Anthracite Particles Research Articles

Comparing the ignition parameters of promising coal fuels

Here we compare the ignition and burnout parameters of lignite, bituminous coal, and anthracite particles, as well as slurry droplets. We also study the fire hazard of traditional fossil fuels and promising fuel types (coal-water slurry, coal processing waste, and waste-derived slurry). The micro-explosion of multi-component droplets is considered in terms of safety at an energy enterprise, i.e., under the actual furnace conditions. Dimensionless integral fire hazard indexes of fuels are calculated and compared with those of lignite as the most reactive fuel. Coal processing wastes are found to be the safest. The relative fire hazard indexes of bituminous coal particles and coal-water slurry are comparable. Adding used turbine oil to the waste-derived fuel mixture makes it more fire-hazardous. Finally, we explore the micro-explosive dispersion of waste-derived slurry droplets before and during combustion in terms of the risk of their spontaneous ignition.

Influence of Submicron Anthracite Particles on the Conditions of Aerosol Synthesis and the Properties of Carbon Nanotubes

Properties of single-walled carbon nanotubes (SWCNTs) obtained by the floating catalyst CVD method using ethyl alcohol and coal (anthracite and semi-anthracite) particles are investigated. Structural and vibrationalcharacteristics of synthesis products are determined. It is revealed that enrichment of the reaction mixture by anthracite particles increases the concentrations of CO and CH4 in the reaction zone, which contributes to the growth of the SWCNTs. A comparison of the Raman spectra of the samples shows an increase in the content of small-diameter semiconductor SWCNTs, whereas a set of chirality indices of the resulting nanotubes remains unchanged.

Mathematical modeling of burn-out of the coal particle coke residue

Combustion of solid fuels in general includes a number of stages: heating, drying, devolatilization, ignition, and burn-out of coke. The stage of coke residue burn-out is the leading one. In this paper, analytical solutions for the burn-out of the coke part of an anthracite particle were developed using the asymptotic procedures, and combustion of anthracite particles with the size of 100 µm and less (presented size for the flare process) and 12 mm or more (characteristic size for burning in a fluidized bed) was calculated. In the first case, combustion occurs in the kinetic regime, and in the second, it occurs in the diffusion regime. The models of the “hard” ash frame, as well as the model “with segregating” ash, have been implemented.

Catalytic Fluidized-Bed Co-Combustion of Peat and Anthracite

Results of the studies of catalytic combustion of peat, anthracite, as well as the mixture at the peat to anthracite weight percent ratio 40/60 are discussed. The degree of the mixture burning-off was shown to increase when peat evolving large quantity of volatile substances is added to anthracite. The burn-up degrees of the solid fuel particles less than 1.25 mm in size were 98.2 % of peat, 50.9 % of anthracite, 74.2 % of the peat and anthracite mixture at 700–750 °C and 1 m height bed of the industrial aluminum-copper-chromium oxide catalyst IC-12-70. In combusting coarse particles (equivalent diameter 11.6–18.6 mm) of molded peat and anthracite mixture, the burn-up degree was 80.5 % at the top of the fluidized catalyst bed. The burn-up degree of the coarse particles fed to the bottom of the fluidized bed was estimated with allowance for the burn-up degree of fine particles moving through the bed. With the coarse molded particles of the peat and anthracite mixture fed to 1 m height catalyst bed, the burn-up degree was shown to reach no less than 95 %. When the catalyst used is 2 mm in size, the peat and anthracite particles comprised in the molded fuel must be no more than 1–1.5 mm in size in order to prevent from ash accumulation in the fluidized catalyst bed.

