Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
  • C06B23/002—Sensitisers or density reducing agents, foam stabilisers, crystal habit modifiers
  • C06B23/003—Porous or hollow inert particles

Definitions

• sensitisation In most fluid explosives or slurry explosives, voids are introduced into the explosives in order to reduce their natural densities and thereby increase their sensitivity to a required level for detonation. This process is known as sensitisation.
• Sensitisation is an important part of the art of manufacturing fluid explosives or slurry explosives.
• Known methods of sensitisation include the use of chemical gassing, whereby gas bubbles are generated at the required rate and to the required extent to effectively sensitise the explosive.
• Another well-known method is to add so-called mechanical voids,, to an unsensitised explosive.
• Mechanical voids that are well known include expanded perlite and microspheres.
• Microspheres may include organic spheres such as polystyrene, or microballoons including glass microballoons or polymeric microballoons.
• a microballoon comprises a hollow body or shell (usually made of glass or a suitable polymeric material) and a gas contained in the hollow body.
• the gas is known as a. blowing agent.
• Explosive manufacturers usually buy pre-expanded microballoons which they then mix with an explosive to produce a sensitised product.
• Pre-expanded microballoons are prepared by subjecting unexpanded microballoons to heat and other treatments causing them to expand and thus having a reduced density compared to the unexpanded microballoons. Almost all kinds of expansion are too complex for the manufacturer of explosives to carry out with the result that they purchase pre-expanded microballoons.
• Microspheres such as polystyrene can also be pre-expanded in the same manner to reduce their density.
• thermal expansion of polymeric microspheres are known.
• Known methods of dry expansion involve relatively high capital cost, in particular because of the precautions that must be taken against fire or explosion of the blowing agent (usually a hydrocarbon gas) that is liberated during the expansion.
• the blowing agent usually a hydrocarbon gas
• steam expansion does not have this hazard because of all the water present in both droplet and vapour form during the entire time when the hydrocarbon gas is liberated.
• One known method of steam expansion comprises preparing a slurry of microspheres which is fed to a pipe together with steam thereby causing the microspheres to expand.
• US patent 4,513,106 teaches that a disadvantage of this method is that the expanded particles leaving the pipe have to be cooled directly with water in order not to agglomerate which results in a final product having unsatisfactory high water content. It is stated that if cooling water is not used or is replaced by cooling air or a cooled apparatus mantle, a product of fused particles will be obtained. US 4,513,106 discloses a method of overcoming this problem whereby a slurry of unexpanded microspheres is introduced into a pressure zone to which steam is fed to partly expand the microspheres. The partially expanded microspheres then leave the pressure zone under a pressure drop whereby the spheres are further expanded and accelerated into steam with a velocity of at least 1 meter per second.
• the accelerated stream is injected into a gas volume whereby the stream is disintegrated and cooled.
• the expanded non-agglomerated spheres are then separated from the gas.
• US Patent 6,113,715 discloses a method whereby unexpanded microspheres are expanded in situ in an emulsion explosive during the formation of the emulsion explosive i.e. during the emulsification process itself.
• explosive as used in this specification includes, in addition to its normal meaning a non-sensitised explosive or explosive pre-cursor which becomes a sensitised explosive when sensitised by the addition of expanded microspheres.
• microspheres are suitable to expand when contacted with steam.
• the microspheres Prior to expansion the microspheres are preferably provided in a suitable carrier fluid, preferably a liquid to provide a slurry, which slurry is then introduced into the steam for expansion.
• the carrier liquid preferably comprises water.
• the carrier liquid may also contain oil such as mineral oil or fuel oil. The oil preferably reduces the viscosity of the final product and thereby enables it to remain fluid with volume fractions of microballoons high enough to otherwise impart a paste-like consistency to the sensitised explosive.
• the carrier liquid may comprise a mixture of oil and water.
• the carrier liquid may also contain additives which may affect the properties of the explosive; for example, the carrier liquid may contain a cross-linker for a watergel explosive.
• a motive fluid may also be used to propel the microspheres (including a slurry thereof) thereby to introduce the microspheres as a stream into the steam.
• the motive fluid may comprise a gas, preferably air.
• a slurry of microspheres is both atomised and injected into the steam using compressed air.
• the steam is a stream of steam and preferably it is at a temperature of above 105°C, preferably between 110 and 130°C.
• the mass ratio of steam to slurry may be any suitable ratio. In one embodiment it may be from 1 :5 to 5:1 , preferably it is about 1 :2.
• the stream of steam may include one or more other fluids therein, preferably a gas such as air or the like.
• the one or more other fluids may be introduced into the stream of steam prior to introducing the microspheres into the stream of steam.
• the STP volume ratio of air to dry steam may be form 0 to 5:1 , preferably about
• the microspheres and stream of steam may be mixed in any suitable manner but preferably they are mixed by introducing both the microspheres and the steam into a tubular member.
