WO2023205823A1

WO2023205823A1 - Sleeve and method for thermally-insulating a blast hole

Info

Publication number: WO2023205823A1
Application number: PCT/ZA2023/050021
Authority: WO
Inventors: Gerhard Johann STENZEL
Original assignee: Glencore Operations South Africa (Pty) Limited
Priority date: 2022-04-21
Filing date: 2023-04-21
Publication date: 2023-10-26

Abstract

A hot-hole, blasting sleeve (1) comprising a flexible, thin-walled, elongate body of composite material, defining an inner chamber (5), the body dimensioned and configured for placement in a conventional borehole. The wall comprises a high-tensile strength, liquid-impermeable inner layer (4), a woven, thermally-insulating middle layer (3) and a high tensile strength, liquid impermeable outer layer (2). The body further has an operatively leading end (6) and an operatively trailing end (7), with an opening located towards the trailing end (7) and suitably configured and dimensioned to enable loading of an explosive charge there through. The leading end (6) is closed off and arranged to retain an explosive charge while blocking the ingress of liquid and the corresponding contamination of such charge within the tubular body to limit sleeve failure prior to detonation.

Description

SLEEVE AND METHOD FOR THERMALLY-INSULATING A BLAST HOLE

Field of the Invention

[001] The invention relates to a blast hole. More particularly but not exclusively, the invention relates to a novel sleeve and corresponding method for thermally-insulating a blast hole.

Backaround to the Invention

[002] In modern mining or earth moving operations, such as open cast coal mining, blasting is typically conducted by firstly drilling so-called blast holes (also referred to as blasting holes, boreholes or shot holes) to predetermined depths at discrete locations or in predetermined patterns into ground to be moved or ore bodies containing natural resources such as coal or minerals. The drilled blast holes are then loaded with predetermined charges of explosive compositions, typically in solid, particulate slurry, emulsion or gel form and up to predetermined depths, volumes or masses. This predetermination is aimed at ensuring that the ground is moved or ore bodies are broken down in the desired manner, leaving earth, rubble and/or fragmentation that is easily removed from the earth moving or mining location after detonation of the explosive compositions, thereby facilitating efficient excavation of the earth or natural resource.

[003] Of the various explosive compositions that are utilized in mining operations, ammonium nitrate based explosive compositions (also referred to as ANFO) is one of the more commonly used compositions today. Most of the explosive compositions used in mining applications, including ammonium nitrates, must however be kept free of water in order to ensure that the detonation quality in fragmentizing rock is satisfactory. Contamination of the explosive compositions by water, such as water collecting in blast holes, can affect and reduce the blast outcome, cause misfires and/or result in significant and costly loss of explosives. While the bulk of the water that ordinarily collects in blast holes is typically pumped out before a hole is loaded with a predetermined charge of the explosive compositions, some water ordinarily remains in or flows back into the blast holes, especially in instances where there are time delays or even prolonged periods of time between the pumping and loading activities and/or the detonation of the explosive charges after loading the blast holes.

[004] In addition to unwanted water, fissures can form in the blast hole walls due to adjacent blasts and/or natural causes, causing the explosive compositions to leak or drain out through the fissures, thereby affecting the blast outcome negatively and leading to the loss of explosive composition.

[005] Water resistant blast hole liners, in order to avoid the contamination or loss of the costly explosive compositions in mining operations, are commonly utilised to line the blast holes. Blast hole liners generally comprise of a simple polymer or plastic tubing in an array of lengths and/or diameters to suit blast holes of differing depths and diameters and/or explosive charges of differing volumes or masses. The liners are typically of predetermined length, closed at one end and open at the opposing end, alternatively, are provided in an endless roll, allowing a user to determine and cut off the requisite length and to seal it off at one end based on the specific depth of the blast hole and/or volume or mass of the charge of the explosive. The liners are typically closed or sealed off with cable ties or knots, stitching and/or adhesives.

