Influence of Organic Sulfur on Low-Temperature Oxidation of Coal and its Transition Characteristics

Abstract

The low-temperature oxidation spontaneous combustion of coal was caused by the active groups in its structure. The oxidation mechanism of carbon and oxygen functional groups in coal had been extensively studied, but there were few reports on the study of sulfur functional groups initiating the coal spontaneous combustion. To investigate the influence of organic sulfur functional groups on the spontaneous combustion of high-sulfur coal and explore its transformation characteristics, the low-temperature oxidation experimental system was used to study the spontaneous combustion tendency of coal with similar metamorphic degrees and different organic sulfur contents. The variations of element forms and organic sulfur functional groups were analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy during low-temperature oxidation of coal and model compounds. The results showed that the forms of organic sulfur in coal mainly included mercaptans, thioethers, thiophenes, sulfones (sulfoxides), and sulfates, and the low-temperature oxidation of coal was not only related to the content of organic sulfur but also related to its type. The coal samples, which possess a low content of total sulfur and a small proportion of active organic sulfur groups such as mercaptans and thioethers, had a lower concentration of indicator gas and a smaller tendency to coal spontaneous combustion. After low-temperature oxidation, the content of mercaptan, thioether, thiophene, methyl(methylene), and pyridine in coal decreased, and the content of oxygen-containing groups such as sulfone (sulfoxide), sulfate, carboxyl, and nitrogen oxide increased. The elements of S, C, and N all changed to a high-valent state. In the oxidation reaction of model compounds, mercaptans were more reactive than thiophenes in the low-temperature region, and the oxidation of thiophene could direct form sulfone (sulfoxide), while the oxidation of mercaptan formed disulfide first. It is speculated that low-valence sulfur migrated to a high-valent state by providing sulfhydryl radicals (•SH) and sulfur radicals (C–S•) combined with active oxygen atoms. After the low-temperature oxidation reaction of model compounds, some organic sulfur existed in the form of aromatic sulfur or sulfur oxides and a small part of sulfur escaped as SO2 and H2S gases in the solid oxidation product.

Combustion properties and pollutant analysis of coal-blended bio-heavy oil fuel

“…This is mainly because coal is a fossil raw materials, which is a product obtained during the processing of crude oil, and thus, has no oxygen-containing functional group. 34,36 While bio-heavy oil is a raw material obtained from biomass processing and is enriched with oxygen-containing functional groups, enhancing its combustion potential. 29 …”

“…In addition, there is a big difference between the chemical compositions of bio-heavy oil and coal, which affects the fuel combustion process. 29,34,35 As shown in Table 1, bio-heavy oil has lower sulfur (0.073%) and nitrogen (0.18%) contents and higher oxygen (11.005%) content than coal. This contributes to cleaner exhaust emissions and enhanced fuel performance.…”

“…This is mainly because coal is a fossil raw materials, which is a product obtained during the processing of crude oil, and thus, has no oxygen-containing functional group. 34,36 While bio-heavy oil is a raw material obtained from biomass processing and is enriched with oxygen-containing functional groups, enhancing its combustion potential. 29 Utilizing a micro-computerized automatic touch calorimeter, we probed the impact of both moisture content and various bio-heavy oil blending ratios on the combustion calo-ric value of the fuels.…”

Experimental Study of Three-Dimensional Time Domain of Water Evaporation from Goaf

“…As shown in Figures 2 and 3, the inhibitor in the goaf moisture evaporation system mainly consists of coal, experimental box, PVC pipe (20), fan (21) and fan speed regulator. The experimental acquisition system is mainly composed of the coal body moisture sensor (1~15), air temperature and humidity sensor (16,18), Pitot tube (17,19), handheld wind pressure and wind speed measuring instrument, monitoring substation and computer. The PVC pipe size specification is 1000 (mm) × 110 (mm).…”

“…It is well known that the oxidation process of coal continues even at room temperature. When the heat produced by the oxidation of the coal body is greater than the heat dissipated, the coal temperature begins to rise [18,19]. When the temperature rises to the critical temperature of coal spontaneous combustion, the coal oxidation process will be accelerated [6,20,21].…”