Energy Science & Engineering最新文献

The Longwall top coal caving (LTCC) technology is regarded as one of the most crucial approaches for exploiting thick coal seams. A crucial and effective approach for improving the recovery rate of top coal and reducing coal resource losses in LTCC faces is to reasonably select process parameters based on actual mining and geological conditions of different mines. The main focus of this paper is the engineering background of the 12,309 LTCC face in Wangjialing Coal Mine. A numerical model is developed using FALC3D and PFC3D software, employing a finite difference method and discrete element method. This model takes into account predetermined cutting and caving ratios, as well as drawing intervals. To examine the caving process and roof particles, three different drawing sequences were examined: sequential drawing, segmented sequential drawing, and intermittent drawing. The findings suggest that, in terms of the reset shape of the drawing body before individual and entire caving, the segmented sequential drawing method exhibits noticeable drawbacks compared to the other two methods. From the perspective of the drawing weight, following “closing drawing opening when seeing gangue”, the sequential drawing, segmented sequential drawing, and intermittent drawing methods can yield 32.42 t, 26.87 t, and 35.78 t of top coal, with corresponding recovery rates of 73.39%, 60.81%, and 82.97%. Therefore, it can be concluded that intermittent drawing is suitable for implementation on LTCC working face 12,309.

To study the effect of coal pressure on gas extraction under fluid-solid coupling, the effect of gas extraction radius under different pore sizes and treatment methods was simulated by using COMSOL Multiphysics software, the time evolution law of gas pressure on coal surface was obtained, and the numerical simulation results were verified by the observation of flow rate and concentration in experimental mine combined with fluid-solid interaction. The results show that the distance of extraction radius increases with the increase of borehole diameter, and the relation between extraction time and extraction radius is a power function, but the increase gets smaller and smaller until it becomes zero. For Φ98 mm borehole and Φ120 mm borehole, hydraulic treatment can increase the efficiency of gas extraction by 31.3% and 22.7%, respectively. For hydraulic treatment and conventional treatment, the ratio of gas drainage effect by enlarging hole size is 6.3% and 13.8% respectively. Compared with the areas without gas extraction under the four conditions, the descending speed of gas pressure from fast to slow is Φ120 mm hydraulic flushing treatment, Φ98 mm hydraulic flushing treatment, Φ120 mm conventional treatment, Φ98 mm conventional treatment. Compared with four different conditions, after 180 days of extraction the coal gas pressure decreased by 75.3% within reasonable hole spacing. At the same time, in multi-hole pumping, the influence area of adjacent borehole is larger than that of single-hole pumping, and the spacing of borehole should be less than twice the radius of pumping.

Nowadays, the seismological monitoring system in China is a valuable tool in the rockburst risk evaluation for deep coal mines. In the past, only parameters, like source location and energy, are widely used to estimate the risk level of rockburst. Sometimes, it is effective; however, some other important physical parameters, such as apparent stress drop, static stress drop, P-wave velocity, and moment tensor, should also be included in order to improve the accuracy of risk assessment. In this study, these parameters are calculated using mine tremor signals recorded in the LW35001 workface of Liangbaosi Coal Mine. These calculations provide an overall identification of periodical stress distribution and rock mass energy-releasing type under high concentrated stress. Via linear moment tensor inversion procedure, the source mechanism of mine tremors and stress state of the rock mass is determined whether it is risk or not to underground roadway. This comprehensive analysis provides a specific guidance for rockburst prevention for coal mine management, that is, knowing when and where measures must be taken to decrease the risk level or induce the occurrence of rockburst under control.

