The Emissions Of Pollutants During Sludge And Coal Co-Combustion

Huge quantity of sludge from sewage treatment is becoming a serious problem to environment and a rigorous challenge to sustainable economic development. So how to disposal these sewage sludge properly and efficiently is meaningful. Co-combustion of sludge and coal is one of an effective ways of sludge disposal, however, this technology is still during resaerch phase because of high ash content, impurity dopant and poisonous materials in sludge, and the industrial application still needs time.Experiment of co-combustion of sludge and coal was carried out at a tube type resistance furnace in laboratory, we focus on trace elements such as Hg, Pb, Cd and so on, and also pollutants of NO and SO₂. In order to get typical results, three kinds of coal and two kinds of sludge were used, and the morphological distribution of Hg2+and Hg0 in flue gas was analyzed with Ontario-Hydro method during different mixing ratio of coal and sludge co-combustion at different temperatures, experiment results show that the higher sludge mixing ratio in co-combustion, the higher mercury concentration in flue gas. The Cl and S element have importment effect on volatility of mercury during co-combustion of sludge and coal, and it has been proved that Cl could promote the mercury volatilization, S could restraint mercury volatilization during co-combustion of sludge and coal. Because the higher content of trace elements in sludge and complex nature, theconcentration of trace elements (As, Cd, Se, Cu, Zn, Pb, Ni, Mn, Cr) in ashes of co-combustion at different temperature were detected, experiment results show that the higher sludge mixing ratio in co-combustion, the higher trace elements concentration in ash. With temperature increasing, volatilization of element As, Cd and Se promoted, and concentration decreased in ash. The mixing ratio of coal and sludge during co-combustion had great influence on volatilization of element Cu, Zn and Pb. Volatilization of element Ni, Mn and Cr had no relationship with temperature. The higher temperature of co-combustion, the lower concentration of trace elements in ash. The higher content of Cl element in sludge can react with most of trace elements at a high temperature, and these resultant of reaction could volatilize more easily, so the concentration decreases in ash.There are also some researches about concentration changes of NO and SO₂ in flue gas during different mixing ratio of coal and sludge co-combustion at different temperatures experiment results show that the the higher temperature in co-combustion, the higher of NO concentration in flue gas during co-combustion of anthracite coal and sludge. Because there are some interactions between N and S element during sludge co-combustion with bituminous coal, so the higher mixing ratio of sludge, the smaller of NO and SO₂ concentration in flue gas. It could cause combustion lag easily when temperatures rised, also NO and SO₂ concentration curves is fluctuate intensely.