Upgrading Of Low Rank Coal Research Articles

Low-rank coal upgrading to optimize its utilization as fuel

Abstract Indonesia’s coal resources and reserves are mostly categorized as low-rank coal, lignite and sub-bituminous coals. Most of them have a high content of moisture, a low calorific value, and a high tendency to low-temperature oxidation and self-combustion, making them difficult to transport over long distances. To increase the utilization of the low-rank coals, a drying treatment was carried out by heating the coal at a temperature and pressure of 160°C and 3.5 Bar respectively for about 15 minutes. Two low-rank coal samples, from South Sumatra (A coal) and South Kalimantan (B coal) were used in this research. The result indicates that the degree of dewatering of A coal is 89.00% while B coal is 95.5%. B Coal has a higher inherent moisture content which generally has more capillary water which is relatively easier to remove. The higher the degree of dewatering the higher the calorific value degree of improvement. The calorific value of the A coal increased by 27.16% and the B coal increased by 40.65%. The combustion characteristic obtained from the thermogravimetry-differential thermal analysis shows that the A and B upgraded coals have a lower tendency to spontaneous combustion than that of the raw coals.

Study on coarse-grained coal water removal characteristics via steam flash drying for low-rank coal upgrading

Low-rank coal drying plays a crucial role in achieving clean and efficient coal utilization. This study introduces steam flash drying, a novel method specifically designed for upgrading low-rank coal. Unlike conventional drying techniques, steam flash drying utilizes steam as the heat medium, generating a certain amount of condensation. This paper presents a comprehensive analysis of the calculated condensate quantity and the experimental measurement of coal particles' water-holding capacity to determine the initial moisture content before drying. Furthermore, the study investigates the steam flash drying effect on different-sized coal particles at a temperature of 497 K. The findings demonstrate that particles above 3 mm have lower water-holding capacity. The initial moisture content is determined by the particles' water-holding capacity and the combined raw coal water content and condensate content. The research reveals a diminishing flash-drying effect with increasing particle size, characterized by a rapid decrease followed by a gradual decline, observed at a critical point of 6 mm. By strategically adjusting the particle size distribution and employing mixing techniques, the coal drying effect can be significantly enhanced by 22%, ultimately leading to a remarkable 17% increase in processing capacity per unit volume. As a result, this study provides a theoretical foundation and optimization strategies for the clean and efficient utilization of coal through steam flash drying.

Cleaning and upgrading of low-rank coal using a novel rotary triboelectric separator with the polyvinyl chloride as friction medium

In this work, a novel laboratory rotary triboelectric separator was designed for the beneficiation of low-rank coal using polyvinyl chloride as the friction medium. The friction charge polarity of the different components in the low-rank coal was determined by charge-to-mass ratio measurements. The separation performance of the rotary triboelectric separator was investigated by separating the simulated materials. The surface properties of the simulated minerals were analyzed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The influence of different conditions on the separation of low-rank coal was studied using rotation speed, feed rate and plate voltage as variables. Under the optimum operating conditions, the ash removal rates of 0.25–0.5 mm, 0.125–0.25 mm and −0.125 mm low-rank coals were 50.05 %, 61.88 % and 25.56 %, respectively. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of the separated products indicated that several harmful trace elements (i.e., Cd, Cr, Pb and Sb) were removed distinctly. Our results will provide an effective way for the separation and upgrading of low-rank coal.

Synergistic Co-liquefaction of waste plastic express bags and low-rank coal based on supercritical water-ethanol system: Waste treatment and resource upgrading

