Coal Moisture Research Articles

Using Ground and Intact Coal Samples To Evaluate Hydrocarbon Fate during Supercritical CO2 Injection into Coal Beds: Effects of Particle Size and Coal Moisture

To investigate the potential for mobilizing organic compounds from coal beds during geologic carbon dioxide (CO2) storage (sequestration), a series of solvent extractions using dichloromethane (DCM) and using supercritical CO2 (40 °C and 10 MPa) were conducted on a set of coal samples collected from Louisiana and Ohio. The coal samples studied range in rank from lignite A to high volatile A bituminous, and were characterized using proximate, ultimate, organic petrography, and sorption isotherm analyses. Sorption isotherm analyses of gaseous CO2 and methane show a general increase in gas storage capacity with coal rank, consistent with findings from previous studies. In the solvent extractions, both dry, ground coal samples and moist, intact core plug samples were used to evaluate effects of variations in particle size and moisture content. Samples were spiked with perdeuterated surrogate compounds prior to extraction, and extracts were analyzed via gas chromatography–mass spectrometry. The DCM extracts generally contained the highest concentrations of organic compounds, indicating the existence of additional hydrocarbons within the coal matrix that were not mobilized during supercritical CO2 extractions. Concentrations of aliphatic and aromatic compounds measured in supercritical CO2 extracts of core plug samples generally are lower than concentrations in corresponding extracts of dry, ground coal samples, due to differences in particle size and moisture content. Changes in the amount of extracted compounds and in surrogate recovery measured during consecutive supercritical CO2 extractions of core plug samples appear to reflect the transition from a water-wet to a CO2-wet system. Changes in coal core plug mass during supercritical CO2 extraction range from 3.4% to 14%, indicating that a substantial portion of coal moisture is retained in the low-rank coal samples. Moisture retention within core plug samples, especially in low-rank coals, appears to inhibit accessibility of supercritical CO2 to coal matrix porosity, limiting the extent to which hydrocarbons are mobilized. Conversely, the enhanced recovery of some surrogates from core plugs relative to dry, ground coal samples might indicate that, once mobilized, supercritical CO2 is capable of transporting these constituents through coal beds. These results underscore the need for using intact coal samples, and for better characterization of forms of water in coal, to understand fate and transport of organic compounds during supercritical CO2 injection into coal beds.

Predicting the steam drying behavior of brown coals and lignites

Abstract Our drying model explicitly accounts for the three forms of moisture in low-rank coals – monolayer, multilayer, and bulk – as a basis to predict the distinctive drying behavior and energy requirements of individual low-rank coal samples. The mass loadings of the moisture forms are estimated from a database of equilibrium moisture contents that were correlated to parameters from a coal’s proximate and ultimate analyses. The drying analysis is validated with laboratory tests on steam drying in autoclaves and a fluidized bed that cover broad ranges of steam pressures and temperatures for an assortment of Australian brown coals. Then the analysis determines which forms of moisture and operating conditions most affect drying times. For some selections of samples, drying time will be proportional to total moisture, and for others, there will be exceptions. One key aspect is whether or not the target moisture level requires removal of any monolayer moisture at all. Coals with abundant bulk and multilayer moisture can achieve targets on residual moisture by vaporizing only a portion of the multilayer moisture. Consequently, their drying times will be relatively modest. But coals with little bulk moisture and relatively abundant monolayer moisture will require relatively long drying times simply because monolayer moisture is always released much more slowly than multilayer moisture. Hence, the levels of the three forms of moisture in any particular coal sample are determining factors for drying times.

