CA1333548C - Method for granulating potassium-sulphate - Google Patents
Method for granulating potassium-sulphateInfo
- Publication number
- CA1333548C CA1333548C CA000541528A CA541528A CA1333548C CA 1333548 C CA1333548 C CA 1333548C CA 000541528 A CA000541528 A CA 000541528A CA 541528 A CA541528 A CA 541528A CA 1333548 C CA1333548 C CA 1333548C
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- Prior art keywords
- sulphate
- potassium
- granules
- product
- grain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
- C01D5/004—Preparation in the form of granules, pieces or other shaped products
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Fertilizers (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Detergent Compositions (AREA)
- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
A method for roller-granulating potassium-sulphate, using starch as an aid to granulation. The method involves dry activation-grinding of some of the potassium-sulphate, moistening the material to be granulated with practically pure water, building up the green granules by rolling upon a granulating pan or in a tumbling barrel, and drying the said green granules, at a temperature of between 105 and 120°C, to a residual moisture of between 0.1 and 0.5%. In order to improve the wetability of the primary particles, and to reduce the amount of water needed for moistening, a soluble salt of lignin-sulphonic acid is added in an amount of between 0.1 and 1 kg/t of fresh material to be granulated.
Description
-It is known that modern fertilizer technology req-uires granulated nutrient-carriers. In contrast to other sin-gle and multiple nutrient fertilizers, granulating processes for potassium-sulphate became known only relatively recently.
It has been found that growing primary particles together to form an adequate grain structure is difficult to achieve.
As a possible solution to the problem of producing granular potassium-sulphate, German Patent 28 10 640 des-cribes a compacting process in which the material to be gran-ulated is compacted in a special way between the rolls of a high-pressure roller-press to form so-called shells. The shells are crushed and the satisfactory grain is screened out. The product is obtained in the desired grain-size and, with after-treatment, it is of good quality.
The compacting process has been found very satis-factory for producing granulated potassium-sulphate. In spite of this, it would be desirable to provide for a roller-granu-lating process for this fertilizer, since the compacting pro-cess delivers angular grains which do not mix very well with the rounded grains of other fertizilers. Furthermore there is an increase in abrasion in the mixture with repeated tran-shipment.
International mixing of individual granulated fert-ilizers in dealer warehouses is becoming increasingly popular in Europe, since mixing close to the point of use makes it possible to adjust the nutrient ratio to the respective de-mand. This procedure, however, means that all fertilizers - 2 - ~
which are to be mixed must be largely of the same grain-size and also, as far as possible, of the same (granule) density, in order to facilitate mixing and to reduce the danger of segregation during transhipment and spreading.
Nearly spherical grains are also preferred because bulk-material of this nature flows better into and out of storage than chip-like materials.
Various substances are suggested as aids to granul-ation. German OS 26 03 917 makes use of calcium compounds - which can be combined with potassium-sulphate to form syngen-itic double-salts.
German OS 27 48 220 discloses the use of mono- and dibasic ammonium-, sodium- or potassium-phosphate in the granulation of potassium-chloride, potassium-nitrate, potas-sium-sulphate, potassium-carbonate, and langbeinite.
German Patent 20 21 963 attempts to solve the prob-lem of rollergranulating potassium-sulphate by using starch as an aid to granulation. In this connection, it is found that starch alone acts far too weakly. In order to moisten the granulating mixture, therefore, it is necessary to use a salt-solution containing magnesium-sulphate and possibly also potassium-sulphate. During drying of the green granules, double salts are supposed to form and these, upon crystal-lizing, cement the primary potassium-sulphate particles.
It has now been found, surprisingly enough, that the action of starch as an aid to granulation may be sharply improved if, instead of a salt-solution, practically salt-~ 1333~8 free drinking water is used to moisten the potassium-sulph-ate, some of which has been subjected to additional dry-grinding. Highly abrasion-resistant granules were obtained by using 2 to 3 kg of paste starch to 1 t of satisfactory grain.
