CA2448820C - Abrasion resistant, tropicalised potash fertiliser granulate, method of its production and device for carrying out the method - Google Patents
Abrasion resistant, tropicalised potash fertiliser granulate, method of its production and device for carrying out the method Download PDFInfo
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- C05—FERTILISERS; MANUFACTURE THEREOF
- C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
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Abstract
This invention relates to an improved potash fertiliser granulate with reduced moisture absorption capacity and increased strength (reduced susceptibility to abrasion). This product is free of oxidic additives and can be produced by a simple and economical method.
Description
Abrasion resistant, tropicalised potash fertiliser granulate, method of its production and device for carrying out the method Description This invention relates to an abrasion resistant, tropicalised potash fertiliser granulate, a method of its production and a device for carrying out the method.
Brief description of the state of the art Potash fertiliser granulates are used throughout the world and are valuable substances which are employed as nutrients in agriculture. Problems which occur again and again with this type of fertiliser granulate are on one hand the low mechanical strength of the granulates which leads to the unwanted formation of fine-grained dusts and the low resistance to moisture or the high moisture absorption of normal fertiliser granulates, which leads both to increases in weight and to impairment of the product integrity, which can cause problems particularly with the use of fertiliser granulates.
To overcome these problems, various methods are known in the state of the art.
Potash fertiliser granulates are normally pressed by compacting fine-grained salts on roller presses to form so-called scabs with a thickness of about 5 to 12 mm. Then the flat scabs are further processed in a crushing and classifying process. The coarse-grained crushing product in the range of grain size from about 1 to 5 mm represents the required finished product (granulate) and the undersized particles are fed back into the granulating process (compaction followed by crushing) (Ulimanns Enzyklopadie der technischen Chemie (Ullmann's Encyclopaedia of technical chemistry), 4th edition, Vol.
13, page 471).
Brief description of the state of the art Potash fertiliser granulates are used throughout the world and are valuable substances which are employed as nutrients in agriculture. Problems which occur again and again with this type of fertiliser granulate are on one hand the low mechanical strength of the granulates which leads to the unwanted formation of fine-grained dusts and the low resistance to moisture or the high moisture absorption of normal fertiliser granulates, which leads both to increases in weight and to impairment of the product integrity, which can cause problems particularly with the use of fertiliser granulates.
To overcome these problems, various methods are known in the state of the art.
Potash fertiliser granulates are normally pressed by compacting fine-grained salts on roller presses to form so-called scabs with a thickness of about 5 to 12 mm. Then the flat scabs are further processed in a crushing and classifying process. The coarse-grained crushing product in the range of grain size from about 1 to 5 mm represents the required finished product (granulate) and the undersized particles are fed back into the granulating process (compaction followed by crushing) (Ulimanns Enzyklopadie der technischen Chemie (Ullmann's Encyclopaedia of technical chemistry), 4th edition, Vol.
13, page 471).
2 This sort of granulate consists of edged to tapered grains with a surface which is comparatively rough due to the crushing process. With loading and unloading and transport stages it is inevitable with this type of granulate that there will be abrasion due to mechanical stressing, leading to the formation of unwanted undersized particles (fine dusts). On further processing or with the application of the granulates, these materials lead to the release of dust, which is undesirable with regard to industrial safety and product efficiency.
Furthermore, potash fertilisers can be basically classified as hygroscopic.
They absorb moisture from the air, which however at temperate latitudes, affects the strength and storage capabilities of the granulates in manageable orders of magnitude. But in zones with tropical climates with relatively high air humidity, a significantly higher water absorption of the granulates occurs, leading to lowering of the grain strength, increase of the fine-grained proportion and to hardening of the product during storage.
With regard to the problems described above, there are rework methods for potash fertiliser granulates. For example, for the reduction of the formation of fine grains due to mechanical abrasion and the breakdown and hardening of the granules due to moisture absorption, there is the suggestion in DE-OS-1 36 956 for minimising the abrasion involving a combined application of the process steps of dust extraction in a fluidised bed and wetting the granulate surface with water. With this combination of process steps the objective is an improvement in the abrasion properties of the granulates and to facilitate the production of non-dusty potash fertilisers. The quoted dust extraction in the fluidised bed occurs at air speeds of 1 to 4 m/s. The water added to the granulate heated to 400 to 80 C amounts to 0.5 to 2% weight referred to the total mass, preferably 1% weight. Drying of the granulate then takes place with a residual moisture content of 0.1 to 0.2% weight by exploiting the thermal content of the granulate or by introducing preheated air currents. The granulates with this residual moisture content are cooled to room temperature and then processed further, for example, packaged. Also, addition of
Furthermore, potash fertilisers can be basically classified as hygroscopic.
They absorb moisture from the air, which however at temperate latitudes, affects the strength and storage capabilities of the granulates in manageable orders of magnitude. But in zones with tropical climates with relatively high air humidity, a significantly higher water absorption of the granulates occurs, leading to lowering of the grain strength, increase of the fine-grained proportion and to hardening of the product during storage.
With regard to the problems described above, there are rework methods for potash fertiliser granulates. For example, for the reduction of the formation of fine grains due to mechanical abrasion and the breakdown and hardening of the granules due to moisture absorption, there is the suggestion in DE-OS-1 36 956 for minimising the abrasion involving a combined application of the process steps of dust extraction in a fluidised bed and wetting the granulate surface with water. With this combination of process steps the objective is an improvement in the abrasion properties of the granulates and to facilitate the production of non-dusty potash fertilisers. The quoted dust extraction in the fluidised bed occurs at air speeds of 1 to 4 m/s. The water added to the granulate heated to 400 to 80 C amounts to 0.5 to 2% weight referred to the total mass, preferably 1% weight. Drying of the granulate then takes place with a residual moisture content of 0.1 to 0.2% weight by exploiting the thermal content of the granulate or by introducing preheated air currents. The granulates with this residual moisture content are cooled to room temperature and then processed further, for example, packaged. Also, addition of
3 organic substances after cooling is possible, preferably mineral oil in amounts of 0.2 to 1 g/kg of granulate, whereby evaporation of the residual water is delayed and additional binding of dust is ensured during application later.
