CFD Modeling Of The Liquid-liquid Flow Field In Sieve Plate Extraction Columns Based A Low-Reynolds-number Turbulence Model

Liquid-liquid extraction is widely used in petroleum,chemical,food,pharmaceutical and other industries because of its reliable and efficient separation.Sieve plate extraction columns of the liquid-liquid extraction has a simple structure,a low manufacturing cost,a large amount of treatment,dealing with corrosive solutions and so on.Therefore,the design of the energy-efficient and high efficiency sieve plate extraction tower has always been a major research topic in the field of extraction.However,the core problem is how to accurately capture the location and size of the recirculation zone and the maximum velocity between the sieve plates in order to obtain the liquid-liquid flow information.In this paper,CFD simulation of the liquid-liquid flow field in the sieve plate extraction tower is carried out by a low-Reynolds-number turbulence model,and the structure of the tower is optimized to guide the design of the energy-efficient and high efficiency sieve plate extraction tower.The main research contents and conclusions are as follows:(1)Flow patterns of the continuous phase in the sieve extraction plate was simulated by a low-Reynolds-number turbulence model,and the simulation results were compared with the experimental results of PIV(Particle Imaging Tachometer).The results revealed that a low-Reynolds-number turbulence model could capture the location and size of the reflux zone and the maximum speed between the sieve plates,and the maximum relative error of the velocity was only 3.8%.(2)The model was based on Eulerian-Eulerian approach along with a low-Reynolds-number turbulence model in the sieve plate extraction column.The CFD model has been validated by comparing the hold-up of the dispersed phase in the sieve plate column with the corresponding values calculated by the correlations reported by Laddha and Degaleesan under the different values of the flowrate of the dispersed phase.Model predictions were found to be within ±10%.(3)The substandard reason of the acetic acid content of the raffinate phase in the sieve plate under the acetic acid recovery unit of a petrochemical PTA was analyzed and calculated.The results revealed that the accumulated layer of the dispersed phase under the plate was too large,which reduced the effective mass transfer area as a result of affecting the extraction performance.(4)The CFD simulation of the simplified structure of the sieve plate was carried out by using the two-phase flow model.The influence of the inner structure(plate spacing,weir height,sieve diameter,downcomer,etc.)on the liquid flow pattern was analyzed.The research results revealed that the accumulated layer of the dispersed phase under the plate does not vary significantly with the change of the orifice diameter and the structure of the downcomer under a certain opening area.However,the accumulated layer of the dispersed phase under the plate decreased to a minimum value and then increased the rise of the plate weir height.When the weir height is 6mm,the effective mass transfer area of the two phases under the sieve plate is large,and the liquid flow pattern in the tower is obviously improved.According to the simulation results,the tower internals of the actual sieve plate extraction tower of this PTA enterprises were optimized.The results showed that the acetic acid content of the raffinate phase after the transformed tower was less than 0.1%,which reached the design requirements.