Vol. 15, Issue 1 (Jan-June 2005)

Abstracts

• Konstantinos G. Tsakalakis (National Technical University of Athens, School of Mining and Metallurgical Engineering, GR-157 80 Zographos, Athens, Greece), Ioannis E. Ioakim (Public Power Corporation (PPC) SA, Western Macedonia Lignite Center, GR-502 00 Ptolemaïs, Greece): "Power generation methods using conventional fossil fuels." Mining & Metallurgical Annals, vol. 15, no. 1, Jan-June 2005, pp. 15-44.

This paper deals with (a) the combustion of the conventional fossil fuels, (b) the methods of power and electricity generation, and (c) the carbon intensity of the fossil fuels using their higher and lower heating values (HHV, LHV). The above issues allow for the calculation of gas and air-particulate emissions to the environment from the power generation processes.

In addition, the conventional procedure for power generation is here examined and the modern methods of energy production, such as the methods of the combined cycle and the combined heat and power (cogeneration), are also briefly presented. These new methods contribute significantly to the reduction of the gas and solid emissions and to the reduction of the consumption of non-renewable fossil fuels.

The gas emissions and the fuel consumption per unit of energy produced can also be calculated using suitable diagrams and equations, which are given herein.

Finally, some simple examples referring to the Greek lignite are also presented. In these examples, the method for the elaboration of the mass and energy balances, in a typical lignite-fired power plant, is extensively described. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2005.

• Christos Roumpos (Public Power Corporation (PPC) of Greece SA, Mines Engineering and Development Department, GR-104 43 Athens, Greece): "Optimisation of the combined project of a lignite mine exploitation and power plant operation." Mining & Metallurgical Annals, vol. 15, no. 1, Jan-June 2005, pp. 45-64.

The optimisation of the combined project of a lignite mine exploitation and a power plant operation is related to the respective power plant capacity and, consequently, to the mine production rate. Based on the economic measure of the project viability expressed by the Net Present Value of the project cash flow, a mathematical optimisation model has been developed. The effect of basic parameters of the model in the power plant optimal capacity is then investigated. From the mathematical analysis, it is concluded that the deposit reserves have a particular effect on the selection of an optimal power plant capacity. Suitable application of the model allows for the programming and evaluation of the lignite deposit exploration, as well as for the selection of mining equipment. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2005.

• Andreas G. Benardos (National Technical University of Athens, School of Mining and Metallurgical Engineering, GR-157 80 Zographos, Athens, Greece), Panagiotis G. Benardos (National Technical University of Athens, School of Mechanical Engineering, GR-157 80 Zographos, Athens, Greece): "Application of artificial neural networks in rock engineering." Mining & Metallurgical Annals, vol. 15, no. 1, Jan-June 2005, pp. 65-81.

The development of models that will efficiently simulate the mechanisms that govern the rock mass or rock behaviour and their interaction with the various construction activities, has always been one of the ultimate goals of many researchers. The introduction of artificial intelligence techniques as that of artificial neural networks (ANN) can further enhance the analysis effectiveness especially in Rock Engineering and Rock Mechanics applications. This paper gives an insight review regarding ANN development. Furthermore, it presents a case study regarding the modelling of TBMs penetration rate with respect to the geological and geotechnical conditions, as well as the machine characteristics by the use of trained neural networks. It is finally proved that the ANNs generalisation produced precise estimation of the penetration rate, with accuracy levels that are even higher than the ones obtained using conventional prediction models. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2005.

• Georgios Alevizos and Michael Galetakis (Technical University of Crete, Department of Mineral Resources Engineering, GR-731 00 Chania, Crete, Greece): "Mineralogical study of anhydrite-gypsum occurence in the area of Vathi at Western Crete - Quality variation and mining particularities." Mining & Metallurgical Annals, vol. 15, no. 1, Jan-June 2005, pp. 83-102.

Anhydrite-gypsum deposits occur in several locations on the island of Crete. The most important of them, from an economical point of view, are located in the area of Altsi in Eastern Crete and in the area of Sougia and Stomio in Western Crete. The deposit of Stomio, that is investigated in this study, is the biggest gypsum-anhydrite deposit of Crete with total proven reserves of more than 100 million tons of anhydrite and 10 million tons of gypsum. The gypsum-anhydrite deposit of Stomio belongs to phyllite nape, which is the first allochthonous unit over the autochthonous crystalline limestones, known as Platten-Kalk. The phyllite nape consists of a Gypsum-Rauhwacke formation and a phyllite-quartzite series.

The deposit is exploited occasionally by small scale quarrying operations. A plant for gypsum preparation and calcination is operating in the area. The main problems concerning the exploitation of the deposit are closely related to the varying quality of the extracted material. For a preliminary quality assessment of the deposit, samples were collected from different heights of a working quarry face. Samples were described macroscopically and analysed for their mineralogical composition using polarised microscopy, X-ray diffraction and differential thermal analysis methods. Their chemical composition was also determined by X-ray fluorescence.

Microscopic examination combined with mineralogical and chemical analysis results have shown that gypsum formation possibly occurred from the hydration of anhydrite, when it was uplifted and exposed to meteoric or ground water. More specifically, the analytical results indicate that:

• Samples collected from the top of the face, near the contact with the upper dolomite formation, consist mainly of well-formed gypsum crystals and rarely gypsum crystals with anhydrite relics. Dolomite is also present as minor mineral. The gypsum concentration exceeds [U1] 85%.
• Samples collected from the middle of the face, consist mainly of anhydrite crystals with gypsum relics. Dolomite is present as minor minerals. Samples contain more than 53% anhydrite.
• Samples collected from the bottom of the face consist mainly of anhydrite crystals. Gypsum crystals with anhydrite relics and dolomite are also present as minor minerals. Samples contain more than 87% anhydrite. Mineral in traces, like quartz, muscovite and magnesite were determined by XRD analysis.

Based on the analytical results, the upper part of the deposit can be characterized as high grade gypsum that could be excavated selectively and used in the building industry. The middle part of the deposit (low grade gypsum) could be used in the cement industry. Finally the remaining deposit consists of anhydrite and must be examined for potential uses in the chemical industry. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2005.

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