NO760975L - - Google Patents

Description

Method for the production of

fertilizers with delayed

nutrient release.

The invention relates to an improvement of the process for converting granulated single- and multi-nutrient fertilizers by enveloping the grains in the fertilizer with delayed nutrient release by means of a pre-treatment method. connections.

One method for the production of fertilizers with delayed nutrient release is to coat the corresponding granules with inert agents that are not or poorly soluble in water in quantities that are sufficient to effectively coat the grain surface. The granules from which one must exit,

however, usually have a relatively large specific surface area, because so-called hardening phenomena occur during cooling, whereby cracks and indentations can be produced in the surface of the particles, so that the specific surface area of such granules is greater than that of spherical particles.

In the case of the usual technical granules, due to these phenomena, the consumption of casing material is significantly greater than what would be expected for the aforementioned ideal conditions.

It has now been found that a significant saving in casing material can be achieved when the fertilizer granules serving as starting material are first subjected to a build-up granulation and then the products produced in this way are treated with a water-soluble material in a sleeve-forming manner.

The granulate is thus primarily heated to temperatures where, with the mixtures used, it sets'

optimum post-granulation conditions and then supplies the granulate to the build-up granulator, simultaneously introducing high-

concentrated solutions or melts of fertiliser.1 salts such as urea, ammonium phosphates, ammonium sulphate, potassium salts or mixtures of these compounds with each other at temperatures where these media have a good fluidity and allow it to granulate together' and subject 'the granules thus formed, possibly after one or more dryings, for enveloping with the inert agent.

For such operations, granulates of the most diverse fertilizers of one or more predominantly water-soluble components, e.g. urea, ammonium sulphate, NO, NK, PK or NPK fertilisers.

These fertilizers can be formed according to usual methods, e.g. by crystallisation, granulation, breaking or by pressing and coating processes, by atomisation or preferably by prilling.

Before the build-up granulations according to the invention, these granules are heated to temperatures, which are also otherwise set when granulating these substances. The optimum granulation temperature varies with the different types of fertiliser. It depends on the each time present resp. set humidity of the granulation material and of the components present therein. The determination of the optimum granulation temperature or the preheating temperature of the granulate is not the subject of the invention.

The preheated granulate is then sprayed into the build-up granulator with the above-mentioned hot solutions or melts. With this method of working, a rough grain surface* is obtained, which comes very close to the spherical surface.

The usual devices can be used as build-up granulators. The build-up granulation can be carried out particularly advantageously in fluidized bed devices. The special advantage of these fluidized bed apparatuses is that you can use these devices not only for granulation, but also, depending on the mode of operation, for drying or for subsequent wrapping. Thereby, one can either work in batches with periodic time-varying of the two treatment techniques or continuously, transporting the substance to be treated one after the other through regions of the corresponding treatment techniques.

The fertilizer solution or melt to be sprayed is then used which matches the component or components of the main fertiliser, or comes as close as possible. Of course, other fertilizer solutions are also possible for certain effects. Optionally, trace fertilizer additives can also be added in this way to the fertilizer solutions or melts used for build-up granulation. The quantity ratios between the fertilizing solution

which is to be sprayed on and the original granules appear from the ■ grain size of the starting material and the desired grain size of the finished product (compare the discussion of the results under examples 1 and 2).

With this method of treatment, a build-up granulation takes place, as the cracks and hollowings are fulfilled. The method according to the invention thus reduces the specific surface of the granules and improves the binding and adhesive ability of the wrapping material so that it is possible to limit the amount required for optimal wrapping. In addition, an under-powdering with finely divided substances before applying the coating can be disregarded. Thereby, the manufacturing costs of the enveloped fertilizer are lowered both by saving this procedural step and also by saving the otherwise necessary sub-powdering agent.

With a sufficiently long stay in the granulation zone, the grain size of the individual grains also balances out. During the build-up granulation according to the invention, a grain collective with. narrowly limited grain size range.

As inert material for encasing those pre-treated in this way. Granules are only such water-insoluble agents which, if used in sufficient quantities, have a sleeve-forming effect. An effective sleeve around the surface of the particles only exists when the release of the enclosed nutrients is delayed to an appropriate extent.

The degree of delay is preferably considered to be the N leaching sample or the part of dissolved nitrogen under standardized conditions of the total nitrogen present. Depending on the type of fertilizer desired, one strives for a leaching part of 70 - 1%, preferably of 30 - 3% • The leaching rate decreases with an increasing amount of coating agent. If the amount of encapsulating agent is kept constant, the degree of leaching decreases with increasing mean grain diameter or with decreasing specific surface area of the particles. It depends on the type and method of application of the encapsulant and further, as is apparent from the invention, on the pre-treatment of the granules.

