AU600758B2 - Improvements in or relating to explosive compositions containing ammonium nitrate - Google Patents

Description

TjV0 I 'H l i i. d N L01 ,t t .r J i' I O. AUS R II COMMONWEALTH OF AUSTRALIA Name of Applicant: Address of Applicant: Actual Inventor(s): Address for service: The Patents Act 1952-1969 RICHARD JOHN JOHNSON P.O. Box 184, Mt. Pleasant, Via Mackay. Qld. 4740.

RICHARD JOHN JOHNSON G.R. CULLEN COMPANY p 4 3 Dalgety llou:>P, COMPLETE PATENT SPECIFICATION FOR THE INVENTION ENTITLED: IMPROVEMENTS IN OR RELATING TO EXPLOSIVE COMPOSITIONS CONTAINING AMMONIUM NITRATE The following statement is a full description of the invention including the best method of performing it known to us: 41 A c -2- THIS INVENTION relates to explosive compositions and in particular relates to explosive compositions containing ammonium nitrate.

I Explosive compositions utilizing ammonium nitrate

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j (AN) as the oxidizing agent, in conjunction with an oxidizable fuel are well known in the art of explosives.

Examples of such known explosive compositions include ANFO explosives (a dry flowable powder of ammonium nitrate and fuel oil), Ammonium nitrate/vegetable oil water-in-oil emulsions, and aqueous gels and slurries having typically 00 00 70% AN by weight.

°os Conventional ANFO explosives are generally in the 0 00 0o Q 0 0 0 0 0o form of a dry powder and are thus easy to place in a 0 00 o0 0 borehole without the need for expensive equipment and/or 00 00 0 000 S highly experienced operators. ANFO explosives are high 0 energy explosives since typically 99% of the w;eight of the 0 0 composition is fuel and oxidant. However, ANFO explosives 0 0 are highly sensitive to water due to the hygroscopic nature Ott of ammonium nitrate, resulting in the unsuitability of ANFO 2 explosives for use in wet boreholes. Even when a wet Sborehole is pumped out, residual water and/or continuing seepage into the borehole may result in diminshed explosive performance or non-detonation (blinds). A blind may be hazardous in that detonation may only be delayed; the 2 subsequent late detonation may be unexpected by the operators, particularly when multiple boreholes have been fired, -3- Thus in the past it has been the practice to employ gel, emulsion or slurry explosives where moisture in the boreholes is encountered. Such explosives are however both costly to manufacture due to the process conditions required and costly to use, since pumping equipment is required to charge the boreholes. Also such explosives cannot be transported in bags; they must be either tankered to sites for large jobs, or cartridged.

Typical gel and slurry compositions in accordance with che prior art include those disclosed in the following o o patents: oo 0 U.S. 3798091, assinged to HERCULES INC., wherein a gelled 000- O0 oo aqueous slurry explosive is provided with a chromium 0 04 0 acetate crosslinked guar gum thickening agent. The 00 0 0 oxidizer is a mixture of CN and AN.

U.S. 3925123, assigned to IRECO CHEMICALS, wherein an Saqueous inorganic oxidizing salt solution forms a continuous phase around the fuel particles, the slurry r' being thickened by a mixture of starch and gums including 2 guar gum.

2O 0" U.S. 4032375, assigned to IRECO CHEMICALS, wherein a 9 4, solution or slurry of oxidizing salts of which at least is CN is blended with at least 3% by weight sulphur. The balance of the oxidizing salt is ammonium nitrate. The 2 composition comprises from 5 to 20% water, and is thickened, usually with guar gum.

U.S. 4008110, assigned to ATLAS POWDER CO., wherein a water 1 1 -4gel explosive is provided comprising 3-30% by weight ov a nitro alkano as an organic dispersed phase and 0,2 to 2 weight of a gelling agent. The composition contains typically 22% water.

U.S. 4055450, assigned to ICI AUSTRALIA LTD, wherein a gelatinuous explosive is provided containing an inorganic oxidizing salt, a gelling agent, 0-5% water and 1-30% of a liquid amine as a solubilizing agent.