[006] A liner in use is placed with its sealed or closed end downwardly in the blast hole, often loaded down with dirt and/or stemming to assist in locating and retaining the liner at a sufficient or predetermined depth in the blast hole. The liners are often further sealed, just above the dirt or stemming, so as to separate the stemming from the explosive composition, before the explosive charge is loaded into the liner. The known liners are however often inadequate to block the ingress of water fully or over prolonged periods, or to provide protection against the loss of explosive compositions when overloaded with stemming and/or explosive composition, due to the breaking or rupturing seals or splitting of liner side walls.

[007] In addition to the above shortcomings of the known liners, there is also a risk of liner failure when using the known liners in blast holes with elevated temperatures such as in open cast, coal mining operations or near volcanic formations. In these operations, the elevated temperatures in blast holes are typically caused by geothermal heating (e.g. volcanic activity), geothermal gradients and burning coal seams. In deep mining, rock face temperatures also increase relative to the depth of the blast hole into the rock face and the depth of the mining operation underground. Elevated temperatures or temperature increases inside a blast hole can lead to a premature and uncontrolled detonation of an explosive composition in the blast hole. Premature or uncontrolled detonations present a serious safety risk to mining operations and surrounding activities.

[008] In addition, blast holes and rock face environments might contain sulphides that can form reactive ground conditions through oxidation in which explosive material can inadvertently detonate. In these cases, the rock undergoes a spontaneous exothermic reaction when it comes into contact with nitrates. Such reactions typically involve the chemical oxidation of sulphides (usually of iron or copper) by nitrates. The resulting reaction can cause the liberation of potentially large amounts of heat. Thus, even in conditions where rock face and/or blast hole temperatures are believed to be below the safety threshold temperature limit for explosives, chemical reactions within the geological formation can cause localized hot spots within the formation that exceed the allowable temperatures. The unpredictable nature of such chemical reactions cause dangerous conditions to exist without being detected and can result in premature or uncontrolled detonation of explosives.

[009] The known blast hole liners, such as those discussed above, are accordingly not suitable for blast holes with elevated temperatures, or for blast holes that have the potential to foster exothermic reactions, as these liners do not sufficiently insulate explosive compositions sufficiently from the elevated temperatures inside the blast hole. This in turn can affect the stability of the explosive charge in these liners adversely and lead to premature or uncontrolled detonations. In addition, the above blast hole liners often lose their structural rigidity or even melt, especially at higher temperatures, increasing the risk of premature and uncontrolled detonation.

[0010] Further, many of the known blast hole liners in mining applications are often simply not strong enough to contain the amount of explosive composition required in certain deeper blast holes securely, causing the liner to open, burst, rip or split when fully charged with the requisite volume or mass of explosives. In addition, the side walls of blast holes can be relatively irregular, uneven and even jagged at times, with various protrusions, edges or particles disparately located along the length of the hole. In turn, the liners that are commonly employed comprise thin-walled material so as to conform substantially to the irregularities within the blast hole, provide suitable compaction of the contained explosive composition and load the bulk of the interstices in the wall of the hole. These liners are accordingly susceptible to tearing or perforating when they are secured within the blast holes.

Object of the Invention

[0011] It is accordingly an object of the invention to provide a novel and relatively inexpensive, thermally-insulating blast hole sleeve that overcomes or at least reduces the above shortcomings of some of the known blast hole liners, or to provide a useful alternative to the existing liners.

Summary of the Invention

[0012] According to the invention there is provided a hot-hole, blast sleeve comprising a flexible, thin-walled, elongate body of composite material, defining an inner loadbearing chamber, the body dimensioned and configured for placement in a conventionally drilled, blast hole, the body having: a wall, comprising: a high tensile strength, liquid-impermeable inner layer; a woven, thermally-insulating middle layer; and a high tensile strength, liquid-impermeable outer layer; a first, operatively trailing end; a filler opening, located towards the trailing end and suitably configured and dimensioned for enabling the loading of an explosive charge there through; and a second, opposed, operatively leading end, located distal from the trailing end and operatively arranged to retain an explosive charge while blocking the ingress of liquid and the corresponding contamination of such charge within the tubular body; the wall being reinforced towards at least some of its extremities to limit sleeve failure prior to detonation.

