This invention relates generally to the field of explosives and blasting agents, and in particular to an ammonium nitrate blasting agent and its method of production.
Explosives or blasting agents, and in particular ammonium nitrate explosives, are used for a wide variety of different industrial applications ranging from mining, to mineral exploration, to civil engineering applications. Currently, there are three major classifications of commercial explosives that are based upon ammonium nitrate. These three classes are ANFO (explosives grade ammonium nitrate prills and fuel oil), watergels (slurry explosives) and ammonium nitrate based emulsions. Each form of explosive has its own particular advantages and disadvantages.
ANFO is a low cost explosive with a low velocity of detonation and with poor water resistance. ANFO also has a relatively low density of approximately 0.85 g/cc, resulting in relatively low bulk strength. Manufacturing explosives grade ammonium nitrate prills is typically carried out in large prilling towers that create particle sizes having a Tyler screen size of approximately −8 to +30. Since the prills have a natural tendency to cake or adhere to one another, after formation the prills are typically dried and coated with various anti-caking agents to help produce a free flowing product.
Watergels are manufactured from aqueous ammonium nitrate solution with or without various explosive sensitizers. Watergells may be formed with variable densities and may have a wide range of bulk strengths. Both high and low velocity products may be manufactured that exhibit relatively good water resistance. The disadvantages of watergels lies in the their high manufacturing costs, which makes them considerably more expensive than ANFO.
Emulsions, the third major class of ammonium nitrate based explosives, are also manufactured from an aqueous solution of ammonium nitrate that is sensitized with glass bubbles or microspheres, and that also contains a quantity of ANFO or ammonium nitrate prills. Emulsions may be manufactured having variable densities and with a wide range of bulk strengths. Emulsions may have high or low velocities of detonation and have excellent water resistant properties. As in the case of watergels, emulsions are expensive to manufacture resulting in pricing considerably higher than ANFO products.
Accordingly, there continues to exist a need for a low cost ammonium nitrate based explosive or blasting agent that is devoid, or generally devoid, of the disadvantages associated with ANFO while at the same time exhibits some of the advantages associated with watergels and emulsions.
The invention therefore provides an ANFO blasting agent that may be manufactured with a density that may be tailored to suit a variety of different specific applications or requirements. The blasting agent of the invention exhibits velocities of detonation beyond those of traditional ANFO, and may be formed with varying degrees of sensitivity. The inventive product has also been shown to exhibit relatively good water resistance when compared to standard ANFO. Manufacturing is accomplished by means of a process that is both safe and that provides the ability to make the blasting agent on demand in a cost effective manner.
Accordingly, in one of its aspects the invention provides a blasting agent comprising from 90 to 98 percent by weight of an ammonium nitrate component and from 2 to 10 percent by weight of an organic carbonaceous fuel component, said ammonium nitrate component comprised of ammonium nitrate crystals having a particle size of from about 1 to about 500 microns and including a crystal habit modifier at a concentration of from 0.01 to 2.0 percent by weight of said ammonium nitrate component.
In a further aspect the invention provides a blasting agent comprising (i) from 90 to 98 percent by weight of an ammonium nitrate component, said ammonium nitrate component comprised of ammonium nitrate crystals having a particle size of from about 1 to about 500 microns and including a crystal habit modifier at a concentration of 0.01 to 2.0 percent by weight of said ammonium nitrate component; (ii) from 2 to 10 percent by weight of an organic carbonaceous fuel component; (iii) a gelling agent at a concentration of from 0.1 to 10 percent by weight of said ammonium nitrate component; and, (iv) a cross linking agent at a concentration of 0.001 to 1.0 percent by weight of said blasting agent.
In another aspect the invention provides a method of producing an ammonium nitrate blasting agent, the method comprising the steps of (i) combining together a crystal habit modifier with an aqueous solution of ammonium nitrate; (ii) with said mixture of said crystal habit modifier and said ammonium nitrate solution, forming ammonium nitrate crystals having a particle size of about 1 to about 500 microns; and,
(iii) combining said ammonium nitrate crystals with an organic carbonaceous fuel at a ratio such that said organic carbonaceous fuel is from 2 to 10 percent by weight of said blasting agent.
In yet another aspect the invention concerns a method of producing an ammonium nitrate blasting agent comprising the steps of (i) forming an ammonium nitrate component through mixing a aqueous solution of ammonium nitrate with a crystal habit modifier, said crystal habit modifier having a concentration of from 0.01 to 2.0 percent by weight of said ammonium nitrate component; (ii) injecting said ammonium nitrate component through a nozzle in the presence of a secondary air flow to form ammonium nitrate crystals having a particle size of from about 1 to about 500 microns; and, (iii) transporting said ammonium nitrate crystals to a mechanical mixing process and mechanically mixing an organic carbonaceous fuel component with said ammonium nitrate crystals, said organic carbonaceous fuel component having a concentration of from 2 to 10 percent by weight of said blasting agent.
