Raw Coal Research Articles

Evolution of oxygen-containing functional groups on coal char surface during gasification in H2O/CO2

Gasification converts coal into syngas (CO and H2) for downstream utilization. The most important reaction in an autothermal gasifier is the char−H2O/CO2 reaction. The evolution of C(O) complexes on the coal char surface directly determines the pathways and rates of CO and H2 generation. This study mainly used a fixed bed reactor to prepare Zhundong coal char with different reaction levels in H2O and CO2, and its surface carboxyl, lactone, phenolic hydroxyl, and hydroxyl functional groups were systematically analyzed by using Boehm titration, FT-IR, and XPS. The results show that the contents of the four oxygen-containing groups in raw coal are in the order of carboxyl＞lactone＞phenol hydroxyl＞hydroxyl. In H2O gasification, the lactone groups were more susceptible to H2O resulting in a significant increase in carboxyl content at the early stage of the reaction. The hydroxyl, as a very active group in the reaction, and the amount of its generation and consumption was very obvious. The phenolic hydroxyl−the least thermally stable group among these four types of groups, was unable to participate in the inter-transformation between oxygen-containing functional groups during the gasification. During CO2 gasification, the hydroxyl was rapidly consumed at the initial stage of the reaction and then shown a slow growth trend, and the newly generated hydroxyl would continue to undergo dehydrogenation to form new functional groups. At the end of the reaction, the transformation of other oxygen-containing functional groups into more stable carbonyl groups leads to a sudden increase in the content of carboxyl and lactone. In this work, Boehm titration was introduced into the determination of oxygen-containing functional groups on the surface of char during gasification in H2O/CO2.

New insights into dynamic disaster monitoring through asynchronous deformation induced coal-gas outburst mechanism of tectonic and raw coal seams

The coalbed methane energy resources waste, environmental pollution and miner's health remain challenging problems in worldwide mining operations accompanied by coal-gas outbursts; thus, the safe and efficient yield of these resources plays a vital role in the world's energy market. The tectonic coal development is a significant geological feature of coal and gas outburst sites, and the study of coal and gas outburst mechanism should be based on more precise geological occurrence characteristics. In this paper, the geological characteristics of coal and gas outburst sites were analyzed. The failure law of coal body under the stratified occurrence of tectonic coal and raw coal seam with different thickness was studied. The mechanical equilibrium equation of non-synchronous deformation of tectonic coal and raw coal was constructed, the initiation criterion of coal and gas outburst was established based on the support body model, and a case study was carried out. The results show that with the thickness increase of the tectonic coal seam, the peak displacement of the driving face increases. The outburst start-up and development of coal and gas outburst, coal and gas extrusion outburst and coal and gas collapse outburst were deeply analyzed, as well as the internal reasons of the occurrence of coal-gas outburst portent are explained, based on the support body model. The development process from the start to the end of coal and gas outburst is revealed, and a new perspective is proposed for the prevention and control of coal and gas outburst: improving the strength of support body is also of great significance for the prevention and control of coal and gas outburst.

Experimental study on variation characteristics of combustion heat load in circulating fluidized bed under fuel high-temperature preheating modification

This study introduces an innovative application of fuel high-temperature preheating modification technology to circulating fluidized bed (CFB), intending to enhance the variable load rate of CFB and reduce its NOx emissions. The variable combustion heat load (CHL) experiments were conducted on a novel CFB experimental platform comprising a preheating modification device (PMD) and CFB. The findings indicate that implementing fuel high-temperature preheating modification technology allows the CFB to operate stably within the range of 30%–100% CHL while maintaining superior combustion efficiency. Moreover, it reduces NOx emissions by over 28% compared to conventional combustion. The decrease in NOx emissions can be attributed to the fuel's preheating modification process inhibiting NOx production and establishing conditions conducive to NOx reduction in CFB. Furthermore, after employing the fuel high-temperature preheating modification technology, the CHL change rate of CFB reached 1.79%/min and 2.27%/min for the transition from 50% CHL to 75% CHL and from 75% CHL to 100% CHL, respectively. These rates represent an increase of 1.59 and 1.80 times compared to the rates observed in conventional combustion processes. The increase in the CHL change rate of different CHL variation intervals is primarily due to the production of high-temperature coal gas and modified char following fuel preheating modification. High-temperature coal gas exhibits a rapid combustion rate, while modified char has a smaller particle size, more developed pore structure, and enhanced reactivity than raw coal.

