Coal Water Research Articles

Radiological Impact Assessment of Mining on Soil, Water and Plant Samples from Okobo Coal Field, Nigeria

Anthropogenic, including mining activities leaves the environment contaminated with potentially toxic substances and remote hazards if not properly checked. The quest in this study is the levels of naturally occurring radionuclides in Okobo coal, Nigeria and their possible distribution in coal mine vicinity soils, water and plants (cassava). Samples were characterized for levels of radionuclides and radiological detriments using high resolution gamma spectrometer, Gamma ray liquid scintillation and applicable radiological hazard indices. The range of mean activity concentrations (Bq·kg-1) for the environmental samples are as follows: 226Ra (8.39 ± 1.0 to 77.6 ± 4.0), 232Th (0.470 ± 0.4 and 77.8 ± 2), and 40K (29.1 ± 0.4 and 289 ± 6), with their respective mean values of 32.7 ± 2.1, 54.0 ± 1.5 and 158.8 ± 3.1 (Bq·kg-1). Radiological detriments including radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), radioactivity level index or gamma index (Iγ) and the ELCR for coal sample is 96.94 Bq·kg-1, 0.26, 0.30, 0.69, and 1.56 respectively. Reported values were below the safety limits stipulated by UNSCEAR and implied that the environment is relatively safe with low levels of natural radioactivity. Overall, this background study has demonstrated that Okobo coal mine is a less radio-hazard contributor to environmental samples. Exceptions to this generalization are representative gamma index (Iγr) and annual effective dose equivalent values for some cassava and soil samples, which may call for future impact monitoring.

The impact of inlet flash evaporation conditions on erosion damage characteristics of coal gasification black water angle valve and prevention strategies

In view of the three-stage flash evaporation system of the coal gasification plant, a combination of theoretical analysis and numerical simulation was used to establish the erosion damage evaluation model in the black water angle valve. The influence of the inlet flash evaporation ratio on the inlet velocity, the outlet flash evaporation ratio and the outlet velocity of the low-pressure black water angle valve are systematically studied, the mechanism of erosion damage to the carbon steel valve body by the solid medium in black water was analyzed according to the micro-cutting theory. The results show that the inlet velocity w 1, the outlet flash evaporation ratio x 2, the outlet velocity w 2 of angle valve have linear correlation with the inlet flash evaporation ratio x 1.The upstream volume erosion ratio of the angle valve at the inlet flash ratio x 1 = 3 wt.% is 114 times as much as that at zero inlet flash ratio. Meanwhile, the downstream volume erosion ratio of the angle valve at x 1 = 3 wt.% is only 2.7 times as much as that at zero inlet flash ratio. The prevention strategies to reduce the erosion damage to black water angle valve are proposed by inhibiting the inlet flash evaporation ratio and reducing the inlet flow rate etc. This study is expected to provide guidance for the erosion resistance design and operation of the black water angle valve.

桃园煤矿II 1042工作面煤层底板注浆量与富水性研究

桃园煤矿II 1042工作面煤层底板注浆量与富水性研究

Tissue Preservation Index (TPI) and Gelification Index (GI) with the Quality of Coal as well as the Connection to the Acid Water Mining

Tissue Preservation Index (TPI) and Gelification Index (GI) are products in coal related to the quality of coal and acid water mining. Research is conducted to know the relationship between the two by means of correlation using polynomial method and pressing method on the environmental diagram of the depositional environtment/facies. The correlation result is obtained that the higher the value of TPI, the value of Inherent Moisture and Volatile Matter is lower and the value of ash content and Fixed Carbon is higher. The higher the value of the GI, then the value of ash content and Fixed Carbon is higher and the value of Volatile Matter is getting lower. The lymnic deposition facies are areas that are located far from the sea and covered by a barrier and composed of land sediment with an active hydrological system. This is what causes minimal acidic water to occur because the sea sulfide does not intervene in the surrounding rocks. In addition, high GI value levels in the research area cause the oxidation process to be low and result in low rock acidity conditions.

A Multi-Scale Modeling of CH4 and H2O Adsorption on Coal Molecules and the Water Blocking Effect in Coalbed Methane Extraction

Coalbed methane (CBM) is of great economic value. However, at the same time, CBM is facing a multitude of technological challenges. The water blocking effect (WBE) is one of the physical effects that controls the production of CBM. To alleviation WBE, it is necessary to study its mechanisms at the molecular level. In this study, we used a combined first-principles calculation and molecular simulation approach to investigate the adsorption and diffusion of both methane and water in coal. The results suggest that water does not compete with methane in the adsorption on coal surfaces, yet the presence of water significantly slows down the diffusion of methane within the micropores of coal. This work not only explains the fundamental mechanisms of the WBE but also provides a simulation framework for building strategies to alleviate WBE.

