Low-grade Coal Research Articles

Interpreting crystallographic and microcrystalline structural effect for demineralization of low-grade thermal coal in multi-stage chemical leaching: A cleaner combustion approach

Chemical leaching is one of the most efficient methods for improving low-grade coal due to its ability to remove both inorganic and organic minerals economically. This study examined the qualitative demineralisation using the XRD and FTIR analyses. Moreover, microcrystalline analysis was investigated by analysing the Micro-Raman spectra, and ash composition was analysed using XRF Spectroscopy analysis for coal samples. Furthermore, a correlation was established between a Raman parameter (AD/AG) and a crystallite parameter (Lc). The demineralisation mechanism was postulated in light of the findings to explain how significant impurities (SiO2 and Al2O3) with iron-bearing elements (Fe2O3 and FeS2) were curtailed during multi-stage leaching. The maximum deashing and demineralisation were obtained by treatment with 40% (w/v), i.e. 10 M NaOH, followed by HCl with HNO3 solution in a 3:1 ratio, with an average particle size of 180 μm. 79% ash reduction and 48% enhancement in GCV were achieved compared to raw coal.

Upcycling low-grade coal fly ash for the production of fly ash fibers and their applications in fiber-reinforced cement composites

Fly ash (FA) fibers were produced from low-grade coal FA, which exhibited high SO3 content, in combination with dolomite and basalt. To identify the optimal combination of these raw materials, glass samples were cast with varying ratios of these materials. Subsequently, an alkaline resistance test was conducted by immersing the ground glass samples in a 1 M Ca(OH)2 solution for a duration of 75 days. The results of the alkaline resistance test revealed that the formulation consisting of 70 wt% FA, 20 wt% dolomite, and 10 wt% basalt, exhibited the highest alkaline resistance with a weight loss of less than 2 wt%. Based on this formulation, FA fibers were then produced and utilized as a reinforcing phase in fiber-reinforced cement composite (FRCC) samples, ranging from 0.1 to 0.8 wt%. Mechanical testing showed that, after 28 days of air curing, the FRCC samples containing 0.8 wt% FA fibers exhibited the highest modulus of elasticity (MOE) at 16,890 ± 434 MPa, along with a modulus of rupture (MOR) of 13.86 ± 0.98 MPa and an impact strength of 1792 ± 134 J/m2. These results meet industry requirements, with a MOR and MOE exceeding 5 MPa and 7000 MPa, respectively, as well as an impact strength exceeding 1000 J/m2. Using the Archimedes method, the density of the FRCC samples containing 0.8 wt% FA fibers, is 1.71 ± 0.03 g/cm3, falling within the industry standard range of 1.5 to 2.2 g/cm3. Furthermore, according to the cost analysis, the production cost for FA fibers is $324.40 per ton, compared to $5000 and $1000 per ton for commercially available fibers. Consequently, utilizing FA fibers would result in significant savings for the raw material costs for FRCC production.

Possibility of utilizing waste activated sludge as a renewable energy source

This paper gives results of a study of biofuel granules made from a waste activated sludge of wastewater treatment. A novel method to enhance waste activated sludge dewaterability with untreated and calcined water treatment sludge of thermal power plants is proposed, and the potential reuse of dewatered sludge as biofuel is evaluated. The water treatment sludge destroyed membrane, resulting in the release of intracellular water by converting bound water into free water, thus enhancing sludge dewaterability. Biofuel granules can be used for technological needs, electricity generation and in heating and hot water supply systems at industrial and domestic facilities. Biofuel granule is a renewable energy that can substituted low grade coal from biomass sources.

