Hydrothermal carbonization of maize straw for hydrochar production and its injection for blast furnace

The aim of this paper was to investigate the characterized hydrochar of maize straw prepared via the hydrothermal carbonization (HTC) process as a solid fuel for blast furnace injection. The effect of HTC conditions on the yield, physicochemical properties and combustion reactivity of hydrochar were evaluated by varying the HTC temperature over the range of 220–340 °C and the HTC time over the range of 15–120 min. The results showed that with the increase in HTC temperature and time, the yields, H/C and O/C values of hydrochar decreased, and the higher heating value increased. These characteristic changes in hydrochar are similar to those in bituminous coal because of dehydration and decarboxylation. The physicochemical properties and structure analyses showed that the specific surface area increased first and then decreased; meanwhile, the CC, CO and aromatic functional groups gradually increased. The carbonaceous structure of hydrochar became more compact, orderly and stable. Compared to the feedstock of maize straw, the combustion of hydrochar was expected to have higher ignition energy and become more stable with its higher ordering degree of the carbonaceous structure. HTC could be used as an effective method to convert maize straw biomass to a high quality solid injection fuel for the blast furnace.