tower and solidified by cooling with counter current flow of air. Our process is different from that of this patent as our process does not contain ammonium nitrate feed, do not heat and melt the raw materials, and don’t involve addition of sylvite and additives. Ours is drum granulation process whereas CN1891678A is tower granulation process. Hence the present invention is different from the above patent.
Chinese Patent No.CN1280969A proposes a process for producing granular composition N-P-K fertiliser directly from urea solution includes such steps as spraying the 65-99.7% urea solution at 80-140 Deg.C on base of pre-crushed raw materials for making NPK fertiliser , then granulating followed by drying, cooling and screening. In this process the author mentioned the products of low grades such as 10-10-10, 8-9-8, 12-12-24. Our process is different from the above-mentioned patent, as our focus is on high nutrient grades such as 17-17-17 and we did not adopt spraying of urea solution on the fertiliser bed, and also did not adopt pre-crushing of raw materials. In this patent there is no mention of sulphuric acid usage, pipe reactor process. Hence the present invention is different from the above patent.

EP0007132A1 (U.S. Patent No 4398936) relates to the process of preparing granular NPK fertiliser, in which a solid potassium salt such as KCl is mixed with an ammonium nitrate containing liquid phase which also contains ammonium phosphate and the mixture is granulated by means of granulating screw and the patent claims that the process is suitable for production of NPK fertilisers like 17-17-17, 15-15-15, 20-10-10, 15-5-5. But the patent is very specific about the particle size of Potassium source i.e., Potassium salt having average particle size of 55 microns is considered for granulation hence if higher size potash is taken it needs to be ground to 55 micron size, before adding to the NP melt. This patent did not mention on usage of sulphuric acid in to pipe reactor. Our invention is different from this patent in various features such as drum granulation, does not ask for grinding of potash to 55 micron size, recommend usage of sulphuric acid into pipe reactor. Our process describes the melt and fused granulation to achieve good quality product in terms of granulometry, Sphericity, crushing strength.

Patent no CN 1035 88543 describes production of Urea and sulfuric acid based fertiliser by preparing Urea sulfuric acid solution in presence of a stop blast agent (zeolite powder, Sepolite or MAP) and reacting this solution with potassium chloride in a reactor vessel for 40 to 70 minutes where gaseous ammonia is also introduced to maintain PH and then granulated, dried and cooled. In the present invention Urea sulfuric acid solution formation, the reactor vessel and the usage of stop blast agent do not arise hence our invention is different from the above patent.

Patent no CN 1003 48550 describes a preparation method for Urea based compound fertiliser by reacting Urea with sulphuric acid and water in a reactor with residence of 40 minutes to form Urea sulphate solution and the solution is cooled to 60-80degC and then sprayed upon the material bed in granulator containing <1mm particle size base fertiliser powder consisting of ammonium phosphate, potash and bentonite or any other filler. In our invention Urea and sulphuric acid reaction does not arise in the reactor and hence there is no requirement for open reactor and cooling of the solution. In our invention we feed Urea in the form of prills to granulator where it gets partially melted and forms integrated granules with potash while hot slurry of ammonium phosphate, ammonium sulphate are sprayed upon. Hence our invention is different from the above patent.

Patent no CN 1073 53071 describes preparation of Urea based NPK fertiliser by preparing Urea solution of 70%-99.7% at temperature of 80-140 deg C and spraying the solution in to granulator bed consisting other fertiliser material such as ammonium phosphate, potash, ammonium sulphate, ammonium chloride and granulating the mixture. NPK 17-17-17 was mentioned in the above patent but the main focus is on spraying the Urea solution of 70-99.7% having a temperature of 80-140 deg C. In the present invention we are not spraying the Urea solution into the granulator bed, we are using Urea in the form of prills to granulator where it gets partially melted and forms integrated granules with potash while hot slurry of ammonium phosphate, ammonium sulphate are sprayed upon. Hence our process is different from the above patent.

Patent no US 4610 715 describes Usage of FormUrea 80% (Formaldehyde 57%+Urea 23%+water 20%) reacting with phosphoric acid in two open reactors in series with different residence times and at different temperatures and PH conditions. The resultant slurry is sprayed on the bed of other fertiliser materials in granulator consisting of ammonium sulphate, potassium sulphate etc. In our process of the present invention we have not used the Urea formaldehyde and we have not used the open reactors. We used Pipe reactor with the residence time , 10-30 seconds for reacting ammonia phosphoric acid and sulphuric acid. Hence our invention is different from the above patent.

Patent no CN 1026 03387 relates to a method of producing compound fertiliser by high tower tube granulation comprising the steps of a) reacting ammonia with phosphoric acid or sulphuric acid or nitric acid or combination of these acids with ammonia gas in a tubular reactor to make mixed slurry b) separating steam from the above slurry c) other solid materials are mixed with this slurry in a melt mixer d) spraying this eutectic slurry in to granulation tower through a rotary granulation nozzle e) cooling the falling droplets from the tower with cold air. Our invention is different from this patent as we are not using tower granulation and our focus is on fused granulation in rotary granulator at 85-90 deg C. Hence our invention is different from the above patent.

