Effects of pyrolysis pressure on the properties and gasification reactivities of biomass chars

Biomass chars were prepared under different pyrolysis pressures in a pressurized fixed bed reactor. The evolution of chemical composition and physical structure of the biomass chars with the change of pyrolysis pressure were observed by BET, XRD, CHNS elemental analyzer and ICP-AES. The reactivities of biomass chars were evaluated by a thermogravimetric analyzer. The results show that the yields of biomass chars increase with increasing pyrolysis pressure, but reach a plateau above 1.0 MPa. With increasing pyrolysis pressure C content in biomass chars increases, while H content and BET surface area decrease. The degree of graphitization of corn stalk char and sawdust char increases with increasing pyrolysis pressure, while that of rice husk char shows almost no dependence on pyrolysis pressure. The average gasification rates of corn stalk char and sawdust char all decrease with increasing pyrolysis pressure, while pyrolysis pressure has little influence on the gasification rate of rice husk char. Compared the evolution of BET surface area and carbon crystallite structure of biomass chars with biomass char gasification rate, it shows that the difference of carbon crystallite structure of biomass chars, which was brought out by the change of pyrolysis pressure, mainly contributes to the difference of gasification rate of biomass chars prepared under different pyrolysis pressures.