Maximum Combustible Recovery Research Articles

Effects of particle size on the flotation behavior of coal slime

In order to investigate the influence of particle size on the flotation behavior of coal slime, industrial analysis, elementary analysis, and particle size composition analysis were carried out on coal slime. The coal slime is divided into three sizes: −0.5 + 0.25, −0.25 + 0.074, and −0.074 mm, and full −0.5 mm particle sizes. Through contact angle measurement, wetting heat measurement, and step-by-step release test to investigate the hydrophobicity of each particle size; in addition, the flotation kinetics test of different particle sizes coal slime was also carried out. The results show that the particle size has a significant effect on the flotation behavior of fine coal slime. The medium particle size −0.25 + 0.074 mm has the best hydrophobicity, followed by −0.5 + 0.25 mm, again −0.5 mm, and finally −0.074 mm particle sizes. Use Origin software to fit six kinetic models to the test data of coal slime flotation kinetics, and analyze the maximum combustible recovery [Formula: see text], flotation rate constant (k), and correlation coefficient ([Formula: see text]) of each particle size, The results show that the first-order model with rectangular distribution of floatabilities can better describe the flotation of coal slime of each particle size.

Separation of unburned carbon from coal fly ash: Pre-classification in liquid–solid fluidized beds and subsequent flotation

Coal fly ash, which is the solid waste produced during the coal combustion and utilization, causes serious environmental problems. The preparation of concrete from coal fly ash has been proven helpful in potentially improving its value and reducing its environmental impact to a certain extent. However, the presence of unburned carbon components affects the performance of coal fly ash-based concrete. In this study, unburned carbon is separated from coal fly ash by pre-classification and subsequent optimized flotation, wherein the factors influencing are explored. The results show that under the pre-classification function of the inflatable-inclined liquid–solid fluidized bed, the underflow product is enriched in unburned carbon particles, with loss-on-ignition (LOI) and yield (Yo) values of 11.58 % and 72.87 %, respectively. Further, the underflow product is flotated for a cleaner carbon product, which is affected by the stirring rate (W) and the amount of collecting agent (C) and foaming agent (Fo). Optimized flotation (i.e., C = 18 kg/t, Fo = 6.5 kg/t, W = 1600 rad/min) results in the maximum combustible recovery rate of the flotation concentrate (89.89%), with LOI of 41.80 % and Yo of 18.51 %, yielding unburned carbon products for fuel. After mixing the flotation tailings with the pre-classified overflow production, the LOI of the formed ash-rich product is 1.73% with Yo of 81.49%, prepared into concrete. Thus, the proposed pre-classification and flotation process can improve the quality of coal fly ash. The results provide a theoretical basis for the harmless and resource treatment of coal fly ash.

Improvement of low-quality fine coal by ultrasonic hydrophobic flocculation

ABSTRACT In this study, the effect of ultrasonic pretreatment on hydrophobic flocculation of fine coal was investigated and named as ultrasonic hydrophobic flocculation (USHF) technique. First, it was found that the ultrasonic power of 150 W and the ultrasonic pretreatment time of 180 sec was required to achieve for more combustible and good-quality coal. Then, the effects of ultrasound on the hydrophobic flocculation of coal with kerosene as bridging liquid were investigated and optimum kerosene concentration value was obtained 4 g/dm3 under the experimental conditions. Also, it was found that a stirring speed of 750 rpm was sufficient to achieve the maximum combustible recovery and minimum ash content values of fine coal particles. The effects of sodium silicate, sodium hexametaphosphate, and sodium pyrophosphate used as inorganic dispersants on the ultrasonic hydrophobic flocculation of coal were also studied. Sodium silicate was more effective than other dispersants in the presence of kerosene. Thus, it was concluded that the ultrasonic pretreatment is an effective method for the beneficiation of fine particle coal. Coal with an ash content of 17.63% was enriched and clean coal was recovered with an ash content of 9.75% with the efficiency of 94.35% by ultrasonic hydrophobic flocculation technique.

Effect of different reagent regime on the kinetic model and recovery in gilsonite flotation

Gilsonite is a natural fossil resource, similar to an oil asphalt high in asphaltenes. To determine the effect of reagent regime on the kinetic order and rate of flotation for a gilsonite sample, experiments were carried out in both rougher and cleaner flotation process. Experiments were conducted using different combinations of reagent: oil – MIBC; gasoline – pine oil; and one test without any collector and frother. According to results, kinetic in the test performed using the oil – MIBC and without any collector and frother were found to be first-order unlike the kinetic in the test conducted using the gasoline – pine oil. Five kinetic models were applied to the modeling of data from the flotation tests by using MATrix LABoratory software. The results show that all experiments are highly in compliance with all models. The kinetic constants (k) in rougher stage were calculated as 0.1548 (s−1), 0.2300 (s−1) and 0.2163 (s−1) for oil – MIBC, gasoline – pine oil, and test without any collector and frother, respectively. These amounts in the cleaner stage were 0.0450 (s−1), 0.1589 (s−1) and 0.0284 (s−1), respectively. The relationship between k, maximum combustible recovery (R∞) and particle size was also studied. The results showed that the R∞ and k were obtained with a coarse particle size of (−250+106) μm in the rougher and (−850+500) μm in cleaner flotation processes.

