GB2084557A - Production of Granular Fertilizer Materials - Google Patents

Abstract

In the production of a granular fertilizer material by granulating powdered raw material for the fertilizer in a granulator in the presence of moisture, the granulation is carried out in the presence of a granulation aid which is a material comprising one or more alkali metal or ammonium salts of long chain fatty acid and obtained by the saponification of an oxidised product of a hydrocarbon. The granulation aid which is preferably one derived from an oxidised paraffinic wax, serves to reduce the amount of fines and/or oversize product produced in the course of granulation and, thus, reduces the amount of material to be recycled through the granulator. The granulation aid is conveniently introduced into the granulator as an aqueous solution or emulsion thereof.

Description

SPECIFICATION Production of Granular Fertilizer Materials This invention is concerned with improvements in and relating to the production of granular fertilizer materials.

Granular fertilizers are commonly produced from powdered raw material therefor by introducing the powdered raw material together with steam and/or water into a granulator wherein the raw material is converted, by rotary action, into granules, i.e. agglomerates of the powdered raw material. One commonly employed form of granulator comprises an elongate drum inclined at a small angle to the horizontal and provided with internal flights or lifters, the raw material being fed to the upper end of the drum and the desired granulate being recovered from the lower end of the drum, granulation being effected by rotation of the drum about its longitudinal axis. In the following description reference will be made to this form of granulator but it is to be understood that other forms of granulation apparatus, for example dish or pan granulators, may also be employed.

Ideally, granulation would be carried out so that all of the granulate had a particle size within the desired limits (e.g. 1 to 4 mm) but, in practice, this ideal solution is rarely if ever achieved and, consequently, it is necessary to screen the granulate, generally after drying and cooling, to separate the granulate into three streams, namely oversized material, material within the desired particle size range, and undersized material (fines).

Conventionally, the oversize material is crushed and recycled together with the fines through the granulator.

As will be appreciated, it would be desirable to reduce the amount of material (crushed oversize and fines) recycled through the granulator for a number of reasons. Thus, for example, reduction in the amount of recycled material would make it possible to produce a given tonnage per hour of granular fertilizer using a small granulator (which is generally a costly item of capital equipment) or conversely to produce a larger throughput of fertilizer for a given granulator. Further, since the consumption of steam per unit weight of finished product would be reduced there would be less water to be removed in the drying stage and hence less energy required for the production of a given amount of finished product. In addition the reduction (and possibly elimination) of the recycled fines material would reduce mechanical problems and hence labour requirements.

It has now been found, in accordance with the present invention, that improved granulation of fertilizer materials, leading to a granulate having a higher content of granules of the desired size, may be acheived by carrying out the granulation in the presence of a small amount of certain materials comprising one or more alkali metal soaps of long chain fatty acids.

According to the invention, therefore,there is provided a process for the production of a granular fertilizer material by granulating powdered raw material for the fertilizer material in a granulator in the presence of moisture in which the granulation is carried out in the presence of a material comprising one or more alkali metal or ammonium soaps of long chain fatty acids, e.g.

acids containing from 10 to 40 carbon atoms, obtained bythe saponification of an oxidised product of a hydrocarbon, especially a petroleum derived hydrocarbon.

The granulation process of the invention will be generally carried out as a continuous process in which there are continuously fed to the granulator (i) powdered fertilizer raw materials (ii) the material comprising one or more alkali metal soaps of long chain fatty acids, and (iii) moisture.

The material comprising the fatty acid soaps is most conveniently supplied to the granulator as an aqueous solution, emulsion or dispersion and this may serve to supply all or a part of the moisture introduced into the granulator and thus, for example, the total moisture introduced into the granulator may comprise the water of the aqueous solution or emulsion together with steam separately supplied to the granulator or injected together with the aqueous solution, emulsion or dispersion.

An essential feature of the present invention is the use, as a granulation assistant, of a material comprising one or more alkali metal soaps of long chain fatty acids and obtained by the saponification of an oxidised hydrocarbon such as an oxidised oil or wax. This material suitably contains at least 10% by weight, preferably at least 25% by weight of alkali metal soaps of long chain fatty acids and may indeed consist substantially of such alkali metal soaps. However the material can comprise other long chain aliphatic components such as, for example, paraffins, unsaponified long chain fatty acids and lactones and esters thereof, provided that the material contains sufficient fatty acid soap to form a stable emulsion with water.