The role of pore water plays in coal under uniaxial cyclic loading

Geofluids are common in underground coal mines and have a significant influence on the deformation of coal rock, where the pore pressure of geofluids varies during swelling or shrinkage processes. In order to characterize the role of pore water in coal, the uniaxial behavior of saturated coal under cyclic compression was investigated considering different loading rates, amplitudes, and numbers of cycles. The results show that Young's modulus (E) increased in the first cycle and then stabilized in the remainder of loading cycles. Also, the increment of E in the first cycle was inversely correlated with the loading rate. For the first time, it is found that the radial residual strain gradually decreased in each subsequent loading cycle. This is different from that of water weakening property of coal by immersion of the coal in water without pressurization. In the unloading phase, the pore pressure decayed more slowly than the stress, leading to a high level of deviatoric stress. As a result, the acoustic emission events appeared even at the minimum of cyclic loading. The transverse relaxation time (T2) distribution shows that the pore water pressure mainly changed the primary pores, while its influence on the secondary pores was negligible. From a poromechanical perspective, high pore pressure developed in pores of poor connectivity during initial cyclic loading, causing stress orientation rotation and tensile damage. With further cyclic loading, the pore water was continuously discharged as the pores were compacted into flat cracks. As a result, the onset stress of dilatancy gradually increased in the subsequent loading cycles due to the enhanced frictional resistance to crack slip.

Directional permeability evolution in intact and fractured coal subjected to true-triaxial stresses under dry and water-saturated conditions

Investigations of the directional permeability evolution of intact and fractured coal are conducted under different simulated geological conditions. The effects of fracture geometry, water adsorption and stress conditions on the permeability evolution of coal as a function of stress are systematically studied. The results indicate that permeability anisotropy is more pronounced in fractured coal than in intact coal. The permeability order, i.e., the kfa > kbu > kbe relationship, is maintained following the introduction of macrofractures into coal. The fracture compressibility in the butt cleat plane flow direction is higher than that in the other two flow directions for both intact and fractured coal. The presence of water in coal can reduce the permeability by up to one order of magnitude, and a more significant permeability decrease is observed in coal specimens containing rough macrofractures. Permeability hysteresis for both intact and fractured coal is somewhat dependent on the stress condition. The hysteresis effect of coal is more significant under triaxial stress conditions and less pronounced under true-triaxial stress conditions.

Weak interaction between water molecule and different rank coals: a DFT-D3 study

Weak interaction between water molecules with different rank coals(anthracite, bituminous, subbituminous and lignite) was studied by density functional theory with dispersion correction (DFT-D3) in quantum chemistry method. The equilibrium configurations of water molecule on the surface of coal molecules were optimised, analysis of electrostatic potential on the surface of coal molecule was conducted, and interaction energy between coal molecular surface and water molecular was calculated, as well as interaction types of water on the different rank coals molecular surface were confirmed by calculating the reduced density gradient function (RDG). Research shows that the order of maximum adsorption interaction energy is lignite > subbituminous > bituminous > anthracite, and the hydrogen bond and Van der Waals play a dominant role in the adsorption of water on coal molecule surface. [Received: June 17, 2016; Accepted: March 22, 2017]

一种煤矿透水事故两级悬浮快速排水新方法在骆驼山矿的实践与应用

一种煤矿透水事故两级悬浮快速排水新方法在骆驼山矿的实践与应用

Promotion of Coal Slime Water Sedimentation and Filtration via Hydrophobic Coagulation

ABSTRACT Highly turbid coal slime water is characterized by high concentrations of fine particles with negative electric charges and a high clay content. These characteristics hinder the sedimentation and dewatering of highly turbid coal slime water. Therefore, we investigated the initial settling velocity, light transmittance, and filter cake moisture content, as well as the effects of quaternary ammonium surfactants on sedimentation and filtration of coal slime water. Amendment with quaternary ammonium surfactants promoted the sedimentation and filtration of coal slime water by enhancing the hydrophobicity of particles and decreasing the electric charge on particle surfaces. In addition, factors such as kinetic energy input (i.e., mixing), reagent type and dosage, solution pH, the size and mineral composition of coal slime water particles affected sedimentation and filtration. For example, under prolonged treatment with quaternary ammonium containing long alkyl chains, the contact angle of slime particles increased, leading to improved sedimentation and dewatering. Further, high quartz and clay mineral contents exerted unfavorable effects on sedimentation and filtration. Also, the optimal solution pH conducive to sedimentation and filtration ranged from 8 to 10. The results of this study should help improve coal slime sedimentation and filtration processes because the study addresses current technological limitations.

