Modeling of a CO2-stripper

1
Modeling of a CO2-stripper
Marie Solvik Supervisors Sigurd Skogestad and
Marius Støre Govatsmark
2
CO2-stripper
PC
PC
LC

• Objectives
• Produce pure ethane product
• Keep the CO2 content in the sales gas within the
  limit.

LT, XLT
FC
F, z, hf

• 75 stages including reboiler and reflux tank
• Bottom product purified ethane
• Distillate Offgas (CO2, ethane and some
  methane)

LC
QR
There exist a dynamic model of the system in
D-spice
B, xB
3
2-component flash tank made in Matlab

• SRK equation of state with binary interaction
  parameter found by Kornberg (2007)
• 2 components- ethane and CO2
• Compared to simulation done in ProSim

z1 Pbarg TK x1 y1 K
0.99 34.0 288.7 0.9927 0.9873 0.9946
0.90 34.0 283.8 0.9248 0.8752 0.9463
0.80 34.0 279.0 0.8428 0.7572 0.8984
0.60 34.0 271.5 0.6503 0.5497 0.8453
0.40 34.0 267.8 0.4202 0.3798 0.9039
0.20 34.0 268.0 0.1810 0.2190 1.2099
z1 Pbarg TK x1 y1 K
0.99 34.0 288.7 0.9924 0.9868 0.9943
0.90 34.0 283.7 0.9231 0.8727 0.9453
0.80 34.0 278.9 0.8419 0.7561 0.8980
0.60 34.0 271.6 0.6528 0.5520 0.8455
0.40 34.0 267.8 0.4225 0.3812 0.9023
0.20 34.0 268.0 0.1780 0.2166 1.2168
4
3-component flash tank made in Matlab

• Added an extra component, methane to the model
• Compared with actual process data from the top of
  the column and a flash tank model made in D-spice

Real time composition of ethane(red) and CO2
(green) from Aspen process explorer.
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D-spice versus Matlab
  yC2 yCO2 Pbarg T?C
Operating point 1 (3h)        
Aspen 0.455 0.525 34.7 -3.3
Matlab 0.528 0.458 34.7 -3.3
Malab 0.443 0.527 34.7 -6.0
D-spice 0.455 0.525 34.7 -3.7
Operating point 2 (15h)        
Aspen 0.515 0.456 34.5 -2.0
Matlab 0.556 0.420 34.6 -2.7
D-spice 0.515 0.456 34.5 -3.1
6
Column model made in Matlab

• SRK function of state
• Builds on the flash tank model
• 75 stages
• Time-consuming

7
Conclusion

• The column model needs to be improved before
  finding optimal operating points
• Flash tank model made in D-spice showed accurate
  results when comparing with actual plant data and
  with Matlab model.