A particularly preferred form of material containing alkali metal soaps of long chain fatty acids is a saponified product of an oxidized paraffinic wax. Oxidized paraffinic waxes are wellknown materials. They are commonly prepared by the air oxidation of a paraffinic wax by blowing air through a melt of the wax, e.g. at a temperature of from 100 to 2000C, in the presence of an oxidation catalyst, for example a manganses/potassium catalyst such as potassium permanganate or a mixture of an oil-soluble manganese salt (e.g. manganese stearate or manganese naphthenate) with an oil-soluble salt of potassium (e.g. potassium stearate or potassium naphthenate) or a potassium compound (e.g. potassium hydroxide or potassium carbonate) capable of reacting with fatty acids produced during the oxidation.The starting paraffinic wax may be a so-called "microcrystalline" wax (in which it is believed that the long chain paraffins are largely in the iso form) or a paraffinic scale wax (in which it is believed that the long chain paraffins are largely straight chain paraffins). The products (oxidate acids) themselves are complex mixtures containing unreacted starting material and oxidized products such as acids, lactones and esters. The degree of oxidation of an oxidized paraffinic wax is commonly indicated by its acid number (the number of milligrammes of potassium hydroxide to neutralise a one gram sample of the oxidate) and for use in the present invention, the oxidized wax suitably has an acid number of from 25 to 100, preferably from 30 to 75, most preferably from 35 to 50.

In accordance with the present invention, the oxidized paraffin wax is employed in saponified form that is, it is converted to an alkali metal (e.g.

sodium or potassium, especially the former) or ammonium soap thereof, for example by reaction with an appropriate alkali metal or ammonium hydroxide or carbonate. The saponification may be carried out by direct reaction of the saponifying agent (i.e. hydroxide or carbonate) with the molten oxidate (e.g. at a temperature of from 90 to 1 500C) or by reaction of the oxidate with an aqueous solution of the saponifying agent (e.g. at a temperature of from 70 to 1 200C). the alkali metal saponified products are water-soluble or water-dispersibl, i.e. can be formed into stable aqueous emulsions or suspensions, suitably having, for example, a solids content of from 30 to 80% by weight preferably from 30 to 50% by weight and these latter are preferred for use in accordance with the invention.

As noted above, the granulation process of the invention, is carried out using a small amount of granulation assistant (material comprising soaps of long chain fatty acids) and, thus, the amount of granulation assistant employed will generally be less than 2% by weight suitably from 0.25 to 1.5% by weight, preferably from 0.3 to 1% by weight, based on the weight of fertilizer raw materials introduced into the granulator. The granulation process of the invention may be carried out to produce a wide variety of granular fertilizers materials using conventional nitrogenproviding and/or phosphorus-providing and/or potassium-providing constituents such as urea, basic slag, ammonium sulphate, ammonium nitrate, potassium nitrate, ammonium phosphate, calcium phosphate and potassium chloride.The raw materials for the desired fertilizer in powdered form, (e.g. having a particle size of from 1 to 4 mesh) are blended in the appropriate ratios and then granulated in accordance with the invention.

As is conventional, the granulate from the granulator will generally be dried by passing it through a suitable drier (such as a rotary drum or fluidized bed drier) to an appropriate moisture content, e.g. 2.5% or less. After drying the dried granulate will then generally be cooled, for example in a rotary drum cooler, and then screened to remove oversize and fines products which are then recycled, asdescribed above, through the granulator.

As noted above, the use of the granulation assistant of the invention has been found to markedly reduce the amount of material which has to be recycled with concomitant advantages as described above. In particular, it has been noted that the use of the granulation assistant in accordance with the invention markedly reduces the amount of fines in the granulate from the granulator thereby markedly reducing the dust level in and around the granulator and subsequent processing apparatus, i.e. drier, cooler and screens.Further it has been noted that when carrying out a granulation in accordance with the invention, the amount of steam required to assist the granulation is reduced and the moisture content of the final product from the drier may also be reduced as compared with a similar process carried out in the absence of the granulation assistant of the invention. (It is believed that a similar beneficial effect may be obtained from the use of the granulation and in other applications, e.g. in the manufacture of particulate insecticides).

