Showing papers in "International Journal of Coal Preparation and Utilization in 2018"
TL;DR: In this paper, the effect of ultrasonic irradiation as a pretreatment method for high-ash coal flotation and its kinetics was evaluated and applied prior to flotati...
Abstract: This research work was undertaken to assess effect of ultrasonic irradiation as a pretreatment method for high-ash coal flotation and its kinetics. Ultrasonic treatment was applied prior to flotati...
28 citations
TL;DR: In this paper, the influence of hardness and impact velocity on the crush-ratio of coal and gangue can be analyzed using impact-crush technology for underground coal mines.
Abstract: Utilizing the difference in hardness, coal and gangue can be separated by the impact-crush technology for utilization underground. The influence of hardness and impact velocity on the crush-ratio d...
22 citations
TL;DR: In this paper, a coal sample with high fluorine content (357 μg/g) was selected for the present work, and the modes of occurrence of fluorine were examined by sequential chemical extraction, screening tests, and float-and-sink tests; the removability of the fluorine in coal was investigated by bench-scale flotation tests.
Abstract: Fluorine is one of the trace elements in coal that is harmful to the ecological environment and human’s health. Flotation, a method of fine-coal processing, may be useful in reducing the fluorine content in coal before coal combustion. For this purpose, a coal sample with high fluorine content (357 μg/g) was selected for the present work. The modes of occurrence of fluorine were examined by sequential chemical extraction, screening tests, and float-and-sink tests; the removability of fluorine in coal was investigated by bench-scale flotation tests. Results indicated that fluorine tends to enrich in large-density fractions and fine-size fractions; fluorine mainly occurred in residual-associated form and carbonate- and Fe/Mn-associated form. Flotation can play an important role in the removal of fluorine from coal. In this study, the optimal amount of flotation reagents was determined by statically designed experiments. Under the optimum condition of 100 g/t diesel oil, 150 g/t 2-octanol, and 200 g/...
19 citations
TL;DR: In this article, emulsified kerosene and high-shear agitation were used to improve flotation performance of microcrystalline graphite, and the flotation conditions were determined first and then optimized through a Box-Behnken design to minimize the concentrate ash content and to maximize the concentrate yield.
Abstract: In this investigation, emulsified kerosene and high-shear agitation were used to improve flotation performance of microcrystalline graphite. The flotation conditions were determined first and then optimized through a Box-Behnken design to minimize the concentrate ash content and to maximize the concentrate yield. Two quadratic models were developed to correlate the flotation variables, including agitation speed, agitation time, and collector dosage. As a result, both responses and the predicted optimal results were obtained. The lowest ash content of 7.81% and the highest yield of 91.00% were achieved by using an agitation speed of 27,173 rpm, an agitation time of 20 min, and a collector dosage of 79 kg/t. The analysis of variance indicated that the models of concentrate ash content and concentrate yield were significant terms to both responses.
17 citations
TL;DR: In this paper, a Turkish lignite sample was evaluated by conventional methods with sink-and-float tests and a Reichert spiral, and the fine size fractions were cleaned with enhanced gravity separation techniques, a multigravity separator (MGS), and a Falcon concentrator.
Abstract: The use of low-rank coals as an energy source may cause environmental problems. Washability of a Turkish lignite sample was evaluated by conventional methods with sink-and-float tests and a Reichert spiral. Also, the fine size fractions were cleaned with enhanced gravity separation techniques, a multigravity separator (MGS), and a Falcon concentrator. The as-received lignite sample was sieved into five size fractions (-100 +25.4 mm; -25.4 +12.7 mm; -12.7 +1.2 mm; -1.2 +0.15 mm; -0.15 mm) and the washability characteristics of the first three fractions were separately investigated with sink-float tests. The -1.2 +0.15 mm size fraction was cleaned using a Reichert spiral. Tests with the MGS and the Falcon concentrator were conducted with a -0.15 mm fine size fraction. Sink-float tests results showed that the tested coal can be classified as difficult-to-clean coal due to the presence of high near-gravity material at lower separation densities than 1.7 g/cm3. However, the production of cleaner coal w...
