US3394038A - Method of producing ammonium nitrate explosive compositions having high package densities - Google Patents

Description

United States Patent Ofiice 3,394,038 METHOD OF PRODUCING AMMONIUM NITRATE EXPLOSIVE COMPOSITIONS HAVING HIGH PACKAGE DENSITIES Joseph J. Miunick and Gordon W. Bell, Marion, 11]., assignors to Commercial Solvents Corporation, a corporation of Maryland No Drawing. Continuation of application Ser. No. 421,644, Dec. 28, 1964. This application Apr. 25, 1967, Ser. No. 634,070

13 Claims. (Cl. 149--21) ABSTRACT OF THE DISCLOSURE Ammonium nitrate explosive compositions are prepared by grinding a dense ammonium nitrate (e.g., having a particle density from about 1.3 to 1.7 grams per cc.) to a particle size of about 8 to 200 mesh and mixing the particles, immediately after cessation of grinding, with a liquid hydrocarbonaceous fuel, the ground ammonium nitrate being kept in a state of continuous relative motion between the particles immediately upon completion of said grinding and until said mixing is complete. The resultant explosive compositions possess high package densities-for example, greater than about 1.0 gram/cc. or, when additionally containing whole, porous ammonium nitrate particles, greater than about 1.09 grams/cc.

This application is a continuation of application Ser. No. 421,644, filed Dec. 28, 1964, now abandoned.

This invention relates to the production of nitrocarbonitrate explosive compositions having good sensitivity and velocity from ammonium nitrate particles having a relatively high density, e.g. a particles density of at least about 1.3 and up to about 1.7 gm./cc.

Nitrocar'bonitrate explosive compositions basically include ammonium nitrate (AN) as an oxidizing agent and hydrocarbon oil as a sensitizing agent. Sodium nitrate can be substituted for up to about 50% of the AN. Other additives can be included, for instance, solid carbonaceous material, e.g. powdered coal, which can partially replace the liquid hydrocarbon to provide a desired oxygen balance and anti-caking agents to inhibit caking.

A first object of the present invention is the provision of nitrocarbonitrate explosive compositions having good sensitivity and velocity (detonation rate) as well as high package density, e.g. greater than about 1.09 gm./cc., from ammonium nitrate particles having a relatively high particle density. A second object is the provision of a low cost, easily pourable nitrocarbonitrate explosive composition containing relatively large amounts of anti-caking and free flowing agents and/or a relatively small amount of sensitizing agent while at the same time having good sensitivity and velocity as well as good package density (e.g. greater than about 1.0 gm./cc.), from ammonium nitrate particles having a relatively high particle density. Other objects will be apparent from the following description of the present invention.

In connection with the first object of the present invention, explosive compositions of relatively high package density are particularly advantageous for use in bore holes containing water since they can sink in the water. Prior attempts to use ammonium nitrate particles of relatively high particle density to produce nitrocarbonitrate explosive compositions having a relatively high package density were not satisfactory.

One approach involved the use of dense ammonium nitrate particles having a particle size greater than 30 mesh. The results were not satisfactory since the density 3,394,038 Patented July 23, 1968 desired for the nitrocarbonitrate explosive was not obtained and the ammonium nitrate particles did not satisfactorily mix with either liquid or solid carbonaceous material to produce the intimate mixture required for a good explosive.

Another approach involved grinding a portion of the dense ammonium nitrate particles and mixing it with larger sized particles. This did not result in a satisfactory explosive since the composition was not very homogeneous. Another approach involved grinding the ammonium nitrate particles and pelletizing them. This was not satisfactory since hydrocarbon oil added to the pellets was rapidly absorbed into the pellets in immediate contact with the oil, leaving very little oil for the other pellets. The resultant inhomogeneity produced explosives lacking in both sensitivity and power compared to the usual nitrocarb-onitrate explosives.

