Dynamic simulation and Control of a CO2 Compression and Purification Unit
for Oxy-Coal-Fired Power Plants
Authors
A. Chansomwong, K.E. Zanganeh, A. Shafeen, P.L. Douglas,E. Croiset,
L.A. Ricardez-Sandoval,
3rd Oxyfuel Combustion Conference September 12, 2013
Content Research Background
• Motivation • Objectives and Scope of Work • CO2 compression and purification unit (CO2CPU)
Methodology Dynamic modeling Results
• Transient behaviour of the CO2CPU • Control structure selection • Preliminary results from
Summary Ongoing work
2
3
Motivation CO2CPU is an important unit which determines the CO2 product quality, the energy consumption and the capital cost of oxy-coal-fired power plant
Research on the dynamic behaviour of CO2CPU is still limited; mathematical models and details of basic control strategy development were not provided in literature.
A controllability analysis is necessary to obtain an efficient and profitable operation.
Integration of process design and control will make the designed process flexible, efficient and easy to control once it is in operation or expanded to the commercial scale.
Study on dynamic simulation and control of an CO2CPU for an oxy-coal-fired power plant
4
Objectives Develop and validate a dynamic model of the CO2CPU
Characterize the dynamic behaviour of the CO2CPU
Propose a suitable control configurations for the CO2CPU
Scope of work Dynamic models to be implemented in gPROMS* (general Process Modelling System)
Literature data** to be used for steady state validation
Decentralized control structure will be proposed based on feedback controller
* gPROMS ModelBuilder 3.5.3. Process Systems Enterprise, London, UK.2012
** Dillon D.J, White V., Allam R.J., Wall R.A., Gibbins J., 2005. Oxy Combustion Processes for the CO2 Capture from Power Plant, IEA Greenhouse Gas R&D Programme, Report 2005/9 (E/04/031).
5
gPROMS
* gPROMS ModelBuilder 3.5.3. Process Systems Enterprise, London, UK.2012
• Equation-oriented modelling software
• Built-in finite different method to solve differential equations
• Add-on physical properties package, Multiflash
6
CO2 Compression and Purification Unit
* Dillon D.J, White V., Allam R.J., Wall R.A., Gibbins J., 2005. Oxy Combustion Processes for the CO2 Capture from Power Plant, IEA Greenhouse Gas R&D Programme, Report 2005/9 (E/04/031).
7
*Schultz, J.M., 1962. The Polytropic analysis of centrifugal compressors. Journal of Engineering Power 8
Dynamic modeling 1. Compressor
Assumptions
Real gas compression with infinitely fast dynamics
Hold-up and inertia of gas within a compressor can be neglected
9
Dynamic modeling 2. Separator
Assumptions Vapour-liquid equilibrium No vapour hold-up in the drum Negligible pressure drop Well insulated
( )cvd MF V L
dt= − −
( )cv ii i i
d M xF z V y L x
dt
×= × − × − ×
ii
i
yK
x≡
Li
i Vi
Kφφ
=
cv
A hM
MW
ρ × ×=
2v vc A ghL
MW
ρ× × ×=
Tube side:
Shell side:
* Coulson & Richardson’s Chemical Engineering Design. Vol.1, 6th ed 10
Dynamic modeling 3. Heat exchanger
, , ( )t t
tt p t t t p t in t out
dTC V FC T T Q
dtρ ρ= − −
Shell-and-tube configuration Countercurrent flow Negligible heat loss and thermal resistance of the tube wall
, , ( )s s
ss p s s s p s in s out
dTC V F C T T Q
dtρ ρ= − +
0.14
0.8 0.330.21 Re Prt t tw
Nuµµ
= ⋅ ⋅
0.14
1 3Re Prs h s sw
Nu jµµ
= ⋅ ⋅
Energy balance Heat transfer coefficient
LMTDQ UA T= ∆where , 1
1 1
t s
U
h h
=
+
, ( )i iNu hd k=
Dynamic modeling 4. Multi-stream heat exchanger
• Complex flow arrangement including counter-flow, parallel-flow and cross-flow
• Encountering both condensing and boiling two phase flows
• Two phase flow model is complex due to the fact that the two distinct phases have its own properties and velocity, and also interact with each other at the interface.