Modern design solutions in the design of boiler units, ovens and fireboxes burning solid fuel in a fluidified bed

Coal fuel has always played an important role in Russia’s fuel and energy balance due to its extensive reserves, availability in a number of regions and relatively low cost. Currently, coal flaring technology is widely used in domestic boiler plants, but it should be noted that this approach is more applicable for high-quality high-calorie coals with low ash content. In addition, flaring is sensitive to changes in the composition of the fuel and deviations from the specified values can lead to a decrease in the reliability of the boiler unit. There are also regions where there are deposits of low-grade coal that are not suitable for flaring. The problem of boiler sensitivity to the use of unspecified fuels, as well as the involvement of local low-grade fuels, can be solved by introducing circulating fluidized bed (CFB) combustion technology.

Optimization of extrinsic parameters for beneficiation of coal with the help of Cronobacter sp

ABSTRACT Beneficiation increases the calorific value of low-grade coal and extracts environmentally sensitive elements. Bacteria may be used as eco-friendly coal cleaning tool, but the treatment is influenced by several extrinsic and intrinsic factors. This study examined five extrinsic factors, namely particle size of coal, pulp density, bacterial biomass concentration, number of bacterial beads (immobilized bacterial cells) and the duration of treatment. For optimization, the test runs were designed using Taguchi L16 orthogonal array, determining optimal values through S/N ratio analysis and individual parameter contribution using ANOVA. The optimal conditions obtained for sub-bituminous coal beneficiation using Cronobacter sp. are 80–120 mesh particle size, 30% pulp density, 750 mg bacterial biomass/g coal, 25 bacterial beads, and six days of treatment resulting in 13.36% ash yield reduction. Particle size had the highest impact (69.4%), followed by treatment duration (13.1%), pulp density (6.3%), bacterial biomass (6.3%), and bacterial bead number (4.8%). A regression model attributed only 42% influence of these extrinsic factors on inorganic removal from coal. Therefore, further research on other factors, particularly intrinsic ones, in inorganic matter liberation is imperative. These findings can be used for designing experiments that optimize the extraction of cleaner fuel from various types of low-grade coal.

Numerical Simulations of Gasification of Low-Grade Coal and Lignocellulosic Biomasses in Two-Stage Multi-Opposite Burner Gasifier

Thermochemical processes utilizing biomass demonstrate promising prospects for the generation of syngas. In this work, a gasification process employing combination of an indigenous low-grade coal with two distinct biomass sources, namely rice husk (RH) and wood sawdust (WS), was explored. The gasification of the selected feedstock was performed using a double-staged multi-opposite burner (MOB) gasifier. A 3D computational fluid dynamics (CFD) model was employed to analyze the effect of kinetic and diffusion rates on the overall gasification performance of an entrained flow biomass gasifier. DPM was employed to track the particles’ trajectory, while the gas phase was treated as the continuous phase, and its behavior was predicted using a standard k-epsilon turbulent model. To calculate both the homogeneous and heterogeneous reaction rates, the finite rate/eddy dissipation model was implemented. The findings indicate that the char conversion efficiency exceeded 95% across all instances. Among the different reaction schemes, scheme E (which involved complete volatile and char combustion reactions) produced better results in comparison with published results, with less than 1% error. Hence, scheme E was validated and utilized for the rest of the simulated cases. The feeding rate has an inverse effect on the overall performance of the gasifier. An increase in feed rate decreases the CO and H2 composition in syngas. The maximum CO value was observed to be 57.59% at a 1.0 O/C ratio with a 0.005 kg/s feed rate, and the maximum H2 value was observed to be 16.58% in the same conditions for Lakhra coal samples. In summary, Lakhra coal exhibited better performance than other biomass samples due to its better fixed carbon and volatiles in its composition.

