污泥焚烧过程中Pb的迁移行为及吸附脱除

在一维固定燃烧炉上进行了城市污水污泥层燃模拟实验,重点研究了不同焚烧工况条件下重金属Pb的迁移行为和形态转化特征,并利用4种固体吸附剂(CaO、Al2O3、粉煤灰和高岭土)对污泥焚烧过程中Pb的排放进行脱除,同时把结果与热力学模型计算进行了对比. 热力学平衡计算得到污泥焚烧过程中Pb主要以PbO(g)形式挥发,当氯化物存在时,Pb主要以PbCl2(g)形式挥发,并且Cl有促进Pb挥发的趋势;当硫化物存在时,Pb主要以PbSO4(s)形式存在,阻滞了Pb的挥发;固体吸附剂Al2O3、SiO2、CaO的加入有稳定的(PbO)(Al2O3)(s)、PbSiO3(s)和CaPbO4(s)化合物生成,延缓了PbO(g)生成温度,并且Al2O3对Pb脱除效果优于SiO2和CaO. 焚烧实验得到,随着焚烧温度的升高,焚烧底渣中Pb的残留量有减小趋势,并且底渣中Pb的易还原态比例逐渐增加,残渣态比例有下降趋势;焚烧时间的延长,对焚烧过程中Pb的挥发影响不大,但底渣中Pb的残渣态比例有所减小.焚烧过程中水分的增加导致Pb的氯化态向氧化态转变,阻滞了Pb的氯化物挥发,而空气过剩系数的增加,导致Pb的残留率下降.污泥焚烧过程中固体吸附剂CaO、Al2O3、粉煤灰和高岭土的加入有利于Pb的残留并固定在焚烧底渣中,从控制Pb挥发角度来看,CaO及Al2O3的效果要优于粉煤灰和高岭土.

Migration behavior of Pb and its vaporization control during sewage sludge incineration process

Staged incineration was carried out on laboratory-scale tube furnace for the sewage sludge incineration treatment. Partitioning, transformation and removal of Pb were investigated under different combustion conditions and four solid sorbents including CaO, Al2O3, fly ash and kaolin were added in sewage sludge incineration process in order to reduce the Pb emissions effectively. The calculation of thermodynamics equilibrium was conducted to identify the Pb removal simultaneously. Thermodynamic equilibrium calculation results indicated that Pb mainly volatilized as the form of PbO (g) during sludge incineration process. PbCl2 (g) was the main volatile substance in the presence of Cl compounds which can promote Pb volatilization. PbSO4 (s) generated while sulfide compounds existed, which would inhibit the volatilization of Pb during incineration. Stable compounds including (PbO)(Al2O3)(s), PbSiO3(s) and CaPbO4(s) were formed and the temperature of PbO(g) formation was delayed by adding the sorbents Al2O3, SiO2 and CaO. Al2O3 was more efficient for removal of Pb than SiO2 and CaO. The results of incineration experiments showed that the residue of Pb in incineration bottom ash had a decreasing trend with increasing incineration temperature and the proportion of reducible Pb fraction increased in the bottom ash, while that of residual fraction showed a descending trend. The increasing incineration time had little influence on the volatilization of Pb, but the proportion of Pb residual fraction decreased in thebottom ash. Pb would change from chloride states to the oxidation states as a result of the increasing moisture, which inhibited the volatilization of Pb chloride. With the increasing excess air coefficient, the residual rate of Pb decreased in the bottom ash. With the increase ratio of the solid adsorbent, the residual rate of Pb increased gradually and immobilized in the bottom ash. The CaO and Al2O3 were superior to fly ash and kaolin in the controlling of Pb volatilization.