start-up and control of an autothermal reforming (atr)...

Department of Chemical and Environmental Engineering

Illinois Institute of Technology

Start-up and Control of an

Autothermal Reforming (ATR) Reactor

Donald J. Chmielewski and Yongyou Hu

Department of Chemical & Environmental Engineering

Illinois Institute of Technology, Chicago, IL

Dennis Papadias Chemical Engineering Division

Argonne National Laboratory, Argonne, IL

Presented at the Annual Meeting of the AIChE: November 2005



Outline

Introduction / Motivation

Reactor Modeling and Analysis

• 1-D Transport and Kinetic Model

• Model Validation

Controller Design

• 0-D Model and Temperature Regulation

• Start-up Transition Control

Route to Predictive Control



Fuel Cell System

Fuel

Processor Fuel Cell

Stack

Spent-Fuel

Burner

Thermal & Water Management

Air

Air

Fuel

H2

Exhaust

H2O CO2

Electric Power

Conditioner



Hydrogen Storage vs. On-Board Reforming

Transportation

Applications

PEMFCReformerLiquid Fuel

Storage Tank

Cm

Hn

H2

CO

H2O

CO2

PEMFCHydrogen

Storage Tank

H2



PEMFC and CO Poisoning



Fuel Processing Reactors

PEMFCPreferential

Oxidation

(PrOx)

Water-

Gas

Shift

(WGS)

Reformer

Hydrocarbon Feed

Large Hydrocarbons Cracked:

Low H2 to CO ratio Most CO converted to CO2: ~ 1% CO remaining

CO levels down to ~ 10 ppm



Partial Oxidation

Hydrocarbon Fuel

Air (at a sub-

stoichiometric rate)

PO

Reactor

Total Oxidation: OHnmCOOnmHC nm 222 2/)2/(

Steam Reforming: 22 )2/( HnmmCOOmHHC nm

Water Gas Shift: 222 HCOOHCO

22

2

COOH

COH



Partial Oxidation

Hydrocarbon Fuel

Air (at a sub-


PO

Reactor

Oxidation: OHnmCOOnmHC nm 222 2/)2/(



22

2

COOH

COH



Water Gas Shift Reaction

At High temperatures equilibrium favors:

222 HCOOHCO

At Low temperatures equilibrium favors:

222 HCOOHCO

More H2O in the feed will also favor the forward direction



Autothermal Reforming

Hydrocarbon Fuel Air (at a sub-


ATR

Reactor




22

2

COOH

COH

Steam



Autothermal Reforming

Hydrocarbon Fuel Air (at a sub-


ATR

Reactor




CO

H

Less

More 2

Steam 222 ,,, COOHCOH



Outline





Controller Design






Fuel Processor System at Argonne

Water

WG

1

AirWater

Fuel

AirW

G2

WG

3

WG

4

PrO

x1

PrO

x2

PrO

x3

ATR

Water

WG

1

AirWater

Fuel

AirW

G2

WG

3

WG

4

PrO

x1

PrO

x2

PrO

x3

ATR



ATR Reactor at Argonne

Vaporized gasoline,

Steam

Liquid water

Heat exchangerAir (25 °C)

Hot air

Nozzle

7 m

m1

2 m

m1

2 m

m

96 mm

Catalyst bed

Heater rod

Thermocouple1 2 3 4

5 6 7

8 9 10

Metal wall

thickness=1.7 mm

High Space Velocity

(GHSV ~ 50,000/h)

Noble Metal Catalyst

(Rh on a Gd-CeO2 substrate).

Operating Temperature

~ 700 – 1000o C



Reactor Model (Axially Dependent, Nonlinear Dynamic Version)

)()()(,

)()(

0s

jg

jg

jccc

gj

g

kAx

m

N

i

iijj

g

j

s

j

g

jc rMk1

)()()(

,0

)()()()(

)()( ˆ0 sggccc

gg

pg TThA

x

Tcm

)()()(

)()( )(ˆ wsw

w

ww

pw TTxh

t

TSc

Mass Balances:

Catalyst Phase:

Gas Phase:

Energy Balances:

Gas Phase:

n

1i

c

)()(

llreactor wa fer toHeat trans

)()()(

,

)()()(

...)(1ˆ

ii

sg

cc

sw

ww

s

axe

ss

p

s

rHTTh

TTxhx

T

xt

Tc

Solid Phase:

Reactor Wall:



Model of Reaction Kinetics (1)

)()(

11 2

s

O

s

fuel yyAr

Total Oxidation Reaction :

OHnmCOOnmHC nm 222 2/)2/(

1A

Rate Expression:

where

Oxidation rate is Fuel Diffusion Limited.




