US3052578A - Ammonium nitrate base blasting agent - Google Patents

Description

Sept. 4, 1962 C. O. DAVIS ET AL AMMONIUM NITRATE BASE BLASTING AGENT Filed June 14, 1961 EFFECT OF WATER N WEIGHT 0F ANHDNIUH NITRATE PER UNIT VOLUME POUNDS 0F AMHONTUH NITRATE PER CUBIC FOOT l0 I5 I WATER (BASED ON TOTAL WEIGHT 0F BLEND) I INVENTORS CLYDE OLIVER DAVIS HARTWELL HENRY FASSNACHT WILLIAM EARLE KIRST CHARLES HARDING NOREN BY 3 a g ATTORNEY rates atent ire AlVflVlONIUM NITRATE BASE BLASTING AGENT Clyde Oliver Davis and Hartwell Henry Fassnacht, Wenonah, and William Earle Kirst, Woodbury, 'N.J., and Charles Harding Noren, Aurora, Col0., assignors to E. I. du Pout de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 14, 1961, Ser. No. 116,984 5 Claims. (Cl. 149-60) The present invention relates to a novel blasting agent. More particularly, this invention relates to a blasting agent especially adapted for use in large-scale blasting operations, such as quarrying, open-pit mining, and stripping operations. This application is a continuation-in-part of our copending application Serial No. 644,595, filed March 7, 1957, now abandoned.

The main function of an explosive charge in a blasting operation is to provide the energy needed to release material from its natural formation and, to the extent practicable, to render that material in a form in which it can be handled or processed further with minimum difficulty. The cost of the explosive and of preparing the site for the blasting operation are basic to the ultimate cost of recovering the desired material in usable form. For the foregoing reason, much effort has been expended in the past to reduce the cost of the explosive and also to reduce the cost of preparing the site for blasting. The attainment of both goals has not always led in the same direction. For example, the costs of preparing a site for blasting can be reduced if fewer boreholes are required per ton of material released. Because the energy required to release the material remains the same, fewer boreholes are practical only if the energy per borehole can be increased and if the material to be blasted will break properly with wider hole spacings. One method of accomplishing such increased energy per borehole is by drilling larger boreholes. Within limits, some economy can be effected by such procedure, but the additional cost of drilling larger boreholes prevents unlimited extension of this technique. An alternative method involves using explosives of higher bulk strength. In the past, however, higher bulk strength has been obtainable only by using a larger percentage of high explosive compounds, such as nitroglycerin and trinitrotoluene, in the explosive composition. These ingredients are expensive to manufacture, thus make the composition higher priced.

As a result of the foregoing, the industry has, to a large extent, had to balance the various factors to achieve the maximum blasting efliciency. Therefore, in areas where large boreholes are less practicable, the explosives generally used are those containing high explosive ingredients to provide the bulk strength required to give good blasting results with a smaller volume of explosive per ton of material released. In areas where larger boreholes are feasible, the less-sensitive and lower cost explosive compositions are used despite their lower bulk strength.

The compositions which have had the greatest adoption by the industry because of their relative insensitivity and their low cost are compositions consisting primarily of ammonium nitrate in admixture with a combustible, nonexplosive fuel. When adequately primed and when present in large diameter, i.e., in a cross-sectional area of at least 3 square inches, such compositions can be detonated to produce the energy required to shatter and throw ore and rock. The bulk density of the ammonium nitratefuel compositions ranges from about 0.8 to a maximum or about 1.1 grams per cubic centimeter. Because such compositions have essentially no water-resistance, they are generally packaged in rigid, water-impermeable containers, usually of metal or multi-ply paperboard heavily waxed or otherwise waterproofed. The quantity of this blasting agent which can be introduced into a borehole is thus limited to the volume of the containers which can be introduced into the borehole. To take advantage of the remaining space in the borehole, free-flowing pellets of a Water-resistant high explosive, i.e., TNT, are frequently introduced into the borehole after the ammonium nitrate-fuel packages have been loaded. The cost of the water-impervious container and of the high explosive pellets greatly increases the cost of the charge per borehole.

