AU594423B2

AU594423B2 - Charging of explosives into boreholes

Info

Publication number: AU594423B2
Application number: AU68176/87A
Authority: AU
Inventors: Michael James Cox; Isadore Edward Francke; Jeremy Guy Breakwell Smith
Original assignee: AECI Ltd
Current assignee: Orica Explosives Technology Pty Ltd
Priority date: 1986-03-05
Filing date: 1987-01-30
Publication date: 1990-03-08
Anticipated expiration: 2007-01-30
Also published as: BR8700949A; MW587A1; CA1312777C; NZ219213A; GB2187490B; GB8700482D0; ZW1487A1; GB2187490A; AU6817687A

Description

AECI 567 PATENTS ACT 1952 594423 P/00/0 11 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: 91 7 187 Complete Specification-Lodged: Accepted: Lapsed: Published: LThis docu mnt contanifs th e amendments miade under Section 49 and is cor',Ct for printing.

P I6rfty: ,Rellied Art: jName of Applicant: 6 A0 Addre3ss of Applicant: Actual Inventor: TO BE COMPLETED BY APPLICANT AECI LIAITED 16th Floor, Office Tower, Carlton Centre, Commissioner Street, Johannesburg, Transvaal Republic of South Africa Isadore Edward FRANCKE Jeremy Guy EREARWELL SMITH Michael James COX Patents Section ICI Australia Limited 1 Nicholson Street Melbourne 3001 Victoria Australia Address for Service: Complete Specification for the Invention entitled: "CHARGING OF EXPLOSIVES INTO BOREtIOLES" The following statement Is a full description of this Invention, Including the best method of performing It known to me:-* Note., The description Is to be typed In double spacing, pica type face, In an area not exceeding 250 mm In depth and 160 mm In width, on tough white paper of good quality and It Is to be Inserted Inside this form.

14590178-L t409978-LPrinted by tHompsoN, Commionwealth Government Printer, Canberr a THIS INVENTION relates to the charging of explosive into boreholes. More particularly, the invention relates to a method of charging a pumpable explosive into a borehole, and to a borehole charging assembly 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 punpable explosive into the borehole; and while the explosive is being pumped into the borehole, mixing a sensitizing agent into the explosive to enable gas bubbles of size 70 to 200 microns in diameter to be formed in the explosive.

Pumping the explosive may be by means oi any suitable pump.

Thus, the pumping 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 transport 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 agent into the explosive may include passing the sensitizing agent 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

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-3pumlp. Mien the sensitizing agent is pumpable, as mentioned above, the method may include pumping the sensitizing agent from a container into the pump which is used to pump the explosive down the borehole. This container, and the container used for the explosive, may be a tank, hopper, or the like.

The mixing may include passing the explosive delivered by the pump 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 or more such static mixers, and they will be typically provided, eg in series, downstream of the pump used to pump the explosive down 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 200 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 interconnected borehole charging assembly as described hereunder, mounted together on mobile transport means'.

The method may be used for charging boreholes underground, in which case it may include the preliminary steps of formulating the explosive as a repumpable unsensitized formulation underground, and then pumping this formulation into a hopper or tank on an underground vehicle from which, in accordance with the invention, it is pumped into the borehole while being sensitized. Naturally, in similar situations above ground, the method may include the similar preliminary steps of

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-4formulating the' unsensitized explosive on site as a repumnpable formulation, and then pumping it into a tank or hopper on a vehicle, from which it is pumped into a borehole.

According to another aspect of the invention there is provided a borehole charging assembly, for charging a pumpable explosive into a borehole, which assembly comprises a container for pumpable unsensitized explosive, a container for sensitizing agent, a pump for pumping the explosive, and a mixing device, the containers having outlets connected to the pump inlet and the mixing device being connected in series with the pump to the pump outlet.

The pump may be an orbiting helical positive displacement pump. There may be a plurality of mixing devices cdniiected in series with the pump, downstream of the pump, the mixing devices and pump being arranged such that the assembly is capable of pumping an explosive containing gas bubbles of size 7 to 200 microns in diameter.

