Coal Pretreatment Research Articles

Pre-oxidation modification of bituminous coal-based hard carbon for high-quality sodium ion storage

Bituminous coal, with its moderate anthracene content, high reactivity, and ease of modulation, stands out as a favorable choice as a precursor for hard carbon. However, due to the highly condensed aromatic rings in bituminous coal, it tends to form highly graphitized structures after high-temperature carbonization. Therefore, pretreatment of bituminous coal is necessary to suppress the graphitization process. Here, we combine pre-oxidation techniques with high-temperature carbonization to produce a cost-effective, high carbon yield, and superior performance coal-based hard carbon. When utilized as anode for sodium-ion batteries, the prepared coal-based hard carbon exhibits a high reversible capacity of 313.5 mAh g−1, along with excellent rate capability and long cycling stability.

Enhanced vanadium bioleaching from stone coal employing Aspergillus niger: Optimization of stone coal pretreatment method

Vanadium is a rare metal with excellent properties. The recovery of vanadium from low-grade stone coal and vanadium-containing solid wastes using microbial leaching, has become an increasingly popular technology. In this paper, Vanadium was obtained from stone coal using Aspergillus niger as the leaching strain, and the process of vanadium bioleaching was strengthened. Compared with plasma treatment and ultrasonic pretreatment of stone coal, the leaching effect of stone coal after roasting at 900 °C was the best, and the leaching rate of vanadium was as high as 94.52 %. The vanadium bioleaching mechanism was explored by SEM-EDS, XRD, XPS and FTIR analysis. The findings indicated that Aspergillus niger has the ability to adhere to the surface of stone coal, resulting in subsequent corrosion and degradation. The roasting treatment of stone coal and bioleaching of Aspergillus niger jointly lead to the decrease of crystallinity, the increase of interplanar spacing and the decrease of stability of stone coal. Meanwhile, the valence state and binding form of vanadium changed, and V (III) was oxidized to V (IV) and V (V). The mineral structure may be distorted as a result of the distinctive peak's vibratory stretching and the influence of functional categories that include oxygen, which in turn causes the change of the coordination form of the internal metal ions, which affects the symmetry of the mineral and facilitates the dissolution of vanadium from the stone coal. Research indicates that roasting and Aspergillus niger bioleaching have a great deal of promise to increase vanadium recovery from stone coal.

Flow characteristics of microwave treated Indian coal: A deep learning modelling

To meet the escalating energy needs of the growing population, the power stations are gradually shifting towards abundant low-quality coals and lignites. This study proposes a sustainable methodology to utilize such low-quality coals by cutting down the coal pretreatment costs. Instead of utilizing the treated coal as a whole, this study proposes to blend the treated coal with the untreated coal for further utilization. These blended samples are then used to prepare coal water slurry, with concentrations varying in the range of 10 to 60% by mass. The rheology of the blended samples shows a reduction in viscosity by ∼ 23% when the blended sample contains 50% treated coal. The sustainability of the process is verified by a trained artificial neural network, that includes an extensive validation of predicted results with experimental data and Irvine (1988) model. The artificial neural network indicates a maximum of 11.5% reduction in the headloss when the blended sample is transported at 50% solid concentration. The specific enthalpy consumption is found to be the minimum for the blended samples transported at 50% solid concentration.

MIL pretreatment on breaking hydrogen bond and swelling of coal: Experiment and simulation

Since direct combustion of low-rank coal is inefficient, expansion and dissolution are essential for better use of coal as an energy source. In this study, [C8mim]FeCl4 molecular configuration was synthesized by quantum chemical simulation method, and Magnetic ionic liquid (MIL) was used to modify coal to improve its swelling efficiency. The FT-IR and Raman properties of MIL were measured by simulation combined with practical methods. Dmol3 was used to study the hydrogen bond changes of coal molecules induced by MIL. When MIL interacts violently with organic matter in coal, the cross-linking network structure generated by non-covalent bonds is destroyed, resulting in the break of covalent bonds such as hydrogen bonds. Further experimental study shows that the pore structure and surface morphology of modified coal samples will be damaged, indicating that the MIL has the ability to dissolve hydrogen bonds and pretreat low-rank coal. It was found by TGA that MIL treatment can increase the tar yield of coal by up to 4.79% and reduce ash content by 3.51%. Through the integration of molecular modeling and experimental analysis, this study elucidates the fundamental principles underlying MIL pretreatment of coal, thereby providing a viable strategy for efficient quality improvement utilization of low-rank coal.