DE-OS-210 650 explains as a supplement to the above quoted German disclosure document that to achieve an optimum gain in strength, the potash fertiliser granulates are brought to a temperature of preferably 800 to 100 C in a mixer before being wetted with water. Furthermore, a minimum dwell period of 10 s in an atmosphere of high moisture content should be maintained.
Although the methods outlined above are, where applicable, able to rectify strength problems of the potash fertiliser granulates, the problem of moisture absorption during transport or loading and unloading processes and during periods of storage is not solved by such methods.
The problem of the absorption of moisture is however addressed in EP-A-1048634.
Here it is disclosed that an increase in the strength of the granulate and a reduction in the moisture absorption of the granulate can be achieved if 0.1 to 2% weight of an additive is added to the fine salt of potash fertiliser used for granulation before the compacting process. This additive, which is preferably added in a quantity of 1 to 1.5%
weight, is preferably dry magnesium oxide or dry calcium oxide. Alternatively, burnt chalk and bumt dolomite is mentioned in the above quoted European application.
The addition of these additives, which is also described in the corresponding American application, US-A-6,379,414, results in granulates which exhibit a moisture absorption of 1.3 to 1.5% weight during storage at 20 C in 70% relative humidity after eight days. A
disadvantage to this approach however is that the added additive is also sensitive to moisture. It is therefore to be expected that with high relative moisture contents, as with the above described test conditions, hydration of the additive will occur, which is
DE-OS-210 650 explains as a supplement to the above quoted German disclosure document that to achieve an optimum gain in strength, the potash fertiliser granulates are brought to a temperature of preferably 800 to 100 C in a mixer before being wetted with water. Furthermore, a minimum dwell period of 10 s in an atmosphere of high moisture content should be maintained.
Although the methods outlined above are, where applicable, able to rectify strength problems of the potash fertiliser granulates, the problem of moisture absorption during transport or loading and unloading processes and during periods of storage is not solved by such methods.
The problem of the absorption of moisture is however addressed in EP-A-1048634.
Here it is disclosed that an increase in the strength of the granulate and a reduction in the moisture absorption of the granulate can be achieved if 0.1 to 2% weight of an additive is added to the fine salt of potash fertiliser used for granulation before the compacting process. This additive, which is preferably added in a quantity of 1 to 1.5%
weight, is preferably dry magnesium oxide or dry calcium oxide. Alternatively, burnt chalk and bumt dolomite is mentioned in the above quoted European application.
The addition of these additives, which is also described in the corresponding American application, US-A-6,379,414, results in granulates which exhibit a moisture absorption of 1.3 to 1.5% weight during storage at 20 C in 70% relative humidity after eight days. A
disadvantage to this approach however is that the added additive is also sensitive to moisture. It is therefore to be expected that with high relative moisture contents, as with the above described test conditions, hydration of the additive will occur, which is
4 associated with swelling. This sort of swelling of the granulates would however severely damage the grain structure of the granulates or lead to the breakdown of the granulates containing the additive. This sort of swelling effect is, for example, described in "Feuerfestkunde" (Refractory theory) (Harder und Kienow), Springer-Verlag 1960, and can amount up to 53% by volume. It is therefore thoroughly conceivable that the addition of the additives in fact causes precisely an opposite effect, in particular with very high relative humidity, as in tropical zones.
It is therefore the object of this invention to provide an improved potash fertiliser granulate which with high relative humidity remains capable of storage without the above quoted problems occurring. Furthermore, the improved potash fertiliser granulate should exhibit an adequate strength, so that the formation of undersized grains is largely prevented. In addition, this invention assumes the task of providing a method for the production of this sort of potash fertiliser granulate and of providing a device for carrying out the method.
Brief description of the invention In another aspect, the present invention provides a method for producing improved potash fertiliser granulates, comprising the treatment of a potash fertiliser raw granulate with a solution containing silicate or carbonate, followed by the application of kinetic energy in the form of vibrations.
In another aspect, the present invention provides a potash fertilizer granulate obtained using the method of the present invention.
In another aspect, the present invention provides a device for producing an improved potash fertiliser granulate, including an appliance for applying a solution to a raw granulate and an appliance for transferring kinetic energy in the form of vibrations to the raw granulate which has been treated with the solution.
The term potash fertiliser as used in this application includes the usual known fertilisers containing potassium, such as for example potassium nitrate, potassium chloride, potassium sulphate, potassium carbonate and the mixed salts derived from potassium, such as potassium magnesium chloride, potassium magnesium chloride sulphate, potassium magnesium sulphate, etc. Those potash fertilisers are particularly preferred which preferably contain potassium chloride or potassium sulphate and mixtures of these components as the principal constituents.
Brief description of the figures Figure 1 shows a flow chart of a normal method for producing potash fertiliser granulate.
Figure 2 shows a flow chart of a method according to the invention for the production of a potash fertiliser granulate.
Figure 3 shows preferred devices for coating the granulates. Figure 3a shows a schematic view of a vibrating fluidised bed dryer/cooler and Figure 3b shows a schematic side view of a weir, adjustable in height with removable operating appliance.
Figure 4 shows a further flow chart of a method corresponding to this invention.
Detailed description of the invention Starting from the known moisture sensitivity of potash fertiliser granulates, examinations were carried out to establish the reason for the moisture absorption of the potash fertiliser granulates. Here, it was found that the alkaline earth chlorides present in potash fertiliser granulates, which are the usual components accompanying the natural salts, influence very significantly the moisture absorption of the potash fertiliser granulates even in slight amounts. Magnesium chloride and calcium chloride have a very strong influence on the moisture absorption capacity of potash fertiliser granulates.
This influence is shown in the following table.
Content of alkaline earth chlorides Moisture absorption of the potash (MgC12+CaCI2 content) fertiliser granulate*
None (< 0.05% mass) 0.45% mass 0.1 % mass 1.40% mass 0.2% mass 2.55% mass 0.5% mass 5.60% mass *Standard conditions: 20 C, 70% RH, 8d Even a content of only 0.1 % mass of alkaline earth chloride results in a very noticeable moisture absorption of the potash fertiliser granulate.