17 citations
TL;DR: In this article, thermal gravimetric analysis and Fourier infrared-spectrum technology were used to analyze the change rules for the critical temperature and stage characteristics during a coal's spontaneous-combustion oxidation-reaction process.
Abstract: In this article, thermal gravimetric analysis and Fourier infrared-spectrum technology were used to analyze the change rules for the critical temperature and stage characteristics during a coal’s spontaneous-combustion oxidation-reaction process. Different-metamorphic-degree-coal change rules and influence factors of the characteristic temperatures were studied. The characteristics of the coal temperature showed an increase trend with an increase of the heating rate. The characteristics of the coal temperature decreases; when the heating rate and oxygen concentration were different, the value of the characteristic temperature was anthracite > bituminous > lignite. The critical temperature of the coal’s functional characteristic peak-absorption strength was related to the coal metamorphic degree. Variation characteristics about the changes of the coal’s functional characteristic peak-area values and the coal functional groups’ characteristic peak-absorption intensity were similar. The changing tren...
15 citations
TL;DR: In this paper, column-flotation operating parameters such as air flow rate, collector, and frother dosage were optimized to obtain the maximum recovery of vitrinite maceral.
Abstract: The separation of vitrinite is being primarily carried out through density-gradient concentration (DGC) method. However, this technology is limited to laboratory-scale operations, since gravity plays a trivial role in the separation of ultrafine particles. In the present investigation, processing of vitrinite macerals on a large scale was explored using column flotation. Two coal samples (medium coking and non-coking) of less than 500 µm size were processed at neutral pH in single-stage column operation. Column-flotation operating parameters such as air flow rate, collector, and frother dosage were optimized to obtain the maximum recovery of vitrinite maceral. Enrichment of vitrinite in flotation products was confirmed through petrography studies with respect to feed. The column-flotation results were compared against to theoretical value obtained from sink-and-float analysis. The extent of vitrinite enrichment using flotation column was further investigated through surface-characterization techni...
15 citations
TL;DR: In this article, large-scale experiments were conducted using an FGX-3 dry separator to beneficiate a Chinese coal, and the separation results indicated that the FGX separator provided ash reduction from 48.7% in the feed to 31.28% in clean coal with a mass yield of 65.12%.
Abstract: Large-scale experiments were conducted using an FGX-3 dry separator to beneficiate a Chinese coal. The separation results indicated that the FGX separator provided ash reduction from 48.7% in the feed to 31.28% in the clean coal with a mass yield of 65.12%. The clean-coal yield increased as the size range decreased from 80-50 mm to 3-0 mm. Coal with particle sizes between 80 mm and 6 mm responded favorably, while the 6-3 mm size range could not be beneficiated effectively, and coal below 3 mm size did not respond to any separation. The calculation of separation efficiencies indicated that the coarser the particle size the lower the separation density and the lower the Ep value. The amount of 1.8 float material in the tailings was less, which meant lower loss of the low-density, low-ash content particles to the tailings.
13 citations
TL;DR: In this paper, the Fuerstenau upgrading equation was used to fit the results of flotation kinetics of various size fractions in the flotation process to investigate the selectivity of different size fractions.
Abstract: To investigate the selectivity of different size fractions in the flotation process, the Fuerstenau upgrading equation was used to fit the results of flotation kinetics of various size fractions an...
12 citations
TL;DR: In this article, the spontaneous combustion liability of the lignite samples with 74 and 500 μm particle sizes maintained under three different storing conditions (deep freezer, deep freezer, and deep freezer) was investigated.
Abstract: During the present experimental work, the spontaneous-combustion liability of the lignite samples with 74 and 500 μm particle sizes maintained under three different storing conditions (deep freezer...
11 citations
TL;DR: In this article, a set of experiments were designed through design expert software for the process of ultrafine coal in a laboratory Kelsey Jig, where four different process parameters were considered for the present study, including pulse frequency, spin frequency, feed flow rate, and ragging size.
