Moisture Content Of Coal Research Articles

Experimental study of the moisture content influence on CH4 adsorption and deformation characteristics of cylindrical bituminous coal core

Moisture content in coal is an important factor affecting the coal seam gas extraction. It directly affects the storage and flow of gas in bituminous coal. In this paper, the cylindrical bituminous coal cores of Xutuan coal mine in Huaibei coal mine group were studied as experimental objects, using the laboratory self-designed experimental device Gas Adsorption and Strain Testing Apparatus system. The influence of the bituminous coal moisture content on gas adsorption characteristics was studied. Drying experiments of coal samples showed that they lose the original moisture content following the exponential decay function of time. At wetting, the saturated moisture content in coal samples increased following the Exponential Association function of time. The experimental results show that the average original moisture content and average saturated moisture content of raw coal samples are 1.3 and 2.4%, respectively. On this basis, the gas adsorption experiments on samples with different moisture contents under different gas pressures were carried out. With the moisture content increase, the gas adsorption capacity and saturation value decreased and the decrease rate gradually reduced. The single exponential decay function describes the gas adsorption capacity dependence on moisture content. Moisture content also affects the adsorption deformation of bituminous coal. At high moisture content, the adsorption deformation of bituminous coal is less.

The fluorescence interference in Raman spectrum of raw coals and its application for evaluating coal property and combustion characteristics

Fluorescence interference in Raman spectrum is a big barrier for rapid and precise analysis of coal structures by Raman spectroscopy. Dealing with fluorescence interference suitably is one of the key tasks before efficient application of Raman spectroscopy in coal assessment. In this study, Raman spectra and coal combustion characteristics of 32 kinds of Chinese coals were respectively obtained in a micro-Raman spectrometer and Thermal Gravimetric Analyzer. The degree of fluorescence interference in Raman spectrum was firstly defined and quantified as the drift coefficient α using a simple method without curve-fitting the spectrum. The correlations between the degree of fluorescence interference and coal property, coal combustion characteristics were set up and multivariable analysis was done. The results indicate that the degree of fluorescence interference is well related to the coal structures, and it is synthetically determined by volatile, moisture and ash content in coal. With the increase of volatile, moisture content in coal, the fluorescence interference increases continuously, and it can be reduced but not eliminated by drying the moisture in coals. Significant mathematical relations between the drift coefficient α and volatile, moisture content, coal combustion characteristic temperatures have been found. Coal with more evident fluorescence interference in Raman spectrum usually has lower degree of coalification, more polar functional groups, and burns at a lower temperature. The drift coefficient α can act as an efficient probe for coal property and coal combustion characteristics. This study provided a new and simple approach for evaluating coal property and coal combustion characteristics by fluorescence interference in Raman spectrum.

Neutron Gamma-Method for Monitoring Ash Content of Coal

A brief analysis is given of the modern instrumental methods of monitoring the ash content of coal. Their particulars and drawbacks are examined. A neutron gamma-method of monitoring the ash content is proposed on the basis of integrated use of prompt γ-radiation accompanying inelastic scattering of fast neutrons and radiative capture of thermal neutrons by nuclei of the primary elements comprising the organic and mineral components of coal. The instrumental-methodological parameters of monitoring (sizes of the analyzed samples, energy intervals of the detected gamma radiation) making it possible to the increase the sensitivity of the method with respect to the ash content and to minimize the impact of the variability of the moisture content of coal on its material composition, are optimized. The method has been certified and recommended for representative monitoring of the quality of coarse coal.

