电厂烟气脱硫废水零排放工艺中试研究

Pilot-scale study on zero liquid discharge technology of flue gas desulfurization wastewater in coal-fired power plants

电厂烟气脱硫废水零排放是行业的热点和难点问题。本文通过脱硫废水水质特性分析,集成预处理、深度处理、预浓缩和蒸发结晶模块建立了脱硫废水零排放工艺,并进行了每天25 m^3的中试试验。结果表明:该工艺各模块可优势互补,高效稳定运行,实现脱硫废水零排放;由预沉池和序批式反应器构成的预处理模块通过投加石灰、氢氧化钠、碳酸钠和絮凝剂,实现了悬浮物、硬度、有机物和重金属的同步去除,悬浮物、Ca^(2+)、Mg^(2+)和有机物去除率分别达到97.3%、38.1%、98.5%和74.3%;深度处理模块包括过滤器、超滤(微滤)和纳滤单元,能够高效截留二价离子和有机物,纳滤单元出水Ca^(2+)、Mg^(2+)和硫酸盐质量浓度分别为5.2、0.4、84.3 mg/L,降低了膜结垢风险,并保证了工业盐品质;经电渗析单元、离子交换单元与蒸发结晶后,所得工业盐纯度达到《工业盐国家标准》(GB 5462—2015)中二级工业湿盐的要求。

Zero liquid discharge(ZLD)of wastewater generated by flue gas desulfurization(FGD)system of coal-fired power plants is a hot and difficult issue in the industry.A ZLD process of FGD wastewater integrated with pre-treatment,intensive softening,pre-concentration and evaporation-crystallization units was established,through quality analysis for desulfurization waste water.Moreover,a 25 m^3/d pilot-scale test was carried out.The results show that,all units of the process operated efficiently and stably,and realized ZLD.The pretreatment module consisting of primary sedimentation tank and sequencing batch softening reactor realized simultaneous removal of suspended substance(SS),hardness,organic matter and heavy metals by adding lime,sodium hydroxide(NaOH),sodium carbonate(Na2CO3)and flocculants.The removal efficiency of SS,Ca^2+,Mg^2+and organic compounds reached 97.3%,38.1%,98.5%and 74.3%,respectively.The intensive softening unit,including filter,ultrafiltration(microfiltration)and nanofiltration unit,could efficiently intercept divalent ions and organic compounds.The concentrations of Ca^2+,Mg^2+and sulfate in the effluent of nanofiltration unit were 5.2,0.4 and 84.3 mg/L,respectively,which reduced the risk of membrane fouling and guaranteed quality of industry salt product.After electrodialysis,ion exchange and evaporation crystallization,the purity of the obtained industrial salt met the requirements of the secondary industrial wet salt in the National Standard for Industrial Salt(GB 5462-2015).