Study On Gas-Liquid Mixing Intensification And Flow Signal Characteristics In A Rigid-Flexible Stirred Tank

The stirred aeration reaction tank is used as a common fluid mixing unit device in the chemical industry.The mixing performance of its equipment directly affects the economics and process efficiency of fluid mixing and related process industries.Recently,the intrinsic correlation between the hydrodynamic behavior of gas-liquid two-phase flow and the external control parameters of the reactor is systematically studied from the macroscopic,mesoscopic and microscopic levels.However,the fluid flow in the stirred tank with baffles appears as a three-dimensional highly turbulent dynamic system with a typical quasi-periodicity.The nonlinear chaotic evolution process spanning several orders of magnitude vortices and eddies is presented on the spatio-temporal scale.It is also accompanied by the occurrence of unsteady random fluctuations in the patterns.All these make it difficult to match the optimization design parameters of stirred reactor structure with the requirements of specific reaction process and to propose an effective scheme of fluid chaotic mixing enhancement.Moreover,there is a lack of research on the characteristics of flow signals with stochastic,non-stationary,time-frequency and local characteristics.Therefore,the study of fluid mixing enhancement and flow behavior characteristics is an important subject in the field of design optimization and amplification of stirred reactors.In this thesis,the model of the air-jet coupled rigid-flexible combination impeller is propose to enhance fluid chaotic mixing based on the objectives of macroscopic chaotic mixing enhancement and microscopic flow signal characteristic expression.Meanwhile,the fractional Fourier transform is used to extract the characteristic parameters of fluid flow signals.The purpose of this study is to establish a gas-liquid mixing enhancement model and generate the characteristic expression of random fluctuation signals in stirred tank.Based on the above research,the external control parameters of stirred-flexible stirred reactor were optimized.Then the pilot-scale study of air-jet coupled rigid-flexible impeller in the leaching process of manganese ore was carried out.The conclusions are as follows:?1?The operation mode of air-eccentric jet coupling rigid-flexible impeller is used to strengthen the fluid mixing efficiency,destroy the symmetry flow field appearing in the fluid mixing process,increase the disordered movement of the fluid,and make more fluids enter the chaotic state.The results show that the degree of chaotic mixing under the rigid-flexible impeller system is greater than that of the rigid impeller system.When the eccentricity is equal to 0.6 and the air jet flow is equal to 1.6 m³/h,the LLE value of the rigid-flexible pitched blade turbine?RF-PBT?is the largest in the experimental system.?2?Based on the idea of jet enhancement,a new type of tube gas distributor was proposed to synergistically enhance the mixing degree of fluid in the rigid-flexible combined reactor.Meanwhile,a mixing performance quantitative analysis method based on mixing index is proposed after studying the distribution characteristics of local void fraction.The results show that the increases in flexible piece length,agitation speed and gas flow rate could all enhance the mixing degree.In addition,the reductions of axial spacing and angle were also able to improve the mixing performance of gas-liquid two phases to a certain extent.?3?According to the power consumption,local characteristic distribution and homogenization of energy distribution in the stirred reaction system,the gas-liquid two-phase mixing performance in a rigid-flexible stirred reactor with a ring gas sparger was studied.The operating mode is optimized based on the correlation coupling analysis of power consumption,mixing time and local phase boundary area,ie.HE=RSDPt_m.The results show that RPD decreases and then remains at a specific value with increasing gas flow number?Fl?and agitation speed for power consumption.In addition,from the relative standard deviation?RSD?of the relative power demand?RPD?value,when the length of the flexible piece is 3 cm,the RSD value of the RPD is the smallest.As for local void fraction,two peaks values distribution of vertical local void fraction are detected near the impeller location and below the liquid surface at a certain distance.From the standpoint of changes in HE values,the preferred mode of operation is RF-RDT,2.5 s^-1,3 cm,1.8 m³/h.?4?Aiming at the signal and characteristics of fluid flow in gas-liquid mixing process,the fractional Fourier transform?FRFT?,which was based on the optimum order calculated by stepping search method,was proposed to extract the characteristics of fluid flow signals.Meanwhile,the largest Lyapunov exponent?LLE?,which is an indication of the chaotic degree of mixing process,was adopted to quantify fluid flow behavior.The maximum amplitude?MA?and LLE value were taken together to inquire into the relationship between the characteristics of fluid flow signals and the characterization of fluid flow behavior.In addition,differences between the two adjacent values?AD?and the maximum differences?MD?are employed to further analyze the differences in behavioral characterization with MA and LLE.The results show that the MA value performs the same increasing trend as the LLE value when the gas flow rate and agitation speed increase.AD and MD values of the MA are one to two orders of magnitude greater than those of the LLE.The FRFT method is facilitates capturing small changes owing to changes in external conditions.?5?In view of the problems of long-term leaching and removal of manganese ore,low efficiency,large discharge of manganese slag,and high manganese content in manganese slag,the pilot study on the leaching and iron removal process of manganese ore by air jet coupled with rigid-flexible combination impeller is carried out.The effects of air-jet coupled rigid-flexible combination impeller on power consumption,manganese ore leaching and iron removal time were investigated.The results show that the presence or absence of air jets or air jet flow has no significant effect on the leaching time of manganese ore.The leaching time is about 3 hours,and the power consumption per hour is not much different.In the iron removal process,the iron removal time is related to the valve opening degree?air jet flow?,that is,the magnitude of the air jet flow is inversely related to the iron removal time to some extent.Finally,based on the regular pattern of iron removal time,it is found that the optimum acidity of pyrolusite oxidation and iron removal is about 5.00 g/L.In addition,the operation mode of the air jet coupling rigid-flexible combination impeller can reduce the input of pyrolusite to about 85%of the original dosage.