Combinations of spherical vessels and pipes are frequently employed in industries. Scholars have primarily studied gas explosions in closed vessels and pipes. However, knowledge of combined spherical vessel and pipe systems is limited. Therefore, a flame acceleration simulator was implemented with computational fluid dynamics software and was employed to conduct natural gas explosions in three structures, including a single spherical vessel, a single spherical vessel with a pipe connected to it, and a big spherical vessel connected to a small spherical vessel with a pipe. These simulations reflected physical experiments conducted by at Nanjing Tech University. By changing the sizes of vessels, lengths of pipes, and ignition positions in linked vessels, we obtained relevant laws for the time, pressure, temperature, and concentrations of combustion products. Moreover, the processes of natural gas explosions in different structures were obtained from simulation results. Simulation results agreed strongly with corresponding experimental data, validating the reliability of simulation.

In this study, we use coal as a carbon source from Zhangjiamao and doped with different nitrogen sources for co-pyrolysis. Nitrogen-rich tar was successfully prepared, and the content and variety were also increased. From the elemental analysis, the nitrogen content of all the tars was significantly enhanced, among which the nitrogen content of the tars after co-pyrolysis with melamine was enhanced by 5.21%, and the nitrogen content of coke was enhanced by 10.87%. According to the GC/MS results, it was found that the nitrogen compounds in the tar after full pyrolysis were richer and more abundant than those in Py-GC/MS. For the free radical reaction, the reaction process is extremely rapid, and the ¹⁵N substitution product after isotope labeling was successfully captured by adding ¹⁵NH₄Cl for isotope labeling, which can be more intuitively and accurately illustrated from the m/z change. Among them, 26 nitrogen-containing compounds were screened out, which accounted for 66.28% of the content, and they were categorized. It was found that the five-membered nitrogen heterocycles were the most abundant, accounting for 34.88%. In addition, five other nitrogen-containing compounds containing different functional groups and the tar from the co-pyrolysis of tar-rich coal were also analyzed by GC/MS, among which the tar from melamine had the highest content of nitrogen-containing compounds, with 70.48%. Finally, the functional groups of nitrogen-containing compounds were further analyzed by XPS and FTIR, and the results were consistent with those of GC/MS analysis. In this paper, nitrogen-rich tar was prepared by co-pyrolysis of tar-rich coal and nitrogen compounds. This achievement provides a valuable reference for the high-value utilization of coal tar.

Magnesium (Mg) dust and magnesium–aluminum (Mg–Al) alloy dust are commonly produced and form a dust cloud in industrial manufacturing processes, which considerably increases explosion risk. This study examined three metal dusts: Mg, 48 mass% Mg–Al alloy, and 91 mass% Mg–Al alloy. A 20-L spherical explosion device was used to investigate the effect of different Mg concentrations. The results revealed that for all the samples, the explosion pressure (P_ex) first increased and then decreased for a dust cloud concentration of 100–1000 g/m³. With the increase of dust particle size, the P_ex of samples decreased. With the increase of ignition delay time, the P_ex of samples first increased and then decreased, reaching the peak at 60 ms. Under identical conditions, when Mg concentration increased, the alloys became less stable. Thermogravimetry-differential scanning calorimetry findings revealed that the oxidation process of samples could be divided into three stages. The initial oxidation temperature of the alloys was lower than that of the pure Mg; however, in its primary oxidation stage, the mass gain rate of the Mg dust was more rapid than that of the Mg–Al alloys. In the oxidation of the alloys, elemental Mg reacted with oxygen first.

In gas drilling operations, the blooey line is highly susceptible to erosion-induced leakage. This study focuses on the use of field-welded V-shaped elbows in blooey lines, establishing a numerical method for erosion prediction and validating its accuracy through experimental data. The numerical results reveal that, due to the inclined configuration of the V-shaped elbow, particles from the central inlet flow directly impact the outer wall of the outlet pipe opposite the inlet, and then rebound and strike the inner wall. Meanwhile, solid particles near the pipeline wall on both sides of the inclined plane collide with the outer wall and exit in a helical flow pattern along the outlet pipe. The maximum erosion rate (3.6 × 10⁻⁴ kg/(m²·s)) occurs at the intersection of these spiral particle flows. Based on erosion predictions under various operating conditions, an empirical formula was established to correlate the erosion rate with the gas injection rate at a rate of penetration (ROP) of 1 m/h, along with corresponding conversion relationships for different ROPs. The predicted residual thickness of the V-shaped elbow showed a 6.8% relative error compared to field measurements. The proposed method can be programmed to enable real-time monitoring of the residual wall thickness and the remaining service life of the blooey line before leakage occurs, assisting field operators in determining optimal pipeline replacement schedules to ensure operational safety.

To address the challenge of quantitatively coupling fire smoke evolution and occupant evacuation in the underground powerhouses of large-scale pumped-storage power stations, full-scale three-dimensional numerical models were developed using PyroSim for fire dynamics and Pathfinder for egress behavior. A multi-factor coupled ASET–RSET safety margin matrix was constructed, integrating fire heat release rate (HRR), sprinkler intervention, egress passage blockage, and occupant load. The results show that visibility continuously dropping below 10 m at a characteristic hazardous height of 4.5 m serves as the governing criterion determining the available safe egress time (ASET). Under a 10 MW fire without sprinklers, the ASET is 343.0 s, whereas activating the sprinkler system effectively suppresses smoke and reduces temperatures, extending the ASET to 380.9 s. With both exits unobstructed, the required safe egress time (RSET) for the baseline 130 occupants is 303 s and increases marginally to only 304 s as the crowd scales to 250 occupants, thereby maintaining a positive safety margin under all scenarios. Conversely, the blockage of a single-sided passage induces a pronounced bottleneck shift. Specifically, blockage of the main access tunnel exhibits acute sensitivity to crowd enlargement: the RSET surges to 441.8 s for 250 occupants, resulting in a severe safety margin deficit that cannot be fully rectified even with sprinkler intervention. Accordingly, two distinct risk boundaries—management-sensitive and structure-constrained regimes—are identified. An optimal egress routing scheme characterized by “hierarchical zoning, lateral priority, and nearest-ascending egress” is proposed, accompanied by a two-dimensional cooperative prevention and control strategy: “source control to delay ASET and capacity expansion to reduce RSET.” This work provides quantitative support for performance-based fire safety design and emergency management in deep-buried underground powerhouses.