A review on microbial metabolism to increase coalbed methane generation and coal pretreatment to improve its bioavailability

A review on microbial metabolism to increase coalbed methane generation and coal pretreatment to improve its bioavailability

Non-pyrolysis microwave heating as coal pretreatment for in-situ combustion: reactivity and microstructure

ABSTRACT Microwave heating without pyrolysis is a promising technology as coal pretreatment for in-situ combustion. In order to study the reactivity of the modified coal from non-pyrolysis microwave heating, Shenmu bituminous coal was subjected to microwave at 700 W for limited time (90 s and 180 s) and the samples were tested by the thermal analyzer, NOVAtouch analyzer and X-ray diffractometer in this work. The weight loss curves of original coal and modified coals are similar, but the weight loss rate is faster for combustion stage when t m is longer. As t m increases, ignition temperature barely changes, while burnout temperature dramatically decreases. Both the specific surface area and pore volume decrease with increasing t m. When t m increases from 0 to 90 s, the microcrystalline structure is less ordered, while aromaticity is larger; when t m increases from 90 s to 180 s, the microcrystalline structure is more ordered, while aromaticity is smaller. When t m increases, the side chains decrease first and then increase, while the reactive oxygen-containing groups keep increasing. This work is essential for grasping the effect of microwave pretreatment on the ISC performance.

The Effect of Hydrothermal Pre-Treatment of Coal, Biomass and Coal-Biomass Mixture on Fuel Properties

Odun talaşı, Trakya linyiti ve ağırlıkça %50 odun talaşı-Trakya linyitinden oluşan karışıma ayrı ayrı hidrotermal ön işlem uygulanmıştır. Her birinin yakıt özelliklerindeki ve termokimyasal dönüşüm karakterlerindeki değişim gözlemlenmiştir. Ayrıca, karışımın hidrotermal ön işlemiyle biyokütlenin kömür üzerinde sinerjik etkisine bakılmıştır. Optimum şartların 230 °C ve 90 dk olduğu ve otojenik basınçta gerçekleşen hidrotermal ön işlem sonrası tüm yakıtlarda sabit karbon yüzdesi ve ısıl değer artmış, kül içeriği azalmıştır. Linyit ve odun talaşına kıyasla, karışıma beraber hidrotermal işlem uygulandığında daha yüksek elementel karbon içeriğine, daha düşük oksijen yüzdesine ve daha yüksek ısıl değere sahip bir yakıt elde edilmiştir. Karışıma uygulanan hidrotermal işlem, karışımın yapısal özelliklerini ve uçucu madde tipini modifiye etmiştir. Bu nedenle hidrotermal ön işlem görmüş karışımın piroliz ve yanma reaksiyonlarındaki reaktivitesi artmış, kütle kaybı hızının maksimum olduğu pik sıcaklıklar da ötelenmiştir.

Thermal desorption of mercury from lignite in a high-temperature furnace and in power plant mills

In this article, the binding forms of two lignite samples are determined by thermal desorption using a high-temperature furnace. Each mercury compound, such as HgCl2, has a specific binding strength whose decomposition requires a certain thermal energy. Hence, the release of mercury from pure substances and lignite samples was analyzed in a high-temperature furnace. The released mercury is determined with a Mercury Vapor Monitor. The obtained characteristic temperature range and peak of the mercury release were compared between lignite samples and mercury pure substances. For the lignite samples investigated, the binding form of mercury was then identified as Humic Acid. These organic compounds vaporize at lower temperatures. About half of the mercury bound in the lignite was already released at 350 °C. Furthermore, the question arises whether mercury is already released during the grinding-drying process in the coal mill of a power plant. At two power plants, lignite samples were taken simultaneously at the feeder before entering the coal mill and at the dust line afterwards. The samples were analyzed for mercury concentration. The results show that up to one third of the mercury was already released in the coal mill. The vaporized mercury enters the combustion chamber detached from the lignite. The stated analysis methods and the results presented in this article contribute to the understanding of the mercury binding forms in lignite. It also shows the potential of thermal coal pretreatment as a favorable alternative mercury separation technology to others such as activated carbon dosing.

