U.S. patent application number 12/823406 was filed with the patent office on 2010-10-14 for ammonium nitrate crystals, ammonium nitrate blasting agent and method of production.
This patent application is currently assigned to Nexco Inc.. Invention is credited to Christopher Preston.
Application Number | 20100258222 12/823406 |
Document ID | / |
Family ID | 35206775 |
Filed Date | 2010-10-14 |
United States Patent
Application |
20100258222 |
Kind Code |
A1 |
Preston; Christopher |
October 14, 2010 |
AMMONIUM NITRATE CRYSTALS, AMMONIUM NITRATE BLASTING AGENT AND
METHOD OF PRODUCTION
Abstract
A blasting agent comprised of an ammonium nitrate component and
an organic carbonaceous fuel component. The ammonium nitrate
component includes ammonium nitrate crystals having a particle size
of from about 1 to about 500 microns and further includes one or
more crystal habit modifiers.
Inventors: |
Preston; Christopher; (North
Bay, CA) |
Correspondence
Address: |
TAROLLI, SUNDHEIM, COVELL & TUMMINO L.L.P.
1300 EAST NINTH STREET, SUITE 1700
CLEVELAND
OH
44114
US
|
Assignee: |
Nexco Inc.
|
Family ID: |
35206775 |
Appl. No.: |
12/823406 |
Filed: |
June 25, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11313007 |
Dec 20, 2005 |
7767045 |
|
|
12823406 |
|
|
|
|
10886872 |
Jul 8, 2004 |
|
|
|
11313007 |
|
|
|
|
Current U.S.
Class: |
149/46 |
Current CPC
Class: |
C06B 31/285 20130101;
C06B 31/28 20130101; C06B 23/002 20130101 |
Class at
Publication: |
149/46 |
International
Class: |
C06B 31/28 20060101
C06B031/28 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2004 |
CA |
2,503,819 |
Apr 8, 2004 |
CA |
2,464,278 |
Claims
1-22. (canceled)
23. A blasting agent comprised of an ammonium nitrate component and
an organic carbonaceous fuel component, said ammonium nitrate
component including ammonium nitrate crystals having a particle
size of from about 1 to about 500 microns and including one or more
crystal habit modifiers.
24. The blasting agent as claimed in claim 23 wherein said one or
more crystal habit modifiers are amines.
25. A blasting agent comprised of from 75 to 98 percent by weight
of an ammonium nitrate component and from 2 to 8 percent by weight
of an organic carbonaceous fuel component, said ammonium nitrate
component including ammonium nitrate crystals having a particle
size of from about 1 to about 500 microns and including one or more
crystal habit modifiers at a concentration of from 0.001 to 2
percent by weight of said blasting agent.
26. The blasting agent as claimed in claim 25 further including
water at a concentration of from less than 1 percent to 15 percent
by weight of said blasting agent.
27. The blasting agent as claimed in claim 25 wherein said one or
more crystal habit modifiers are amines.
28. The blasting agent as claimed in claim 25 wherein said one or
more crystal habit modifiers are dodecylamine or
octadecylamine.
29. The blasting agent as claimed in claim 25 including a gelling
agent.
30. The blasting agent as claimed in claim 29 wherein said gelling
agent is guar at a concentration of from 0.1 to 10 percent by
weight of the ammonium nitrate crystals.
31. The blasting agent as claimed in claim 25 further including a
cross-linking agent.
32. The blasting agent as claimed in claim 25 having a density of
from 0.55 to 1.4 g/cc.
33. The blasting agent as claimed in claim 25 having a velocity of
detonation of from 3,000 to 7,000 meters per second.
34. The blasting agent as claimed in claim 25 including
polyisobutylene.
35. The blasting agent as claimed in claim 25 further including
water at a concentration of from less than 1 percent to 15 percent
by weight of said blasting agent, guar at a concentration of from
0.1 to 10 percent by weight of the ammonium nitrate crystals, and a
cross-linking agent, said one or more crystal habit modifiers being
amines and said blasting agent having a density of from 0.55 to 1.4
g/cc.
36. The blasting agent as claimed in claim 23 wherein said ammonium
nitrate crystals are crystals formed through injecting an aqueous
solution of ammonium nitrate and said one or more crystal habit
modifiers, together with compressed air, through a nozzle in the
presence of a secondary air flow.
