OUT OF SIGHT INSIGHTS Solving Process Mysteries Using a ...
Transcript of OUT OF SIGHT INSIGHTS Solving Process Mysteries Using a ...
OUT OF SIGHT INSIGHTS
Solving Process MysteriesUsing a Simulation Lens
Kenneth R. Cox
Department of Chemical and Biomolecular Engineering
Rice University, Houston, Texas USA
6 October 2005
The Lure of the Great Mystery
“There is nothing more stimulating
than a case where everything goes
against you”
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�Sherlock Holmes
6 October 2005 Rice University/Houston,Texas/USA Page 2
The Classic Whodunnit
* No Witness
* Puzzle to be solved
* Clues not obvious
* Several suspects
* Eureka moment
* Order restored
6 October 2005 Rice University/Houston,Texas/USA Page 3
Typical Oilfield Brine System
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�Morgenthaler, Khatib, French, and Cox (1991)
6 October 2005 Rice University/Houston,Texas/USA Page 4
Assembling the Clues
T
P
P
T
from Evidence
CarbonDioxide
Oil
ScaleCarbonate Water
Scene ofthe Crime
Reconstructed
CarbonDioxide
Water
6 October 2005 Rice University/Houston,Texas/USA Page 5
Le Chatlier’s Principle
Ca2+(aq)+CO2−3 (aq) ⇋ CaCO3(s)
CO2(g) ⇋ CO2(aq)
CO2(aq)+H2O(aq) ⇋ H2CO3(aq)
H2CO3(aq) ⇋ H+(aq)+HCO−
3 (aq)
HCO−
3 (aq) ⇋ H+(aq)+CO2−3 (aq)
6 October 2005 Rice University/Houston,Texas/USA Page 6
Pressure Dependence of Calcite Solubility
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�Cox and Moore(1985)
6 October 2005 Rice University/Houston,Texas/USA Page 7
Hydrogen Ions are Components, too
CO2(g) ⇋ CO2(aq)
CO2(aq)+H2O ⇋ H+(aq)+HCO−
3 (aq)
HCO−
3 (aq) ⇋ H+(aq)+CO2−3 (aq)
H2O ⇋ H+(aq)+OH−(aq)
PCO2 = HCO2[CO2]
K1 =[H+][HCO−
3 ]
[CO2]
K2 =[H+][CO2−
3 ]
[HCO−
3 ]
Kw = [H+][OH−]
6 October 2005 Rice University/Houston,Texas/USA Page 8
Hydrogen Ions are Components, too
[CO2−3 ]
[CO2]=
K1K2
[H+]2
6 October 2005 Rice University/Houston,Texas/USA Page 9
The Moment of Insight
“Exactly! It is absurd – improbably
– it cannot be. So I myself have
said. And yet, my friend, there it is!
One cannot escape from the facts.”
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�Hercule Poirot
6 October 2005 Rice University/Houston,Texas/USA Page 10
Evaporation of Water with Temperature
6 October 2005 Rice University/Houston,Texas/USA Page 11
Solubility of Water in Carbon Dioxide
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�Cox and Moore(1985)
6 October 2005 Rice University/Houston,Texas/USA Page 12
An Education Challenge
“The world is full of obvious things
which nobody by any chance ever
observes”
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�Sherlock Holmes
6 October 2005 Rice University/Houston,Texas/USA Page 13
Relative Volatility of Gases
Plot the equilibrium partial pressure
of carbon dioxide over a 0.125 N
aqueous ammonia solution at 60◦C.
Use the molar ratio of CO2 to NH3
as the x-axis. Vary this molar ratio
from 0.1 to 0.9. Use the best
available method in HYSYS.
6 October 2005 Rice University/Houston,Texas/USA Page 14
Relative Volatility of Gases
Use the best available physical property method to
confirm the experimental partial pressure data in the
table below
6 October 2005 Rice University/Houston,Texas/USA Page 15
A Surprising Result?
6 October 2005 Rice University/Houston,Texas/USA Page 16
What is going on?
NH3(g) ⇋ NH3(aq)
NH3(aq)+H2O ⇋ NH+4 (aq)+OH−(aq)
H2O ⇋ H+(aq)+OH−(aq)
PNH3 = HNH3[NH3]
KNH3 =[NH+
4 ][OH−]
[NH3]
Kw = [H+][OH−]
[NH3]total = [NH3]+ [NH+4 ]
6 October 2005 Rice University/Houston,Texas/USA Page 17
What is going on?