The optimal amount of encapsulant for a desired degree of leaching of a fertiliser, when determining the other working conditions, can easily be determined by professionals in small trial batches.

As an agent, which provides effective sleeves around the grains. of a fertiliser, we are talking about water-insoluble plastics and/or waxes, e.g. lead vinyl chloride-vinylidene chloride dispersions, waxy polyethylenes with or without additives or copolymers of ethylene with - Cg - a - olefins, as well as 'preferably molten sulphur, optionally with the addition of wax.

With powdered substances, such as e.g. As you know, with sulphur-blossom you cannot achieve sleeves with a sufficient delay in nutrient release.

The pre-products formed by build-up granulation, possibly post-dried, already have improved storage properties with regard to baking tendency and grain strength.

However, the storage properties are unexpectedly good

the wrapped products.

The advantages of the method can be seen from the experiments described below.

Example 1.-

Commercially heated to 80 - 90°C urea prills are sprayed into a fluidized bed apparatus with a 90% aqueous urea melt on it. 115 - 120°C in weight ratio 1:1 (calculated anhydrous) with the help of 150 - 160°C hot. atomizing air.

Samples of the thus constructed prills as well as samples. of the commercially available prills are enveloped in a fluid layer with each 25% and 30% molten sulfur of approx. 150°C, the percentages in this case referring to the final product and subjected to an N leaching test.

Thereby, 20 g of the enveloped fertilizers are poured over with 100 ml of water. During the course of 20 hours, the water is kept in motion at room temperature. From the results of a nitrogen determination in an aliquot of the solution, the quantity of the plant nutrient used is then calculated. in resolution.

Example 2.

While maintaining the other conditions, experiment 1 is repeated, however a (referred to freedom of water) weight ratio of 1:3 between urea f-prills and 'urea melt' is observed and the build-up granulated products are equipped with sulfur sleeves of 20, 25 resp. 30 parts by weight per 80, 75 resp. 70 parts by weight building granules.

The two test results are listed in the table.

From the experimental results it can be concluded:

1. During build-up granulation, the center of gravity of the grain spectrum is shifted towards coarser grains. Thus, more than 9J>% of the granulate is observed during build-up granulation per part by weight ..urea-prill, 2. With an increasing amount of build-up melt, the degree of leaching decreases with constant consumption of the enveloping agent, ■ for example, at 25% sulfur and 0 parts by weight melt per weight part prill approx. 73.5% leaching,

at 25% sulfur and 1 part by weight melt per weight part prill approx. 30% leaching, at 25% sulfur and 3 parts by weight 'melted per weight part prill approx. 12% leaching.

An analogous relationship is seen between the center of gravity of the grain size range of any aggregates and the degree of leaching at a constant sulfur content.

3. When comparing trial series 2 with each other with trial series 1, approximately

that for setting a leaching rate of approx. 17% at a 1:1 prill-melt-to-cladding weight ratio requires 30% molten sulphur,

while at a 1:3 prill-melt weight ratio only approx. 20% molten sulphur.

With a suitable choice of pretreatment, you can therefore

save considerable amounts of sulphur.

By saving sulfur in the fertilizer mixture, however, it is also possible to increase the overall sum of main nutrients in the product to be produced.

Claims (6)

1. Process for the production of fertilizers with reduced nutrient release by encasing fertilizer granules, the components of which are predominantly water-soluble with a water-insoluble material, characterized by subjecting them. fertilizer granules serving as starting material primarily for a build-up granulation and then treating the thus produced products with a water-insoluble material in a sleeve-forming manner. 2. Method according to claim 1, characterized in that granules of fertilizers such as urea, ammonium sulphate, NP, NK, PK or NPK are used as starting material. 3- Method according to claims 1 and 2, characterized in that highly concentrated solutions or melts of fertilizer salts are used for build-up granulation. preferably urea melts. 4. Method according to claims 1 to 35, characterized in that the build-up granulation is carried out in a known manner in granulation drums or plates, or preferably in fluidized bed devices. 5. Method according to claims l to h, characterized in that one wraps the build-up granulate on. known method uses molten sulphur, possibly with the addition of wax. 6. Method according to claims 1 to 4, k. a r a, k - t e r i , s e ' r t v e d ' that water-insoluble plastics with a sleeve are used to enclose the build-up granules forming properties. 7- Fertilizer with delayed nutrient release produced according to claim 1 and/or one or more of claims 2 to 6.