0 CI: cnnetedEach container may be a fluid container, having its outlet conete by a fluid flow line to the pump inlet.

The pump outlet may 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 pump for pumping sensitizing agent from said container 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 the flow line between said further pump and the container for the sensitizing agent.

ti In a particular embodiment of the invention there may be a single mixing device, and the mixing device may be a static mixer, eg a static mixer of the type comprising a tubular housing one or typically several mixing elements arranged in series in the housing. As mentioned above, the static mixer may be connected directly to the outlet of the pump for pumping 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 connrected 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 like for insertion into a borehole to be 0 charged.

0 The explosive may be an emulsion explosive in which an Soxidizing salt-containing component forms the discontinuous phase, the continuous phase comprising a fuel component which is immiscible with "O the discontinuous phase. Such explosives, when the oxidizing o 0 salt-containing component contains water and is in the form of an aqueous solution are known as 'water-in-fuel' 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 ammonium nitrate alkali metal nitrates alkaline earth metal nitrates -6ammonium perchlorate urea alkali metal perchlorates and alkaline earth metal perchlorates.

When 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, together with the anmonium nitrate, form a melt which has a melting point which is lower than that of the ammonium nitrate, the further compounds 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 the oxidizing salt component to avoid excessively high processing temperatures during formation of the base Semulsion. When selecting the proportion of water used in the emulsion o to which the sensitizing solution is added, the proportion of any water in such sensitizing solution as is used can be borne in mind, to determine the proportion of water which will be present in the final explosive product.

o O o The fuel of the fuel component of the 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 fuel may comprise at least one member of the group consisting in S-7mineral oils, fuel oils, lubricating oils, liquid paraffin, microcrystalline waxes, paraffin waxes, xylene, toluene, petrolatum, slack wax and dinitrotoluene.

When the emulsion is intended to be repumpable, any constituents thereof such as microcrystalline waxes, paraffin waxes, petrolatun, slack waxes, or the like which, if used in excess, can affect its repunpability, 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 selected from the group consisting in sorbitan sesquioleate, sorbitan monooleate, sorbitan monopalmitate, sodium monostearate, sodium c'" tristearate, the mono- and diglycerides of fat-forming'fatty acids, soya bean lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl acid phosphate, laurylamine 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 o o o o derivatives. The emulsifiers act as surfactants and stabilizers to promote the formation of the emulsion and to resist crystallization and/or coalescence 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/cm 3 mentioned above.

f-a.-

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f crc 0*e -8- This type of explosive, without the density reducing agent, ie the 'sensitizing agent referred to above, will be contained in one of the tanks or hoppers, and the sensitizing agent, which will function as a density reducing agent, will be contained in the other tank or hopper.

llu c* Typical emulsions or use in accordance present invention will comply with the following with the method of the broad formulation: Constituent Ammonium nitrate Sodium nitrate Calcium nitrate Water Sorbitan monooleate Fuel oil Acetic acid Thiourea Sodium acetate

FORMULATION

Function Oxidizing salt Oxidizing salt Oxidizing salt Solvent Emulsifier Fuel Buffer Catalyst Stabilizer Typical proportion in formulation on a mass basis (m/m) 60,0 75,0 0,0 20,0 0,0 20,0 9,0 22,0 0,5 1,0 0,0 0,1 0,1 o o o Ii 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 P95 Mineral oil available from BP South Africa (Proprietary) Limited may be substituted for the fuel oil, and other known emulsifiers of the type recited above may be substituted for the sorbitan monooleate. Other catalysts such as thiocyanate can be substituted for the thiourea, and other buffers such as citric acid for the acetic acid.

Furthermore, if desired, finely divided solid fuels such as aluminium or ferrosilicon can be added to the emulsion.

For emulsions of the type set out in the above table, any suitable sensitizing agent may be used, but the invention contemplates particularly employing a pumpable sensitizing solution in the form of an aqueous solution of sodium nitrite. In this gassing solution the sodium nitrite will typically make up 10-40% by mass, the water, correspondingly, making up 60-90% 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 I, 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 regari it should be noted that the mixing device, eg the static mixer, should be selected so that bubbles are produced having an average size of between and 200 microns, with all the bubbles produced preferably being within this range and 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 explosive, with the associated danger, is kept to a minimum.

The invention will now be described, by way of illustrative non-limiting 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 assembly in accordance with the present invention,' 'in its operative condition in use in accordance with the method of the present invention, for above ground use; and FIGURE 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 reference numeral 12.

