Coal Grains Research Articles

Optimization of a Radiometric Density Meter for Monitoring of a Coal Separation Process in a Jig

It should be possible to optimize discrete filters applied in an electronic circuit of a radiometric density meter monitoring coal separation processes in a jig. The signal from the meter can be used to (1) evaluate the degree in which coal grains loosen during cyclic water pulsations and (2) to determine the density of the separation layer in the jig. The signal transmitted by the radiation detector is variable due to stochastic decay of the radiation source and changes in media density. The authors present a simulation model of the radiometric meter and discuss results of optimization procedures based on industrial tests.

Determination of Transmission Coefficient for the Filtration Deposit Made of Coal Grains

Abstract The study presents the method of determining constant coefficient b2, occurring in general filtration equation (1), in the second part of the denominator, that is in the expression for deposit resistance In the considerations, lack of the deposit’s compressibility was assumed, which means that the deposit porosity is constant. With such an assumption, constant coefficient b2 is equivalent with transmission coefficient, which occurs in commonly known and accepted equation – as the baseline equation – for fluid flow through a porous layer according to Darcy (Piecuch 2009, 2010). This study is another publication in the cycle of basic tests of the filtration process which constitute next publications of the authors, published in Rocznik Ochrona Środowiska [Annual Set the Environmental Protection] as well as in the magazine Gospodarka Surowcami Mineralnymi [Mineral Resources Management], to which the reader interested in these problems can refer. Another study will be the publication discussing the filtration process with the creation of sediment on the filtration deposit, hence in the general filtration equation (1) the value of sediment resistance RO will appear in the denominator. Relevant cycle of publications will study the possibilities of use of gravitational deposit filters in which the porous deposit will be the set of coal grains, while the fed mixture will also be the post-production suspension of coal grains.

Organic Sulfur Reduction on Lignite Coal Using Multistage Artificial Biotreatment (A-Bmt)

This study focuses on the biodesulfurization of lignite specifically the reduction of organic sulfur, namely aliphatic mercaptans/thiolsviabioprocess methods. The process was conducted by using multistage artificial biotreatment (A-Bmt) andPseudoclavibactersp.SKC/XLW-1 strains as biocatalysts. The aims are to improve the recovery of clean coal by reducing the organic sulfur both in nodules and globular forms on the maceral surface during the stage of coal biooxidation prior to column bioflotation stage, in which it is still possible to achieve higher recovery of fine coal grains without sulphide mineral. The results shows that the A-Bmt method carried out through biooxidation stage followed by column bioflotation stage has better performance compared to the method without biooxidation stage. The results of this study show that the content of organic sulfur are lower by 25%.

Estimating the fusible content of individual coal grains and its application in coke making

Quantification of the amount of inertinite that is fusible during coke making has long been a goal for many researchers and coke makers alike. This study has used matched halves of coal and coke to first determine the fusibility cut-off, and has then used CSIRO's CGA optical imaging system to obtain quantitative compositional information on individual coal particles at the size they are used for coke making.The reflectance cut-off between fusible and infusible inertinite was determined by cutting coal lumps in half and coking one half. Comparison of matched structures in images of the coal and coke lumps allowed the fusible/infusible reflectance cut-off for inertinite to be determined for each of the coals. This study found that rather than there being a single reflectance cut off point between fusible and infusible inertinite for each coal there is a consistent difference (range) between the end of the vitrinite reflectance distribution and the fusible/infusible inertinite reflectance boundary for each individual particle within a coal.This reflectance range was then used to estimate the amount of fusible and infusible inertinite in individual particles of coal which had been crushed for use as coke oven feed for six Australian coking coals (consisting of matched pairs of coals of similar ranks from different Australian coal measures). Also determined was size detail for the individual inertinite structures within each particle and the amount of infusible inertinite structures greater than 1.5mm in length.The CGA results obtained suggest that two of the coals (from the Rangal Coal Measures) contained a greater proportion of large infusible inerts than did the coals of comparable rank from other Australian measures. If this is proven, the information may assist coal producers to develop specific milling strategies for these coals.