More evidence on primary sulfate emission from residential coal combustion in northern China: Insights from the size-segregated chemical profile, morphology, and sulfur isotope

This study addresses the ongoing debate concerning the origin of ambient sulfate in northern China, and provides more evidence for primary sulfate from the perspective of source emission. An extensive field experiment was conducted, involving the collection of size-segregated particulate matter emitted under various coal types and combustion conditions for subsequent analysis. Our findings reveal that residential coal combustion (RCC) emits significant amounts of primary sulfate, constituting approximately 26.48 ± 15.43% of the particulate mass. Moreover, these emissions exhibit a strong association with NH4+, leading to the formation of stable ammonium sulfate compounds. The emission of sulfate is intricately linked to both coal quality and combustion conditions. Notably, the oversight of δ34S isotope enrichment in RCC particulate matter, which distinctly differs from the raw coal, introduces uncertainties in the quantitative assessment of sulfate sources and formation pathways. Therefore, more in-depth explorations are necessary to elucidate the precise processes involved in RCC sulfate transformation and to accurately determine its environmental impact.

Investigation of the impact of sodium dodecylbenzene sulfonate modification on the wettability of coking coal

ABSTRACT To investigate the impact of sodium dodecylbenzene sulfonate (SDBS) modification on coking coal’s wettability, our research focuses on coking coal and uses SDBS as the surfactant in the experiment. The surface tension, scanning electron microscope, FTIR, contact angle measurement, and reverse osmosis experiment are employed to measure the microscopic characteristics and wettability of raw coking coal, water-soaked coal, and coal soaked in 0.0005%, 0.005%, and 0.05% SDBS solutions. Finally, the dust reduction efficiency was determined by spray dust reduction experiments. We analyzed the effect of varying mass fractions of SDBS on coking coal’s wettability. The findings indicate that the surface of coal samples soaked in water and SDBS solution become rough. Adding clean water and SDBS solution improves the coal samples’ wettability. Among various coal samples soaked in different solutions, the one treated with 0.005% SDBS solution exhibits the smallest contact angle, significantly higher moisture absorption, and the most pronounced wetting effect. Soaking the coal samples in 0.005% SDBS solution can achieve the highest dust reduction efficiency. In summary, soaking the coal samples in no matter clean water or SDBS solution can enhance the wettability of coal dust, while soaking in 0.005% SDBS solution has a better effect.

Enhancement of CH4/N2 separation capacity of coal-based porous carbons via hydrothermal coupled KOH activation

The separation of CH4 and N2 is an important technology for the effective utilization of low-concentration CBM. To improve CH4/N2 separation properties of coal-based porous carbons, Shaanxi long-flame coal was hydrothermally treated followed by KOH activation for the preparation of porous carbons. The impact of hydrothermal treatment on the pore structure and CH4/N2 separation properties of porous carbons was investigated. The results show that hydrothermal decomposes the macromolecular structure of coal, which enlarges the pore size of the raw coal and facilitates the KOH penetrate deeper into the coal particles. Meanwhile, more release of methylene/methyl groups and in-stiu growth of carbon nanotubes develop the pore structure during the activation process of treated coal. The pore structure of porous carbons can be precisely controlled by adjusting the water-coal ratio in the hydrothermal process. Among them, C-TC1.25 shows a 22% increase in CH4 adsorption capacity over C-RC, which is mainly due to a significant increase in the micropore volume at 0.5–1.0 nm and generation of carbon nanotubes as gas transport channels. At 298 K and 101 kPa, C-TC1.25 exhibits a CH4 adsorption capacity reaching 1.72 mmol/g, which surpasses that of most known adsorbents, while the IAST selectivity is as high as 5.5. The breakthrough experiment confirms that the porous carbons effectively enable separation of CH4/N2 mixed gas. Kinetic studies show the CH4 adsorption process on C-TC1.25 conform to the pseudo-first-order model and exhibit surface-attached physical adsorption.

