radiation and convection heat transfer in oxyfuel combustion
TRANSCRIPT
Radiative and Convective Heat Transfer in Oxy Coal CombustionTransfer in Oxy-Coal Combustion
John Smart Phil O‘Nions Gerry Riley Ed JamiesionJohn Smart, Phil O Nions, Gerry Riley, Ed Jamiesion
RWEnpower
RWEnpower’s OxyFuel facility
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Introduction
The work presented on radiative and convective heat transfer in oxy-coal combustion where coal is burnt, not in air but in a stream of 100% O2 diluted with recycled flue gas as comburent
The recycled flue gas can be either wet or dry dependent on where the recycled flue gas taken from in the system.
The recycled flue gas could be take wet from the outlet of the ESP (where the moisture content would be circa 18% by volume) or after an FGD system (where the moisture contentvolume) or after an FGD system (where the moisture content would be circa 8% by volume).
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Objectives of Current Experimental Programme
Simulate an oxyfuel recycle gas process using a once through combustion system – once through selected for flexibility
Both wet and dry recycle to be studied
Oxygen content in burner primary flow kept constant @ 21% v/v
Input parameters studied:
Recycle Ratio (RR) (65% 77%)- Recycle Ratio (RR) - (65% - 77%)
- Oxygen enrichment level (28% - 42 v/v)) dependent on RR and furnace exit Oand furnace exit O2
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Objectives of Current Experimental Programme (cont )(cont.)
Three coals to be studied – Two Russian and one South African
Co-firing of coal with biomass – Shea Meal and Sawdust (20% mass)
Measure heat transfer characteristics of flames compared to air –pradiative and convective
Carbon-in-Ash
Oxy-Overfire Air (OFA) to be Studied for heat transfer optimisation
Work performed on RWEn Combustion Test Facility (CTF) at DidcotDidcot
International Flame Research Foundation (IFRF) Burner
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Driver for Studying Heat Transfer Distributions – Radiative and Convective
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Schematic of CTF
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IFRF Experimental Burner
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Schematic of Once Through Oxy-Fuel System
Boiler SteamS
CoalPrimary AirBoiler Skid
HeatersMixing Skid
CO2Primary Flow
O2Vaporiser
Vaporiser
Secondary Flow
Tertiary Flow
Flow Control Skid
NOx/SOx
OXY OFA(Not used on this burner)
Secondary Air
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Secondary Air
Schematic of CTF Test Furnace
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Oxyfuel System
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Results: Radiative HT- South African coal – Dry RecycleRecycle
Furnace Heat Flux MeasurementsSouth African coal, Oxyfuel (3% O2)
500 SAcoal/Air - 3% O2
450
500
kW/m
2
Oxyfuel RR 65%
Oxyfuel RR 68%
Oxyfuel RR 70%
Oxyfuel RR 72%
Oxyfuel RR 75%
350
400
Hea
t Flu
x k Oxyfuel RR 75%
250
300
Rad
iativ
e H
200
50
0 500 1000 1500 2000 2500 3000 3500Axial Distance from Burner mm
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Axial Distance from Burner, mm
Normalised Convective & Radiativeheat fl R ssian Coal Dr Rec cleheat flux – Russian Coal - Dry Recycle
Dry Oxyfuel Operation Normalised to Air OperationPeak Radiation Flux Convective heat transfer and calculated flame temperaturePeak Radiation Flux, Convective heat transfer and calculated flame temperature
Russian coal
1.4
1.6
1.4
1.6Normalised Flame Temperature (calculated)Peak Normalised Heat Flux (measured)Normalised Convective HTC (measured)
Measured Convective Heat Transfer Coefficient indicates 74% Recycle is "Air-equivalent"
1.2
diab
atic
er
atur
e 1.2
adia
tive
and
Hea
t Flu
xMeasured Peak Radiative data indicates 74% Recycle is "Air-equivalent"
New Build Retrofit Avoid
0.8
1
orm
alis
ed A
dla
me
Tem
pe
0.8
1
Nor
mal
ised
Ra
Con
vect
ive
H
0.4
0.6
No F
0.4
0.6
N
Calculated dry oxyfuel adiabatic flame temperatures are equivalent to air at 69% recycle
1360% 65% 70% 75% 80%
Effective Recycle Ratio
IFRF Burner - RR 66%, 38% Inlet O2
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IFRF Burner – RR 77%; 28% Inlet O2
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Flame Animations (South African Coal) ( )
• Images for different simulated recycle rates under low O2 settings
70% rr, Total flow 656.99kg/h Sec 501kg/[email protected]% O2(time: 13:14)
68% rr, Total flow 615.71kg/h Sec 457kg/[email protected]% (time: 13:44)
65% rr, Total flow 554.74kg/h Sec 400kg/[email protected]% O2(time: 14:19)
72% rr, Total flow 709.04kg/h Sec 552kg/[email protected]%O2(time: 12:41)(time: 13:14)(time: 13:44)(time: 14:19) (time: 12:41)
• Images for different simulated recycle rates under high O2 settings
1665% rr, Total flow 567.69kg/h Sec 412kg/[email protected]% O2(time: 14:36)
75% rr, Total flow 806.57kg/h Sec 650kg/[email protected]% O2(time: 12:29)
72% rr, Total flow 722.64kg/h Sec 567kg/[email protected]%O2(time: 12:54)
70% rr, Total flow 670.91kg/h Sec 516kg/[email protected]%O2(time: 13:27)
68% rr, Total flow 624.70kg/h Sec 470kg/[email protected]%O2(time: 14:04)
Flame Imagesg
• Temperature profiles for different simulated recycle rates under lower O settingslower O2 settings
65% RR: Sec.f 368kg/[email protected]% 68%RR: Sec.f 62% RR: Sec.f 322kg/[email protected]% g @(time: 15:18, 29-10) 422kg/[email protected]%
(time: 15:05, 29-10)
62% RR: Sec.f 322kg/[email protected]%(time: 12:32, 30-10)
75% RR: Sec.f 600kg/[email protected]%(ti 13 41 29 10)
72% RR: Sec.f 513kg/[email protected]%( )
17Note: Images and temperature profiles shown here are averaged for 10 instantaneous readings over about 2 minutes.
