Low-ash Coal Research Articles

Features of Distribution of Rare-Earth Elements in Coals of the Far East

For the first time, the distribution of rare earth elements (REE) has been studied in detail for a number of coal facilities (30 deposits, 650 samples of coal and 210 samples of carbonaceous rocks). The ubiquitous presence of elevated concentrations of REE in coals has been noted. The REE mineral cluster in coals includes the association: ash content of coals – SiO2 – K2O – Al2o3 – TiO2 – Sc – Y – Dy – Ho – Er – Tm – Yb – Lu, and the association La – Ce – Pr – Nd – Sm – Eu – Gd – Tb. The presence of these elements of the mineral part of the coals is preferably in the composition of phosphate minerals – monazite and apatite (according to electron microscopy with microanalysis, the correlation of REE with P2o5). The content of individual REE in humic acids isolated from coals and fractions of coals of different densities has been studied. The specific role of organic matter(s) in the concentration of REE, their presence in the humus component of S and in low-ash coals is shown. Selective accumulation (fractionation) of heavy REE by organic matter has been experimentally established for the first time. Two genetic types of REE mineralization have been identified in coals: mainly terrigenous (hydrogenic) and tufogenic. The increased concentrations of REE in coals are due to the influence of the petrofund. The deposits were ranked according to the degree of prospects for REE based on an assessment of the resource potential of associated REE in the coals of the studied brown coal deposits. REE raw materials (lanthanides in coal ash) differ significantly from traditional types of rare earths ores by an incomparably large relative amount of heavy REE (on average 3–4 times), sometimes reaching 46% of the total REE content. Thus, coal ash is a unique non–traditional source of heavy lanthanides – more rare, valuable and expensive. The coals of the studied deposits should be considered as associated raw materials for rare earths.

A novel approach to the separation of macerals in inertinite-rich coal: Charged micro-nanobubble flotation

The classification and utilization of coal macerals have become a vital focus for the advancement of the modern coal chemical industry and mineral processing. Flotation is a well-established technique for large-scale mineral separation, but as for maceral separation, it is often limited by a low recovery rate and poor selectivity. This study investigates the utilization of charged micro-nanobubble (CMNB) flotation to separate the vitrinite from a typical low-ash and inertinite-rich coal in Xinjiang. Results show that CMNB flotation demonstrated notable index advantages over conventional flotation. Optimal flotation was achieved by the CMNBs produced from a 0.75 mM sodium dodecyl sulfate (SDS) solution, with a yield, concentrate vitrinite content, and vitrinite recovery of 49.58 %, 74.31 %, and 77.28 %, respectively. It was revealed that the CMNBs not only promoted the aggregation of vitrinite particles but also increased the adhesion of vitrinite particles and their aggregates to conventional flotation bubbles, resulting in enhanced flotation performance.

Studies on increased utilization of high-ash Indian coal in coke-making

ABSTRACT Due to low-ash coking coal scarcity, India depends on high-cost imported coal for coke making. The present work aims to increase the Indian coal input in the original coal blend for coke making. One typical Indian high-ash and one imported low-ash coal were used as reference materials, presently used in coal blend for coke production in IISCO Steel Plant Burnpur (ISP), West Bengal, India. Coal samples were ground, changing various parameters. The ash distribution in different particle sizes was evaluated. It is observed that decreasing the particle size up to −88 µs can reduce ash content from (18–23%) to (12–14%), which is generally considered suitable for the blended coal mixture used for coke making in the coke-oven battery in ISP. Reduced ash containing fraction of high- ash coal was utilized to evaluate the dilatation behavior and economics of the coking process by considering blending with different percentages of beneficiated Indian coal. From the behavioral study, it was observed that 20% blending would be economical for coke making without hampering the original blend property. The improved dilatation behavior was observed by incorporating 20% dry beneficiated Indian coal in the original blend. The CRI, CSR, and Micum index properties are identical with the normal blend and within the acceptable limit.

