Search

This contribution presents the results of structural investigations on the cured and high temperatures of three series of geopolymers. The specimens were synthesized at 80 °C from coal fly ash and three activators of variable composition based on sodium hydroxide and sodium silicate solutions. Structural and microstructural analysis was performed, especially using in-situ measurements of XRD patterns and IR spectra as a function of temperature. The cured compounds' phase content and compressive strength changed slightly depending on the starting chemical composition. All analyzed materials experience a mass loss due to water removal at 300 °C, followed by increased porosity from disintegrating compounds above 300 °C. Higher alkali content improves strength (400–600 °C) possibly due to nepheline formation. The amorphous phase gradually softens during heating, influenced by alkali content. Structural analyses were supported by model calculations of a number of aluminosilicate structures. The cluster analysis using the k-means algorithm was used to divide the PCA space into regions that represent structural similarities, and analyzing specific point positions in the space allowed for several conclusions to be drawn about the studied materials, including that changes in chemical composition and thermal treatment can promote the transformation from sodalite to nepheline and that the glass network has elements that are nepheline-like and may promote its crystallization. [ABSTRACT FROM AUTHOR]

Coal, extensively used in many countries across various industries, particularly as a fuel in the energy sector, poses significant environmental challenges due to process-related implications and their complex characteristics. A notable obstacle arises from its heterogeneous and complex submicron–nano-molecular structure, often leading to operational issues that are challenging to predict. This research aims to comprehensively assess the environmental impact of bituminous coal sourced from the Barapukuria Coal Mine (NW Bangladesh). This study focuses on elucidating the intrinsic properties of coal, with specific attention to its thermal behavior, structural composition, and surface morphology, aiming to understand the implications for energy production. Advanced techniques, such as TGA/DTG, CHNS-O, XRD, FTIR, XRF, ICP-OES, XPS, SEM with EDX, and TEM, were employed. Rigorous experimentation and analysis provided valuable insights into combustion and pyrolysis processes, illuminating the release of environmentally hazardous pollutants and their negative consequences associated with the utilization of Barapukuria coal for energy generation. Thermogravimetric analysis indicates coal bond breakdown at 573–933 K, releasing gases and liquids during the breakdown stage, resulting in mass loss from moisture evaporation, protogenic gas release, and volatile matter loss. Despite being of the bituminous type, the coal exhibits a mean carbon concentration of 78.24% and a low sulfur content of 0.42%, signifying relative environmental friendliness compared to high-sulfur coals, which is crucial for preventing acid rain. The average higher heating value (31.04 ± 0.74 MJ kg−1) and calorific value (30.20 ± 0.95 MJ kg−1) indicate that the studied coals have high energy potential. This study also suggests that optimizing thermochemical conversion for power generation may enhance energy efficiency and mitigate potential environmental impacts. The research findings contribute to the scientific understanding of coal thermal properties, serving as a foundation for informed decision-making in energy production strategies that prioritize both efficiency and environmental sustainability. [ABSTRACT FROM AUTHOR]

The spontaneous combustion period of coal in deep mines is short, so the risk of coal spontaneous combustion (CSC) is high, and it is cause environmental pollution. To explore the relationships between the microstructure and thermal effect of coal in deep mine, the relation among microstructure, activation energy and thermal effect of CSC was analysed using differential scanning calorimetry, Fourier infrared spectroscopy and synchronous thermal analyser, respectively. Results show that the process of coal self-combustion can be divided into 3 stages: the slow oxidation stage, accelerated oxidation stage and rapid combustion stage. In the slow oxidation stage, the XJL coal sample experienced the largest thermal release, and the main functional group was C–H–. In the accelerated oxidation and rapid combustion stages, the ZL coal experienced the largest thermal release; the functional groups are mainly C=C, –CH3, –CH2. In simpler terms, aromatic hydrocarbon significantly impacts the heating process of TK coal combustion. The structure of these hydrocarbons shows the highest correlation with the thermal release, followed by oxygen-containing functional groups for gas coal. These findings can help manage the risks of CSC and prevent potential dangers. [ABSTRACT FROM AUTHOR]