Abstract: Processing of ultrafine ( 50 %) coal was investigated in a laboratory Kelsey Jig. A set of experiments were designed through design expert software. Four different process parameters were considered for the present study, including pulse frequency, spin frequency, feed flow rate, and ragging size, while other parameters were kept constant. In a single pass through a KCJ, an absolute 8% reduction in the ash with 53% yield was obtained. Statistical modeling studies and process optimization were also performed. Two different process schemes were studied to process the high-ash coal fines involving (a) a Kelsey Jig and (b) a hydrocyclone followed by a Kelsey Jig. It was observed that the removal of particles below 45 µm by a desliming process results in a reduction of 12% ash with 60% yield at the optimized condition. The Ecart probable value was estimated for particle sizes of 300 x 45 micron. The Ecart probable value 0.08 over a particle-size range of 300 µm x 45 µm with a sepa...
TL;DR: In this article, the most important parameter in the designing of a dryer is the exiting moisture content of the material a.k.a. exiting moisture in coal, which is a very significant topic due to its high economic value.
Abstract: Drying of low rank coal is a very significant topic due to its high economic value. One of the most important parameter in the designing of a dryer is the exiting moisture content of the material a...
TL;DR: In this article, the effect of pulp temperature on coal flotation was investigated and the results showed that flotation performance was lower in higher pulp temperatures (50 and 75°C), while flotation performances were higher in lower pulp temperatures(5 and 25°C).
Abstract: In this study, the effect of pulp temperature on coal flotation was investigated. Waste vegetable oil was used as collector. Experiments were carried out at different temperatures (5, 25, 50, and 75°C) and the pros and cons of each temperature for flotation performance were revealed. While flotation performance was lower in higher pulp temperatures (50 and 75°C), flotation performance was found higher in lower pulp temperatures (5 and 25°C). Highest combustible recovery values were obtained at 25°C pulp temperature, and the lowest ash product was obtained at 75°C. However, the lowest combustible recovery value was obtained in flotation at 75°C.
TL;DR: In this article, a three-level and five-variable Box-Behnken design combined with response surface methodology (RSM) was used to develop an approach to analyze the behavior of different variables of coal-oil agglomeration where pulp density, oil dosage, aggregated time, particle size, and oil type were varied.
Abstract: In this study, a three-level and five-variable Box-Behnken design combined with response surface methodology (RSM) was used to develop an approach to analyze the behavior of different variables of oil agglomeration where pulp density, oil dosage, agglomeration time, particle size, and oil type were varied. The response of coal–oil agglomeration to this variation was investigated using the Box-Behnken design. The efficiency of this process was evaluated by calculating percent ash rejection (%AR) and percent organic-matter recovery (%OMR). The optimal conditions established were pulp density (3%), oil dosage (15%), agglomeration time (15 min), and particle size (0.15 µm) using linseed oil with a predicted %AR and %OMR as 66.02% and 95.93%, respectively, with a desirability of 94.20%. The optimal condition was experimentally validated as 64.60% for ash rejection and 93.94% for organic-matter recovery. The coefficient of determination (R2) was found to be .870 and .926 for %AR and %OMR, respectively.
TL;DR: In this article, the viscosity measurements of coal-clay-mixture suspensions and corresponding batch flotations were performed with increasing CaCl2 concentrations (ranged in 1-20 mM).
Abstract: Slime coating is known to have one of the detrimental effects of clay in coal flotation. In this study, the viscosity measurements of coal–clay-mixture suspensions and corresponding batch flotations were performed with increasing CaCl2 concentrations (ranged in 1–20 mM). It was found that at 4–6 mM concentration a significant transfer from Newtonian to non-Newtonian behavior occurred; meanwhile, the clay recovery increased dramatically. In this process, clay recovery through true flotation with entrainment excluded gradually increased. Cryo-SEM analysis, furthermore, confirmed that more coating clay appeared in higher CaCl2 concentrations. Thus, the rheology measurement could be used as a method for determining whether the slime coating occurred in flotation pulp with low salinity.
TL;DR: The microscopic structure and texture of coke are intrinsically important to the cold strength index (M10 and M40) and hot strength indices (CRI and CSR) properties of the coke as mentioned in this paper.
Abstract: The microscopic structure and texture of coke are intrinsically important to the cold strength indices (M10 and M40) and hot strength indices (CRI and CSR) properties of the coke. Traditionally, Bl...