Effects of Aqueous Solution and Immersion Duration on Spontaneous Combustion Characteristics of Weakly Caking Coal

ABSTRACT Coal spontaneous combustion (CSC) severely affects the development of the coal industry and threatens the safety of coal miners. This study investigated how immersing coal in aqueous solution affects the CSC risk and evaluated the effect of the immersion duration. Fourier transform infrared spectrometry and thermogravimetric−differential scanning calorimetry analysis were performed. Coal samples were immersed in water from an underground coalmine or in distilled water for 30 or 60 days. Changes in microscopic functional groups and thermokinetic behaviors were determined. Immersion in distilled water for 60 days led to 4.41%, 2.26%, and 6.25% smaller masses of C=O, –CH3, and free hydroxyl groups, respectively, relative to their levels in raw coal. Additionally, the characteristic temperatures T 4 , T 5 , and T 6 were 8.8%, 9.0%, and 9.2% lower, respectively, and the average apparent activation energy was 15.67% lower. Immersion in water from an underground coalmine for 60 days led to 5.68%, 2.58%, and 6.54% higher masses of C=O, –CH3, and free hydroxyl groups, respectively, and 12.8%, 13.0%, and 13.5% higher characteristic temperature, respectively; the average apparent activation energy was 20.43% lower. These findings suggest that the coal immersed in water from an underground coalmine was the most susceptible to CSC.

Study on the Mechanical Degradation and Destruction Characteristics of Coal Oxidation

ABSTRACT Deep coal bodies are often in high stress and high temperature environments. To study the effects of stress and temperature on the mechanical degradation and failure characteristics of coal samples, nuclear magnetic resonance experiments were carried out before and after coal sample oxidation to analyze the effect of oxidation on the porosity of the coal samples. Through mechanical property experiments, the changes in the mechanical properties of the coal samples at different oxidation temperatures is analyzed. Then coal samples of different particle sizes are screened and statistically analyzed to determine the relationship between the fractal dimension of the broken block size and the oxidation temperature. A stress model for the oxidized coal samples is established to analyze its mechanical degradation and its breaking mechanism. Based on the results, As the oxidation temperature increases, The total porosity of the coal samples show an overall increasing trend, the elastic modulus, secant modulus, Poisson’s ratio, and shear modulus show a downward trend, and the destructive strain energy density decreases from 43.33 kg•m−3 to 15.47 kg•m−3, indicating the oxidized coal sample increases in plasticity and decreases in stiffness, resulting in a decrease in the amount of load the sample can carry. The fractal dimensions of the broken block size from raw coal to 200°C coal samples are 2.008, 2.092, 2.150, 2.159, 2.175, 2.183, 2.314, and 2.328. Oxidation leads to the formation a network of tiny fractures inside the coal samples; thus, the broken block size becomes more complex with worsened integrity. A model for the ability of the oxidized coal samples to resist destruction is established, and the diameters of unoxidized areas in oxidized coal samples are calculated to be 45.053, 44.956, 43.031, 41.931, 37.442, 28.081 and 13.778 mm. An analysis of the breaking mechanism of oxidized coal samples was carried out. Our results are beneficial for the safe operation of deep coal seam mining.

Failure Behavior and Fracture Evolution Mechanism of Coal with Fissures around Holes.

