Study on co-pyrolysis and co-gasification of hydrothermal carbonized biomass and coal

The co-thermochemical conversion of coal and biomass can contribute to the low carbonization of current fossil energy system. In this work, the bituminous and lignocellulosic biomass were selected to study the co-pyrolysis and co-gasification of coal and biomass, with the consideration of different hydrothermal carbonization (HTC) temperature and biomass blending ratio. The synergistic effect of co-pyrolysis and co-gasification was analyzed by using the thermogravimetric analyzer, and the H₂ release property was investigated by the online mass spectrometer. The model-fitting method was adopted to analyze the overall kinetics during pyrolysis and gasification stage, respectively. The results showed that the synergistic effect of coal and biomass in co-gasification stage was much stronger than that in co-pyrolysis stage. The gasification synergy was enhanced with the biomass blending ratio, while the HTC pretreatment could weaken the synergy. The H₂ production was inhibited during co-pyrolysis. The first-order reaction model could well describe the co-gasification process, while the n-order reaction model was suitable for the co-pyrolysis process. For the blends of raw or the slight HTC biomass and coal, the overall pyrolysis activation energy (E_a) was greater than that calculated by the weighted average, whereas the overall gasification E_a showed the opposite trend. For the blends of the severe HTC biomass and coal, the E_a of co-pyrolysis and co-gasification were both close to the weighted average value.