Potential of hydrothermal carbonization route to enhance the combustion-related properties of bamboo

In this study, hydrothermal carbonization (HTC) was proposed as an effective thermochemical pre-treatment for enhancing the quality of bamboo species. This goal was achieved by solubilization of the most problematic alkali metals, by this way improving the next use of the pre-treated biomass in combustion processes. Three different HTC temperatures (160, 180 and 200ºC) and reaction times (1, 4, and 8 hours) were employed, working at a constant biomass loading (10 wt%). The starting biomass and corresponding HTC-derived solids were characterized for the chemical compositions and for proximate analysis. Additionally, the estimation of ash composition (before and after HTC treatment), along with the fouling and slagging trends, were considered, to quantify the effectiveness of the HTC towards the solubilization of inorganics elements. Mild HTC conditions, 160ºC and 1 h residence time, was proved as the optimal choice to achieve the best removal of boosting fouling inorganics (such as K, Mg, and P), at the same time keeping a lower energy cost, and reducing the solubilization of compounds (such as Si), which could limit the alternative uses of the resulting liquid as a soil fertilizer. In this context, the fouling index of the HTC-pretreated biomass obtained under the best identified reaction conditions (0.27) was much lower than that obtained from the raw bamboo (0.91), thus demonstrating the effectiveness of the proposed pre-treatment for improving the combustion properties. This approach is not limitedly aimed at the improvement of the combustion properties of the starting biomass, but also opens the way to a more developed biorefinery scheme that involves the subsequent fractionation/exploitation of the structural macrostructural components of biomass, through thermal processes that may be sensitive to the relevant presence of inorganics.