Combustible Recovery Research Articles

ENRICHMENT OF SİVAS/GEMEREK LIGNITE COAL BY OIL AGGLOMERATION USING DIFFERENT VEGETABLE OILS

The aim of this study was to investigate the use of various vegetable oils (almond oil, hazelnut oil, poppy oil, soybean (soya) oil, sunflower oil) for Sivas/Gemerek (in Turkey) lignite coal by oil agglomeration. The study examined the effect of bridging liquid type and dosage on oil agglomeration. Vegetable oil dosages of 2%, 5%, 10% and 20% were investigated in oil agglomeration experiments. The agglomeration of lignite coal with these bridging liquids was evaluated based on yield, combustible recovery and ash rejection. The agglomeration performances of these vegetable oils were compared. The highest ash rejection (70.30%) was observed by using soybean (soya) at 20% of the bridging liquid dosage. The yield and combustible recovery of lignite coal were achieved 36.46% yield and 38.05% combustible recovery in this soybean (soya) oil dosage, respectively. The lignite coal ash content was reduced from 19.08% to 15.54% under these optimum conditions.

Development of magnetic flotation hybrid separation process for cleaner coal preparation

The magnetic flotation hybrid separation process, which combines column flotation and magnetic separation, was anticipated to beneficiate a representative coal sample acquired from the El-Maghara coal mine with a relatively high ash percentage of 27.21%. The system was designed to introduce a high gradient magnetic field to a flotation column to hinder the flotation of magnetic particles even if attached to flotation bubbles, improving the coal demineralization process and producing high quality coal. The Box-Behnken design and response surface methodology were employed to investigate and optimize the combined influence of various operating parameters on the process performance. The effects of the main operating parameters such as magnetic field strength, slurry circulation flow rate, air flow rate, collector dosage, and frother concentration were investigated. Ash percentage, combustible recovery, and separation efficiency were defined as process responses. Upgrading the coal sample under the optimum conditions of 1.2 T magnetic field strength, 1500 ml/min circulation flow rate, 11.64 ml/min air flow rate, 0.87 kg/ton diesel collector, and 42 ppm methyl isobutyl carbinol frother, the predicted and two confirmation experiments data were 7.78%, 7.89%, 7.71% ash percentages with maximum recoveries of 75.86%, 76.37%, 75.94%, and maximum separation efficiencies of 77.17%, 78.51%, 78.71% respectively.

Dodecylamine enhanced coal gasification fine slag flotation and its molecular dynamics simulation

Coal gasification fine slag (CGFS) is produced by the raw gas flow through the top of the gasifier, and is formed after preliminary washing and purification, precipitation, and dehydration. The CGFS cannot be directly used as building materials or in other industries because of its higher ignition loss than the standard of building mixed raw materials. Neither can it be used for direct combustion because of low carbon content, high moisture content and low calorific value. Currently, its treatment is mainly landfill-based disposal which causes environmental pollution and carbon resources waste. The utilization of CGFS is becoming increasingly urgent and its premise is the separation of ash material and residual carbon. Froth flotation is a common method used for separating fine materials. In this study, kerosene (D1) and a dodecylamine-kerosene mixture (D2) were used as collectors and the flotation performance of CGFS sampled from Ningxia Coal Industry Company was investigated. The results indicate that D2 is better than D1 in that it gives higher yield of concentrate, ash of tailings, and combustible recovery. Pore structure analysis (BET) and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) were used to characterize the flotation products, which provided a basis for the separate utilization of carbon ash from CGFS. In this paper, a certain percentage of functional groups were grafted onto graphene based on the results of XPS analysis to replace the residual carbon model, and the D2 collector is proved to be more efficient than D1 by two models. Molecular dynamics (MD) simulations was used to simulate the adsorption morphology of D1 and D2 on the surface of residual carbon and the adsorption morphology of D2 on the surface of residual carbon with four functional groups. The results show that D2 has stronger adsorption energy with residual carbon than D1, and the electrostatic forces play a certain role. The adsorption energy of D2 with four functional groups decreases from carboxyl, carbonyl, hydroxyl, to ether bonds. Some dodecylamine molecules help kerosene to form smaller oil droplets that act on the carbon residue surface through van der Waals (vdW) force and electrostatic force, while other dodecylamine molecules form hydrogen bonds with oxygen-containing functional groups on the carbon surface to cover some hydrophilic points. This significantly increases the hydrophobicity of the residual carbon and enhances its flotation effect.

