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