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Rotary kiln is also known as lime rotary kiln.
Rotation speed:0.1–5 r/min
Applied materials: roasting cement clinker in the industries of metallurgy, refractory matter and chemical plant.
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The spontaneous combustion of coal is one of the biggest challenges in coal mining. It can cause a series of problems, including significant environmental contamination, temporary or permanent mine closures, environmental problems and even fatalities (Singer et al. 1991; Zhang et al. 2011; Bell et al. 2001; Heffern and Coates 2004; Chatterjee 2006; Pone et al. 2007). In China, around 53.1 % of the state-owned coal mines have a propensity towards spontaneous combustion. Also, more than 90 % of coal mine fires resulted from spontaneous combustion of coal (Zhang et al. 2011). Therefore, research on the coal spontaneous combustion mechanism is of importance for fire prevention, detection and extinguishment
The occurrence and development of coal spontaneous combustion is an extremely complex, dynamic, auto- acceleration physical and chemical process. It is affected by a large number of factors such as coal type, moisture content, circumstance temperature, air leakage intensity etc. The effects of sulfur on coal spontaneous combustion have been recognized by most researchers. As the necessity for extending mining depths has grown, the mining of sulfur content coal seams has been significantly increased. Therefore, study of the effects of the sulfur on coal spontaneous combustion has become increasingly vital
Three forms of sulfur exist in coal: pyrite, sulfate and organic sulfur (Lu and Liu 1999). Pyrite plays a vital role in coal spontaneous combustion. The specific heat of pyrite is only one-third of that of coal; but with the same heat absorption, the temperature rise of pyrite is three times higher when compared to coal. Reactions of pyrite and oxygen, with the help of moisture, are shown in Fig. 1
These reactions can occur at low temperatures and additionally, all of the reactions are exothermic reactions. The heat generation from these reactions doubles that of coal with the same oxygen (Garcia 1999; Martínez et al. 2009). Thus, the presence of pyrite is a big promoter for the spontaneous combustion of coal
Numerous previous studies have been conducted in terms of the characteristics of sulfur in coals. Hakvoort (1995) studied the existing states of sulfur in coal providing fundamentals for the subsequent research. Mondragón et al. (2002) studied the evolution of H2S produced in the reaction of coal and found that the strongest reduction in the amount of H2S evolved was observed in the samples oxidized at 30 °C. The contributive factors for retention effect of sulfur in coal were studied via three bituminous coals by Folgueras et al. (2004). Stanger and Wall (2011) investigated the impacts of sulfur during pulverized coal combustion based on carbon capture. Müller et al. (2013) modeled the evolution of sulfur during coal combustion and divided the whole process into three stages. Chamberlain et al. (2013) experimentally studied the changes of sulfur species (SO2, H2S, SO3 etc.) during the oxidation of coal and quite different concentration distributions were observed at different stages
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