Thermal characterization studies of high-temperature flue gas waste heat drying and combustion system for sludge

Municipal sludge treatment often faces high energy demand due to its high moisture content and low calorific value. This study develops a sludge incineration system that directly utilizes high-temperature flue gas waste heat for drying, minimizing energy consumption and enhancing heat transfer efficiency. The system shows clear advantages over conventional indirect drying methods: a dryer efficiency of 6.22 (%·kg)/(h·m3), specific energy consumption of 0.73 MJ/kg, and overall system efficiency of 8.8%. Under primary air temperatures of 100 °C–120 °C and sludge lower heating values of 9–11 MJ/kg, the critical furnace-entry moisture content is 46.7%–53.5%, while heat exchange efficiencies reach 82%–86% (WN60) and 79%–82% (WN80). It is notably higher than indirect systems. These results confirm the system's capacity to treat sludge across a wide moisture range, with superior efficiency, compact design, and strong potential for sustainable application.