[0013] The leading end may be proved with a welded seal towards the extremities of at least one of the liquid-impermeable layers and, preferably, towards the extremities of each of the liquid-impermeable layers, to create a liquid-impermeable, closed body end and provide a corresponding liquid-impermeable, closed inner chamber for retaining the explosive charge therein.

[0014] The leading end, alternatively, may be knotted end to provide a liquid- impermeable, closed body end.

[0015] The body wall may comprise at least one elongated, layered sheet material with at least two opposed elongate sides, joined substantially along the two sides with a reinforcing rib weld to provide a substantially tubular, load-bearing inner chamber, the rib weld configured to reinforce the body longitudinally when loaded with a preselected explosive charge.

[0016] The trailing end may be provided with a reinforcing rib, extending and configured along at least part of the opening extremities to reinforce the tubular body when the chamber is loaded with the explosive charge.

[0017] The trailing end may be provided further with at least one retaining formation, configured to receive and retain securing means, selected from the group comprising a rope, cord, strap and the like, for securing the sleeve within a blast hole. The retaining formation may comprise an eyelet, loops or the like.

[0018] The inner layer may comprise a high tensile strength, liquid-impermeable, thermal resistant material selected from the group including polyvinyl chloride, polypropylene and the like.

[0019] The middle layer may comprise a woven, thermally-insulating material selected from the group including polyester, nylon, elastane and the like. Preferably, the thermally-insulating material would enable hot-hole blasting at external temperatures of between about 80 and 150 degrees Celsius (°C) and, more preferably, up to 150°C, while maintaining a stable temperature within the inner chamber of below about 60 to 90°C for prolonged periods of time. [0020] The outer layer may comprise a high tensile strength, liquid-impermeable, thermal resistant material selected from the group including polyvinyl chloride, polypropylene and the like.

[0021] The collective thickness of the three layers may be between about 0.25 mm and 3 mm and, preferably, between about 0.35 mm and 0.75 mm. The sleeve may have a minimum weight of between about 150 g/m² and 1500 g/m² and, preferably, between about 300 g/m² and 850 g/m². The sleeve may have a minimum tensile strength measured in accordance with ISO 1421 :1998 of between about 750 N 150 mm and 4500 N I 50 mm and, preferably, between about 1500 N I 50 mm and 3000 N I 50 mm in the warp direction, and between about 500 N I 50 mm and 4500 N I 50 mm and, preferably, between about 1000 N I 50 mm and 3000 N I 50 mm in the weft direction. The sleeve further may have a minimum tear strength measured in accordance with ISO 4674- 1 :2016 (Method B) of between about 100 N and 550 N and, preferably, between about 200 N and 400 N in the warp direction, and between about 75 N and 500 N and, preferably, between about 150 N and 350 N in the weft direction. The sleeve may have a minimum adhesion strength measured in accordance with ISO 2411 :2017 of between about 10 N / 25 mm and 75 N / 25 mm and, preferably, between about 20 N / 25 mm and 50 N / 25 mm.

[0022] The sleeve may be provided with a temperature sensor arrangement, configured to measure the temperature at least periodically within the inner chamber once it has been loaded with an explosive charge during the period prior to detonation. Preferably, the body may be provided with a temperature sensor arrangement, configured to measure the temperature at least periodically at preselected locations along the length of the inner chamber. More preferably, the temperature sensor arrangement may be configured to measure the temperature continually at between 2 m and 10 m intervals along and, most preferably at about 5 m intervals along the length of the inner chamber.

[0023] The temperature sensor arrangement may comprise a plurality of temperature measuring probes, spaced apart and connected electrically to a flexible electric cable, the cable preferably secured towards the trailing end and attached to the inner chamber at preselected intervals along the length of the inner chamber. More preferably, the cable may be secured to the inner chamber at between 2 m and 10 m intervals and, most preferably at about 5 m intervals along the length of the inner chamber.