Recently the use of a flexible packaging material, e.g., polyethylene or polyvinyl chloride film, for the ammonium nitrate-fuel mixture has gained some acceptance in areas Where large boreholes are used and the holes are essentially dry. The flexible packaging material protects the contents adequately from atmospheric moisture. When the composition thus packaged is loaded into the borehole, the flexible material permits the composition to spread to fill substantially the borehole from side to side. However, these packages cannot be made as waterproof as rigid containers and do not have the resistance to tear or puncture needed for use in boreholes containing moisture. Also, the density of the composition in the borehole is only about 0.8 gram per cubic centimeter. An alternative to the foregoing for dry boreholes involves dumping prilled ammonium nitrate-fuel mixtures directly into the borehole. Again, this practice is being used only in dry boreholes and, again, the density of the composition in the borehole is only about 0.8 gram per cubic centimeter. Thus, in either case, the bulk strength of the charge is undesirably low.

Accordingly, an object of the present invention is to provide a blasting agent wherein low-cost ingredients are used, and wherein the foregoing disadvantages are overcome. Other objects will become apparent as the invention is more fully described.

We have found that the foregoing objects are achieved when we provide as a blasting agent an essentially uniform blend of solid ammonium nitrate, a fuel, and an aqueous solution of dissolved ammonium nitrate, the total water present being between 5 and 20% by weight based on said blend. We have further found that a highly effective blasting operation is attained when the described blasting agent is loaded in a borehole in a manner such that it substantially fills every portion of said borehole not otherwise occupied by solid materials, and an adequate primer is imbedded in said blend to initiate the blend.

The present invention is based on the surprising discovery that, contrary to the well established belief in the industry, the presence of a relatively large amount of water in an ammonium nitrate-fuel mixture will not prevent propagation of explosion in a confined column of such mixture provided that the water is present in the form of an aqueous solution of ammonium nitrate, and the blend thus produced is substantially uniform in composition throughout. The blasting agent of the present invention is advantageous, however, not because water may be present in an ammonium nitrate-fuel mixture, but because the effective blasting energy of an ammonium nitrate-fuel mixture can be increased by the incorporation of an aqueous solution of ammonium nitrate, the ammonium nitrate dissolved in said solution preferably constituting at least 60% by weight of said solution. The increased blasting energy is obtained because the quantity of the energy-producing ammonium nitrate-fuel mixture per unit volume is increased when a portion of the ammonium nitrate is in the form of an aqueous solution. In any such blend, the aqueous solution will be saturated; the quantity of ammonium nitrate in the solution will depend on the temperature and the quantity of other water-soluble ingredients present. At a temperature of 50 F., a temperature slightly below the average temperature within a borehole, the ammonium nitrate in a saturated aqueous solution will constitute approximately 62% by weight of the solution. At average summertime atmospheric temperatures, i.e., about 70 F., the ammonium nitrate will constitute about 66% by weight of a saturated aqueous solution. When an aqueous solution of ammonium nitrate is blended with solid ammonium nitrate, either in the presence of a fuel or without, the aqueous saturated solution occupies the voids between the granules of the solid ammonium nitrate, thereby increasing by the amount of ammonium nitrate in the solution the total amount of ammonium nitrate per unit volume.

In order to illustrate the foregoing, reference is now made to the accompanying drawing which shows graphically the effect of water on the weight of ammonium nitrate per unit volume. The data was obtained by preparing the different ammonium nitrate-saturated aqueous ammonium nitrate blends and then determining the weight of each blend which would fill a specific volume. As shown on the graph, the number of pounds of ammonium nitrate per cubic foot of space rises from about 63.1 when no water is present to about 81 when 10% water is presentan increase of 28% in the amount of ammonium nitrate which can be thus incorporated in a borehole. The graph shows that the beneficial effect of the increased quantity of ammonium nitrate per unit volume is obtained over the range to 20% by weight of water with the maximum at about In order to further describe the present invention, reference is now made to the following examples. To demonstate the efficiency of various embodiments of the present blasting agent, a number of boreholes 2 /2 inches in diameter and from 40 to 45 inches in depth were drilled at a downward angle of about 45 in the face of a granite formation. The top of the borehole was located about 3 feet above the floor of the test area so that the bottom of the borehole was at approximately floor level. For each test, a primer pellet of a 95/5 RDX/wax composition 2 inches in diameter by 3 inches in length (200 grams) having a central cap-well containing a No. 6 electric blasting cap was inserted to the bottom of the borehole, and the described composition was then poured or tamped into the borehole. Velocity measurements by conventional means Were made to determine the propagation of explosion by the blasting agent. In the examples, all proportions given are by weight, and all blends were prepared at 70 F.

