Raw Coal Research Articles

Study on the influence of coal on coal-to-ethylene glycol process considering the integration of reactor, distillation column, and heat exchanger network

The ethylene glycol (EG) process has low energy efficiency and high emissions. The raw coals purchased from different mines have different compositions and affect the reactor/column parameters and the integration of the heat exchanger network (HEN). An integrated reactor-distillation column-HEN model is built for optimizing the coal-to-ethylene glycol (CTEG) process considering the variation of raw coal. The particle swarm optimization (PSO) algorithm is used to solve this model and target the optimal raw coal for the CTEG process based on the interaction of MATLAB and Aspen Plus software. The influence of raw coal is obtained based on the sensitivity analysis performed for key reactor parameters and energy consumption. For the identified optimal raw coal, the mass fraction of carbon, hydrogen, oxygen, and ash are 84.02%, 6.80%, 1.00%, and 5.00%, respectively; the water added in the coal-water slurry is 62.15 t·h−1, and the water-gas ratio is 0.32, the corresponding energy consumption and the CO2 emission per unit product are 0.093 kgce⋅kmol−1 and 0.247 kgCO2⋅kmol−1, both decreased by 32.61%. The proposed method can be used to optimize the design and operation of the CTEG process and extended to optimize the other coal-based processes to achieve cleaner production.

Experimental Study on the Improvement of Char Physicochemical Properties and Reactivity by Activation Process in CFB.

Solid carbon can be transformed into activated char with higher reactivity through the activation process in a circulating fluidized bed (CFB) to improve the Boudouard reaction. A new technology for reducing CO2, the activated-reduction technology, was proposed. In order to investigate the influence of relevant parameters (carbon dioxide addition, oxygen concentration, and O2/C) of the activation process on the physicochemical properties and reactivity of activated char, the experiments were carried out on a bench-scale CFB. The relationship between the parameters and the reactivity of activated char is explored. The result shows that compared with the raw coal, the pore structure of activated char is developed, the number of active sites increases, the degree of graphitization decreases, and higher reactivity is possessed. For the activation process, less of the O2/C and moderate oxygen concentration promote the increase in activated char reactivity, which is conducive to the reduction of CO2. The results of the correlation discussion show that the reactivity is difficult to be characterized by a single simple parameter. The reactive specific surface area (RSSA) obtained by multiplying the mesoporous specific surface area and I D3+D4/I all has a good effect on describing the reactivity.

Pyrolysis of shenmu coal to prepare blue-coke used as reductant

Blue-coke is a form of granular char prepared by medium-low temperature pyrolysis of low-rank coal. As a reductant, it has been widely used in calcium carbide production, ferroalloy, copper pyro refining, and ferrosilicon production in China due to the abundant reserves of raw coal and its excellent performance. However, there is little research on the pyrolysis process of granular coal to produce blue-coke and its characteristics as a reductant. Thus, the effects of pyrolysis temperature, heating rate, particle size and holding time at the final temperature on blue-coke preparation were investigated in a rotary kiln reactor. The quality index of blue-coke as a reductant and its properties, including the element composition, surface function groups, carbon forms, reactivity and lower heating value under different pyrolysis temperatures, were analyzed in detail. It is demonstrated that the pyrolysis temperature had a more significant impact on the quality of blue-coke compared to other pyrolysis conditions. With the rise of pyrolysis temperature, the blue-coke’s C/O and C/H increased. With the particle size and heating rate increased, the temperature gradients developed within the granular coal during the pyrolysis process led to the volatile release shifting to higher temperature zone and more secondary reaction occurrence. Nevertheless, the secondary reaction was restrained in the rotary kiln with good heat and mass transfer. The indexes of blue-cokes as reductants were met by the chars produced at temperatures from 550 oC to 750 oC with a holding time 60 min at this temperature and a heating rate of 10 oC/min. As the key index of blue-coke, the electrical resistivity decreased with the increase of pyrolysis temperature. It was found to be closely related to the removal of H and O heteroatom at the pyrolysis temperature below 700 °C. While at the higher temperature, the development of graphitized carbon structure took a major role on it. Nonetheless, the crystallite sizes of the blue-coke obtained under this low temperature pyrolysis were small and the carbon forms were turbostratic. These resulted in the blue-coke's high combustion reactivity, which would gradually decline with the rise of pyrolysis temperature.

