Moisture Content Of Coal Research Articles

Permeability evolution in tectonic coal: The roles of moisture and pressurized water‐injection

AbstractWater often influences the exploitation of Coalbed methane (CBM) as well as the hydraulically enhanced permeability; it is therefore useful to objectively quantify the permeation properties of a CBM reservoir with different moisture contents. Based on the occurrence of CBM and the laws governing gas flow in CBM reservoirs, gas seepage experiments were carried out on the coal collected from the Baijiao mine in Sichuan, China. Various moisture contents were evaluated using natural coal samples, dry coal samples heated in an oven for various periods, and coal samples wet by soaking them in different pressure water under a constant effective confining stress. Results showed that: (1) The coal moisture decreased gradually with the drying time and increased with the soaking time. When coal is soaked in high pressure water (5–20 MPa), the moisture content in coal will increase from 2.60 to 3.85% with the increasing of water pressure. (2) The permeability of soaked coal decreased with the increasing of gas pressure, while the permeability of natural coal firstly decreased and then increased with the pore pressure decrease. (3) For the coal with higher moisture contents, gas permeability is more sensitive to the reduction of pore pressure, which may be due to the alteration of fracture structure induced by high‐pressure water injection. (4) Moisture content of coal affects the slippage effect in coal pores, and a higher moisture in coal will result in the decrease effective pore throat, incurring a stronger slippage flow and a higher apparent permeability of coal. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Effect of moisture content on flow behavior and resistance characteristics of dense-phase pneumatic conveying

The flow characteristic of high pressure dense-phase pneumatic conveying of pulverized coal is essential to the safe and stable operation of the gasifier. In this paper, the effects of coal moisture content on conveying behavior and resistance characteristics of dense-phase pneumatic conveying were explored. Meanwhile, a model of the additional pressure drop of particles was proposed and compared with the experimental data. The results show that though the resistance and cohesiveness increase with increasing moisture content, its influence is different in dense and dilute phase. In the dense-phase region, the coal with lower moisture content shows a larger solid mass flow rate and solid concentration; while in the dilute-phase region, the moisture content has minor effect on conveying characteristics. For the coal with lower moisture content in dense-phase region, the solid mass flow rate and solid concentration are larger, and the gas velocity has a small effect on solid friction factor, due to its smaller cohesiveness and resistance, which is showed in our experiments and inferred from our model. The additional pressure drop model was proposed for straight pipes and bends, whose parameters are probably effective than the existing parameters in this kind of model, as the deviation in the vertical rise pipe, horizontal pipe and bend pipe is controlled within ±30%, and the corresponding vertical down pipe are controlled within ±40%.

Coupling Technology of Deep-Hole Presplitting Blasting and Hydraulic Fracturing Enhance Permeability Technology in Low-Permeability and Gas Outburst Coal Seam: A Case Study in the No. 8 Mine of Pingdingshan, China

The current study aims to analyze the principles of integrated technology of explosion to tackle the problems of coal seam high gas content and pressure, developed faults, complex structure, low coal seam permeability, and high outburst risk. Based on this, we found through numerical simulation that as the inclination of the coal seam increases, the risk of coal and gas outburst increases during the tunneling process. Therefore, it is necessary to take measures to reduce the risk of coal and gas outburst. We conducted field engineering experiments. Our results show that the synergistic antireflection technology of hydraulic fracturing and deep-hole presplitting blasting has a significant antireflection effect in low-permeability coal seams. After implementing this technology, the distribution of coal moisture content was relatively uniform and improved the influence range of direction and tendency. Following 52 days of extraction, the average extraction concentration was 2.9 times that of the coal seam gas extraction concentration under the original technology. The average scalar volume of single hole gas extraction was increased by 7.7 times. Through field tests, the purpose of pressure relief and permeability enhancement in low-permeability coal seams was achieved. Moreover, the effect of gas drainage and treatment in low-permeability coal seams was improved, and the applicability, effectiveness, and safety of underground hydraulic fracturing and antireflection technology in low-permeability coal seams were verified. The new technique is promising for preventing and controlling gas hazards in the future.

