Search

This work systematically quantifies groundwater's effect on the roof stability of underground openings in shallow coal mines and indirectly assesses the potential for sinkhole formation. A specific stratigraphy was analyzed where the opening instability can lead to sinkhole formation, given the geological conditions, the overburden stratigraphy, and the depth of the openings. The groundwater recharge was investigated as an individual rainfall infiltration (short-term) and as groundwater dynamics (long-term), representing the accumulation of infiltrated rainwater with time. In the latter case, two approaches were employed for the porewater pressure calculation: (a) phreatic line with hydrostatic conditions and (b) steady-state flow based on constant groundwater head on the vertical boundaries at the model's edges. The safety analysis was based on a simplified statics model relating the stability to the bending of the roof, and numerical analysis was employed for the stress analysis. The short-term safety remained unaffected as rainfall water accumulated on the aquitard to form perched water. The long-term safety deteriorated due to the increase of the tensile stresses in the roof of the underground openings with the rise of the groundwater table. The phreatic line approach is the most conservative, resulting in lower safety than steady-state flow. [ABSTRACT FROM AUTHOR]

The development of three-dimensional geological models has proven to be critical for conceptualizing complex subsurface environments. This is crucial for mining areas due to their various hazards and unstable conditions. Furthermore, three-dimensional (3D) models can be the initial step for the development of numerical models in order to support critical decisions and sustainable mining planning. This paper illustrates the results and the development phases of a 3D geological model within the boundaries of the Kardia lignite deposit in western Macedonia, Greece. It also highlights the usefulness of a Geographic Information System (GIS) methodology in the subsurface geological and hydrogeological analysis regarding the Underground Coal Gasification (UCG) methodology. In addition, the work focuses on the integrated geospatial framework that was developed to support the Coal-to-Liquids Supply Chain (CLSC) integration in unfavorable geological settings. A 3D subsurface geological model of the study area was developed to identify a suitable area for in situ coal conversion and UCG considering criteria related to specific coal thickness and depth. In this context, the suggested integrated geomodelling workflow can positively contribute to the implementation of conventional and innovative mining, saving time and reducing the cost to improve the quality of information needed to support decisions related to UCG implementation. [ABSTRACT FROM AUTHOR]

Mining operations can drastically affect the stability of nearby areas. A representative case for this has been the Mavropigi mine, a part of an open-pit lignite mining complex in northwestern Greece. Mavropigi is a vast excavation that has reached 150 m depth and has posed severe challenges and stability issues that caused problems in the area. In 2010, noteworthy surface tension cracks appeared near the excavation, leading to extensive monitoring and countermeasures, while various studies were conducted. The present work aims to revisit the case study of Mavropigi from a different than the previous perspectives. Previous studies were based only on continuum approaches, thus understating or ignoring the effect of discontinuities. Nevertheless, the area has an intense tectonic past and faults that interact with soil movements. In this work, advanced, discontinuous numerical modelling through the distinct element method was used to understand better the role of slope-fault interaction in the case study of Mavropigi and assess the faults' effect on the area's response. The results emphasised the influence of faults on ground movements. The fault's existence increases the impact of the mine operations on the surrounding area significantly and intensifies the possibility of structural damage in nearby constructions. The analysis confirms that the open-pit mine's effect on the surrounding area can be amplified under complex geological conditions, in this case, the presence of faults nearly parallel to the slope inclination. [ABSTRACT FROM AUTHOR]

Featured Application: This work has application in coal and lignite mining excavations and areas, especially during decarbonization and towards a post-coal and post-lignite era. Areas that hosted coal and lignite mines are now being reclaimed—often by installing renewable energy systems—and targets are being set to fulfill new energy principles in relation to energy production, harvesting, and storage. The appropriate and sustainable exploitation of these areas is directly related to their safety and stability. A new perspective is presented for evaluating the slope stability of coal and lignite mines due to rainfall. The case of Greek lignite mining areas is employed to illustrate the methodology. Initially, past climatic records of rainfall are documented and analyzed; rainfall intensity varies from light (0.8 mm/h) to heavy (up to 9 mm/h). Few extreme phenomena are documented, with the maximum intensity being 17 mm/h. Furthermore, climatic projections of future trends are performed with open-access tools to anticipate possible deviations from the baseline conditions. Although the mean temperature is expected to increase, projections show that the past rainfall range is not expected to change. Finally, the effect of rainfall infiltration on the stability of a typical open-pit lignite mining slope is investigated by finite element analysis. The precipitation range defined by the environmental analysis is used. The SF is practically constant for the lower rainfall intensities (0.8–2.2 mm/h). For the higher intensities of 6.4 mm/h, 9 mm/h, and 17 mm/h, the SF decrease is almost the same (from 2.08 to 1.9), with reduction rates of 8.3%, 8.9%, and 9.3%, respectively. The effect of the critical geotechnical properties—groundwater table depth, unsaturated zone properties, and soil permeability—is also examined for a complete evaluation. [ABSTRACT FROM AUTHOR]

