Effects of Hydrothermal Carbonization Process Parameters on Physicochemical Properties and Combustion Behavior of Maize Stalk Hydrochars

Hydrothermal carbonization (HTC) is an effective method to improve the performance of biomass fuels. In this work, the reusable maize stalk (MS) hydrochars were prepared at different carbonization conditions, and the effects of carbonization parameters on physicochemical properties, recovery rate, coalification mechanism and combustion behavior of MS hydrochars were investigated. The results show that with the increase of temperature and time, the particle size, O/C and H/C ratios, flammability index and comprehensive combustion characteristic index of MS hydrochars decrease gradually, while the calorific value, ignition temperature (T_i), and burnout temperature (T_f) increase gradually. The combustibility and combustion reactivity of MS hydrochars are significantly better than anthracite. Under the optimal carbonization conditions (260 ºC, 40 min, solid–liquid ratio of 2%), MS hydrochar has a high carbon content and calorific value, and the carbon content and calorific value of MS are 66.85 and 22.36 MJ·kg⁻¹, respectively. HTC technology can effectively transform MS biomass into high energy density solid fuel, which provides a theoretical basis for expanding the application field of hydrochars.