Effect of NaCl presence caused by salting out on the heterogeneous-homogeneous coupling non-equilibrium condensation flow in a steam turbine cascade

Abstract

Steam turbine is one of the most important components in fossil-fired and nuclear power plants, its efficiency is of great importance for saving energy and decreasing consumption. The steam density rapidly decreases when the steam expanses, and NaCl dissolved in steam starts precipitating. However, the presence of NaCl will not only affect the non-equilibrium condensation decreasing the steam turbine efficiency, but also erode the steam turbine blade reducing the steam turbine safety and shortening maintenance cycle. The main objective of the current work is to investigate the effect of the NaCl presence on the non-equilibrium condensation process and the loss in steam turbine cascade. Firstly, a non-equilibrium condensation model including homogeneous and heterogeneous condensation process is presented and its accuracy is checked in a steam turbine cascade by comparing with available experimental data. And the results show the accuracy and robustness of the model is quite trustworthy. Secondly, the influence of NaCl concentration on the non-equilibrium condensation flow is investigated in a steam turbine cascade. The results show that the NaCl presence has a significant effect on condensation flow. With the NaCl concentration increasing, the droplets nucleation rate decreases, diminishing the tiny droplet emerging, which weakens homogeneous condensation. As a result, the condensation loss caused by the homogeneous condensation decreases, and even the condensation loss caused by the homogeneous condensation becomes zero when the NaCl particle number reaches 7.5×1014 per kilogram in steam flow. However, the condensation loss caused by the heterogeneous condensation shows a reverse tendence, which increases with the NaCl concentration. At last, the condensation loss and entropy generation caused by the non-equilibrium condensation are checked in steam turbine cascade under different NaCl concentration conditions. The results show that the condensation loss reduces by 9.2% and increases by 42% at the 7.5×10141/kg and 10171/kg NaCl concentrations, respectively. Meanwhile, when the NaCl particle number reaches 7.5×1014 per kilogram, the isentropic efficiency is highest, about 0.884, compared with other cases considering condensation effect. This study proves that the NaCl concentration has a nonnegligible effect on the condensation loss and entropy generation, which must be considered in future steam turbine study.