Abstract: The energy balance of Greece is strongly dependent on imported oil. The rather late introduction of natural gas has increased the diversity of the energy mix while the share of renewable sources in primary energy supply still needs to increase according to the existing potential. Yet, Greece as one of the most of the EU developed countries encounters a serious task: the need to increase its electricity production of almost 5% per year but at the same time to reduce the CO2 emissions according with the National and International (20-20-20) regulations and allocation plans. Therefore reducing CO2 emissions has become a major priority for national government. In addition, from 2013, there will be the full implementation of the wholesale market in the European Trading Scheme (ETS) which is currently in the last stages of a transition phase.In Greece electricity is mainly generated from lignite, thus making the electricity sector one of the main contributors to GHG emissions with a level above 40% of the total country and higher than the corresponding average of the rest of the EU countries. The possible implementation of Carbon Capture and Storage (CCS) technologies would then become very decisive due to the large use of the lignite as fuel in the country electricity mix. CCS technology has the potential of increasing the flexibility on the achievement greenhouse gas emissions reduction by allowing to continue to use fossil fuels, which still guarantees feasibility in the energy sector. This work presents a roadmap with the modeling of the main technologies associated to the CCS and its implementation into the Greek energy system considering existing National and International Strategic energy plans under different scenarios. The implementation of CCS technologies would have a large influence on the national electrical power production, having the responsibility for large shares of the emissions reduction that can potentially achieved in this sector. For this purpose, TIMES (The Integrated MARKAL/EFOM System) has been chosen as the principal tool for building a techno-economic model of the Greek energy system and its possible evaluation over time (2040). [Copyright &y& Elsevier]

Abstract: The mobility of inorganic pollutants is of key concern for a range of industrial and engineering applications of fly ash produced during the combustion of lignite in power generation. This paper investigates the role that the geochemical features of lignite, the ash composition and the partitioning of elements during combustion play in determining leaching properties of lignite fired by-products. The work is based on surveys on three lignite-fired power plants in Greece. Calcium-rich ashes show a high abatement potential for SO2 and other gaseous pollutants. For most elements, the concentrations in the parent lignite and the ashes follow the same trend. Relative enrichments in Cd, Co, Cr, Cu, Mo, Ni, Pb, U, V, W, Zn fingerprint the regional and local geological settings of the lignite basins. The total and leachable concentrations of highly volatile elements are strongly influenced by the interaction with ubiquitous free lime. A broad array of elements is highly insoluble in alkaline ash, while a few oxyanionic-forming elements display substantial mobility. Their mode of occurrence in the parent lignite plays a primary role in the leaching of combustion ashes. The outcomes of this study may assist in addressing the impact of co-firing high ash or high Ca alternative fuels on the leaching properties of combustion by-products. [Copyright &y& Elsevier]

Abstract: The Achlada and Mavropigi lignite deposits in northern Greece provide the main coal source for the next generation of Greek power plants. A comparative characterization of these two lignite deposits is presented, covering the coal rank and the features of the maceral components, based on detailed coal petrography, and the mineralogical and geochemical features of the coals and their ashes, based on XRF and XRD analyses. The data are used to interpret the palaeoenvironments of the lignite beds, as well as factors that may affect their burnout behavior. Both deposits have a lignite C rank. The Mavropigi lignite is mainly a matrix lignite lithotype, whereas the Achlada deposit consists both of matrix and xylite-rich lithotypes. The Achlada lignite was formed in a fluviatile environment, mainly in the abandoned channels of a meandering river system during flooding periods; hence it is enriched in inorganic matter, with ash values >30wt.%. The Mavropigi lignite formed in a reed-marsh environment under limno-telmatic conditions, and displays ash values <30wt.%. The inorganic matter of the two deposits is different in composition due to the contrasting environments, and these differences should be taken into account in optimizing their utilization for power production. A preliminary assessment indicates that the Achlada lignite may have more favorable slagging and fouling properties than the Mavropigi lignite, although experimental studies are required for more solid conclusions to be reached. [ABSTRACT FROM AUTHOR]

