Abstract
Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C9–C11), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained:
Plate distributor at presence of silica particles:
Ring distributor at presence and absence of silica particles:
There is a good agreement between experimental and predicted values with a percent of error less than 2 %.
It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.
Nomenclatures
Symbol | Definition | Unit (SI) |
---|---|---|
Pressure drop through the hole | Pa | |
Pressure drop through the pipe | Pa | |
Pressure drop due to friction | Pa | |
Initial liquid height (without gas) | (m) | |
H | Final liquid height (with gas) | (m) |
C* | Saturated concentration | kmol/m3 |
C* | Concentration at equilibrium (solubility) | kmol/m3 |
CL | Liquid concentration | (kmol/m3) |
CV | Volumetric solid concentration | vol. % |
L | Height of column | m |
L\D | Height of column/Column diameter | (−) |
J | Mass transfer rate | kmol/m2. s |
kL | Liquid side mass transfer coefficient | m/s |
KL | Mass transfer individual coefficient | m/s |
KLa | Volumetric mass transfer coefficient | (1/s) |
KLaL | Liquid side mass transfer coefficient per unit volume of liquid | (1/s) |
Ksensor | sensor time constant | (1/s) |
T | Temperature | K |
Ug | Superficial gas velocity | (m/sec) |
εg | Gas holdup | (−) |
εL | Liquid holdup | (−) |
εs | Solid holdup | (−) |
Abbreviations
Symbol | Definition | Unit (SI) |
---|---|---|
SBCRs | Slurry bubble column reactors | (−) |
BCRs | bubble column reactors | (−) |
I.D | Inside diameter | (m) |
C9–C11 | Liquid paraffin | (−) |
G–L | Gas-Liquid | (−) |
G–L–S | Gas-Liquid-Solid | (−) |
F-T | Fischer–Tropsch | (−) |
ODM | Oxygen Dissolved Metter | (−) |
PC | personal computer | (−) |
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