The fracture of coal is the main channel of gas flow and an important factor affecting the stability and efficiency of gas drainage boreholes. The coal structure, the development of hole cracks, and the degree of deformation are different. It affects the strength and mechanical deformation characteristics of coal to a great extent. In order to investigate the law of fracture evolution around the borehole of fractured coal, uniaxial and triaxial compression tests of raw coal samples have been carried out. The stress field evolution characteristics of fractured coal under compression were analyzed by Particle Flow Code (PFC2D). The strength, deformation, and fracture evolution behavior of fractured coal around boreholes under different confining pressures were studied. The results show that the compressive strength and fracture morphology evolution characteristics of coal around the hole are obviously related to the confining pressure and fracture occurrence of raw coal. The borehole structure itself has an important influence on the distribution location of the shear failure zone of the fracture around the hole, and its influence degree increases with the decrease of borehole confining pressure. During the deformation of coal with cracks around the hole, the initiation, propagation, and union behavior of cracks are related to the crack angle β. The cracks with β 0 and 180° are most easily closed during compression and the cracks with β 90° have little effect on the crack propagation zone. When the crack angle β is 45°, it is most easy to sprout and expand at the end; when the coal is compressed to the ultimate strength, the increase rate of the tensile crack increases, and the polymerization and combination behavior of the crack is more obvious. The evolution cloud map of the stress field can better reflect the evolution characteristics of fracture development, expansion, and fracture in the process of coal loading. Studying the failure behavior and fracture evolution mechanism of the coal around the hole can better predict and control the gas migration and extraction effect, which is of great significance to prevent the occurrence of gas accidents.

Inhibition Effect of Coal Spontaneous Combustion by Composite Inhibitory Foam Based on CaCl2-Melatonin Inhibitor.

Inhibitory foam technology plays an important role in inhibiting coal spontaneous combustion. To enhance the stability and inhibitory performance of inhibitory foam for coal spontaneous combustion, a novel physicochemical composite inhibitor was developed in this work. CaCl2 was chosen as an inorganic salt physical inhibitor to compound with the chemical inhibitor melatonin (MLT) due to its corresponding good foam stability. When the mass ratio of CaCl2 to MLT was 4:1, the lowest CO release concentration of 7337.06 ppm at 200 °C was observed in the composite inhibitor-treated coal. Furthermore, the addition of 20 wt % of the composite inhibitor resulted in a foam half-life of 3067 min, which was 5.89 times longer than that of the water-based foam. In comparison with the water-based foam, the inhibitory foam based on 20 wt % CaCl2-MLT composite inhibitor exhibited more excellent foam stability, wetting ability, and inhibition performance. The release of CO at 200 °C was 7854.6 ppm, showing a reduction of 63.2% compared to the raw coal. Moreover, the composite inhibitory foam could significantly delay the onset of the characteristic temperature and reduce the weight change during the decomposition stage by 12.8%.

Preliminary Study of Carbonized Bituminous Raw Coal for Supercapacitor Electrode

Bituminous grade coal is a promising and cost-effective raw material for supercapacitor electrode application. Carbonization plays a crucial role in transforming the organic components present in raw coal into a carbon-rich structure with an enhanced capacity for charge storage. In this research, we study carbonized bituminous coal (CBC) as a preliminary evaluation of its electrochemical properties. The carbonized bituminous coal was synthesized through a simple heat treatment at temperatures of 700 and 900°C under a continuous flow of argon gas for 2 hours. The structural behavior of carbonized bituminous coal was analyzed using several characterizations, including x-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopy. Furthermore, the electrochemical properties were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge in a 3 M electrolyte solution of potassium hydroxide (KOH) with a three-electrodes configuration. The specific capacitances of 49.75 F g−1 and 20.00 F g−1 at a current density of 0.5 A g−1 were achieved for the sample produced at the carbonization temperature of 700 and 900°C, respectively. These values are considerably higher than the specific capacitance of raw bituminous coal (0.687 F g−1) at 0.5 A g−1. This result may offer valuable insight for the further development of coal-based supercapacitor electrodes.

