Tom 24 2008 Zeszyt 4/3
S.V. MUCHNIK*, V.N. OPARIN*
Experience and prospects of turbo-blasting at open-pit mines
Introduction
The process of blasting of industrial explosives is known to have two subsequent stages of development, a stage of detonation and a stage of secondary chemical reactions (Antonov, Gladilin 1975; Soloviev 1980) that are frequently identified with deflagration (Denisov 1989). They differ both in heat liberation rate and nature and quantity of useful yield.
Deflagration is caused by partial dispersion of non-detonated particles of a fuel and an oxidizer into the nonstationary flow of detonation products. The rate of deflagration is con- fined by the diffusion and natural-convective mechanisms of heat transfer and mass transfer.
All along of a high density of the detonation products in a blasting chamber (~103kg/m3), it is indispensable that the mentioned mechanisms clamp down reactions of deflagration until explosion gas intrusion into the atmosphere. As a result, a share of nonreacted fuel releases in the air and is out of useful yield of a blast.
We advanced an opinion that explosion heat losses may be decreased by increasing the rate of deflagration in a blasting chamber by mechanical interfusion of detonation products (Muchnik 2001). In consequence of this action, the mechanisms of mass and heat transfer are supplemented with forced convection.
This hypothesis was proved in the course of large-scale industrial experiments carried out during open mining at coal, ore and nonmetallic deposits of Russia. As a result, a previously unknown phenomenon was revealed: explosion energy grew largely under the forced convection of detonation products in a hole by a gyroconvector. Based on that, the authors have developed a technology for improvement of industrial blasting efficiency. The tech- nology has been named turbo-blasting; it is schematically illustrated in Figure 1.
* Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia.
The gyroconvector is a metal plate tortile in helical fashion for 360° (one full turn). Size of the plate depends on a borehole diameter. For instance for holesf 0.200–0.320 m, the optimal plate size is 0.200´ 0.020 ´ 0.002 m.
Figure 1a demonstrates the structure of a charge with a gyroconvector. The explosive charge is always initiated directly by a relay detonator. Below, spaced at no less than a half borehole diameter, the gyroconvector is installed. It should be completely imbedded to the charge, and its long axis should be parallel to the charge column axis.
After the relay detonator action, the detonation wave (Fig. 1b) followed with the high-speed flow of detonation products propagates along the charge of explosive. When the detonation waves arrives at the gyroconvector and streams around the helix, it generates the torsion torque (Fig. 1b shows resolution of forces on the helix, the resultant force F).
The gyroconvector is brought into the rotation by the force Fw, and is pushed forward by the force Fz.
After the detonation wave has passed (Fig. 1c), the gyroconvector mechanically rotates progressively lengthwise the borehole after the wave front. In so doing, the gyroconvector induces convection and speeds up deflagration reactions.
The gyroconvector rotates in such direction that it forces the gas-dispersion products of detonation onward, along its movement. When the charge is initiated directly, the flow runs downward the borehole and prevents from blast gas release through the hole mouth. As a result, the detonation products stay in the borehole for a longer period of time, which increases the heat of deflagration reactions and enhances the explosion-generated shock.
Relay detonator Gyroconvector Explosive charge
a)
Flow of detonation products
Detonation wave front
Gyroconvector
Fz D b)
Fw u F
u D
Induced convection of detonation products Gyroconvector Detonation wave front
c)
Fig. 1. Turbo-blasting and its stages:
a) installation of gyroconvector in explosive charge and relay detonator;
b) actuation of gyroconvector by detonation wave followed by the flow of detonation products;
c) progressive rotation of gyroconvector lengthwise the borehole and induction of forced convection of detonation products
Rys. 1. Roboty strzelnicze turbo i ich etapy:
a) instalacja ¿yrokonwektora w ³adunku wybuchowym i sp³once przekaŸnikowej;
b) aktywacja ¿yrokonwektora przez falê detonacyjn¹, po której nastêpuje przep³yw produktów detonacji;
c) postêpuj¹ca rotacja ¿yrokonwektora wzd³u¿ otworu wiertniczego i wprowadzenie wymuszonej konwekcji produktów detonacji
Figure 2 exemplifies tests carried out to compare turbo-blasting of aluminum-containing explosives with and without the gyroconvector (a check blast) (Muchnik 2002).
A block abcd for blasting, length of 180 m, width b of 35 m, height ed of 27 m, was divided into two equal parts 90 m long each: trial part (turbo-blasting with gyroconvector) and check part (standard blasting). Explosive charges were placed in blasting chambers in boreholes with a diameter of 0.32 mm (5 rows, Fig. 2 shows the first and last rows by double lines), drilled with an incline in a square grid 7´ 7 m. The explosive was an aluminum- -containing mix of equal portions of grammonite 79/21 and granulite AC-8. Average charge for one borehole contained 1250 kg of explosive.