Effects of coal moisture control and coal briquette technology on structure and reactivity of cokes

In this work, the influences of coal moisture control (CMC) and coal briquette technology on structure and reactivity of cokes were investigated by adding a certain proportion of briquette into raw coal with different moisture. The coking experiments were carried out in a tested coke-oven of 70 kg, and the properties of as-obtained coke were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and so on. The coke reactivity index (CRI), coke strength after reaction (CSR) and the optical texture of different cokes were also measured. The results indicated that the two technologies both can improve the structure of coke and reduce the reactivity of coke. The improved coke properties can be attributed to forming a more compact microcrystalline structure of coke to enhance its pore wall structure, its optical texture index (OTI) and its graphitization degree. Noticeably, the introduction of CMC technology in coal briquette process can produce the superposition effect to the great improvement of the coke properties. In addition, the results also indicated that the introduction of CMC technology in coal briquette process can reduce the sulfur content of coke due to the overflowed sulfur in the form of gas during the coking, and can almost be equivalent to substitute 10% briquette in coal briquette process in the improvement of the CRI and CSR from coke, implying the reduced amount of briquette to save coal resources.

NO and N2O emissions in oxy-fuel combustion of coal in a bubbling fluidized bed combustor

Emissions from coal oxy-fuel combustion are receiving significant attention during the last years. This paper is focused on the analysis of fuel-N emissions in fluidized bed combustion systems. Experiments were carried out in a bubbling fluidized bed unit in the temperature interval 850–950°C. Different coals (anthracite, bituminous and lignite) were used as fuels and different sorbents were employed for in-bed sulfur retention. In the experiments, NO, N2O and NO2 were measured. NO2 was not detected in any of the operating conditions. The influence of temperature on NO and N2O emissions was the same as in conventional combustion: NO emission increased as temperature increased while N2O emission decreased. Nevertheless, the total fuel-N conversion to nitrogenous species seemed to be lower than in combustion with air. As in air-firing combustion, the highest levels of NO and N2O were registered with the highest rank coals. The Ca-sorbent was found to have a key role on NO reduction via catalytic reaction and this catalytic effect seemed not to be affected by the high CO2 levels present in oxy-fuel combustion. Also, the moisture content in the coal affected the NO formation, which decreased with an increase in the coal moisture content. A similar effect was observed by increasing the oxygen concentration fed to the combustor.

Effect of Coal Moisture on the Treatment of a Lignitic Coal through a Semi-Pilot-Scale Pneumatic Stratification Jig

Dry processing methods are well known to be sensitive to the moisture content of the processed material. It is well known that cohesive forces among the particles originating from the surface moisture hinder the individual movement or appropriate stratification of particles during separation. Furthermore, high surface moisture also hampers the flow of feed material. In this study, the effect of total/surface moisture on separation of lignitic coals was investigated by using Allair stratification jig with the aim of finding possible critical surface moisture content for optimum separation. Coal samples in the size of −13 + 4 and −4 mm were processed at different particle total/surface moisture levels to recover as clean coal concentrate as possible along with obtaining tailings with minimum levels of combustibles. It is envisaged that a critical surface moisture on both classification (effective screening) and separation is available around 5.5% surface moisture (corresponding to 15% total moisture) for −13 + 4 mm whereas effective separation is not possible for the −4 mm size range even at minor changes in surface moisture of particles.

Assessing the Water Migration and Permeability of Large Intact Bituminous and Anthracite Coals Using NMR Relaxation Spectrometry