In the following, this invention, which has been based on the above quoted findings, is described in detail. Firstly, the method according to the invention is discussed. Details, which are provided in conjunction with the method according to the invention, also apply correspondingly to the product according to the invention and the device according to the invention (equivalent in each case, where applicable) and vice versa.
According to the invention, a normal raw granulate of a potash fertiliser granulate is used. Preferably, this raw granulate includes the fraction of the grain size of 1 to 5 mm quoted at the start. This is first treated with a solution containing silicate or carbonate.
Such preferred solutions are aqueous solutions, in particular aqueous solutions containing silicate of potassium, soda, silicate of sodium or potash.
Preferred solutions contain the components containing silicate or carbonate in an amount of 5 to 25%
weight, preferabiy 10 to 20% weight and especially 14 to 20% weight. This solution is applied to the raw granulate using methods known in technology, for example by spray application or by mixing in an intensifier-type mixer. The amount of the solution to be used is preferably 1 to 2.5% weight referred to the total mass of raw granulate and applied solution, preferably 1.3 to 2.0% weight and particularly preferably 1.5 to 1.8%
weight. The treatment of the raw granulate with the solution described above leads to a transformation of the alkaline earth chlorides contained in the raw granulate to silicate compounds or compounds containing carbonate which are not hygroscopic. Due to this process stage a substantial reduction of the moisture absorption capabiiity of the raw granulate is already obtained. A surprising feature is that a positive effect can be obtained due to this type of simple wet chemical reaction, without additional additives such as magnesium oxide, calcium oxide, burnt chalk or burnt dolomite having to be added to the granulate as suggested in the European patent application mentioned above. At the same time the application of the amount of liquid leads to further binding of any included fine-grain content so that the application of the liquid as such furthermore has a positive effect on the raw granulate.
After application of the solution described above, according to the invention kinetic energy is then applied by treatment with vibration. This vibration treatment, in contrast to compaction methods which are carried out in presses with high pressures, involves relative simple equipment and leads to the required grain deformation. Due to the rather point-type energy application by the vibration method, smoothing of the surface of the granulate grains is achieved, resulting in rounding of the grains and a reduction of the specific surface area. This produces a clearly improved abrasion resistance with a simultaneous further reduction of the moisture absorption capacity.
Overall, the positive effect of the stage with treatment of the solution containing carbonate or silicate solution is again reinforced by the second stage of the method according to the invention and furthermore also the mechanical properties of the granulates are improved. Consequently, the abrasion of the granulates during transport, loading and unloading is again clearly reduced, the flow properties of the granulates under handling are improved and the tendency to hardening during storage is reduced by reducing the flat contact points.
In contrast to compaction where crystal deformation is forced due to high compression pressures on the rollers (180 to 300 bar), surprisingly in the method according to the invention, the grain deformation of the moistened granulates can be achieved by vibrations in the frequency range from 10 to 70 Hz, preferably from 15 to 30 Hz, with amplitudes from 2 to 20 mm, preferably from 2 to 10 mm and particularly preferably from 5 to 8 mm.
It has been found that the moistened granulate should be subjected to a dwell period in the vibration treatment zone of 10 to 180 s in order to ensure adequate compaction.
Longer dwell periods are basically however not detrimental, but rather only disadvantageous with regard to the economics of the method.
The adequate relatively short dwell periods open up however additional possibilities for the integration of the process step of vibration treatment into other process stages, which can lead to further simplification of the process and to a reduction in the investment and operating costs. For example, it is possible to carry out the vibration treatment in a vibration zone which is not made available specially for this purpose, but instead to position it in a feed section of a vibration-aided fluidised-bed dryer.
Taken overall, the method according to the invention comprises the two main stages of application of a solution containing carbonate or silicate and the vibration treatment for grain deformation and grain compaction as described above.
Following the process steps, essential to the invention and quoted above, the usual post-treatments can be carried out which are briefly described below.
Following the vibration treatment, drying of the moistened granulates can take place.
This drying can be carried out in normal equipment, such as for example, fluidised-bed apparatus or in vibration-aided fluidised-bed dryers. Normally the next process stage following drying is cooling, whereby the granulate at a temperature of over 100 C is cooled to about 40 C and therefore the vapour is extensively extracted.
The following treatment stage of the granulate is normally formed by a coating with organic substances, such as for example oils, amines, oil/amine mixtures and waxes, to ensure free-flowing properties and the storage capability of the granulates over still longer time periods by the partial coating of the granulate surface. The process controls and equipment needed for this are known to the skilled person. Coating is normally carried out in mixers, as shown in Figure 1 for example. Altematively, the coating can be located in a vibration-aided fluidised-bed dryer, as indicated in Figure 2.
To achieve this, a weir, as shown in Figure 3 and which is adjustable in height, is provided in the transition area of drying/cooling with an overhang strip of at least 10 cm width mounted in the application direction, under which an airless nozzle device can be installed which can also be replaced during the process. The nozzles can be individually pressure controlled depending on throughput and adjusted such that the height at about 10 to 15 cm of the granulate fluidised bed is not penetrated. Depending on the consistency of the coating agent, melting on may be necessary, e.g. with waxes or tempering with oil/amine mixtures.
If a coating is provided in the method according to the invention, then this coating takes place using the usual organic substances, whereby, for example, palmitin or stearin waxes are preferred. Normally, fatty amines with a chain length of 16 to 18 C
atoms, mineral oils, fatty acids (e.g. palmitin acid) or waxes (e.g. stearin) are used for an organic coating. The coated amount is generally I to 3 kg of coating substance per t of granulate, preferably about 2 kg of coating substance per t of granulate.
The product according to the invention is explained in more detail in the following.
The potash fertiliser granulate according to the invention is a product which can be obtained by the method of this invention described above. This product is characterised in that in comparison to the state of the art, the abrasion resistance is increased and the moisture absorption reduced, as shown in the following examples.
Simultaneously, the product according to the invention contains no additionally introduced additives, as mentioned at the start, in particular no MgO and no CaO, which are added as moisture-absorption inhibiting additives in the European application discussed above.
