The Combustion Behavior Of Single Sludge Pellet And Character Of Heavy Metal In Bottom Ash

As the speedy development of national economy and the improvement of environmental awareness, the amount of effluent discharge has increased substantially, the rate of polluted water disposal is also improving. Given the fact that our state pays more attention on water than sludge, the phenomenon that cities are besieged by sludge is becoming serious. Compared with agriculture use and landfill, high temperature incineration is more attractive for its maximum volume reduction and energy recovery. How to incinerate the sewage sludge effectively and cleanly has became a hot area of research recently. Aimed at clean and effective incineration of sludge, a series of experiments have been done to study the combustion behavior of single sludge pellet and character of heavy metal in bottom ash.By building up an experimental apparatus, the factors affecting the combustion behavior including moisture content of the fuel, particle size, flame and oxygen concentration were experimentally studied. It revealed that the moisture content affects the flame shape and burnout of sewage sludge a lot. For sludge sample with low moisture content, the flame is higher and more visible than that of high moisture content samples. The results of the effect of particle size show that for every thin layer dehydration, devolatilization and char combustion run serially, but it may behavior in parallel because of the variety of experiment conditions and composition of fuel. Besides, the effect of flame is studied and the result indicates limited influence caused by the existence of flame.Based on the experimental conclusions, heat flux model, two-step pyrolysis model and char combustion model are selected and integrated. The simulation results show that both surface and center temperature are in good agreement with experimental data at low temperature and heating section, including the plateaus near the boiling point. When it comes to high temperature, the model prediction is about 70 K lower than the experimental data in quantitative for surface and center temperature because of the ignoring of the thermocouple wire conduction and the lack of accurate description of some physical properties.This paper studied the effect of moisture content and additions on characteristics of heavy metals in dry sewage sludge and solid residues formed during combustion and it turned out that the effect depends on the character of heavy metal.