FI61680B - FOERFARANDE FOER FRAMSTAELLNING AV GOEDSELMEDEL MED FOERDROEJD AVGIVNING AV NAERINGSAEMNEN - Google Patents

Description

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(44) Date and date of issue. -

Patent · och regicterstyrelsen Araekw utitgd och uti ^ kriftwi pubiictrad 31.03.82 (32) (33) (31) Pyyd · ”/« tuolkeu * —Begird priorlut 21.03.75

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 2512386.8 (71) Veba-Chemie Aktiengesellschaft, Gelsenkirchen-Scholven, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Hans Heumann, Herne, Heinrich Hahn, Buerenk, Gels Herne, Heinz Liebing, Herne, Manfred Schweppe, Herne, Federal Republic of Germany-Förbundsrepubliken Tyskaland (DE) (7 * 0 Oy Kolster Ab (5 * 0 Method for the production of fertilizers with delayed nutrient delivery

The invention relates to a process for the preparation of slow-release nutrient fertilizers by coating fertilizer granules, the components of which are predominantly water-soluble, with a water-insoluble substance. In this method, granulated mono- and multi-nutrient fertilizers are converted by coating into fertilizer granules that slowly release nutrients.

This treatment is particularly suitable for those fertilizers which are water-soluble.

One method of preparing fertilizer delivery products with delayed nutrient delivery is to coat the corresponding granules with water-insoluble or poorly soluble inert substances used in an amount sufficient to effectively coat the surface of the granule. However, the starting granules usually have a relatively high specific surface area, because during cooling the so-called melting phenomena, resulting in cracks and bumps in the surface of the particles, so that the specific surface area of such granules is larger than that of ball-shaped particles.

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As a result of these phenomena, the consumption of the coating material in ordinary technical granules is substantially higher than would have been expected under the said ideal conditions.

It has now been found that a considerable saving of coating material is obtained by first passing the starting fertilizer granules with highly concentrated solutions or melts of water-soluble fertilizer salts to structural granulation, after which the products obtained are treated in a coating-like manner with a water-insoluble substance.

The granulate is thus first heated to a temperature at which the post-granulation properties of the mixture used are optimal, after which it is fed to a structural granulator to which simultaneously concentrated highly concentrated solutions or melts of fertilizer salts, such as urea, ammonium phosphates, and they are allowed to granulate together, and the granulate thus obtained is optionally, after one or more drying, subjected to a treatment in which it is coated with an inert substance.

Such a treatment is suitable for granules of a wide variety of fertilizers consisting of one or more, mainly water-soluble components, such as urea, ammonium sulphate, NP, NK, PK or NPK fertilizers.

These fertilizers can be prepared by conventional methods, e.g. by crystallization, crushing, impregnation or by pressing or granulating, killing or, preferably, spraying into granules.

Prior to the structural granulation according to the invention, these granules are heated to temperatures which are also otherwise used in the granulation of these substances. The optimal granulation temperature varies with different types of fertilizer. It depends on the prevailing or controlled humidity of the granulating substance and the components present in it. It is not an object of the invention to determine the optimal granulation temperature or the preheating temperature of the granulate.

The preheated granulate is sprayed in a structural granulator with the above-mentioned hot solutions or melts. This procedure achieves a rough grain surface that is approximately spherical.

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Ordinary equipment can be used as structural granulators. Particularly advantageously, the structural granulation can be carried out in vortex bed devices. A particular advantage of these vortex layer devices is that they can be used not only for granulation but also - depending on the driving style - for drying or also for final coating. In this case, it is possible to work in batches by changing these three treatment steps periodically, or continuously, in which case the substance to be treated is transported successively through the areas of the respective treatment steps.

The fertilizer solution or melt to be sprayed is preferably selected to be compatible with or as close as possible to the constituents of the main fertilizer. However, it is self-evident that other fertilizer solutions are also possible for certain effects. In some cases, residual fertilizers can also be added to the fertilizer solutions or melts used for structural granulation in this way.

The ratio of the amounts of fertilizer solution to be sprayed and the initial granulate is obtained from the grain size of the starting granulate and the desired grain size of the finished product (compare the description of the results of Examples 1 and 2 below).

The process according to the invention achieves structural granulation in which cracks and molten points are filled. The method according to the invention thus reduces the specific surface area of the granulate, and improves the bonding and adhesion of the coating materials, so that it is possible to limit the amount required for their optimal coating. In addition, the process according to the invention avoids powdering with the finest substances, which generally has to be carried out before coating. The manufacturing costs of the fertilizer thus coated are reduced by saving both this work step and the pre-powdering agents required therein.

With a sufficiently long treatment in the granulation zone, the grain sizes of the individual granules are also smoothed. The structural granulation according to the invention gives fertilizer granules with a very uniform grain size, which can be considered as an additional advantage.

As the inert substance in this way, only those water-insoluble substances which, when used in sufficient amounts in each case, act to form the coating are suitable for coating the pretreatment granulate. An effective coating on the surface of the particles only exists when the release of the entrapped nutrients is slowed down as calculated.

