US3032450A - Ammonium nitrate explosive and its production - Google Patents

Description

United States Patent Ofiice 3,032,450 Patented May 1, 1962 ware No Drawing. Filed Apr. 1, 1958, Ser. No. 725,480 19 Claims. (Cl. 149-7) This invention relates to an ammonium nitrate explosive and to its production. In one of its aspects, the invention relates to the conversion of an ammonium nitrate fertilizer which has been clay-coated and which is not readily detonatable to a readily detonatable explosive by removing the clay coating and adding a combustible liquid. In another of its aspects, the invention relates to a method of converting such a fertilizer grade ammonium nitrate as has been described in a manner as described by heating and agitating together a combustible which is liquid under the conditions of operation and said ammonium nitrate until the clay-coating thereon has been substantially replaced with said combustible material. In another of its aspects, the invention provides an improved ammonium nitrate explosive by heating the combustible-coated nitrate to a temperature at which the nitrate passes through a phase transition which causes cracking of the nitrate and allows the oil to soak into the individual particles thereof.

The conventional clay-coated ammonium nitrate which is the ordinary commercial product used for fertilizer is not readily detonatable and when mixed with the proper amount of combustible material, such as petroleum hydrocarbon, which is used in the preparation of detonatable ammonium nitrate, the said commercial product produces a rather difficulty detonatable material.

Explosives with ammonium nitrate as the oxidizer are old in the art. The ammonium nitrate is intimately mixed with or soaked with a combustible material such as peat, petroleum distillates or residues, coke, and similar materials. It has been established that detonation characteristics are favorably affected by low moisture content of the ammonium nitrate, this ordinarily being below 1.5 weight percent, and by intimate contact between the ammonium nitrate and the combustible material.

It is known that there are a number of variables which afiect the ease of detonation of ammonium nitrate explosives. Included among these variables, which are known to one skilled in the art of ammonium explosives, are the following which are applicable to ammonium nitrate and mineral oil mixtures: fineness of ammonium nitrate; fineness of combustible, when it is a solid at ordinary temperatures; 'diiferences in the method of coating the ammonium nitrate with the combustible; differences in the specific types of combustible materials used; variation of the moisture content.

The ready and general availability of fertilizer grade ammonium nitrate makes it desirable as a material for use in explosives. However, as noted, the clay-coated commercial product is unsuited for explosive purposes.

I have now found that if the conventional clay-coated ammonium nitrate fertilizer is agitated with a petroleum hydrocarbon, such as a gas oil or diesel fuel, until the clay coating has been removed from the nitrate particles and the oil coated thereon, that the ammonium nitrate which is thus freed of the clay coating and soaked with the liquid hydrocarbon has good detonating properties.

It is an object of this invention to provide an ammonium nitrate explosive. It is another object of this invention to provide a method for the preparation of an ammonium nitrate explosive. It is a further object of the invention to provide a method for producing an ammonium nitrate explosive from a fertilizer grade ammonium nihydrocarbons being found in the exit sweep gas.

trate. A still further object of the invention is to produce a combustible-coated ammonium nitrate particle. A further object still is the production of a combustiblecoated ammonium nitrate particle in which the coating is, at least in part, found within cracks in the surfaces of the particle.

Other aspects, objects and several advantages of the invention are apparent from this description and the claims.

According to the present invention, there is provided a method for the preparation of a detonatable ammonium nitrate composition from a coated ammonium nitrate product unsuitable for use as an explosive because of its poor detonatability which comprises intimately contacting said coated ammonium nitrate with a combustible which is liquid under the treating conditions for a time and in a manner so as to remove the coating from the ammonium nitrate and to coat the same with said combustible, and recovering said combustible-coated ammonium nitrate from the treating mass.

Thus, the process of the present invention comprises the steps of removing the clay coating from the ammonium nitrate and forming an explosive composition of uncoated ammonium nitrate which is soaked with a combustible which is liquid under the treating conditions and such that it will not hinder the detonation of the final product of the invention, the combustible being usually a petroleum hydrocarbon such as diesel oil, gas oil, etc. The process can be practiced readily by forming, for example, in a jet-agitated vessel, a slurry of coated ammonium nitrate prills with diesel fuels or oils, such as a gas oil, the moving hydrocarbon removing the clay from the prills and forming a suspension of the clay in the hydrocarbon. The clay is removed by draining the excess hydrocarbon and suspended clay from the prills. This is accomplished in a batch operation by draining off the excess liquid hydrocarbon and suspended clay. Continuous operation is within the scope of the invention and can be practiced by providing an agitating zone adjacent a conveyor zone, the coated prills being fed to the agitation zone for agitation with the oil and passed through the conveying zone wherein the prills are allowed to settle and the supernatant oil layer is decanted. The prills are allowed to drain until the oil-soaked prills are about five to ten percent by weight oil and the remainder, ammonium nitrate. The explosive composition is then ready for use. Agitation is ordinarily discontinued while draining away the hydrocarbon containing the suspended clay. However, some agitation, at least of the hydrocarbon phase, can be provided to insure good suspension of the clay therein, in the event some settling of the clay which is, in the specific instance, undesirable, is occurring. Ordinarily, some clay in the final product, not usually more than that suspended in the oil coating, will not be objectionable. Indeed, the final product appears to be quite suitable when it contains some clay.

