US 3540953 A
Description (OCR text may contain errors)
United States Patent BLASTING COMPOSITIONS CONTAINING AMMO- NIUM NITRATE PRILLS, FUEL, AND A CARBO- NACEOUS BLACK Roy E. Schulze and Paul H. Rydlund, St. Louis, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Apr. 4, 1969, Ser. No. 813,736
Int. Cl. C06]: 19/00 U.S. Cl. 149-2 8 Claims ABSTRACT OF THE DISCLOSURE Blasting agents or explosive compositions containing high density ammonium nitrate prills, a carbon black and a liquid hydrocarbonaceous fuel.
This invention relates to explosive compositions and particularly to explosive compositions containing a predominant proportion of high density ammonium nitrate prills.
Ammonium nitrate has been used extensively in blasting agents and explosives for many years. Although this material is a relatively strong oxidizing agent, it is not readily detonatable. Therefore, ammonium nitrate blasting agents or explosive compositions usually contain this material in uniform intimate contact with various fuels, modifiers and sensitizers which in themselves are either explosive or non-explosive. Recently, fertilizer grade ammonium nitrate has enjoyed widespread usage in the explosive field. This material in the form of prills or solidified droplets is conventionally mixed with a liquid hydrocarbonaceous fuel, such as fuel oil, in the preparation of substantially oxygen balanced blasting agents. The regular grades of fertilizer grade ammonium nitrate prills are porous and have a particle density up to about 1.45. Other commercially available types of fertilizer grade ammonium nitrate prills are hard, smooth, relatively nonporous and have a particle density in the neighborhood of 1.5-1.6 or more. In spite of the recognized advantages that should result from using high density prills for the formulation of correspondingly dense blasting agents or explosives, the hard ammonium nitrate prills have not heretofore been found to be suitable components of explosive compositions. Their smooth, practically imperforate surfaces militated against the requisite intimate contact between the ammonium nitrate and the other constituents of the explosive mixtures. Previous attempts to utilize high density ammonium nitrate prills in explosive compositions have centered about physical modification of the dense prills by roll-crushing, grinding, comminuting, water etching and the like to improve their oil reception, and using the physically modified material in explosive formulations. Thus, prior to the advent of the present invention practically all ammonium nitrate blasting agents utilized low density ammonium nitrate or physically modified high density ammonium nitrate.
It is therefore an object of the present invention to provide improved ammonium nitrate blasting agents or explosive compositions overcoming the disadvantages of the prior art. A more specific object is to provide improved explosive compositions in which dense ammonium nitrate prills per se are used as the sole or primary oxidizing agent.
These and other objects are accomplished in accordance with the present invention, generally speaking, by the formulation of explosive compositions containing high density prilled ammonium nitrate, a carbon black or a carbonaceous black and a liquid hydrocarbonaceous fuel. More specifically, the present invention is directed to explosive compositions or blasting agents containing whole prills of ammonium nitrate having a particle density of at least 1.5, a finely divided carbonaceous black, fuel oil or the like together with appropriate sensitizers and modifiers. The compositions thus obtained consist primarily of free-flowing high density ammonium nitrate prills substantially uniformly coated with a mixture of carbon black and a liquid hydrocarbon such as fuel oil.
The term carbonaceous black is used herein in a generic sense to include solid, particulate material containing a predominance of elemental carbon.
Although neither carbonaceous black nor fuel oil can be successfully used alone as sensitizers for high density ammonium nitrate, it has now been found that high density ammonium nitrate prills can be readily sensitized With a carbonaceous black in association with a liquid hydrocarbon fuel when the carbonaceous black and the liquid fuel are mixed or formulated with the high density ammonium nitrate in well-defined proportions. The Weight ratios of the ammonium nitrate, carbonaceous black and the liquid fuel can vary somewhat but in order to insure the advantageous results of the present invention the carbonaceous black and liquid hydrocarbon fuel together must be between about 4% and about 10% by weight of the ammonium nitrate and the weight ratio of the carbonaceous black to the liquid hydrocarbonaceous fuel must be between about 2.5 :1 and about 112.5. When more than 10% of the combined solid-liquid fuel is employed the fuel is not efiiciently utilized. On the other hand, compositions containing less than about 4% of the combined fuel are not completely reliable. Likewise, compositions containing carbonaceous black or liquid fuel in excess of that set forth above are not free-flowing and homogeneous. Various amounts of conventional modifiers and sensitizers can be incorporated into the compositions of this invention but when such additives are present the weight ratios between the ammonium nitrate, carbon black and liquid fuel must be maintained. In the absence of significant amounts of additional components, the advantages of the present invention are achieved with compositions within the following appropriate ranges:
Percent Ammonium nitrate -96 Carbonaceous black 1.2-7.2 Liquid hydrocarbon 1.2-7.2
The ammonium nitrate employed is in prilled form and must have a particle or prill density of at least 1.5. The
high density ammonium nitrate prills used are those which are commercially available and have a particle size such that they pass through a 8 mesh screen and at least about 90% of them are retained on a 20 mesh screen (USS). Thus, substantially all of the ammonium nitrate prills vary in size between 0.84 and 2.38 mm.
