Coal Powder Research Articles

Influence of porosity on the reactivity of inertinite and vitrinite toward sodium hypochlorite: Implications for enhancing coal seam gas development

Sodium Hypochlorite (NaClO) oxidation has been reported as a promising method for coal seam permeability enhancement and extracting valuable hydrocarbons from coal. Different coal macerals, particularly vitrinite and inertinite behave differently in NaClO with varying reaction extent exhibited. The reasons for variability are not completely understood. This study aims to reveal the controlling factors of different coal maceral oxidation by comparing their molecular structures and pore characterization. A Permian coal from Bowen Basin, Australia, was collected and separated into vitrinite-rich concentrate (bright coal) and inertinite-rich concentrate (dull coal). Their reaction phenomena with NaClO are examined and their molecular structures and pore structures are compared with multiple techniques. The vitrinite-rich and inertinite-rich concentrates share similar organic molecular structures although there is some marginal difference with the bright coal being slightly more aliphatic with higher oxygen content. By contrast, their pore structures are significantly different such that the dull coal is more porous with higher content of mesopores and better connectivity. For coal powders vitrinite is more reactive than inertinite and yet for coal particles inertinite is more reactive. Given that inertinite is more porous, these results suggest that the porosity of the inertinite is the key property making the inertinite more reactive. Therefore, it is proposed that the different extent of oxidation for different macerals from isorank coal is controlled primarily by the difference in their porosity rather than molecular structures.

Thermogravimetric and Kinetic Analysis of Co-Combustion of Waste Tires and Coal Blends.

The waste tire is a fuel with the potential to partially replace coal due to the high heat value. In the present study, the combustion characteristics of the tire powders, bituminous coal, and their blends were examined using the thermogravimetric analyzer. The influence of heating rate on tire powders combustion and the burnout characteristics of their blends were studied. The increase of the heating rate caused the combustion temperature of the tire powders to become high but reduced the maximum weight loss rate. The combustion characteristics of the blends of coal and tire powders approached the combination of those of the individual sample, suggesting that the interaction effects between coal and tire powders were slight. Furthermore, the influence of different ratios on ignition characteristics, burnout temperature, and combustion effect of the blends was studied at the optimal combustion rate. The addition of tire powders improved the ignition characteristics, reduced the burnout temperature and increased the burnout rate of coal to a certain extent. An increase in the proportion of tire powders led to a decrease in the activation energy in the temperature range of 349–465 °C, whereas it caused an increase from 465 °C to burnout, which could be attributed to the fact that the volatile matter was more combustible than fixed carbon within 349–465 °C, and the combustion effect of fixed carbon in the tire powders gradually manifested in the combustion from 465 °C to burnout when the tire powders content increased.

Experimental research with the help of thermal derivatographic analysis on coal powder that can be blowed in the furnace

In an integrated steel flow, the costs related to the consumption of metallurgical coke represent approx. 25% of the production cost of the shards obtained by continuous casting. As the price of coal returns to about 50% of that of coke, the technology of insufflating coal dust at the blast furnaces mouths, which transfers the coking process to the blast furnace, can reduce the cost of slag by 4-5%. It cannot be used to blow into the furnace any type of coal. The coal used must meet certain requirements, based on its physical and chemical properties. By thermo-derivatographic analysis, important properties of coals can be established. The authors present in this paper the results of thermal derivatographic analyzes performed on certain types of coal.

Micromorphology and safety properties of meager and meager-lean coal for blast furnace injection

Four types of meager and meager-lean coal and one type of high-quality anthracite were selected based on the safety requirements for blast furnace coal injection and domestic coal quality to conduct microstructure and component analyses. The analyses of the organic and inorganic macerals and the chemical compositions of the selected coal samples indicate that the four types of meager and meager-lean coal have low volatilization, low ash content, and low sulfur content; these qualities are suitable for blast furnace injection. Grindability test was conducted on the four types of meager and meager-lean coal and the anthracite mixed coal samples. Results indicate that the mixture of meager and meager-lean coal and anthracite is beneficial to improve the grindability of pulverized coal. The explosive tests reveal that the selected coal samples are non-explosive or weakly explosive. When the proportion of meager and meager-lean coal is less than 40wt%, the mixed coal powder would not explode during the blowing process. The minimum ignition temperature test determines that the minimum ignition temperatures of the four types of meager and meager-lean coal and anthracite are 326, 313, 310, 315, and 393°C, respectively. This study provides a guiding research idea for the safety of meager and meager-lean coal used in blast furnace injection.

