脱硫废水分盐结晶零排放技术研究

Research on desulphurization wastewater salt separation-crystallization and zero emission technology

燃煤电厂产生烟气中含有大量SO2,目前国内多采用湿法脱硫工艺处理烟气,脱硫废水高含盐量、高腐蚀性影响其安全、稳定处理。分析了脱硫废水传统处理工艺及存在的弊端,重点阐述了某百万超超临界燃煤发电机组采用的"膜法分盐+MVR结晶"工艺实现厂区内脱硫废水零排放的原理和优缺点,分析其应用效果。结果表明:该电厂脱硫废水含盐量较高,且硬度离子较高。脱硫废水首先进入预沉池去除悬浮物,进入缓存池进行水质调节。随后进入"一级反应箱(利旧现有三联箱)→一级澄清池→二级反应箱→二级澄清池(利旧现有澄清池)"去除绝大部分硬度离子。从纳滤浓水回流返回一级加药澄清单元处理,澄清池出水进入后续"过滤-离子交换-脱碳"工艺段,进一步去除残余悬浮物、硬度、碱度。脱硫废水处理浓缩工艺段选择分盐技术,制取有经济价值的工业纯盐而不是工业杂废盐,最终选择"纳滤+反渗透"膜法路线。通过对比MVR技术和多效蒸发技术的经济、技术、可行性、温度性,选用MVR结晶技术,在结晶器中进一步蒸发浓缩,回收NaCl结晶盐。干燥后的结晶盐进入包装机,结晶盐品质满足精制工业盐一级标准(纯度≥98.5%,含水率<0.5%)。某百万燃煤电厂脱硫废水零排放项目实现脱硫废水零排放:最终产出含盐量TDS浓度<50 mg/L、Cl-浓度<20 mg/L的优质回用水近20 m3/h,每年为厂区提供6.4×104t回用水;最终产出近1 t/h的高纯度结晶盐;自动化程度高,脱硫废水全流程控制整合至全厂DCS系统。

There is a large amount of SO2 in the flue gas produced by coal-fired power plants.At present,wet desulfurization process is widely used to treat flue gas in China.The high salt content and high corrosiveness of desulfurization wastewater affect its safety and stability.The traditional treatment process of desulfurized wastewater and its disadvantages were analysed,and principle,advantages and disadvantages of"membrane salt separation+MVR crystallization"process was studied which was adopted by a million ultra supercritical coalfired power generation unit to realize zero discharge of desulfurized wastewater in the plant area.At last its application effect was analysed.The results show that the desulfurization wastewater of this power plant has high salt content and high hardness ion.First,the desulfurization wastewater enters the pre sedimentation tank to remove the suspended solids,and then enters the buffer tank for water quality regulation.Then,most of the hardness ions will be removed in"primary reaction tank(used existing triple tank)→primary clarifier→secondary reaction tank→secondary clarifier(used existing clarifier)".The concentrated nanofiltration water is returned to the primary dosing clarification unit for treatment,and the effluent from the clarifier enters the subsequent"filtration ion exchange decarbonization"process section to further remove the residual suspended solids,hardness and alkalinity.In the concentration process of desulfurization wastewater treatment,salt separation technology is selected to produce industrial pure salt with economic value instead of industrial waste salt,and finally the route of"nanofiltration+reverse osmosis"membrane method is selected.By comparing the economy,technology,feasibility and temperature of MVR technology and multi effect evaporation technology,MVR crystallization technology is selected to further evaporate and concentrate in the crystallizer and recover Na Cl crystal salt.The dried crystal salt enters the packaging machine,and the quality of crystal salt meets the first level standard of refined industrial salt(purity≥98.5%,moisture content<0.5%).The zero discharge project of desulfurization wastewater in a million coal-fired power plant realizes zero discharge of desulfurization wastewater.The TDS concentration of final output of high-quality reuse water is less than 50 mg/L,and Cl-concentration less than 20 mg/L is nearly 20 m3/h.Reuse water providing for plant is 64 thousand per year,and the final output of high-purity crystal salt is nearly 1 t/h.The degree of automation is high,and the full process control of desulfurization wastewater is integrated into the DCS system of the whole plant.