FR2584179A1 - Device for stopping a detonation for a system for loading bulk explosives by pumping - Google Patents

Abstract

The invention relates to a device for stopping a detonation for a system for transferring bulk explosive by pumping in mines, quarries and public works, of the type which comprises a loading tube 13 communicating with at least one bulk-explosive reservoir and intended for partially penetrating into a mine hole 17 to be filled at least partially with explosives, and a pump 14 designed to bring about a particular flow of explosive in this tube 13. This tube 13 is subdivided, over at least a part of its length sufficient for stopping a detonation, into at least two branch conduits 23 of an inside diameter smaller than the critical diameter detonation determined by the density of the pumped explosive.

Description

 The present invention relates to a device for stopping a detonation for a system for charging explosives in bulk by pumping.

 During the loading of bulk explosives by pumping. the presence of a detonator at the bottom of the borehole increases the risk of an untimely explosion. To limit the consequences of such a consecutive explosion for example to electrical disturbances (storm ...) it is important that a detonation initiated in the borehole (which can contain up to several hundred kilos of explosive in open-cast operations) can not be transmitted through the loading cannula to the bulk explosive stock, generally consisting of one or more tanks, the total mass of which on the same site may be several tons and of which the explosion could have catastrophic consequences.

 Given the high speed of propagation of the detonation in a cylindrical explosive charge (several kilometers per second), as well as the destructive effects of the shock wave caused by the detonation, the realization of an arresting system detonation by simple mechanical processes is difficult to envisage.

 The solution currently adopted to limit the risks of transmission of the detonation through the loading cannula consists in limiting the diameter thereof to a sludge less than the critical detonation diameter of the pump explosive: Indeed the critical diameter of detonation An explosive is a value of the diameter of a cylindrical charge of that explosive below which the detonation is unable to propagate into the charge.

 This solution has been adopted in the French regulation of the pumping of explosives in mines and quarries: in the presence of a detonator downhole. the diameter of the pumped explosive loading cannula must be limited to 25 mm, which is in principle less than the critical detonation diameters of all explosives authorized for pumping loading in France.

 The limitation of the diameter of the cannulas to 25 mm has the effect of significantly reducing the pumping rate and correspondingly increasing the loading time of the mines. The duration of exposure of personnel to the risks of inadvertent departure is increased, and the economic interest of the loading of bulk explosives by pumping can be called into question, in particular in the case of open shots by vertical mines. deep with priming downhole.

 But in terms of pumpable explosives, which are for example boiled or emulsified explosives, the choice of the critical diameter of detonation as criterion of limitation of the diameter of the cannulas is debatable: the value of the critical diameter of detonation, which is an intrinsic characteristic of a given explosive is determined under special experimental conditions (light encapsulation, standardized density, ....), and usually "once and for all" in the approval examination of the product. this characteristic is representative of the explosive under its normal conditions of use.

In particular, the confinement provided by the reinforced rubber of the loading cannulas may have the effect of slightly reducing the value of the critical diameter of detonation. But it can also depend closely on the density of the explosive in its conditions of use. This density of the pumpable explosives can undergo important variations according to:
- the pressure to which the product is subjected in the cannula during pumping. This influence, however, generally goes in the direction of security. Indeed, pressures of the order of a few bars, commonly reached at the pump outlet, may be sufficient to desensitize the explosives.

 - commercial imperatives that require manufacturers to adjust the densities of their products, which is done by mechanical processes (aeration stirring), or chemical (variation of the amount of reducing agent or emulsifier).

 Ultimately, not only does the current rule of limiting the diameter of pump cannulas have major drawbacks in terms of practical pumping conditions, but it does not guarantee in certain cases the non-transmission of the detonation from the bottom of the hole. from mine to explosive tanks.

 To overcome these disadvantages, while tolerating fluctuations in the critical diameter of the pumped explosive and without affecting the pumping rate, the invention aims to stop the detonation between the blast hole and the explosive stock.

 The present invention proposes for this purpose a device for stopping a detonation installed on a loading system by pumping explosives in bulk, in mines, quarries and public works, of the type which comprises a loading cannula in connection with at least one tank of explosive in bulk and intended to penetrate at least partially into a borehole to be filled. at least in part, explosive, and a pump adapted: to cause a certain flow of explosive in this cannula which is subdivided over at least a part of its length into at least two bypass pipes of internal diameter less than the critical diameter detonation determined for the density of the pumped explosive.