Determination of Sulfur Content in Mineral Mass for Prediction of Hazardous Properties of Coal Mine Seams

Introduction. Sulfur is found in the organic and mineral parts of all types of solid fuels, and its concentration determines the extent of the hazardous characteristics of mine seams. Therefore, research on the determination of sulfur content in fossil fuels has not lost its relevance. The total sulfur content and its varieties has been studied in most cases in terms of the efficiency of fuel processing processes, the quality and environmental safety of coal products. Less attention was paid to the hazardous properties of mine seams, forecasting and developing preventive measures for endogenous fires in coal mines. This work aims to develop an engineering method to calculate the elemental sulfur content in the mineral mass of coal to predict the hazardous properties of mine seams.Materials and Methods. According to the results of the correlation analysis, we established how the sulfur content in the combustible part of the fuel depended on the total sulfur. We analyzed data on coals from almost all mine seams of the Donetsk and Lviv-Volyn coal basins. We presented the ash ratios for the formation and basin samples, as well as the information about the total sulfur and sulfur content in the combustible part. This allowed us to estimate the sulfur content in mineral impurities by calculation. The initial data for developing the method were taken from reference and regulatory documents.Results. Seven sets were considered, which included from 149 to 1827 mine seams. For each, reference and calculation data were summarized:- sulfur content — total (Std) and in the combustible part of the fuel (Sг);- conditional points for adjusting the indicators to avoid obtaining negative average values;- empirical equations that describe the calculated and corrected dependencies based on the ratio of Std and Sг;- correlation of these indicators;- ranges of change in ash yield.All this information was presented for clean and raw coals, for ash yields of more and less than 10%. In one case, satisfactory results were noted for determining the calculated sulfur content in a conditionally non-combustible mass. This was a set of 149 mine layers. For 13 of them, the difference in indicators (Std – Sг) was greater than or equal to zero. For 136 — less than zero. For 81, the sulfur content in the conditionally non-combustible part of the fuel Sн was less than zero. At the same time, there was a sufficient level of correlation (0.79) and a limited range of changes in ash yield (2.4–10). The empirical equation corresponding to this set was recommended for predicting the hazardous properties of mine seams with an ash yield of less than 10%.Discussion and Conclusion. The results of this study can be used to improve regulations for the safe conduct of mining activities, taking into account sulfur content in organic matter and in mineral impurities of fossil coal.

Correlation and stage change of key groups and thermal effects of spontaneous coal combustion due to long-term ultraviolet illumination

This study aimed to unveil the correlation between the changes in active groups and thermal effects during the spontaneous coal combustion under prolonged ultraviolet (UV) irradiation. In situ Fourier transform–infrared spectroscopy (FTIR) and microcalorimetry (C80) experiments were conducted. Thermodynamic analysis, Pearson's correlation analysis, and Grey Relational Analysis (GRA) were employed to analyze the raw coal (R0) and the coal after UV irradiation for 3, 6, 9, and 12 months (R3, R6, R9, and R12). The results indicated that UV irradiation promotes the generation of Ar-CH, –CC-, CO, and –OH, while causing the consumption of –CH3. This promoting effect gradually increases within the first 6 months and then diminishes after 6 months. A thermodynamic analysis revealed a consistent trend in the apparent activation energy during Stages I and II, where R0<R12<R3<R9<R6. This result suggests that UV exposure promotes coal–oxygen reactions. In the correlation analysis, it was observed that the key active groups for R0 and UV-irradiated coal are not consistent across different stages, with –OH and –CO identified as the key active groups in Stages I and II of UV-irradiated coal, respectively. The correlation between –OH and –CO exhibits a distinct stage-wise variation with prolonged UV exposure.

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal.

