多效平板膜蒸馏用于反渗透浓水浓缩的中试研究

Pilot study of multiple effect flat membrane distillation for concentration of reverse osmosis concentrated water

膜蒸馏是一种新型膜分离技术,能同时进行热量与质量的传递。膜蒸馏将膜分离技术与传统蒸发过程结合起来,以多孔疏水膜作为汽、液两相间的屏障,膜两侧的蒸汽压力差为传质推动力,使水蒸气透过膜孔在膜的另一侧冷凝,可实现溶液的浓缩、分离或提纯。采用多效平板膜蒸馏中试装置进行反渗透高盐水的浓缩,优化后的实验条件为:加热温度70℃,末端真空压力8~9 kPa,进水流量63 L/h。结果表明:膜蒸馏过程可以实现盐水的高倍浓缩,浓缩液TDS可达240 g/L,产水通量随浓缩液TDS的增加由7 L/(m^(2)·h)降至2.65 L/(m^(2)·h),水回收率高达97.5%。运行期间,膜蒸馏产水水质比较稳定,电导率在20μS/cm以下,脱盐率超过99.9%,满足回用要求。膜蒸馏的动力消耗较低,可利用低品位的热源,有效节约成本。

As a new membrane separation technology,membrane distillation can transfer heat and mass simultaneously. Membrane distillation combines membrane separation technology with traditional evaporation process,using porous hydrophobic membrane as barrier between the vapor and liquid,and using vapor pressure difference between two sides of the membrane as mass transfer driving force to condense steam on the other side of membrane through membrane pores,thus achieving concentration,separation or purification of solution. A multiple effect flat membrane distillation pilot unit was used for the concentration of reverse osmosis concentrated water,and the optimized conditions were:temperature of 70 ℃,terminal vacuum pressure of 8-9 kPa,and feed water flow of 63 L/h. The results showed that membrane distillation process could achieve high concentration of brine,TDS of concentrated solution reached 240 g/L,the production flux decreased from 7 L/(m^(2)·h) to 2.65 L/(m^(2)·h) with the increase of TDS,and recovery rate was up to 97.5%. During the operation,water quality produced by membrane distillation was relatively stable,with conductivity below 20 μS/cm and desalination rate over 99.9%,meeting the reuse requirements. The power consumption of membrane distillation is low,which can save cost effectively by using low grade heat source.