It has now been surprisingly discovered that explosive compositions having good sensitivity and velocity as well as a relatively high package density, e.g. greater than about 1.09 gm./cc., can be produced using dense ammonium nitrate particles having a size from about 8 to 200 mesh (U.S. Sieve Series) with at least about 20 weight percent, preferably about 25 to 60 weight percent, of the particles in the size range of about 100 to 200 mesh. The dense ammonium nitrate particles having the desired size distribution can 'be provided by grinding larger particles and, in accord with this invention, immediately thereafter keeping the ground ammonium nitrate particles in a state of continuous relative motion between the particles until they are mixed with other additives to be included in the formulation of the explosive composition. If the ammonium nitrate is permitted to stand for any period of time e.g. greater than about 1 minute in a normal atmosphere, after grinding, the final explosive composition produced therefrom will not have a package density within the desired range, e.g. above about 1.09 gm./cc., but instead the density would be in the range from about 1.0 to 1.05 gm./cc. When the ground ammonium nitrate is kept moving, the density of the final composition will be significantly enhanced, e.g. as high as from about 1.10 to 1.15 gm./cc. I

or higher, with densities as high as about 1.18 gm./cc. being obtained after the explosive composition has been tamped.

The ammonium nitrate particles utilized in the present invention can be a fertilizer grade ammonium nitrate. Generally, fertilizer grade ammonium nitrate contains various additives or fine particulate coatings added to inhibit caking and to promote free flowing characteristics of the material. Either the granular or prilled form of the dense ammonium nitrate larger than the size desired can be ground to the desired size distribution for use in the present invention. Moreover, in connection with the first object of this invention, the ground, dense ammonium nitrate can be used in part with porous ammonium nitrate which has not been ground. For instance, up to about Weight percent of the ammonium nitrate can be porous ammonium nitrate but generally, the ammonium nitrate can comprise from about 50 to weight percent of the ground, dense ammonium nitrate having the particle size distribution set forth above and from about 0 to 50 weight percent of porous ammonium 'ni-trzge, e.g. Whole prilled ammonium nitrate. In connection with the second object of the invention to provide the low-cost, easily pourable compositions, solely the ground, dense ammonium nitrate is used.

The dense ammonium nitrate used in the present invention can be advantageously ground to the desired particle size distribution in a hammer mill generally using a to A; -inch screen, preferably round holed, with a 3 p mill speed from about 2000' to 6000 rpm. The process of the present invention can be conducted under ambient temperature and pressure conditions and preferably in an atmosphere having a relative humidity not greater tha about 65%. v

The moving ammonium nitrate, at least a part of it having been ground to provide particles having the desired size distribution, is advantageously immediately combined (e.g. less than minutes, preferably less than about 1 minute) with a normally liquid carbonaceous fuel in an amount sufiicient to provide the desired sensitivity for the composition. Generally, from about 0.1 or 0.5 to 8% by weight of the liquid hydrocarbon is added to the ground ammonium nitrate. The maximum sensitivity for the explosive composition is usually Within a preferred range of 1.2 to 3%, depending somewhat on the ammonium nitrate particle size, in providing nitrocarbonitrate explosive compositions having a package density greater than about 1.09 gm./cc. The liquid hydrocarbon may be of any chemical characteristic, e.g. paraffinic, olefinic, naphthenic, aromatic, saturated or unsaturated. Hydrocarbons which are highly viscous at atmospheric temperatures can be heated to permit preparation of compositions. Preferred liquid hydrocarbons include No. 2 fuel oil and furnace oil which are readily available and which are relatively inexpensive. Other hydrocarbons include kerosene, crude oil and lubricating oil fractions. The liquid hydrocarbon is preferably added immediately after grinding. The ground ammonium nitrate must not be permitted to surge or stand before it is mixed with the liquid hydrocarbon and other components of the explosive composition.

A solid carbonaceous fuel, e.g. powdered coal, can be added to the explosive composition in an amount sufiicient to adjust the oxygen balance to give maximum power. Generally from about 0.1 to by weight, preferably about 3 to 8% byweight of a solid fuel can be added. The powdered coal advantageously has a particle size generally from about to 60 mesh for at least about 80 percent of the particles.