37. The blasting agent as claimed in claim 36 wherein said
secondary air flow is non-cyclonic.
38. The blasting agent as claimed in claim 25 wherein said ammonium
nitrate crystals are crystals formed through injecting an aqueous
solution of ammonium nitrate and said one or more crystal habit
modifiers, together with compressed air, through a nozzle in the
presence of a secondary air flow.
39. The blasting agent as claimed in claim 38 wherein said
secondary air flow is non-cyclonic.
40. A blasting agent comprised of from 75 to 98 percent by weight
of an ammonium nitrate component, from 2 to 8 percent by weight of
an organic carbonaceous fuel component, and water at a
concentration of from less than 1 percent to 15 percent by weight
of said blasting agent, said ammonium nitrate component including
ammonium nitrate crystals having a particle size of from about 1 to
about 500 microns and including one or more crystal habit modifiers
at a concentration of from 0.001 to 2 percent by weight of said
blasting agent, said crystal habit modifiers comprised of amines,
said ammonium nitrate crystals being crystals formed through
injecting an aqueous solution of ammonium nitrate and said one or
more crystal habit modifiers, together with compressed air, through
a nozzle in the presence of a secondary airflow, said organic
carbonaceous fuel blended with said ammonium nitrate crystals
through injecting said fuel through injection ports on the
nozzle.
41. A blasting agent comprised of an ammonium nitrate component and
an organic carbonaceous fuel component, said ammonium nitrate
component including ammonium nitrate crystals having a particle
size of from about 1 to about 500 microns, said organic
carbonaceous fuel component comprising one or more crystal habit
modifiers.
42. The blasting agent as claimed in claim 41 where said one or
more crystal habit modifiers are dodecylamine or octadecylamine.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent application
Ser. No. 11/313,007 filed Dec. 20, 2005 which is a
Continuation-in-Part of U.S. patent application Ser. No.
10/886,872, filed Jul. 8, 2004 (now Abandoned) and corresponds to
Canadian Patent Application Nos. 2,464,278, filed Apr. 8, 2004 and
2,503,819, filed Apr. 7, 2005 and the contents of which documents
are herein incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates generally to explosives and blasting
agents, and in particular to an ammonium nitrate blasting.
BACKGROUND OF THE INVENTION
[0003] 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.
[0004] 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.
[0005] Watergels are manufactured from aqueous ammonium nitrate
solution with or without various explosive sensitizers. Watergels
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 their high manufacturing costs,
which makes them considerably more expensive than ANFO.
[0006] 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.
[0007] 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. There is also the need for an
ammonium nitrate crystal product that may be readily transported
and used for the production of such a blasting agent.
SUMMARY OF THE INVENTION
[0008] The invention therefore provides stabilized ammonium nitrate
crystals and 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 generally 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.
[0009] Accordingly, in one of its aspects the invention provides a
blasting agent comprised of an ammonium nitrate component and an
organic carbonaceous fuel component, said ammonium nitrate
component including ammonium nitrate crystals having a particle
size of from about 1 to about 500 microns and including one or more
crystal habit modifiers.
[0010] The invention further provides a blasting agent comprised of
from 75 to 98 percent by weight of an ammonium nitrate component
and from 2 to 8 percent by weight of an organic carbonaceous fuel
component, said ammonium nitrate component including ammonium
nitrate crystals having a particle size of from about 1 to about
500 microns and including one or more crystal habit modifiers at a
concentration of from 0.001 to 2 percent by weight of said blasting
agent.
[0011] In another aspect the invention provides a blasting agent
comprised of from 75 to 98 percent by weight of an ammonium nitrate
component, from 2 to 8 percent by weight of an organic carbonaceous
fuel component, and water at a concentration of from less than 1
percent to 15 percent by weight of said blasting agent, said
ammonium nitrate component including ammonium nitrate crystals
having a particle size of from about 1 to about 500 microns and
including one or more crystal habit modifiers at a concentration of
from 0.001 to 2 percent by weight of said blasting agent, said
crystal habit modifiers comprised of amines, said ammonium nitrate
crystals being crystals formed through injecting an aqueous
solution of ammonium nitrate and said one or more crystal habit
modifiers, together with compressed air, through a nozzle in the
presence of a secondary airflow, said organic carbonaceous fuel
blended with said ammonium nitrate crystals through injecting said
fuel through injection ports on the nozzle.