Recently, with the ongoing development of the express industry, the consumption of waste plastic express bags has been increasing year by year, which has brought considerable pressure on municipal waste management. At the same time, in China, where coal is the main energy resource, the upgrading of low-rank coal is a more reliable and prospective way. An effective method for waste treatment and resource upgrading by synergistic co-liquefaction of waste plastic express bags and low-rank coal in a supercritical water-ethanol system has been developed. The effects of different experimental factors (temperature, residence time, plastic-coal ratio, water-ethanol ratio) on the conversion ratio and synergistic effect of co-liquefaction were investigated. The results showed that elevated temperature, lower water-ethanol ratio as well as suitable residence time, and plastic-coal ratio of 1:1 were conducive to the conversion ratio. Temperature ≥375 °C and suitable plastic-coal ratio (1:1) had a significant positive synergistic effect on the conversion ratio, whereas the other conditions exhibited no or negative synergistic effect on the conversion ratio. The maximum conversion ratio and positive synergistic efficiency were 85.11% and 12.25% at 425 °C, 60 min, water-ethanol ratio of 1:1, and plastic-coal ratio of 1:1, respectively. It was observed after FT-IR and elemental analysis based on the solid residue that the oxygen-containing functional groups in the residue disappeared, the oxygen content decreased, the carbon content increased, and the higher heating value (HHV) increased significantly, and the residue could be further used (such as gasification or pyrolysis) without the need for landfill. The GC-MS results of the oil products suggested that the oil products contained high content of hydrocarbons and phenols, as well as esters, alcohols, and other compounds. The hydrocarbons and phenols mainly derived from the decomposition of long chains in plastics and the decomposition of aromatic structures in coal, and the hydrocarbon and phenolic contents produced at 400 °C were 27.74% and 32.62%, respectively. Thus, the oil product can be used further as a chemical raw material. It cannot be ignored that the ethanol medium after reaction can also be further recycled by rotary evaporation. The synergistic co-liquefaction of waste plastic express bags and low-rank coal based on supercritical water-ethanol system is a promising method for waste treatment and resource upgrading.

A coarse-grained simulation insight of the adsorption process of mixed collector at low-rank coal/water interface

ABSTRACT Low-rank coal upgrading poses significant challenges, and conventional collectors like kerosene and diesel exhibit suboptimal performance. While mixed collectors have shown improved flotation outcomes, their interaction mechanism with low-rank coal remains poorly understood. Molecular simulation methods have limitations in studying this mechanism due to the simplified representation of coal models and the neglect of simultaneous adsorption competition among different functional groups. Additionally, All-Atom molecular dynamics (AAMD) simulation suffers from high collector concentrations and pre-placement near the coal surface, hindering the observation of dynamic adsorption processes. To address these limitations, this study employs the Coarse-Grained molecular dynamics (CGMD) method, which closely approximates the actual collector usage in flotation. By utilising a comprehensive low-rank coal classic model, we investigate the dynamic adsorption process, equilibrium adsorption configuration, optimal adsorption site, coal-collector interaction energy, and induced adsorption process between collectors. The CGMD method offers valuable insights into the compounding mechanism of mixed collectors and serves as a theoretical reference for collector mixing.

Enhancing Flotation Performance of Low-Rank Coal Using Environment-Friendly Vegetable Oil

Flotation is widely used for low-rank coal upgrading, although it is always inefficient due to its rough surface morphology and rich oxygen-containing functional groups. In this study, the environment-friendly vegetable oil 1030# was used to enhance the flotation performance of low-rank coal. The mechanism of 1030# enhancing the flotation of low-rank coal was revealed through surface property analysis of coal particles and bubble–particle adhesion tests. The flotation results showed that the flotation yield of low-rank coal increased with the increase in the collector dosage, and the flotation yield of 1030# as a collector is obviously higher than that of diesel. Scanning electron microscopy (SEM) and chromatography–mass spectrometry (GC-MS) were used to analyze the surface morphology of coal particles and components of the reagent. The SEM results showed that the surface of low-rank coal is loose and contains a large number of pores and cracks, which is not conducive to the spreading of chemicals on the coal surface and the mineralization of bubbles and particles. GC-MS results showed that 1030# mainly contained methyl oleate with more unsaturated double bonds than diesel. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface functional groups of the low-rank coal before and after reagent treatment. The results of FTIR and XPS showed that the coal surface of low-rank coal before reagent treatment contained a large number of oxygen-containing functional groups with poor surface hydrophobicity, while the surface of low-rank coal after reagent treatment had reduced oxygen-containing functional groups and increased hydrophobicity. The contact angle of the low-rank coal surface also showed the same variation trend as the FTIR and XPS results. The adhesion force between the bubble and coal surface in different collector solutions was measured. The maximum adhesion between the bubble and coal surface increased with the increase in the collector, and the maximum adhesion force with 1030# treatment was higher than that of diesel. This indicated that 1030# with a large number of polar components is more easily spread on the surface of low-rank coal, thus improving the hydrophobicity of low-rank coal.