Converting raw coal powder into polycrystalline nano-graphite by metal-assisted microwave treatment

A metal-assisted microwave treatment that converting raw coal powders into nano-graphite is presented. Specifically, four major factors are identified for successful conversion: (1) high temperature; (2) reducing environment; (3) catalyst; and (4) microwave radiation. Specifically, it is determined that the combination of the carbon sources (raw coal powders), the high temperature (microwave induced electric sparking), the reducing environment (the Ar/H2 mixture), the catalyst (Cu foil), with the microwave radiations can generate nano-graphites. This novel approach utilizes the sparking induced by the microwave radiation on the fork-shape metal foils to generate high temperature (> 1000 ºC) within few seconds. The small thermal load makes this method cost effective and has potential for higher temperature using metals with higher melting temperature. Refinement of this technique is possible to yield a higher quality and quantity of nano-graphite materials for a wider range of applications.

Impact of microarc carburizing and boriding of steel on diffusion layer structure

Intensification of carburizing and boriding of steel parts is achieved by microarc surface alloying. For carburizing, the parts are immersed in coal powder followed by electric current passing. For boriding, a coating with diffusant is used. Acceleration of diffusion is achieved by action of microarc discharges on the steel surface. The aim of this work was to study the effect of diffusion parameters on thickness, structure, and phase composition of coatings. The samples were made of 20 steel. Surface current density was 0.45 – 0.53 A/cm2. Duration of the process was 2 – 8 min. At the beginning of heating, temperature of the samples increases, and then stabilizes at 930 – 1250 °C due to cessation of micro-formation during combustion of coal particles. After carburizing, a eutectoid mixture is formed on the surface, then, the zone with ferrite-perlite structure is located, which transfers into the original structure. The maximum layer thickness (60 – 390 microns) is reached after 6 – 7 min of heating and then does not increase due to a decrease in the carbon potential during combustion of coal particles. Similar relationship is obtained when boriding: the maximum layer thickness (60 – 340 microns) is reached after 6 – 7 min and then does not increase due to depletion of diffusant source in the coating. At current density of 0.45 A/cm2, the layer consists of a base (a dispersed ferrite-carbide mixture) containing fine inclusions of iron borides and boron carbide. At current densities of 0.49 and 0.53 A/cm2, the layer has heterogeneous structure, with areas of high-hard boride eutectic located at the base. At high current density, diffusion of carbon and boron along the grain boundaries forms Fe – C – B triple eutectic. At lower current density, surface temperature is lower than eutectic formation temperature, so heterogeneous coating structure is not formed. The work results make it possible to choose modes of microarc heating to obtain the required parameters of diffusion layer.

Effect of External Factors on Diffusion Acceleration Mechanism During Steel Microarc Surface Impregnation

The considerable duration of steel chemical heat treatment (CHT) processes makes it necessary to intensify them. For this purpose, it is advisable to use microarc surface impregnation that provides acceleration of CHT in all stages. During microarc alloying steel products are immersed in a metal container filled with coal powder, followed by passage of an electric current in the circuit. Microarc discharges occur within the powder and are concentrated around the product with formation of a microarc halo and rapid heating to the diffusion saturation temperature. When the coal powder is heated a saturated atmosphere based on carbon monoxide is formed within the container that leads to steel product carburization. Preliminary application of a coating containing a diffusant to the surface provides preparation of multi-component coatings. This technology provides acceleration of CHT in all stages. The surface being treated is affected by microarc discharges that lead to accelerated formation of active diffusant atoms and ions and their movement towards a treated surface. On transfer into the metal there is an effect of electrotransport whose operating factors are a force for action of an electric field on the diffusant ions, and the strength of the interaction of atoms and diffusant ions with directional flow of conduction electrons that drives them in the direction of their own movement (“electron wind”) as well as heat transfer, whose impact is described by a vacancy mechanism (Wirts model), the mechanism of entrainment of ions by electrons under the action of a temperature gradient, as well as the mechanism of diffusing atom attraction by phonons of the crystal lattice (“phonon wind”). Experimental studies are conducted for the intensity of diffusion flow depending on the direction of the electric current for various alloying elements, as well as a calculated estimate of the values of these forces. It is found that the main factor determining intensification of diffusion saturation during microarc alloying is the “electron wind” strength. Calculated values of alloying element diffusion coefficients for various versions of microarc heating correspond to the scheme proposed for acting forces.