Effects of inorganic sodium on the soot generation of coal particle: Insights with PLIF and DFT calculation

Inorganic sodium in low rank coal exerts significant influence on the soot generation in the early stage of combustion. The effect of inorganic sodium on the PAHs, soot formation and OH generation of coal particle was investigated on a concentrating light heating platform using Planar Laser Induced Fluorescence (PLIF) of OH radicals and PAHs. The generation characteristics of PAHs during coal particles pyrolysis with the temperature of 500 °C and 800 °C were also investigated. Raw coal, acid-washed (AW) coal and AW impregnated with different mass ratio of NaCl (1 %, 3 % and 5 % NaCl-loaded) were studied. Theoretical calculations using density functional theory was performed to explore the effect of sodium on the conversion of small molecule to macromolecular substances during early coal combustion. The results showed that the NaCl addition inhibited the OH radical and soot generation in the early stage of coal combustion, as demonstrated by the reduced OH intensity, and decreased soot intensity by observing the flame luminosity for the NaCl-loaded coals, compared with AW coal. Simultaneously, the PAHs generation was significantly reduced for NaCl-loaded coals, both at the early stage of coal combustion and under pyrolysis conditions, compared with AW coal. The quantum chemistry calculation revealed that the formed C-Na structure enhanced coal structural stability, making the chemical bonds less prone to cleavage, thereby inhibiting the volatile and PAHs release during the early stage of coal combustion. On the other hand, the released Na+ can catalyze the addition reactions of small ring PAHs (naphthalene, naphthalene derivatives) to larger ring PAHs (phenanthrene, pyrene), which would promote the PAHs and soot generation in homogeneous reactions, explaining the highest PAHs with 3-to-5 rings for 5 % NaCl-loaded coal among NaCl-loaded coals. The above two kings of reaction pathways were related to soot formation, but considering the results of reduced soot yield after NaCl addition, the former dominated. Furthermore, the results from the two pathways also illustrated that the Na inhibit the OH formation, which was corresponding to the decreased OH intensity for NaCl-loaded coals, as detected by OH-PLIF, and thus was detrimental to soot consumption. Therefore, the presence of Na in the early stage of combustion inhibited the release of volatiles and PAHs, which was the main reason for the decreased soot generation amount of NaCl-loaded coal.

Efficient production of activated carbon with well-developed pore structure based on fast pyrolysis-physical activation

As the most commonly used method for industrial activated carbon preparation, physical activation is usually accompanied by significant loss of raw materials, especially when the pore structure of activated carbon is well developed. This not only reduces yields, but also increases costs. To enhance both yield and pore structure of activated carbon, we proposed a facile and scalable method called "fast pyrolysis-physical activation". After fast pyrolysis, although the initial pore volume of the semi-coke decreases, the rapid release of volatiles promotes the increase of mesopore and macropore volumes and the development of micron-scale cracks, which is beneficial for CO2 mass transfer and reduces diffusion resistance. Therefore, compared to slow pyrolysis, the activated carbon produced through this method has a higher pore volume (increased by 25.9 %–30.0 %) and a larger SBET (increased by 26.7 %–38.3 %), while the yield remains almost unchanged. Consequently, due to the increase in pore volume and high yield of the activated carbon, the CO2 adsorption capacity (25 °C, 1 bar) of ACB-K700 increases from 2.02 mmol/g to 2.37 mmol/g compared to ACB-M700, and the total CO2 adsorption capacity of activated carbon prepared from the same mass of raw coal (1 g) increases from 1.07 mmol to 1.16 mmol. Due to the pre-formed pores inside the semi-coke, the gas activator molecules are able to penetrate deep into the particles, which not only reduces the ineffective etching that occurs on the surface, but also promotes the development of pore structure. In conclusion, this study provides a new pore development model for physical activation, and also provides a new method to produce activated carbon rapidly and massively, while the pore structure is well developed.