TL;DR: In this paper, the effect of particle size on coal flotation conditioning was examined with a focus on the effect on the particle size of coal particles on the flotation performance of coking coal.
Abstract: How to improve coal flotation performance has been examined with a focus on the effect of particle size on flotation conditioning. A coking coal sample collected from the flotation feed of a coal p...
TL;DR: The identification of optimal separation densities and blending protocols for these precombustion cleaning facilities greatly influences the economics of the fuel supply chain and India's quest for additional low-cost energy as mentioned in this paper.
Abstract: The energy sector in India is highly dependent on coal as a fuel. At present, most of the domestically produced thermal coal is burned raw or after minimal beneficiation. This practice often results in higher operating and maintenance costs, poorer utilization efficiencies, and increased greenhouse gas emissions. To improve the prevailing conditions, the Government of India is taking steps to increase clean coal production by promoting the installation of coal preparation plants across the country. The identification of optimal separation densities and blending protocols for these precombustion cleaning facilities greatly influences the economics of the fuel supply chain and India’s quest for additional low-cost energy. Traditionally, preparation plants have utilized float-sink (washability) data to determine suitable density separation set points for their processing circuits. Very often, these set points are based on the cumulative ash content required to meet contract specifications within Indi...
TL;DR: In this article, high-ash Indian coals and washery discards were extracted using an organic solvent and complete characterization study was carried out in order to measure its coking potential.
Abstract: High-ash Indian coals and washery discards were extracted using an organic solvent. Complete characterization study was carried out in order to measure its coking potential. The study revealed that swelling and thermoplastic properties of the extracts are better as compared to the parent coals. A new concept for studying the thermoplastic behavior of coal is introduced to access the coking potential of parent and extracted coal. A series of carbonization tests was performed considering organic extracts as one of the blend components. The carbonization study reflects that the addition of an optimum amount of extracts in the base-coal blends helped in improving the properties of metallurgical coke.
TL;DR: Based on sieve and float-sink tests of sampled materials, distributions of size, ash, and density were investigated in this paper, where six sampling splits were arranged in the front discharge section and three final products were obtained.
Abstract: Compound dry separator has been widely used for coal preparation in China. This work discusses the distribution of coal properties along the front discharge section based on pilot-scale experiments. Six sampling splits were arranged in the front discharge section and three final products were obtained. Based on sieve and float-sink tests of sampled materials, distributions of size, ash, and density were investigated. During the separating process, fine particles are much easier to be discharged at first and coarse particles mainly concentrate in clean coal and tailings. Hence, the content of fine particles in raw coal has an important influence on clean coal. The high-density minerals in clean coal are mainly derived from −6+0.5 mm fine gangue, which cannot be separated effectively. The low and high separation densities of −6+0.5 mm fine coal were much higher than those of −50+6 mm coarse coal at the same operating conditions. Moreover, the middlings obtained in compound dry separator can also be ...
TL;DR: In this article, a coal of lower HGI needs more energy to be ground, while a coal with higher HGI requires less energy to ground, based on the Hard Groove Grindability Index.
Abstract: Grindability of a coal is generally represented in terms of the Hard Groove Grindability Index (HGI); a coal of lower HGI needs more energy to be ground. Samples of this study were taken from the A...
TL;DR: In this article, the relationship of pyrolysis characteristics of raw coals and vitrinite-rich concentrates with coal rank and elemental composition were studied by thermogravimetric analysis and ultimate analysis.
Abstract: The vitrinite-rich concentrates were produced from five coking coals with different ranks (Donghuantuo gas coal, Tangshan 1/3 coking coal, Zhongliu fat coal, Hongsheng coking coal, and Lvjiatuo coking coal) by float-sink separation under centrifugal force The relationships of the pyrolysis characteristics of raw coals (RC) and vitrinite-rich concentrates (VC) with the coal rank and elemental composition were studied by thermogravimetric analysis and ultimate analysis The results show that vitrinite-rich concentrate have greater weight loss and a higher weight-loss rate than the corresponding raw coals Also, VCs have higher H, C, and N content and lower O and S content With an increase of coal rank, the weight-loss rate (ΔTG) and maximum weight-loss rate (DTGmax) of VC decreases, and the temperature with DTGmax (Tmax) of VC increases, and the C/H ratio of VC also increases The analysis of thermogravimetric parameters and elemental composition of VC shows that the ΔTG and DTGmax decrease linear
TL;DR: In this paper, the optimization of process variables from the lab scale to the pilot scale with a chemical-leaching technique is reported, and almost a 68% ash reduction could be achieved while maintaining the optimum process conditions.