Sustainable preparation of high-calorific value and low-N and S energy products through the low-temperature alkali fusion of coal gasification fine ash

Coal gasification fine ash (CGFA) is characterized by high yield, high carbon content, and difficult recovery. This results in waste of coal resources and serious environmental pollution. To address this issue, a novel green deashing process is proposed in this study to modify CGFA into deashed carbon (DAC) with a high calorific value and an ash content of less than 5% through a low-temperature alkaline fusion process. Compared with traditional alkaline fusion (which is carried out at 600–1000 °C), low-temperature alkaline fusion treatment can efficiently remove ash minerals in the temperature range of 300–450 °C, which is beneficial to the efficient recovery of residual carbon in DA, while simultaneously improving the physicochemical properties and energy characteristics of DAC, thereby improving its combustion performance. At an alkali fusion temperature of 350 °C, a NaOH:DA ratio of 4.5:1, and a reaction time of 40 min, the resulting DAC product had ash content of 2.28%, combustible material recovery (CMR) of 82.03%, higher heating value (HHV) of 31.07 MJ kg−1, and SBET of 445.43 m2 g−1. In comparison, it was found that low-temperature alkali fusion significantly improved the deashing of CGFA when compared to existing deashing technologies. These results strongly suggest that this innovative deashing method can modify CGFA into a high-calorific value and low-N and S fuel, thereby providing a cost-effective and sustainable utilization method for CGFA.

Compare graphite flotation and coal flotation in Reflux Flotation Cell

The Reflux Flotation Cell (RFC) has been developed as a game-changing technology to improve fine particle flotation, coarse particle flotation and plant capacity. It has been proved successful for coal flotation. This study compared graphite flotation and coal flotation in the RFC under the operation conditions established for optimizing coal flotation with an objective of extending the RFC to mineral flotation. It was interesting to find that graphite flotation in the RFC produced much lower combustible recovery than coal flotation especially at a high gas flux despite the same surface property and feed size of graphite and coal particles tested. Through the modelling of fluid flow, it was found that the lower combustible recovery from graphite flotation was due to the lower sphericity of graphite particles. The flaky graphite particles promoted a greater dynamic drag force and a greater particle settling velocity compared to coal particles with a greater sphericity. This increased the relative velocity between particles and bubbles in the RFC downcomer, unfavourable for bubble-particle attachment in graphite flotation in the RFC. In addition, a higher gas flux environment in the RFC downcomer produced a higher bubble slip velocity, further increasing the relative velocity between particles and bubbles, exacerbating graphite flotation. Furthermore, the extra gas in the inclined channels pushed more graphite particles to the tailing stream given the higher particle settling velocity. This study indicates a direction of how to optimize graphite flotation in the RFC.

Revisiting the enhanced selectivity in low-rank coal flotation by composite collector comprising kerosene and sorbitan mono oleate

In this study, the impact of KS collectors (blends of kerosene and span80) on flotation selectivity and the underlying mechanism were investigated to comprehensively understand the non-ionic composite collectors in low-rank coal flotation. Results demonstrate that Gaudin's selectivity indices are in the range 3.19–3.61 for kerosene at dosages in the range 2–10 kg/t, but 6.58–10.81 for KS collectors at dosages in the range 2–6 kg/t. This improved flotation selectivity was because the increase of gangue recovery was overshadowed by that of combustible recovery with the KS collectors. Results also revealed that, owing to span80, coal surface hydrophobicity was enhanced, thereby improving the true flotation recovery. Meanwhile, as a result of strengthened froth stability by span80, both water recovery and the degree of entrainment increased, resulting in the increased gangue recovery. In addition, proper usage of span80 for low-rank coal flotation was also highlighted in this study.

Study on the mechanism of adsorption and hydrophobic modification of glycerol monooleate/kerosene mixed collector on low-rank coal surface

A new collector (GK) consisting of GMO (glycerol monooleate)/kerosene was developed to address the problem that low-rank coal is difficult to be recovered by flotation with conventional non-polar oil collector. The flotation test proved that GK collector has excellent flotation performance for low-rank coal (combustible recovery rate close to 90 % while the ash content of clean coal is about 6 %). The contact angle, infiltration time, wetting heat and XPS analysis demonstrated that GK collector can significantly improve the hydrophobicity of low-rank coal, resulting in a great improvement of flotation efficiency. Molecular dynamics simulation shows that the hydrophilic head of GMO molecules can adsorb with low-rank coal directly through hydrogen bonding or indirectly through water bridges. The presence of GMO molecules in GK collector can increase the overall interaction strength of collector oil droplet with low-rank coal surface by more than half. A schematic diagram of collector adsorption on the surface of low-rank coal is drawn, which gives a complete overview of the stacking and hydrogen bonding connection modes at the molecular level of low-rank coal, water, GMO and kerosene adsorbed at the interface. The adsorption mechanism of this mixed collector on the surface of low-rank coal was clarified.