It is preferred to utilize high density ammonium nitrate prills that have been stabilized by the incorporation of small amounts of magnesium nitrate or calcium nitrate in accordance with the general procedure of U.S. Pat.
3,030,179 granted Apr. 17, 1962 to McFarland and Stites. Although prills which have been phase-stabilized by this or by other methods are preferred to enhance storage characteristics, any type of high density ammonium nitrate prills can be employed in accordance with the present invention. It is only necessary that the prills have a particle density of at least 1.5 and are hard, smooth and relatively non-porous.
The carbonaceous black used as a component in the present compositions can be any of the commercially available blacks which are usually produced by the partial combustion of hydrocarbon gases or liquids. This solid fuel can be carbon black, channel black, furnace combustion blacks, furnace thermal blacks, acetylene black, lamp black, and the like. In addition, charcoal burned paper, bone black and coal dust can be utilized with equal success. Since coal dust normally has a higher hydrocarbon content than the other carbonaceous blacks, less liquid fuel is normally required with coal dust than with the other solid carbon fuels. However, the requisite weight ratio of solid to liquid fuel is still maintained when coal dust is used as the solid fuel.
While fuel oil, and particularly No. 2 fuel oil, is set forth above as a typical liquid fuel for compounding with ammonium nitrate, various other types of commercially available liquid hydrocarbons can be used. In fact, any liquid hydrocarbon that can be mixed in liquid form is suitable for the formulation of such blasting agents. These include diesel oil, kerosene, lube oil, coal oil and the like. It is only necessary that the liquid fuel employed be readily combustible and capable of distribution over the ammonium nitrate surfaces while preferably having a flash point of at least 175 F.
Various modifiers, densifiers and sensitizers can be conveniently incorporated into the compositions of this invention to enhance their characteristics or to render them particularly suitable for specific purposes. Such additives include for example, aluminum, magnesium, aluminum-magnesium alloys, ferrophosphorus, ferrosilicon, lead and its salts, sulfur, trinitrotoluene, ground smokeless powder, sawdust, corn meal, wheat flour, and other conventional blasting agent components.
The compositions of the present invention can be formulated merely by bringing high density ammonium nitrate prills, a carbonaceous black and fuel oil into contact with one another and mixing until the ammonium nitrate prills are substantially uniformly coated. The sequence of addition is not critical but for ease of operation it is preferred to add the liquid hydrocarbon to the prills and mix these two components until the oil is evenly distributed over the surface of the prills. The carbonaceous black is then preferably added to the oiled prills and mixing continued until the carbonaceous black is substantially equally distributed over the surface of the prills. Any additives that are to be incorporated into the compositions are preferably added subsequent to the oil and carbonaceous black. The compositions of the present invention can be prepared in conventional apparatus and either continuously or by batch processes, When a batch method of operation is used, a ribbon blender and many other commercially available mixers are satisfactory. -For continuous operation, it is preferred to use a screw conveyer in which the carbonaceous black and fuel oil are added to the ammonium nitrate as it progresses along the path of the conveyer. When the present compositions are thus made continuously, the conveyer can be positioned to charge the finished product directly into the bore hole.
The product thus obtained is free-flowing and consists predominately of ammonium nitrate prills uniformly coated with a combination of a carbonaceous black and a liquid hydrocarbon fuel. The product is cap-insensitive and can thus be transported safely. It can be readily initiated, however, with a /2 lb. booster of nitroglycerine, tetryl or PETN. When thus initiated the present composi- About 1980 parts of phase-stabilized ammonium nitrate prills having a particle density of about 1.6 and a size distribution such that they passed through a 8 mesh screen and at least 90% were retained on a 20 mesh screen, were charged into a ribbon blender. After being charged with ammonium nitrate the blender was put into operation and mixing continued throughout the formulation process, About 40 parts of N0. 2 fuel oil were sprayed over the surface of the ammonium nitrate prills and the prills and oil were mixed for about 2 minutes. At the end of this period the fuel oil was substantially evenly distributed over the surfaces of the prills. About 70 parts of carbon black were then added to the oiled prills and the components mixed for about 5 minutes to insure uniform distribution of the carbon black throughout the mix and over the surfaces of the prills.