Although extensive literature has emerged on the use of nuclear magnetic resonance (NMR) relaxation spectrometry for the determination of various petrophysical properties of clastic rocks, relatively few papers have reported the use of NMR to determine the moisture migration process and permeability of large intact coals. In this study, evaporation experiments simultaneously with NMR measurements were conducted for seven coal core plugs. Differences in the relaxation time distribution at the various saturation stages provide both qualitative and quantitative information on the saturation state and migration of moisture in the coal samples. Moisture migration accrues first in the larger pores, whereas the smaller pores appear to remain water-saturated. The evaporation of moisture in large intact coals undergoes three continuous processes: Migration of free water, macro-capillary water, and micro-capillary water, among which, the migration rates of both macro-capillary water and micro-capillary water are related to the coal pore size distribution and porosity. The results of the NMR measurements also indicate that coal permeability has a relationship with the moisture migration characteristics, which make it possible to develop an NMR-derived permeability model. The Timur–Coates and the Schlumberger-Doll Research (SDR) equations, which are commonly used in NMR logging evaluations of the permeability of clastic rock reservoirs, were discussed concerning their application to coals. It is found that a modified SDR permeability evaluation model $$[K_\mathrm{SDR}=0.0224(\hbox {T}_\mathrm{2gm}^\mathrm{b})^{0.182}(\hbox {T}_\mathrm{2gm}^\mathrm{a})^{1.534}]$$ , which is a double-exponential relationship with the $$T_{2}$$ geometric mean in the full water-saturated state and in the bound water state, fits the analyzed coal samples well. The NMR-derived methods provide a framework for the determination of the moisture migration and permeability of coals.

Fluidization of Wet Brown Coal Particles with Wide Particle Size Distribution

Though the amount of brown coal resources in the world is abundant, and its moisture content is often high (more than 30%, wet basis). Thus, fluidized bed drying systems, using superheated steam for fluidizing gas, has been developed as a large capacity and low energy consumption drying technology. Brown coal particles used in fluidized beds are classified into B particles according to Geldart’s classification. However, particle properties, size, density and cohesiveness change with moisture content. Therefore, it is important to know the influence of moisture content on its fluidization characteristics. In this work, experiments were carried out to evaluate the effect of moisture content and particle size distribution on fluidization characteristics by using a fluidized bed cold model. For fluidization characteristics, minimum fluidization velocity, minimum complete fluidization velocity and minimum complete mixing velocity were measured. As a result, a quantitative relationship between the particle size distribution and fluidization characteristics was obtained. Also, a quantitative relationship between moisture content and fluidization characteristics was obtained by introducing an angle of repose as an index of cohesiveness.

湿潤褐炭粒子の流動層における伝熱特性

世界の可採石炭埋蔵量は約9000億トンであり，約半分は亜瀝青炭，褐炭などの高水分炭と言われている．特に褐炭では重量の半分近くが水分であるため，褐炭を高効率かつ大容量で予備乾燥させ，発電効率を向上させる技術が望まれている．蒸気を流動化ガスとする流動層乾燥方式は潜熱回収が可能であり，高効率な褐炭乾燥法に適していると考えられる．蒸気流動層乾燥装置では層内伝熱管に飽和温度150˚C程度の水蒸気を供給して褐炭粒子を間接加熱し，乾燥させる．ところが，褐炭粒子は幅広い粒度分布を有するとともに水分含有率が高く付着性を有しているため，蒸気流動層乾燥装置の設計においては，流動特性とともに伝熱特性を精度よく評価する必要がある．本研究では，窒素を流動化ガスとする基礎試験装置により，水分含有量の異なる2種類の褐炭を用い，流動化ガス速度，層内伝熱管のピッチを変化させて，管外伝熱係数への影響を把握した．さらに，伝熱面積の増加を目的に伝熱管にフィンを取りつけ，フィン間隔を変化させ，その効果を把握した．その結果，管外伝熱係数は粒子の見かけ密度と粒径を水分含有量の関数として与えることによりAndeen and Glicksmanの式で予測できること，伝熱管密度が大きくなったときの管外伝熱係数は付着性のない粉体ではやや増加するが，付着性のある粉体では低下すること，伝熱管フィン有効度はフィン表面伝熱係数が平滑管表面の伝熱係数と同一であると仮定して計算した値に比べると小さいことを明らかにした．

湿潤褐炭粒子の蒸気流動層における乾燥特性

湿潤褐炭粒子の蒸気流動層における乾燥特性

Pilot-scale experimental and CFD modeling investigations of oxy-fuel combustion of Victorian brown coal

