Moisture Content Of Coal Research Articles

A comprehensive analysis of coal toughness index: Relationships among coal toughness index, uniaxial compressive strength and proximity parameters

Coal and gas outbursts are significant safety hazards in underground coal mining, particularly in deep Australian coal seams. While the traditional outburst risk management relies on threshold limit values of seam gas content, recent experiences have shown that this approach overlooks important factors such as coal toughness and strength. This study evaluates the effectiveness of the coal toughness test, also known as the Protodyakonov strength test, as a predictor of outburst risk. After upgrading the test rig and updating testing procedures, the toughness index f was compared with conventional strength parameters, revealing a strong positive correlation with uniaxial compressive strength (UCS) and drop hammer impact strength. An analysis of 98 coal samples taken from seven seams at three Australian mines revealed that lower moisture content and higher apparent relative density are associated with increased coal toughness. Specifically, the Pearson and Spearman correlation coefficients of −0.79 and −0.78 were observed, respectively, indicated a strong negative relationship between coal moisture content and toughness. Additionally, coal seams with lower volatile matter content exhibited higher toughness values. The study proposes adopting the coal toughness index as a robust alternative to the conventional indicators such as UCS, especially when obtaining intact coal samples is difficult. Incorporating the toughness index into the outburst risk assessment can improve safety by adopting a more comprehensive and reliable approach.

Intelligent non-destructive measurement of coal moisture via microwave spectroscopy and chemometrics

The rapid and non-destructive measurement of coal moisture content is essential in the coal industry for production, transportation and utilization purposes. Existing measurement methods have still drawbacks, such as being time-consuming, producing destructive samples and yielding unstable outcomes. To address these issues, this paper explored the utilization of broadband microwave spectrum for intelligent coal moisture measurement. A multi-type outliers detection method based on the Monte-Carlo cross-validation (MCCV) strategy was used to prevent masking effect of microwave spectra. In order to effectively extract microwave spectral features and establish correlations with coal moisture, a novel neural network model, UC-PLSR, is proposed by combining U-Net, Convolutional Block Attention Module (CBAM) and Partial Least Squares Regression (PLSR) algorithm. Furthermore, a design scheme/case of a microwave measurement device for coal moisture was presented, offering guidance for the development of rapid coal moisture measurement instruments or on-site measurement systems. Experimental results demonstrated that the proposed model outperformed traditional chemometrics methods, achieving superior prediction accuracy and generalization capability with R2 = 0.8756, MAE = 1.2523 and RMSE=1.6560.

Effect of coal moisture content on gas desorption and diffusion: A theoretical model and numerical solution

Effect of coal moisture content on gas desorption and diffusion: A theoretical model and numerical solution

Characteristics of the gas diffusion in water-bearing coal with different damage degree and its influence mechanism

The moisture content and degree of damage in water-bearing coal affect the gas diffusion characteristics in coal, which limits the effect of gas extraction. The experiments were carried out on water-bearing coal with different damage degrees using a self-built coal and gas adsorption–desorption system to study the gas diffusion characteristics of water-bearing coal with varying degrees of damage. The results show that the pore volume of tectonic coal is positively correlated with the degree of damage. The increased moisture content in coal decreases gas desorption performance, embodied in the simultaneous reduction of desorption amount, desorption speed, and diffusion coefficient. Under the same water content condition, the gas desorption amount, gas desorption rate, and gas diffusion coefficient of coal with different damage degrees all show a downward trend, and the decline range is positively correlated with the water content. The relation between the amount of gas desorption, the time, and the moisture content of the water-bearing coal with different damage degrees has been set up. The study results provide a solid theoretical foundation for evaluating and predicting the gas extraction characteristics of coal seams with varying degrees of damage.

