Note: Descriptions are shown in the official language in which they were submitted.
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EXPLOSIVE
THIS INVENTION relates, broadly, to ammonium nitrate/fuel oil explosives,
also known as ANFO or ANFEX explosives, and hereinafter also referred to as
ANFO
explosives. More particularly, the invention relates to a process for
producing an ANFO
explosive, and to an ANFO explosive when produced by the process.
Water and oil emulsion components, such as those used in the production of
ANFO explosives, are known to be unstable in that separation of the oil and
water
phases after mixing thereof occurs readily. Such separation is particularly
problematic
when the emulsion is pre-mixed and then transported to an ANFO explosive
manufacturing site or operation, since re-mixing of the emulsion is required
before it can
be used in manufacture of the ANFO explosive. Conventional approaches to
overcoming or inhibiting this instability include adding surfactants to the
emulsion and
continuous stirring of the emulsion. Continuous stirring of the emulsion is,
however, a
cumbersome exercise. The use of surfactants is a viable alternative, but
surfactants are
expensive and in bulk operations, such as the manufacturing of large
quantities of
ANFO explosive, the use of large quantities of surfactants is thus not an
economically
attractive option.
It is thus an object of the present invention to provide a cost-effective
process for the production of an ANFO explosive, which addresses, in
particular, the
separation of water and oil components of a water/oil emulsion used in the
production of
a fuel oil for the ANFO explosive production.
According to the invention, there is provided a process for producing an
ammonium nitrate/fuel oil explosive, the process including:
admixing an oil with water to form a fuel comprising an emulsion;
introducing ozone into the emulsion, thereby to obtain an ozonated emulsion;
and
admixing the ozonated emulsion with solid particulate ammonium nitrate to
absorb
the emulsion into the ammonium nitrate, thereby to form an ammonium
nitrate/fuel oil
explosive.
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The introduction of the ozone into the emulsion may include bubbling ozone
or an ozone-containing gas through the emulsion. Bubbling the ozone or the
ozone-
containing gas through the emulsion may be conducted at a sufficiently high
rate such
as to cause ozonation of the emulsion.
The introduction of the ozone into the emulsion causes the viscosity of the
emulsion to increase. The introduction of ozone into the emulsion may
therefore be
conducted for a sufficient treatment period so as to obtain an emulsion of
desired
viscosity. More particularly, the introduction of ozone into the emulsion may
be
continued for a treatment period of from about 1 hour to about 24 hours, e.g.
for about
3 hours. On becoming ozonated, the emulsion typically attains a black or milky
black
appearance, and the bubbling of the ozone through the emulsion will therefore
typically
continue until such an appearance has been attained. It is expected that, in
becoming
ozonated, the viscosity of the emulsion will increase above that of the oil
used in
emulsification. The extent to which the viscosity increases is understood also
to be
dependent on the quantity of water used to form the emulsion.
Typically, the ozone is obtained by passing compressed air, oxygen,
nitrogen, or mixtures thereof through an ozone generator. The product gas from
the
ozone generator typically contains 3% to 6%, by volume, ozone; this product
gas can
then be bubbled through the emulsion.
The introduction of the ozone, or ozone-containing gas, into the emulsion
may be conducted simultaneously with the admixing of the oil and the water.
It will be appreciated that, depending on, amongst others, the relative
proportions of oil and water used, the emulsion may thus be either a water-in-
oil
emulsion or an oil-in-water emulsion.
Sufficient of the oil and the water may be used such that the oil forms
50%-98% by mass of the emulsion, with the balance thus being water.
Preferably,
sufficient of the oil and the water is used such that the oil forms 72%-89% by
mass of
the emulsion, e.g. about 75% by mass thereof. Thus, when the oil forms 75% by
mass
of the emulsion, the water will form 25% by mass thereof.
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The oil may, in particular, be used lubricating oil. Still more particularly,
the lubricating oil may be of the type employed, or rather previously
employed, for the
lubrication of motor vehicle parts. The motor vehicle parts may, in
particular, be those
of utility vehicles of the kind used in mines or similar machinery, which
require
lubrication.
The admixing of the oil and the water may be effected by means of high-
shear mixing. This may be achieved by using a high-shear mixer or another
emulsification method or means.
