AU779181B2 - Improved N-P fertiliser compositions - Google Patents

Description

-1- Regulation 3.2

AUSTRALIA

PATENTS ACT, 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

rdl0n& AE T'.-IJir;mS LimlJ D BOP FERTILIASER LIMITED- Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: CHRISTOPHER ALLAN WILSON A J PARK SON, Level 11, 60 Marcus Clarke Street, Canberra ACT 2601 Improved N-P Fertiliser Compositions The following statement is a full description of this invention, including the best method of performing it known to me/us The present invention relates to improved fertiliser compositions.

There is frequently a need to provide easily broadcast (yet preferably wind drift resistant) fertiliser compositions of a particulate nature having a desired concentration of nitrogen and phosphorous values.

The most common fertiliser in New Zealand to provide phosphorus values is that of superphosphate which arises from the use of a procedure whereby rock phosphate is subjected to acidification with sulphuric acid.

Superphosphate however is low or devoid of nitrogen values where the acidification is with sulphuric acid.

It is well documented that superphosphate is of very limited compatibility with urea due to reaction with the mono calcium phosphate component and thus *'..:compositions have not usually been available where, by virtue of a simple blending of urea and superphosphate, there can be a provision of adequate N and P values.

Recently (in 1994) the French Company, AZF Grande Paroisse disclosed its urea super phosphate process which utilises the ability of urea to form eutectics at certain concentrations with sulphuric acid. Such eutectic compositions can then be used in addition of sulphuric acid to manufacture a superphosphate simulating product from subsequently provided rock phosphate. The outcome of such a blend S: however is that N values of a level of about 20% w/w and P values of about 5% w/w are provided. As a consequence that process is primarily used for granulating NPK fertilisers where there is a subsequent addition of K (potassium) values.

The present invention relates to processes and products capable of themselves of providing a higher P value than the aforementioned process with a useful N value and which themselves lend to subsequent processing to provide a blend having a desired P and N value.

In a first aspect the present invention consists in a method of preparing a (preferably granulatable) composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including the steps of i) blending urea with rock phosphate, and ii) subjecting the blend of step to acidification.

Preferably said acidification is with sulphuric acid.

Preferably said acidification is with concentrated sulphuric acid.

In a second aspect the present invention consists in a method of preparing a (preferably granulatable) composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including the step of acidifying the rock phosphate (to provide said P values) in the presence of urea (to provide said N values).

In still a further aspect the invention consists in a method of preparing a (preferably granulatable) composition having N values derived from urea and P 10 values derived from rock phosphate, said method comprising or including the step of blending acidulated rock phosphate with urea.

Preferably (irrespective of whether the procedure is of said first or second or third aspect) said method additionally includes a step of granulating the reaction *oo* product.

Preferably said granulation step includes the addition of water to any extent necessarily required (whether at the acidification and/or granulation stage or, indeed, any desired intermediary stage).

S. .Preferably said granulation is conducted whilst the product of said S" acidification is still at an elevated temperature.

In still a further aspect the present invention consists in a method of preparing granules of a composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including the steps of either a) blending urea with rock phosphate, and b) subjecting the blend of to acidification, or (ii) acidifying rock phosphate in the presence of urea, (II) allowing ageing of the product of step (III) optionally kneading the ageing and/or aged product of step (II), (IV) granulating the product of step (II) or (III)(if any), and oorlin an rallowing the cooling of the granules produced by step

(IV).

Preferably the ageing of the product of step is for a period of greater than minutes but less than 90 minutes and most preferably about 1 hour.

Preferably the temperature at which ageing occurs is about 125 C.

Preferably the temperature at which granulation takes place is at about Preferably said granulation includes the addition of such amount of water as is required to achieve effective granulation.

Preferably said granulation is to a size of granule less than 4.6 mm.

Preferably said ageing occurs on a conveyor, eg; a moving floor of a den.

Preferably said granulation takes place in a drum.