The features and advantages of the invention will become apparent from the following description given by way of nonlimiting example, with reference to the accompanying drawings in which:
FIG. 1 represents a device of the known art in the case of an open pit mine;
Figures 2 and 3 show two characteristic curves of given explosive d-them;
- Figure 4 is a longitudinal sectional view of the device of the invention;
FIG. 5 is a cross-sectional view along arrow V of the device of the invention shown in FIG. 4.

- Figure 6 is a longitudinal sectional view of a variant of the device of the invention;
FIG. 7 is a cross-sectional view along the arrow VII of the variant of the device of the invention shown in FIG. 6.

 - Figure 8 shows a device used to experiment the invention.

 According to the embodiment chosen and shown the device of the known art shown in Figure 1 comprises two tanks 10 containing a certain amount of explosive 11, a cannula 13 from these reservoirs, a winder 12 cannula 13 and a pump 14 arranged on a truck 15.

 In the rest of the description, the expression "pumping" corresponds here to an explosion of the pump through the cannula 13.

 The free end 16 of the cannula 13 descends into a vertical borehole 17, in the bottom of which has previously placed a detonator 18.

 A trigger device 19 located on the surface is connected to this detonator by any known means.

 At the beginning of the loading the end of the cannula is at the bottom of the borehole, it then goes up gradually, for example thanks to a progressive rewinding of the cannula (13) on the reel (12), to always stay in touch with the surface of the explosive spilled into the borehole 117).

 In normal operation, after having pumped part of the borehole (17) with bulk explosive, the explosion command is carried out remotely by the triggering device.

 But during this pumped loading phase the presence of the detonator (18) at the bottom of the borehole (17) increases the risk of accidental explosion due for example to mechanical shocks or electrical disturbances.

 To limit these risks, the solution of the prior art is to limit the diameter of the cannula (13) below a threshold corresponding to the critical diameter of detonation of 1 pumped explosive.

 A curve of variation of this critical detonation diameter with normal pressure density is shown in Figure 2 for two pumpable explosives of the slurry type.

 A curve of variation of the density as a function of the pressure of one of these slurries is represented in FIG.

The device of the invention allows, in case of an untimely explosion, to stop the detonation before it reaches the stock of explosive. This device tolerates fluctuations in the critical diameter of the pumped explosive and does not affect the pumping rate,
According to the embodiment chosen and shown in FIGS. 4 and 5, the device of the invention makes it possible to obtain an improved safety compared to the devices of the known art while not modifying the flow rate of the explosive. . This device comprises a loading cannula 13 divided over at least a part of its length, sufficient to stop an explosion, into two bypass conduits 23 of diameters smaller than the critical detonation diameter of the explosive, separated from each other and connected in their ends by two endpieces 24.But this number of bypass conduits 23 can be increased.

 In Figures 6 and 7 the bypass pipes are four in number.

In both cases, we can consider increasing the section of the cannula while maintaining excellent safety conditions,
To demonstrate the validity of the solution implemented in the device of the invention, propagation tests of the detonation were performed using a simulation device shown in Figure 8 for two pumpable explosives.

This simulation device consists of
a first tube 26, simulating the cannula 13, of polyvinyl chloride or "PVC" having 53 mm and 63 mm respectively of internal and external diameters and 850 mm of length;
a second tube 27, simulating one of the bypass conduits 23, made of "PVC" having 20 and 25 mm internal and external diameters and 1000 mm in length.

 The reduction of the inner diameter from 53 to 20 m is carried out progressively by means of an inner cone connection sleeve 28.

The explosive 29 filling the device is ignited by means of a detonator 30 for example and a relay 31 of plastic explosive. The length of the first tube 26 is sufficient for the detonation regime to be permanent at the level of the section reduction. The possible propagation of the detonation in the second tube 27 is subject to a triple control by:
- marking of lead plates;
- resistant probe along the length of the second tube 27
- verification of the non-priming of a detonating cord strand at the end of the second tube 27.

The results are shown in Table 1 at the end of the description where
the number of detonations of the explosive in the second tube 27 on the number of tests carried out;
the ratio of the propagation length L over the total length L of the second tube 27.

 In all cases, the detonation stopped in the second tube 27 after a distance not exceeding 15% of its total length, most of the tube 27 remaining intact after testing.

 A diameter of the ducts 23 decreased by 10 mm relative to the critical diameter of the explosive to its density of use provides an acceptable level of safety.

