FR2461518A1 - Fertiliser granules prepn. - by spraying a hot slurry of ammonium sulphate onto dry minerals in a rotating drum - Google Patents

Abstract

process. Solid mineral salts are introduced at one end of a rotating cylinder and treated with a freshly prepd., hot slurry of slightly acidic ammonium sulphate. The mixt. passes to the lower end of the cylinder where it is sieved into fines, medium sized granules and oversized particles. The fines and oversized particles are recycled, the latter after crushing. Only sufficient water is used as is necessary to bind the granules together, and the slurry is added at high temp. There is a considerable saving in energy costs. The percentage of fines and oversized particles is reduced.

Description

 The present invention relates to a method and an apparatus for manufacturing granular fertilizers, and in particular fertilizers of the binary type NP or of the ternary type NPK, that is to say of fertilizers containing the elements nitrogen and phosphorus or nitrogen. , phosphorus and potassium.

 Fertilizers of this type are particularly prized by farmers because of their presentation in the form of granules, because they avoid the disadvantages of a powdered fertilizer, which flies away easily when applied in the fields in high wind, as well as the disadvantages of a liquid fertilizer, which requires the handling of a large weight of an inert vehicle.

 The manufacture of granulated fertilizers has been carried out for many years by drying a liquid slurry of a determined mixture of mineral salts, such as diammonium phosphate, superphosphate, ammonium nitrate, neutral sulfate dQammoniumt potassium chloride, to name only the most commonly used salts in this kind of industry.

 The drying of this slurry, which is in the form of a more or less viscous aqueous solution depending on its partly dissolved solid content, is generally carried out in a rotary cylinder or granulator whose diameter is of the order of 2 meters and the length of the order of 5 to 10 or 20 meters, and whose axis is slightly inclined relative to the horizontal to facilitate the circulation of the materials which circulate there.

 The slurry is introduced at the upstream end of the cylinder where generally a flow of hot air circulates against the current, which dries the slurry and transforms it, during its mixing and its advance in the rotary cylinder, into granules of all dimensions.

 The granules thus formed are collected at the downstream end of the rotary cylinder, screened into fine, medium and large, the granules of medium dimensions forming the desired market product, while the granules of large dimensions are crushed and recycled as well as the fines to the upstream end of the cylinder.

 Such a process consumes a great deal of energy because it requires the elimination by drying of most of the water present in the feed slurry of the rotary cylinder and necessary for the formation of granules; on the other hand, the production of a specific installation of granulated fertilizers is limited by recycling particles which are too fine or too large and which can reach a flow rate which is a multiple of the average particles having the desired particle size.

 Attempts have been made to reduce these drawbacks by introducing the slurries into the rotary cylinder at increasing temperatures and by providing, inside this cylinder, arrivals of pressurized steam, which makes it possible to reduce the amount of heat. brought by the current of hot air circulating in the cylinder.

 The present invention makes it possible to improve the thermal balance of a given installation while maintaining the recycling of granules of unsatisfactory dimensions at a reduced rate.

It thus makes it possible to increase the capacity of workshops for manufacturing granular fertilizers without increasing their energy consumption.

 The method according to the invention consists in injecting directly into the mass of solid mineral salts introduced into the rotary cylinder, a slurry of slightly acidic ammonium sulphate which has just been prepared.

 This slurry is prepared in a reactor from concentrated sulfuric acid, the amount of water necessary for the granulation of the fertilizer in the rotary cylinder and ammonia.

 The quantity of water required for granulation is introduced either entirely into the concentrated sulfuric acid, or partly into the latter and partly into the ammonia which it dilutes, therefore before the neutralization reaction between the acid and ammonia.

 Therefore, in the process according to the invention, not only the heat of dilution of sulfuric acid in water but also the heat of neutralization of this acid with ammonia is used to evaporate the dilution water and to reheat ammonium sulphate which is injected as soon as it is produced, into the mass of the other mineral salts introduced at the upstream end of the rotary cylinder in the form of powders or granules.

 In other words, and without the Applicant being bound by this explanation, it can be assumed that the hot liquid ammonium sulphate which has just been produced and which is introduced into the solid mass at a temperature close to the ambient temperature of the other mineral salts introduced into the rotary cylinder will serve as a binder for the particles of these other mineral salts to form complex granules, the average composition of which corresponds to the formulation of granulated fertilizers desired.

 To carry out this injection of freshly prepared ammonium sulphate into the rotary cylinder, the Applicant has developed a tubular jacket with double jacket in which the neutralization reaction takes place and which is extended in the rotary cylinder by a discharge injector angled opening into the mass of mineral salts moving in the cylinder.

The invention will be illustrated by means of a particular implementation shown in the accompanying drawings in which:
Figure 1 shows an overview of an installation for manufacturing granular fertilizers according to the invention; and
Figure 2 is a vertical section along the axis AA 'of Figure 1 of the reactor of the apparatus according to the invention.

