The Optimization Design Of Biological Three-Phase Internal Loop Fluidized Bed Using The CFD

Biological three-phase internal loop fluidized bed has excellent hydrodynamics property, as well as the favorable mass transfer. However, Its design and scale-up preferably depending on experience parameters. Therefore, consolidated design theory of fluidized bed is still far from well formed. This study using the computational fluid dynamics( CFD) to explore the influence of operating parameters and structural parameters in the biological three-phase internal loop fluidized bed, has great importance on its scale-up design. This study build mathematical model which can effectively reflect the characteristics of fluid in the biological three-phase internal loop fluidized bed reactor using computational fluid dynamics with Eulerian model.And then prove that CFD model can effectively predict the complex gas, liquid and solid three-phase flow hydrodynamics in internal loop fluidized bed reactor with example. On this basis, this study explore the effect of operation parameters and structure parameters on the performance of biological three-phase internal loop fluidized bed.The simulation results which explore the influence of operating parameters demonstrate that the gas holdup increased firstly, then decreased with solid loading ratio continuously going up, and maximum value reached at 13%. When the superficial gas velocity changed in the range of 0~0.05m/s, gas holdup increased with the increase of superficial gas velocity, peaking at 0.05m/s. When superficial gas velocity was greater than 0.05m/s, no longer gas holdup increased with the increase of superficial gas velocity, but basically remained unchanged. Liquid circulation velocity decreased with the increase of solid loading ratio, along with the increase of superficial gas velocity. In terms of gas holdup, Liquid circulation velocity as constraint conditions, the fluidized bed reactor was in its best condition with solid loading ratio 13% and superficial gas velocity of 0.05m/s. The greater size of solid particles was more conducive to broken bubble, at the same time it also increased the interfacial area, so the gas holdup increased with the greater size of solid particles. The influence of size of solid particles in liquid circulation was obvious. We should choose the solid particles which have relatively small sizes when the greater liquid circulation velocity is demanded in the actual industry, favorable to improve the liquid circulation velocity.The simulation results which explore the influence of structural parameters demonstrate that diameter ratio of rising area and reactor(Dr/D) mainly influences the liquid circulation liquid, while maximum and distribution of liquid circulation velocity can be optimized when Dr/D was 0.7. Height-diameter ratio(H/D) mainly influences gas-liquid flow patterns, and gas sparger of the reactor with lower H/D should be optimized to obtain better hydrodynamic characteristic.Distance between draft tube and liquid level(H1) mainly influences the flow structure of rising area and liquid level, and distribution of liquid velocity can be optimized when H1 is 100 mm,H is 1000 mm. Distance between draft tube and bottom area(H2) mainly influences the flow characteristic and rolling velocity in downcomer area and bottom area. H2 should be higher than the gap distance of downcomer, but rolling velocity of liquid on the sludge in bottom area rapidly decreases with higher H2, at the same time the higher H2 will cause the hydraulic die area easily.