Note: Descriptions are shown in the official language in which they were submitted.
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~ECI ~67
T~IIS INVENTION relates to the charging of explosive into
boreholes. ~lore particularly, ~he invention relates to a method of
charging a pumpable explosive into a borehole, and to a borehole
charging assen~ly for charging a pumpable explosive into a borehole.
According to one aspect of the invention there is provided a
method of charging a pumpable explosive into a borehole, which method
comprises
pumping the pwnpable explosive into the borehole; and
while the explosive is being pumped into the borehole, mixing a
sensitizing agent illtO the explosive to enable gas bubbles of size 70 to
200 microns iTl di~meter to be ~ormed in tile explosive.
Pumping the explosive may be by means of any suitable pump.
Thus, the pwnping may be by means of an orbiting helical positive
displacement screw pump, such as a Mono pump, the pumping taking place
from a container containing unsensitized pumpable explosive mounted on
mobile ~ransport means such as a lorry, rail truck, or like vehicle.
The sensitizing agent may also be pumpable, being eg a fluid
material such as a chemical gassing solution. The mixing of
the explosive and the sensitizing agen-t into the explosive may include
passing the sensitizing agen~ together with the explosive through the
pump which is used to pump the explosive down the borehole, so that the
sensitizing agent and explosive are at least partially mixed in the
3 ~3~2777
~un~ en the sensitizing agent is pwnpable, as melltiorlcd a~ove, the
method ma~ include pumping the scnsitizing agent from a container into
the pump which is used to pump the explosive down the borchole. This
container, and the container used for the explosive, may be a tank,
hopper, or the li~e.
The mixing may includé passing the explosivè delivered by the
punlp which is used to pump the explosive down the borehole together with
the sensitizing agent through a mixing device. The mixing device may be
a static mixer. There may be one oI more such static mixers, and they
will be typically provided, eg in series, downstream of the pwnp used to
pump the explosive do~l the borehole, and the mixture will issue from
said mixing device or devices as an explosive which is starting to
become sensitized by gas bubbles of size 70 to Z00 microns in diameter,
and which mixture passes directly from the mixing device or devices into
the borehole.
The containers, pump or pumps and mixing device or mixing
devices, all conveniently form part of an interco Mected borehole
charging assembly as described hereunder, mown~ed together on mobile
transport means.
The method may be used for charging boreholes undergrowld, in
which case it may include the preliminary steps of formulating the
explosi~e as a repumpable unsensitized formulation undergrownd, and then
pumping this formulation into a hopper or tank on an undergrownd vehicle
from which, in accordance with the invention, it is pumped into the
borehole while being sensitized. Naturally, ~n similar situations above
growld, the method may include the similar preliminary steps of
7 r~ r~
ormulatillg the unsellsitized explosive on site as a rcpumpable
fo~ulatioll, alld then pumping it into a tank or hopper on a vehicle,
from which it is pumped into a borehole.
~ccording to another aspect of the invention there is provided
a borehole chargillg assembly, for chargillg a pun~able explosive into a
borehole, which assembly comprises a container for pumpable unsensitized
explosive, a container ~or sensitizing agent, a pump for pwnping the
explosive, and a mixing device, the containers having outlets connected
to the pump inlet and the mixing device being comlected in series with
the pump to the pump outle~.
The pump may be an orbiting helical positive displacement
pump. There may be a plurality of mixing devices comlected in series
with the pwnp, downstream of ~he p~np, the mixing devices and pump being
arranged such that the assembly is capable of pumping an explosive
containing gas bubbles o size 7 to 200 microns in diameter.
~ ach container may be a fluid container, having its outlet
colmected by a fluid flow line to the pump inlet.
The pump outlet m~y be connected directly to the inlet of the
mixing device into which it feeds; and the flow line from the container
for the sensitizing agent to the pump may include a further pun~ for
pumping sensitizing agent from said contahler to the pump for pumping
explosive. The assembly may include a flow meter, for metering flow of
sensitizing agent from the container for the sensitizing agent to the
pumps, the flow meter being provided eg in ~he flow line between said
further pump and the container for the sensitizillg agent.
S ~ 7 rl 7
1ll a ~)articular embodilncnt of the invelltion tl~erc rnay be a
sillgle mixin~ d~ice, and the mixing device may be a static mixer, eg a
static mixer of the type comyrising a tubular housing one or typically
several mixing elements arr,~n~ed in series in the housing. As mentioned
above, the static mixer may be connected directly to the outlet of the
pump for pun~ g the explosive.
