Abstract: In order to reveal the effect of particle size on gas methane desorption from coal seam,physical simulation experiments were carried out the difference of gas desorption capacity and desorption.Differences between the cylindrical coal sample and the granular coal sample of anthracite (high metamorphic) coal and those of long flame coal (low metamorphic) in the effects on the gas desorption amount and the desorption rate were studied under different adsorption pressure conditions.The results show that there is a positive correlation between both the cumulative gas desorption amount and the desorption rate and the coal's metamorphism in the whole desorption process,that the cumulative gas desorption amount from granular coal is always greater than that from column coal,and the difference between the two increases first and then decreases,that particle size has an obvious effect on both the cumulative gas desorption amount and the desorption rate under the same metamorphic degree and pressure,and that the two granular coal sample grades of 0.5-1 mm and 1-3 mm are about to reach the limit of granularity in the desorption amount.

Key words: gas desorption, particle size effect, cylindrical coal, granular coal, simulation test, desorption law