WO1981001704A1

WO1981001704A1 - Ammonium nitrate process and products

Info

Publication number: WO1981001704A1
Application number: PCT/US1979/001073
Authority: WO
Inventors: G Williams; J Smith
Original assignee: Nitram Inc
Priority date: 1979-12-12
Filing date: 1979-12-12
Publication date: 1981-06-25
Also published as: GB2075487B; BR7909055A; DE2953920A1; GB2075487A

Abstract

A process for making high strength prills of ammonium nitrate by the following steps: (a) feeding a stream of ammonium nitrate-water solution (1) into an evaporation apparatus (A); (b) concentrating the solution to a concentration of 90-100%, preferably about 96% to make a low density product or about 99% to make a high density product; (c) adding aluminum sulfate (6) to the ammonium nitrate to provide a concentration of 4 to 50 parts per million of aluminum; (d) spraying the ammonium nitrate into a prilling tower (B); (e) passing the prills through a drying/cooling apparatus (C); (f) passing the prills through a screening apparatus (D); and, (g) applying at least one coating agent to the prills (E). A high strength low density porous prilled product of ammonium nitrate made by the foregoing process, wherein the concentration in step (b) is about 96% ammonium nitrate, containing about 4 to 50 parts per million of aluminum and which is useful as an ANFO explosive. A high strength high density nonporous prilled product of ammonium nitrate made by the foregoing process, wherein the concentration in step (b) is about 99% ammonium nitrate, containing about4 to 50 parts per million of aluminum and which is useful as an agricultural fertilizer.

Description

AMMONIUM NITRATE PROCESS AND PRODUCTS

Field of the Invention

The invention is in the field of processing ammonium nitrate compositions and the products thereof.

DESCRIPTION OF THE PRIOR ART

The general concept of adding aluminum sulfate to ammonium nitrate explosives is known. For example, U.S. Patent No. 1,464,667 to Snelling disclosed adding aluminum sulfate containing large amounts of water of crystallization (column 1, lines 25-27) to explosive materials, such as ammonium nitrate, for the purpose of reducing the flame temperature.

The general concept of adding elemental aluminum as a sensitizer to ammonium nitrate explosives is also known. For example, U.S. Patent No. 2,168,562 to Davis disclosed this concept (column 2, line 7).

U.S. Patent No. 3,317,276 to Brown et al disclosed the concept of stabilizing substantially pure ammonium nitrate by crystallization from a liquid mixture with boric acid, an alkali-metal salt thereof, an ammonium salt thereof, or a mixture thereof in an amount sufficient to substantially reduce the sensitivity of the ammonium nitrate to II-IV and/or III-IV crystal type transitions. Ammonium nitrate was crystallized from a liquid mixture comprising (a) boric acid, an alkali-metal salt thereof, an ammonium salt thereof, or a mixture thereof, plus (b) monoammonium or diammonium phosphate, and preferably also up to about 1 percent diammonium sulfate.

U.S. Patent No. 3,639,643 to Mollerstedt et al disclosed a method for eliminating the 32°C. phase transition in granules containing free ammonium nitrate by incorporating into the liquid nitrate solution, prior to conversion of the nitrate into solid form, between 0.1 and 10% by weight of a colloidal hydrate or hydroxide of silicon or iron or aluminum. Example 3, relating to large diameter granules of ammonium nitrate, described a 94% aqueous solution of ammonium nitrate to which was added aluminum sulfate and then ammonia so that it contained 0.5% colloidal Al(OH)₃ based on the quantity of nitrate.

Finally, British Patent No. 891,562 described mixing a hot pure ammonium nitrate solution having a concentration of at least 95% by weight with from 0.1 to 1% by weight, calcu lated on the pure ammonium nitrate, of hydrated aluminum sulfate to obtain a homogeneous mixture at a temperature of 165 to 170°c and then granulation of the mixture.

SUMMARY OF THE INVENTION

The invention is a process and two products made the process.

The inventive process is a method of making high strength prilled products of ammonium nitrate by the steps of: (1) feeding a stream of an ammonium nitrate-solution into an evaporation apparatus; (2) concentrating the ammonium nitrate-water solution in the evaporation apparatus to a concentration of about 90 to 100% by weight ammonium nitrate; (3) adding aluminum sulfate to the ammonium nitrate to provide a concentration of 4 to 50 parts per million of aluminum; (4) spraying the ammonium nitrate containing aluminum sulfate into a prilling tower where the falling prills are cooled by a rising stream of air; (5) passing the prills to a drying/ cooling apparatus where they are dried and cooled; (6) passing the prills to a screening apparatus where the oversize and undersize particles are removed; and, (7) applying at least one coating agent to the outer surface of the prills.