Low-temperature oxidation and self-heating accelerated spontaneous combustion properties of a Yima formation bituminous coal with various moisture contents

By thermogravimetry (TG) experiments, evolution behaviors and properties of thermal oxidation processes at low temperature (< 230.0 °C) of a bituminous coal with five moisture contents were investigated. A novel Acceleration Temperature Point Method (ATPM), defined as the transition point from low-temperature oxidation to rapid self-sustained heating-up period, was proposed to determine the role of moisture content in accelerating such process. Results show that segments of water evaporation and gas desorption dominate in stage 1 (65.0–150.0 °C), while segments of generation of coal-oxygen complex and structure oxidation dominate in stage 2 (150.0–275.0 °C). In the moisture range of 9.16–12.06%, the promoted effect of physical desorption capacity becomes weak with increasing moisture content. This is owing to five aspects: the equilibrium of vapor pressure and wetting capability of physically bound water, the change of mass and heat transfer between gas phase (water vapor)-condensed phase (bulk coal particle), the diffusing effect of gaseous water, the heat from dissolving and swelling of gaseous water into bulk coal pores, and the heat of pyrolysis derived from coal particles. Taking Acceleration Temperature Point (ATP) as a barometer to evaluate the spontaneous combustion susceptibility, the critical moisture content of Gengcun bituminous coal is 9.16%.

Experimental Study on Mechanical Properties of Briquette Coal Samples with Different Moisture Content

Coal seam water injection is an important technical method to prevent and control coal and gas outburst and other disasters. Water can soften coal and change its mechanical properties. In order to study the mechanical properties of coal samples with different moisture content, briquette coal samples with five moistures content (4%, 6%, 8%, 10%, and 12%) were selected to carry out triaxial compression tests under different confining pressures (0.1, 0.2, 0.4, 0.8, and 1.2 MPa). Then, the mechanical response mechanism of the water-bearing briquette coal was analyzed. The results show that the slope of the linear elastic stage of the stress-strain curve gradually decreases with the increase of moisture content. Water-bearing coal exhibits strain strengthening characteristics under high confining pressure, which transforms the water-bearing coal from brittle to ductile state. The peak stress under different moisture content conditions shows a linear relationship with the confining pressure. The internal friction angle decreases linearly with the increase of moisture content. The cohesion varies parabolically with the increase of moisture content and reaches the maximum value when the moisture content is 8%. The coal body with moisture content between 7% and 9% has a high bonding force, which is beneficial to the consolidation of the coal body. Therefore, ensuring a reasonable moisture content of coal through coal seam injection can provide a basis for preventing coal and gas outburst.

Air Dispersion Modelling of Coal Particles Released During Handling of Cargo at Port

Mormugao Port Trust (MPT) handles 1087 t/h of coal with the help of 6 mooring dolphins situated at around 600-m distance in sea from the port next to the city of Vasco da Gama, Goa, India. During the said operations, the particles are released at lower height (2 to 5 m from sea water level) unlike other emissions. Since the city is situated next to the port, particles released during the handling of coal reach the Vasco city due to dispersion and affect health of the people in the city. The objective of this study was to identify the key variables which affect the dispersion of the particles released during coal loading and unloading operations. Detailed simulation studies are carried out to study the effect of wind speed, atmospheric temperature, atmospheric humidity, moisture content of coal, and the release height of the material from cranes, on dispersion of particles. For this purpose AERMOD software was used. All the necessary data required for the study was collected from Mormugao Port Trust, Vasco, Goa. Wind speed and moisture content of materials are key variables identified as they influence the dispersion significantly. With wind speeds greater than 8 m/s, the concentrations of PM10 and PM2.5 exceed beyond permissible limits up to 1 km radius. Variation in release height from 1 to 3 m does not have significant effect on particle dispersion. Change in atmospheric temperature and atmospheric humidity has no influence on dispersion of particles. The model results are validated with the field data obtained during the actual handling of coal at Mormugao Port Trust.

