Lecture 3: Oxyfuel Combustion Science: Mass and energy ...

Lecture 3: Oxyfuel Combustion Science: Mass and energy balances, heat transfer, coal

combustion and emissions

Professor Terry Wall and Dr Jianglong Yu

University of Newcastle, Australia

APP OFWG capacity building course

University of Newcastle, Australia

Oxy- fuel flowsheet for first generation technology, showing additional units for a retrofit in red

Air Separation unit (ASU)

Air

Recycled Flue Gas (RFG)

Nitrogen

V Boiler or Ash removal /

cooler / Purification /

Oxygen

Fuel CO2 (SO2)

CO2 –rich Flue Gas

Recycled Flue Gas (RFG)

Conc. Stream of CO2

Vent

Gas Turbine cooler /

condenser / FGD compression

Steam

2 ( 2)

Steam Turbine

Power

Oxy- fuel flowsheet for first generation technology, showing additional units for a retrofit in red

Issues with Oxy-combustion CCSASU

g

ASUCO2 handlingPurification; compression; transportation; storage

Replacement of nitrogen with recycled CO2

Combustion environment of fuel•Fuel reactivityR t fit•Retrofit

•Impurity formation and emissionI it i t CO handlingImpurity impact on CO2 handling

Lecture context and content

Oxyfuel science used here to compare air and oxy-fuel furnace f f t fit f i ti i fi d b il hilperformance, for retrofit of an existing air-fired boiler while

maintaining heat transfer, considering

Conditions for matched heat transfer– Conditions for matched heat transfer– Changed burner flows, with flame and heat transfer impacts– Coal reactivity and burnout impacts

Developments and gaps in knowledge will be suggested

Mass and energy balances and heat transfer

AFT of air and oxy cases

2600

2200

erat

ure

(K)

air

1800

flam

e Te

mpe oxy-wet

oxy-dry

1400

Adia

batic

10000.18 0.22 0.26 0.30 0.34 0.38

O2 fraction at burner inlet

Oxy-fuel: differences of combustion in O2/CO2compared to air firingp g

•To attain a similar AFT the O2 proportion of the gases through the burner is ~ 30%g g

•The high proportions of CO2 and H2O in the furnace gases result in higher gas emissivitiesgases result in higher gas emissivities

•The volume of gases flowing through the furnace is reducedreduced

•The volume of flue gas (after recycling) is reduced by about 80%by about 80%.

Recycle gases have higher concentrations in theffurnace

Gas property differences 1: EmissivityTriatomic gas (H2O+CO2) emissivity ~ beam length

comparisonscomparisons

30 500 1050 MWe

0.8

1

(-)

Oxy-fuel fired furnace

30 500 1050 MWe

0

0.6

mis

sivi

ty (

Air fired furnace

0.2

0.4

Gas

Em

00 10 20 30 40 50 60 70 80 90

Beam Length (L) (m)

Gupta et al (2006)

Beam Length (L) (m)

CFD radiative transfer inputs

0.8 4 grey gas modelOxy-fuel fired furnace

0.6

0.7

(-)

4 grey gas model,

4-GGM

Gupta et al, (2006)

0 4

0.5

issi

vity

( Gupta et a , ( 006)

3 grey gas model,

0 2

0.3

0.4

Em 3-GGM

Smith et al, (1982)30 MWe 500 MWe0.2

0 10 20 30 40 50 60Beam length (L) (m)

]1[)( )(

0,

22 Lppk

ii

OHCOieTa

Property/ratio Gas property differences 2: Heat capacity etc

Impact for air to oxyfuel retrofitHigher O2 thru burner

Lower burner velocity, higher coal residence time in furnace

Slower flame propagation velocity

Properties from Shaddix 2006Gas property ratios for CO2 and N2 at 1200 K

Properties from Shaddix, 2006

Burner flow comparisons for a retrofit

Therefore secondary RFG reduced

27 O2 % v/v fixed for same

RFG reduced

2HT

Fi d l it

~3% v/v O2Fixed velocity 2

Burner

1 MWt test conditionsParameter Full load Partial load

Air case Oxy case Air case Oxy case

Coal flow rate kg/hr 120 120 72 72

Primary velocity m/s 20 23 17 21

Secondary velocity m/s 35 21 18 12

Secondary swirl number - 0.2 0.2 0.2 0.2

Primary momentum flux kg/s m2/s2 35 7 54 1 20 9 36 8Primary momentum flux kg/s.m2/s2 35.7 54.1 20.9 36.8

Secondary momentum flux kg/s.m2/s2 270.2 74.1 38.2 16.4

Momentum flux ratio (Pri/Sec) - 0.13 0.73 0.55 2.25

Preheated air/RFG: primary 350 - 400K and secondary 450 - 550 K, Wall 1200 K

IFRF Flame types from swirl burners

Type-0 Lo SType 0 Lo S

Type-1 Hi S (S>0.6) , Lo v

T 2

Lo v2

Type-2Hi S, Hi v2

1 MWt – Temperature contours at full load

X 1.5m

Air-case

Type-0 flame

Oxy-case

Coal combustion in Sandia’s entrained flow reactor under the intermediate gas temperature conditions.intermediate gas temperature conditions.