The Order of Kinetic Models, Rate Constant Distribution, and Maximum Combustible Recovery in Gilsonite Flotation

Kinetic models are the most important tool for predicting and evaluating the performance of flotation circuits. Gilsonite is a natural fossil resource similar to an oil asphalt, high in asphaltenes. Here, in order to determine the kinetic order and flotation rate of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments were conducted using the combinations of oil–MIBC and gas oil–pine oil, with one test without collector and frother. Five kinetic models were applied to the data obtained from the flotation tests using MATLAB software. Statistical analysis showed that the results of the experiment with oil–MIBC were highly in compliance with all models. Kinetic constants (k) were calculated as 0.1548 (s−1) and 0.0450 (s−1) for rougher and cleaner stages, respectively. Rougher and cleaner tests without collector and frother also matched all models well (R2 > 0.98), with k values of 0.2163 (s−1) and 0.284 (s−1), respectively. The relationship between flotation rate constant, maximum combustible recovery, and particle size showed that the maximum flotation combustible recovery and flotation rate were obtained in the size range of −250 + 106 μm in the rougher and cleaner stages. The combustible recovery and flotation rate were higher in the rougher flotation process than in the cleaner stage.

Effect of NaCl on the flotation response of low-rank coal

ABSTRACTIn this study, the effect of adding NaCl on the flotation enhancement mechanism of low-rank coal was investigated. A gradual reduction in the negativity of the zeta potential of low-rank coal with NaCl addition was conducive to reducing the bubble–particle attachment time and enhancing low-rank coal recovery. In addition, the reduced bubble size and improved foam stability with NaCl addition were moderately beneficial to coal recovery. The flotation rate constant, k, and the maximum combustible recovery, ε∞, increased remarkably as the NaCl concentration increased, indicating that the flotation kinetic of low-rank coal was enhanced by the addition of NaCl.

Cleaning of high pyritic sulfur fine coal via flotation

Large quantities of fine coal have been produced during mining and processing activities of coals. Use of these fine coals after cleaning is important in terms of recovering of economically valuable energy source and prevention of environmental pollution. In the present study, amenability of a high ash-sulfur coal sample to flotation process was investigated. Coal particle size and collector dosage were selected as variables. Increasing coal particle size affected sulfur and ash rejections adversely. On the other hand, more combustible matter was recovered at coarser particle sizes. Maximum combustible recovery, ash rejection, pyritic sulfur rejection and sulfate sulfur rejection were achieved to be 82.56%, 82.84%, 90.04% and 81.45%, respectively. Polished section examinations and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis confirmed the rejection of significant level of ash and sulfur from the coal.

Flotation Performance of Low-rank Coal in the Presence of Cetyltrimethyl Ammonium Bromide

ABSTRACT The flotation enhancement mechanism and flotation kinetics of low-rank coal in the presence of cetyltrimethyl ammonium bromide (CTAB) were investigated. The contact angle of the coal sample increased by 46.07% and the attachment time between coal particles and a single air bubble decreased by 85.79% with increasing the concentrations of CTAB from 0 to 1 × 10–4 M. Low concentrations of CTAB enhanced the flotation performance of low-rank coal, and the concentrate yield significantly increased by up to 8.59 percentage points with increasing the concentrations of CTAB from 0 to 1 × 10–5 M at the cost of a lower increase in the ash content. However, the selectivity was reduced at high CTAB concentrations (5 × 10–5 M and 10–4 M). Six kinetic flotation models were employed to fit the flotation test data using the 1stOpt analysis software; the flotation rate constant (k), the maximum combustible recovery (ε ∞), the correlation coefficient (R 2) and the modified flotation rate constant (k m) were calculated. Most models showed that the modified rate constant and the maximum combustible recovery of low-rank coal increased with the increasing concentrations of CTAB.

