修复植物化学链气化中重金属迁移热力学平衡分析

Thermodynamic Equilibrium Analysis of Heavy Metal Migration in Chemical Looping Gasification of the Phytoremediating Plant

采用热力学平衡计算的方法,研究了富集重金属Cd、Pb、Zn的修复植物在热解/气化和化学链气化过程中重金属的形态分布和迁移变化规律,考察了不同气氛、温度和载氧体的影响。结果表明:铁矿石载氧体的化学链气化明显促进了3种重金属氧化物和碳酸盐的形成,对重金属的氯化物、氢化物和氢氧化物的气态挥发也具有促进作用。在以SiO 2、Al 2O 3分别作为惰性载体的钙基(CaSO 4)载氧体化学链气化中,3种重金属几乎都以硫化物生成,高温下的重金属挥发态大幅度减少,其中以SiO 2作为载体时有利于PbS的形成;2种载氧体的惰性成分SiO 2、Al 2O 3能与重金属反应生成更加稳定且不易挥发的重金属硅酸盐和铝酸盐,达到固化的效果。在水蒸气气氛下铁矿石载氧体化学链气化中,3种重金属熔融态的生成受到抑制,气态挥发物更加容易生成,其中固态PbO与PbSiO 3含量明显增加;而钙基载氧体下水蒸气明显促进了3种重金属熔融态的形成,抑制了高温下重金属的气态挥发,其中Zn的铝酸盐和硅酸盐的生成得到明显促进。与热解/气化相比,化学链气化对重金属固化率有一定的优势,特别是钙基载氧体下的化学链气化。

Thermodynamic equilibrium calculation method was used to study the morphological distribution and the migration rules of heavy metal Cd,Pb and Zn enriched in phytoremediating plants during the process of pyrolysis/gasification and chemical looping gasification,and the effects of atmosphere,temperatures and oxygen carriers.The results show that the formation of oxides and carbonates of three heavy metals were obviously promoted in the chemical looping gasification with iron ore oxygen,and the formation of gaseous volatilization of chloride,hydrides and hydroxides of heavy metals were also promoted.For chemical looping gasification with calcium-based oxygen carrier(CaSO 4)and SiO 2 and Al 2O 3 inert carriers,almost all the three heavy metals were generated by sulfides,and the volatilization at high temperature was significantly reduced.When SiO 2 was used as the carrier,the formation of PbS was promoted.The inert carriers SiO 2 and Al 2O 3 in both two oxygen carriers reacted with heavy metals,producing more stable and non-volatile heavy metal silicates and aluminate,to achieve effects of solidifying heavy metals.For chemical looping gasification with the iron ore oxygen carrier under the steam atmosphere,the formation of the molten states of three heavy metals was inhibited,the gaseous volatiles were easier to generate,and the formation of solid PbO and PbSiO 3 was significantly promoted.However,with the calcium-based oxygen carriers,the steam obviously promoted the formation of molten state of three kinds of heavy metals,greatly inhibited the volatilization of heavy metals at high temperature,and significantly promoted the formation of aluminates and silicates of Zn.Compared with pyrolysis/gasification,chemical looping gasification shows advantages in the solidification of heavy metals,especially under calcium-based oxygen carriers.