Abstract: In a typical coal washery, middlings are generated as a byproduct of a dense media cyclone having a size range of -13+0.5 mm and an ash content of 40–45%. Nearly 40% of the feed material is discharged as middlings. Middlings have good carbon values but embedded minerals in it and, hence, it is difficult to wash using conventional physical-cleaning techniques. Here in this article, the optimization of process variables from the lab scale to the pilot scale with a chemical-leaching technique is reported. Almost a 68% ash reduction could be achieved while maintaining the optimum process conditions. Higher reaction temperature, increased alkali concentration, and lesser reaction time favor the leaching process. Moreover, the alumina-to-silica ratio reduced from 0.53 to 0.25 and the phosphorus content significantly reduced by 90%.
TL;DR: In this paper, a systematic method of measuring crystalline silica (α-quartz) in bulk coal samples using NIST-SRM 1878a as a calibration standard with more accuracy by FT-IR and distribution of quartz in various screen sizes, float-and-sink fractions, for both the feed and clean coal.
Abstract: In Indian coals, quartz is abundantly found and its proportion usually varies from 5–20% by weight. Beneficiation of high-ash thermal coals of India has become the prerequisite for improving the overall economics and efficiency of power generation. A detailed survey of literature reveals that no systematic work has been done of beneficiated coal for Indian coals with respect to quartz, as also for correlation with abrasion. Therefore, to understand this effect different sizes of crushed coal were subjected to float-sink treatment at specific gravities in the range of 1.30– 1.80. This study highlights the systematic method of measuring crystalline silica (α-quartz) in bulk coal samples using NIST-SRM 1878a as a calibration standard with more accuracy by FT-IR as well as distribution of quartz in various screen sizes, float-and-sink fractions, for both the feed and clean coal. The results show that there is a linear relationship between ash % and quartz % with respect to specific gravity for all scr...
TL;DR: In this article, the surface free energy and interfacial interaction energy were calculated to identify the interaction mechanism between coal and dodecane/nonyl benzene from the perspective of thermodynamics.
Abstract: The collector consumption for anthracite coal flotation is higher than that of coking coal. In the present study, dodecane and nonyl benzene were evaluated for anthracite flotation. The surface free energy and interfacial interaction energy were calculated to identify the interaction mechanism between coal and dodecane/nonyl benzene from the perspective of thermodynamics. The results showed that anthracite coal was rich in benzene ring groups, and flotation performance of anthracite coal using nonyl benzene was better than that of using dodecane. The interfacial interaction free energy between anthracite coal and nonyl benzene was much higher than that of dodecane. Nonyl benzene interacts with aromatic sites on the coal surface through Pi-bonding, resulting in a high flotation recovery.
TL;DR: In this paper, a novel flotation method, using polyaluminum chloride (PAC) is described that showed better ash rejection, and the aggregation due to PAC addition was verified with a concentration around 20 mg/L, and PAC selectively aggregated the high-ash gangue minerals (> 2.0 g/cm3) but did not aggregate the low-ash coal (< 1.4 g/ cm3).
Abstract: It is difficult to obtain a low-ash clean coal from a coal sample containing a high proportion of gangue minerals by traditional flotation methods due to the severe gangue contamination of the concentrate. In this article, a novel flotation method, using polyaluminum chloride (PAC) is described that showed better ash rejection. The aggregation due to PAC addition was verified with a concentration around 20 mg/L, and PAC selectively aggregated the high-ash gangue minerals (> 2.0 g/cm3) but did not aggregate the low-ash coal (< 1.4 g/cm3). With higher concentrations of PAC, both coal and gangue minerals were dispersed. The scanning electron microscope pictures of the flotation concentrate indicated that the contamination of gangue minerals was reduced using a low concentration of PAC. The zeta-potential measurements showed that charge neutralization with a low PAC concentration was the main aggregation mechanism of the gangue minerals. The zeta potential of the low-ash coal was highly positive when ...