By crushing a large part of the potassium-sulphate particles to less than 50 ~m, this additional grinding increases the particle-surface per unit of mass and activates the stressed particles.
Recrystallizing is presumably accelerated by the immediately preceding mechanical action. It may also be imag-ined that activated potassium-sulphate dissolves very quickly in the water used for moistening and the starch-paste, col-loid-dissolved starch being partly expelled from the solution and being fixed upon the surfaces of the potassium-sulphate particles. This film may possibly promote the growth of potassium-sulphate which has passed into solution upon the surfaces of undissolved potassium-sulphate particles, whereas the starch which has remained in solution suppresses nuclea-tion in the film of solution between the particles.
The method according to the invention is character-ized in that approximately 20 to approximately 40% of the potassium-sulphate, in relation to the amount of product (satisfactory gra~) d~charged, is subjected, prior to the production of the moist granulating mixture, to dry activation-grlnding in a mill which grinds more than half of the material to less than 50 pm. The amount activated is combined, in the mixer, with the main amount of material to be granulated. The X
133354~
mixture is moistened with water to which l to 5 kg of starch per t of satisfactory grain have been added in the form of a paste and the mixture is rolled. The green granules are dried, at a temperature of between 105 and 120C, to a resid-ual moisture of 0.1 to 0.5% and the product (satisfactory grain) is finally screened out of the dried granular material and dis-charged, whereas the rejected granules (unsatisfactory grain), after being crushed, is returned to the mixer.
The method may be further characterized in that either some of the potassium-sulphate which is fed to the process freshly as the satisfactory grain is discharged, or some of the unsatisfactory potassium-sulphate grain screened out of the granulated product, is subjected, after crushing, to dry activation-grinding.
The method according to the invention may also be characterized in that a water-soluble salt of a lignin-sulph-onic acid is added, in an amount of between 0.1 and l kg per t of discharged satisfactory material, to the potassium-sul-phate mixture to be granulated, together with the pasted starch.
As in the case of any granulating process, the method according to the invention delivers over-size and under-size dried granulated material which must be screened out and returned, whereas the satisfactory grain is dis-charged as the product. In the stationary case, the unsatis-factory grain forms a part-circuit with a partly circular flow. Fresh potassium-sulphate is added to the process as the -1333~48 satisfactory grain is discharged.
It has been found, in principle, immaterial whether some of the fresh potassium-sulphate or an equal amount of potassium-sulphate, recirculating as unsatisfactory grain, is subjected to activation-grinding. In order to regain its granulatability, the returned material must be moistened by rolling with the fresh material. In order to compensate for the disadvantage of drying and remoistening in the returned-material part-circuit, it is desirable to use a filter-wet crystalline material as fresh potassium-sulphate. This is possible if the dry activation-grinding is applied to the un-satisfactory grain. The result is scarcely any different from that obtained by using dry and partly activated, fresh potassium-sulphate.
Although the fact that lignin-sulphonate saves water is known from the preparation of concrete in construct-ion work and other fields, the addition of lignin-sulphonate to the granulating mixture cannot be generally recommended, since these salts often have a structure-loosening effect.
In granulating potassium-sulphate, not only was the expected saving in water achieved, but also, surprisingly enough, a noticeable increase in resistance of the granules to abrasion. The moisture needed for rolling build-up was re-duced, by the addition of O.S kg of sodiumlignin-sulphonate per t of satisfactory grain, by about 20% as compared with no addition.
If it is considered that even such a fine potas-sium-sulphate as is obtained with the industrial potassium-sulphate process, with a main grain-size of between 90 and 250 ~m (58%), cannot be compacted to green-strength granules by rolling, and that addition of starch ln the form of a paste to the granulating material moistened with water provides little improvement, then the progress achleved with the method according to the invention becomes clear.
It is not the individual measures, but the combina-tion of activation-grinding and the addition of starch that produces structural compacting during rolling and a mechanic-ally strong bond between the primary particles within the granules upon drying. In contrast to this, green granules from untreated potassium-sulphate have such a loose structure that most of them cannot withstand drying. Although the ad-dition of 1% of starch in the form of a paste does improve the structure in green granules, they lose most of their res-istance to abrasion upon drying. Testing reveals an abrasion coefficient of 32%.
