operational experience during coal combustion in a 50 kwth...

Politecnico Di Milano Milan, Italy

1st - 2nd September 2015

Alberto Abad

Raúl Pérez-Vega, Francisco García‐Labiano, Pilar Gayán, Luis F. de Diego, Juan Adánez

Combustion & Gasification Group

Instituto de Carboquímica (ICB-CSIC), Zaragoza, Spain

abad@icb.csic.es

Operational experience during coal combustion in

a 50 kWth Chemical Looping Combustion unit

A. iG-CLC: in-situ gasification of coal in the fuel reactor

B. CLOU: Chemical Looping with Oxygen Uncoupling

Coal

CO2 + H2ON2 (+O2)

MexOy

H2O(l)

CO2

Air

Reactor

Fuel

Reactor

MexOy-1

Condenser

Air

CLC: Direct coal feeding to the fuel reactor

H2O(v)

and/or

CO2

Ash

Two options

CO2

Introduction

A. iG-CLC: Gasification of coal in the fuel reactor

Oxygen-Carrier

Coal

iG-CLC (solid fuel)

H2O and/or CO2

H2O

CO

H2

H2O

Char

Volatiles

Syngas-CLC (gas fuel)

Syngas

CO

H2

CO2

H2O

Coal

O2

CO2 H2O

Volatiles

CLOU (solid fuel)

CO2

CO2

Oxygen-Carrier

Char

CO2

H2O

CO2

H2O

Oxygen-Carrier

First, coal is dried and devolatized

Remaining solid char is gasified to give gaseous H2

and CO

Volatiles and Gasification Products react with oxygen-carrier as a gas-solid reaction

► Coal H2O + Volatile matter + Char

► Char + H2O H2 + CO

► Char + CO2 2 CO

► + n MexOy CO2 + H2O + n MexOy-1

Volatile matter

H2 + CO

H2O

CO2

Introduction

B. CLOU: Chemical-Looping with Oxygen Uncoupling

Here, coal is also dried and devolatized

But the oxygen-carrier is able to release gaseous OXYGEN (O2)

Volatiles and Char react with OXYGEN (O2) as in common combustion with air

► Coal H2O + Volatile matter + Char

► + O2 CO2 + H2OVolatile matter

Char

Oxygen-Carrier

Coal

iG-CLC (solid fuel)

H2O and/or CO2

H2O

CO

H2

H2O

Char

Volatiles

Syngas-CLC (gas fuel)

Syngas

CO

H2

CO2

H2O

Coal

O2

CO2 H2O

Volatiles

CLOU (solid fuel)

CO2

CO2

Oxygen-Carrier

Char

CO2

H2O

CO2

H2O

Oxygen-Carrier

► 2 MexOy 2 MexOy-1 + O2

Introduction

Coal

CO2 + H2ON2 (+O2)

MexOy

H2O(l)

CO2

Air

Reactor

Fuel

Reactor

MexOy-1

Condenser

Air

H2O(v)

and/or

CO2

Ash

CO2

Which is desirable in CLC?

High CO2

capture

efficiency

High

combustion

efficiency

A Carbon

Stripper is

necessary

To minimize

the use of an

Oxygen

Polishing Unit

Carbon

Stripper

C

CO2

MexOy-1 + C

+ CO + H2 + CH4 CO2

Oxygen

Demand

Oxygen

polishing

O2

WT = O2 for unburnt gases

O2 for coal combustion

WT

Introduction

Coal reaction rate

CS efficiency

Coal

CO2 + H2ON2 (+O2)

MexOy

H2O(l)

CO2

MexOy-1

Condenser

Air

H2O(v)and/or

CO2Ash

CO2

Carbon

Stripper

C

CO2

+ CO + H2 + CH4 CO2Oxygen

polishing

O2

CO2 capture

efficiency

Oxygen

Demand

Availability of oxygen in FR

OC OC

coal coal

R m

m

W

Oxygen carrier reaction rate

OC to fuel ratio

Inventory of

solids in FR (kg/MW)

Residence time

of solids in FR

Solids circulation

Coal feeding rate

Amount of solids in FR

FR Temperature

Oxygen carrier

Type of coal

Gas velocity in CS

Introduction

Objective

To optimize the design and operation

of the CLC process of coal

• The effect of operating conditions, such as temperature, solids

circulation rate, solids inventory and carbon stripper

efficiency on the CO2 capture and the Oxygen demand were

analyzed in a 50 kWth CLC unit burning coal

• Operating conditions were linked to fluid dynamics of the fuel

reactor for desing purposes

ICB-CSIC-s50 facility

N2 Air

Air

H2OH2O

Loop Seal(LS-CS)