The product according to the invention, obtained according to the main process stages as described above, exhibits preferably an abrasion value of < 4%, particularly preferred < 3.8% and especially preferred < 3%. The abrasion value is determined according to the potash standard (works standard KALI 97 - 147, 08/87). This abrasion value is the proportion < 0.5 mm in % mass of the amount used, which is determined after exposure of the sample material in a vibration device (frequency 240 min'', amplitude 30 mm) in a pan with 36 steel balls by sieving. The abrasion values according to the Busch method, which is also used, are normally on average 10 to 15% below those of the method according to the potash standard.
The moisture absorption, measured under standard conditions of a temperature of C, a relative humidity of 70%, with a storage period of 8 days, amounts to preferably less than 2% with the product according to the invention, particularly preferably less than 1.5% and especially preferably less than 1%. By additional application of the coating layer describe above, i.e. by partial coating with the organic substances described above, the moisture absorption can be reduced still further, preferably to a value less than 1.8%, particularly preferably less than 1% and especially preferably still less than 0.8%.
These values apply to potash fertiliser granulate which is not partially coated with a water repellent organic substance.
Here, it is surprising that according to the invention the potash fertiliser granulate does not need to contain any oxidic additives, such as calcium oxide or magnesium oxide, which are described in the European application mentioned above as essential components for the reduction of the moisture absorption. Since however the addition of such materials is associated with the problems described at the start, this invention makes an overall improved potash fertiliser granulate available.
The method according to the invention furthermore has the result that, as described at the start, the specific surface area of the granulate grains is reduced and the grain shape slightly modified. Whereas the usual granulates are angular shapes running to a taper (due to the fracture surfaces arising with the usual treatment), the product of this invention exhibits a rather rounded grain shape due to the modification of the granulate grain area due to the application of kinetic energy by the vibration treatment process.
Overall, a product results with an improved storage stability, in particular because the moisture absorption is reduced which prevents unwanted hardening of the granulate (baking). Simultaneously, the production of dust when handling the granulate is reduced due to the increased granulate strength, improving the application conditions and contributing to improved handling safety.
Overall, the product according to the invention is characterised by a hitherto unattained combination of mechanical strength and low moisture absorption, whereby it is ensured that no oxidic additives need to be employed.
In the following the device for carrying out the method of this invention is more precisely described.
The device according to the invention comprises as the essentiai eiements first an apparatus with which the liquid described in conjunction with the method according to the invention (containing carbonate or silicate) is applied to the raw fertiliser granulate.
This apparatus is preferabiy a mixer in which the raw fertiliser granulate is moved while the liquid is added. The addition of the liquid can either occur through an inlet opening in the mixer or preferably by spray nozzles provided, whereby an improved distribution of the liquid to be applied is achieved. This type of mixer is basically not restricted, but intensifier-type mixers are preferred.
The second element of the device according to the invention is a vibration appliance in which the raw granulate grains, which are exposed to the liquid, are treated to apply the kinetic energy by vibration oscillations. This element of the device according to the invention is preferably a vibrating conveyor, equipped such that the raw fertiliser granulate grains treated with the liquid are subjected to a frequency of 15 to 70 Hz at an amplitude of 2 to 20 mm, with a dwell time of 10 to 180 s. The ranges for these parameters described above in conjunction with the method according to the invention also apply to the device according to the invention. Alternatively, the apparatus for applying the kinetic energy is arranged as an entry zone on a vibration-aided dryer. This simplifies especially the equipment needed, because normally drying in a dryer follows the application of kinetic energy through vibration, for example, a fluidised-bed dryer or a vibration-aided dryer.
Optionally, the device of this invention includes furthermore a device for applying the above described coating layer of an amine, oil, wax or a mixture of these.
This device, which can be fitted for example below the dryer unit, is preferably also a spray nozzle appliance, provided for example in a weir, adjustable in height, in the transition drying/cooling section of a fluidised-bed dryer. The application preferably occurs by replaceable airless jetting appliances, whereby the nozzles preferabiy can be pressure controlled individually in relation to the throughput. Normally, adjustment is made such that the granulate fluidised bed, about 10 to 15 cm high, is not penetrated.
Where applicable, this unit also includes an apparatus for heating the organic coating agent to be applied, because, for example with waxes, melting on is needed and with oils or oil/amine mixtures tempering is required.
This invention is illustrated further based on the following embodiments.
Example 1 A dry potash fertiliser salt raw granulate, produced on a roller press, with a magnesium chloride/calcium chloride content of 0.16% is sprayed according to Figure 2 in a mixer with a 15% weight soda solution for a feed of 1.5% weight, mixed thoroughly and thereby the alkaline earth chlorides are subjected to a transformation reaction, resulting in the carbonates. The moistened raw granulate is surface deformed, smoothed and compacted in the following vibrating conveyor and also in the entry section of the vibrating fluidised-bed dryer. The vibrating conveyor is run at a frequency of 30 Hz and an amplitude of 5 mm. The granulate is dried in the vibrating fluidised-bed dryer/cooler and the dust extracted in the airflow. In the transition section of the dryer/cooler there is the jetting appliance with which 2 kg of amine/oil mixture (ratio of amine :
oil = 1:1) is applied to one tonne of granulate. In technical testing the granulate produced in this way exhibits a single grain strength of 36.2 N, an abrasion of 2.8% and a moisture absorption (standard conditions, as described above) of 0.75%. As a comparison raw granulate was treated in accordance with Figure 1. Here, a single grain strength of 34.1 N, an abrasion of 4.5% and a moisture absorption of 1.90% resulted. The raw granulate exhibited a single grain strength of 34.4 N, an abrasion of 6.8% and a moisture absorption of 2.05%. It should be pointed out that in this connection, the values described above were measured in each case on a granulate on which no amine/oil mixture had been applied.
It is therefore apparent that the method according to the invention is able to provide a superior potash fertiliser granulate in accordance with this invention which exhibits an increased strength and a reduced moisture absorption compared to the granulate produced by the usual method, whereby at the same time no additional oxidic additives need to be employed.
After application of the amine/oil mixture a moisture absorption in the product according to the invention of 0.6% resulted and with the comparison product 1.05%
(whereby the abrasion values were approximately the same and were about 0.2%).