Effect of Critical Variables on Air Dense Medium Fluidized Bed Coal Drying Efficiency and Kinetics

Calorific value, as a key component for fuel quality assessment, directly affects the thermal power plants' efficiency. While high-quality coal is consumed as metallurgical coal, low-rank coals are used by coal-fired power plants. The high moisture content of the thermal coals significantly influences their heating values. In this study, the drying performances of the fixed bed and air dense medium fluidized bed (ADMFB) dryers were investigated under the superficial air velocity of 15-18 cm/s, inlet air temperature of 55-75 oC, and up to 80 minutes of operation. Low air consumption is an intrinsic characteristic for ADMFB, while a low-temperature range for drying air was selected to address the coal-fired power plants' waste heat. It was found that an increase in air velocity and temperature favored the drying efficiency of both systems (i.e., 18 cm/s and 75 oC), with the temperature being more effective than the air velocity. The ADMFB dryer removed comparatively more moisture than the fixed bed for the shorter drying durations. For example, for 10% moisture reduction at 75 °C, the ADMFB dryer needed 5 minutes less time than the fixed bed. The fitting quality and goodness of serval well-known thin-layer models for describing fluidized bed and ADMFB coal drying kinetics were assessed by several models and statistical evaluators, respectively. It was found that the Middilli & Kucuk model best describes the fixed bed coal drying (i.e., R2=0.999, RSE=0.001, RMSE=0.008), while the Page model much properly simulates the ADMFB coal drying (i.e., R2=0.998, RSE=0.002, RMSE=0.009).

КРАЙОВИЙ КУТ ЗМОЧУВАННЯ КАМ’ЯНОГО ВУГІЛЛЯ ВОДОЮ

It is known that in the process of coking a compacted coal charge during its ramming in an industrial ramming-loading-pushing machine, the moisture of the charge plays the role of a compaction agent. On the basis of this, the authors put forward a reasonable assumption that the higher the ability of coal grains to hydration, the stronger the contact between them and, accordingly, the greater the density of the formed rammed coal cake. Therefore, the determination of the ability to hydrate the surface of coal used in the charge for ramming is of both theoretical and practical importance. For the numerical determination of this indicator, the authors have chosen the contact angle of wetting, determined by the method of "sessile drop" of water on a carbon substrate. The article presents the results of a study of the ability of various brands of coal to hydrate. The article describes the characteristics of the studied grades of coal and their contact angle of wetting with water (Ɵ) after 1, 2 and 3 minutes of keeping the drop on a polished surface. Since according to the literature data, the organic mass of coal is hydrophobic, and mineral impurities, as a rule, are hydrophilic, the authors investigated the degree of influence of the "ash content of coal" (Аd ) indicator on the value of Ɵ. To determine the influence of the wetting angle and the internal moisture content of coal after 14 hours of moisture saturation in water (Wins) on the strength (ϭss) of the rammed sample, the corresponding graphical dependence was determined. The data obtained indicate that any significant relationship between Аd and Ɵ is absent, the correlation coefficient is insignificant (r = 0.28). Thus, the predominant factor in the hydration of cleaned coal is the properties of its organic matter. The correlation between Ɵ and the yield of volatile substances Vdaf and the content of vitrinite Vt is also insignificant – the correlation coefficient is up to 0,43 and 0,50 respectively. A close relationship of the contact angle was found with the reflection coefficient of vitrinite Ro (r = 0.72), the internal moisture content of coal after 14 hours of saturation in water, Wins (r = 0,65), and the shear strength of the rammed coal sample ϭss (r = 0,68). Keywords: coal, ability to hydration, contact angle of wetting, organic mass of coal, mineral impurities, density, strength. Corresponding author V.M. Kuznichenko, e-mail: : ko@ukhin.org.ua