Example I A blend of 80% ammonium nitrate, saturated aqueous solution of ammonium nitrate and 5% petroleum oil (containing a small quantity of an emulsifier-triethanolamine to facilitate blending) was tamped into the borehole. The density of the blend in the borehole was about 1.34 grams per cubic centimeter and the water represented about 5% of the total blend. Upon initiation of the primer, the blend detonated at a velocity of 1980 meters per second and produced a large crater 3 feet high, 5 feet wide, and 37 inches deep in the granite formation.

Example II A blend of 56% ammonium nitrate, 31.5% saturated aqueous ammonium nitrate solution, and 12.5% sugar was poured into a borehole. The blend had a smooth, creamy consistency and flowed very freely. The amount of water was 10.5% based on the blend, and the density of the blend in the borehole was 1.54 grams per cubic centimeter. Upon initiation, the blend detonated at a velocity of 1740 meters per second and produced a crater 3 feet high, 5 feet wide, and inches deep.

Example III A blend of 47.5% ammonium nitrate, 47.5 saturated aqueous ammonium nitrate solution, and 5% motor oil (containing a small quantity of an emulsifiertriethanolamine) was poured into a borehole. The slurry poured freely, but showed no signs of segregation of ingredients on standing. The water constituted 15.6% of the blend and the density of the blend in the borehole was 1.42 grams per cubic centimeter. Upon initiation, the blend detonated at a velocity of 3970 meters per second and produced a crater 3 feet high, 5 feet wide and 33 inches deep.

Example IV A blend of 56% ammonium nitrate, 38% saturated aqueous ammonium nitrate solution, 4.8% fuel oil, and 1.2% corn starch was poured into a borehole. The blend was readily pourable and its density in the borehole was about 1.35 grams per cubic centimeter. The water constituted 12.6% of the blend. Upon initiation, the blend detonated at a velocity of 3400 meters per second and produced a crater 3 feet high, 5 feet wide, and 45 inches deep.

In another series of tests carried out as described for the previous examples, except that the boreholes were drilled into the floor of the graphite formation instead of the face, and were 2% inches in diameter and 30 inches in depth, the following results were obtained.

Example V A blend of 48% ammonium nitrate, 32% saturated aqueous ammonium nitrate solution and 20% cornmeal was poured into the borehole. The proportion of water was 10.6% and the blend had a density of about 1.45 grams per cubic centimeter. No velocity measurements were obtained, but a conical crater 3 /2 feet in diameter by 30 inches in depth was produced when the blend was initiated.

Example VI A standard amatol composition ammonium nitrate-20% T T) was loaded into the borehole in lieu of the blend for comparative purposes. The borehole was loaded to the same depth as in Example V. Upon initiation, a crater approximately equal to that described in Example V was produced. This composition is representative of the high explosive-sensitized ammonium nitrate compositions which the present blend can replace.

Example VII A blend of 37% ammonium nitrate, 40% saturated aqueous ammonium nitrate solution, 8% of finely divided aluminum, and 2% of corn starch was poured into a spiralwound paperboard tube one end being closed, having a diameter of 27 8 inches and a length of 12 inches, and containing a SO-gram primer pellet of a 5 RDX/Wax composition and a No. 6 electric blasting cap. The density of the slurry was 1.35 grams per cubic inch and the water content was 13% by weight of the total blend. The open end was capped and the cartridge thus produced was submerged in water. Upon initiation of the primer, the slurry detonated at a velocity of 3850 meters per second.

