直接接触式膜蒸馏不同操作温度下的能耗分析研究

Exergy Analysis of Direct Contact Membrane Distillation under Different Operating Temperatures

膜蒸馏(MD)过程伴随相变,能量利用效率是决定其是否具有竞争力的重要因素。考察了直接接触式膜蒸馏(DCMD)法海水淡化过程中操作温度对跨膜通量和()效率的影响,计算和分析了不同操作温度下的系统()损失和()效率。结果表明,膜透过侧冷却至常温以下时,冷却部分的()损失较大,占总能耗的35%以上;料液侧温度在50℃以下时膜组件的()损失占总()损失的50%以上,升高至55℃以上时则加热部分()损失比例升高至50%以上。合适的膜蒸馏操作温度可提高系统的()效率,透过侧温度为环境温度(25℃)、膜两侧温差为33.5℃左右时,可获得相对较高的系统总()效率、膜组件()效率和膜通量,膜组件()效率可达50%以上,系统总()效率为0.5%以上。提高膜组件以外其它部分的()效率是提高系统总()效率的关键。

Membrane distillation（MD） is a separation process accompanied with phase change and such that energy utilization is an important aspect for its competitive application.In this paper,the effects of feed temperature（Tf）,permeate temperature（Tp） and transmembrane temperature difference on transmembrane water flux and exergy efficiency of direct contact membrane distillation（DCMD） were investigated.A parameter,K,which is defined as the ratio of transmembrane water flux to transmembrane temperature difference,was introduced to evaluate the effect of operating temperature on thermal efficiency of DCMD.The exergy loss and exergy efficiency of the system were calculated and analyzed under different operating temperatures.The results show that K-value increases with an increase in Tf but is hardly affected by the change of Tp.The results of exergy calculation show that the exergy loss in the cooling section of the system is over 35 percentage of the total exergy loss when Tp is below ambient temperature（25℃）.The exergy loss in the heating section of the system is over 50 percentage of the total exergy loss when Tf is above 55℃,while the exergy loss in membrane module is above 50 percentage of the total exergy loss when Tf is below 50℃.In general,operating under 25℃ of permeate temperature combined with nearby 33.5℃ of transmembrane temperature difference is favorable to achieve relatively high exergy efficiency of membrane module and of the total system,that is,above 50% and 0.5%,respectively.Besides the of membrane module,improving exergy efficiency of other sections of DCMD system,such as the cooling section and the heating section is of key essential to achieve high exergy efficiency of the total system.