基于BP神经网络的煤炭含水率预测研究

基于BP神经网络的煤炭含水率预测研究

Study on the evolution of internal and external water of lignite during microwave drying and the moisture reabsorption characteristics of dried lignite

ABSTRACT Lignite with high moisture content needs to be dried. The variations of internal and external water of Mindong lignite during microwave drying were studied. The effects of coal particle size (<0.2 mm, 1–4 mm, 8–12 mm) and target moisture content (20%, 15%, 10%) on the moisture re-absorption characteristics of dried samples were analyzed. It was found that microwave heating quickly removes the moisture of lignite, showing an exceptionally positive effect on the removal of internal water. During the drying process, the pore volume of lignite first decreases and then increases, while the content of oxygen-containing functional groups such as hydroxyl and carboxyl group on the surface of lignite decreases. When dried lignite is under a normal atmosphere, lower moisture content and smaller particle size lead to more water to be reabsorbed; The external water contents of coal samples (8–12 mm) with target moisture content of 20%, 15% and 10% are 5.45%, 5.44% and 5.21%, respectively, which shows the similar external water content. The experimental results are conducive to exploring the moisture migration path during drying and re-absorption of dried lignite. Considering the balance of drying and re-absorption, microwave drying of lignite should have optimum target moisture contents and material particle sizes, depending on the specific conditions and requirements. The research provides theoretical guidance for the industrial application of lignite drying.

Studies on the influence of moisture on the sorption and structural properties of hard coals

In the conducted research, the effect of moisture on CO2 sorption and transport processes and changes occurring in the coal pore structure were investigated in detail. The measurements were carried out under isothermal (313 K) and isobaric conditions (0.1−0.8 MPa) on the original device - a manometric sorptomat. Coal sorption capacities, Langmuir sorption isotherms, effective diffusion coefficients and structural parameters were analysed. The obtained sorption capacities of the tested samples relative to CO2 for pressures 0.1, 0.3 and 0.8 MPa confirmed that moisture significantly (even up to 6 times) reduces the sorption capacity of coal relative to CO2, and the largest reduction in sorption capacities was noted on coal with the lowest vitrinite reflectance. It was observed that the increase of the sorption equilibrium pressure decreases the effect of the reduction of the sorption capacity of coal under the influence of moisture, and above 1.0 MPa this effect disappears completely. The critical moisture content was estimated, above which there is no further reduction of the coal sorption capacity due to the increase in moisture content. It was observed that the influence of moisture on CO2 diffusion in its pore space is not clear. Structural analysis were carried out by low-pressure CO2 adsorption at 273 K and 0−0.1 MPa. After increasing the coal moisture content, the surface area decreased by 50 % and a decrease in the volume of available pores with diameters in the range of 0.5−0.6 nm was noted.

A machine learning approach to improve ignition properties of high-ash Indian coals by solvent extraction and coal blending

Indian coals are of poor quality, having high ash content and lower calorific value as compared to foreign coal reserves. To circumvent the problems of high ash content and low calorific value in coal, this study endeavours to explore two methods of improving ignition characteristics of Indian coals: solvent extraction and coal blending. The thermal decomposition behaviour of four Indian coals with and without solvent extraction were investigated through a thermogravimetric analyser under non-isothermal conditions. Kinetic parameters and activation energies of the coals were determined by using Arrhenius, Coats-Redfern, Doyle-Ozawa and Friedman methods. It was found that solvent extraction of the coal reduced the activation energy by approximately 50%. Pearson correlation analysis performed on the chemical composition and ignition properties of 16 typical Chinese coals and 48 of their blends showed that moisture, volatile matter, fixed carbon, calorific value, oxygen, and carbon content of coals were the most relevant factor to ignition temperature and activation energy. Accordingly, three-layer back-propagation neural network models were trained and tested and found to be reasonably accurate. The selected neural networks were used to predict the ignition characteristics of 17 Indian coals. 16 Indian coals were then hypothetically blended with 84 coals from various other countries to form 1344 blends, whose ignition characteristics were further predicted using the trained neural network models. 220 of these 1344 blends were found to have better ignition properties than the original Indian coals. The maximum reductions observed in ignition temperature and activation energy were 79.08 K and 179.38 kJ/mol respectively.

