In this study, Erianthus arundinaceus energy grass was examined by conducting hydrothermal carbonization (HTC) using a laboratory-scale autoclave in the temperature range of (180–240 °C) and the retention time of (0–120 min). The parent material and hydrochars were investigated in terms of mass yield, proximate and elemental analyses, the higher heating value (HHV), X-ray diffraction, Fourier transform infrared, and X-ray fluorescence (XRF) analyses. Furthermore, CO2 gasification was conducted on the pyrolysis char prepared from the parent material and the hydrochars using thermogravimetric analysis. It was found that increasing the HTC temperature and residence time caused the mass yield to decrease and the HHV to increase. Hydrochar crystallinity increased with HTC temperature up to 210 °C as a result of the deformation of the amorphous components, while under 240 °C, the crystallinity declined from its peak at 210 °C due to the commencing of cellulose degradation. The XRF analysis showed that the alkali index was increased due to increasing temperature and residence time. Gasification reactivity of the pyrolyzed hydrochar prepared at 180 °C was enhanced due to longer residence time (120 min), while those from very short residence time (0 min) showed a weaker reactivity than the parent material. Changing the HTC temperature showed minimal effect on the reactivity. At higher HTC temperature (240 °C), the catalytic activity was restricted by the highly ordered structure. This was not the case at 180 °C and long residence time of 120 min, where the reactivity was mainly controlled by the increased minerals.

In this study, Newlands coal, spirulina microalgae samples, and mixtures of them were gasified in a fixed-bed downdraft reactor by CO2 at the atmospheric pressure and in the temperature range of 950–1000 °C. The effects of the reaction temperature, the CO2 partial pressure, and the blending ratio on the syngas yield were studied. Results showed that the CO2 partial pressure did not affect the gas production yield until its value exceeded 0.05 MPa. The cogasification experimental results showed higher values than the predicted ones in terms of the gas production yield, especially H2 and CO components when the blending ratio of algae is 50% wt. This synergetic effect was mainly attributed to the catalytic activity of the high content of alkali and alkaline metals in algae. The increase of the reaction temperature led to a higher gas production yield as the Boudouard reaction is an endothermic reaction that went to a higher extent with the temperature increase.

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In this study, a mixture of breeding lines of Erianthus arundinaceus energy grass was pretreated prior to gasification. Although biomass torrefaction and subsequent pelletizing of torrefied biomass (TOP process) have been studied in details, the torrefaction of pellets (TAP process) still in its infancy. Therefore, samples prepared by TAP, torrefaction‐only and pelletizing‐only were compared in terms of fuel characteristics and gasification kinetics. Results showed that the mass yield decreased with increasing torrefaction temperature, whereas the higher heating value (HHV) continued to increase with temperature, which can be seen in the evolution of O/C and H/C atomic ratios. Tradeoff between mass yield and HHV points to 250°C as the optimum torrefaction temperature, as mass yield above 76% could be achieved. TAP process was superior not only in terms of producing fuel with higher energy density, but also the gasification reactivity was higher than that of torrefied‐only or densified‐only samples, suggesting TAP is promising to be employed within the gasification process. Yet, conducting TAP under higher torrefaction temperatures may weaken the reactivity due to the more release of potassium during pyrolysis. Lastly, gasification kinetics data revealed that the pretreated samples exhibited slightly higher activation energy.