Theoretical Energy Consumption Analysis for Sustainable Practices in Iron and Steel Industry

Exploring theoretical energy consumption introduces a fresh perspective for energy-saving research within the iron and steel industry, with a primary focus on the energy expended during material transformation. Building upon the theory of theoretical energy consumption, this study meticulously investigates the theoretical energy consumption associated with each stage of the iron and steel making process, including coking, sintering, pelletizing, ironmaking, steelmaking, and hot rolling. The findings reveal that, under specific conditions, the theoretical energy consumption for each process is as follows: coking (2.59 GJ), sintering (1.36 GJ), pelletizing (1.02 GJ), ironmaking (8.81 GJ), steelmaking (−0.16 GJ), and hot rolling (0.76 GJ). Additionally, this study delves into the analysis of influencing factors on theoretical energy consumption. Using the coking process as an illustrative example, it is observed that the theoretical energy consumption in coking decreases with a reduction in both moisture and volatile content in coal. Under the specified conditions, the minimum theoretical energy consumption for each process is as follows: coking (2.51 GJ), sintering (0.98 GJ), pelletizing (0.67 GJ), ironmaking (8.38 GJ), steelmaking (−0.58 GJ), and hot rolling (0.07 GJ), respectively. This comprehensive analysis serves as a valuable resource for advancing sustainable practices in the iron and steel industry.

Study of Palm Oil Shell Utilization as Metallurgical Coke with Variation of Bondcrete Additive

Coke, an essential ingredient in the steel and metallurgical industries, is typically derived from bituminous coal. However, in Indonesia, where bituminous coal is rare, coke production is dependent on coal imports due to the high moisture content of local coal. An alternative approach is to use biomass, such as palm oil processing waste, for "biomass coke" to produce a more environmentally friendly coke with lower greenhouse gas emissions. Palm kernel shell waste rich in lignocellulose proved suitable for this purpose due to its compressive strength and carbon content. Pyrolysis, a technique for creating porous micro-structured carbon from palm kernel shells, was used to produce this coke substitute, offering a more sustainable energy source with a lower carbon footprint than fossil fuels. Bio-coke exhibits low moisture content (5.84%) and ash content (13.20%) due to the moisture and ash reduction effects of bondcrete adhesive during combustion. It also demonstrates substantial compressive strength (14 mPa), a high calorific value (6795 cal/g), and a favorable pore structure with a large surface area, indicating a positive influence of bondcrete adhesive on coke properties without compromising energy potential.

Effects of the CADW in low-metamorphic coal and analyse on its action mechanism

The CO2-alkaline-water two-phase displacing gas and wetting coal (CADW) measure can effectively prevent coal and gas outburst and reduce mine dust concentration, while relevant research on its effects and action mechanism is insufficient. In this work, effects of the CADW in low-metamorphic bituminous coal and its action mechanism were investigated deeply. The experimental results revealed that, after using the CADW, the risk of gas outburst was reduced evidently compared with conventional water injection. The residual methane and mixed gas in JZ coal reduced by -79.50% and -33.39% severally. The water-injection effect was also enhanced obviously. During injecting water, the maximum pore pressure at 20, 40, 60 mm away from the drilling increased by 10.80%, 5.96%, 1.80%, respectively. The water-injection rate, total volume and radial moisture content of JZ coal all increased distinctly, with the increment of 4.45%∼28.14%, 10.30% and 3.45%∼15.82% respectively. The increment of moisture content rose with distancing the drilling. In addition, the CADW could notably improve the water-lock effect, the permeability of JZ coal was reduced by 88%. As a result, the methane migration, from deeper coal seam to the exposed working face, was inhibited effectively. The results can provide significative guidance for the application of the CADW technique, gas outburst prevention and dust concentration reduction.

