深度脱水污泥焚烧过程中调理剂的热转化行为及其对重金属挥发的影响

Thermal conversion of conditioner and its effect on the volatilization of heavy metals during the dewatering sludge incineration

采用化学热力学平衡分析方法,应用污泥实测数据模拟计算了深度脱水后污泥焚烧过程中调理剂的热转化过程及逸出产物,并预测了含Cl调理剂与CaO耦合作用对重金属迁移转化及排放的影响.研究结果表明,污泥添加单一调理剂Al_2(SO_4)_3、Fe_2(SO_4)_3、FeSO_4、AlCl_3及FeCl_3后,Fe和Al在高温下主要以Al_2O_3(s)和Fe_2O_3(s)存在,主要气态产物是HCl和SO_2.调理剂CaO和FeCl_3共存且含量增加时,焚烧过程中HCl(g)逸出过程变慢,并且Fe_2O_3(s)易于和CaO(s)作用导致Fe_2O_3(s)存在温度区间变窄.污泥未添加调理剂焚烧过程中,重金属Cd、Pb、Cr、Tl、Hg、As易于以Cd(OH)_2(g)、PbO(g)、CrO_2(OH)_2(g)、AsO(g)、Hg(g)、Tl(g)形式挥发,而Cu、Zn、Ni以其氧化物形式存在而难挥发.调理剂FeCl_3及CaO添加到污泥后,重金属(Cd、Pb、Cu、Zn、Ni、Hg、Tl)的分布受FeCl3的影响大于CaO,导致其形成重金属氯化物而挥发,而Cr和As与CaO作用生成CaCr_2O_4(s)、Ca_3(AsO_4)_2(s)热稳定化学物,抑制了Cr、As的挥发.当脱水污泥与含硫化物掺烧时,重金属(Pb、Cu、Zn、Ni)挥发受到Cl的影响大于S,在低温区间其主要以硫酸盐为主,在中高温区间以氯化物存在,而Hg和Tl不受硫化物影响.

Thermodynamic equilibrium calculations were performed to reveal the partitioning of the conditioners and their emissions during sewage sludge incineration. Actual compositions of sewage sludge and various combustion conditions were applied in simulations. Effects of co-existence of Fe Cl_3 and CaO on the migration of heavy metals were also considered. Results showed that Fe and Al were in the form of Al_2O_3（ s） and Fe_2O_3（ s） respectively at high temperature after single conditioners（ Al_2（SO_4）_3,Fe_2（ SO_4）_3,FeSO_4,AlCl_3 and FeCl_3） mixed with the sludge. The major gaseous products were HCl（ g） and SO_2（ g）. The emission concentration of HCl（ g） decreased when Ca O and FeCl_3 were added to sludge simultaneously and the formation temperature range of Fe_2O_3（ s） was suppressed owing to the reaction of Fe_2O_3（ s） and Ca O（ s）. Without addition of conditioners,heavy metals were easy to volatilize in the forms of Cd（ OH）_2（ g）,PbO（ g）,CrO_2（OH）_2（ g）,As O（ g）,Hg（ g） and Tl（ g）,and it was notably that Cu,Zn and Ni oxides were difficult to volatilize. When FeCl_3 and CaO mixed with the sludge,the distribution of heavy metals（ Cd,Pb,Cu,Zn,Ni,Hg,and Tl） was moresignificantly influenced by FeCl_3 than CaO. Metals（ Cd,Pb,Cu,Zn,Ni,Hg and Tl） formed as chlorides were easy to volatilize,but volatilizations of Cr and As were inhibited because of generation of Ca Cr2O4（ s） and Ca3（ As O4）2（ s）. Additionally,heavy metals（ Cu,Pb,Ni and Zn） were affected by Cl than S when the sludge was mixed with sulfide,Fe Cl3 and Ca O. In that case,metal sulfates mainly existed at low temperature,but metal chlorides dominated in the mid-to-high temperature ranges. Particularly,metals such as Hg and Tl did not react with S.