Study On Deposition And Migration Of Corrosion Products In Supercritical Unit Steam Water System

Supercritical thermal power units will still play an important role in the future energy structure,but the low temperature corrosion and particle deposition in steam water side of units affect the safe and efficient operation of supercritical units.Therefore,understanding and mastering the migration law of Fe ions in the steam water system of supercritical units is the key to further improve the operation economy and safety of supercritical units.Due to the complex interaction between fluid flow and heat transfer in the steam water system of supercritical unit,especially in the transcritical region,the fluid parameters will change dramatically,and the evolution law of particle deposition and migration in the transcritical region is still unclear.In addition,there are multi loop cycles in supercritical units,and the variation range of working fluid parameters is large,and the migration path and morphology of Fe ions are complex.At present,there is no method to evaluate the migration of Fe ions in this complex cycle.In order to solve the above problems,the experimental system of supercritical particle deposition was designed and built,and the evolution behavior of particle deposition in transcritical flow field was simulated.The Fe ion migration model in complex system was established,and the Fe ion migration law in subcritical and supercritical steam water system was evaluated and tested respectively.The main work of this paper is as follows:(1)Design and construction of supercritical particle deposition experimental system.The variation of flow field and temperature field with pipe diameter and heat flux was studied numerically,and the space-time distribution of flow field and temperature field in the test section was obtained.The structural parameters of the test section,hot and cold fluid mixing,heating power and other key parameters were optimized,and the supercritical experimental system was built.Through the design of the analysis method of the experimental sample,a global monitoring method of Fe ion is developed,and all the input Fe ions in the test section can be tracked.(2)In order to obtain the particle deposition law in the transcritical flow field,the evolution law of temperature boundary layer and flow boundary layer in the transcritical process was analyzed by numerical analysis method;Based on the change rate of Prandtl number,the heat transfer deterioration criterion of fluid in transcritical region is established.The discrete phase model was used to study the deposition behavior of particles in the transcritical region.The influence of thermophoresis on the deposition behavior of particles with different sizes was obtained.The evolution of the boundary layer of particle concentration in the transcritical process was analyzed.The optimal model of particle deposition in the transcritical region of water was obtained.(3)In order to evaluate the migration law of Fe ions in steam water of thermal power units,a Fe ion migration model considering network propagation and local disturbance was established based on the law of mass conservation.The network topology of the propagation path and direction of Fe ions was analyzed.The kinetic model of low temperature corrosion reaction and the optimization model of particle deposition in transcritical region were used as the mass source in the network;Through the model calculation,the propagation characteristics and disturbance characteristics of particulate Fe and dissolved Fe in the system network under steady-state conditions are analyzed.(4)In order to verify the Fe ion migration model in steam water of thermal power units,a scheme of boiler steam water sampling and experimental analysis was designed for Subcritical Boiler and supercritical boiler.In the sampling process,the filter’s capture of particles was considered,and the actual Fe ion content in steam water sample was reduced by weighting the filter fluid and particles.The calculated results of Fe ion migration model are verified by the experimental data obtained under the condition of full load of boiler.The verification results show that the calculated results of Fe ion migration model are in good coincidence with the experimental data.