If 30% of the potassium-sulphate used is subjected to activation-grinding, if the activated material is added to the untreated sulphate, and this is followed by moistening!
rolling and drying, this produces granules which, when test-ed, show 18% abrasion.
Although activation-grinding alone improves the strength of the granules almost as much as the proposal con-tained in German Patent 20 21 963 (without after-treatment), total success is achieved only by the addition of 2 to 3 kg of pasted starch per t of product. Under test, granules thus produced exhibit only 4 to 8% abrasion. It is also worthy of note that, when thrown into water, these granules do not dis-integrate; instead they dissolve like large individual cryst-als. This indicates that the primary particles which build up the granules grow together particularly firmly. Such cohesion between primary particles can be obtained in granules pro-duced by other method only by complex after-treatment of the material, for example by spraying with water, solutions, vapours or the like and renewed drying.
In contrast to the method according to German Patent 21 21 963, the method according to the invention also makes it possible to save energy by using filter-wet potas-sium-sulphate, the optimal moisture-content of the material being adjusted by matching the additional amount of water to the ratio between the dry returned material and the moist fresh material.
The following examples are intended to explain the method according to the invention, without restricting its principle to the numerical data provided.
Example 1 In this case, the substance to be granulated is a non-crystalline potassium-sulphate. 3% by mass of the sulph-ate has a grain-size in excess of 500 ~m, 70% by mass is be-tween 200 and 500 ~m, 19% by mass is between 100 and 200 ~m, and 3~ by mass has a grain-size of less than 100 ~m.
40 parts by weight of this potassium-sulphate are 13335~8 ground in a ball-mill for activation until 2/3 thereof has assumed a grain-size of less than 45 ~m. The activated potas-sium-sulphate is co~bined, in the mixer, with 60 parts by weight of potassium-sulphate of the original grain-size and is mixed with 0.3 parts by weight of starch which has been converted into a paste by boiling in 4 parts by weight of water. During the mixing process, drinking water is added until preliminary granulation is visible. This requires about 6 parts by weight of water.
The granules are formed and compacted by rolling on a granulating pan. They are then dried at 100C to a residual moisture of 0.2%. The test-material screened out had a burst-ing strength of 24 N/grain after 1 day and of 35 N/grain after 30 days. Abrasion measured 7% after 1 day and 6% after 30 days.
Example 2 Based upon the same substance and the same dry preparation as in Example 1, the starch-paste is mixed with the moistening water before being placed in the mixer. The rolled green granular material is dried at 105C to a resid-ual moisture of 0.4%. Bursting strength after 1 day rose to 26 N/grain; abrasion was 6%.
Example 3 The basic substance in this example is a dry com-mercial potassium-sulphate containing the following grain-sizes:
-13335~8 > 500 ~um 2%
200 - 500 ~m 25~
90 - 200 ~m 41%
~ 90~um 32%
500 parts by weight of returned unsatisfactory grain are crushed to a grain-size of less than 500 ~m. 150 parts by weight of the commercial potassium-sulphate are sub-jected to activation-grinding in a rod-mill. 73% of the acti-vated potassium-sulphate had a grain-size of less than 45 ~m.
The returned material, and the activated potassium-sulphate, are passed, together with 350 parts by weight of untreated potassium-sulphate, to a ploughbar-mixer. The dry material is mixed with 105 parts by weight of water in which 1.5 parts by weight of paste starch are dissolved colloidally, followed by thorough mixing. The moist mixture is passed to a rotating drum, 5 more parts by weight of water being sprayed onto the inlet-end thereof. As the material rolls through the drum, almost spherical green granules, with smooth surfaces, are produced. The material emerging from the rolling drum is dried to a residuaL moisture of 0.2%.