• An eductor may be used to introduce the microspheres and steam into the tubular member or other mixing device.
• the microspheres (preferably in the form of a slurry and mixed with a motive fluid) may be sprayed into the stream of steam and preferably the resulting mixture is introduced into a tubular member where further mixing of the microspheres and steam take place.
• the stream of expanding microspheres and water is preferably conveyed at very high velocity down the tubular member.
• the high velocity usually ensures high turbulence in the tubular member, thus ensuring good heat transfer from the steam to the microspheres, which may result in almost instantaneous expansion of the microspheres.
• the residence time of the microspheres in the steam and the maximum temperature of the stream of wet expanded microspheres is in use controlled to achieve the desired extent of expansion.
• the explosive may comprise an explosive which normally includes water therein.
• the explosive may comprise a slurry explosive, preferably a pumpable composition.
• the slurry explosive may comprise a mixture of a fluid explosive and a granular material.
• the granular material may comprise an ammonium nitrate product, preferably ammonium nitrate fuel oil (ANFO) but it may also comprise other products such as granular nitrate, a granular propellant or even a granular or particulate explosive such as TNT.
• ANFO ammonium nitrate fuel oil
• the explosive is preferably provided at a temperature which quenches the
• the explosive is at a temperature below
• the temperature of the explosive may be at ambient temperature. In the case of an emulsion the temperature of the
• explosive may be from ambient temperature to about 60 to 75°C.
• the explosive may preferably also serve
• stream of wet expanded microspheres and optionally air may comprise
• both the stream of wet expanded microspheres and the explosive are introduced in substantially the same direction into the tubular member.
• the microspheres and the stream of steam are introduced co-Iinearly or co-axially into the tubular member. In one embodiment of the invention thus is achieved by means of a co-axial eductor.
• the process preferably comprises a continuous process.
• Figure 1 is a diagrammatic drawing of an apparatus suitable for carrying out a method of sensitising an explosive according to the present invention
• Figure 3 is a diagrammatic drawing of yet another apparatus for carrying out a method of sensitising an explosive according to the present
• an apparatus 10 suitable for preparing a sensitised explosive comprises an eductor 11 defining an inlet 12 an outlet 13 and a suction port 14.
• a tubular member in the form of an expansion pipe 15 is connected to the outlet 13 of the eductor 11 and to a suction port 16 of a second eductor 17.
• the pipe 15 has a length of approximately 1 meter and a diameter of 75mm.
• the eductor 17 also defines an inlet 18 and an outlet 19.
• a hose 20 is connected to the outlet 19.
• the hose 20 is curved to have a general S-shape, and the inlet 21 of the hose 20 is not in line with the outlet 23 of the hose 20.
• the hose is 1.6m long with a 100mm diameter.
• an alternative apparatus100 suitable for carrying out a method of sensitising an explosive according to the invention comprises a container 101 for an aqueous slurry of unexpanded microballoons and a pump
• the expansion pipe 108 also serves as a suction port of an inline and co-axial Penberthy eductor 109.
• an explosive is introduced into the eductor 109 through the inlet 110 which explosive serves as the motive fluid for the eductor 109.
• the eductor 109 is coupled to a tubular member 111 in the form of a pipe and the stream of expanded wet microballoons from the expansion pipe 108 and explosive introduced through the inlet 110 are introduced co-axially to flow in the same direction into the tubular member 111 wherein they are mixed thoroughly.
• the tubular member 111 comprises a pipe (length of 1 ,5m and diameter of 76mm with a 90°C short radius elbow towards the exit end 113 of the member 111.
• a hose 114 is coupled to the tubular member 111 for delivering the mixture of sensitised explosive to a suitable point e.g. a truck, storage tank or borehole etc.
• FIG. 3 an alternative apparatus 200 suitable for carrying out a method of sensitising an explosive according to the invention is shown.
• the apparatus 200 is very similar to the apparatus 100 of Figure 2 and the same reference numbers are used to denote corresponding parts.
• the orifice sprayer 104 (of Figure 2) is replaced with an eductor 201.
• the eductor 201 defines an inlet 202 through which air (as the motive fluid is .introduced).
• the slurry of unexpanded microballoons is sucked into the eductor 201 through the suction port 203.
• the eductor 201 is coupled to the mixing tee 106. In this case only steam (not steam and air) enters the mixing tee 106 through the inlet 107.
• a slurry of unexpanded, thermally expandable polymeric microballoons was prepared by mixing (on a mass basis) 10 parts unexpanded microballoons of the type sold under the trade name of Expancel 551 WU with 5.7 parts of a carrier liquid in the form of water. This mixture comprised 45% dry weight Expancel 551 WU and 55% by weight water. The volume ratio of Expancel 551 WU: water was 1 :1.33. The Expancel 551 WU was in the form of a wet cake . containing about 29% water.
