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MODELING AND EXPERIMENTAL STUDY OF ROTARY KILNS EQUIPPED WITH LIFTERS Alex BONGO NJENG Dimensional Analysis 08-03-16
MODELING AND EXPERIMENTAL STUDY OF ROTARY KILNS EQUIPPED WITH LIFTERS
Alex BONGO NJENG
Dimensional Analysis
08-03-16
INTRODUCTION
2
RESEARCH WORK
3
CMGPCE Laboratory
RAPSODEE Centre
MC
JLD
SVMD
&
4
EXPERIMENTAL SETUPS
CNAM - LGP2ES2 m in length
Mines Albi - Centre RAPSODEE4 m in length
BACKGROUND
5
Rot
ary
Kiln
Sugar
Food
Processing
Phar
mac
euti
cal
Indu
stries
Cement
Lime
Clay
Phosphate
Iron
ore
Aggr
egat
es Coal
MineralsProcessing
ChemicalProcessing
Rare Metal
Indu
stries
Nuclear
fuel
Asph
alt
ProcessingSpecialty
Paper
Haz
ardo
usW
aste
Cereal Grain
VegetablesWaste
Gas
-sol
ids
Reactor
Paddy
Alfal
fa
Processing
Dry
erK iLNRotary
RESEARCH METHODOLOGY
6
DIMENSIONAL ANALYSIS: SUMMARY
๏ Modeling of the flow characteristics of solids materials within continuously fed rotary kilns equipped with lifters:
๏ Mean Residence Time,
๏ Hold-Up,
๏ Axial Dispersion Coefficient,
๏ Modeling of the heat transfer mechanisms in continuously fed rotary kilns equipped with lifters:
๏ Convective heat transfer Coefficient (wall-to-gas),
๏ Wall-to-solid Heat Transfer Coefficient.7
HYDRODYNAMIC CHARACTERISTICS
8
KEY FACTORS
9
Main factors to be taken in consideration:
• Kiln design: L, Di
• Kiln operating conditions:N, M, S, Dex, Slift
12 variables
• Solid characteristics:ρbulk, ρtapped, θ
• Physical property: g
ShorliftSlift
=⇡D2
i
4� n
lift
� 1
2Shorlift
Dex
= Di
� 2hexit
BUCKINGHAM’S II THEOREM
10
If there is a physically meaningful equation:
involving a certain number r=12 physical variables, then the original equation can be rewritten in terms of a set of p=r-n=12-4=8 dimensionless parameters.
?
F (N, M, S, Dex
, Slift
, L, Di
, ⇢bulk
, ⇢tapped
, ✓, g) · t = 1
p: number of dimensionless grouping to definer: number of variablesn: number of fundamental units among the variable
DIMENSIONLESS GROUPING ( )
๏ Dynamic ratio between inertial and gravitational forces:
๏ Solids characteristics:
๏ Geometric ratio:
๏ Solids transport coefficients:
11
✓
S
⇢bulk⇢tapped
M
⇢bulkD2i
pgL
N2Di
g
Dex
Di
4Slift
⇡D2i
L
Di
tpgL
HU [%]⇢bulkL⇡D2
i4
DpD2
i gL
MRT: tpgL
= F
"✓N2D
i
g
◆,
✓D
ex
Di
◆,
✓✓
S
◆,
M
⇢bulk
D2i
pgL
!,
✓4S
lift
⇡D2i
◆,
✓⇢bulk
⇢tapped
◆,
✓L
Di
◆#
⇢bulk, g, L, S
CORRELATIONS
12
t = kp
gL
✓N2D
i
g
◆↵
✓D
ex
Di
◆�
✓✓
S
◆�
M
⇢bulk
D2i
pgL
!� ✓
4Slift
⇡D2i
◆✏
✓⇢bulk
⇢tapped
◆⇣
✓L
Di
◆⌘
HU [%] = k⇢bulk
L⇡D2i
4
✓N2D
i
g
◆↵
✓D
ex
Di
◆�
✓✓
S
◆�
M
⇢bulk
D2i
pgL
!� ✓
4Slift
⇡D2i
◆✏
✓⇢bulk
⇢tapped
◆⇣
✓L
Di
◆⌘
D = kq
D2i gL
✓N2Di
g
◆↵✓dpDi
◆�
(S)�
M
⇢bulkD2i
pgL
!� ✓4Slift
⇡D2i
◆✏✓ ⇢bulk⇢tapped
◆⇣ ✓ L
Di
◆⌘
k α β γ δ ϵ ζ η[1]
MRT 0,0026 -0.4422 -0.3597 0.9276 -0.1130 -8.8835 2.4641 1.1HU 45.65 -0.4439 -0.3987 0.7780 0.9584 -3.8197 16763 0D -8.92 10-4 0.3033 -0.1362 0.6477 -1.2280 -13809 -4.7868 0
