To prevent spontaneous coal burning at a goaf in the People’s Republic of China, the effectiveness of a grouting system was simulated (PRC). The colliery has been in operation for more than 27 years, and it is known to have a complicated air circulation network with airflow leakages that could lead to spontaneous combustion of at goaves. To begin, MIVENA, a coalmine aeration simulator, was used to test the mine aeration network’s ability to control airflows into and out of goaves and working faces. In the second technique, FLUENT simulation to forecast spontaneous burning of coal with seepage flow of air in the goaf #3205. It was seen that the goaf could be subdivided into three different regions based on the concentration of oxygen in the goaf. Lastly, the arithmetical simulation outcomes indicate that the slurry grouting approach can be effective as well as an economical approach to reducing permeability in the area of the goaf to prevent residual coal from spontaneous combustion.
Keywords: spontaneous combustion, Simulation, FLUENT, MIVENA, goaf areas
It is clear that goaf areas are the key areas when looking at the underground coal mines fire. In these areas, it is possible to induce a spontaneous fire in the goaf areas. Following the data about coal production in China, Ninety percent of total coal production is from underground mines, and there are about six hundred state-owned main coal mines out of which 25.1 percent are highly gaseous mines, and approximately 17 percent are fume out-burst coalmines. In Chinese coal mines, fatal accidents happened, especially in the past ten years. Since the mines yielded a large volume of coal that meets local demand, it caused insufficient efforts to keep safety operation at goaf areas and working faces. Precisely, most accidents were indirectly or directly associated with spontaneous combustion of coal in goaf mine areas (Wang et al, 2015.55).
Chen and Qi looked at the distributing circumstance of abutment force as well as the way airflow in goaf, and later they came up with the theoretical method to predict the velocity of airflow in goaf region as well as the spontaneous combustion region where the velocity of airflow is below 0.24 m/min. In 2013, Pan and others studied a goaf and subdivided it into three sectors linked to impulsive coal combustion using the distribution of oxygen and concentration of carbon monoxide. They categorized the goaf zone to asphyxiation and radiating zones by oxygen concentrations less than 7 percent and larger than 18 percent, respectively (Wang et al, 2015.55). In this study, a preventing approach for the spontaneous burning of coal at a goaf area in Haizi Colliery China has been analyzed, for it is a distinctive lignite coal mine in PRC and can experience spontaneous combustion because of fusain found in coal beds.
The mine area of Haizi Colliery is approximately 6.44 km2 comprising 1,200-5,200 m alongside the strike as well as tendency of 0 – 1,700 m. The coal layers are divided by three normal lines that form an isolated block region like a triangle zone bearing coal. The current depth that represent working face is about −320 m as from the surface level (Hu et al, 2015. 462). The self-ignition temperature of the yielded lignite coal is around 275°C. And the time from when the coal contacted air to the time when spontaneous combustion occur has been estimated to be roughly 1 – 1.5 month. According to the mine’s operational record of 2002 – 2013, spontaneous ignition occurrence has been regularly studied at a working face. The features of coal from Haizi are recorded in Table 1. Proximate and density examination of Haizi.
2. Analysis of Mine Ventilation Network
The centralized aeration system in Haizi Colliery is utilized with a key intake channel for fresh airflow as well as an exhausting channel used only for draining airflow. The intake tube has a diameter of about 6 m which is equal to 28.3 m2 in surface area. It is also is utilized for hoisting workers and elevating coal, and the exhaust channel is about 9.6 m2 in surface area. There are two key centrifugal fans; one is standby, and other is running (Hu et al, 2015. 462). They were fitted out to provide sufficient ventilation. Each fan is operated by a 220 kW motor with a rotating speed of 740 rpm. It has a total airflow intake of 3564 meters cubed per minute operated by an aggregate loss of pressure Pa.
In the current study, MIVENA, the coal mine ventilation system simulator has been used to forecast airflows and aeration characteristics centered on the system data. To be specific, the air circulation of #3205 working face, is the total-mechanized residual coal cutting faces, which was dedicated by altering conditions with the operation of working face. Later, the simulated statistics was used to regulate air movement in the working face bearing in mind the whole aeration in the system (Hu et al, 2015. 462).
According to the safety regulations for coal mines ventilation in China, the velocity of airflow should meet the range of 0.25- 4 m/s. Here, Haizi Colliery assessed the amount of air thru the goaf. It was about 480 m3/min which meets the requirements indicated above, for the air seepage was estimated to be 368 m3/min (Wang et al, 2015.55). The challenge which was experienced was that several shortcuts or bypass airways are present at the bottom of the mine with comparatively large aeration resistance in the left wing. The arithmetical simulations were done for the aeration cases, using several useful approaches to solve the challenge (Hu et al, 2015. 462). Based on results of the simulation, the effective way out was to put an additional intake channel freshly excavated in this region, for the newly dug airway can result in a decrease in air movement resistance of 30 percent at the #3205 working face. It was projected that the pressure reduces from 319 Pascal to 270 Pascal at the face; so it was also anticipated to control airflow leakage easily into the goaf zone than before.
Using the process indicated above, air seepage can be decreased to 200 meters cubed per minute from 338 meters cubed per min at the #3205 operational face. At working faces, once excavation is done (such as #1709 and #2207 working faces), stopping barriers were erected immediately to avoid leakage of the air into goaf regions as well as to improve the efficiency of fresh-air usage in the coal mine (Hu et al, 2015. 462). After optimizing coal mine ventilation air movements as well as lowering pressure near working faces, authors concentrated on studying the goaf area as well as preventing impulsive combustion of coal in the goaf area.
Zones at Goaf Area
The state of goaf area changes steps by step with the advancing of the working face. Air seepage at the working faces provides O2 to the coal in the goaf zone as well as coal joints close by the goaf, and it can result in spontaneous combustion of coal in the goaf zone that is categorized into three zones. The zones are oxidized, radiating, as well as asphyxiation zone. These zones can be described by flow speed of air seepage, the concentration of oxygen in the goaf region, as well as the rate of temperature increase that are assessed by the approach elaborated in the Coal Mine Safety Standards of China (Wang et al, 2015.55).
The table below represent the Chinese safety Regulations for different goaf zones.
O2 ≥ 8%
0.02 m/s ≥ ≥ 0.001 m/s