The rapid surge in global energy needs has paved way for the development of various alternatives to natural resources every now and then. However, dependence on coal-based energy has not reduced ...greatly. Thus, massive quantities of coal fly ash (CFA) are generated worldwide, which is a serious threat to ecology owing to constraints associated with its storage and disposal. There exists a pressing and ongoing need to develop new, and green product streams from CFA to reduce the threat to the environment. The present review begins with an emphasis on the generation, physicochemical properties, and potential dangers of CFA. Then, it focuses on impending applications such as synthesis of geopolymers (alternative to cement), silica aerogels (insulating materials), carbon nanotubes (carbon allotropes) for electronic devices, and the separation of radioactive isotopes as well as rare earth elements from CFA. Furthermore, the review analyses factors restraining the motive for effective management strategies that drives utilisation of CFA (either in raw and processed state) for new product streams. Finally, the review elucidates the role of CFA as an emerging input in delivering eco-friendly amenities and future derivatives.
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•Coal fly ash (CFA) as a cost effective source of aluminosilicate was discussed.•Reviewed literature pertaining the current utilisation options of CFA.•Thorough emphasis on the influential factors of synthesis procedures were presented.•The directions of future research with new product streams were proposed.•Challenges and opportunities of CFA were reported.
•Experimental methods of a 15-t experimental furnace and STA-FTIR were developed.•The entire process of 1st and 2nd coal spontaneous combustions was analyzed.•Temperature, mass, heat energy ...intensity, and gaseous products were investigated.•Functionalities of the microstructure in 1st and 2nd combustions were determined.
To investigate the entire process of first and second coal spontaneous combustion, a 15-t experimental furnace for coal spontaneous combustion and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy were employed. The process of experimental tests was as follows: First, coal temperature was increased from 31.0 °C (room temperature) to 452.7 °C without intervention. Second, the coal sample was cooled to approximately 90.0 °C in an anaerobic atmosphere. Third, air was supplied until the sample reached 418.0 °C. Finally, the coal was cooled again to 100.0 °C in an anaerobic atmosphere. The variations of temperature, mass, heat energy intensity, and gaseous products were investigated. The results indicated that the temperature change rate first increased and then decreased during the first and second coal spontaneous combustion. Compared with the first coal spontaneous combustion, the rates of temperature and mass loss change with a heating rate of 2.5 °C/min were higher at the combustion stage of the second coal spontaneous combustion, but the variations of the exothermic reaction rate and mass loss with other heating rates (5.0, 10.0, and 15.0 °C/min) were lower. The differences among CO, CO2, alkanes, and alkenes during the first and second coal spontaneous combustions were insignificant until 300.0 °C. However, the emission of CO and CO2 during the second coal spontaneous combustion was significantly higher than during the first coal spontaneous combustion, whereas the release of alkanes and alkenes was substantially weaker when the temperature was higher than 300.0 °C. Moreover, the amount of H2O during the first coal spontaneous combustion was higher than that during the second coal spontaneous combustion.
Coal spontaneous combustion (CSC) is the combustion of the outcrop or shallow part of a coal seam due to long-term oxidation or artificial factors. Because of the continuous development of surface ...cracks, oxygen is constantly transported to the high-temperature zone, promoting diffusion to the deep coal seam. This study independently established a semi-closed experimental system. Coal samples from Lu'an, Shanxi Province, China were selected as the research objects, and 15 points were established in the coal seam to probe the law of temperature change to determine the high-temperature zone. It further revealed the distribution law of oxygen and gaseous products in the high temperature region during CSC. Finally, various index systems were determined. The results show that CO, CO2, CH4, and C2H4 gas concentrations increased during the heating stage and decreased during the cooling stage. Furthermore, there are “mutation” processes and “delay” in the points between the same layers of various gases. The determination indices in the heating stage were φ(CO)/φ (CO2), Graham number, and Grignard fire coefficients R2 and R3. In contrast, the cooling stages were φ(C2H4)/φ (CH4), Graham number, and Grignard fire coefficients R1 and R2.
•The high temperature area in the entire process of coal fire combustion heating and cooling was determined.•The oxygen distribution characteristics in different stages of the combustion process were explored.•The change law of oxidation gas in the holistic heating and cooling stage of coal fire combustion was analyzed.•The coal fire index early warning parameters in three dimensions were determined.
•Anions determines the destruction of functional groups and desulfurization capacity.•Influence of acid radical electronegativity is smaller than van der Waals force.•Anion chain length is ...proportional to the destruction of FTIR structure parameters.•Thermodynamic evolution behavior of samples is mastered.
