power point del aa
TRANSCRIPT
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Team 1
Michael GlasspoolSarah Wilson
Nicole Cosgrove
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Production Goals Produce 30,000 Metric Tonnes / year
Operate for 350 days / year
Produce acrolein at 0.0177 kmol / s
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Allowable Process Conditions1,2
Process typically run between 320 390C
Run between atmospheric pressure and 303.975 kPa (3
atm) Use air as an oxygen source
Typical Conversion between 65 90 %
Propylene flammability range 2 11.1 %
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Process Optimization Process was optimized in a series of reports
Modeling started off simple and became more
complex Pressure drop calculations and energy balances were
added over the course of the semester to accuratelymodel the system
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Material BalanceAssume an 80 % propylene conversion Flow enough air to stay below LFL of 2%
C3H6 + O2 C3H4O + H2O
Species NameChemical
Formula
Inlet Molar
Flow rate
(kmol/s)
Inlet Mass
Flow rate
(kg/s)
Outlet Molar
Flow rate
(kmol/s)
Outlet Mass
Flow rate
(kg/s)
Propylene C3H6 0.0221 0.9308 0.0044 0.1862
Oxygen O2 0.2433 7.7864 0.2256 7.2202
Nitrogen N2 0.9154 25.6304 0.9154 25.6304
Acrolein C3H4O 0.0000 0.0000 0.0177 0.9921
Water H2O 0.0000 0.0000 0.0177 0.3188
Total - 1.1808 34.3476 1.1808 34.3476
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Preliminary Energy Balance This model assumes a single reaction
Adiabatic and Isothermal cases were modeled
Variable Isothermal Adiabatic
Inlet Temp (K) 623.15 623.15
Outlet Temp (K) 623.15 777.84
Hrxn (J/s)x10-6
-6.02 0
Heat Duty (J/kmol reacted)x10-6
-340 0
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Simple Kinetic Expression3
Rate expression was first order in propylene and half
order in oxygen
sec/212 catOp kgkmolCCkr
2
1
336 sec/)/5.16206exp(101778.5
mkmolkgmTk catrxtr
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Simple Kinetics ResultsAssuming steady-state, isothermal plug flow, the
reactor was modeled in POLYMATH and Aspen Plus
Number of Tubes 1
Tube Diameter (m) 10
Tube Length (m) 759.89
Reactor Volume (m3) 59681.87
Catalyst Bulk Density (kg/m3
rxtr) 1000
Catalyst Weight (kg) 59681870
Catalyst Void Fraction 0.4Reactor Temperature (K) 623.15
Reactor Pressure (kPa) 101.325
Heat Duty (W) -6014660
Calculated Heat Duty (W) -6020000
Residence Time (s) 395.3
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Simple Kinetics Results
0
10
20
30
40
50
60
70
80
90
100
0.00E+00 1.00E+04 2.00E+04 3.00E+04 4.00E+04 5.00E+04 6.00E+04
PropyleneConversion(%)
Reactor Volume (m3)
723 K
713 K
703 K
693 K
683 K
673 K
663 K
653 K
643 K
633 K
623 K
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Major Findings The reactor volume was too large
Increasing the temperature can drastically decrease
the reactor volume Reactor temperature would be raised to 663.15 K, the
maximum temperature
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Pressure Drop CalculationA pressure drop calculation was added using the ErgunEquation, assuming an isothermal plug f low reactorwith a catalyst void fraction of 0.40 4
To
T
o
o
bulkc
o
F
F
T
T
P
P
AdW
dP
GDD
G
ppo
o 75.1)1(150)1(
3
c
i
Woi
A
MF
Gi
,
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Pressure Drop Results By increasing the inlet pressure to 3 atm, the reactor
