The effects of internals and low aspect ratio on the fully developed flow region and bubble properties in a pilot-plant bubble column

Abstract

This work investigates, for the first time, the effects of the presence of internals and low dynamic liquid levels on the bubble dynamics in industrial-size pilot plant bubble columns. Experimental work that conducted in a bubble column of 0.6 m inner diameter and 3.9 m height with an air-water system was utilizing our advanced four-point fiber optical probe technique to measure the radial profiles of the bubble properties. The superficial gas velocity varied from 0.2 to 0.45 m/s to cover the churn turbulent flow regime. PVC pipe of 0.06 m diameter used to represent the heat exchanging internals, occupying 24% of the column cross-section area, and three different aspect ratios (H/D = 3, 4, and 5) were used. Data obtained show that the presence of internals slightly increases the overall gas holdup and significantly affects the radial profiles and distribution of the bubble properties, particularly in the fully developed flow region. However, the presence of internals increases the local gas holdup, the bubble pass frequency, and the interfacial bubble area, especially in the wall region, while decreases the bubble chord length and the bubble rise velocity. The variation in the aspect ratio (H/D) and the presence of internals exhibited a slight impact on the bubble dynamics in the sparger region, whereas the effect of internal on the local gas holdup was concentrated in the wall region. Meanwhile, the axial location (Z), where the fully developed flow region occurs, appears a high sensitivity toward the internals existence and the variations in the aspect ratio and the superficial gas velocity. However, the presence of internals and the increase in aspect ratio both show that the fully developed flow region begins at lower axial locations, while an increase of the superficial gas velocity delays the transition to fully developed flow to a higher axial location.