Patent no US 4134 750 of Jan 1979 described the process for manufacture of granular ammonium phosphates, ammonium phosphate sulphates and Urea ammonium phosphate sulphates using a specially designed pipe reactor. In this patent the author shown the examples for different fertilisers but not for the high grade NPK products such as 17-17-17. He just mentioned 17-17-17 in a table of typical grades that are produced in their pipe reactor but has not described the process for this grade nor given an example for that. one example was shown for NPK 13-13-13 (in example III) which is different from our invention as there are many differences between their process and our invention. The author of the above patent used following concepts 1) pre-heated the phosphoric acid before feeding to pipe reactor to the temperature in the range of 58 to 69 deg C 2) operated the pipe reactor at temperature in the range of 242-269 deg C. 3) Eliminated the usage of dryer for drying the granulator discharge material 4) Did not use Urea for the product 13-13-13 that was shown under example III. 5) For 13-13-13 he maintained N/P Mole ratio of 1.0 for final product 6) He mentioned usage of Urea solution or Urea melt in to pipe reactor for high nitrogen grades. These all are different from our invention in the aspects 1) We do not preheat the phosphoric acid before feeding to pipe reactor and only feed the phosphoric of ambient temperature 2) We operate the pipe reactor at 140-145 degC. 3) We use rotary dryer for heating the material coming out of the granulator. 4) We use Urea for producing high grade NPK fertilisers such as 17-17-17. 5) For 17-17-17 we maintain N/P Mole ratio of the final product at 1.30-1.40 typically 1.35. 6) We use Urea in the form of prills and feed it to the granulator along with the recycle fines. 7)we focussed on good quality parameters such as sphericity, crushing strength, Uniform size and low hygroscopicity. Hence our invention is different from the above patent.

US patent no 2205/0144997A1 describes process for granular ammonium phosphate based fertiliser that contains an extended slow release nitrogen component introduced during the granulation process using an alkaline water soluble Urea-formaldehyde (UF) resin where as in our invention we do not use any such material. The field of the invention of this patent was “ an improved NP/NPK fertiliser having an extended or slow release nitrogen component” whereas our field of invention is a process for manufacture of urea based high grade NPK fertiliser such as 17-17-17 with good sphericity, crushing strength, uniform size and durability. In the above patent the author has shown two examples one for NPK 16-4-8 and another is for NPK 10-5-10, in both the cases alkaline water soluble UF resin was used and was introduced in to granulator for imparting slow release nature to the some part of Nitrogen. In para (0041) it is mentioned their process is suitable for 17-17-17 grade also. The author mentioned in para (0046) that other optional raw materials such as ammonium nitrate, potassium chloride or urea may be introduced into the mixer/granulator through inlet 6. Raw materials formulations have been mentioned for both the examples but Operating parameters in the process were not mentioned. In example -2 it is mentioned that a) Granulator bed is preheated to 183 deg C temperature before introducing the UF resins and liquid raw materials b) UF resin was preheated to 82 deg C before feeding to granulator. In para (0025)it is mentioned that the essential feature of the patent is the provision of an alkaline water soluble UF resin as one of the raw materials so as to provide an extended-release nitrogen component to the resulting NP or NPK granular fertiliser. Our focus is not on slow release nitrogen, we do not use water soluble UF resin, we do not preheat the granulator material bed and our focus is on manufacturing high grade NPK fertilisers such as 17-17-17 in pipe reactor route using sulphuric acid as one of the liquid feed in to pipe reactor and feeding Urea in the form of prills to granulator where it gets partially melted and form integrated granules with potash while hot slurry of ammonium phosphate, ammonium sulphate are sprayed upon. Hence our patent is different from the above patent.

Patent no CN 1035 725 describes process for potassium sulphate type ternary compound fertiliser which involves a) direct reaction of potassium chloride with concentrated sulphuric acid at 1:1 mole ratio at the temperature of 90-110 degC for 60 minutes to prepare potassium hydrogen sulphate followed by dilution with hot water b) Mixing this solution with phosphoric acid in a mixing tank followed by neutralising with gaseous ammonia in a neutralisation tank c) the neutralised slurry is concentrated, sprayed and granulated. In our invention we do not react potassium chloride with sulphuric acid in a reactor tank, we feed the potassium chloride in solid form to granulator where it forms integrated granules with Urea, ammonium phosphate and ammonium sulphate under the influence of high temperature at 85-90 deg C. Hence our invention is different from the above patent.

Patent no CN 1063 96928 describes production method for slow release compound fertiliser that comprises a) preparation Potassium hydrogen sulphate slurry in a reaction kettle b) mixing this solution with phosphoric acid another reaction kettle and neutralising with ammonia to prepare NPK compound fertiliser slurry c) preparation of Urea + formaldehyde+ water solution in a kettle d) pumping both slurry and solution to granulator on the bed of recycle fines. The focussed fertiliser is slow release type with NPK grade 16-16-16 fertiliser. In our invention we do not react Potassium Chloride with sulphuric acid and we do not make Urea solution with formaldehyde and our focus is not on slow release property. Hence our invention is different from the above patent.