222 HCOOHCO

Water-Gas Shift Reaction:

Rate Expression:

029.22073)()(

)()(

33 10;22

2

3

T

e

e

s

CO

s

Hs

OH

s

CO

RT

E

KK

yyyyeAr

Wheeler, Jhalani, Klein, Tummala, Schmidt, J. Catal. (2004).

Parameters Adapted from:




22 )2/( HnmmCOOmHHC nm

Steam Reforming Reaction:

Rate Expression:

2

)(

2

2)()(

22

2

2

2

1

s

fuel

RT

H

s

OH

s

fuel

RT

E

yeKyyeAr

Activation Energies from:

Dubien, Schweich, Mabilon, Martin, Prigent, Chem. Eng. Sci. (1998).

A2 and K2: Fit to Experimental Data:



Micro-Reactor Tests (Steady-State Analysis)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.75 1.25 1.75 2.25 2.75 3.25

H2O/C ratio (-)

H2,

CO

2 m

ola

r fr

ac

tio

n (

dry

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

CO

mo

lar

fra

cti

on

(d

ry)

O2/C=0.45

CO2

CO

H2

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.30 0.35 0.40 0.45 0.50 0.55 0.60

O2/C ratio (-)

H2,

CO

2 m

ola

r fr

ac

tio

n (

dry

)

0.05

0.08

0.10

0.13

0.15

0.18

0.20

CO

mo

lar

fra

cti

on

(d

ry)

CO2

H2

CO

H2O/C=1.5



Reactor Start-up: A 2 Step Procedure

Partial Oxidation Mode (to quickly increase temperature)

ATR Mode (for greater CO conversion)

Hydrocarbon Fuel Air

ATR

Reactor

Steam

Hydrocarbon Fuel

Air

PO

Reactor



Reactor Start-Up: CPOX Mode

0

100

200

300

400

500

600

700

800

900

1000

20 40 60 80 100 120 140 160 180 200

Time (s)

Te

mp

era

ture

(°C

)

Experimental Data

Simulation

@ 7 mm

@ 19 mm

Inlet temperature



Reactor Start-Up: ATR Mode

0

100

200

300

400

500

600

700

800

20 40 60 80 100 120 140 160 180 200

Time (s)

Te

mp

era

ture

(°C

)

Experimental Data

Simulation

@ 7 mm

@ 19 mm

Inlet temperature



Exit Concentrations

0.00

0.05

0.10

0.15

0.20

0.25

50 70 90 110 130 150 170 190

Time (s)

Mo

lar

fra

cti

on

dry

(-)

Experiment H2

Experiment CO

Simulation H2

Simuation CO

CPOX Mode: ATR Mode:

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

30 50 70 90 110 130 150 170 190

Time (s)

Mo

lar

fra

cti

on

dry

(-)

CO Simulation

H2 Simulation

CO Experimental

H2 Experimental

@ reactor exit @ GC



Steady-State Axial Profiles

0.00

0.05

0.10

0.15

0.20

0.25

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Dimensionless x-axis (x/L)

Mo

lar f

ra

cti

on

s w

et

(-)

H2

CO

H2O

CO2

Fuel

CPOX Mode: ATR Mode:

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Dimensionless x-axis (x/L)

Mo

lar f

ra

cti

on

s w

et

(-)

H2

CO

H2O

CO2

FuelO2



Outline





Controller Design






Need for Temperature Regulation

Vaporized gasoline,

Steam

Liquid water

Heat exchangerAir (25 °C)

Hot air

Nozzle

7 m

m1

2 m

m1

2 m

m

96 mm

Catalyst bed

Heater rod

Thermocouple1 2 3 4

5 6 7

8 9 10

Metal wall

thickness=1.7 mm

0 200 400 600 800 10000

100

200

300

400

500

time (sec)

Inle

t A

ir T

em

pera

ture

(deg C

)

Inlet Air Temperature Trajectory

Primary Disturbance:

