Nikos Papayannakos, Professor National Technical University of Athens
School of Chemical Engineering Unit of Hydrocarbons and Biofuels Processing
8 March 2013
UGent Francqui Chair 2013 / 5th Lecture
Scaling down/up three phase reactors
Contents : • Origin of Chemical Engineeing
• Scale down
• Hydrotreatment
• Operation of Small Scale Reactors
• Conclusions
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A View on the Origins of Chemical Engineering
The idea of an Engineer associated with
Chemical Processes existed before 1839 First Appearance of the term Chemical Engineering : Dictionary of Arts, Manufacturers and Mines, published in 1839
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1901 G.E. Davis Published a Handbook of Chemical Engineering / Second edition 1904
A View on the Origins of Chemical Engineering
First official attempts to initiate the Chem Engng profession
1881 G.E. Davis Proposed the formation of a Society of Chemical Engineers in London
1887 G.E. Davis Presented a series of 12 Lectures on the Operation of Chemical Processes
( Unit Operations ) at the Manchester Technical School
1888 M.I.T. / Professor Lewis Moll Norton The first course was offered : Course X – Chemical Engineering
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G.E. Davis 1850 – 1906
Industrial Alkali inspector from Manchester, UK
Most responsible person for applying the term Chemical Engineering to the emerging profession
In his Handbook he stressed the value of • A Unit Operations approach • Safety practices • Large Scale Experimentation (Pilot Plant precursor)
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Scope of Scaling Down • Study at Smaller Scale a Process/Reactor operation
with a view to obtain reliable information for Process/Reactor – Simulation – Design – Scale up
• Benefits of Scaling down – Production of data at much smaller effort and time – Improved Safety ( Smaller is safer ) – Improve the knowledge of Process Characteristics
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Scaling Down Characteristics
• Easy to achieve controllable process parameters T, P, flow rates
• Use of less materials : catalysts, feeds • Less energy consumption and disposal problems • Higher vessel surface to volume ratios
• Lower superficial velocities to keep the same space velocities for CF Reactors
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Hydrotreatment Process I
First Commercial Applications 1950 – 19551,2 based on data from • Pilot Plants Scale Up • Bench Scale Units Catalyst Testing 1 J.J.van Deemter, 3rd Eur. Symp. Chem. Reac. Eng., Pergamon, London, 1964 2 L.D. Ross, Chemical Engineering Progress, 61 (10), 1965
Widely used in refineries
Improvement of petroleum product quality
Arrange the required product distribution
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Trends of current research - Needs
– Test / Develop Catalysts • Activity – Deactivation • Selectivity (Hydrogenation/Hydrocracking/HDS/HDN/HDO)
– Spectrum of feeds / Bio-Oils
– Follow up – Improve performance of existing Units – Design new Reactors (Industry, Data)
Hydrotreatment Process II UGent/FCh13/5L
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HDT Simulation and Design Tools Prediction of Reactor Performance • Engineering Software • Reliable data from small scale Units
Small Scale Units / HDT Reactors Catalyst Volume Bed Height
• Pilot Scale 1 - 4 lt 2 – 4 m N.D. • Bench Scale 50 – 250 cc 10-70 cm N.D./ D. • Mini Scale 5 – 10 cc 5–10 cm D.
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Scaling Down to Mini Scale Reactors
Simulation of the Operation of Industrial Three Phase Hydrotreaters
Using Data from Mini Scale Reactors
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Simulation of the Operation of Three Phase Hydrotreaters
Mass Transfer Hydrodynamics
Reaction Kinetics
Industrial Reactors Laboratory Reactors
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Sulfur Limits in Diesel Oil (EU)
Year ppm
1994 2000
1996 500
2000 350
2005 50
2010 10
350 % 500 %
Catalyst Activity
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Deep Hydrodesulfurization/Hydrocracking Existing HDS Catalysts of Moderate Activity
Operating Conditions
• Reaction temperature X • Gas and Liquid Flow Rates √
• Simple and reliable kinetic equations – Lumped Power law forms
