AU2004212562A1 - Segregation reducing agent in explosive compositions - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Roche Blasting Services Pty Ltd A.C.N. 009 687 487 Invention Title: SEGREGATION REDUCING AGENT IN EXPLOSIVE COMPOSITIONS The following statement is a full description of this invention, including the best method of performing it known to me/us: SEGREGATION REDUCING AGENT IN EXPLOSIVE COMPOSITIONS FIELD OF THE INVENTION This invention relates to an explosive composition which includes a density controlling component. More particularly it relates to the use of a segregation reducing agent in such an explosive composition.

BACKGROUND

ART

Explosive compositions essentially comprise an oxidiser component and a fuel component. The oxidiser component often comprises an ammonium nitrate (hereinafter referred to as AN) compound and the fuel often comprises a fuel oil (hereinafter referred to as FO) such as diesel or the like. A combination of AN and FO is known as ANFO and a 94:6 mass ratio of AN: FO provides an explosive composition with a near perfect oxygen balance.

ANFO is not water resistant and to allow ANFO to be used in damp or wet conditions, the ANFO may be coated with a water-in-oil emulsion. ANFO coated in such an emulsion is known as heavy ANFO or an emulsion blend explosive. HeavyANFO typically contains 20 to 50wt% of the water-in-oil emulsion. The emulsion may comprise a discontinuous phase of an aqueous oxidiser component dispersed in a continuous phase of an oil component. An emulsifier is usually required to stabilise the water-in-oil emulsion.

It is well known to reduce the density of an explosive composition by adding a density controlling component to the explosive composition. Explosive compositions with a significantly reduced density below 0.8 grams/cc, are suited to be used in conditions where less shock energy or vibrancy is required.

Many different types of density controlling components are known, and such known components are, for example, plant-derived matter such as sawdust, seed shells, or non-plant derived matter such as microballoons or polystyrene spheres.

One disadvantage of explosive compositions containing a density controlling component is that the density controlling component tends to segregate from the rest of the explosive composition. In the past adhesive or bonding agents were used to overcome this problem, but these agents have the disadvantage that they stick to mixing equipment. In US 4,875,950 and US 4,957,569 this problem was overcome by using water-in-oil emulsions to reduce such segregation. US 5,409,556 teaches that water on its own, or water-in-oil emulsions can be used to reduce such segregation. A disadvantage of waterin-oil emulsions as a segregation reducing agent is that they are relatively expensive, they have a relatively high viscosity, and they are not always readily available.

The prior art also teaches that it is desirable to design products that are oxygen balanced. Accordingly an ammonium nitrate, fuel oil water-in-oil emulsion is normally used as the segregation reducing agent for the purpose of maintaining oxygen balance.

It is also known that where sawdust is used as a density controlling agent for ANFO, the diesel used in the ANFO at least partially wets the sawdust which is sufficient to prevent segregation of the sawdust from the ANFO. However, it was found that diesel does not perform satisfactorily as a segregation reducing agent when density controlling components with a bulk density of less than that of sawdust is used. Sawdust, when used as a density controlling agent can have a bulk density of over 0.4g/cc, especially when wet with oil.

The inventors of the present invention have now identified certain segregation reducing agents which may be suitable to be used to reduce segregation of density controlling agents which has a density of less than 0.4g/cc. It has surprisingly been found that it is not always necessary to achieve oxygen balance and good results were obtained with products which were not oxygen balanced. However, it is not outside the scope of the invention to design the product to be oxygen balanced.

DISCLOSURE OF THE INVENTION According to the present invention there is provided the use of a segregation reducing agent in an explosive composition which includes a density controlling component, to reduce segregation of the density controlling component in the explosive composition; the use being characterised therein that the density controlling component has a bulk density of less than 0.4g/cc, and the segregation reducing agent is an agent selected from the group consisting of a non-emulsified oil with a viscosity higher than that of diesel, and a sugar based material.

In this specification all viscosities were measured according to ASTM D445.

The explosive composition may, in addition to the density controlling component, also comprise a mixture of an oxidiser component; and a fuel component.

The oxidiser component may comprise any suitable component. Preferably it comprises an ammonium nitrate (AN) product. The AN product may be any prilled or granular material of industrial or agricultural quality. Prilled AN is preferred, and porous prilled AN (PPAN) is even more preferred. Preferably the PPAN has a bulk density of about 0.8g/cc. PPAN known in the trade as

EXPAN

TM is most preferred.