Abstract: The mineralogy of five lignite layers and the associated roof, floor and intercalating strata has been analysed using low-temperature oxygen-plasma ashing and quantitative X-ray diffraction techniques. The lignite contains quartz, kaolinite, illite and smectite, and in some cases small proportions of feldspar, thought to represent mainly detrital minerals in the original peat deposits. One sample also contains crystalline calcium oxalates, with weddellite present in the raw lignite and whewellite in the low-temperature ash (LTA) of the same lignite sample. Minor proportions of gypsum are present in some of the raw lignite samples, possibly in part derived from precipitation of dissolved Ca and SO4 in the pore waters on drying. All the LTAs, however, contain much higher proportions of bassanite and/or gypsum compared to the other minerals present, consistent with production of calcium sulphate artefacts from interaction of abundant organically-associated Ca and S in the lignite during the plasma-ashing procedure. The inorganic strata are mainly carbonate rocks, consisting almost entirely of calcite with minor aragonite, small proportions of illite, traces of pyrite and in some cases siderite. Some non-carbonate rocks are also associated with the lignite seams; these are dominated by plagioclase feldspar and mica, along with illite, kaolinite and a relatively minor proportion of quartz. The mineral assemblages can be related to the palaeoenvironmental conditions under which the various sediments (including lignite) were deposited. Comparison of the mineral abundances in the samples to the chemical composition of the materials shows that the quantitative XRD technique provides results consistent with ash analysis data. Although abundant in the associated rocks, calcite does not occur in the lignite samples. While part of the relatively abundant Ca in the lignite occurs as either gypsum or weddellite, most of it appears to be organically-bound. Mine products that incorporate calcareous rocks of the type associated with the lignite may, however, contain separate calcite phases and display high carbonate CO2 contents. [Copyright &y& Elsevier]

Abstract: The chemical and mineralogical composition of fly ash samples collected from laboratory scale circulating fluidised bed (CFB) combustion facility have been investigated. Three fly ashes were collected from the second cyclone in a 50kW laboratory scale boiler, after the combustion of different solid fuels. Characterisation of the fly ash samples was conducted by means of X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Quantitative analysis of the crystalline (mineral) and amorphous phases in each ash sample was carried out using the Rietveld-based Siroquant system, with an added spike of ZnO to evaluate the amorphous content. SiO2 is the dominant oxide in the fly ashes, with CaO, Al2O3 and Fe2O3 also present in significant proportions. XRD results show that all three fly ashes contain quartz, anhydrite, hematite, illite and amorphous phases. The minerals calcite, feldspar, lime and periclase are present in ashes derived from Polish coal and/or woodchips. Ash from FBC combustion of a Greek lignite contains abundant illite, whereas illite is present only in minor proportions in the other ash samples. [Copyright &y& Elsevier]

This paper presents a roadmap performed in 2010 as part of a European project for the modelling of carbon capture and storage technology, and various scenarios with different taxations and permit prices for the CO2 emissions considering the Greek national plans, then the gradual decommissioning of various lignite or other units of electricity power plants. In addition, this study presents a first check, 10 years after its writing, of the current situation of the Greek energy system, regarding the correspondence of the roadmap designed in 2010 to what has been finally executed during this period, including the possibility of other energy sources complimenting or substituting the national strategic energy plans. For this purpose, the integrated MARKAL-EFOM system (TIMES) was employed to model the Greek energy system and evaluate its development over time, until 2040, by analyzing three different scenarios with respect to taxation and permit prices for carbon emissions. The results obtained show that, if this study had been considered and executed by the different stakeholders during that period, then the implementation of CCS in the new licensed power plants from 2010 and onwards could reduce the use of lignite and imported hard coal power production in a much smoother and beneficial way in the next years, and until the present, without compromising any major power plants. This implementation would also make the transition to a lignite free economy in Greece much faster and better, while complimenting the EU regulations and also enhancing the possible greater use of alternative energy sources in the green energy mixture. [ABSTRACT FROM AUTHOR]

