This paper attempts to use analogs of coals and Coal bed Methane (CBM) properties in Sedimentary basins to mutual advantage from the knowledge of each other.
An attempt has been made here to showcase as to why two Coal bearing formations, Lower Eocene, Cambay in India and Miocene, South Sumatra, Indonesia can be compared with each other in terms of coal quality and CBM characteristics.
Cambay basin, with an area of 56,000 sq kms is an elongated NNW-SSE rift basin in the western part of India. The basin fill comprises Mesozoic(?) sediments capped by Late Cretaceous Deccan volcanics and a thick tertiary pile of fluvio deltaics. Thick Lignite to sub bituminous coal is found in Middle (two thick seams) and Lower Eocene section (three thick seams of 20-35 m range and one thin seam of 1-10m). Chemically, the Middle Eocene lignite-sub bituminous coal is characteristically low in moisture (4-5%), quite low in ash (1-11%) and high in volatiles (43-55%). The Lower Eocene coals are sub bituminous with 10-20% moisture, low ash(5-10%), low Sulphur(<1%) content. The gas content of the Lower Eocene coals are 6 cubic metre / tonnne, with permeability 1-3 Md with seams slightly over pressured. Depth ranges of both these coal horizons are between1000-1800m approximately.
South Sumatra basin, double in size wrt Cambay basin with an area of 100,000 sq kms, is a NE-SW trending, backarc basin. Series of half grabens punctuated with basement highs, holds Miocene and Eocene Coals in the grabens of a mostly Tertiary sedimentary pile. The Miocene coals (formed in tide dominated coastal plain) are sub bituminous, with VRo 0.4-0.5, low ash(<10%), Moisture(10-18%), high volatile matter of around 40% at depths 300-1000m, with 20-30 seams with gas content of 7 cubic metre / tonne. The Older Eocene Coals are1-10 m thick at depths 1000-2000m formed in peat bogs in fluvial settings.
The Indonesian Coals of Miocene age are very comparable in coal properties and gas content to the Middle and Lower Eocene Coals of Cambay basin and can supplement each other in studies for CBM exploration and exploitation. Of great similarity are the coal quality, ash% and gas content. To take the comparisons further ahead, detailing of thickness, extent, geometry and depositional environments of each of these basins would be advantageous.
Ground control condition is one of the most important issues in mechanized longwall mining. The Alpu lignite field in Turkey presents a challenging situation because of its thick, weak and clay content surrounding strata. The purpose of this study is to figure out the ground control condition of the study area by the following steps: classification of the geotechnical units, rock mass classification, cavability index, required shield capacity and floor bearing capacity. Geotechnical classification of the strata layers and rock mass classification was determined by the lithology of the boreholes and laboratory test analyses of them. Caving behavior of the roof strata was predicted by the polish scientists method. Then by applying the “US National Institute for Occupational Safety and Health (NIOSH)” roof rating system at possible roof strata, results were compared. Roof strata were classified as “immediately caving” strata in all production alternatives. Required shield capacity was estimated by detached block method. The caving height was calculated based on the bulking factor of the lignite and roof strata. Low strength floor strata act as a limitation to mining height increasing in all production alternative. Possible mining height was determined as five and six meters with the LTCC method. Required shield capacity in each production alternative was raised by increasing cutting height. To avoid failure during the production, supports should be advance with pressure by touching the roof and soon after the cutting. In addition, cutting height should be limited to the critical height.
Since the 1980; longwall mining has become rival to many surface mining operation performances by achieving more safety, high production and most productive in underground coal mining (Galvin, 2016). The longwall mining method is preferred for stratiform and flat lying orebody and orebody dip needed to be less than 20°. Under the hydraulic roof support, coal is cut with shearer and the broken cut coal is loaded by armored face conveyor (AFC) to the belt conveyor which is parallel to the face advance (Brady and Brown, 1985).