The Peluit Heat Utilization for Low-Rank Coal Upgrading

<p class='IJASEITAbtract'>BATAN is developing a power reactor called the Peluit. In addition to electrical generation, the reactor's heat is used for cogeneration. A possible cogeneration process is coal upgrading. Indonesia holds 161,0 billion tons of coal reserves, 60% of which is low-rank coal with a moisture content of over 25%. During combustion, the low-rank coal produces extremely low heat and high CO₂ emissions. To increase the coal quality, a drying process is needed. Peluit is designed to generate superheated steam on the secondary side with temperatures above 500°C. It can be used for coal upgrading. Peluit can be built side by side with a coal-fired plant and provide it with good quality coal. Various studies on coal drying using conventional heat have been done and found it ineffective and inefficient. This research aims to determine the total amount of dried coal producible by utilizing Peluit superheated steam. The ChemCAD software package is used for modeling and simulation. Superheated steam is assumed at 500°C, 15 kg/s, and 5 bars. The dry coal combustion heat value is assumed to increase from 4840 kcal/kg to around 6170 kcal/kg. The temperature of the rotary drum is maintained at 150°C to prevent spontaneous dried coal combustion, and the moisture content is set at 10%. Approximately 600 tons/day of low-rank coal can be dried with this method, and its moisture content is reduced from 40% to 10%.<em></em>

Effect of hydrothermal pretreatment on surface physicochemical properties of lignite and its flotation response

Flotation is the common method for fine low rank coal upgrading while it is always inefficient due to the rough surface morphology and rich oxygen-containing functional groups. Hydrothermal pretreatment is widely used in dewatering for low rank coal. The physicochemical properties of coal surface considerably vary following the hydrothermal pretreatment. In this study, hydrothermal pretreatments at different temperatures for different times were applied to enhance lignite flotation. The hydrothermal pretreatment at 200 °C can significantly improve the flotation efficiency, while the temperature raised to 300 °C, the flotation recovery did not increase or even decrease. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Zeta potential, Brunauer–Emmett–Teller, and particle size distribution analysis were conducted to explain the underlying mechanism. The contents of pore and crack on coal surface considerably decreased and more fresh and smooth surfaces exposed following hydrothermal pretreatment, according to SEM analysis. The FTIR spectroscopy and XPS showed that the contents of oxygen-containing functional groups were decreased, while the hydrophobicity of lignite was increased following pretreatment. The decrease of Zeta potential also indicated the decrease of oxygen-containing functional groups and increase of hydrophobicity on coal surface. However, excessive temperature of hydrothermal pretreatment could increase the pore diameter and fine particle fraction, leading to a higher collector consumption and lower bubble–particle collision efficiency. Consequently, the flotation recovery was not improved or even decreased at the hydrothermal pretreatment temperature of 300 °C.

Model study of carbonisation of low rank coal briquettes: Effect of briquettes shape

Carbonisation is a promising process to upgrade low rank coal briquettes to clean coal, where the shape of briquettes in the carbonisation reactors may be significantly different, including sphere, ellipsoid, cylinder, half-ellipsoid. However, the influence of briquette shape variation on carbonisation performance has not been studied. In the present study, an integrated numerical model is developed and applied to investigate the effect of briquette shape on carbonisation behaviour of low rank coal briquettes in a pilot-scale coke oven. This model integrates a DEM model to simulate packing structure evolution of briquettes in four different shapes; and a CFD model to simulate the carbonisation process. This model is validated against the experimental data. The simulation results indicate that briquettes with different shapes have different packing statuses during the carbonisation in terms of bed height and packing density. Specifically, the half-ellipsoidal and cylindrical briquettes show an upward trend of packing density during the carbonisation, which is opposite to ellipsoidal and spherical briquettes. Moreover, the half-ellipsoidal briquette bed shows the best carbonisation performance in comparison with other shapes of briquettes, as it has a more rapid bed temperature increasing rate and faster devolatilisation efficiency. This work is helpful to design proper briquettes and carbonisation operation for improving carbonisation efficiency in low rank coal upgrading.

Life Cycle Assessment of Low-Rank Coal Utilization for Power Generation and Energy Transportation

In China, the electricity load is concentrated in the east, but low-rank coal resources are concentrated in the west. To solve this contradiction, in this study, three cases for energy transmission about power system with and without solar energy were studied by life cycle assessment (LCA). Case 1 directly combusts low-rank coal to generate electricity in western China and transmits it to eastern China by grid. Cases 2 and 3 upgrade low-rank coal and transport it to eastern China for power generation. With the evaluating indicators and various stages of LCA, the impact of each case on the environment was compared clearly. The results show that over 90% of the pollutant emission comes from coal combustion throughout the life cycle. The pollutant emission of upgraded coal transportation is less than 5%. With low-rank coal upgrading then combusting, the total emission is less than that of direct combustion. In particular, with solar energy added, the emission of combustion can be further reduced. On the bases of LCA, analytic hierarchy process (AHP) was used to establish the connection of these four evaluation indicators to comprehensively evaluate the performance of the three cases through the objective function of AHP, which provided guidance for the energy transmission and utilization in the eastern and western China. Finally, sensitive analysis shows the main major factors affecting system performance on the system. The results show that the Case 3, which integrates with solar energy, performs best in the whole life scale.