Abstract: The chemical and mineralogical composition of fly ash samples collected from different parts of a laboratory and a pilot scale CFB facility has been investigated. The fabric filter and the second cyclone of the two facilities were chosen as sampling points. The fuels used were Greek lignite (from the Florina basin), Polish coal and wood chips. Characterization of the fly ash samples was conducted by means of X-ray fluorescence (XRF), inductive coupled plasma-optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), particle size distribution (PSD) and X-ray diffraction (XRD). According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, SiO2 is the dominant oxide in fly ash with Al2O3 and Fe2O3 found in considerable quantities. Results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite. The ICP-OES analysis showed rather low levels of trace elements, especially for As and Cr, in many of the ashes included in this study compared to coal ash from fluidised bed combustion in general. [Copyright &y& Elsevier]

Abstract: Diatomite with variable chemical and mineralogical composition occurs in the Komnina Lignite Basin. The diatomite layers, which overly lignite seams of Upper Miocene age, are rich in silica or calcium. These layers correspond respectively to quartz-rich and calcite-rich layers. The diatomite mainly consists of opal-A, while other minerals are quartz, feldspars, calcite, smectite, illite, kaolinite, chlorite, cristobalite, and muscovite. The well-preserved nature of the diatom species indicates a weak silica diagenesis. This is also indicated by the mineralogical composition of diatomite, especially the absence of opal-CT. The organic material present in the lake acted as coating and prevented diatom dissolution. The shallow lake, where the diatoms were deposited, did not allow diagenesis of diatomite. Diatoms were deposited in the Komnina Lake as a result of the acidic pH, the warm-humid conditions, and the silica-rich environment that occurred due to volcanic activity in the nearby area (Aridea). Remains of volcanic ash have been identified in the lignite deposits of the wider Ptolemais area. The association of diatomite with lignite was brought about by tectonic movements that occurred in the wider area of Monastir–Florina–Ptolemais–Kozani–Elassona–Sarantaporo in the Upper Miocene, resulting to the development of individual small shallow lakes. The paleoenvironment changed to acidic from the previous alkaline pH, the vegetation died off, the silica produced from the volcanic activity and the calm water conditions allowed the deposition of diatoms. [Copyright &y& Elsevier]

In many circles, brown coal continues to be viewed as a cheap source of energy, resulting in numerous investments in new opencast brown coal mines. Such a perception of brown coal energy is only possible if the external costs associated with mining and burning coal are not considered. In past studies, external cost analysis has focused on the external costs of coal burning and associated emissions. This paper focuses on the extraction phase and assesses the external costs to agriculture associated with the resulting depression cone. This paper discusses the difficulties researchers face in estimating agricultural losses resulting from the development of a depression cone due to opencast mineral extraction. In the case of brown coal, the impacts are of a geological, natural-climatic, agricultural-productive, temporal, and spatial nature and result from a multiplicity of interacting factors. Then, a methodology for counting external costs in crop production was proposed. The next section estimates the external costs of crop production arising from the operation of opencast mines in the Konin-Turek brown coal field, which is located in central Poland. The analyses conducted showed a large decrease in grain and potato yields and no effect of the depression cone on sugar beet levels. Including the estimated external costs in the cost of producing electricity from mined brown coal would significantly worsen the profitability of that production. [ABSTRACT FROM AUTHOR]

Surface lignite mines of the Balkan Peninsula face growing pressure due to the CO2 emissions reduction initiatives, rapidly increasing renewable-power capacity, and cheap natural gas. In this frame, the development of a modern mine land rehabilitation strategy is considered as a prerequisite for mitigating the social and economic impacts for the local communities. In the case of western Macedonia lignite mines, these prospects are investigated based on a PEST (political, economic, social, technological) analysis of seven alternative land uses. Urban (industrial) development, green houses, and industrial heritage parks are considered as the most appropriate land uses for mitigating the socioeconomic impacts due to the loss of employments. For the land uses occupying large areas (i.e., agriculture, forestry, livestock farming, and photovoltaic parks), an optimisation algorithm is proposed for determining the mix of land uses that maximise revenue, equity, and natural conservation and minimise investment. The algorithm was applied using the opinions of 10 experts, who were involved in mine land reclamation projects carried out in the western Macedonia region in the recent past. According to the results obtained, photovoltaic parks are rated as a more attractive investment than extensive agriculture, as regards the anticipation of revenues, while livestock farming and forests are necessary to safeguard the ecosystem's functions. [ABSTRACT FROM AUTHOR]