EXPERIMENTAL VARIABLES & MATERIALS
13
Parameters Notation Order of magnitude Unit
Kiln length L 1,95-4 m
Kiln diameter D 0.1-0.2 m
Rotation speed N 1-12 rpm
Kiln slope S 1-5 degree
Mass flow rate M 0.6-7.5 kg/h
Exit dam height h 0-33.5 mm
Lifters SL, RL, NL - 3SL, 6SL -
MaterialsBulk
density[kg.m-3]
Tapped density[kg.m-3]
Size
[mm]
Repose Angle
[°]
Sand 1422 1543 0,55 39
Rice 889 934 3.8*1.9 36
NaCl 1087 1184 0,6 35,4
Dyed rice 889 934 3.8*1.9 36
Beech chips 260 284 10*4.5
*2 42
MEAN RESIDENCE TIME
14
Calculated t [min]0 20 40 60 80 100
Exp
erim
entalt[m
in]
0
20
40
60
80
100Sand
4 RL4 SL
Calculated t [min]0 20 40 60 80 100
Exp
erim
entalt[m
in]
0
20
40
60
80
100Broken Rice
4 RL4 SLNL
Calculated t [min]0 20 40 60 80 100
Exp
erim
entalt[m
in]
0
20
40
60
80
100Beech chips
6 SL3 SLGNL
Good agreement within the ±20% margins
FILLING DEGREE
15
Calculated HU [%]0 5 10 15 20 25
Exp
erim
entalHU
[%]
0
5
10
15
20
25Beech chips
6 SL3 SLGNL
Calculated HU [%]0 5 10 15 20 25
Exp
erim
entalHU
[%]
0
5
10
15
20
25Broken Rice
4 RL4 SLNL
Calculated HU [%]0 5 10 15 20 25
Exp
erim
entalHU
[%]
0
5
10
15
20
25Sand
4 RL4 SLHT-100(NL,4SL,4RL)HT-300(NL,4SL)HT-500(4SL)
Good agreement within the ±20% margins
AXIAL DISPERSION COEFFICIENT
16
Calculated D [m2.s-1]10-6 10-4
Exp
erim
entalD
[m2.s
-1]
10-7
10-6
10-5
10-4
10-3Sand
4 RL4 SL
Calculated D [m2.s-1]10-6 10-4
Exp
erim
entalD
[m2.s
-1]
10-7
10-6
10-5
10-4
10-3Broken Rice
4 RL4 SLNL
Calculated D [m2.s-1]10-6 10-4
Exp
erim
entalD
[m2.s
-1]
10-7
10-6
10-5
10-4
10-3Beech chips
6 SL3 SLGNL
Good agreement except in cases of slipping motion
HEAT TRANSFER MECHANISMS
17
KEY FACTORS
18
Convective heat transfer :• Kiln design: D• Kiln operating conditions:ω, lg, T
• Solid characteristics:ρg, μg, cpg, kg
Wall-to-solid heat transfer :• Kiln design: D• Kiln operating conditions:ω, lψ, T, HU
• Solid characteristics:ρb, cpg, kb
BUCKINGHAM’S II THEOREM
19
If there is a physically meaningful equation:
involving a certain number r=9 variables, then the original equation can be rewritten in terms of a set of p=r-n=9-4=5 dimensionless parameters.
?p: number of dimensionless grouping to definer: number of variablesn: number of fundamental units among the variable
F (cpg, ⇢g, µg, kg, !, D, lg, Tg) · hew�g = 1F (cpb, ⇢b, [HU ]%, kb, !, D, l , Tw) · hcw�cb = 1
CORRELATIONS
20
K α β γ δ
Nuew-g 0.1085 0.0275 -0.4839 -1.9284 -0.2208
Nucw-cb 2.1371 0.4531 -0.3507 0.9693 1.4177
Re! =!⇢D2
µgPr =
cpgµg
kg
Nuew�g =hew�gD
kg= KRe↵!Pr�
✓lgD
◆� ✓10�10 cpg⇢gT
1g
!µg
◆�
21
MATERIALS AND METHODS
300 °C Materials Bulk density[kg.m-3]
Sp. heat cap. [J.kg-1.K-1]
Therm. conduc.[W.m-1.K-1]
Therm. diffus.[m2.s-1]
Emissivity[1]
[-]
Bulk Sand 1422 835 0,1786 0.01 10-5 0,76
Gas Air 1,177 1OO5 0,0262 2.21 10-5 0.01 (esttimated)
Wall Inconel 800 7950 427 14,660 0.43 10-5 0.85 (esttimated)
