SYSTEM FOR MAKING AN AQUEOUS SLURRY-TYPE BLASTING COMPOSITION

Abstract: Blasting composition, method and system for making such. The blasting composition is a homogeneous slurry-type blasting agent containing a major amount of water and a relatively small amount of a particulate fuel, preferably a particulate metal fuel. The blasting composition is made by premixing the fuel with water and a gelling agent to form a stable suspension of fuel in the water, metering the suspension of fuel into a dry particulate mixture of an inorganic metal oxidizer and a gelling agent, and slowly tumbling the mixture a short time sufficient to obtain a uniform composition without desensitizing the composition to detonation.

Description: Description SYSTEM FOR MAKING AN AQUEOUS SLURRY-TYPE BLASTING COMPOSITION Technical Field This invention relates to a homogeneous slurry-type blasting composition, and to a method and system for making such. Background Art Aqueous and oil-based inorganic nitrate slurry explosives are extensively used in strip mining of coal and other construction uses. These slurry-type explosives gen¬ erally contain a major amount of an inorganic nitrate and a fuel together with water or oil and a thickening or gelatin¬ izing agent. The most common way of making slurry-type explosive compositions has generally involved employing an aqueous solution of ammonium nitrate or alkali or alkaline earth metal nitrates -to which the other components are added. Finely divided aluminum flakes are commonly used in such compositions; however, "dusting" of this particulate material during manufacture of blasting compositions pre- sents an extreme hazard. It is also difficult to obtain a homoqeneous mix of the metal nitrate and metal particles without segregation. If the components are not uniformly mixed, the explosive composition either does not detonate or performs unsatisfactorily. It has remained a problem to develop a slurry-type explosive composition which can be manufactured quickly, without the need for special equipment, at reasonable cost, and with safety. The following U.S. patents disclose slurry-type blasting compositions and methods of making them; however, none of them employ a method or composition as described and claimed herein. U.S. Patent No. 3,294,601 discloses a slurry-ty blasting composition of ammonium nitrate as an oxidize hexamethylenetetramine as a fuel, water, and a thickening gelling agent. No particulate metal as a fuel is employe The blasting composition is formed by mixing the ammoniu nitrate, gelling agent together in a steam-jacketed vess to melt them and slowly adding to the dry, hot melted mix ture hexamethylenetetramine dissolved in boiling water, th mixture being blended until a cohesive mass is formed. U.S. Patent No. 3,765,967 discloses a slurr explosive prepared by dissolving an inorganic metal per chlorate in water together with a thickener and particulat pentaerythritol tetranitrate and adding finely divide aluminum to the aqueous slurry. U.S. Patent No. 5,985,593 discloses a method o making a slurry explosive by solubilizing nitromethane in a aqueous gel of sodium perchlorate which includes a solubil izing agent for the nitromethane, such as ethylene glycol. U.S. Patent No. 3,787,254 discloses a water-bas slurry composition made by distributing a liquid hydrocarbo fuel in an emulsion-like form of a mixture of ammoniu nitrate and calcium nitrate, and then adding a thickening o gelling agent. Aluminum metal is added as a secondary fue for certain of the compositions. U.S. Patent No. 3,886,010 discloses a water-bas slurry composition made by incorporating a small amount of thickener to an aqueous oxidizing solution of ammonium ni trate and thereafter adding a dry mix of a particulate soli fuel, such as finely divided aluminum, to the solution b stirring and mixing, the dry mix including a supplementa thickening agent and a cross-linking agent. U.S. Patent No. 3,378,415 discloses an explosiv slurry made by melting together the liquefiable component o the composition, i.e., ammonium nitrate and sodium nitrate and then mixing in a dough-type mixer the mixture of th metal nitrates and a carbonaceous fuel, such as starch o woodmeal; a particulate metal, such as aluminum powder o flake; water; and a thickening agent, if needed. It i essential to melt the liquefiable ingredients first and then add the fuel and other ingredients to avoid spontaneous ignition thereof. U.S. Patent No. 3,235,425 discloses a sequence of steps for mixing a slurry-type blasting composition by mix¬ ing together a dry mixture of ammonium nitrate and a gelling agent, then adding the resulting dry mix to water, and thereafter mixing in a smokeless powder. None of the patents disclose a sequence of mixing steps to avoid dusting of particulate metal such as aluminum used as a fuel in the production of blasting compositions nor a method which avoids desensitizing the