The measure of delayed nutrient delivery is preferably the N-wash test, i.e. the portion of nitrogen that is soluble in the total amount of nitrogen under standard conditions (see Example 1). Depending on the type of fertilizer desired in each case, the amount to be washed out is 70 to 1%, preferably 30 to 3%. The amount washed out decreases as the amounts of coating material increase. When the amount of coating material is kept constant, the amount to be washed out decreases as the average grain diameter increases, i.e., as the specific surface area of the particles decreases. This depends on the quality and method of application of the coating material, and further - as the invention shows - on the pretreatment of the granulate.

The optimum amount of coating required for a fertilizer with the desired degree of washout can be easily determined for each person skilled in the art in a simple manner by selecting a few test portions after selection of other treatment conditions (cf. also experiments 1 and 2).

Suitable substances for effective coating of fertilizer granules are water-insoluble plastics and / or waxes, for example polyvinyl chloride-vinylidene chloride dispersions, waxy polyethylenes with C3 to C8-4 olefins and additions or copolymers of ethylenes containing them, possibly wax has been added.

Substances in powder form, such as sulfur flower, cannot, as is known, be coated with a sufficient effect of slowing down nutrient delivery.

In addition, structurally granulated preforms, possibly post-dried, have improved storage properties in terms of caking tendency and grain strength,

However, the storage properties of coated products are unexpectedly good.

The advantages of the method are shown in the following dried experiments.

Example 1

Generally available commercial urea granules heated to 80-90 ° C are sprayed in a vortex bed with a 90% aqueous urea melt at 115-120 ° C in a weight ratio of 1: 1 (calculated on dry weights) using spray air at 150-160 ° C.

5 61 680 Samples The granules thus obtained, as well as the commercial granules, are coated in a vortex layer, one sample to 25% and the other to 30% with molten sulfur (150 ° C) and the percentages for the N-wash test apply to the final product.

In this case, 20 g of coated fertilizer are poured with 100 ml of water. The water is kept in motion for 20 hours at room temperature. From the results of the nitrogen determination from the composition of the solution, the proportion of plant nutrient entrained in the solution can then be calculated.

Example 2

While maintaining the other conditions, experiment 1 is repeated, however, the weight ratio (based on dry weights) is taken to be 1: 3 between the urea granules and the urea melt, and the granulated products are provided with 20, 25 or 30 parts by weight of sulfur coating per 80, 75 or 70 parts by weight of structural granules.

The test results for both experiments are tabulated.

Table

Experimental results of Examples 1 and 2 Example 1 + 2 1 2 parts by weight of urea melt for each part by weight of urea structures 013

Grain size distribution% <1.0 mm 0.1 1.0 - 1.6 mm 27.8 1.8 1.6 - 2.0 mm 66.9 50.5 1.7 2.0 - 2.5 mm 5.0 46 , 1 23.2 2.5 - 3.15 mm 0.2 1.6 70.7> 3.15 mm - - 4.4 N washing test with water% of total nitrogen, dissolved in 20 hours when 20% sulfur has been used for coating 81-84 - 17-24 25% sulfur 67-80 30 10-14 30% sulfur 52-59 17 5-7 (calculated on the final product).

Based on the experimental results, the following can be stated: 6 61 680 1. With structural granulation, the center of gravity of the grain spectrum shifts in the direction of a coarser grain. Thus, in structural granulation where there is a certain amount of urea melt for each part by weight of urea granules, more than 93% of the account has a grain size as follows:

Part by weight of urea melt Grain size range 0 1.0 - 2 f0 mm 1 1, 6 - 2.5 mm 3 2.0 - 3.15 mm 2. As the amount of building melt increases, the amount of washable part decreases when the consumption of coating material remains constant, for example when using 25 % sulfur and 0 parts by weight of melt for each part by weight of granules has a wash removal of about 73.5%, using 25% sulfur and 1 part by weight of melt for each part by weight of granules has a wash removal of about 30%, and using 25% sulfur and 3 parts by weight of melt for each part by weight of granules have a wash removal of about 12%.

An analogous relationship can be taken into account between the center of gravity of the respective equipment and the washable amounts, while the sulfur content remains constant.

3. A comparison of test set 2 and test set 1 approximates that to adjust the washable amount to about 17% sulfur, 30% molten sulfur is required to coat the granules when the weight ratio of granules to melt is 1: 1, while a weight ratio of granules to melt of 1: 3 requires only about 20% fused sulfur.

With the appropriate choice of pretreatment, large amounts of sulfur can also be saved.

By saving sulfur in the fertilizer mixture, it becomes possible to use more main nutrients in the product to be manufactured.

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Claims (6)

61 680 7 A process for preparing slow-release nutrient fertilizers by coating fertilizer granules whose constituents are predominantly water-soluble with a water-insoluble substance, characterized in that the starting fertilizer granules are first with an insoluble substance. Process according to Claim 1, characterized in that fertilizer granules which are urea, ammonium sulphate, NP, NK, PK or NPK granules and are used as starting material. Process according to Claim 1 or 2, characterized in that a urea melt is used for the structural granulation. Method according to one of Claims 1 to 3, characterized in that the structural granulation is carried out in a known manner in granulation drums or discs or, preferably, in vortex bed devices. Method according to one of Claims 1 to 4, characterized in that the structural granules are coated in a known manner with molten sulfur and, optionally, finally with wax. Method according to one of Claims 1 to 4, characterized in that the structural granulate is treated with water-insoluble plastics which have coating-forming properties. '' V K 'r