Waste heat utilization using organic rankine cycle from a pressurized pulverized combined cycle power plant

Power plants release a massive amount of waste heat at very low temperatures. Posing a challenge for efficient conversion into useful work through conventional methods. By selecting appropriate working fluids, low-grade power cycles can solve this problem by converting waste heat to electricity. The present work dealt with waste heat utilization using the Organic Rankine Cycle (ORC) from a 400 MWe coal based supercritical Pressurized Pulverized Combined Cycle (PPCC). The working fluid for the ORC is the refrigerant R245fa. High-ash (HA) Indian coal and low-ash (LA) South African coal are used as fuel to assess the plant’s ability to produce electricity under ambient conditions in India. The simulation flowsheet program “Cycle-Tempo” models and simulates different plant layouts. The thermodynamic assessment unveiled that the standalone plant has energy and exergy efficiencies of 43.46% and 39.87% for HA & 45.42% and 43.84% for LA, respectively. According to this study, the proposed plant has energy and exergy efficiencies of 44.63% and 40.94% for HA & 46.69% and 45.07% for LA, respectively. Moreover, using ORC, the waste heat generates additional electricity of 9.38 MWe, with an energy efficiency of 12.92% and exergy efficiency of 34.63%.

Source differences in the components and cytotoxicity of PM2.5 from automobile exhaust, coal combustion, and biomass burning contributing to urban aerosol toxicity

Abstract. Although air quality guidelines generally use the atmospheric concentration of fine particulate matter (PM2.5) as a metric for air pollution evaluation and management, the fact cannot be ignored that different particle toxicities are unequal and significantly related to their sources and chemical compositions. Therefore, judging the most harmful source and identifying the toxic component would be helpful for optimizing air quality standards and prioritizing targeted PM2.5 control strategies to protect public health more effectively. Since the combustions of fuels, including oil, coal, and biomass, are the main anthropogenic sources of environmental PM2.5, their discrepant contributions to health risks of mixed ambient aerosol pollution dominated by the respective emission intensity and unequal toxicity of chemical components need to be identified. In order to quantify the differences between these combustion primary emissions, 10 types of PM2.5 from each typical source group, i.e., vehicle exhaust, coal combustion, and plant biomass (domestic biofuel) burning, were collected for comparative study with toxicological mechanisms. In total, 30 types of individual combustion samples were intercompared with representative urban ambient air PM2.5 samples, whose chemical characteristics and biological effects were investigated by component analysis (carbon, metals, soluble ions) and in vitro toxicity assays (cell viability, oxidative stress, inflammatory response) of human lung adenocarcinoma epithelial cells (A549). Carbonaceous fractions were plenteous in automobile exhaust and biomass burning, while heavy metals were more plentiful in PM2.5 from coal combustion and automobile exhaust. The overall ranking of mass-normalized cytotoxicity for source-specific PM2.5 was automobile exhaust > coal combustion > domestic plant biomass burning > ambient urban air, possibly with differential toxicity triggers, and showed that the carbonaceous fractions (organic carbon, OC; elemental carbon, EC) and redox-active transition metals (V, Ni, Cr) assisted by water-soluble ions (Ca2+, Mg2+, F−, Cl−) might play important roles in inducing cellular reactive organic species (ROS) production, causing oxidative stress and inflammation, resulting in cell injury and apoptosis, and thus damaging human health. Coupled with the source apportionment results of typical urban ambient air PM2.5 in eastern China, reducing toxic PM2.5 from these anthropogenic combustions will be greatly beneficial to public health. In addition to the air pollution control measures that have been implemented, like strengthening the vehicle emission standards, switching energy from coal to gas and electricity, and controlling the open incineration of agricultural straws, further methods could be considered, especially by preferentially reducing the diesel exhaust, lessening the coal combustion by replacement with low-ash clean coals, and depressing the rural crop straw biomass burning emissions.