Also, according to the present invention, there is provided the important and now preferred feature of drying the ammonium nitrate during the removal of the clay coating therefrom for some time thereafter. This is accomplished by heating the oil-ammonium nitrate mixture preferably with agitation and preferably providing for the removal of vaporized water with an entrainer gas, for example, in a sweep stream of natural gas. The liquid hydrocarbon used in this modification is preferably a low volatility fraction such as described since this facilitates operation without high concentration of vapors of liquid Otherwise, more volatile combustible materials can be used which would be those known in the art. The liquid hydrocarbon or other combustible material, if desired, can contain particles of carbon black or other materials which are found to preferentially deposit with the combustible on the nitrate particle.

When heating is practiced according to the invention, it is practiced for, at least, one of several reasons.

One reason for heating the oil-coated prills is to pass the prills through a phase transition point which occurs at about 90 F. Such heating is useful even though no substantial dehydration is practiced. Thus, the passing through a phase transistion point at about 90 F. causes a rather large volume change to take place which aids in cracking the prills and allowing the oil to enter them more readily. This is also advantageous in the formation of a uniform mixture and in contacting intimately the oil and the nitrate.

Another reason for heating is, of course, the dehydration of the final product to bring it within the desired known low water content iimit. The heating can be accomplished at any time during the operation, for example, during agitation or thereafter. When heating is practiced, it is practiced to increase substantially the vapor pressure of the water and preferably, the temperature will be at or above the boiling point of water, for example, in a range of from about 210 to about 225 F. The heating time usually is in the range of live minutes to two hours, more usually in the range from about ten minutes to one-half hour. The excess oil, if any is prescut when heating occurs, is drained and the oil or combustible material coated prills cooled, thus yielding a composition ready for use in blasting.

The blasting compositions formed by the process of this invention can be used in a conventional and known manner, they can be packed in bags or other containers for placing in the hole, and, for use in wet locations, the containers are preferably water-proof. These containers can be, for example, paper, cloth or plastics such as polyethylene.

Example I Prilled uncoated ammonium nitrate as used in the preparation of coated ammonium nitrate of fertilizer grade and having an average particle size of 14 mesh was soaked with 7 weight percent diesel fuel and then detonated in cardboard tubes with Primacord as an initiator. A similar mixture made with clay-coated ammonium nitrate prills would not detonate under the same conditions. indeed, it would not detonate when'dynamite booster was used. Several mixtures of the uncoated ammonium nitrate soaked with 7 Weight percent diesel fuel and several of the similar mixtures with clay-coated ammonium nitrate prills which would not detonate, were prepared to confirm the first-reported findings of this example.

Example If A mixture of coated ammonium nitrate of fertilizer grade and diesel fuel and a mixture of uncoated ammonium nitrate and diesel fuel were prepared and detonated confined in an iron pipe. The initiators were dynamite boosters set off with a small amount of Primacord. (Samples confined in an iron pipe can be detonated in certain instances where the lower degree of confinement of a cardboad tube will not result in detonation.) The uncoated ammonium nitrate and diesel fuel mixture detonated with 54 plastic cards between the initiator and the explosive. The clay-coated ammonium nitrate-diesel fuel mixture detonated with a maximum of 12 cards between the initiator and the explosive. Several of each of the mixtures were prepared to confirm the findings reported in this example.

Petroleum hydrocarbons particularly suited for use in this invention are those boiling in the range of 250 F. to 800 F., preferably from about 300 F. to 700 F. These ranges include distillates known in the petroleum refining art as kerosene, gas oil, diesel fuel, stove oil, and numerous others.

The ammonium nitrate is at least for the most part available as prills within the range of 10 to 20 mesh in size. Some of the fertilizer is available as crystallized ammonium nitrate, and a small part is available as a ground product. These latter products may contain a considerable amount of particles finer than 20 mesh and as fine as mesh.