Longwall top coal caving (LTCC) is a comparatively new method for mining thick coal seams. LTCC currently has reached high production and efficiency in longwall mining mostly in China. The procedure is almost the same as the traditional longwall mining method. The Shearer cuts coal seam from the lower section of it onto AFC that installed near the cutting face and in front of the hydraulic support. A rear conveyor belt is added behind the support in the modern LTCC, so the caved coal in the upper part of the seam can flow to the rear conveyor from the canal which is controlled by the rear canopy of the support (Alehossein and Poulsen, 2010). A schematic model of the top coal caving method is illustrated in Fig. 1.
Historically, invert-emulsion drilling fluids (IEFs) require organophilic clays to provide viscosity and suspension characteristics. While effective, these chemicals are prone to stratification in certain conditions, slow chemical-reaction times, high pressure spikes, and high equivalent circulating densities (ECDs). This paper describes the first application of clay-free IEFs in the Norwegian continental shelf (NCS), with an emphasis on an impressively low and consistent ECD contribution. Further, a treatment was developed to allow the IEFs to be used to drill into a section exhibiting temperatures greater than 160 C. IEFs have been used in the NCS for almost 50 years. These systems commonly use organophilic clays and lignites as their primary viscosifiying and filtration-control agents.
ABSTRACT: Fully understand the microstructures and the rock mechanical property are extremely important for the coal seam characterization, explorations, coal bed methane (CBM), enhanced coal bed methane (ECBM), and CO2 storage. However, how the different coal rank relate to the microstructure and rock mechanical property are still in-sufficient. Thus, in this study, we conducted the 3D high resolution microCT scanning (3.43 μιη voxel sizes) and nanoindentation test on high to low rank coals - anthracite, bituminous, sub-bituminous, lignite, and peat. The coal microstructure are quantified after the image segmentation process which show the low rank coal has the most abundant pore system (including large pores and tiny pores) and high rank coal has the more fixed carbon content. Furthermore, the coal indentation modules decreased from high to low rank coal, we thus suggested the safety issues for the low rank coal seam should be in priority concern.
The typically rock mechanical tests are always centimeter to meter scale, such as UCS, triaxial and acoustic test. However, the un-homogeneous rock such as coal always has heterogeneous morphology and results the mechanical properties are also heterogeneous even in micro / nano scale (Roshan et al., 2017). Thus the small scale rock mechanical properties are extremely important, particularly for the multiscale fracturing mechanism analysis and modelling. The nanoscale mechanical properties nowadays can be obtained by the newly nanoindentation test, which has been successfully applied to natural reservoir rocks in earth science such as sandstone (Zhu et al., 2009), limestone (Lebedev et al., 2014; Zhang et al., 2018a; Zhang et al., 2016a), shale (Kumar et al., 2012; Liu et al., 2018), and coal (Zhang et al., 2018b; Zhang et al., 2018c). However, there is still blank about how such small scale mechanical property correlate with the coal's rank and the related anisotropy.
In this paper, we thus conducted the nanoindentation tests on the different rank coal samples (anthracite, bituminous, sub-bituminous, lignite, and peat) and discussed how the morphology (microCT) based on coal ranks was correlated to the obtained rock mechanical property.
Utilization of coal reserves in the protection area of the coal mine gives the possibility of unusual mining methods. Just use methods room pillar in lignite coal mining is quite unusual opportunity. Application of the room pillar method can become very beneficial to the place where it can be somehow limited extraction using longwall face. This method is respectful of the overburden and excavated areas stay stable. The paper deals with the issue of stability and stabilization of coal pillars by using rockbolt support. The problem with this method is currently designing pillars so as to sufficiently handle pass the load.
Coal mining under the end slopes of surface lignite mines is becoming quite an important topic especially in areas where coal mining is slowly finishing up. The first experience with the method of pillar mining was acquired in the North Bohemian ČSA Mine, where this method was tested for mining in protected zones. This method is based on the room-and pillar mining method, where the principle is driving parallel galleries, while pillars that ensure stability are left between galleries. Therefore, it is not the case of caving mining, but the pillars remain stable even after the excavation. This brings a number of problems that must be solved. These include the size of galleries, which is partly influenced by mining mechanisms (milling machines), as well as the stability of the pillars, which depends on the strength of coal, thickness and the properties of the overlying rocks, but also the dimensions of the pillars. The advantage of this method is continuous extraction while the stability of the extracted space is ensured.
