From Pulper rejects to paper mill resources through double-stage thermal pyrolysis

This study investigates the transformation of pulper reject (PR), a challenging industrial waste from paper recycling, into energy resources via dual-stage pyrolysis. As paper recycling rates rise, the sustainable management of PR becomes increasingly critical. Despite its strong commitment to circular economy principles, the paper industry generates significant waste. Integrating PR valorization into the energy demands of paper mills enhances resource efficiency while reducing environmental impact. Characterization of PR from an Italian paper mill confirmed its potential for thermal and chemical valorization despite its heterogeneity. Pyrolysis tests achieved high conversion rates, yielding energy-rich gas and oil with low heating values of 33 MJ/kg and 32 MJ/kg, respectively. The system demonstrated resilience to feedstock variability, ensuring consistent performance. Process simulation scaled these findings to an industrial level, showing that 1800 kg/h of wet PR could generate over 1300 kg/h of superheated medium-pressure steam and approximately 2 MWe of electrical power. Environmental assessments indicated a 76 % reduction in CO2 emissions compared to fossil fuels, qualifying the gaseous fuel as a renewable Recycled Carbon Fuel under REDIII regulations established by the European Union. This study highlights the technical and environmental feasibility of PR valorization, supporting decarbonization in the paper industry. Further research should refine kinetic models and waste characterization to enhance process scalability and optimize industrial applications.