Coal Moisture Research Articles

Dewatering coal with supercritical Carbon Dioxide

ABSTRACT Supercritical CO2 (sCO2) dewaters coal through two mechanisms. For bituminous coal of 9.5% average moisture content the water is dissolved out of the coal and the concentration of water in the bulk sCO2 approximates its solubility limit. For lignite (54% average moisture content) the water extracted by the sCO2 exceeds its solubility limit in sCO2, which implies that a part of the water is displaced from, rather than dissolved out of the coal. Thus, there is a clear distinction between wet coals where most of the water is displaced, as compared to drier coals where the water is dissolved out. Hence, sCO2 dewatering will be especially efficient for high-moisture coals where there is significant free water available for displacement. Precedent for this process is available from the dewatering of wood flakes.

Switching Coal-Fired Thermal Power Plant to Composite Fuel for Recovering Industrial and Municipal Waste: Combustion Characteristics, Emissions, and Economic Effect

Combustion characteristics were studied experimentally for single droplets of fuel slurries based on wet coal processing waste with municipal solid waste components (cardboard, plastic, rubber, and wood) and used turbine oil. We established the ignition delay time for three various groups of fuel compositions in motionless air at 600–1000 °C. The minimum values are 3 s, and the maximum ones are 25 s. The maximum temperatures in the droplet vicinity reach 1300 °C during fuel combustion for compositions with 10% of used oil. The combustion temperatures of fuel compositions without oil are 200–300 °C lower. The concentrations of anthropogenic emissions in flue gases do not exceed those from dry coal combustion. Adding used oils to composite fuels reduces the concentrations of dioxins and furans in flue gases when municipal solid waste in the fuel burns out due to high combustion temperatures. Based on the experimental research findings, we have elaborated a strategy of combined industrial and municipal waste recovery by burning it as part of composite fuels, as illustrated by three neighboring regions of the Russian Federation with different industrial structures and levels of social development. This strategy suggests switching three typical coal-fired thermal power plants (one in each of the regions) to composite liquid fuel. It will reduce the hazard of waste to the environment and decrease the consumption of high-quality coals for power generation. Implementing the developed strategy for 25 years will save 145 Mt of coal and recover 190–260 Mt of waste. The positive economic effect, considering the modernization of fuel handling systems at thermal power plants and the construction of a fuel preparation plant, will make up 5.7 to 6.9 billion dollars, or 65–78%, respectively, of the main costs of three thermal power plants operating on coal within the identical period.

Влияние естественной влажности на характерное время десорбции метана из углей различной степени метаморфизма

Goal. To study the effect of natural internal moisture content on the kinetics of methane desorption from coals of varying degrees of metamorphization. Methodology. For the research, coal was used after a long (more than 100 days) preliminary exposure in a dry, closed indoors. The measurements were carried out on several samples of Donbass coals with different volatile content. Two groups of coal samples were used - dry, with natural internal humidity and one sample with artificial humidity of 1.5%. The volumetric method was used for measurements. The method includes three stages: 1st  saturation of coal with compressed methane, 2nd  preliminary discharge of compressed gas from a container with coal after its saturation, and 3rd  collection of methane released by coal into a storage vessel. Before registration of desorption, pressurized gas was discharged from the free volume of containers into the atmosphere. The desorption unit contains a low-temperature trap (78°C) for water vapor and a warming radiator for methane entering the storage vessel. To determine the numerical values of the characteristic time of desorption of methane from coal, we used information on the change in gas pressure in the storage vessel during desorption. To analyze the results, a method based on the concept of a change in the characteristic relaxation time of desorption during methane emission was used. Results. Experimental results show that in wet coals the ratio between the amount of methane in coal and the intensity of its outflow at any desorption site is less than in dry coals. It was found that in coals of the metamorphic series the presence of natural moisture leads to a decrease in the intensity of methane emission, a decrease in the characteristic desorption time and a decrease in the activation energy of methane desorption by 0.4 - 2.5 kJ / mol. The features of the kinetics of desorption indicates competition energetics of interactions between methane and water with the surface of the pores of coal. Scientific novelty. It was found that even without artificial humidification, but in the presence of natural internal moisture in coal, the degassing time during desorption is reduced (in comparison with dry coal). Practical significance. The research results can be used to optimize the duration of hydraulic saturation of the coal seam and the water consumption during coal degassing.