To ensure the long-term stability of the mine excavations, they must be secured (stabilized) by means of supports. Due to the right-angled profile of the working and the applied technology of driving using road headers, separate roof bolting in combination with welded meshes is used to ensure the stability.
The applied methods of dimensioning separate roof bolting as well as the methods of calculating the stable pillars between the mining galleries are mostly based on empirical and empirical-analytic procedures based on knowledge and in-situ measurements. The method of pillar mining and separate roof bolting has not been applied yet in the conditions of this lignite deposit, therefore, the results of in situ measurements are not available, either. For that reason, we adjusted the results of general analytical and empirical methods for determining the minimum parameters of roof bolting to the results of mathematical modelling [1, 2].
The paper presents geotechnical engineering studies for the design of a new lignite open-pit mine in central Poland. The lignite deposit occur in a deep tectonic rift formed in Mesozoic rock characterized by complex geological conditions. The rift is approximately 10 km long, 1 km wide and 50-250 m deep and filled with Neogene and Quaternary sediments. The design of the open-pit mine required geotechnical analysis to reveal possible problems that may occur during its construction and operation. The author of this paper had opportunity to perform slope stability studies and geotechnical analyses within the project conducted by Poltegor-Institute. The calculation procedure enabled determination of slope stability on the design of excavation and spoil dump. It included 21 analyses using Flac v.7 of which 14 regarded the slopes of the pit, 6 the slopes of the external spoil dump and one covered both areas. The results indicated that the factor of safety Fs ranges 0.75-1.65 for the pit and 1.12-1.60 for the dump. In risk areas slope inclination were lowered due to likelihood of developing of landslide processes. These included spoil dump area close to S-8 road. Due to relatively limited geotechnical data in same areas especially on northern slope and western part of spoil dump detailed geotechnical investigations will be necessary. The instability problems can be caused by the groundwater conditions and the presence of high compressibility organic peats in the spoil dump bedrock layers. Comprehensive identification and monitoring of geotechnical risks for the mine slopes and storage of overburden should be a continuous process. This activity should start from the beginning stages of construction and should be conducted also during exploration and continuing to mine final reclamation to reduce potential natural hazard impact on mining and the natural environment.
Lignite opencast mining has a significant contribution to the production of electricity in a number of European countries. Germany, Greece, Poland, Czech Republic, Bulgaria and Romania, produce approx. 96% of lignite in the European Union, a total of 433.8 mln t [4, 11]. In Poland 30% of electricity is produced from brown coal and it is one of the cheapest sources of energy. Over 45 billion tons of lignite was documented in Poland till this time. Till now only 2.6 billion were mined. Some of the older lignite mines will end the current deposits in the near future. The largest Belchatow mine will end production in 2038, the Turow mine a few years later. The plans to build a new coal mines were not finally decided but it requires in advance detailed recognition of geotechnical engineering conditions. Lignite mining in Poland, due to high, 200–300 m exploitation depth is often associated with geohazards. In the paper slope stability analyses for the design of a new mine in Zloczew are described. The preliminary design project of this mine was realized in 2014 by Poltegor-Institute . The exploitation of lignite layers in a deep tectonic rift will require mining of large volume of limestone and marl rocks located on the south slope. The geotechnical engineering part of the design focused on description of potential geohazards. Paleolandslide deposits located on the South slope and low strength clayey soils on the North slope could pose slope stability problems during the coal exploitation. Others geotechnical problems could be connected with storage of large masses of overburden on the external spoil dump. Complex geological structure, rainfalls, changes in groundwater levels, seismic shocks and karsts processes could influence stability of slopes . In the paper, conclusions connected with these problems together with the results of analysis are presented.