As indicated in several of the foregoing examples, the blend can be made very fiowable, either as a slurry or having a creamy consistency. A blend having such characteristics can be loaded into a borehole with a minimum of difficulty. For example, the blend can be poured directly into the borehole, and, without any further tamping, will completely fill all unoccupied portions of the borehole to the level desired. Alternatively, such slurry or cream can be pumped through tubing or pipe from a mixing or conveying unit to the borehole. For example, trucks having mixing means can be loaded with the components and driven to the blasting site, all mixing occurring enroute. Alternatively, the trucks can be loaded with a premixed blend prepared at a storage and mixing station. Portable mixers at the blasting site can also be used. Further, in boreholes containing water, the blend may be poured or pumped through a pipe or tube leading to the bottom of the borehole. The blend, being of much higher density than the water, will displace the water upward and completely fill the borehole from side to side from the bottom up to the desired level. The water on top will act as stemming or may be displaced by earth or rock stemming. Because of the high density, i.e., at least 1.3 grams per cubic centimeter, of the blend, further entrance of water through the strata surrounding the borehole is retarded if not entirely halted. For further protection of the blend, the borehole may be lined with a tubing of a flexible sheeting, such as polyethylene or polyvinyl chloride.

It is, however, essential that the borehole be substantially free of voids in the portion containing the blend. Our findings have led us to believe that discontinuities of the blasting agent will result in failure of propagation of the explosion. The foregoing is supported by the known (failures which have resulted when packaged compositions of ammonium nitrate-fuel have been exposed to water in a borehole, as for example, through leakage of the container. In such cases, the dissolving of a portion of the ammonium nitrate would cause a decrease in the bulk of the contents in the container, thus producing a discontinuity of blasting agent between adjacent containers. A layer of water between units of relatively insensitive compositions will effectively halt propagation of explosion in cases where propagation of explosion will invariably be continued as an uninterrupted column or mass. Further, the presence of voids, such as surround rigid explosive packages in a borehole because of the irregularities and larger diameter of the borehole, provides channels for the rapid escape of gases under pressure from the reaction zone. Inasmuch as the reaction of ammonium nitrate and a fuel is known to be pressure dependent, failure to maintain the required high pressure at the reaction zone will cause the reaction induced by the detonation of the primer to slow and finally stop long before much of the mass of the ammonium nitratefuel has begun reacting. To some degree, the foregoing difficulty can be overcome by using a continuous primer, for example as a core surrounded by a sensitized ammonium nitrate composition. The provision of such continuous core of primer composition obviously greatly increases the quantity of high cost, highly sensitive explosive required, increases the loading problems, and, requires that the entire unit be treated as a high explosive unit.

We have found that a primer of about 200 grams of high explosive is adequate to initiate the present blend when the blend is confined in a borehole and is free of discontinuities. The same primer will not initiate the blend when the blend is packaged in a container of even larger diameter outside the borehole, even when under water confinement. Thus the safety inherent with the present blasting agent is apparent. For insurance against failure due to ground shift from previous blasts or defective initiation, the customary blasting practice of including more than the minimum required primer in the borehole will preferably also be followed in the use of the present blend. The usual practice is to locate primers every 20 or 30 feet along the borehole, all primers beng initiated in sequence, for example, by a line of detonating fuse.

Therefore, included in the concept of this invention is a method of blasting which comprises providing at least one primer and initiation means in a borehole, and providing as the main charge in said borehole a blend of ammonium nitrate, an aqueuos solution of ammonium nitrate, the ammonum nitrate content of said solution preferably being at least 60% by weight, and a (fuel, the total amount of water being from to 20% by weight based on the weight of the blend, and the composition of the blend being uniform throughout its mass and hav- 6 ing a density of at least 1.3 grams per cubic centimeter, wherein the portion of the borehole containing the said blend is essentially free of voids.

