Pyrolysis characteristics and char reactivity of Oedogonium sp. and Loy Yang coal

Abstract

The proposition of combining the application of algae in wastewater treatment, CO² fixation, and energy production maximizes the opportunity of algal bioremediation. In this paper, the freshwater macroalga Oedogonium, a key target species for the bioremediation of waste waters, was investigated for its utilization in energy production via gasification or co-gasification with coal. The pyrolysis characteristics of Oedogonium and the effects of pyrolysis conditions on char reactivity were investigated in this paper, and an Australian lignite was also studied for comparison purposes. The pyrolysis process of Oedogonium and coal can be divided into three stages: moisture evaporation, volatile release, and decomposition of the remaining carbonaceous compounds. However, the devolatilization of Loy Yang coal was slower and occurred over a wider temperature range compared to Oedogonium. As the heating rate increased, the pyrolysis curves for both Oedogonium and Loy Yang coal shifted to higher temperatures. To investigate the effects of pyrolysis conditions on char reactivity, a tube reactor was employed to generate char samples under a range of pyrolysis conditions. The produced char samples were characterized using a CHN analyzer and scanning electron microscopy technique. It was found that char samples almost maintain their original shape following pyrolysis at a low heating rate. However, evidence of char swelling was observed in the structure of chars prepared at a high heating rate. Pyrolysis conditions also had a significant influence on the reactivity of the derived chars. Char reactivity for both fuels was enhanced at a higher heating rate and lower pyrolysis temperature. Oedogonium char reactivity was around 2–5 times that of Loy Yang char prepared under the same pyrolysis conditions. However, the differences in reactivity became less significant as the pyrolysis temperature increased. Oedogonium has a higher devolatilization rate and higher char reactivity than Loy Yang lignite. It implies that it is easier to be gasified, and the co-gasification with lignite is advantageous.