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This paper selects the unsoaked air-dried coal (USC), air-dried coal with 1 month’s water soaking (S 1 ), air-dried coal with 3 months’ water soaking (S 3 ) and air-dried coal with 5 months’ water soaking (S 5 ) as the research objects to analyze the adsorption law of coal to CH 4 , oxygen, nitrogen, and mixed gas, and the changes of free radical concentrations, aliphatic hydrocarbons, and oxygen-containing functional groups under gas atmospheres with different CH 4  concentrations during low-temperature oxidation process by using ESR and FTIR. The experimental results show that the effect of soaking time on CH 4  adsorption amount is greater than that on O 2  and N 2  adsorption amounts. It can be seen by investigating the O 2  concentration after the desorption process that there is no significant relationship between the O 2  concentrations of three kinds of coals and different soaking time under the mixed gas with 0% CH 4  concentration. However, there appears a certain law for O 2  concentrations under the mixed gas with 25% and 45% CH 4 . The oxygen concentration of S 1  is obviously higher than those of S 3  and S 5 . Furthermore, there exists an upper limit of CH 4  concentration to inhibit free radicals concentration of S 1 , about 35%. Obviously, the CH 4  concentration points of S 3  and S 5 , at which the decrease rate of free radicals concentration slows down, appear earlier than that of S 1 . The concentrations of -CH 2  – and -CH 3  of S 1  gradually decrease in the initial stage and start to rise once the temperature exceeds 120°C. The change law of aliphatic hydrocarbon of S 3  is similar to that of aliphatic hydrocarbon of S 1 . The concentration of aliphatic hydrocarbon of S 5  starts to increase from 25% in the initial stage. The -OH concentration decreases sharply as starting oxidizing, and then the decrease gradually slows down. With the CH 4  concentration increasing, the -OH concentration slowly increases, thus the decrease of -OH concentration reduces. Furthermore, the results show that the declining rate of -OH concentration in S 1  is higher than those of -OH concentrations in S 3  and S 5 . The -COOH of S 1  rapidly decreases in the stage of 40–120°C. But with the increase of CH 4  concentration, the decrease rate is obviously smaller. The decrease rate of S 3  further slows down at the initial stage, and there is no increase in the -COOH content of S 5 .

combustion science and technology

Adsorption Characteristics of Soaked Air-dried Coal and Reaction Characteristics of Free Radical Functional Groups in CH 4 -containing Oxidizing Atmosphere