Application of image processing and different types of imaging devices for three-dimensional imaging of coal grains

Precise particle size measurements are important in many aspects of engineering geology, e.g. in mineral processing and the study of methane hazard in coal mines. The volume of grains, estimated exclusively on the basis of dimensions of the grains differs tens of percent from the volume obtained from 3D digital measurements. This confirms that full three-dimensional automatic imaging can be used in the measurements of the particles.The paper discusses the technique of three-dimensional imaging performed with the use of three types of devices. Coal particles representing the 0.5–1.0mm grain fraction were chosen as the research material. The measurements were performed by means of: X-ray computed tomography, confocal microscopy and optical profilometry. The last two techniques are less costly and more easily available than computed tomography.For the X-ray CT scanner, full three-dimensional imaging was performed. In the case of the other two techniques, only those parts of the particles that were captured by the heads of the relevant devices in question were measured. The invisible parts of the particle were reconstructed with the assumption that the bottom part of the particle is similar (in some scale) to the top part of the particle. The results obtained by means of X-ray CT scanner were used as the correct volume and size values.The results indicate that measurements carried out carefully and with use of the more easily available and less costly equipment, combined with careful data processing, can be used instead of methods that are expensive and harder to employ. The percentage deviation between the volume calculated with use of the data obtained with the X-ray CT scanner and the volume calculated with use of the data obtained with the other two devices varies from 0.2% to ca. 5%.

Investigation into the Flow Properties of Coarse Solid Fuels for Use in Industrial Feed Systems

Material feeding and handling systems have been cited as one of the most common causes of process downtime where thermochemical conversion processes are concerned. New and emerging fuels come in a variety of forms, and if such fuels are to be deployed widely it is imperative that material feeding and handling systems are designed appropriately. This study proposes an approach for designing material feeding and handling systems for use with coarse solid fuels. The data obtained from this study indicates particle size to be one of the key issues affecting the flowability of bulk solids further to the uniformity in particle shape. Coarse bulk solid samples were shown to flow more freely than their milled and pulverised counterparts, generating higher degrees of flowability. The results from this study were also applied to a new feed system used for feeding solid fuels to high pressure processes named the Hydraulic Lock Hopper. In this study the Hydraulic Lock Hopper demonstrated the feeding of wood pellets, torrefied spruce pellets, and ground anthracite coal grains against a pressure of 25 barg in two modes of operation. Energy savings compared to conventional lock hopper systems were recorded in the region of 80%.

Analysis of Sorption-Induced Permeability Reduction Considering Gas Diffusion Phenomenon in Coal Seam Reservoir

The sorbed gas diffuses in a coal matrix, where diffusion varies considerably with pore structure and pressure. The diffusion is an essential factor due to high sorption affinity of \(\hbox {CO}_{2}\) on coal grain surface. The sorption within the matrix causes swelling or shrinkage of matrix, in which the amount of sorbed gas affects gas diffusion. In this study, in order to observe permeability change occurred when the sorbed gas diffuses in a coal matrix, experiments were conducted with a bituminous coal sample. Firstly, gas partial pressure was measured through a diffusion experiment with a transient flow method. Secondly, flowing experiments were conducted to examine the permeability reduction yielded by sorption phenomena according to the various pore pressures. The results were then analyzed for the effect of diffusion coefficient on permeability change. The diffusion coefficient of \(\hbox {CH}_{4}\) in low-pressure section was greater than that of \(\hbox {CO}_{2}\) owing to the difference in their molecular weight. However, as pressure increased, the diffusion coefficient of \(\hbox {CO}_{2}\) became greater because of higher sorption affinity of \(\hbox {CO}_{2}\) compared to \(\hbox {CH}_{4}\). Finally, it was revealed that the gas diffused instantaneously in the case of crushed coal in which its diffusion coefficient had infinite value due to the destroyed pore structure. Meanwhile, in the coal core sample in which pore structure was preserved as original state, it was ascertained that diffusional flow occurred gradually corresponding to concentration gradient, and hence, the permeability was reduced accordingly. This phenomenon was also confirmed through pore images obtained from X-ray CT.

