Study On Combustion Charateristics And Pollutants Emission Of Dried Sludge In Fluidized Bed

With the continuous progress of China’s economy and technology, the discharging of industrial wastewater and domestic sewage discharge increases every year, so sludge from sewage treatment is also increasing. Sludge has very unstable nature and contains many toxic ingredients, so it may become great harm to the environment and humans. Sludge incineration is the most thorough technology of sludge disposal, but it also will produce a variety of pollutants. The development of sludge incineration technology is not mature in our country, and we lack of comprehensive and reliable experimental data. Therefore, this paper describes the study incineration characteristics and pollutants emission and control of sewage sludge.First, industrial analysis and elemental analysis were performed, the result showed that sludge had high concentration of fugitive constituent and ash and had low concentration of fixed carbon and calorific value. The thermogravimetric analysis experiments of dry sludge combustion under normal air atmosphere were carried out. The effect of heating rates were analyzed through experiments. Four main weight loss stages were observed during experiment, which were room temperature to 120℃, 220℃ to 400℃, 400℃ to 550℃ and 650℃ to 850℃. The sludge combustion kinetic model were calculated by Coats-Redfern. The results showed that the most probable mechanism function was G（α）=（1-α）-1-1.Secondly, sludge combustion experiments in fluidized bed using quartz sand as bed materials were carried out. The emisson characteristics of NOx, SO₂ and HCl with combustion temperature, excess air factor, amount of limestone injection and concentration of FeCl3 were analyzed through experiment. The results reveal that higher combustion temperature can promote the formation of NOx, increase the emisson characteristics of SO₂ and HCl. Excess air factor promotes the emisson of NOx and SO₂, but has no effect on the formation of HCl. The emisson of NOx and increase as the amount of limestone injection. Emissions of SO₂ and HCl can be controlled by limestone,but effect is not obvious. The emisson of NOx, SO₂ and HCl increases with the increase of concentration of FeCl3.Finally, the migration characteristics of heavy metals during sludge incineration were researched through analysis on the content of Pb, Cr, Cd and Hg in ash by ICP-OES. The results reveal that more than 95% of Hg was carried out by flue in the combustion, and most of Pb, Cr, Cd remained in ash. The concentration of Pb, Cr and Cd reduces with the increase of combustion temperature and combustion time. The lowest volatility of Pb causes that the residual rate of Pb in the ash is the highest, and the highest volatility of Cd causes that the residual rate of Cd in the ash is the lowest. The effect on Cr is the least by the combustion temperature and combustion time, because Cr will generate stable oxide.