Evaluation of combustion kinetics of corn stover hydrochar by cone calorimeter

Disposal of waste biomass has been an alarming issue for the U.S. over the past few years. A sustainable circular bio-economy has been a prime need to shift towards alternative fuels from traditional fossil fuels. Unfortunately, waste biomass contains high inorganics and low carbon content that makes biomass unfavorable for combustion. This study focused on converting the waste corn stover into carbon-rich biopolymer through Hydrothermal Carbonization (HTC) and evaluating the reaction kinetics in cone calorimeter at five heat fluxes (10-50 kW/m2). The biomass goes through HTC at 200, 230, and 260 °C for 30 mins and the hydrochars are characterized. Results indicate that the hydrochars possess higher lignin but lower cellulose/ hemicellulose biopolymers than biomass. The O/C and H/C ratios are significantly reduced augmenting heating value. The hydrochars are combustible at lower critical heat flux and ignition temperature. However, hydrochars also show higher ignition time and thermal response parameter because of high composition of lignin biopolymer (highly inert). The peak heat release rate of the hydrochars is more sensitive to external heat fluxes and sensitivity increases with increasing HTC temperature. The biomass is more thermally hazardous than hydrochars. The combustion of all hydrochars is mostly driven by the loss of volatile matter than the fixed carbon. Moreover, the activation energy for oxidation of fixed carbon and volatile matter are significantly reduced through HTC, suggesting smoother combustion of biopolymers. Regression analysis also confirmed that degradation of biomass/hydrochar follows first order rate kinetics. This study shows a sustainable route to synthesize biopolymers with increased combustibility than biomass.