TL;DR: In this article, the authors investigated the impact of optical sorting on lignite processing and showed that significant impacts on process economics and recovery could be achieved by implementing optical sorting to lignitite cleaning.
Abstract: Impact of the optical sorting on lignite processing has been discussed. Experimental study covered sink-float tests, visible light-color (VIS) sorting, and near-infrared (NIR) sorting of an unconventional lignite sample. Results showed that significant impacts on process economics and recovery could be achieved by implementing optical sorting to lignite cleaning. Operational and investment costs per ton of clean lignite were also investigated when optical sorting was implemented. Also, within approximately similar ash levels, it was observed that NIR sorting results had better efficiency and ash removal performance than VIS sorting.
TL;DR: In this article, the cylindrical section of a 710/500mm three-product cyclone was adopted to treat 0.75-0.125mm fine coal, the cylinder-cone cyclone is a surge section.
Abstract: Dense medium cyclone is effective in beneficiation of fine coal with great separation precision. Small diameter cyclones (usually 150 mm to 350 mm) are preferred in industrial application. But the handling capacity of small cyclone is low which bring about the problems of maintain and operation. The separation efficiency of large diameter cyclones with greater handling capability in fine coal treatment is questionable. In this study, the cylindrical section of a 710/500 mm three-product cyclone was adopted to treat 0.75-0.125 mm fine coal, the cylinder-cone cyclone was a surge section. Influence of inlet pressure, feed rate was studied in an industrial environment. According to the results, the separation efficiency was sharp at relatively low feed pressures (110 KPa to 160 KPa). The separation effect increased with the feed rate. The favorable Ecart probable (Ep) value of 0.054 was obtained at the inlet pressure of 120 KPa and feed rate of 42 t/h. Results of the studies showed that large diameter cyclo...
TL;DR: In this article, a comparison of liquid-solid fluidized bed separator (LSFBS) and a dense medium cyclone (DMC) are used for cleaning coal of -1+0.25 mm size.
Abstract: Both a liquid-solid fluidized bed separator (LSFBS) and a dense medium cyclone (DMC) are used for cleaning coal of -1+0.25 mm size. However, a comparison of LSFBS and DMC’s performance in separation of difficult-to-separate coal has seldom been reported. Difficult-to-separate coarse coal from the Tangkou plant was processed using LSFBS and DMC. The products with the same ash content were analyzed by the float-sink tests to compare the separation efficiencies. According to the results, the concentrate yield and Ep value obtained by the DMC were 48.85% and 0.045, respectively, while the values obtained by LSFBS were 32.86% and 0.12, respectively. The results showed that DMC was more efficient than LSFBS for separating the Tangkou difficult-to-separate coal with a higher yield and a lower Ep value.
TL;DR: In this paper, a mathematical quadratic model was established to predict the relationship between the segregation index and operational factors, and the optimum segregation index was obtained when the initial bed height, fluidization number, vibrational amplitude and frequency were optimally set to 80 mm, 1.5, 2.0 mm, and 16 Hz, respectively.
Abstract: Efficient cleaning of fine lignite is difficult through conventional coal-separation technology. This study focused on the dry cleaning of fine lignite using vibrated fluidized bed separation. Various operational factors that influence the segregation efficiency of fine lignite include the initial bed height, fluidization number, vibrational amplitude, and frequency. The factors were optimized using response surface methodology, which was based on the Box–Behnken design. Results indicated that the satisfied segregation efficiency could be achieved under suitable operational conditions. The optimum segregation index was obtained when the initial bed height, fluidization number, vibrational amplitude, and frequency were optimally set to 80 mm, 1.5, 2.0 mm, and 16 Hz, respectively. In this case, the favorable recovery efficiency of clean coal was achieved as well. A mathematical quadratic model was established to predict the relationship between the segregation index and operational factors. Predicte...