WO2007071175A1

WO2007071175A1 - Granulation of sulfate of potash (sop)

Info

Publication number: WO2007071175A1
Application number: PCT/CN2006/003478
Authority: WO
Inventors: David Zeng; Qiang Wan; Guoqing Teng
Original assignee: The Mosaic Company
Priority date: 2005-12-19
Filing date: 2006-12-19
Publication date: 2007-06-28
Also published as: CN1793064A

Abstract

The present invention relates to a granulated sulfate of potash (SOP) product and methods of producing the granulated SOP using cornstarch as a binder. The granulated SOP utilizing the cornstarch binding agent results in granular SOP with good granular hardness, good configuration, uniform granular size, dust free, and a highly soluble in water product.

Description

GRANULATION OF SULFATE QF POTASH (SQP)

FIELD OF THE INVENTION

The present invention relates to a granulated sulfate of potash (SOP) product and methods of producing the granulated SOP. More particularly, the invention relates to granulated SOP and methods of manufacturing the granulated SOP using corn-starch as a binder.

BACKGROUND OF THE INVENTION

Plants can obtain some of the nutrients they need from the atmosphere and water, such as carbon, hydrogen and oxygen. Other essential necessary nutrients, such as nitrogen, phosphorus and potassium, are potentially obtained from the soil. Often, these nutrients are deficient in soil or are not present in a form that is readily utilized by plants. Therefore, methods have been developed to provide the plants with these and other nutrients needed for productive growth. The provision of these plant nutrients can come in the form of fertilizer containing the required nutrients being added to the soil. Fertilizer products can be a single nutrient product or a multi-nutrient product. Multi- nutrient products are called mixed or complex fertilizers and can be blended fertilizer products. Fertilizers can come in various forms, including powder, liquid and granular. The powder form of fertilizers is common in agriculture. However, if blended fertilizer products are to be made, granular fertilizer products are required to prevent the blended fertilizers from segregation and to prevent excessive amount of dusts. SOP is a good source of potassium for crops. The SOP grades typically range from about 50 to 54 percent K₂O, and SOP also contains about 17 percent sulfur. Lower ranges of K₂O are possible, but not necessarily desirable. SOP is generally made using a recrystallization process based upon reaction of KCl and H₂SO₄ or evaporation or crystallization of brine from natural salt lakes. SOP is a popular fertilizer, due, for example, to its low chloride content and water solubility. Further, SOP offers a high concentration of nutrients that are readily available to the crops.

Because of its unconsolidated loose nature, SOP fertilizer is generally handled in powder form and cannot be granulated with adequate chemical and physical qualities using traditional granulation technology. Adequate moisture content and nutrient analysis (high potassium content) can be difficult to achieve in a granulated SOP. Further, desired surface smoothness and hardness can be difficult to achieve in granulated SOP. However, granulated SOP is desirable for making bulk blend fertilizers, as granulated SOP has a relatively uniform particle size to be compatible with other raw materials such as granular urea and phosphates. Bulk blended fertilizers of different particle sizes can lead to segregation or separation of the components.

