纳滤膜深度处理火电厂脱硫废水实验

Experimental study on FGD wastewater advanced treatment by nanofiltration method

传统化学沉淀法处理的脱硫废水出水难以满足烟气脱硫除尘工艺水回用指标,要实现火电厂废水零排放,亟需对其进行深度处理。采用纳滤膜深度处理燃煤锅炉电厂脱硫废水,分别研究了纳滤过程中操作压力、操作温度、操作时间、原水典型残留物以及浓缩比对处理效果的影响,并分析了纳滤浓缩结晶产物的成分。结果表明:合适的操作条件为操作压力2.5 MPa,操作温度25℃,此时纳滤出水中总盐度、氯化物、氟化物、硫酸盐和钙离子的质量浓度分别为2 720、719.9、1.97、213、24.8 mg/L,重金属达到痕量级别,该水质满足湿法脱硫系统工艺水回用指标,在此条件下可实现电厂节约用水,减少排放量的目的;采用纳滤进行深度处理时,原水中Al3+和PAM会使纳滤膜通量和盐分截留率下降,保持合理的纳滤浓缩比,及时去除浓缩结晶产物硫酸钙是控制膜污染和减少膜清洗次数的关键。

The desulphurization wastewater treated by conventional chemical precipitation method was difficult to meet the requirement of reclaimed water used as process water for the FGD system. Advanced wastewater treatment process was urgently needed for the realization of zero liquid discharge of FGD wastewater. The nanofiltration membrane technology was used as advanced treatment for the FGD wastewater from coal-fired power plants in this paper. The effects of operating pressure, operating temperature, operating time, typical residual pretreatment reagent and concentration factor on the treatment effect were studied, and the crystalline precipitates were analyzed. The experimental results showed that, condition with operating pressure of 2.50 MPa and operating temperature of 25 ~C was the appropriate operating condition. Under this condition, the residual concentration of TDS, chloride, fluoride, sulfate and calcium in the effluent were 2 720, 719.9, 1.97, 213 and 24.8 mg/L, respectively, and the heavy metals were in trace amounts. The effluent quality met the requirement of reclaimed water used as process water for the FGD system, and it realized the goal of saving water and reducing wastewater emissions. In addition, the permeate flux and the rejection rate of dissolved salts reduced with the existence of residual A1^3＋ and PAM, and keeping a right concentration factor and removing the precipitated gypsum were the keys of controlling the fouling of membrane and reducing the clean frequency.