US. 4096003, assigned to ATLAS POWDER CO., wherein an aqueous gel exploeive is provided, containing as an 01 0essential component 1-10 weight percent of an alkyl or 0 a ooooi alkanol amine nitrate.

C.A. 1053470, assigned to CANADIAN MINISTRY FOR NATIONAL DEFENCE, wherein a gel-slurry containing antifreeze and 0a guar gum is provided, the oxidizer being ammonum nitrate dispersed in the aqueous gel.

U.S. 4198253, assigned to CANADTAN INDUSTRIES LTD, wherein a slurry explosive is provided containing from 5 to weight water.

AU 8654622 in the name of E.I. DU PONT DE NEMOURS, and wherein an explosive is provided having sufficient water content to be both flowable and water retentive.

AU 8537556 in the name of AECI LTD, and wherein an aqueous emulsion explosive is provided wherein the aqueous phase comprises the oxidizing agent and is discontinuous within a continuous fuel phase.

U.S. 4380482 assigned to E I DUPONT DE NEMOURS, and wherein a water bearing explosive comprising oxidizer, fuel and sensitizer is further provided with a source of iodide or iodate ions to stabilize the gel. All of the above compositions have inferior specific energy to ANFO explosives due to the presence of water as an inert diluent.

Where the cost of use of gel, emulsion or slurry explosives exceeds an economic level, then recourse must be had to other, more expensive solid explosives such as 3 dynamite, gelignite and RDX Such explosives however do o not have the same explosive energy as ANFO explosives due 0 0 o000 to their high inert substance content such as diatomaceous o et o ac earth in the case of dynamite.

a o o0 It is thus an object of the present invention to provide an explosive composition which substantially overcomes the stated deficiencies of the prior art.

It is a further object of the present invention to provide an ammonium nitrate based powder explosive composition which is suitable for use where wet boreholes are encountered.

Accordingly, there is provided a dry flowable powder explosive composition comprising: an inorganic oxidizing agent, (ii) a carbonaceous reducing fuel; and (iii) a gelling agent, wherein said oxidizing agent includes at least 50% by weight of ammonium nitrate and said oxidizing agent

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00 0 0 0 C' 0 00 0 0 00 00 0 0 0 000 00 0 0 00 0 00 0 000 00 -6comprises 80%-96% of the total weight of the composition.

Preferably the oxidizing agent is in the form of ammonium nitrate particles of a size such that voids are formed in the resulting composition. Such voids serve to sensitize the composition. However, it is envisaged that powdered ammonium nitrate may be used in circumstances where a sensitized composition is not required.

It is especially preferred to use ammonium nitrate prills having a particle size distribution such that at 1o least 60% of the particles are between 1 and 2.5 mm, prills" being defined as particles formed as spherical pellets from an ammonium nitrate melt.

Preferably, the oxidant consists of ammonium nitrate and comprises from 80 to 96% by weight of the total 15 composition. It is particularly preferred to use about 94% ammoniun nitrate based on the total composition. Use of such proportions of ammonium nitrate provide excellent handling and VOD (velocity of detonation) characteristics, providing explosive compositions suitable for use in most borehole blasting applications. Such compositions have VOD's of about 4500 n/s at 50 mm diameter.

However, where modification of the V0D characteristics is required, other oxidants may replace part of the ammonium nitrate. Examples of suitable co-oxidants for use in compositions of the present invention include Calcium nitrate Sodium Nitrate (SN) and perchlorates of sodium or potassium.

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0 0 00 0 0 0 00 00 0 0 00 0 o0 00 0 0O 0 0 0 0 0o to 00 Q 0 4 00 0 000 0 40 00 0 0 00 000 0 0 00 4 0 4 0 0 0 44 00o 0 *0 -7- The use of up to 50% by weight of total oxidant of CN provides an explosive having reduced gas generation and VOD, relative to a composition comprising ammonium nitrate as the sole oxidant. Such a composition is suitable for use where the blast is intended to move masses whilst minimizing fragmentation of the mass. CN containing ammonium nitrate explosives in accordance with the present invention may have a VOD as low as 3000 m/s at 50 mm diameter.

