Abstract
The internal circulation system in Internal Circulation (IC) reactor plays an important role in increasing volumetric loading rate and promoting the mixing between sludge and wastewater. In order to design the internal circulation system, the flow behaviors of gas-liquid inside vertical riser should be studied in detail. In the present study, the Multiple Flow Regimes model is adopted to capture the phase interface for different flow conditions. The flow patterns, internal circulation flow rate, gas holdup, and frictional pressure drop of vertical riser are investigated. The results show that the bubble flow inside a vertical riser is in a stable flow condition. There exists a maximum value for internal circulation flow rate with the increasing superficial gas velocity. The parameters of Martinelli models for gas holdup and frictional pressure drop are improved based on Computational Fluid Dynamics (CFD) results. The deviations between the calculated gas holdup and frictional pressure drop by improved model and experimental value are reduced to 14% and 13.2%, respectively. The improved gas holdup and frictional pressure drop model can be used for the optimal design of internal circulation system.
Highlights
The internal circulation system in Internal Circulation (IC) reactor can increase the volumetric loading rate and biogas production obviously [1]
The deviations between the calculated gas holdup and frictional pressure drop by improved model and experimental value are reduced to 14% and 13.2%, respectively
The frictional pressure drops calculated by Martinelli model and improved model in this study were compared with the experimental results of Zhou et al [34]
Summary
The internal circulation system in Internal Circulation (IC) reactor can increase the volumetric loading rate and biogas production obviously [1]. Pereboom [2] proposed a mathematical equation for the calculation of the superficial liquid velocity of vertical riser Based on this equation, the internal circulation flow rate can be obtained. Processes 2019, 7, 936 there is no universal formula for the frictional pressure drop calculation because of the lack of a deep understanding of the flow behaviors inside the vertical riser. The MFR model was used to investigate the effects of the superficial gas velocity and immersion ratio on the flow patterns and internal circulation flow rate. The gas holdup and frictional pressure drop of gas–liquid two-phase flow were predicted and analyzed. Based on the CFD simulation results, the key parameter models for the design of internal circulation system of IC reactor, such as gas holdup and frictional pressure drop, were assessed and improved
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