Preferably the product is screened prior to presentation to a cooler with oversized granules being returned after breaking into the means of granulating, eg; granulation drum preferably.

Preferably said sulphuric acid is 98.5% w/w sulphuric acid that is presented to both the urea and rock phosphate (the rock phosphate and urea being present together), and preferably water is added to reduce the concentration of the sulphuric acid (nevertheless still above a dilute sulphuric acid concentration), for example, down to about, for example, 70-80% w/w sulphuric acid.

Preferably the ratio of 98.5% w/w sulphuric acid to rock phosphate is within the range of from 0.52 to 0.58 by weight.

Preferably the acid strength reduction in the preferred mixer within which the acidification takes place is adjusted to such water content as will assist in the maintenance of a proper consistency for downstream granulation after ageing.

Preferably the urea and/or rock phosphate presented to acidification (preferably by step is of a particle size substantially less than 150 microns.

In another aspect the present invention consists in a fertiliser composition having available N values greater than 3% w/w and available P values greater than 8% w/w where it is a blend of iv) urea, and v) a granulated reaction product of a process in which either a mix of urea and rockphosphate lias been subjected to acidification or rock phosphate has been acidified in the presence of urea.

Preferably said granulated reaction product is a product of a kind produced by a process in accordance with the present invention.

In still a further aspect the present invention consists in a fertiliser composition having N values greater than 3% w/w and available P values greater than 8% w/w where it is a blend of iv) urea, and v) granules having both available P levels and available N levels, the N levels at least in part having been derived from urea and the P levels :i 10 having at least in part been derived from rock phosphate, oooo wherein the available N value contribution of the granules in the overall composition does not provide greater than 5% w/w of the available N values present, yet such granules providing at least most (if not all) of the available P values of the overall composition.

Preferably the fertilising composition has an available N level in the range of from 2 to 5% w/w and available P levels in the range of from 8 to 10% w/w.

In still a further aspect the present invention consists in the use of granules as aforesaid as a fertiliser or as a blending component of a fertiliser composition (eg; to be still higher in N value content).

The invention also consists in related methods of applying N and P value fertiliser to a desired locus of application.

A preferred form of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 shows a flow diagram of a typical superphosphate process, Figure 2 shows a modification of such a standard superphosphate process which lends itself to the preparation of granules in accordance with the present invention, Figure 3 shows a down stream procedure whereby the output from a process as depicted in Figure 2 can be blended with urea (each in a compatible form) to provide for a desired N and P value composite product, -Figure 4 is a plot of granule strength (resistance to relate weights in kg) against percentage nitrogen added by way of the urea addition, and Figure 5 is a plot of acid strength against mixer temperature.

In a standard superphosphate process (Figure rock phosphate, for example, ground to substantially below 150 microns is fed via a weigh feeder 1 into a mixer 2 where concentrated sulphuric acid (98.5% w/w) is used to acidify the phosphate.

Appropriate water additions (if any) may be made into the mixer in order to provide a requisite moisture content requiring little addition of water at a subsequent granulation step.

The output from the mixer 2 is then aged through a den 3 which serves the function of allowing the exothermic reaction to proceed beyond the stage it has reached in the mixer 2 whereupon, as the material is conveyed through the den, it is S: then presented to a conditioner 4 where kneading and other manipulation occurs.

Then the material, still at an elevated temperature, is presented into a granulation drum 5 to which might be added any desired water addition to achieve effective granulation.

The output from the granulation drum 5 is then screened by a screen 6 and the product with granules of a requisite size, for example, less than 4.6 mm is the output whilst oversized material is returned via a lump breaker 7 back into the granulation drum The arrangement in the process of the present invention as depicted in Figure 2 is substantially similar save for the pre-mixing (in a preferred form of the present invention) of urea with the rock phosphate after each has been fed via a weigh feeder 1 to the mixer 2.