Optimization of the oil agglomeration for high-ash content coal slime based on design and analysis of response surface methodology (RSM)

Oil agglomeration is an alternative technique for the cleaning and upgrading of low-rank coal or high-ash content coal slimes. Therefore, this approach was used to beneficiate coal slime with high-ash content of 31.34% in this work. The single-factor tests of oil agglomeration were performed to determine the appropriate ranges for various operational factors, including pulp concentration, reagent concentration, and agitation speed. The separation results suggested that considering the yield and ash content of clean coal, and combustible material recovery, the optimal pulp concentration and reagent concentration should be adjusted as 12%–16%, and 20%–24%, respectively, and the optimal agitation speed should be controlled as 800–1200 r/min. The Response surface methodology (RSM) based on Box–Behnken design (BBD) was adopted to investigate the significance of various operational factors, and the interactions between various operational factors on the response of combustible material recovery. A mathematical model was established to predict the response, and the results indicated that the established model was proved to be highly accurate in the prediction of response. The optimization of the solutions suggested that the maximal combustible material recovery of 97.49% was obtained with the pulp concentration of 12%, reagent concentration of 20%, and agitation speed of 1200 r/min. This work provides an experimental foundation for the operation design and process optimization in the oil agglomeration of coal slimes.

Application of the Oily-Bubble flotation of Shengli lignite and its optimization

ABSTRACT The upgrading of low-rank coal is important for its utilization. The lignite used in this study had extremely low surface hydrophobicity and responded poorly to the conventional flotation process. Therefore, to enhance its flotation, a laboratory device known as oily-bubble flotation was used. With this device, the combustible matter recovery at a collector dosage of 6.4 kg/t reached 32.94% which was comparable to that of the conventional flotation at the collector dosage of 50 kg/t. For improving recovery, utilization of electrochemical conditions for pulp, i.e., pH, and NaCl and CaCl2 solutions, was used to further enhance the oily-bubble flotation performance. Based on the response-surface methodology, a functional model for combustible matter recovery was established, and the regulator scheme in oily-bubble flotation was optimized to achieve a combustible recovery of 59.19% with pH and NaCl and CaCl2 concentrations of 6.03, 61.26 mmol/L, and 80 mmol/L, respectively. Results showed that an increased combustible matter recovery of 78.69% could be obtained using this optimization scheme.

Thermodynamic analysis of a novel solar-hybrid system for low-rank coal upgrading and power generation

Abstract This work proposed and analyzed an integrated solar hybrid system for upgrading and utilization of low-rank coals using coal pre-drying, low-temperature pyrolysis and power generation, efficiently converting the low-rank coal into exportable value-added coal while generating electric power locally. The collected solar energy could be utilized in a cascade way to feed coal pre-drying and low-temperature pyrolysis. The low-energy density raw syngas discharged from the pyrolyzer is efficiently utilized by co-combusting with upgraded coal in the conjunct boiler and a large amount sensible heat of the upgraded coal is effectively recovered through pre-heating the condensate/feed water in the steam turbine unit. A case study for Zhundong lignite upgrading and utilization using the proposed system integrated with a typical 600 MW supercritical power plant was performed. The thermodynamic analysis results showed that, the overall energy and exergy efficiencies could reach 90.0% and 89.8%, respectively, with the product energy distribution ratio at 47.8 MJ/(kW h). The equivalent conversion efficiency of the coal upgrading process soars to 98.8% and the net solar-to-UGC efficiency reaches 49.4%. This proposed concept may provide a science and technology foundation for efficient utilization of the low-rank coal resources and a promising way to advance the solar energy utilization.