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

MURUGOV A. A. ENERGY AS A COMPREHENSIVE FACTOR OF MODERNIZATION DURING INDUSTRIAL REVOLUTION IN EUROPE: A REVIEW OF WESTERN HISTORIOGRAPHY

The current study attempts to assess the energy base held by Europe in the XVIII – early XIX centuries. The research is based on the English and Russian assessment of foreign historiography devoted to energy balance in Europe. Chronologically, the historiographical base features the period from 1970s up to modern days. The main instrument of the analysis presented in the article is quantitative calculation of the power sources of energy in the countries of Western Europe. The article shows the increase dynamics of coal energy, wood, water, wind, steam, muscular energy and draft animals in Europe. Then, available power growth rate is compared with the rate of GDP that occurred in the study period. The research of the structure and nature of energy has revealed a strong statistical dependence of GDP on the amount of energy used in the era of industrial revolution in Europe and especially in the UK. The research stresses the importance of energy as a key factor of modernization and technological development of material culture.

Experimental investigation on spontaneous imbibition of water in coal: Implications for methane desorption and diffusion

During the process of coal mining and coalbed methane extraction, the application of hydraulic techniques generally leads to the spontaneous imbibition of water in coal seams. To study spontaneous imbibition of water in coal and evaluate its influence on methane desorption and diffusion, experiments of spontaneous imbibition in coal containing methane were conducted under different adsorption equilibrium pressure and water imbibition ratios. The displacement effect of water during imbibition was investigated, and methane desorption was also tested under atmospheric-pressure conditions. Imbibition test results show that adsorbed methane can be displaced by water. The displacement amount and its efficiency increase with water imbibition ratio, but an upper limit on the displacement amount exists because of the limited imbibition capacity. Desorption test results show an inhibitory effect of water blocking on methane desorption and diffusion. The desorption time increases and diffusivity decreases with the imbibition ratio. However, the time-dependent characteristics of desorption ratio indicate that the desorption process is temporarily delayed rather than completely stopped by water blocking. Moreover, the residual methane amount decreases with the water imbibition ratio based on long-time-scale desorption, suggesting that spontaneous imbibition of water can promote methane desorption on the whole. The scale effects of coal samples and actual conditions on methane adsorption, desorption and imbibition are also discussed. These findings show the multiple effects of spontaneous imbibition on methane desorption in coal and help in better understanding the overall effects of water-based treatment techniques on coalbed methane extraction and coal seam gas control for mining safety.

Economic impacts of coal seam water for agricultural enterprises, lessons for efficient water management

While the coal seam gas industry is relatively new in Australia its growth has been significant. To date, development has been located almost entirely in Queensland. Significant quantities of coal seam water are produced as a by-product of this industry. Once treated, it provides a potential benefit for agricultural use. How much water is being produced, where, and what proportion can practically be used for this purpose depends on a number of social and environmental limitations. One of these limitations is that much of this water is only available for a restricted timeframe, perhaps only 20 years, and much of this water is only available in proximity to large treatment plants. While these provide short-term benefits, these may have been improved through more efficient storage and distribution. The lessons for improved groundwater management and alternative storage mechanisms have the potential to yield major improvements for sustainable agriculture.

Characterizing strata deformation over coal pillar system in longwall panels by using subsurface subsidence prediction model

The ground control stability problem due to underground large mine openings often associates with large movements and deformations of strata. The situation becomes more complicated when relative subsidence research involves zones above the coal pillar. Continues fractures in strata created by such subsidence progress may become the pathway of fresh air delivery or water migration in the strata aquifer which would cause the problems of underground coal combustion or water resource losing. Hence, knowing the subsurface strata movement characteristics over gob and coal pillar to make any subsidence predictions are desired for mining engineers to estimate any damages happened in the subsurface strata in advance. This paper proposes a prediction model for investigating subsurface strata movements over the pillar. Using the calculated subsidence results, the related strata fraction distributions are characterised. For validation reason, extensometer boreholes are used to identify the subsurface strata caving progress in a long-wall panel. The measurement results agree with the predications derived by the model shows the reliability of the model. Such research efforts can well help to understand the moving behaviour of all strata over the coal pillars and assist mining engineer to efficiently deal with the possible crack pathways over the coal pillar.

