regulatory control layer for co2 capturing...
TRANSCRIPT
Plantwide Control Course
Regulatory control layer for CO2 Capturing process
Ref.: M. Panahi and S. Skogestad, Economically efficient operation of CO2 capturing process. Part II. Design of control layer, Chemical Engineering and Processing, 52, 112-124 (2012)
by: Mehdi Panahi
Department of Chemical Engineering Ferdowsi University of Mashhad
Plantwide Control Course, Ferdowsi University of Mashhad, M. Panahi
Plantwide control Hierarchy
Real time optimization (RTO)
Model Predictive control (MPC)
Primary controlled variables, economic variablescs=y1s
Secondary Controlled variables, stabilizing variablescs=y2s
Systematic plantwide control procedure of Skogestad
I Top Down • Step S1: Define operational objective (cost) and constraints• Step S2: Identify degrees of freedom and optimize operation
for disturbances• Step S3: Implementation of optimal operation
– What to control ? (primary CV’s) (self-optimizing control)• Step S4: Where set the production rate? (Inventory control)
II Bottom Up • Step S5: Regulatory control: What more to control (secondary
CV’s) ?• Step S6: Supervisory control• Step S7: Real-time optimization
Proposed control structure with given flue gas flowrate (region I)
Region II: in presence of large flowrates of flue gas (+30%)
Flowrateof flue gas
(kmol/hr)
Pumpsduty(kW)
Self-optimizing CVs in region I CoolerDuty(kW)
Reboilerduty(kW)
Objectivefunction
(USD/ton)CO2 recovery
%Temperature
oftray no. 16
°COptimal nominal
point219.3 3.85 95.26 106.9 321.90 1161 2.49
+5% feedrate 230.3 4.24 95.26 106.9 347.3 1222 2.49
+10% feedrate 241.2 4.22 95.26 106.9 371.0 1279 2.49
+15% feedrate 252.2 4.64 95.26 106.9 473.3 1339 2.49
+19.38% feedrate,reboiler duty
saturates
261.8 4.56(+18.44%)
95.26 106.9 419.4 (+30.29%)
1393(+20%)
2.50
+30% feedrate (reoptimized)
285.1 4.61 91.60 103.3 359.3 1393 2.65
Saturation of reboiler duty (new operations region, region II); one unconstrained degree of freedom left
Maximum gain rule for finding the best CV: 37 candidates
Temp. of tray no. 13 in the stripper: the largest scaled gain
RGA analysis for selection of pairings
2 2
dyn. -2s
2 2
6.85s+1.74 -0.76s 0.0382400s +107s+119.7s +11.4s+1G (s)=
(-9.51s-1.02)e 0.45s+0.0754218s +17.3s+1 205s +18.8s+1
+é ùê úê úê úê úë û
dyn.RGA (0)=0.77 0.230.23 0.77
é ùê úë û
10-3
10-2
10-1
100
101
102
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Frequency [rad/min]
||RG
A -
I||su
m
Diagonal pairing alt.1
Off-diagonal pairing alt.2Recycle amine Reboiler duty
CO2 recovery
Temp. no.16 in the stripper
2SS
0.5232 1.48G 10
8.47 5.17- -é ù
= ´ ê ú-ë û
SSRGA =0.27 1.271.27 0.27
é ùê úë û
- ++ -
1. Dynamic RGA
2. Steady-State RGA
”Break through” of CO2 at the top of the absorber (UniSim simulation)
Liquid mole fraction of CO2 in trays of the Absorber
0,015
0,02
0,025
0,03
0,035
0,04
0,045
0,05
0,055
0 50 100 150 200 250 300 350 400 450
Time (min)
mol
e fr
actio
n
tray 15tray 14tray 13tray 12tray 11tray 10tray 9tray 8tray 7tray 6tray 5tray 4tray 3tray 2tray 1
tray 1
tray 15
Proposed control structure with given flue gas flowrate, Alternative 1
Performance of the proposed control structure, Alternative 1
Proposed control structure with given flue gas flowrate,Alternative 2 (reverse pairing)
Performance of the proposed control structure, Alternative 2
Proposed control structure in region II, Alternative 3
Performance of the proposed control structure, Alternative 3
Modified Alternative 2 = Alternative 4
Performance of the proposed control structure, Alternative 4
Performance of the proposed control structure, MPC