The Response Characteristics of Pore Volume and Specific Surface Area of Different Phases of Carbon Dioxide Injection into Anthracite Coal Pores

After the coal sample reacts with CO2, the porosity and pore volume change. Compared with dry raw coal sample, the porosity of coal after CO2 adsorption is increased. With the increase of CO2 injection pressure, the porosity of coal will gradually increase, especially when CO2 enters the supercritical phase. In terms of pore capacity of coal samples, CO2 adsorption time, CO2 adsorption pressure and CO2-H2O treatment do not show obvious regularity in the changes of pore capacity of coal samples, but in general, the increase of CO2 adsorption pressure and CO2-H2O treatment have a positive effect on the increase of pore capacity of coal samples, especially ScCO2-H2O. The mesoporous pore capacity increased by 137.1%. In terms of macro pore volume of coal sample, the change of macro pore volume after CO2 adsorption is more regular. Extending CO2 adsorption time, increasing CO2 adsorption pressure and CO2-H2O treatment all have positive effects on the increase of macro pore volume of coal sample. Under 8MPaScCO2-H2O, macro pore volume reaches a maximum of 0.016462ml/g. The increase also reached 130.4 percent. On the mesoporous specific surface area of coal sample, increasing CO2 adsorption pressure, prolongating CO2 adsorption time and CO2-H2O treatment can increase the mesoporous specific surface area of the sample. The mesoporous specific surface area of the sample at 8 MPa ScCO2-H2O is 0.631 m2/g, which reaches the maximum in this experiment, with an increase of 334.27%.

Occurrence of Differences between Alkali and Alkaline Earth Metals (AAEMs), Including Sodium, Potassium, Calcium, and Magnesium, in the Maceral Groups of the Xiheishan Coal, Zhundong Coalfield, Xinjiang, China

This study investigated the differences and correlation between the occurrence characteristics of alkali and alkaline earth metals (AAEMs) among different maceral groups in high-alkali, high-inertinite coal, and provides scientific guidance for the co-separation of AAEMs and inertinite groups in Xinjiang coal. The total AAEMs of inertinite-enriched samples were significantly higher than those in raw coals and vitrinite-enriched samples. Five-step sequential extraction showed that Na mainly occurs as water-soluble sodium (Na-Water) in raw coal and inertinite-enriched samples, accounting for about 53% of the total content, while it exists as organic sodium (Na-NH4Cl and Na-EDTA) in vitrinite-enriched samples, accounting for about 52% of the total content. Ca and Mg are both mainly present in organic form (Ca/Mg-NH4Cl and Ca/Mg-EDTA) in all the samples, with slightly higher proportions present in vitrinite-enriched samples. The contents of K are low in all the samples, which exist in an insoluble state (K-I). Combined microscopy and SEM-EDS analyses have revealed that the localized enrichment of Na in raw coal and inertinite-enriched samples occurs in the inertinite cell cavity, which primarily exists as NaHCO3 combined with quartz crystals, with a maximum content of up to 5.85 wt%. In this study, although EDS spectra could not directly characterize organic Ca and Mg, dolomite and calcite minerals were repeatedly found in the inertinite cell cavity. Moreover, the contents of Ca and Mg in the vitrinite-enriched samples were significantly lower than those in the other samples, which suggests that Ca and Mg are enriched with the inertinite groups. The localized enrichment of AAEMs could not be detected in any of the vitrinite-enriched samples. In summary, though there are significant differences between the occurrence modes of AAEMs in different maceral groups of high-alkali coal, AAEMs have a strong affinity with inertinite, which may be due to the inertinite’s abundant pore structures.