Hydrothermal dewatering of low-grade coal: Product evaluation and primary component analysis of ash deposition

The hydrothermal dewatering (HTD) process was carried out using 16 coal samples obtained from several regions in Indonesia. This research aims to identify the dominant parameters that influence ash deposition during coal combustion in a boiler or gasifier due to the HTD process. This research was conducted due to the lack of clear and comprehensive information regarding this issue. Therefore, to understand the effect of HTD on ash deposition, an analysis of the chemical composition of ash and the ash melting temperature (AFT) was carried out. To verify the data obtained from the experimental analysis, statistical methods such as paired sample t-test and primary component analysis were applied to obtain the dominant parameters influencing ash deposition due to HTD. Eight parameters, namely SiO2, Fe2O3, slagging viscosity index (SR), Babcock index (Rs), initial deformation temperature, softening temperature, hemispherical temperature, and fluid temperature under oxidative conditions, have the greatest influence on ash deposition due to the HTD process. Based on the average values of SR and Rs, raw coal and processed coal samples have the same ash deposition trend. On the other hand, based on AFT under oxidation conditions, processed coal has a higher AFT, indicating that the tendency for ash deposition is lower than raw coal. Therefore, the HTD process can be used to improve the quality of low-grade coal. As an implication, low-grade coal, which has not been widely utilized in Indonesia, due to several constraints regarding its characteristics, through the HTD process can be optimized where coal utilization is a bridge towards the use of green energy which is being intensively pursued.

Optimization of low-grade coal and refuse-derived fuel blends for improved co-combustion behavior in coal-fired power plants.

This study is aimed at utilizing three waste materials, i.e., solid refuse fuel (SRF), tire derived fuel (TDF), and sludge derived fuel (SDF), as eco-friendly alternatives to coal-only combustion in co-firing power plants. The contribution of waste materials is limited to ≤5% in the composition of the mixed fuel (coal + waste materials). Statistical experimental design and response surface methodology are employed to investigate the effect of mixed fuel composition (SRF, TDF, and SDF) on gross calorific value (GCV) and ash fusion temperature (AFT). A quadratic model is developed and statistically verified to apprehend mixed fuel constituents' individual and combined effects on GCV and AFT. Constrained optimization of fuel blend, i.e., GCV >1,250 kcal/kg and AFT >1,200 °C, using the polynomial models projected the fuel-blend containing 95% coal with 3.84% SRF, 0.35% TDF, and 0.81% SDF. The observed GCV of 5,307 kcal/kg and AFT of 1225 °C for the optimized blend were within 1% of the model predicted values, thereby establishing the robustness of the models. The findings from this study can foster sustainable economic development and zero CO2 emission objectives by optimizing the utilization of waste materials without compromising the GCV and AFT of the mixed fuels in coal-fired power plants.

Concentration contextualisation, temporal patterns and sources of hydrogen sulphide at a site on the South African Highveld

South Africa is one of the largest atmospheric sulphur emitting countries, but the contribution of H2S to this regional burden is not known. Also, no H2S source apportionment for South Africa have been undertaken, although H2S has adverse effects on the environment and human health both directly and after being oxidised. Measurements were conducted for 2 years at a site on the Mpumalanga Highveld (South Africa), which is influenced by multiple sources. A mean of 3.1 ppb H2S was obtained, which is similar than concentrations reported for some large Northern Hemisphere cities and areas close to gas processing plants. Well defined seasonal and diurnal patterns indicated that low-level emission sources likely made a significant contribution to the ambient H2S concentrations. In this study, a receptor method was developed to enable identification of sources and quantification of their contribution to atmospheric H2S levels above the baseline concentrations. The results indicate that emissions from urban areas on the Mpumalanga Highveld, associated with sources in towns, as well as semi- and informal settlements (e.g. ineffective household combustion of low grade coal, sewage waste water treatment facilities, landfills, small industries and traffic) contributed most to atmospheric H2S levels in excess of baseline concentrations (34.6%), followed by pyrometallurgical smelters (19.8%) and a petrochemical operation near Secunda (17.9%). The Johannesburg-Pretoria megacity, coal-fired power stations, burning coal dumps and cattle feedlots contributed 10.9, 4.7, 3.8 and 0.4%, respectively, to H2S concentrations in excess of the baseline levels, respectively. The results from this study will be informative for legislation that is currently being considered, wherein regional ambient H2S standards for South Africa are suggested.