The char-CO2 reaction behaviour is important for oxy-fuel combustion of coal gangue and weathered coal or biomass. The thermal conversion characteristics of coal gangue, weathered coal, pine sawdust and their blends in CO2/N2 atmosphere were investigated using thermogravimetric analysis, focusing on the reaction behaviour of char and CO2. The results showed that the thermal conversion of coal gangue, weathered coal and pine sawdust all had two main stages, but pine sawdust had shorter time of thermal conversion. Mass loss of coal gangue/pine sawdust blends included two obvious stages with four overlapped peaks, which was different from coal gangue/weathered coal mixtures with two separated peaks. The addition of weathered coal or pine sawdust could improve the char-CO2 reactivity of coal gangue. However, the interactions were absent for all the coal gangue/weathered coal mixtures, and interaction between coal gangue and pine sawdust was obvious during the reaction of char and CO2, which was affected by the blending ratio of pine sawdust. [ABSTRACT FROM AUTHOR]

Pyrite is common in coal gangue formed in a reduced environment and has a significant influence on the recycling utilization of coal gangue. Four types of pyrite with different structures and morphologies, namely octahedral pyrite framboid, pentagonal dodecahedral pyrite framboid, irregular grain pyrite, and euhedral octahedral crystalline pyrite, were selected from coal gangue to study their thermal behavior and phase transformation processes during heat treatments in different atmosphere via high-temperature XRD, TG-DSC, SEM-EDS, and XRF. The results show that pyrite in coal gangue can be decomposed into pyrrhotite when heated in an inert atmosphere. Pyrites with different morphologies and structures exhibit distinct thermal behavior. The higher S/Fe ratio promotes the better crystallinity of pyrite and thus lowers the phase transformation temperature from pyrite to pyrrhotite. The thermal decomposition temperature of the sulfur-rich and well crystalline pyrites was approximately 600 °C, and the transformation temperature of sulfur-deficit pyrites to pyrrhotite was approximately 640 °C. The S release rate from the former two pyrites was also slower than that from the latter two. The pyrites can be oxidized to nano-hematite when heated in an air atmosphere at above 400–500 °C, with the transformation proceeding in the sequence of pyrite–nano-microsphere magnetite–nano-microsphere hematite. The nano-hematite aggregates had a pseudomorph of the original pyrite crystals. This study has great significance for the high-level recycling utilization of coal gangue, such as iron removal and direct material. [ABSTRACT FROM AUTHOR]

It is necessary to study the thermophysical properties and heat transfer mechanism of coal for underground coal gasification (UCG). The long-flame coal from Ningtiaota coal mine was pyrolyzed and oxidized at different temperatures (200, 250, 300, 350 °C in nitrogen, and 100, 150, 200, 225, 250, 275, 300, 325 °C in air), respectively. The influence of pre-treatment temperature and real-time temperature on thermal diffusivity, specific heat capacity, and thermal conductivity of coal was studied by laser-flash method. The results show that there are strong correlations between temperatures and thermophysical properties. During the real-time testing, with the rise of real-time temperature, the thermal diffusivity of different pre-treated coal decreases and the change rate gradually decreases. Meanwhile, specific heat capacity and thermal conductivity increase, and obvious stage characteristics are shown around 210–240 °C. Pyrolysis and oxidation can significantly degrade the thermal diffusivity and thermal conductivity of coal samples, and the degradation degree of oxidized coal is higher. The specific heat capacities of pyrolyzed and oxidized coal are normally higher than raw coal, and the effect of oxidation on the specific heat capacity increases with real-time temperature. The results can provide an important reference for exploring coal's thermophysical properties change mechanism during the process of UCG. [ABSTRACT FROM AUTHOR]