• Refractory Sulfur Compounds :
Substituted Dibenzothiophenes (DBT)
Reaction Kinetics
• Kinetics of DBTs HDS depends on matrix effects
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Sterical effects
Reagent Structure Relative activity (Houalla et al., 1980)
dibenzothiophene S
1.0
2,8- dimethyldibenzothiophene
S
0.91
3,7- dimethyldibenzothiophene S
0.48
4,6- dimethyldibenzothiophene S
0.067
4- methyldibenzothiophene S
0.090
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Kinetic Equations (1) Compounds - S + sHDS H2 Hydrocarbons + H2S
(2) Non Saturated Hydrocarbons + sHYD H2 Saturated Hydrocarbons
(3) Oxygenated Hydrocarbons + sHYD H2 Saturated Hydrocarbons
SH,LHDS,SH
H,Ln
TRE
i,HDSi,HDS22
2HDS
i,LHDS
Ck1
CCekR
+= ⋅
−
SH,LHYD,SH
H,Ln
TRE
HYDi,HYD22
2HYD
i,LHYD
Ck1
CCekR
+= ⋅
−
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Liquid Phase Mass Balances Boundary condition at the inlet Boundary condition at the outlet Gas Phase Mass Balances Boundary condition at the inlet
[ ] [ ] −===
−= 000
iLLiLLi
LAX xCuxCuddxCD 0=
=L
i
dzdx
( )SHLHDS,SH
Hnin
LRT
E
i,HDSL
BEDiL
i
i
L
Vi,LGiLAX
iLL
xCkxx
Cekβε
ρ xCHyP
βεaK
ddxCD
dd
dxCud HDS
HDSHDS
22
2
11
+
⋅
−
−
⋅+
= +−
( )( )
−
−−= iL
i
i
L
Vi,LGiGG xCHPy
βεaK
dyCud
1
−===
00 ii yy
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• Cylindrical particles Ni-Mo/γ-Al2O3
• Gas oil 14000 ppm S • P : 54 bar • T : 320 – 350 °C • G/L : 250 – 1000 Nl/kg • WHSV : 0.5 – 4 h-1
• For the diluted beds SiC 250 μm was used
Characteristics : • The cross section area of the bench reactor is 10 times higher • The superficial velocities and the bed height was the same in both reactors
Bench 50 g
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Mini 5.5 g
Experiments with Mini and Bench scale reactors
Definition of Apparent Activity
BED 1
BED 2
Same
T, P, G/L WHSV, CS,in
R = kHDSexp(-E/RT) f(ci,Pi)
kHDS,1 kHDS,2
Bed 1 = Reference bed
Apparent Activity : η = kHDS,2 / kHDS,1
CS,1 CS,2
CS,0 CS,0
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Comparison of Mini Scale and Bench scale reactor performance
Mini Reactor Bench scale reactor
0,0
0,2
0,4
0,6
0,8
1,0
1,2
η
Non Diluted Diluted Diluted
Non Diluted
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 1 2 3 4 5
WHSV (h-1)
η
T1 downflowT2 downflowT3 downflowT1 upflowT2 upflowT3 upflow
Performance of the Mini Reactor
Mini Reactor
No significant flow effects
The same performance in upflow and downflow mode
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Distribution of Sulfur groups in up/downflow
0
5
10
15
20
25Al
kyl-t
h
BT
C1-
BT
C2-
BT
C3-
BT
C4-
BT
DBT
C1-
DBT
C2-
DBT
C3-
DBT
+
CS
(ppm
)
DownflowUpflow
36 ppm total S
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Sensitivity Tests
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1 10 100 1000Pe
η
WHSV=2 1/h, T=320 °CWHSV = 2 h-1, T1 Diluted Bed
Effect of Péclet on the activity
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.001 0.01 0.1 1kLaV (s-1)
ηWHSV=1 1/h, T=320 °C, 65 ppm S
WHSV=2 1/h, T=320 °C, 526 ppm S
WHSV = 1 h-1, T1, Diluted Bed
WHSV = 2 h-1, T1, Diluted Bed
Effect of kLaV on the activity
Non-diluted (Upflow) Pe : 9 – 20
Diluted (Upflow/Downflow) Pe : 87 -115
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Estimation of mass transfer for Mini and Bench reactors
Bench
Reactor upflow Mini
Reactor upflow
Bed Non Diluted Diluted Non Diluted
P
(bar)
T
(ºC)
uLS
(mm/s)
uGS
(mm/s)
aV / l
(m-2)
aV / l
(m-2)
aV / l
(m-2)
51 T1 0.029 1.38 35000 31700 74100
51 T3 0.061 1.43 36900 33400 78400
( ) ( ) xCHPy
laDxC
HPyak.T.M iL
i
i
opt
Veff,iiL
i
ioptvilg
−
=
−=
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Interfacial M.T. coefficient in Diluted Bench and Mini Reactors the same • Same particles, conditions and feeds
• Same superficial velocities and bed lengths
Wetted catalyst
Wetted catalyst
bubble
bubblebubble
Η2
Η2Sbubble
Η2
Η2S
CL
CL
Bench reactor
Mini reactor
Radial mass transport resistance of the reactants H2 and S-compounds
Mass transfer effects UGent/FCh13/5L
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Gas oil kinetics experiments at deep HDS conditions
• Mini Reactor • HAGO and trilobe Ni-Mo catalyst • Dilution with 60 μm SiC • WHSV: 0.5 – 4.0 h-1
Τ (ºC) P (bar) G/L (Nl/kg) uGS (mm/s) uLS (mm/s) Evaporation
(% wt.)