The fuel component may comprise any suitable fuel such as a liquid or a solid fuel. In a preferred embodiment of the invention the fuel component comprises a liquid fuel, preferably an oil, preferably a mineral oil, for example diesel.

In one embodiment of the invention the combined oxidising and fuel components may comprise ammonium nitrate fuel oil (ANFO) which is a combination of ammonium nitrate (AN) and fuel oil In one embodiment of the invention the combined oxidising and fuel components may comprise heavy ANFO which is a combination of ANFO with an emulsion. The emulsion may comprise an aqueous emulsion of an oxidiser component (preferably a salt such as AN or a combination of salts, such as AN, calcium nitrate and sodium nitrate) as a discontinuous phase in a continuous oil phase. The emulsion may also include an emulsifier, for example a PIBSA derived emulsifier.

In one embodiment of the invention the explosive composition may comprise an emulsion explosive. In another embodiment of the invention the explosive composition may comprise a watergel (an oil in water) explosive.

The explosive composition may have a density of less than 1.1 g/cc, preferably in the range of 0.8 to 0.2g/cc, preferably below 0.5g/cc and more preferably from 0.49g/cc to 0.25g/cc. In one embodiment of the invention the density of the explosive composition may be 0.45g/cc or below.

The density controlling component preferably has a bulk density of less than 0.3g/cc and may comprise any suitable density controlling component. The density controlling component may for example comprise expanded cereal grains such as puffed wheat, puffed rice, popcorn etc. Popcorn is preferred.

Alternatively it may comprise shells of seeds such as peanut shells, sunflower seed husks, oats husks or hulls of de-hulled plant grain. Hulls of de-hulled plant grain is preferred and preferably such hulls which have a density of less or equal to 0.14g/cc.

The de-hulled plant grain preferably comprises rice hulls with a density of less than or equal to 0.14g/cc. Preferably the rice hulls have been treated to remove the rice hull fines to reduce the density of the rice hulls to less than or equal to 0.1 g/cc.

The density controlling component is preferably added to constitute less than of the explosive composition, or preferably below 20wt%. Most preferably using less than 12wt% of the density controlling composition can be used to prepare an explosive composition with a density of less than The segregation reducing agent preferably has a density of between 0.8 and 1.1 g/cc, which is lower than that of emulsions.

The non-emulsified oil preferably has a viscosity of above about 3 mm 2 /sec at 400C which is the viscosity of diesel. Preferably it has a viscosity of at least 2 /sec at 400C, preferably from 20 to below 200mm 2 /sec at 400C. The oil may comprise any suitable oil, but a mineral oil is preferred. Preferably the oil comprises waste engine oil, but it may also comprise crude oil, bunker oil or shale oil. Preferably the oil in the form of the segregation reducing agent is present in an amount from 7, preferably, to 15wt% of the total explosive composition.

The sugar based material may comprise a viscid sugar based material, such as molasses. Preferably the viscid sugar based material has a viscosity higher than that of diesel. Preferably it has a viscosity of at least 20mm 2 /sec at 400C.

According to another aspect of the present invention there is provided an explosive composition comprising a mixture of an oxidiser component; a fuel component; a density controlling agent with a bulk density of less than 0.4g/cc; and a segregation reducing agent selected from the group consisting of a nonemulsified oil with a viscosity higher then that of diesel, and a sugar based material.

The explosive composition may be oxygen balanced. Altematively, the explosive composition may not be oxygen balanced.

The invention will now be further described by means of the following nonlimiting examples.

Examples Example 1 The PPAN product known as EXPAN T 100 was mixed with 2wt% of diesel to form ANFO.

Waste engine oil with a density of ±0.885g/cc at 200C and a viscosity of 30mm 2 /sec at 400C in an amount of 5wt% was added to the ANFO and it was mixed thoroughly before adding 10wt% rice hulls (density controlling component) having a poured density of 0.11 g/cc. The hulls were mixed with the ANFO and waste engine oil mixture and the density determined as 0.425 g/cc.

The oxygen balance was -5.3g O/g substance.