One or more anti-caking agents can be added to the explosive compositions of the present invention in an amount sufiicient to prevent caking and provide free fiowing compositions. Generally, fertilizer grade ammonium nitrate contains various additives of fine particulate coatings added to inhibit caking and to promote free-flowing characteristics of the material. Ammonium nitrate, as referred to herein, includes ammonium nitrate containing up to 3% of various anti-caking additives in addition to a moisture content which generally ranges up to 1%. The anti-caking agents, however, can be added in amounts from about 0.1 to 5 or 10% by weight, preferably from about 1 to 3.9 weight percent, in providing explosive compositions having a package density greater than about 1.09 gm./cc. The anti-caking agents are generally in powdered form to provide a very thin coating. Suitable anti-caking agents include inert, inorganic, solid materials which do not adversely affect the density of the explosive composition and have been employed heretofore in the ammonium nitrate industry to inhibit caking tendencies, such as fine clay, barytes, chalk, and the like. Organic agents may also be added such as wax, ground apricot pits, corn starch and the like, Kieselguhr and diatomaceous earth can be used in the free-flowing compositions. A particularly effective anti-caking agent which is the subject of cop'ending application Ser. No. 421,695, now US. Patent 3,368,929, is calcium chloride in discrete particle form e.g. pellets, having a size generally from about 6 to 20 mesh (U.S. Sieve Series) usually for at least about 90% of the particles which can be added generally in an amount from about 0.1 to 5% by weight. Powdered clay can be advantageously used in conjunction with calcium chloride to further enhance the anti-caking characteristics of the compositions without causing an adverse effect on their density.

After addition of the solid carbonaceous material and anti-caking agent to the ammonium nitrate-hydrocarbon oil mixture,"theexplosive 'composition'can'be mixed for a period of time sufficient to thoroughly mix all the ingredients, e.g. on the order of 3 to 25 minutes or more but the total processing should be completed in 2 hours or lesshThe mixing of the ground ammonium nitrate, liquid hydrocarbon, solid carbonaceous material and anticaking agent may be accomplished in a tumbling action mixer or in a'positive action blender.

Preferably, the-explosive composition of the present invention is packaged in moisture proof containers to prevent misfi'res in water-filled or moisture laden bore holes. Where dry bore holes are assured the container need not be water-proof, but a vapor barrier. in the package is advantageous. If desired, one or more containers of the explosive composition may be opened and the contents poured directly into the bore hole as a free-flowing material. For convenience and reliability, however, a container is preferred. The container preferably is vibrated before closing to provide maximum density of the composition. 1 The following examples more fully illustrated the present invention but it is not intended that the present invention be liimted to the specific proportions, ingredients, etc., thereof.

Examples I-lV In these examples, the calcium chloride, powdered coal, fuel oil No. 2 and ammonium nitrate used typically have the following specifications. The calicum chloride is of pelleted grade having a maximum moisture content of 0.3% and a size distribution, U.S. Sieve Series as follows:

Percent The powdered coal has an apparent density of about 0.75 to 0.85 and a size distribution, U.S. Sieve Series, as follows:

1 Percent 10 +20 maximum 15 20 +60 30 to -60 +pan maximum 60 The fuel oil No. 2 is of the following character:

Flash point (Cleveland Open Cup) 140 F. minimum.

Gravity, A.P.I. 30 to 38. Atmospheric distillation:

Initial boiling point 370 to 416 F. End boiling point 630 to 675 F. Pour point +10 to 0 F. Specific gravity, 60 F./60 F 0.840 to 0.875.

Viscosity at F., Saybolt seconds 33 to 38.

The ground, dense ammonium nitrate (AN) is of a specification as follows:

Apparent bulk density (densim- The prilled AN (porous AN) is of a specification as follows:

Apparent bulk density 0.78 to 0.85 gm./cc. Screen analysis, U.S. Sieve Series:

+8 1o +12 40 to 70%.

Screen analysis, U.S. Sieve Series:

-12 +16 25 to 50%. 16 +20 5 to +pan 2%.