The salt gradient solar pond (SGSP) is used to store solar energy for low-temperature applications. This study investigates experimentally the density and temperature profile of Magnesium sulfate (MgSO4) in a trapezoidal-shaped SGSP. Four identical trapezoidal solar ponds were constructed by using plywood. The sides of the pond were completely covered with polythene sheets and given a black coating. The experiments were conducted using four identical solar ponds for seven days with different concentrations of magnesium sulfate and identified that the 16% concentration of MgSO4 (SGSP-M16) is the optimum concentration. Further, the experiment is extended to a 16% concentration of MgSO4 with coal cinder (SGSP-C). The temperature difference between the lower convective zone (LCZ) and upper convective zone (UCZ) is of about 13.7 °C and 17.6 °C for SGSP-M16 and SGSP-C, respectively. It is also observed that maximum temperatures of 54 °C and 59.1 °C in the heat storage zone for SGSP-M and SGSP-C, respectively. This higher temperature in SGSP-C is owing to the low volume heat capacity and low thermal diffusivity of the coal cinder. [ABSTRACT FROM AUTHOR]

The study of biomass is extremely important, aiming to discover the potential of alternative source that are capable of promoting the development of new technologies. The thermal behavior and chemical characteristics of the Capsicum waste from the use for the manufacture of sauces and condiments were investigated using thermogravimetric analysis, higher heating values, ignition (Ti) and burnout temperatures (Tb) and kinetic study using isoconversional models. Torrefaction and pyrolysis conditions were applied. Characterization based on ultimate and proximate analysis, gravimetric and gravimetric yield factor were also realized. Thermal analysis showed a biomass conversion between 150 °C and 500 °C. Proximate analysis identified an average volatile content of 46.5%, and carbon and fixed carbon were 22.3 and 31.1%, respectively. Gravimetric yield varied between 28 and 58%. Considering the intersection model, ignition and burnout temperature varied between 342–354 °C and 470–503 °C, respectively. The deviation model found an ignition temperature between 210 and 249 °C. Biomass proved to be a possible source of biofuel with a significant economic potential. [ABSTRACT FROM AUTHOR]

At present, inhibitors have been widely used in the field of coal fire prevention and control, but there are some defects in the use of them. So it is necessary to find a new practical and economical inhibitor. Dissolvable tiny-foam extinguisher (DTE) is environment-friendly, high in thermal stability, and fast in cooling. In view of the good performance of the product, the thermal behavior effects of DTE on coal spontaneous combustion were investigated through experimental tests. A scanning electron microscopy was used to study changes in the surface microstructure of raw coal after DTE treatment. Laser thermal conductivity analysis and simultaneous thermal analysis were used to test the effects of DTE at mass fraction of 0%, 5%, 10%, and 15% on the thermophysical properties, mass loss, characteristic temperature, and heat release of coal during heating. The surface of the DTE-treated coal sample was covered in a dense film. The treated coal sample had lower thermal diffusivity and thermal conductivity values and a higher specific heat capacity. Moreover, coal treated with DTE showed no obvious oxygen absorption or mass gain during initial heating, and the dry cracking temperature was greatly increased by 37 °C, 53 °C, and 100 °C, respectively. The initial heat release temperature increased by more than 170 °C, and the amount of the initial heat absorption was more than 52.2 times that of untreated samples. Oxidation kinetics were applied to calculate the activation energy of the coal during thermal decomposition and ignition, and the activation energies of the treated samples at the thermal decomposition and combustion stages increased by 161%, 179%, and 173%, respectively. From these results, we concluded that DTE could inhibit heat accumulation by blocking oxygen contact with the coal and greatly reducing heat release during heating. Besides, only a small quantity of DTE was needed to effectively inhibit coal self-ignition. These results provide reference for the field application of DTE in restraining coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