The difference in flotation kinetics of various size fractions of bituminous coal between rougher and cleaner flotation processes

In order to investigate the difference in flotation kinetics of various size fractions of bituminous coal between rougher and cleaner flotation processes, clean coal was collected as a function of time in both rougher and cleaner flotation processes. The size composition of clean coal was then analyzed. Six flotation kinetic models were applied to the modeling of data from the flotation tests by using MATrix LABoratory software. The relationship between flotation rate constant, maximum combustible recovery and particle size was also studied. The results show that the maximum flotation combustible recovery and flotation rate are obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate are higher in the cleaner flotation process than that in the rougher flotation process. Except the classical first-order flotation kinetic model, the other five kinetic models gave an excellent fit to the flotation data. The rougher flotation process can be described using the first-order and second-order models while the cleaner flotation process can only be described using the first-order model. It is found that the first-order model with rectangular distribution of floatability provides the best fit of the experimental data obtained from both the rougher and cleaner flotation processes among the tested models.

Ash Depression in Fine Coal Flotation Using a Novel Polymer Aid

The current study investigated the effects of novel hybrid polyacrylamide polymers as ash (slime) depressants in fine coal flotation to enhance combustible recovery and ash rejection. Coal samples at P80 of approximately 45 um with ~25% ash content were floated in the presence of in-house synthesized hybrid aluminum hydroxide polyacrylamide polymers (Al(OH)3-PAM, or Al-PAM). All flotation experiments were carried out in a 5-L Denver flotation cell. Various influencing factors were examined to optimize the flotation process in the presence of the Al-PAM polymers, including the Al-PAM dosage, Al-PAM conditioning time, impeller rotation speed and pulp pH. Comparative and synergistic studies were also performed using organic polyacrylamide polymers (PAMs), commercial dispersants and Al-PAM/dispersant system. Results showed a significant improvement in both combustible recovery and ash rejection at an Al-PAM dosage of 0.25 mg/L. The maximum combustible recovery obtained, at natural pH, with Al-PAM and Al-PAM/dispersant system was determined to be 70% and 66% at ash content of 7.74% and 7.4%, respectively. Zeta potential values of both the raw coal and concentrate products showed a large shift toward more positive values (from ˉ50 mV to ˉ13 mV), indicating a significant decrease in ash-forming minerals (slimes) when Al-PAM polymers were applied.

A Study of Kinetics on Oily-Bubble Flotation for a Low-Rank Coal

ABSTRACTThe flotation performance and kinetics for a low-rank coal were investigated using air bubbles and oily bubbles. Five flotation kinetic models were applied to the test data to estimate the relationships between the flotation rate constant, the maximum recovery, and the collector dosage. The results showed that the oily-bubble flotation (OBF) obtained lower ash content and higher combustible recovery with less collector dosage than the air-bubble flotation (ABF). But this advantage of OBF gradually diminished with the collector dosage. It was found that the flotation of a low-rank coal in ABF and OBF can be best described with the second-order kinetic model and classical first-order model, respectively. The OBF had higher maximum combustible recovery values and lower maximum ash recovery values. The flotation rate constants of OBF were higher in all the models except the fully mixed reactor model. Furthermore, the effect of collector dosage on the low-rank coal flotation kinetics was evaluated. It was indicated that the maximum recovery values and modified rate constants increased with the collector dosage. The similar trend was observed in the flotation rate constants for all of the models except the fully mixed reactor model.

Effect of particle size on cleaning of high-sulphur fine coal by oil agglomeration

An oxidized fine coal sample with high sulphur content was subjected to oil agglomeration process in order to determine the effect of coal particle size (−0.5, −0.25, −0.125mm) on the performance of the process at different oil dosages (5, 10, 15, 20%). Maximum combustible recovery, ash rejection, pyritic sulphur rejection and sulphate sulphur rejection were achieved to be 75.23%, 97.56%, 99.23% and 98.15%, respectively. Increase in coal particle size affected the ash and pyritic sulphur rejections adversely. However, higher combustible recovery was obtained at coarser coal particle sizes. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis and polished section examination of feed coal, clean coal and tailings support the success in rejection of considerable amount of ash and sulphur sources from the coal. Microscopic examination also showed an increase in agglomerate size with increases in coal particle size and oil dosage.

Effect of pH, air velocity and frother concentration on combustible recovery, ash and sulphur rejection using column flotation

