Coalbed methane as one type of clean energy has become an important gas resource recently. High-pressure water injection in coal seams is an effective approach for improving gas extraction efficiency, which is determined by the gas displacement characteristic and pore structure of coal. To investigate the gas displacement characteristics in coal and its pore response and influential factors, gas adsorption and water injection experiments were conducted under different conditions. The results show that the gas displacement caused by the water injection undergoes three stages: rapid increase, slow increase, and almost constant. The wetting process in water injection includes three processes: wetting, soaking, and spreading, and the wettability of coking coal is best, followed by lean coal and anthracite. The amount of gas driven by the water increases with increasing water injection pressure, and it is more favorable to increase the injection pressure to improve the gas displacement effect under the relatively low injection pressure. The lower the coal rank, the better the gas displacement effect due to the higher porosity of the coal, and the longer the early gas displacement stage. The high adsorption equilibrium pressure can improve the gas displacement effect; for the relatively high adsorption equilibrium pressure, the gas displacement effect is better. After water injection in coal, the large fractures and pores dramatically increase in size, especially for the low metamorphic coals coking coal, contributing to the majority of the increase in porosity. The results of this study can provide a theoretical foundation for the wide application of water injection technology for efficient gas drainage in coal mines.
With the widespread use of substations around the world, oil jet fire accidents from transformer oil-filled equipment in substations caused by faults have occurred from time to time. In this paper, a series of transformer oil jet fire experiments are carried out by changing the external heat source (30 cm and 40 cm) and the inner diameter of the container (5 cm, 8 cm and 10 cm) to study the axial centerline temperature distribution of the transformer oil jet fire plume of the transformer oil-filled equipment in the substation. The experiment uses K-type thermocouple, electronic balance and CCD to measure and assess the temperature distribution of the axial centerline of the fire plume of the transformer oil jet. The result demonstrates that the axial centerline temperature of the fire plume increases with the external heat release rate and the inner diameter of the container. In addition, a novel axial temperature distribution prediction model of the transformer oil jet fire plume is established. This model can effectively predict the oil jet fire plume temperature of transformer oil- filling equipment in substations, and provide help for substation fire control.
Transformer oil jet
fire is one of the most dangerous types of
fires in substations. The combustion behavior of transformer oil jet
fire produces uncontrollable hazards to personnel and equipment and
even triggers a domino effect. However, the jet fire combustion behavior
of such materials as transformer oil has not been revealed before.
Investigation of the combustion behavior of transformer oil jet fire
has positive implications for the prevention and control of substation
fires. In this paper, KI25X transformer oil was used as fuel. A series
of transformer oil jet fire experiments were conducted with variable
orifice diameters (5, 10, and 15 mm) with heat release rates ranging
from 200 to 659.2 kW. The results showed that the entrainment coefficient
of transformer oil jet fire was greater than that of pure gas phase
jet fire. The entrainment coefficient of transformer oil jet fire
was 0.029. Using dimensionless theory, it was proposed that the imaginary
point source was proportional to the 0.317 power of Froude number.
Based on the point source model, a dimensional analysis model with
Reynolds number was developed. The radiation fraction of transformer
oil jet fire was proportional to the −0.133 power of Reynolds
number. This study played an important role in improving the jet combustion
behavior of transformer oil.
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