Fundamental combustion behaviors of dried sewage sludge

It is important to use combustible waste products as sustainable energy resources for reducing the usage of fossil fuels. One of the simplest ways to do that is the thermal recycling, in which waste products are burned in boilers to drive steam turbines and so on. To design boilers with high efficiencies and low environmental impacts, the residence time for char burnout in combustion zone should be appropriately estimated for each solid fuel. Sewage sludge accounts for 20% of industrial waste products discharged in Japan, although the large part of it is just incinerated without thermal recycling. Then, the objective in this study is to investigate fundamental combustion behaviors of sewage sludge as a solid fuel, in particular, to estimate char burnout in sewage sludge combustion, compared with other solid fuels like woody biomass. Thermo-gravimetrical analysis was combined with iso-thermal combustion experiments of dried sewage sludge samples. Effects of temperature and oxygen concentration were examined, and experimental results were analyzed based on reaction kinetics.