高温熔盐流量标定平台物理和控制方案的优化

摘要

Background: High temperature flow meter has been widely applied in the molten salt reactor, solar power generation, high temperature hydrogen production,etc. With the limitation of the material characteristics, the flow meter can only be used in a temperature below 535℃. To be applied in high temperature more than 650℃ environment, the ultrasonic waveguide plate had been modified to raise the temperature resistance. However, there is no standard flow meter or calibration equipment for flow calibration.Purpose: This study aims to design a stable and controllable molten salt flow platform for flow calibration with temperature less than 800℃, pipe diameter about 50 mm, measuring range 1?5 m·s?1, and calibration error less than 5%.Methods:Argon gas was used to control the velocity of the molten salt in the pipe connecting two tanks. The proportion-integration-differentiation (PID) closed-loop control system was employed to control the gas mass flow rate to achieve stable differential pressure and get more than 40-s calibration time. MATLAB simulation was conducted to get the optimization parameters and determine the control scheme of the calibration platform. Some factors affecting the stability of the flow rate are analyzed.Results: The optimized scheme, by setting an initial liquid level difference, has been proven to be capable of reducing the total consumption of molten salt (<0.1 m3) and driving gas, and reducing the requirements of the mass flow meter. After calculation, it can get 40-s stable molten salt flow, reached velocity of 4m·s?1, and with a theoretical calibration error about 1.2%.Conclusions:The physical model of a high temperature molten salt flow meter calibration platform based on gas pressure control deduces a specific expression of the system flow rate. Optimized parameters provide reference for flow meter components selection.%高温熔盐流量计在高温熔盐反应堆、太阳能发电、高温制氢等熔盐集热储能装置中具有良好的应用前景.而目前市场上流量计受材料特性的影响,最高只能在535℃以下使用,并不能满足这些应用场合的高温运行环境要求.研究表明通过改进超声波流量计波导片增加其耐温性能,可满足大于650℃ 的高温测量要求,然而目前并没有标准的流量计或标定装置能对其进行标定.钍基熔盐堆(Thorium Molten Salt Reactor,TMSR)项目迫切需要建立一个熔盐流量标定平台,提供熔盐的标准流量标定,它的基本参数需满足目标流速1?5 m·s?1、工作温度小于800℃、管径约50 mm、标定误差小于5%、熔盐用量小于200 L等.构建了基于气压控制熔盐流速的物理模型,推导出系统流速的具体表达式,分析控制管道熔盐压差的比例、积分和微分(Proportion-Integration-Differentiation,PID)算法对流速稳定性的影响.通过MATLAB软件仿真,确定了可行性的控制方案参数,并为仪控元件的选型提供了依据.