For good layout, profiles of disintegration in trail and check parts of the block are overlapped (Fig. 2). The profile of broken rock disintegration is shown by dot-dash line ahj in the check part and by solid line fij in the trial part. It is seen that under the standard blasting, major portion of broken rock ahjcda remained within the block contour abcd, whereas after the turbo-blasting, half as much rock fijcdf was left within this contour. The dashed part I (or fijhae) implies the extra broken rock owing to the higher energy and explosion-generated impulse as a result of using the gyroconvector.
Another factor is loosening of the rock mass adge beyond the contour owing to the gyroconvector as well (dotted line ad marks position of the slope in the check part and line eg is for the same in the trial part).
The third factor is the slope outcropping. In the check part of the block, rock completely covers the slope ad up to the upper edge a, while in the trial part the outcrop ef covers 2/3 of the slope eg.
On application of gyroconvectors to the direct dumping method with total rock volume of 4.44 mln m3, the following results were obtained (Fig. 3). The check explosion index of removing a rock mass into internal dump is 25 % (Fig. 3a), when the trial blasting produced the index of 34–35% with using grammonite 79/21 and 42–47% with aluminum-containing granulite AC-8 (Fig. 3b). Thus, due to additional energy release, the blast effect may grow by a factor of 1.4–1.8 depending on the granular explosive. For the three years period of application, 17 large-scale turbo-blasts have dumped 0.44 mln m3of rock mass in addition.
Fig. 2. Disintegration of broken rock under turbo-blasting (fij) and under check large-scale explosion (ahj).
Hatchwork indicates extra rock disintegrated by turbo-blasting
Rys. 2. Rozpad kruszonej ska³y pod wp³ywem robót strzelniczych turbo (fij) i w przypadku kontrolnego wybuchu du¿ej skali (ahj). Pole zakreskowane wskazuje dodatkowy rozpad ska³ wskutek robót strzelniczych
turbo
The long-continued testing of the gyroconvector with different industrial explosives and at different coal, ore and nonmetallic deposits have shown that the higher turbo-blasting heat Qgrelative to the reference value Q for the given explosive can be estimated by the reduced factor eg= Q/Qg, at that:
eg= 0,73 + 0,02D2/Q
Percentage of additional heat to the initial Q:
DQ = 100(1/eg– 1)%
The highestDQ is generated under blasting aluminum-containing explosives and simple free-from-trotyl explosives (DQ = 28–32%), the lowest DQ is produced on explosion of emulsion explosives (for poremit 1, DQ = 8–9%). The reason is different shares of heat released in the zone of chemical reactions. When the heat almost completely releases in detonation, we have that the forced convection of gas-dispersion products produces no appreciable effect. In case that detonation generates low heat, the forced convection speeds-up exothermal reactions of deflagration and enhances DQ. For example, after the gyroconvectors had been introduced at the large coal deposit Sibirginskoe, South Kuzbass, the average annual consumption of explosives (grammonite 79/21, granulite AC-8 and granulotol) decreased from 1.07 to 0.87 kg/m3(i.e. by 18.7%) during the first three years and kept the same in the course of the next three years of the trubo-blasting application.
All in all in Russia by now, the rock mass volume broken with the trubo-blasting totals
~101 mln m3.
It is expedient to reduce explosive consumption with the turbo-blasting by trying to achieve the higher yield of rock mass per running meter of boreholes at the same weight of
b)
Fig. 3. Turbo-blasting and direct dumping method:
a) check profile of broken rock disintegration;
b) broken rock disintegration with application of gyroconvector Rys. 3. Roboty strzelnicze turbo i metoda bezpoœredniego zwa³owania:
a) profil kontrolny rozpadu ska³; b) rozpad ska³ z zastosowaniem ¿yrokonwektora
the charges. In this case, the reduction value both of blasthole meterage drilled and of particular explosive consumption as against the standard project can be calculated by the formula:
d = - +
- -
é ëê ê
ù ûú ú+
100 0 075
1 0 27
0 27 0 075
2 0
2
Q D
Q
Q
Q Q D
. .
. ( . )
.075 1
D2
Q - ìí
ï îï
üý ï þï
[%]
In large-scale explosion of packaged explosives that have a small diameter, the trubo- -blasting allows even more diminishing diameters of the cartridges, which facilitates charging of faulted holes (Obgolts 2005). The initial capacity P0of the holes decreases to Pg and the condition that Pg³ egP0should be met.
With the gyroconvector it is possible to increase the blast heat selectively height-wise a bench. In the bench composed of hard-to blast rocks in the bottom and easy-to-blast rocks on the top, the gyroconvector should be placed 1 m above the interface of these rocks. In this case,DQ will release in the difficult-to-destroy section and, as the commercial test show, no oversizes will be produced and the bench bottom will be mined qualitatively (Muchnik 2003).