Characterization and acid resistance test of one-part geopolymer from fly ash and water treatment sludge

Development of geopolymers from wastes or by-products introduces a sustainable approach to replace ordinary Portland cement (OPC)-based concrete with an eco-material of lower green-house gases emissions. However, safety concerns related to the conventional two-part geopolymer has limited large-scale applications of the product. In this context, a novel one-part geopolymer from coal fly ash and water treatment sludge has been presented. The transformation of raw materials to geopolymer was observed by FTIR, SEM and XRD analyses. Acid resistance test has proved that the new binder had great durability against sulphuric acid attack. After 28 days immersion in 5% H2SO4 solution, weight of all samples was hardly changed. Compressive strength, on the other hand, has not decreased but significantly increased as curing time increased. The properties were also compared to those of control samples cured in water. It was demonstrated that strong acid immersion did not create any noticeable effect on the weight and strength of one-part geopolymer system developed from coal fly ash and water treatment sludge.

基于多层正则极限学习机的煤矿突水光谱判别方法

基于多层正则极限学习机的煤矿突水光谱判别方法

Combustion peculiarities of coal-methane-air mixtures in a recuperative burner

Numerical modeling of the combustion of a lean methane-air mixture containing fine coal particles entering the “Swiss-roll” type recuperative burner is considered. The mathematical model is constructed under the following assumptions: the flow field is two-dimensional; the gas mixture is an ideal incompressible gas consisting of oxygen, methane, coal volatile substances, carbon monoxide, carbon dioxide, water vapor, hydrogen and nitrogen. In the gas phase four oxidation reactions, in which methane, volatile matter of coal, carbon monoxide, hydrogen participate and the reaction of carbon dioxide decomposition take place. On the surface of the coal particle, there are three oxidation reactions involving oxygen, carbon dioxide and water vapor, resulting in the formation of carbon monoxide. It is assumed that coal contains 8% of ash, 12.9% of volatile substances and 79.1% of carbon. It is shown that for a two percent methane-air mixture the reaction zone shifts toward the center of the burner as the feed rate of the mixture increases. An increase in the content of coal particles leads to a shift of the reaction zone into the inlet part of the burner, and the heat release in the burner increases.

Determining the Quality of Mine Gushing and Mixed Water Using Coupled AHP and Fuzzy Comprehensive Evaluation Methods

This study focused on analysis of the chemical characteristics of mine waters. The aim of this study is to correlate the degree of different ionic components in mine water and the influence of their convergence using a combination of the three-scale AHP and fuzzy evaluation methods for the comprehensive evaluation of water quality. Ion chromatography (ICS 1100) has been used to analyze the content of the water sample while portable pH/EC/TDS/Tem- perature meters (SX 811 and SX 813) were used to test physical-chemical parameters. The results of this study show that chemistry of in No.11 gushing mine is dominated by HCO3-Na and HCO3-Ca, and had a pH between 7.1 and 8.00, belonging to neutral or slightly alkaline water. In addition, water were found to have the hardness between 18 mg/L and 542.5 mg/L. Results also show that the TDS of the roof sandstone and goaves water are higher than Cambrian limestone water, while the turbidity of the mixed water is 20 NTU in the sump, again higher than in other samples such as Cambrian limestone water. Total dissolved solids and the total hardness of Cambrian limestone groundwater mainly depend on the content of K+ + Na+, Ca2+, B={b1,b2,…,bj} and SO2-4. Thus, chemical composition changes remarkably after mine water mixing. Results showed that the coal roof sandstone water is class V while that in the sump is class III, and the Cambrian limestone groundwater is class I. In gushing, the quality of water can vary greatly; thus, water from the coal face roof sandstone and the Cambrian limestone should be stored and treated separately before being utilized.

International Trials of Vertical Flow Reactors for Coal Mine Water Treatment

Vertical flow reactors (VFRs) were tested at coal mine sites in New Zealand, South Korea, and the USA. The objective was to evaluate the iron removal efficiency and iron removal mechanisms during field trials at low pH and circumneutral pH, and to evaluate the potential use of VFRs as stand-alone systems or in combination with other passive treatment technologies. Total iron and manganese removal efficiencies at circumneutral pH (6–8) often exceeded 90%, with effluent concentrations less than 1 mg/L. This is attributed to both homogeneous and heterogenous Fe(II) oxidation and filtration of the precipitated ferrihydrite. Iron removal efficiencies at moderately acidic conditions (pH 3–4.5) averaged close to 40%, with an average 71.0% removal in one of the trials after iron removal capacity was stabilized. Microbial Fe(II) oxidation and precipitation as schwertmannite together with aggregation of colloidal and nano-particulate Fe(III) are suspected to be the main removal mechanisms. Iron solubility limited removal under very acidic conditions (pH < 3). The reproducibility of the results with respect to previous research confirmed that VFRs can be used as stand-alone passive treatment systems for iron removal from mine waters with a footprint less than half of the area required by a conventional aerobic wetland. A VFR can also provide useful iron pretreatment for other passive treatment systems under circumneutral conditions, but would have to be combined with alkaline generating systems to achieve full iron removal from acidic mine waters.