It has also been noted that the final product from the granulation process of the invention has a reduced tendency to cake on storage.

Accordingly it may not be necessary to treat a granular product obtained in accordance with the invention with anticaking agents such as clays or fatty amines but, of course, if desired, such treatment may be carried out.

In order that the invention may be well understood the following example is given by way of illustration only.

Example (a) An emulsion of a sodium salt of an oxidised paraffinic wax product having the properties listed below was prepared as described below.

Properties of oxidised paraffinic wax.

(Hypax 450 L manufactured by applicants) Drop melting point 550C Acid No. (mg KOH/gm) 45-55 Saponification value (mg KOH/gm) 110-120 Viscosity at 98.90C 34 43 centistokes 400 Parts by weight of the molten oxidate (8000) were mixed with 400 parts by weight of hot water (800 C). 30.8 Parts by weight of a 50% aqueous sodium hydroxide solution were added to the resultant mixture of the whole mass was stirred for 1 hour at 800C. 169.14 Parts by weight of hot water (800 0) were then added to the stirred reaction mixture and the whole was then mixed for one hour at 800C to give an emulsion of the sodium hydroxide saponified product of the oxidate. This product will hereinafter simply be referred to as the "sodium soap emulsion".

(b) The effectiveness of the sodium soap emulsion produced as described in (a) above was tested on a full scale fertilizer granulation plant as follows.

The granulation plant was a conventional plant comprising a rotary granulator, a rotary drier, screens for sieving the material from the drier, and means for recycling crushed oversize and fines through the granulator.

A mixed N:P:K fertilizer (N:P:K=8:20:16) was produced from urea, potassium chloride, monoammonium phosphate and diammonium phosphate using steam as granulation aid.

In the first stage of the test the plant was allowed to reach steady state conditions under conventional operating conditions (i.e. without the addition of the sodium soap emulsion). At steady state, yaw material was fed to the granulation at a rate of 20 tons/hour and the recycle ratio was 1:1. In order to achieve this it was necessary to introduce steam into the granulator at a rate such that the temperature in the granulator was 1 870F (86.1 OC) and the moisture content of the produce from the drier was 2.259%.

The sodium soap emulsion was then injected into the granulator at a rate of 1.5% by weight based on the total throughput of material through the granulator. Granulation was then effected for some time, with appropriate control of the steam input, until a steady state was again achieved (after about 4 hours). In bringing the granulation to a steady state whilst introducing sodium soap emulsion it was found that the amount of steam introduced into the bed could be reduced and at the final steady state steam had only to be introduced at a rate such as to provide a granulation temperature of 1280F (53.30C) so that there was a marked reduction in steam requirement with the result that the moisture content of the product from the drier fell to 1.5% by weight. Further, the recycle ratio was reduced by 10% indicating improved granulation.

Claims (6)

Claims

1. A process for the production of a granular fertilizer material by granulating powdered raw material for the fertilizer in a granulator in the presence of moisture in which the granulation is carried out in the presence of a material comprising one or more alkali metal or ammonium soaps of long chain fatty acids obtained by the saponification of an oxidised product of a hydrocarbon.

2. A process as claimed in claim 1 in which the said oxidised product is an oxidised paraffinic wax.

3. A process as claimed in claim 2 in which the oxidized wax has an acid number of from 25 to 100.

4. A process as claimed in any one of the preceding claims in which the said alkali metal or ammonium salt containing material is introduced into the granulator in the form of an aqueous solution or emulsion thereof.

5. A process as claimed in any one of the preceding claims in which the said alkali metal or ammonium soap-containing material is employed in an amount of less than 2% by weight, based on the weight of the fertilizer raw materials introduced into the granulator.

6. A process as claimed in claim 1 substantially as hereinbefore described with reference to the examples.