A novel method for preparing high-quality biochar from straw via coupled water quenching and pyrolysis for steel metallurgy

A method coupling water quenching and pyrolysis is proposed to prepare high-quality biochar from straw, aiming to reduce the steel industry's dependence on coal. Pyrochar derived from tobacco straw at 400 °C, 600 °C, and 800 °C (designated as TC-400P, TC-600P, and TC-800P) was subjected to water quenching to obtain water-quenched char (TC-400Q, TC-600Q, and TC-800Q), and their physicochemical properties, combustion characteristics, and application potential were systematically analyzed. The results indicate that water quenching exhibits a superior deashing effect on pyrochar. After water quenching, the coal-like properties, calorific value, energy recovery, specific surface area, and porosity of pyrochar are significantly enhanced. However, excessively high or low pyrolysis temperatures can affect the deashing efficiency during water quenching. Notably, water quenching has the most pronounced upgrading effect on TC-600P, achieving an ash removal rate of 53.41 %, while increasing its calorific value from 24.27 MJ/kg to 28.20 MJ/kg. The substantial ash removal enhances the thermal stability of pyrochar, making its combustion performance more comparable to metallurgical coal and improving its applicability in sintering, pelletizing, and blast furnace injection. This method is simple, efficient, and holds significant potential for low-carbon metallurgy.