| The external loop spray ethoxylation reactor diffuses the liquid material into the gas phase with a small droplet state by using the atomization nozzle,which can realize the full contact of the gas phase and liquid phase.As a result,the problem of low mass transfer efficiency in the traditional gas-liquid contact reaction process can be overcomed while the safety is improved.However,Most of the domestic and foreign scholars focused on the reaction kinetics and catalyst for ethoxylation at present.The published literature on external loop spray ethoxylation reactor was only the technology introduction.In addition,study on atomization performance and reaction preformance of the ethoxylation reaction nozzle in the equipments were also rare.A series of study on atomization and reaction performance of ethoxylation nozzles were carried out.A new type of atomization nozzle for ethoxylation reaction was developed.The atomization mechanism was studied by theoretical analysis,experimental verification and numerical simulation.The atomization performance test platform was designed and established,and the atomization performances of different nozzles were studied.The influence of different swirl cores and sizes on all the atomization performances were analyzed.In addition,the VOF-IBM numerical method was developed and the nozzle structure was optimized by orthogonal test and fuzzy evaluation.Finally,a mathematical model for external loop spray ethoxylation was established,which was corresponding to spray performances of the nozzles.The reliability of the mathematical model was verified by the thermal mode experiment,which provides important technical guidance for the optimization design,safe operation and process improvement.The main research work and conclusions are as follows:(1)A new type of swirl groove ethoxylation reaction nozzle was developed to meet the requirements of low pressure drop,large flow rate,small droplets size,large range and solid cone spray.Ethoxylation reaction nozzle is a kind of spray form which combines direct and centrifugal spray.The spray process is clearly demonstrated by numerical simulation and verified by the emperiment.The atomization mechnism is as follows:the liquid through the straight groove is ejected first due to the larger axial velocity.Then,under the action of gravity and air resistance,the liquid accumulates in the head and the liquid column behind becomes thinner.After that,liquid through swirl grooves is ejected and rotated outward.However,the inertia force doesn't overcome the surface tension so that the liquid film shrink into liquid bag.Soon the liquid through swirl grooves develops fully and forms divergent ligaments due to the relatively high air velocity,which belongs to the initial atomization process of the ethoxylation reaction nozzles.Finally,the liquid ligaments are broken into smaller droplets under the action of inertia force,aerodynamics force,viscous force and surface tension.The above is a dynamic and continuous process.Based on the atomization mechanism,the theoretical calculation model for the atomization performances of the nozzle was established.(2)According to the technical requirement of ethoxylation reaction,centrifugal pressure nozzle,four spiral groove nozzle,six spiral groove nozzle and solid X nozzle are chosen to test the flow characteristics,spray shape,spray cone angle,Sauter mean diameter and droplets size distribution respectively by the self-designed spray nozzle performance testing platform.It is found that the comprehensive performance of the spiral groove nozzle is better.In addition,the visual circulation experiment was carried out in the experimental device with same size and structure as an industrial device.it is found that spiral groove nozzle has a good spraying condition,uniform droplets distribution,large coverage and no dead angle.According to the experimental data,the calculation formula of the atomization performance is fitted and the design software is compiled by VB,which can be applied in the optimal design of the nozzle.(3)The atomization performances of the nozzles with different structural size were tested by using the test platform.The influences of swirl groove shape,groove number,inclination angle,groove length and area ratio of swirl grooves and direct groove on spray performance are analyzed respectively.The experimental results show that flow rate increases with the increase of pressure drop,but each nozzle has a discharge coefficient.Spray cone angle increases first and then decreases with the increase of pressure drop and the critical pressure drop is between 0.20 and 0.25MPa.The nozzles,whose inclination angle is less than 45 degree,have a spray cone angle range of 88 to 123 degree.Taking into account the difficulty and efficiency of the manufacturing process,inclination angle should be 45 degree.Due to the differnet internal structure of the nozzle,the radial distribution is classified as unimodal,bimodal and trimodal distribution.The circumferential inhomogeneity ?1 is less than 12%and ?2 is less than 6%.Sauter mean diameter decreases with the increase of pressure drop and the Log-hyperbolic distribution is suitable for reaction nozzle.(4)Initial breakup model(IBM)is written as a user defined function(UDF)and embedded in CFD code.Volume of fluid(VOF)approach combined with IBM is developed to get the atomization performances of the nozzles,which is corresponding to the internal structure.The orthogonal test is designed.The primary and secondary order of the factors on spray perfomances are gained by using VOF-IBM method.The influence of inclination angle on discharge coeffient is the largest.Groove number and area ratio of swirl grooves and direct groove have greatest effect on Sauter mean diameter.According to technical requirement and fuzzy evaluation method,the most suitable nozzle has four square swirl grooves,30 degree inclination angle,15mm groove length and 15.52 area ratio.(5)The thermal model experiment of the two optimized spiral groove nozzles was carried out in the industrial ethoxylation reactor.The macroscopic quality index and reaction condition are basically the same and in the best range.The mathematical model for external loop spray ethoxylation was established,which was corresponding to particle diameter of the nozzles,and calculated by Matlab.The changes of pressure and EO gas mole fraction were obtained and in the best and safe range.Comparing mole fraction of the starter and additionproducts for different nozzles,it is found that the micro quality of the products could be improved further,and the best Sauter mean diameter is between 472?m to 543?m. |
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