Ammunition and explosives – Blasting – Borehole loading
Reexamination Certificate
2000-11-22
2003-04-01
Miller, Edward A. (Department: 3641)
Ammunition and explosives
Blasting
Borehole loading
C149S046000, C149S108400
Reexamination Certificate
active
06539870
ABSTRACT:
The present invention relates to an improved method of blasting with blasting agents. More particularly, the invention relates to a method of reducing the formation of toxic nitrogen oxides (NO
x
) in after-blast fumes by using a blasting agent that contains particulate silicon metal (hereafter silicon powder).
The blasting agent used in the method of the present invention can be of the ANFO type, a water-in-oil emulsion or a water gel. In addition, the emulsion or water-gel can contain significant amounts of ammonium nitrate (AN) or ammonium nitrate-fuel oil (generally in a ratio by weight of 94:6) prills (ANFO). The water-in-oil emulsion (hereafter emulsion) comprises a water-immiscible organic fuel as a continuous phase, an emulsified inorganic oxidizer salt solution as a discontinuous phase, an emulsifier, gas bubbles or an air entraining agent for sensitization, and silicon powder in an amount from about 1% to about 20% by weight of the composition for reducing the amount of nitrogen oxides formed in after-blast fumes. The water-gel blasting agent comprises a continuous phase of inorganic oxidizer salt solution throughout which is dispersed a liquid or solid fuel(s) and gas bubbles or gas entraining agent for sensitization. The oxidizer salt solution preferably is thickened or gelled to render it viscous. To this water-gel is added the silicon powder in the same weight range as for the emulsion.
BACKGROUND
Emulsion and water-gel blasting agents are well-known in the art. They are fluid when formed (and can be designed to remain fluid at temperatures of use) and are used in both packaged and bulk forms. They commonly are mixed with ammonium nitrate prills and/or ANFO to form a “heavy ANFO” product, having higher energy and, depending on the ratios of components, better water resistance than ANFO. Such blasting agents normally are reduced in density by the addition of air voids in the form of hollow microspheres, other solid air entraining agents or gas bubbles, which materially sensitize the emulsion to detonation. A uniform, stable dispersion of the air entraining agent or gas bubbles is important to the detonation properties of the blasting agent. Gas bubbles, if present, normally are produced by the reaction of chemical gassing agents. Sensitization also can be obtained by incorporating porous AN or ANFO prills.
A problem associated with the use of blasting agents in mining blasting operations is the formation of nitrogen oxides, a yellow orange-colored smoke, in the gasses produced by the detonation of the blasting agent. These gasses will be referred to herein as “after-blast fumes.” Not only is the formation of nitrogen oxides a problem from the standpoint that such fumes are toxic but also these fumes are visually and aesthetically undesirable due to their yellow/orange color. Many efforts have been made to eliminate or reduce the formation of such fumes. These efforts typically have been directed at improving the quality of the blasting agent and its ingredients to enhance the reactivity of the ingredients upon initiation. Other efforts have focused on improving blast pattern designs and initiation schemes. Still other efforts have focused on improving the borehole environment by dewatering or using a more water resistant emulsion blasting agent.
Typically, after-blast fumes are formed in soft or well-fractured rock and where water may be present in the boreholes. These conditions often are found in surface coal mining operations. Thus geological conditions that can influence the formation of after-blast fumes include soft rock formations; sand and mud seams; cracks, fissures and cavities; and borehole water.
Theoretically, after-blast fumes are caused when the gasses produced by the explosive reaction experience reduced pressures and temperatures, resulting in thermodynamically non-ideal gaseous reactions. Under more ideal reaction conditions, N
2
would be formed rather than NO and NO
2
. In addition to geological conditions, other factors can influence or contribute to NO
x
formation (generated as the result of a non-ideal detonation reaction). Such factors include certain mining methods (long sleep times, deep boreholes, large patterns), blast design (delay sequence, pattern spacing, short crest burdens), blasting agent selection (water resistance, packaged versus bulk product, energy) and blasting agent formulation (oxygen balance, energy, sensitivity, ingredients). If a mine is experiencing frequent after-blast fumes, the method of the present invention will help to reduce such fumes.
Of these factors, the present invention deals primarily with the blasting agent formulation factor. The addition of silicon powder is found to reduce significantly the formation of after-blast NO
x
fumes in side-by-side comparative formulation testing, even when compared to aluminum powder. The silicon powder contributes energy to the blasting agent and apparently acts as a more effective reactant or scavenger of NO
x
than aluminum powder. In fact, silicon powder is as effective, or more so, than the use of urea as an additive for reducing NO
x
fumes, as is described in U.S. Pat. No. 5,608,185. Although silicon powder has been used, or suggested for use, in blasting agents as a metallic fuel, see, for example, U.S. Pat. Nos. 4,357,184 and 4,026,738, no mention is made of its use for purposes of reducing after-blast fumes.
Coal mining operations are facing increasing pressure from regulatory agencies and from local residents and communities to reduce after-blast fumes. Because of the various factors that can cause or contribute to after-blast fumes, the solution is not a simple or easy one. The present invention is a clear step toward a solution and one that provides a significant reduction in after-blast fumes, as is shown in the comparative examples presented below.
SUMMARY
The present invention is directed to an improved method of blasting whereby the formation of nitrogen oxide after-blast fumes is reduced. This helps satisfy the need for better fume characteristics in blasting. The method reduces the formation of nitrogen oxides in after-blast fumes resulting from the detonation of a blasting agent in a borehole. The method comprises formulating the blasting agent to contain from about 1% to about 20% silicon powder.
DETAILED DESCRIPTION
As indicated above the addition of silicon powder to a blasting agent significantly reduces the amount of nitrogen oxides formed in the detonation reaction between the oxidizer and fuel in the blasting agent. How the silicon powder performs this function is subject to hypotheses. Whether it reacts with the nitrogen oxides during the detonation reaction, acts as a scavenger of the nitrogen oxides after the reaction or functions in some other way is not clear.
The silicon powder used in the present invention typically is of a size range of −200 U.S. mesh. It is used in the amount of from about 1% to about 20% by weight of the blasting agent. The degree of effectiveness generally is proportional to the amount of silicon powder employed. However, for reasons of optimizing oxygen balance, energy and effectiveness, the preferred range is from about 2% to about 10%.
The blasting agents preferably are selected from three common types: ANFO, emulsions and water-gels. As previously described, ANFO typically is simply a blend of porous ammonium nitrate prills and fuel oil in a weight ratio of 94:6, respectively.
Emulsion Blasting Agents. In emulsions, the immiscible organic fuel forming the continuous phase of the composition is present in an amount of from about 3% to about 12%, and preferably in an amount of from about 3% to less than about 7% by weight of the composition, depending upon the amount of ANFO or AN prills used, if any. The actual amount of organic fuel used can be varied depending upon the particular immiscible fuel(s) used, upon the presence of other fuels, if any, and the amount of urea used. The immiscible organic fuels can be aliphatic, alicyclic, and/or aromatic and can be saturated and/or unsaturated, so long as they ar
Dyno Nobel Inc.
Miller Edward A.
LandOfFree
Blasting method for reducing nitrogen oxide fumes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Blasting method for reducing nitrogen oxide fumes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Blasting method for reducing nitrogen oxide fumes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3011483