DE1592359A1 - Process for the production of ammonium nitrate granules - Google Patents

Description

PATENT ADVOCATE DR. HANS-GUNTHER EGGERT, DIPLOMA CHEMIST

5 KOLN-LINDENTHAL PETER-KINTGEN-STRASSE 2

Cologne, 20.4o1967 Eg / Ax

Nitrates et Engrais ,

61, Rue Galilee, Paris 8 ^e (France).

Process for the production of ammonium nitrate granules

.Ammonium nitrate comes in the form of granules or "prills" in the. Trade, its nitrogen content depending on the intended agricultural or technical use is different. The granules must be well dried so that they can be stored and not caked and hardened = So far, the granulate is made by atomizing a saturated, aqueous ammonium nitration solution at the top made of a tower. Based on an aqueous ammonium nitrate solution, a concentration of about 95 ^ is obtained one at the foot of aes tower a granulate, which is about 4 $ Contains water and then in an expensive and extensive Apparatus is dried, the dimensions of which require the erection of large structures »

Ui the plant costs caused by this drying It was recently proposed to reduce a 3 very highly concentrated 99.8% ammonium nitrate solution to be used and to produce ilitrate practically in the molten state atomize, obtaining a granulate at the base of the tower which contains 99 »8 ^ ammonium nitrate and 0.2 / 0 water. In order to achieve this very high concentration, you have to Complicated apparatuses are used, and the handling of the liquid at a temperature in the vicinity of the

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Decomposition temperature of Arni..oniuiunitrat is with a serious danger associated.

The invention makes it possible to overcome the disadvantages of using of highly concentrated ammonium nitrate]. by starting from solutions of medium concentration and reducing the cost and size of the equipment, by using fluidized bed technology.

According to the invention, the moisture content can be brought to a very low fourth (about 0.1 or 0.2 $) with a very small specific fluidized bed area by adjusting the concentration of the solutions to be atomized on the one hand and subjecting the granules to a sequence of selective heat treatments on the other . This is based on an aqueous ammonium nitrate solution having a concentration of equal to or less than 97 * 5% by weight, preferably less than 95% by weight of ammonium nitrate. For purely economic reasons there is no interest in using a concentration below 90% by weight. This solution, which is atomized at the top of a tower, produces granules at the foot of the tower, the water content of which is about 1% below the water content of the starting solution. This granulate consists of ammonium nitrate crystals and a liquid phase, which is a saturated solution at the respective temperature of the granulate.

With the drying process according to the invention, a to rapid crystallization of this saturated solution can be avoided. When the crystallization is not controlled is, it causes a premature clogging of the pores of the granulate through which the enclosed moisture escapes. The granulate is therefore subjected to a series of selective heat treatments as follows:

a) maturation

This first heat treatment, which has the purpose of homogenizing the water content inside each grain, must be like this be carried out that the granules without significant

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Loss of moisture is brought to a temperature close to the later actual drying temperature. For this purpose, this warming must be reasonably slow and for a duration which is at least 1 minute and can be up to 4 minutes and more. she can in fluidized beds of small thickness (e.g. 50-βθ mm) or in any other suitable manner.

If the granulate at the puss of the granulating tower has already been delivered to a If temperature is obtained which is close to the dry temperature, one can of course do the ripening process without Apply a heat treatment, but the time of natural, sufficiently slow maturity must be adhered to before the actual drying.

b) Drying with a constant course

After ripening, drying takes place at a constant rate. This is the process step in which most of the drying takes place. The drying is carried out in such a way that the surface evaporation is as constant as possible in order to avoid premature crystallization of the enclosed solution. This heat treatment can be carried out in any suitable manner, but a fluidized bed dryer is preferably used, in detr. gerelfte the ammonium nitrate after its introduction is dried so that its temperature between 45 and 70 ⁰ C, preferably at about 55 ° C. The temperature obtained in practice depends on the height of the fluidized bed and on the temperature of the drying air. Good drying is achieved with a fluidized bed about JOO mm high and with air at 110 ° C. The residence time of the granules in the dryer can be between 4 and 8 minutes and is preferably 6-7 minutes. At the exit of the dryer, the moisture content of the grain is around $ 0.5-1.

c) Slow diffusion

The granulate becomes the same as the troc '"c; iUii; r with a constant course dried in a fluidized bed at a temperature which, however, is clearly the temperature of the previous stage, *

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namely at about 80-100 ° C, the height of the layer preferably is about 550 mm. The residence time depends on the desired final moisture content and is in the order of magnitude of 6 minutes with a final moisture content of $ 0.1-0.2. The dry ammonium nitrate can then be cooled in a conventional cooler and then filled into bags will.