It can be seen therefore that little in the way of capital plant in addition is required to achieve the outcome to be forthcoming from the present invention over the plant for the superphosphate process although there is preferably the addition of a cooler 8 to reduce the temperature of the granulated material. Indeed, at least at the time of the granulation the material still down only to about 100°C having past through over a period of, for example, 52 minutes the den 3 at which stage it is still at a temperature of about 125°C as a result of the exothermic reaction.

-The product Which isthe outcomie ofthe procedure of Figure2 preferably has a nitrogen value of about 2 to 5% w/w and a P value percentage of the same level as that in ordinary superphosphate, ie; about or not much less than about 8-10% w/w.

The outcome product (as shown in Figure 3) can then compatibly be blended with additional urea to bring the N value content up to any that might be required.

Whilst output product from the procedure of Figure 2 might itself have an N value as high as about 5% w/w preferably levels much higher than a more usual 2 or 4% w/w are derived from the subsequent blending procedure as depicted in Figure 3.

It is envisaged therefore that a product resulting from the procedure of Figure 3, irrespective of whether or not it has any other elemental values incorporated 10 therewith for example, optionally potassium, will have a P value ranging from 5 to 10% w/w and an N value range of from 3% w/w to 20% w/w.

It is believed therefore that the present invention provides not only granules (the result of a procedure typified by a flow diagram of Figure 2) which can be used for subsequent blending purposes or can themselves be used as a compound fertiliser.

Trial Analysis 1. Rock, Initial trials used a rock blend including Christmas (ie; from Christmas Island). This was unsatisfactory as the iron and aluminium affect the reaction rates and prevent use of AR's acid to rock ratios by weight) over 0.52. Straight BuCraa (a rock phosphate from Morocco) was also trialed but slower reaction rates meant that AR was curtailed and could not be raised over 0.52. Both Nauru: BuCraa and Nauru: Khouribga (also from Morocco) blends could be run effectively at a range of AR's up to 0.58. Chemically the Nauru: BuCraa blend (Nauru being from Nauru) gives acceptable phosphate solubility and processability.

2. Urea content, A range of urea additions resulting in N levels in the product of up to 5% w/w have been produced. At the high end there are difficulties with the liquidity in granulation and also with the hygroscopic nature of the product. Low levels of addition, of 0.5 or 1% w/w will improve physical properties of granules but -will-not-reduce-mono-calcium phosplate-(MCP)levels sufficiently to allow dry blending with urea. The optimum appears to be at a product N content of about 3%.

Lower levels may in some instance be useful for physical improvement of superphosphate. See Figure 4.

3. Urea addition, In the trial work urea was added either to the weighed ground rock or blended with the rock before milling. Both methods were viable but the propensity for segregation of urea and rock in storage meant that variable N levels were experienced. As a consequence the best option found was to add the urea by weighfeeder to the weighed ground rock feed to the mixer.

4. Reaction conditions, Acid to Rock Ratio Through a wide range of trials we have found that we can achieve an AR of at least 0.58 with optimum rock blend and acid strength. The limiting factor on the achievable maximum AR for the 3% wlw N product is primarily the reactivity of the rock blends. In trials that have contained Christmas B (a rock phosphate from Christmas Island that is high in iron and aluminium oxide) or 100% w/w BuCraa, the AR has had to be significantly lowered to reduce the quantity of acid in the ex-den product and get a product dry enough for granulation. The acid content in the ex-den product should be less than 10% w/w Phosphoric Acid with no Sulphuric Acid present to enable granulation. The optimum AR for the Christmas B or 100% w/w BuCraa rock blends is only 0.52 which results in both lower yield and lower P solubility.

Acid Strength The operational acid strength is ideally between 70% to w/w with the optimum being 72% w/w for a 20% w/w Nauru (ie; rock phosphate from Nauru), 80% w/w BuCraa rock blend. This limits our mixer temperature to between 115 125 deg.C. The upper limit on acid strength is due to the quantity of water in the reaction system becoming so low that the reactions in the system become too slow. This results in the product ex-den being too liquid (too much acid solution remaining) for granulation. The temperature of the ex-den product, which is controlledby acid str-gth, isalso abbe the optimum level for good granulation.

