performance studies of trickle bed reactors
DESCRIPTION
PERFORMANCE STUDIES OF TRICKLE BED REACTORS. Mohan R. Khadilkar Thesis Advisors: M. P. Dudukovic and M. H. Al-Dahhan Chemical Reaction Engineering Laboratory Department of Chemical Engineering Washington University St. Louis, Missouri. CREL. Trickle Bed Reactors. - PowerPoint PPT PresentationTRANSCRIPT
PERFORMANCE STUDIES OF TRICKLE BED REACTORSPERFORMANCE STUDIES OF TRICKLE BED REACTORS
Mohan R. KhadilkarMohan R. Khadilkar
Thesis Advisors: M. P. Dudukovic and M. H. Al-DahhanThesis Advisors: M. P. Dudukovic and M. H. Al-Dahhan
Chemical Reaction Engineering LaboratoryChemical Reaction Engineering Laboratory
Department of Chemical EngineeringDepartment of Chemical Engineering
Washington UniversityWashington University
St. Louis, MissouriSt. Louis, Missouri
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Trickle Bed ReactorsTrickle Bed Reactors
CATALYST
BED
GAS LIQUID
GAS
LIQUID Re (Liquid)
Re(G
as)
10
100
1000
10000
1 10 100 1000
TRICKLE PULSE
DISP .
BUBBLE
WAVYSPRAY
............. ......... ... .. ... ... ...
Liquid Film or Rivulet
Liquid Filled pores
Dry Pellet
Capillary Condensation
Catalyst Wetting Conditions in Trickle Bed Reactor
Flow Map (Fukushima et al., 1977)
Operating Pressures up to 20 MPaOperating Flow Ranges:High Liquid Mass Velocity (Fully Wetted Catalyst) (Suitable for Liquid Limited Reactions)Low Liquid Mass Velocity (Partially Wetted Catalyst) (Suitable for Gas Limited Reactions)
Cocurrent Downflow of Gas and Liquid on a Fixed Catalyst Bed
Limiting Reactant criterion:
Gas limited reaction if
Liquid limited reaction if
1*
AeA
BieB
CD
CD
D C
D CeB Bi
eA A* 1
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FLOW REGIMES AND CATALYST WETTING EFFECTSFLOW REGIMES AND CATALYST WETTING EFFECTS
DOWNFLOW (TRICKLE BED REACTOR) DOWNFLOW (TRICKLE BED REACTOR) UPFLOW (PACKED BUBBLE COLUMN) UPFLOW (PACKED BUBBLE COLUMN)
100
1000
10000
10 100 1000
Re (Liquid)
BUBBLE (I)
PULSE
BUBBLE (II)
CHURN
PSEUDOSPRAY
PSEUDOPULSE
10
100
1000
10000
1 10 100 1000
Re (Liquid)
TRICKLE PULSE
DISP .BUBBLE
WAVYSPRAY
PARTIAL WETTING COMPLETE WETTING
CATALYSTLIQUIDGAS
(Trickle Flow Regime) (Bubble Flow Regime)
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MotivationMotivation
A clear understanding of the differences between the two modes of operation is needed, particularly for high pressure operation. Are upflow reactors indicative of trickle bed performance under different reaction conditions?
