Optimizing sludge-to-fuel conversion: The synergistic effects of coal gangue and pomelo peel on pellet formation and combustion performance

Incineration is a common method for municipal sludge disposal; however, its effectiveness is hindered by high moisture content, substantial ash production, and low calorific value. This study proposes a systematic approach that integrates sludge dewatering and incineration processes by incorporating coal gangue to assist with sludge dewatering and blending it with pomelo peel waste for densification, ultimately producing high-quality fuel pellets. The addition of coal gangue significantly improved sludge permeability, reducing moisture content to 57.17 %, capillary suction time by 30.4 % and increasing calorific value by approximately 56 %. However, coal gangue content exceeding 50 % hindered drainage. Pomelo peel, used as a binder and combustion enhancer, improved the mechanical properties and combustion performance of the pellets, achieving a maximum calorific value of 14,289 kJ kg−1 and compressive strength of 113.25 N min−1. Excessive pomelo peel (over 30 %) reduced wear resistance and adversely affected elasticity and density. Under optimized conditions (51.28 % sludge, 25.64 % coal gangue, 23.07 % pomelo peel, 100 MPa pressure), the pellets exhibited a denser structure, smoother surface, and combustion duration 5.09 times longer than powdered fuel. Pearson correlation and clustering analyses indicated that enhancing ductility and abrasion resistance is crucial for improving combustion performance, emphasizing the binder's significant impact on molding pressure. This research provides valuable insights into optimizing fuel pellet production from sludge.