Effect of moisture on the desorption and unsteady-state diffusion properties of gas in low-rank coal

Currently, resource integration in coal-burning facilities and clean energy reconstruction are being strongly pushed forward in China. As a clean fossil energy, unconventional natural gas, such as coalbed methane (CBM), exhibits promise as an energy development strategy. In China, there are abundant CBM resources in the considerable reserves of low-rank coal. Therefore, the study of low-rank coal is the key to realize the high-yield and high-efficiency development of CBM resources in China. In this paper, a new water injection device was designed to prepare coal samples with a variety of moisture contents, and a novel method to measure the gas desorption properties in coal containing water was introduced. On this basis, the gas desorption law in low-rank coal with different moisture contents was tested, and the effect of moisture on the gas diffusion properties in low-rank coal was analyzed. The results indicate that the initial gas desorption volume of low-rank coal is extremely large and that the gas desorption law in the moisture-containing low-rank coal can be described by Airey's empirical equation. It is also observed that the ultimate gas desorption volume, initial gas desorption rate and initial effective gas diffusion coefficient all shift toward the direction that is beneficial to CBM development. Therefore, reducing the moisture content in low-rank coals through certain techniques can dramatically enhance the gas migration behavior and achieve the purpose of high-yield CBM development.

Investigation of steam effect on ignition of dispersed coal particles in O2/N2 and O2/CO2 ambiences

In this paper, we intensively investigate the influence of steam on the hetero-homogeneous joint ignition of dispersed coal particle streams in both O2/N2 and O2/CO2 conditions of an optically accessible flat-flame burner. Two differently ranked coals and one bituminous char were tested for a comparison. The effects of moisture content in the raw coal, steam content or diluents (N2/CO2) in the ambience, and fuel types were systematically examined under isothermal conditions. First, it is seen that the moisture content in raw coal delays its ignition because of endothermic vaporization, which becomes weakened at the high ambient temperature. Secondly, three main mechanisms are categorized to explore the profound effects of ambient steam content on ignition of coal particles, i.e., (i) the promotion effect of OH radical on the oxidation of volatile hydrocarbons, (ii) the inhibition effect of gaseous H2O molecule on the equilibrium of hydrocarbon oxidation, (iii) the negative effect of endothermic surface gasification reaction (C-CO2/C-H2O). In O2/N2 ambience (1500 or 1800 K), as the steam content increases, the ignition delay of coal particles is rapidly reduced in an early stage of 0%–5% due to the positive effect of OH radicals, followed by an inappreciable reduction in 5%–13% stage because of both the steam inhibition effect and the endothermic surface gasification. However, in O2/CO2 ambience with sufficiently high steam content (5%–18%), the ignition delay even becomes longer with the further increment of steam. It is because of the synergistic effect between C-H2O and C-CO2 reaction at high temperatures (1500 K and 1800 K). Finally, for fuel types, the OH radical promotion effect of two lignite samples is obviously higher than that of low-volatile char samples, whereas with steam addition the sodium-rich Zhundong coal exhibits lower ignition delay than Hulunbel lignite due to catalytic effect.

Influence of coal moisture on initial gas desorption and gas-release energy characteristics

Coal and gas outbursts (hereinafter referred to as ‘outbursts’) result in serious damage and often occur in tectonically-deformed coal that is rich in gas. It has been demonstrated that the level of outburst risk declines with increasing coal moisture content. Moreover, an outburst generally lasts for mere tens of seconds and the required energy is mainly provided by the gas expansion energy. However, the gas desorption and energy release characteristics of tectonically deformed coal with different moisture contents during the first dozen seconds have not often been studied. In this study, a set of self-designed gas desorption equipment was used to carry out gas adsorption-desorption experiments in the first dozen seconds (about 13 s) on coal with different moisture contents. The results show that the drop rate of the gas pressure increases with an increase in coal moisture content, and the total amount of gas desorption and the mass flow rate of gas desorption reduce correspondingly in the gas desorption process. Moreover, the gas velocity also slows with increasing moisture content. Under different gas pressures, the total gas expansion energy (TGEE) and the total gas energy (TGE) released from the coal decrease with the increasing moisture content. Correspondingly, it takes a shorter time for coal to release 90% of the TGEE and the TGE. For all of the coal samples, the time taken for releasing 90% of the TGEE is shorter than that for releasing 90% of the TGE. Meanwhile, the ratio of TGEE in the TGE increases with the increasing moisture content. The TGEE accounts for 14–16% of the TGE released from coal samples of different moisture contents under different gas pressures.