Mechanism on Activation of Coal Gangue Admixture

Coal gangue, an industrial waste, is rich in silicon and aluminum phase and may be used as a mineral admixture in concrete after moderately stimulating activity, allowing for efficient solid waste utilization. This study used a mortar strength and activity evaluation method to investigate single or compound activation methods to find the optimum activation method of coal gangue. FLIR, XRD, and SEM were used to investigate the activation mechanism of different modes, providing a theoretical foundation for the study of coal gangue as a concrete admixture. Results showed that mechanical ball milling, microwave, and chemical activator could activate coal gangue, and the composite activation effect was the best. The fineness of the coal gangue powder was more than 300 mesh, according to the optimal compounding method. Accordingly, the particle surface was smooth, the internal defects were reduced, and the microwave irradiation temperature was 700°C–800°C, causing the coal gangue particles to form a bonding surface and gradually agglutinate and densify. Meanwhile, the layered structure of kaolin minerals was destroyed, and a significant amount of glassy active SiO2 and Al2O3 was produced, enhancing the gel ability and activity of coal gangue. Finally, 8% Ca(OH)2 was added in the production of mortar specimens, which increased the alkalinity of the slurry, stimulated the rapid cracking and secondary hydration of the coal gangue, and enhanced the strength of mortar. At this time, the activity rate of coal gangue powder reached the highest, which was 90.5%.

Selection the measuring system for registering the metal parts temperature at microarc heating and its thermophysical analysis

Measuring the temperature of metal parts during thermal and thermochemical treatment is necessary for the control of the correctness of the technological process. Currently, new methods of thermochemical processing of parts under high-energy conditions, such as microarc surface alloying, are proposed. Heating is carried out by the action of microarc discharges on the surface of parts immersed in coal powder when an electric current flows. It reduces the processing time from a few hours to a few minutes, but makes it difficult to measure the temperature, because heating occurs in dynamic mode. The aim of the work was to select a measuring system for recording the metal parts’ temperature during microarc heating, and the thermophysical analysis of the heating process. The S-type sensor was selected. The measuring system also includes a digital multimeter and a personal computer. The density of the electric current on the surface of the samples was 0.53 A/cm2 The registered heating curve consists of several stages. At the first stage the heating speed was about 8 °C/s. At the second stage it increases to 16 °C/s, but then decreases to 3.5 °C/s. Then the temperature increases monotonously with an average speed of 9 °C/s. At the fourth stage the sample temperature is stabilized at 1250 °C. The thermophysical process’ model of the heating metal parts under the influence of microarc discharges was proposed. The analysis showed that the calculated data coincide with the experimental data.

SWOT-assessment of recycling materials for cheap explosives used in the development of fields in the Russian Arctic zone

The recycling potential is being actualized due to the trends in the production and use of powder and liquid combustible materials from the waste of a mining enterprise in the production cycle of mining, enrichment and processing (polymer packaging and containers of explosives, large tires and rubber products during the operation of mining vehicles, coal powder and coke breeze during enrichment and coking of coal, waste oil products during the operation of vehicles and mechanization equipment). In the material under consideration, a SWOT analysis of the possibility of using the recycling technology of materials in the manufacture of the simplest explosives in the northern and arctic regions of Russia is carried out, including consideration of geological, natural, climatic, economic-geographical, environmental, technological and technical aspects. On the basis of the presented detailing of the indicators of the considered aspects of the SWOT analysis, their role is shown and the value is highlighted when using the technology of recycling materials for the simplest explosives in the development of medium and small deposits. The possibility of obtaining recycled material used for the manufacture of the simplest explosives at mining enterprises from alternative manufacturers is shown.

The effect of composite reducing agent on the reduction process and the tail gas of carbon-containing pellets

In order to explore a reasonable way for the efficient utilization of coal resources in the ironmaking process. In this paper, lignite and bituminous coal are used as reducing agents, and two types of vanadium-titanium magnetite composite reducing agent pellets are prepared for different content ratios and mixed forms of the two coal powders. Under the simulated rotary kiln pre-reduction conditions, the influence of the ratio and mixing of pulverized coal on the metallization rate and tail gas composition of the reduction process was explored. The results show that increasing the proportion of high volatile lignite is beneficial to the reduction of pellets and can obtain pellets with a higher metallization rate. Under the new pre-reduction process conditions of the rotary kiln, the vanadium-titanium magnetite double-layer pellet with 75wt% lignite inside and 25wt% bituminous coal outside has the highest metallization rate of about 76%. At the same time, this new type of composite reducing agent pellets reduced gas emissions. This pellet is of great significance to the coal-based ironmaking process.