As explosives almost completely burn in a borehole, nitrogen peroxide exhaust into the atmosphere is virtually exterminated. This is understood by the absence of characteristic yellow color of the blast gases during the turbo-blasting. Comparative experiences show that the gyroconvectors when used increase density of the blast gases that acquire a habit to propagate over the bottom of a bench and to effuse to the subjacent benches. We think it is possible to consider this fact as an evidence of increase in relatively heavy and harmless carbon dioxide instead of light and poisonous carbon oxide. Turbo-blasted granutol burns in full in the hole, which is confirmed by the absence of claps and flames usually visible when this explosive is blasted at the night-time.
As a rule, enterprises manufacture gyroconvectors in their own workshops. Installation of gyroconvectors into a service position in the charged blasthole takes additionally 1 or 3 seconds. However, in spite of simplicity and production effectiveness of the turbo-blasting, it is recommended to launch industrial production of packaged explosive cartridges with the built-in gyroconvectors with the goal of expanding the application range of the turbo- -blasting and reaching appreciable resource-saving and ecological effect.
Conclusion
It has been established that the forced convection of detonation products increases combustion efficiency of an explosive charged in a borehole. The authors propose the simplest design of a gyroconvector that is placed under the delay detonator in the explosive charge and is actuated by the detonation wave. While moving along the borehole after the
detonation wave, the gyroconvector induces flows of the forced convection of detonation products and forces them into the bottom of the hole. As a result, the blast-generated heat and impulse transferred to the rock mass grow.
The technology of blasting with the gyroconvectors has been named as turbo- -blasting. The formula for calculating the resource-saving effect of the turbo-blasting is offered. Volume of rock mass broken by the turbo-blasting in Russian is about of
~101mln m3.
REFERENCES
[1] A n t o n o v E.A., G l a d i l i n A.M., 1975 – Propagation of plane detonation waves in the presence of zone of secondary chemical reactions. Vzryvnoe Delo 75 (32), 48–60.
[2] D e n i s o v Yu.N., 1989 – Gas Dynamics of Detonation Structures. Moscow, Mashinostroenie.
[3] M u c h n i k S.V., 2001 – Improvement of overburden direct dumping efficiency by application of turbo- -blasting. Ugol 12, 21–24.
[4] M u c h n i k S.V., – Turbo-blasing of borehole explosive charges in open-pit mines. Journal of Mining Science (38), 470–472.
[5] M u c h n i k S.V., 2003 – Application of turbo-blasting to redistribution of blast energy height-wise a bench.
Gorny Zhurnal 6, 24–27.
[6] O b g o l t s A.A., L a p i n a O.P., G r i s h i n A.N., M u c h n i k S.V., 2005 – Safe and efficient use of grammonite P21 in the watered areas of open pits. Bezopasnost Truda v Promyshlennosti 6, 9–12.
[7] S o l o v i e v V.S., et al., 1980 – Detonation of explosives with afterburning. The 6th International Symposium on Burning and Blasting Proceedings. Alma-Ata-Chernogolovka, IKhF AN SSSR.
DOŒWIADCZENIA I PERSPEKTYWY ROBÓT STRZELNICZYCH TURBO W KOPALNIACH ODKRYWKOWYCH
S ³ o w a k l u c z o w e
Kopalnia odkrywkowa, kamienio³omy, materia³y wybuchowe, roboty strzelnicze turbo
S t r e s z c z e n i e
Opracowanie ukazuje potencja³ konserwacji zasobów i zmniejszenia wp³ywu ekologicznego po robotach strzelniczych w kopalniach odkrywkowych poprzez zastosowanie wymuszonej konwekcji produktów detonacji w otworze. Ukazano sposób kierowania wymuszon¹ konwekcj¹ gazowych dyspersyjnych produktów detonacji, jak równie¿ zaprezentowano konwektor i opisano projekty ró¿nych ³adunków stosowanych w górnictwie odkryw- kowym. Opisano podstawowe cechy technologii robót strzelniczych turbo oraz podano historiê ich zastosowañ, popart¹ faktycznymi danymi o istniej¹cych oszczêdnoœciach zasobów i œrodowiskowych korzyœciach zastoso- wania tej technologii w kamienio³omach rud i zasobów niemetalowych oraz w kopalniach odkrywkowych wêgla w Rosji.
EXPERIENCE AND PROSPECTS OF TURBO-BLASTING AT OPEN-PIT MINES
K e y w o r d s Open pit, quarries, explosives, turbo-blasting
A b s t r a c t
The highlight of the paper is the potentiality of resource conservation and mitigation of ecological impact after blasting at open pit mines by application of the forced convection of detonation products in a hole. It is expounded how to drive the forced convection of gas-dispersion detonation products, as well as a convector and the designs of various charges to be used in the open pit mining are described. The prime elements of the turboblasting technology are described, and its case history is presented, backed by the actual data on the existent resource-saving and nature-oriented pay-off of the technology application at ore and nonmetallic quarries and coal open pits in Russia.