After the satisfactory material to be discharged has been separated, the unsatisfactory material is returned to the start of the process. The product shows a bursting strength of 31 N/grain and 6% abrasion.
Example 4 The procedure in this case is the same as in Example 3, as far as the moistening process.
In this case, 0,3 parts by weight of sodiumlignin-sulphonate are dissolved in the moistening water, in addition to the 1.5 parts by weight of starch. Using the otherwise similar procedure of the preceding example, this recipe pro-duces granules having a bursting strength of 34 N/grain after 1 day and of 41 N/grain after 30 days, together with 6 abrasion after 1 day and 3% after 30 days.
Example 5 Commercial potassium-sulphate, of the grain-size given in Example 3, has, in the undried condition, a moist-ure-content of 11%, i.e. 100 parts by weight of the dry mat-erial contains, in the filter-wet condition, 12.5 parts of water. The total addition of potassium-sulphate may be ef-fected in the moist condition if the unsatisfactory : satis-factory-grain ratio is not less than 2 : 3.
The flow of returned material in the process amounts to 400 parts by weight per hour. A flow of 180 parts by weight per hour is branched off and is passed through the activation-mill. After the air-separating ball-mill, the two dry partial flows are reunited and are passed to a continuous mixer together with 600 parts by weight of moist potassium-sulphate. Also fed into this mixer continuously is a solution of 1.8 parts by weight of starch and 0~.12 parts by weight of megnesiumlignin-sulphonate in 21.6 parts by weight of water.
Upon entering the rolling drum, the material thus produced has a water-content of 96 parts by weight to 1000 parts by weight of dry material, corresponding to a maisture content of 8.9%. Five more parts by weight of water per hour are sprayed into the rolling drum. The water-content of the green granules is about 9.2% and they are dried at 100C to a residual moisture of 0.2%. After screening , 600 parts by weight of satisfactory grain are discharged as the product.
The 400 parts by weight of unsatisfactory grain, after being crushed to less than 250 pm, are returned to the start of the process. With this method of operation, 0.165 t of H2O/t of product are to be vapourized as compared with a saving of 0.124 t of vapourized H2O/t of dry material in the moist potassium-sulphate used. Thus the granulating process need only deliver 0.041 t of vapourized H2O/t of product more than potassium-sulphate drying without granulation. Tests showed a bursting strength after 1 day of 7% and, after 30 days, 4%.
Under test, granules thrown into water do not dis-integrate. They dissolve within about two hours, like cryst-als of the same size.
It has been found that growing primary particles together to form an adequate grain structure is difficult to achieve.
As a possible solution to the problem of producing granular potassium-sulphate, German Patent 28 10 640 des-cribes a compacting process in which the material to be gran-ulated is compacted in a special way between the rolls of a high-pressure roller-press to form so-called shells. The shells are crushed and the satisfactory grain is screened out. The product is obtained in the desired grain-size and, with after-treatment, it is of good quality.
The compacting process has been found very satis-factory for producing granulated potassium-sulphate. In spite of this, it would be desirable to provide for a roller-granu-lating process for this fertilizer, since the compacting pro-cess delivers angular grains which do not mix very well with the rounded grains of other fertizilers. Furthermore there is an increase in abrasion in the mixture with repeated tran-shipment.
International mixing of individual granulated fert-ilizers in dealer warehouses is becoming increasingly popular in Europe, since mixing close to the point of use makes it possible to adjust the nutrient ratio to the respective de-mand. This procedure, however, means that all fertilizers - 2 - ~
which are to be mixed must be largely of the same grain-size and also, as far as possible, of the same (granule) density, in order to facilitate mixing and to reduce the danger of segregation during transhipment and spreading.
Nearly spherical grains are also preferred because bulk-material of this nature flows better into and out of storage than chip-like materials.
Various substances are suggested as aids to granul-ation. German OS 26 03 917 makes use of calcium compounds - which can be combined with potassium-sulphate to form syngen-itic double-salts.
