| There are different tendencies of spontaneous combustion for different metamorphic degree of coal; but they both have exothermic properties. Thus, the change of oxidation characteristics and main functional groups for different metamorphic degree of coal was investigated during the heating process. In addition, the performance of inhibitor is explored for inhibition of oxidation and exothermic behavior of coal by inerting of functional group and absorption of heat. The main findings are shown as follows:(1) STA-FTIR technology was used to observe the change of oxidation characteristics of coal. According to experimental results, with the decrease in metamorphic degree of coal, the volatile matters were increased, and the characteristic temperatures were gradually decreased. The apparent activation energy and frequency factor of different stages were lower, and heat release rate and total released heat is higher. In addition, there was a full combustion process and generation of great amounts of CO2 and less CO with lower metamorphic degree of coal, and the initial temperature and peak temperature for gases releasewere lower.(2) The differences of functional group of coal were investigated by DRIFTS during the heating process. From the results, the proportions of main functional group for any kind of metamorphic degree of coalwas oxygen containing functional group > aromatics > fat hydrocarbon. With the increase ofmetamorphic degree of coal, the proportions of fat hydrocarbon and aromatics were gradually increased, but the proportion of oxygen containing functional group decreased. Additionally, we found that fat hydrocarbon and oxygen containing functional group were the main functional groupsduring oxidation reaction of coal during heating process. Moreover, the activity of these functional groups became higher with lower metamorphic degree of coal.(3) Based on the inert function of functional group and inhibition of exothermic reaction for coal, the solid inhibitor, Zn/Mg/Al-CO3-LDHs,is prepared to combine with six types of coal byin-situ co-precipitation method, forming the complex materials of Zn/Mg/Al-LDHs/coal composites(CLCs). The structure of LDHs and CLCs could be identified by FT-IR, XRD, and SEM/EXD. The chemical and physical inhibition mechanisms of LDHs were also explored by STA-FTIR and DRIFTS. We found that the –OH of LDHs was able to generate the weak hydrogen bond which could react with the active–COOH functional group of coal. In addition, the surface adsorption and binding equilibrium is formed amongZn2+, Mg2+, and Al3+ and coal that could delay the oxidation and decomposition reaction to some extent for main functional groups of coal during heating process, decreasing the oxidation reaction rate of coal. Moreover, LDHs have multistage endothermic reaction based on thermal decomposition during heating process that could adsorb the heat from oxidation reaction to decrease the temperature of coal. Therefore, the spontaneous combustion of coal is further prevented and controlled.(4) Based on physical inhibition mechanism of cooling and decalescence, a temperature-sensitive liquid inhibitor P(NIPAm-co-SA)was synthetized, and the optimum polymerization conditions of P(NIPAm-co-SA)was determined by orthogonal tests. The chemical characteristics of P(NIPAm-co-SA)were identified by FTIR. The phase change and prevention and control mechanism of spontaneous combustion of coal via the effects of P(NIPAm-co-SA)was analyzed by performance of temperature, fluid change, and heat. According to the results, P(NIPAm-co-SA) possessed excellent sensitivity to temperature and high thermal stability. The LCST of P(NIPAm-co-SA) is 59℃. At lower temperature, P(NIPAm-co-SA)was able to dissolve into water, and it has outstanding fluidity to easily permeate into the interior of coal, forming a cladding layer. Moreover, when the temperature of P(NIPAm-co-SA) reaches to LCST, the endothermic reaction occurred due to phase change and the water could be exhausted during the process. At the same time, the concentration, viscosity, properties of fluid change were also obviously changed. So P(NIPAm-co-SA) could adhere to the coal surface, isolating the contact of the oxygen. In addition, a great amount of water vapor could lower the temperature of coal. Therefore, P(NIPAm-co-SA) has excellent inhibiting effect and is a highly efficient water extinguishing agent.(5) We use the STA-FTIR technique to determine the inhibiting effect ofZn/Mg/Al-CO3-LDHs, thermosensitive hydrogel, and three types ofcommercialinhibitors(ammonium phosphate, sodium phosphate,magnesium chloride) based on various critical factors, such as characteristic temperatures, total heat release, released gases, and apparent activation energy. According to the results, the inhibiting effect of self-made Zn/Mg/Al-CO3-LDHs and P(NIPAm-co-SA) is obviously better than commercial inhibitors for different metamorphic degree of coal. Therefore, they could be used as green and environment-friendly material to prevent the spontaneous combustion of coal. |