The global recognition of eco-friendly products like plant-based dyes is escalating, driven by their exceptional biological and Ayurvedic attributes. This study isolates colorants from mango turmeric (Curcuma aromatica) using ultrasonic irradiation, supplemented with bio-mordants to enhance color retention. Through the utilization of Response Surface Methodology and Central Composite Design, a technique that was optimized was completed to maximize coloring variables using statistical analysis. Results from 32 experimental runs reveal that optimal color depth (K/S = 19.399) was achieved with ultrasonic-treated silk fabric (20 min exposure) using 65 mL of irradiated aqueous extract (20 min) with a pH of 5, supplemented with 1.5 g/100 mL salt of sodium chloride, maintained the temperature 75°C for the 45 min. Precoloring treatment with acacia, pomegranate, and pistachio extracts at specified concentrations enhanced colorfastness. Postdyeing, alterations in the concentrations of these extracts led to further improvements in colorfastness. Notably, adding Al⁺³ and Fe⁺² salts, alongside tannic acid, exhibited notable effects in both pre- and postdyeing stages. While the colorfastness properties of unmordated silk fabric was lower than mordanted dyed silk fabric. Irradiation with ultrasonic waves significantly boosted the amount of dye that could be extracted from rhizomes of mango turmeric. Moreover, the application of bio and synthetic mordants in a strategic manner led to colorfastness ratings on silk fabric that ranged from excellent to satisfactory. This research underscores ultrasonic technologies and bio-mordants' efficacy in sustainable dyeing processes, offering insights for developing eco-friendly textile coloration methods.

The characteristics of gas seepage in broken coal and rock composed of different particle sizes and grades were investigated in this study. On the basis of Darcy's law and non-Darcy seepage theory, equations of gas permeability in the nonlinear seepage of broken coal and rock, as well as the porosity of broken coal and rock, under triaxial compression were determined. The stress loading path of gas seepage in broken coal and rock was developed. The characteristics of gas seepage in broken coal and rock composed of different particle sizes and grades were analyzed, and the results showed that the gas permeability after compression was proportional to the particle size of the broken coal and rock. Under triaxial compression, the gas permeability of the broken coal and rock composed of graded-particle sizes was lower than that of the broken coal and rock composed of different single-particle sizes. The gas permeability of the broken coal was lower than that of the broken rock mass, and the gas permeability and porosity of the broken coal and rock can be described by the exponential decay function. At a constant porosity, the gas permeability of the broken coal and rock was proportional to the size grading index under triaxial compression. The coefficient of viscosity and gravity of the flow are key factors influencing the flow permeability in broken coal and rock. This study provides a reference for on-site practice such as the efficient extraction of gas in goafs.

The speed of using renewable resources is expanding day by day. Renewable energy systems have many benefits for energy supply that do not include diesel, natural gas, or coal. Despite the many advantages, the use of renewable resources also includes basic challenges. With the presence of these sources, many technical issues must be considered in the network, the most important of which are voltage quality and network losses. The presence of these power plants can reduce fossil fuel costs and help reduce emissions. However, the high-capacity connection of these types of power plants in the transmission networks despite the uncertainty may cause the congestion of transmission lines, increase losses and decrease voltage quality. Therefore, to reduce the need to build transmission lines, energy storage devices can be installed and energy can be stored and returned to the network in certain hours. The purpose of this paper is to build the maximum capacity of wind power plants in the transmission network in such a way that its profitability is guaranteed. For this purpose, in addition to considering the costs related to the power plant, the costs of storage devices and the construction of possible new lines have been considered. Also, improving the technical conditions of the network and reducing the maximum emission after installing these units is considered as a multiobjective function. The problem tested on the standard IEEE test transmission network and the results show that it is possible to determine the maximum profitable capacity of wind power plants.

In the strategy to combat climate change that has been caused by the world's overdependence on fossil fuels, current research is focusing on the decarbonisation of the energy sector through the production of renewable cleaner energy, such as biofuels. Spent coffee grounds (SCGs), the waste stream of the coffee brewing industry, are a potential feedstock for the production of valuable products, including biofuels. However, the environmental implications for the valorisation of this valuable waste need to be investigated. This study assesses the environmental impacts of six biomass-to-fuel processing technologies using SCGs as a feedstock, with the aim of identifying the most environmentally friendly technology. A cradle-to-gate life-cycle assessment (LCA) was conducted on fast pyrolysis, fermentation, anaerobic digestion (AD), hydrothermal liquefaction (HTL), gasification, and biodiesel production. The mass and energy balances obtained from Aspen Plus simulations served as the life-cycle inventory data. Using the ReCiPe 2016 midpoint (H) and Eco-Indicator 99 as the assessment methods, potential environmental impacts were calculated in OpenLCA software. Electricity generation and carbon dioxide emissions were the biggest contributors of environmental impacts. For each category, the maximum result was set to 100% and the results of the other variants were displayed in relation to this result. AD, with the smallest total weighted score (160), was the most environmentally friendly biomass-to-fuel processing route, while HTL, with the biggest total weighted score (893), was the worst. A sensitivity analysis indicated that the environmental performance of biofuel production from SCGs was highly influenced by energy input flows and the source of energy generation.