German OS 27 48 220 discloses the use of mono- and dibasic ammonium-, sodium- or potassium-phosphate in the granulation of potassium-chloride, potassium-nitrate, potas-sium-sulphate, potassium-carbonate, and langbeinite.
German Patent 20 21 963 attempts to solve the prob-lem of rollergranulating potassium-sulphate by using starch as an aid to granulation. In this connection, it is found that starch alone acts far too weakly. In order to moisten the granulating mixture, therefore, it is necessary to use a salt-solution containing magnesium-sulphate and possibly also potassium-sulphate. During drying of the green granules, double salts are supposed to form and these, upon crystal-lizing, cement the primary potassium-sulphate particles.
It has now been found, surprisingly enough, that the action of starch as an aid to granulation may be sharply improved if, instead of a salt-solution, practically salt-~ 1333~8 free drinking water is used to moisten the potassium-sulph-ate, some of which has been subjected to additional dry-grinding. Highly abrasion-resistant granules were obtained by using 2 to 3 kg of paste starch to 1 t of satisfactory grain.
By crushing a large part of the potassium-sulphate particles to less than 50 ~m, this additional grinding increases the particle-surface per unit of mass and activates the stressed particles.
Recrystallizing is presumably accelerated by the immediately preceding mechanical action. It may also be imag-ined that activated potassium-sulphate dissolves very quickly in the water used for moistening and the starch-paste, col-loid-dissolved starch being partly expelled from the solution and being fixed upon the surfaces of the potassium-sulphate particles. This film may possibly promote the growth of potassium-sulphate which has passed into solution upon the surfaces of undissolved potassium-sulphate particles, whereas the starch which has remained in solution suppresses nuclea-tion in the film of solution between the particles.
The method according to the invention is character-ized in that approximately 20 to approximately 40% of the potassium-sulphate, in relation to the amount of product (satisfactory gra~) d~charged, is subjected, prior to the production of the moist granulating mixture, to dry activation-grlnding in a mill which grinds more than half of the material to less than 50 pm. The amount activated is combined, in the mixer, with the main amount of material to be granulated. The X
133354~
mixture is moistened with water to which l to 5 kg of starch per t of satisfactory grain have been added in the form of a paste and the mixture is rolled. The green granules are dried, at a temperature of between 105 and 120C, to a resid-ual moisture of 0.1 to 0.5% and the product (satisfactory grain) is finally screened out of the dried granular material and dis-charged, whereas the rejected granules (unsatisfactory grain), after being crushed, is returned to the mixer.
The method may be further characterized in that either some of the potassium-sulphate which is fed to the process freshly as the satisfactory grain is discharged, or some of the unsatisfactory potassium-sulphate grain screened out of the granulated product, is subjected, after crushing, to dry activation-grinding.
The method according to the invention may also be characterized in that a water-soluble salt of a lignin-sulph-onic acid is added, in an amount of between 0.1 and l kg per t of discharged satisfactory material, to the potassium-sul-phate mixture to be granulated, together with the pasted starch.
As in the case of any granulating process, the method according to the invention delivers over-size and under-size dried granulated material which must be screened out and returned, whereas the satisfactory grain is dis-charged as the product. In the stationary case, the unsatis-factory grain forms a part-circuit with a partly circular flow. Fresh potassium-sulphate is added to the process as the -1333~48 satisfactory grain is discharged.
It has been found, in principle, immaterial whether some of the fresh potassium-sulphate or an equal amount of potassium-sulphate, recirculating as unsatisfactory grain, is subjected to activation-grinding. In order to regain its granulatability, the returned material must be moistened by rolling with the fresh material. In order to compensate for the disadvantage of drying and remoistening in the returned-material part-circuit, it is desirable to use a filter-wet crystalline material as fresh potassium-sulphate. This is possible if the dry activation-grinding is applied to the un-satisfactory grain. The result is scarcely any different from that obtained by using dry and partly activated, fresh potassium-sulphate.
Although the fact that lignin-sulphonate saves water is known from the preparation of concrete in construct-ion work and other fields, the addition of lignin-sulphonate to the granulating mixture cannot be generally recommended, since these salts often have a structure-loosening effect.