Development of a new fine particle dry separator

Dry coal cleaning has generated renewed interest in scientific and coal mining communities alike due to water scarcity in many parts of the world and the numerous tailings ponds that have resulted from traditional wet coal preparation methods. Commercially available dry separation technologies such as air tables and air jigs are mostly effective in cleaning coarse coal with particle size larger than 6.35 mm. The smaller-than-6.35 mm fraction, which might be up to 20 to 40 percent of raw coal, is sent to the clean coal or tailings streams in a dry separation plant without any cleaning. The main objective of this study is to develop, design and fabricate a new density-based dry separator to effectively clean fine coal in the size range of smaller than 6.35 mm to larger than 1 mm. A difficult-to-clean coal sample with particle size smaller than 6.35 mm and flat-shaped shales as main rocks were used in this study. Using a laboratory-scale fluidization bed, the optimum air flow rate for fluidization of fine particles in air tables was found, which was much less than that for coarse coal. The perforations diameter and open area of the separating deck of the air table were also found to be critical for fine particle separation. These findings led to the development of a new air table named SIU Airtable for cleaning fine coal sized smaller than 6.35 mm and larger than 1 mm. The new air table has a unique air distribution and fluidization system for fine particles, along with adjustable vibration frequency and direction. It also has an optional extended section to lower the moisture content of high-moisture fine coal using part of the fluidization air. The experiments showed that an ash rejection of about 49 percent could be achieved with a combustible recovery of around 89 percent, indicating suitable separation. Furthermore, increasing ash rejection to 70 percent gives a combustible recovery of 72 percent, indicating that the separation performance of the new air table is close to the fine coal washability data.

Experimental study on thermo-responsive inhibitors inhibiting coal spontaneous combustion

Due to its strong fluidity and easy evaporation characteristic, high water-cut physical inhibitors (HWPIs) cause the decrease in moisture content of coal, so that its inhibitory effect on coal spontaneous combustion weakens or even fails. Aiming at solving the problem, this paper proposes to inhibit coal spontaneous combustion using thermo-responsive inhibitors (TRIs). These inhibitors are sensitive to specific temperatures and can retain their effects as long as the temperatures have not been reached. Besides, when the temperatures are reached, they are able to absorb heat and undergo physical and chemical changes to release H2O and inert gases (defined as gases that are not involved into the coal oxidation reaction in this paper) such as NH3 and CO2, so as to inhibit the low-temperature oxidation of coal. Based on the temperature-programmed experiment of coal spontaneous combustion, this paper analyzed the effects of types and amounts of TRIs on coal spontaneous combustion by using differential scanning calorimetry (DSC), scanning electron microscope (SEM), thermogravimetry-derivative thermogravimetric analysis-differential scanning calorimetry (TG-DTG-DSC) and nitrogen adsorption test methods. The results show that CaCl2•6H2O achieves the most stable inhibitory effect, as its inhibiting rate rises steadily in the heating process to reach a maximum value of 79.9% at 200 °C.

Influence of increased primary air ratio on boiler performance in a 660 MW brown coal boiler

A computational fluid dynamics model was established based on a 660 MW brown coal boiler, to study the effects of primary air ratio (PAR) on boiler performance. To improve model prediction, moisture content in brown coal is specially considered. Confidence in the model was established by carrying out mesh independence test and validation against real life data and theoretical calculations. Then it was used to simulate 10 cases with different PAR. Results show that with PAR increasing from 0.325 to 0.55, overall boiler performance deteriorates and total radiative heat flux decreases by 35.2 MW. However, the temperature distribution and heat flux in main burners region and above separated over fire air region show a parabolic trend. The results indicate that boiler performance deteriorates with PAR increasing, and well explain why boiler thermal load is still reduced, even if PAR is increased to maintain the drying capacity in high moisture content cases. Momentum ratio of primary and secondary air is pointed out to be the main cause of this phenomenon. At last, a feasible solution is proposed to raise primary air temperature, not the ratio of it, to maintain the drying capacity. Therefore, the adverse effects caused by increased PAR can be avoided.