To understand the effects of bed dilution with fines on reactor performance
To develop guidelines regarding the preferred mode of operation for scale-up/scale-down of reactors for gas or liquid reactant limited reactions
Objectives Objectives
Experimentally investigate the performance of DOWNFLOW Experimentally investigate the performance of DOWNFLOW (Trickle Bed) and UPFLOW (Packed Bubble Column) reactors (Trickle Bed) and UPFLOW (Packed Bubble Column) reactors for a test HYDROGENATION reaction for a test HYDROGENATION reaction
Study the effects of PRESSURE, FEED CONCENTRATION and Study the effects of PRESSURE, FEED CONCENTRATION and GAS VELOCITY on the performance of both modes of operationGAS VELOCITY on the performance of both modes of operation
Study the effect of FINES on the performance of the two modes Study the effect of FINES on the performance of the two modes at different feed concentrations and pressuresat different feed concentrations and pressures
Compare MODEL PREDICTIONS with experimental data at Compare MODEL PREDICTIONS with experimental data at different pressuresdifferent pressures
Reaction SchemeReaction Scheme::C CH
CH
2
3
HC CH
CH
3
3
H+2
Pd/Alumina
Limiting Reactant criterion:
B (l) + A(g) P(l)
D C
D CeB Bi
eA A*
1
D C
D CeB Bi
eA A*
1Liquid limited reaction if
Gas limited reaction if
Catalyst : 2.5 % Pd on Alumina (cylindrical 0.13 cm dia.)Fines : Silicon carbide 0.02 cm
Range of Experimentation :
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• Superficial Liquid Velocity (Mass Velocity) : 0.09 - 0.5 cm/s (0.63-3.85 kg/m2s)• Superficial Gas Velocity (Mass Velocity) : 3.8 -14.4 cm/s (3.3x10-3-12.8x10-3 kg/m2s)
• Feed Concentration : 3.1 - 7.8 % (230-600 mol/m3)• Operating Pressure : 30 - 200 psig (3-15 atm)• Feed Temperature : 24 oC
Alpha-methylstyrene cumene
Experimental SetupExperimental Setup
High PressureGas Supply
Feed Tank
Damper
LT
DPT
TT
TT
LT
TT
PT
PT
LT
LTLC
Waste Tank
GasChromatograph
Reactor
Vent
High PressureGas Supply
Solvent
Rotameter
High PressureDiaphragm Pump
Gas-LiquidSeparator
Computer
Demister
PC
PC
PC PC
PC
PC
PC
Distributor
CoolingJacket
Rotameter
Vent
Saturators
Timer
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Downflow and Upflow Experimental Results at Low Pressure Downflow and Upflow Experimental Results at Low Pressure (Gas limited Reaction) without Fines(Gas limited Reaction) without Fines
DOWNFLOW OUTPERFORMS UPFLOW DUE TO PARTIAL EXTERNAL WETTING LEADING TO IMPROVED GAS REACTANT ACCESS TO PARTICLES
0
0.2
0.4
0.6
0.8
1
0 100 200 300 400Space time , s
Con
vers
ion(
X)
UPFLOW
DOWNFLOW
CBi=7.8%v/v, P=30psig
Gas Limited
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Downflow and Upflow Experimental Results at High Pressure Downflow and Upflow Experimental Results at High Pressure (Liquid limited Reaction) without Fines(Liquid limited Reaction) without Fines
UPFLOW OUTPERFORMS DOWNFLOW DUE TO MORE COMPLETE EXTERNAL WETTING LEADING TO
BETTER TRANSPORT OF LIQUID REACTANT TO THE CATALYST
00.10.20.30.40.50.60.70.80.9
1
0 50 100 150 200Space time, s
Con
vers
ion(
X)
DOWNFLOW
UPFLOW
CBi=3.1(v/v)%,P=200psig
Liquid Limited
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ABOUT EQUAL PERFORMANCE DUE TO COMPLETE WETTING
00.10.20.30.40.50.60.70.80.9
1
0 50 100 150 200Space time,s
Con
vers
ion(
X)
DOWNFLOW
UPFLOW
CBi=6.7 %(v/v), P=30 psig
Downflow and Upflow Experimental Results at Low Pressure Downflow and Upflow Experimental Results at Low Pressure (Gas limited Reaction) with Fines(Gas limited Reaction) with Fines
Fines Packing Procedure: Vol. of Fines ~Void volume (Al-Dahhan et al. 1995)
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SAME PERFORMANCE DUE TO COMPLETE WETTING
00.10.20.30.40.50.60.70.80.9
1
0 50 100 150 200
Space time,s
Con
vers
ion(
X)
DOWNFLOW
UPFLOW
CBi=3.18%(v/v), P=200 psig.
Downflow and Upflow Experimental Results at High Pressure Downflow and Upflow Experimental Results at High Pressure (Liquid limited Reaction) with Fines(Liquid limited Reaction) with Fines
Fines Packing Procedure: Vol. of Fines ~Void volume (Al-Dahhan et al. 1995)
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Effect of Pressure on Downflow PerformanceEffect of Pressure on Downflow Performance
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 50 100 150 200 250
Space time,s
Con
vers
ion(
X)
p=100psig
p=200 psig
p=30psig
Ug=3.8cm/s, CBi=4.8%v/v
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Effect of Pressure (as transition to liquid limitation occurs) on Effect of Pressure (as transition to liquid limitation occurs) on Upflow Reactor Performance.Upflow Reactor Performance.
