Abstract:New experiments on air‐water countercurrent flow limitations in a vertical pipe are presented. The experiments were carried out to investigate the effect of test procedure on the occurrence of the two countercurrent flow limitations; namely the onset of flooding and complete carry‐up limits. The results revealed the existence of significant hysteresis effects at both limits particularly for high liquid feed rate. For low liquid feed rate, hysteresis effects were only observed at the complete carry‐up limit. So… Show more
“…Apparently, this coalescence process leads to the blocking of certain channels for the gas phase and therefore makes it difficult to transfer back to nonflooded operation when the gas flow rates are decreased. The dependency of the hysteresis on the liquid flow rate is in good qualitative agreement with the observations of previous investigations on single tubes. , On the other hand, previous work with tube bundles did not show any hysteresis, which might be due to the lower liquid flow rates applied in the experiments, thicker walls allowing better liquid drainage at the outlet, and differences in the outlet section itself. 12 Flooding and deflooding behavior based on pressure drop changes (closed symbols for increasing and open symbols for decreasing gas flow): ▪/□ u Ls = 0.65 cm/s, ·/○ u Ls = 4.75 cm/s; 25 cpsi, ⌀ = 43 mm, decane/air.…”
The flooding performance of square channel monoliths for a wide range of geometric parameters and liquid properties has been evaluated. Hydrodynamic flooding is determined by a strong increase in pressure drop for increasing gas flow rate. Inefficient drainage of the liquid at the outlet of the monolith as well as liquids with high surface tension and monoliths with smaller channel sizes lower the flooding limits significantly, indicating a dominating impact of capillary forces. Increased liquid viscosity lowers the flooding limits, but the effect is less pronounced. The column diameter has a rather negligible effect on flooding. For higher liquid flow rates, a hysteresis effect was observed, shifting the deflooding gas flow rates to lower values. Misaligned stacking of monolith sections leads to a decrease of the flooding limits (approximately 15%), independent of the number of stacks. Common flooding correlations need to be adapted with the Bond number to describe the experimental data. For the type of outlet device applied in this work and the alignment of the outlet device with the channel walls, the experimental data are well correlated by C F,0.25,0 /Bd ) [204.4 + 297.1F LG 1.5 -171.4e -F LG ] -1 for d h /l c > 1.15. A comparison with the requirements of applications revealed that channel sizes of 2.9 and 4.1 mm (50 and 25 cpsi) are well-suited for hydrotreating and reactive stripping operations. For the more demanding needs of catalytic distillation, the larger channel size is more favorable.
“…Apparently, this coalescence process leads to the blocking of certain channels for the gas phase and therefore makes it difficult to transfer back to nonflooded operation when the gas flow rates are decreased. The dependency of the hysteresis on the liquid flow rate is in good qualitative agreement with the observations of previous investigations on single tubes. , On the other hand, previous work with tube bundles did not show any hysteresis, which might be due to the lower liquid flow rates applied in the experiments, thicker walls allowing better liquid drainage at the outlet, and differences in the outlet section itself. 12 Flooding and deflooding behavior based on pressure drop changes (closed symbols for increasing and open symbols for decreasing gas flow): ▪/□ u Ls = 0.65 cm/s, ·/○ u Ls = 4.75 cm/s; 25 cpsi, ⌀ = 43 mm, decane/air.…”
The flooding performance of square channel monoliths for a wide range of geometric parameters and liquid properties has been evaluated. Hydrodynamic flooding is determined by a strong increase in pressure drop for increasing gas flow rate. Inefficient drainage of the liquid at the outlet of the monolith as well as liquids with high surface tension and monoliths with smaller channel sizes lower the flooding limits significantly, indicating a dominating impact of capillary forces. Increased liquid viscosity lowers the flooding limits, but the effect is less pronounced. The column diameter has a rather negligible effect on flooding. For higher liquid flow rates, a hysteresis effect was observed, shifting the deflooding gas flow rates to lower values. Misaligned stacking of monolith sections leads to a decrease of the flooding limits (approximately 15%), independent of the number of stacks. Common flooding correlations need to be adapted with the Bond number to describe the experimental data. For the type of outlet device applied in this work and the alignment of the outlet device with the channel walls, the experimental data are well correlated by C F,0.25,0 /Bd ) [204.4 + 297.1F LG 1.5 -171.4e -F LG ] -1 for d h /l c > 1.15. A comparison with the requirements of applications revealed that channel sizes of 2.9 and 4.1 mm (50 and 25 cpsi) are well-suited for hydrotreating and reactive stripping operations. For the more demanding needs of catalytic distillation, the larger channel size is more favorable.
“…However, this method only suits for transparent towers. In addition, the delay in reaction and the hysteresis effect , may make it unsuitable in practice. Flooding can also be identified by noticing the increase in liquid holdup using γ ‐scan and X‐ray scan.…”
The development of simple and efficient monitoring methods for flooding supervision is an important but difficult task for the safe operation of packed towers. A data-driven online flooding monitoring method named Bayesian integrated dynamic principal component analysis (IDPCA) is assessed. In the first step of IDPCA, using the fuzzy c-means clustering method, the multivariate samples collected during plant operation are first classified into several groups. Then, in each subset a dynamic principal component analysis (DPCA) model is constructed to extract the process characteristics. To improve the monitoring performance, Bayesian inference is utilized to combine these DPCA models in a suitable manner. Consequently, the control limits are formulated using the probabilistic analysis. The superiority of IDPCA is illustrated using a lab-scale packed tower by comparison with the conventional principal component analysis (PCA) and DPCA methods.
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