Modeling challenges
11
Dynamic modeling 4. Multi-stream heat exchanger
A dynamic model that is not overly complicated but accurate enough to capture the heat transfer
phenomena is required 12
Two-phase flow model
Lumped parameter model
Discretized model
Homogenous model
Separated flow model
Two-fluid model
Two-phase region is well-mixed. Complexity
and Accuracy
13
Dynamic modeling 4. Multi-stream heat exchanger
Assumptions • One-dimensional fluid flow • Homogenous two phase region • Vapour-liquid equilibrium • Negligible pressure drop • Neglected axial conduction • Negligible thermal resistance of the wall
( ) 0vt z
ρρ
∂ ∂+ =
∂ ∂( ) ( ) 4
TP
H v Hh T
t z D
ρ ρ∂ ∂+ = ∆
∂ ∂
( )1v lρ α ρ α ρ= + −where
vA v
v lA
z dA A
A Az dAα
∆= =
+∆
∫∫
α is a void fraction defined as:
( )0.803
1
1 0.49 ttXα =
+
0.5 0.10.91 v l
ttl v
xX
x
ρ µρ µ
− =
*Abdul-Razzak, A. et.al, 1995. Characteristics of refrigerant R134a liquid-vapour two-phase flow in horizontal pipe. ASHRAE Transaction Sysmposium, 101, pp.953-964. *Lockhart, R.W., Martinelli, R.C., 1949. Proposed correlations of data for isothermal two-phase, two-component flow in pipes. Chem. Eng. Prog., 45, pp. 39-48.
14
15
Results Steady state comparison
gPROMS Dillon et al., 2005* Relative error (%) Process variables Product Vent Product Vent Product Vent
Temperature (K) 308.98 292.77 316.15 293.32 2.27 0.19 Pressure (bar) 110 1.1 110 1.1 - - Mass flow rate (kg/s) 128.06 37.54 126.97 38.61 0.86 2.77 Composition (%mol) CO2 0.9521 0.2439 0.9584 0.2462 0.65 0.95
O2 0.0165 0.1834 0.0105 0.1942 56.67 5.54 Ar 0.0062 0.0727 0.0061 0.0712 1.69 2.06 N2 0.0206 0.4988 0.0203 0.4872 1.50 2.38
H2O 0 0 0 0 - -
SO2 0.0045 0 0.0045 0 0.13 - NO 0.0001 0.0012 0.00013 0.00118 7.83 4.71 CO2 recovery (%Wt) 91.31 91.13 0.20 CO2 Purity (%mol) 95.19 95.84 0.68
* Dillon D.J, White V., Allam R.J., Wall R.A., Gibbins J., 2005. Oxy Combustion Processes for the CO2 Capture from Power Plant, IEA Greenhouse Gas R&D Programme, Report 2005/9 (E/04/031).
16
Results Transient behaviour
P
94.5
95
95.5
91
92
93
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 P
uri
ty (
%m
ol)
CO
2 R
eco
very
(%
wt)
Time (hr)
Recovery
Purity
Ramp up 10% P within 5 min
68 69 70 71 72
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
247
248
249
250
251
0 0.5 1 1.5
Tem
per
atu
re (
K)
Time (hr)
Temperature
53
54
55
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
217.5 217.75
218 218.25 218.5
0 0.5 1 1.5 Tem
per
atu
re (
K)
Time (hr)
Temperature
17
Results Transient behaviour
Q
Ramp up 20% cooling duty of C02 within 5 min
95
95.5
96
88
89
90
91
92
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 P
uri
ty (
%m
ol)
CO
2 R
eco
very
(%
wt)
Time (hr)
Recovery
Purity
244
245
246
247
248
0 0.5 1 1.5 2 2.5 3 3.5
Tem
per
atu
re (K
)
Time (hr)
Temperature
65
75
85
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
215
216
217
218
0 0.5 1 1.5 2 2.5 3 3.5
Tem
per
atu
re (K
)
Time (hr)
Temperature
40
45
50
55
60
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
18
Results Control Structure Selection using Relative Gain Array
Code Manipulated
variables Code Controlled variables
M1 Pdischarge of K02 C1 CO2 Product purity M2 C02 Cooling duty C2 CO2 Recovery M3 V1 C3 D03 Liquid height M4 V2 C4 D04 Liquid height
( )1 T−= ⊗› K K
RGA Matrix Open –loop gain matrix
