Abstract
It is imperative to have an in-depth understanding of the effect of extraneous moisture on the spontaneous combustion of coal not only for the control and prevention of coal spontaneous combustion in the coal mining industry, but also for the optimization design and application of the technological process. In this study, the type of moisture in a coal body has been redefined for the first time from the perspective of disaster prevention and control, i.e., original occurrence of moisture in the coal matrix and the extraneous moisture from the technological process. A suit of coal bodies with different extraneous moisture was prepared by soaking long-flame coal with a low water content. Using a temperature-programmed oxidation test, the effects of extraneous moisture on the temperature increase rate of coal bodies and the emission characteristics of gaseous products during coal spontaneous combustion were studied. Moreover, combined with the characterization of thermal analysis and of pore structure test, the action the mechanism of extraneous moisture on the coal spontaneous combustion process was also explored. The experimental results indicated that the effect of the extraneous moisture content varied with the development of coal spontaneous combustion. In the slow oxidation stage, extraneous moisture played a physical inhibition role in the coal oxidation. In the accelerated oxidation stage, extraneous moisture exhibited a catalytic effect on the coal–oxygen reaction or directly participated in the reaction. After entering the rapid oxidation stage, a delayed effect appeared. When the coal temperature exceeded 180 °C, the spontaneous combustion characteristics of coals with different initial moisture contents gradually tended to achieved balance.
Highlights
During coal production, its spontaneous combustion adversely threatens the life safety of mining personnel and production safety of mining enterprises [1,2]
It can be seen that the mechanistic actions of the extraneous moisture varied with the increase of coal temperature and the process of coal spontaneous combustion can be divided into three stages
The heating rate of coal samples decreased with the increase in the extraneous moisture content; that is, the coal samples with a high moisture content exhibited a slow heating rate, mainly related to the coagulation of extraneous moisture in the porous structure on the coal particle surface at this stage, thereby inhibiting the diffusion of oxygen and reducing the contact area between coal and oxygen
Summary
Its spontaneous combustion adversely threatens the life safety of mining personnel and production safety of mining enterprises [1,2]. The internal moisture in coal refers to the moisture originally present, which exists in an absorption or agglomeration mode in the capillary pores with a diameter of less than 10−5 cm in internal coal. Energies 2020, 13, 1969 present moisture that is adsorbed on the coal surface or within the capillary pores with a diameter of greater than 10−5 cm. It is considered that there is a critical value between the external moisture and internal moisture, at which moisture has the greatest promoting effect on coal spontaneous combustion; above or below this threshold, the oxidation of coal will be inhibited to a certain extent [7,8]
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