The clay coating on the ammonium nitrate is usually diatomaceous earth, although a relatively minor portion of the fertilizer is coated with kaolin, fullers earth or other clays. The amount used varies to some extent, but 3 /2 percent (based on the total) is a representative amount.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention, the essence of which is that a fertilizer grade clay-coated ammonium nitrate is rendered suitable for use as an explosive by replacing the clay-coating of the ammonium nitrate with a combustible material such as a hydrocarbon, substantially as set forth and described herein.

I claim:

1. A method for the conversion of a clay-coated fertilizer grade ammonium nitrate to an explosive which comprises admixing said ammonium nitrate with a liquid petroleum hydrocarbon, agitating the mixture until substantially the entire clay coating has been removed from the particles of the ammonium nitrate and the particles have been coated with the liquid petroleum hydrocarbon, removing any liquid in excess of that wetting the particles, and recovering an explosive liquid-coated ammonium nitrate.

2. A method according to claim 1 wherein said liquid petroleum hydrocarbon has a boiling point in the range of about 250 F. to about 800 F.

3. A method according to claim 2 wherein the excess liquid is removed until the liquid-coated ammonium nitrate particles are in the range of about 5 to about 10 weight percent liquid petroleum hydrocarbon.

4. A method according to claim 3 wherein the liquidcoated ammonium nitrate particles are heated to pass the ammonium nitrate through a phase transition which occurs at about F.

5. A liquid petroleum hydrocarbon ammonium nitrate explosive prepared according to the method of claim 4.

6. A method for the conversion of a clay-coated fertilizer grade ammonium nitrate to an explosive which comprises admixing said ammonium nitrate with a liquid petroleum hydrocarbon, agitating the mixture until substantially the entire clay coating has been removed from the particles of the ammonium nitrate and the particles have been coated with the liquid petroleum hydrocarbon, removing any liquid in excess of that wetting the particles, and heating the liquid-coated ammonium nitrate particles to pass the ammonium nitrate through a phase transition.

7. A liquid petroleum hydrocarbon ammonium nitrate explosive prepared according to the method of claim 6.

8. A method for the preparation of an explosive composition which comprises intimately contacting ammonium nitrate particles with a liquid petroleum hydrocarbon and heating the thus-formed mixture at least to a temperature at which the ammonium nitrate passes through a phase transition, thereby producing cracks in the surfaces of the ammonium nitrate particles, the cracks being, at least in part, filled with said liquid petroleum hydrocarbon.

9. A method for the preparation of an explosive composition which comprises intimately contacting ammonium nitrate particles with a liquid petroleum hydrocarbon and heating the thus-formed mixture to pass the ammonium nitrate through a phase transition which occurs at about 90 F.

10. An explosive composition prepared according to claim 8.

11. An explosive composition prepared according to claim 9.

12. A method according to claim 1 wherein during the removal of the coating, said ammonium nitrate and said liquid petroleum hydrocarbon are heated and an entrainer gas is passed through the mass to facilitate removal of water from said ammonium nitrate.

13. A method according to claim 1 wherein the mixture is heated during agitation.

14. A method according to claim 1 wherein the mixture is heated to a temperature in the range of approximately 210-225 F.

15. A method according to claim 1 wherein said liquid petroleum hydrocarbon is diesel fuel.

16. A method according to claim 1 wherein said liquid petroleum hydrocarbon is gas oil.

17. A method according to claim 1 wherein an entrainer gas is passed through the mixture during said step of agitating.

18. A method according to claim 17 wherein the entrainer gas is natural gas.

19. A method for the conversion of a clay coated fer- References Cited in the file of this patent UNITED STATES PATENTS OBrien Sept. 2, 1913 Kirst et al Feb. 26, 1935 Taylor et a1 Mar. 18, 1952 OTHER REFERENCES Perry: Chemical Engineers Handbook, 3rd Edition,

20 3rd Impression, 1950, p. 1118.

Daugherty: Chemical and Engineering News, October 7, 1957, pp. 62 and 63, 52-05 S & L.

Claims (1)

1. A METHOD FOR THE CONVERSION OF A CLAY-COATED FERTILIZER GRADE AMMONIUM NITRATE TO AN EXPLOSIVE WHICH COMPRISES ADMIXING SAID AMMONIUM NITRATE WITH A LIQUID PETROLEUM HYDROCARBON, AGITATING THE MIXTURE UNTIL SUBSTANTIALLY THE ENTIRE CLAY COATING HAS BEEN REMOVED FROM THE PARTICLES OF THE AMMONIUM NITRATE AND THE PARTICLES HAVE BEEN COATED WITH THE LIQUID PETROLEUM HYDROCARBON, REMOVING ANY LIQUID IN EXCESS OF THAT WETTING THE PARTICLES, AND RECOVERING AN EXPLOSIVE LIQUID-COATED AMMONIUM NITRATE.