Molecular dynamics simulations of interaction between sub-bituminous coal and water

The high moisture content of sub-bituminous coal is associated with the interactions between coal and water. Because of complex composition and structure, the graphite surface modified by hydroxyl, carboxyl and carbonyl groups was used to represent the surface model of sub-bituminous coal according to XPS results. Density profiles for oxygen atoms and hydrogen atoms indicate that the coal surface properties affect the structural and dynamic characteristics of the interfacial water molecules. The interfacial water exhibits much more ordering than bulk water. The results of radial distribution functions, mean square displacement and local self-diffusion coefficient for water molecule related to three oxygen moieties confirmed that the water molecules prefer to absorb with carboxylic groups, and adsorption of water molecules at the hydroxy and carbonyl is similar.

Ultrasonic technique for online measurement of bulk density of stamp charge coal cakes in coke plants

Coke oven batteries utilize stamp charged coal cakes for production of high quality blast furnace coke. Crushed coal blends are mechanically stamped to produce coal cakes. It is crucial to have a good control over this stamping operation so as to achieve a uniform bulk density (≈1100–1200kg·m−3 wet basis) of coal cake post stamping. This can facilitate robust and energy efficient coking operation. The dynamic nature of the stamping operation necessitates an online bulk density measurement technique. An ultrasonic technique which enables online measurement of bulk density during the stamping operation is described. The ultrasonic response was found to have a straight line correlation with bulk density (wet basis) and moisture content of stamped coal with an R2 value of 0.98. The effect of moisture content in the coal on the ultrasonic measurements is also discussed. A lab scale prototype was developed with integrated sensors to emulate online measurement. The prototype was found to have a measurement error of less than ±1.6%. This method can also be suitably adapted for online bulk density measurement of granular solids other than crushed coal.

Study of the Change in the Coal-and-Liquid-and-Gas Interfacial Angle

The use of surfactants has a significant impact on the safety of mining operations in order to prevent dynamic processes, prevent dust. The interfacial angle is the main indicator characterizing the interfacial interactions for heterogeneous multicomponent solid bodies, coal and solutions. The problem of development of modern methods for determining the interfacial angle at the coal-water-gas boundary is considered. The results of the research study of the change in the coalliquid-gas interfacial angle are presented. The influence of various coal properties and characteristics on the interfacial angle value is shown. The influence of the interfacial angle on wetting and filtration processes, the features of the experimental methods for the interfacial angle determination are shown. A model of the coal surface consisting of four main components is proposed. The main attention is paid to the moisture content of coal and capillaries as the main factors determining the properties of coal. An analytical method for determining the interfacial angle of coalwater-gas is proposed.

Effect of hydrothermal dewatering on the moisture content of brown coal

ABSTRACTBrown coal was dewatered under hydrothermal dewatering (HTD) conditions. The variation in moisture content and distribution of brown coal were studied. The results showed that equilibrium moisture content decreased from 28.2% to 9.6% after hydrothermally treated at 300 ºC. Three types of moisture existed in brown coal and its HTD products according to the coal-water binding energy (Eb): Surface adsorption water (Eb < 2000 kJ/kg), interparticle water (2000 < Eb < 9000 kJ/kg), and interior adsorption water (Eb > 9000 kJ/kg). Drying rates of these types of moisture​ respectively followed logarithmic, linear, and indicial equations.

Volatilization of mercury in coal during conventional and microwave drying and its potential guidance for environmental protection

During the thermal drying process of coal, the sufficient attention has been paid to the changes in the properties of coal before and after the drying process. However, the volatility characteristics of harmful trace elements in coal during the drying process are always neglected to date, whereas the volatilization of harmful trace elements not only has significant effects on the surrounding atmosphere environment but also influence the following utilization of dried coal. In this study, the volatility characteristics of both the moisture and mercury in the coal sample during conventional (electric blast oven) and microwave (microwave oven) drying processes were investigated. In addition, the changes in the surface properties of coal before and after the drying process were studied using X-ray photoelectron spectroscopy (XPS) analysis. The results show that the moisture content of coal decreases in non-line format (decreases slowly at the first and then quickly according to the drying time) in the conventional drying process, while it decreases in line format in the microwave drying. The microwave drying process needs much shorter time required to obtain the dried coal of a certain moisture content than the conventional drying process. Under the same volatilization rate of moisture, the volatilization rate of mercury in the microwave drying process is always greater than that in the conventional drying process. Nearly half or more (49.73% and 59.26%, respectively) of the mercury in the coal slime evaporates into the atmosphere after the drying processes. XPS results show the content of CC and CH groups on the coal surface increased, but the CO content decreased after the drying processes and the microwave drying process has a stronger ability to remove oxygen-containing functional groups than the conventional drying process.

