Alterations in the coal matrix pore structure caused by gas adsorption are a critical factor affecting the efficiency of coalbed methane (CBM) extraction. This study investigates the adsorption behaviors of CH4, CO2, and N2. The evolution characteristics of micropore structure and permeability in a coal matrix under different pressures are discussed using molecular simulation methods. The alterations in the coal matrix pore structure are controlled by pore-filling and structural reconfiguration effects. CO2 shows the most pronounced effects on both processes, leading to increased complexity in pore morphology and a 35.7% decrease in the number of transport pores. CH4 exerts a moderate impact, which reduces both the porosity and surface area of the coal matrix. The number of pore throats displays a nonlinear variation characteristic. In contrast, N2 adsorption has a minimal influence on the pore structure, exerting only a weak filling effect. A permeability model established in this study, which accounts for adsorption-induced pore structure evolution, reveals that although CO2 exhibits strong adsorption and displacement effects, the gas transport capacity of coal post-adsorption declines by more than 90%. Meanwhile, N2 exhibits limited CH4 displacement efficiency and has a negligible effect on coal matrix permeability.
This study investigates the suppression mechanism and microkinetic evolution of heptafluoropropane (HFC227ea) in methane-air premixed combustion with a low ammonia fraction. Experimental results show that HFC227ea reduces the maximum explosion overpressure (Pmax) and the maximum pressure rise rate ((dP/dt)max), with strong dependence on the overall equivalence ratio ((p). Suppression is most pronounced under stoichiometric ((p = 1.0) and fuel-rich ((p = 1.4) conditions, whereas inhibition weakens under fuel-lean conditions ((p = 0.6) because of excessive O2 that promotes chain-branching reactions. Microkinetic analysis shows that suppression is governed by an oxygen-dependent kinetic competition mechanism. Suppression efficiency is controlled by competition between fluorinated radicals that scavenge H/OH/O radicals and the dominant chainbranching reaction (H + O2 = O + OH). Inhibition arises from nonlinear coupling between the initial endothermic decomposition of HFC-227ea and subsequent radical-scavenging reactions, which chemically terminate combustion chains by depleting H/OH/O radicals. This coupled process disrupts the energy-radical balance required to sustain combustion. Reaction flux analysis shows that this mechanism remains consistent across different ammonia-methane blending ratios, indicating the chemical stability of fluorinated intermediates such as CF3CHF and CF3 in complex fuel systems. These findings provide a theoretical basis for the safe application of ammonia-methane blended fuels.
Understanding the synergistic effects of inorganic minerals and pore structure on coal pore wettability remains a critical knowledge gap. This study investigates the pore-scale wettability mechanism of five high-rank coals by integrating quantitative inorganic mineral analysis, pore morphological characterization, and low-field nuclear magnetic resonance (LF-NMR) T 2 relaxation spectroscopy. A series of water-droplet-coal wetting experiments, organized into three groups, was conducted to establish a cross-scale framework linking physical pore structure, mineral composition and wetting response. The results indicate that the dual mechanism of strong adsorption on hydrophilic mineral surfaces and capillary forces in micropores drives the wetting process. In terms of mineral aspect, clay minerals exhibit significantly higher wettability than non-clay minerals, and clay content shows a significant negative correlation with wetting parameters R g,24h measured by LF-NMR. Notable, when clay content ranges from 2% to 10%, its regulatory effect on pore wettability is particularly sensitive. In terms of pore structure, an exponential saturation model was employed to fit the pore wetting kinetics. The derived kinetic parameters, including the rate constant k and equilibrium pore diameter R eq are consistent with the trends observed in R g,24h . And the 24 h observation is confirmed to represent quasi-steady state for all samples. Additionaly, Pore wettability is governed by absolute pore capacity when pore volume differences exceed approximately two-fold, whereas at smaller differences, micropore complexity and connectivity dominate. Micropores play a critical role due to capillary force-driven physical contributions. Furthermore, a critical pore diameter of 42.16 nm is identified, above which wetting transitions from capillary-driven to surface-spreading or gravity-dominated regimes. A two-dimensional pore-wet coupling model is proposed, and five representative wettability types were defined. Among them, samples C4 and C5 exhibit synergistic enhancement (type A), while C1 shows mutual inhibition (type B). These results provide a new multidimensional coupling paradigm for understanding wettability in heterogeneous porous media.
The chemical state of silver was found to affect the catalytic activity of ethanol-SCR reaction. The hydroxyl (OH) groups on the surface of Al2O3 support as anchor sites for Ag species, were benefit for the dispersion of silver and the formation of active sites. The surface OH contents of the Al2O3 support were synergistically regulated by varying the calcination temperature and hydrothermal treatment, to control the coordination environment of silver and optimize the catalytic performance. The result showed that the OH contents of Al2O3 mainly govern the dispersion of Ag species. The decrease in OH groups led to increased proportion of metallic Ag species, resulting in significant decrease in the NOx reduction activity. Additionally, hydrothermal treatment of support promoted the formation of well dispersed oxidized Ag species, significantly enhancing the NOx reduction performance in the high-temperature range of 400-500 degrees C. Cycling tests revealed that the Ag species on the catalyst surface would migrate and redisperse under conditions of oxygen-rich at temperatures above the Tammann temperature of silver (344 degrees C). The transformation causes hysteresis in the catalytic activity during heating and cooling, further revealing the dynamic evolution of Ag species under reaction conditions. The results reveal the mechanism through which OH contents in the support govern the structure and performance of Ag/Al2O3 catalysts, providing a theoretical basis and novel insights for the development of high-efficiency diesel vehicle exhaust purification catalysts.
A scaled-down heat-tube air preheater is prepared in this paper, to study experimentally the local and overall characteristics of ammonium bisulfate (ABS) ash accumulation. The morphology, composition, distributions of ash accumulation are analyzed based on the approaches of visualization, SEM, EDS, XRD, as well as the pressure loss and heat transfer in the air preheater. The influences of key parameters including the flue-gas temperature (190-280 °C) and the ABS-ash ratio (1/120-1/30) on the ash accumulation features are also discussed. It is found that the fly-ash without ABS does not form a stable ash accumulation layer on the vertical smooth tube. By contrast, the addition of ABS makes the fly-ash particles rapidly accumulating on the tube and forming a bell-shaped dense accumulation layer, due to the liquid-phase ABS significantly enhancing the adhesion of fly-ash particles. The acidic decomposition products of ABS react chemically with the basic oxides in the fly-ash to form the sulfate compounds, which not only change the composition of the ash accumulation but also promote the compactness of the ash accumulation layer. The thickness of ash accumulation firstly rises then decreases with the flue-gas temperature increases, and reaches a maximum of 26.2 mm at Tg,i = 220 °C when the ABS reaches a more fully melted state. With the ABS-ash ratio increases from 1/120 to 1/30, the thickness of ash accumulation significantly increases by 217%, but the ABS-ash ratio has a limited impact on the reaction path of ABS with fly-ash components. Besides, the backflow vortex causes the ash accumulation layer at the second row of tube (Row #2) to be thickest.
