Fuels

The article presents a comparison between the pressure conditions of a real low-pressure gas network and the results of hydraulic calculations obtained using various simulation programs and empirical equations. The calculations were performed using specialized gas network analysis software: STANET (ver 10.0.26), SimNet SSGas 7, and SONET. Additionally, the simulation results were compared with calculations based on the empirical Darcy–Weisbach and Renouard equations. In the first part of the analysis, two calculation models were compared. In one model, the geodetic elevation of individual network nodes was included (elevation-aware model), while in the second, calculations were performed without considering node elevation (flat model). For low-pressure gas networks, accounting for elevation is critical due to the presence of the pressure recovery phenomenon, which does not occur in medium- and high-pressure networks. Furthermore, considering the growing need to increase the share of renewable energy, the study also examined the network’s operating conditions when using natural gas–hydrogen mixtures. The following hydrogen concentrations were considered: 2.5%, 5.0%, 10.0%, 20.0%, and 50.0%. The results confirm the importance of incorporating elevation data in the modeling of low-pressure gas networks. This is supported by the small differences between calculated results and actual pressure measurements taken from the operating network. Moreover, increasing the hydrogen content in the mixture intensifies the pressure recovery effect. The hydraulic results obtained using different computational tools were consistent and showed only minor discrepancies.

Biomass briquettes are increasingly used as renewable solid fuels, yet their durability under humid storage remains a key limitation. This study evaluated the mechanical performance and water resistance of briquettes made from fine (0–1 mm) and coarse (0–3 mm) charcoal fractions using molasses as a primary binder, polyvinyl alcohol (PVA, 3–7%) as a synthetic binder, and liquid soap (1–9%) as a surfactant additive. Compressive strength was measured in the dry state, after four days of water immersion, and after re-drying, while water absorption was monitored over immersion times from 15 min to 4 days. Fine-fraction briquettes showed higher strength and lower water uptake than coarse fractions, with optimal PVA contents of 6–7% providing maximum dry and post-drying strength. Moderate soap addition (2–3%) improved binder dispersion and early wet strength, whereas higher levels (>5%) reduced durability. Water absorption kinetics indicated that particle size controlled early swelling, while binder composition influenced the rate but not the final saturation. The best performance in humid storage was achieved by 0–1 mm + 4% PVA and 0–1 mm + 5% PVA + 3% soap formulations. These results support the formulation of eco-friendly binder systems that balance strength, moisture resistance, and cost for large-scale biomass briquette production.

Coal mining has entered the stage of deep mining, and the prevention and control of gas disasters are facing significant challenges. Coal seam water injection, as an effective means of preventing and controlling gas disasters, has dual effects of pressure relief, permeability enhancement, and displacement sodium dodecyl benzene sulfonate (SDBS), as an anionic surfactant, can reduce surface tension to a certain extent in its aqueous solution and is therefore commonly used in coal seam water injection technology. In order to clarify the effect of SDBS on the water absorption capacity of coal and whether it will affect the gas adsorption capacity of coal, imbibition tests were conducted on dried coal samples in different concentrations of SDBS solutions, as well as gas adsorption tests on dried coal samples after imbibition was completed. Research shows that the key concentration range of SDBS for practical application is 0.050–0.075 wt%. When the concentration of SDBS solution is lower than 0.050 wt%, as the concentration of SDBS solution increases, the spontaneous imbibition capacity of coal increases significantly, and the adsorption capacity of coal to gas decreases significantly. When the concentration of SDBS solution is higher than 0.075 wt%, the spontaneous imbibition water capacity and gas adsorption capacity of coal hardly change significantly with the increase in solution concentration. Considering the effects of SDBS on coal water absorption and gas adsorption capacity, as well as environmental protection factors, it is recommended to use SDBS as a surfactant with a solution concentration of 0.050 wt%.