Low rank coal drying technology for decreasing electricity cost production: case study of Nagan Raya power plant

Considering the depletion of black coal resources, utilization of low rank coal currently is emerging to meet the growing of electricity consumption globally. Some coal fired power plants urge to use the domestic low rank coal due to some financial reasons. They are several coal drying technologies have been proposed. This study analyzes the utilization low rank coal to decrease the electricity cost production at Nagan Raya coal fired power plant. The Coal Moisture Control Fluidized Bed (CMC-FB) technology is selected as a basis for both technical and financial calculation. Based on the pilot project in Fukuoka, this technology is technically feasible and well suited for Nagan Raya power plant. A financial modelling shows that coal drying technology implementation can potentially decrease the electricity cost production for the utility and also make benefits for the investor. Further research is recommended to investigate other proven technologies. Additionally the effect of coal drying implementation to the environment should be noticed.

Wind tunnel investigation on the dust emission characteristics of high moisture coal piles

With the increasing requirements of environmental protection, a large number of new wet dust suppression technologies are used in the port in recent years, such as watering at the bottom of the Dumper Shed, etc. So the moisture content of coal is more than 10% often appear. Relevant studies show that the amount of dust from coal (conventional moisture content) pile is directly proportional to the high power of wind speed. But studies on high moisture content coal are rare. In this study, Wind tunnel test was carried out to study the dust emission behavior of coal with high moisture content (13.7% and 14.3%). The results show that the relationship between coal dust and wind speed tends to be linear under high moisture content. The study can provide a basis research for the estimation of coal dust emission in port.

Conditions and characteristics of droplets breakup for industrial waste-derived fuel suspensions ignited in high-temperature air

This research is focused on the ignition and combustion mechanisms and characteristics of single droplets of seven different composite liquid fuels, based on wet coal processing waste (fine coal + 50 wt% of water) with 40 wt% of vegetable oils (castor, rapeseed) and used petroleum-based oils (lubricants – motor, compressor, and turbine oils; working fluid – hydraulic oil; insulating fluid – transformer oil). The combustion of waste-derived fuel suspensions is initiated by introducing single droplets into heated motionless air with a temperature of 700–1,000 °C. Threshold conditions (component composition, concentration of combustible liquid, and temperature) were detected, for which micro-explosions during the induction period resulted in the full breakup of droplets, combustion of products (vapors and fine particles) and their subsequent rapid burnout. A high-speed video recording system is used to establish consistent patterns of physical and chemical processes, as well as ignition and combustion characteristics (ignition delay times, burnout time, velocity of breakup products, and size of their burnout area) for a group of fuels under the conditions of droplet breakup. A hypothesis about how the composition of the component affects the breakup of droplets during ignition was formulated based on the results of analyzing the properties (initial boiling point and evaporation rates of oils, their surface tension and surface free energy, as well as wettability of dry coal processing waste) of separate fuel components.

Numerical investigation of coal self-heating in longwall goaf considering airflow leakage from mining induced crack

Self-heating of coal is a long-standing hazard and pollution source in longwall goaf and abnormal air leakage into goaf is a key yet complex drive to the hazard. To investigate such a problem with more insights, a numerical model without considering coal moisture is established based on a Shendong longwall. Abnormal air leakage into goaf mainly sources from the edge cracks resulting in presence of high level oxygen (8 %∼13 %) in start-off area of the longwall. Two heating liable regimes were identified: one is behind longwall face and another one locates in the start-off zone. Heating in the start-off zone develops more quickly than that in heating regime one. On day 25 the maximum temperature of regime two can rise to 500K while it can only increase to approximately 340K in regime one. The heating spot behind longwall face tends to be self-suppressed with longwall advancing while the heating in the start-off zone can develop to a spontaneous combustion incident due to constant airflow leakage from the mining induced cracks. A wide range of inertisation plans including different locations, strategies, and flowrates of nitrogen injection were conducted. An optimum inertisation plan is to proactively inject inert gas with a low flowrate (e.g. 122m3/h) from a seal along the start-off line. A high flowrate of nitrogen stream is preferable to suppress an on-going heating and the reactive inertisation should be maintained for a long run otherwise the heating is very likely to re-develop.

