Study On Condensation Characteristics Of Gas Mixture Containing CO₂ In Stator Cascade

With the rapid development of productivity,electricity is an indispensable secondary energy for human society,and among many power generation methods,thermal power generation is still the most widely used.Therefore,clean and efficient utilization of coal resources is of great significance to improve efficiency,save energy and protect the environment.Academician Guo Liejin’s team proposed the coal supercritical water gasification hydrogen production process and H₂O/CO₂ hybrid gas mixture power generation polygeneration technology based on this problem.The gas mixture expands and does work in the steam turbine.Condensation is easy to occur in the last few stages of the low-pressure cylinder,and the existence of wet steam containing CO₂ will reduce the efficiency of the steam turbine and affect its safe and stable operation.In this topic,the safe,stable and efficient operation of the mixed gas mixture steam turbine is very critical.In this paper,the single/two-component condensation model written in C language is used to carry out numerical simulation research in the form of adding UDF in Fluent,and it is compared and verified with the existing experimental data.The verified condensation model was used to perform numerical calculations on the condensing flows of steam turbines with pure steam working medium,H₂O/CO₂ gas mixture and gas mixture with different CO₂concentrations.Comparative analysis was carried out on the generation of initial condensing zone,velocity distribution in the flow passage,humidity in the flow passage,etc.,and the following conclusions were drawn:Under the same inlet and outlet conditions,the condensation flow characteristics of the mixed working medium with a CO₂ concentration of 18.45%are basically the same as that of the pure steam,and the main difference is concentrated in the vicinity of the initial setting zone.When the gas mixture condenses,the position of the pressure jump is closer to the downstream than that of the pure steam,and the maximum pressure of the sudden jump is slightly lower than that of the pure steam,indicating that the humidity of the gas mixture appears in the position of the initial condensation zone is relatively back,and the overall humidity in the flow passage and the average humidity at the exit are less than that of the pure steam.The temperature at the outlet of the gas mixture is also lower than that of the pure steam.The maximum speed that the gas mixture can reach in the flow passage is lower than that of pure steam.Under the same inlet and outlet conditions,the condensation flow ratio of working medium with CO₂ concentration from 0 to 50%is basically the same,and the main difference is still concentrated in the vicinity of the initial setting zone.With the increase of CO₂concentration,the initial condensation zone moves downstream along the suction,the maximum pressure reached by the pressure jump decreases gradually,and the maximum velocity that the working medium can reach also decreases gradually.On the whole,the increase of CO₂ concentration slows down and delays the occurrence of condensation,but also leads to the slowing down of the flow rate of working medium.The analysis of condensation flow characteristics in the low pressure cylinder of a mixed medium（H₂O/CO₂）steam turbine have important guiding significance for the safety of the steam turbine.