Parametric optimisation and performance evaluation of gasifier-CI engine on dual fuel and dual feed material gasification

Gasification-based energy derived is one of the appealing resources for producing heat and power generation. The objective of this paper is to conduct an experimental study on downdraft air co-gasification of Madhuca longifolia wood and Indian low-grade coal (50:50 wt %) to generate producer gas and its application in dual-fuelled mode CI engine. Besides, the optimisation using the response surface methodology (RSM) has been applied to Gasifier-Engine to determine the best engine performance and emission response by optimising the input variables, i.e. gasifier equivalence ratio, engine compression ratio, and engine load. The RSM-based analysis predicted that optimum input operating parameters could be attained for co-gasification for Equivalence ratio (ER), compression ratio (CR), and engine load (EL) at 0.43, 16, and 100%, respectively. Based on optimal input variables, the performance response values of the gasifier-engine are 29.52% Brake thermal efficiency (BTE), 3.30 kW Brake power (BP), 0.3851 kg/kWh Brake specific fuel consumption (BSFC), 0.0186 vol% CO, 0.958 ppm UHC, 0.9768 vol % CO2, and 109.415 ppm NOx. The results show that the projected regression model has a high accuracy of R2 > 90% and a high correlation coefficient of 0.8927.

Improvement of Coking Property of Low-Grade Coals by Mild Reduction Treatment

Improvement of Coking Property of Low-Grade Coals by Mild Reduction Treatment

Pure hydrogen gas production in a coal supercritical water gasification system with CO2 as transporting medium

Supercritical water gasification (SCWG) technology was a clean coal conversion and utilization technology, which could decompose low-grade coal into gaseous products and make efficient and clean use of them. However, system with H2O transporting had much energy consumption on heating transporting medium and side reactions at heating process would weaken the gasification effect. Considering the advantages of low critical point and low specific heat capacity of CO2, and the precedent of CO2 as a transport medium in non-supercritical systems, CO2 was expected to become a transport medium in supercritical water gasification systems and to achieve the goal of improving the gasification effect of heating process and reducing energy consumption. A supercritical water coal gasification system of was established with lignite as raw material in this paper. Production yields of gasification with CO2 as the transporting medium at different working conditions were investigated. CO2 and H2O were used as the transporting medium of the system, contrastively. Compared with H2O-transporting system, production of H2 and CO2 in CO2-transporting system decreased while that of CH4 and CO increased as well. Furthermore, both energy and exergy efficiency of CO2-transporting system were higher than that of H2O-transporting system. The result proved the superiority of CO2 as the transport medium of supercritical water gasification system.

Development and Characterization of Coal-Based Thermoplastic Composite Material for Sustainable Construction

The exploitation of coal and the disposal of waste plastic present significant environmental and economic challenges that require sustainable and profitable solutions. In response, we propose a renewable construction composite material of coal-based thermoplastic composite (CTC) that can be made from low-grade coal and plastic waste. We developed and tested the hot-press fabrication method for this CTC, using coal with a maximum particle size of 4.75 mm and recycled high-density polyethylene (HDPE). The effects of the coal fraction (50–80 wt%) on compressive properties, thermal properties, microstructure, and ecological and economic efficiencies of the CTC were investigated. Test results revealed that the compressive strength and modulus decrease as the coal fraction increases. However, the thermal properties, including thermal conductivity and specific heat, increase with higher coal contents. Compared to concrete, the CTC has about half the thermal conductivity and twice the specific heat, making it a more energy-efficient construction material. Microstructure testing helped to reveal the mechanisms behind the above behaviors of CTC from the observation of binder volume, bonding quality between coal and HDPE, and porosity variation. The life cycle analysis indicated that the CTC production reduced embodied energy, carbon footprint, and cost by up to 84%, 73%, and 14%, respectively. Therefore, we recommend the CTC with 50–70% coal fraction as an innovative construction material with satisfied mechanical and thermal properties, better cost efficiency, and a reduced ecological impact.

Structural Characterization and Molecular Model Construction of High-Ash Coal from Northern China.