Oxidation of Pokrovskoe coal in laboratory and natural conditions. 1. Kinetics of oxidation and technological properties

The oxidation of coal from the Pokrovskoe mine consists of stages of initial and intense oxidation in both laboratory and natural conditions. The oxidation temperature has a significant influence on the properties of the coal. In laboratory oxidation, the surface layer of the coal grains is significantly modified, with loss of plastic-viscous properties and reduction in ignition temperature. In addition, at different temperatures, different chemical processes will predominate. The oxidation of Pokrovskoe coal is assumed to result predominantly in peroxide formation in natural conditions (from –1 to 22°C), whereas oxidation in a drying chamber (at 140°C) is accompanied by decomposition of the peroxides and the formation of coal-oxygen complexes. Hence, the oxidation of coal is different in laboratory and natural conditions, and correspondingly the change in technological properties of the coal will be different. The rate constants, the preexponential factors, and the activation energy for the oxidation of Pokrovskoe coal are calculated by methods developed in physical chemistry. The rate constants of oxidation are k0–1 = 0.0041 × 10–4 and 2.7933 × 10–4 min–1 in natural and laboratory conditions, respectively; the corresponding values of the preexponential factors are k0 = 266.0 and 267.8 min–1. In the range 7.3–140°C, the activation energy is Ea = 11.3 kcal/mol.

MONITORING OF COAL SEPARATION IN A JIG USING A RADIOMETRIC DENSITY METER

Application of a radiometric density meter for monitoring of the coal separation process in a jig has been discussed in the paper. The signal from the meter can be used to evaluate the degree of coal grain loosening during cyclic water pulsations and to determine the separation density in a jig. The signal from the radiation detector is highly nonstationary due to stochastic decay of the radiation source and various changes in media density. The paper discusses the optimisation of analogue and discrete filters applied in an electronic circuit of a density meter. The minimum dynamic error of measurement can be achieved in the case of filters with parameters adapting to changes in the measured density. Results of industrial tests of the jig control system with the radiometric density meter have also been presented.

Distributed flotation kinetics models – A new implementation approach for coal flotation

Composition-dependent flotation kinetic models with distributed flotation rate constants for predicting the flotation response of the various components of coal have been available for quite some time. However, the full potential of these models have not been realised because the floatability distribution of particles, a key requirement for the utilisation of the models, has not been readily accessible experimentally to allow the validation of these models.A new approach has been developed that allows the coal flotation feed to be fractionated into particles classes of size and composition using a microscopic characterisation tool called Coal Grain Analysis. Previous work had determined the contact angles of discrete coal maceral groups and associated minerals. Combining this information with the particle composition data from the Coal Grain Analysis methodology provides a pathway for estimating the contact angles of heterogeneous coal particles via Cassie’s Equation. The approach provides a unique opportunity to estimate the flotation rate constants for the different particle classes.

A correlation of the lower flammability limit for hybrid mixtures

Hybrid mixtures are widely encountered in industries such as coal mines, paint factories, pharmaceutical industries, or grain elevators. Hybrid mixtures explosions involving dust and gas can cause great loss of lives and properties. The lower flammability limit (LFL) is a critical parameter when conducting a hazard assessment or developing mitigation methods for processes involving hybrid mixtures. Unlike unitary dust or gas explosions, which have been widely studied in past decades, only minimal research focuses on hybrid mixtures, and data concerning hybrid mixtures can rarely be found. Although methods to predict the LFL have been developed by using either Le Chatelier's Law, which was initially proposed for homogeneous gas mixtures, or the Bartknecht curve, which was adopted for only certain hybrid mixtures, significant deviations still remain. A more accurate correlation to predict an LFL for a hybrid mixtures explosion is necessary for risk assessment. This work focuses on the study of hybrid mixtures explosions in a 36 L dust explosion apparatus including mixtures of methane/niacin, methane/cornstarch, ethane/niacin and ethylene/niacin in air. By utilizing basic characteristics of unitary dust or gas explosions, a new formula is proposed to improve the prediction of the LFL of the mixture. The new formula is consistent with Le Chatelier's Law.

The influence of composition of coal briquettes on changes in volume of the heated coal charge

Two coal blends of different composition made of lower, medium, and higher rank coals (further in the text LRC, MRC, and HRC appropriately) in the ratio of 70:20:10 and 20:70:10 were carbonized in a laboratory unit for coke-making with the use of X-raying. The carbonization of the blends was carried out with the briquettes having the same composition as the blend and with the briquettes made of HRC with 2wt% of coal tar pitch (CTP), with 2wt% of low density polyethylene (LDPE), and with 2wt% of polypropylene (PP). Markers were introduced into the charges of the blends to enable measurements on X-ray pictures that are connected with volumetric changes. The same blends were pyrolyzed in thermobalance coupled with a TG/FT-IR interface.It has been proven experimentally that the addition of briquettes to the coal charge having the same composition as the charge leads to an increase in volume of the charge near the heating wall. The introduction of the briquettes made of higher rank coal with addition of CTP, LDPE, and PP reduces the increase in volume of the two charges at the stage of coal grain swelling.The briquettes made of the blend of HRC with LDPE are most exposed to gasification by decomposition products from blend 1; the composition of volatiles does not influence the gasification of the briquettes made of the blend of HRC with PP. The briquettes made of the blend of HRC with CTP substantially increase their thickness under the influence of a greater amount of volatile products.