An investigation of performance characteristics and energetic efficiency of vertical roller coal mill

ABSTRACT This study shows the performance of a currently running vertical roller coal mill (VRM) in an existing coal-fired power plant. In a power plant, the coal mill is the critical equipment, whose effectiveness impacts the overall power plant efficiency. Uniform coal feeding mass flow rate and required particle size and temperature at the outlet channel throughout with better classifier performance are crucial indicators that characterize the coal mill performance. To understand the performance of a vertical roller coal mill, the real operational tests have been performed considering three different coal sources. Obtained results indicate that grinding pressure, primary air (PA) temperature and mill motor current have a tendency to rise by increasing coal feeding mass flow rates for all used coal. Moreover, coal volatile matter and moisture content are improved by increasing the mill outlet temperature for each coal type. Additionally, effect of enhancement of the classifier speed has been found favorable on the combustion performance indicators. CMC coal shows relatively better performance since it has lower moisture content and higher hard grove index. Ultimately, the energetic efficiency of coal mill has been investigated and performance value has been found to be a maximum value of 96.2%.

Explicit equation derivation for predicting coal moisture content in convective drying process by GMDH-type neural network

ABSTRACT Predicting the instant moisture content of the low-rank coals under the different drying conditions is crucial to construct the optimal system design and operation related to drying processes. Even if the thin-layer drying models are at the center of the field studies, the disadvantage of these type models is that the prediction results are valid only for the conditions of the drying experiment. Conversely, artificial intelligence models can provide accurate prediction results under a wide range of different conditions. Nevertheless, they are not practical because of their implicit forms and require both the specific software and experts. In this study, the GMDH-type neural network is applied for the first time in developing explicit model equations for the prediction of coal moisture at any time during the drying process. 223 experimental instances are used, representing coal moisture contents obtained under the different drying conditions. The considered parameters are bed height (80–150 mm), coal sample size (20–50 mm), drying air velocity (0.4–1.1 m/s), drying air temperature (70–160 °C), and drying time (0–270 minute). The developed equation is nonlinear and provides satisfactory prediction accuracy (R2 is 0.96–0.99) for different drying conditions. Additionally, its usage is quite practical due to the explicit form.

Numerical Simulation of a Coke Oven Using Decoupling Techniques

Cokemaking is an important unit operation in an integrated steel plant as coke quality has a strong influence on blast furnace performance. A two-dimensional (2D) model coupling physico-chemical phenomena inside combustion and coking chambers of a coke oven has been presented. It was implemented using the computational fluid dynamics software Ansys Fluent and was solved by a serial decoupling approach to improve convergence and to reduce computational time. The model predictions for gas temperatures inside the combustion chamber and the effect of coal moisture content on evolution of coke bed temperatures are in reasonable agreement with published experimental data. The computational time required for the 2D model is six times lower than that for a corresponding three-dimensional model. This model is useful for model-based optimization of cokemaking and for designing coke ovens with reduced computational burden.