High-ash coal, also known as low-grade coal, has becomes a viable alternative in recent years to high-quality coal because available resources have become increasingly scarce due to extensive mining activity. This work aims to provide a comprehensive understanding of the structural characteristics of high-ash coal and construct a plausible molecular structure to elucidate its chemical reactivity in future applications. Its properties were investigated using Solid-state 13C nuclear magnetic resonance (13C NMR), X-ray photoelectron spectroscopy analysis (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The molecular structure was constructed and validated using Material Studio, LAMMPS Software Package, and MATLAB program. The characterization results revealed that high-ash coal contains 72.15% aromatic carbon, significantly surpassing the percentage of aliphatic carbon (27.85%). The ratio of bridgehead carbon to peripheral aromatic carbon was calculated as 0.67, indicating that the pentacene is the main carbon skeleton form in the high-ash coal structure. Furthermore, oxygen-containing functional groups presented as C=O/O-C-O, C-O, and COO- within the structure along with pyridine and pyrrolic structures. Consequently, the molecular structure comprises pentacene with aliphatic carbon chains, such as methylene, that connect the benzene rings and form a three-dimensional network. The results of a simulated IR spectrum and contact angle simulation aligned with the experimental results, validating the molecular structure of high-ash coal. The chemical formula for the high-ash coal model was determined as C203H189N7O61S with a molecular weight of 3734.79.

A comparative evaluation of co-gasification of blends of low grade and washed coals with high-rank coal in a fixed bed reactor

ABSTRACT Coal is the most valuable gasification resource due to its abundance and low cost for commercial applications. But utilization of low-rank Indian coals for gasification is challenging due to difficulty in washing. For utilizing low-grade high ash raw coal, blending is one of the effective methods to control the gasification performances. So, the present study explores the gasification of such a low-rank raw coal blend and compares the results with washed coal blend. The blending effects on raw gas yield (kg/kg of coal) and heating value (Kcal/Nm3) were investigated for coal blends-WH (washed coal with high-rank coal) and RH (raw coal with high-rank coal). In WH, raw gas yield is 1.210 to 1.225 (kg/kg of coal), whereas, in RH is 1.189 to 1.213 (kg/kg of coal), though the fixed carbon content of WH (40.75–41.74%) is lower than RH (44.73–45.25%). In washed coal, raw gas yield is minimum (0.75 kg/kg of coal). The heating value is lower in WH (2730–2871 Kcal/Nm3) than in RH (2884–2978 Kcal/Nm3). Statistical correlation is developed between gaseous components of raw gas and heating value; H2/CO ratio is the most significant parameter. RH gasification is economically viable than WH.

Simulation modelling of sampling and replacement of coal suppliers for thermal power plants

This paper embarks to the persistent suboptimal coal quality issues experienced in thermal power plants that hinder operational efficiency and sustainability. The research is divided into three main segments: formulation of a transport problem, creationof a coal supplier selection model, and construction of a MATLAB Simulink® simulation for detecting and refusing low-grade coal. The proposed supplier selection model, important for thermal power plants, considers factors such as potential transport delays and the necessity of reserve refueling to prevent fuel shortages. This model is expected to decrease fuel shortages and enhance the reliability and efficiency of thermal power plants. Additionally, a coal quality detection model has been developed using a sampling approach based on the Cochran formula, aiming to increase defect detection accuracy, thus reducing the likelihood of utilizing poor-quality coal. The model's unique feature is its dynamic adjustment of coal sample selection based on combustion results, enabling real-time response to coal quality inconsistencies. Upon detecting poor-qualitycoal, the power plants promptly switch to an alternate supplier, minimizing operational disruptions. The validity of the models was confirmed via simulation on various examples

Alkali leaching in dissolved oxygen for efficient desulphurization of low-grade Lakhra coal

ABSTRACT Coal is still a great source of energy, but its high sulfur content causes environmental pollution and problems in its processing. This study used a method of combined oxidation and alkali leaching to desulfurize low-grade, high-sulfur Lakhra coal at different ranges of temperature, alkali concentration, leaching time, partial pressure of oxygen, and agitation speed. The optimum values for the leaching reaction were observed to be an alkali (NaOH) concentration of 0.8 mM, a leaching time of 1.5 h, an oxygen partial pressure of 150 psi, and an agitation speed of 800 rpm. The ash content of the coal initially increased at higher values of reaction time and temperature, and then became saturated at a certain peak. The raw coal was characterized for ultimate and proximate analysis, and the product was characterized for ash content and total sulfur content.