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200Space time,s
Con
vers
ion(
X)
p=30psig
p=100psig
p=200psig
CBi=3.1%,Ug=3.8 cm/s
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Slurry KineticsSlurry Kinetics
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300Time(min)
Co
nve
rsio
n(X
)
#1p=30psig,CBi=3.9%
#2p=100psig,CBi=3.99%
#3p=200psig,CBi=4%
#4p=300psig,CBi=3.45%
LHHW FORM
rk C C
KC KCvs amsh
ams cume
2
1 21( )
Pressure (psig) kvs
(m3iq./m3cat./s)
*(mol/m3 liq)r-1
K1 K2
30 0.0814 0 0 0100 1.14 4.41 11.48 1200 0.022 0.0273 0.021 2
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El- Hisnawi (1982) modelEl- Hisnawi (1982) model
•Reactor scale plug flow equations Liquid phase gas reactant concentration
•Constant effectiveness factor Modified by external contacting efficiency
•Allowance for rate enhancement on externally dry catalyst Direct access of gas on inactively wetted pellets.
REACTOR SCALEL G
L G
........................
........................
........................
........................
..................
......
........................
................... .............................
Liquid
Film
Dry
Direct Access
to Dry AreasAccess of Gas
via Liquidof gas
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Beaudry (1987) modelBeaudry (1987) modelDRY HALF-WET FULLY WET
Catalyst Pellet
Flowing Liquid
• Pellet scale reaction diffusion equations
For fully wetted and partially wetted slabs
• Effectiveness factor weighted based on contacting efficiency
• Overall effectiveness factor changes along the bed length
Evaluation of overall effectiveness with change in concentration and contacting
Overall Effectiveness factor at any location
o ce od ce ce odw ce ow ( ) ( )1 2 12 2
CBCA
0 2V/S
01x
0 1y
CB
CA
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10,0''
;10,0')1(' 2
2
222
2
2
yCdy
CdxC
dx
CdAA
AAA
A
Upflow and Downflow Performance at Low PressureUpflow and Downflow Performance at Low Pressure (Gas Limited Condition) (Gas Limited Condition)
Experimental Data and Model PredictionsExperimental Data and Model Predictions
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400
Space time(s)
Con
vers
ion(
X)
down,El-Hisnawi
upflow,El-Hisnawi
downflow,Beaudry
upflow,Beaudryi
downflow,exp
upflow,exp
Ug=4.4cm/s,Co=7.6%(v/v),p=30psig
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Upflow and Downflow Performance at High Pressure Upflow and Downflow Performance at High Pressure (Liquid Limited Conditions): (Liquid Limited Conditions):
Experimental Data and Model PredictionsExperimental Data and Model Predictions
00.1
0.20.3
0.40.5
0.60.7
0.80.9
1
0 50 100 150 200 250
space time(s)
Con
vers
ion(
X)
down,El-Hisnawi
up, El-Hisnawi
down, Beaudry
up, Beaudry
downflow,exp
upflow,exp
Ug=3.8cm/s,Co=3.1%(v/v),p=200psig
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SummarySummary DOWNFLOW PERFORMS BETTER AT LOW PRESSURE.
(Hydrogenation of alpha-methylstyrene is a gas limited reaction.
Partial wetting is helpful in this situation.)
UPFLOW PERFORMS BETTER AT HIGH PRESSURE.
(Hydrogenation of alpha-methylstyrene becomes a liquid limited reaction. Complete wetting is beneficial to this situation.)
THE PREFERRED MODE FOR SCALE-UP (UPFLOW OR DOWNFLOW) DEPENDS ON THE TYPE OF REACTION SYSTEM AS WELL AS ON THE RANGE OF OPERATING CONDITIONS THAT AFFECT CATALYST WETTING.