Segregation of the fertilizer components can occur during fertilizer blending, transportation, storage and application. Application of the product/fertilizer in this segregated state can lead to uneven distribution of nutrients, which is undesirable. Granular forms having the same size range as other components in the blended fertilizer work to obviate the problem of segregation of fertilizer components. Traditional granulation technology methods include granulating SOP using clays as the binding material. Due to the chemical nature of crystalline SOP, SOP molecules tend to repel each other, and thus are difficult to granulate with sufficient quality using traditional binding agents, such as clays. Nevertheless, attempts at making granulated SOP have been made, using compaction pressure and clays as the binder. The use of clay as a binding material results in low K₂O analysis (less than 40% K₂O), and the low ranges of potassium result in difficulty in formulating fertilizer programs. Further, the granular configuration using clay as a binder results in granule breakdown, excessive amounts of dusts and poor solubility. Nevertheless, clay can still be used as a binding agent for SOP; up to 20 percent of the total volume of the SOP product.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a process for producing a granulated SOP product, the process comprising milling the SOP, the SOP generally being in powdered form. The process includes preparing a corastarch-and-water suspension and spraying the milled SOP with the cornstarch- and- water suspension. The cornstarch- and- water suspension acts as a binder and promotes the granulation of the SOP. A maximum of about 4.0 weight percent cornstarch relative to SOP is combined with the SOP. The granulated SOP is dried and packaged. Alternatively, the granulated SOP granules can be coated to assist in preventing break-down of the granules. In another aspect, the invention pertains to a granulated SOP composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart depicting an embodiment of a process for making a granulated SOP product. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to using a starch as a binding agent to granulate the powdered SOP into granules with desired chemical and physical properties. In particular, the invention relates to the use of cornstarch as the binding agent in granulating the SOP. The SOP may be provided in powder form and may contain at least 50 percent K₂O. The granulation technology of the present invention uses a minimal amount of cornstarch to granulate the fine SOP to produce granular SOP with high potassium (K) content. The potassium content may be greater than 48.0 percent K₂O. The granulated SOP utilizing the cornstarch binding agent results in granular SOP with good granular hardness, good configuration, uniform granular size, dust free, and a highly soluble-in-water product. SOP can be produced by a variety of means, including treating caustic potash or potassium carbonate (K₂CO₃) with sulfuric acid (H₂SO₄), reacting sulfuric acid with potassium chloride (KCl), or treating muriate of potash (MOP) with sulfate of magnesia or with sulfuric acid. For particular crops, SOP is the preferred fertilizer, by providing potassium without also containing high levels of chlorine. MOP, for example, contains higher levels of chlorine than SOP and may result in injury to the particular plant or crop. For example, tobacco plants can be adversely affected by high levels of chlorine in the soil. SOP fertilizer has a generally loose, unconsolidated nature, and, therefore, is often handled in powder foπn and generally cannot be granulated with adequate chemical qualities, such as nutrient content and moisture content. Further, it is generally difficult to granulate SOP with adequate physical qualities, such as granular configuration, surface smoothness and hardness.

Due to the chemical nature of crystalline SOP, SOP molecules tend to repel each other and thus are difficult to granulate with sufficient quality using conventional binding agents such as clays. Compaction pressure and using clay as the binder has been tried as a means of granulating the SOP. However, the SOP that is produced using this method may result in SOP with a low potassium content (less than 40 percent K₂O). Further, the process using compression and clay as the binder results in poor granular configuration exhibiting granule breakdown, excessive amounts of dust and poor solubility in water. Referring to FIG. 1, the SOP powder is first weighed and fed into a vessel 102, where the SOP is milled 104. Milling of the SOP 104 breaks up any large lumps of powder SOP so that, for example, the proper granule size can be formed and so that the surface area of the powder SOP is available for binding with the starch. The particle size of the powder SOP is less than 1.0 millimeters in diameter, preferably less than about 0.6 millimeters in diameter, and more preferably less than 0.4 millimeter in diameter.

The starch binder is weighed 110 into another vessel. The starch binder, in this example, cornstarch, is mixed with warm water 112. The cornstarch is mixed while the warm water 116 is added to the vessel. The water temperature may be between 2O⁰C and 60⁰C, preferably between 45°C and 55°C, and preferably about 50⁰C. Steam 114 may be added to the vessel containing the cornstarch and water mixture to heat the mixture to a temperature of at least 70⁰C. The cornstarch is preferably mixed 112 with the warm water and dissolved to form a cornstarch-water suspension. Mixing time for the cornstarch-water suspension depend on the volume of vessel. The heated cornstarch-water suspension is transferred from the mixing vessel to a spray nozzle in the granulator. As the SOP is mixed in the granulator, the cornstarch suspension is sprayed uniformly onto the SOP. A gear pump can be used to spray the cornstarch suspension on the SOP. The granulator agglomerates the finer particles of SOP into larger, free flowing granules of starch covered powdered SOP.

A top spray granulator can be used for spraying the cornstarch-water suspension into the SOP fluidized powder. The temperature of the granulator during the spraying of the cornstarch-water suspension and granulation of the SOP 106 can be maintained at a temperature of between about 50°C and 7O⁰C, and preferably about 6O⁰C. The granulator continues to mix, and more of the powdered SOP is bound by the cornstarch-water suspension, forming more granules of SOP 106. The time for granulating is about 5 minutes to about 20 minutes, and preferably 7 minutes to 15 minutes. The agglomerated SOP is then dried 108 by heated air flowing into the drier as it continues mixing. The granulated SOP 106 is dried 108 at a temperature of between about 7O⁰C and 100⁰C, and preferably about 85°C. A rotary drying drum can be used to diy the granulated SOP. Drying time for the granulated SOP is half hour in the drier. Once the granules of SOP are dried 108, the granules of SOP are de-dusted 118 and the dust is gathered and washed 122. A cyclone dust collector and a Vencuri scrubber can be used to remove the dust. The SOP dust wash is recycled and added to the water 116 that is used to dissolve 112 the cornstarch and form the cornstarch-water suspension.

