Effect of Alkali and Alkaline Earth Metallic Species on Gas Evolution and Energy Efficiency Evolution in Pyrolysis and CO2-Assisted Gasification

In this study, the same moles of alkali and alkaline earth metallic species were introduced into pine wood to investigate their effects on biomass pyrolysis and carbon dioxide-assisted gasification. First, thermogravimetric analysis was conducted to examine the pyrolytic behavior of pine wood loaded with alkali and alkaline earth metallic species. A semi-batch fixed bed platform was used to quantify gaseous product parameters, including gas mass flowrate, gas yield, recovered energy, energy efficiency, and net carbon dioxide consumption. Thermogravimetric results indicated that the loading of alkali and alkaline earth metallic species promoted the thermal decomposition of pine wood at low temperatures, but an inhibitory effect was observed at high temperatures. In terms of pyrolysis, adding alkaline earth metals increased syngas yields, and recovered energy, as well as energy efficiency, whereas alkali metals had the opposite effect. For the gasification, the loading of alkali metals showed a stronger catalytic than the pine wood loaded with alkaline earth metals. Based on the evolution of carbon monoxide, the effects of alkali and alkaline earth metallic species on enhancing the biochar's gasification reactivity were in the sequence of sodium > potassium > calcium > magnesium. In addition, the addition of alkali metals exhibited a stronger capacity for carbon dioxide consumption, which contributed to the management of the greenhouse gas. Considering only energy efficiency, adding alkaline earth metals in biomass pyrolysis is an optimal choice due to the higher overall energy efficiency obtained in less time.