cfd model of a fluidized bed chemical · interconnected multi-phase cfd chemical looping model glt...

Lehrstuhl für Energieanlagen und EnergieprozesstechnikP f D I V S hProf. Dr.‐Ing. V. Scherer

CFD model of a fluidized bed chemicalCFD‐model of a fluidized bed chemical looping system:

Design of a heat and mass flow control

H. Kruggel‐Emden; S. Wirtz; V. Scherer

2nd International Conference on Energy Process Engineering | Frankfurt | June 20, 2011

Lehrstuhl für Energieanlagen und EnergieprozesstechnikProf. Dr.‐Ing. V. Scherer

Chemical looping combustion- A solid oxygen carrier (metal oxide) is circulated in the

O2, N2 CO2, H2Ooxidized

i

A solid oxygen carrier (metal oxide) is circulated in the system and is alternately oxidized/reduced

- Air reactor: Oxidation of the oxygen carrier

carrierAirReactor

FuelReactor- Fuel reactor: Bonded oxygen of the carrier reacts with

the gaseous, liquid or solid fuel

Airreducedcarrier Fuel

Gaseous products are CO2 + H2O

=> No additional separation of N2 necessary: good efficiencies

=> Low formation of thermal NOx due to low temperatures



Scale up of chemical looping processes

Existing CFB power plants:e.g. Lagisza III – 460MW

?

Hereby necessary:Simulation methods

0 1kW 1kW 10kW 100kW 1MW ?? ??

Simulation methods


0.1kW 1kW 10kW 100kW 1MW ?? ??


Applicable simulation methods for fluidized systems

- Macroscopic models

- Multi-phase CFD

- Fuel reactor - gaseous fuel [Jung/Gamwo 2008, Deng et al. 2008, Jin et al. 2009,…]Solid fuel conversion [Mahalatkar et al 2009]- Solid fuel conversion [Mahalatkar et al. 2009]

- Fuel reactor model validation [Mahalatkar et al. 2011]- Interconnected modeling [Shuai et al. 2011, Mahalatkar et al. 2010, Kruggel-g gg

Emden et al. 2010]

- Particle based models & CFD



Interconnected multi-phase CFD chemical looping modelG l t

oxsm ,

exhaustairm

General parametersTime step Δt [s] 0.0002Mean particle diameter dp [mm] 0.1525Angle of internal friction ξ [°] 30Maximal packing limit ε [-] 0 6

Air-reactor Fuel-

reactor

Maximal packing limit εs,max [ ] 0.6Restitution coefficient e [-] 0.9Kinetic model Spherical shrinking coreThermal power P [MW] 0.5 (0.4, 0.3)

bubsm ,

XBuffer

fuelmredsm ,

bubsX ,

airm bufsm ,feedsm ,




oxsm ,

exhaustairm


Air-reactor Fuel-

reactor


bubsm ,

X

Buffer specificationsInitial mass [kg] 0Initial state of reduction X [-] 0.65Initial temperature [K] 1200

Buffer

fuelmredsm ,

bubsX , Initial temperature [K] 1200Initial mass flow dm/dts,feed [kg/s] 3.5Initial mass flow dm/dts,red [kg/s] 0Feed temperature [K] 1200Feed state of reduction X[-] 0.65

feedsm ,airm bufsm ,

Feed state of reduction X[ ] 0.65




oxsm ,

exhaustairm


Air-reactor Fuel-

reactor


bubsm ,

X

Air reactor specificationsWidth of vessel [m] 0.225Height of vessel [m] 8.0G id b [ ] 1500

Buffer

fuelmredsm ,

bubsX , Grid number [-] 1500Inlet gas temperature [K] 300Inlet gas velocity [m/s] 1.45Inlet gas composition [kg/kg] N2: 0.77; O2: 0.23Initial bed height [m] 0


Initial bed height [m] 0Inlet solid velocity [m/s] 0




oxsm ,

exhaustairm


Air-reactor Fuel-

reactor


bubsm ,

X

Fuel reactor specificationsWidth of vessel [m] 0.25Height of vessel [m] 0.8W i h i ht [ ] 0 4

Buffer

fuelmredsm ,

bubsX , Weir height [m] 0.4Initial bed height [m] 0.21Initial solids packing [-] 0.42Initial temperature [K] 1223Initial state of reduction X [-] 0 5


Initial state of reduction X [ ] 0.5Grid number [-] 2500Inlet gas temperature [K] 300Inlet gas velocity [m/s] 0.061Inlet gas composition [kg/kg] CH4: 1 (0.594, 0.354);


4CO2: 0 (0.406, 0.646)


Governing gas/solid reactionsOxygen Carrier Materials: Mn O -Mg-ZrO NiO/MgAl O Fe O /MgAl O

Unreacted zone

O2HCO12MnOCHOMn 22443 432 OMn4O212MnO

Oxygen Carrier Materials: Mn3O4-Mg-ZrO2, NiO/MgAl2O4, Fe2O3/MgAl2O4

Reacted

4NiO2HCOCH4NiO 224 4NiO2O4Ni 2

O2HCOO8FeCHO12Fe 2243432 zone

O2HCOO8FeCHO12Fe 2243432 32243 O2Fe1O2O8Fe

Reaction model and kinetic data

32~1exp3 /ngas )X-(C

TREkbdX/dt

Q Zafar, A Abad, T Mattisson, B Gevert, M Strand, Chem. Eng. Sci. 2007, 62, 6556.Q Zafar, A Abad, T Mattisson, B Gevert, En. & Fu. 2007, 21(2), 610.

n, k, E, b - Derived according to experimental data from:


A Abad, et al., Chem. Eng. Sci. 2007, 62(1-2), 533.