The assembly may be mounted on mobile transport means. Thus,
the assembly as a whole may be mounted on mobile transport means such as
a lorry, rail truck, sled, or the like, and conveniently includes a
power supply drivingly connected to each pump. In use, the out let of
the pump for pumping the explosive may be be connected, via the mixing
device, to a hose or the liké for insertion into a borellole to be
charged.
The explosive may be an emulsion explosive in which an
oxidizing salt-containing component forms the discontinuous phase, the
continuous phase comprising a fuel component WhiC}I is immiscible Wit]
- the discontinuous phase. Such explosives, when the oxidizing
salt-containing comyonent contains water and is in the form of an
aqueous solution are known as 'water-in-fuel1 emulsions, and when the
oxidizing salt-containing component contains little or no water can be
regarded as 'melt-in-fuel' emulsions.
The discontinuous phase may comprise at least one oxidizing
salt selected from the group consisting in :
~mmonium nitrate
alkali metal nitrates
alkaline earth metal nitrates
1312 ~ ~ 7
.m~loniwn perchlorate
urea
alkali metal perchlorates and
al~aline earth metal perchlorates.
Whell the discontinuous phase comprises ammonium nitrate, it
may comprise one or more further compounds such as sodium nitrate,
calcium nitrate, urea or the like which, to~ether with the ammonium
nitrate, form a melt which has a melting point which is lower than that
of the ammonium nitrate, the further colnpounds being capable of reacting
as oxygen releasing salts or fuels. The discontinuous phase may in
certain cases comprise water, which is kept to a minimum to avoid wasted
energy arising from steam generation, but which is employed to
facilitate melting/dissolving of tile oxidizing salt component to avoid
excessively high processing temperatures during formation of the base
emulsion. When selecting the proportion of water used in the emulsion
to which the sensitizing solution is added, the proportion of any water
in such sensitizing solution as is used can be bom~ in mind, to
determine the proportion of water which will be present in the final
explosive product.
The fuel of the fuel component of ~he emulsion may form from
2-25~ by mass of the emulsion, preferably about 3-12%.
The fuel of the fuel component of the emulsion will be
immiscible with and insoluble in water, and may be non-self-explosive,
comprising eg at least one member of the group consisting in
hydrocarbons, halogenated hydrocarbons and nitrated hydrocarbons. Thus
the uel may comprise at least one member of the group consisting in
7- ~3~2777
r,~ eral oils, fuel oils, lubricating oils, li~uid paraffin,
microcl~stalline waxes, paraffin waxes, xylene, toluene, petrolatum,
slack wax and dinitrotoluene.
When the emulsion is intended to be repun~able, any
constituents thereof such as microcrystalline waxes, parafIill waxes,
petrolat~nn, slack waxes, or the like whic}l, if used in excess, can
affect its repun~ability, will be used in sufficiently small proportions
so that they do not adversely affect this repumpability.
The fuel component of the emulsion may comprise at least one
emulsifier s~lected from the group consistillg in sorbitan sesquioleate,
sorbitan monooleate, sorbit~l monopalmitate, sodium monostearate, sodium
tristearate, the mono- and diglycerides of fat-forming fa~ty acids, soya
bean lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl
acid phosphate, laulylamine acetate, decaglycerol decaoleate,
decaglycerol decastearate, 2~oleyl-4,4'-bis(hydroxymethyl)-2-oxazoline,
polymeric emulsifiers containing polyethylene glycol backbones with
fatty acid side chains and polyisobutylene succinic anhydride
derivatives.
The emulsifiers act as surfactants and stabilizers ~o promote
the formation of the emulsion and to resist crystallization and/or
coalescense of the discontinuous phase.
The method may include dispersing a density reducing agent
therein to reduce the density of the emulsion to within the desired
range of 1,0-1,5 g/cm3 mentioned above.
This t~e of explosive, witllout the density reducing agent, ie
the sensitizing agent referred to above, will be contained in one of
the tal~ks or hoppers, and the sensitizing agent, which will function as
a density reducillg agent, will be contained in the other tank or hopper.