Liquefied natural gas (LNG) exports from the United States have risen dramatically since the LNG-export ban was lifted in 2016, and the United States is now the world's largest exporter. This LNG is produced largely from shale gas. Production of shale gas, as well as liquefaction to make LNG and LNG transport by tanker, is energy-intensive, which contributes significantly to the LNG greenhouse gas footprint. The production and transport of shale gas emits a substantial amount of methane as well, and liquefaction and tanker transport of LNG can further increase methane emissions. Consequently, carbon dioxide (CO₂) from end-use combustion of LNG contributes only 34% of the total LNG greenhouse gas footprint, when CO₂ and methane are compared over 20 years global warming potential (GWP₂₀) following emission. Upstream and midstream methane emissions are the largest contributors to the LNG footprint (38% of total LNG emissions, based on GWP₂₀). Adding CO₂ emissions from the energy used to produce LNG, total upstream and midstream emissions make up on average 47% of the total greenhouse gas footprint of LNG. Other significant emissions are the liquefaction process (8.8% of the total, on average, using GWP₂₀) and tanker transport (5.5% of the total, on average, using GWP₂₀). Emissions from tankers vary from 3.9% to 8.1% depending upon the type of tanker. Surprisingly, the most modern tankers propelled by two- and four-stroke engines have higher total greenhouse gas emissions than steam-powered tankers, despite their greater fuel efficiency and lower CO₂ emissions, due to methane slippage in their exhaust. Overall, the greenhouse gas footprint for LNG as a fuel source is 33% greater than that for coal when analyzed using GWP₂₀ (160 g CO₂-equivalent/MJ vs. 120 g CO₂-equivalent/MJ). Even considered on the time frame of 100 years after emission (GWP₁₀₀), which severely understates the climatic damage of methane, the LNG footprint equals or exceeds that of coal.

In recent years, there has been a lot of research and debate on how solar energy can be used instead of conventional sources of heating to power residential heating. In this study, the Trombe wall (TW) technique, based on natural convection and energy storage, was examined to predict mass flow rate, temperature field, and velocity field for the TW system under steady conditions. A numerical simulation model was investigated for further validation using k-ε turbulence and discrete ordinates (DO) radiation models. Independent grid studies were conducted to ensure that there were no changes after varying the grid numbers. The effect of the air gap was carried out to enhance TW thermal performance. CFD simulation shows good agreement with published data in the literature, and the optimum air gap was set at 0.1 m. The results pave the way for future studies to improve passive solar heating systems, which will eventually help move towards more sustainable residential heating solutions.

As China's demand for imported oil continues to grow, large-scale oil storage facilities have become increasingly important. Currently, China primarily uses underground salt cavern spaces and newly excavated underground water-sealed caverns for oil storage, which places high demands on the rock formations. China has abundant and widely distributed gypsum mineral resources, and utilizing abandoned gypsum mines for oil storage could not only turn waste into treasure by controlling underground space but also generate significant economic and social value. This article aims to systematically evaluate the mechanical properties of gypsum rock through long-term immersion tests in crude oil to assess the impact of crude oil immersion on the mechanical performance of gypsum rock and explore the feasibility of using gypsum mines as long-term stable oil storage caverns. The results show that oil immersion treatment reduces the uniaxial tensile strength of gypsum samples, but has little effect on their compressive strength and long-term strength. From a mechanical performance perspective, it is feasible to use gypsum mine voids for crude oil storage.