This paper presents the first trial in the world for experimental and modeling investigation of oxy-fuel combustion of Victorian brown coal in a 3MWth pilot-scale facility. Two coal samples with different moisture contents, wet (40wt% moisture) and air-dried (24wt% moisture), were tested in air- and oxy-firing modes with oxygen level varying from 27% (vol) to 40% in furnace. The commercial software, FLUENT 13, was employed to interpret the experimental data by taking into account a series of validated refined sub-models for oxy-fuel combustion. The modeling results showed reasonable agreement with the measurements of flue gas temperature profile as well as in-situ flame photographs in furnace. As has been confirmed, a rather identical flue gas temperature profile was achieved between air-firing and oxy-27% O2 for the dried Victorian brown coal. For the wet brown coal with 42wt% moisture, 30% O2 in oxy-fuel mode is however essential to match air to achieve an identical flue gas temperature profile. Even so, under above optimum retrofit conditions, the radiative heat transfer and CO emission profiles were still slightly mismatched between air-firing and oxy-firing cases regardless of the moisture content within coal. The radiative heat transfer was increased in wet coal oxy-firing because of the higher gas emissivity for the abundant CO2 and H2O within the flue gas. The CO emission concentration in oxy-fuel mode was raised, due to the enhanced C–CO2 and C–H2O gasification reactions that occurred readily at relatively low temperatures for Victorian brown coal char. The presence of no less than 30% oxygen in primary gas is also essential to minimise particle ignition delay caused by the large specific heat capacity of CO2 and steam. For flue gas properties, it has been confirmed that, under the optimised oxy-fuel conditions, the typical CO2 purity reached approximately 80% in dried flue gas, in which the excess oxygen remained at ∼4% whereas steam reached 35%, relative to 10% in air-firing flue gas. By shifting coal combustion from air-firing to oxy-fuel mode, the flue gas recirculation ratio varied from 48% to 64% for the use of wet and dried coals, which are considerably lower than the literature results for bituminous coal.

Emission factors for fugitive dust from bulldozers working on a coal pile

A study of a Powder River Basin (PRB) coal pile found that fugitive emissions from natural and human activity each produced similar levels of downwind fine + coarse (i.e., smaller than 10 µm, or PM10) particle mass concentrations. Natural impacts were statistically removed from downwind measurements to estimate emission factor Ev for bulldozers working on the pile. The Ev determined here was similar in magnitude to emission factors (EFs) computed using a U.S. Environmental Protection Agency (EPA) formulation for unpaved surfaces at industrial sites, even though the latter was not based on data for coal piles. EF formulations from this study and those in the EPA guidance yield values of similar magnitude but differ in the variables used to compute Ev variations. EPA studies included effects of surface silt fraction and vehicle weight, while the present study captured the influence of coal moisture. Our data indicate that the relationship between PRB coal fugitive dust Ev (expressed as mass of PM10 emitted per minute of bulldozer operation) and coal moisture content Mc (in percent) at the study site is best expressed as Ev =10f(Mc) where f(Mc) is a function of moisture. This function was determined by statistical regression between log10(Ev) and Mc where both Ev and Mc are expressed as daily averages of observations based on 289 hours sampled during 44 days from late June through mid-November of 2012. A methodology is described that estimates Mc based on available meteorological data (precipitation amount and solar radiation flux). An example is given of computed variations in daily Ev for an entire year. This illustrates the sensitivity of the daily average particulate EF to meteorological variability at one location. Finally, a method is suggested for combining the moisture-sensitive formulation for Ev with the EPA formulation to accommodate a larger number of independent variables that influence fugitive emissions.Implications: Fugitive coal dust emission factors (EFs) derived by this study contribute to the small existing knowledge base for a type of pollutant that will become increasingly important as ambient particulate standards become tighter. In areas that are not in attainment with standards, realistic EFs can be used for compliance modeling and can help identify which classes of sources are best targeted to achieve desired air quality levels. Reconciling emission factor formulations that are sensitive to different factors (i.e., those from the EPA and this study) produces a more powerful tool for estimating fugitive emissions at a broad range of sources.