Assessment of the flotation activity of reagents in terms of the hydrogen bond energy in molecular complexes with active sites of the coal surface

The hydrogen bond energy of molecular complexes between a flotation reagent and coal’s organic mass is calculated for the first time. The electron density distribution in molecules of 2-methyl-1,3-dioxane and 2-methyl-1,3-dioxa-2-silacyclohexane is determined. It is shown that the silicon atom in the molecule of 2-methyl-1,3-dioxa-2-silacyclohexane increases the electron density at oxygen atoms from −0.279 to −0.424 and −0.432 in positions 1 and 3 of the molecule, respectively. This increases the hydrogen bond energy of the reagent in molecular complexes with water and model compounds of the coal’s organic mass. In molecular complexes of 2-methyl-1,3-dioxa-2-silacyclohexane with model compounds of the coal’s organic mass, the hydrogen bond energy is considerably higher than in corresponding complexes of 2-methyl-1,3-dioxane. As a result, the adsorption of 2-methyl-1,3-dioxa-2-silacyclohexane on the coal surface is 35–45% greater than for 2-methyl-1,3-dioxane. Consequently, the coal grains become more hydrophobic, and their flotation is improved. With the same consumption of reagents, the use of 2-methyl-1,3-dioxa-2-silacyclo-hexane rather than 2-methyl-1,3-dioxane increases the concentrate yield and reduces the losses of the coal’s organic mass with the wastes. Analogous flotation properties of coal are found for other cyclic acetals and their silicon analogs. Experimental data confirm that the hydrogen bond energy in complexes between the flotation reagent and the coal’s organic mass may be used to assess its effectiveness.

Lignite oxidative desulphurization

AbstractThe process of lignite desulphurization via its treatment by an oxidant (air or air–steam mixture) has been studied. The research objective was useful determination of steam application in oxidative lignite desulphurization. It has been proved that the water steam should be included in the oxidant composition to increase the hydrogen sulphide and combustible constituent content in the gases obtained during the processes under research. The impact of factors which affect the reactions between solid (in our case – lignite) and gaseous reagent (oxidant, i.e. air and or air–steam mixture) upon the research process has been investigated, if these reactions occur in the kinetic area. Such factors are linear rate of oxidant movement and coal grain size. The values of oxidant movement linear rate and coal grain size, which the reaction transfer from pyrite sulphur and organic content of lignite from diffusion into kinetic area occurs by, have been determined. Under these “transfer” conditions, the values of coefficients of oxidant mass transfer (β, m/s) as well as Sherwood criteria and boiling layer differences have been calculated.

Influences of magmatic intrusion on the macromolecular and pore structures of coal: Evidences from Raman spectroscopy and atomic force microscopy

Magmatic intrusion into coal-bearing sequences can significantly affect the rank of the intruded coal and change the macromolecular and pore structures. Here, we use Raman microscope and Atomic force microscope (AFM) to obtain quantitative information on these transformations. Six coal samples of different ranks taken from a magmatic intrusion zone of Huainan Coalfield, China, were studied. The Raman spectra were fitted with a combination of 8 Lorentzian bands and 1 Gaussian band. We found that the macromolecular structures in coals of different ranks have significant relationships with Raman spectral parameters, particularly the band area ratios (ID1/IG, ID2/IG, ID3/IG, ID4/IG and IG/IAll). With the increase of coal rank, ID1/IG, ID2/IG, ID3/IG and ID4/IG show trends of decreasing intensity, suggesting an enhanced orientation of aromatic hydrocarbons. Observations by Atomic force microscopy indicate that the pore parameters (e.g. amount, size, shape) are quite different for different ranks of coals. The pore size of low-rank bituminous coal is much larger than high-rank anthracite and pore abundance is higher in the former. In addition, there is also good correspondence between the surface topography of coal grains and coal rank.