Selective removal of sodium and calcium from low-rank coal – Process integration, simulation and techno-economic evaluation

This paper has addressed the techno-economic feasibility regarding the selective removal of sodium (Na) and calcium (Ca) from low-rank sub-bituminous coal, aiming to reduce the ash slagging and fouling propensity in the pulverized coal-fired boilers. Four novel process integrations were proposed and simulated in Aspen Plus. Both the novel counter-current three-stage water washing process and an acid-water two-stage washing process have proven to improve the ash fusion temperature satisfactorily, reducing the mass fraction of Na2O in ash from 4.32wt% to 0.85 and 0.19wt%, respectively. In addition, the use of acid-water washing removed 12.5% CaO and 19.5wt% total ash. For the recycle and treatment of wastewater, the water gain is desirable for the use of an evaporator, owing to the dewatering of the initially high-moisture coal (25wt%) in the centrifugal and the high water recovery rate from the evaporator. However, the good performance of evaporator was counteracted by the considerable capital cost caused by the huge heat transfer area requirement. Instead, the use of reverse osmosis (RO) resulted in a water loss up to 228.4kg/t coal. Additionally, prior to the RO treatment unit, the recycle and reuse of the unsaturated water for maximum six times and four times for three-stage water washing and acid-water two-stage washing, respectively, was critical in reducing both the water and power consumption. The water consumption dropped to 38.1kg/t coal and 48.1kg/t coal for the three-stage water washing and acid-water two-stage washing process, respectively. Both are remarkably lower than 85.0kg-water/t black coal. In terms of the power consumption, it decreased to ~9.4kWh/t coal for the three-stage water washing process and further down to 5.8kWh/t for the acid-water washing case, which was even slightly lower than 6.3kWh/t for the black coal. Furthermore, the integration of acid-water washing and RO was also demonstrated to be economically viable by its high NPV, IRR and short payback period. Sensitivity analysis indicate that, the original Na content in raw coal is the most influential variable on the water and power consumption of the overall process, followed by the initial moisture content in the raw coal. For a low-rank coal containing >2150–2520ppm Na and/or <19wt% moisture, the washing process proposed would turn economically unviable compared to the existing black coal washing process. A minimum selling price of 136 RMB/t (−32% deviation) was also necessary to keep both NPV and IRR positive as well as the payback period shorter than the project lifetime.

Performance Analysis on an Entrained‐Flow Gasifier by Coal Moisture

AbstractThe performance of a 300‐MW‐class Shell entrained‐flow gasifier along with moisture contents in low‐rank coal was studied by a rigorous dynamic model. The developed model predicted the steady‐state reference data well. The gas and slag temperature profiles decreased with higher coal moisture content, which led to an increase of the slag thickness on the gasifier wall. The high‐moisture coal resulted in reduced power generation together with reduced low heating value (LHV) of syngas, higher amount of oxygen supply, and less energy recovery in the membrane. The amount of coal required to produce the same total LHV of syngas was smallest when the coal was dried to 5 % moisture. Therefore, the coal‐drying level for appropriate power production was between 5 and 10 %.

