Bubble column and designing models with flow
- 1. 1 2 < L/D < 20 UG,sup up to 50 cm/s UG,sup >> UL,sup Liquid Gas Gas Inlet Liquid/Slurry Inlet Gas Liquid Pool Sparger A bubble column is a liquid pool sparged by a process stream. Bubble Column Reactor
- 2. Advantages Simple construction, and low capital cost; No moving parts, and minimum maintenance; Ability to handle solids; Ease of temperature control. Disadvantages High pressure drop of the gas due to high static head of the liquid; G/L area decreases if the ratio of height to diameter exceeds 12, because of bubble coalescence Bubble Column Reactors
- 3. 3 Bubbly Flow Churn-Turbulent Flow (“Heterogeneous”) Bubble columns: flow regimes
- 4. Bubble columns: flow regimes
- 5. Types of Bubble Columns
- 6. 6 Bubble column design issues • Design parameters: – Gas holdup. Directly related to rise velocity. Correlations of the form a ~ usg a rl b sc ml d are commonly used. – Mass transfer coefficient kla. Correlations of the form kla ~ usg a rl b sc ml d mg e Df Drg are commonly used. – Axial dispersion occurs in both the liquid and gas phase, and correlations for each are not available. – Mixing time. Correlations are available for a limited number of systems. – Volume, flow rates and residence time. – Flow regime: homogeneous, heterogeneous, slug flow.
- 7. 7 Bubble column design issues - cont’d • Accurate knowledge of the physical properties is important, especially the effects of coalescence and mass transfer affecting chemicals. • Although good correlations are available for commonly studied air-water systems, these are limited to the ranges studied. • Correlations may not be available for large scale systems or systems with vessel geometries other than cylinders without internals. • Furthermore, experimental correlations may not accurately reflect changes in performance when flow regime transitions occur.
- 8. Dynamic macroscopic flow structures : Chen et al. (1994) and Lin et al. (1996) Qualitative description of existing flow regimes: Diaz et al. (2006, 2008) Flow Structures in Bubble Column
- 9. Two Circulation Cells (cooling tower mode) Aspect ratio (H/W) Air Superficial Velocity (mm/s) 0 5 10 15 20 0 5 10 15 20 20 0 5 10 15 20 0 5 10 15 20 25 x (cm) z (cm) 0 5 10 15 20 0 10 20 30 40 50 60 70 80 0 5 10 15 20 0 10 20 30 40 50 60 70 80 0 5 10 15 20 0 10 20 30 40 50 60 70 80 0 5 10 15 20 0 10 20 30 40 50 60 70 80 5 10 15 20 0 5 10 15 20 25 30 35 40 45 5 10 15 5 10 15 20 25 30 35 40 45 5 10 15 20 0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 5 10 15 20 25 30 35 40 45 1 2.25 4 1.33 8.33 12.5 16.7 Plume Oscillation Single Circulation Two distinct zones are observed No Plume Oscillation
- 10. Air lift Reactor