Микропузырьковая безреагентная гидрофобизация поверхности угля

The paper describes methodological features of coal surface hydrophobization the using a microbubble gas-liquid medium to intensify the process of flotation concentration of coal. Air microbubbles were generated using decompression of liquid saturated under air pressure. The influence of water saturation pressure with gas on the size of the bubbles and their stability over time has been established. It is shown that addition of microbubbles leads to formation of an intermediate hydrophobic air layer on the surface of coal, which is the basis for catching bubbles of the flotation size. The results of coking coals flotation using a microbubble gas-liquid mixture are presented. By means of the method of differential particle size analysis, the preferred flotation of fine coal particles < 50 microns in size by micro-bubbles of air was established. It was found that for low-ash coals, the efficiency of reagentless microbubble flotation can be comparable with the results of concentration using traditional petrochemical reagents. In the reagent mode, the micro-bubbles are attached to the oil-hydrophobized surface of small particles with the formation of carbon-air complexes.

Comparative assessment of different grades of coal for methanol production: Simulation, optimization, environmental and economic analysis

The present study reports the modeling and simulation of methanol production through the gasification of freshly mined three coal samples having different wt.% of ash, viz., low-ash coal (LAC), medium-ash coal (MAC), and high-ash coal (HAC), collected from three different locations in India. The effect of the input parameters such as steam-to-coal mass ratio and gasification temperature on process performance parameters such as stoichiometric number, syngas yield, green house gas emissions from the process stream or net stream carbon dioxide equivalent, and methanol yield was studied through process sensitivity analysis and input parameters are optimized for the maximum methanol yield and minimum green house gas emission. Primary economic investigation at optimized conditions revealed that an internal rate of return of 5.93% is achieved for HAC at minimum plant scale and setting the methanol selling price of 400 USD/ton whereas IRR obtained as 3.20% and 5.87% for LAC and MAC, respectively, at this condition. The coal sample, HAC, performed better due to a high internal rate of return (i.e., 7.53% at base case) and subsequently low production cost. The present study's findings can be decisive for the countries with substantial low-grade high-ash coal reserves concerning coal diversification for its sustainable consumption in methanol production.

Analysis of char structure and composition from microwave and conventional pyrolysis/gasification of low and middle rank coals

The structure and composition of residual coal char after pyrolysis dictates its reactivity towards gasification. The nature of the char is a result of the parent coal composition and structure as well as the reaction conditions during pyrolysis. Further, due to the unique characteristics of selective dielectric heating, char development during microwave CO2 gasification may differ from conventional thermal gasification, and little is known about the effect of microwave heating on the char structure development. In this work the heating method used is compared (microwave vs conventional thermal) to generate char samples from four different coal types. These coal chars generated by pyrolysis and gasification were characterized by ultimate analysis, surface area analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and dielectric characterization to investigate the chemical and structural differences between microwave- and conventionally-generated chars. The results reveal notable chemical and structural differences between the chars from microwave and conventional pyrolysis and gasification. In general, the conventional chars had greater pore structure development as seen by higher specific surface areas compared to microwave chars, possibly due to rapid thermal collapse of coal pore structure. Microwave pyrolysis chars had greater ordering of the carbon crystal structure for low-ash coals, while graphitization was inhibited for coals with high ash percentage yield. The observations from this study highlight the differences in char characteristics from microwave and conventional pyrolysis and gasification, which can aid microwave gasifier design, implementation, and integration for efficient syngas production and coal ash utilization.