Ecological risk assessment of heavy metals in coal gasification slags and their leaching toxicity

ABSTRACT The coal gasification process produces a large amount of coal gasification slag (CGS), which accumulates heavy metals from the raw coal. The CGS not only occupies land resources during long-term storage but also poses potential ecological pollution risks. In this study, eight different CGS samples from various regions of China were analyzed to determine their chemical composition and evaluate their environmental risks. Two leaching methods recommended by the Ministry of Ecology and Environment of China were employed to conduct leaching experiments, aiming to assess the hazardous waste level of CGS. The results indicated that the risk index of YL-FS and XJ-CS reached 101.87 and 87.15, respectively, classifying them as medium-risk materials. The remaining samples were categorized as low-risk materials. CGS itself is not classified as hazardous solid waste. The leaching results revealed that the concentration of Be in the leaching solution of NMG-CS and XJ-CS exceeded 0.005 mg/L, placing them in Class II of general industrial solid waste. The remaining samples exhibited minimal leaching toxicity and were classified as Class I general industrial solid waste.

Fire zone forefront residual tar combustion characteristics and functional group transformation mechanism: Appling the based on thermogravimetric and in-situ high-temperature FTIR

When preventing spontaneous combustion disasters in extinguished coal fire zones, the influence of the tar re-ignition phenomenon is often overlooked. Therefore, in this study, using thermogravimetric analysis and high-temperature (630 °C) in-situ infrared technology, the combustion reactivity and real-time evolution mechanism of key functional groups for tar were deeply discussed under oxygen-lean conditions. Additionally, a novel two-step baseline drift correction method for spectral graphs at high temperatures is proposed. The results showed that tar combustion could be divided into two stages: pyrolysis-volatilization mass loss and crosslinked structure oxidation combustion. Reduced oxygen concentration limits the violent and stable rapid combustion of tar-crosslinked structures and reduces the re-ignition tendency of tar. Among, with a decrease in oxygen concentration, H (burnout performance), Cb (the reaction ability in the early stage of ignition) and S (overall combustion performance) decreased, while Ti (mass loss endpoint temperature), Th(burnout temperature), and HF (combustion stability) increased. This provides information for the selection of a reasonable process to prevent tar re-ignition. The contents of methylidene and aldehyde carbonyl in tar increased by approximately 2 and 3.7 times, respectively, compared to those of raw coal. In the first thermal decomposition stage of tar, the aromatic hydrocarbons were relatively stable under the action of the structural framework, whereas aliphatic hydrocarbons continued to decrease. Before burnout, a decrease in oxygen concentration increased the crosslinking ability of tar and delayed the tar burnout process. The contents of aromatic hydrocarbons and aldehyde groups are highly sensitive to the evolution of the oxygen concentration. Specifically, the Kubelka–Munk value of the aromatic hydrocarbons increased from 0.015 to 0.10, while that of aldehyde carbonyl groups increased from 0 to 0.23. Additionally, in the early stage of tar combustion, the volatile mass loss was basically not affected by the time-scale effect, and mass loss endpoint residual mass was approximately 48.11 %. In the later stage of tar combustion, owing to the cumulative of time-scale effect, the tar re-ignition tendency increased, H, Cb, and S increased, and HF decreased from 1.388 to 1.098. This research is helpful guiding disaster prevention and control of tar re-ignition in a fire area, which leads to reburning in the surrounding area.

Influences of clean fracturing fluid viscosity and horizontal in-situ stress difference on hydraulic fracture propagation and morphology in coal seam

The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.

Study on coal pulverization characteristics and gas desorption mechanism based on impact crushing experiment

The coal's particle size distribution properties after pulverization and the gas desorption behavior driven by pulverization are of profound meaning to the study of coal and gas outburst mechanism. In this paper, based on the impact crushing experiment, the tectonic coal and primary coal are crushed under different impact energy conditions. After screening the broken coal, the particle size distribution law is analyzed, and the characterization function suitable for the particle size distribution of coal particles after crushing is determined. The relationship between crushing work and new surface area and fractal dimension of coal body is discussed. The consequences indicated that the mass proportion of tectonic coal below 0.074 mm particle size is much huger than that of raw coal. G-S, R–R, and fractal distribution model describe the best particle size distribution of the two coals in the scope of 0.074∼4 mm. The new surface area added increases with the crushing work, and the tectonic coal is 1.34–1.96 times that of the raw coal. The fractal dimension diminishes first and then increases with the crushing work ratio. In addition, the gas desorption amount of coal particles with different particle sizes after coal pulverization was measured, and a dynamic model suitable for coal pulverization-driven gas desorption was established, and the experimental results were verified. The research results of this paper can provide experimental and theoretical basis for the analysis of energy dissipation in coal and gas outburst.