FINES NEUTRALIZE PERFORMANCE DIFFERENCES DUE TO MODE OF OPERATION AND REACTION SYSTEM TYPE , DECOUPLE HYDRODYNAMICS AND KINETICS, AND HENCE ARE TO BE PREFERRED AS SCALE-UP TOOLS.
THE TESTED MODELS PREDICT PERFORMANCE WELL
(although improvements in mass transfer correlations are necessary)
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Unsteady State Operation in Trickle Bed ReactorsUnsteady State Operation in Trickle Bed Reactors
“Modulation of input variables or parameters to create unsteady “Modulation of input variables or parameters to create unsteady state conditions to achieve performance better than that attainable state conditions to achieve performance better than that attainable with steady state operation”with steady state operation”
MotivationMotivation
Performance enhancement in existing reactorsPerformance enhancement in existing reactors Design and operation of new reactorsDesign and operation of new reactors Lack of systematic experimental or rigorous modeling studies in Lack of systematic experimental or rigorous modeling studies in
lab reactors necessary for industrial applicationlab reactors necessary for industrial application
Two ScenariosTwo Scenarios– Gas Limited ReactionsGas Limited Reactions– Liquid Limited ReactionsLiquid Limited Reactions
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ObjectivesObjectives
To experimentally investigate trickle bed performance under unsteady state operation (flow modulation) for gas and liquid limited conditions for a test hydrogenation system
To develop model equations for unsteady state phenomena occurring in trickle-bed reactors
To simulate unsteady state transport processes in trickle-bed reactors including bulk and interphase momentum, mass, and energy transport for the test reaction system
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Strategies for Unsteady State OperationStrategies for Unsteady State Operation
Flow Modulation Flow Modulation (Gupta, 1985; Haure, 1990; Lee and Silveston, 1995)(Gupta, 1985; Haure, 1990; Lee and Silveston, 1995)
– Liquid or Gas Flow– Isothermal/Non-Isothermal– Adiabatic
Composition Modulation Composition Modulation (Lange, 1993)(Lange, 1993)
– Pure or Diluted Liquid/Gas– Isothermal/Non-Isothermal – Adiabatic
Activity Modulation Activity Modulation (Chanchlani, 1994; Haure, 1994)(Chanchlani, 1994; Haure, 1994)
– Enhance activity due to pulsed component– Removal of product from catalyst site– Catalyst regeneration due to pulse
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Gas Limited ReactionsGas Limited Reactions
Partial Wetting of Catalyst Pellets -DesirablePartial Wetting of Catalyst Pellets -Desirable– Internal wetting of catalystInternal wetting of catalyst– Externally dry pellets for direct access of gasExternally dry pellets for direct access of gas– Replenishment of reactant and periodic product removalReplenishment of reactant and periodic product removal
– Catalyst reactivationCatalyst reactivation
Liquid Limited ReactionsLiquid Limited Reactions
Partial Wetting of Catalyst Pellets-UndesirablePartial Wetting of Catalyst Pellets-Undesirable– Achievement of complete catalyst wettingAchievement of complete catalyst wetting– Controlled temperature rise and hotspot removalControlled temperature rise and hotspot removal
Possible Advantages of Unsteady State OperationPossible Advantages of Unsteady State Operation
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Test Reaction and Operating ConditionsTest Reaction and Operating Conditions
C CH
CH
2
3
HC CH
CH
3
3
H+2
Pd/Alumina
Operating ConditionsOperating Conditions
• Superficial Liquid Mass Velocity : 0.1-3.0 kg/m2s• Superficial Gas Mass Velocity : 3.3x10-3-15x10-3 kg/m2
• Feed Concentration : 2 .7 - 20 % (200-1500 mol/m3)• Cycle time (Total Period) : 40-900 s• Cycle split (ON Flow Fraction) : 0.1-0.6• Max. Allowed temperature rise : 25 oC• Operating Pressure : 30 -200 psig (3-15 atm)• Feed Temperature : 20-35 oC
Alpha-methylstyrene hydrogenation to isopropyl benzene (cumene)
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Experimental ResultsExperimental Results
Liquid Limited Conditions ( = 2)High Pressure,