-9- The lower acid strength limit of 70% is due to the high solubility of the urea phosphate. The extra water delays the onset of crystallization and results in the product being too wet for granulation.

Hydrolysis of urea, effect on MCP levels and mixability with urea The hydrolysis of urea to form ammonia and then MAP is an important process in the reduction of the total acidity of the final product and in reverting MCP.

The parameters affecting these reactions are denning time, temperature and water content. The removal of all MCP arises when 60% w/w hydrolysis of the urea (or 2% w/w NH 4 -N level) is achieved. Given the present restrictions on acid strength this would require increasing the denning time to greater than 50min as we are only Sachieving 30% w/w hydrolysis at this point. At 30min. Denning time only 15% w/w hydrolysis is obtained. The acceptable level of P in the form of MCP appears to be less than 1.5% P as indicated from trial data in Table 1 Table 1 shows mix quality when a 15% w/w urea blend is made and stored.

Table 1 2 w/w MCP as P Stability after 1 week 2.34 Wet and lumpy 2.06 Wet and lumpy 1.47 Free Flowing When product is poured to storage without further cooling hydrolysis type reactions continue which subsequently improve the mixability with urea. Indicative results from trials were an increase in ammonia N from 0.5% to 0.9% w/w, which infers MCP as P reduced from 2.0% to 1.1% w/w.

S Mixer Temperature To control the granulation conditions the mixer temperature has significant effect on the down stream chemical reaction, in particular the hydrolysis rate of urea and the subsequent reversion of MCP.

If mixer temperatures of 135deg.C can be obtained a product with no MCP, which would be stable, when mixed with urea and stored for long periods, can be produced.

We are, however, able to lower the MCP content sufficiently to allow the product to be stable for at least 1 week when mixed with urea by optimizing the level of urea hydrolysis within the constraints of acid strength for granulation.

6. Granulation, During the trails additional cooling was introduced into the granulation circuit. This consisted airflow through the conditioner to reduce the temperature and, by crystallisation, the liquid phase in the product. Without this additional cooling granulation was not possible as the product remained too wet to ~process. Adjusting this cooling provides another parameter that the operator can use to fine tune the process. We have shown however that a long processing circuit can provide sufficient natural cooling in favourable conditions.

Product cooling and Screening of Fines Screening of fines The current granulated superphosphate urea contains about 5% w/w of less than 1mm size. Clearly it is best to screen before storage so that this material may be regranulated as it is produced. Cooling (hardening) is desirable prior to screening. Hot product will likely lead to clogging of the screening system.

Conclusion For best results a Nauru/BuCraa rock blend is used with urea added via a weighfeeder to the weighed ground rock at 11% with respect to rock which will result in 3% N in the finished product. An acid to rock ratio of 0.58 at 72% acid strength will give reasonable chemical conversion i.e. 77% c/s P 69% w/s P.

Temperature control of the product in the granulation circuit will optimise granulation by controlling liquidity.

Claims (24)

1. A method of preparing a granulatable composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including the steps of i) blending urea with rock phosphate, and ii) subjecting the blend of step to acidification.

2. A method as claimed in claim 1 wherein said acidification is with sulphuric acid.

3. A method as claimed in claim 2 wherein said acidification is with concentrated sulphuric acid.

4. A method of claim 2 wherein the acid is from 70% to 75% w/w. A method of claim 2, 3 or 4 wherein the acid to rock ratio is such that after ageing and before granulation there will be less than 10% phosphoric acid present and substantially no sulphuric acid present.

6. A method of any one of claims 1 to 5 wherein the granulatable composition has N values greater than 3% w/w and available P values greater than 8% w/w. S7. A method of any one of the preceding claims wherein the composition is low in 0. mono calcium phosphate.

