Effect of Pressure and Heating Rate On Biomass Devolatilization and Gasification

The goal of present study is to characterize the effect of pressure and heating rate on the devolatilization behavior of different biomass species.  Three biomass species (southern Pine, corn stover, and switchgrass) were studied. A combination of two complementary gasification devices are utilized in this study: (i) pressurized entrained flow reactor (PEFR) provides high heating rates (≥ 10^{3 o}C/sec) and short residence times (1-20 sec), and (ii) pressurized thermo-gravimetric analyzer (PTGA) provides lower heating rates (0.1-1 ^oC/sec), but larger residence times (5-100 min). The pressurized thermogravimetric analyzer connected to a mass spectrometer and a Fourier-transform infrared analyzer provides information on the evolution of gaseous species during pyrolysis.

The char yield appeared to increase with an increase in pyrolysis pressure. The yields of the lighter gas components (CO, CO₂, H₂, CH₄, H₂O) increased as the pressure was increased. The increase in the amount of char and lighter gases was accompanied by a decrease in the formation of tar species. This was supported by an observed decrease in furan and furfural and higher hydrocarbon fragments with increasing pressure. There were clear differences in the evolution of gaseous species between the woody and herbaceous and agricultural residue feedstocks. The evolution of char morphology is strongly influenced by pyrolysis pressure and heating rates. The results suggest a complex role of pyrolysis conditions and biomass ash content on the char reactivity.