Effect of coal moisture content on coke’s quality and yields of products during coal carbonization

The coal with low moisture during carbonization could not only increase the yield of coke, but also promote the coke quality and reduce the energy consumption. In this paper, the influence of the moisture in the blend coal (1.8%–10.13%) on the product yields and coke quality during coal carbonization were investigated. The results show that the coke yield is increased from 75.90% to 77.16%, and the coke qualities such as coke strength after reaction with CO2 (CSR), coke reactivity index (CRI), fragmentation index (M25) and abrasion index (M10)) are also improved when the moisture of the blend coal decreases from 10.13% to 1.80 % in a bench scale reactor. Due to the secondary reaction, tar become lighter when the moisture is decreased. In order to further prove the above results, the blend coal with 1.8% and 9%–10% (common moisture used in coke plant) moisture is carbonized in a coke oven with 6 m height, the results show that CRI are 23.4% and 27.3%, CRS are 67.1% and 62.2% under 1.8% and 9%–10% moisture of blend coal. Moreover, the variation of the moisture in blend coal has a limited influence on dust emission at the ascension pipe and the charging car.

Pengembangan Blok Fungsi Kendali PI-Fuzi pada IEC 61499

Automation system in the form of automatic control is needed in one or several operating units in the process industry. Several control system algorithms have been widely implemented in the process industry, one of them is PI (Proportional and Integral) controller. This PI controller has a simple structure, but the adaptive ability of the controller is still not better for the controlled process. Therefore, the development of PI controller is needed to have a better adaptive ability to the process, in order to produce the responses that are also better and more robust. This research develops PI controller by adding the Fuzzy controller algorithm or also known as PI-Fuzzy controller. The PI-Fuzzy controller in this study is applied to the IEC 61499 Programmable Logic Controller (PLC) standard and to see its performance, the PI-Fuzzy controller based on IEC 61499 is tested and validated on an industrial scale process, namely coal mill. The test was carried out for three hours in real-time on the 4DIAC-IDE software, then the response results were compared with the response results of the PI controller. The PI-Fuzzy controller function block based on IEC 61499 made in this study showed good performance in controlling industrial-scale processes. This is demonstrated in testing and validation using a coal mill, with able to achieve the working range of each parameter. The mean value of coal flow parameter is 13.584 kg/s, coal mass accumulation is 2,196 kg, coal output temperature is 83.296 0C, coal moisture is 0.021, and coal fineness is 75.338 %.

Formation of methane hydrate from water sorbed by anthracite: An investgation by low-field NMR relaxation

Transverse relaxation time spectra T2 were studied for the samples (a) of wet coal in which methane hydrate was obtained, (b) wet coal exposed under the pressure of methane without the formation of the hydrate, and (c) initial wet coal. In all these cases, the samples of wet coal contained only water adsorbed in the fine pores of the coal substance. It was demonstrated that hydrate formation and the competitive sorption of methane at the positions previously occupied by water causes replacement of a part of water from coal mesopores into larger pores. The data obtained confirm a previously proposed multistage model (Smirnov et al., 2018) of hydrate formation in natural coal, which includes the stages of replacement of a part of sorbed water from coal pores by gas, the formation of microscopic water fragments in larger coal pores, and the formation of hydrate from this water.

