超临界二氧化碳干气密封端面成膜机理及凝析控制研究

Supercritical Carbon Dioxide Brayton (S-CO2) has been the most promising power cycle system because of its high cycle efficiency, while the higher efficiency of which is limited by the high leakage of the key power equipment in the system. Dry gas seal (DGS) is an important shaft sealing type which can be used to improve the efficiency of the S-CO2 power equipment for its low leakage. It is difficult for the existed DGS to work efficiently in the condition of high pressure and special supercritical fluid of S-CO2 system. This project aims to investigate the S-CO2 real gas behavior, coupling law of multi-field, phase transition mechanism of condensate and the control strategy, and then improve the stability, sealing performance and phase change of condensate resistance of the existed DGS. The multi coupled Thermal-Hydro-Mechanical (THM) model of the S-CO2 DGS will be established by considering the special effect of high pressure supercritical fluid, the heat balance of sealing system and the deformation sealing ring, which can be used to study the effect of the real gas behavior, coupling law of multi-field, phase transition mechanism of condensate, and to reveal the coupling mechanism between seal ring deformation and end face groove. Present the design method for the S-CO2 DGS end face groove with high stability, low leakage and strong resistance ability of phase transformation condensate, which is expected to meet the independent research requirements of key components in S-CO2 energy system.

超临界二氧化碳（S-CO2）布雷顿循环因效率高而成为目前发电领域最具应用前景的电力循环系统，而系统中关键动力设备的高泄漏损失严重制约其效率提高。干气密封因其低泄漏而成为S-CO2动力设备提高效率的重要轴封型式，但是现有干气密封还难以满足S-CO2高压工况和超临界流体特殊性质的密封需求。本项目以S-CO2干气密封为对象，以提高稳定性、密封性和抗相变凝析能力为目标，开展S-CO2干气密封真实气体行为、多场耦合规律、相变凝析机理及控制策略研究。考虑高压超临界流体的特殊效应，以及密封系统热平衡和密封环变形等因素，建立S-CO2干气密封热流固多场耦合模型，探究S-CO2真实气体行为、多场耦合规律和相变凝析机理及其对密封性能影响规律，揭示密封环变形与端面型槽之间的耦合作用规律，提出高稳定性、低泄漏和强抗相变凝析能力的S-CO2干气密封端面设计方法，满足我国S-CO2能源系统中关键基础件的自主研发需求。

随着超临界二氧化碳（sCO2）在布雷顿循环发电系统、页岩气开采和高效清洁驱油中的广泛应用，sCO2透平机械轴端密封采用干气密封已成为国际趋势，但是现有干气密封还难以满足超临界CO2高压工况和超临界流体特殊性质的密封需求。本项目以高压超临界CO2干气密封为对象，以提高密封性和稳定性为目标，开展超临界CO2干气密封实际物性表征、实际流体效应和气膜动态特性及其影响因素研究。首先在文献中大量关于不同压力和温度下CO2物性实测数据的基础上，获得了REFPROP物性数据库中所提供各物性的精度，并基于神经网络算法获得近临界区CO2密度、粘度和导热系数的修正模型，；其次，综合考虑高参数超临界流体的离心惯性效应、阻塞效应、湍流效应和实际气体效应修正超临界CO2干气密封压力场和温度场的数值求解模型，深入探讨了各实际流体效应对超临界CO2干气密封流动传热特性和开启力、泄漏率等稳态性能参数的影响，指出实际气体效应和湍流效应影响最为显著，而惯性效应和阻塞效应的影响较弱；然后，基于多变量摄动法求解了超临界CO2干气密封的气膜动态特性，以及各实际流体效应和变量摄动型式对气膜稳定性的影响；最后，开发了高参数干气密封实验测试平台，以期用于干气密封数值计算结果的验证。本项目的研究内容和结果可完善干气密封的设计方法，为我国超临界CO2能源系统动力设备中关键密封的设计提供依据。