An acid solution improves the pore-plugging problem in hydraulic fracturing, which in turn improves the permeability of the coal seam. The study aimed to investigate the effect of mixed acid on the micronano mechanical properties and permeability of the coal seam. The surface morphology of acidified coal was analyzed from the micronano scale using atomic force microscopy (AFM) and scanning electron microscopy. Additionally, the micronano scale mechanical characteristics of acidified coal were examined using the mechanical mode in an atomic force microscope. Furthermore, the complexity and connectivity of the micronano pores of samples were investigated using the low-temperature nitrogen adsorption and mercury intrusion porosimetry methods and the fractal theory. The results indicated that the surface minerals of acidified coal were dissolved, loosening the coal and increasing the complexity of the pore structure. Mineral deformation and pore deformation weakened the mechanical properties of coal at the micronano scale, and the mean elastic modulus of acidified coal (B# and E#) decreased by 28.78 and 25.66% compared to that of raw coal. The acid solution effectively enlarged the pore diameter, transitioning from micropores to mesopores and macropores, and the total pore volume of acidified coal increased by 1.88 times and 1.25 times, Kn increased from 0.064 to 0.581 and 0.37, respectively. The type of methane diffusion in the diffusion pores changed from Knudsen diffusion to transition-type diffusion. The tortuosity of the pore structure of acidified coal decreased, the fractal dimension of the tortuosity of the pore structure decreased, and the permeability increased by nearly three times. The research results indicate that the mechanical properties of coal decrease after acidification and that the microstructural changes can promote methane migration (diffusion-seepage), which can provide theoretical guidance for coalbed methane extraction in low-permeability coal reservoirs.

Ecological environment quality assessment and spatial autocorrelation of northern Shaanxi mining area in China based-on improved remote sensing ecological index

The northern Shaanxi coal mining area is an important coal production base in China and an ecologically fragile area, and it is of great significance to explore the ecological environment quality and spatial evolution trend of the mining area. Based on Sentinel-2 and MODIS image data, an improved remote sensing ecological index was constructed by principal component analysis method: normalized difference vegetation index, normalized difference water index, normalized differential buildup and bare soil index, and net primary productivity. The ecological environment quality of the northern Shaanxi coal mining area and its influencing factors, as well as the spatial autocorrelation analysis of ecological environment quality, were discussed. The results showed that: 1) The vegetation coverage in the study area showed an overall increasing trend, but it was greatly affected by the average annual temperature. The NDVI index at the mine area is higher than the NDVI index at the non-mine area. 2) The water area gradually decreases with the year, which has a certain negative correlation with the total raw coal production. 3) The NDBB index showed a decreasing trend with the year, and compared with the non-mining area. 4) The coupling of year-by-year precipitation and temperature leads to interannual fluctuation of NPP value. 5) The change of ecological environment quality in the study area is the result of the comprehensive effect of natural factors and human factors. The implementation of ecological protection projects such as geological environmental protection and land reclamation in mining areas also has a certain impact on the trend of ecological environment quality. 6) There was a significant spatial autocorrelation in the quality of the ecological environment in the study area. There are significant “High-High” gathering areas of ecological environment quality within the coal mining area.

Three Decades of Oasis Transition and Its Driving Factors in Turpan–Hami Basin in Xinjiang, China: A Complex Network Approach

As a predominant ecosystem-providing area and distinctive landscape in arid regions, an oasis plays an important role in maintaining land stability, human production, and daily activities. Studying the dynamics of oasis and its driving factors is vital to supporting arid regions’ sustainable development. As a typical mountain–desert–oasis landscape, the Turpan–Hami (Tuha) Basin, located in Xinjiang, China, includes complex interactions among different land types. For this study, we revealed the spatio-temporal patterns and transition processes of the oasis using a complex network method between 1990 and 2020 in the Tuha Basin. In the oasis transition network, the degree value, betweenness centrality, and average path length were calculated to express the transition relationship, key oasis type, and oasis structural stability, respectively. Six factors related to climate change and human actives were selected to investigate the driving forces behind oasis transitions, including the average temperature and precipitation in the growing season, the total power of agricultural machinery (TAMP), the production of raw coal (PRC), the total output value of the plantation industry (TPI), and the population (Pop). Our results show that the oasis area of the Tuha Basin, including the natural oasis and artificial oasis, all grew from 1990 to 2020, with the natural oasis expanding more than the artificial oasis. The transitions between oasis types became more frequent as the area of oasis land types increased throughout the study period. Grassland acted as the most important oasis type in the network, with the highest betweenness centrality, but its importance declined due to the increasing complexity of the oasis transition network from 1990 to 2020. The transitions between oasis types became simpler, and the oasis structural stability decreased. Through driving force analysis, the oasis changes showed a positive correlation with the temperature (p-value &lt; 0.05, r = 0.88), and urbanization and industrialization factors prompted transitions to built-up areas and cropland from grassland and shrubland. In summary, our results suggest that to create a harmonious symbiotic relationship between the natural environment in dryland and human activities, preventing grassland degradation and excessive reclamation of land cover is an available way. Meanwhile, the protection of shrubland and water resources is also important. This study provided reference and theory support for promoting the sustainable development of oases.

