太阳能热发电站中熔融盐冻堵管道的熔化过程  

The melting process of a freezing molten salt pipe of concentracted solar power plant

作　　者：廖志荣[1,2] 李鑫[1] 徐超[3] 张强强[1] 常哲韶 李志[1,2] LIAO ZhiRong LI Xin XU Chao ZAHNG QiangQiang CHANG ZheShao LI Zhi(Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China University of Chinese Academy of Sciences, Beijing 100049, China)

机构地区：[1]中国科学院电工研究所中国科学院太阳能热利用及光伏系统重点实验室,北京100190 [2]中国科学院大学,北京100049 [3]华北电力大学能源动力与机械工程学院,北京102260

出　　处：《科学通报》2017年第9期960-966,共7页Chinese Science Bulletin

基　　金：国家自然科学基金(51522602);北京市自然科学基金(3164052)资助

摘　　要：熔融盐工质沸点高、低蒸汽压及良好的传热储热特性使塔式电站是最具商业前景的太阳能热发电技术之一.但是熔融盐的凝固点高,导致采用熔融盐作为吸热传热工质的太阳能热发电站中有可能发生熔融盐在管道内凝固,使得冻堵管道的解冻成为一个棘手的问题.在利用电伴热熔化管道内熔融盐的过程中,最关键的问题在于熔融盐的固液相变,本文利用焓法模拟了水平管道内熔融盐的熔化过程,发现由于自然对流的存在使得先熔化的熔融盐聚集到管道的上端.研究发现,电伴热的安装位置影响熔化过程的不均匀性以及管内熔融盐完全熔化所需时间.电伴热功率与完全熔化所需的时间呈非线性关系.随着电伴热功率的逐渐增大,缩短熔融盐完全熔化所需时间的效果减弱.Concentrated solar power plants are potential to provide based load power of the future electrical power system. Commercial concentrated solar power plants using molten salt as the heat transfer fluid and the energy storage medium have been built and show great promising. However, due to high freezing point, the molten salt has a freezing possibility and may block the pipe. In practical, an electrical heat tracing is installed along the flow path of the molten salt to protect against freezing. Once the molten salt is freezing inside the pipe, the electrical heat tracing can be used to melt the molten salt. This paper studied the melting process of a molten salt（60% NaNO_3 and 40% KNO_3, referred to as Solar Salt） inside a horizontal pipe by an electrical heat tracing. The molten salt is a binary mixture, its freezing point（511 K） is higher than melting point（494 K）. A solid-liquid mixture mushy zone exists between the melting point and the freezing point during the melting process. The enthalpy method was used to simulate the solid-liquid phase change phenomenon of the molten salt. The effect of the natural convection inside the pipe was also considerate. The effect of the installation position and the heating power of the electrical heat tracing on the melting process and the melting time were studied. During the heating process, the molten salt close to the electrical heat tracing melts first and forms a mushy zone. With the assistance of the natural convection, the molten salt in the mushy zone flows upward and gathers in the upper zone of the pipe. Thus, the upper zone of the pipe has a higher liquid fraction than the lower zone, which results in a liquid fraction gradient inside the pipe. The results show than the installation position of the electrical heat tracing effects the gradient of the liquid fraction during the melting process. The increase in the angle between the gravity and the installation position, g, increases the liquid fraction gradient. It takes a same time to completely melt th

关 键 词：太阳能热发电 熔融盐 解冻熔化 焓法 数值模拟 

分 类 号：TM615[电气工程—电力系统及自动化]