Research on prediction of coal water medium separation effect based on multi-models

To improve the separation efficiency of raw coal and ensure clean use, the accurate calculation of the partition coefficients (PCs) in coal water medium sorting is required. Single models have been used to predict the partition coefficient (PC) for decades, but their accuracy remains constrained. This study proposes a multi-model (MM) calculation method based on the Gompertz model (GM), the Logistic model (LM), the Arctangent model (AM), and the Approximate formula (AFM) to improve the accuracy of the predicted coal water medium sorting PCs. Four groups of coal samples and two specific cases were used to verify the accuracy of the MM calculation method. The PCs of the MM method had a minimal Ef (0.91–8.84), a maximal R2 (0.9648–0.9994), a maximal F-value (199.17–11352.31), and the highest significance of all the models. The MM method was found to be the most suitable of all the models for predicting any coal water medium separation process. Further, when calculating the PC for cleaned coal ash, the separation density of MM is closer to the actual separation density than that of either the GM, LM, AM, or AFM models. The MM method, therefore, produces more accurate results compared to a single model. MM is expected to predict the PC based on the required cleaned coal ash, and then regulate the sorting density to improve the production efficiency.

Influence of mudstone on coal spontaneous combustion characteristics and oxidation kinetics analysis

To explore the spontaneous combustion characteristics and hazards of the low-temperature oxidation (LTO) stage in the process of spontaneous combustion of coal and mudstone, the pore structure, spontaneous combustion characteristic parameters, and exothermic characteristics of coal and mudstone were tested and studied, and the oxidation kinetic parameters were calculated. The results show that mudstone has a larger specific surface area and pore volume than coal. From the fractal characteristics, the pore structure of mudstone is more complex than that of coal. According to the comparison of theoretical and actual gas generation and oxygen consumption rate curves, it is found that there is an interaction between coal and mudstone in the LTO process. With the increase of mudstone mass ratio, gas production, and its oxygen consumption rate increase. Among them, CM-4 (Coal:Mudstone = 1:1) has the highest exothermic intensity and the exothermic factor (A) and fire coefficient (K) increase with the increase of mudstone content. The apparent activation energy of the mudstone sample is lower than that of the raw coal, indicating that the sample after adding mudstone is more likely to have spontaneous combustion in the LTO stage.

Design and study of mine silo drainage method based on fuzzy control and Avoiding Peak Filling Valley strategy

Coal is a non-renewable fossil energy source on which humanity relies heavily, and producing one ton of raw coal requires the discharge of 2–7 tons of mine water from the ground. The huge drainage task increases the cost of coal mining in coal mines significantly, so saving the drainage cost while guaranteeing the safe production of coal mines is a problem that needs to be solved urgently. Most of the fuzzy controllers used in the traditional dynamic planning methods applied to mine drainage are two-dimensional fuzzy controllers with limited control effect, so the traditional two-dimensional fuzzy controllers are improved by introducing the rate of change of gushing water to form a three-dimensional fuzzy controller with three-dimensional control of instantaneous section—water level—rate of change of gushing water, and at the same time, the optimized dynamic planning method is designed by combining the Avoiding Peak Filling Valley strategy and the optimal dy-namic planning method is used in conjunction with the un-optimized dynamic planning method. The optimized dynamic planning method is applied to the same coal mine water silo gushing water experiments; experimental comparison found that the pumping station system before the optimi-zation of the electricity consumed is 52,586 yuan/day, while after the optimization of the electricity consumed is reduced to 41,692 yuan/day, the cost per day consumed compared with the previous reduction of 20.69%, a year can be saved 3,969,730 yuan. Therefore, the mine water bin drainage method based on fuzzy control and Avoiding Peak Filling Valley strategy proposed in this paper can be used as an improvement method of the existing mine drainage method, which can further ex-pand the economic benefits of coal mines and realize safe production while realizing cost savings.