Low Liquid Feed Concentration
Gas Limited Conditions ( = 20)Low Pressure,
High Liquid Feed Concentration
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 200 400 600 800
Space time (s)
Con
vers
ion(
X)
Steady State
Unsteady State (Cycle = 60s, S=0.5)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 100 200 300 400 500Space time (s)
Con
vers
ion
(X)
Unsteady State (Cycle=60s, S=0.5)
Steady State
D C
D CeB Bi
eA A*
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Effect of Cycle Split on Performance EnhancementEffect of Cycle Split on Performance Enhancement
Gas Limited Conditions ( = 20)Operating Conditions : Pressure=30 psig
Liquid Reactant Feed Concentration= 1484 mol/m3
Cycle Split (St)= Liquid ON Period/Total Cycle Period(T)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.2 0.4 0.6 0.8 1Cycle Split (ON time/Total Cycle Time)
Con
vers
ion
(X)
SteadyState
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Phenomena occurring under unsteady state operation Phenomena occurring under unsteady state operation with flow modulation in a trickle-bed reactorwith flow modulation in a trickle-bed reactor
time,t
Catalyst (Internally and Externally wetted)
Liquid Full (Holdup=Bed voidage)
Catalyst (Internally wet, externally partially wet)
Liquid films (Holdup = dynamic +static)
Gas accesing liquid and dry catalyst
Catalyst (Internally wet, externally dry)
Liquid films (Holdup = only static)
Gas Accesing dry catalyst
LIQUID PULSE ON
LIQUID PULSE TRANSITON ZONE
LIQUID PULSE OFF
Temperature, Low (=Feed Temperature)
Temperature, Rise (>Feed Temperature)
Temperature, High (>Feed Temperature)
(a)
(b)
(c)
(Only Scenario II)
(Only Scenario II)
GOALGOAL: : To Predict Velocity, Holdup, Concentration and Temperature ProfilesTo Predict Velocity, Holdup, Concentration and Temperature Profiles
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The Model StructureThe Model Structure
z=L
z=0GAS LIQUID
SOLID
C1G
C2G
.
.CnG
C1L
C2L
.
.CnL
NiGS
NiGS
NiLS
NiLS
NiGL
EGS
EGS
ELS
ELS
EGL
EGL
NiGL
t
Cz
u C N a N aG iG IG G iG iGL
GL iGS
GS( )
t
Cz
u C N a N aL iL IL L iL iGL
GL iLS
LS( )
Bulk Phase EquationsBulk Phase Equations
SpeciesSpecies
EnergyEnergy
c B CPB e
CP LSLS
GSGS
E
tk
T
zE a E a
( )( )
11
2
2
( ) ( )L L L L IL L L GLGL
LSSL
E
t
u H
zE a E a
( ) ( )G G G G IG G G GLGL
GSGS
E
t
u H
zE a E a
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Advantages of Maxwell-Stefan Multicomponent Advantages of Maxwell-Stefan Multicomponent Transport Equations over Conventional ModelsTransport Equations over Conventional Models
Multicomponent effects are considered for individual component transport [k]’s are matrices
Bulk transport across the interface is considered
Nt coupled to energy balance (non zero) Transport coefficients are corrected for high fluxes
[k] corrected to [ko] = [k][[exp([])-[I]]-1
Concentration effects and individual pair binary mass transfer coefficients considered
Thermodynamic non-idealities are considered by activity correction of transport coefficients
Holdups and velocities are affected by interphase mass transport and
corrected while solving continuity and momentum equations
D Dij ij
[ ]ln
ij ij ii
j
xx
Flow Model EquationsFlow Model Equations
uiL,uiG
L,G,P
Staggered 1-D Grid
ZN
u
z
u
zt
zc
p
zG L
L iL G iG( )( ) ( ) ( )* *1 1
MomentumMomentum
ContinuityContinuity
PressurePressure
L
LL
IL L
iGL
GL i iLS
LS it
u
zN a M N a M
G G G IG G
iGL
GL i iGS
GS it
u
zN a M N a M
L L
ILL L IL
ILL L L
LD Liq IG IL IL i
GLGL i i
LSLS i
u
tu
u
zg
P
zF K u u u N a M N a M , ( ) ( )
G G
IGG G IG
IGG G G
GD Gas IL IG IG i
GLGL i i
GSGS i
u
tu
u
zg
P
zF K u u u N a M N a M , ( ) ( )
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Stefan-Maxwell Flux Equations for Interphase Stefan-Maxwell Flux Equations for Interphase Mass and Energy TransportMass and Energy Transport
N J x J xq
iL
iL
i k kL
k
n
ix
1
1
Gas-Liquid FluxesGas-Liquid Fluxes
Liquid-Solid and Gas-Solid FluxesLiquid-Solid and Gas-Solid Fluxes
N J y J yq
iV
iV
i k kV
k
n
iy
1
1
E h T T N H TLL I L i
LiL
Li
n
. ( ) ( )
1
E h T T N H TVV G I i
ViV
Gi
n
. ( ) ( )
1
E h T T N H TLSLS L ILS i
LSiL
Li
n
. ( ) ( )
