Numerical Simulation Of Fast Liquid Mixing At High Flow Rate Ratio And Continuous Tubular Nitrification

Nitrification reaction is usually a strong exothermic reaction.The nitrification products are generally flammable and explosive,so controlling the mass and heat transfer performance in the nitrification process is the critical factor to improve the intrinsic safety of the process.Aiming at the key nitrification reaction unit in the annular tubular nitrification process,this paper researched and developed the rapid mixing and reaction equipment suitable for the low-flow fresh feed and large-flow circulating material,to strengthen the mass transfer and heat transfer efficiency in the reaction process and improve the technological safety of such reaction process.Firstly,the computational fluid dynamics(CFD)method is used to study the mixing process between two streams at high flow rate ratio in a fast injection mixing unit.The Reynolds time-mean Navier-Stokes equation method and the large eddy simulation method are used in this paper.The effects of the structural parameters and operating conditions on the mixing performance was investigated.Besides,the variation of the mixing performance of the mixer during amplification was also investigated.On this basis,we proposed the optimal structural design for the rapid mixing process of liquid at high flow rate ratio.Secondly,taking hydroxynitrate esterification on N-butylethanolamine(BEA)as the research object,particle swarm optimization algorithm(PSO)was used to study the kinetics of the reaction process of nitrate esterification,and the corresponding reaction kinetics parameters were obtained.Finally,we coupled with the reaction kinetics and carried out the numerical simulation of the nitrification reaction process in the optimized nitrification reaction unit.The characteristics of the concentration distribution and temperature distribution during the reaction process were studied,and the safety of the reaction process in the nitrification reaction equipment was discussed.The results show that the mixing effect of the cross-flow swirl jet mixer is much better than that of the coaxial swirl jet and the coaxial swirl static mixer.It is not only simple in structure but also beneficial to process amplification.The distance required for the physical mixing to 99% of two streams at high flow rate ratio is less than 13 mm.Increasing the number of swirling holes and the flow ratio were benefit to the mixing effect.The comparison between the standard k-ε model and LES results shows a big difference in the intensity of segregation within the mixing distance of 0-9 mm.The calculated results of the two models gradually converge within 9-25 mm,and the segregation degree within 25-100 mm is the same.The geometrical enlargement of the cross-flow swirl jet mixer shows that the shape of the high-concentration area did not change with the increase of geometric size,and the overall change trend of the segregation strength and the the streamline trajectory of the low-flow jet was consistent.The magnifying effect of the cross-flow swirl jet mixer is small,which has an obvious strengthening effect on the mixing process.Finally,the kinetic parameters of nitrification reaction of N-butylethanolamine were fitted by the PSO algorithm,and the heat release curve fitted was in good agreement with the experimental data.The high-temperature point of reaction between BEA feed and nitric acid is mainly concentrated at the BEA feed inlet,and the temperature range can be controlled between 283-333 K.The final reactor outlet temperature is 285.5K.The temperature rise of mixed materials after reaction is controlled below 3℃,which significantly improves the intrinsic safety of nitrification reaction process.