Patent no RU 241125 relates to methods for producing NP & NPK fertilisers on the basis of a mixture of low concentration phosphoric acids of 19-21% P2O5 and medium concentrated Phosphoric acid of 38-40% P2O5 in order to reduce the energy consumption at the stage of evaporating phosphoric acid and with an intention to increase the productivity of phosphoric acid plant and also to reduce the corrosive effects on the equipment and the fluorine impurity in the finished product. In this patent the author described the examples for producing NP grades 16-20-0-15S, 16-25-0-13S, 14-34-0-9.5S and NPK grades 14-14-14-11.7S and 10-20-20-11.7S using tubular reactor, ammoniator granulator and tumble dryer. The author has not mentioned the usage of urea in the process hence the grades that can be produced are limited to maximum Nitrogen content of 16% only. More over the author of this patent has not focussed on the sphericity, uniform size and crushing strength of the granules that can be produced. Our invention describes clearly the process for manufacture of Urea based high grade fertilisers such as 17-17-17 through pipe reactor route with addition of sulphuric acid with an objective of producing spherical, uniform sized granules with good crushing strength. Hence our invention is different from the above patent.

Patent no RU 2532 931 relates to the development of a new complex fertiliser and method thereof enabling to increase yields of both flax or linseed. The developed complex fertilisers contain N: 12-15%, P2O5: 15-20%, K: 25-30% and micro nutrients B: 0.2%, Zn: 0.4% in one grade and B: 0.2% and MgO: 3.7% in another grade. In this patent the author focussed much on agronomical trials using 3 fertilisers namely a ) 12-15-25-0.2%B, 0.4%Zn b) 12-15-25-0.2%B, 3% MgO c) 13-19-26 0.2%B, 3% MgO and 2 controls 1) without fertiliser 2) using NPK 16-16-16 fertiliser. The author provided examples for finished product composition and raw material quantities required per ton of product for the fertilisers a) 12-15-25-0.2%B, 0.4% Zn using only ammonia as N component b) 12-15-25-0.2%B, 0.4%Zn using ammonia and ammonium nitrate as N components c) 12-15-25-0.2%B, 3.0% MgO using ammonia and ammonium nitrate as N components d) 13-19-26-0.2%B, 3.0% MgO using ammonia and Urea as N components. The author also suggested specific names of Boron, zinc and Magnesium containing micro additives in this patent. There was no mention of process to manufacture NPK 17-17-17 or on improvement of its physical properties such as Sphericity, Uniform granule size and crushing strength. Our invention describes clearly the process for manufacture of Urea based high grade fertilisers such as 17-17-17 through pipe reactor route with addition of sulphuric acid with an objective of producing spherical, uniform sized granules with good crushing strength. Hence our invention is different from the above patent.

OBJECTIVE OF THE INVENTION

The key objective of the invention is to produce good quality high grade granulated NPK fertilisers such as 17-17-17 while using Urea and Potash as constituents whose presence in the so far existing prior art processes are leading to low crushing strength and high hygroscopic nature of the NPK fertilisers.

The main objective of the invention is to improve the quality parameters such as Sphericity, crushing strength, Uniformity, size range and to reduce the hygroscopic nature of the Urea and potash containing fertiliser products thus increasing the durability.

The subsequent objective of the present invention is to provide a new and innovative process for the production of granular NPK fertiliser which is devoid of the drawbacks and disadvantages that exist in the prior arts such as irregular shape, low crushing strength, varied & wider size range and high hygroscopicity..

One more objective of the invention is to adopt the right combination of ammonium phosphate, ammonium sulphate and Urea that give better granulation properties as well as better physical properties of the product while meeting the total nitrogen requirement of 17% in the product.

Another objective of the invention is to introduce melt granulation technique in the granulator where Urea and potash form eutectic solution in Ammonium phosphate and ammonium sulphate which encourages the formation of round, spherical and uniform composition, the granules thus formed exhibit good crushing strength and low hygroscopicity after drying and cooling and thereby have increased durability.

Further objective of the invention is development of the key feature of maintaining granulator bed temperature in the range of 85-90 Deg.C so as to obtain melt granulation of Urea, potash, ammonium phosphate and ammonium sulphate in the granulator.

Another objective of the invention is choosing the pipe reactor process for conducting the reaction between ammonia & phosphoric acid so as to reduce the heat losses and also to utilise the heat of reaction that is generated, to raise the granulator bed temperature.

Further objective of the invention is injecting sulphuric acid into the pipe reactor as one more reactant so as to increase the heat of reaction in the pipe reactor and operate the pipe reactor contents at above 140-145 Deg.C and utilise this heat to maintain the granulator bed temperature in the range of 85-90 Deg.C where the contents reach as stage of melt phase.

One more objective of the invention is to maintain low moisture content in granulator discharge material i.e. in the range of 2.0-3.0% in contrast to the 3-4% that is maintained in conventional processes that have been existing in prior arts where moisture granulation occurs and the product exhibits hygroscopic nature. The low moisture at 2-3% is sufficient for granulation because the melt phase also contributes some liquid phase and thus meets the requirement for good granulation.

Further objective of the invention is under melt granulation conditions the contents can be granulated at low moisture content itself i.e at 2.0-3.0%, there is no need to maintain higher moisture up to 4.0%.

Other objective of the invention is that commercial potash of size as high as 0.6-1.7 mm also can be used as it is, no need to grind the potash to lower size.
Other objective of the invention is that recycle ratio in the present process is very less at 3:1 compared to the recycle rate of more than 5:1 in case conventional processes.