After sufficient granules of SOP have dried, the granules of SOP are allowed to cool 126 to a temperature of less than about 45⁰C, and preferably less than about 40⁰C. The granular SOP is de-dusted 120 again, with the dust being collected and washed 122. The wash containing the SOP dust is recycled and used as part of the water 122 used to mix and dissolve the cornstarch 112 and form the cornstarch- water suspension. The granulate SOP is now sieved 128 so that properly sized SOP granules are obtained. A screen may be used to obtain granulated SOP of between about 2-4 millimeters. A Tyler screen of 5-mesh to 9-mesh can be used to screen 128 the SOP and obtain the 2-4 millimeter granule size SOP. The powder material remaining after sieving is recycled by adding the powder SOP at the milling step 104. The granulated SOP thus obtained may have a granular hardness of at least 15 Newtons.

The granulated and cooled SOP granules go into a coating drum 138 for coating by the coating agent. 134. The coating agent dissolved and heated by steam coil in a vessel 132 and then spray onto the surface of the granules. Then the granules go into finished production bin 140 for bagging. The dust in the system is removed by dedusting system 142 and 146 for recycle.

EXAMPLES

Test 1- Formation of Granular SOP with a Cornstarch Binder

This process describes the formation of granulated SOP from SOP powder and cornstarch binder based on the process described herein. Approximately 1,200 grams of powdered SOP having a particle size of less than 1 millimeter was placed in the granulator. The powdered SOP generally had a particulate size less than 1 millimeter. Approximately 40 grams of cornstarch was placed in a container and mixed thoroughly with about 40 milliliters of warm water. The water was at a temperature of about 5O⁰C. The cornstarch-water suspension was then heated, with stirring, by hand, to a temperature of about 7O⁰C. When the cornstarch-water suspension reached a temperature of about 70⁰C and was thoroughly mixed, the cornstarch-water suspension was transferred to a sprayer.

The granulator containing the weighed sample of SOP was started and the cornstarch- water suspension was unifoπnly sprayed on the SOP. A pan granulator or a rotary drum granulator can be used. In this example, a pan granulator was used to granulate the SOP. The rotation velocity of the granulator was set at 13 to 17 rounds/minute. The cornstarch-water suspension acts as a binder, and the granulator started to agglomerate the powdered SOP to form granules. The temperature of the SOP and cornstarch-water suspension during granulation was about 60⁰C.

Once the SOP granules formed, the granulator was stopped and the SOP product was sieved through Tyler type screens to obtain 2-4 millimeter size granules of SOP. The material was then dried in an oven with a temperature of about 300⁰C. The time to granulate the SOP was 7 to 15 minutes and it took about 4 hours to dry the granulated SOP.

Once the granulated SOP was formed, an analysis of the granulated SOP was conducted. The K₂O analysis of the granulated SOP gave a result of about 48.51% and a moisture content of about 0.11%. The granular hardness of the granulated SOP using cornstarch as a binder was 15.9 Newtons.

Test 2- Formation of Granular SOP with a Cornstarch Binder

This process describes the formation of granulated SOP from SOP powder and cornstarch binder based on the process described herein. Approximately 1 ,050 grams of powdered SOP having a particulate size less than about 1 millimeter was placed in the granulator. Approximately 25 grams of cornstarch was placed in a container and mixed thoroughly with 25 milliliters of warm water. The water was at a temperature of about 50°C. The cornstarch-water suspension was then heated, with stirring, to a temperature of about 70⁰C. When the comstarch-water suspension reached a temperature of about 70°C and was thoroughly mixed, the cornstarch-water suspension was transferred to a sprayer.