Experimental study on the dispersion behavior of a microemulsion collector and its mechanism for enhancing low-rank coal flotation

As the poor dispersion of oily collectors and the inferior hydrophobicity of the mineral surface, the low-rank coal has an unsatisfactory flotation performance when using traditional collectors. In this paper, an ionic liquid microemulsion was used as a collector to enhance its floatability. Flotation test results demonstrated the microemulsion collector exhibited a superior collecting ability. A satisfactory separation performance of 78.66% combustible material recovery was obtained with the microemulsion collector consumption of 6 kg/t, which was equivalent to the flotation performance of diesel at a dosage of 25 kg/t. The dispersion behavior of the microemulsion collector was investigated using the Cryogenic-Transmission Electron Microscopy. The interaction mechanism of the microemulsion collector on enhancing the low-rank coal flotation was elucidated through the Zeta potential and contact angle measurements, the Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The microemulsion collector exhibited superior dispersibility, which was dispersed into positively charged oil droplets with an average size of 160.21 nm in the pulp. Furthermore, the nano-oil droplets could be more efficiently adsorbed on the low-rank coal surface through electrostatic attraction, resulting in the improvement of its hydrophobicity. Thus, the microemulsion collector shows great application potential in improving the flotation performance of low-rank coal.

A conceptual flotation circuit for fine coal processing based on combination of the tree analysis and kinetic data

In this research study, we focus on the tree test results as well as the first-order kinetic model to evaluate flotation test data to propose a conceptual design of a flotation circuit for a specific coal sample. Results from the tree test showed it was possible to achieve a product with ash content less than 10% with 8% as combustible recovery and indicated for this coal sample, to obtain low ash – low recovery condition. Kinetic test results showed some of the streams had the same constant, so it could combine streams with similar rates according to configuration aspects. The proposed circuit includes stages (1- rougher, 2- rougher -scavenger, 3- cleaner, 4- cleaner -scavenger, and 5-recleaner) and recleaner concentrate indicated as the final product and rougher -scavenger tailings and cleaner -scavenger tailings also indicated as a final tailing. It is worth noting the proposed circuit is a conceptual design, so the validation of data on a larger scale for the obtainment of the optimized circuit is crucial.

Effect of nanobubbles on flotation of El-Maghara coal

ABSTRACT To extensively explore the advantage of using nanobubbles in the El-Maghara coal flotation process, the effect of nanobubbles on both column and mechanical flotation was investigated under different operating parameters such as diesel oil collector dosage, MIBC frother concentration, superficial feed velocity, superficial air velocity, and superficial wash water velocity in column flotation; besides the slurry flow rate through nanobubbles generator into a 25-liter mechanical flotation cell. The representative coal flotation feed acquired from the El-Maghara deposit located in Sinai, Egypt with chemical characterization using proximate analysis containing 25.27% mineral matter forming ash during coal combustion and with particle size distribution measurement using laser particle size analyzer is 57 µm d90. Also, the flotation kinetic experiments were done to show the influence of nanobubbles on the flotation time required to obtain high-quality coal products with high combustible recovery. Nanobubbles enhanced the flotation performance and kinetics by up to 24% combustible recovery based on the operation parameters reducing flotation time from 4 to 2.25 min for 80% combustible recovery.

Study on dissociation characteristics and enhanced gravity separation of coking coal middlings

ABSTRACT This work innovatively introduced EGS technology into the re-separation process of coking coal middlings based on the dissociation characteristics. The EGS separation characteristics were compared with conventional FF and a novel pre-desliming EGS technology was proposed to achieve clean and efficient separation of coking coal middlings. The density composition and washability of the coking coal middlings crushed under the upper limit size of 6, 3, 1, and 0.5 mm show that the dissociation of the coking coal middlings has been basically completed when crushing to −0.5 mm. The clean coal ash can be reduced to 13.37% with a yield of 42.46% through the pre-desliming EGS technology. The optimal combustible recovery of 71.84% and ash removal rate of 81.36% can be obtained by EGS and pre-desliming EGS methods, respectively, which indicates the superiority of EGS compared to conventional FF. The pre-desliming EGS technology has already demonstrated its great potential in the re-separation of coking coal middlings with the advantages of low-cost, no-pollution and high-efficiency.

New Insight into Temperature Effects on Low-Rank Coal Flotation Using Diesel as a Collector.