In granulating potassium-sulphate, not only was the expected saving in water achieved, but also, surprisingly enough, a noticeable increase in resistance of the granules to abrasion. The moisture needed for rolling build-up was re-duced, by the addition of O.S kg of sodiumlignin-sulphonate per t of satisfactory grain, by about 20% as compared with no addition.
If it is considered that even such a fine potas-sium-sulphate as is obtained with the industrial potassium-sulphate process, with a main grain-size of between 90 and 250 ~m (58%), cannot be compacted to green-strength granules by rolling, and that addition of starch ln the form of a paste to the granulating material moistened with water provides little improvement, then the progress achleved with the method according to the invention becomes clear.
It is not the individual measures, but the combina-tion of activation-grinding and the addition of starch that produces structural compacting during rolling and a mechanic-ally strong bond between the primary particles within the granules upon drying. In contrast to this, green granules from untreated potassium-sulphate have such a loose structure that most of them cannot withstand drying. Although the ad-dition of 1% of starch in the form of a paste does improve the structure in green granules, they lose most of their res-istance to abrasion upon drying. Testing reveals an abrasion coefficient of 32%.
If 30% of the potassium-sulphate used is subjected to activation-grinding, if the activated material is added to the untreated sulphate, and this is followed by moistening!
rolling and drying, this produces granules which, when test-ed, show 18% abrasion.
Although activation-grinding alone improves the strength of the granules almost as much as the proposal con-tained in German Patent 20 21 963 (without after-treatment), total success is achieved only by the addition of 2 to 3 kg of pasted starch per t of product. Under test, granules thus produced exhibit only 4 to 8% abrasion. It is also worthy of note that, when thrown into water, these granules do not dis-integrate; instead they dissolve like large individual cryst-als. This indicates that the primary particles which build up the granules grow together particularly firmly. Such cohesion between primary particles can be obtained in granules pro-duced by other method only by complex after-treatment of the material, for example by spraying with water, solutions, vapours or the like and renewed drying.
In contrast to the method according to German Patent 21 21 963, the method according to the invention also makes it possible to save energy by using filter-wet potas-sium-sulphate, the optimal moisture-content of the material being adjusted by matching the additional amount of water to the ratio between the dry returned material and the moist fresh material.
The following examples are intended to explain the method according to the invention, without restricting its principle to the numerical data provided.
Example 1 In this case, the substance to be granulated is a non-crystalline potassium-sulphate. 3% by mass of the sulph-ate has a grain-size in excess of 500 ~m, 70% by mass is be-tween 200 and 500 ~m, 19% by mass is between 100 and 200 ~m, and 3~ by mass has a grain-size of less than 100 ~m.
40 parts by weight of this potassium-sulphate are 13335~8 ground in a ball-mill for activation until 2/3 thereof has assumed a grain-size of less than 45 ~m. The activated potas-sium-sulphate is co~bined, in the mixer, with 60 parts by weight of potassium-sulphate of the original grain-size and is mixed with 0.3 parts by weight of starch which has been converted into a paste by boiling in 4 parts by weight of water. During the mixing process, drinking water is added until preliminary granulation is visible. This requires about 6 parts by weight of water.
The granules are formed and compacted by rolling on a granulating pan. They are then dried at 100C to a residual moisture of 0.2%. The test-material screened out had a burst-ing strength of 24 N/grain after 1 day and of 35 N/grain after 30 days. Abrasion measured 7% after 1 day and 6% after 30 days.
Example 2 Based upon the same substance and the same dry preparation as in Example 1, the starch-paste is mixed with the moistening water before being placed in the mixer. The rolled green granular material is dried at 105C to a resid-ual moisture of 0.4%. Bursting strength after 1 day rose to 26 N/grain; abrasion was 6%.