ExamAle 2 A dry potash fertiliser salt raw granulate, produced on a roller press, with a magnesium chloride/calcium chloride content of 0.6% is treated in accordance with Figure 4 in an intensifier-type mixer or equivalently on a vibrating conveyor with a 20%
weight potassium metasilicate solution and intensively and thoroughly mixed. The potassium metasilicate solution was produced from a potassium metasilicate with a density of 1.24 to 1.26 g/cm3. The applied amount of solution containing silicate was 1.7%
weight. The different facilities used in this example, were used alternatively and can be selected in practical operation according to constructional prerequisites.
Then the moistened raw granulate was surface deformed and then dried in the following vibrating fluidised-bed dryer with a granulate deformation section of at least 1 m and reduced air feed at a frequency of 18 to 25 Hz at an amplitude of 7 to 8 mm.
The coating was then applied, in this example with a palmitin melt heated to 80 C
with an additive amount of 2 kg of paimitin per t of granulate.
Before the application of the paimitin coating, the granulate produced in this way exhibits in the technical tests a single grain strength of 32.9 N, an abrasion of 3.6% and a moisture absorption of 1.9% (measured in each case in accordance with the standard method mentioned at the beginning). The comparison granulate, produced in accordance with Figure 1, exhibited a single grain strength of 28.2 N, an abrasion of 4.8% and a moisture absorption of 6.2%. The raw granulate showed a single grain strength of 31.0 N, an abrasion of 7.9% and a moisture absorption of 6.5%. It was therefore found again that the product according to the invention particularly exhibited a very substantially reduced moisture absorption.
After application of the paimitin coating the values for the abrasion on the product according to the invention and on the comparison product were in each case approximately equal (0.2%). The moisture absorption was reduced in the comparison product to about 4.2%, but in the product according to the invention to 1.6%.
Overall it has been shown that the method according to the invention provides an improved potash fertiliser granulate. Since particularly the addition of oxidic additives can be omitted, the product is improved with regard to the long-term storage capability, because the swelling effects mentioned at the start cannot occur in the granulate according to the invention. The device according to the invention is characterised by a relatively simple structure and therefore facilitates economical production of the product according to the invention and economical implementation of the method according to the invention.
It is therefore the object of this invention to provide an improved potash fertiliser granulate which with high relative humidity remains capable of storage without the above quoted problems occurring. Furthermore, the improved potash fertiliser granulate should exhibit an adequate strength, so that the formation of undersized grains is largely prevented. In addition, this invention assumes the task of providing a method for the production of this sort of potash fertiliser granulate and of providing a device for carrying out the method.
Brief description of the invention In another aspect, the present invention provides a method for producing improved potash fertiliser granulates, comprising the treatment of a potash fertiliser raw granulate with a solution containing silicate or carbonate, followed by the application of kinetic energy in the form of vibrations.
In another aspect, the present invention provides a potash fertilizer granulate obtained using the method of the present invention.
In another aspect, the present invention provides a device for producing an improved potash fertiliser granulate, including an appliance for applying a solution to a raw granulate and an appliance for transferring kinetic energy in the form of vibrations to the raw granulate which has been treated with the solution.
The term potash fertiliser as used in this application includes the usual known fertilisers containing potassium, such as for example potassium nitrate, potassium chloride, potassium sulphate, potassium carbonate and the mixed salts derived from potassium, such as potassium magnesium chloride, potassium magnesium chloride sulphate, potassium magnesium sulphate, etc. Those potash fertilisers are particularly preferred which preferably contain potassium chloride or potassium sulphate and mixtures of these components as the principal constituents.
Brief description of the figures Figure 1 shows a flow chart of a normal method for producing potash fertiliser granulate.
Figure 2 shows a flow chart of a method according to the invention for the production of a potash fertiliser granulate.
Figure 3 shows preferred devices for coating the granulates. Figure 3a shows a schematic view of a vibrating fluidised bed dryer/cooler and Figure 3b shows a schematic side view of a weir, adjustable in height with removable operating appliance.
Figure 4 shows a further flow chart of a method corresponding to this invention.
Detailed description of the invention Starting from the known moisture sensitivity of potash fertiliser granulates, examinations were carried out to establish the reason for the moisture absorption of the potash fertiliser granulates. Here, it was found that the alkaline earth chlorides present in potash fertiliser granulates, which are the usual components accompanying the natural salts, influence very significantly the moisture absorption of the potash fertiliser granulates even in slight amounts. Magnesium chloride and calcium chloride have a very strong influence on the moisture absorption capacity of potash fertiliser granulates.
This influence is shown in the following table.
Content of alkaline earth chlorides Moisture absorption of the potash (MgC12+CaCI2 content) fertiliser granulate*
None (< 0.05% mass) 0.45% mass 0.1 % mass 1.40% mass 0.2% mass 2.55% mass 0.5% mass 5.60% mass *Standard conditions: 20 C, 70% RH, 8d Even a content of only 0.1 % mass of alkaline earth chloride results in a very noticeable moisture absorption of the potash fertiliser granulate.
In the following, this invention, which has been based on the above quoted findings, is described in detail. Firstly, the method according to the invention is discussed. Details, which are provided in conjunction with the method according to the invention, also apply correspondingly to the product according to the invention and the device according to the invention (equivalent in each case, where applicable) and vice versa.
According to the invention, a normal raw granulate of a potash fertiliser granulate is used. Preferably, this raw granulate includes the fraction of the grain size of 1 to 5 mm quoted at the start. This is first treated with a solution containing silicate or carbonate.
Such preferred solutions are aqueous solutions, in particular aqueous solutions containing silicate of potassium, soda, silicate of sodium or potash.
Preferred solutions contain the components containing silicate or carbonate in an amount of 5 to 25%
weight, preferabiy 10 to 20% weight and especially 14 to 20% weight. This solution is applied to the raw granulate using methods known in technology, for example by spray application or by mixing in an intensifier-type mixer. The amount of the solution to be used is preferably 1 to 2.5% weight referred to the total mass of raw granulate and applied solution, preferably 1.3 to 2.0% weight and particularly preferably 1.5 to 1.8%
weight. The treatment of the raw granulate with the solution described above leads to a transformation of the alkaline earth chlorides contained in the raw granulate to silicate compounds or compounds containing carbonate which are not hygroscopic. Due to this process stage a substantial reduction of the moisture absorption capabiiity of the raw granulate is already obtained. A surprising feature is that a positive effect can be obtained due to this type of simple wet chemical reaction, without additional additives such as magnesium oxide, calcium oxide, burnt chalk or burnt dolomite having to be added to the granulate as suggested in the European patent application mentioned above. At the same time the application of the amount of liquid leads to further binding of any included fine-grain content so that the application of the liquid as such furthermore has a positive effect on the raw granulate.