The use of up to 50% by weight of total oxidant of SN provides an ammonium nitrate based explosive having an accelerated VOD at reduced gas volume. Such an explosive is particularly suitable for use where shock waves are the desired product, for example, for seismic work or for 1 fragmentation without excessive blast. Such compositions may have a VOD as high as 4800 m/s. at 50 mm diameter.

Where necessary, the present compositions may be sensitized by the addition of a sensitizing agent such as finely divided sulphur or aluminium powder in an amount of from 5-10% by weight of the composition. The sensitizing 20 agent serves to increase the combustion temperature of the explosive. The result of this increase in combustion temperature is a kinetic increase in the VOD, improving the shock characteristics of the explosive and thereby improving fragmentation.

The carbonaceous fuel may be any compound or composition providing source of carbon which is available -8for oxidation by an oxidant upon detonation of the composition. Examples of suitable liquid carbon sources include animal, vegetable or mineral oils including epoxidized vegetable oils. Suitable particulate carbon sources include ground coal, ground vegetable matter and ground rubber.

A preferred liquid carbonaceous fuel is the petroleum distillate fraction supplied for use as diesel engine fuel. The preferred particulate carbonaceous fuel is ground coal, with it being particularly preferred to 00 0,0 select from ground hard coals such as sea coal (hard 0 00 ooo bituminous coal) and anthracitic coals including gilsonite.

o 00 Mixtures of carbonaceous fuels are also o contemplated for use in the present invention. The o preferred mixture is a mixture of a solid carbon;ceous fuel and a liquid carbonaceous fuel, with it being particularly preferred to use a mixture of ground sea coal rnd diesel fuel in ratios of from 1:6 to 1:1 by weight, Such a fuel mixture utilizes the absorptive affinity of the ammonium Snitrate for diesel fuel to provide intimate contact between the fuel and oxidant for ease of detonation whilst i retaining the surface area characteristics inherent in the use of particulate fuels such as sea coal for improved VOD.

The amount of carbonaceous fuel used in compositions of the present invention is generally between i and 7% by weight based on the total composition, the choice of amount being determined by the desirability of an a 0 o0 O 00 0 o 0 0 00 0 0 0 0 00 0 0 00 00 ?0 00 00 0 5 0 00 00 0 04 0 3 001 0 I1 S o -9oxygen balance (OE) of 1. At this ideal oxygen balance, there is sufficieut oxidant available to completely combust the oxidizable carbonaceous fuel, without undue waste of oxidant.

It is especially preferred to use an amount of carbonaceous fuel of about 5% by weight of the composition.

Where the carbonaceous fuel of choice is an epoxidized oil, the expoxy oxygen is available to favourably contribute to the oxygen balance of the composition. In such compositions the amount of 10 expoxidized oil used may exceed 7% of the weight of the composition, The gelling agent as defined herein may be any organic compound or composition which when included in the present composition is capable of forming a hydrated gel in the presence of water, the gel so formed forming at least a partial barrier to further hydration of the explosive composition. Therefore the gelling agent is useful in protecting the bulk of the dry flowable powder in the advent of water seepage into the borehole. Suitable gelling agents for use in the present compositions include hydratable vegetable gums such as guar gums and seaweed extracts.

It is particularly preferred to select the gelling agent from the group comprising a guar gum derived from a guar flour having an 85% soluble fraction and carrageenan.

The preferred guar gum has a guaran content of 85%, guaran

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0, 0o 00 0j 0o 0 00 00 o o 0 consisting of linear chains of (1 4)-P-D-mannopyranosyl units with~C-D-galacto-pyranosyl units attached by (1;6) linkages. The ratio of D-galactose to D-mannose units is 1:2. Such a guar gum has 5-8 times the thickening power of starch by weight.

Guar gum is the preferred gelling agent for most compositions envisaged by the present invention and is suitable for all.

However, where the amount of ammonium nitrate in 1 the composition is particularly high, it may be preferred to use carragenan due to the enhanced grlling action of carragenans upon hydration in the presence of ammonium ions. Carragenans are a heterogeneous natural colloid polymer comprisingc<-D-galactopyranosyl sulphate esters as the functional gelling prosthetic group. Carragenans form a network gel or hydration in the presence of hydrophobic cations such as potassium and ammonium.