Throughout this description, the term fuel has been used to refer to a non-explosive combustible material which will react with ammonium nitrate to form oxidized products. Preferably, the oxidized products will be gases, such as are obtained from the combustion of carbonaceous materials, e.g., hydrocarbons, carbohydrates, urea, etc. However, the use of fuels which produce nongaseous products, such as powdered metals and alloys, e.g., aluminum, magnesium, iron, ferrosilicon, and the like, is also within the scope of this invention as is shown by Example VII. In summary, any of the non-explosive combustible materials used by the art as fuels in ammonium nitrate explosive compositions are included. The proportion of fuel required will vary according to its oxygen requirements for complete oxidation. Generally, an oxygen-balanced blend is preferred, i.e., the proportion-s of fuel and inorganic nitrate are such that all the fuel will be converted to fully oxidized products by the complete reduction of the oxidizing salt to stable products. Blends having an oxygen balance between +10 and 10% are acceptable. The fuel may be either liquid or solid. For flowable compositions, liquid fuels are preferred because they contribute to the mobility of the blend. The fuel may be either water soluble, water absorbent, or Water insoluble. When a water-soluble fuel, such as sugar, is used, concentration of the ammonium nitrate in the aqueous solution will be reduced somewhat, depending on the relative solubilities of the components and their proportions in the blend. However, for effective blasting energy, the concentration of the ammonium nitrate in the aqueous phase preferably will be at least 60% by weight. As shown by the examples, the ammonium nitrate concentration generally will be considerably higher. With water-insoluble fuels, the addition of a small quantity of an emulsifying agent is desirable to aid in the dispersal of the fuel throughout the blend. The choice of emulsifier is dependent entirely on the fuel and the economics involved, and is not critical to the present invention.

The use of other inorganic nitrates in conjunction with ammonium nitrate as the oxidizing salt is within the scope of this invention. As is commonly known in the industry, replacement of up to 30% of the ammonium nitrate by sodium nitrate, potassium nitrate, barium nitrate, etc., is frequently desirable to modify the biasing action. Such modifications are apparent to those skilled in the art and are not departures from the spirit of this invention. Accordingly, we intend to be limited only by the following claims.

We claim:

1. A blasting agent consisting essentially of a uni-form blend of solid ammonium nitrate, from about 5 to about 20% by weight of a non-explosive combustible fuel selected from the group consisting of liquid hydrocarbons, carbohydrates and urea, and a saturated aqueous solution of ammonium nitrate, the total water in said blend representing from 5 to 20% by weight of said blend and the ammonium nitrate in the blend representing at least 60% by weight of the blend, said blend having a density of at least about 1.3 grams per cubic centimeter and the weight ratio of ammonium nitrate to fuel in said blend being such as to provide an oxygen balance of between +10 and 10%.

2. The blasting agent of claim 1 wherein said fuel is a liquid hydrocarbon fuel.

3. The blasting agent of claim 1 wherein said fuel is sugar.

4. The blasting agent of claim 1 wherein said fuel is a carbohydrate.

5. The blasting agent of claim 2 wherein said fuel is a liquid petroleum oil.

No references cited.

Claims (1)

1. A BLASTING AGENT CONSISTING ESSENTIALLY OF A UNIFORM BLEND OF SOLID AMMONIUM NITRATE, FROM ABOUT 5 TO ABOUT 20% BY WEIGHT OF A NON-EXPLOSIVE COMBUSTIBLE FUEL SELECTED FROM THE GROUP CONSISTING OF LIQUID HYDROCARBONS, CARBOHYDRATES AND UREA, AND A SATURATED AQUEOUS SOLUTION OF AMMONIUM NITRATE, THE TOTAL WATER IN SAID BLEND REPRESENTING FROM 5 TO 20% BY WEIGHT OF SAID BLEND AND THE AMMONIUM NITRATE IN THE BLEND REPRESENTING AT LEAST 60% BY WEIGHT OF THE BLEND, SAID BLEND HAVING A DENSITY OF AT LEAST ABOUT 1.3 GRAMS PER CUBIC CENTIMETER AND THE WEIGHT RATIO OF AMMONIUM NITRATE TO FUEL IN SAID BLEND BEING SUCH AS TO PROVIDE AN OXYGEN BALANCE OF BETWEEN +10 AND -10%.

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