Tgbu
Ts Tgbd
Tgu
Tw
Tw
Tw
Tw
1. Set the variable parameters to desired value, and achieve steady state (of the bulk flow)
2. Start the logging of temperatures (wall, gas and solids) ~30 min before starting heating the bulk bed)
3. Collect the power supply, the ambient temperature and freeboard gas temperatures at the inlet end, every 30 min.
4. Set the desired temperature at wall and turn on the heating in zone 2 or in the two zones (1 and 2)
5. Achieve steady state of wall, gas and solids temperature
6. Collect and weigh the solids hold up
[1] Thammavong, P., Debacq, M., Vitu, S., Dupoizat, M., 2011. Experimental Apparatus for Studying Heat Transfer in Externally Heated Rotary Kilns. Chemical Engineering & Technology 34, 707–717.
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EXPERIMENTAL VARIABLES
Parameters Notation Order of magnitude Unit
Kiln length L 1,95 mKiln diameter D 0,101 m
Rotation speed
N 2-12 rpmKiln slope S 3 degreeMass flow
rateM 0.7-2.6 kg/h
Exit dam height
h 23.5-33.5 mmLifters SL, RL, NL - -
Temperature Tw 100-500 °C
CONVECTIVE HEAT TRANSFERT
23
Good agreement within the ±20% marginsCalculated Nu [-]
0.005 0.01 0.015 0.02 0.025 0.03
Exp
erim
entalNu[-]
0.005
0.01
0.015
0.02
0.025
0.03
100°C300°C500°C
AXIAL DISPERSION COEFFICIENT
24
Calculated hcw−cb [W.m−2.K−1]0 200 400 600 800 1000 1200
Exp
erim
entalhcw
−cb
[W.m
−2.K
−1]
0
200
400
600
800
1000
1200
J= 48.97 W.m-2.K-1
100°C300°C500°C
Good agreement within the ±20% margins
CONCLUSIONS
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CONCLUSION - HYDRODYNAMIC
๏ Residence Time Distribution (RTD): 🔆 about 170 experiments used for the model validation
๏ Mean Residence Time Modeling ✅ successfully represents the Exp. MRT of this study and other works
๏ Hold-up / Filling degree correlation show good agreement with experimental data
๏ Axial Dispersion Model ✅ successfully represents the Exp. RTD within rolling motion
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๏ Analysis of the temperature profiles following a heating operation: 90 experiments
๏ Experimental determination of the heat transfer coefficient between wall and solid particles:
๏ Lumped system formulation Methods
๏ Global heat balance using supply power measurements
๏ Convective heat transfer model in good agreement with experimental data but need a few other data for consolidation
๏ Wall-to-solid heat transfer model ✅ successfully represents the experimental data
๏ Some difficulties encountered to take into account effect of the temperature and proceed the calculations in the mean time
27
CONCLUSION - HEAT TRANSFER
VALUATION OF THE RESULTS
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VALUATION OF THE RESULTS
29
EA21
A THOROUGH EXPERIMENTAL RESIDENCE TIME DISTRIBUTION STUDY IN ROTARY KILN
Alex BONGO NJENG1,2, Marie DEBACQ1, Jean-Louis DIRION2, Marc CLAUSSE1,3, Stéphane VITU1
1 Conservatoire National des Arts et Métiers, Laboratoire de Génie des Procédés pour l’Environnement, l’Energie et la Santé (EA21), Paris, France.2 Université de Toulouse, Mines Albi, UMR CNRS 5302, Centre RAPSODEE, Albi, France.
3 ESIEE Paris, Noisy le Grand, France.
IntroductionRTDs and associated mean residence
times were investigated in a pilot rotary kiln(L = 1.95 m and D = 0.1 m), equipped withstraight lifters (SL) or rectangular lifters(RL). The bulk material was nodular sand(angle of repose θ=39°, density ρ=1460kg.m–3), the tracer was sodium chloride, bothwithin a size range of 0.4-0.8 mm.
In presence of lifters, four otheroperational variables were studied: (1) thekiln rotational speed, (2) the kiln slope, (3)the height of the dam at the exit end, and (4)the feed rate of solid.
Rotary kilns are gas-solid reactorswidely used in mineral process applications(cement, lime, ore reduction) as well as solidwaste pyrolysis or uranium dioxideproduction for the manufacture of nuclearfuel. The device is generally an inclinedcylinder, which can be either directly orindirectly heated, equipped or not withlifters, and rotated axially.
Among parameters affecting theperformance of a rotary kiln, one of the mostimportant is the mean residence time ofsolids (MRT). Hence, it is worth tocharacterise the influence of operationalvariables on this key parameter.