DESCRIPTION OF DRAWINGS

Fig-1 is Process flow diagram for the conventional Pre-neutralizer route of conducting the reactions between phosphoric acid-ammonia and sulphuric acid-ammonia. This is well known and established process. Liquid raw materials viz liquid ammonia (1), phosphoric acid (2a) and Sulphuric acid (2b) are fed to pre-neutraliser (3a) where they react and form ammonium phosphate sulphate slurry. This slurry is pumped to Granulator (5) where the recycle material along with solid raw materials such as Urea and potash are fed and forms as material bed rolling in the granulator. Slurry sprayed in to the granulator falls on the rolling bed and forms a layer on the recycle material granules and powder. Some quantity of liquid ammonia (4) is also fed to the granulator (5) for reacting with the slurry on the surface of the solid material in the granulator. The wet granules from the granulator enter in to the dyer drum (6) where the material gets contacted with the hot air from the combustion chamber (26). Combustion air fan (27) provides air to burn the LPG(29) to heat the air provided by the dilution air fan (28). This hot air when comes in contact with the wet granules in the dryer, takes the moisture from the wet granules and thus dries the material. The dried material from the dryer is lifted to the screen floor by the dryer discharge elevator (7) and feed the material to the screens (8). Oversize material from the screens gets crushed in the pulverisers (9) and falls on the recycle material conveyor (18). Also the fines from the screens falls on the recycle material conveyor. On the recycle conveyor belt, the solid raw materials are also fed from the Solid raw material bins (14) through the raw material weigh feeders (15) at controlled flow rate. Recycle material along with the solid raw material feeds are lifted by the granulator elevator (17) to the granulator floor and feed in to the granulator drum (5). The product size material from the screens is collected by the product bin and it is fed in to the cooler drum (19) through the product regulating conveyor (16). Product granules after cooling is considered as final product and goes to packing section or storage.

The dust laden air streams from the dryer, cooler and screens are subjected to cyclonic separation in the cyclones (10&11) to recover the dust and the exhaust air goes to scrubber(20) and then to stack(22). Exhaust Gases from the granulator also are pulled by the Exhaust fan (21) through the scrubber (20) to recover ammonia and dust and then go to stack.

Fig-2 is Process flow diagram for the Pipe reactor route of conducting the reaction between phosphoric acid-ammonia and sulphuric acid-ammonia. Here the liquid raw materials such as liquid ammonia (1), Phosphoric acid (2a) and sulphuric acid (2B) are fed to the pipe reactor (3b) to conduct the reactions between Phosphoric acid-ammonia and Sulphuric acid-ammonia in the Pipe reactor and the resultant slurry is sprayed on the material bed in the granulator (5). The rest of the process remains same as the previous para. There is an additional tank called as pipe reactor feed tank (25) which receives the scrubber liquor from the scrubbers and where the fresh phosphoric acid is also added to adjust the specific gravity and N/P mole ratio before sending to pipe reactor as phosphoric acid to pipe reactor.

The reaction of liquid raw materials in the pipe reactor as shown in Fig 2 is related to our invention whereas other part of Fig 2 and all of Fig-1 are the available ones in the prior art. Also the present invention is related to the spraying the high temperature slurry from pipe reactor on the rolling bed in granulator and achieving fused granulation/melt granulation of Urea and potash with ammonium sulphate and ammonium phosphate in the granulator.

Labels for Process flow diagram (Fig-1 & Fig-2)
1. Ammonia feed
2A. Phosphoric acid feed
2B. Sulphuric acid feed
3A. Pre-Neutralizer
3B. Pipe Reactor
4. Ammonia Feed to granulator
5. Granulator drum
6. Dryer drum
7. Dryer discharge elevator
8. Screens
9. Pulverisers
10&11 Cyclones
12. Product Bin
13. Raw material elevator
14. Raw material bins 15. Feeders
16. Product regulating conveyor
17. Granulator elevator
18. Recycle material conveyor
19. Cooler drum
20. Venturi Scrubber
21. Exhaust Fan
22. Stack
23. Phosphoric acid tank
24. Scrubber vessel
25. PR feed tank
26. Combustion chamber
27. Combustion air fan
28. Dilution air fan
29. LPG

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the manufacturing of Urea based NPK fertilisers such as 17-17-17 with good sphericity, crushing strength, uniform size and durability nature while using Urea and Muriate of potash as constituents of the product. The Urea containing NPK fertilisers that are produced vide prior arts lack in crushing strength and also exhibit hygroscopic behaviour because of which it becomes powder, absorb moisture and loses the integrity of the granule during storage period either in bulk or in bagged form. The fertiliser granules produced under the present invention process will not pose such problems due to better crushing strength, good size range and low hygroscopicity. The innovative feature of the present process is achieved by the melt granulation of Urea, potash in the ammonium phosphate sulphate slurry in the granulator at a sufficiently higher temperature than the conventional granulation processes. The temperature that is required to achieve melt granulation is obtained from Pipe reactor slurry where the temperature is maintained at around 145 Deg.C. This temperature is obtained in the Pipe reactor by feeding sufficient sulphuric acid which is one of the raw material for the process in to the pipe reactor and allowing reaction of ammonia with sulphuric acid in the pipe reactor in addition to the reaction between ammonia and phosphoric acid in the pipe reactor.