Modelling and control of pulverizing system considering coal moisture

The pulverizing system serves an important function in the safe and efficient operation of thermal power units. The effect of coal moisture and pulverized coal moisture on the pulverizing system was considered in establishing a mass and energy balance-based dynamic mathematical model of a coal mill. The parameters of the model were identified by using the genetic algorithm and later validated with measurements. An extended Kalman filter was designed to estimate and verify the internal states of the coal mill. Based on the dynamic mathematical model of coal mill, pulverized coal moisture was used as a feed-forward signal, and a feed-forward compensation controller was designed to optimize the coal mill outlet temperature. Simulation results showed that the dynamic characteristic of the mill can be forecasted effectively with the established model. Moreover, pulverized coal moisture was reduced with feed-forward compensation, thereby improving the efficiency of the boiler.

Phase Transformation of Coal at High Temperature

Anthracite and bitumite were processed respectively at 1400°C,1700°C, 2000°C, 2200°C, 2400°C and 2600°C,and their chemical composition,resistivity,microstructure, phase composition,and the internal migration of molecular functional group were tested and characterized. The results indicate that moisture, ash and volatile in coal have gradually shifted and lost with the elevation of heat treatment temperature, while the higher temperature, the quicker and completer phase change. Heat treatment can make the coal transform from approximately insulative phase to conductive phase,. Furthermore, as the temperature increases, the conductive phase transformation effect is better. The higher the heat treatment temperature of coal, the more amorphous carbon transforming into crystalline carbon completely, but the less types of phases .

Coal Pyrolysis for High-Quality Tar and Gas in 100 kg Fixed Bed Enhanced with Internals

Using internals in kilogram-laboratory fixed bed pyrolysis of coal has been newly reported to greatly upgrade the pyrolysis performance in terms of the yield and quality of the produced tar and pyrolysis gas. This work is devoted to further verifying such a finding through pyrolysis tests in enlarged fixed bed reactors with and without internals at obviously increased coal treatment capacities of about 100 kg of coal per test. The reactors were electrically heated, and the tests were via batchwise operation, while Yilan sub-bituminous coal was used. Comparing the results from reactors without and with the particularly designed internals demonstrated that the use of internals increased the heating to the coal bed by about 20%, while the tar yield was 87.0% of the Gray-King (G-K) tar yield, which was obviously higher than 46.9% of the G-K tar yield from the reactor without internals. In the tar from the internal-enhanced reactor, the content of light tar (boiling point below 360 °C) was about 71 wt %. Raising the furnace temperature from 900 to 1100 °C increased the tar yield from 80.5% to 90.3% of the Gray-King tar yield for the reactor with internals. Parametric studies were performed for coal particle size, heating furnace temperature, and coal moisture content.

Soft sensing of coal moisture

This study presents a soft sensing model of coal moisture for utility boilers. The model is based on the energy and mass balance of matter in the inlet and outlet of a positive-pressure, direct-firing, MPS-type mill. Compared with the results obtained with a proximate analysis method, the results calculated with the soft sensing method are consistent with proximate analysis data. Meanwhile, the accuracy and reliability of the soft sensing method can be improved by data fusion of the calculated coal moisture from other running mills.

Evaluation of Carbon Dioxide Adsorption on Malaysian Coals for Potential Sequestration

Adsorption experiments of carbon dioxide (CO2) were contacted on two coal samples from Sungai Buloh and Silantek mines in Malaysia. A fixed bed adsorption unit was used to determine CO2 adsorption capacity of the coal samples. The experiments were conducted at different pressure ranges (5-40 bar) and temperature at 25°C. The CO2 adsorption capacity of Silantek coal sample showed adsorption capacity of 4.178 mmol/g at 40 bars and 25 °C, which is higher than Sungai Buloh sample. Different adsorption isotherms were employed to examine the experimental results, Langmuir isotherm of Silantek coal sample illustrated better correlation than Freundlich isotherm for the same sample. In contrary, Freundlich isotherm of Sungai Buloh coal sample illustrated better fitting than Longmuir isotherm correlation for the same sample. This is related to the coal rank and moisture content and ash content.