Inlet Temperature



Open-Loop System

ATR

System T3

Inlet Air Flow

T4

T5

T2

T1

Inlet Air

Temperature

Inlet Steam Flow

} } Unmeasured

(but simulated)

Measured

(and simulated)

• Step Tests Performed Using the 1-D Nonlinear Model

• CPOX and ATR Modes Simulated



First Order Plus Dead Time Modeling (CPOX Mode)

Air Flow Rate Inlet Temperature Steam Flow Rate

1,

s

eK

F

T

i

s

i

inAir

ii

1,

s

eK

T

T

i

s

i

inAir

ii

1,

s

eK

F

T

i

s

i

inSteam

ii

0 20 40 60 80 100800

850

900

950

1000

1050

time (sec)

AT

R T

em

pera

ture

(oC

)

T1

T2

T3

T5

T4

0 20 40 60 80 100800

850

900

950

1000

1050

T1

T2

T3

T4

T5

AT

R T

em

pera

ture

(oC

)

time (sec)0 20 40 60 80 100

650

700

750

800

850

900

950

1000

1050

time (sec)

AT

R T

em

pera

ture

(oC

)

T1

T2

T3

T4

T5



First Order Plus Dead Time Modeling (ATR Mode)

0 20 40 60 80 100800

850

900

950

1000

1050

T3

T1

T2

T3

T4

T5

AT

R T

em

pera

ture

(oC

)

time (sec)0 20 40 60 80 100

800

850

900

950

1000

1050

time (sec)

AT

R T

em

pera

ture

(oC

) T1

T2

T3

T4

T5

0 20 40 60 80 100650

700

750

800

850

900

950

1000

1050

AT

R T

em

pera

ture

(oC

)

time (sec)

T2 T

1

T4

T5

T3

Air Flow Rate Inlet Temperature Steam Flow Rate

1,

s

eK

F

T

i

s

i

inAir

ii

1,

s

eK

T

T

i

s

i

inAir

ii

1,

s

eK

F

T

i

s

i

inSteam

ii



Feedback Control

ATR

Reactor

T3 Inlet Air Flow

+ +

+ +

T4

T5

T2

T1

+

- PI

Control

T3, set point

Inlet Air Temperature

T3, measured

Sensor Noise

Temperature Fluctuations in Reactor



Feedback Control

ATR

Reactor

T3 Inlet Air Flow

+ +

+ +

T4

T5

T2

T1

+

- PI

Control

T3, set point

Inlet Air Temperature

T3, measured

Sensor Noise

Temperature Fluctuations in Reactor

Manipulated

Variable

Control Variable

Disturbances



Simulated Disturbances

0 200 400 600 800 10000

100

200

300

400

500

time (sec)

Inle

t A

ir T

em

pera

ture

(oC

)

Inlet Air Temperature Trajectory

0 200 400 600 800-80

-60

-40

-20

0

20

40

60Temperature Fluctuations and Sensor Noise

time (sec)

Dis

turb

ance I

nput



Analysis of the Feedback Controller

Regulation During Partial Oxidation Mode:

0 200 400 600 800800

900

1000

1100

1200CV (T

3) Response: Open vs. Closed-loop

time (sec)

Tem

per

atu

re (

oC

)

Open-loop

Closed-loop

0 200 400 600 800-50

0

50

100

150MV (Air Flow) Response: Open-loop vs. Closed-loop

time (sec)

Inle

t A

ir F

low

Rate

(sl

pm

)

Closed-loop

Open-loop



Analysis of the Feedback Controller

Regulation During ATR Mode:

0 200 400 600 800800

900

1000

1100

1200CV (T

3) Response: Open- vs. Closed-loop

time (sec)

Tem

per

atu

re (

oC

)

Open-loop

Closed-loop

0 200 400 600 8000

50

100

150

200MV (Air Flow) Response: Open vs. Closed-loop

time (sec)

Inle

t A

ir F

low

Rate

(sl

pm

) Open-loop

Closed-loop



Outline





Controller Design






Transition from CPOX to ATR Mode

TF w.r.t.

Air Flow

T3 Air Flow

+ + +

- PI

T3, set point

Steam Flow Rate

+ +

TF w.r.t.