Prediction of Combustion Behavior in a Boiler Fired by Mixture of Vietnamese Anthracite and Coal Gas Using CFD

The domestic anthracite is the most important fuel for Vietnamese thermal power plants. Due to high carbon percentage and low volatile matter it is difficult to ignite and to burn out the domestic anthracite. The rest carbon in ash is very high, in some cases approximately 40 %. To solve this problem some methods have been tested. In this research a mixture of anthracite and coal gas is considered. The purpose of the research is to describe a combustion behavior in a boiler, namely temperature, carbon and volatile matter distributions using CFD. The mixture consists of 4.3 % coal gas and 95.7% anthracite in mass. The boiler is divided into two combustion zones, the main zone 1 and the zone 2, to extend combustion area and through it to improve burning conditions for anthracite particles and to reduce NOx formation. All the anthracite mass and 1/3 coal gas volume are delivered into the zone 1, the rest of coal gas is into the zone 2. The CFD simulation is used for the zone 1. The simulation findings show that anthracite particles are ignited earlier, the mixture combustion develops in a larger space with higher temperatures, the carbon burning rate is remarkably improved due to coal gas. That means the domestic anthracite can be used better in boilers if some coal gas, 4 or 5 %, is mixed and the obtained ash can have lower unburned carbon, below 10%, and be more friendly for the environment.

Silicon Carbide Formation Enhanced by In-Situ-Formed Silicon Nitride: An Approach to Capture Thermal Energy of CO-Rich Off-Gas Combustion

Carbothermic smelting of ores to produce metals or alloys in alternating current open/semiclosed and closed submerged arc furnaces, or in closed direct current furnaces, results in large volumes of CO-rich off-gas being generated. Most of the CO-rich off-gas is cleaned and flared on stacks, since the storing of large volumes is problematic due to the associated toxic and explosive risks. Flaring of CO-rich off-gas results in significant wastage of energy. In this study, an alternative method to partially capture the thermal energy associated with off-gas combustion, in the form of silicon carbide (SiC) generated from waste materials (quartz and anthracite fines), is proposed. SiC can partially replace conventional carbonaceous reductants used to produce alloys such as ferrochromium. The influences of quartz and anthracite particle size, treatment temperature, and gaseous atmosphere (nitrogen or air) on SiC formation were investigated. A quartz-anthracite mixture with 90 pct of the particles < 350.9 µm carbothermically treated at 1873.15 K (1600 °C) resulted in almost complete conversion of quartz to SiC in both nitrogen and air atmospheres. The study indicated significant potential for industrial application of the process.

Experimental Study of High-Temperature Fracture Propagation in Anthracite and Destruction of Mudstone from Coalfield Using High-Resolution Microfocus X-ray Computed Tomography

The coalfield fire is determined by fractures of coal and rock that provide tunnel for gases and heat exchange. To study fracture propagation at high temperatures, high-resolution X-ray computed tomography (CT) was used to scan anthracite and mudstone samples collected from the Qinshui coalfield, Shanxi Province, northern China. The samples were scanned at 100 °C intervals as they were subjected to temperatures of up to 500 °C. Three-dimensional images were reconstructed by the CT software to analyze changes in the fractures and pores in the samples. The experimental results show that fracturing of anthracite began at 200 °C. The generation rate of fractures in the coal samples increases slowly below 300 °C, but above 300 °C there is a sharp increase in fracture development. This indicates that the thermal fracturing temperature threshold for anthracite is 300 °C. During the experiment, it was found that preexisting fractures, voids, and regenerative fractures formed around the hard portions of anthracite particles or along the weak boundaries between particles. Some regenerative fractures developed along the fabric of the relatively crystalline particles within the particle and terminate at the edge of the particle or where the fracture encounters a harder portion of coal. Some fractures even expanded enough to be transformed into voids as temperatures rose. In the mudstone, the porosity changed suddenly at 300 °C. This indicated that there was a void generated at 200 °C, but the void expanded when the temperature was increased. However, changes in the void were not obvious from 200 to 300 °C.

