有机工质朗肯循环驱动反渗透海水淡化建模研究

发布时间：2018-12-18 18:42

【摘要】：在当前淡水资源匮乏、能源短缺与环境污染的形势下,发展高效的清洁能源海水淡化技术成为热点。有机工质朗肯循环因其在低品位热源利用方面的优势,可将工业余热、太阳能、生物质能、地热能等同反渗透海水淡化耦合联系起来,成为当下节能与海水淡化交叉领域研究的热点。本文围绕有机工质朗肯循环驱动反渗透海水淡化技术开展研究。针对有机工质朗肯循环侧,首先针对前人研究相对较少的带回热有机工质朗肯循环建立分别基于热力学第一定律与热力学第二定律的平衡、评价模型。随后采用耦合热源的窄点温差方法求解并比较带回热循环与普通循环的运行参数、输出功及各部件的(火用)损。最后得出结论,带回热有机朗肯循环相对普通循环具有更高的(火用)效率与更低的运行压力水平,膨胀机输出功可提升5.1%,膨胀机进口压力可降低17%；带回热循环能提升(火用)效率的原因主要在于降低了凝汽器处的(火用)损,而优化凝汽器的运行可进一步提升系统(火用)效率。因此,本文又针对有机工质朗肯循环凝汽器处的传热优化问题展开研究,采用气液两相流理论对内分液结构流型调控管建立数学模型,并分析证明了其可实现流型调控与管内气液两相流冷凝的传热强化。模型计算结果与实验数据吻合较好,最终得出结论在气相流速较低、液相流速较高的条件下可在竖直管内实现最优化流动与传热的第二类工况。针对反渗透海水淡化侧,本文首先采用经典反渗透海水淡化理论对组成海水淡化厂的最基本单元——卷式膜元件建立数学模型,随后采用实验数据与海水淡化厂实测数据从多角度验证了模型的准确性。采用模型分析得出结论,适当增加供水压力,尽量降低供水盐度,合理选择供水容积流量,是提升产水回收率,降低盐通率进而提升膜元件工作性能的有效措施。本文随后在膜元件的数学模型基础上,建立评价有机工质朗肯循环驱动反渗透海水淡化厂经济性的数学模型,采用模型比对了该类海水淡化厂与常规海水淡化厂的产水成本,得出结论,引入有机朗肯循环驱动可降低海水淡化厂的产水成本,另外,提高海水淡化厂各部件的能源效率、增大厂容量、选址于盐度较低海域也是提升海水淡化厂经济性的有效措施。
[Abstract]:In the current situation of shortage of fresh water resources, energy shortage and environmental pollution, the development of efficient clean energy seawater desalination technology has become a hot spot. Because of its advantages in the utilization of low-grade heat sources, the organic working fluid Rankine cycle can combine industrial waste heat, solar energy, biomass energy and geothermal energy with reverse osmosis seawater desalination. Energy conservation and seawater desalination become the research hotspot. This paper focuses on the Rankine cycle driven reverse osmosis seawater desalination technology. Aiming at the Rankine cycle side of organic working fluids, the evaluation model based on the first law of thermodynamics and the second law of thermodynamics is established for the Rankine cycle of organic working fluids, which has been studied relatively little before, which is based on the first law of thermodynamics and the second law of thermodynamics, respectively. Then, the narrow-point temperature difference method of coupled heat source is used to solve and compare the operating parameters, output work and exergy losses of the return thermal cycle and the ordinary cycle. Finally, it is concluded that the Rankine cycle has higher exergy efficiency and lower operating pressure than the ordinary cycle, the output work of the expander can be increased by 5.1 and the inlet pressure of the expander can be reduced by 17 percent. The main reason for bringing back the heat cycle to improve exergy efficiency lies in the reduction of exergy loss at the condenser, and the optimization of the operation of the condenser can further enhance the exergy efficiency of the system. Therefore, in this paper, the optimization of heat transfer in Rankine circulating condenser with organic working fluid is studied, and the mathematical model of flow pattern control tube with internal separation structure is established by using the theory of gas-liquid two-phase flow. It is proved that it can realize the heat transfer enhancement of flow pattern regulation and gas-liquid two-phase flow condensation in pipe. The results of the model are in good agreement with the experimental data. Finally, it is concluded that the optimal flow and heat transfer can be realized in the vertical tube under the condition of lower gas flow rate and higher liquid flow rate. Aiming at the reverse osmosis seawater desalination side, this paper first uses the classical reverse osmosis seawater desalination theory to establish the mathematical model of the most basic unit of seawater desalination plant, the reel membrane element. Then the accuracy of the model was verified from different angles by using the experimental data and the measured data of seawater desalination plant. By using model analysis, it is concluded that increasing water supply pressure properly, reducing water supply salinity as far as possible, and reasonably selecting water supply volume flow are effective measures to increase water yield, reduce salt flux and improve the performance of membrane components. On the basis of the mathematical model of membrane element, a mathematical model to evaluate the economy of reverse osmosis desalination plant driven by organic working fluid Rankine cycle is established, and the water production cost of this kind of desalination plant is compared with that of conventional seawater desalination plant. It is concluded that the introduction of organic Rankine cycle drive can reduce the water production cost of seawater desalination plant, in addition, improve the energy efficiency and increase the capacity of seawater desalination plant. It is also an effective measure to improve the economy of seawater desalination plant.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P747

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