5Typical emulsions or use in accordance with the method of the
present invention will comply with the following broad fonmulation:
FO~LA~ION
Constituent FunctionTypical proportion in
formulation on a mass
basis (m/m)
~nonium nitrate Oxidizing salt60,0 - 75,0
Sodium nitrate Oxidizing salt0,0 - 20,0
Calcium nitrate Oxidizing salt0,0 - 20,0
15 Water Solvent 9,0 - Z2,0
Sorbitan monooleate Emulsifier 0l5 - 4,0
Fuel oil Fuel 1,0 - 5,0
Acetic acid Buffer 0,0 - 1,0
Thiourea Catalyst 0,1 - 1,0
Sodium acetate - Stabilizer 071 - 1~0
The thiourea acts to catalyse the reaction between the
ammonium nitrate and sodium nitrite described hereunder, and the acetic
acid buffers the pH of the oxidizing salt component to a desirable
value.
For this particular type of explosive, the ammonium nitrate
and sodium nitrate components may be partially replaced by perchlorates
of the type mentioned above, calcium nitrate, or the like. Mineral oil
such as P9S Mineral oil available from BP South Africa (Proprietary)
7 7 1
Limited m.ly be substituted for the fuel oil, alld other hlown emulsifiers
o~ the type recited above may be substituted for the sorbitan
monooleate. Other catalysts such as thiocyanate can be substituted or
the thiourea, and other buffers such as citric acid for the acetic acid.
Furthermore, if desired, finely divided solid fuels such as aluminiun~ or
ferrosilicon can be added to the emulsioll.
For emulsions of the type set out in the above table, any
suitable sensitizing agent may be used~ but the invention contemplates
yarticularly employing a pumyable sensitizing solution in the form of an
aqueous solutioll of sodium nitrite. In this gassing solution the sodium
nitrite will typically make up 10-40~ by mass, the water,
correspondingly, making up 6~-~0% by mass.
To the emulsions of the type set out in the table above,
typically 0,5-3,0 parts by mass of this gassing solution will be added.
In accordance with the method, thus, the pump will be used to
withdraw the emulsion from the emulsion hopper, and the gassing solution
from its tank, the flow lines from said hopper and tank entering the
inlet or throat of the pump, and the flow being assisted by gravity and
the drop in pressure below ambient pressure at the pump inlet caused by
operation of the pump. Initial mixing of sensitizing solution and
emulsion will take place in the pump itself, and final mixing to
acceptable homogeneity in the mixing device downstream of the pump. The
sodium nitrite in the gassing solution will react with ammonium nitrate
in the emulsion to produce nitrogen (N2) bubbles, which act to reduce
the density of the emulsion, thereby to sensitize it. In this regard it
should be noted that the mixing device, eg the static mixer, should be
-lo~ 131~7 ~ ~
seleeted so that bubbLes are produced having ~ average siLe of between
and 2~ microns, w;th all the bubbles produced preferably being
~ithin tlliS r~lge ~nd evenly and homogeneously dispersed throughout the
emulsion. The explosive, in its sensitized form, will flow immediately
from the mixing device into the borehole, so that time spent handling a
sensitized e~plosive, with the associated danger, is kept to a minimum.
The invention will now be described, by way of illustrative
non-lLmiting example, with reference to the accompanying diagrammatic
drawings and worked example.
In the drawings,
FIGURE 1 shows a schematic side elevation of a borehole charging
assenlbly in accordance with the present invention, in its operative
condition in use in accordance with the me~hod of the present invention,
for above ground use; and
FIGU~E 2 shows a similar view of another assembly according to the
invention for underground use.
In Figure 1 of the drawings, reference numeral 10 generally
designates a borehole charging assembly in accordance with the present
invention. The assembly is mounted on a lorry generally designated by
referellce numeral 12.
The assembly 10 con~rises a ~iono pump 14 mounted by brackets
16 Oll the load bed 18 of the lorry. The Mono pump has a drive shaft 20,
connected by drive transmission means (not shown) to a power supply
(also not shown) both mo~l~ed on the load bed 18.
3~777
The p~np l~ has an inlet in the fo~m of a flanged pipe 22
co~ected b~ a shut-off valve 24 having an operating handle 26, to a
flanged pipe 28 constituting the outlet of an emulsion hopper 30. A
chemic~l gassing solution tank 32 is mounted alongside the hopper 30,
and has an outlet provided by a pipe 3~ which is connected via a
shut-off valve 36 having an operating handle 38, to a hose 40 which
feeds through a flow meter 41 and a further pump into a branch pipe 42
of the pipe 22, leading into the pipe 22. The br~lch pipe 42 has a
non-return valve 43 which prevents flow from the pipe 22 to the hoMer
32. This furtller pump, designated 44, is a small centrifugal pump such
as a Jabsco pwnp. Although shown suspended from the hose ~0 in the
drawings, the Jabsco pump will in ~act be mounted on the load bed 18 of
the lorry 12.