[0012] In still a further aspect the invention concerns a blasting
agent comprised of an ammonium nitrate component and an organic
carbonaceous fuel component, said ammonium nitrate component
including ammonium nitrate crystals having a particle size of from
about 1 to about 500 microns, said organic carbonaceous fuel
component comprising one or more crystal habit modifiers.
[0013] Further aspects and advantages of the invention will become
apparent from the following description taken together with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] 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:
[0015] FIG. 1 is a schematic flow diagram of a method of producing
the ammonium nitrate blasting agent of one of the preferred
embodiments of the present invention;
[0016] FIG. 2 is an enlarged schematic view of an air atomizing
nozzle utilized pursuant to one embodiment of the method shown in
FIG. 1;
[0017] FIG. 2a represents an electron microscope image of particles
created through use of the method of producing ammonium nitrate
crystals described herein;
[0018] FIG. 3 is an enlarged schematic view of a laval-type nozzle
that may be utilized pursuant one embodiment of the method shown in
FIG. 1;
[0019] FIG. 4 is a chart plotting velocity of detonation against
charge diameter for an ammonium nitrate blasting agent pursuant to
one of the preferred embodiments of the present invention at a
density of 1.25 g/cc and compared to standard ANFO; and
[0020] FIG. 5 is a table showing examples of various compositions
of blasting agents that may be constructed in accordance with the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] 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.
[0022] A method of producing an ammonium nitrate blasting agent in
accordance with one of the preferred embodiments of the present
invention is generally shown schematically in FIG. 1. The method
consists primarily of three steps or stages; namely, the mixing of
an aqueous solution of ammonium nitrate and one or more crystal
habit modifiers, the formation of fine grained ammonium nitrate
crystals, and the combination of the ammonium nitrate crystals with
an organic carbonaceous fuel, with or without various other
additives, to form an ammonium nitrate blasting agent. Each of
these primary stages will now be described in more detail.
[0023] With reference to FIG. 1, an aqueous solution of ammonium
nitrate may be formed through the addition of industrial grade
(chemically pure) ammonium nitrate and water to a tank or vessel 1.
In an alternate embodiment of the invention, a pre-mixed solution
of ammonium nitrate and water may be purchased or otherwise
acquired and added to tank 1. It should be noted that when ammonium
nitrate or industrial grade ammonium nitrate are referred to
herein, it is intended that the product be relatively pure and
generally devoid of impurities (including clays and iron) that may
be present in other forms of ammonium nitrate. Typically tank 1
will include an impeller or mixing means 2 that ensures a thorough
mixing of the contents of the tank. In the case of FIG. 1, impeller
2 is rotated by means of a motor or drive mechanism 3 at a desired
speed that takes into account the flow of materials into and out of
the tank, as well as the tank's volume. It will, of course, be
recognized that a wide variety of other mixing or agitating means
could be used in place of impeller 2.
[0024] 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 industrial grade 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.
[0025] In accordance with one of the preferred embodiments of the
invention, one or more crystal habit modifiers are combined with
the ammonium nitrate solution through adding the crystal habit
modifier or modifiers to tank 1 so that impeller or mixing means 2
may distribute the crystal habit modifier throughout the solution.
In one embodiment the preferred crystal habit modifier or modifiers
are commercially available primary amines, such as dodecylamine
(C.sub.12H.sub.25NH.sub.2) or octadecylamine
(C.sub.18H.sub.37NH.sub.2), or mixtures containing such
commercially available or other generally similar products.
Examples of commercially available products that may be used in
these regards include Armeen 12D.TM. and Armeen 18D.TM. by Akzo
Nobel.TM.. It will, however, be appreciated by those skilled in the
art that other amines, including secondary and tertiary amines,
could equally be used while remaining within the broad scope of the
invention. Where other amines are utilized, preferably such amines
are fatty acid amines that range from about C.sub.10 to
C.sub.22.
