Radiative and Convective Heat Transfer in Oxy Coal Combustion - - PowerPoint PPT Presentation

Radiative and Convective Heat Transfer in Oxy Coal Combustion Transfer in Oxy-Coal Combustion

John Smart Phil O‘Nions Gerry Riley Ed Jamiesion John 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 content volume) 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 O and 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 – p radiative 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 Didcot Didcot



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 Steam S Coal Primary Air Boiler Skid

Heaters

Mixing Skid

CO2 Primary Flow O2

Vaporiser 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 Recycle Recycle

Furnace Heat Flux Measurements South African coal, Oxyfuel (3% O2)

500

SAcoal/Air - 3% O2

450 500

kW/m2

Oxyfuel RR 65% Oxyfuel RR 68% Oxyfuel RR 70% Oxyfuel RR 72% Oxyfuel RR 75%

350 400

Heat Flux k

Oxyfuel RR 75%

250 300

Radiative H

200 50 500 1000 1500 2000 2500 3000 3500

Axial Distance from Burner mm

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Axial Distance from Burner, mm

Normalised Convective & Radiative heat fl R ssian Coal Dr Rec cle heat flux – Russian Coal - Dry Recycle

Dry Oxyfuel Operation Normalised to Air Operation

Peak Radiation Flux Convective heat transfer and calculated flame temperature Peak Radiation Flux, Convective heat transfer and calculated flame temperature

Russian coal 1.4 1.6 1.4 1.6

Normalised 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 diabatic erature 1.2

adiative and Heat Flux

Measured Peak Radiative data indicates 74% Recycle is "Air- equivalent"

New Build Retrofit Avoid

0.8 1

• rmalised Ad

lame Tempe 0.8 1

Normalised Ra Convective 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

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60% 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/h@29.0% O2 (time: 13:14) 68% rr, Total flow 615.71kg/h Sec 457kg/h@31.6% (time: 13:44) 65% rr, Total flow 554.74kg/h Sec 400kg/h@35.8% O2 (time: 14:19) 72% rr, Total flow 709.04kg/h Sec 552kg/h@26.5%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

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65% rr, Total flow 567.69kg/h Sec 412kg/h@38.0% O2 (time: 14:36) 75% rr, Total flow 806.57kg/h Sec 650kg/h@25.4% O2 (time: 12:29) 72% rr, Total flow 722.64kg/h Sec 567kg/h@28.9%O2 (time: 12:54) 70% rr, Total flow 670.91kg/h Sec 516kg/h@31.3%O2 (time: 13:27) 68% rr, Total flow 624.70kg/h Sec 470kg/h@33.9%O2 (time: 14:04)

Flame Images g

• Temperature profiles for different simulated recycle rates under

lower O settings lower O2 settings

65% RR: Sec.f 368kg/h@34.8% 68%RR: Sec.f 62% RR: Sec.f 322kg/h@39.4%

g @ (time: 15:18, 29-10)

422kg/h@30.5%

(time: 15:05, 29-10)

62% RR: Sec.f 322kg/h@39.4%

(time: 12:32, 30-10)

75% RR: Sec.f 600kg/h@22.1%

(ti 13 41 29 10)

72% RR: Sec.f 513kg/h@25.5%

( )

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Note: 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)

16 18 20 Hz)

Air Only

16 18 20 (Hz Low O2 setting Root Mid 6 8 10 12 14 16 tion frequency (H 6 8 10 12 14 16 tion frequency 2 4 6 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Oscillat Root Mid 2 4 6 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 (%) 10 12 14 16 18 20 equency (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)

2 4 6 8 10 Oscillation fre

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60 65 70 75 80 Recylce 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 Flux Russian coal B, 18%H2O, 3% O2

550 450 500 550 x kW/m2

Russian B/Air, 3%O2 - dry OF 65% RR - dry OF 72% RR - dry OF 75% RR - dry OF 68% RR - wet OF 72% RR - wet

350 400 Heat Flux

OF 75% RR - wet OF 65% RR - wet

250 300 Radiative 200 500 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 Flux 250 300 350 diative He 200 250 500 1000 1500 2000 2500 3000 3500 Rad

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Axial Distance from Burner, mm

Wet (18%) and Dry Recycle Normalised Peak Radiative and Convective Heat Flux Radiative and Convective Heat Flux

Normalised Peak Radiative and Convective Heat Flux Russian coal, 3%O2, Dry v's Wet combustion

1.4 nd

Peak radiative - dry Peak radiative - wet

1.0 1.2 convective an diative HF

Convective - dry Convective - wet Li (P k di ti

0.6 0.8 Normalised c peak rad 0.4 60% 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 0001 BOFCom: Contract No. RFCR-CT-2006-0001

 The UK Technology Strategy Board - Oxycoal-UK: Contract No.

TPC/00/00404/00/00 TPC/00/00404/00/00

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Thank you for your attention.

Questions?

Background – Recycle Ratio

Recycled Flue Gas (mRFG)

ASU

Air

Wet Recycle Dry

Recycle

ASU Boiler

N2

Fuel

CO2 - Rich Product (mPFG) N2

H20

MRFG

RFG

RR = ---------------------- MRFG + MPFG 26