多相流蒸发法高浓缩率海水淡化系统的热力性能分析与优化

发布时间：2019-04-16 18:57

【摘要】：结垢问题是困扰热法海水淡化技术的主要问题之一。本文将多相流防、除垢技术应用到海水淡化中，惰性固体颗粒的加入不仅起到强化传热和防除垢的作用，同时能够提高海水淡化系统的操作浓缩比。浓缩比的提高，不仅可以使海水淡化系统造水比提高，还可以减少海水的预处理量。较高的浓海水盐度可使淡化后的浓海水再利用的后处理成本有效降低，并且淡化后得到的高浓度海水也可以作为产盐原料，在浓海水资源得到有效利用的同时也为解决污染提供了一种有效途径。本文建立了包括蒸发器、预热器、闪蒸罐、冷凝器和蒸汽喷射器在内的多相流蒸发法高浓缩率海水淡化系统的的数学模型。模型中考虑了热力损失、压力损失、盐水浓度变化引起的温差损失。此外，以系统单位产量淡水成本最小作为优化目标建立了该系统的的优化模型。以上数学模型及优化模型的求解均在MATLAB程序下完成。对于无TVC顺流多相流蒸发法高浓缩率海水淡化系统，分析了固体颗粒体积分率、首效加热蒸汽温度、预热量以及浓缩比对系统的热力性能影响。计算结果表明固体颗粒体积分率对蒸发器传热面积影响较大，固体颗粒的加入能够强化传热，减小各效蒸发器的传热面积，降低淡水成本。以四效无预热考虑冷凝水闪蒸系统为例，在本文计算条件下，当固体颗粒体积分率从0增大到12%时，各效蒸发器总传热系数分别增加了8.74%、9.37%、9.02%、9.77%；各效蒸发器传热面积减少了8.19%；淡水成本下降了1.21%。首效加热蒸汽温度对蒸发器传热面积影响较大；预热量对生蒸汽耗量和造水比影响较大；浓缩比对淡水成本影响较大。对于无TVC平流多相流蒸发法高浓缩率海水淡化系统，分析了海水温度和末效蒸发器温度对其热力性能的影响，，并与无TVC顺流流程做了对比分析。对无TVC无预热顺流系统和无TVC无预热平流系统进行了优化与非优化对比分析。并对顺流无预热且忽略冷凝水闪蒸系统、顺流无预热且考虑冷凝水闪蒸系统、顺流有预热且考虑冷凝水闪蒸系统、平流无预热且忽略冷凝水闪蒸系统、平流无预热且考虑冷凝水闪蒸系统、平流有预热且考虑冷凝水闪蒸系统的优化性能进行了比较分析。结果表明平流有预热且考虑冷凝水闪蒸系统生蒸汽耗量最小，造水比最高且淡水成本最小，但是结垢风险大。针对带TVC顺流多相流蒸发法高浓缩率海水淡化系统，分析了工作蒸汽压力，引射蒸汽温度，抽汽位置对海水淡化系统热力性能的影响，并对TVC-MED海水淡化系统和MED海水淡化系统进行了比较分析。计算结果表明TVC-MED海水淡化系统的性能要优于MED海水淡化系统；在本文的计算条件下，TVC放在第二效蒸发器后热力性能最优，淡水成本最小，为3.25￥·t-1。
[Abstract]:Scaling problem is one of the main problems which puzzles the thermal seawater desalination technology. In this paper, multi-phase flow anti-scaling technology is applied to seawater desalination. The addition of inert solid particles can not only enhance heat transfer and scale control, but also improve the operation and concentration ratio of seawater desalination system. The increase of concentration ratio can not only increase the water production ratio of seawater desalination system, but also reduce the pre-treatment amount of seawater. The higher salinity of concentrated seawater can effectively reduce the cost of reusing desalinated sea water, and the high concentration seawater can also be used as raw material for salt production after desalination. The effective utilization of the water resources in the thick sea also provides an effective way to solve the pollution. In this paper, a mathematical model of multiphase flow evaporation high concentration desalination system including evaporator, preheater, flash vaporizer, condenser and steam ejector is established. The thermal loss, pressure loss and temperature difference loss caused by salt water concentration change are considered in the model. In addition, the optimization model of the system is established by taking the minimum cost per unit output of the system as the optimization objective. All the above mathematical models and optimization models are solved by MATLAB program. The effects of solid particle integration rate, first-effect steam temperature, preheat and concentration ratio on the thermal performance of a high concentration seawater desalination system with no TVC downstream multiphase evaporation are analyzed. The calculation results show that the integral ratio of solid particles has a great effect on the heat transfer area of the evaporator. The addition of solid particles can enhance the heat transfer, reduce the heat transfer area of each effect evaporator and reduce the cost of fresh water. In this paper, when the integral ratio of solid particles increases from 0 to 12%, the total heat transfer coefficients of each effect evaporator are increased by 8.74%, 9.37% and 9.02%, respectively. 9.77%; The heat transfer area of each evaporator has been reduced by 8.19%, and the cost of fresh water has decreased by 1.21%. The heat transfer area of the evaporator is greatly affected by the steam temperature of the first effect heating, the preheat has a greater effect on the steam consumption and the ratio of water production to water, and the concentration ratio has a great effect on the cost of fresh water. The effects of seawater temperature and end effect evaporator temperature on the thermal performance of a high concentration seawater desalination system without TVC advection multiphase evaporation are analyzed and compared with those of TVC free downstream flow. The optimization and non-optimization analysis of TVC-free and non-preheating-free advection systems are carried out for both TVC-free and non-preheating-free advection systems. There is no preheating and neglect of condensate flash system in downstream, no preheating and consideration of condensate flash system in downstream flow, no preheating and consideration of condensate flash system in downstream flow, no preheating in advection and neglect of condensing water flash system. The optimization performance of advection without preheating and considering condensation water flash system is compared and analyzed, and the optimization performance of advection water flash system with preheating and consideration of condensate flash system is compared and analyzed. The results show that the preheating of advection and the consideration of condensate flash system have the lowest steam consumption, the highest water production ratio and the lowest fresh water cost, but the risk of scaling is high. In view of the high concentration rate seawater desalination system with TVC downstream multiphase flow evaporation, the effects of working steam pressure, ejecting steam temperature and pumping position on the thermal performance of seawater desalination system were analyzed. TVC-MED seawater desalination system and MED seawater desalination system were compared and analyzed. The results show that the performance of the TVC-MED desalination system is better than that of the MED desalination system, and the thermal performance is the best and the fresh water cost is the lowest when TVC is placed in the second effect evaporator under the calculation conditions in this paper.
【学位授予单位】：河北工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P747

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