Kinetic analysis and mathematical modeling of low-rank coal drying by using swirl fluidized bed dryer on varied angles of guide vane and temperatures

ABSTRACT Low-rank coal is currently widely used as fuel to cover the increasing needs of boilers. This kind of coal must be upgraded due to its high moisture content to increase its quality. The drying using a fluidized swirl bed has not been studied to reduce the moisture content of Low-Rank Coal. In contrast, the drying kinetic model has never been found. This study used the angle of guide vanes (AGV) 10°, 20°, and 30° to produce swirl flow. Experiments with varying temperatures used temperatures of 40°C, 45°C, and 50°C. The purpose of this work was to determine the drying characteristics, the best-drying kinetics models, the effective moisture diffusion value, SMER, MER, and SEC on swirl fluidized bed drying. The study results show that the Khazaei and Rational drying kinetic model was the most suitable for the two experimental variations. For experiments with varying AGV, the R2 values obtained are 0.9989–0.9992 and 0.9980–0.9983, while for the variable temperature, the values are 0.9990–0.9992 and 0.9983–0.9992 for each model. The research also found that the smaller AGV angle and higher temperature result in a faster drying rate and consume less energy.

Optimization of briquetting conditions and influencing factors of high-strength sludge briquette

With the increase of sewage sludge production in China, there is an urgent need for a clean and efficient sludge treatment, and the coupling utilization of sludge and coal to produce briquette is a potential sludge treatment method. In this work, sludge (with blending ratio higher than 40 wt%, dry basis) and one Chinese low-rank pulverized coal were used as raw materials to prepare sludge briquette by cold pressing method without binder. The effect of sludge moisture content (SMC), briquetting load (BL), blending ratio (BR), and particle size distribution of coal (PSD) on the compressive strength of the briquette were explored. Through FTIR, contact angle, Zeta potential, and SEM analysis, the briquetting mechanism of sludge briquette was clarified. The response surface method (RSM) was used to optimize the briquetting process conditions. The results showed that the order of influence of various factors on the compressive strength of the briquette is as follows: BL > PSD > SMC > BR. The results also showed that the interaction among SMC, BL, and PSD is the main factor affecting the compressive strength of sludge briquette. According to regression analysis, the optimum briquetting conditions are SMC of 14.11%, BL of 46.54 MPa, the weight proportion of sludge of 60%, and the weight proportion of R1 in coal of 52.68%. The quadratic regression model was established by RSM, and the predicted value is close to the experimental value.

Effect of Solvent Treatment on the Composition and Structure of Santanghu Long Flame Coal and Its Rapid Pyrolysis Products.

Easily soluble organic components in Santanghu long flame coal (SLFC) from Hami (Xinjiang, China) were separated by CS2 and acetone mixed solvent (v/v = 1:1) under ultrasonic condition, and the extract residue was stratified by carbon tetrachloride to obtain the light raffinate component (SLFC-L). The effect of solvent treatment on the composition and structure of the coal and its rapid pyrolysis products was analyzed. Solvent treatment can reduce the moisture content in coal from 9.48% to 6.45% and increase the volatile matter from 26.59% to 28.78%, while the macromolecular structure of the coal changed slightly, demonstrating the stability of coal's complex organic structure. Compared with raw coal, the relative contents of oxygen-containing functional groups and aromatic groups in SLFC-L are higher, and the weight loss rates of both SLFC and SLFC-L reached the maximum at about 450 °C. In contrast, the loss rate of SLFC-L is more obvious, being 33.62% higher than that of SLFC. Pyrolysis products from SLFC at 450 °C by Py-GC/MS are mainly aliphatic hydrocarbons and oxygenated compounds, and the relative contents of aliphatic hydrocarbons decreased from 48.48% to 36.13%, while the contents of oxygenates increased from 39.07% to 44.95%. Overall, the composition and functional group in the coal sample were changed after solvent treatment, resulting in a difference in the composition and distribution of its pyrolysis products.