Detailed

of the Invention

[0024] A non-limiting embodiment of the invention shall now be described with reference to the accompanying drawings wherein:

Figure 1 is a two-dimensional side view of a hot-hole, blast sleeve of composite material in accordance with the invention;

Figure 2 is a cross sectional view of the hot-hole, blast sleeve, cut along the line A - A as illustrated in Figure 1 ;

Figure 3 is a cross sectional side view of the hot-hole, blast sleeve as illustrated in Figure 1 , wherein the sleeve is suspended at a preselected depth within a blast hole and loaded with an explosive charge; and

Figure 4 is a cross sectional side view of the hot-hole, blast sleeve as illustrated in Figure 3, wherein the sleeve is provided with a temperature sensor in accordance with the invention.

[0025] A hot-hole, blast sleeve 1 , suitable for use in hot-hole blasting in accordance with the invention and as illustrated in Figures 1 and 2, comprises a thin-walled body with a wall of composite flexible sheet material comprising a flexible, liquid-impermeable outer layer 2, a flexible woven, thermally-insulating middle layer 3, and a flexible liquid- impermeable inner layer 4 with respectively preselected, liquid-impermeable and thermally-insulating capabilities, the body having an inner load-bearing chamber 5 that is dimensioned and configured to retain a preselected charge of an explosive charge (not shown) therein. It is envisaged that the explosive charge (not shown) could be in a slurry or gel form, such as ammonium nitrate-fuel oil (ANFO).

[0026] The outer layer 2 comprises a high tensile strength, yet flexible thermoplastic material of polyvinyl chloride (PVC) to block the ingress of liquid through it. PVC has inherent thermal insulation characteristics that allow the outer layer 2 to be resistant to the elevated temperatures that is present in a hot blast hole. The outer layer 2 is further resistant to the abrasions that are caused by the sharp, uneven and jagged edges within the hole once while the sleeve 1 is being lowered therein. The middle layer 3 comprises a woven, thermally-insulating material of polyester that is resistant to elevated temperatures. The middle layer 3 serves to provide further resistance to the elevated temperatures that is present in a hot blast hole. The inner layer 4 comprises high tensile strength, yet flexible material of polyvinyl chloride (PVC) that blocks the substantial discharge of any charge loaded within the chamber 5 from the sleeve 1. The thermalinsulating properties of the three layers 2, 3, 4 enable the blast sleeve 1 to maintain a stable temperature within the inner chamber of below about 60°C, while being exposed to elevated external temperatures of between about 80°C and 150°C for prolonged periods of time, without compromising its structural integrity.

[0027] The collective thickness of the three layers 2, 3, 4 is between about 0.35 mm and 0.75 mm. The sleeve 1 is further configured to have a minimum weight of between about 300 g/m² and 850 g/m². The sleeve 1 is configured to have a minimum tensile strength measured in accordance with ISO 1421 :1998 of between about 1500 N I 50 mm and 3000 N I 50 mm in the warp direction, and between about 1000 N I 50 mm and 3000 N I 50 mm in the weft direction. The sleeve 1 is further configured to have a minimum tear strength measured in accordance with ISO 4674-1 :2016 (Method B) of between about 200 N and 400 N in the warp direction, and between about 150 N and 350 N in the weft direction. The sleeve 1 is additionally configured to have a minimum adhesion strength measured in accordance with ISO 2411 :2017 of between about 20 N / 25 mm and 50 N I 25 mm.

[0028] The sleeve 1 extends between a first, operatively leading end 6 and a second, operatively trailing end 7, the leading end defined by a closure, typically located towards the bottom of the sleeve, while the training end is defined by an opening, typically located towards the top of the sleeve. The closure 6 is configured to ensure that there is no ingress of liquid that might be present in the hot blast hole, as well as blocking the discharge of the explosive charge that is retained in the chamber 5. The closure 6 is constructed by welding the bottom of the sleeve 1 shut. The weld on the closure 6 has a minimum width of between about 20 mm and 60 mm. Alternatively and due to the relatively flexible materials that the sleeve 1 comprises of, the closure 6 can be created by tying a knot at the bottom of the sleeve 1.