PH2S (bar) CL,H2S (mol/l)
T1 51 450 0.66 0.044 26 1.2 0.016
T2 61 520 0.65 0.042 30 1.2 0.017
T3 71 610 0.66 0.040 35 1.2 0.016
T2 61 790 0.98 0.035 42 0.80 0.011
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Simulation with 5 pseudo-compounds, the same reactivity • Optimization using the points CS>10 ppm and WHSV ≥ 2 h-1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 1 2 3 4 5
WHSV (h-1)
η
T1T2T2, G/L+T3
8 March 2013
Apparent activity vs. product CS, One or Five preudo-compounds • Optimization using the points with CS>10 ppm and WHSV ≥ 2 h-1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1 10 100 1000CS (ppm)
η
T1T2T2, G/L+T3
Ultra-Deep HDS
± 5%
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Extrapolation to industrial applications
Adiabatic regime Continuous catalyst deactivation Various feed qualities
600
605
610
615
620
625
0 5 10 15 20
Reactor Length (m)
Tem
pera
ture
(K) Q
UEN
CH
A
QU
ENC
H B
L1 = 2.64 L2 = 5.66 L3 = 8.17
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INDUSTRIAL PERFORMANSE (CS,out, Tprofile,
HC)
OPERATION VARIABLES(ML, Q, T, P)
OPTIMIZER
MODEL
NEURAL NETWORKS
FEED QUALITY (wi, d15, CS,in,
TTAIL)
MODELDEACTIVATION,
KINETIC PARAMETERS
PREDICTION
INDUSTRIAL PERFORMANSE (CS,out, Tprofile,
HC)
OPERATION VARIABLES(ML, Q, T, P)
OPTIMIZER
MODEL
NEURAL NETWORKS
FEED QUALITY (wi, d15, CS,in,
TTAIL)
MODELDEACTIVATION,
KINETIC PARAMETERS
PREDICTION
INDUSTRIAL PERFORMANSE (CS,out, Tprofile,
HC)
OPERATION VARIABLES(ML, Q, T, P)
OPTIMIZER
MODEL
NEURAL NETWORKS
FEED QUALITY (wi, d15, CS,in,
TTAIL)
MODELDEACTIVATION,
KINETIC PARAMETERS
PREDICTION
A hybrid model for the simulation of industrial hydrotreaters
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0.0
0.5
1.0
1.5
0 100 200 300 400 500 600t (days on stream)
η
Training DataTest data
22 % deactivation/year
Prediction of deactivation UGent/FCh13/5L
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Dependence of conversion on reactor diameter.
Reaction : Acetic acid HDO Reaction Conditions : 0.07 MPa, 150 oC, Gas Phase : Hydrogen (80 %) – Nitrogen
Liquid Phase : Acetic Acid Catalyst : sulphided NiMo/Al2O3
Reaction Conditions : 15 MPa, 450 oC, Gas Phase : Hydrogen (80 %) – Nitrogen -
Acetic Acid Catalyst : sulphided NiMo/Al2O3
Joshi N., Lawal A., Chemical Engineering Science, 2012, 84, 761-771
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Is it possible to build a reactor in which all the catalyst particles to be equally accessible by the liquid and gaseous reactants ?
Avoid problems associated with low fluid velocities :
• Catalyst by-passing
• Poor gas and liquid distribution through the catalyst bed
Question :
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Spiral Reactor – Reactor dimensions – Internal Diameter : 0.20 cm – Catalyst Length : 50 - 450 cm – Typical Loaded Catalyst Mass: 0.5 – 10.0 g – Flow mode: ascending and descending – No thermowell inside
– Advantages – Structured and repeatable loading – > 10 times higher velocities – Uniform radial temperature – Easy construction
partile
Reactor w
alls
Reactor w
alls
particle
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• Effective reactor Scaling Down must be carefully designed
• The Mini reactors produce more reliable data for deep HDS
simulation than the corresponding Bench Scale one • The lower apparent activity of the Bench Scale reactor for low
gas and liquid flow rates is attributed to mass transport limitations
• Conventional kinetic formulations can not be used for ultra
deep desulphurization ( exit sulphur concentration < 15 ppm ) • Spiral reactor appears very promising for upscale/downscale
applications involving three phase catalytic reactions.
Concluding Remarks UGent/FCh13/5L
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Acknowledgements Thanks are due to : • G. Bellos • K. Gotsis • L. Kallinikos • K. Metaxas • G. Stefanidis • C. Templis
and to : • I.F.P., Air Liquide, EL.PE. and M.O.
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