CHEMICAL REACTION ENGINEERING LABORATORY
Data Base Expansion for Bubble Data Base Expansion for Bubble Column FlowsColumn Flows
reported for DOE in period from 1995 to 2001
& summarized by Peter Spicka
CHEMICAL REACTION ENGINEERING LABORATORY
OutlineOutlineTopical review of the data reported for DOE since 1995• Gas Holdup and Liquid Recirculation• Solid Loadings and Sparger Effect• Scale-Up of Bubble Columns• Eddy Diffusivities• Summary
GoalsGoalsContract DE-FC 22-95 PC 95051Contract DE-FC 22-95 PC 95051• Development of reliable data base for evaluation of parameters in CFD
based models• Development of improved engineering models for flow mixing and mass
transfer in bubble columns
CHEMICAL REACTION ENGINEERING LABORATORY
Gas holdup and Liquid RecirculationGas holdup and Liquid Recirculation
Commonly used correlationsCommonly used correlations
009.0296 16.019.098.044.0 GLgU
17.027.0
3
487.0
4.01
L
G
L
LLg gU
nRrccn
nr
122
2
31,0 4.1 BgCL UUDU
310 737.0 CgL DUU
NN
L
L
R
r
U
rU
2
0
21
Reference Axial Liquid Velocity
Overall gas holdup
Reilly et al. (1986)
Hammer et al. (1984)
Gas holdup radial profile
Luo & Svendsen (1991)
Centerline axial liquid velocity
Joshi & Sharma (1979)
Zehner (1982b)
Axial liquid velocity profile
Garcia-Calvo et al. (1994)
Hydrodynamics is driven by:• buoyancy, drag, inertia, pressure,
viscous, interface forces… • strong coupling between the forces• many different scales
The scale-up is tricky and only very sophisticated CFD simulations can resolve all the aspects - feasible in future ?
Main aspects of multiphase flow
Simplifications:
• Steady–state one-dimensional flow
• Only gas holdup, liquid velocity and turbulence radial profiles are determining factors
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid Recirculation I.Gas Holdup & Liquid Recirculation I. Effect of UEffect of Ugg and Liquid Properties and Liquid Properties (DOE Quarterly Reports 7-11, 1996)(DOE Quarterly Reports 7-11, 1996)
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
0.0 0.2 0.4 0.6 0.8 1.0r/R
Axi
ally
Ave
rag
ed
Axi
al V
elo
city
, cm
/s
Air-Water
Air-Drakeoil
Ug=10 cm/s
Gas holdup profiles
Air-water air-Drakeoil
Observations:• Increased Ug results in higher holdup and less uniform holdup profile • Gas holdup is lower in air-Drakeoil system due to higher liquid viscosity (20 cP)• The higher holdup in air-water system results in higher recirculation rate
Axial velocity profiles
air-water air-water vs. air-Drakeoil
air-water
air-Drakeoil
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid RecirculationGas Holdup & Liquid Recirculation II. II.Effect of Column Diameter & Internals Effect of Column Diameter & Internals (DOE Quarterly Reports 8 & 9, 1996)(DOE Quarterly Reports 8 & 9, 1996)
-30.0
-20.0
-10.0
0.0
10.0
20.0
30.0
40.0
50.0
0.0 0.2 0.4 0.6 0.8 1.0r/R
Tim
e A
vera
ged L
iquid
Axi
al V
elo
city
, cm
/s Without internals
With internals
Ug=10 cm/s
Overall gas holdup in 6”, 8” and 18” columns
18”8”6”
Internals layout
Axial velocity profiles
6”& 8” columns with and without internals in 18” columns
Observations:• Overall gas holdup and liquid recirculation increases with column diameter • Effect of internals on axial velocity is less pronounced• Internals reduce radial eddy diffusivity ( Chen et al., 1999)
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid RecirculationGas Holdup & Liquid Recirculation III.III.Gas Distributor Effect Gas Distributor Effect (DOE Quarterly Report 18, 1999)(DOE Quarterly Report 18, 1999)
Gas distributors:D1D1
Porosity = 0.1 %163 holes of 0.4 mm ID
Equilateral triangle 1 cm apart
D2D2
Porosity = 0.1 %4 holes of 2.6 mm ID
Distributed on a cross
Porosity = 0.1 %Single hole of 5.1 mm ID