Dependence evaluation of factors influencing coal spontaneous ignition

AbstractCoal spontaneous combustion is determined by a variety of factors. Testing can describe the changes incoal spontaneous combustion with various factors, however, the dependence of spontaneous combustion on various factors is unclear. Therefore, reliability theory was used to deduce the functional relationship of the dependence of coal spontaneous combustion on various factors, and construct a model algorithm for predicting the probability of occurrence of coal spontaneous combustion, which is adopted to evaluate and rank the degree of influence of various factors on coal spontaneous combustion. Effective prevention methods are proposed by strengthening the role of the most important factors. The results show that, by taking the duration of coal heating to 150°C as the measurement standard of coal spontaneous combustion, the duration of the initial stage of coal heating increases linearly with the increase of specific heat capacity, thermal conductivity, and moisture content of coal. With the increase of oxygen concentration, oxidation rate, and initial temperature of the coal, the duration of the initial stage of coal heating decreases exponentially. With the increase of gas flow seepage velocity in the coal body, the duration of the initial heating stage changes in a parabolic manner. At the same time, the probability of spontaneous combustion decreases exponentially with the increase of specific heat capacity and moisture content of the coal. The probability of coal spontaneous combustion increases linearly with the increase of coal thermal conductivity, oxygen concentration, gas seepage velocity, and rate of oxidation. The dependence of coal spontaneous combustion probability on different factors can be expressed as follows: coal temperature > gas seepage velocity > specific heat capacity > oxidation rate > oxygen concentration > moisture content > thermal conductivity.

Study on water seepage law of confined coal body and optimization of water injection parameters

To optimize water injection parameters, it is necessary to understand the water seepage characteristics of coal and establish an evaluation method for the coal seam water injection effect. Using low-field nuclear magnetic resonance (NMR) technology and a peripheral loading pressure experimental system, real-time Carr-Purcell-Meiboom-Gill sequence tests were conducted on coal samples under different water injection schemes. The dynamic migration characteristics of pressurized water in coal under a constant water injection pressure and injection flow were studied. The results showed that under a fixed water injection pressure, the change in water content with injection time was in concordance with first-order kinetics, indicating that the process is controlled by diffusion. Combined with the fitting results of the wetting rate constant and water injection pressure, the best water injection pressure was obtained. Moderate water injection flow, an increase in water injection volume, and an extension of the water injection time can improve the wetting effect. Under constant water pressure, water seepage in the coal includes two processes: the rapid migration of free water to the pore fractures of coal and the spontaneous water absorption process in the coal. Under constant water flow, the water seepage process in the coal is consistent with the Boltzmann equation. Based on the time constant and inflection point of the time growth obtained by the Boltzmann equation, the seepage process was divided into the water inflow, water transportation, and water adsorption stages. The peak area of the adsorbed water is proportional to the mass of coal moisture. This relationship can realize the mutual conversion between the NMR water signal quantity and moisture content in coal.

Design of a Coal Drying System with Solar-Assisted Heat Pump and Waste Heat Utilisation

The increase in global energy demand has directed researchers towards making low-quality coals into an environmentally friendly energy source by reducing their high moisture content. Drying coal is a high-energy and time-consuming process, so reducing the required energy and drying time is crucial for drying technology. Coal drying increases the thermal value of coal and makes it easier to transport. In this study, a coal drying system was designed using waste heat recovery systems, R-134a refrigerant as working fluid, air source heat pumps, and vacuum tube solar collectors to provide hot air. Firstly, the moisture content of the coal and the desired moisture content after drying were determined, and then the heat required to dry the coal was calculated. Next, the capacity of the solar collector required to provide the necessary heat to the heat pump was determined, and the type and capacity of the heat pump that could produce the required heat were selected. Finally, the coal dryer was designed based on the specific requirements of the power plant and the type of coal used. As a result, the coal drying system designed with solar-assisted heat pumps and waste heat utilization can increase the efficiency of coal-fired power plants by reducing the moisture content of coal before combustion.