 The rotary cylinder or granulator 1 is of the type previously described and comprises at its upstream end 2, slightly higher than its downstream end 3, a feed hopper 4 in solid material and an injector 5 extending a reactor 6, and, at its downstream end, a device 7 for extracting the granules and separating the mist.

 The granules leaving the granulator Is dried and then passed to the screen where only the medium-sized granules corresponding to a determined range, the maximum and minimum of which vary according to the formulation produced, are retained as a merchant product.

 The coarsest particles are crushed and returned, as well as the finest, in the hopper 4 and all of these particles, which are too large or too fine, constitute recycling. The recycling rate is defined by the ratio of the weight of large and fine particles to the weight of medium particles. In the method according to the invention, this rate is always less than 2 and generally between 1 and 1.3.

 The device for manufacturing ammonium sulphate comprises a mixer 8, a reactor 9 and an injector 10.

 The mixer 8 consists of an axial pipe 11 for supplying concentrated sulfuric acid, generally 98%, which is closed at its end and diffuses the acid by means of radial perforations 12. This axial pipe opens into a cylinder 13 more large diameter, fed radially at 14 by a water inlet. The sulfuric acid diluted in the mixer 8 leaves through the orifice 15 and will feed the reactor 9.

 The reactor 9 is in the form of a double jacket tube, the inner jacket 16 and the outer jacket 17 being in the form of two coaxial tubes of the same length having a length to diameter ratio between 5 and 10. L internal shell 17 has an axial inlet 18 and outlet 19 and consists of a tube having a longitudinal diffuser 20 near its inlet 18 and which is provided over its entire width with a number of radial orifices 21, distributed uniformly along circumferences located at equal distances from each other and preferably offset by 45 "with respect to one of the neighboring circumferences. The external envelope 17 is partitioned by a transverse wall 22 into two cylindrical compartments 23 and 24, provided respectively with a pipe 26 or 27 for supplying liquid or gaseous ammonia which can optionally be diluted with water.

 The outlet orifice 19 of the reactor 9 is connected, for example by means of a conical element 28, to the injector 10, which consists of a tube penetrating inside the granulator 1 and bent to open out nearby from the wall of the latter, at an angle to the vertical so that the end of the injector is embedded in the mass of solid matter flowing in the granulator 1. The end of the injector is preferably provided with a deflector 29.

Such a device operates in the following manner
The mixture of concentrated sulfuric acid and water is adjusted in the mixer 8 by measuring their flow rates and the thus diluted acid is introduced into the inlet port 18 of the reactor 9 where it is diffused by the diffuser 20 in the form axial jets inside the internal envelope 16.

The dilution of sulfuric acid is preferably, in the case of a 98% acid, maintained at a rate of H 2 SO 4 /
H2SO4 + H2O by weight between 0.60 and 0.80 and in particular between 0.65 and 0.72.

 The supply of ammonia, which is preferably liquid and diluted with part of the water necessary for granulation, is also regulated by measuring its flow rate and dividing it, for example into equal parts, in compartments 23 and 24 of the outer shell 17, from which the ammonia enters the inner shell 16 via the radial orifices 21. There is thus a meeting at a right angle of the currents of dilute sulfuric acid and ammonia in the reactor.

 The respective flow rates of acid and ammonia are adjusted so that a slight acidity is obtained.

It has in fact been observed that there was no granulation in the event of introduction into the granulator of neutral ammonium sulphate. It is preferred to obtain neutralization conditions such that a mixture of neutral ammonium sulfate and acid ammonium sulfate containing approximately 50 to 80% by weight of the first is obtained,
The pressures in the reactor are of the order of 2 to 5 bars; the ammonium sulphate slurry leaving through the injector has a temperature of the order of 250 to 350 ° C., and a pH of the order of 1.5 and it is practically anhydrous.

During the dilution reactions of sulfuric acid in the mixer and its neutralization by ammonia in the reactor, the dilution water is vaporized to an extent sufficient to reduce, or even eliminate, any addition of steam additional in granulator 1
To illustrate the range of different formulations of granulated complex fertilizers which can be produced according to the present invention, the operating conditions of the reactor, the proportions of the raw materials used, the granulation conditions, the characteristics of the finished product and the grain size for different formulations.