Weather and climate are parameters vital for the development and flourish of human activities, and they crucially affect mining activities. Coal and lignite (brown coal) mining operations can be aided by appropriate weather or stopped by an extreme weather event that might have catastrophic consequences for a mining area. The same stands for closed and abandoned coal mines, as extreme weather events can have severe consequences. This work aims to obtain a comprehensive overview of the climatic conditions by documenting and reporting them in various European coal and lignite mining regions. Specifically, the chosen regions cover Europe from the north (the United Kingdom) to the south (Greece), from the east (Poland, the Czech Republic) to the west (Spain), and through Europe's center (Germany). A climate baseline is created for the chosen regions to serve as a reference for safety assessment and for evaluating future climate changes. Initially, the general climate of each region was evaluated; additionally, an extensive climate database from 1990 to 2020 was created, including the mean annual temperature and precipitation. Mean values and general trends of increase or decrease during the last 30 years are of interest and were compared for all areas. [ABSTRACT FROM AUTHOR]

Fly ash from two lignite-fed power stations in Greece (Megalopolis and Meliti) has been utilized to synthesize zeolitic materials with upgraded adsorption capacity. Two different siliceous fly ash samples were subjected to hydrothermal treatment at fixed solid/liquid ratio and constant temperature. The zeolitic products have been characterized for their microstructure, chemical, and mineralogical composition by means of SEM, AAS, and XRD, respectively. The primary zeolitic crystals identified were phillipsite and thomsonite, in Megalopolis and Meliti fly ash, respectively. In light of their prospective utilization as liquid-phase sorbents, the specific surface area and porosity of materials were also determined, by means of N 2 -porosimetry. The zeolitic samples were tested for their actual heavy metal-removal capacity by water sampled from active lignite mines in Northern Greece. Artificial aquatic samples with known concentration of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) were also tested, showing that the synthetic zeolitic materials are good to uptake a wide variety of potential pollutants with up to 100% efficiency. The efficiency of the synthetic zeolitic materials was comparatively assessed, showing that the more intense the presence of phillipsite in the synthetic materials, the greater the uptake rates for certain groups of trace elements. [ABSTRACT FROM AUTHOR]

Abstract: The chemical and mineralogical composition of lignite fly ash (FA) varies as a function of the prevalent conditions in both the processes of power production and lignite mining. The differentiation of the qualitative and quantitative composition of the highly-calcareous lignite fly ash, as a function of its particle size distribution, is verified in this paper. According to the results of the conducted research, a fine-grained fraction of considerable amount presents properties that obstruct the sustainable exploitation of calcareous lignite fly ash in cement industry applications. On the other hand, the same grain fraction (because of its hydraulic properties) can be utilized in other sort of applications, based on different criteria, i.e. in road constructions. The coarse-grained fraction (which reflects a low proportion to the total fly ash output) presents the same undesired characteristics as well. Rather, the intermediate grain fraction (75–150μm) presents the highly desirable properties when fly ash is utilized as a pozzolanic additive. In addition, the mechanism of the formation of the intermediate grain fraction strongly prevents the factors that cause the variation of fly ash-quality. It is therefore the optimum part of the whole amount of lignite FA, to be utilized as additive in cement manufacturing. The outcomes of this paper will hopefully contribute towards the crucial goal of the expansion of the utilization of calcareous lignite fly ash by proposing a more effective way of using this material, basically by taking advantage of its fundamental chemical and mineralogical properties. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, two Class C, lignite fly ashes (FAs) were utilized for the fabrication of Al/fly ash metal matrix composites (MMCs) using the powder metallurgy (PM) technique. Aluminum–fly ash and aluminum/silicon alloy (Al–12% Si)–fly ash mixtures, containing 5, 10 and 15wt.% of – both pozzolanic and hydraulic – FAs were prepared and compacted. The green products were tested for their thermal behavior in order for the sintering temperature to be determined. Then, they were sintered for 2 and 6h. The density of composites was decreasing with the increase of the percentage participation of fly ash particles into them. Apart from that, although FA clusters had been developing in the metal matrix, there was a significant enhancement in the hardness of MMCs when increasing FA content, which is mainly attributed to the intense calcareous nature of the reinforcement material. Volume and mass changes throughout calcination were also estimated as a function of increasing FA weight percent and it seems that CaO (%) of FAs plays a crucial role regarding the post-sintering raise in the mass and volume of composites. Microscopic studies of green and sintered compacts clearly indicated the effectiveness of the sintering process. Additionally, the composites were characterized in terms of their chemical composition and mineralogical structure. The rise of Ca–Si- and Si-mineral phases is intense, particularly for the composites with the highest percentage presence of CaO in FAs (15wt.%) and does not differentiate as a function of the sintering time. [Copyright &y& Elsevier]