4 4 4 44 4 I 4 4 4( 441i 16 on the connected (also not The assembly 10 comprises a Mono pump 14 mounted by brackets load bed 18 of the lorry. The Mono pump has a drive shaft by drive transmission means (niiot shown) to a power supply shown) both mounted on the load bed 18.

V11 The pump 14 has an inlet in the form of a flanged pipe 22 connuected by a shut-off valve 24 having an operating handle 26, to a flanged pipe 28 constituting the outlet of an emulsion hopper 30. A chemical gassing solution tank 32 is mounted alongside the hopper and has an outlet provided by a pipe 34 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 branch pipe 42 has a lion-return valve 43 which prevents flow from the pipe 22 to the hopper 32. This further punip, designated 44, is a small centrifugal pump such as a Jabsco pump. Although shown suspended from the hose 40 in the drawings, the Jabsco pump will ini fact 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 connected 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 4 loading hose 56 shown inserted into a borehole 58 in rock 60 to be 4 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, -12and the hose 56, which is conveniently permanently attached to the outlet 54 of the mixer 52, and carried in a coiled state on the load'bed 18, will then be uncoiled and inserted into the appropriate borehole 58.

The pumps 14 and 44 will then be driven by their power supplies (not shown), which may be mounted on the load bed 18 of the lorry 12, simultaneous operation of the pumps 14 and 44 automatically withdrawing, after opening of the valves 24, 36, emulsion from the hopper 30 and gassing solution from the tank 32.

Mixing of gassing solution and emulsion will start in the pump 14, and will progress in the mixer 52 to adequate homogeneity, nitrogen bubbles simultaneously starting to be formed in the emulsion, in the size range 70-200 microns and homogeneously dispersed in the emulsion.

These gas bubbles are eg nitrogen bubbles formed by reaction of sodium nitrite in the gassing solution with ammonium nitrate in the emulsion, for the formulation set out in the Example hereunder. This chemical 0 gassing and density reduction, eg to a density of 1,0-1,5 g/cm 2 io sensitizes the emulsion to detonation by means of a blasting cap or the 0 C 0 like.

°The sensitized emulsion is pumped directly from the assembly 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.

-13- 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. Unless 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 following composition was used: Constituent Proportion in parts m/m Ammonium nitrate 64 Sodium nitrate 12 Water 17,3 Sorbitan monooleate Fuel oil Acetic acid 0,1 Thiourea Sodium acetate 0,1 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.

.14- In accordance with the method described above, with reference to the drawings, and using the assembly shown in the drawing, the sensitizing 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 emulsion were mixed with 1,2 parts by mass of sensitizing solution.

The method and assembly were found to provide a conveniently employed inexpensive and relatively safe method and means for charging boreholes. In particular, the invention has the advantage that the base emulsion is transported in its relatively safe unsensitized state and is partially sensitized for an extremely short period before charging thereof into the boreholes, being indeed fully sensitized only several minutes after it has been charged into the boreholes.

Claims

1. A method of charging a pumpable explosive into a borehole, which method comprises pumpinig the pumpable explosive into the borehole; and while the explosive is being puimped into the borehole, mixing a sensitizing agent into the explosive to enable gas bubbles of size 70 to

2-20 microns in diamneter to be formed in the explosive. 2. A method as claimed in Claim 1, in which the pumping is by means of an orbiting helical positive displacement screw pump and takes place from a container containing unsensitized pumpable explosive mounted on mobile transport means.

3. A method as claimed in Claim 1 or Clai-m 2, in which the mixing of the sensitizing agent into the explosive includes passing the sensitizing agent together with the explosive through the pump which is used to pump the explosive down the borehole.

4. A method as claimed in Claim 3, in which the sensitizing agent is pumpable, the method including pumping the sensitizing agent from a containier into the pump which is used to pump the explosive down the borehole.

S. A method as claimed in any one of the preceding claims, in which the mixing includes passing the explosive delivered by the pump which is used to pump the explosive down the borehole together with the sensitizing agent through a mixing device. *1 16

6. A method as claimed in Claim 5, in which the mixing device is a (mixer.

7. A method of charging a pumpable explosive into a borehole, substantially as described herein. 3c7t' day of 7 Dated this

1989. 0 0 000 V 0 AECI LIMITED By its Patent Attorney J R Davy 1