Feasibility Analysis of Drying Sludge Using Flue Gas Waste Heat

Using sewage sludge as fuel has been considered an effective way to handle the sludge. However, due to the high water content, sludge is required to be dried before it can be burnt. In this paper, a paddle sewage sludge dryer was proposed to add after bag house gas filter (BHF) and before flue gas quench (FGQ), which can use the waste heat of the flue gas (FG) and therefore, improve the overall efficiency of the biomass-based plant and sludge handling. A mathematical model was developed to simulate the heat transfer in the paddle dryer, which was validated through the comparison with measured data. Based on this model, the impacts of flow rate of sludge and stirrer speed on the moisture content of exit sludge, temperature of exit sludge were studied. The results show that the increase of stirrer speed or the decrease of sludge mass flow rate all can reduce the moisture content of exit sludge.