Example 3 The basic substance in this example is a dry com-mercial potassium-sulphate containing the following grain-sizes:
-13335~8 > 500 ~um 2%
200 - 500 ~m 25~
90 - 200 ~m 41%
~ 90~um 32%
500 parts by weight of returned unsatisfactory grain are crushed to a grain-size of less than 500 ~m. 150 parts by weight of the commercial potassium-sulphate are sub-jected to activation-grinding in a rod-mill. 73% of the acti-vated potassium-sulphate had a grain-size of less than 45 ~m.
The returned material, and the activated potassium-sulphate, are passed, together with 350 parts by weight of untreated potassium-sulphate, to a ploughbar-mixer. The dry material is mixed with 105 parts by weight of water in which 1.5 parts by weight of paste starch are dissolved colloidally, followed by thorough mixing. The moist mixture is passed to a rotating drum, 5 more parts by weight of water being sprayed onto the inlet-end thereof. As the material rolls through the drum, almost spherical green granules, with smooth surfaces, are produced. The material emerging from the rolling drum is dried to a residuaL moisture of 0.2%.
After the satisfactory material to be discharged has been separated, the unsatisfactory material is returned to the start of the process. The product shows a bursting strength of 31 N/grain and 6% abrasion.
Example 4 The procedure in this case is the same as in Example 3, as far as the moistening process.
In this case, 0,3 parts by weight of sodiumlignin-sulphonate are dissolved in the moistening water, in addition to the 1.5 parts by weight of starch. Using the otherwise similar procedure of the preceding example, this recipe pro-duces granules having a bursting strength of 34 N/grain after 1 day and of 41 N/grain after 30 days, together with 6 abrasion after 1 day and 3% after 30 days.
Example 5 Commercial potassium-sulphate, of the grain-size given in Example 3, has, in the undried condition, a moist-ure-content of 11%, i.e. 100 parts by weight of the dry mat-erial contains, in the filter-wet condition, 12.5 parts of water. The total addition of potassium-sulphate may be ef-fected in the moist condition if the unsatisfactory : satis-factory-grain ratio is not less than 2 : 3.
The flow of returned material in the process amounts to 400 parts by weight per hour. A flow of 180 parts by weight per hour is branched off and is passed through the activation-mill. After the air-separating ball-mill, the two dry partial flows are reunited and are passed to a continuous mixer together with 600 parts by weight of moist potassium-sulphate. Also fed into this mixer continuously is a solution of 1.8 parts by weight of starch and 0~.12 parts by weight of megnesiumlignin-sulphonate in 21.6 parts by weight of water.
Upon entering the rolling drum, the material thus produced has a water-content of 96 parts by weight to 1000 parts by weight of dry material, corresponding to a maisture content of 8.9%. Five more parts by weight of water per hour are sprayed into the rolling drum. The water-content of the green granules is about 9.2% and they are dried at 100C to a residual moisture of 0.2%. After screening , 600 parts by weight of satisfactory grain are discharged as the product.
The 400 parts by weight of unsatisfactory grain, after being crushed to less than 250 pm, are returned to the start of the process. With this method of operation, 0.165 t of H2O/t of product are to be vapourized as compared with a saving of 0.124 t of vapourized H2O/t of dry material in the moist potassium-sulphate used. Thus the granulating process need only deliver 0.041 t of vapourized H2O/t of product more than potassium-sulphate drying without granulation. Tests showed a bursting strength after 1 day of 7% and, after 30 days, 4%.
Under test, granules thrown into water do not dis-integrate. They dissolve within about two hours, like cryst-als of the same size.
