We collected 8 kinds of low rank coal (LRC) with distinguished macrolithotypes

carried out some experiments like the low-temperature liquid nitrogen adsorption and isothermal methane adsorption

discussed the LRC adsorption pore characteristics

and established the relationship between fractal model suitable for LRC adsorption pores and fractal dimension with pore structures and adsorption capacities.From this

the LRC absorption/desorption curves are divided into four categories with 4 corresponding pore types:taper-shaped pores with one end closed being dominant in bright coal

ink-bottle-shaped pores dominating semi-bright coal

open-cylindric pores and wedge-shaped ones occurring in semidull coal

and open-cylindric pores being predominant in dull coal.Results show that (1) compared with the BET model

the FHH model is more appropriate for the characterization of LRC pores in respect of fractal nature;(2) the various macrolithotypes in FHH model show different adsorption characteristics at relative pressure 0~0.5 and 0.5~0.5 and have fractal dimensions D

21

and D

22

respectively

with D

21

representing the surface roughness of adsorption pores and D

22

the irregularity of the pore structures.As D

21

gets bigger

the pore specific surface area increases

whereas the bigger D

22

gets

the smaller the average pore size becomes

the higher the micropore content is

and the larger the pore heterogeneity is;(3) D

21

is more effective than D

22

in controlling the adsorption capacity of LRC.When the coal is characterized by high D

21

and low D

22

the adsorption capacity is the strongest

and the adsorption capacity enlarges as the fractal dimension of cumulative specific surface area increases.The LRC adsorption process subsequently shows transition from predominance of monomolecular layer adsorption to predominance of polymolecular layer adsorption with increasing pressure.