Sulfur-containing pollutants are released during coal thermal conversion processes and must be controlled to satisfy the requirements of industrial production and protect the environments. This study investigated the release behaviors of sulfur species in Zhundong (ZD) coal during combustion and gasification. H2O-washed ZD coal and Shenmu (SM) coal were also investigated as reference samples to compare with ZD coal and to obtain general release properties. The experiments were carried out using online thermogravimetric analysis coupled with mass spectrometry. Theoretical calculation of the released gas was obtained by a novel method and equivalent characteristic spectrum analysis. The mass flow rate, the release proportion and the release temperature range of individual sulfur-containing pollutant were evaluated. The results show that water washing process did not change the combustion reactivity and the sulfur release temperature ranges of ZD coal, but the maximum gasification rate and the SO2 release rate were decreased. H2S, COS and SO2 were observed in gasification of the coals, while COS and SO2 were observed in combustion. SO2 was always the main sulfur-containing gaseous product in both combustion and gasification. Some sulfur starts to release as SO2 at high temperature (at about 1000 °C for ZD coal and H2O-washed ZD coal, and at about 1100 °C for SM coal) due to the decomposition of sulfate, at which temperature carbon had already burned out in combustion, and the coal conversion in gasification reached about 90%. With combustion temperature lower than 1000 °C, the release of SO2 from ZD coal, H2O-washed ZD coal and SM coal can be decreased by 46.14%, 38.95% and 4.36%, respectively. With gasification temperature lower than 1000 °C, few SO2 from ZD coal and H2O-washed ZD coal and SM coal can be released. It was observed that the releases of sulfur species were related to their occurrence, reaction evolution, temperature and atmosphere. Controlling the temperature is helpful in reducing the release of SO2 in both combustion and gasification. This work also shows that it is possible to achieve high carbon conversion of ZD coal gasification at a moderate temperature and simultaneously reduce the release of sulfur. [ABSTRACT FROM AUTHOR]

The TG method is applied to eleven coal samples of varying rank collected from across the Jharia coalfield, India, to determine spontaneous heating susceptibility. Previous literature does not agree as to the TG experimental parameter that characterizes the spontaneous heating susceptibility of coal. A series of TG experiments were performed on triplicate samples of each coal to determine the susceptibility of coal to spontaneous heating. Each prepared sample had the following properties: mass–10 mg, size distribution − 212 µm, and was subjected to a sample gas flow rate of 40 mL min−1 and a balance gas flow rate of 60 mL min−1 under the following four different heating rates: 1, 5, 15 and 30 °C min−1. The study concludes that the heating rate of 5 °C min−1 should be used to determine the spontaneous heating susceptibility. The experimental data obtained are subjected to chemo-metric tools, i.e. principal component analysis and hierarchical clustering analysis to establish any linkage between the coal characteristics parameters and spontaneous heating susceptibility indices. These analyses reveal that the self-heating (Tsh) and ignition temperature (Tign) determined from the TG experiment results may indicate the susceptibility of coal to spontaneous heating, which is corroborated by well-established standard experiments as well as with field observations. [ABSTRACT FROM AUTHOR]

The influence of water immersion on the spontaneous combustion characteristics of anthracite with high concentrations of sulfur-bearing minerals was studied using simultaneous thermogravimetry–mass spectrometry (TG-MS), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. In addition, variations in the structural parameters, mass, heat release and gas evolution processes before and after water immersion were investigated. The results showed that the coal sample contained a large amount of pyrite (FeS2). After 45 days of immersion, the pyrite content in the coal decreased, and the infrared absorption peak of Si (Al)–O at 1116 cm−1 disappeared. The TG curves did not show a mass increase. Moreover, the initial reaction temperature of immersed coal was 39 °C lower than that of raw coal, and the heat release increased by 127.3 J g−1. The gas products in the samples varied mainly in quantity but not in species. MS and FTIR analyses revealed that SO2 was the main gas produced, and the maximum SO2 gas evolution temperatures of both coal samples were similar to the peak temperatures in the differential thermogravimetry and differential scanning calorimetry (DSC) curves. Furthermore, the infrared 3D spectrogram revealed that gas generated by immersed coal was detected at a lower temperature, the peak temperature occurred earlier, and the evolved intensity was stronger. [ABSTRACT FROM AUTHOR]

Mn-based solid oxygen carriers supported on MgAl2O4 were prepared by the microwave-assisted combustion method followed by wet impregnation of the active phase. The oxygen carriers were characterized by X-ray diffraction, temperature-programmed reduction and scanning electron microscopy with energy-dispersive spectroscopy of the surface. The study aimed to evaluate the influence of the thermal treatment on the structure and reactivity of the oxygen carriers. Reactivity tests using coal as fuel were carried out in a thermobalance at temperatures of 750–850 °C to evaluate the behavior of the carriers. The results revealed that oxygen carriers, which were subjected to only a heat treatment after the impregnation step (MnC1), showed more reactive surfaces presenting a greater number of non-reactive and irreversible phase and thus displaying lower oxygen transport capacity as well as poorer reactivity. The carriers prepared by heat treating the support after the combustion reaction and again after the impregnation step (MnC2), showed higher oxygen transport capacity and greater reactivity with coal at 850 °C. The better reactivity is associated with the formation of Mg6MnO8 and Mn2O3 phases. [ABSTRACT FROM AUTHOR]