Efficient flotation of low-rank coal is of great significance for the development of green and low-carbon cycles. Temperature is a crucial parameter of flotation, but the mechanism of its effect on flotation lacks understanding. In this paper, the mechanism was studied by kinetic flotation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, low-temperature liquid-nitrogen adsorption (LP-N2A), X-ray photoelectron spectroscopy (XPS), and molecular dynamics simulation. The flotation combustible recovery gradually decreases as temperature rises. Compared with 60 °C, the combustible recovery at 5 °C increases by 18.13%. The desorption energy for oil droplets decreases as the temperature rises. As a result, the oil droplets are easier to desorb at high temperatures. The SEM and LP-N2A results demonstrate that the pores and fractures of the coal sample are well developed. Also, the oil-water interfacial tension and viscosity of oil droplets decrease as the temperature rises, while the diffusion ability increases. These increase the volume of oil droplets that penetrate into the pores, resulting in poor spreadability of oil droplets on the coal surface. The average volume of bubbles gradually increases as temperature rises, which renders the flotation foam unstable and worsens the flotation. Therefore, the flotation performance is better at low temperatures.

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.

An Investigation into the Enrichment of Coal Wastes of Western Lignite Company (WLC) by Physical and Physico-Chemical Methods

Mechanical excavation and the successive processes coal production are the main reason for the occurrence of fine waste coals. These wastes are normally discharged without being processed from coal washing plants. Therefore, it causes not only economic loses but also severe environmental problems. It was attempted to enrich waste coals of WLC by using physical and physico-chemical methods and the results were compared.
 From the tests the optimum carbon content and the combustible recovery values were obtained as 85% and 97%, respectively, when heavy media and the coarse particle size group were chosen. From the tests with the medium particle size group using spiral and Knelson separators, combustible recovery of up to 90% was reached together with a carbon content of 80%. Moreover, a carbon content of 86.5% with a combustible recovery of 56.6% was obtained by using MGS. In the fine particle size group, the highest combustible recovery was obtained by using spiral and Knelson separators. The highest carbon content in the fine particle size group was obtained through MGS and Jameson Cell.

Capture performance and quantum chemistry simulation of composite collectors for coal gasification coarse slag

ABSTRACT For the purpose of using coal gasification coarse slag, carbon/ash separation by flotation is necessary. In this work, kerosene and dodecylamine polyoxyethylene ether (AC1202) were combined to create a composite collector known as AK, which was used in flotation experiments. The findings reveal that when the dosage of the AK collector was raised to 14 kg/t, the tailings ash reached as high as 83.76% and the combustible recovery increased by 69.84% to 81.42%, which is almost 28.62% higher than that of kerosene. The characteristics of various collectors, the strength of the adsorption between various collectors and particles, and the variation in particle hydrophobicity after the action of various collectors are used to elucidate the mechanism of the improved flotation effect with composite collectors. A new technique for separating the carbon and ash from coal gasification coarse slag is provided by the use of the AK collector.

Preparation of a novel silica-polyvinylpyrrolidone hybrid regulator and its role in ultrafine low-rank coal flotation

ABSTRACT In upgrading low-rank coal, various promoters have been employed with their fascinating abilities to alter the surface properties of particles. For decades, regulators have been proven as effective promotors in flotation. In recent years, coal flotation has benefited from the development of hybrid regulators. The interaction between coal and gangue particles can be regulated through the adjustable properties of hybrid regulators. However, when it comes to ultrafine low-rank coal (ULC), flotation becomes more difficult. The performance of micromolecule surfactants and oily collectors is not obvious when the grain size becomes finer and the coal rank becomes lower. The polymers and nanoparticles are valued for their performance. The emphasis of this study is on the preparation of silica-polyvinylpyrrolidone hybrid regulator (SiO2-PVP) and its role in low-rank coal flotation. The effect of the hybrid regulators on ULC is revealed by surface properties and chemical interactions. The contact angle, floc size, functional group, and surface topography of ULC were regulated by SiO2-PVP. The flotation response proved the benefits of SiO2-PVP to combustible recovery and clean coal. Thus, SiO2-PVP is a reliable hybrid promoter for ULC flotation. This study will be helpful to understand the effect of the polymer-nanoparticle regulator on low-rank coal flotation.