According to the present invention, Urea based Complex NPK fertilisers more precisely high nutrient grade NPK fertilisers such as 17-17-17 can be produced with high sphericity, good crushing strength and with low hygroscopicity through Pipe cross reactor by injecting sulphuric acid in to the Pipe reactor.

Innovativeness of our process is that high sphericity, good crushing strength of the final product are the result from the melt granulation phenomena of the Urea, potash, ammonium phosphate and ammonium sulphate mix and the low hygroscopicity of the product is the result from the low N/P mole ratio of the ammonium phosphate in the final product consisting of ammonium phosphate, ammonium sulphate, Urea and potash.

The material bed in the granulator contains recycle material as well as Urea and potash that are fed as solid raw materials. The hot slurry sprayed on the material bed raises the material temperature and causes the formation of melt mix of Urea and potash

To achieve melt granulation of material in the granulator bed it is required to operate the granulator bed at a temperature more than 85 degC. There are two ways of bringing more heat to the granulator one is through recycle material and the second one is through reaction slurry. There is limitation in bringing heat through recycle material because we maintain an optimum temperature at dryer discharge considering the moisture content of final product and the temperature of final product after cooling in the product cooler. So the recycle material will have a maximum of around 70 degC but not more than that. So the option available for us is to play with the reaction slurry. In order to achieve more than 85degC of granulator bed material we need to spray the reaction slurry at a temperature as maximum as possible. In the experiments that we conducted in pilot plant indicated that when the pipe reactor skin temperature is maintained more than 140 degC then the granulator material bed temperature maintains 85 deg C and above.

In the conventional Pre-neutraliser process we operate the slurry with a minimum of 20% moisture so as to maintain the fluidity and pumpability of slurry to granulator without difficulties. The temperature that can be achieved in the pre-neutraliser under this moisture condition is in the range of 116-124 degC only and not more than that because of the heat losses due to evaporation of water in Pre-neutraliser. Even with introduction of sulphuric acid into Pre-neutraliser higher temperatures cannot be maintained because of the compulsion to maintain fluidity and pumpability of the slurry to pump it up to granulator without the choking problems of slurry line.

By adopting pipe reactor technology we can maintain the reaction slurry temperature higher than that of Pre-neutraliser slurry. Here as we increase ammoniation the temperature of the contents in the pipe reactor increases but we have limitation to restrict the ammoniation to the extent of N/P mole ratio of the slurry to 0.5 to 0.7 for the reason to maintain less hygroscopicity of the final product.

As we wish the pipe reactor to be operated at the N/P mole ratio of 0.5-0.7, the exothermic heat contributed by reaction between and ammonia and phosphoric acid is lesser compared to N/P mole ratio operation of 1.4-1.45. Without sulphuric acid injection in to pipe reactor, it is not possible to achieve the reaction temperature in the pipe reactor at 140 degC at this mole ratio of 0.5 to 0.7.
The advantage of Low mole ratio operation in pipe reactor is immediate solidification of slurry after falling on the recycle material bed in the granulator where it is further ammoniated to the N/P mole ratio of around 1.0. The solubility of ammonium phosphate at N/P mole ratio 1.0 is very low compared to that at other mole ratio values hence the solidification is fast. Moreover the ammonium phosphate of N/P mole ration is less hygroscopic than that of other mole ratios.

So the innovativeness of our process is to inject sulphuric acid in to the pipe reactor to an extent such that the formed ammonium sulphate contributes an equal quantity of ammoniacal nitrogen in the product as that of ammonium phosphate while it additionally contributes generation of high reaction heat in pipe reactor.

The sulphuric acid thus injected reacts with ammonia and forms ammonium sulphate in addition to the reaction between phosphoric acid and ammonia to form ammonium phosphate. Both the reactions are highly exothermic and generate heat. Pipe reactor skin temperature of more than 140 DegC can be achieved thus more heat is available to evaporate most of the water from the slurry while getting sprayed on the recycle bed and also to raise the granulator bed temperature to 85degC and above. The slurry moisture at pipe reactor discharge falling on the recycle bed in the drum granulator would be as low as about 5% to 8%.

On the other hand the ammonium sulphate thus formed in the pipe reactor contributes to part of the ammoniacal nitrogen requirement of the product whereas the remaining part of the ammoniacal nitrogen requirement is contributed by ammonium phosphate.

The innovativeness of this process is that the ammoniation of phosphoric and sulphuric acid mix generates high heat of reaction in pipe reactor and raises the temperature of the reaction products to a temperature more than 140DegC, through conventional reaction without sulphuric acid in pipe reactor or by using Pre-neutraliser process it is not possible to get this much high temperature of slurry.

High temperature pipe reactor liquor increases the granulator bed temperature to 80Deg.C-90 DegC, where urea prills that are present in the granulator bed starts melting (called as surface melting) and produces adequate liquid phase required for granulation. Some of the urea interacts with Free acid and forms urea phosphate and urea sulphates, this liquid phase forms the very strong bridges between solid particles i.e., recycle material and the potash in the bed. There by gradual increase in the size of granules occur through mostly by accretion and to some extent by agglomeration. This type of granulation is called fusion granulation this continues in the granulator and also up to some length of the drier.