In the process of multi-seam mining, the measure of water exploration is usually employed for the upper coal seam to prevent and control water accumulation. The residual coal immersed in water for a long time in the upper layer is dried under the action of air leakage, leading to the enhancement of the risk of coal spontaneous combustion. Therefore, it is necessary to study the water soaking–drying process (WSD) on the spontaneous ignition characteristics of coal. In this study, a laser thermal conductivity analyzer was used to investigate the changes in thermal properties of bituminous coal collected from mines in western China after WSD. The results show that compared with the raw (unsoaked) coal samples, the thermal diffusivity, specific heat capacity, and thermal conductivity of the bituminous coal are considerably reduced after WSD; the maximum reductions in the three parameters are 11.11%, 6.64%, and 12.39%, respectively. These reduced thermal parameters indicate that after WSD, bituminous coal is more prone to self-heating, resulting in an increase in the rate of coal–oxygen compound reactions and a significantly increased risk of spontaneous combustion. [ABSTRACT FROM AUTHOR]

Thermal behavior and chemical properties of selected raw and NaOH-pretreated rice husk varieties were investigated. NaOH-pretreatment process involved soaking 5 g rice husk samples in 40 mL of 2%w/v NaOH, shaking (400 rpm) and heating (50 °C) for 3 h. NaOH-pretreated samples were water-washed, oven-dried, and milled for use in the determination of their thermal behavior and surface functional groups. Alkaline wash-water was also analyzed for sugar components. Thermal decomposition temperatures, degradation rates, and the subsequent mass losses varied from one rice husk variety to another. These thermal properties increased after NaOH-pretreatment of the rice husk varieties, reducing their char yields (17.1–20.4% db). These changes mainly had to do with the lignin, hemicellulose, and ash removal from the rice husk varieties, as confirmed by their FTIR analysis, as well as by the sugar composition analysis of their alkaline wash-water. Consequently, the FTIR spectra differed between the raw and NaOH-pretreated rice husk varieties. [ABSTRACT FROM AUTHOR]

In order to further understand the effect of the water content on spontaneous combustion of coal, the thermal oxidative degradation kinetics of coals with different water contents were studied by Kissinger method, Flynn–Wall–Ozawa method, and Starink method. The results show that the water has no substantial effect on the thermal decomposition mechanism of the coal, and reaction orders are similar (n = 1) with different water contents. However, the activation energy Ea of coals has a certain relationship with the water content. When the water content of the coal is less than 6.0 mass%, with the increase of the water content, the activation energy Ea decreases. With the water content of coal exceeding 6.0 mass%, the activation energy Ea is increased with the increase of the water content. The change tendency of activation energy Ea is consistent with the mass increase of coals in the coal oxidation stage, which means that lower activation energy Ea is easier to make spontaneous combustion of coal. From this study, we hope to provide an efficient method for further understanding the mechanism of the water influence on spontaneous combustion of coal. [ABSTRACT FROM AUTHOR]

