Co-pyrolysis behavior of microalgae biomass and low-quality coal: Products distributions, char-surface morphology, and synergistic effects

•Products distributions and synergistic effects were investigated during co-pyrolysis of coal and Green algae.•A process mass spectrometer was applied to track the releasing characteristics of volatiles.•Both positive and negative synergistic effects were observed on the yield and composition of volatiles.•Fractal analysis on the morphology of co-pyrolysis char indicating GA promoted homogeneity of the char surface. In this work, the distributions and releasing properties of the primary volatile products during co-pyrolysis of low-rank coal and green algae (GA) has been studied using fixed-bed reactor with online mass spectrometry. Surface morphology of the char was described quantitatively by SEM combined with fractal theory. Different forms of synergistic effects existed from both the yields of products and composition of the main gaseous products. Positive synergistic effects from tar yield were observed under 25% of GA from 600 to 850 °C, indicating GA promoted the formation of tar. Opposite synergistic effects on the content of H2 and CO were gained when the mass ratio of GA was 50%. The fractal dimensions of co-pyrolysis char were less than the calculated values except under 650 °C, which meant the GA promoted the homogeneity of char surface. This work could provide essential data for proper operation parameters selecting for co-pyrolysis.