Gas production performance of underground coal gasification with continuously moving injection: Effect of direction and speed

Underground coal gasification (UCG) is an in-situ gasification technology where the controlled retreating injection point (CRIP) method is usually adopted to optimize the cavity evolution and gas production stability. However, the reported studies only focus on the gasification behavior of the moving injection backward under fixed time intervals. In this work, the gas production performance and reaction region evolution were studied for UCG with continuously moving injection for different directions and different speeds. For moving backward injection, when a uniform moving speed is used, gas production is not satisfactory with a heating value of 1 MJ/m3. In order to optimize the gas production, the injection should move backward for a fixed distance at regular time intervals rather than continuously, and the distance should be long enough for a new distribution of combustion zone, gasification zone and pyrolysis zone. For moving forward injection, when the moving speed and oxygen flow rate match well, the maximum heating value is larger than 11 MJ/m3, and the gas production is stable. The moving forward method is recommended for low ash coal to avoid “ash cover pipe” problem, and the injection pipe should be manufactured with high temperature resistant material. The moving backward method is recommended for low volatile coal to avoid “gas product leakage” problem, and the retreatment distance should be specially designed to avoid re-ignition.

CFD modeling of ash deposition distribution in an industrial radiant syngas cooler to enhance the operation performance

Radiant syngas cooler (RSC) is a crucial heat recovery equipment for entrained-flow coal gasification. Ash depositions in the industrial RSC endanger its operation efficiency and operation safety. In this work, the critical viscosity model and the ash shedding model are coupled to explore the ash deposition behavior in the industrial RSC for a 2000 t/d entrained-flow coal gasifier. Simulation results are in good agreement with the industrial conditions. The results show that ash depositions in RSC are mainly distributed in the upper part and the bottom cone, and the maximum ash thickness are 9.67 mm and 36.71 mm respectively. Due to ash depositions, the outlet temperature of RSC increases by 19.76%, the total heat transfer rate decreases by 21.88%, and the steam yield decreases by 22.41%. Employing low-ash coal as gasification raw coal is a good suggestion to enhance the operation performance of the industrial RSC. Moreover, when the industrial RSC is fully loaded, an appropriate increase in syngas mass flow rate can also contribute to a better operation performance.

Insight into structural evolution and detailed non-isothermal kinetic analysis for coal pyrolysis

In this study, the pyrolysis of low-ash coal (SF) and high-ash coal (NM) was investigated using a thermogravimetric analyzer. The semi-pyrolyzed char was collected to analyze its structural characteristics, and different model-fitting approaches were adopted for non-isothermal kinetics. Partial demineralized coal was also prepared to clarify the mineral–organics–gas correlation. The results showed that coal pyrolysis was a two-step sequence in which the aliphatic chain decomposed first (<600 °C), and then the aromatic ring condensed (>600 °C) with the formation of H2. Moreover, the amorphous structure in coal char was generated before the graphitization. HF leaching can promote the generation of H2 during the secondary pyrolysis of high ash coal. Inner minerals can promote graphitization under high-temperature pyrolysis. The nth-order model showed the best fitting performance, and the activation energy (Ea) increased with temperature based on piecewise analysis. Moreover, the Ea distribution became more concentrated after demineralization, especially for high-ash coal. Finally, the coal pyrolysis mechanism was summarized based on the solid structural evolution with consideration of the gas release property and inner minerals effect.

Новые возможности развития угольной отрасли: технология очистки отходящих газов от SO2, NOX, CО2

Based on a brief overview and analysis of global trends and the development of the coal industry, the article examines the causes and factors constraining the provision of conditions for the sustainable development of the industry. It is shown that despite the negative consequences resulting from the burning of coal, it remains the main cheap and widespread source of energy. The current state of the global coal industry is analyzed and ways of solving its further effective development are shown. One of the key solutions for the development of the coal industry is to reduce the environmental burden of harmful gases (SO2, NOx, CO2). A significant reserve for the development of the coal industry could be the involvement of high-calorie low-ash cheap coals. However, this requires the development and implementation of highly efficient, innovative technologies for deep purification of waste gases of TTP from SO2, NOx, CO2. One of such solutions is a new technology of complex deep purification of waste gases of the TTP, providing a high level of utilization of SO2, NOx, CO2 with the production of commercial products.