The resulting product was free-flowing, non-tacky and uniformly black. This material was cap-insensitive and in fact did not detonate with five No. 8 electric blasting caps when initiated in 9 ounces of the composition contained in a plastic cup.
The composition thus prepared was charged into iron pipes having an internal diameter of about 6 inches and about 2 ft. long. When thus confined and initiated with a 1 lb. pentolite, the charge had a detonation velocity of 12,000 ft. per second. The total energy released by initiation of the composition thus prepared was determined by the underwater bubble method and was found to have an underwater bubble energy of 030x 10% K calories.
The underwater bubble energy is a relative measure of the energy released by initiation of an explosive or a blasting agent and is determined by detonating a test charge under water. When an underwater explosion occurs, a bubble of gaseous detonation products is formed. The outward momentum of the water keeps expanding the bubble even after the gas has reached ambient pressure. At zero momentum, a vacuum will exist. The bubble collapses and the resultant implosion effect sends out an additional shock wave. By sensing the time lapse between the initial explosition and eventual bubble collapse with water compatible transducers, the gaseous products energy associated with the bubble can be indirectly calculated. This method is more fully described by Cole, H. C., Underwater Exposions, Princeton University Press, Princeton, NJ. (1948), pages 228-285, and by Sadwin, L. D., Underwater Evaluation of the Performance of Explosives, International Symposium on Mining Research, Rolla, Mo., February 1961.
EXAMPLE 2 About 942 parts of ammonium nitrate of the type used in the above example was mixed in a ribbon blender with about 20 parts fuel oil, about 35 parts carbon black and about 3 parts aluminum dust in substantial accordance with the procedure of Example 1. This blasting agent when charged into an iron pipe 3 ft. long and having an inside diameter of about 2 inches and initiated with a /2 lb. pentolite booster had a detonation velocity of about 9900 ft. per second.
A numeral of other compositions within the scope of the present invention were prepared and their energy level determined by the underwater bubble energy test as described above. The composition and the energy level of these compositions are set forth below in tabular form.
TABLE 1 Prilled Example Monsanto Fuel Carbon Lamp Coal Coconut Burned Underwater No. oil black black dust charcoal paper bubble energy 3. 5 0.30 X 10 Koalories. 3.1 l OBOX l0 Kcalories.
X 10 K calories. X 1 K calories. X 10 K calories. X 10 K calories.
The above description, and particularly the examples, are set forth by way of illustration only. Other variations and modifications can be made without departing from the spirit and scope of the invention herein described.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. An explosive composition comprising a predominant proportion of ammonium nitrate prills having a particle density of at least 1.5 and between about 4 and about 10% based on the weight of the prills of a liquid hydrocarbonaceous fuel and a carbonaceous black, the weight ratio of the carbon black to the liquid hydrocarbonaceous fuel being between about 2.5 :1 and about 1:25.
2. An explosive composition of claim 1 in which at least 90% of the ammonium nitrate prills have a diameter greater than about 0.84 mm.
3. An explosive composition of claim 1 in which the carbonaceous black is coal dust.
4. An explosive composition of claim 1 in which the carbonaceous black is lamp black.
5. An explosive composition of claim 1 in which the carbonaceous black is charcoal.
6. An explosive composition of claim 1 in which the carbonaceous black is burned paper.
7. An explosive composition containing between about 90 and about 96% by weight of ammonium nitrate prills having a particle density of at least 1.5, between about 1.2 and about 7.2% by weight of fuel oil and between about 1.2 and about 7.2% by weight of carbon black, the weight ratio of the fuel oil to the carbon black being between about 25:1 and about 122.5.
8. An explosive composition comprising a predominant proportion of ammonium nitrate prills having a particle density of at least 1.5 and between about 4 and about 10% based on the weight of the prills of fuel oil and carbon black, the weight ratio of the carbon black to the fuel oil being between about 25:1 and about 122.5, and aluminum.
References Cited UNITED STATES PATENTS 2,975,046 3/1961 Cooley et a1. 14946 X 2,978,864 4/1961 Stengel 149--46 X 2,997,378 8/1961 Cox et a1 149-46 X 3,046,888 7/1962 Gordon 14946 X 3,103,457 9/1963 Grossrnann 149-46 3,291,659 12/1966 Yancik 149-46 X 3,394,038 7/1968 Minnick 14946 X BENJAMIN R. PADGETI, Primary Examiner S. J. LECHERT, JR., Assistant Examiner US. Cl. X.R. 149-43, 46, 112