Flotation of flocculated coal grains for effective enrichment

The deposition of coal slurry by means of various flocculants is experimentally studied. The flotation of flocculated coal grains is investigated. Effective conditions of coal flotation are developed.

Triboelectric charging behavior of wood particles during pellet handling processes

Electrostatic charges accumulated on wood particles through triboelectrification during their transportation and handling processes can cause hazardous electrical discharge which may further trigger dust explosion. In this work, tribo-charging behavior of different kinds of wood particles was investigated by a vibrating plate charging method. It was found that reduction in the work function difference between contact bodies might contribute to the reduction of tribo-charge generation, while the reduction of electrical resistivity of wood pellets could effectively accelerate the charge dissipation. As the particle size decreases, accumulated charges increase significantly. In contrast, higher moisture content of wood particles leads to lower charge accumulation due to an accelerated charge dissipation rate. Tribo-charging behaviors of white pellets, torrefied pellet, steam treated pellets and dark pellets have also been investigated. Compared to the white pellets, they all have shown a reduction on charge accumulation to some extent. However, results suggested that all of them have nearly equivalent tribo-charge density as coal and wheat grains used as references in this study.

A comparison of the influence of adsorbed gases on gas stresses leading to coal and gas outburst

The present work analyzes the influence of seepage and desorption processes on the initial conditions of coal and gas mini-outbursts. A series of laboratory experiments incorporating coal briquettes and three different gases, namely carbon dioxide, methane or nitrogen were carried out. Experiments relied on mini-outburst inducing. Space and time pressure distributions along the briquettes were recorded. A comparative analysis of the results revealed that the observed differences in mini-outbursts initial conditions cannot be explained by means of a simple coal or gas property such as sorption capacity, desorption rate, seepage rate, or viscosity of gas. On the contrary, the efficiency of accumulated gas releasing processes – desorption and diffusion inside of the coal grains and seepage through the briquette coupled processes – seems to explain the observed variations.

Kinetics of coal and char oxycombustion studied by TG–FTIR

Coal and char oxycombustion is a complex process because of very high reaction rate of oxygen with coals and chars carbon. Very important process during oxycombustion is diffusion of O2 to surface of coal and char grain. This process can be minimized using small samples and high flow of the gas, but it is also dependent on temperature. For this reason, it is impossible to eliminate diffusion processes which cause significant impact on calculated kinetic parameters. This paper describes the results of thermogravimetric studies of oxycombustion process with evolved gas analysis by FTIR. Ultimate and proximate analysis of coal and char were made. Thermogravimetric experiments of coal and its char oxycombustion were conducted using five heating rates, namely 2.5, 5, 10, 20 and 40 K min−1, and gas mixture composed of 20 % O2 in CO2. Activation energies of coal and char oxycombustion were calculated by isoconversional methods: integral Vyazovkin and differential Friedman. Activation energies for three ranges of heating rates were calculated. This paper shows influence of heating rate on calculated activation energy. The reason of this phenomenon is due to change of the mechanism of coal and char oxycombustion from the chemical kinetic control regime to mixed chemical kinetic–diffusion control regime.

The Use of Tri-Block Copolymer Surfactants as Promoters to Improve Flotation Recovery of Poorly Floating Coal Components

The use of tri-block copolymer surfactants as flotation promoters to enhance the recovery of poorly floating components of coal is examined. Previous study of the flotation response of different coal components using the coal grain analysis tool showed that coarse particles of inertinite, inertinite-rich, and vitrinite-rich composites were poorly recovered compared with liberated vitrinite. Improved recovery of these poorly floating components by using targeted reagents could boost the saleable product coal and, hence, economic outcomes. This approach requires only minor modifications to existing fines circuits. The reagents used were surfactants from the group of tri-block copolymers of polyethylene oxide/polypropylene oxide. The tests were complemented by the coal grain analysis tool that allowed the impact of the reagents on the recovery of the problem components to be properly assessed. Laboratory and full-scale flotation experiments were conducted by adding small amounts of the promoters before adding conventional collector (diesel). Flotation recovery was significantly increased with only a small product ash penalty in each case. Coal grain analysis showed that recovery was improved for most components, especially the coarse composite grains.