In order to inhibit the intrinsic metal in coal to catalyze the spontaneous combustion of coal, three different types of metal-chelating agents were selected to react fully with coal, and thermogravimetric and differential scanning calorimetry curves of coal samples and gas generated during coal oxidation were obtained through temperature-programmed experiments. The effects of these additives on coal spontaneous combustion were analyzed by characteristic temperature, exothermic peak parameters, and CO and CO2 emission laws. The results show that the addition of oxalic acid promotes the spontaneous combustion of coal, ethylenediaminetetraacetic acid, and phytic acid and can inhibit the spontaneous combustion of coal, and the inhibition effect of phytic acid is better. The mechanism of phytic acid inhibition of coal samples was analyzed by Fourier transform infrared spectroscopy. It was found that phytic acid can capture metal ions in coal to form stable chelates. The oxygen-containing functional groups in coal combine to form an ether, ester, and hydrogen-bonded cross-linking structure, which improve the stability of coal macromolecules. In the oxidation reaction, phytic acid reduces the free radical content of the system and inhibits the chemical adsorption of coal to oxygen, thereby delaying the spontaneous combustion of coal. The inhibitory effect of phytic acid on the spontaneous combustion of coal with different metamorphic degrees was compared. It was found that phytic acid had a significant inhibitory effect on low rank coal. The minerals in the coal were analyzed by water and hydrochloric acid treatment, and it was found that the phytic acid was mainly combined with the exchangeable minerals in the coal. It is considered that phytic acid is a new type of high-efficiency low rank coal spontaneous combustion inhibitor, and it is very friendly to the environment. The results can provide new ideas for preventing the spontaneous combustion of coal.

Abstract:To improve the prevention of spontaneous coal combustion, reduced iron powder and other ingredients should be added together to form an iron-based deoxidizing inhibitor, with the dual effect of oxygen consumption and inhibition. The oxygen consumption rate of the inhibitor was studied through experiments. According to the theory of coordination resistance, the coordination resistance of Fe 3+ was studied via the density functional method. Subsequently, a comparative experiment of the effects on spontaneous coal combustion was conducted. The research shows that several kinds of common resistance agents that are added to the reduced iron powder can consume oxygen. However, the rate of oxygen consumption varies. Fe 3+ produced by the reduced iron powder indicates a strong coordination resistance. When compared with traditional inhibitors of Mg 2+ , Fe 3+ has a stronger inhibition effect on the N, P, and S reactive groups in coal. The overall inhibitory effect is better than that of traditional inhibitors, because of the increased oxygen consumption and the coordination resistance of Fe 3+ on the basis of traditional inhibitors.

A new method is proposed based on temperature-controlled self-reaction to generate and release inhibitors in the form of foam at a specific temperature, which can overcome the disadvantages of short effective time and low efficiency in the inhibition of the spontaneous combustion of coal when inhibitors are released in advance, and greatly increase the action range of inhibitor through foam diffusion. The proposed temperature-controlled foaming system was prepared with hollow spheres as solution carriers, NaHCO3 and acetic acid as basic reactants, reaction-generated CO2 as foaming gas, sodium dodecyl sulfate and sodium carboxymethyl cellulose as foaming additives, NaCl, MgCl2 and CaCl2 as additives to enhance inhibition effect, and temperature sensitive paraffin as insulating material to generate and release inhibitor foam. The effects of releasing foam on restraining the spontaneous combustion of coal were studied based on the experimental analysis of the optimum ratio of reactants and additives, hollow sphere parameters, released temperature of the foam and variation rule of CO generated by coal oxidation. The obtained results showed that the released temperature of foam was 59–61°C and the covered area of pulverized coal by inhibitor foam was 12.9–13.9 times higher than when it was directly wetted by inhibitor solution. The total effects of inhibition and inerting were achieved after pulverized coal was wetted with inhibitor foam and the efficiency of restraining the spontaneous combustion of coal reached 88.51–97.06% when temperature was increased to 160°C.

The KBr pellet press method for detecting the infrared spectrum of coal is one of the commonly used methods for analyzing the types and content of functional groups in coal. However, KBr crystalline water or moisture has a significant impact on the peak position, peak shape, and peak area of the organic O–H based stretching vibration wave in coal. In this paper, the theoretical characteristics of infrared spectra of phenols and alcohols have been simulated and analyzed using the Gaussian 16 series of programs. Four infrared spectral analysis techniques, in situ infrared, KBr pellet press, dry KBr pellet press, and paste methods, have been used to detect the infrared spectra of coal. The results show that the stretching vibration peaks of free O–H radicals without hydrogen bonding are located between 3700 and 3600 cm–1. After the O–H form hydrogen bonds with each other, the O–H stretching vibration frequency moves toward the low frequency direction, and the lower the wavenumber, the more O–H content. The conventional KBr gasket manufacturing process will absorb moisture in the air to interfere with the hydroxyl absorption peak of coal, and the experimental process requires absolute drying. The relative content of hydroxyl in coal can be compared and analyzed based on the peak position, peak shape, and peak area of the hydroxyl stretching vibration wave. Quantitative analysis of hydroxyl groups in coal also requires combination of elemental analysis and X-ray photoelectron spectroscopy.

We propose an experimental adsorption device, imitating the environment of a coal-mine goaf and the composition of the flue gas in Tashan Mine Power Plant. The characteristics of the coal adsorbing flue gas were studied with the atmospheric volumetric method. The factors affecting the seal of CO 2 were analyzed and the effect of power plant flue gas on fire prevention in the goaf was investigated at normal temperature and pressure. It can be inferred from the experiment that N 2 , SO 2 , and H 2 O can also reduce CO 2 adsorption capacity. The increase or decrease in pH can increase the adsorption capacity of CO 2 , which is apparently larger when the pH is decreasing than when the pH is increasing. The O 2 adsorption capacity can evidently be reduced when the power plant flue gas is injected into the goaf. The activation energy of coal burned in air is greater than that of coal burned in flue gas, indicating that the use of power plant flue gas, with N 2 and CO 2 as the main components, to replace the traditional inert gas can not only save N 2 generation cost, but also reduce the emission of greenhouse gases, while the power plant flue gas can be adsorbed by coal.