Analisis Kualitas Batubara Bonto Matinggi Sulawesi Selatan Untuk Kebutuhan Industri Semen

Coal in Indonesia is widely used for both export and domestic industrial needs. Domestically, it is widely used for the textile industry, power plants, and the cement industry. Coal consumption for the cement industry in Indonesia in 2022 is up to 15 million tons. In the cement industry, coal is used as a basic material for fuel in kilns. For its utilization, coal needs to know its properties. These properties can be known by proximate analysis, sulfur content analysis and calorific value. Therefore, this research aims to find out and determine whether the quality of Bonto Matinggi coal is in accordance with the coal specifications needed in the cement industry. The research method was carried out by taking two coal samples directly in the research area, namely SA I coal sample and SA II coal sample. The coal samples were then prepared and further analyzed. Analysis of coal sample quality was carried out by proximate, sulfur and calorie analysis methods. The results of proximate analysis show that the moisture content in air dried both samples have a value that is not too significant with an average value of 6.29% adb; ash content of 19.99% adb; volatile matter of 46.79% adb and fixed carbon of 39.86% adb as well as sulfur content of 0.39% adb and calories with an average of 4,692.92 cal/g. The coal in the study area does not qualify as a basic material for fuel in kilns in the cement industry. The coal in the study area, if classified according to the Classification of in Seam Coal 1998, is classified as low grade coal (according to ash content) and the coal rank includes bituminous rank (medium rank).

Reconstructing the nanoscale porous structures in coal-based membranes by ultrafast high-temperature sintering for solar-driven water treatment

Lignite, a low-grade coal, accounts for over 40% of the global coal reserves. The use of lignite has been limited compared to other grades due to its low calorific value, high impurities content, and elevated volatile matter. Exploring a scalable and environment-friendly approach to upgrade lignite will offer new opportunities. In this work, Ultrafast High-Temperature Carbonization (UHC) has been developed to carbonize lignite and modify its nanoscale structure to construct a conductive porous membrane. The whole process takes only 30 s with an ultrafast heating rate reaching up to 9000 °C/min and a maximum temperature over 1500 °C. Upon heating the pore structures in the coal membrane evolves into micro- and mesopores with a specific surface area of over 300 m2/g. The carbonized coal-based membrane provides superior performance as a solar evaporator for water treatment, due to its interconnected porous structures, hydrophilicity, and over 85% absorption of full-band visible light. Under 1 sun solar irradiation, the membrane shows over 98.2% removal rate of salts, heavy metal ions, and volatile organic compounds (VOCs).

Bio-coke: A sustainable solution to Indian metallurgical coal crisis

Coal is the predominant global energy source, where its consumption as metallurgical coke from fast-depleting prime coking coal is vital. In India, the complete depletion of prime coking coal and ultimate dependence on low-grade low-volatile coking coal reserves are the primary concern, so the need to explore alternative fuels, preferably with less climatic concern. Accordingly, a process for the synthesis of bio-coke, a novel product, using varying blending ratios (90:10, 80:20, 70:30, 60:40, and 50:50) of such inferior grade coal and biochars (derived at 550°C) of coconut shell (CSC), groundnut shell (GSC), sawdust (SDC), and sugarcane bagasse (SBC) in the presence of starch and molasses binders was developed via carbonization (at 800–1100°C). Obtained bio-cokes from coal and biochars with molasses possess better strength and plastic properties for metallurgical applications than those prepared with starch, and can be a sustainable substitute for metallurgical coke.