After application of the solution described above, according to the invention kinetic energy is then applied by treatment with vibration. This vibration treatment, in contrast to compaction methods which are carried out in presses with high pressures, involves relative simple equipment and leads to the required grain deformation. Due to the rather point-type energy application by the vibration method, smoothing of the surface of the granulate grains is achieved, resulting in rounding of the grains and a reduction of the specific surface area. This produces a clearly improved abrasion resistance with a simultaneous further reduction of the moisture absorption capacity.
Overall, the positive effect of the stage with treatment of the solution containing carbonate or silicate solution is again reinforced by the second stage of the method according to the invention and furthermore also the mechanical properties of the granulates are improved. Consequently, the abrasion of the granulates during transport, loading and unloading is again clearly reduced, the flow properties of the granulates under handling are improved and the tendency to hardening during storage is reduced by reducing the flat contact points.
In contrast to compaction where crystal deformation is forced due to high compression pressures on the rollers (180 to 300 bar), surprisingly in the method according to the invention, the grain deformation of the moistened granulates can be achieved by vibrations in the frequency range from 10 to 70 Hz, preferably from 15 to 30 Hz, with amplitudes from 2 to 20 mm, preferably from 2 to 10 mm and particularly preferably from 5 to 8 mm.
It has been found that the moistened granulate should be subjected to a dwell period in the vibration treatment zone of 10 to 180 s in order to ensure adequate compaction.
Longer dwell periods are basically however not detrimental, but rather only disadvantageous with regard to the economics of the method.
The adequate relatively short dwell periods open up however additional possibilities for the integration of the process step of vibration treatment into other process stages, which can lead to further simplification of the process and to a reduction in the investment and operating costs. For example, it is possible to carry out the vibration treatment in a vibration zone which is not made available specially for this purpose, but instead to position it in a feed section of a vibration-aided fluidised-bed dryer.
Taken overall, the method according to the invention comprises the two main stages of application of a solution containing carbonate or silicate and the vibration treatment for grain deformation and grain compaction as described above.
Following the process steps, essential to the invention and quoted above, the usual post-treatments can be carried out which are briefly described below.
Following the vibration treatment, drying of the moistened granulates can take place.
This drying can be carried out in normal equipment, such as for example, fluidised-bed apparatus or in vibration-aided fluidised-bed dryers. Normally the next process stage following drying is cooling, whereby the granulate at a temperature of over 100 C is cooled to about 40 C and therefore the vapour is extensively extracted.
The following treatment stage of the granulate is normally formed by a coating with organic substances, such as for example oils, amines, oil/amine mixtures and waxes, to ensure free-flowing properties and the storage capability of the granulates over still longer time periods by the partial coating of the granulate surface. The process controls and equipment needed for this are known to the skilled person. Coating is normally carried out in mixers, as shown in Figure 1 for example. Altematively, the coating can be located in a vibration-aided fluidised-bed dryer, as indicated in Figure 2.
To achieve this, a weir, as shown in Figure 3 and which is adjustable in height, is provided in the transition area of drying/cooling with an overhang strip of at least 10 cm width mounted in the application direction, under which an airless nozzle device can be installed which can also be replaced during the process. The nozzles can be individually pressure controlled depending on throughput and adjusted such that the height at about 10 to 15 cm of the granulate fluidised bed is not penetrated. Depending on the consistency of the coating agent, melting on may be necessary, e.g. with waxes or tempering with oil/amine mixtures.
If a coating is provided in the method according to the invention, then this coating takes place using the usual organic substances, whereby, for example, palmitin or stearin waxes are preferred. Normally, fatty amines with a chain length of 16 to 18 C
atoms, mineral oils, fatty acids (e.g. palmitin acid) or waxes (e.g. stearin) are used for an organic coating. The coated amount is generally I to 3 kg of coating substance per t of granulate, preferably about 2 kg of coating substance per t of granulate.
The product according to the invention is explained in more detail in the following.
The potash fertiliser granulate according to the invention is a product which can be obtained by the method of this invention described above. This product is characterised in that in comparison to the state of the art, the abrasion resistance is increased and the moisture absorption reduced, as shown in the following examples.
Simultaneously, the product according to the invention contains no additionally introduced additives, as mentioned at the start, in particular no MgO and no CaO, which are added as moisture-absorption inhibiting additives in the European application discussed above.
The product according to the invention, obtained according to the main process stages as described above, exhibits preferably an abrasion value of < 4%, particularly preferred < 3.8% and especially preferred < 3%. The abrasion value is determined according to the potash standard (works standard KALI 97 - 147, 08/87). This abrasion value is the proportion < 0.5 mm in % mass of the amount used, which is determined after exposure of the sample material in a vibration device (frequency 240 min'', amplitude 30 mm) in a pan with 36 steel balls by sieving. The abrasion values according to the Busch method, which is also used, are normally on average 10 to 15% below those of the method according to the potash standard.
The moisture absorption, measured under standard conditions of a temperature of C, a relative humidity of 70%, with a storage period of 8 days, amounts to preferably less than 2% with the product according to the invention, particularly preferably less than 1.5% and especially preferably less than 1%. By additional application of the coating layer describe above, i.e. by partial coating with the organic substances described above, the moisture absorption can be reduced still further, preferably to a value less than 1.8%, particularly preferably less than 1% and especially preferably still less than 0.8%.
These values apply to potash fertiliser granulate which is not partially coated with a water repellent organic substance.
Here, it is surprising that according to the invention the potash fertiliser granulate does not need to contain any oxidic additives, such as calcium oxide or magnesium oxide, which are described in the European application mentioned above as essential components for the reduction of the moisture absorption. Since however the addition of such materials is associated with the problems described at the start, this invention makes an overall improved potash fertiliser granulate available.