size was minimized and pressure drop was more easilymodeled
Reactor Temperature (K) 663.15
Initial Pressure (kPa) 303.975
Catalyst Weight (kg) 2628582
Catalyst Density (kg/m3) 6350
1
Reactor Volume (m3) 752.6362
Reactor Diameter (m) 17
Reactor Length (m) 3.31587
Pressure Drop (kPa) 0.2965
Percent Pressure Drop (%) 0.0975
1 Perry, Dale L., and Sidney L. Phillips. Handbook of Inorganic Compounds. CRC Press, 1995.
Number of Tubes 509668.7
Number of Reactors 6
Tubes per Reactor 84945
Total Flow Rate (kmol/s) 1.1808
Flow Rate per Reactor (kmol/s) 0.1968
Total Catalyst Weight (kg) 2628582
Catalyst per Reactor (kg) 438097
Total Reactor Volume (m3) 752.637
Volume per Reactor (m3) 125.4395
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Reaction Kinetics Real reaction kinetics were found as modeled by Tan et
al 5
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Kinetic Development Rate constants were given at different temperatures
Temperature (C) 350 375 390
ka 5.28 x 10-5
9.99 x 10-5
1.46 x 10-4
k12 (2.19 0.14) x 10-4 (3.86 0.37) x 10-4 (5.38 0.35) x 10-4
k13 (2.70 0.18) x 10-4
(2.94 0.31) x 10-4
(2.70 0.27) x 10-4
k14 (2.73 0.21) x 10-5
(4.52 0.55) x 10-5
(6.28 0.71) x 10-5
[ka] = (mol*m3)
1/2/(kg*s)
[kij] = m3/(kg*s)
1/T (1/K) ln(ka) ln(k12) ln(k14) ln(kCO2) ln(kCO)
0.001605 -9.849 -8.426 -10.509 -8.237 -12.149
0.001543 -9.211 -7.860 -10.004 -8.183 -11.1280.001508 -8.831 -7.528 -9.676 -8.346 -10.327
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Kinetic Modeling Assumptions The reaction was assumed to take place in a steady
state, isothermal plug flow reactor
The catalyst void fraction was assumed to be 0.45 witha bulk density of 1565.5 kg/m3 6
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Kinetic Modeling Results The new kinetics reduced the volume necessary to
produce an 80 % conversion
This allowed the reaction to take place in only onereactor
The best acrolein selectivity was found at the higherend of the temperature range (390C)
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Molar Flow Rate throughout
Reactor
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Acrolein Selectivity
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Incorporation of an Energy BalanceAn energy balance was added to account for
temperature changes throughout the reactor
Molten salt (Ua = 227 W/m2-K) was used as a coolantto prevent a runaway reactor temperature7
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Energy Balance Assumptions The flow rate of coolant was kept high enough to
maintain a constant coolant temperature of 658.15 K
Heat capacities and heats of reaction were assumed tobe constant
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Energy Balance Results The addition of the energy balance reduced the overall
volume necessary to reach 80 % conversion
The pressure drop was also reduced from 10.64 % to9.98 %
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Reactor Temperature Profile The temperature throughout the reactor was modeled
to determine the reactor hotspot
The effect of changes in the inlet and coolanttemperatures were also explored
For the base case, the reactor hotspot occurred at thebeginning of the reactor and reached a temperature of
672.5 K
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Reactor Temperature Profile
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Reactor Gain The reactor gain was analyzed to determine the
thermodynamic stability of the reactor 7
For a 1C change in inlet temperature, the gain wasfound to be 0.0754
Inlet
HS
T
TGain
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Reactor Gain Profile
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Energy Balance Results The coolant temperature effected the selectivity of the
reactor
The highest selectivity was found when the coolanttemperature and the inlet temperature were equal
To
(K)
Ta
(K)
Facrolein
(kmol/s)
FCO2
(kmol/s)FCO (kmol/s)
Facetaldehyde
(kmol/s)Selectivity
663.15 658.15 0.017681 0.007796 0.001124 0.002031 1.615
663.15 663.15 0.018495 0.007347 0.001307 0.002107 1.719663.15 668.15 0.019248 0.006897 0.001511 0.002176 1.819
658.15 658.15 0.017646 0.007834 0.001114 0.002028 1.608
668.15 658.15 0.017718 0.007757 0.001135 0.002034 1.622
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Final Reactor DesignVariable Value Units
Inlet Propylene Flow Rate 0.027213 kmol/s
Inlet Oxygen Flow Rate 0.299583 kmol/s
Inlet Nitrogen Flow Rate 1.12716 kmol/s
Overall Pipe Diamter 4.5 m
Tube Diameter 0.0258226 m
Number of Tubes 30228 -
Reactor Length 2.42366 m
Void Fraction 0.45 -
Inlet Pressure 303.975 kPa
Inlet Temperature 663.15 K
Coolant Temperature 663.15 K
Overall Heat Transfer Coefficient 227 W/m2-KCatalyst Bulk Density 1565.5 kg/m3
Catalyst Weight 59997.8 kg
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Temperature Profile in Final
Reactor Design
662
664
666
668
670
672
674
676
678
680
0 10000 20000 30000 40000 50000 60000 70000
ReactorTemperatur
e(K)
Catalyst Weight (kg)
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Flow Rate Profile in Final Reactor
Design
0
0.005
0.01
0.015
0.02
0.025
0.03
0 10000 20000 30000 40000 50000 60000 70000
FlowR
ate(kmol/s)
Catalyst Weight (kg)
Propylene
Acrolein
CO2
CO
Water
Acetaldehyde
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References1) Guest, H.R.. "Acrolein and Derivatives." Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed.2) Machhammer, et al. Method for Producing Acrolein and/or Acrylic Acid. US Patent 7,321,058. January 2008.
3) Dr. Concetta LaMarca. Memo 2: Simple Kinetics. 2008.
4) Fogler, H. Scott. Elements of Chemical Reaction Engineering. 4th Ed. Prentice Hall. 2006.
5) Tan, H. S., J. Downie, and D. W. Bacon. "The Reaction Network for the Oxidation of Propylene over a BismuthMolybdate Catalyst." The Canadian Journal of Chemical Engineering 67(1989): 412-417.
6) "Bismuth molybdate, powder and pieces." CERAC Online Catalog Search. CERAC Incorporated. 05 Mar 2008.
7) Dr. Concetta LaMarca. Memo 5: Energy Balance. 2008.
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Any Questions?
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