Each of compositions Nos. 83, 86, 87 and 89 was not sensitive to a No. 8 blasting cap but was sensitive to 20 grams of Composition C-4 primer explosive. The ingredients in and the character of each of these explosive compositions is set forth in Table I.

TABLE I Example I 1 Dense AN with a particle density of 1.5 gm./cc.

- Porous AN with a particle density of 1 .35 gn1./cc.

3 Primed with tetryl, rated at 2" diam. pipe.

4 Primed with tetryl, rated at 3" diam. pipe.

5 Primed with Mine Gel 2, rated at 3 diam. pipe.

6 Primed with seismo booster, rated at 4 diam. can.

Composition No. 83 is produced in -a batch mixer. The whole prilled AN and of the No. 2 fuel oil are placed in the mixer and mixed for one minute. The coal, clay and calcium chloride are then added to the mixer. (Dense AN granules are ground in a hammer mill using a W inch round hole screen with a mill speed of 5300 r.p.m. It is passed directly into the screen and into the mixer.) The ground AN is not allowed to surge at any point before it is mixed with the other ingredients. The remainder of the No. 2 fuel oil is slowly added with the ground AN in the mixer and mixing is continued for 5 minutes after the ground AN is added. Thereafter the composition is dumped into a hopper and packaged. It can be packaged in polyethylene/burlap bags, polyethylene/muslin bags, spiral paper cartridges, and other packages with a vapor barrier. The packages are to be vibrated to maximum density before closing. For water resistant closure the bags are to be closed by twisting the polyethylene, bending the twist and wire tying it to effect a double seal.

Composition No. 86 was manufactured in a batch mixer. The ammonium nitrate was ground in a hammer mill using a inch round hole screen and conveyed directly into the mixer. The ground coal, clay and calcium chloride were added into the mixer as soon as possible after the mixing had started. No. 2 fuel oil was added through a nozzle during grinding after about /3 of the ammonium nitrate was ground directly into the mixer. The ammonium nitrate was not allowed to surge and was ground directly into the mixer. The composition was packaged in essentially the same manner as composition No. 83.

Composition No. 87 is an exemplification of the second object of the present invention which provides an easily pourable explosive composition solely from relatively dense AN particles which composition has good sensitivity and velocity while at the same time providing a composition with a good package density (e.g. greater than about 1) although it contains relatively large amounts (e.g. greater than about 3.9 weight percent) of anti-calcing and free flowing agents and a relatively small amount (e.g. less than about 1.2 weight percent) of liquid hydrocarbon sensitizing agent.

Composition No. 87 is a low-cost, free flowing blasting agent. It was manufactured by conveying AN which was hammer-milled through a 7 inch screen to a mixer ceocrook,

as it was ground and adding the fuel oil to the mixer during the grinding of the remainder of the AN. The mixing was continued for 5 minutes after the last of the AN was added. The calcium chloride, dried ground apricot pits and ground coal were then added and the mixing was continued for 5 minutes. The corn starch and kieselguhr were then added and the mixing was continued for about 5 minutes until the composition was homogeneous. The composition was dumped from the mixer and packaged in 4-ply, multiwall, paper bags with a plastic coated inner ply. Exposure of this composition to humid air during the processing was minimized, e.g. less than two hours.

Composition No. 89 is a seismographic grade nitrocarbonitrate for use in off-shore seismographic exploration. It was prepared in a tumbling action mixer. The order of addition of the materials to the mixer was as follows: Ammonium nitrate (ground immediately before mixing), furnace oil, coal and barytes. The mixing time after addition of coal and barytes was sufficient to thoroughly mix all the ingredients and it wasnot less than 3 minutes. The composition was packaged in steel cans, filled and vibrated so that the loaded steel can would submerge when placed in sea water.

