Using microwaves to break up rock saves energy

In a project funded by the austrian Science Fund FWF, a research group from Leoben investigated how mining methods for hard rock could be improved by using microwave irradiation so as to make classical mechanical excavation easier and save energy.

The excavation of hard rock such as granite is a serve that consumes a big batch of time and energy, whether it be in mining or in tunneling. several steps are necessity. First of all, cracks are created in covenant rock candy to make it break up into individual pieces that can then be excavated and removed. In the history of mine, this first gradation was frequently carried out with the assistant of arouse – because inflame cracks the rock. An interdisciplinary project of the Chairs for Mechanics, Physics and Mining Engineering at the ‘Montanuniversität Leoben ‘ ( Leoben University of Mining Sciences ) investigated a mod version of that scheme, using microwaves to heat the rock .
“ All conventional excavation methods have one thing in common : you first base want to break the rock, i.e. create more surfaces, but entirely a small separate of the energy in truth goes into that fragmentation. The lion ‘s share is lost in the form of heat, ” says principal detective Thomas Antretter from the Institute of Mechanics at the Montanuniversität. Currently, the rock candy is either blasted or fragmented mechanically with heavy machinery and then excavated. “ This is a giant star barren of energy. We do not want to replace mechanical excavation completely, that would be impossible. But we can make it easier, ” says Antretter.

25 times stronger than a microwave oven
The fact that microwaves can be used to warm up food is well known. It is less obvious, however, that microwaves can besides be used to heat up rock candy. “ You could actually put a piece of rock in a microwave oven and it would become warm, ” explains Antretter. “ In ordain to create real cracks, however, you need a great distribute more energy. ” For the practice tests, they used a microwave unit with an output of 25 kW, which is about 25 times the energy produced by a microwave oven. Applied by means of a device that looks like a hosiery, the microwaves are channeled through this excavate conductor .
Antretter ‘s group was responsible for the computer simulations. “ The simulations were quite comprehensive examination, because first we had to compute the electromagnetic processes, the radiotherapy and propagation of electromagnetic waves, and then we had to conclude from these computations how the granite would heat up. ”

Antretter was particularly concerned in granite because of the difficulties it entails in excavation due to its severity. Granite consists of feldspar, quartz glass and mica. “ These minerals have different properties and heat up to different degrees. apart from that, they besides differ in their electrical properties, meaning that they absorb microwaves differently. ” This besides had to be computed anterior to the experiments .
“ The results for office waste were then used to compute the mechanical aspects, ” explains Antretter. “ In order to do that, we needed to calculate how the temperature is going to develop in the rock over time. Based on that, we can compute the mechanical strains and stresses, again as a routine of meter. ” The results were compared with the critical tension levels for the individual components of the rock in order to find out when the rock would break and produce the craved cracks .
Short pulses more effective

Thomas Antretter ‘s team simulated inadequate, intense pulses lasting only one-tenth of a second and compared them with longer pulses of lower intensity that lasted 100 seconds. The department of energy output was the same in both cases. “ In the simulations, the short pulses showed a little more effect with the same amount of energy, ” reports Antretter. In parallel, tests were made at the neighbouring Chair of Mining Engineering, where the researchers have access to a microwave unit. “ There, they actually irradiated rock samples under different conditions and for different lengths of clock time. It turned out that you can create ace patterns and that they will correlate well with the results of our model. ”
The idea of using microwaves to break up rock has been around for some time, recalls principal detective Antretter. “ But one could never quantify the effect precisely, the tests were done on a trial and error basis. And so they forgot about it again. ”
There are a number of open questions concerning execution in practice, such as open fire safety issues. “ But from a strictly technical point of view, there is nothing that prevents implementation, ” says Antretter .
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More information:
Michael Toifl et al. Numerical study of the influence of irradiation parameters on the microwave-induced stresses in granite, Minerals Engineering (2016). Michael Toifl et aluminum. Numerical study of the influence of radiotherapy parameters on the microwave-induced stresses in granite, ( 2016 ). department of the interior : 10.1016/j.mineng.2016.09.011 R. Meisels et alabama. Microwave propagation and absorption and its thermo-mechanical consequences in heterogenous rocks, International Journal of Mineral Processing ( 2015 ). department of the interior : 10.1016/j.minpro.2015.01.003
Michael Toifl et alabama. 3D numerical discipline on microwave induced stresses in inhomogeneous hard rocks, Minerals Engineering ( 2016 ). department of the interior : 10.1016/j.mineng.2016.01.001

P. Hartlieb et aluminum. Thermo-physical properties of selected hard rocks and their relation back to microwave-assisted comminution, Minerals Engineering ( 2015 ). department of the interior : 10.1016/j.mineng.2015.11.008 Citation : Using microwaves to break up rock saves energy ( 2017, August 21 ) retrieved 9 May 2022 from hypertext transfer protocol : //
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