Operation of the interconnected modeloxsm ,

Air-t

Fuel-

exhaustairmoxsT ,

reactor reactor

bubsm ,

X

q

redsX ,

Buffer

fuelmredsm ,

bubsX ,


dm/dts,buf=fixed=3.5kg/sCarrier: Mn3O4-Mg-ZrO2

=> Heat and mass flow control essential



Temperature control design

oxsm ,

exhaustfuelmexhaustairm

oxsT , act

oxgset

oxgoxgoxgpactoxs

setoxsoxsoxsp TTmcTTmcQ ,,,,,,,,

Excess heat flux and excess heat flux density

Air-reactor Fuel-

reactor

t

surf dQTnQAKpq

0/1/

setoxs

setoxg TT ,, where

B ff

qbubsm ,

bubsX ,

Kp and Tn from an open loop step response

Kp=0 35·Tg/Ks/TuBuffer

fuelmredsm ,

Kp=0.35 Tg/Ks/Tu

Tn=1.2·Tg

feedsm ,airm bufsm , KL Chien, JA Hrones, JB Reswick, in: Transact. of the Am. Soc. of Mech. Eng.74 Cambridge 1952


74, Cambridge 1952


Temperature control designOpen loop step response for Mn3O4-Mg-ZrO2

exhaustairm

oxsT ,

oxsm ,

1 2

1.6

2

Open loop step response for Mn3O4 Mg ZrO2

dm/dts,buf Kp Tn

2 k / 1 85 3 24Air-reactor

0.4

0.8

1.2

x(t)

dm/dt s,buf=2kg/sdm/dt s,buf=4kg/s

)(tx 2 kg/s 1.85 3.24s

4 kg/s 0.61 2.76s

6 kg/s 1.91 2.40s

setqq 00 1 2 3 4 5 6 7

t [s]

dm/dt s,buf=6kg/s

(A)Closed loop progression of Ts,ox (left), solid mass flow rate dm/dts,ox (right)

1300

1400

1500

[K] 6

8

10

(t) [k

g/s]

dm/dt s,buf=2kg/sdm/dt s,buf=4kg/sdm/dt s,buf=6kg/s

1100

1200

T(t)

[

T s,ox (dm/dt=2kg/s)T s,ox (dm/dt=4kg/s)T s,ox (dm/dt=6kg/s)T s,ox,set

airm

setbufsbufs mm ,,, 2

4

dm/d

t s,o

x


10000 4 8 12 16

t [s]

, ,

(C)

00 2 4 6 8 10

t [s](D)


Temperature control designOpen loop step response for NiO/MgAl2O4

exhaustairm

oxsT ,

oxsm ,Open loop step response for NiO/MgAl2O4

dm/dts,buf Kp Tn

0 5 k / 0 61 2 765

6

7dm/dt=0.5kg/sdm/dt=1kg/sdm/dt=1.5kg/s

Air-reactor

)(tx 0.5 kg/s 0.61 2.76s

1.0 kg/s 0.88 3.00s

1.5 kg/s 1.17 3.00s1

2

3

4

x(t)

Open loop step response for Fe2O3/MgAl2O4

setqq 00 1 2 3 4 5 6 7

t [s](A)

1.6

2

2.4

dm/dts,buf Kp Tn

2 kg/s 1 91 2 40s

0.4

0.8

1.2x(t)

dm/dt=2kg/sdm/dt=4kg/sdm/dt=6kg/s

airm

setbufsbufs mm ,,,

2 kg/s 1.91 2.40s

4 kg/s 2.06 2.40s

6 kg/s 7.61 2.40s


00 1 2 3 4 5 6 7

t [s]

dm/dt 6kg/s

(B)


Mass flow control design

M fl di PI lloxsm ,

exhaustfuelmexhaustairm

Mass flow rate according to a PI-controller

tact

redsset

redsact

redsset

redsbufs dXXTnXXKpm

0,,,,, )(/1)(

Air-reactor Fuel-

reactorKp and Tn derived from a simplified model

0

exhaustfuelm

B ff

bubsm ,

bubsX ,

redsX ,

exhaustfuelmbubsV ,bubsX ,

tBuffer

fuelmredsm ,

bufsm ,act

redsX ,oxsm ,oxsX ,

setredsX ,


fuelm



Mass flow control design

t

t

actreds

setreds dtXXTnKpf

0,, )(,Optimization of:

P t f PI t ll ith t [3 4 5 ]

exhaustfuelmbubsV ,bubsX ,

through a genetic algorithm

Parameters of a PI-controller with tdel =[3s , 4s, 5s]bufsm ,

actredsX ,

oxsm ,oxsX ,

setredsX ,

Xox[-]

ms,buf[kg]

Kp[-]

Tn[s]

Kp[-]

Tn[s]

Kp[-]

Tn[s]

fuelmMn3O4/MnO 0.25 60 52.1 9.7 39.5 11.5 31.9 13.5

NiO/Ni 0.18 85 60.0 12.1 46.3 16.3 38.2 20.5

Fe2O3/Fe3O4 0.01 50 19.1 8.8 14.1 10.3 11.6 11.82 3 3 4



Chemical looping system: Load change P=(0.5;0.4;0.3)MW Solid mass flow (left) and temperatures (right) for Mn3O4-Mg-ZrO2 as carrierSolid mass flow (left) and temperatures (right) for Mn3O4 Mg ZrO2 as carrier

25

30

35

40

/s]

dm/dt s,reddm/dt s,feeddm/dt s,bufdm/dt s,ox

1200

1300

1400

1500

5

10

15

20

dm/d

t [kg

/

800

900

1000

1100

T [K

]

T s,bufT s ox

Heat flux density (left) and degrees of reduction (right) for Mn3O4-Mg-ZrO2 as carrier

00 50 100 150 200

t [s](A)

700

800

0 50 100 150 200t [s]

T s,oxT s,ox,set

(B)

0

-20000

-10000

0

m2 ] 0.4

0.5

0.6

0.7

-40000

-30000q [W

/m

0.1

0.2

0.3X

X s,redX s,oxX s,red,set


-500000 50 100 150 200

t [s](C)

00 50 100 150 200

t [s](D)


Chemical looping system: Temperature setpoint changeSolid mass flow (left) and temperatures (right) for Mn3O4-Mg-ZrO2 as carrier

1200

1300

1400

1500

20

25

30

35

/s]


Solid mass flow (left) and temperatures (right) for Mn3O4 Mg ZrO2 as carrier

00

800

900

1000

1100

T [K

]

T s,bufT s ox

5

10

15

20

dm/d

t [kg

/

0 7

600

700

0 20 40 60 80 100 120 140 160 180t [s]

T s,oxT s,ox,set

(B)

00 50 100 150 200

t [s](A)

Heat flux density (left) and degrees of reduction (right) for Mn3O4-Mg-ZrO2 as carrier

0.4

0.5

0.6

0.7

-30000

-20000

-10000

0

m2 ]

0.1

0.2

0.3X

X s,redX s,oxX s,red,set-60000

-50000

-40000q [W

/m


00 20 40 60 80 100 120 140 160 180

t [s](D)-70000

0 50 100 150 200t [s](C)


Chemical looping system: Reduction rate setpoint changeSolid mass flow (left) and temperatures (right) for Mn3O4-Mg-ZrO2 as carrier

30

35

40

45

/s]


1100

1300

1500

Solid mass flow (left) and temperatures (right) for Mn3O4 Mg ZrO2 as carrier

5

10

15

20

25

dm/d

t [kg

/

500

700

900

T [K

]

T s,bufT s ox

00 50 100 150 200 250 300

t [s](A)

3000 50 100 150 200 250 300

t [s]

T s,oxT s,ox,set

(B)

0 0 7Heat flux density (left) and degrees of reduction (right) for Mn3O4-Mg-ZrO2 as carrier

-30000

-20000

-10000

00 50 100 150 200 250 300

2 ] 0.4

0.5

0.6

0.7

70000

-60000

-50000

-40000

q [W

/m2

0.1

0.2

0.3X

X s,redX s,oxX s,red,set


-80000

-70000

t [s](C)

00 50 100 150 200 250 300

t [s](D)


Chemical looping system: Other carrier materialsSolid mass flow NiO/MgAl2O4 (left) and Fe2O3/MgAl2O4 (right)

30dm/dt s,reddm/dt s,feed

25dm/dt s,reddm/dt s,feed

Solid mass flow NiO/MgAl2O4 (left) and Fe2O3/MgAl2O4 (right)

15

20

25

dm/d

t [kg

/s]

dm/dt s,feeddm/dt s,bufdm/dt s,ox

10

15

20

dm/d

t [kg

/s]

dm/dt s,feeddm/dt s,bufdm/dt s,ox

0

5

10

0 10 20 30 40 50 60 70 800

5

0 10 20 30 40 50 60 70 80 90

t [s](A)t [s](A)



Conclusions

An interconnected multiphase CFD-model was derived

T t d fl t l i l t d dTemperature and mass flow controls were implemented and necessary

parameters derived

Various setpoint changes for a selection of carrier materials were considered

The applied controllers allow steady operation of the chemical looping model

Detailed investigations of the dynamics in further refined model frameworks g y

become possible


cfd model of a fluidized bed chemical · interconnected multi-phase cfd chemical looping model glt...

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