The first inventive product is a high strength low density porous prilled product of ammonium nitrate made by the foregoing process wherein the concentration at the end of step (2) is about 95.5 to 96.6% by weight ammonium nitrate, the prilled product having a bulk density of about 750 to 850 kilograms per cubic meter, and the prilled product contains about 4 to 50 parts per million of aluminum. The high strength low density porous prilled product is useful as an ANFO explosive.

The second inventive product is a high strength high density nonporous prilled product of ammonium nitrate made by the foregoing process wherein the concentration at the end of step (2) is about 99% by weight ammonium nitrate, the prilled product having a bulk density of about 850 to 1000 kilograms per cubic meter, and the prilled product contains about 4 to 50 parts per million of aluminum. The high strength high density nonporous prilled product is useful as an agricultural fertilizer.

The inventive products exhibit reduced breakdown in the drying/cooling apparatus, increased hardness, better oil absorption by the low density porous product, reduced caking during storage, and reduced tendency to form dust. The inventive process causes less air pollution (as measured by the opacity of the prilling tower discharge air) and has increased operating efficiency (as evidenced by reduced recycling per unit of output).

BRIEF DESCRIPTION OF THE DRAWING

The figure shows a schematic diagram of the apparatus and steps used in the process of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive process is shown schematically. in the figure. Referring to the figure, an ammonium-water solution 1 of any concentration, but preferably 83-85% ammonium nitrate concentration at a temperature of about 220°F (114°C), is fed through line 3 to the concentration or evaporation section operated at about 290-300°F (143-149°C) where water 5 is driven off by use of an external heat source 4, such as steam heat. Although the pH of the feed stream 1 can vary over a wide range, it is preferable to operate with a slight excess of ammonia with a pH of approximately 6.0 to 6.5. The ammonium nitrate can be concentrated to a concentration of about 90- 100% by weight, but about 95.5 to 96.6% by weight is preferable for making a porous low density prilled product and about 99% by weight is preferable for making a nonporous high density prilled product. A second stage evaporation apparatus may be used when making the 99% ammonium nitrate concentration

Aluminum sulfate 6, preferably in the form of 35% solution in water, is added or injected into the ammonium nitrate leaving the evaporation section. The aluminum sulfate can be added at any point of the process prior to pril ling, but the preferable addition point is just exit the evaporation section. Aluminum sulfate is added to give concentrations of about 4 to 50 parts per million (ppm) of aluminum, but the preferred concentration is about 7 to 40 ppm of aluminum and the most preferred range is about 15-20 ppm of aluminum.

The ammonium nitrate containing the aluminum sulfate is fed through line 7, still at a temperature of about 290- 300°F, and is sprayed into the prilling section B where the falling prills are cooled by a rising stream of air 8 as they pass down the tower. The ammonium nitrate can be cooled to any temperature from its solidification point down; however, the preferred temperature at the exit of the prilling section is in the range of about 185-195°F (85-91°C). The ammonium nitrate prills 9 from the prilling section are passed to the drying/cooling section C where they are dried and cooled. The preferable moisture content leaving the section is about 0.15 to 0.20% by weight; however, higher moistures can give an acceptable product. It is preferable to cool the product leaving this section C to below about 100°F (38°C); however, slightly higher temperatures may be necessary during warm summer months. The air stream 11, used in the drying/cooling section C, is passed to a scrubbing section H and then exits to the atmosphere at 22. The scrubbing liquor 23 is passed to a weak liquor holding tank G where it is recycled back to the scrubbing system.

The ammonium nitrate prills 12 from the drying/cool ing section C are passed to the screening section D where oversize and undersize materials 13 are removed. Prills which are about 1.2 to 3.0 millimeters in diameter are preferred. Therefore, materials which are under 1.2 mm are considered undersize and materials which are over 3.0 mm are considered oversize.