- en régime turbulent

Once the diameter of these ducts is set, their number must be evaluated so that the explosive flow rate is at least conserved. according to the laws of
Poiseuille, the flow of a fluid in a tube of diameter d is - Q = kl wd in laminar regime; kl, kt
constant - Q = kt w0,5 d2,5 in turbulent regime: w = loss of
charge per unit
length
- The conservation of flow rates by multiplication of the cannula of diameter do in n ducts of diameter d1 imposes in laminar regime

- in turbulent regime

 To know the number of necessary bypass pipes, it is sufficient to carry out evaluations aimed at specifying the flow regime and the pressure loss per unit length for each pipe diameter.

 These ducts 23 reduced section must be kept at a sufficient distance or separated so that their presence effectively prevents any inadvertent explosion is transmitted from one conduit to another.

 The minimum length of the bypass ducts causing with a good certainty the stop of the detonation is at least equal to 20 times the internal diameter of these ducts.

 The invention is of course not limited to the details of the embodiments which have just been considered as examples.

 In particular the borehole (17) may not be vertical (for example horizontal or oblique) and the loading process may be different from that described above.

In a configuration like that shown in Figure 1, the device can be positioned between hole 17 and winder 12, in which case it is the entire length of the cannula 13, downstream of the winder to be divided. The practical conditions of use then dictate that the spacer 25 can slide along the n conduits 23 of the cannula;
It can also be positioned between the reel 12 and tanks 10 which is more practical convenience, but it must be tolerated in this case the explosion of the additional charge constituted by the explosive located in the cannula on the reel. This solution requires a screen to be positioned between the reel and tanks to limit the risk of detonation of the latter under the effect of projections due to the explosion of the pump or the reel.

TABLE 1: TESTS OF STOP DEVICES OF THE
DETONATION

<tb> REDUCTION <SEP> OF
<tb> SECTION
<tb> (53 <SEP> to <SEP> 20 <SEP> mm)
<tb> EXPLOSIVE <SEP> DENSITY <SEP> DIAMETER
<tb> CRITICAL <SEP> RESULT <SEP> L / L0
<tb><SEP> (mm)
<tb> EXPLOSIVE <SEP> 1 <SEP> 1.19 <SEP> 45 <SEP> 0/2 <SEP> 0.13
<tb> 0.14
<tb> EXPLOSIVE <SEP> 2 <SEP> 1.17 <SEP> 25 <SEP> 0/1 <SEP> 0.14
<tb> EXPLOSIVE <SEP> 2 <SEP> 1.29 <SEP> 55 <SEP> 0/1 <SEP> 0.07
<tb> EXPLOSIVE <SEP> 2 <SEP> 1.33 <SEP>><SEP> 70 <SEP> * <SEP> *
<tb> * impossible to achieve with a diameter explosive
critical greater than 53 mm.

Claims (9)

 1. Device for stopping a detonation installed on an explosive pump loading system in bulk, in mines, quarries and public works, of the type comprising a loading cannula (13) in connection with at least one a tank (10) of explosive (11) in bulk and intended to partially penetrate into a borehole (17) to be filled, at least in part, with explosive (11), and a pump (14) adapted to cause a certain flow of explosive in this cannula (13), characterized in that this cannula is subdivided over at least a part of its length, sufficient to stop a detonation, in at least two bypass ducts (23) of lower internal diameter to the critical detonation diameter determined for the density of the pumped explosive (11).  2. Device according to claim 1 characterized in that these conduits (23) have an internal diameter at least 10 mm less than this critical diameter of detonation.  3. Device according to any one of claims 1 or 2 characterized in that connecting sleeves are disposed between the cannula and ducts.  4. Device according to any one of claims 1 to 3 characterized in that the different ducts (23) are not in contact with each other.  5. Device according to any one of claims 1 to 4 characterized in that the diameter of the ducts is sufficient for the flow of explosives in bulk form of slurry or emulsion.  6. Device according to any one of claims 1 to 5 characterized in that the cannula t13) being formed of two sections on either side of a winder (12), is divided into several ducts between the winder ( 12), on which it is stored, and the borehole (17).  7. Device according to any one of claims 1 to 5 characterized in that the cannula (13) being formed of two sections on either side of a winder (12) is divided into several ducts between the winder (12), on which it is stored, and a reservoir (10) in which is stored the explosive (11), a screen being disposed between the reservoir (10) and the winder (1 2)  8. Device according to any one of claims 1 to 5, characterized in that the cannula (13) is subdivided into a plurality of ducts between the reservoir (10) and the borehole (17).  9. Device according to any one of claims 1 to 5, characterized in that the length of the bypass ducts (23) is at least equal to 20 times the inner diameter of these ducts,