Loop Seal(LS-AF)

Air Reactor (AR)

Air Reactor exhaust gases

(N2 + O2)

Fuel Reactor exhaust gases

(CO2 + H2O)

Fuel Reactor (FR)

CarbonStripper

(CS)

DoubleLoop Seal

(LS-D)

Coal

ScrewFeeders

Solidscirculation

measurementdevices

Solidsreservoir

N2 / CO2

Oxygen carrier (100-300 mm):

ILMENITE: Fe2TiO5 / FeTiO3

Coal (200-300 mm):

South African Bituminous coal

Moisture 3.5

Ash 15.7

Volatile matter 25.5

Fixed carbon 55.3

C 66.3

H 3.6

N 1.8

S 0.5

LHV (kJ/kg) 24930

Nominal thermal power:

• 20 kWth for CLC of coal

• 50 kWth for CLOU

Main dimensions of the ICB-CSIC.s50 facility

FR AR CS Height (m) 4.00 4.80 0.71 Diameter bottom (m) 0.10 0.30 0.15 Diameter up (m) 0.08 0.10 -

Experimental

Experimental

Experimental Series

I II III IV V

Operating condition unit 1 2 3 1 2 3 6 7 8 9 10

FR Temperature ºC 944 990 1006 964 982 990 905 963 970 991 962

Solids circulation rate kg/h 140 140 140 150 150 150 100 100 100 100 75

Thermal power kWth 17.5 17.5 17.5 13.5 13.5 13.5 12.5 12.5 12.5 12.5 6.9

Coal feeding rate kg/h 2.5 2.5 2.5 2.0 2.0 2.0 1.8 1.8 1.8 1.8 1.0

OC to fuel ratio () 1.1 1.1 1.1 1.5 1.5 1.5 1.1 1.1 1.1 1.1 1.5

FR solids inventory kg/MWth 253 306 443 522 525 481 680 535 506 466 722

CS gas velocity m/s 0.20 0.20 0.35 0.50 0.50 0.50 0.35 0.35 0.35 0.35 0.35

Gas c

on

cen

trati

on

(vo

l.%

, d

ry,

N2 f

ree)

0

20

40

60

80

100

Tem

pera

ture

(ºC

)

0

200

400

600

800

1000

Time (min)

0 100 200 300

0

5

10

15

20

25

0

200

400

600

800

FR

AR

CO2

CO

CH4

CO2

O2

Temperature

Temperature

Heating period Coal combustion

H2

Gas c

on

cen

trati

on

(vo

l.%

)

Startingconditions

Results

Steady state

CO2 capture

efficiency

Oxygen

Demand

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

CO

2 c

ap

ture

eff

icie

nc

y (

%)

50

60

70

80

90

100

CO2 capture

efficiency

• CO2 capture increased with fuel reactor temperature because a higher char conversion was reached

Results

Effect of fuel reactor temperature

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Series IV ( ): 12.5 kWth

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

CO

2 c

ap

ture

eff

icie

ncy (

%)

50

60

70

80

90

100

ugasCS = 0.2 m/s

+10 % in CO2 Capture

ugasCS = 0.35 m/s

CO2 capture

efficiency

Results

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Effect of gas velocity in CS

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

CO

2 c

ap

ture

eff

icie

nc

y (

%)

50

60

70

80

90

100

ugasCS = 0.5 m/s

+6 % in CO2 Capture

ugasCS = 0.35 m/s

ugasCS = 0.2 m/s

CO2 capture

efficiency

Results

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Effect of gas velocity in CS

• The higher CS gas velocity led to the higher CO2 capture efficiency

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

CO

2 c

ap

ture

eff

icie

nc

y (

%)

50

60

70

80

90

100

.mOC = 100 kg/h

mOC = 150 kg/h.