1 N c k xLSt LS LS [ ][ ].
N c k xGSt GS GS [ ][ ]. E h T T N H TGS
GS G IGS iGS
iG
Gi
n
. ( ) ( )
1
Bootstrap Condition for Multicomponent TransportBootstrap Condition for Multicomponent Transport• Interphase Energy Flux for the Gas-Liquid Transport and Bulk to Catalyst Interphase Energy Flux for the Gas-Liquid Transport and Bulk to Catalyst Interface TransportInterface Transport
• Net Zero Volumetric Flux for Liquid-Solid and Gas-Liquid Interface for Net Zero Volumetric Flux for Liquid-Solid and Gas-Liquid Interface for Intracatalyst FluxIntracatalyst Flux
[ ], i k G ik i ky , ik k nc y ( )/
, y i i
i
y:i i i
VG i
LLy H T H T ( (@ ) (@ ))
[ ], ikCP ik ci kx:k
k
k
nc
ncmx
MM( )/
and
mx cii
ii
xM
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Catalyst Level EquationsCatalyst Level Equations
Approach I: Rigorous Single Pellet Solution of Intrapellet Profiles along with Liquid-Solid and Gas-Solid Equations
Approach II: Apparent Rate Multipellet Model Solution of Liquid-Solid and Gas-Solid Equations
G CiCP L
xc
CiCP L G CiCP L G CiCPL
cx x
dtB
x x x
xcRtCP
i ncnt
i ncnt
j
j ncnt
j ncnt
j ncnt
jncnt, ,
,
, , ,{[ ][ ] [ ]}
( )
( )
1
11
11 1
11
2 11
20
cx x
dtN a N a RtCP
int
int
iLS
jLS
j a biGS
jGS
j a bAppnt
1
1 1 1 11
1 0, ,
G
Type I: Both Sides Externally Wetted
Type II: Half Wetted Type III: Both Sides Externally Dry
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Holdup and Liquid Velocity ProfilesHoldup and Liquid Velocity Profiles
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 10 20 30 40time (s)
Liq
uid
Hol
dup
...
z=0.0
z=0.25
z=0.45
z=0.65
z=0.85
z=1.0
0
0.01
0.02
0.03
0.04
0.05
0.06
0 10 20 30 40
time (s)
Liq
uid
Vel
ocity
(m/s
) …..
z=0.0
z=0.25
z=0.45
z=0.65
z=0.85
z=1.0
Operating Conditions: Liquid ON time= 15 s, OFF time=65 s Liquid ON Mass Velocity : 1.4 kg/m2s Liquid OFF Mass Velocity: 0.067 kg/m2s Gas Mass Velocity : 0.0192 kg/m2s
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Pseudo-Transient Simulation ResultsPseudo-Transient Simulation Results Alpha-methylstyrene Concentration ProfilesAlpha-methylstyrene Concentration Profiles
0
50
100
150
200
250
0 0.2 0.4 0.6 0.8 1Axial Position (m)
-MS
con
cent
ratio
n (m
ol. m
-3)
0.75
1.644
2.844
6.324
10.644
16.164
29.814
40.314
46.674
0
50
100
150
200
250
0 5 10 15time, (s)
-MS
conc
entra
tion,
(mol
. m
-3 )
..