Effects and influencing factors of the CO2-alkaline-water two-phase displacing gas and wetting coal

To prevent the risk of coal and gas outburst and improve the coalbed methane (CBM) recovery, the CO2-alkaline-water two-phase displacing gas and wetting coal technique (CADW) was researched. Effects of the CADW in the residual CH4 and CO2, pore pressure, moisture content and permeability in coal under different conditions were studied detailedly. The results showed that, compared with the CO2 displacing CH4, after adopting the CADW, the amount of residual gas in the Qincheng (QC), Liangshun (LS) and Zhongxing (ZX) coals increased significantly, with the increment of 203.99%, 75.15%, 61.35%. The desorbed CH4 and CO2 of the three coals accounted for 86.37%, 69.12%, 64.60% and 4.30%, 3.38%, 13.43% of the injected CH4 and CO2 respectively. Compared to the conventional water injection, after using the CADW, the pore pressure, water injection volume and moisture content in coal all increased obviously. The maximum pore pressure of QC, LS and ZX coals increased by 2.05–6.96%, 4.37–5.44% and 2.88–9.25% respectively. The water injection volume of QC, LS and ZX coals increased by 10.69%, 33.51%, 43.45% respectively. The moisture content increased by 2.81–13.01%, 20.00–42.58%, 16.69–114.34% radially, and its increment increased with distancing the borehole. Besides, the permeability in three coal samples all decreased by one order of magnitude, with the reduction of 84.21%, 86.49% and 89.47%. Additionally, increasing the water injection pressure and time can distinctly improve effects of the CADW, which will reduce with rising ground stress and reducing temperature. The results can provide important reference for better preventing the coal and gas outburst risk and increasing the CBM recovery.

Operation control and optimization of high efficiency hot primary air temperature adjustment device

Aiming at the problems existing in the control logic of the current hot primary air temperature adjustment device, such as adjustment lag, poor adjustment quality, deviation of the pulverizing system operation from the normative value and insufficient energy-saving effect in the adjustment process, a standard-based calculation method was proposed. It is a logical optimization scheme that dynamically adapts to the moisture content of raw coal and the coal volume of the pulverized. It has the advantages of faster adjustment speed, high system energy saving effect, and ensures the standard operation of the coal mill.

Assessment of physical properties and antimicrobial activity of activated charcoal impregnated with silver nanoparticles against Escherichia coli

Activated charcoal possesses small pores that help in the increment of the surface area available for chemical reactions. In this study, coal samples were taken from Kalimati, Dharan, and Eastern Nepal with the goal of determining the antibacterial activity of activated charcoal against Escherichia coli. This study also measured the moisture content, volatile substances, fixed carbon, and pH of coal using proximate analysis. This study was carried out by the activated carbon impregnation with silver nanoparticles by varying with the different AgNO3 concentrations: a) 0.1 mol/liter (mol/L) b) 1 mol/L c) 1.5 mol/L one at a time. By the proximate analysis, it was found that the moisture content was 2.2%, the volatile matter was 15%, the fixed carbon was 53.8%, and the pH was 5.83. The antimicrobial activity was performed by agar well diffusion methods. With 25 mg nanoparticles the zone of inhibition against E. coli was found to be 7 mm, 8 mm and 10 mm respectively and with 50 mg nanoparticles the zone of inhibition against E. coli was found to be 9 mm, 9 mm and 12 mm with concentration 0.1 mol/L, 1 mol/L and 1.5 mol/L of AgNO3 respectively. According to Pearson correlation (r = 0.697) and a simple linear regression (R2 = 0.798), there was a positive relationship between the concentration of AgNO3 and the zone of inhibition observed against E. coli. The highest zone of inhibition (ZOI) of activated charcoal impregnation against E. coli was 12 mm at 1.5 mol/L of AgNO3 with 50 mg silver nanoparticles, which was comparatively less against seven standard antibiotics (13-29 mm ZOI).

Research on Optimization of Large Flow Hydraulic Punching Process in Zhaozhuang Mine

Taking hydraulic punching test of Zhaozhuang Mine as engineering background, by comparing the field application effects of different hydraulic punching processes, the relationship between coal moisture content around the borehole blockage and gas extraction effect was monitored and analyzed. The following conclusions were drawn: the occurrence of borehole blockage was the result of the comprehensive action of coal slag particle size and slag discharge capacity of punching return water. Blocking the borehole led to the accumulation of a large amount of punching high-pressure water and coal slag in the borehole, which compressed and infiltrated the surrounding coal body and reduced gas extraction efficiency of borehole. Under the condition of the same amount of coal produced by punching, the different punching methods led to the great difference in the influence radius of punching. The large flow three-stage coal-breaking hydraulic punching system developed according to the borehole blockage mechanism can effectively reduce the particle size of coal slag, increase the punching flow, effectively avoid borehole blockage, and improve gas extraction efficiency of borehole.