A novel dry beneficiation process for coal

ABSTRACT More than two-thirds of coal in China is present in dry areas and cannot be separated by traditional wet coal preparation techniques. Dry coal beneficiation is an effective technique to realize coal separation and upgradation, as it does not consume water, has a low cost and is pollution-free. In this study, an air dense medium fluidized bed (ADMFB) and FGX separator were arranged in series to achieve 100–0 mm coal size dry separation. Raw coal (100–50 mm and 50–0 mm) was separated by ADMFB and the FGX separator, respectively. The fluidization characteristics of ADMFB and the separation effect were analyzed. When the gas velocity was 0.11 m/s, the yield of clean coal was 90.96% with an ash content of 7.86%. With respect to the FGX separator, the coal transport process and the distribution of the ash segregation degree under different vibration parameters were studied. The separation effect was optimal when the vibration amplitude reached 2.2 mm and the vibration frequency was 18 Hz. The clean coal yield was 90.30%, and the ash content was 13.28%. Effective coal separation (100–0 mm) was first achieved by the combined ADMFB–FGX separator separation system.

Kinetic behavior of heterogeneous sorption deformation on coal: Effect of maceral/micro-lithotype distribution

The greenhouse effect has attracted increasing attention globally. The geologic sequestration of CO2 is considered as an effective method for reducing the amount of CO2 in the atmosphere. Carbon-dioxide enhanced coalbed methane (CO2-ECBM) recovery is extremely attractive owing to its ability to store CO2 in coal seams while simultaneously enhancing the production of methane. However, the injection of CO2 can induce a deformation of the coal matrix, which has a significant effect on the fluid flow and stability of the coal seams. In this study, the sorption kinetics experiments indicated the high anisotropy and heterogeneity of local sorption deformation in coal samples and a unique kinetic behavior of sorption deformation which was rarely reported and analyzed in detail in previous studies. This kinetic behavior demonstrated a rapid increase of sorption strain followed by a slight or significant falloff until the equilibrium state reached. The characteristics of component distribution in coal samples were investigated using CT scanning and micro-lithotype and EDS analysis. An extensive analysis of the experiment results indicated the following: 1) Carbon dioxide dissolved during the first sorption process induced a rearrangement of the coal structure, leading to a drastic variation of deformation behavior between the first and subsequent sorption process. 2) The unique kinetic behavior of sorption deformation could be induced by either the loss of moisture in coal or the interaction of different coal components. The mechanism of these two factors induced coal shrinkage was different and had a distinct effect on the global behavior of sorption deformation. 3) The quantitative relationship between compressional and dilative components directly verified the significant compression of inertinite-rich regions by the slow swelling of vitrinite-rich regions. 4) The kinetic behavior of sorption deformation was affected by the combination of the macroscopic bedding structure and the heterogeneous component distribution in coal.

Combustion of Wet Coal Processing Waste and Coal Slime as Components of Fuel Slurries

ABSTRACT Coal processing waste is generated annually in large volumes by the coal exporting countries. More than 70% of run-of-mine coal is enriched. At the same time, typical coal processing waste (slime, flotation waste, mid-coal and tailings) make up at least 10–15% of the raw coal mass. Approximately 220–300 million tons of coal processing waste is generated annually at coal-preparation plants in Russia and China. The results of experimental researches in recent years illustrate the growing interest in such wastes as promising energy components. In this paper, we performed a comparative analysis of the main physical properties, ignition and combustion characteristics of several types of coal processing waste. The comparison is made for typical flotation waste (filter cakes or coal slime) generated in Russia and China. It is shown that for wastes from different countries the ignition delay times differ by no more than 50% and the heat of combustion by 9–15%. Concentrations of main anthropogenic emissions were determined. Generalization is made using criterion expressions to illustrate the advantages and disadvantages of coal processing waste incineration in comparison with pulverized coal combustion.

