Second-generation bioenergy to decouple fossil fuel dependency and environmental deterioration: Dynamic and optimal mechanisms and gas-to-ash products of combustion of Pennisetum hydridum

Second-generation biofuels may show great potential for decoupling fossil fuel reliance and environmental deterioration. This study aimed to characterize the dependency, drivers, and gas-to-ash products of the combustion of Pennisetum hydridum (PHY). The activation energy of the two main combustion stages and their best-fit mechanism models were 221.01 kJ·mol⁻¹ (F4) and 191.59 kJ·mol⁻¹ (D1) in the air combustion and 202.26 kJ·mol⁻¹ (F3.5) and 199.09 kJ·mol⁻¹ (D3) in the oxy-fuel combustion. High atmospheric concentration of CO₂ delayed the peaks of the mass loss curve, increased the release of C-containing products (CO, CH₄, and some small molecule organic matters), decreased or delayed the release of N-containing products (HCN and NH₃), and reduced the slagging risk of ash, presenting a loose and porous structure. Owing to the high K content, part of K formed K₂SO₄ and KCl, finally decomposed into gaseous products, with remaining K being retained in the ash as silicates and aluminosilicates. The maximized energy performance and the minimized emissions of gaseous products were jointly optimized in the combustion range of 500–993 °C. Findings of this study can provide insights into a better development of the comprehensive utilization of PHY from the perspective of bioenergy efficiency and eco-friendly disposal.