z=0
z=0.1
z=0.2
z=0.3
z=0.4
z=0.5
z=0.6
z=0.7
z=0.8
z=0.9
z=1.0
Alpha-methylstyrene Concentration buildup in the reactor to steady state or during ON cycle of flow modulationFeed Concentration : 200 mol/m3
Pressure : 1 atm. Reaction Conditions : Gas Limited ( = 10)
(Intrinsic Rate Zero order w.r.t. Alpha-MS)
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time,s
Pseudo-Transient Cumene and Hydrogen Pseudo-Transient Cumene and Hydrogen Concentration ProfilesConcentration Profiles
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1
Axial Position (m)
Cum
ene
conc
entra
tion
(mol
.m -3
)
0.75
1.644
4.044
8.124
14.004
21.084
29.814
34.254
44.034
0
2
4
6
8
10
12
14
16
0 5 10 15 20
time (s)
Liq
. Pha
se H
ydro
gen
Con
c (m
ol.m
-3
)
z=0
z=0.1
z=0.2
z=0.3
z=0.4
z=0.5
z=0.6
z=0.7
z=0.8
z=1
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Profiles show build up of Cumene and Hydrogen profiles to steady state or during ON part of the pulse
Alpha-methylstyrene and Cumene Concentration Alpha-methylstyrene and Cumene Concentration Profiles During Flow ModulationProfiles During Flow Modulation
Supply and Consumption of AMS and Corresponding Rise in Cumene Concentration
Operating Conditions: Cycle period=40 sec, Split=0.5 (Liquid ON=20 s) Liquid ON Mass Velocity : 1.01 kg/m2s Liquid OFF Mass Velocity: 0.05 kg/m2s Gas Mass Velocity : 0.0172 kg/m2s
0.341
10.479
20.644
29.291
39.455
0.1
0.2
0.3
0.4
0.5
0
10
20
30
40
50
Cum
ene
Con
c., m
ol/m
3
time, s Axial Location, m
0.1
0.3
0.5
0.7
0.9
0.2275.353
10.15615.852
20.43325.313
29.83134.725
37.225
0
40
80
120
160
200
Alp
ha-M
S co
nc.,
mol
/m3
time, s
Axial Location, m
CREL
Catalyst Level Hydrogen and Alpha-methylstyrene Catalyst Level Hydrogen and Alpha-methylstyrene Concentration Profiles During Flow ModulationConcentration Profiles During Flow Modulation
0.03
5
5.07
81
10.3
263
15.1
737
21.0
159
24.9
087
30.1
751
35.0
302
39.7
204
0.10.2
0.30.4
0.50.6
0.70.8
0.91
0
20
40
60
80
100
120
140
160
Alp
ha-M
S co
ncen
trat
ion,
m
ol/m
3
time,s
Axial Location, m
0.1
0.3 0.
5 0.7 0.
9
0.035
5.0781
15.1737
20.0057
25.459730.1751
35.0302
02468
1012
14
Hyd
roge
n C
once
ntra
tion
, m
ol/m
3
time,s
Axial Position, m
Concentration of Hydrogen during Liquid ON (1:20s, Wetted Catalyst ) and Liquid OFF(20:40 s,
Dry catalyst) for negligible reaction test case
Concentration of Alpha-MS in previously dry pellets during Liquid ON
(1:20s, Wetted Catalyst ) and Liquid OFF(20:40 s, Dry catalyst)
CREL
ConclusionsConclusions
• Performance enhancement under unsteady state operation is demonstrated to be significantly dependent on reaction and operating conditions
• Rigorous modeling of mass and energy transport by Maxwell-Stefan equations and solution of momentum equations needed to simulate unsteady state flow, transport and reaction occurring in a trickle bed reactor has been accomplished. This algorithm can be used as a generalized simulator for any multicomponent, multi-reaction system and converted to a multidimensional code for large scale industrial reactors.
• Pseudo-transient and transient operation is simulated for the case of liquid flow modulation to demonstrate performance enhancement under unsteady state conditions. Product formation rate is enhanced due to increased supply of liquid reactant to dry pellets (during ON cycle) and gaseous reactant to previously wetted pellets (during OFF cycle). Exothermic enhancement and higher hydrogen solubility can also be taken advantage of in the OFF cycle due to systematic quenching during the ON cycle.
CREL