用于膜蒸馏的大型平面膜组件性能数值模拟研究

Study on the performance of large-scale flat sheet membrane module used in membrane distillation by numerical simulation

以典型膜蒸馏系统中的大型多层平面膜组件为研究对象,通过数值模拟的方法研究该类组件的性能。工作中建立了该类组件的数学模型,并将该模型与系统中其它设备的数学模型联立求解。模拟计算结果表明,大型膜组件在膜蒸馏系统中会表现出与实验室用小型组件完全不同的性能规律。组件通量随外供热量的增加呈线性规律上升;在外供热量一定的情况下, 提高热回收换热器的KA值固然能提高组件通量,但随着KA值的增大,这一手段的效果会越来越不显著;增加组件膜面积使组件通量减小,但总产量是增加的;膜两侧流体流量的增加会导致组件通量的下降。流体停留时间的大大增加使大型膜组件内存在范围很宽的流体温度分布,因此才能够进行膜蒸馏系统的能量回收。上述组件性能随设计和操作条件的变化正是能量回收率变化的结果。

This paper investigates the performance of a large-scale flat sheet membrane module used in membrane distillation by means of numerical simulation. The mathematical model of this module was built and solved along with＇what of other components in a typical membrane distillation system. Analysis of the simulation results revealed some features of this type of module, which are quite different from those of small module used in laboratory. The module flux is linearly increased with the increase of heat energy added to the system. The module flux can be increased by means of improving the KA value of the heat recovery exchanger, but this method will become less effective with the increase of KA value. While the module with larger membrane area shows less flux, its production rate is always larger than the one with less membrane area. With a specific amount of heat energy added to the system, increasing the flow rate in the module will greatly reduce the module flux. Due to the prolonged residence time, the feed and permeate fluid experience great temperature variations within large-scale membrane module, and this makes the system heat recovery possible. The variations of the module performance with design and operation parameters mentioned above are just the results of the changes of the heat recovery rate in the system.