Sulfur fixation for raw coal with combined microwave irradiation and ultrafine Ca(OH)2 method

Sulfur fixation technology for raw coal can reduce SO2 emission during coal combustion. A method combining microwave irradiation and ultrafine Ca(OH)2 slurry was proposed, where raw coal was pulverized to mix with the slurry, and then treated by microwave irradiation. For anthracite coal (sulfur content = 1.90 wt%) with particle size distributed in the range of 75–180 μm, the treatment fixed 67.98 % of the sulfur in coal ash. Results prove that there is a synergy between microwave irradiation and ultrafine Ca(OH)2 for coal pretreatment, and finer coal particles had higher fixation rate. Under the same treatment condition, the sulfur fixation rate was increased to 74.68 % by adding 1 mol/L NaOH. Applying more NaOH or less Ca(OH)2 both made the fixation rate decrease. The combined treatment was also applied to bituminous coal (sulfur content = 0.79 wt%), and a fixation rate of 87.93 % was obtained. A continuous pretreatment system was developed for practical utilization of the method. Coal treated by the system was made into honeycomb briquette and burnt in a domestic coal stove, where a sulfur fixation rate of 74.97 % was obtained, compared to that of 4.55 % from untreated coal briquette.

A study on the applicability of pulverized coal combustion flue gas desulfurization of alkali metal-based pretreatment desulfurization agent

An experiment was conducted to reduce sulfur oxides by burning low-calorie, low-sulfur sub-bituminous coal treated with an alkali metal-based coal pretreatment desulfurization agent. As a result of pre-combustion treatment with 0.3% desulfurization agent, it was possible to reduce sulfur dioxide by 96.83ppm from 97.10ppm to 0.27ppm on average compared to raw coal at 6% reference oxygen concentration, and the maximum reduction rate was found to be 99.70% on average. Additional research is needed on whether such a reduction rate is possible even in the case of high-sulfur coal treatment, but by using an alkali metal-based pre-combustion desulfurization agent, the emission of sulfur dioxide could be dramatically reduced for low-sulfur sub-bituminous coal. In the future, it will be possible to minimize the emission of sulfur dioxide to the atmosphere by operating in combination with FGD, which is a post-treatment facility.

Enhancing Biomethane Production From Lignite by an Anaerobic Polycyclic Aromatic Hydrocarbon Degrading Fungal Flora Enriched From Produced Water.

The coal-degrading ability of microorganisms is essential for the formation of biogenic coalbed methane. The ability to degrade the aromatic compound of coal is more important because it is perceived as the main refractory component for bioconversion. In this paper, a polycyclic aromatic hydrocarbon (PAH) degrading fungal community (PF) was enriched from produced water using phenanthrene as sole carbon source. The goal was to improve both the microbial structure of the methanogenic microflora and its coal-degrading ability. Two strategies were pursued. The first used coal pretreatment with PF (PP), followed by methane production by methanogenic microflora; the second used methane production directly from coal by mixed culture of PF and methanogenic microflora (PM). The results showed that methane productions of PP and PM increased by 29.40 and 39.52%, respectively. After 7 days of cultivation, the fungal community has been altered in PP and PM, especially for Penicillium the proportions of which were 67.37 and 89.81% higher than that in methanogenic microflora, respectively. Furthermore, volatile fatty acid accumulations increased by 64.21 and 58.15%, respectively. The 13C-NMR results showed that PF addition promoted the transformation of aromatic carbons in coal to carboxyl and carbonyl carbons, which contributed greatly to the production of methane together with oxygen-containing functional groups. These results suggest that methane production can be increased by indigenous PAH-degrading fungi by improving the fermentation of aromatics in coal and the generation of volatile fatty acids. This provided a feasible method for enhancing biomethane generation in the coal seam.

Impact of conditions of coal supply to hard-to-reach northern areas on its useful properties

Hard-to-reach northern areas of Russia are supplied with coal via complex and extended delivery chains. Long-term storage and large haulage distances between the coal production sites and the heat power generation points result in degradation of useful properties of coal and its high quantitative losses. The authors discuss the causes of change in the fuel quality as it travels from production faces to boiler-houses, as the consequences of lower quality fuel burning. The current approaches to alteration of coal properties are reviewed. The influence of oxidation and cryogenic effects is analyzed. Assuming the delivery chains as the integrated systems in blocks and their performance evaluation by the final result allows disengaging new reserves in quality management. An element of the refreshed quality management can be technological and managerial procedures in open pit coal mining and in pre-treatment of coal before shipment.