Preparation and characterization of coal gangue/Al cermet materials

In this study, the calcined coal gangue was mixed with Al powder at different mass fractions (5wt%〜35wt%). After being pressed at 80MPa and sintered at 1200°C for 2h, the coal gangue/Al cermet material was obtained. The phase composition, microstructure and mechanical properties of the material were studied. The results show that the main components of the prepared materials are Al, mullite, AlN, alumina and silicon. With the increase of coal gangue powder, the hardness of coal gangue/Al cermet gradually increases, while the static compression strength first increases and then decreases. When the mass fraction of gangue is 25wt%, the coal gangue/Al cermet material has the best performance. Density is 2.23g/cm3, hardness is 752HV, static compression strength is 127.3MPa.

A Novel Method of On-Line Coal-Rock Interface Characterization Using THz-TDs

The core problem in unmanned/intelligent working face of coal mining is the automatic adjustment of shearer arm where the coal-rock interface detection is the key. The cutting location of shearer drum affect the proportion of coal and rock powder around the cutting teeth of shearer drum. Therefore, the method of on-line coal rock interface characterization using Terahertz Time Domain spectroscopy (THz-TDs) we proposed aims to estimate the ratio of rock by Terahertz response. Firstly, anthracite and quartz sandstone were uniformly mixed according to 39 different ratios in this study, the samples' responses were obtained by terahertz system, and then the obtained time domain data was converted into frequency domain data by fast Fourier transform. The absorption coefficient spectrum and the refractive index profile of the 39 samples were calculated by optical parametric model. Secondly, corresponding quantitative model between mixed coal/rock powder and THz signal was built by using back propagation neural network (BPNN) and least squares support vector machine (LSSVM). We expected to use the ratio of rock powder detected by the model to estimate the depth of shearer drum teeth embedded in the rock layer. Finally, we found that both two mathematical arithmetic is feasible to quantitatively detect different proportion of coal and rock mixtures. The results show that the depth of shearer drum teeth embedded in the rock layer could be estimated by the novel method, which means the coal-rock interface could be on-line characterized by using THz-TDs and the height of the drum could be adjusted in time.

Study the kinetics involved in solid state reduction of mill scale with lean grade coal and optimization of process parameters involved in reduction through rotary kiln furnace

Abstract Present investigation envisages kinetics involved in solid state reduction of mill scale surrounded by lean grade coal powder in static and dynamic processes. Research aims to evaluate the reduction potential of economically available lean grade coal from Rajasthan in the reduction of mill scale. Experiments were carried out by mixing equal proportion of mill scale and coal and charging into the rotary kiln furnace. The variables studied are time and temperature. The reduction was done at temperatures ranging from 950 °C to 1050 °C. The degree of reduction of mill scale was calculated at 60 to 240 min. The experiments were statistically designed to assess each variable quantitatively and compared. The results indicated an increase in the degree of reduction with time and temperature. With the increment in temperature up to 1000 °C and holding time 240 min, 77.71% of metallization is achieved. The results showed a definite relation between reduction with time and temperature. Using the technique of empirical relation of transformation, the kinetics involved in solid state reduction of iron is studied for the processes. It is empirically calculated that the kinetics of reduction for the process of reduction in rotary kiln using the experimented setup. The Taguchi method, and analysis of variance (ANOVA) for the selected parameters to investigate the major effects and to assess the optimal process parameters show that, temperature is the most significant parameter amongst all whereas the mill scale size is the least affecting parameter. Based upon the analysis the optimized parameters obtained were temperature (at 1000 °C), mill scale to coal ratio (minimum 1:3), time (minimum 180 min), and mill scale size (minimum 425 to 600 µm). The microstructural characterization (XRF, XRD and FE-SEM. FE-SEM) conforms the formation of porous mass due to the solid state reaction between mill scale and coal.

Evaluation of polymer binders in briquetting of coal fines for combustion applications

Coal briquetting traditionally makes use of high-dosage, nonpolymeric binders (such as coal tar pitch or molasses) or polyvinyl alcohol (PVA) at low dosages for the binding of fine and ultrafine coal. Due to constraints associated with the manufacturing and cost of PVA-bound briquettes, a novel polyacrylic binder was developed that could possibly be added in low dosages at room temperature. A set of formulations of two polyacrylic components (components A and B) was developed, from which an optimal binder mixture was determined. This formulation comprises 40wt.% component A and 10wt.% component B with a 0.04wt.% cross-linking additive, and the balance water. The uniaxial briquette compressive strength was used to obtain the optimal binder mixture. The binder mixture was added to the coal powder in dosages from 0.1 to 1.2wt.%. Mechanical tests and thermogravimetric analysis in an oxidized environment at a maximum temperature of 930°C were conducted. Binder-bound briquettes were compared to binderless briquettes and PVA-bound briquettes. Briquettes made from the polyacrylic formulation had uniaxial compressive strengths double that of the binderless briquette yield strength, as well as the minimum recommended compressive strength of 0.375 MPa. The organic binders did not affect the combustion of the briquettes, since the results compared well with the binderless briquettes. The polyacrylic formulation is considered to be a possible substitute for PVA in terms of mechanical and thermal properties and raw material cost.