The pump 14 has an outlet at 45 provided with a flange 46 via
which it is colmected to the flange 48 of the inlet 50 of a static mixer
52. The outlet at 54 of the static mixer is connected to an explosive
loading hose 56 sllown inserted into a borehole 58 in rock 60 to be
broken, and wherein other boreholes are also designated 58.
,
Suitable support means, such as legs, struts or the like (not
shown) are provided, whereby the hopper 30 and tank 32 are mounted on
the load bed 18 of the lorry 12.
In use, the hopper 30 and the tank 32 will respectively be
charged with emulsion and gassing solution from suitable sources of
supply. The lorry 12 will then be driven to the rock face 62, which may
be above ground or underground in a mine, wherein the boreholes 58 have
been drilled. The lorry 12 will be stopped in a convenient position,
-12- 13~27~7
alld the hose 5h, whicll is conveniently pennanently attached to the
outlet 54 Or the mixer 52, ~Id carried in a coiled state on the load bed
18, will then be uncoiled and inserted into the appropriate borehole 58.
The pwnps 1~ and 44 will then be driven by their power supplies (not
sho~n), which may be mowlted Oll the load bed 18 of the lorry 12,
simultaneous operation of the ~wnps 14 and 44 automatically withdrawing)
after opening of the valves Z4 9 36 J emulsion from the hopper 30 and
gassing solution from the tank 32.
Mixing of gassing solution and emulsion will start in the pump
1~, and will progress in the mixer 52 to adequate homogeneity, nitrogen
bubbles simultaneously starting to be fonmed in the emulsion, in the
size range 70-200 microlls and homogeneously dispersed in the emulsion.
These gas bubbles are eg nitrogen bubbles formed by reaction of sodium
nitrite in the gassing solu~ion with ammonium nitrate in the emulsion,
for the fonnulation set out in the Example hereunder. This chemical
gassing and density reduction, eg to a density of 1,0-1,5 g/cm2,
sensitizes the emulsion to detonation by me~ls of a blasting cap or the
like.
The sensitized emulsion is pumped directly from the assembly
10 via the hose 56 into the borehole 58, after which it can be detonated
when desired.
The bubbles will continue to form in the mixer 52, in the hose
56 and in the borehole 58. Bubble formation will be complete several
minutes after the explosive has been charged into the borehole 58.
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Figure 2 of the drawings shows a substantially similar
assembly to that of Figure 1, except that the lorry 12 is replaced by an
underground vehicle 64. ~nless otherwise specified the same reference
numerals refer to the same parts. For both Figures 1 and 2 it is
contemplated that the emulsion will be formulated on site (above ground
or underground as the case may be) as a repumpable emulsion and then
pumped into the hopper 30 to be taken by the vehicle 12, 64 to the
boreholes 58.
The assembly described above with reference to Figure 2 of the
drawings has been successfully tested with the explosive and sensitizing
agent formulations set out in the following Example:
EXAMPLE
A water-in-oil or water-in-fuel emulsion having the foll~wing
composition was used:
Con tituent Proportion in parts m/m
Ammonium nitrate 64
Sodium nitTate 12
Water 17,3
Sorbitan monooleate 1,0
Fuel oil . 5,0
Acetic acid 0,1
Thiourea o,5
Sodium acetate O,1
As a gassing solution a solution of sodium nitrite was used,
comprising one part by mass of sodium nitrite dissolved in five
parts by mass of water.
3~277 ~
In accor~ ce with the method described above, with reference to
the drawings, and using the assembly shown in the drawing, the
sensitizirlg solution was used to sensitize the base or unsensitized
emulsion, while pumping the emulsion into boreholes. It should be
noted that 98,8 parts of base ernulsion were mixed with 1,2 parts by
mass of sensitizing solution.
The method and assembly were found to provide a conveniently
employed inexpensive and rela~ively safe method and means for
charging boreholes. In particular, the invention has the advantage
that the base emulsion is transported in its relatively safe
unsensiti%ed state and is partially sensitized for an extremely
short period belore charging thereof into the boreholes, being
indeed fully sensitized only several minutes after it has been
charged into the boreholes.