The blend was allowed to fall through a distance of 2.5 meters five minutes after blending, as if down a borehole to determine the segregation. The blend was fairly dry after a short time min) and partial separation of the hulls from the prills took place while falling.

Laborating tests showed that the explosive composition detonated without any difficulty.

Example 2 The same procedure as in example 1 was followed except that in this case 7.0wt% waste engine oil was used. The density of the final mixture of ANFO with oil and rice hulls was 0.436 g/cc. The oxygen balance was -11.9g O/g substance.

The blend was still wet after 10 minutes and no separation of the hulls from the prills took place during falling.

Laborating tests showed that the explosive composition detonated without any difficulty.

Example 3 The same procedure as in example 1 was followed except that in this case 7wt% hypoid gear oil was used. The hypoid gear oil had a density of 0.893g/cc at 20 0 C and a viscosity of 145mm/sec at 40 0 C. The density of the final mixture of ANFO with gear oil and rice hulls was 0.417g/cc. The oxygen balance was -11.9g O/g substance.

The blend was still wet after 10 minutes and no separation of the hulls from the prills took place during falling.

Laborating tests showed that the explosive composition detonated without any difficulty.

Example 4 The same procedure as in example 1 was followed except that in this case 7.0wt% HVI 55 oil was used. The HVI 55 oil had a density of 0.858g/cc at 200C and a viscosity of 20 mm 2 /sec at 400C. The density of the final mixture ANFO with oil and rice hulls was 0.450 g/cc. The oxygen balance was -11.9g O/g substance.

The blend was still wet after 10 minutes and no separation of the hulls from the prills took place during falling.

Laborating tests showed that the explosive composition detonated without any difficulty.

Example The PPAN product known as EXPAN T M 100 was mixed with 2wt% of diesel to form ANFO.

This blend was mixed thoroughly and 7wt% of molasses with density of 1.401 g/cc at 40"C and a viscosity of 5300 mm 2 /sec was added before adding rice hulls. The hulls were mixed with the ANFO molasses mixture and the density determined as 0.58g/cc. The oxygen balance was +10.0g O/g substance.

The blend was still intact after 10 minutes and no separation of the hulls from the prills took place during falling.

Laborating tests showed that the explosive composition detonated without any difficulty.

Claims (13)

1. Use of a segregation reducing agent in an explosive composition which includes a density controlling component, to reduce segregation of the density controlling component in the explosive composition; the use being characterised therein that the density controlling component has a bulk density of less than 0.4g/cc, and the segregation reducing agent is an agent selected from the group consisting of a non-emulsified oil with a viscosity higher than that of diesel, and a sugar based material.

2. The use of claim 1 wherein the explosive composition, in addition to the density controlling component, also comprises a mixture of an oxidiser component; and a fuel component.

3. The use of claim 2 wherein the oxidiser component comprises an ammonium nitrate (AN) product.

4. The use of claim 3 wherein the AN product comprises porous prilled AN (PPAN). The use of any one of claims 3 or 4 wherein the fuel component comprises an oil.

6. The use of claim 5 wherein the combined oxidising and fuel components comprise ammonium nitrate fuel oil (ANFO) which is a combination of ammonium nitrate (AN) and fuel oil (FO).

7. The use of any one of the preceding claims wherein the explosive composition has a density of less than 1 .lg/cc.

8. The use of any one of the preceding claims wherein the density controlling component has a bulk density of less than 0.3g/cc.

9. The use of claim 8 wherein the density controlling component comprises hulls of de-hulled plant grain with a density of less than or equal to 0.14g/cc.

10. The use of any one of the preceding claims wherein the density controlling component constitutes less than 30wt% of the explosive composition.

11. The use of any one of the preceding claims wherein the segregation reducing agent has a density of between 0.8 and l.lg/cc.

12. The use of any one of the preceding claims wherein the segregation reducing agent is a non-emulsified oil with a viscosity higher than that of diesel.

13. The use of claim 12 wherein the non-emulsified oil comprises waste engine oil.

14. The use of any one of claims 1 to 11 wherein the segregation reducing agent is a sugar based material in the form of molasses. An explosive composition comprising a mixture of an oxidiser component; a fuel component; a density controlling agent with a bulk density of less than 0.4g/cc; and a segregation reducing agent selected from the group consisting of a non-emulsified oil with a viscosity higher then that of diesel, and a sugar based material.