PNH3
[NH3]total=
HNH3
1+ KNH3Kw
10−pH
At high pH:PNH3
[NH3]total⇒ HNH3
At low pH:
log
(
PNH3
[NH3]total
)
⇒ log
(
HNH3Kw
KNH3
)
+ logpH
6 October 2005 Rice University/Houston,Texas/USA Page 18
Bookkeeping of Component Paths
“I suggest you count your bees, you
may find that one of them is
missing”
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�Inspector Clouseau
6 October 2005 Rice University/Houston,Texas/USA Page 19
Which Way Does Water Go?
H2, CH4
C2’s, C3’s
H2, CH4
C2’s
C3’s
C2’s
C3’s
dem
etha
nize
r
deet
hani
zer
168 K
302 K
258 K
360 K
230 K 311 K
6 October 2005 Rice University/Houston,Texas/USA Page 20
Relative Volatilities based on Pure Compounds
Liquid
Vapor
T = 25 C T = 25 C
Vapor
Liquid
T
P
T
P
Water 1−Propene
Water 1−Propene
P = 23.776 torrN/V = 1.2808 mol/m^3
P = 8682.7 torrN/V = 580.41 mol/m^3
6 October 2005 Rice University/Houston,Texas/USA Page 21
Water More Volatile than Propylene!
Vapor
T
P
in in
X = 0.0001 X = 0.0001
Vapor
T
P
PropyleneWater
C7= Liquid C7= Liquid
T = 25 C T = 25 C
P C3 = 0.798 torrN/V = 0.0769 mol/m^3
P H2O = 1.427 torrN/V = 0.0431 mol/m^3
6 October 2005 Rice University/Houston,Texas/USA Page 22
Water Less Volatile than Ethylene
Vapor
T
P
in in
X = 0.0001 X = 0.0001
Vapor
T
P
Water
C7= Liquid C7= Liquid
T = 25 C T = 25 C
N/V = 0.0769 mol/m^3 P H2O = 1.427 torr
Ethylene
P C2 = 3.841 torrN/V = 0.2077 mol/m^3
6 October 2005 Rice University/Houston,Texas/USA Page 23
Partial Pressures over 1-Heptene Solvent
6 October 2005 Rice University/Houston,Texas/USA Page 24
Component with Intermediate Volatility
H2, CH4
C2’s, C3’s
H2, CH4
C2’s
C3’s
C2’s
C3’s
dem
etha
nize
r
deet
hani
zer
168 K
302 K
258 K
360 K
230 K 311 K
6 October 2005 Rice University/Houston,Texas/USA Page 25
Formation of Corrosive Phases
HA
H + A+ −HA
H + A+ −
HA
HA
HA
Non−volatile Acid
(eg, Carboxylic Acids) (eg, H2S, CO2)
Volatile Acid
T
P
T
P
6 October 2005 Rice University/Houston,Texas/USA Page 26
Kister’s Leading Causes of Tower Malfunctions
Fractionator malfunctions due to plugging – mostly
scale products and corrosion products
Column Type Rank
Atmospheric Crude Towers 1
Vacuum Towers 5
FCC Main Fractionator 1
Alky Unit Main Fractionator 1
6 October 2005 Rice University/Houston,Texas/USA Page 27
The Role of Physical Property Experts
TOUGH DECISIONS VS.DEPTH OF UNDERSTANDING
1980 - PRESENTA
vg E
xper
tise
of U
sers
Number of Choices
EOS MODELS GE MODELS
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✲
✲
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✲Peng Robinson
SRK
Kabadi Danner
Lee Kesler
Zukevitch-Joffee
BWR-Lee Starling
PR-MHV2
PR-Wong Sandler
Nothnagel
Ideal Gas
Hayden-O’Connell
NBS/NRC Steam
Boston-Matthias
NRTL
Margules
UNIQUAC
van Laar
Wilson
Bromley-Pitzer
Electrolyte NRTL
Redlich-Kister
UNIFAC
Ideal Liquid
SH-RST
Chien-Null
Pitzer
More than 50 Choices!More than 50 Choices!
6 October 2005 Rice University/Houston,Texas/USA Page 28
Lessons for the Day
• Familiar heuristics fail with electrolyte systems
• Process simulators usually get it right
• Property experts are useful
• Major opportunity to educate young engineers
• Need to analyze and catalog published cases
6 October 2005 Rice University/Houston,Texas/USA Page 29
The Final Word on Mysteries
“The most beautiful experience we
can have is the mysterious. It is the
fundamental emotion which stands
at the cradle of true art and true
science”
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�Albert Einstein
6 October 2005 Rice University/Houston,Texas/USA Page 30