Understanding the pyrolysis synergy of biomass and coal blends based on volatile release, kinetics and char structure

The devolatilization characteristics, kinetics, and volatile-char interaction mechanism during co-pyrolysis of a bituminous coal (BC) and four kinds of biomass were deeply investigated by the integrated pyrolysis method to achieve new understanding of the pyrolysis synergy. 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 °C. In addition, co-pyrolysis of BC and the biomass produced more C–O and C=O bearing compounds, but less CO, CH4 and C2+ aliphatics. Compared with the woody biomass, blending the two herbs in BC generated less CO2 and arenes, but more porous structures in the chars. The study on the pyrolysis kinetics suggested that co-pyrolysis processes obeyed 1.5 order reaction mechanism and the synergy in terms of E was related to both biomass types and reaction temperatures. Furthermore, a new volatile-char interaction mechanism was proposed to interpret the existence of the external molecular interaction between BC volatiles and the bio-chars in the temperature range of 380–650 °C.