Insights into moisture content in coals of different ranks by low field nuclear resonance

The moisture occurrence in coal reservoirs has important significance in the evaluation of gas-bearing properties and production of coalbed methane (CBM). In order to investigate the occurrence mechanism of moisture content of coals, a series of experiments including mercury intrusion porosimetry (MIP), low temperature nitrogen gas absorption/desorption (N2GA) and nuclear magnetic resonance (NMR) are conducted in this study to characterize and quantify pore structure properties. The nature of occurrence of moisture content in coal reservoir pores is then divided into four categories by NMR saturation and centrifugation experiments. The bound water content in the adsorption pore accounts for the highest proportion. Based on the relevance of bound water content and its influencing factors, moisture occurrence in coal reservoirs of different ranks is revealed by SPSS statistical methods. The moisture content of low-rank coal is mainly controlled by elemental oxygen and specific surface area, whereas for medium- and high-rank coals, this is controlled mainly by minerals. Our study finds application in CBM evaluation and development.

Influence of alkaline solution injection for wettability and permeability of coal with CO2 injection

The technology for combining CO2 injection with alkaline solution injection into coal bodies is proposed and investigated to address the disadvantages of traditional CO2 injection technologies, such as the production of dangerous amounts of excess residual gas and prevention of water injection into the deeper coal seams. After the CO2 injection, the wettability of coal sample is greatly improved, especially the alkaline solution. CO2 injection can effectively displace methane in coal, while alkaline solution can dissolve CO2 molecules adsorbed in coal and improve the wetting effect of coal. The increase of moisture will lead to the decrease of coal permeability, which can reduce gas emission. The permeability loss ratios for coal samples injected with CO2 were more than 90% much higher than those for coal samples not injected with CO2. After alkaline injection, the moisture content of coal into which CO2 had been injected increased 6.13 times compared to raw coal. Therefore, this technology may consume excess CO2 gas from the coal body and improve the effect of water injection into deeper coal seams.

Analysis of Upgrading Process of South Sumatera Low Rank Coal

This research aims to find a method of removing moisture of Indonesian low rank coal by using a combined equipment of evaporator and heater. The heating equipment was controlled at varied temperatures of 343 K, 353 K and 363 K. This method is expected to increase heating value and reduce moisture content of coal. Based on this study, the removal of moisture content of Indonesian low rank coals was affected by the heating temperature and particle size of coals. Ambient air was passed through the evaporator tubes to decrease the temperature until reaching the dew point temperature of the air and then through the heating elements of a heater before entering the fluidised bed of pulverized coal. The results of this research showed that the heating value of coal can be increased up to 35.4% and also the moisture content can be reduced up to 29.8%, both at heater temperature of 363 K and particle size of (-20 +40) mesh.

Decision tree regression model to predict low-rank coal moisture content during convective drying process

ABSTRACT Coal is still a significant energy source for the world. Due to the utilization of low-rank coal, drying is a key issue. There are lots of attempts to develop efficient drying processes. The most prominent method seems as thermal drying. For thermal drying processes, the most important subject is the coal moisture content change with time. In this study, convective drying experiments were utilized to develop a new model based on decision tree regression method to predict coal moisture content. The developed model gives satisfactory results in prediction of instant coal moisture content with changing drying conditions. With the decision tree depth of six, the best test results were achieved as 0.056 and 0.802 for MSE and R 2 analyses, respectively.

Improving permeability of coal seams by freeze-fracturing method: The characterization of pore structure changes under low-field NMR

The method of improving permeability of coal seams by freeze-fracturing is presented to accelerate the diffusion of coalbed gas into exploited wells. The pore structure of coal sample changes caused by freeze-fracturing were characterized by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), and a permeability-calculation model was employed to estimate the permeability of coal sample. The pore size distribution, porosity, and permeability of coal before and after freezing were analyzed. Results show that freeze-fracturing can complicate the coal pore structure, and its complexity is positively correlated with the freezing temperature and coal moisture content. The main manifestation is the growth and expansion of coal pores, with higher pore connectivity, generation of gas seepage pores with pore diameter > 100 nm, and expansion of original pores into larger ones. By comparing the connectivity and seepage space of the pore structure of coal before and after freezing, it is concluded that freeze-fracturing can promote the coal seam permeability significantly, which is beneficial for the exploitation of coalbed gas.