Direct optical observation of coal particle fragmentation behavior in a drop-tube reactor

An experimental plant – called Single Particle Disintegrator (SPaltor) – is presented that allows an observation of coal particle fragmentation during the thermochemical conversion process. The SPaltor is a lab-scale drop-tube reactor which runs at atmospheric pressure and temperatures up to 1600°C. A high-speed camera, a long-distance microscope, and a high-power LED outside the reactor in combination with two mirrors arranged inside the reactor in a 45°-position are used to monitor the inside of the reactor. In this setup, the particle behavior of three different feedstocks were recorded at nitrogen atmosphere. Two recordings are presented in this paper for a reactor temperature of 1400°C. While a brown coal particle shows no fragmentation, but a bright gas tail due to devolatilisation, an anthracite particle disintegrates into smaller fragments in the first third of the heated zone. For detailed investigation of primary fragmentation, three non-swelling feedstocks were used: A brown coal from Germany, a high-volatile bituminous coal from South Africa, and an anthracite from Germany. Two key figures were used for the description of fragmentation behavior: Fragmentation probability and fragmentation number. The influences of temperature (800–1400°C), particle size (0.8–3.15mm), reactor height (0–90cm), and calculated residence time (0.25–0.5s) were investigated. Increasing these parameters led to an increase of fragmentation of the anthracite and the high-volatile bituminous coal. In contrast, fragmentation was never observed for the brown coal in any experiment. For the chosen particle sizes, the residence time in the heated zone is smaller than 0.5s and comparable to free-fall conditions. The heating rate referring to the particle center varies heavily with particle size and coal type.

Removal of oxygen demand and nitrogen using different particle-sizes of anthracite coated with nine kinds of LDHs for wastewater treatment.

This paper reports the application of anthracite particles of different sizes and coated with nine kinds of layered double hydroxides (LDHs) varying in MII–MIII cations, as alternative substrates in the simulated vertical-flow constructed wetland columns. Effects of LDHs-coating and particle size of modified anthracites were examined to evaluate their abilities in removing oxygen demand and nitrogen from sewage wastewater. Results showed that LDHs modification effectively enhanced the removal of nitrogen and organics. The removal efficiencies of total nitrogen (TN) , ammonia and chemical oxygen demand (COD) were best improved by 28.5%, 11.9% and 4.1% for the medium particle size (1–3 mm), followed by 9.2%, 5.5% and 13.6% for the large size (3–5 mm), respectively. Only TN removal was improved up to 16.6% for the small particle size (0.5–1 mm). Nitrate tended to accumulate and fluctuate greatly across all the treatments, probably due to the dominancy of aerobic condition in the vertical-flow columns. Overall, MgFe-LDHs was selected as the best-modified coating for anthracite. The results suggested LDHs modification would be one of the promising strategies to provide new-types of highly efficient and lasting wetland substrates.

Ultrasonic-Assisted Solid-Phase Extraction Pre-concentration and Determination of Nicotinamide and Nicotinic Acid by High-Performance Liquid Chromatography Using Anthracite

This study introduces a novel method of ultrasonic-assisted solid-phase extraction, pre-concentration, and reversed-phase high-performance liquid chromatography to determine nicotinamide (NAM) and nicotinic acid (NAC) from an aqueous solution using anthracite particles (ANTCs). Results demonstrated that ANTCs were quite efficient for use in extraction and pre-concentration of traces of NAM and NAC at 25 °C. Tests investigated the effects of the parameters: pH, buffer and its volume, electrolyte concentration, composition and volume of the desorbing solvent, accepted tolerable volume, amount of adsorbent, ultrasonic radiation time, and evidence of some co-existing ions on pre-concentration and determinations of NAM and NAC. The method showed good linearity for determination of these compounds in the range of 0.0025–10 μg mL−1 with regression coefficients of 0.999. Evaluations for limits of detection were 6 × 10−4 and 7 × 10−4 μg mL−1 for NAM and NAC, respectively. Intra- and inter-day relative standard deviations for 0.2 and 5 μg mL−1 were below 3.5 % and 4.6 %, respectively. Samples of rice, coffee, spice, spaghetti, tea, and B-complex syrup with potential niacin content were used as real samples, and NAM and NAC in the samples and spiked samples were pre-concentrated and determined successfully.