The dryer that dries the material coming out of the granulator is conventional rotary dryer with co-current hot air flow like in any NP/NPK granulation plants. It is of fixed speed and is provided with flights inside called as carrying flights and lifting flights. The material that enters the dryer is carried forward by the carrying flights of spiral shape and distribute to the lifting flights. Lifting flights lift the material and pours down vertically where the material forms like a curtain and the maximum contact would be possible with hot air that enters the dryer at 200-220 DegC, both material and hot air travels in co-current passion.

While this granular material passes through the drier, due to contact with hot air it loses the moisture present within each granule. By the time material reaches the discharge end of the drier the moisture content reduces to 1.0-1.2%. At this stage the granules look to be soft because of high temperature at around 85 degC but they can withstand the abrasion on the screens during the screening. The product size fraction gets hardened while cooling in the product cooler.
This product that is produced through this process is uniform in size, spherical in shape and hard in integrity, and superior in some other physical properties related to hygroscopicity with low moisture absorption, low moisture penetration. Improvement in the physical properties by the new formulation are considered to be because of right proportion of ammonium sulphate and urea, low N/P mole ratio of product, high temperature during the granules formation, melt formation of constituents, fused granulation and finally, low moisture content of the product.

PILOT PLANT EXPERIMENTAL DATA

Experiments are conducted at the pilot plant of Coromandel International Ltd, Visakhapatnam, India where the pilot plant is having Pre-Neutraliser, Pipe reactor , Pipe reactor feed tank, scrubber, rotary granulator, rotary dryer, rotary cooler, Screens and all equipments and vessels as listed in the legend of Fig-1 and Fig-2. By changing the process route viz Pre-neutraliser route and Pipe reactor route experiments were

conducted described below and measured the physical characteristics of the product viz crushing strength, SGN, Uniformity index, Sphericity and hygroscopicity.

The physical characteristics of the product obtained from Exeriment-4 proves to be superior while meeting the specifications of the nutrient specifications. Such a process does not exist in the prior arts for high grade NPK fertiliser grades such as 17-17-17 , hence it is considered as the innovative process for obtained good quality product.

The key features of the invented process

1. Urea based NPK 17-17-17 fertiliser produced through Pipe Reactor reaction route
2. This process involves direct addition of concentrated sulphuric acid to pipe reactor along with Ammonia and Phosphoric acid.
3. This process involves urea addition at 18-19%.
4. This process adopts equal proportion of AN% & UN% in the product, i.e 8.4-8.5% and 8.4-8.5% respectively.
5. This process adopts maintaining the final product N/P mole ratio in the range of 1.30-1.35.
6. This process involves High slurry temperature i.e., 140-145 Deg.C at pipe reactor discharge.
7. This process adopts maintaining the granulator discharge material moisture content in the range of 2-3%.
8. This process involves Low slurry moisture at i.e., 5.0-8.0% on to granulator bed.
9. This process uses the Fusion granulation technique by creating conditions for partial melting of solid urea with high temperature slurry.
10. In this process we can use Potash of particle size up to 1.7 mm and there is no need to restrict the particles to be of lower size.
11. This process maintains granulation bed temperature at 80-90 Deg.C
12. Product moisture is 1.0 to 1.5%
PREFERRED EMBODIMENTS OF THE INVENTED PROCESS
• As disclosed above the disclosure in one aspect discloses a process to produce good quality high grade granulated NPK fertilisers such as 17-17-17 while using Urea and Potash as constituents whose presence in the so far existing prior art processes are leading to low crushing strength and high hygroscopic nature of the NPK fertilisers.
• In another aspect this invention discloses a process to improve the quality parameters such as Sphericity, crushing strength, Uniformity, size range and to reduce the hygroscopic nature of the Urea and potash containing fertiliser products thus increasing the durability.
• In another aspect the present disclosure provides a new and innovative process for the production of granular NPK fertiliser which is devoid of the drawbacks and disadvantages that exist in the prior arts such as irregular shape, low crushing strength, varied & wider size range and high hygroscopicity..
• In another aspect this invention discloses adaptation of the right combination of ammonium phosphate, ammonium sulphate and Urea that give better granulation properties as well as better physical properties of the product while meeting the total nitrogen requirement of 17% in the product.
• In another aspect the present invention discloses introduction melt granulation technique in the granulator where Urea and potash form eutectic solution in Ammonium phosphate and ammonium sulphate which encourages the formation of round, spherical and uniform composition, the granules thus formed exhibit good crushing strength and low hygroscopicity after drying and cooling and thereby have increased durability.
• In another aspect this invention discloses development of the key feature of maintaining granulator bed temperature in the range of 85-90 Deg.C so as to obtain melt granulation of Urea, potash, ammonium phosphate and ammonium sulphate in the granulator.
• In another aspect this invention discloses the choose of the pipe reactor process for conducting the reaction between ammonia & phosphoric acid so as to reduce the heat losses and also to utilise the heat of reaction that is generated, to raise the granulator bed temperature.
• In another aspect this invention discloses injection sulphuric acid into the pipe reactor as one more reactant so as to increase the heat of reaction in the pipe reactor and operate the pipe reactor contents at above 140-145 Deg.C and utilise this heat to maintain the granulator bed temperature in the range of 85-90 Deg.C where the contents reach as stage of melt phase.
• In another aspect this invention discloses the way to maintain low moisture content in granulator discharge material i.e. in the range of 2.0-3.0% in contrast to the 3-4% that is maintained in conventional processes that have been existing in prior arts where moisture granulation occurs and the product exhibits hygroscopic nature. The low moisture at 2-3% is sufficient for granulation because the melt phase also contributes some liquid phase and thus meets the requirement for good granulation.
• In another aspect this invention discloses that at melt granulation conditions the contents can be granulated at low moisture content itself i.e at 2.0-3.0%, there is no need to maintain higher moisture up to 4.0%.
• In another aspect this invention discloses that commercial potash of size as high as 0.6-1.7 mm also can be used as it is, no need of grinding the potash to lower size.
• In another aspect of this invention is that recycle ratio in the present process is very less at 3:1 compared to the recycle rate of more than 5:1 in case conventional processes.
Table-1 : Examples of Pilot plant trial data of Urea based NPK 17-17-17 at 1.0 Ton/hr