Determination of moisture in brown coals

The measurement results of moisture in high-moisture brown coal performed by different (gravimetric and chemical) methods are presented. The experimental results are compared. Conclusions on procedures chosen for the measurements of brown coals are proposed, and the promising lines of the measurements of moisture in coals are outlined.

Using hyperspectral indices to measure the effect of mine dust on the growth of three typical desert plants.

To examine the influence of coal dust from mining on vegetative growth, three typical plants from near an open-pit coalmine in an arid region were selected, and their spectral signals were determined. The present study was conducted near the Wucaiwan open-pit coalmine in the East Junggar Basin in Xinjiang. We extracted nineteen vegetation indices and examined their correlation with the dust flux. The objective was to determine which parameters that quantify vegetation damage could provide a basis for environmental monitoring in arid regions. The results indicate that when coal dust damages vegetation, both chlorophyll and moisture are reduced, and the amount of carotenoids increases with increasing coal dust. The pigment-specific normalized difference (PSNDb), structure-insensitive pigment index (SIPI) and plant water index (PWI) were the most sensitive indices, and sacsaoul was most sensitive to coal-dust pollution.

Experimental Study of Coal Moisture Content Measurement System Based on Standing-Wave Ratio

In this paper, a measurement system is designed to deal with the problem of measurement of the coal moisture content. Based on the measurement principle including standing-wave ratio and permittivity, develop the whole measurement system from the hardware and software aspects. The measurement system of coal moisture content based on standing-wave ratio has the advantages of less measuring time, higher accuracy and larger measurement range according to the results. And it can apply in the coal moisture content measurement in many industry fields.

Optimization of drying of low-grade coal with high moisture content using a disc dryer

In this study, low-grade coal with high moisture content was dried in a novel disc dryer equipped with a heating plate and rotary blades. Raw coal was fed into the center of the disc dryer and then was transferred from the center of the heating plate to the outside of the plate by the rotary blades during the drying process. According to a numerical analysis using a model of a single solid spherical particle without any porosity, the temperature of the coal particles reached that of the heating plate within 5min. The analysis also showed that at a heating plate temperature of 150°C, the moisture content of the raw coal was lowered from 34% to below 3% within 5min, and all of the raw coal was dried after 10min of drying time. Experimental studies were used to investigate the influence of the following factors on the effectiveness of the novel disc dryer: heating plate temperature, coal feed rate, rotational speed of the rotary blades, drying environment, and position of the coal on the heating plate. When the heating plate temperature was high, the moisture content of the dried coal was greatly decreased. However, on the basis of energy-efficiency considerations, it was recommended that the temperature of the heating plate be maintained at 150°C. Furthermore, a decrease in the coal feed rate could lower the moisture content, and a high rotational speed of the rotary blades could slightly reduce the moisture content as well. In addition, the reduction in moisture content could be remarkably enhanced by using a vacuum pump to remove the evaporated water vapor from the inside of the dryer. The position of the coal on the heating plate was also important. The temperature of the raw coal could be increased without evaporation up to a certain distance from the center of the dryer. However, the moisture of the raw coal began to evaporate in a region near the outside of the heating plate before discharging, where the raw-coal temperature reached about 100°C. Overall, it was concluded that the size and temperature of the heating plate should be considered in the design and operation of a disc dryer for drying low-grade coal. In addition, the dispersion of raw coal on the heating plate was important during the drying process. The disc dryer could enhance the conductive heat transfer coefficient between raw coal and a heat source and mixing of the coal to reduce drying time.