[0026] It will also be appreciated that the relative amount of
ammonium nitrate and crystal habit modifier in the ammonium nitrate
solution may vary within a relatively broad range. Factors such as
the particular crystal habit modifier that is used, the amount of
carbonaceous fuel that is later added to create a blasting agent,
the amount of water present in both the ammonium nitrate solution
and a subsequently produced blasting agent, the presence of
additive in either the ammonium nitrate solution and/or a
subsequently produced blasting agent and the oxygen balance that is
desired will influence the ratio of ammonium nitrate to crystal
habit modifier. However, the applicant has found that in accordance
with one of the preferred embodiments of the invention the ammonium
nitrate solution may contain from approximately 70 to 90 percent
ammonium nitrate by weight with the crystal habit modifier being
added to the solution at a concentration that results in the
crystal habit modifier representing from about 0.001 to about 2
percent by weight of a blasting agent that is subsequently
produced.
[0027] 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. FIGS. 2 and 3
represent examples of but two forms of nozzles that may be used in
the crystallization stage. In FIG. 2, the heated ammonium nitrate
solution or liquor (including the crystal habit modifier) is
injected through a centralized port 4 within an atomization nozzle
5. At the same time, compressed air is injected through laterally
adjacent ports 6 and 7, causing a turbulent mixing of the solution
of the ammonium nitrate liquor with a secondary air flow. As the
solution cools very fine grains of crystalline ammonium nitrate is
formed. As in the case of tank 1, the nozzle is preferably
maintained at a temperature of between approximately 85 and 100
degrees Celsius. Maintaining the nozzle at the desired temperature
range may be accomplished through various forms of heating devices
and methods, including direct and indirect heating means. In the
example shown in FIG. 2, nozzle 5 is equipped with a
circumferential steam jacket 8 that delivers the required heat. In
order to ensure the purity of the crystallized ammonium nitrate
product, the compressed air injected through the nozzle is
preferably environmentally controlled so that dust and other
particulate matter is filtered out. The secondary air is also
maintained within a desired temperature range of between about 20
and about 50 degrees Celsius, and the moisture content of the
secondary air flow is preferably maintained within defined
limits.
[0028] An alternate form of nozzle that may be used in the
crystallization stage is shown in FIG. 3. Here the heated ammonium
nitrate liquor (again including the crystal habit modifier) is
injected through a high velocity convergent-divergent laval-type
nozzle 9 in the presence of an environmentally controlled source of
pressurized air. As in the case of the nozzle shown in FIG. 2, the
pressurized air is preferably devoid of excessive amounts of
particulate material and is maintained within a temperature range
of from about 20 to about 50 degrees Celsius, and within defined
humidity ranges. As indicated in FIG. 3, as the compressed air
passes into nozzle 9 it enters a convergent zone 10 having a
reduced cross-sectional area and that acts in many ways like a
choke. After passing through the convergent zone 10 the compressed
air immediately enters a divergent zone 11 where the ammonium
nitrate liquor is injected at an angle of approximately 90 degrees
to the air flow. It will be appreciated that as the compressed air
passes at high velocity through the diverging zone the ammonium
nitrate liquor injected into the nozzle will experience turbulent
mixing with the high velocity air. In operation, nozzles of the
type shown often develop supersonic air speeds within their mixing
zones, thereby providing a very high degree of turbulent mixing and
the ability for high volume throughput. Once again, as in the case
of the atomizing nozzle shown in FIG. 2, to maintain nozzle 9
within a desired temperature range of approximately 85 to
approximately 100 degrees Celsius, direct or indirect heating of
the nozzle may be necessary. In the embodiment shown in FIG. 3,
heating of the nozzle is accomplished through the use of a steam
jacket 12.
[0029] Regardless of whether the nozzle shown in FIG. 2, the nozzle
shown in FIG. 3, or some other mechanically equivalent structure is
utilized, the turbulent mixing of the ammonium nitrate liquor with
a stream of compressed air causes very fine crystallization of the
ammonium nitrate, such that crystals having a particle size
distribution of from about 1 to about 500 microns are formed. This
may be contrasted to traditional explosives grade prills that have
particle sizes in the range of 1400 to 1800 microns. The selection
of the particular nozzle to be used will to a large degree depend
upon required production rates, with air atomizing nozzles (FIG. 2)
being used for lower production rates. 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.
[0030] The fine grained ammonium nitrate crystals formed in
accordance with the above described methods have been found to
exhibit qualities that make them particularly attractive for use in
the manufacturing of explosives.
[0031] However, it will be understood that such crystals could also
be used for non-explosive applications, including those in the
agricultural and cleaning industries.