BOARD
NPK formula 17.17.17 18.22.12 14.20.20 20.10.10
Raw material feed (Kg / tonne) - Reactor
H2S 4 98% 75 68 70 70
Dilution water 11 12 12 10
NH3 liquid 22 23 20 25
Dilution water 22 24 24 20
total 33 36 36 30
% dilution H2S04 69.6 65.3 66 70
H2 504 ratio 3.4 2.95 3.5 2.8
NH3 - Granulator
Nitrate at NH4 245 24I 144 365
NH4 112 neutral sulfate
phosphate diam 373 419 440 189
Simple superphosphate 80
Potassium chloride 284 190 334 167
Material humidity
first solids
(in%) 1.12 1> 36 1.28 1.34
GRANULATION
Recycling rate 0.9 1 1.1 1.1 TB of the product leaving the granulator 80 "76" 840 82
H2O content of the product at the outlet of the granulator 1.55 1.45 1.55 1.70
FINAL PRODUCT
Total N 17.01 17.89 14.53 20.07
N nitric 4.52 4.20 2.86 6.13
N ammonia 12.49 13.69 11.67 13.94
P205 total 17.00 21a90 19.97 10.49
K20 17.46 12.41 18.97 10.56% H20 (1 h 1000C) 0.51 0.60 0.68 0.50
TABLE (continued)
NPK formula 17.17.17 18.22.12 14.20.20. 20.10.10 surface pH 5.95 5.90 5.70 6.20
GRANULOMETRY (mm) + 4 0.6 0.5 0.1 0.4 + 3.15 28 8.9 9.1 23.7 + 2.5 91 88.1 86.7 90.8 + 2 99 99 , 2 98 99.1
It appears from the data in the preceding table that, with a recycling rate close to 1, according to the invention, various formulations of complexed fertilizers are obtained, which have remarkably low moisture content and of which 90% on average do not pass. not through a 2.5 mm sieve, but pass through the 4 mm sieve and are retained by the 2 mm diameter mesh opening.

 Such a result illustrates the great flexibility of the process of the invention.

 It should also be noted that the reactor used for the implementation of this process is made of or coated with a suitable material resistant to the action of sulfuric acid.

 It goes without saying that the present invention has been described purely for explanatory purposes and in no way limitative and that any useful modification may be made thereto without departing from its scope as defined by the claims below.

Claims (10)

 1 - Process for the preparation of granular fertilizers by the introduction of an ammonium sulphate porridge into the minerals at the upstream end of a rotary cylinder in which the porridge is dried and transformed into granules , screening of the granules leaving the downstream end of the rotary cylinder into medium and large fines2, collection of the medium particles which constitute the product produced and recycling of the large, after grinding, and of the fines at the upstream end of the cylinder, characterized in that directly injects a slightly acidic ammonium sulphate slurry, which has just been prepared, into the mass of the other mineral salts introduced into the rotary cylinder in solid form.  2 - Method according to claim 1, characterized in that the ammonium sulfate slurry is produced in a reactor from concentrated sulfuric acid, the amount of water necessary for the granulation of the fertilizer in the rotary cylinder and ammonia to be injected, directly at the outlet of the reactor, into the mass of the other mineral salts, in particular in the form of powders.  3 - Process according to claim 2, characterized in that the quantity of water necessary for the granulation of the fertilizer in the rotary cylinder is introduced entirely into the concentrated sulfuric acid or partly into the latter and partly in liquid ammonia before bringing the acid and ammonia into contact in the reactor, preferably so that the dilution rate H2SO4 / H2SO4 + H2O by weight is between 0.60 and 0.80.  4 - Process according to any one of claims 1 to 3 characterized in that the contact between sulfuric acid and ammonia takes place at a right angle.  5 - Process according to any one of claims 1 to 4, characterized in that the reaction for neutralizing ammonia with sulfuric acid in the presence of water is carried out so as to obtain a mixture of neutral sulfate and sulfate ammonium acid preferably in a proportion of 50% to 80% by weight of the first.  6 - Apparatus for the preparation of granulated fertilizers according to the process which is the subject of claim 1, comprising a rotary cylinder, a hopper for supplying solid matter and a injector for supplying liquid slurry, both located at the upstream end of the cylinder, a series of screens collecting the granules leaving the downstream end of the cylinder and allowing their separation into fine, medium and coarse and the recycling of large particles after grinding and fines at the upstream end of the cylinder , characterized in that the injector introduces, inside the mass of solid mineral salts coming from the feed hopper, a liquid slurry of ammonium sulphate prepared in a tubular jacketed reactor where sulfuric acid arrives axially in the internal envelope and the ammonia is released from the external envelope towards the internal envelope by a series of radial orifices.  7 - Apparatus according to claim 6, characterized in that the reactor has a length / outside diameter ratio between 5 and 10.  8 - Apparatus according to claim 6 or 7, characterized in that the external envelope of the reactor where the arrival of ammonia is divided into two separate compartments which are both in contact by radial orifices with the envelope internal, where the arrival of sulfuric acid takes place, preferably these two compartments comprising a number of radial orifices increasing with the direction of flow of the slurry.  9 - Apparatus according to any one of claims 6 to 8, characterized in that the radial orifices of the reactor are distributed uniformly along the circumferences, located at equal distance from each other over the entire length of the internal envelope of the reactor .  10 - Apparatus according to claim 9, characterized in that the orifices arranged along a circumference are offset by 45 "relative to those of the neighboring circumferences.