Chlorine migration during hydrothermal carbonization of recycled paper wastes and fuel performance of hydrochar

Abstract

Wastes from recycled paper industry (WRP) was hydrothermally carbonized to remove impurities to produce alternative biofuel. The chlorine behaviors during hydrothermal carbonization (HTC) and the fuel properties of the generated hydrochar were evaluated. The degradation of lignocellulosic components improved free -OH bond and small free cellulosic fragments facilitating dechlorination. Meanwhile, dechlorination process stimulated degradation of biomass. The carbon content and density of WRP were improved by HTC resulting in high heating value increasing from 5044.40 MJ/m3 to 17,004.88 MJ/m3. Pollutants emission from hydrochar combustion would be effectively controlled because of the removal of sulfur and chlorine. Hydrochar enjoyed higher ignition temperature and average combustion rate while lower burnout temperature, indicating that the combustion range has been narrowed, thus improving the combustion efficiency. The increase of HTC temperature facilitated hydrochars combustion and reduce energy consumption during hydrochar combustion. Mild HTC operating conditions (220 ℃ for 90 min and 240 ℃ for 60 min) were supposed to effectively improve the combustion intensity with stability meanwhile reached the highest dechlorination efficiency. These results evidence the feasibility of converting WRP to clean biofuel via HTC.