Alam, A. K. M. Badrul (Horonobe Research Institute for the Subsurface Environment, NOASTEC) | Aramaki, Noritaka (Hokkaido University) | Tamamura, Shuji (Horonobe Research Institute for the Subsurface Environment, NOASTEC) | Ueno, Akio (Horonobe Research Institute for the Subsurface Environment, NOASTEC) | Murakami, Takuma (Horonobe Research Institute for the Subsurface Environment, NOASTEC) | Fujii, Yoshiaki (Hokkaido University) | Kaneko, Katsuhiko (Horonobe Research Institute for the Subsurface Environment, NOASTEC)
Oxidation of lignite with H2O2 solution to produce dissolved organic carbon (DOC) for generating biomethane by methanogen cultivation is an important stage of subsurface cultivation and gasification methods. To obtain more insights into this process, changes of lignite mechanical properties were investigated after its oxidation to produce DOC. Core specimens 30 mm in diameter and 60 mm in height were immersed into 1 wt.% H2O2 to achieve a liquid-to-solid ratio of 5:1. Values of pH and Eh were measured at arbitrary time intervals together with concentrations of H2O2 and DOC. P-wave velocity and density were measured before and after immersion. A series of uniaxial compression tests was carried out for both chemically reacted (H2O2-immersed) and non-reacted (H2O-immersed) specimens. The concentration of DOC, which is the substrate of methanogen cultivation, increased due to the oxidation of lignite at decreased pH by H2O2. P-wave velocity showed positive correlations with strength, static tangent modulus, and dynamic Young’s modulus. The average P-wave velocity (Vp) decreased by about 1.5% from its initial value due to the average density decrease of 0.6% resulting from the above chemical reaction. This decrease was associated with microcracking caused by swelling and grain boundary change due to leaching. The influence of the above chemical reaction on the mechanical properties of lignite is small, despite the formation of DOC to produce biogenic methane.
Lignite seams of the Tenpoku coal field in Hokkaido, Japan, are considered to be used for biomethane production by subsurface cultivation and gasification (SCG, Aramaki et al., 2015; Tamamura et al., 2016), with the formation of dissolved organic carbon (DOC) from lignite by induced oxidation using hydrogen peroxide (H2O2) being the first stage of this method. Subsequent stages feature methanogen cultivation to produce biomethane, using the DOC as a substrate, and the last stage corresponds to gas recovery. The formation of DOC for methanogen cultivation via chemical reactions can change the mechanical properties of lignite, which is the subject of this research.
ABSTRACTFireside corrosion is a serious concern for power generation industry since the harsh conditions lead to an accelerated corrosive attack of plant components. Especially superheater tubes are prone to this type of corrosion as they are subjected to ash deposits and also the corrosive atmosphere. While the demand for increased efficiency requires higher operating temperatures and thus leads to higher corrosion rates, the use of CO2-neutral fuels like biomass will introduce a higher amount of corrosive species into the system. This study therefore aims to investigate the fireside corrosion behavior of different metals under char and lignite conditions and with increased amount of chlorine and potassium. First results are presented that highlight the beneficial effect of high chromium content in the material.INTRODUCTIONFossil fuels will remain a major part of energy generation in the foreseeable future in parallel to renewable energy sources like e.g. solar and wind power. Conventional power plants are required to cover the base load energy when alternative energy sources are not sufficiently available. However, a reduced consumption of fossil fuels and lower CO2 emission is a demand for modern power plants, requiring advanced firing techniques and new material solutions. Lower CO2 emission can be achieved by adding CO2-neutral fuels i.e. biomass to the conventional fuels, however, theses fuels will introduce a relatively high amount of corrosive species like chlorine and sulfur into the firing chamber. As a consequence, metal components within the system, especially the superheater tubes, are prone to an increased corrosive attack.Type II hot corrosion is a special form of corrosive attack that occurs at temperatures below 800°C when sodium and sulphur are present in the combustion environment. It is a rather well investigated process that is being studied for turbine materials over the last 30 to 40 years.1-4 The increased attack in the presence of flue ash is caused by the formation of low melting salts. A major role is played by sodium sulphate Na2SO4 that is produced during the combustion process. It has a melting point of 884°C which is higher than the exposure temperatures at which type II hot corrosion is observed. However, sodium sulphate will form low melting eutectics with other metal sulphates, some of which are: Na2SO4/CoSO4: 