Steam

-




0 50 100 150 2000

400

600

800

0 50 100 150 2000

50

100

Reacto

r T

em

pera

ture

(deg C

)Impact of Steam Injection

Ste

am

Flo

w R

ate

(g/m

in)

time (sec)

With Feedback Controller

Without Feedback Controller

Steam Flow Rate




0 50 100 150 200

400

600

800

0 50 100 150 2000

50

100

0 50 100 150 200

Impact of Steam Injection Rate

With Feedback Controller

Without Feedback Controller

Steam Flow Rate

time (sec)

Reacto

r T

em

pera

ture

(deg C

)

Ste

am

Flo

w R

ate

(g/m

in)



Feed-forward Control

Gp(s) T3

Air

Flow +

+ +

- PI

T3, set point

Steam Flow Rate

(Measured)

+ +

Gd(s)

Gff(s)

-

)()(

)()( sH

sG

sGsG

p

d

ff



Impact of Feed-forward Control

0 20 40 60 80 100500

600

700

800

900

Reacto

r T

em

pera

ture

(deg C

)

time (sec)

Steam Injection: With and Without Feed-forward

Feedback Controller Only

Feed-forward / Feedback Controller



Model Mismatch in Feed-forward Control

Gp(s) T3

Air

Flow +

+ +

- PI

T3, set point

Steam Flow Rate

(Measured)

+ +

Gd(s)

Gff(s)

-

)()(

)()( sH

sG

sGsG

p

d

ff

• If the Gd(s) or Gp(s) used to define Gff(s) are

different than the actual plant then mismatch occurs.



Impact of Model Mismatch

0 20 40 60 80 100400

600

800

1000

1200

time (sec)

T3 T

em

pera

ture

(oC

)


Feed-forward Without

Model Mismatch

Feed-forward With Model Mismatch

Impact of Model Mismatch on Feed-forward

0 20 40 60 80 100200

400

600

800

1000

T3 T

em

pera

ture

(oC

)

Impact of Model Mismatch on Feed-forward

time (sec)

Feed-forward Without Model Mismatch


Feed-forward With

Model Mismatch



Conclusions

• Modeling

– 0-D model sufficient for feedback design.

– Nonlinear model likely needed for feed-forward design.

• Feedback Control (CPOX and ATR Modes)

– Good performance w.r.t. inlet conditions and sensor noise.

– Good performance during CPOX to ATR Transition, if transition is

slow enough.

• Feed-forward Control

– Model mis-match is a major concern



Use of Predictive Control (for CPOX to ATR Transition)

• MPC can incorporate a nonlinear model during transition.

• Can enforce explicit bounds on process variables

(i.e., maximum flow rates and minimum temperatures).

• However, fast running model is needed to meet the

computational requirements of on-line optimization.



Reduced Order Modeling

20 40 60 80 100 120 140 160 180 2000

200

400

600

800

1000

Time, s

Tem

per

ature

,oC

@ z = 7 mm

Measured Inlet Temperature

@ z = 19 mm

Experimental Measurements - "*"

High Order CFD Simulation - Solid

Reduced Order Simulation - Dashed

Computational

Effort:

NLM: ~10 min

ROM: ~30 sec



Reduced Order Modeling

0 0.2 0.4 0.6 0.8 1-0.05

0

0.05

0.1

0.15

0.2

Dimensionless Axial Position, 1 unit =7mm

Mo

le F

ract

ion

, w

et b

asis

H2 CO

CO2 Fuel H

2O

High Order CFD Simulation - SolidReduced Order Simulation - Dashed

Computational

Effort:

NLM: ~10 min

ROM: ~30 sec



Acknowledgements

Collaborators

Shabbir Ahmed (ANL) Sheldon Lee (ANL)

Herek Clack (IIT) Jai Prakash (IIT)

Students

Kevin Lauzze (IIT)

Funding

Argonne National Laboratory

Graduate College, IIT

Armour College of Engineering, IIT

Chemical & Environmental Engineering Dept, IIT



ATR Reactor Model

0

100

200

300

400

500

600

700

800

900

20 40 60 80 100 120 140 160 180

Time (s)

Tem

pera

ture

(°C

)

7 mm

19 mm

Inlet temperature

Partial Oxidation Start-up: (Liquid Water Spray at 75 s)

start-up and control of an autothermal reforming (atr)...

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