Located in the center
D3D3D4D4
Porosity = 0.15 %163 holes of 0.5 mm ID
Equilateral triangle 1 cm apart
Porosity = 0.04 %61 holes of 0.4 mm IDCircular rings 1.5 cm
apart
D5D5D6D6
Porosity = 1.0 %163 holes of 1.25 mm IDEquilateral triangle 1 cm
apart
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1
Dimensionless radius
Gas
Hol
dup
D1D2D3D4D51.05 Average0.95 Average
z/D = 9.0Ug = 14 cm/s
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
Dimensionless radius, r/R
Gas
Hol
dup
D1D2D3D41.05 Average0.95 Average
z/D = 9.0Ug = 30 cm/s
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
Dimensionless radius, r/R
Gas
Hol
dup
D1D2D3D4D51.05 Average0.95 Average
z/D = 2.1Ug = 14 cm/s
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1
Dimensionless radius
Gas
Hol
dup
D1D2D3D41.05 Average0.95 Average
z/D = 2.1Ug = 30 cm/s
Ug = 14 cm/s Ug = 30 cm/s
Z+
Z-
Observations:• Gas distributor effect is visible only at low Ug (14 cm/s) and near the
column bottom• Flow stabilizes faster when single nozzle distributors are used• At Ug of 30 cm/s, the gas distributor effect is negligible
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid RecirculationGas Holdup & Liquid Recirculation III. III.Gas Distributor Effect Gas Distributor Effect (DOE Quarterly Report 14, 1996; Degaleesan (DOE Quarterly Report 14, 1996; Degaleesan et al.,et al., 1997) 1997)
Liquid Velocity profile
8” column, Ug=12.0 cm/s. Distributors are: Cone (8C), Bubble Cap (8B), and Perforated Plate (8A)
Turbulent kinetic energy profile
Observations:Single nozzle distributors • produce larger bubbles flow is less organized with large spiraling structures• suppressed recirculation and higher turbulent kinetic energy (about 40% higher compared to multiple nozzles
distributors)
Multiple holes distributors • Smaller bubbles, less violent flow and enhanced recirculation
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid RecirculationGas Holdup & Liquid Recirculation IV. IV.Pressure Effect Pressure Effect (DOE Quarterly Report 22, 2000; Kemoun (DOE Quarterly Report 22, 2000; Kemoun et al.,et al., 2001) 2001)
• 6.4” column, axial level z/D = 5.5, distributor D4
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.2 0.4 0.6 0.8 1
Dimensionless radius, r/R
Ga
s H
old
up
P = 1 atm
P = 4 atm
P = 10 atm
P = 1 atm
P = 4 atm
P = 10 atm
P = 1 atm
P = 4 atm
P = 10 atm
z/D = 5.5
14
Ug cm/s
8
2
Findings• Almost uniform gas holdup profiles,
which are not pressure dependent were observed at lower Ug. This finding is in good agreement with Letzel (1997)
• In churn-turbulent regime, gas holdup increases with pressure (in the interval from 1 to10 bars) as well as the steepness of the profile
• Single hole distributor D3 provides visibly higher gas holdup than perforated plate distributors at 4 bars and Ug of 30 cm/s due to increased dispersion and break up of the gas jet produced by the single nozzle (Kling, 1962; Nauze et al., 1974)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1
Dimensionless Radius, r/R
Ga
s H
old
up
D1D2D3D4D60.95*Avg1.05*Avg
6.4” column, 4 bars, Ug= 30 cm/s
6.4” column
CHEMICAL REACTION ENGINEERING LABORATORY
Gas Holdup & Liquid RecirculationGas Holdup & Liquid Recirculation V. V.Effect of Solids Loading Effect of Solids Loading (DOE Quarterly Report 12, 1998)(DOE Quarterly Report 12, 1998)
Influence of Solids Loading Axial Distance
Axial Velocity Profiles
-30
-20
-10
0
10
20
30
40
0.0 0.2 0.4 0.6 0.8 1.0r/R
Ua
x, c
m/s
x=5.6 cm
x=11.9 cm
x=36.9 cm
x=61.9 cm
x=86.9 cm
x=111.9 cm
pp-u8-gls
b)
Dc=4in.Axial Velocity Profiles
-30
-20
-10
0
10
20
30
40
50
0.0 0.2 0.4 0.6 0.8 1.0r/R
Ua
x, c
m/s
u9.6
u8-wt7
u8-wt14
u8-wt20
Z=36.87cmDc=6in.