Catalytic influence of iron oxide (Fe2O3) on coal pyrolysis and char combustion at various temperatures

The conversion of coal into cleaner energy forms is essential for achieving sustainable development. This study investigates the role of Fe2O3 as a catalyst in enhancing the efficiency of coal pyrolysis and char combustion. A fixed-bed tube furnace (TF) was selected for pyrolysis, and a Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectroscopy (TG-FTIR) was used for combustion analysis. The produced syngas and tar were characterized using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC/MS). Our results show higher volatile release volume (VRV) from coal with catalyst compared with without catalyst and the rise with temperature within the 600–1000 ℃ range. Although hydrogen production decreased with the addition of the catalyst, at 1000 ℃, the catalyst's impact was negligible. The catalyst notably facilitated the breakdown of heavy aromatic rings in tar, eliminating triple-bond aromatic structures. In contrast, tar from raw coal exhibited a 20% yield of such structures. Scanning Electron Microscopy (SEM) revealed a cubic structure of Fe2O3 in char, with an increased surface area compared to raw coal char (338.75 m2/g vs. 313.51 m2/g). TG-FTIR analysis indicated a lower activation energy for catalysts with char combustion. Overall, Fe2O3 improves tar structure, increases char surface area, and lowers activation energy.

Optimization of CO2/N2 injection ratios in goaf by saturation adsorption capacity

The inerting technology is a common means to prevent fires in goaf of coal mine, in which adsorption capacity is the key index to measure the inerting effect. Therefore, this paper obtained the coal spontaneous combustion (CSC) stage of Qianyingzi coal mine through programmed heating experiments, and determined the physical adsorption stage temperature (below 323.15 K) matching the actual environment. The oxidation characteristics of coal samples with different adsorption degrees were further studied by adsorption experiment and TG-DSC test. The results indicate that the combustion activation energy of coal samples follows the sequence of second-stage adsorption coal > dried coal > raw coal > first-stage adsorption coal. This implies that the CO2 saturated adsorption can exert a specific inhibitory impact on coal combustion. Therefore, the index of the saturation adsorption capacity (SAC) was proposed to evaluate the inerting effect. We further studied the adsorption capacity of coal at different ratios of CO2/N2 by molecular simulation under different pressures (0–5 MPa). The results show that CO2 dominates in both single-component adsorption and competitive saturated adsorption. The average of ratios (AOR) and average of differences (AOD) threshold are determined. The priority of SAC is obtained in the order of single-component (CS), CO2/N2 mixture ratio at 4:6 (C4:6), CO2/N2 mixture ratio at 2:8 (C2:8) from largest to smallest. Furthermore, a fuzzy optimization method for injection ratio of CO2/N2 under different pressures was established. During dynamic changes in environmental pressure, it is appropriate to inject CO2 separately at 0.2–2.5 MPa. At 3 MPa, a mixture of CO2/N2 at a ratio of 2:8 is the best for prevent fires in goaf. Similarly, an inert gas with a CO2/N2 ratio of 4:6 is injected at 3–5 MPa.

A novel gas injection method with swirl flow in underground gasification for improving gas production and controlling pollution yields

Underground coal gasification (UCG) is a promising technology, which can convert deep coal seams into high calorific value gas products through in-situ controllable combustion, for the traditional coal mining technology. However, the structure of raw coal is dense, and it is difficult for the injected gasification agent to penetrate from the coal surface to the inside of coal in the gasification channel, which leads to worse gasification performance. Different from conventional straight flow injection, swirl flow injection is proposed to improve the effective contact between the gas and the coal surface to enhance the gasification reaction efficiency. In this work, various types of novel swirl nozzles were independently designed. The characteristics of gas production, temperature distribution and tar pollutant are studied with different swirl angles. As the swirl number increases from 0 to 1.41, there is a significant enhancement in the residence time of oxygen in the axial direction and a reduction of the mass transfer between oxygen and the coal wall in the radial direction. As the oxygen flow rate increases from 0.5 to 2 L/min, swirl flow injection exhibits stronger gasification performance than traditional straight flow injection, such as maximum gas calorific value and tar generation control capability.