The undersize and oversize material 13 is dissolved in sump F in a weak ammonium nitrate solution stream 20 and fed through line 18 to the weak solutions tank G along with the scrubbing liquor 23 from the scrubbing section H. The concentration of the weak liquor in tank G is maintained by adding makeup water 10 and recycling a portion of the weak liquor 19 to the evaporation section A through line 2. Another portion of the weak liquor 21 is recycled to the scrubbing section H. The prills 14 from the screening section D have coating agents applied to their outer surfaces and are mixed thoroughly in the coating section E. Either liquid and/or solid coating agents can be used, but the preferable method is a liquid coating agent 15 followed by a solid coating agent 16. A preferred liquid coating agent is "Petro Ag Special", a 50% aqueous solution of a polyalkylated polynuclear sulfonate marketed by Petro Chemical Inc. A preferred solid coating agent is kaolin clay. The product 17 from the coating system E can be stored or shipped for use. An important advantage achieved by this invention is the ability of the production plant to meet federal, state and local environmental pollution control standards. The prilling tower discharge air 8 must satisfy such pollution standards. These standards are frequently expressed in terms of the opacity of the discharge air. For this purpose, opacity is measured using a standardized smoke meter. The prilling process inherently produces microscopic drops (plume) which pass out of the tower in the discharge air, thus causing measurable opacity. The present invention, through the use of a very low concentration of aluminum sulfate as described, produces an unexpected lowering in the opacity of the discharge air from the prilling tower. Test data showing the reduction in opacity are summarized in the table below.

^•ia

I

The concentration of aluminum sulfate used in the process is adjusted within the range of about 4 to 50 ppm of aluminum, preferably within the range of about 7 to 40 ppm of aluminum, to obtain the desired product quality and desired plume opacity. The concentration of aluminum required may change within a few hours depending on weather conditions plus three plant operating parameters, namely, air flow to the prilling tower (which may be adjusted), concentration of ammonium nitrate, and concentration of free ammonia in the melt being fed to prilling tower B. As these parameters vary, the operator adjusts the feed rate of aluminum sulfate sol ution 6 within the previously described range to give the desired product quality and plume opacity.

As described previously the inventive process can be adjusted to produce two inventive products. The first inventive product is a high strength low density porous prilled product of ammonium nitrate. This product is made by concentrating the ammonium nitrate-water solution in evaporation apparatus A to approximately 95.5 to 96.6% by weight ammonium nitrate and then running the remaining steps of the process as described above. The low density product has a bulk density of about 750 to 850 kilograms per cubic meter. It contains about 4 to 50 parts per million of aluminum, preferably about 7 to 40 parts.per million of aluminum, and most preferably about 15 to 20 parts per million of aluminum. The porous nature of the low density prills result from the evaporation of the water in the prill. The low density prills, which are useful as an ANFO (Ammonium Nitrate Fuel Oil) explosive, have the following most preferred analysis:

One of the advantages of the porous low density prills is their high strength which results from adding the very low concentration of aluminum sulfate as a strengthening agent. Although the exact mechanism is unknown at present and the inventors do not wish to be bound by any theory, it may be theorized that the aluminum atoms modify and strengthen the crystal structure of the ammonium nitrate. In any event, it is totally unexpected that such a very low concentration of aluminum sulfate could achieve this strengthening effect. Test data showing this effect are summarized in the table above .

The second inventive product is a high strength high density nonporous prilled product of ammonium nitrate. This product is made by concentrating the ammonium nitrate-water solution in one or two stages in evaporation apparatus A to approximately 99% by weight ammonium nitrate and then running the remaining steps of the process as described earlier. The high density prilled product has a bulk density of about 850 to 1000 kilograms per cubic meter. It contains about 4 to 50 parts per million of aluminum, preferably about 7 to 40 parts per million of aluminum and most preferably about 15 to 20 parts per million of aluminum. The high density prills are useful as an agricultural fertilizer.

One of the advantages of the nonporous high density prills is their high strength which results from adding the very low concentration of aluminum sulfate as a strengthening agent. Again, it is totally unexpected that such a very low concentration of aluminum sulfate could achieve this strengthening effect.

Another economic advantage of the invention is improved plant operation efficiency. This derives from two effects. First, the higher strength of the prills results in lower amounts of ammonium nitrate in recycle stream 19 going to the evaporation section A since there is less prill breakage in the screening apparatus D. This means there is a reduction of fines or undersize particles from the screener D per unit of output. The most immediate benefit of reduced recycle is lower heat consumption (per unit of prill product) to evaporate the recycle stream 19 in evaporation apparatus A. This offers the potential of increasing plant throughput if evaporation capacity is limiting.