a)
G-L system G-L-S system
Dc inch(cm) 4 (10.2) 6 (14) 4 (10.2) 6 (14)
Composition air - 50% iso-propanol
air - water air - 50% iso-propanol - alumina
air - water - glass beads
Ug [cm/s] 4-12 2.4-12 2-8 2-14
Solids [wt. %] ‑ ‑ 10 7, 14 and 20
Particle size [m]
- - 40-106 125-177
Sparger perf.plate,bubble cap
perf. plate sintered plateperforated plate
perforated plate
Comparison of G-L and G-L-S systems
•Ug has smaller effect on axial velocity profiles in slurries and its effect decreases with increased concentration of slurries
•All observed differences can be attributed to altered viscosity and density of the pseudo slurry phase
CHEMICAL REACTION ENGINEERING LABORATORY
Eddy DiffusivitiesEddy DiffusivitiesEffect of Effect of UgUg, solids loading , solids loading (DOE Quarterly Reports 13 & 14, 1998)(DOE Quarterly Reports 13 & 14, 1998)
Axial Eddy Diffusivity
0
50
100
150
200
250
300
0.0 0.2 0.4 0.6 0.8 1.0
r/R
Dzz
, cm
^2/s
u12
u14-wt7
u14-wt14
u14-wt20
Axial Eddy Diffusivity
0
50
100
150
200
250
300
0.0 0.2 0.4 0.6 0.8 1.0
r/R
Dzz
, cm
^2/s
u2-wt7
u8-wt7
u14-wt7
Effect of Ug Effect of solids loading
Eddy diffusivity • Flow in bubble columns is of transient nature• Fluctuating character of flow and backmixing
can by captured by eddy diffusivity, defined in Langrangian framework as:
ijjijiij yvyvdt
dyy
dt
dtD
2
1
2
1
6” column , GLS system, glass particles of 150 m
Findings of the study• With increased Ug, the axial eddy
diffusivity increases• Maximum Dzz occurs at r/R = 0.75• Solids loading does not affect the axial
eddy diffusivity profiles significantly
CHEMICAL REACTION ENGINEERING LABORATORY
Eddy DiffusivitiesEddy DiffusivitiesEffect of Effect of UgUg and and DcDc – – correlations correlations (DOE Quarterly Report 13, 1998)(DOE Quarterly Report 13, 1998)
3.03.08.0
2 6.1062325
gCC
zz UDD
scmD 3.03.08.0
2 0.13350
gCC
rr UDD
scmD
These correlation are valid for air-water systems in large columns size (Dc> 10 cm) and churn-turbulent regime ( Ug > 5 cm/s)
CHEMICAL REACTION ENGINEERING LABORATORY
Scale–Up Issues I.Scale–Up Issues I.((DOE Quarterly Report 13, 1998)DOE Quarterly Report 13, 1998)
CREL contribution Ibased on CARPT/CT, a new correlation for centerline axial velocity was developed:
nRrccn
nr
122
2
004.0146.0598.03 Re10188.2 LGG MoFrn2492.02 Re1032.4 Gc
44.065.2
44.0
0
65.21cn
L
L
R
rcn
U
rU
Wu et al. (2001a) Wu et al. (2001b)
Chronology:Energy balance models:• Whalley & Daviddson (1974)• extended by Joshi & Sharma (1979)
who proposed circulation structuresMomentum balance models:• Rietema & Ottengraf (1970)• Zehner (1980)Implementation of turbulence:• universal mixing length by Ueyama &
Miyauchi (1979)• Anderson and Rice (1989) proposed
a‘three zones’ concept• Geary and Rice (1992) proposed
model which depends on bubble size
4.04.02.2/ gCC UDscmU
CREL contribution IIIn a separated effort ( not directly funded by DOE), new correlations for radial gas holdup and axial liquid velocity were proposed
CHEMICAL REACTION ENGINEERING LABORATORY
Scale –Up Issues II.Scale –Up Issues II.((DOE Quarterly Report 13, 1998: Degaleesan, 1997)DOE Quarterly Report 13, 1998: Degaleesan, 1997)
1653.00717.50929.5 2
2
2
Pwhere
PDD rrrr 5847.0005035.02404.34979.3 34
4
4
Pwhere
PDD zzzz
CREL contribution IIICorrelations for radial profiles of axial and radial eddy diffusivities were proposed
(Valid for churn-turbulent regime and Dc> 10 cm)
CHEMICAL REACTION ENGINEERING LABORATORY
Summary I.Summary I.
Extensive data base has been created which Extensive data base has been created which encompass broad range of operating conditions:encompass broad range of operating conditions:
• Column diameters: 4, 6, 8 and 18 inch column
• Range of UG : from 2 to 30 cm/s
• Range of pressure: 1, 4, and 10 bars for 6.4” column• Distributors: perfor. plate (various porosities), sintered
plate,cross sparger, cone, buble cap • Liquids : water, Drakeoil, 50% isopropanol in water• Internals in 18”column)
CHEMICAL REACTION ENGINEERING LABORATORY
Summary II.Summary II.• Gas holdup and liquid recirculation is affected primarily by superficial gas
velocity• Secondary effects are due to: liquid physical properties; column diameter and;
solids concentration• Heat exchange tubes do not affect significantly gas holdup and liquid
recirculation profiles• Gas distributor does has minimum effect gas holdup and liquid velocity in fully
developed region• Gas holdup is not affected by pressure in bubbly regime but it rises with
pressure in churn-turbulent regime and becomes increasing parabolic• Correlations have been developed for the gas holdup, liquid velocity and eddy
diffusivity radial profiles
Future workFuture work
• Data base extension to higher pressure and temperature• Experiments at low H/Dc to identify sparger with most desirable properties• New models need to be proposed as to which variable is dominant one that
governs the establishment of gas holdup and liquid velocity profile
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