We claim:

1. A process for producing ammonium nitrate explosive compositions from ammonium nitrate particles having a particle density from about 1.3 to 1.7 gm./ cc. comprising grinding the ammonium nitrate into particles having a size distrbution in the range of about 8 to 200 mesh with at least about 13 weight percent being in the range from about 100 to 200 mesh and immediately mixing the ground ammonium nitrate with a liquid hydrocarbonaceous fuel in an amount sufiicient to provide the desired sensitivity for the composition, said ground ammonium nitrate being kept in a state of continuous relative motion between the particles immediately upon completion of said grinding and until said mixing is complete.

2. Process of claim 1 wherein said liquid fuel is added in an amount of from about 0.1 to 8% by weight based on the total weight of the composition.

3. Process of claim 2 further including mixing a solid carbonaceous fuel into said composition in an amount sufficient to adjust the oxygen balance of said composition to provide the desired power.

4. Process of claim 3 wherein said solid fuel is added in an amount of from about 0.1 to 10% by weight based on the total weight of said composition.

5. Process of claim 3 wherein said solid fuel is added in an amount of from about 3 to 8% by weight based on the total weight of said composition.

6. Process of claim 3 further including mixing an anticaking agent into said composition in an amount sufiicient to prevent caking of the composition.

7. Process of claim 6 wherein said anti-caking agent is calcium chloride in particle form including particles having a size from about -6 to 20 mesh, said agent being included in an amount of about 0.1 to 5 weight percent, based on the total composition.

8. Process of claim 6 wherein said anti-caking agent is a combination of clay and calcium chloride in particle form including particles having a size from about 6 to 20 mesh said agent being included in an amount of about 0.1 to 5 weight percent, based on the total composition.

9. Process of claim 6 wherein said anti-caking agent is barytes, said agent being included in an amount of about 0.1 to weight percent, based on the total composition.

10. process for producing ammonium nitrate explosive compositions having a package density greater than about 1.09 gm./cc. from ammonium nitrate consisting essentially of about 20 to 1 00 weight percent of dense particles having a particle density greater than about 1.3 gm./ cc. and 0 to about weight percent of porous particles having a size distribution in the range of about 8 to 20 mesh and an apparent bulk density of about 0.78

to 0.85 gm./cc. which comprises grinding the dense particles of ammonium nitrate into particles having a size distribution in the range of about 8 to 200 mesh with at least about 13 weight percent being in the range of about 100 to 200 mesh, immediately mixing the ground ammonium nitrate with from about 1.2 to 3.0 weight percent normally liquid hydrocarbonaceous fuel, from about 0.1 to 10 weight percent powdered coal, from about 1.0 to 3.9 weight percent inert, inorganic, solid, anti-caking material, and with the said porous ammonium nitrate particles when present, said ground ammonium nitrate being kept in a state of continuous relative motion between the particles immediately upon completion of said grinding and until said mixing is complete.

11. The process of claim 10 wherein the ammonium nitrate consists essentially of about 50 to 100 weight percent of said dense particles and O to about 50 weight percent of said porous particles.

12. The process of claim 11 wherein the weight ratio of said dense particles to said porous particles is approximately 2:1.

13. A process for producing a low cost, easily pourable explosive composition having a package density greater than about 1.0 g-m./cc. from ammonium nitrate consisting essentially of particles having a particle density greater than about 1.3 gm./cc. which comprises grinding the ammonium nitrate into particles having a size distribution in the range of about 8 to 200 mesh with at least about 13 weight percent being in the range of about 100 to 200 mesh, immediately mixing the ground ammonium nitrate with from about 0.1 to 1.2 weight percent normally liquid hydrocarbonaceous fuel, from about 0.1 to 10 weight percent powdered coal, and from about 3.9 to 5.0 weight percent inert, inorganic, solid, anti-caking material, said ground ammonium nitrate being kept in a state of continuous relative motion between the particles immediately upon completion of said grinding and until said mixing is complete.

References Cited UNITED STATES PATENTS 2,975,046 3/1961 Cooley et al. 149--46 X 2,997,378 8/1961 Cox et al. 149-46 X 3,095,335 6/1963 McCl oud 149-112 X BENJAMIN R. PADGETT, Primary Examiner.

S. J. LECHERT, JR., Assistant Examiner.