[0029] The opening 7 is configured to receive the explosive charge once the sleeve has been lowered sufficiently into a hot blast hole. The opening 7 is configured and dimensioned to receive a loading device such as a hose end therein, and for the charge of an explosive charge to be loaded directly into the chamber 5.

[0030] The sleeve 1 is provided with a set of retaining formations in the form eyelets 8, located in the upper portion of the sleeve and configured to retain securing means such as rope, strap, cord or the like securely therein. The eyelets 8 have a minimum diameter of between about 5 mm and 25 mm. The opening 7 of the sleeve 1 has a rim 9, reinforced with a rib 10, extending around the opening to ensure, in association with the eyelets 8, that the sleeve can hold the weight of a preselected charge of explosives.

[0031] The sleeve 1 is further provided with a reinforcing rib weld 11 , extending longitudinally substantially along the length of the sleeve to ensure further structural strength. The reinforcing rib weld 11 has a minimum width of between about 20 mm and 60 mm.

[0032] In operation, the sleeve 1 of a preselected length is inserted leading end 6 first and lowered up to a preselected depth before it securely suspended within a hot blast hole 12 with its opening 7 sufficiently exposed to receive a charge of explosives therethrough, respectively as illustrated in Figure 3. In such operation, with the sleeve 1 being lowered into the blast hole 12, a rope 13 (normally nylon ski rope with a diameter of about 6 to 10 mm) is threaded through the eyelets 8 and tied to an anchor rod 14 (normally a wooden stick with a diameter of about 30 to 50 mm), the rod having a length beyond the diameter of the blast hole. Once secured, the inner chamber 5 is loaded with a preselected charge of an explosive composition 15 via the opening 7, up to a predetermined level, volume or mass of explosives. Once the chamber 5 has been loaded as required, a booster-and-detonator arrangement 16 is typically lowered into the explosive composition 15 for detonation.

[0033] As illustrated in Figure 4, the sleeve 1 is further provided with a temperature sensor arrangement 17, configured to measure the temperature within the inner chamber 5 along the length of the sleeve 1 in substantially real-time during the period after the explosive charge has been loaded and prior to detonation. The temperature sensor arrangement 17 comprises a temperature display module 17a and a plurality of temperature measuring probes 17b, spaced apart and connected electrically to a flexible electric cable 17c at between 2 m and 10 m intervals and, typically, at about 5 m intervals. The cable 17c is secured towards the trailing end 6 and attached to the inner chamber at between 2 m and 10 m intervals and, typically, at about 5 m intervals along the length of the inner chamber. The temperature sensor arrangement 17 is further provided with an alarm (not show) able to generate an alert, should the temperature as measured by any of the probes exceed a predetermined value.

[0034] It will be appreciated that many variations in detail are possible without departing from the scope and/or spirit of the inventions as defined in the consistory statements and/or as described in the specific embodiment hereinabove, such as increasing any one or more of the above dimensions and/or physical properties of the layers so as to adjust the liquid impermeable and/or thermally-insulating capabilities of the sleeve.

