Co-Pyrolysis of Coal and Different Biomass Resources : Pyrolysis Characteristics, Gas Release, and Volatile-Char Interaction Mechanism

The volatile-char interaction mechanism and devolatilization characteristics during co-pyrolysis of a bituminous coal (BC) and four different types of the biomass were deeply investigated with the integrated approaches. The results showed that co-pyrolysis of BC and the biomass presented obvious synergy in the respects of volatile release, gas formation, pyrolysis kinetics, and char structure. Co-pyrolysis of BC and the biomass increased the maximum devolatilization rate and activated energy (E), but had no influence on initial and maximum devolatilization temperatures compared to individual pyrolysis below 380 oC. Co-pyrolysis of BC and the biomass produced larger amounts of C–O and C=O bearing compounds, but less CO, CH4 and C2+ aliphatics. Blending the two herbs in BC could generate less CO2 and arenes, but more porous structures in the chars compared with the woody biomass. The kinetic study suggested that co-pyrolysis of BC and the biomass obeyed 1.5 order reaction mechanism and the synergy in terms of E values was related to both biomass species and reaction temperatures. Furthermore, a new volatile-char interaction mechanism was proposed to interpret the existence of the strong external molecular interaction between BC volatiles and the bio-chars at the secondary pyrolysis stage within 380–650 oC