Water Explosives for Mining
Continuous Hard Rock Breaking by Blasting with Water Charges: Technological and Technical Prerequisites for Automated and Environmentally Friendly Open Pit Mines
Tech Area / Field
- MAN-ROB/Robotics/Manufacturing Technology
- OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences
3 Approved without Funding
Kyrgyz-Russian Slavonic University, Kyrgyzstan, Bishkek
- Canadian Institute of Mining, Metallurgy and Petroleum / CIM - Central Asia, Bishkek Branch of the Canadian Institute of Mining, Metallurgy and Petroleum, Canada, QC, Montreal\nThe University of Montana / MontanaTech, USA, MT, Butte
Project summaryThe project objective is to create technological and technical prerequisites for environmentally appropriate technology and maximum safe mining of gold, diamond, uranium, and other minerals, especially under unfavorable geological, climatic, and socio-economic conditions by using automated, unattended systems.
Means for achievement of the goal are the method and device for creation and keeping of continuous flows of hard rock broken by controlled blasting with water charges. The device is the automated drill-and-blast planer equipped with a generator for formation of charges, their explosion, and delivery of water transformation products into the blastholes.
The basis of the Project is the two following facts:
- positive R&D results of the Project #KR-341;
- arisen, as a result of performed works, opportunity to extend capabilities of continuous mining of hard rock, to make it high-profitable, more safe, and environmentally appropriate owing to the use of water as a working medium for physical explosions, which have an equivalent or more breaking capability than hydrogen and oxygen.
Today, there are known two techniques: hydrothermal method [C.W. Beehler. Hydrothermal mining process. USA Patent 497513, May 16, 1893.] and hydrox cylinder [N.P. Komar’s hydrox cylinder. From E.O. Mineli, N.F. Kusova et all. Coal-breaking by hydrox cylinder in mines. M., Nedra, 1978, pp. 6-7.] for breaking of coal and soft rock using stored energy of activated water. These techniques have not found wide use since they are applied in isolation from the common mining technologies, unsuitable for hard rock, have a cyclical character, and are performed manually with high capital and labor inputs.
One of the workable methods for transformation of water into explosive, i.e. to make a physical explosion for obtaining a super-high-speed flow of superheated or dissociated steam that able to break the rock inside the blastholes, is the heating of the water charges by the electric arc. A speed of water steam flow, heated up to 1000-7000 K and discharged from the Laval nozzle, can amount up to 1.5 - 7.5 km/sec [I. Zinger-Bredt. Some of properties of hydrogen and water steam – possible working medium for rockets. IIL, Moscow, 1962, p.20.].
Taking into account that in proposed technology blasts in holes are made with an interval of 0.5-1.0 min, the three variants of the problem solution are outlined:
- to carry out a rapid heating of water with the electric arc in open chamber with a nozzle by a quick high-power supply from the energy storage device, for example, pulse condenser;
- to carry out a relatively slow heating of water up to the specified temperatures and pressures in confined chamber equipped with a control valve which is opened at the specified moment for explosive release of working medium into the blastholes;
- combination of two mentioned variants.
For achievement of the project objectives, the following tasks should be solved:
- to study the processes and operations of the continuous hard rock mining with the aim to create technological and technical prerequisites for safe, maximum profitable, automated open pit mines with the continuous rock breaking in surface layer of the bench faces using water charges;
- to determine thermodynamic parameters of water during formation of charges, explosive transformation into superheated steam flows, movement of flows into the blastholes, and interaction of shock wave with the rock;
- to determine the optimum ratio between amount of energy, heating temperature of water charges, pressure, and mass flow of the working medium for controlled hard rock breaking without oversize;
- to develop a working prototype of the drill-and-blast planer for continuous hard rock breaking by water charges;
- to test the generator on rock with different strengths;
- to work out the requirements specification on the prototype drill-and-blast planer equipped with the blast generators.
Current conceptions of the mechanism of continuous hard rock breaking by blasting allow for a conclusion that simultaneous shock action of supersonic pulsed flows of dissociated steam on the blasthole walls will be equal or considerably greater than during blast of charges of oxygen and hydrogen under similar conditions and with the same consumption of the working medium.
Results of the comparative study of cost-effectiveness of traditional (cyclical) and new (continuous) technologies and systems for hard rock mining by blasting with 1) ammonium nitrate and diesel fuel, 2) hydrogen and oxygen, and 3) water, are presented in Tables 1-3.
Costs of hard rock mining for a single mine with a productivity of 0.75×106 m3 per year using traditional and new technologies are shown in Tables 1-3.
Effectiveness of continuous hard rock mining by blasting with water charges.
Technological and technical prerequisites for effective continuous hard rock mining by blasting with water charges.
Performed researches have shown that replacement of cyclical methods and systems by the continuous technology, which includes mining with high benches by continuous breaking of rock using the drill-and-blast planers, movement of the broken material under gravity to the toe of the bench, and loading on the belt conveyor without excavators, allows for reducing mining costs by 50%.
Reasons for the economy are as follows:
- fracturing of the rock by chipping, which requires 2.5-3 times less energy than during simultaneous, short-delay blasting of charges having a total weight ranging from several dozens to hundreds tons placed in deep, large diameter holes;
- less metal and energy consumption for the same volumes of broken material;
- replacement of conventional explosives and facilities by water and electric energy;
- exclusion of traditional equipment needed for mass blasting and reducing maintenance personnel by 50%;
- elimination of oversized material and secondary blasting;
- continuity of all production processes and possibility for full automation of all overburden and mining operations;
- as much as possible compliance with the environmental regulations, absence of release of blast gases containing nitric oxides hazardous to health and environment, elimination of negative seismic impact of mass blasting, increase of stability of benches and open-pit walls;
- minimization of waste and dilution as a result of preservation of natural structure of the deposits; possibility of selective excavation;
- when mining kimberlite deposits, size and clarity of diamonds are fully retained owing to the non-damaging technology of layer-by-layer excavation of diamond ores; whereas during mass blasting a considerable amount of large diamonds are broken and loss their quality.
Comparative analysis of cost-effectiveness of traditional (cyclical) and new (continuous) technologies and systems for hard rock mining by continuous blasting with charges of ammonium nitrate and diesel fuel, hydrogen and oxygen, and water.
Variant 1. Traditional cyclical mining technology for hard rock.
Initial data: face productivity - 0.75×106 m3 per year; type of open-pit mine - benching, by horizontal layers, bench height - 15 m; rock hardness according to Prof. M.M.Protodjakonov’s scale - 12; conditions for overburden mining - total preliminary destruction of rock mass by blasting; drilling of holes with a diameter of 160 - 185 mm, depth of 16-18 m by roller-cutter drilling rig; volume of broken rock per one blast - 300 m3; explosive - a mixture of 94% porous ammonium nitrate and 6% diesel oil; consumption of explosive per 1 m3 rock - 0.6 kg; oversize output - 5-12% of the total volume of blasted rock; oversize elimination procedure - repeated blasting with packaged explosives in holes or with laid-on charges; overburden is hauled to dumps by 5 trucks with a capacity of 55 tons; haulage distance - 1.0 km.
Face productivity and properties of overburden in Variants 2 and 3 are the same.
Variant 1. Traditional cyclical mining technology for hard rock
Variant 2. New, continuous mining technology for hard rock using drill-and-blast planer, re-loader, and belt conveyor; explosive – hydrogen and oxygen
Variant 3. New, continuous mining technology for overburden hard rock using drill-and-blast planer, reloader, and belt conveyor; explosive – water charges
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