(time: 13:41, 29-10) (time: 14:18, 29-10)
Flame oscillation frequency for different recycle ratios and total flows and their comparison to the air-firing (Russian Coal)
161820
Hz)
Air Only
161820
(Hz
Low O2 setting
Root Mid
6810121416
tion frequen
cy (H
6810121416
tion frequen
cy
0246
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Oscillat
Root Mid
0246
60 65 70 75 80
Oscillat
R l ti (%)20
High O2 setting
O2 (%)
Note: 1) The data points are average values of 10 instantaneous readings. The “error
b ” i di t th t d d i ti f th d t
Recylce ratio (%)
101214161820
equen
cy (Hz) Root Mid
bar” indicates the standard variation of the data.
2) Low O2%: 22.1(75rr), 25.5(72rr), 32.9(68rr), 34.8(65rr) and 39.4(62rr)
3) High O2%: 24.5(75rr), 28.0(72rr), 30.5(68rr), 37.1(65rr) and 41.7(62rr)
0246810
Oscillation fre
18
0
60 65 70 75 80Recylce ratio (%)
Conclusions (Dry recycle data) Air operation radiative heat flux found to be equivalent to 72 – 75%
recycle ratio (due to different radiative properties of carbon dioxide compared to nitrogen)
Radiative heat flux peak shifts downstream as recycle rate increases
Convective Heat Transfer equivalent to air at 74% recycle ratio (main factors here are temperature and mass flow)
Working range exists (there is a recycle ratio for which both Working range exists (there is a recycle ratio for which both radiative and convective transfer can be reasonable matched between air and oxyfuel operation. It is therefore possible to design a boiler for efficient operation in both oxyfuel and air conditions).
Flame stability decreases with increasing recycle ratio
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Stop Press
Latest results - Wet/Dry comparison
Radiative Heat FluxRussian coal B, 18%H2O, 3% O2
550
450
500
550
x kW
/m2
Russian B/Air, 3%O2 - dryOF 65% RR - dryOF 72% RR - dryOF 75% RR - dryOF 68% RR - wetOF 72% RR - wet
350
400
Hea
t Flu
x OF 75% RR - wetOF 65% RR - wet
250
300
Rad
iativ
e
2000 500 1000 1500 2000 2500 3000 3500
Axial Distance from Burner, mm
R
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,
Latest results – Wet (8%) / Wet (18%) comparison
Radiative Heat Flux
Russian coal B, 3% O2 550
450
500
550
kW/m
2 OF 68% RR, H2O 18% - wet
OF 68% RR, H2O 8% - wet
350
400
450
eat F
lux
250
300
350
diat
ive
He
200
250
0 500 1000 1500 2000 2500 3000 3500
Rad
22Axial Distance from Burner, mm
Wet (18%) and Dry Recycle Normalised Peak Radiative and Convective Heat FluxRadiative and Convective Heat Flux
Normalised Peak Radiative and Convective Heat FluxRussian coal, 3%O2,
Dry v's Wet combustion1.4
nd Peak radiative - dry
Peak radiative - wet
1.0
1.2
conv
ectiv
e an
diat
ive
HF
Convective - dry
Convective - wet
Li (P k di ti
0.6
0.8
Nor
mal
ised
cpe
ak ra
d
0.460% 65% 70% 75% 80%
Effective Recycle ratio
N
Oxyfuel operation normalised to Air operation
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Acknowledgements
The combustion test facility conversion to oxyfuel was financed by RWE npower
The experimental programmes are co-funded by RWE npower and:
The European Commission Research Fund for Coal and Steel -BOFCom: Contract No RFCR CT 2006 0001BOFCom: Contract No. RFCR-CT-2006-0001
The UK Technology Strategy Board - Oxycoal-UK: Contract No. TPC/00/00404/00/00TPC/00/00404/00/00
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Thank you for your attention.
Questions?
Background – Recycle Ratio
Recycled Flue Gas (mRFG)
ASUAir
WetRecycle
DryRecycle
ASU Boiler
N2Fuel
CO2 - Rich Product(mPFG)
N2H20
MRFGRFGRR = ----------------------
MRFG + MPFG
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