The admixing of the oil and the water may be effected in the presence of
an emulsifier/surfactant, hereinafter referred to as a surfactant. When used,
the
surfactant may typically form 0.2%-1.0% by mass of the emulsion. Preferably,
the
surfactant, when used, forms 0.3%-0.8%, e.g. about 0.5% of the emulsion.
At least a portion of the surfactant used may be provided by the oil. In this
regard it will be appreciated that used lubricating oil normally contains some
surfactants,
and these surfactants can thus constitute at least part of the surfactant as
discussed
above. It is envisaged that, normally, it will typically not be necessary to
use any
additional or external surfactant.
The relative proportions of emulsion and ammonium nitrate employed in
producing the ammonium nitrate/fuel oil (ANFO) explosive will be more or less
conventional. More particularly, sufficient of the emulsion and the ammonium
nitrate
may be used in producing the ANFO explosive such that the oil forms 2.5%-22%
by
mass of the ANFO explosive. More preferably, sufficient of the emulsion and
the
ammonium nitrate may be used such that the oil forms 5%-7% by mass of the ANFO
explosive, e.g. about 6% by mass thereof.
The particulate ammonium nitrate may be in the form of porous
ammonium nitrate prills, i.e. porous prilled ammonium nitrate. Typically, the
porous
prilled ammonium nitrate (PPAN) will be of the type conventionally used in the
manufacture of ANFO explosives. The PPAN prills may be employed in a mass
ratio to
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the fuel of 98:2 - 78:22. Preferably, the PPAN is employed in a mass ratio to
the fuel of
94:6 - 91:9, e.g. about 94:6.
Admixing the ozonated emulsion with the porous prilled ammonium nitrate
may be conducted in conventional fashion by pumping the emulsion from a source
tank
and spraying it by means of a nozzle onto the ammonium nitrate which is moved
along
by the flutes of an auger. It is expected that moving the ammonium nitrate in
such a
fashion will provide additional mixing. Alternatively, and typically for
preparing the
ANFO explosive on a batch scale, a concrete mixer or the like may be used.
The invention extends to an ANFO explosive when produced in
accordance with the process described herein.
The invention will now be described, by way of example, with reference to the
accompanying non-limiting illustrative worked Example.
EXAMPLE
A water-in-oil emulsion, comprising, by mass, 25% water and 75% oil, was
prepared by mixing appropriate quantities of water and used lubricating oil in
a high-
shear mixing vessel.
Ozonated air, i.e. a gas obtained by passing compressed air through an
ozone generator and containing 3% to 6% ozone, by volume, was bubbled through
the
mixture for a treatment period of 3 hours, during which the viscosity of the
emulsion
increased above that of the oil used and the emulsion attained a black
appearance. It
will be appreciated that, in accordance with the other embodiments of
invention, any
other suitable gas may be used instead of compressed air to generate an ozone-
containing gas which is then bubbled through the mixture or emulsion of water
and used
lubricating oil.
At the end of the treatment period, bubbling of the ozone through the
emulsion was ceased. A stabilized water-in-oil emulsion was obtained.
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An ANFO explosive was then prepared by admixing the stabilized emulsion
or fuel with porous prilled ammonium nitrate (PPAN) in a mass ratio of PPAN:
stabilized
emulsion (fuel) of 94:6. The admixing was effected by pumping the emulsion
from a
source tank and spraying it by means of a nozzle on to the ammonium nitrate
prills.
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The Applicant believes that the present invention provides a viable and
cost-effective process for the production of ANFO explosive which addresses,
in
particular, the difficulties associated with the separation of water and oil
components of
a water/oil emulsion.
The use of ozone in the formation of the oil/water emulsion, in accordance
with the invention, serves to stabilize the emulsion so that separation of the
emulsion
into separate oil and water phases does not readily occur. When used
lubricating oil is
used as the oil, or as at least a component of the oil, then surfactants
already present in
the used lubricating oil serve to stabilize the emulsion even further,
typically to the
extent that it is not necessary to use any additional, i.e. external or
additional,
surfactant.
The stabilized ozonated emulsion provided by this process is thus
economically attractive, as the need for large quantities of expensive
additional
surfactants to stabilize the emulsion is reduced or even eliminated. The
stabilized
emulsion was found to be stable for long periods of time, being particularly
advantageous when the emulsion needs to be transported in premixed form to an
ANFO explosive production site or operation.
