Hydrodynamics And Mass Transfer Characteristics In Jet Bubbling Reactor

Jet bubbling reactor is the key equipment in carbonylation of methonal to acetic acid process. Since it uses liquid jet to achieve mixing, which makes a much simpler reactor structure and lower cost of maintenance and manufacture, this kind of reactor has gradually been used in reality. Because of the research on this new type of gas and liquid reactor has been started only for a short time, and both jet and gas bubbling would impact on the performance of the reactor significantly, so the reactor hasn’t been well understood yet. Especially the lack information of the internal mixing, mass transfer and flow behavior has seriously suppressed the design, optimization and scaling up of the reactor. Therefore, this thesis employed the cold model experiment, and computational fluid dynamics (CFD) simulation method to study its hydrodynamic characters. The main research contents and achievements of this thesis are as follows:(1) With the electrolyte tracer technique and energy input analysis, the impact of aeration rates and jet Reynolds numbers on mixing time in the jet bubbling reactor has been systematically researched. The results showed that with the same aeration rates, mixing time would decrease at first, and then become constant when the jet Reynolds number kept increasing. While with the constant jet Reynolds number, mixing time would also decrease at first and then increase with the increasing of aeration rates. In addition, we could conclude that liquid jet and gas bubbling would not only impact each other but also restrict, it has been found that if the total power input remained constant, liquid mixing time decreased at first and then increased, the turning point was around where gas input power occupied 60% of the total input power. At the turning point, the synergy effect between liquid jet and gas bubbling reached the highest level. An empirical correlation was proposed as follows: tM=85.87×PL-0.12 PG-0.19.In addition, it has been found that the triangle structure jet had the same hydrodynamic behavior but a much better mixing performance.(2) With the dissolved oxygen electrode method and energy input analysis, the impact of aeration rates and jet Reynolds numbers on mass transfer coefficient in the jet bubbling reactor has been systematically researched. The results showed that with the constant jet Reynolds number, mass transfer coefficient would increase at first and then remain consistent with the increasing of aeration rates. With the same aeration rates, mass transfer coefficient would increase with the increasing of jet Reynolds number. Introducing liquid and gas power input, an empirical correlation was proposed as follows:KLa=0.0041×PL0.26 PG0.33.Based on the analysis of power input, the turning point was found to be around where gas input power occupied 56% of the total input power and at this moment jet and bubble cooperated best. Same condition was found in the research of mixing characteristics mentioned above. In addition, a better mass transfer performance appeared with the new structure through the experimental investigation.(3) With the axial velocity experimental results,3 different zones consisting of jet controlled zone, bubbling controlled zone and near-wall zone had been found in the reactor. Besides, they were concluded in 3 different flow patterns. Based on the experimental results, A tanks-in-series model was proposed on the basis of this result. The model could describe the 3 zones mentioned well and give each zone’s volume, liquid flowing direction and the exchanging rates between different zones. Simultion results showed that with the synergy of jet and bubbling, this flow region in jet controlled zone was like’spindle’and the volume decreased with the increasing of aeration rates. The bigger radial flow coefficient λ was, the better flow behavior in the reactor would be. We found that with the increase of gas input power ratio x, λ increased firstly and the decreased. When gas input power was 67% of the total input power, λ would be the highest one and at this moment the synergy was the best.(4) With CFD method, simulated results of gas holdup were compared with the experimental data and average error was within ±25%. According to this result, we could conclude that the modeling, meshing as well as the method of model were accurate, and the model could be used for research of other parameters. With the data of phase distribution, axial liquid velocity distribution and the liquid flow pathlines, the’spindle’down flow region has been verified further. In addition, jet rates sudden decrease and fast liquid upstream flowing phenomenon had been found near the gas distributor. At the same time, so much whirlpool turbulence circulation in the reactor has been observed and these were the vital factor of strengthening mixing and mass transfer.(5)The principle of scaling up was proposed based on the experimental results. We should guarantee the liquid power input per volume is equal, with this condition, then make recycle ratio stable and ensure aeration rate the equal.