The gelling agent is preferably used in an amount greater than 1% by weight of the total composition.

Since the preferred gelling agents are in themselves sources of carbon oxidizable by an oxidizing agent, they may contribute to the total carbon of the composition when calculating the oxygen balance of the composition. However, it is particularly preferred to limit the amount of gelling agent from 1-2% by weight of the composition since this range of amounts provides adequate gel performance whilst maximizing the amount of

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-11the preferred fuels which are less expensive than the gelling agents.

Where exceptional water resistance is required, up to 5% of the gelling agent may be included in the compositions. It is preferred to select carragenan as the gelling agent in such circumstances.

In the manufacture of the present compositions, the components may be blended by any means achieving a n o g f heterogenous mixture including by the use of agitator 0 i 0 bowls, rotary blenders, and auger, drum or barrel rollers.

0 0 Preferably, the components are charged to a rotary blender 0 0co 0 0 0 oo of the RIBANDS type and blended to yield the finished 0 oo 0 000 product.

o, The compositions of the present invention are 0 o 0 0 0 ,0 15 amenable to shipping to the blast site on bulk.

Alternatively, the present compositions may be safely 0" prebagged and thence delivered in bags.

Typical compositions of the present invention include compositions comprising 92-96 weight percent ammonium nitrate, 3-7 weight percent diesel fuel or powdered sea coal and 1-2 weight to guar gum.

Where a sensitizing agent is employed, a typical Scomposition would include compositions comprising 80-90 weight percent ammonium nitrate, 5-10 weight of sulphur or powdered aluminium sensitizer, 1-7 weight percent of diesel fuel or powdered sea coal and 1-2 weight percent guar gum.

L -12- The invention is further described with reference to the following non-limiting examples.

Example 1 An explosive composition is prepared by feeding the following constituents to a RIBANDS blender 94 kg NH 4 NOprills (ii) 4 kg diesel fuel (iii) 2 kg guar gum.

oo The constituents were blended for 15 minutes to 0 0 0 °ooo° 1) yield a flowable powder explosive having a VOD of 4500 0 (.0 0 o m/s. When damped down with water, a mould of this 0 V0 0 0 0 o t compsotion exhibited gelling of the outside of the mound.

00 0O 0 o0 After 10 minutes the thickness of the gel layer was 5 mm.

Example 2 00 0 0 °0 0 15 A sensitized explosive composition was prepared by

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feeding to a RIBANDS type blender S06a 85 kg NHN0 3 prills 7 kg sulphur powder oo 6 kg diesel fuel 0 a a o; 20 2 kg guar gum.

The composition was blended for 15 minutres to provide an explosive composition having a VOD of 4800 m/s at 50 mm diameter.

The behaviour of the composition in the presence of water was the same as that of the product composition of Example 1.

The present compositions substantially retain the luuu I -13advantages inherent in convention ANFO explosives, such as ease of handling and placement and high specific energy (energy per kilogram). At the same time, the present compositions exhibit a resistance to water present in boreholes to a degree that would mitigate against the use of conventional ANFO explosives.

The water resistance of the present explosive j compositions is a result of the gelling action of the o o composition when contacted by water, the gel forming a S oo0 °o 10 substantially water-impervious layer against the walls of °o the borehole, preventing the access of water to the bulk of o the composition.

oo 0 0 0 0The present compositions are superior to the current gel and slurry types in terms of specific energy,

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cost of manufacture and cost of application to the 0 0 boreholes, the present compositions being formable by 000 0oo simple blending and being able to be placed by pouring or funnelling.

oo Whilst the above has been given by way of o0 0 20 illustrative example of the invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set fort! in the following claims.

Claims (15)

1. A dry flowable powder explosive composition comprising: an inorganic oxidizing agent (ii) a carbonaceous reducing fuel; and (iii) a gelling agent, wherein said oxidizing agent includes at least 50% by weight of ammonium nitrate and said oxidizing agent comprises 96% of the total weight of the composition.