Velocity characterization of dense phase pneumatically conveyed solid particles in horizontal pipeline through an integrated electrostatic sensor

Dense phase pneumatic conveying of pulverized fuel particles under high pressure is one of the key techniques in large scale gasification of coal and petroleum coke. The real time and continuous measurement of dense phase gas–solid flow parameters such as particle velocity, concentration and mass flow rate has great significance for the in-depth understanding of particle flow dynamic behaviors and the optimized design of the conveying system. In this paper, an integrated electrostatic sensor is designed and used to explore the flow characteristics of anthracite and petroleum coke particles on a dense phase pneumatic conveyor. The ring electrodes in the integrated sensor are capable of measuring the “mean” velocity of solid particles over the whole cross-section of the pipeline, while the arc electrodes are employed to determine the local velocity of particles near them. The experimental results on a dense phase pneumatic conveyor under high pressure demonstrate that the flow characteristics depend on the physical properties of solid particles and carrying gas. Petroleum coke particles are much easier to be suspended in the gas flow than the anthracite particles, but its flow stability is worse. The local velocities from the arc electrode pairs mounted on the top of the pipeline are usually higher than those from the arc electrodes on the bottom for a stratified flow. The velocity from the ring electrode pair, indicating the mean velocity of particles over the whole cross-section, is usually higher than the local velocities from the arc electrode pairs for a suspension flow. In addition, the relationship between the mass flow rate and charge level of dense phase pneumatically conveyed solid particles is very complicated due to the complexity of the particle flow and the charge level cannot be used to measure particle concentration or mass flow rate.

Devolatilization of a single fuel particle in a fluidized bed under oxy-combustion conditions. Part A: Experimental results

Devolatilization of a single fuel particle and the related flame combustion were studied in a two-dimensional fluidized bed with a quartz wall, allowing visual observation of the conversion process. The aim was to evaluate the devolatilization behavior (ignition, flame temperature, flame life-time, devolatilization time) of different fuels (4 ranks of coal from lignite to anthracite and wood) when replacing O2/N2 by O2/CO2 in O2 volume concentrations from 0% to 40%, at a fixed bed temperature of 1088K using 6mm spherical fuel particles. The volatiles’ flame was recorded by a color video camera to analyze ignition and extinction. The flame temperature was estimated by two-color pyrometry. Two thermocouples were inserted in the fuel particle to measure the temperature at the center and near the surface. Homogeneous and heterogeneous ignition modes, times of devolatilization, and flame duration (flame-life) under different gas atmospheres were analyzed. Results indicate that the mode of ignition of bituminous coal, lignite coal and wood changes when N2 is replaced by CO2. The ignition-delay time is much longer, and the flame temperature is lower in the O2/CO2 atmosphere than in an O2/N2 atmosphere for all the tested fuels. The devolatilization time of the anthracite particle is almost unaffected by the surrounding atmosphere, while for the other fuels this time is generally longer in O2/CO2 than in O2/N2 at the same O2 concentration. The presence of a flame during the volatiles combustion did not accelerate the particle heating, not even at the highest O2 concentration tested (40vol%), however, after the extinction of the flame, the rate of particle heating is significantly affected by the oxygen concentration.

Accuracy of the single-film model in the prediction of coal char conversion rates under oxy-fuel and conventional combustion conditions

The accuracy of the single-film model in the calculation of char burning rates and particle temperatures in conventional and oxy-fuel combustion conditions has been investigated taking as a reference the results obtained with a model with detailed gas-phase kinetics. Both models have been applied to subbituminous coal and anthracite char particles in different sizes (60–1000μm), in N2 and CO2-rich atmospheres with a low and a high oxygen concentration. For 120μm char particles, the models’ predictions have been also compared over an ample range of ambient gas temperatures (1373–1823K) and oxygen concentrations (4–50%). High particle diameters, bulk gas temperatures and oxygen concentrations result in CO-flames closer to the particle surface; however, the specific effects of the flame strongly depend on the coal rank and combustion conditions. In general, the single-film model accuracy is quite high in terms of burning rate predictions, except for fine anthracite particles burning at moderate bulk gas temperatures and high O2 concentrations; greater deviations have been found regarding particle temperatures, even in cases where the corresponding combustion rates are very similar. The oxy-combustion of the reactive coal char is found to be faster than its conventional combustion, except for the finest particles; although qualitatively similar, the difference in rates is overestimated if the single-film model is considered.