Thermogravimetric Analysis of Moisture Desorption from Coal

In coke production, the moisture content of the initial coal is an important parameter. The moisture present in the pores of coal changes the properties of the coking batch. Note also that, together with methane and/or carbon dioxide, water may form gaseous hydrates in the coal bed. In the present work, to study the state of the moisture in coal, attention focuses on eight samples of natural gas saturated to constant moisture content in an atmosphere where the relative partial pressure of water vapor is 91%. The moisture sorbed from the atmosphere has a U-shaped dependence on the metamorphic stage of the coal, with a minimum at coking coal (K coal). In similar conditions, the more mature T and A coal contains twice as much moisture as K coal, while the younger D and G coal contains about four times as much moisture. Thermogravimetric analysis of coal samples saturated to constant moisture content permits calculation of the rate of mass loss and activation energy for the evaporation of moisture in the heating of the given samples. For each coal sample, the temperature range where the evaporation of moisture may be described by a first-order Arrhenius equation is determined. The upper limit of this range is compared with the temperature corresponding to maximum rate of mass loss and also with the temperature corresponding to the maximum thermal effect.

Product Competitiveness of Upgrading Brown Coal (UBC) Process in Indonesia

The utilization of coal in Indonesia is in a running of improvement to become the biggest energy source. In 2025, 30% of total energy used is targeted as stated in Indonesian Government Regulation No. 79 of 2016. In Indonesia, the potential coal is mostly found in low and moderate calorific coal, it is classified as brown coal. Commonly, brown coal has high moisture content. Upgrading Brown Coal (UBC) process is a method for reducing the moisture content of brown coal by up to 80%. This study provides an overview of the UBC product competitiveness compared with brown coal. It will generate some technical recommendations on the current energy policies. Business as Usual (BAU) scenario and UBC product scenario were applied to show the difference in the amount of coal needed to generate electricity with the same capacity and the total of green house gas emission potential (GEP). The calculation was performed using the LEAP program (Long-range Energy Alternative Planning system). The use of UBC product was potentially reduce the feed consumption by 50% compared to usual brown coal. Furthermore, the GEP calculated between the two scenarios was 1.141 billion kg CO 2 -eq/year as net saving. UBC process can be developed to improve the quality of brown coal, so that the UBC product will be much more competitive.

Influence of coal properties on the performance of fixed-bed coal-burning braziers

Informal fixed-bed coal-burning braziers are used extensively in low-income communities of South Africa for space-heating and cooking needs. An investigation was carried out on the effects of coal moisture content and coal quality on the thermal and emissions performance of domestic coal-burning braziers in three field-procured braziers (with three different air ventilation rates), using the bottom-lit updraft (BLUD) and top-lit updraft (TLUD) ignition methods. Results showed that an increase in coal moisture content (from 2.4 wt.% to 8.6 wt.%) led to 18% and 30% decreases in fire-power when using the TLUD and BLUD methods, respectively. The combustion efficiency increased by 25% with an increase in moisture content. Measured carbon monoxide (CO) emission factors increased with an increase in moisture content, while carbon dioxide (CO2) emission factors remained unchanged. The use of A-grade coal resulted in a 49% increase in PM emissions compared with D-grade coal at high ventilation rates, despite no statistically significant differences (p &gt; 0.05) in CO and CO2 emission factors produced between coal grades.

Heat Transfer in a Fluidized Bed with Immersed Tubes Using Moist Coal Particles

The moisture content of coal (MCC) has an important effect on the thermophysical properties and the granular flowability. However, it brings both active and negative influence to the heat transfer between the fluidizing moist coal and the immersed tubes in the fluidized bed. Four groups of bituminous coal with same size distribution (0.25–2.8 mm) but different MCC (7.86–15.18%) have been examined to study the variation of the heat transfer in an experimental setup. The average heat transfer coefficients $$(h_{\mathrm{avg}})$$ for the four groups of test samples have the same changing trend by increasing the superficial velocity $$(U_{\mathrm{g}})$$ . However, the maximum heat transfer coefficients $$(h_{\mathrm{max}})$$ display different peak values. With the increase in MCC, the $$h_{\mathrm{max}}$$ rises at first and begins to fall when reaching a critical value. To predict the $$h_{\mathrm{avg}}$$ accurately with different MCC, the angle of repose has been imported to measure the variation of the granular flowability. A novel semiempirical correlation has been thereupon proposed by the dimensional analysis, and it accords well to the experimental data from this study and the previous research.