Sl no Process route adopted Pre-Neutraliser route Pipe Reactor route
Expt-1 Expt-2 Expt-3 Expt-4 Expt-5
1 PHOSPHORIC ACID USED
2 Concentration P2O5% 0.532 0.532 0.532 0.532 0.532
3 Specific gravity 1.66 1.66 1.66 1.66 1.66
4 PRE-NEUTRALISER:
5 Phosphoric acid to PN tank, lpm 2.05 2.05 Pre-neutraliser not used
6 Scrubber liquor to PN tank, lpm 7.8 7.8
7 Sulphuric acid, lpm (93% conc & 1.82 spg) 0.725 1.42
8 Liquid ammonia to PN tank, Kg/hr 71 96
9 PN slurry temperature , Deg.C 116 120
10 PN slurry Sp.gr. 1.52 1.54
11 PN slurryr N/P MR 1.4 1.4
12 PR FEED TANK:
13 Phosphoric acid to PR feed tank, lpm Pipe reactor not used 2.05 2.05 2.05
14 Scrubber liquor to PRFT, lpm 7.8 7.8 7.8
15 PR Feed tank liquor N/P MR 0.45 0.45 0.55
16 PR Feed tank liquor Sp.gr. 1.45 1.4 1.48
17 Sulphuric acid, lpm (93% conc & 1.82 spg) 0.725 Nil Nil
18 SCRUBBER:
19 Phosphoric acid to scrubber, lpm 1.2 1.2 1.2 1.2 1.2
20 Scrubber liquor Sp.gr. 1.1 1.1 1.1 1.1 1.1
21 water to scrubber, lpm 6.72 6.72 6.72 6.72 6.72
22 Scrubber liquor N/P MR 1.3 1.3 1.3 1.3 1.3
23 FEEDS TO PIPE REACTOR:
24 Liquid Ammonia, kg/hr Pipe reactor not used 67 61 85
25 PRFT liquor, lpm 9.17 9.5 9.84
26 PRFT liquor N/P MR 0.45 0.45 0.45
27 Sulphuric acid, lpm (93% conc & 1.82 spg) Nil 0.725 1.42
28 FEEDS TO GRANULATOR:
29 PN Slurry to Granulator, lpm 9.27 10.04 Preneutraliser not used
30 Targetted MR at PR discharge Pipe reactor not used 1 0.85 0.85
31 Pipe Reactor skin temperature, Deg.C 122-124 130-132 142-145
32 Liquid ammonia, Kg/hr 21 20 18.5 23.4 20.6
33 Urea Kg/hr 217.4 172 225 225 189
34 MOP (Potassium chloride) kg/hr 285 285 285 285 285
35 Recycle solids tons/hr 4.5 4 3.5 3.2 3
36 PROCESS PARAMETERS IN GRANULATOR
37 Granulator discharge material H2O% 3.0-4.0 3.0-3.5 2.5-3.5 2.5-3.5 2.0-3.0
38 Granulator discharge material temperature deg C 63 68 71 75 87
39 Product bleed off rate tons/hr 1.0 1.0 1.0 1.0 1.0

Table- 1 continued...
Sl no Process route adopted Pre-Neutraliser route Pipe Reactor route
Expt-1 Expt-2 Expt-3 Expt-4 Expt-5
40 PRODUCT SIEVE ANALYSIS (wt. %)
41 + 4 mm 9.09 6.7 1.9 2 2.7
42 -4 mm to +2mm 46.47 54.23 34.4 47.4 84.9
43 -2mm + 1mm 36.01 29.82 51.4 43.6 11.4
44 -1mm 8.43 9.25 12.3 7 1
45 NUTRIENT ANALYSIS:
46 %AN 7.46 9.39 6.9 6.8 8.56
47 %UN 9.7 7.67 10.04 10.04 8.43
48 %TN 17.16 17.07 16.94 16.84 17
49 %TP2O5 17.13 17.1 17.07 17.08 17.12
50 %K2O 17.01 17 16.96 17.03 17.05
51 % H2O 1.8-2.0 1.6-1.8 1.5-1.6 1.3-1.5 1.0-1.2
52 Product N/P MR 1.60-1.62 1.60-1.62 1.40-1.45 1.40-1.42 1.30-1.35
53 PHYSICAL PROPERTIES OF PRODUCT
54 Bulk density kg/CuM 935 952 971 986 1000
55 Product Crushing Strength Kgf/granule 0.8-1.0 1.0-1.3 1.1-1.3 1.4-1.6 1.8-2.0
56 SGN of the product 239 242 195 220 284
57 Uniformity Index 25.6 27.2 14.5 24.2 33.5
58 Sphericity 48-50 45-48 38-40 40-43 56-58
59 HYGROSCOPIC PROPERTIES WHEN EXPOSED TO 80% RELATIVE HUMIDITY AND 300C FOR 72 HRS IN A CYLINDRICAL JAR AS PER IFDC STANDARD METHOD
60 Moisture absorption, mg/cm2 174 159 154 149 140
61 Moisture penetration, cm 3.9 3.4 3.1 2.3 2.1