Claims

Claims . A hot-hole, blasting sleeve comprising a flexible, thin-walled, elongate body of composite material, defining an inner load-bearing chamber, the body dimensioned and configured for placement in a conventional blast hole, the body having: a wall, comprising: a high-tensile strength, liquid-impermeable inner layer; a woven, thermally-insulating middle layer; and a high tensile strength, liquid impermeable outer layer; a first, operatively trailing end; a filler opening, located towards the trailing end and suitably configured and dimensioned for enabling the loading of an explosive charge there through; and a second, operatively leading end, located distal from the trailing end and operatively arranged to retain an explosive charge while blocking the ingress of liquid and the corresponding contamination of such charge within the tubular body; the wall being reinforced towards at least some of its extremities to limit sleeve failure prior to detonation. . A hot-hole, blasting sleeve as claimed in claim 1 wherein the leading end is provided with a welded seal towards the extremities of at least one of the liquid-impermeable layers to create a liquid impermeable body end and provide a corresponding liquid- impermeable inner chamber for retaining an explosive charge therein. . A hot-hole, blasting sleeve as claimed in claim 1 wherein the body is knotted towards the leading end to create a liquid impermeable body end and provide a corresponding liquid-impermeable inner chamber for retaining an explosive charge therein. . A hot-hole, blasting sleeve as claimed in claim 1 wherein the body wall comprises of at least one elongate, layered sheet material with at least two opposed elongate sides, joined substantially along the two sides with a reinforcing rib weld to provide a substantially tubular inner chamber, the rib weld configured to reinforce the body longitudinally when loaded with a preselected charge of an explosive charge. . A hot-hole, blasting sleeve as claimed in claim 1 wherein the trailing end is provided with a reinforcing rib, extending and configured along at least part of the opening extremities to reinforce the tubular body when the chamber is loaded an explosive charge.

6. A hot-hole, blasting sleeve as claimed in claims 1 to 5 wherein the trailing end is further provided with at least one retaining formation, configured to receive and retain securing means, selected from the group comprising a rope, cord, strap and the like, for securing the sleeve within a blast hole.

7. A hot-hole, blasting sleeve as claimed in claim 6 wherein the retaining formation is selected from a group including an eyelet, loops and the like.

8. A hot-hole, blasting sleeve as claimed in claim 1 wherein the inner layer comprises a high tensile strength, liquid impermeable, thermal resistant material selected from the group including polyvinyl chloride, polypropylene and the like.

9. A hot-hole, blasting sleeve as claimed in claim 1 wherein the middle layer comprises a woven thermally-insulating material selected from the group including polyester, nylon, elastane and the like. 0. A hot-hole, blasting sleeve as claimed in claim 1 wherein the thermally insulating material is selected to enable blasting in hot holes with temperatures of between 80 to 150 degrees Celsius (°C). 1. A hot-hole, blasting sleeve as claimed in claim 1 wherein the outer layer comprises a high tensile strength, liquid impermeable, thermal resistant material selected from the group including polyvinyl chloride, polypropylene and the like. 2. A hot-hole, blasting sleeve as claimed in claim 1 wherein the collective thickness of the three layers is between about 0.25 mm and 3 mm. 3. A hot-hole, blasting sleeve as claimed in claim 1 wherein the sleeve has a minimum weight of between about 150 g/m² and 1500 g/m²

14. A hot-hole, blasting sleeve as claimed in claim 1 wherein the sleeve has a minimum tensile strength of between about 750 N I 50 mm and 4500 N I 50 mm, in the warp direction, and between about 500 N 150 mm and 4500 N 150 mm, in the weft direction.

15. A hot-hole, blasting sleeve as claimed in claim 1 wherein the sleeve has a minimum tear strength of between about 100 N and 550 N, in the warp direction, and between about 75 N and 500 N, in the weft direction.

16. A hot-hole, blasting sleeve as claimed in claim 1 wherein the sleeve has a minimum adhesion strength of between about 10 N / 25 mm and 75 N / 25 mm.

17. A hot-hole, blasting sleeve as claimed in claim 1 wherein the body is provided with a temperature sensor arrangement, configured to measure the temperature at least periodically within an inner chamber loaded with an explosive charge during the period prior to detonation.

18. A hot-hole, blasting sleeve as claimed in claim 17 wherein the temperature sensor arrangement is configured to measure the temperature along the length of the inner chamber at a plurality of intervals, the arrangement comprising a plurality of temperature measuring probes operatively located and electrically connected at between 2 and 10 m intervals along the length of the inner chamber to a flexible insulated electric cable.

19. A hot-hole, blasting sleeve as claimed in claim 18 wherein the cable is welded to the closed end and attached to the inner chamber at a plurality of intervals along the length of the inner chamber.