[0032] In order to convert the crystallized ammonium nitrate into a
blasting agent, the ammonium nitrate crystals are 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, however, other carbonaceous fuels can also be used.
Such other fuels include 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 and may include tackifiers, such a Paratac.TM. and
polyisobutylene. It will also be appreciated by those skilled in
the art that in some cases the presence of the crystal habit
modifier in sufficient quantity to achieve a desired oxygen balance
in the blasting agent could remove the need for the use of a
carbonaceous fuel per se.
[0033] Where an organic carbonaceous fuel is added to the ammonium
nitrate crystals, in one of the preferred embodiments of the
invention the fuel is preferably added at an amount of from about 2
to about 8 percent by weight of the total explosive composition,
(with the ammonium nitrate representing from about 75 to 98 percent
of the blasting agent), and most preferably from about 4 to about 6
percent by weight of the blasting agent with the preferred ratio of
inorganic oxidizing salt (ammonium nitrate) to organic carbonaceous
fuel preferably being generally about 94:6. Ratios in this general
range help to ensure that the explosive composition or blasting
agent contains sufficient organic carbonaceous fuel to be oxygen
balanced. The oxygen balance is preferably more positive than -10
percent, and most preferably in the range of about -5 to +5
percent. It will of course be recognized that other ratios of
ammonium nitrate and fuel could equally be used while remaining
within the broad scope of the invention. It should also be noted
that altering the amount of crystal habit modifier, together with
the addition of water and/or other additives, will in many cases
have an impact on the amounts of ammonium nitrate and fuel that may
be utilized while maintaining an oxygen balance and velocity of
detonation within desired ranges.
[0034] Referring again to FIG. 1, in one embodiment of the
invention the fuel is added to the ammonium nitrate crystals by
means of a mechanical mixing process. The particular form of
mechanical mixing may be varied, however, it is expected that in
most cases the mixing will be accomplished through use of a ribbon
or drum blender 15 driven by a motor 16. As also indicated in FIG.
1, one or more additives may be mixed with the blasting agent
during the mechanical mixing stage. Such additives may include
water, gelling agents, cross-linking agents and/or (as described
above) the organic carbonaceous fuel. Where the additive added is a
gelling agent, preferably it is added at a concentration of about
0.1 to 10 percent by weight of the ammonium nitrate crystals. The
gelling agent would typically be a hydrophilic colloid, such as
guar gum, which swells or hydrates in the presence of water.
Derivatives of guar gum, such as hydroxyethyl or hydroxypropyl guar
or self-complexing guar gums (which contain a pre-blended
cross-linking agent), may also be used. Other forms of thickeners
or gelling agents, such as polyacrylamide, carboxy methyl
cellulose, carboxy ethyl cellulose, and biopolymers (such as
Xanthan gum) may also be used.
[0035] 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
pyroantimonate, 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 tartrate, sodium dichromate or sodium
tetraborate may be used.
[0036] Water may also be combined with the ammonium nitrate
crystals during the mechanical mixing stage. Where water is added,
preferably the water concentration of the blasting agent ranges
from less than 1 percent to about 15 percent by weight of the total
explosive composition.
[0037] 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 or for use in mining
or other blasting operations, or may be sent to any one of a wide
variety of other storage or processing facilities.
[0038] In an alternate embodiment of the invention, the fuel may be
added to the ammonium nitrate component during the crystallization
stage. For example in FIG. 3 a pair of arrows 18 indicate the
position at which fuel may be injected into the nozzle to cause the
fuel to be mixed with the ammonium nitrate crystals as and
immediately after they are formed. Depending upon the flow rate
through the nozzle, a number of fuel injection ports may be spaced
about the circumference of the nozzle. The high degree of
turbulence within the nozzle helps to ensure an even distribution
of fuel throughout the ammonium nitrate crystals and results in
enhanced blasting characteristics of the explosive. In yet a
further embodiment of the invention, fuel may be added to the
ammonium nitrate by both injecting through the nozzle and through
mechanical mixing with a ribbon blender, drum blender or similar
device.
[0039] For illustrative purposes, FIG. 5 shows some examples of
particular compositions of blasting agents that may be constructed
in accordance with the invention.
[0040] 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 FIG. 4. FIG. 4 also shows a related
curve for standard ANFO and demonstrates the increase in velocity
of detonation provided by means of the current invention.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
* * * * *