Study of the Granulometric and Morphological Composition of Coal Powders

Study of the Granulometric and Morphological Composition of Coal Powders

Study of the Granulometric and Morphological Composition of Coal Powders

Study of the Granulometric and Morphological Composition of Coal Powders

Improving coal powder wettability using electrolyte assisted surfactant solution

Evidence has shown that the prevalence of Coal Worker’s Pneumoconiosis (CWP) has been increasing among coal workers due to over-exposure to coal dust. Water spray is a widely used approach to suppress the coal dust in underground coal mines. The high surface tension of water prevents the water droplets to effectively capture coal particles. Although the addition of surfactant into water has been implemented in the mining industry to increase dust suppression efficiency. However, it is still a challenge to most of the mining industries for meeting the latest regulation. Studies have shown that the suppression efficiency could be improved significantly by using the surfactant with the addition of electrolyte. Thus, the selection of an optimum compounding solution is important. In this study, a standardised sink test method, which is reliable and accurate, was first proposed for evaluating the wettability of surfactant solutions. After that, the established standardised sink test method together with the commonly used surface tension test is used to evaluate the effectiveness of adding four different electrolytes to three types of surfactants. The finding of this paper provides the insight of an easy-conduct sink test method which may benefit other researchers who conduct similar tests. And the result reveals that the addition of electrolyte can significantly improve the coal powder wettability in anionic and cationic surfactant solutions. This study provides a starting point for the development of a more efficient low-cost dust suppression solutions.

Analysis of enhancing moisture-proof and waterproof performance for lignite powder briquette

ABSTRACT There are abundant resources of low-rank coal powder in the world. Powder briquetting technology has opened up a new avenue for large-scale utilization of low-rank coal. Water repellency is of great importance for the storage and transportation of lignite briquettes. In this paper, different water repellents were investigated to improve the moisture and water resistance of briquettes. The results showed that the moisture-proof and waterproof effect of briquette with the silicone emulsion was better than other briquettes. After 132 h of moisture absorption experiment, the briquette with the silicone emulsion absorbed only 1.8 wt% of water finally and was less 4.7 wt% than the briquette without water repellent. After 24 h of water immersion experiment, the water absorption of briquette with the silicone emulsion reached 19.74%. The addition of water repellent improved the water immersion strength and re-drying water immersion strength, of which briquette with the silicone emulsion were 4.91 KN/piece and 9.37 KN/piece. The waterproof mechanism was explored by scanning electron microscopy and wettability. It was proved that the addition of silicone emulsion, polyurethane, and acrylic emulsion played a positive role in the waterproofing of lignite briquette.

Large Eddy Simulation on the Effects of Coal Particles Size on Turbulent Combustion Characteristics and NOx Formation Inside a Corner-Fired Furnace

Abstract The effects of pulverized coal particles’ sizes on the coal combustion characteristics are numerically studied in a laboratory-scale tangentially fired furnace. The turbulent gas flow and the coal particle motion are solved by employing the large eddy simulation (LES) and the discrete phase model (DPM). The mixture fraction probability density function (MF-PDF) is coupled to simulate the non-premixed pulverized coal combustion. It is found that the coal combustion efficiency is positively affected by the dispersion of coal powders. The particle dispersion and the coal combustion are augmented by the intensive impingement caused by the corner-injected flow. Large coal particles, with their greater inertia, enhance particle agglomerations, which limit the combustion of volatile and char. Accordingly, the average flame temperature decreases with the growing particle sizes. Also, the O2 concentration increases slightly because of the incomplete coal combustion, and the CO2 concentration decreases gradually. In contrast, the CO concentration increases markedly in the furnace center due to the presence of a reducing atmosphere. The NO concentration exhibits an exponential decline with the increased particle size. A relatively stable combustion and a relatively low NOx formation are acquired inside such a corner-fired furnace when the particle Stokes number is a little greater than 1.