Strength and microstructural analysis of geopolymer prepared with coal-based synthetic natural gas slag

PurposeThe coal-based synthetic natural gas slag (CSNGS) is a solid waste remaining from the incomplete combustion of raw coal to produce gas. With the continuous promotion of efficient and clean utilization of coal in recent years, the stockpiling of CSNGS would increase gradually, and it would have significant social and environmental benefits with reasonable utilization of CSNGS. This study prepared a new geopolymer by mixing CSNGS with PC42.5 cement in a certain mass ratio as the precursor, with sodium hydroxide and sodium silicate solution as the alkali activators.Design/methodology/approachThe formulation of coal-based synthetic natural gas slag geopolymer (CSNGSG) was determined by an orthogonal test, and then the strength mechanism and microstructure of CSNGSG were characterized by multi-scale tests.FindingsThe results show that the optimum ratio of CSNGSG was a sodium silicate modulus of 1.3, an alkali dosage of 21% and a water cement ratio of 0.36 and the maximum unconfined compressive strength of CSNGSG at 7 d was 26.88 MPa. The increase of curing temperature could significantly improve the compressive strength of CSNGSG, and the curing humidity had little effect on the compressive strength of CSNGSG. The development of the internal strength of CSNSG at high temperatures consumed SiO2, Al2O3 and CaO and the intensity of corresponding crystalline peaks decreased.Originality/valueMoreover, the vibration of chemical bonds in different wavenumbers also revealed the reaction mechanism of CSNSG from another perspective. Finally, the relevant test results indicated that CSNGS had practical application value as a raw material for the preparation of geopolymer cementing materials.

Orthogonal Experimental Study on the Ratio of Similar Materials of Coal Body

According to the coal samples collected from Zhaogu No.2 Coal Mine as raw coal samples, the similar materials of coal body were studied by using river sand, pulverized coal, Portland cement and calcium carbonate. The orthogonal test method of four factors (bone glue ratio, aggregate ratio, rubber ratio, water mixing rate) and three levels was used to obtain the physical and mechanical parameters such as density, uniaxial compressive strength, elastic modulus, cohesion, internal friction angle and tensile strength of coal similar materials. The range analysis method was used to obtain the key influencing factors and variation rules of the physical and mechanical properties of coal similar materials. Finally, the method of multiple linear regression analysis was used to obtain the similar material ratio that was most consistent with the mechanical properties index of raw coal. The ratio of calcium carbonate: cement: river sand: coal powder: water = 1: 5: 0.9: 5.9: 3.2. The density error, compressive strength error, elastic modulus error and cohesion error of coal sample and raw coal are small, which proves that the similar material is similar to the mechanical properties of raw coal, and provides guidance for subsequent research.

Heat Storage Using Solar Pond Technology and Post-Mining Brine – Preliminary Analysis

This paper presents an analysis of the feasibility of using solar pond technology for thermal energy storage, particularly using post-mining brine water. Solar ponds are not considered as a potential heat/cool storage technology for heating systems mainly because of the requirement to constantly supply the pond with fresh water and salt solutions, which involves significant investment and operating costs. On the other hand, brine water from the dewatering of deep mines is a by-product of the extraction of various raw materials, including copper, iron, non-ferrous metals, and coal. The treatment of these waters yields highly concentrated salt solutions, which, when combined with solar pond technologies, can lead to strong synergies. The article presents preliminary selected simulation results of the solar pond system and presents a proposal for its systemic use. A forecast of the potential energy, environmental, and socio-economic benefits of the technology is also presented.

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.