composition during manufacture. Disclosure of Invention It is a primary object of this invention to pro¬ vide a method of quickly formulating an aqueous, slurry-type blasting agent safely and economically. It is a further object of this invention to pro- vide a method of formulating a homogeneous, aqueous, slurry- type blasting agent using flaked aluminum, with little or no dusting of the aluminum. It is a further object of this invention to pro¬ vide an aqueous, slurry-type blasting composition wherein the two components of the blasting composition can be sepa¬ rately packaged and mixed together quickly and safely with¬ out the need for sophisticated equipment and without desen¬ sitizing the composition. It is a further object of this invention to pro- vide an aqueous, slurry-type blasting agent employing no toxic ingredients and which can be handled in an open plant. It is a further object of this invention to pro¬ vide an aqueous, slurry-type blasting agent employing a high proportion of water and a relatively small amount of parti- culate aluminum and still obtain a blasting composition having good blasting characteristics. It is a further object of this invention to provide a two-component aqueous slurry-type blasting agent employing dry, particulate ammonium nitrate, the endothermi reaction occurring when the dry ammonium nitrate is mixe with the aqueous fuel suspension providing greater therma stabiliy and insensitivity. These and other objects are accomplished b premixing a fuel with water and a gelling agent to form stable suspension of the fuel in the water, mixing togethe (in dry form) a particulate nitrate oxidizer together with gelling agent, and blending the suspension and dry mixtur by subjecting them to a slow tumbling action for a brie period of time. The blasting composition comprises 50-8 percent by weight ammonium nitrate, 0.5-10 percent fuel preferably flaked aluminumin an amount ranging from 1^-4 per cent, 15-35 percent by weight water, 0.5-10 percent gellin agent, preferably 1-2 percent, 0.02-0.5 percent of a cross linking agent and, optionally, 0.05-1 percent of a glycol such as ethylene or propylene glycol. Brief Description of the Drawings The drawing illustrates a schematic diagram of batch mixing system for formulation of. an aqueous, slurry type blasting composition of the type disclosed herein. Best Mode for Carrying Out the Invention The inorganic nitrate which is preferably employe as the nitrate component of the explosive composition o this invention is ammonium nitrate; however, other inorgani nitrates can be employed alone or in admixture with th ammonium nitrate, such as the alkali or alkaline earth meta nitrates; e.g., sodium nitrate, potassium nitrate, calciu nitrate. If a mixture is used, it should generally contai a predominant amount of ammonium nitrate in preference t the other nitrates. The nitrate used can be in any form; i.e., crushed, prill or a combination of the two, reasonabl oil- and water-free. Fertilizer-grade ammonium nitrate i suitable. The particulate nitrate is usually processe through a hammermill or other means to grind it to a unifor particulate size before being blended with the other compo OΛ'. nents in the explosive composition. Although a dry gelling or thickening agent may be added to the oxidizer, it is preferable to add the gelling agent and cross-linking agent to the aqueous suspension to avoid any problems of (1) pre- mature cross-linking, should the ammonium nitrate become damp, or (2) toxicity, which is a problem with certain of the cross-linking compounds. The thickening agents may be any of the conventional thickening agents employed in the preparation of slurry explosives, such as guar gum, starches and synthetic polymers, such as the polyacrylamid.es. Cross- linking agents may also be added for the thickening agent. Cross-linking agents are especially useful where the stabil¬ ity or integrity of the composition needs to be maintained. The cross-linking agents are generally metal salts, such as ferric nitrate, sodium dichromate, ammonium, antimony salts, etc. The inorganic nitrate, with or without the gelling agent and cross-linking agent, in dry form, forms one compo¬ nent of the two-component explosive composition. The second component of the explosive composition is comprised of a fuel, preferably a finely divided metal, such as aluminum, which is premixed with water and a gelling or thickening agent which suspends and causes the aluminum to be absorbed by the water. Preferred is de-dusted alumi¬ num flake which includes a coating of a polyfluorocarbon and/or a metal stearate to prevent reaction with water. Alcoa 1651, manufactured by the Aluminum Company of America, is suitable, as are other commercially available aluminum flake products. This particulate aluminum is susceptible to dusting if disturbed, for example, by vibration, and is extremely hazardous to use if dusting cannot be