Maximum stable bubble size and gas holdup in high-pressure slurry bubble columns

✍ Scribed by Xukun Luo; D. J. Lee; Raymond Lau; Guoqiang Yang; Liang-Shih Fan

• Publisher: American Institute of Chemical Engineers
• Year: 1999
• Tongue: English
• Weight: 323 KB
• Volume: 45
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690450402

✦ Synopsis

Experiments of pressure effects on gas holdup and bubble size in slurry bubble columns at 5.6 MPa and at gas ®elocities up to 45 cmrs indicate that the gas holdup increases with an increase in pressure, especially at high slurry concentration. At ambient pressure, a higher solids concentration significantly lowers gas holdup o®er the entire gas-®elocity range, while at 5.6 MPa, the effect of solids concentration on gas holdup is relati®ely small at gas ®elocities abo®e 25 cmrs. An empirical correlation was de®eloped based on these data and those in the literature to predict gas holdup in bubble and slurry bubble columns o®er a wide range of operating conditions. An analysis of bubble flow characteristics during dynamic gas disengagement indicates that large bubbles play a key role in determining gas holdup due to the large bubble and wake ®olumes that induce the acceleration of small bubbles. Direct measurement of bubble size shows that ele®ated pressures lead to smaller bubble size and narrower bubble-size distributions. Bubble size increases significantly with increasing solids concentration at ambient pressure, while at high pressures this effect is less pronounced. A theoretical analysis of circulation of gas inside the bubble yields an analytical expression for maximum stable bubble size in high-pressure slurry bubble columns. Based on this internal circulation model, the maximum stable bubble size at high pressures is significantly smaller due to the high gas inertia and low gas ᎐ liquid surface tension. The smaller bubble size and its reduced bubble rise ®elocity account for the obser®ed pressure effect on gas holdup.