Coal-field fire results in much loss of resource and severe harm for human beings. In order to investigate the oxidation and heat transfer characteristics of coal-field fire under axial compression, the coal samples were heated and loaded by stress within axial compression equipped with a temperature-programmed device. Considering the heat generating rates over temperature in temperature-programmed (TP) device, both the critical temperatures Tc and Tg were obtained to divide the process of TP under axial compression into three stages. (Here, Tc is the critical temperature, it indicates that the coal begins to undergo an intense oxidation reaction. Tg represents the burnout temperature, as the temperature reaches Tg, the oxygen supplied to the furnace is almost exhausted and then fuel molecule of coal reacts with oxygen slowly again.) Stage I (less than Tc) represents the process as the temperature of coal increases slowly, Stage II (Tc ~ Tg) the temperature of coal rises rapidly, and Stage III (more than Tg) the temperature of coal combusts steadily. In Stage I, the smaller the apparent activation energy of coal, the lower the critical temperature Tc. The apparent activation energy of coal is the smallest as the axial compression reaches the critical axial compression (4 MPa), and the thermal conductivity of coal decreases with the increasing temperature. In Stage II, the smaller the apparent activation energy of coal, the lower the Tg, and the thermal conductivity of coal goes up and down as 2, 4, 6 and 8 MPa were loaded in turn. Generally, the results show that the average oxygen consumption rate of coal increases as the porosity increases, while the average porosity of coal increases linearly with the decreasing axial compression. Furthermore, the thermal conductivity changes as a cubic function with the increasing axial compression. The results would be meaningful to explain the spread of coal-field fires and provide guidance for the on-site prevention and control for coal-field fires. [ABSTRACT FROM AUTHOR]

Coal spontaneous combustion (CSC) is a global, long-standing thermal hazard in coal mining that causes serious environmental damage, particularly in developing countries. Ionic liquids (ILs) are environmentally friendly, green, economical, and a new type of fire-preventing material that inhibits coal oxidation and alleviates thermal production. In this study, 1-butyl-3-methyl imidazole tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methyl imidazole ([BMIM][I]) at various mass ratios (0.0, 0.5, 2.0, 5.0, and 10.0 mass%) were used to treat three types of coal (lignite, 1/3 coking coal, and anthracite) for CSC. The combustion-mass loss and thermal release rate of ILs treated relative to untreated coal samples were investigated using a synchronous thermal analyzer, and the optimal addition mass ratio of ILs was predicted. Not only do ILs have the most efficient inhibiting effect, but they also consider the economic benefit. Per thermogravimetric-differential scanning calorimetry, for the content of 5.0 mass% [BMIM][BF4], the inhibiting effect is favorable for universal applications. In addition, coal samples treated with 5.0 mass% [BMIM][BF4] were subjected to programmed-temperature heating experiment testing. The oxygen consumption rate, inhibiting effect, as well as apparent activation energy, were determined. The inhibiting effect at 120.0–150.0 °C was the most obvious, which provided the basis of the application for CSC prevention. [ABSTRACT FROM AUTHOR]

In this work, the pyrolysis characteristics and release of sulphur contaminant were studied under different mass percentages (25%, 50% and 75%) of Zhundong coal in the sample mixtures. The results showed that the yields of volatile products during co-pyrolysis were higher than those calculated from linear combination of corresponding yields of pure sludge and Zhundong coal, which mean that a certain synergistic effect occurs in co-pyrolysis process. The yields of H2S, COS and SO2 decreased with the increase in the content of Zhundong coal in the samples. What's more, when the content of Zhundong coal were 50%, a great significance on the yields of sulphur contaminant occurs in the process of co-pyrolysis. [ABSTRACT FROM AUTHOR]

Thermal stability, structural peculiarities and thermal destruction of functional groups of the matrix, which are responsible for the stabilization of the nanosystems, of the gold- and silver-containing medicinally important water-soluble nanocomposites synthesized from therapeutic humic substances, isolated from brown coal of Baga Nuur field of Mongolian sources, have been studied. A crucial problem in biomedical and engineering application of the silver- and gold-containing nanocomposites is their stability upon heating, for example, during sterilization at high temperatures in medicine or laser action, which can heat a system, in plasmon technologies. All compounds have been investigated by complex modern physical–chemical methods (electron paramagnetic resonance and infrared spectroscopies, X-ray diffraction analysis, transmission electron microscopy and others). Thermal analysis of Ag0 and Au0 nanocomposites on the basis of humic matrices, as well as the initial humic substance, has been carried out. It is shown that the thermal decomposition of the nanocomposites depends on the nature of the metal. It is found that stable zero-valent nanoparticles of noble metals with an average particle size of 6–17 nm are formed in a natural matrix. The nanocomposites obtained are aggregatively stable for a long time, preserving their properties intact, that is extremely important for promising medicinal substances. [ABSTRACT FROM AUTHOR]