Adsorption—Desorption Behavior And Facies Control Of Coals

Adsorption and desorption behaviors of coal controlled by coal facies have been analysed through the experiments on the stratified seam-samples from No.2, No.4 and No.9 coal seams in Xiqu, Gujiao mining area. Referring to the GI-TPI diagram, five basic types of coal facies were identified by Q cluster analysis. The peat bogs were evolving in cycles and jump, which indicated pulsant changes of the bog water. The adsorption data were fitted by the models of Langmuir and D-A and the coal facies control of adsorption was analysed. Likewise, the desorption characteristics were discussed by fitting the desorption data by models of Langmuir and Weibull. The study suggests that coal developed from herbs has a stronger adsorption ability than those from the woody plants. Maceral with original structural pores is advantageous to both adsorption and desorption. The research found that the adsorption ability of coal in the low moor under the barrier-lagoon(facies A) is the poorest, the desorption ability is relatively strong and the desorption rate is medium. Both adsorption and desorption abilities of coal in the forest swamp under the barrier-lagoon(facies B) are relatively strong and the desorption rate is the highest. The adsorption ability of coal in the low moor under the lower delta plain(facies C) is strong while the desorption ability is relatively poor and the desorption rate is the lowest. The adsorption ability and desorption ability of coal in the wet forest swamp under the upper delta plain(facies D) are relatively strong as well as the desorption rate. To the contrary, the adsorption ability of coal in the dry forest swamp under the upper delta plain(facies E) is very poor and both the desorption ability and desorption rate are relatively low. According to the types of original plants, pore structure, ash yield, etc, geological causes contributing to these differences of adsorption and desorption among coal facies are further discussed. Finally, it is forecasted that the CBM exploitation conditions are good in No.2-Ⅳ stage of No.2 coal seam and the whole No.9 coal seam while poor in No.4 coal seam.