Air‐lift reactor analysis: Interrelationships between riser, downcomer, and gas‐liquid separator behavior, including gas recirculation effects

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Abstract
An approach to air‐lift reactor analysis is presented that examines the three parts of the air‐lift—the riser, downcomer, and gas‐liquid separator—as three interconnected and interrelated elements. Downcomer flow configurations are described and characterized by either straight or oscillating bubble flow patterns. The downcomer gas flow rate is determined using a two‐sparger system, and a correlation is presented relating the downcomer superficial gas velocity to the downcomer gas holdup. Gas recirculation is calculated and related to the geometric and operating conditions of the gas‐liquid separator. It is shown that an increase in residence time in the gas‐liquid separator decreases the gas recirculation rate. Correlations are presented relating gas holdup and liquid velocities to superficial gas velocity.A sparger was added near the entrance of the downcomer, in addition to the conventional placement near the entrance of the riser. Results of such a two‐sparger system are discussed in relation to reactor stability and liquid velocities.