The influence of ash-content pulverized coal particles on their burning characteristics in tuyere hearth

Effect of ash content in coal dust on the burning characteristics in tuyere zone of blast furnace is studied. The ash is considered as an individual fraction in addition to two fractions of coal dust. It is shown, that the variation of pulverized coal fractional composition allows increase of carbon monoxide yield and fuel particles burnout. The presence of ash results in oxygen zone extension and increase of coke residue burnout. At the same time the total coal dust burnout is lower than that of low-ash coal. Fine pulverized coal combustion is characterized by increased production of carbon monoxide and reduction of carbon dioxide percentage.

Selective screening of coal to improve the washability characteristics at different levels of size reduction

ABSTRACT In coal beneficiation, ash content is the main focus area as it plays a vital role in controlling the yield and quality of the washed clean coal. Indian sub-bituminous and bituminous coals are of low-grade with intrinsically distributed ash-bearing minerals, which makes it difficult to segregate the low ash coal. Different stages of crushing and grinding techniques have been used to produce the desired feed size of coal washeries, i.e., −13 mm. During blasting and crushing, cracks propagate through the weaker interfaces within the coal particles. Petrographic analysis suggests the formation of good amount of naturally liberated maceral-rich particles of −13 mm size at different stages. These particles generated at mine site and primary crusher are subjected to further crushing during subsequent stages of secondary and tertiary crushing, resulting in more fine generation and higher energy consumption. Hence, an attempt has been made to check the washability characteristics of coals at different stages of crushing and effect of prescreening of coarse (−13 + 0.5 mm) and fine (−0.5 mm) fraction on washability characteristics of coal and overall clean coal yield. It was observed that −13 mm particles generated at early stage of crushing show good washability characteristics compared to the crushed lump coal (+13 mm) for the separation of 17.8–18% ash clean coal; and hence, prescreening of −13 mm prior to tertiary crushing improves the process efficiency.

Techno-economic analysis of co-combustion of Indian coals with municipal solid waste in subcritical and supercritical based steam turbine power generating carbon-negative systems

Incineration of municipal solid waste (MSW) can generate thermal energy for electricity generation and reduces its accumulation in the environment. MSW has low calorific value and its utilization would lead to low thermal efficiency in power plants due to higher auxiliary power consumption. Alternatively, this problem can be overcome by co-utilizing MSW with coal in thermal power plants. The capture of the generated CO2 from MSW can lead to carbon-negative energy production. Hence to evaluate its feasibility, energy and techno-economic analysis of subcritical and supercritical based steam turbines using MSW and its co-utilization with Indian high ash and low ash coals are performed using Aspen plus software (v 8.8). The effect of integrating post combustion carbon capture on the net thermal efficiency of power plants and its subsequent impact on levelized cost of electricity (LCOE) are analysed. The feedstock with an equal proportion of coal and MSW had shown a reasonable LCOE in the range of 60–67 $/MWh without carbon capture. The results had shown that the addition of 25% MSW to low ash coal could give a similar plant thermal efficiency and LCOE to that of high ash coal under subcritical conditions without carbon capture.

Reaction kinetics of coal char in oxy-fuel combustion environment and characterization of reacted char