prevented during mixing of the explosive composition. It was found that premixing the aluminum particles with water and a gell¬ ing agent substantially eliminated dusting. The gelling or thickening agent employed can be the same as that blended with the dry inorganic oxidizer. Preferred is one of the guar gums, preferably used ' without a cross-linking agent. It is also desirable to add a small amount of a glycol, such as propylene glycol, to the suspension to aid in dispersing the gelling agent. The amount of water blended with th particulate aluminum and gelling agent should be only enoug to form a concentrate of aluminum suspended in an aqueou system. An impeller, vortex mixer is preferred for prepara tion of the concentrate. This concentrate can be package in suitable cartridges and shipped to the intended blendin site for blending with the first component. At the us site, the two components of the explosive composition ar blended together with additional water to produce an aque ous, slurry-type blasting agent which can be used wit safety. Reference is made to the drawing illustrating schematic diagram of the equipment used for blending th explosive composition. The particulate ammonium nitrate o other inorganic nitrate or mixture thereof is delivered int a bin 10 by an auger 12 coming from a bulk facility holdin the nitrate. The inorganic nitrate drops into a hammermil 14 which grinds the inorganic oxidizer to a uniform particl size. The ground inorganic nitrate exits from the hammer mill and is conveyed by auger 16 to a mixer 18, similar to conventional mortar mixer. A dry gelling agent may be adde to the oxidizer in the mixer. The mixer incorporates mixin blades within it which slowly tumble the dry, particulat mixture. The mixer is pivotally mounted at pivot point 1 to frame members 20 for dumping the mixture, after blendin of the second component, into a bin and auger packer 22 a illustrated. A scale 24 is included beneath hopper 10 fo measuring a predetermined weight of the dry particulat oxidizer to be fed into the mixer 18. When formulating th explosive composition, a predetermined weight of the dr particulate oxidizer, as weighed by the bag scale 24, is fe into the hammermill 14 and into the mortar mixer 18. The second component of the explosive compositio (the concentrate of particulate aluminum suspended in a aqueous slurry) is poured into the mortar mixer simultane ously with or prior to ' the addition of a predetermine amount of additional water. Once the second component i added to the dry particulate mixture in the mixer, the mixe is activated to slowly tumble the mixture only for a short period of time, generally 2 to 30 seconds. If the mixture is mixed too rapidly, the sensitivity of the explosive com¬ position is destroyed. If mixed too slowly, a non-uniform composition is obtained. If the mixture is mixed too rapid¬ ly, the aluminum will dust. After the short mixing time of the two components, the mixture, having a molasses-like con¬ sistency, is dumped into the auger packer 24, where it is packed in polyethylene or other plastic packages or car¬ tridges. The mixer 18 is provided with an interlock mechan¬ ism which prevents mixing until the proper amounts of the two components have been added to the mixer. The final explosive composition should have a composition consisting essentially of 50-80 percent by weight ammonium nitrate or other inorganic nitrate or mixtures thereof, 0.5-10 percent particulate aluminum, preferably 1-4 percent, 15-35 percent water, 0.5-10 percent gelling agent, 0.02-0.5 percent cross- linking agent and 0.05-1.0 percent of a glycol, such as ethylene or propylene glycol. The equipment needed to formulate the explosive composition is unsophisticated and the components, particu¬ larly the aluminum-containing component, can be packaged as a gel in concentrated form for transport to the formulation site. The ammonium nitrate or other inorganic nitrate can be acquired from any suitable source. The composition can' be formulated quickly with no dusting problems and with safety. The final composition uses a relatively small amount of particulate aluminum.. No other fuel is needed. A relatively high proportion of water is used in contrast to other commercially used slurry-type explosive compositions. The aluminum content may be varied to vary the sensitivity of the explosive composition. Above about 3 percent alumi¬ num the explosive composition is cap-sensitive. Below about 3 percent, a booster is necessary. It is important that the aqueous suspension of aluminum be added to the dry particu¬ late mixture to avoid dusting of the particulate aluminum and to insure a uniform, homogeneous composition which does not segregate. ( _ OMPI Example 1 The explosive composition described is general prepared in batches weighing from 200 to 400 pounds eac In a given day 20,000 pounds of the composition may be pre pared. To formulate 20,000 