Effect of hydrothermal treatment on structure and liquefaction behavior of Baiyinhua coal

Baiyinhua (BYH) coal, a kind of lignite, was hydrothermally treated in an autoclave reactor at 200–350°C for 30min and the liquefaction behavior of the treated samples were investigated. To uncouple the complex behavior of the changes in structural characteristics and functional groups of treated samples, the structural change in BYH coal was investigated by thermogravimetry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results reveal that oxygen content and volatile matter in treated sample reduce and carbon content increases. The decrease in atomic ratio of oxygen to carbon and hydrogen to carbon of treated sample indicates the improvement in coalification degree. CO2 and CO account for the overwhelming majority of gaseous products from hydrothermal treatment, which can be attributed to the significantly decrease of carboxyl and carbonyl content. The hydrothermal treatment involves the breakup of some weak bonds within coal structure, and the main structure of BYH coal does not change significantly. A desirable upgraded coal was obtained by hydrothermal treatment of BYH raw coal at 250°C. The liquefaction behavior of coal can be improved by hydrothermal treatment at 250°C, and the oil yield increases from 32.9wt% (dry ash-free basis) of raw coal to 37.8wt% (dry ash-free basis). This work illustrates that hydrothermal treatment is a promising approach for upgrading of low rank coal.

95.亜/超臨界水処理による低炭化度炭の改質

95.亜/超臨界水処理による低炭化度炭の改質

82.液相分解法による低炭化度炭からの改質炭 : 粘結性の検討

82.液相分解法による低炭化度炭からの改質炭 : 粘結性の検討

1-2-1 溶剤中および機械的加圧下の熱処理による低品位炭の高品位化(1-2 熱分解・石炭改質,Session 1 石炭・重質油等)

1-2-1 溶剤中および機械的加圧下の熱処理による低品位炭の高品位化(1-2 熱分解・石炭改質,Session 1 石炭・重質油等)

Pyrolysis and catalytic upgrading of low-rank coal using a NiO/MgO–Al2O3 catalyst

The catalyst NiO/MgO–Al2O3 was prepared by loading magnesium and nickel onto the surface of γ-Al2O3 beads, respectively, and was adapted to in situ upgrade the high temperature pyrolysis vapor derived from coal pyrolysis. The catalyst synthesis process, and structural variation were characterized by the XRD, SEM, and physical adsorption analyzer. In order to examine the catalytic effect on the different nickel loading ratio in the catalysts, the solid–liquid–gas product distribution, variation of gas and components of coal tar were studied by simulated distillation, GC/MS, elemental analysis and so on. The results shows both the tar yield and the content of the light fraction in the tar can be increased by catalytic up grade. The catalyst has a strong ability to convert the heavy component and polycyclic aromatic hydrocarbons in the tar to lower molecular weight components.

Fluid bed drying as upgrading technology for feasible treatment of Kolubara lignite

An overview of the current status of low-rank coal upgrading technologies is presented in the paper, particularly with respect to drying and dewatering procedures. In order to calculate the significant parameters of the moisture removal process, a model of convective coal drying in a fluid bed, based on the two-phase (bubbling) fluidization model proposed by Kunii and Levenspiel, is developed and presented. Product-specific data (intraparticle mass transfer, gas-solid moisture equilibrium) related to the particular coal variety addressed here (Kolubara lignite) are obtained through preliminary investigations. Effective thermal conductivity of the packed bed as defined by Zehner/Bauer/Schl?nder is used to define heat transfer mechanisms occurring in the suspension phase of the fluid bed. A completely new set of experimental data obtained has been successfully used to validate the model additionally.

Upgrading of low rank coal by hydrothermal treatment: Coal tar yield during pyrolysis

Hydrothermal treatment of coal was carried out in a lab autoclave at 533K for 30min and coal pyrolysis was completed in a tube reactor at 873K for 15min with the heating rate of 5K/min. The thermal analysis of the raw and treated coal was compared by thermogravimetric analyzer. The distribution of carbon in coal was detected by solid state 13C nuclear magnetic resonance. The free radical concentrations in coal were determined by electron paramagnetic resonance spectrometer. The results show that hydrothermal treatment is an effective method for upgrading and deoxygenation of low rank coal. The pyrolysis water yields decrease from 9.21wt.% of the raw brown coal to 7.40wt.% of the treated brown coal. The pyrolysis tar raises about 18% for the treated brown coal and 5% for the treated sub-bituminous. After hydrothermal treatment, the treated coal has lower contents of oxygen functional group and higher percentage of alkyl carbons in comparison with the raw coal, the free radical concentrations in treated coal increase, especially for brown coal, which is the result in the increment of tar yield.