Experimental study on freeze–thaw damage characteristics of coal samples of different moisture contents in liquid nitrogen

In this study, the surface crack-propagation law and pore damage characteristics of coal samples of different water contents after they undergo leaching in liquid nitrogen are investigated using a 4 K scientific-research camera, HC-U7 non-metal ultrasonic detector, nuclear magnetic resonance testing technology, and self-made multi-functional three axial fluid–solid coupling test system. Experimental investigations are conducted on coal samples of different water contents before and after they undergo liquid-nitrogen freezing and thawing in order to determine the propagation law of surface fissures, the development law of internal micro-fissures, the development process of internal pores, the change law of the pore-size distribution, and the law of coal-sample deformation and gas seepage during the stress process. The test results show that, with the increase in water content in the liquid-nitrogen leaching process, the frost heave force on the coal surface increases, and the greater the increase ratio of the coal porosity, the faster is the development of micro-cracks and pores. Under the action of liquid nitrogen, the number of micro-pores, meso-pores, and macro-pores in the coal sample increased, and with the formation of new cracks and the connection of the original cracks, liquid-nitrogen freezing and thawing can promote the development of the pore structure in the coal body. The permeability changes of coal samples of different water contents during unloading failure exhibit obvious stage characteristics. The above results demonstrate that the moisture content of coal has a significant effect on the development of surface cracks and pore-damage characteristics of coal after liquid-nitrogen freezing and thawing, and there is a positive correlation between the surface crack expansion and internal damage of the coal samples of different moisture contents leached in liquid nitrogen.

A Pilot Plant Study of Coal Dryer: Simulation and Experiment

High moisture content in low-range coal causes low calorific value. To increase the quality, drying by a coal dryer to minimize moisture content is proposed. Here, a case study of a cyclone-like conical tube coal dryer pilot plant was reported. Drying heating uses combustion heat generated from volatile matter combustion. This approach will solve the two problems simultaneously: decreasing moisture content and volatile matter. The computational fluid dynamic (CFD) approach is used to study fluid dynamics inside the coal dryer using ANSYS Fluent 2020R2 software. The CFD simulation results represent the phenomenon of coal drying inside the coal dryer validated by the pilot plant experimental result. The simulation was carried out in steady and unsteady conditions to understand the drying phenomena. The simulation firmly fits the experimental result, especially in an unsteady state system, indicating that the simulation result is promising for further coal dryer design. The optimal condition produces a high moisture content reduction of 86.37%, uniform fluid distribution, and significant volatile matter combustion

Intelligent Measurement of Coal Moisture Based on Microwave Spectrum via Distance-Weighted kNN

Realizing the rapid measurement of coal moisture content (MC) is of great significance. However, existing measurement methods are time-consuming and damage the original properties of the samples. To address these concerns, a coal MC intelligent measurement system is designed in this study that integrates microwave spectrum analysis and the distance-weighted k-nearest neighbor (DW-kNN) algorithm to realize rapid and non-destructive measurement of coal MC. Specifically, the measurement system is built using portable microwave analysis equipment, which can efficiently collect the microwave signals of coal. To improve the cleanliness of modeling data, an iterative clipping method based on Mahalanobis distance (MD-ICM) is used to detect and eliminate outliers. Based on multiple microwave frequency bands, various machine learning methods are evaluated, and it is found that coal MC measurement using broad frequency signals of 8.05–12.01 GHz yields the best results. Experiments are also carried out on coals from different regions to examine the regional robustness of the proposed method. The results of on-site testing with 27 additional samples show that the method based on the combination of microwave spectrum analysis and DW-kNN has a potential application prospect in the rapid measurement of coal MC.