ABSTRACT The work primarily focuses on combustion kinetics of devolatilized coal char fines (75–120 µm), including the estimation of kinetic parameters and char morphological transformation in oxy-fuel environment (O2-CO2 and O2-N2). Experimental work has been carried out to study the effect of higher CO2 concentration and elevated O2 concentrations on the ignition, burnout behavior of pulverized coal char both non-isothermally and isothermally. The coal chars obtained from pyrolyzing three different types of coal are used in experiments; a high ash (HA) coal, a medium ash (MA) coal, and a low ash (LA) coal. Three different kinetic models, namely VM, GM and RPM, have been employed to determine the kinetic parameters. The kinetic parameters are observed to be a strong function of oxygen concentration for all the three models. The estimated activation energy employing non-isothermal analysis for LA coal char using VM lies in the range of 203–212 kJ/mol. In comparison, the activation energy predicted by GM for HA coal char lies in the range 137–144 kJ/mol. Moreover, the activation energy estimated for MA coal char by RPM varies in the range of 134–142 kJ/mol. It is also explored during the non-isothermal analysis that an increase in char particle size from 75–120 µm to 250–300 µm shows a small increase in the values of apparent activation energy and pre-exponential factor. The activation energy values calculated employing the isothermal method are 106–126 kJ mol−1 (using RPM) for coal char MA and 96–135 kJ mol−1 (using GM) for coal char HA. Both the isothermal and non-isothermal kinetic analysis reveals that the combustion of coal char LA follows VM while coal char MA and HA follows RPM and GM in order. SEM images and BET surface area analysis for partially converted coal chars are further analyzed to justify the suitability of different reaction mechanism followed by various coal chars.

Lithium and redox-sensitive (Ge, U, Mo, V) element mineralization in the Pennsylvanian coals from the Huangtupo coalfield, Shanxi, northern China: With emphasis on the interaction of infiltrating seawater and exfiltrating groundwater

Geochemistry of low-ash and medium-sulfur coal and non-coal horizons from the Huangtupo coalfield, Shanxi, northern China was investigated. The economic potential of coal mining for critical elements (e.g., U, Li) was investigated in the present study. Uranium, Mo, and Sr are slightly enriched in the Pennsylvanian Huangtupo coal; with U and Mo reaching their highest concentrations in the topmost coal bench underlying the limestone roof. These enrichments are probably related to a marine invasion in the basin. The Al2O3/TiO2 ratio and the Zr/TiO2-Nb/Y relationship indicate the input of felsic-intermediate materials. The similar rare earth elements plus Y (REY) distribution patterns between non-coal horizons and Yinshan Upland granite suggests a detrital input from the Yinshan Upland. The Li mineralization, common in coals of the Qinshui basin, is represented by Li enrichments in the lower coal benches associated with the parting and floor mudstones. This mineralization is probably related to the neutralization of infiltrating seawater by acidic groundwater. This acidic water, possibly derived from the Triassic Li-Cs-Ta pegmatites and exfiltrated through the clastic deposits into the coal seam, could cause some additional Li enrichments in the lower coal benches and associated clastic rocks. Some coal benches (e.g., from the Jincheng and Changzhi Mines) in the Qinshui Basin meet the mining grade of lithium (80–120 μg/g, on whole coal and/or rock basis) for coals, making them promising for commercial Li recovery.

ИССЛЕДОВАНИЕ СОРБЦИОННЫХ ХАРАКТЕРИСТИК АКТИВИРОВАННЫХ УГЛЕЙ

The article presents the results of a comparison of the sorption characteristics for gold of crushed activated carbon of the foreign Haycarb brand, obtained from expensive raw materials - coconut shells, and crushed activated carbon of the domestic Shubarkol brand, obtained from relatively cheap raw materials - low-ash coking coal. The activated carbon Shubarkol crushed to a class of -3.6+1.0 mm, was produced in Kazakhstan from coking coal by Shubarkolkomir JSC. To test the crushed coal Shubarkol, industrial crushed coal Haycarb, made from coconut shells, was used as a reference sample. This coal is widely used in gold mining enterprises for the sorption of dissolved gold from cyanide solutions and pulps. For research, a productive solution of the process of heap leaching of gold from oxidized ore of one of the deposits of Kazakhstan was used with the composition, mg/L: gold 0.82; silver 0.44; copper 8.34; pH 11.05. Determination of the sorption characteristics of coals was carried out by the method of saturation with gold when changing solutions. The results of changes in the gold content in the mother solution, its extraction and saturation of coals with precious metal after each sorption cycle from the productive heap leaching solution using crushed coals of the Shubarkol and Haycarb brands are presented. It follows from the obtained data that Shubarkol activated carbon has similar sorption characteristics compared to Haycarb activated carbon. The working capacity for gold of Shubarkol coal was 2.28 kg/ton of sorbent, and of Haycarb coal - 2.57 kg/ton. Thus, crushed coal Shubarkol, obtained from relatively cheap raw materials, can be successfully used at industrial facilities instead of foreign sorbent.