The granulator containing the weighed sample of SOP was started and the cornstarch- water suspension was uniformly sprayed on the SOP. . A pan granulator or a rotary drum granulator can be used. In this example, a pan granulator was used to granulate the SOP. The rotation velocity of the granulator was set at 13 to 17 rounds/minute. The cornstarch-water suspension acts as a binder, and the granulator started to agglomerate the powdered SOP to form granules. The temperature of the SOP and cornstarch-water suspension during granulation was about 60°C. Once the SOP granules formed, the granulator was stopped and the SOP product was sieved through Tyler type screens to obtain 2-4 millimeter size granules of SOP. The material was then dried in an oven with a temperature of about 300⁰C. The time to granulate the SOP was 7 to 15 minutes and it took about 4 hours to dry the granulated SOP. Once the granulated SOP was formed, an analysis of the granulated SOP was conducted. The K₂O analysis of the granulated SOP gave a result of about 49.4% and a moisture content of about 0.66%. The granular hardness of the granulated SOP using cornstarch as a binder was 15.9 Newtons. The potassium content of the granulated SOP was determined using the ISO 5318 method. The moisture content of the granulated SOP was determined using the gravimetric method. A sample of granulated SOP is heated to dryness and the moisture loss is calculated based upon the weights taken before and after drying the sample. The hardness (or crushing strength) of the granulated SOP was determined using standard testing methods for fertilizer granular hardness. A sample of the granulated SOP was screened according to IFDC S- 107 to obtain at least 25 granules of a closely sized faction. The granules size for lab analysis was from range 2.36 to 2.80 mm. A commercial compression tester was used for measuring the hardness. Individual granules were placed on a mounted flat surface, and pressure was applied by a flat- end rod attached to the compression tester. A gauge mounted in the compression tester measures the pressure required to fracture the granule. At least 25 granules were tested and the average of the measurements is taken as the hardness of the granule. The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and the scope of the invention.

Claims

CLAIMSWhat is claimed is:

1. A fertilizer composition comprising sulfate of potash (SOP) and cornstarch.

2. The fertilizer composition of claim 1, wherein the cornstarch acts as a binder of the sulfate of potash (SOP) particles.

3. The fertilizer composition of claim 1, wherein the sulfate of potash (SOP) and cornstarch together form sulfate of potash-cornstarch granules.

4. The fertilizer composition of claim 1, wherein the sulfate of potash (SOP) was in powder form when combined with the cornstarch.

5. The fertilizer composition of claim 4, wherein the cornstarch is a cornstarch and water suspension.

6. The fertilizer composition of claim 1, comprising no more that 4 weight percent cornstarch relative to the sulfate of potash (SOP) weight.

7. The fertilizer composition of claim 1, wherein the K₂O content of the sulfate of potash-cornstarch granules is at least 47 percent.

8. The fertilizer composition of claim 3, wherein the sulfate of potash-cornstarch granules have a granular hardness of at least 14 Newtons.

9. A method for producing granulated sulfate of potash (SOP), the process comprising combining sulfate of potash (SOP) with cornstarch.

10. The method of claim 9, wherein no more that 4.0 weight percent cornstarch relative to sulfate of potash (SOP) is combined with the sulfate of potash (SOP).

11. The method of claim 9, wherein the cornstarch is provided in a cornstarch-and- water suspension, the cornstarch-and-water suspension comprising about equal parts of cornstarch and water.

12. The method of claim 11, wherein the granulated sulfate of potash (SOP) is formed by spraying the sulfate of potash (SOP) with the cornstarch-and-water suspension.

13. The method of claim 11, wherein the sulfate of potash (SOP) is milled prior to combination of the sulfate of potash (SOP) with the cornstarch-and-water suspension.

14. The method of claim 12, wherein the granulated sulfate of potash (SOP) is dried.

15. The method of claim 14, wherein the granulated sulfate of potash (SOP) is sieved.

16. The method of claim 15, wherein the granulated sulfate of potash (SOP) has a minimum size of about 2 millimeters.

17. The method of claim 15, wherein the granulated sulfate of potash (SOP) granules have a maximum size of about 6 millimeters.

18. The method of claim 15, wherein the granulated sulfate of potash (SOP) is sprayed with the cornstarch-and-water suspension, imparting a coating on the granules of sulfate of potash (SOP).

19. The method of claim 18, wherein the coated granules of sulfate of potash (SOP) are dried.