All of these selective heat treatment operations are improved, especially in the case of the most concentrated 95-97 > 5 weight solutions, if a surfactant is added to the ammonium nitrate solution prior to atomization, of which the amine acetates and the alkyl sulfates, such as sodium lauryl sulfate, are the best known. However, it must be ensured that the surface-active agent has a higher decomposition temperature than the solution to be atomized.

example 1

An aqueous ammonium nitrate solution containing 92 $ nitrate and 8 $ water is atomized at the top of a granulation tower. On fies the tower is a .Granulat, the $ 93 $ nitrate and about 7 v / ater containing obtained ⁰ C at a temperature of about 25-50. These granules are first subjected to ripening in a first fluidized bed under the following conditions:

Layer height 50-60 mm

Air inlet temperature 70-75 ° C

Product outlet temperature 55 ° C

Moisture content of the exiting product 6-6.5? «

Residence time 1.5 minutes

Ripening is followed by constant drying in a second fluidized bed under the following conditions:

Height of the layer 250 mm at the entrance

550 mm at the outlet

Air temperature at the inlet 110-115 ° C

Exit temperature of the product 6O-7O ° C

Moisture content of the exiting

Product 009850/1689 ° * 5-i £

Dwell for 6 minutes

BATH ORIGINAL

After constant drying, the granulate undergoes a slow diffusion in a third fluidized bed subject to the following conditions:

Layer height J5OO-550 mm

Air temperature at the inlet 90 ⁰ C

Exit temperature of the product about 85 C moisture content of the exiting Product $ 0.1-0.3

Residence time 5 minutes

Under these conditions, a practically dry product is thus obtained in about 12 minutes. In contrast, if you use the classic method to spray a concentrated aqueous solution with 96% ammonium nitrate and 4% water, you get a granulate with 96.8 % nitrate and 2% v / water at the foot of the tower. If this granulate is dried without special precautions, for example by introducing air at IJO ⁰ C, the moisture content after 5 minutes is 3. lyo, after 10 minutes J>% and after 15 minutes it is still yp. The lowering of the moisture content is extremely slow, and it would take several strokes to dry the granulate completely, if this is possible at all.

Example 2

This example illustrates the benefit of adding a surfactant to the aqueous ammonium nitrate solution before atomization.

A granulate containing vmrdo obtained by spraying an aqueous solution containing 95 / ^ ammonium nitrate and 5 $ v / ater and 0.05 # Ilatriuinlaurylsulfat, was in a fluidized bed (height 00 ^ brain temperature dor air 110-115 ⁰ C) dried according to the method described in Example L. The t'Onohtl ^ koLUjgehal.t des GranuLcits Ln dependence on the Trockexi / oil Ln t given below together with the words that for «La CIruiml.at from a • / erj.leich.'ilösun ^; without surface-active HiL, LeL were determined.

BATH ORIGINAL Ü098S0 / 1689

Drying time moisture content of the granulate,

Comparative product with 0.05? O Na (without surface-trlurnlauryl active coat) sulfate

After 0 minutes, 4.6O 4.60

After 2 minutes 4.24 2.22

After 8 minutes 3.56 0.24

After 15 minutes 3.10 0.15

The annex for the implementation of the procedure according to Invention can be constructed in any suitable manner. Drying floors or drum dryers are suitable, however, three classic v / vortex floors are preferred, which are arranged separately or combined into a single block, with the necessary auxiliary equipment, e.g. a heating battery, a blower for the fluidization, a dust collector, etc., is used.

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Claims (4)

- 7 - 592359 patent claims 1. A process for the preparation of ammonium nitrate granules by spray-drying and additional drying of the resulting at the bottom of the spray tower granules, characterized in that one of an aqueous ammonium nitrate solution of 97 * 5 wt.% Or less, preferably starting and less than 95 wt.%, The generated Granulate subjected to the following selective heat treatments: a) Slow heating in at least 1 minute to the actual drying temperature. b) Drying with a constant course, by which the temperature of the granulate to 45 - 70 ⁰ C, in particular "which is brought to 55 C. by which the temperature of the granules is brought to about 100 ⁰ C 8o- c) Slow diffusion. 2. The method according to claim 1, characterized in that the heat treatment is carried out in fluidized beds will. 3. The method according to claim 1 and 2, characterized in that that the aqueous ammonium nitrate solution to be sprayed contains a surface-active agent. 4. The method according to claim 1 to 5 *, characterized in that that the ammonium nitrate solution to reduce the nitrogen content of the granulate a filler, such as Calcium carbonate, is added. BAD ORiG! NAL 009850/1689