Techno-economic evaluation of electronic waste based oxygen carriers for co-chemical looping combustion of coal and biomass integrated combined cycle power generating systems

Chemical looping combustion (CLC) is an emerging technology to capture CO2 in a cost-effective way. Metal particles such as Fe, Ni, and Cu can separate oxygen from air by forming their oxides and they could thereby act as oxygen carriers for the combustion of fuels producing nitrogen-free CO2 enriched flue gas. To commercialize the CLC based carbon capture technology, low cost oxygen carriers are essential for economical operation. Electronic waste contains enormous metal components, which can be a potential source for the production of oxygen carriers. In the present study, mixed oxygen carrier particles obtained from a printed circuit board (PCB) based electronic wastes are proposed to use in the CLC process. A combustion experiment is conducted to extract metals from the PCB and their composition is identified using an XRF analyzer. These metals are found with 21% Fe2O3, 22.8% CuO and 3% NiO, 9.6% CaO and 10% Al2O3. Using these oxidized printed circuit board metals (OPCB) as oxygen carriers, Aspen plus simulations are performed by integrating a CLC system with a combined cycle power plant having a net capacity of 150 MW for electricity generation. High ash coal (33% ash) and low ash coal (2.1% ash) and rice straw are used in a co-combustion mode for the CLC operation. The effect of co-firing on the net thermal efficiency of the power plants is analyzed. Further economic analyses are carried out for the proposed system and the levelized cost of electricity (LCOE) is estimated for the power plants using various fuels. It is found that the use of electronic waste based oxygen carriers achieved almost an equivalent net thermal efficiency of 42.4% based on the combined cycle power plants, compared to pure Fe2O3 based power plants. Further the economic analysis has shown that the levelized cost of electricity (LCOE) of the CLC integrated combined cycle power system employed with electronic waste based oxygen carriers is 85.9 $/MWh, which is the lowest among other power systems. Metal oxide interaction with fuel ash is investigated experimentally using a thermogravimetric analyzer (TGA). The X-ray diffraction (XRD) analyses of the residue confirmed that there is no formation of complex components due to the ash interaction with OPCB.

Mechanistic investigation on the microwave-assisted leaching of low-grade coal for low-ash coal production

ABSTRACT The coal-derived energy can potentially be explored by utilizing the low-grade coals after beneficiation for power sector application on a long-term basis. However, beneficiating the low-grade coals of Indian origin to produce low-ash coal by physical or physicochemical techniques is very challenging due to their complex mineralogical nature. In this context, chemical beneficiation or leaching has proved to be an effective method. But, the high cost of chemicals associated with the leaching process limits its commercial practice. An in-depth investigation is, therefore, needed to optimize the chemical consumption so that the requirement of the chemicals can be minimized. Herein, a microwave-assisted leaching study was investigated on Indian low-grade coal to produce low-ash coal suitable for power generation. The raw coal and its flotation product were pretreated under optimized microwave pretreatment time (5 min) and subject to leaching at varying alkali concentrations. Among all the combinations, the leaching of microwave pretreated floated coal showed a higher degree of demineralization (69.57%) together with increased carbon content (55.48%) and gross calorific value (6635 kcal/kg) in its leached product. The leached products were also analyzed using different characterization techniques such as Fourier transform infrared spectrometer, X-ray diffraction, and Thermogravimetric analyzer.