Claims (5)
1. A method of producing a granulated potassium sulphate product using starch as an aid to granulation, the method comprising the steps of:
subjecting to dry activation grinding, an amount of potassium sulphate comprising approximately 20 to approximately 40% by weight in relation to the amount of product produced, said grinding being performed in a mill which grinds more than half of the said amount of potassium sulphate to less than 50µm, and producing activated potassium sulphate;
combining activated potassium sulphate from the mill with potassium sulphate not from the mill in a mixer, to produce a mixture;
subsequently moistening the mixture with water to which 1 to 5 kg of starch per t of product has been added in the form of a paste;
rolling the mixture to form green granules;
drying the green granules at a temperature of between 105 and 120°C to a residual moisture of 0.1 to 0.5%;
subjecting the dried granules to screening to produce said product and rejected granules;
discharging the product;
subjecting rejected granules to crushing; and returning said rejected crushed granules to the mixer.
subjecting to dry activation grinding, an amount of potassium sulphate comprising approximately 20 to approximately 40% by weight in relation to the amount of product produced, said grinding being performed in a mill which grinds more than half of the said amount of potassium sulphate to less than 50µm, and producing activated potassium sulphate;
combining activated potassium sulphate from the mill with potassium sulphate not from the mill in a mixer, to produce a mixture;
subsequently moistening the mixture with water to which 1 to 5 kg of starch per t of product has been added in the form of a paste;
rolling the mixture to form green granules;
drying the green granules at a temperature of between 105 and 120°C to a residual moisture of 0.1 to 0.5%;
subjecting the dried granules to screening to produce said product and rejected granules;
discharging the product;
subjecting rejected granules to crushing; and returning said rejected crushed granules to the mixer.
2. A method according to claim 1, in which potassium-sulphate is freshly added as product is discharged and is subjected to dry activation grinding.
3. A method according to claim 1 in which the rejected crushed granules are subjected to dry activation grinding.
4. A method according to claim 2 in which some of the potassium sulphate which is freshly added is used in filter-wet condition.
5. A method according to claim 1, characterized in that the water-soluble salt of a lignin-sulphonic acid is added to the potassium-sulphate granulating mixture in an amount equal to 0.1 to 1 kg of product discharged.
14.
14.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3623104.5 | 1986-07-09 | ||
| DE19863623104 DE3623104A1 (en) | 1986-07-09 | 1986-07-09 | Process for granulating potassium sulphate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1333548C true CA1333548C (en) | 1994-12-20 |
Family
ID=6304764
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000541528A Expired - Fee Related CA1333548C (en) | 1986-07-09 | 1987-07-07 | Method for granulating potassium-sulphate |
Country Status (5)
| Country | Link |
|---|---|
| BE (1) | BE1001043A4 (en) |
| CA (1) | CA1333548C (en) |
| DD (1) | DD266085A5 (en) |
| DE (1) | DE3623104A1 (en) |
| IL (1) | IL83103A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1243397B (en) * | 1990-11-27 | 1994-06-10 | Agrimont Spa | PROCESS FOR THE GRANULATION OF POTASSIC SALTS |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB847502A (en) * | 1956-11-30 | 1960-09-07 | Aschaffenburger Zellstoffwerke | Improvements in the manufacture of waterproof moulded bodies |
| US2907645A (en) * | 1957-01-22 | 1959-10-06 | Hartmann Waldemar | Method of aggregating carbonaceous material |
| IL28110A (en) * | 1966-06-28 | 1971-01-28 | Philips Nv | Pesticide granules and methods of preparing such granules |
| US3620709A (en) * | 1969-04-29 | 1971-11-16 | Int Minerals & Chem Corp | Granulation of potassium sulphate |
-
1986
- 1986-07-09 DE DE19863623104 patent/DE3623104A1/en active Granted
-
1987
- 1987-07-07 DD DD87304711A patent/DD266085A5/en not_active IP Right Cessation
- 1987-07-07 IL IL83103A patent/IL83103A/en not_active IP Right Cessation
- 1987-07-07 CA CA000541528A patent/CA1333548C/en not_active Expired - Fee Related
- 1987-07-08 BE BE8700758A patent/BE1001043A4/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| BE1001043A4 (en) | 1989-06-20 |
| IL83103A (en) | 1991-03-10 |
| DE3623104A1 (en) | 1988-01-21 |
| IL83103A0 (en) | 1987-12-31 |
| DD266085A5 (en) | 1989-03-22 |
| DE3623104C2 (en) | 1988-05-11 |
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| Date | Code | Title | Description |
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| MKLA | Lapsed |