The method according to the invention furthermore has the result that, as described at the start, the specific surface area of the granulate grains is reduced and the grain shape slightly modified. Whereas the usual granulates are angular shapes running to a taper (due to the fracture surfaces arising with the usual treatment), the product of this invention exhibits a rather rounded grain shape due to the modification of the granulate grain area due to the application of kinetic energy by the vibration treatment process.
Overall, a product results with an improved storage stability, in particular because the moisture absorption is reduced which prevents unwanted hardening of the granulate (baking). Simultaneously, the production of dust when handling the granulate is reduced due to the increased granulate strength, improving the application conditions and contributing to improved handling safety.
Overall, the product according to the invention is characterised by a hitherto unattained combination of mechanical strength and low moisture absorption, whereby it is ensured that no oxidic additives need to be employed.
In the following the device for carrying out the method of this invention is more precisely described.
The device according to the invention comprises as the essentiai eiements first an apparatus with which the liquid described in conjunction with the method according to the invention (containing carbonate or silicate) is applied to the raw fertiliser granulate.
This apparatus is preferabiy a mixer in which the raw fertiliser granulate is moved while the liquid is added. The addition of the liquid can either occur through an inlet opening in the mixer or preferably by spray nozzles provided, whereby an improved distribution of the liquid to be applied is achieved. This type of mixer is basically not restricted, but intensifier-type mixers are preferred.
The second element of the device according to the invention is a vibration appliance in which the raw granulate grains, which are exposed to the liquid, are treated to apply the kinetic energy by vibration oscillations. This element of the device according to the invention is preferably a vibrating conveyor, equipped such that the raw fertiliser granulate grains treated with the liquid are subjected to a frequency of 15 to 70 Hz at an amplitude of 2 to 20 mm, with a dwell time of 10 to 180 s. The ranges for these parameters described above in conjunction with the method according to the invention also apply to the device according to the invention. Alternatively, the apparatus for applying the kinetic energy is arranged as an entry zone on a vibration-aided dryer. This simplifies especially the equipment needed, because normally drying in a dryer follows the application of kinetic energy through vibration, for example, a fluidised-bed dryer or a vibration-aided dryer.
Optionally, the device of this invention includes furthermore a device for applying the above described coating layer of an amine, oil, wax or a mixture of these.
This device, which can be fitted for example below the dryer unit, is preferably also a spray nozzle appliance, provided for example in a weir, adjustable in height, in the transition drying/cooling section of a fluidised-bed dryer. The application preferably occurs by replaceable airless jetting appliances, whereby the nozzles preferabiy can be pressure controlled individually in relation to the throughput. Normally, adjustment is made such that the granulate fluidised bed, about 10 to 15 cm high, is not penetrated.
Where applicable, this unit also includes an apparatus for heating the organic coating agent to be applied, because, for example with waxes, melting on is needed and with oils or oil/amine mixtures tempering is required.
This invention is illustrated further based on the following embodiments.
Example 1 A dry potash fertiliser salt raw granulate, produced on a roller press, with a magnesium chloride/calcium chloride content of 0.16% is sprayed according to Figure 2 in a mixer with a 15% weight soda solution for a feed of 1.5% weight, mixed thoroughly and thereby the alkaline earth chlorides are subjected to a transformation reaction, resulting in the carbonates. The moistened raw granulate is surface deformed, smoothed and compacted in the following vibrating conveyor and also in the entry section of the vibrating fluidised-bed dryer. The vibrating conveyor is run at a frequency of 30 Hz and an amplitude of 5 mm. The granulate is dried in the vibrating fluidised-bed dryer/cooler and the dust extracted in the airflow. In the transition section of the dryer/cooler there is the jetting appliance with which 2 kg of amine/oil mixture (ratio of amine :
oil = 1:1) is applied to one tonne of granulate. In technical testing the granulate produced in this way exhibits a single grain strength of 36.2 N, an abrasion of 2.8% and a moisture absorption (standard conditions, as described above) of 0.75%. As a comparison raw granulate was treated in accordance with Figure 1. Here, a single grain strength of 34.1 N, an abrasion of 4.5% and a moisture absorption of 1.90% resulted. The raw granulate exhibited a single grain strength of 34.4 N, an abrasion of 6.8% and a moisture absorption of 2.05%. It should be pointed out that in this connection, the values described above were measured in each case on a granulate on which no amine/oil mixture had been applied.
It is therefore apparent that the method according to the invention is able to provide a superior potash fertiliser granulate in accordance with this invention which exhibits an increased strength and a reduced moisture absorption compared to the granulate produced by the usual method, whereby at the same time no additional oxidic additives need to be employed.
After application of the amine/oil mixture a moisture absorption in the product according to the invention of 0.6% resulted and with the comparison product 1.05%
(whereby the abrasion values were approximately the same and were about 0.2%).
ExamAle 2 A dry potash fertiliser salt raw granulate, produced on a roller press, with a magnesium chloride/calcium chloride content of 0.6% is treated in accordance with Figure 4 in an intensifier-type mixer or equivalently on a vibrating conveyor with a 20%
weight potassium metasilicate solution and intensively and thoroughly mixed. The potassium metasilicate solution was produced from a potassium metasilicate with a density of 1.24 to 1.26 g/cm3. The applied amount of solution containing silicate was 1.7%
weight. The different facilities used in this example, were used alternatively and can be selected in practical operation according to constructional prerequisites.
Then the moistened raw granulate was surface deformed and then dried in the following vibrating fluidised-bed dryer with a granulate deformation section of at least 1 m and reduced air feed at a frequency of 18 to 25 Hz at an amplitude of 7 to 8 mm.
The coating was then applied, in this example with a palmitin melt heated to 80 C
with an additive amount of 2 kg of paimitin per t of granulate.
Before the application of the paimitin coating, the granulate produced in this way exhibits in the technical tests a single grain strength of 32.9 N, an abrasion of 3.6% and a moisture absorption of 1.9% (measured in each case in accordance with the standard method mentioned at the beginning). The comparison granulate, produced in accordance with Figure 1, exhibited a single grain strength of 28.2 N, an abrasion of 4.8% and a moisture absorption of 6.2%. The raw granulate showed a single grain strength of 31.0 N, an abrasion of 7.9% and a moisture absorption of 6.5%. It was therefore found again that the product according to the invention particularly exhibited a very substantially reduced moisture absorption.