Biogenic methane generation from Vietnamese coal after pretreatment with hydrogen peroxide

The application of coal as a methanogenic substrate is limited due to its recalcitrant nature, thus, requiring pretreatment for increasing bioavailability of coal. This paper describes the pretreatment of Vietnamese coal from the Red River Basin. The coal sample was treated with 3% (vol/vol) hydrogen peroxide, which resulted in 45.4% (weight %) solubilization of coal and release of various organics into the liquid phase. This dissolved fraction was analyzed for total dissolved organic carbon, Fourier transform infrared spectroscopy, high-performance size exclusion chromatography, and high-performance liquid chromatography. The detailed analytical investigations revealed the presence of aliphatics and aromatics hydrocarbons in the liquid phase. Short-chain organic acids, including oxalic, citric, malic, malonic, formic, and acetic acids were also observed. The dissolved fraction was subjected to methanogenesis. Methane generation achieved the peak at 218.5 μmol/g coal after 500 days of incubation. The effect of the pretreatment process on inorganic matter of the residual coal samples was also assessed using inductively coupled plasma mass spectrometry. The pretreatment caused a reduction in metal content of the residual coal sample. The findings of the paper can be prospected as a feasibility study of methane production from Vietnamese coal after its pretreatment using hydrogen peroxide.

Surface physico-chemistry governing microbial cell attachment and biofilm formation on coal

An essential but missing component in our understanding of microbial interactions leading to coal bed methane (CBM) formation lies in the relationship between coal and coal-adhering microorganisms. Here, we explored the influence of surface physico-chemistry on the microbial cell attachment on coal, utilising a known coal-oxidising bacterium P. fluorescens Pf-5 as a model. Based on the interfacial free energy of adhesion calculation and direct observation of cell adhesion on coal, natural lignite and subbituminous coals offered the most conducive surface for cell attachment driven by favourable hydrophobic and acid-base interactions. Coal pretreatments dramatically decreased coal surface hydrophobicity and increased its electron-donating potential (γ−), resulting in unfavourable interaction with cells that were hydrophilic and possessed high γ−. An exception to this was peroxide treatment, which maintained a low γ− of the coal surface and allowed favourable coal-cell interaction to occur. Cell colonisation on lignite appeared to be the strongest amongst all coal types, likely due to the relatively high van der Waals surface energy component that influence the adhesion strength in favourable cell-coal interactions. This would partly explain the higher methanogenic potential found in lignite compared to subbituminous coal in previous studies, as more adsorbed cells potentially lead to greater liberation of small organic compounds. Although our cell enumeration results generally correlated with the thermodynamic data, some exceptions were present that signify the biological role in cell-to-coal attachment and biofilm formation. Overall, these findings provide insights into the fundamental parameters that are involved in cell-coal adhesion dynamics at the molecular level.

Wastewater treatment technology with modified sorbent from the complex of household services

The composition and characteristics of wastewater from the complex of household services and the method of wastewater treatment from the surfactants have been studied. To increase the efficiency of local treatment of the wastewater, a method of neutralization on a carbon sorbent modified with sulfuric acid has been analyzed. Wastewater treatment technology with a high content of organic substances having an increased alkaline reaction is a pretreatment of coal with sulfuric acid solutions, which then serves as a resin charge for filters. The spent resin charge is regenerated with a hydrogen peroxide solution. These results have been obtained using artificially prepared and natural wastewater from the complex of household services and form the basis for the development of wastewater treatment facilities for laundries located in hotels, health centers and recreation facilities. The conclusions on the efficient use of the proposed method are made.