There is an urgent need for a green and efficient inhibitor to inhibit coal spontaneous combustion (CSC). Ionic liquids (ILs) have led to a growing interest because of eco-friendliness, sustainability, and excellent designable properties. Herein, we report some ILs, which are composed of EMIM+ cations and different anions (Cl–, BF4–, OAC–, OTf–). Anions show the characteristics of increased chain length and enhanced electronegativity of acid radical. The effect of the chain volume of anions and the strength of acidity on the microstructure of coal were measured by analyzing and comparing the changes of element morphology, Fourier Transform infrared spectroscopy structure parameters, and microcrystalline in this work. The results illustrate that with the increase of the anionic chain volume and the electronegativity of acid radical, the ILs appear the outstanding ability to destroy the lamellar diameter microcrystals and the structural abundance of aliphatic hydrocarbons of coal. With the enhancement of the electronegativity of anionic acid radical, the degree of reduction of CO and COO functional groups of coal and the ability of desulfurization rate are enhanced. The thermodynamic process demonstrates that the dry cracking temperature and ignition temperature can increase by 19.3 °C and 10.0 °C, respectively, resulting in coal may be inhibited during the oxidation. In additional, the thermal kinetic behaviors of samples were investigated by Starink models. Results indicated that the apparent activation energy of the inhibited samples can be increased from 51.96 kJ mol−1 of Un-tc to EMImBF4-tc 60.52 kJ mol−1 in the stages of thermal decomposition and combustion. The regular destruction characteristics of anions and cations on coal molecules to suggest hopeful prospects ILs as a novel and designable materials in the field of prevention CSC fire.
Three types of self‐prepared chemical dust suppressants (CDSs) were investigated for their inhibitory effects on nitrocellulose (NC) cloud dust explosion. The results revealed that NC is extremely ...sensitive to electric sparks and has a high explosion intensity. CaCl2‐CDS effectively increased the particle size to control fly dust substantially inhibiting dust cloud explosions. However, both Na2SO4‐CDS and MgCl2‐CDS exhibited poor abilities and even promoted explosion. Therefore, neither Na2SO4‐CDS nor MgCl2‐CDS is recommended as a CDS for NC. Inappropriately using CDSs may engender severe explosions. Furthermore, a mechanism underlying NC dust cloud combustion and explosion was proposed. NC has three stages of heat release: autoxidation, thermal decomposition, and combustion. Thermal decomposition, combustion, and explosion were triggered depending on the energy provided from autoxidation. CaCl2‐CDS inhibited only combustion. This study reveals the mechanism underlying NC dust cloud explosions and provides useful information for the development of more optimized CDSs.
Coal spontaneous combustion is characterized by high-temperature oxidation and microscopic mechanisms. These are essential aspects to understand when attempting to control or prevent spontaneous ...combustion. Three fresh bituminous coal samples were collected for experimentation from Huainan, China. X-ray diffraction and Fourier-transform infrared spectrometry were conducted to determine the microscopic characteristics of coal during high-temperature oxidation. The mineral structures and functional groups were ascertained to ensure that the original structural characteristics of the coals were obtained. Thermogravimetry–differential scanning calorimetry was used to divide the high-temperature oxidation into four substages and obtain detailed exothermic characteristics. The heat energy release exhibited a positive correlation with an increase in temperature.
Moreover, to investigate the relationship between the functional groups and their exothermic characteristics, correlation analysis was conducted for describing the quantitative phenomena within the four oxidation stages. The results revealed that the oxygen-containing groups were initially the most active and reactive among the 14 types of functional groups. The most rapid stage of spontaneous combustion, in which should be the most cautious and aware of risks, was the oxygen adsorption and mass gain stage because the heat energy output increased rapidly and passed this stage, thus leading to dangerous and possibly unrecoverable situations.
•TG-DSC was conducted to divide the high-temperature oxidation into four substages.•Fourteen types of functional groups were explored and elucidated in four substages.•Quantitative phenomena in four substages were described by correlation analysis.•Oxygen adsorption and mass gain stage were found as the critical stage.
In the mining of multiple coal seams, geological fracture may cause water from aquifers to accumulate in the overlying gob. Residual coal in the overlying gob after water immersion and air exposure ...is regarded as soaked coal, which is at a high risk of coal spontaneous combustion. In the present study, Fourier transform infrared spectrometry and synchronous thermal analysis were performed to investigate the active functional groups, characteristic temperatures, and exothermic properties of bituminous coal (selected due to its abundance in northwestern China) immersed in water for different durations (150, 180, 210, and 240 days). On the basis of reaction mechanism equations, two thermokinetic models were used to calculate the apparent activation energy (AAE) in different stages of coal pyrolysis. Results revealed that soaked coals were more prone to spontaneous combustion than raw coal (WW0) because of changes in the numbers of functional groups and characteristic temperatures. The critical soaking duration of 180 days increased the exothermic strength of coal to its maximum. The AAE of WW0 was higher than that of soaked coals in Stages 1 and 4 of coal pyrolysis, indicating that soaked coals were more likely to react.
