Research On Atomization Mixing Characteristics And The Process Of Phase Transition And Heat Transfer In REAC Wate Injection Swirl-flow Nozzle

China is the largest importer and refiner of heavy crude oil in the world.Fire and explosion accidents caused by equipment corrosion failure commonly occur with the diversification of crude oil,varying working conditions.In particular,the crystal deposition of ammonium salt formed in the refinement of high sulfur and chlorine-containing crude oil causes the blockage and local erosion of tube in hydrogenation air cooler.Although water injection is an effective method for washing ammonium salt,the effect of water injection washing is poor because of the lack of correlation analysis of water injection and heat transfer,and the vaporization characteristics of water injection are not fully considered.Therefore,analyzing swirling atomization mixing characteristics and process of phase transition and heat transfer in water injection swirl-flow nozzle,and establishing quantitative characterization prediction and evaluation methods are the keys to improving the operational reliability of hydrogenation reactor effluent air cooler(RE AC)systems.In this study,the REAC water injection system of a refinery enterprise was used as the research object.Process analysis was conducted on the basis of the failure cases of air cooling tube bundle during water injection and salt washing.The formation mechanism of crystalline deposition corrosion of NH4Cl and NH4HS was revealed,and the optimization scheme of water injection and salt washing was explored.The mixed flow characteristics and liquid film separation of swirling nozzle atomization and mainstream gas phase mixing were studied through simulation experiments and numerical calculations.The characteristics of mixed flow with atomization angle,liquid coverage,and average droplet size were proposed.The effects of different spray parameters on the water-air mixed flow characteristics and droplet heat transfer and evaporation in the process pipeline were analyzed through numerical simulation.The main contents and conclusions are summarized as follows:(1)A process simulation calculation model based on mass conservation and reverse order derivation was established to determine the process flow and typical operating conditions of the hydrogenation REAC system.The change in the partial pressure of NH3,HCl,and H2S with temperature was obtained,and the failure mode in the tube was determined as NH4Cl deposition blockage.The optimum water injection to meet the washing effect is calculated to be 12 t/h using the Peng-Robinson state equation.Considering the heat transfer and vaporization characteristics,the water phase fraction at the water injection point position is 29.59%.(2)The experimental platform of water injection atomization mixing was designed and built,and the information was collected using a high-speed camera and image boundary feature recognition.The atomization angle,liquid coverage and droplet average particle size were proposed as the key characterization parameters to evaluate the water-gas mixing characteristics.The variation laws of the key characterization parameters corresponding to different operating environment were measured and obtained.The effects of interphase momentum exchange on the liquid film separation in the mixed region were analyzed using volume of fluid(VOF)-Largrangian mixed atomization model and large eddy simulation.The experimental data were compared to verify the accuracy of numerical calculation.(3)On the basis of the fully developed flow field of nonreactive components,Taylor analogy breakup and droplet evaporation models were used to conduct the numerical simulation of heat transfer and vaporization of the mainstream mixed droplet injection.The influences of spray parameter variables,such as atomization angle,orifice diameter,droplet size,and water injection mass flow on the mainstream media flow and the characteristics of droplet heat transfer and evaporation were studied.The relative contact area and slip velocity between the droplet and the mainstream medium are the key factors affecting the heat transfer and evaporation of the dropletThe innovations of this study are provided as follows1)The numerical simulation of the diffusion and fragmentation of the swirling atomized liquid film was realized,and during water-gas mixing under atmospheric pressure,the evolution characteristics of the atomized liquid film flow were revealed on the basis of the VOF-Lagrangian mixed atomization model and "H-adaptive" dynamic adaptive grid generation technology;2)A multi-component mixed flow prediction model with liquid droplet heat transfer and evaporation was constructed through the analysis of heat transfer,and the laws of dynamic equilibrium of key spray parameters such as atomization angle,orifice diameter and droplet size on heat transfer in the flow field were obtained.