In addition, the invention provides a method of producing an ammonium nitrate blasting agent comprising the steps of (i) the forming an ammonium nitrate component through mixing an aqueous solution of ammonium nitrate with a crystal habit modifier, said crystal habit modifier having a concentration of from 0.01 to 2.0 percent by weight of said ammonium nitrate component; and, (ii) injecting said ammonium nitrate component, together with an organic carbonaceous fuel component, through a nozzle in the presence of a secondary airflow to form ammonium nitrate crystals having a particle size of from about 1 to about 500 microns, said organic carbonaceous fuel component added at a concentration of from 2 to 10 percent by weight of said blasting agent and becoming intermixed with said ammonium nitrate crystals by means of injection through said nozzle.
Further aspects and advantages of the invention will become apparent from the following description taken together with the accompanying drawings.
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings which show the preferred embodiments of the present invention in which:
The present invention may be embodied in a number of different forms. However, the specification and drawings that follow describe and disclose only some of the specific forms of the invention and are not intended to limit the scope of the invention as defined in the claims that follow herein.
A method of producing an ammonium nitrate blasting agent in accordance with one of the preferred embodiments of the present invention is shown schematically in
With reference to
Preferably the ammonium nitrate solution is formed and maintained (or purchased or acquired and subsequently heated and/or maintained) at a temperature of between approximately 85 and approximately 100 degrees Celsius. To attain such a temperature, in one embodiment of the invention the water added to the tank is pre-heated and/or steam is injected into the tank. Once the water and ammonium nitrate (or the pre-mixed solution) have been added to the tank, maintaining the tank at a temperature of between approximately 85 to 100 degrees Celsius would be typically accomplished through the use of a steam jacket. Alternatively, any one of a variety of other commonly used methods and heating devices (including direct or indirect heating mechanisms) may be used to maintain the temperature of the contents of the tank at the desired temperature. In addition, compressed air (which may be heated or at an elevated temperature) may also be introduced into the tank to provide motive force to move the ammonium nitrate solution to the crystallization stage, as is discussed in more detail below.
In accordance with the invention, a crystal habit modifier is combined with the ammonium nitrate solution through adding the crystal habit modifier to tank 1 so that impeller or mixing means 2 may distribute the crystal habit modifier throughout the solution. In accordance with one of the preferred embodiments of the invention the ammonium nitrate solution contains from approximately 60 to 90 percent ammonium nitrate by weight and the crystal habit modifier is added to the solution at a concentration of from about 0.01 to 2.0 percent by weight of the ammonium nitrate solution. The preferred crystal habit modifier is a commercially available primary amine, such as dodecylamine C5H25NH2. However, other amines, including tertiary amines, could also be used.
After the ammonium nitrate solution and the crystal habit modifier (collectively, the ammonium nitrate liquor) are thoroughly combined together in tank 1, the mixture is transported to a crystallization stage where ammonium nitrate crystals are formed through injecting the mixture through a nozzle 17.
An alternate form of nozzle that may be used in the crystallization stage is shown in
Regardless of whether the nozzle shown in
As the fine grained ammonium nitrate crystals and secondary air travel outwardly from the nozzle during the crystallization stage they are typically sent to a cyclone 13 where the ammonium nitrate crystals are collected and the secondary air stream is sent to a conventional wet scrubber 14 for removal of any ammonium nitrate powder carried over from the cyclone prior to being sent to exhaust.
In order to convert the crystalized ammonium nitrate into a blasting agent, the ammonium nitrate crystals must be combined with an organic carbonaceous fuel. The organic carbonaceous fuel added to the ammonium nitrate crystals is preferably a fuel oil such as No. 2 diesel fuel. Other carbonaceous fuels can also be used, such as fuel oil, heating oil (bunker C), jet fuel, kerosene, mineral oils, vegetable oils (such as corn oil, sunflower oil or soy bean oil), saturated fatty acids (such as lauric acid and stearic acid), alcohols (such as cetyl alcohols and glycols). Semi-solid fuels can also be used, including waxes (such as paraffin wax, petroleum wax, or microcrystalline wax). IN addition, semi-solid fuels may be used in combination with liquid fuels.
The organic carbonaceous fuel is added to the ammonium nitrate crystals at an amount of from about 2 to about 10 percent by weight of the total explosive composition, (with the ammonium nitrate representing from about 90 to 98 percent of the blasting agent), and most preferably from about 4 to about 8 percent by weight of the blasting agent with the preferred ratio of inorganic oxidizing salt (ammonium nitrate) to organic carbonaceous fuel at about 94:6. This ratio ensures that the explosive composition or blasting agent contains sufficient organic carbonaceous fuel to be oxygen balanced. The oxygen balance is preferably more positive than −15 percent, and most preferably in the range of about −10 to +10 percent.