•Functional groups of raw and soaked bituminous coal were analysed.•Characteristic parameters of raw and soaked bituminous coals were determined.•Bituminous coals soaked for 180 days had the highest exothermic strength.•The oxidation of soaked bituminous coals conformed to chemical reaction (n = 4).
Three commercial inhibitors were investigated for their suitability in preventing the spontaneous combustion of noncaking coal (NCC) and gas coal (GC), two coals of low metamorphic grades. ...Simultaneous thermal analysis, Fourier transform infrared spectroscopy, and kinetic analysis demonstrated that Zn/Mg/Al-CO3-layered double hydroxides (LDHs) and diammonum phosphate (NH42HPO4) both exhibited substantial inhibiting effects. Therefore, Zn/Mg/Al-CO3-LDHs and (NH4)2HPO4 may be used for the prevention of spontaneous coal combustion. The reaction mechanisms and kinetic models for NCC and GC mixed with inhibitors were also determined. Na3PO4 demonstrated poor inhibiting ability in NCC and GC and even promoted the combustion of GC. Therefore, Na3PO4 is not recommended as an inhibitor for NCC and GC. Finally, the results indicated that (NH4)2HPO4 and Zn/Mg/Al-CO3-LDHs can be used to decrease CO2 release, limiting the oxidation reaction of coal and attenuating greenhouse gas emissions. This study can serve as a reference for efforts to prevent spontaneous coal combustion and for the development of new inhibitors.
•Inhibiting ability of three inhibitors were determined.•Zn/Mg/Al-CO3-LDHs and (NH4)2HPO4 had an effective inhibiting ability.•STA method identified the inhibition mechanism of coal spontaneous combustion.•Inhibiting effects of inhibitors were determined by the dilution effects of oxygen.
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•Covid-19 pandemic consequences on the global energy sector examined.•AChances and obstacles of the shift towards clean energy.•Lessons, future tactics and policy ...consequences.•Current renewables status and roadmap to sustainable energy.•Investment approaches, and policy landscapes towards renewables.
The novel coronavirus (2019-nCoV) was extended to 213 countries globally by August 2021. The world has been threatened by rising infection rates and emerged as the catastrophic event in the field of health triggering the international emergency panic button. COVID-19′s sudden arrival wreaked havoc on the world economic picture, particularly in the energy sector. A steep drop in oil prices, as well as an imbalance in energy, was the result of strict travel restrictions, fewer transportation options, and people's fears of a flu pandemic. However, confined mobility and a drop in energy demand coated the environment with a silver line and drowned the nation's economic opportunities. Industrial transport, and not to mention every conventional energy-related thing, is completely devastated, but renewables were immunized. Wind, solar, hydrothermal, hydrogen, biomass-based energy systems were on high gear yielding maximum results in counterbalancing the demand–supply chain.
Moreover, the pandemic created an opportunity to showcase the importance of renewable energy and tackle the difficult emergency like now. In addition to this, the mindset of the investors was slowly fading away from conventional fuels and shifting towards renewable energy. However, it is too early to state the booming renewables at the moment, and no idea about its long-time survival. Thus, the present review gives a clear picture of the current status of fossils and renewables, the impact of a pandemic, energy investments, government policy standings, threats, and opportunities, and finally, the key takeaways avoiding energy scarcity in once a lifetime disaster situation.
To study the effects of particle size on gases emitted from weathered coal under high-temperature oxygen deficiency, we investigated the macroscopic spontaneous combustion characteristics of ...weathered coal with various particle sizes during high-temperature oxidation. The gas concentration obtained from weathered coal of different particle sizes through oxidation from normal temperature to 600 °C was tested using a self-developed high-temperature program experiment system, and the variation law of the indicator gas was analyzed. The thermokinetic parameters of weathered coal were calculated in four reaction stages. The results revealed the different experimental phenomena of the coal sample of each particle size. The temperature-increase rate of weathered coal with different particle sizes was presented as a growth trend, and a noticeable stage was observed during the growth process. The concentration of indicator gas neither increased nor decreased monotonically with the change in the particle size. A particle size of 3 mm was obtained as the critical particle size during the high-temperature oxidation of weathered coal. The experimental results provided a pivotal theoretical basis for the early prediction and scientific prevention of the spontaneous combustion of weathered coal during open-pit mining and shallow coal seams.
•The critical particle size of weathered coal in the process of high temperature oxidation was determined.•Effect of particle size on temperature rise rate of weathered coal was analyzed.•Characteristic temperatures of the weathered coal with different particle sizes were calculated.•Apparent activation energy of weathered coal with different particle size was compared.
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