After application of the paimitin coating the values for the abrasion on the product according to the invention and on the comparison product were in each case approximately equal (0.2%). The moisture absorption was reduced in the comparison product to about 4.2%, but in the product according to the invention to 1.6%.
Overall it has been shown that the method according to the invention provides an improved potash fertiliser granulate. Since particularly the addition of oxidic additives can be omitted, the product is improved with regard to the long-term storage capability, because the swelling effects mentioned at the start cannot occur in the granulate according to the invention. The device according to the invention is characterised by a relatively simple structure and therefore facilitates economical production of the product according to the invention and economical implementation of the method according to the invention.
Claims (23)
1. A method for producing improved potash fertiliser granulates, comprising the treatment of a potash fertiliser raw granulate with a solution containing silicate or carbonate, followed by the application of kinetic energy in the form of vibrations.
2. The method according to claim 1, whereby the solutions used contain silicate or carbonate materials in an amount of 5 to 25% weight.
3. The method according to claim 1 or 2, whereby the solutions are added in dosages of 1 to 2.5% weight, referred to the total quantity of raw granulate and solution.
4. The method according to any one of claims 1 to 3, whereby the application of the kinetic energy occurs through a vibration treatment in the frequency range from 15 to 70 Hz at an amplitude of 2 to 20 mm and a dwell period of 10 to 180 s.
5. The method according to any one of claims 1 to 4, whereby the solutions are aqueous solutions and said silicate or carbonate are selected from sodium metasilicate, potash, soda or silicate of sodium.
6. The method according to any one of claims 1 to 5, also including the application of a coating with a water repellent substance.
7. The method according to claim 6, whereby the water repellent substance is oil, an amine, a wax or an oil/amine mixture, whereby an amount of water repellent substance applied to the granulate is 1 to 3 kg/t of granulate.
8. A potash fertiliser granulate, obtained using the method as defined in any one of claims 1 to 7.
9. The potash fertiliser granulate according to claim 8 with a moisture absorption of less than 2%.
10. The potash fertiliser granulate according to any one of claims 8 to 9, also including a partial coating with a water repellent substance.
11. The potash fertiliser granulate according to any one of claims 8 to 10 with an abrasion value of less than 4%.
12. The potash fertiliser granulate according to any one of claims 8 to 11, whereby the potash fertiliser granulate is free of oxidic compounds of magnesium and/or calcium.
13. The potash fertiliser granulate according to any one of claims 8 to 12 with a moisture absorption of less than 1%.
14. A device for producing an improved potash fertiliser granulate, including an appliance for applying a solution to a raw granulate and an appliance for transferring kinetic energy in the form of vibrations to the raw granulate which has been treated with the solution, wherein the solution comprises silicate or carbonate.
15. The device according to claim 14, whereby the appliance for transferring the kinetic energy in the form of vibrations is a vibrating conveyor.
16. The device according to any one of claims 14 to 15, whereby the appliance for applying the solution is an intensifier-type of mixer with spray nozzles.
17. The device according to any one of claims 14 to 16, also including a drying unit.
18. The device according to at least one of claims 14 to 17, also including a coating device for applying an organic water repellent substance.
19. The method according to any one of claims 1 to 3, wherein said vibrations are in a frequency range of from 10 to 70 Hz with an amplitude of 2 to 20 mm.
20. The device according to any one of claims 14 to 18, wherein said vibrations are in a frequency range of from 10 to 70 Hz with an amplitude of 2 to 20 mm.
21. The method according to claim 7, wherein said oil/amine mixture has a weight ratio of 1:1.
22. The method according to claim 6, wherein said water repellent substance is palmitin.
23. The method according to claim 7, wherein said water repellent substance is stearin wax.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10252848A DE10252848B3 (en) | 2002-11-13 | 2002-11-13 | Preparing potassium fertilizer granules comprises treating crude granulate with silicate or carbonate solution, then vibrating mixture |
| DE10252848.9 | 2002-11-13 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2448820A1 CA2448820A1 (en) | 2004-05-13 |
| CA2448820C true CA2448820C (en) | 2009-07-28 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002448820A Expired - Fee Related CA2448820C (en) | 2002-11-13 | 2003-11-10 | Abrasion resistant, tropicalised potash fertiliser granulate, method of its production and device for carrying out the method |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2448820C (en) |
| DE (1) | DE10252848B3 (en) |
| IL (1) | IL158752A0 (en) |
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| BR112017015339A2 (en) * | 2015-01-28 | 2018-01-09 | Koeppern & Co Kg Maschf | ? process for conditioning granules of fertilizer material? |
| DE102016010584A1 (en) | 2016-09-02 | 2018-03-08 | K+S Aktiengesellschaft | Process for the preparation of potassium chlorite granules |
| DE102016010586A1 (en) * | 2016-09-02 | 2018-03-08 | K+S Aktiengesellschaft | Process for the preparation of potassium chloride granules |
| DE102016010585A1 (en) | 2016-09-02 | 2018-03-08 | K+S Aktiengesellschaft | Process for the preparation of potassium chlorite granules |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| DD136956B1 (en) * | 1978-06-01 | 1981-09-30 | Wolfgang Tittel | METHOD FOR PRODUCING NON-DUSTING ABRASIVE CALIDUIN AGENT GRANULES |
| DD141821A2 (en) * | 1979-01-26 | 1980-05-21 | Wolfgang Tittel | PROCESS FOR PREPARING ABRASIVE NON-DUSTING CALIDUENEGRANEAN GRANULES |
-
2002
- 2002-11-13 DE DE10252848A patent/DE10252848B3/en not_active Expired - Fee Related
-
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- 2003-11-05 IL IL15875203A patent/IL158752A0/en active IP Right Grant
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Also Published As
| Publication number | Publication date |
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| DE10252848B3 (en) | 2004-03-25 |
| CA2448820A1 (en) | 2004-05-13 |
| IL158752A0 (en) | 2004-05-12 |
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