Advanced Process Control
A Real World Example
Jim English
UT Graduate, ChE ‘04
April 27, 2006
Introduction
• Who am I?
• Who is Air Liquide?
Why am I here?
• “Real World” example
• Some notes from industry
So what’s the story?
• HyCO = Hydrogen + Carbon Monoxide
• How does the HyCO work? (Go to PFD)
• Amine System (Go to Amine)
HyCO Process Flow
Natural Gas
+
Steam
Reformer
(Reactions)
Hydrogen
PSA
Amine
System
Dryers
(Details)
Cold
Box
CO
Membranes
Reformer Reactions
Natural Gas Reforming:
– CH4 + H2O ↔ 3H2 + CO
Water Shift Reaction
– CO + H2O ↔ H2 + CO2
• Back to PFD
~60’
Amine System
Process
Gas
Outlet
CO2
Reboiler
Amine
System
Stripper
(Inside)
Process
Gas
Inlet
Absorber
Heat
Exchanger
Pictures Inside
Top Wall
Reboiler
X
Reboiler
Stripper
Pictures Inside
Downcomer Tray
X
Stripper
Reboiler
Missing Clips
Pictures Inside
Steam Deflector Plate
Reboiler
Stripper
X
So What Next?
Form the Team
• Research & Development
• Engineering & Design
• Process Control Experts
• Plant Operations
• HyCO Personnel
What’s our Goal?
• Reduce corrosion in the stripper…
• While maintaining absorber’s CO2 removal
But Why?
• If we have to replace stripper packing…
– $50,000 for packing
– Plant shutdown = lost product revenue
– Packing degradation ruined 2 pumps ($$$)
What’s Important?...
• Constraint Variables
• Manipulated Variables
• Disturbance Variables
Which Allows Us To…
CV Target
CV Value
MVPC
MV History
Controller
DV History
MV Setpoint
Amine System Revisited
Process
Gas
Outlet
CV
CO2
CV
CV
Reboiler
MV
Stripper
CV
Absorber
Process
Gas
Inlet
DV
Heat
Exchanger
CV
CV
MV
How do these guys interact?
MVs
Stripper Reboiler
Amine Recirc
Total CO2 Flow
Stripper Ovhd Temp
?
?
?
CO2 Slip
?
?
?
Rich Liquid Loading
?
?
?
Stripper Top DP
?
?
?
Stripper Bottom DP
?
?
?
Absorber DP
?
?
?
CVs
Next came the tough part
• Test & collect process
reaction curves
• Import to Excel &
Matlab
• Fit First Order plus
Time Delay models
Example Step Response
(0.5)
G = 0.5
τ = 4.5
θ = 3.0
θ
(3.0)
τ
(7.5)
Now we Know
MVs
CVs
Stripper Reboiler
Stripper Ovhd Temp
Modeled
CO2 Slip
Modeled
Rich Liquid Loading
Amine Recirc
Total CO2 Flow
Modeled
Modeled
Modeled
Modeled
Stripper Top DP
Modeled
Modeled
Stripper Bottom DP
Modeled
Modeled
Absorber DP
Modeled
Modeled
Inserting Models into MVPC…
Overall Results
235°F
Corrision Temperature
235°F
230°F
230°F
225°F
225°F
Post Implementation
220°F
215°F
220°F
• Reduced average temperature by 5°F (225°F to 220°F)
• 215°F
Decreased
deviation by
T standard
= 225 ± 10°F
T 60%
= 220 (10°F
± 4°Fto 4°F)
avg
avg
Miscellaneous
• Project Updates
• Tools used
• Tasks performed
Conclusions
• Important Factors:
– ENTIRE team
– We reduced the risk of corrosion!
– Project’s success is leading to further MVPC
around the plant’s reformer
Thanks!
Questions?