Select the pairing between controlled variable Ci and manipulated variable Mj that gives a positive relative gain, λij, as close as possible to unity
5 30.92
40.96
6 4 81.00
6 51.04
M1 M2 M3 M4
0.08 6.4 10 1.5 10C1
C2 0.08 6.8 10 0.04
C3 2.3 10 7.3 10 9.2 10C4
2.3 10 0.04 1.7 10
− −
−
− − −
− −
× ×
× −=
− × × − ×
× − − ×
›
* Bristol E.H., 1966, On a new measure of interactions for multivariable process control
19
Results Control Structure Selection using RGA
20
Results Controller Design and Tuning
88
89
90
91
92
93
94
95
0 3 6 9 12 15
CO
2 R
eco
very
(%
wt)
Time (hr)
Unstable response
Recovery
Set point
( ) ( ) ( )cbias c
I
Ku t u K e t e t dt
τ= + + ∫
89.5
90
90.5
91
91.5
92
92.5
0 3 6 9 12 15 C
O2
Rec
ove
ry (
%w
t)
Time (hr)
Stable response
Case 2 Case 3 Case 4 Set point
PI controller:
21
Summary Mathematical models of all unit operations existed in the CO2CPU
are provided
A good agreement between simulation results and literature data were obtained
CO2 recovery is more sensitive to the operating conditions of the CO2CPU more than the CO2 product purity
Stream 8’s temperature was found to be a key variable that determines the CO2CPU performance (i.e. CO2 recovery and CO2 product purity).
22
Ongoing work Fine tune all controllers in the CO2CPU Test controller performance for disturbance rejection Develop a dynamic model of CanmetEnergy’s CO2 capture plant (CanCO2)
23
Acknowledgment The authors gratefully acknowledge the support provided by Natural Resources Canada through CanmetENERGY, Ottawa, under the Canadian government’s funding program “ecoENERGY Innovation Initiative (ecoEII)” and “Program for Energy Research and Development (PERD)”.
Thank You
25
Process variables Flue gas
Flow rate(kg/hr) 600,906
Temperature (°C) 20
Pressure (kPa) 101
Mole fraction
CO2 0.75
O2 0.06
Ar 0.02
N2 0.15
H2O 0.02
26
* Dillon D.J, White V., Allam R.J., Wall R.A., Gibbins J., 2005. Oxy Combustion Processes for the CO2 Capture from Power Plant, IEA Greenhouse Gas R&D Programme, Report 2005/9 (E/04/031).
27
Results Transient behaviour
P
247
248
249
250
251
0 0.5 1 1.5
Tem
per
atu
re (
K)
Time (hr)
217.5 217.75
218 218.25 218.5
0 0.5 1 1.5 Tem
per
atu
re (
K)
Time (hr)
68 69 70 71 72
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
94.5
95
95.5
91
92
93
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 P
uri
ty (
%m
ol)
CO
2 R
eco
very
(%
wt)
Time (hr)
Recovery
Purity
0.58
0.59
0.6
0.61
0 0.5 1 1.5 2 2.5 3 3.5
Vap
ou
r p
has
e fr
acti
on
Time (hr)
Temperature Temperature
Vfrac
0.44
0.45
0.46
0 0.5 1 1.5 2 2.5 3 3.5
Vap
ou
r p
has
e fr
acti
on
Time (hr)
Vfrac
53
54
55
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
Ramp up 10% P within 5 min
244
245
246
247
248
0 0.5 1 1.5 2 2.5 3 3.5
Tem
per
atu
re (K
)
Time (hr)
28
Results Transient behaviour
Q
Temperature
Ramp up 20% cooling duty of C02 within 5 min
95
95.5
96
88
89
90
91
92
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 P
uri
ty (
%m
ol)
CO
2 R
eco
very
(%
wt)
Time (hr)
Recovery
Purity
215
216
217
218
0 0.5 1 1.5 2 2.5 3 3.5
Tem
per
atu
re (K
)
Time (hr)
0.45
0.5
0.55
0 0.5 1 1.5 2 2.5 3 3.5
Vap
ou
r p
has
e fr
acti
on
Time (hr)
Temperature Vfrac
0.5
0.55
0.6
0 0.5 1 1.5 2 2.5 3 3.5
Vap
ou
r p
has
e fr
acti
on
Time (s)
Vfrac
65
75
85
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
40
50
60
0 0.5 1 1.5 2 2.5 3 3.5
CO
2 m
ass
flo
w
rate
(kg
/s)
Time (hr)
CO2
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