Study on the Reoxidation Characteristics of Soaked and Air-Dried Coal

Abstract

After coal seam mining, the residual coal is soaked with the accumulated water in goaf, and its spontaneous combustion characteristics were changed after air-dried. To study the reoxidation characteristics of soaked and air-dried coal, temperature-programmed experiments were carried out, and the cross point temperatures and index gases were investigated. Results showed that the cross point temperature of raw coal (146.3 °C) was reduced to 137.1 °C after it was pre-oxidized at 90 °C. The cross point temperature of water-soaked, and air-dried coal (96 h) was 122.5 °C, while the cross point temperature of water-soaked, air-dried (96 h) and pre-oxidized (90 °C) coal was 111.5 °C. Although CO was produced in the initial slow oxidation phase, it was found that C2H4 and C3H8 were not generated. In the rapid oxidation stage, different pretreatments affected the gas generation and the overall oxidative degree was consistent with the cross point temperature. The generation temperature and the concentration of C2H4 and C3H8 were decreased after the coal was water-soaked, air-dried, and pre-oxidized. Furthermore, the high-energy chemicals and functional groups were studied, which could be used to explain the physical experiment oxidation characteristics of different coals.

The effect of soaking in increasingly alkaline aqueous solutions on the spontaneous combustion characteristics of bituminous coal

“…It is well known that the ignition temperature and temperature for the maximum mass loss rate are critical parameters, because they directly determine the degree of difficulty of spontaneous combustion occurring. [19][20][21][22][23][24][25] TG analysis enables the determination of the values of Using Equations ( 1)-(3), we calculated the values of D i , S and H f , as shown in Table 3. We can see that the values of D i and S for the soaked coal samples were higher than those for the raw coal sample.…”

“…6,19 Some scholars have found that the chemical structure and pore structure of the coal soaked in water have changed. [19][20][21][22][23][24][25] Song et al 6 studied the effect of water immersion on the oxidation activity of long flame coal. They found that pore diameters on the soaked coal surface increased compared with un-soaked coal and the oxidation activity of the coal was enhanced.…”

“…The above studies indicated that water immersion eventually modified the coal surface structure and provided more space for coaloxygen bonding that intensified the coal-oxygen reaction. 6,[21][22][23][24][25] Besides, the increase in active functional groups of soaked coal enhanced oxygen adsorption and the oxidation process readily, increasing the risk of coal spontaneous combustion. 22 The abovementioned literature mainly focuses on the influence of neutral water on the spontaneous combustion of coal.…”

“…As a kind of porous materials, coal spontaneous combustion is affected both by the chemical structure and pore structure 6,19 . Some scholars have found that the chemical structure and pore structure of the coal soaked in water have changed 19‐25 . Song et al 6 studied the effect of water immersion on the oxidation activity of long flame coal.…”

“…They found that water immersion enhances the activity of the functional groups. Sun et al 23 found that the generation temperature and the concentration of C 2 H 4 and C 3 H 8 were decreased after the coal was water‐soaked, air‐dried, and pre‐oxidized. The above studies indicated that water immersion eventually modified the coal surface structure and provided more space for coal‐oxygen bonding that intensified the coal‐oxygen reaction 6,21‐25 .…”