Comparative study of four alternative models for CO oxidation around a burning coal char particle

The steady state combustion of a quiescent char particle is investigated by means of a detailed model which accounts for heterogeneous oxidation and gasification, as well as homogeneous reactions (GRI-Mech 3.0) in the particle’s boundary layer. First, the way and extent in which the mass and energy transfer are altered due to the oxidation of CO are examined by comparison with the predictions of a single-film model in the case of anthracite particles within 60–1000μm. Then, four alternative descriptions of the gas phase (single-film, double-film, global kinetics and detailed kinetics) are evaluated for two coals of very different reactivity towards O2 and CO2, at low and high O2 concentration and in the same broad range of sizes. The overall influence of the CO conversion modeling on the particle burning rate and temperature (i.e. whether the reduction in O2 surface concentration or the heat and CO2 provided by the flame dominate over each other) is found to depend on the conditions considered. The single-film approach reasonably fits the predictions of the most complete model in all cases (and especially in the pulverized-coal size range), whereas the double-film hypothesis and the global kinetics generally overestimate the effects of the flame on the consumption rates and the particle temperatures.

Simultaneous removal of nitrobenzene, 1,3-dinitrobenzene and 2,4-dichloronitrobenzene from water samples using anthracite as a potential adsorbent

Micro-sized anthracite particles (ANTCs) were used as natural adsorbent for efficient removal of nitrobenzene (NB), 1,3-dinitrobenzene (DNB) and 2,4-dichloronitrobenzene (DCNB) from polluted water samples. Results indicated that the adsorption of NB, DNB and DCNB was rapid and reached a steady state after 3min. Effects of solution pH, amount of adsorbent, contact time, ionic strength and reusability on the adsorption capability of the ANTC were investigated. Experimental results showed that the removal efficiency is independent of pH and ionic strength of the test solution. The adsorption isotherms were well described by the Langmuir model and kinetics of removal processes were obeyed the pseudo-second-order mechanism. The adsorbed amounts of NB, DNB and DCNB were determined by high performance liquid chromatographic (HPLC) measurements before and after the removal process. The loading capacity of ANTC for adsorption of NB, DNB and DCNB was determined to be 0.577, 0.672 and 0.853mg/g, respectively. This study showed the potential ability of ANTC as an efficient natural adsorbent for removal of NB, DNB and DCNB from industrial wastewater samples.

An experimental investigation on the effect of convection on the ignition behaviour of single coal particles under various O2 concentrations

An experimental study on the convection effect on the ignition behavior of single coal particles with size of ∼1.5mm was carried out in an electrically heated vertical tube furnace under various O2 concentrations and temperatures ranging from 873K to 1123K. Under all test conditions, anthracite particles ignited heterogeneously. However, the ignition mechanism of the bituminous coal particles was conditionally changed by the convention. For both coals, the ignition delay time decreased and then increased with the increasing convection intensity, and the variation trends were insignificant under strong convections or high furnace temperatures. Under O2-enriched conditions, convection is in favor to coal ignition at low furnace temperatures and even cause asymmetrical hetero-homogeneous ignition. The ignition temperature of bituminous coal decreased and then increased with increasing convection intensity. It slightly decreased with the increasing O2 concentration at a weak convection and remained nearly constant when convection was rather strong. The influencing mechanisms of convection on coal particle ignition were discussed.

