褐煤掺烧促进污泥重金属固化及抑制PM2.5生成协同机理研究

The emission of heavy metals is the most obvious barrier to widely resource utilization of municipal sewage sludge in China. The multi-minerals in lignite, especially Si-Al and Ca-based minerals are expected to coordination control heavy metals when co-combustion with sludge. However, the mechanism of competition between multi-minerals and heavy metals has not been reported. In the proposed project, the typical minerals including Si-Al-based minerals, Ca-based minerals and alkali metals are loaded in the uniform simulated coal sample with different proportions to burn with sludge. The speciation of heavy metals in the ash are analyzed to reveal the mechanisms of competitive reactions between multi-minerals and heavy metals and the effect of minerals interaction on heavy metal speciation under different temperatures. The influences of HCl and H2O on heavy metals captured by minerals are also investigated. The kinetics of heavy metal reactions are elucidated. With regard to the actual industrial process, the coordinated mechanism for heavy metal harmlessness and PM2.5 reduction when lignite co-combustion with sludge are clarified. Finally, in view of further harmless disposal and resource reuse of incineration ash, an efficient method for phosphorus recovery from ash is proposed and built.

重金属排放问题是限制我国城市污泥大规模资源化利用的关键，褐煤中以Si-Al和Ca基矿物为主的多种矿物有望实现与污泥掺烧时对多种重金属的协同固化，但复杂矿物与重金属的竞争耦合机理尚不清楚。本项目基于实验室沉降炉，选择褐煤中典型矿物组分Si-Al基矿物、Ca基矿物以及碱金属，以不同配比加载在性质均一的人工模拟煤样与污泥混烧，分析重金属的化学形态以及排放特性，揭示高温下复杂矿物对重金属的竞争反应机理以及矿物间交互作用对重金属行为的影响规律，研究炉内气态组分HCl和H2O蒸汽对矿物吸附反应的影响作用，揭示重金属反应的化学动力学过程，阐明褐煤掺烧污泥重金属固化、无害化及PM2.5减排的协同作用机理。寻求焚烧灰的资源化处置思路，建立灰中磷的高效回收方法。

本项目针对污泥燃烧过程中重金属的迁移转化特性、多种矿物与重金属的反应机理及影响因素、重金属反应动力学、低阶煤掺烧对重金属及PM2.5的减排特性、污泥中磷的回收利用进行了详细研究。污泥单独燃烧过程中重金属As、Se和Zn 70%-90%随尾部烟气释放，Mn和Cr 20%-30%释放。CaO、CaCO3、MgO、Fe2O3可以较好地捕集烟气中的As、Se和Cr，Si-Al矿物对Zn和Mn有较好的作用。低于1000ºC时CaCO3和Fe2O3使污泥燃烧PM2.5排放减少50%。CaCO3与Fe2O3掺混的复合矿物高温下发生矿物交互作用生成Ca-Fe-O，使其对As和Se的吸附能力提升，当CaCO3与Fe2O3掺混比为3:1时达到最佳吸附效果。良好孔隙结构的分子筛进一步负载Ca2+或Fe3+后表现出良好的捕集重金属性能。通过动力学模拟及实验详细研究获得了H2O及HCl对As/Se形态及CaO/Fe2O3捕集的影响机理，建立了竞争反应动力学模型。通过污泥与不同矿物特性低阶煤的掺烧研究，提出了掺烧煤种选择建议，应用高硅铝高钙铁低硫煤进行掺烧，有望实现对多种重金属的稳定固化及PM2.5减排的协同作用。最后，对污泥燃烧过程中磷的转化路径进行了详细揭示，并提出了磷的高效回收利用方法，应用Ca/Mg矿实现灰中磷富集，添加碳酸钾对灰改性使其变为含高达80%有效磷的钙镁磷肥。本项目的研究对污泥大规模处置有非常重要的意义，为污泥与低阶煤掺烧重金属及PM2.5排放控制奠定了理论基础。