(Murphy and Shaddix 2006)

Sensitivity analysis – full & partial load

Effect of momentum flux

Confirms the significance of momentum flux and Gas properties on flame ignition

1 MWt Temperature comparisons for matching furnace heat transferfurnace heat transfer

Flame

FEGTFEGT

Coal combustion in Sandia’s entrained flow reactor under the intermediate gas temperature conditions.intermediate gas temperature conditions.

(Murphy and Shaddix 2006)

Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion.pulverized coal during oxy fuel combustion.

Shaddix, C. R. and A. Molina (2009)

Devolatilization of coals under fluidized bed conditions in oxygen-enriched airyg

(Borah, Ghosh et al. 2008)

30 MWe Burner plane – Temperature contoursAir case Oxy case

30 MWe – heat transfer results

250

m2)

Front wall Rear wall Side wall1 Side wall2

210

230

flux

(kw

/m

airoxy-fuel

190

face

hea

t f

150

170

Tota

l sur

f

45 51 56 56Furnace wall area (m2)

425 MWe – burner zone temperatures

2200

2000

re (K

)

Air

1600

1800

s te

mpe

ratu

r

Oxy-0.28-3GGMOxy-0.28-4GGM

1400Peak

ga

12000 2 4 6 8 10 12

Burner horizontal level

Summary plot relating gas emissivity changes to burner oxygen ……yg

2.0ai

r) wet recycle dry recycle

1.8

y (o

xy to

a

1.2 MWt

1.6

s em

issi

vity

425 MWe

30 MWe

1.2 MWt

1.4

atio

of g

as

30 MWe

425 MWe1

1.20.20 0.25 0.30 0.35 0.40

O f ti t b i l t ( )

R

0 2

0.4

0.6

0.8

Gas

Em

issi

vity

(-)

Oxygen fraction at burner inlet (-)0

0.2

0 10 20 30 40 50 60 70 80 90

Beam Length (L) (m)

G

Heat transfer: Other relevant study (CFB (Zhejiang 2003))(Zhejiang 2003))

Through early modelling although CO2 has a differentth d i ti d th t tthermodynamic properties, under the same oxygen content,oxy-combustion heat transfer does not differ much from aircombustion because oxy-combustion has a lower flametemperature;temperature;

CFD based modelling indicated that when oxygen content inthe oxy-combustion increases from 21% to 29%, combustionthe oxy combustion increases from 21% to 29%, combustionefficiency and boiler efficiency increase. But further increasein oxygen content does not significantly improve the efficiencyand 30% above oxygen causes other problems and safetyyg p yconcerns. The oxygen content in oxy-combustion thereforevary from 21% to 29%.

….. And O2 fraction at the burner can be determined by flue gas recycle ratio (here, for wet recycle)y g y ( , y )

Coal combustibilityCoal combustibility

1 MWt Combustibility comparison

6 Coal A

Coal B

Parity, equal C-in-ash air/oxy

4

5

ode ?%

Coal C

3

n-ash, Oxy m

1

2

Carbon-in

0

1

0 2 4 6 8 10

Carbon-in-ash, Air m ode (%)

Unburnt carbon in ash: oxy vs air combustion

El t i P D l t & IHI Ki 1995Electric Power Development & IHI, Kimura 1995

Illustrative differences in air and oxyfuel which influence burnoutinfluence burnout

For matched furnace heat transfer:For matched furnace heat transfer:

O f l h l f id ti 20% G dOxyfuel has longer furnace residence time, ~20%

Oxyfuel has lower temperatures, ~ 50 C

Good

BadIn oxyfuel, coal experiences an environment with higher O2

Good

Pyrolysis and oxidation reactivities of Coal A & Coal B in TGA

0.12Coal A N2C CO2

0.08

0.1

min

-1)

Coal A CO2Coal A AirCoal A OxyCoal B N2C l B CO2

Coal BPyrolysis

0 04

0.06

ctiv

ity (m

Coal B CO2Coal B AirCoal B Oxy

Coal BOxidation

Coal AOxidation

Coal A

0.02

0.04

Rea

c Coal APyrolysis

00 200 400 600 800 1000 1200

Temperature (oC)Temperature ( C)

Heat flow during pyrolysis & oxidation of Coal A & Coal B in TGA

200Coal A N2Coal A CO2

100

150

mW

)

Coal A CO2Coal A AirCoal A OxyCoal B N2Coal B CO2

Coal BOxidation

Coal AOxidation

0

50

at fl

ow (m Coal B Air

Coal B OxyOxidationExothermic

-50

0

Hea

Coal BPyrolysis

Coal A Pyrolysis

Pyrolysis & gasificationEndothermic

-1000 200 400 600 800 1000 1200

Temperature (oC)