To achieve this goal, residence timedistribution (RTD) measurements wereoperated using the tracer impulse-responsetechnique.
Parameters RangeKiln rotation speed (N) 2–12 rpm
Kiln slope (S) 1–5°
Dam height (H) 0–33.5 mm
Solid feed rate (Ṁ) 0.5–2.5 kg.h–1
Lifters (removable) Straight–Rectangular
Experimental setupStraight lifters Rectangular lifters
Lifters structure
Hopper
Screw feeder
Rotary Kiln
Electric heatingzone
Recovery tank
Kiln slope adjustment device
Electric motors for screw and kiln rotation
Experimental rotary kiln layout
Rectangular LiftersResults: RTD curves
0
0,05
0,1
0,15
0,2
0 20 40 60 80 100
2 rpm
3 rpm
4 rpm
6 rpm
8 rpm
10 rpm
12 rpm
0
0,05
0,1
0,15
0,2
0,25
0,3
0 20 40 60 80 100
2°
2,5°
3°
4°
5°
0
0,05
0,1
0,15
0,2
0 20 40 60 80 100
33,5 mm
23,5 mm
13,5 mm
0 mm
0
0,05
0,1
0,15
0,2
0 20 40 60 80 100
2,5 kg/h
1,9 kg/h
1,3 kg/h
0,68 kg/h
E(t) [min-1]
t [min]
E(t) [min-1]
t [min]
E(t) [min-1]
t [min]
E(t) [min-1]
t [min]
Straight & Rectangular LiftersResults: MRT
0
20
40
60
80
0 2 4 6 8 10 12 14
Exp. RL Exp. SL Calc. RL Calc. SL
0
20
40
60
80
1 2 3 4 5 6
Exp. RL Exp. SL Calc. RL Calc. SL
0
20
40
60
80
0 10 20 30 40
Exp. RL Exp. SL Calc. RL Calc. SL
0
20
40
60
80
0 0,5 1 1,5 2 2,5 3 3,5
Exp. RL Exp. SL Calc. RL Calc. SLMRT
[min]
MRT [min]
MRT [min]
N [rpm]
MRT
[min]
S [°]
H [mm]
Kiln rotational speed influence
Kiln slope influence
Exit dam height influence
Solid feed rate influence
Effect of operational variablesInfluence of kiln rotation speed:
As the rotation speed increases from 2 to 12 rpm, RTDcurves shift towards lower residence time region (Fig.1) sothat the MRT decreases significantly by 69% (Fig.5).
Influence of kiln slope:By increasing the kiln slope from 2 to 4°, the MRT
significantly decreases (Fig.6) and RTD curves show agradual change in shape (Fig.2).
Influence of exit dam height:The MRT slowly increases with increasing the dam
height (Fig.7), sidewise the spread of corresponding RTDcurves decreases (Fig.4).
Influence of solid feed rate:When the solid feed rate decreases, RTD curves
gradually spread and flatten (Fig.4) while slowly movingforward so that the MRT increases (Fig.8).
Influence of lifters:Rectangular lifters can lift a volume of solid material 3
times bigger than straight lifters. From Fig. 5-8, it isapparent that the MRT decreases by 3 to 4 min whenreplacing rectangular lifters by straight lifters.
Fig.1
Fig.2
Fig.3
Fig.4
Fig.5
Fig.6
Fig.7
Fig.8
ConclusionIn a rotary kiln having longitudinally disposed lifters and using sand as bulk material, it was found that the mean residence time increases with the exit dam height.
Conversely the mean residence time decreases with the increase in either rotational speed or slope of the kiln, or the bulk material feed rate. These results areconsistent with previous research on rotary kilns without lifters.
From experimental data computation, the mean residence time could be correlated in term of operating parameters and physical characteristics of the rotary kiln.Good agreement is found between predicted and experimental results.
Future work will focus on determining effect of the particle size, the total number of lifters and the kiln scaling-up on the mean residence time.
Correlation
Lifters cross section
M [kg/h].
04-13: PosterECCE9
A THOROUGH EXPERIMENTAL RESIDENCE TIME DISTRIBUTION STUDY IN ROTARY KILN
03-14: Powder Technol.
04-14: Powder Technol.
Effect of lifter shape and operating parameters on the flow ofmaterials in a pilot rotary kiln: Part I. Experimental RTD and axial dispersion study
Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: Part II. Experimental hold-up and mean residence time
modeling
18 months
11-14: Oral Pr.2014 AIChE
10, 11-15: Oral Pr.ECCE, AICHE
Modeling of Mean Residence Time of Solid Particles in Rotary KilnsEvaluation of the Wall-to-solids Heat Transfer coefficient in Rotary Kilns
6 months
THANK YOU FOR YOUR ATTENTION
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