8. A method of preparing a granulatable composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including S the step of acidifying the rock phosphate in the presence of urea.

9. A method as claimed in any one of the preceding claims wherein said method additionally includes a step of granulating the reaction product of either step (ii) of claim 1 or the acidification step of claim 8. A method as claimed in claim 9 wherein said granulation step includes the addition of water to any extent necessarily required whether at the acidification and/or granulation stage or, indeed, any desired intermediary stage.

11. A method as claimed in claim 9 or 10 wherein said granulation is conducted whilst the product of said acidification is still at an elevated temperature as a result of the acidification step.

12. A method of preparing granules of a composition having N values derived from urea and P values derived from rock phosphate, said method comprising or including the steps of either a) blending urea with rock phosphate, and H:\Iibrry\patents\dj\specs\4 19167.djj -12- b) subjecting the blend of(i)(a) to acidification, or (ii) acidifying rock phosphate in the presence of urea, (II) allowing ageing of the product of step (III) optionally kneading the ageing and/or aged product of step (II), (IV) granulating the product of step (II) or (III)(if any), and cooling and/or allowing the cooling of the granules produced by step (IV).

13. A method as claimed in claim 12 wherein the ageing of the product of step is for a period of greater than 15 minutes but less than 90 minutes.

14. A method of claim 13 wherein the period is about 1 hour. A method as claimed in claim 13 or 14 wherein the temperature at which ageing occurs is about 125°C.

16. A method as claimed in claim 13, 14 or 15 wherein the temperature at which granulation takes place is at about

17. A method as claimed in any one of claims 13 to 16 wherein said granulation includes the addition of such amount of water as is required to achieve effective Sgranulation.

18. A method as claimed in any one of claims 13 to 17 wherein said granulation is to a size of granule less than 4.6 mm.

19. A method as claimed in any one of claims 13 to 18 wherein said ageing occurs on a conveyor or moving floor of a den.

20. A method as claimed in any one of claims 13 to 19 wherein said granulation takes place in a drum.

21. A method as claimed in any one of claims 13 to 14 wherein the product is screened prior to presentation to a cooler with oversized granules being returned, after breaking, into the means of granulating. S "22. A method as claimed in any one of claims 13 to 21 wherein acidification is with about 98.5% w/w sulphuric acid that is presented to both the urea and rock phosphate.

23. A method of any one of claims 13 to 21 wherein acidification is with about 70 to about 80% w/w sulphuric acid.

24. A method as claimed in claim 22 wherein the ratio of about 98.5% w/w sulphuric acid to rock phosphate is within the range of from 0.52 to 0.58 by weight. A method as claimed in claim 22 or 23 wherein the acid strength reduction occurs in the preferred mixer within which the acidification by adjustment to the water content H:\library\patcnts\dj\spccs\4 191 67.dj -13- thereby to assist in the maintenance of a proper consistency for downstream granulation after ageing.

26. A method as claimed in any one of claims 13 to 25 wherein the urea and/or rock phosphate presented to acidification is of a particle size substantially less than 150 microns.

27. A method of any one of claims 13 to 26 wherein step I(i) is used.

28. A granulated fertiliser composition having available N values greater than 3% w/w and available P values greater than 8% w/w where it is a blend of i) urea, and ii) a granulated reaction product of a process in which either a mix of urea and rock phosphate has been subjected to acidification or rock phosphate has been acidified in the presence of urea.

29. A granulated composition produced using a process of any one of claims 1 to 27. The use of a granulated composition of claim 28 as a fertilizer.

31. A method of applying N and P value fertiliser to a desired locus of application, said method involving the use of a composition produced by a method of any one of claims 1 to 27 or a composition of claim 28. Dated: 28 October 2004 130P FERTILISER LIMITED A J PARK Patent Attorneys for the Applicant i H:\library\patents\djj\specs\419167.djj