Thermal properties of coal during low temperature oxidation using a grey correlation method

The low temperature oxidation of coal is a contradictory and unified dynamic process of coexisting mass and heat transfer. The thermophysical properties are crucial during coal spontaneous combustion. In the current paper, the variations of moisture, ash, volatiles, fixed carbon and thermophysical properties (thermal diffusivity, specific heat and thermal conductivity) of three coal samples from 30 °C to 300 °C were studied, and their grey correlation was analyzed. The results indicated that with the increase of temperature, the free moisture of Coals A and B decreased first but then increased, while the free moisture of Coal C kept decreasing without a later increase. The variation of surface moisture was consistent with that of free moisture. The trend of volatiles and fixed carbon was completely the opposite, showing a significant negative correlation. Ash was less affected by temperature. Along with the rise of temperature, the thermal diffusivity of three coal samples decreased first but later increased, and the specific heat was always in a state of increasing. The change in thermal conductivity was mainly affected by specific heat. By calculating the grey correlation degree, the major factors affecting the thermophysical properties were obtained.

Separation characteristic of hot air heavy medium fluidized bed

The air-density fluidized bed drying and sorting integration experiment system was used to conduct the separation experiment on wet coal. The effects of surface water of coal, drying temperature, drying time, air volume and other factors on separation precision and separation density were investigated. A mathematical correlation model of separation precision and separation density with various influencing factors was established. Studies have shown that the drying temperature and surface water of coal have a significant influence on the separation precision; the increase of drying temperature can improve the separation effect and increase the separation density, the increase of surface water of coal leads to the decrease of separation precision and the decrease of separation density. The increase of drying time contributes to the removal of surface water of coal, which makes the separation precision increase and the separation density increase; As the air volume increases, the separation precision first increases and then decreases, and the separation density decreases first and then increases slightly.

Co-combustion of coal processing waste, oil refining waste and municipal solid waste: Mechanism, characteristics, emissions

This experimental research studies co-combustion of wet coal processing waste (filter cakes) with typical municipal solid waste (wood, rubber, plastic, cardboard) and used turbine oil, as combustible components of composite liquid fuel. Ignition mechanisms and characteristics of single droplets of three fuel composition groups have been investigated in a motionless heated air with using a high-speed video recording system. Analyzing video frames, a physical model of the process under study was developed. The values of the guaranteed ignition delay times have been determined for three fuel groups with different compositions at the ambient temperature 600–1,000 °C. The minimum values of ignition delay times are about 3 s, the maximum ones are about 25 s. In addition to the established difference in the ignition delay times, the various fuel compositions also differ in combustion temperatures. Maximum values reaching 1,300 °C for compositions with 10% of used oil. It has also been determined that fuels with municipal solid waste are notable for lower nitrogen and sulfur oxide concentrations in flue gases as compared to filter cakes in initial state. Adding used oil to such fuel compositions increases the anthropogenic emissions but these worsening environmental characteristics do not exceed the regulated allowable limits of pollutants for solid fossil fuel combustion by thermal power plants. The obtained results are the backbone for the development of an environmentally friendly, cost- and energy-efficient co-combustion technology for municipal solid waste recovery by burning it as part of composite fuels, e.g., in boiler furnaces instead of coal.

Molecular Simulation of CH4 and CO2 Competitive Adsorption in Moisture Coals

Molecular simulations of CH4/CO2 competitive adsorption in moisture coals are carried out. The synergistic effect of micropore walls has a significant impact on the spatial distribution of adsorbates. Water molecules in micropores can prevent CO2 and CH4 from smoothly diffusing and adsorbing in the pore. The micropore is more favorable to the advantage of CO2 in the competitive adsorption. The variation of excess adsorption capacity is related to the density difference between adsorbed phase and free phase. Relative to CH4 density, CO2 density is easier to affect the variation trend of adsorption capacity in the competitive adsorption.