Coal A PyrolysisEndothermic

Temperature ( C)

Volatile yields in DTF at 1400 C

Coal B Coal C Coal DCoal B Coal C Coal DV* (N2) 36.7 30.9 53.5Q factor (N )

1.52 1.43 1.76(N2)V* (CO2) 43.3 32.2 66.2Q factor (CO )

1.79 1.49 2.18(CO2)

V* - Volatile yield at 1400 oCQ factor – Ratio of V* and volatile yield obtained by proximate analysis

Char burnout in DTF taking V*(N2) to estimate char yieldchar yield

100

80

90

100

basi

s (%

)

Coal B

60

70

80

nout

daf

b

40

50

60

Cha

r bur

n AirOxy

400 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Oxygen concentration (atm)

Summary of reactivity data for 63-90 micron size cuts of four coals from DTF experiments at 1400 Cfour coals from DTF experiments at 1400 C

Volatile yield Coal Burnout

5060708090

100

ld a

t 140

0 o C in

f b

asis

), %

889092949698

100

out a

t 140

0 o C

in

af b

asis

), % 8% O2

010203040

65 70 75 80 85

Vola

tile

yiel

DTF

(da

N2CO2 80

82848688

65 70 75 80 85F l C b (d f b i ) t %

Coa

l bur

noD

TF (d

a

Air, 10% O2Oxy, 10% O2

Fuel Carbon (daf basis), wt.%Fuel Carbon (daf basis), wt.%

99

100o C

in

% 21% O2

96

97

98

99bu

rnou

t at 1

400

TF (d

af b

asis

), %

Ai 21% O2

% O

95

96

65 70 75 80 85

Fuel Carbon (daf basis), wt.%

Coa

l b DT Air, 21% O2

Oxy, 30% O2

DTF-char reactivity in TGA

0.005Air 2% O2Oxy 2% O250% O2

Coal B

0 003

0.004

ity (s

-1)

y %Air 5% O2Oxy 5% O2Air 10% O2Oxy 10% O2Ai 21% O2

2

21% O2

0.002

0.003

Rea

ctiv Air 21% O2

Oxy 21% O2Air 50% O2Oxy 50%O2

10% O2

5% O

0.001Cha

r

2% O2

5% O2

0300 500 700 900 1100 1300

Temperature (oC)Temperature ( C)

Char reactivity comparison for air and oxyfuel conditions at the same O levelconditions at the same O2 level

Oxy-fuel (O2/CO2) combustion

Ai (O /N )

L t t

Air (O2/N2) combustion

e Low temperaturesReaction kinetics controlled (Regime I)

actio

n ra

te

Moderately high temperatures Reaction kinetics

Very high temperatures Bulk diffusion

Rea

Reaction kinetics& internal diffusion limited (Regime II)

Bulk diffusion controlled (Regime III)

1/Tp (K-1)

Combustion efficiency (cfb)cy nc

y

on e

ffici

en

ler

effic

ien

O2

Com

bust

io

O2

Boi

C

Emissions and impurity impacts

PM, SOx, NOx, HgPM, SOx, NOx, HgConcentration in the flue gas and in furnace

and Impacts on CO2 handling

Impurity impacts on the purification process in oxy-fuel combustion based CO2 capture and storage system

CRR=92.15%

Li, H., J. Yan, et al. (2009)

Size distribution (mass fraction) of the particles collected using DLPI under oxy and air g y

combustion conditions Sheng, 2008

Formation of Submicron Particulates (PM1) from the Oxygen-Enriched Combustion of biomass

Zhang, 2007

Impurity impacts on the purification process in oxy-fuel combustion

Li, H., J. Yan, et al. (2009).


2-stage-flash

Li, H., J. Yan, et al. (2009).


distillation

Li, H., J. Yan, et al. (2009).

SO2 formation (CFB )

O2

SO2 emission Normalized SO2 emission

O2

(CFD, Zhejiang 2003)

2 2

NOx emission (PF )

El t i P D l t & IHI Ki 1995Electric Power Development & IHI, Kimura 1995

Fuel-N conversion into NOx (PF )

IHI T Ki 1997IHI, T.Kiga, 1997

NOx emission (CFB )

O2

SO2 emission Normalized SO2 emission

O2

(CFD, Zhejiang 2003)

Additional research required

Heat transfer and combustion

Hot spot evaluation and burner impacts (cfd based)Hot spot evaluation, and burner impacts (cfd based)

Quantify potential O2 reduction

Gas quality and furnace

Sulfur gases and corrosion (using pilot-scale data and g ( g pcalculation)

Mercury levels and form, and impact on CO2 handling

Gas quality for transport, compression and storage

Plant impacts, regulation and safety issuesp , g y

Thank you for your attention!Thank you for your attention!

Phase Diagram of CO2

Flame propagation speed (mm/s) vs oxygen content in different atmospherecontent in different atmosphere

(T. Kiga, 1997)

Lecture 3: Oxyfuel Combustion Science: Mass and energy ...

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