565°C, Na2SO4/NiSO4: 671°C, Na3Fe(SO4)3/KjFe(SO4)3: 555°C.5 The acting mechanisms are complex and are strongly dependent of the alloy composition, the ash composition and especially the partial pressure of SO2/SO3, CO/CO2, and O2 in the atmosphere. Usually the attack is not uniform but occurs in the form of separated pits, sometimes associated with a low amount of internal sulphidation. The mechanism involves the acidic dissolution of oxides at high SO3 partial pressures, where sulphates like NiSO4 or CoSO4 are formed. These sulphates will react to form e.g. the low melting eutectic Na2SO4/CoSO4 with a melting temperature of 565°C. Other eutectic phases are of course also possible. The melting point of such low melting eutectics is usually setting the lower limit of type II hot corrosion, while the decrease of SO3 partial pressure is responsible for the upper limit. As a result the corrosion rate for many materials shows a bell-shape behavior with a maximum at a temperature between 650°C and 700°C.6,7
Fukuda, D. (Hokkaido University) | Maruyama, M. (Hokkaido University) | Aramaki, N. (Horonobe RISE) | Kaneko, K. (Horonobe RISE) | Nara, Y. (Tottori University) | Kodama, J. (Hokkaido University) | Fujii, Y. (Hokkaido University)
Evaluation of three dimensionally non-uniform strain distribution in rocks under various conditions such as in water or under freeze-thaw cycles is of significant importance to understand their complex deformations and fracturing mechanisms. For this purpose, we developed an image analysis method which can evaluate or “measure” the three dimensional (3-D) strain distribution in rocks. The proposed method utilizes the 3-D images of rock under initial and deformed configurations, which are obtained by some imaging techniques such as X-ray computed tomography (X-ray CT). In the proposed method, the obtained 3-D images are divided into multiple sub-regions of interest. For each sub-region, the strain is evaluated utilizing 3-D affine transform with unknown coefficients to be determined. In the first step, 3-D voxel level displacements at multiple representative points in each sub-region are computed by 3- D digital volume correlation technique between the comparison images and the initial-guess of the transform coefficients are obtained. In the second step, referring to the initial-guess of unknown transform coefficient, they were optimized in sub-voxel level by finding optimum digital volume correlation between the comparison images, which can evaluate the transform coefficients with higher precision. From the calculated transform coefficients, the strain was directly obtained through the spatial derivative of displacement based on affine transform. In this paper, along with the description of the proposed method, the evaluation of deformation in a lignite specimen due to immersion in water was presented as an application example. As the 3-D imaging technique, micro-focus X-ray CT was applied. The result showed that the induced dilatational strain field due to the initiation and extension of cracks in the specimen was clearly captured. Therefore, authors believe that the proposed method can be applicable to various problems in rock mechanics.
It is of significant importance to understand fracture mechanisms in various rocks for geological and engineering problems which require such as the assessment of long-term integrity of subsurface rock structures excavated in a rock mass. It is now widely accepted that rock fracturing involves with nucleation and propagation of micro cracks from pre-existing heterogeneities, which can be in the form of pores, cracks, inclusions or other defects (e.g., Wong et al., 2001). To date, systematic, theoretical and experimental investigations of initiation, propagation and coalescence of cracks in brittle solids including rocks have been conducted and it has been shown that the fracturing is a process from the proliferation and coalescences of micro cracks to the formation of the main fracture due to locally induced stress concentration or strain localization (e.g., Ortiz, 1988). However, the application of ordinary mechanical testing apparatus for such as uni- (or multi-)axial tests with displacement meters or strain gages mounted on the specimen surface cannot clarify the phenomena occurring inside of the rock specimen during the test. Thus, although it is still possible to obtain many insights from the aforementioned tests, the discussion tends to be largely conjectural and it is often the cases that the surface imaging techniques are applied to the post-fractured specimen and the “fracturing process” cannot be discussed. To solve the above difficulty, non-destructive imaging techniques such as X-ray computed tomography (X-ray CT) and magnetic resonance imaging (MRI) have been found to be one of the most attractive tools and have been applied to the investigation of deformation and fracturing in rocks under various types of loading and environmental conditions (e.g., Lenoir et al., 2007; Kodama et al., 2011; Marica et al. 2006).