Cleaning of Thar coal by froth flotation and water washing

The demand for a constant supply of energy is increasing day by day. To meet these increasing demands the natural resources must be utilized smartly. Coal can be a promising fuel due to its large reserves available in Pakistan. About 175 billion tons of coal reserves are found in Thar region of Sindh province. The major issue is the pre-processing cleaning of coal after it is mined out. A number of methods have been adopted to clean coal.
 Presently, cleaning of Thar coal was carried out using froth flotation and water washing techniques. Three different particle sizes (-60#, -100# and -150#) were employed to study the effect of froth flotation on ash and sulfur reduction. Experiments were carried out in laboratory flotation cell and beakers under different set of conditions (i.e., flotation with and without collector and frother and by simple water washing). Kerosene oil was used as a collector and pine oil as a frother. Characterization of raw and treated Thar coal samples was carried out by ASTM standards. The results exhibited an inverse relationship of particle size towards efficiency of the cleaning process; thus, the optimal combustible recovery was attained at -150# particle size. Furthermore, FTIR results disclosed the presence of aromatic and aliphatic structure in treated coal samples. Thermo-gravimetric analysis was also made to determine the weight loss in raw and treated samples and observed increased combustion efficiency and reactivity of Coal.

Flotation response of coal washery reject fines: Characteristics, process optimization, and oxidation

AbstractThe present paper outlines the characterization, electrokinetic behaviour, and flotation response of rejected coking coal fines with 32.5% ash generated in a coal washery in Eastern India. The response methodology and central composite rotatable design (RSM‐CCRD) were used for the process modelling and optimization of the flotation process using diesel, methyl isobutyl carbinol (MIBC), and sodium hexametaphosphate as a collector, frother, and depressant to maximize ash reduction, yield, and combustible recovery. At optimum condition, a 9.7% clean ash coal was achieved with a 63% yield at collector, frother, and depressant dosages of 0.78, 0.31, and 0.80 kg/ton, respectively. The model prediction and experimental data corroborated sufficiently. Subsequently, within 1 year, the fines oxidized and did not float with the collector. Fourier‐transform infrared spectroscopy (FTIR) confirmed surface oxidation on oxidized coal. The oxidized coal responded favourably to acid oil, a vegetable oil refinery waste. With acid oil as a collector, the oxidized coal can upgrade to 12% clean ash coal with a 60% yield; the combustible recovered is 80%. The work indicates successful upgradation of fresh and oxidized coal using the froth flotation process.

Studies on low-grade coking coal characterisation, flotation response and process optimisation

ABSTRACT The work illustrates the physico-chemical, petrographic characteristics and flotation response of low-grade oxidized coking coal containing 39.5% ash. The maceral composition, surface oxidation, and particle liberation are the factors that affect coal flotation. The oxidized coal requires more collectors than the freshly ground coal. The flotation process modeling and optimization of −0.5 mm coal fraction was carried out using response methodology and central composite rotatable design (CCRD). The diesel, MIBC, and sodium hexametaphosphate are used as collectors, frothers, and depressants to maximize the coal grade, yield, and combustible recovery. At an optimum dosage of 1.35 kg/ton collector, 0.2 kg/ton frother, and 0.5 kg/ton depressant, it is possible to achieve 11.3% ash-clean coal with a 50.72% yield from 39% feed ash coal. The ash, yield, and combustible recovery model prediction matched well with the experimental results. The R2 of the ash, yield and combustible recovery model are 0.9676, 0.9662, and 0.9692, respectively. The work highlights that Indian coal can upgrade for metallurgical use using a flotation process.

Effective purification of the low-rank coal by the collaboration of the microemulsion collector and the CO2 nanobubbles

As the inferior hydrophobicity and low probability of bubble-particle collision, the low-rank coal has poor flotation performance. In this paper, an effective purification method that innovatively combined the use of the microemulsion collector and the CO2 nanobubbles was proposed. The procedure of the purification method and the reagent regime were established through flotation tests. And the flotation results showed that in the presence of the CO2 nanobubbles, a satisfactory separation performance with 83.97 % of combustible matter recovery was obtained at a microemulsion collector consumption of 3.5 kg/t. The collector consumption decreased significantly compared with the diesel oil. The interaction mechanism was elucidated through the Zeta potential measurements, the rheological behavior tests, the fractal dimension analysis, and the extended Derjaguin–Landau–Verwey–Overbeek theoretical analysis. On one hand, the microemulsion collectors can reinforce the adsorption of the oily collectors on the low-rank coal surface to improve its hydrophobicity. On the other hand, the agglomeration of the coal particles was strengthened and the probability of bubble-particle collision was increased due to the selective adsorption of CO2 nanobubbles on the hydrophobically modified surface of the low-rank coal. This research provided new insight into the improvement of the low-rank coal flotation.