Rheological properties of highly concentrated anthracite coal-water slurries stabilized with sodium carboxymethyl cellulose

The rheological behavior of highly concentrated hydrosuspensions based on anthracite stabilized with the use of sodium carboxymethyl cellulose of different molecular weights and degrees of substitution was studied. It was found that the hydrosuspensions of low-ash anthracite exhibited a viscoplastic flow in the presence of sodium carboxymethyl cellulose. It was revealed that the adsorption of sodium carboxymethyl cellulose on anthracite particles and the structurization of the dispersion medium due to the formation of a polymer network contribute to the stabilization of hydrosuspensions.

Variation in the structure of anthracite at a fast heating rate as determined by its optical properties: An example of oxy-combustion conditions in a drop tube reactor

Abstract Most studies dealing with the transformation of anthracite when heated have focused on conditions similar to those of the carbonization process: high temperatures, a reducing atmosphere and a low heating rate. This study focuses on the transformations that occur in anthracite particles when these are subjected to conditions similar to those under which pulverized fuel combustion takes place: a temperature of 1300 °C, high heating rates and a variable oxidizing atmosphere. The techniques employed to assess the transformation of anthracite particles were optical microscopy, true density and isothermal reactivity at 550 °C. Two anthracites of different rank which do not melt under pulverized combustion conditions (HRA and HRB; ISO-11760 [ISO 11760 (2005). Classification of Coals. International Organization for Standardization, Geneva, Switzerland, 9 pp.]) were fed into a Drop Tube Reactor (DTR). The DTR was operated under conventional combustion (O 2 /N 2 ) and oxy-combustion atmospheres (O 2 /CO 2 ) with different oxygen concentrations and the transformations that occurred in the particles were compared. After passing through the reactor the lower rank anthracite underwent a larger enhancement of reflectance than the higher rank one, indicating a higher transformation capacity. The final structure of the particles was determined by the operating conditions and was similar for the two anthracites regardless of the rank of the parent anthracite. The progress of combustion resulted in a slightly enhanced order as determined by its optical properties, a significant drop in reactivity, and a trend of true density to first increase and then decrease for extensively burned chars. The results were found to be very similar for both the combustion and the oxy-combustion series. An additional set of experiments was performed in which the anthracite chars were refired under 5% O 2 /95% CO 2 . The structural transformations in this case were minor for both anthracites indicating that the anthracite char had a limited transformation capacity once most of the volatile matter had left the particles.

Electric conductivity and aggregation of anthracite and graphite particles in concretes

A statistical model of the electric conductivity of a heterogeneous system based on coal and a binding agent is presented. In this system, a conductive phase appears because of particle aggregation. The model was tested in the systems of anthracite and graphite in cement stone. The consistency between the experimental and calculated electric conductivities with a correlation coefficient higher than 0.9 was found on a linear interpolation of model parameters. It was found that the presence of a surfactant (cetylpyridinium chloride) and a high-molecular-weight compound (polyvinyl acetate) changed the number of particles in anthracite and graphite aggregates to affect the specific conductivity of the heterogeneous system.

Production of Carbon Included Sinter and Evaluation of Its Reactivity in a Blast Furnace Environment

Recently, the reduction in the amount of the CO2 emission has become an important issue. It is important to increase the reactivity of iron sources used in a blast furnace to decrease of CO2 emission. Therefore, the carbon composite iron ore agglomerates are significant. The production experiments of a new agglomerate named CIS (Carbon Included Sinter), where green balls were granulated by a model pan pelletizer were carried out using pot tests. The reduction of produced CIS with CO–CO2 gas mixture were examined, and were compared with that of ordinary sinter ore. Also, the softening and melting property tests of 50% CIS–50% sinter mixed layer were carried out and compared with the results using 100% sinter layer. The results are summarized as follows:(1) A new agglomerate, which an anthracite particle was surrounded by a shell with the same components as ordinary sinter ore, was produced by sintering pot test.(2) When CIS was reduced by CO–CO2 gas mixture at 1273 K, the degree of reduction achieved 80% in 120 min, even though ordinary sinter ore achieved less degree of reduction.(3) 250 g CIS–250 g ordinary sinter ore packed bed achieved 1/3 maximum pressure drop of 500 g ordinary sinter ore packed bed in the softening-melting property test.