Referring again to
In addition to gelling agents, the additive combined with the ammonium nitrate crystals at the mechanical mixing stage may include a cross-linking agent at a preferable concentration of from about 0.001 to 1.0 percent by weight of the blasting agent. The preferred cross-linking agent for the invention is potassium pyroantimonate. The potassium pyroantimonate may be in a solid form and added directly to the ammonium nitrate crystals, but is preferably disbursed within a hydrophilic medium, such as ethylene glycol, in the form of a solution of 15 parts potassium pyronatimonte, 45 parts ethylene glycol and 40 parts water. The solution may be further diluted with water or ethylene glycol to suit particular process conditions. Cross-linking of the polymer chains of the gelling agent may be accomplished by divalent or multivalent metal ions such as antimony boron, chromium, or iron under controlled pH conditions. It should also be appreciated that other forms of cross-linking agents, such as boric acid, ferric chloride, potassium antimony tartrade, sodium dichromate or sodium tetraborate may be used.
Finally, water may be combined with the ammonium nitrate crystals during the mechanical mixing stage. Where water is added, preferably the water concentration of the blasting agent is less than from about 1 percent to about 15 percent by weight of the total explosive composition.
After leaving the mechanical mixing stage the blasting agent may be delivered directly to a storage tank, may be loaded into trucks, may be delivered directly to boreholes in a mining operation, or may be sent to any one of a wide variety of other storage or processing facilities.
In an alternate embodiment of the invention, the fuel may be added to the ammonium nitrate component during the crystallization stage. For example in
In accordance with the above method, there is produced an ammonium nitrate blasting agent that has been shown to have enhanced characteristics over those of standard ANFO. For example, the blasting agent of the current invention has been found to have velocity of detonation of from 3,000 to 7,000 meters per second in a confined charge diameter ranging from less than 10 millimeters to 500 millimeters. The velocity of detonation of the blasting agent for various confined charge diameters, and at a density of 1.25 g/cc, is shown graphically in
The ammonium nitrate blasting agent of the present invention may also be formed with a variable final density that can be tailored to suit a variety of different end uses. Furthermore, adjustments to the concentration of the crystal habit modifier allows for ammonium nitrate crystals of differing particle sizes to be created, resulting in a blasting agent that may be either cap sensitive or booster sensitive. Through the use of different organic fuels, the blasting agent may be produced with a consistency that varies from powder, to a waxy particulate, to the type of consistency that is common in emulsions. It has also been found that the blasting agent of the present invention detonates with up to about 15 percent of water by weight of the final composition and thus exhibits enhanced water resistance over standard ANFO.
From a thorough understanding of the invention it will also be appreciated that the blasting agent described herein will have blasting characteristics similar to currently available emulsions, and with good to excellent water resistance. The ammonium nitrate crystal structure produced by the described manufacturing process is small in size and high in specific area, resulting in an explosive composition that has enhanced sensitivity and superior blasting characteristics. As indicated above, the crystal size of the ammonium nitrate in the blasting agent can be varied by the production process to produce crystals in the range of from about 1 to about 500 microns. Such fine crystal size permits the formation of a blasting agent with increased density over and above that normally associated with standard ANFO. This unique crystal structure is obtained by using a crystal habit modifier and through the employment of manufacturing processes that create a highly turbulent environment within which the crystalline ammonium nitrate is formed. The crystal habit modifier also aids in binding the organic fuel to the ammonium nitrate crystals, to further enhance blasting or detonation characteristics. The nozzles that are used to form the blasting agent of the present invention are in stark contrast to the spray-type nozzles currently used in prilling towers. Such nozzles create large ammonium nitrate droplets that form prills in the size range of 1,400 to 1,800 microns.
The method of the present invention provides the advantages of safety, low cost, and the ability to make new blasting agent on demand. Currently, large, high cost prilling towers are used to create explosives grade ammonium nitrate prills that are required to form ANFO. On account of their capital cost, prilling towers and prilling production facilities tend to be centralized, resulting in significant shipping costs associated with transporting the prills to end users. Under the current invention, manufacturing can be localized, even to the extent that the blasting agent may be manufactured on site for immediate use. Such a method not only eliminates the need for high cost centralized manufacturing facilities and the associated costs of transporting prills, but also eliminates the jurisdictional, security and other difficult issues associated with shipping an “explosive” product.
It is to be understood that what has been described are the preferred embodiments of the invention and that it may be possible to make variations to these embodiments while staying within the broad scope of the invention. Some of these variations have been discussed while others will be readily apparent to those skilled in the art.
Number | Date | Country | Kind |
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2,464,278 | Apr 2004 | CA | national |