In one aspect, the invention discloses a process for preparing the granular urea based NPK fertiliser containing Nitrogen (N), phosphorous (P) and Potassium (K) using pipe reactor and a granulator using urea and potash as solid raw materials, the process comprising of:
a) injecting Phosphoric acid and liquid ammonia as liquid reactants into the pipe reactor as per the flows mentioned in experiment-5 of table-1 to form Ammonium phosphate and generate high quantity of exothermic reaction heat,
b) injecting Sulphuric acid into the pipe reactor as another liquid reactant at the rate as mentioned in row 27, experiment-5 of table-1 for reaction with ammonia to form ammonium sulphate and generate high quantity of exothermic reaction heat,
c) maintaining the pipe reactor skin temperature at 142 -145 deg C as obtained in row 31, experiment-5 of table-1,
d) melting of Urea prills placed as solid particles within granulator bed using the heat generated in granulator by spraying the hot slurry from pipe reactor,
e) forming of Urea Phosphates and Urea Sulphates due to interaction of urea with free acids thus forming integrated granules with uniform composition,
f) the said generated Ammonium Sulphate in the pipe reactor contributes to a portion of Ammoniacal Nitrogen in the prepared fertiliser and that the said generated Ammonium Phosphate in the granulator contributes to another portion of Ammoniacal Nitrogen in the prepared fertiliser,
g) allowing formation of eutectic solution of Urea and Potash in Ammonium Phosphate and Ammonium Sulphate in the granulator bed maintained at a temperature in the range of 85-900C, more specifically 87 deg C as obtained in row 38,experiment-5 of table-1, due to spray of hot slurry from the pipe reactor on the rolling bed of Urea +Potash +Recycle material in the granulator with the exothermic reactions and heat generation,
h) allowing accretion and agglomeration by fusion of the solid raw materials and melt granulation to occur with the liquid phase bridging among the solid particles in the granulator, the solid particles being Urea, potash and the recycle fines in the granulator bed, and
i) drying the wet granules from the granulator in a rotary dryer for reducing the moisture content followed by cooling granules in a rotary cooler so as to get final moisture content of the product in the range of 1.0-1.5%, more specifically 1.0 to 1.2% as obtained in row 51, Experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the injection of sulphuric acid in to the pipe reactor at 1.42 lpm per ton of final product along with the other liquid raw materials viz., phosphoric acid and liquid ammonia, generates more exothermic heat and there by Pipe reactor skin temperature reaches as high as 142-145 degC and this high temperature favors melt granulation phenomena in the granulator bed materials viz urea, potash & recycle powder material.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the final product composition of 8.4-8.5% Ammoniacal Nitrogen and 8.4-8.5% Urea Nitrogen is favorable for melt granulation phenomena and thereby it favors the achievement of strength granules in the final product with the crushing strength of 1.8-2.0 kg.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the process further includes maintaining low moisture content in the granulator bed in the range of 2-3% as mentioned in row 37, experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the process accepts the higher potash also, in the all the experiments of table-1 we used of solid Potash having size in the range of 0.6-1.7 mm.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the process further includes a low recycle rate of 3:1. This is proved by row-35, experiment-5 in the table -1 of pilot plant run data where recycle rate was 3.0 tons per hour for obtaining the product at the rate of 1.0 ton per hour.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules are more spherical with the spherity being in the range of 56-58 as obtained in the row 58, experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules are uniform with uniformity index being above 33% as obtained in the row 57, experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules are hard with crushing strength in the range of 1.8 to 2.0 kg as obtained in the row 55, experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules contain -4+2 mm fraction more than 80%, the obtained fraction is 84.9% in our experiment as mentioned in the row 42, experiment-5 of table-1.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules possess low hygroscopic behavior, when tested in a cylindrical jar as per the standard test procedure laid down by IFDC under the conditions, 80% relative humidity and 30 deg C temperature, in a humidity chamber, this is proved by the moisture absorption of 140 mg/cm2 area as obtained in row 60, experiment-5 of table-1 which is lower than the other experimental results.

In another aspect, it is for the process for preparing the granular Urea based NPK fertiliser as described above, wherein the produced granules possess low hygroscopic behavior, when tested in a cylindrical jar as per the standard test procedure laid down by IFDC under the conditions, 80% relative humidity and 30 deg C temperature, in a humidity chamber, this is proved by the moisture penetration of 2.1 cm as obtained in row 61, experiment-5 of table-1 which is lower than the other experimental results.

The examples and illustrations are only for the purpose of understanding and none of them shall limit the scope of the invention. All variants and modifications as will be envisaged by skilled person are within the spirit and scope of the invention.