Experimental investigation on the mechanical characteristics of gas-bearing coal considering the impact of moisture

Water is an inherent component in coal masses. The presence of moisture has a significant impact on the mechanical properties of gas-bearing coal and plays a key role in the development of coal and gas outburst disaster. However, how moisture affects the mechanical behavior of gas-bearing coal is poorly understood. In this research, a series of triaxial compression and acoustic emission (AE) tests were performed on gas-bearing coal under different water treatment conditions. The results show that moisture reduces the change in surface energy of the coal by methane adsorption due to the predominance of water adsorption. Therefore, the influence of moisture is more prominent than that of methane and results in a reduction in strength and enhancement in the gas softening coefficient with increasing moisture content. Simultaneously, AE activity of gas-bearing coal is significantly inhibited by moisture, and two failure types can be determined based on the AE results around peak stress: a sudden rupture type for dry and low-water-bearing coal and a stable rupture type for water-saturated coal. Moreover, a meso-statistical damage model is proposed, which agrees well with the experimental results. An analysis indicates that the moisture in coal can reduce the surface energy and weaken the bonds among coal matrix particles, which not only changes the strength of gas-bearing coal but also restrains the energy release during failure; thus, moisture promotes the development of damage in gas-bearing coal.

Molecular simulation of flue gas and CH4 competitive adsorption in dry and wet coal

For further understanding the microcosmic mechanism of CO2 storage and CH4 recovery during coal-fired power plants flue gas injecting into the coal seams, the dry and wet macromolecular models of coal were established. Then Grand Canonical Monte Carlo (GCMC) molecular simulations were performed to state multicomponent (single, binary, ternary and quaternary systems among flue gas and CH4) and competitive adsorption behaviors. The results show that the adsorption amount of individual gas in the mixed components adsorption systems increases with the pressures and bulk mole fractions increasing. While the advantages of selective separation for competitive ones, especially for CO2, decrease. The order of adsorption amount of gases in the mixture depends on not only adsorption ability but also bulk mole fraction. With the same bulk mole fraction of CH4, the selectivities of CO2/CH4 that in the systems injecting flue gas are larger than that injecting pure CO2. With the same 0.99 mmol/g adsorption amount of CO2, injection of flue gas is more beneficial to desorption of CH4 than injection of CO2 due to the large partial pressure of N2. The advantages of competitive adsorption for CO2 can be explained by stronger favorable adsorption sites therefore stronger van der Waals energy and electrostatic energy between CO2 and coal. Water in coal goes against the gases adsorption, especially for CO2, because the preferential adsorption sites are occupied by water. The conclusions of this research lay a theoretical foundation for the application of flue gas-ECBM technology.

Experimental Study on the Effect of Moisture Content on Bituminous Coal Porosity Based on 3D Reconstruction of Computerized Tomography

Bituminous coal in the Xutuan Coal Mine of the Huaibei Mining Bureau (China) is the research object of this study. The influence of moisture content on the porosity of the bituminous coal was investigated from a microscopic perspective by using a high-solution 3D X-ray micro-analyzer. The threshold segmentation method was used to segment the scanning slices of the coal samples. The threshold values of the various media were in the following order (from large to small): minerals, water, matrices, and fractures. The scanning volume and actual volume proportions of the different media in the coal samples with different moisture contents were calculated. The accuracy of the computerized tomography (CT) scanning method in measuring the coal moisture content was verified by comparison with the results obtained using the weighing method. 3D reconstructed coal samples, with different moisture contents, were analyzed, as well as separately reconstructed fractures and water in the coal samples with different moisture contents. The heterogeneity and anisotropy of the coal mass were explained quantitatively by the CT scanning intensity. A commonly used fracture classification method indicated that the primary fracture in the coal sample was a type A fracture. The results of the analysis of water in the coal fracture indicated that the porosity of bituminous coal decreased with the increase in moisture content in conditions of atmospheric pressure and a short immersion period. However, a certain level of porosity remained evident, and the degree of fracture development of the coal samples remained unchanged. This is attributed to the minor volumetric change in the minerals in the coal samples, as the water does not completely occupy the fractures in the coal samples, and the dissolution of the minerals by water is therefore not significant. The reasons for the moisture content affecting gas adsorption, seepage, and strength of a coal body were analyzed from a microscopic perspective. In addition, the types of fractures and water in the coal samples were classified by employing statistics and analyses of volume, surface area, specific surface area, and aspect ratio of the fractures and the water in the coal samples with different moisture contents.