2. A composition in accordance with Claim 1 wherein said oxidizing agent consists of ammonium nitrate.

3. A composition in accordance with claims 1 or 2 wherein said ammonium nitrate is in the form of prills having a particle size distribution such that at least 60% of the particles are between 1 and 2.5 mm in size.

4. A composition as claimed in any of the preceding claims wherein said ammonium nitrate agent is present in an amount of from 80% to 96% by weight of the composition. 0 0 Q A composition in accordance with claims 1 or 3 1000 wherein said oxidizing agent comprises up to 50% by weight of calcium nitrate. o a 6. A composition in accordance with any one claims 1 ,to 3 wherein said oxidizing agent comprises up to 50% by weight of sodium nitrate.

7. A composition as claimed in any one of the preceding claims wherein said carbonaceous reducing fuel is V selected from the group consisting of animal, vegetable, and mineral oils, epoxidized vegetable oils, ground vegetable ai matter, groi.nd rubber, ground coal, and mixtures tnereof.

8. A composition as claimed in claim 7 wherein said carbonaceous reducing fuel is a petroleum distillate fraction suitable for use as diesel engine fuel.

9. A composition as claimed in claim 7 wherein said carbonaceous reducing fuel is ground sea coal. A composition as claimed in claim 7 wherein said carbonaceous reducing fuel is a mixture of ground sea coal o o and diesel fuel, the weight ratio of coal to diesel fuel on being from 1:6 to 1:1. 000 o of o° l 11. A composition as claimed in any one of the 0 00 0 0 preceding claims wherein said carbonaceous reducing fuel is o0 o used in an amount of from 1 to 7% by weight of the composition.

12. A composition as claimed in claim 11 wherein said o0 0o" carbonaceous reducing fuel is used in an amount of 5% by 00 i Co weight of the composition. o0g 13. A composition as claimed in claim 7 wherein said carbonaceous reducing fuel is epoxidized vegetable oil.

14. A composition as claimed in claim 13 wherein said O a onoa.t epoxidized vegetable oil is used in an amount exceeding 7% of the composition by weight. A composition as claimed in any one of the preceding claims wherein siid gelling agent is selected from the group consisting of hydratable vegetable gums. -16-

16. A composition as claimed in Claim 15 whorein said gelling agent is guar 8um.

17. A composition as claimed in Claim 15 wherein said gelling agent is carrageonan.

18. A composi..ion as claimed in any one of the preceding claims wherein said gelling agent is present in an amount of from 1 to 2% by weight of the composition.

19. A composition as claimed in Claim 17 wherein the amount of carrageenan is up to5 weight percent of the composition. A dry flowable powder explosive composition comprising: 0 0 O o 00 o oo OO O o n 0 0 0 0 '300 O 0 0 00 a 00 0400 A Oi (i) (ii) (iii)

21. A dry comprising:

92-96 wt% NIlN0 3 3 7 wt% diesel fuel 1-2 wt% guar gum. flowable powder explosive composition 92-96 wt% NHiNO 3 3-7 wt% powdered sea coal 1-2 wt% guar gum. flowable powder explosive composition (i) (ii) (iii) A dry comprising: 00o a 0 04o 0 0 80-90 wt% NH.NO 3 (ii) 5-10 wt% sulphur or aluminium powder (iii) 1-7 wt% of diesel fuel, sea coal or a mixture thereof (iv) 1-2 wt% of guar gum. .4- -17- ~23. A compoition in accordance with any 0110 Of Claims to 22 wherein nai 1aiimuoniumf nitrilte j..'in tIIC form of 1ril is having a particle siz.e (Ii Strihution sMICh that greater~ tHa 60Z of the particle-, have a pnrtiXc] aSiZe Of frun I to 2. 5 mm. 24. A method for preparing a dry, flowable powder explosive composition as claimed in any one of the preceding claims wherein the method comprises blending the components of the composition in a rotary blender. Dry, flowable powder explosive compositions as hereinbefore described with reference to Examples I and 2. 26. Methods of preparation of dry flowable powder explosive components, as hereinbefore described with K reference to Examples 1 and 2. DATED this ninth day of April 1990. DO o RICHARD JOHN JOHNSON By his Patent Attorneys G.R. CULLEN CO. 0 V