pounds of the explosive composi tion requires 13,750 pounds of particulate prilled ammoniu nitrate and 358 pounds of guar gum. A batch amount of the ammonium nitrate was fed b auger into bin 10 from a bulk facility and then fed throug a hammermill which crushed the prills. The crushed ammoniu nitrate was then fed by auger 16 into mixer 18 and mixe with a batch amount of guar gum. The dry mixture was tum bled slowly to form a uniform mixture of the oxidizer an dry gelling agent. An aqueous slurry concentrate of particulat aluminum was prepared by blending together with an impeller vortex mixer 358 pounds of a de-dusted flake aluminum (Alco 1651) , 1,076 pounds water, about 10 pounds of a gellin agent (HP 11, hydroxypropyl guar), and 20 pounds of propy lene glycol. The concentrate of the gelatinous mixture o aluminum suspended in the aqueous gel was prepackaged in 30 pound polyethylene cartridges, each cartridge weighing abou 15 pounds, and shipped to the use site. At the use site th packages were slit and added to the batch quantity of th dry particulate mixture of ammonium nitrate in the mixe with slow tumbling. Simultaneously with addition of th aluminum concentrate (or separately) , an additional batc amount of water was added to the composition (4,428 pound water per 20,000 pounds oxidizer). The mixture was blende after introduction of the water and concentrate for a tim less than' 5 seconds and was then fed into an auger packe which packed it into polyethylene cartridges. The set-u time of the composition ranged from 24 to 48 hours. Th blended and formulated explosive composition incorporate the following: Percent Ammonium nitrate 68.75 Guar gum 1.79 Water — (1) Present in the aluminum- containing concentrate 5.38 (2) Added at the time of formulation 22.14 Gelling agent Jaguar HP-11 (Stein-Hall, a division of Celanese Corporation) 0.05 Propylene glycol 0.10 Flake alumimum (Alcoa 1651) 1.79 The explosive composition, on plate dent tests, detonated completely -and gave plate dents comparable to other slurry explosives.

Claims: Claims 1. A method for making a homogeneous, aqueous slurr type blasting composition containing a dry particulate inorgani nitrate oxidizer and a fuel, characterized by: premixing the fuel with water and a gelling agent t form a stable suspension of the fuel in the water; mixing the aqueous suspension of fuel with the dr particulate nitrate oxidizer and an additional amount of water and slowly tumbling the mixture for a brief time suffi cient to uniformly mix the components. 2. The method of claim 1 wherein the fuel is a finel divided metal fuel and wherein the dry nitrate oxidizer is mixe with a dry gelling agent. 3. The method of claim 2 wherein the compositio consists essentially of 50-80 percent by weight particulat inorganic nitrate, 0.5 to 10 percent by weight finely divide aluminum flake, 0.5 to 10 percent by weight gelling agent and 1 to 35 percent water. 4. The method of claim 2 wherein the mixing tim ranges from 2 to 30 seconds and the inorganic nitrate is ammo nium nitrate. 5. The method of claim 4 wherein mixing of th aqueous suspension of fuel with the ammonium nitrate results i an endothermic reaction providing thermal stability and insensi tivity to detonation. 6. An explosive slurry characterized by: 50 to 8 percent by weight, based on the weight of the total composition of an inorganic nitrate oxidizer, 1 to 4 percent by weight of finely divided particulate metal fuel, 0.5 to 10 percent b weight of a gelling agent, and 15 to 35 percent water. 7. The explosive slurry of claim .6, including 0.02 to 0.50 percent by weight of a cross-linking agent for the gelling agent and 0.05 to 1.0 percent by weight of a glycol. 8. The explosive slurry of claim 7 wherein the nitrate oxidizer is ammonium nitrate. 9. A system for making a homogeneous, aqueous, slurry-type blasting composition which contains a particulate nitrate oxidizer, a particulate fuel, and a gelling agent, the system characterized by: grinding means for grinding of the particulate nitrate to a uniform particle size; means for feeding the particulate dry oxidizer to a mixer having tumbling blades therein which subjects the mixture to a slow tumbling action; means for feeding into the mixer a gelatinous concen¬ trate consisting essentially of particulate aluminum- in a stable suspension with water and a gelling agent; and means ' for packing the formulated explosive composition in cartridges. 10. The system of claim 9 wherein the composition consists essentially of 50 to 80 percent by weight nitrate oxidizer, 1 to 4 percent by weight particulate aluminum, 15 to 35 percent by weight water and 0.5 to 10 percent by weight gelling agent. 11. The system of claim 9 wherein the means for packing is an auger packer. OMPI

Inventors: MAES M, REINSCH R, SHAW R
Applicants: ENERGY SCIENCES PARTNERS LTD
Application year: 1981
Main classification: C06B33
IPC codes: C06B21, C06B47