A critical review on direct catalytic hydrogasification of coal into CH4: catalysis process configurations, evaluations, and prospects

Coal catalytic hydrogasification (CCHG) is a straightforward approach for producing CH4, which shows advantages over the mature coal-to-CH4 technologies from the perspectives of CH4 yield, thermal efficiency, and CO2 emission. The core of CCHG is to make carbon in coal convert into CH4 efficiently with a catalyst. In the past decades, intensive research has been devoted to catalytic hydrogasification of model carbon (pitch coke, activated carbon, coal char). However, the chemical process of CCHG is still not well understood because the coal structure is more complicated, and CCHG is a combination of coal catalytic hydropyrolysis and coal char catalytic hydrogasification. This review seeks to shed light on the catalytic process of raw coal during CCHG. The configuration of suitable catalysts, operating conditions, and feedstocks for tailoring CH4 formation were identified, and the underlying mechanisms were elucidated. Based on these results, the CCHG process was evaluated, emphasizing pollutant emissions, energy efficiency, and reactor design. Furthermore, the opportunities and strategic approaches for CCHG under the restraint of carbon neutrality were highlighted by considering the penetration of “green” H2, biomass, and CO2 into CCHG. Preliminary investigations from our laboratories demonstrated that the integrated CCHG and biomass/CO2 hydrogenation process could perform as an emerging pathway for boosting CH4 production by consuming fewer fossil fuels, fulfilling the context of green manufacturing. This work not only provides systematic knowledge of CCHG but also helps to guide the efficient hydrogenation of other carbonaceous resources such as biomass, CO2, and coal-derived wastes.

Environmental Kuznets curve of carbon emissions from China’s forest products industry and decomposition of factors influencing carbon emissions

Carbon emissions from China’s forest products industry were considered based on the data of 2001-2020. Then a carbon emissions Kuznets curve was constructed to judge the relationship between the economic development level and carbon emissions. The logarithmic mean Divisia index (LMDI) was used to analyze the influencing factors of carbon emissions. The carbon emissions from China’s forest products industry showed a trend of rapid growth in the early stage and slow decline in the later stage, increasing from 19.46 million tonnes in 2001 to 54.18 million tonnes in 2020. Consumption of raw coal was the main reason for the increase in carbon emissions. There was an inverted-U relationship between the economic development level and carbon emissions, and the industry output value of CNY 3306.56 billion was the theoretical inflection point. The current economic development level of the industry was in the left-half part of the inverted “U” shape, indicating that carbon emissions from this industry will continue to increase with the increase of industrial output. Economic development was the key factor driving the increase of carbon emissions in the forest products industry, while the energy intensity was the key factor inhibiting the growth of carbon emissions.

Dynamic mechanical response and crack evolution law of raw coal loaded by dynamic-static coupling under three-dimensional constraints

This paper presents the investigation of the dynamic mechanical properties of coal rock under complex stress conditions at depth, based on the improved Separate Hopkinson Pressure Bar Test System. A total of 15 groups of coal samples were used to perform dynamic impact tests under different conditions. The changing rules of dynamic strength, crushing, fractal dimension and damage modes of coal under different stress conditions were analyzed. A total of nine groups of coal samples were selected for numerical simulation using ANSYS/LS-DYNA. The results show that: (1) The stress–strain curves of coal specimens under different strain rates, different confining pressures and axial pressures have basically the same trend and the curves show a certain jump forward. (2) The peak dynamic stress of the coal specimens increased linearly with the increase of strain rate and confining pressure, and the ambient pressure limited the expansion of internal cracks of the coal specimens under impact loading. Based on the experimental and simulated data, the maximum relative errors between the experimental and simulated data were determined to be 2.9578% for Group A, 6.177% for Group B, and 6.382% for Group C, respectively. (3) The damage modes of the coal samples under the three-dimensional dynamic-static combined loading were mainly “X” type and “conical” shear damage. The fractal dimension increases with the increase of strain rate, decreases with the increase of confining pressure, and first decreases and then increases with the increase of axial pressure. This research achievement can provide theoretical support for the prevention of dynamic disasters in deep coal mine engineering.