This study shows the effect of pH, air velocity (Jg) and frother concentration (FC) on combustible recovery, ash and sulphur rejection for four Colombian bituminous coals: Cerrejón (Guajira), Nechí (Antioquia), Jagua (Cesar) and Guachinte (Valle del Cauca) using column flotation. For the experimental development a 23 factorial central composite experimental design was used. The coal samples were processed in a pH range of 4 to 10, Jg in the range of 0.7 to 2.1cm/s and FC in the range 2.1 to 6.3kg/t. Results showed that Cerrejón and Jagua coal presented combustible recovery higher than 50%, (57.6% and 54.7% respectively), at acidic pH (pH 5), with Jg of 1cm/s and 3.2 to 4.2kg/t of FC, respectively, while Guachinte coal presented a maximum combustible recovery of 56.4% at alkali pH (pH 9), Jg of 1cm/s and 3.2kg/t of FC and Nechí coal obtained the highest combustible recovery (46.8%) at pH 7 with 2.1kg/t of FC and Jg of 1.4cm/s. For Guachinte and Nechí coal ash and sulphur rejection were high (90.3% and 88.5%) and (71.3% and 73.8%) respectively at acidic conditions (pH 4 and 5) with Jg in the range of 1.4 to 1.8cm/s, whereas Cerrejón and Jagua coals exhibited high values of ash (85.4% and 94.7%) and sulphur rejection (81.1% and 85.1%) at alkali conditions (pH 9 and 10) with Jg in the range of 1.0 to 1.4cm/s. In general, it was observed that Cerrejón and Jagua coals presented higher values of combustible recovery under acidic conditions than Nechí coal and Guachinte coal.

Investigation of Bituminous Coal Hydrophobicity and its Influence on Flotation

The hydrophobicity of bituminous coal surface has a significant effect on the separation of coal and mineral matters by flotation process. In this work, water contact angles on bituminous coals displaying different brightness in terms of specular reflectance were measured to characterize their surface hydrophobicity. It is found that water contact angle on coal increases with specular reflectance for both bright and dull coals, and the bright coals have higher contact angle and specular reflectance than the dull coals. The oxidation of coal surface will render it less hydrophobic, but has little effect on the specular reflectance. Results from petrographic analysis show remarkable differences in volume percentage of maceral groups for bright and dull coals. Bright coals contain more vitrinite, less inertinite and mineral mater, than the dull coals. X-ray photoelectron spectroscopy (XPS) analysis indicates that the dull surface has more hydrophilic, oxygen-bearing functional groups. These results imply that vitrinite is more hydrophobic than inertinite, and should float better than the latter. The combustible recoveries of bench scale flotation tests increase with the corresponding contact angles and their relationship can be accurately described by a sigmoidal equation. The maximum combustible recovery for vitrinite is 96.76% under the current operation conditions. The results also indicates that in order to reach the targeted combustible recovery in flotation, the contact angle of coal particles needs to reach certain value.

Performance of classic oils and lubricating oils in froth flotation of Ukraine coal

In this study, the appropriate collector and collector amount for Ukraine coal in froth flotation was determined. For this purpose, the performance of classic oils (kerosene, diesel-oil and fuel-oil) and lubricating oils (spindle oil, bright stock and heavy neutral) was evaluated by combustible recovery, ash rejection and efficiency index. It was found that the combustible recovery and ash rejection changed, depending on the type and concentration of oil. The maximum combustible recovery was obtained by using bright stock. It was determined that bright stock, fuel-oil and kerosene were suitable for the flotation of Ukraine coal. On considering the flotation efficiency index values, the best results were obtained with bright stock and diesel-oil. Consequently, it was shown that bright stock and spindle oil could be used as alternative oils instead of classic oils for cleaning of Ukraine coal by the froth flotation.

95/00076 Effect of bubble generating devices on recovery of clean coal from refuse using column flotation

Column flotation testing was conducted on the flotation feed slurry obtained from a preparation plant located in the southern Illinois coal basin using three different bubble generating devices, static sparger, gas saver and foam jet. Each of these devices were tested with three different types of frother and various column operating variables to provide maximum combustible recovery, minimum product ash and maximum pyrite rejection. Alcohol frothers were most effective for use with the static sparger, somewhat less effective for the foam jet and ineffective for the gas saver. Glycol frothers were effective for all three bubble generating systems, providing high combustible recovery (>90 percent), low clean coal ash (4-6 percent ash) and high pyrite rejection (70-80 percent).

Comparison of bubble generating devices for column flotation of fine coal from refuse

Column flotation testing was conducted on the flotation feed slurry obtained from a preparation plant located in the Southern Illinois coal basin. The column flotation tests were conducted using three different bubble generating devices: a static sparger, a gas saver and a foam jet. Each of these devices was tested with three different types of frother and various column operating variables to provide maximum combustible recovery, minimum product ash and maximum pyrite rejection. The results show that column flotation provided improved flotation performance, in terms of combustible recovery as well as ash and pyrite rejection, for each of the bubble generating devices. However, the effectiveness of each bubble generating device was dependent on the type of frother used. Alcohol frothers were most effective for use with the static sparger, somewhat less effective for the foam jet and ineffective for the gas saver. Glycol frothers were effective for all three bubble generating systems, providing high combustible recovery (>90%); low clean-coal ash (4–6% ash) and high pyrite rejection (70–80%).