+7 % in CO2 Capture

CO2 capture

efficiency

Results

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Series IV ( ): 12.5 kWth

Effect of solids circulation rate

• The decrease of the solids circulation rate had a positive effect on the CO2 capture

FR Temperature (ºC)

960 975 990 1005

CO

2 c

ap

ture

eff

icie

ncy (

%)

50

60

70

80

90

100 .mOC = 100 kg/h

ugasCS = 0.35 m/s

mOC = 150 kg/h

ugasCS = 0.5 m/s

.

mOC = 150 kg/h

ugasCS = 0.35 m/s

.

.mOC = 75 kg/h

ugasCS = 0.35 m/s

CO2 capture

efficiency

Results

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Series IV ( ): 12.5 kWth

Series V ( ): 6.9 kWth

Global evaluation

• Similar CO2 capture could be obtained varying the fuel reactor temperature, solids circulation rate and CS gas velocity

► Experiments selected

to evaluate

the oxygen demand

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

Ox

yg

en

de

ma

nd

(%

)

0

2

4

6

8

10

12

14 = 1.1mOC = 450 kg/MW

= 1.1mOC = 470 kg/MW

= 1.5mOC = 480 kg/MW

- 2 % in Oxygen demand

Oxygen

Demand

Results

Effect of oxygen carrier to fuel ratio ()

• The oxygen carrier to fuel ratio has a relevant influence on the Oxygen Demand

Availability of oxygen in FR

OC OC

coal coal

R m

m

WOC to fuel ratio

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Series IV ( ): 12.5 kWth

Series V ( ): 6.9 kWth

FR Temperature (ºC)

880 900 920 940 960 980 1000 1020

Oxyg

en

dem

an

d (

%)

0

2

4

6

8

10

12

14 = 1.1mOC = 450 kg/MW

= 1.1mOC = 470 kg/MW

= 1.5mOC = 480 kg/MW

= 1.5mOC = 720 kg/MW

- 1 % in Oxygen demand

Oxygen

Demand

Results

Series I ( ): 17.5 kWth

Series II ( ): 17.5 kWth

Series III ( ): 13.5 kWth

Series IV ( ): 12.5 kWth

Series V ( ): 6.9 kWth

Effect of the solids inventory in FR

• In addition, a higher solids inventory in the fuel reactor improved the combustion efficiency of the process

Operating variable

CO2 Capture Oxygen demandDesign

condition

FR temperature As high as possibleLow relevance in the interval 900-1000ºC

1000 ºC

Solids circulation rateAs low as possible

( > 1)As high as possible

= 1.5

Solids inventoryLow relevance in the

interval 300-700 kg/MWAs high as possible,

but conditioned by DP700 kg/MWth

Carbon stripper performance

Must be optimized Low relevance>98% separation

efficiency

Results

Selection of operating conditions

► Would it be possible to operate a

CFB with these requirements?

Pre

ssu

re d

rop

(kP

a)

1

10

100

ug r

iser

(m/s

)

0.1

1

10

Cross Sectional Area (m2/MW

th)

0.01 0.1 1

So

lid

s f

lux (

kg

m-2

s-1

)

1

10

100

H2O/C = 0.1 - 0.2 - 0.5 - 1.0 - 2.0 - 5.0

mOC = 100 kg/MW 200

500

1000

2000

5000

2

5

10

= 1

Particle diameter ( m)

100 1000 10000

Gas v

elo

cit

y (

m/s

)

0.01

0.1

1

10

100

umf

ut

Bubbling

Spouted

Turbulent

Pneumatictransport Fast

fluidization

Results

Fluid dynamics & Design parameters

Adapted for ilmenite particles from Kunii & LevenspielChem. Eng. Sci. 1997, 52, 2471-2482

ug = 4 m/s

H2O/C=1

0.2 m2/MWth

700 kg/MWth

30 kPa

= 1.5

15 kg m-2 s-1

Conclusions

• The effect of relevant operating conditions on the CO2 capture and

Oxygen demand of the iG-CLC process was determined in a CLC unit

• The value of several operating conditions for the design of a iG-CLC

unit was determined

• The operating conditions of the fuel reactor fit the fluid dynamics

requirements for CFB units

Politecnico Di Milano Milan, Italy

1st - 2nd September 2015

Alberto Abad

Raúl Pérez-Vega, Francisco García‐Labiano, Pilar Gayán, Luis F. de Diego, Juan Adánez

Combustion & Gasification Group

Instituto de Carboquímica (ICB-CSIC), Zaragoza, Spain

abad@icb.csic.es

Thanks for your attention

Project: ENE 2013-45454-R- Reference: T06