• the slurry of microballoons was pumped at a rate of 3.2kg/minute into the suction port 14 of the eductor 11 of the apparatus 10 of Figure 1.
• the motive fluid of the eductor 11 was a stream of steam at a temperature of about 115°C and a nominal pressure of O. ⁇ bar gauge pressure flowing at 1.0kg/minute through the inlet 12 of the eductor 11.
• the steam was nominally dry steam with little if any liquid water.
• the slurry of unexpanded microballoons was thus introduced into a stream of steam causing thermal expansion of the microballoons thereby providing a resulting stream of water wet expanded microspheres flowing through the ' expansion pipe 15.
• the stream of water wet expanded microspheres comprised expanded microspheres, steam, liquid water in droplet form and air.
• a non-sensitised emulsion explosive in the form of a water-in-oil emulsion explosive entering the eductor 17 through the inlet 18 at a rate of 10OOkg/minute provided the motive fluid for the eductor 17.
• the resulting sensitisation by microspheres turned the non-sensitised emulsion explosive into a sensitised emulsion explosive.
• the non-sensitised emulsion explosive comprised 8.5% (mass by mass) continuous fuel phase of a suitable mixture of mineral oil (obtained under the name of MODEF from Continental Nitrogen & Resources) and an emulsifier of the PlBSAtype (obtained underthe name NBX2000Afrom Nelson Bros.)
• the ratio of these in the fuel phase was 7:1 mass oil: mass PIBSA-type emulsifier.
• the discontinuous aqueous phase comprised an 82% (mass by mass) ammonium nitrate solution.
• the emulsion explosive had a viscosity of about 20 000 cp at 10rpm at a temperature of 75°C.
• the temperature of the emulsion explosive was about 75°C when introduced into the eductor 17.
• the pressure at the exit of the expansion pipe (15) is less than atmospheric pressure. Because the stream issuing from the pipe (15) contains a mixture of steam and water in equilibrium, the drop in pressure to below atmospheric pressure is believed to cause evaporative cooling of the mixture to below the boiling point of water at atmospheric pressure i.e. to below 100°C. This provides an important safety feature for the process, although it is not essential.
• the relatively huge mass of explosive compared to the mass of the hot stream of steam and microballoons will cause substantially immediate cooling. It can easily be shown, as one skilled in the art will realise, that the temperature rise of the final product of this process can easily be limited to a few degrees. It is thus relatively easy to control temperatures at all points in the explosive to safe limits.
• the stream of wet expanded microspheres was introduced into the emulsion explosive and they mixed thoroughly in the hose 20.
• the resultant mixture flowing from the outlet 23 may be received in any suitable vessel or may be introduced directly into a borehole.
• the density of the emulsion explosive prior to introduction of the expanded microspheres was 1 ,3 g/cc and after the introduction of the expanded microspheres the emulsion explosive had a density of 1 ,24 g/cc.
• the slurry of unexpanded thermally expandable polymeric microballoons contained 40% (by mass) microballoons and 60% (by mass) water with a volume ratio of about 1 :1.5.
• Microballoons of the type sold under the trade name Expancel 007WU was used. [This wet unexpanded material is a kind of filter cake. It contained about 30% (by weight) water, varying from batch to batch and printed on the container; that figure is used to calculate what wet weight ratios to use to get 40% dry weight].
• the emulsion explosive was the same as used in example 1.
• the orifice sprayer 103 was estimated to be 0.7kg/min and the rate of air
• the wet or aqueous expanded microspheres can be introduced directly into the explosive without the necessity of intermediate processing such as filtering or drying, intermediate storage, metering of expanded microspheres, etc.
• the process also has the advantage that low density expanded microspheres do not have to be transported, stored or handled. Accordingly the difficulties associated therewith are avoided.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Manufacturing Of Micro-Capsules (AREA)
• Colloid Chemistry (AREA)
• Disintegrating Or Milling (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

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• 2002
  • 2002-11-29 CN CNA028252543A patent/CN1604885A/zh active Pending
  • 2002-11-29 EP EP02787086A patent/EP1458659A2/en not_active Withdrawn
  • 2002-11-29 WO PCT/ZA2002/000191 patent/WO2003051793A2/en not_active Application Discontinuation
  • 2002-11-29 AU AU2002351427A patent/AU2002351427A1/en not_active Abandoned
  • 2002-11-29 MX MXPA04005834A patent/MXPA04005834A/es unknown
  • 2002-11-29 CA CA002470825A patent/CA2470825A1/en not_active Abandoned
  • 2002-11-29 BR BR0215007-7A patent/BR0215007A/pt not_active Application Discontinuation
  • 2002-11-29 RU RU2004121964/02A patent/RU2004121964A/ru not_active Application Discontinuation
  • 2002-12-10 AR ARP020104787A patent/AR037780A1/es not_active Application Discontinuation
  • 2002-12-13 PE PE2002001234A patent/PE20030685A1/es not_active Application Discontinuation

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