Second, reduced opacity of the discharge air 8 from prilling tower B to acceptable levels is achieved by the inventive process even during warm humid weather when other plants may have to reduce or cease operations. The operator is able to achieve these benefits relating to product and operation within broad ranges of weather conditions and plant operating parameters.

The above-described embodiments are intended to be illustrative, not restrictive. The full scope of the invention is defined by the claims, and any and all equivalents are intended to be embraced.

Claims

WHAT IS CLAIMED IS:

1. A process for making high strength prilled products of ammonium nitrate, comprising:

(1) feeding a stream of an ammonium nitrate-water solution into an evaporation apparatus;

(2) concentrating said ammonium nitrate-water solu tion in said evaporation apparatus to a concentration of about

90 to 100% by weight ammonium nitrate;

(3) adding aluminum sulfate to the concentrated ammonium nitrate to provide a concentration of 4 to 50 parts per million of aluminum; (4) spraying the concentrated ammonium nitrate containing aluminum sulfate into a prilling tower where the falling prills are cooled by a rising stream of air;

(5) passing said prills to a drying/cooling apparatus where the prills are dried and cooled; (6) passing said prills to a screening apparatus where oversize and undersize particles are removed; and

(7) applying at least one coating agent to the outer surface of said prills.

2. The process of claim 1 wherein the feed stream in step (1) contains a slight excess of ammonia and has a pH of 6.0 to 6.5.

3. The process of claim 1 wherein step (2) is performed at a temperature of about 290 to 300°F (143 to 149°C).

4. The process of claim 1 wherein step (2) concentrates the ammonium nitrate-water solution to a concentration of about 95.5 to 96.6% by weight ammonium nitrate for making a porous low density prill.

5. The process of claim 1 wherein step (2) concentrates the ammonium nitrate-water solution to a concentration of about 99% by weight ammonium nitrate for making a nonporous high density prill.

6. The process of claim 1 wherein step (3) is performed using aluminum sulfate in the form of a 35% solution in water.

7, The process of claim 1 wherein the aluminum sulfate added to the concentrated ammonium nitrate in step (3) provides a concentration of about 7 to 40 parts per million of aluminum.

8. The process of claim 1 wherein the aluminum sulfate added to the concentrated ammonium nitrate in step (3) provides a concentration of about 15 to 20 parts per million of aluminum.

9. The process of claim 1 wherein the temperature at the exit end of the prilling tower in step (4) is in the range of about 185 to 195°F (85 to 91°C).

10. The process of claim 1 wherein the prills leaving the drying/cooling apparatus in step (5) have a moisture content of about 0.15 to 0.20% by weight and a temperature below about 100°F (38°C).

11. The process of claim 1 wherein the air stream used in the drying/cooling apparatus in step (5) is passed to a scrubbing section.

12. The process of claim 1 wherein the oversize and undersize particles from step (6) are dissolved in a weak ammonium nitrate solution stream, fed to a weak solutions tank, and recycled to the evaporation apparatus in step (2).

13. The process of claim 1 wherein step (7) comprises applying a liquid coating agent followed by a solid coating agent.

14. A high strength low density porous prilled product of ammonium nitrate made by the process of claim 1 wherein the concentration at the end of step (2) is about 95.5 to 96.6% by weight ammonium nitrate, said prilled product having a bulk density of about 750 to 850 kilograms per cubic meter, and said prilled product containing about 4 to 50 parts per million of aluminum.

15. The prilled product of claim 14 wherein said product contains about 7 to 40 parts per million of aluminum.

16. The prilled product of claim 14 wherein said product contains about 15 to 20 parts per million of aluminum.

17. A high strength high density nonporous prilled product of ammonium nitrate made by the process of claim 1 wherein the concentration at the end of step (2) ia about 99% by weight ammonium nitrate, said prilled product having a bulk density of about 850 to 1000 kilograms per cubic meter and said prilled product containing about 4 to 50 parts per million of aluminum.

18. The prilled product of claim 17 wherein said product contains about 7 to 40 parts per million of aluminum.

19. The prilled product of claim 17 wherein said product contains about 15 to 20 parts per million of aluminum.