Abstract: The fractal dimensions of four biomass chars from rice shell, leaves of Platanus orientalis L., corn stalk and cotton stalk were calculated using Menger sponge model and thermodynamic model based on measured results of their pore structure by mercury porosimetry. The results showed that thermodynamic model was close to pore structures of biomass chars. The fractal dimensions of biomass chars were bigger,i.e. irregularity and changed with varieties of biomass. The fractal dimension of biomass char from leaves of P.orientalis L. was the biggest in four biomass chars, meanwhile that from corn stalk was the smallest. The fractal dimensions of biomass chars were influenced by factors such as pyrolysis temperature, pyrolysis rate, and pyrolysis time for preparation of chars. The influence of pyrolysis temperature was the biggest in above factors. The influences of pyrolysis conditions depend on the plasticity of biomass.

Key words: biomass char, pore, fractal characteristics