Unusual origin of choline phenylalaninate ionic liquid nanostructure

Choline amino acid ionic liquids have received much attention recently due to their environmental friendliness and low toxicity. Some of these ionic liquids have shown outstanding capacity for biomass and coal pretreatment, yet it remains unclear what structural features underpin performance. Despite sharing many structural features with other choline amino acid ionic liquids proven to be effective at lignin extraction, choline phenylalaninate (ChPhe) is surprisingly among the poorest solvents at such application. Using multi-contrast neutron diffraction we show that the liquid nanostructure of ChPhe – consisting of apolar domains in a continuous polar network – primarily consists of small clusters stabilised by inter-anion hydrogen bonds between amine and carboxylate groups. Within the apolar regions, phenyl side-chain rings adopt no preferred arrangements, signaling the absence of π-π stacking, but instead show evidence of competing cation-π interactions. This is the first example of self-assembled ionic liquid nanostructure not of solvophobic origin. The unusual suite of interactions also explains its water miscibility but inability to retain nanostructure upon water dilution, as well as its poor performance for biomass pretreatment, and provides a new strategy by which to engineer and tune ionic liquid nanostructure for the design of application-specific, renewable solvent systems.

Fe3O4 Nanoparticles Supported on Modified Coal toward Catalytic Hydrogenation of Coal to Oil.

Iron-supported catalysts exhibit good catalytic performance in direct coal liquefaction (DCL), but the effect of the carrier on the performance of the composite catalyst is unclear. In this paper, a simple solid-state synthesis strategy for the preparation of coal-loaded Fe3O4 nanoparticles (Fe3O4/Coal) and the hydrochloric acid treatment of coal-loaded Fe3O4 nanoparticles (Fe3O4/Coal-HCl) is presented. The resulting composite was used as a catalyst for DCL. The effects of supports on the structure and performance of iron-supported catalysts have been illustrated. After the acid pretreatment of the catalyst carrier coal, the surface structure and functional groups changed, which affected the aggregation morphology of the Fe3O4 active component. The Fe3O4/Coal-HCl catalyst improved the catalytic performance of DCL with conversion and oil yield of 98.02 and 49.96 wt %, respectively. The result shows that pretreatment can be an effective way to modify the surface of the catalyst carrier coals, thereby further improving the catalytic performance of composites. The iron-based composites prepared by the solid-state route show great potential as supported catalysts in DCL.

Ionic liquids for coal dissolution, extraction and liquefaction

AbstractCoal is the most abundant fossil fuel. Direct combustion of low‐ and medium‐rank coals causes alarming environmental impacts. Therefore, it is crucial for coal to undergo pretreatments before its efficient utilization [such as coal to liquid (CTL) processes]. Conventional pretreatment methods suffer from several limitations including the use of volatile organic solvents, environmental hazards, strong reaction conditions (e.g. high temperature and pressure), consumption of large quantities of nonrecoverable chemicals (e.g. bases used in aqueous alkaline digestion), or being only effective for specific coals. On the other hand, coal pretreatment by nonvolatile ionic liquids (ILs) could lead to partial coal dissolution/swelling and structure disruption, which is a critical step before coal liquefaction, hydrogenation, pyrolysis or the inhibition of oxidation/combustion. In addition, ILs are suitable solvents for extracting sulfur compounds from coal, asphaltenes from Direct Coal Liquefaction Residues (DCLR) and phenolic compounds from coal tar. This review will discuss these aspects of coal pretreatments by ILs, and identify how ILs could lead to a cleaner and more efficient utilization of coal resources. © 2020 Society of Chemical Industry

Technology of Thermal Preparation of Coal for Ecologically Pure Combustion of Fuel in Small Boilers

The problems of ecologically clean coal combustion are connected with the need to reduce the formation of pollutants to the environment during thermal transformation of fuel. Currently, about 180-190 million tons of coal are burned in Russia to produce heat and electricity, with more than 60% in the eastern regions of the country. Most of the coal (about 80%) is consumed by large thermal stations, which are equipped with pollutant trapping systems. The remaining part is burned in numerous boiler houses that operate in both urban and rural areas to provide heat to social facilities and the population. The analysis shows that the role of boiler houses increases significantly in the territories with a low population or in remote and decentralized areas. In this regard, the coal pretreatment technology before burning including the thermal preparation of coal is important. The use of thermally prepared fuel (semi-coke) will significantly reduce emissions of NOx and SOx, as well as improve the “culture” of thermal energy production at small boilers by switching to fully automated technologies, as well as significantly reducing the financial burden of utilities by reducing the wage fund and emission fees.

Improving mining efficiency in thick gently dipping coal seams by means of top coal pretreatment

Improving mining efficiency in thick gently dipping coal seams by means of top coal pretreatment