Thermal behavior and the evolution of char structure during co-pyrolysis of platanus wood blends with different rank coals from northern China

Co-thermochemical conversion of biomass and coal has been extensively investigated as an effective means to reduce the emission of greenhouse gas. Successful evaluation on the thermal behavior and product characteristics of the co-pyrolysis process is of crucial importance for predicting performance and improving efficiency of this technology. In this study, thermal behavior of platanus wood, two different rank coals (Pingzhuang lignite and Shenmu bituminous) and their blends during pyrolysis were studied via thermogravimetric analyzer. Raman spectroscopy technique was further employed to study the evolution of char structure. Thermogravimetric experiments indicated that the pyrolysis characteristics of their blends cannot be accurately forecasted based on individual component and blending ratio. The non-additive behavior of thermogravimetric curves of the blends suggested the existence of synergistic effects, which can promote the volatiles yields during the co-pyrolysis process. The most obvious synergistic effects were observed when the coal blending ratios were 30% for Pingzhuang lignite and 50% for Shenmu bituminous, respectively. In addition, iso-conversional method was used to solve activation energy. Non-additivity performance in the mean activation energy values of the blends was observed. The Raman results revealed that as the platanus wood blending ratio increased the Raman peak intensities of the char samples from pyrolysis of the blends also increased, which was probably attributed to the competition of oxygen-containing groups increment and disproportional impact of alkali and alkaline-earth metal species. The intensity ratios of some major Raman bands can provide useful information on char structure evolution. The generation of smaller aromatic rings structures (3-5 fused rings) was favored in these char samples with the higher platanus wood blending ratio.