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

2 RWEnpower’s OxyFuel facility

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). 3

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) Recycle Ratio (RR) - (65% - 77%) (65% 77%) - Oxygen enrichment level (28% - 42 v/v)) dependent on RR and furnace exit O and furnace exit O 2 4

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 5

Driver for Studying Heat Transfer Distributions – Radiative and Convective 6

7 Schematic of CTF

8 IFRF Experimental Burner

Schematic of Once Through Oxy-Fuel System Coal Steam Primary Air Boiler Boiler S Skid Mixing Skid Heaters Primary Flow CO 2 Vaporiser Secondary Flow O 2 Vaporiser OXY OFA Tertiary Flow (Not used on this burner) NOx/ SOx Flow Control Skid Secondary Air Secondary Air 9

10 Schematic of CTF Test Furnace

11 Oxyfuel System

Results: Radiative HT- South African coal – Dry Recycle Recycle Furnace Heat Flux Measurements South African coal, Oxyfuel (3% O 2 ) SAcoal/Air - 3% O2 500 500 Oxyfuel RR 65% Oxyfuel RR 68% 450 kW/m 2 Oxyfuel RR 70% Oxyfuel RR 72% Oxyfuel RR 75% Oxyfuel RR 75% Heat Flux k 400 350 Radiative H 300 250 50 200 0 500 1000 1500 2000 2500 3000 3500 Axial Distance from Burner mm Axial Distance from Burner, mm 12

Normalised Convective & Radiative heat flux – Russian Coal - Dry Recycle heat fl R ssian Coal Dr Rec cle 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 1.6 1.6 Normalised Flame Temperature (calculated) Measured Convective Heat Peak Normalised Heat Flux (measured) Transfer Coefficient indicates 74% Normalised Convective HTC (measured) Recycle is "Air-equivalent" 1.4 1.4 Retrofit New Build Avoid adiative and diabatic Measured Peak Radiative Heat Flux erature 1.2 data indicates 74% 1.2 Recycle is "Air- equivalent" ormalised Ad Convective H lame Tempe Normalised Ra 1 1 0.8 0.8 No N F 0.6 0.6 Calculated dry oxyfuel adiabatic flame temperatures are equivalent to air at 69% recycle 0.4 0.4 60% 65% 70% 75% 80% Effective Recycle Ratio 13

14 IFRF Burner - RR 66%, 38% Inlet O 2

15 IFRF Burner – RR 77%; 28% Inlet O 2

Flame Animations (South African Coal) ( ) • Images for different simulated recycle rates under low O 2 settings 68% rr, Total flow 615.71kg/h 70% rr, Total flow 656.99kg/h 72% rr, Total flow 709.04kg/h 65% rr, Total flow 554.74kg/h Sec 501kg/h@29.0% O 2 Sec 457kg/h@31.6% Sec 552kg/h@26.5%O 2 Sec 400kg/h@35.8% O 2 (time: 13:14) (time: 13:14) (time: 14:19) (time: 14:19) (time: 13:44) (time: 13:44) (time: 12:41) (time: 12:41) • Images for different simulated recycle rates under high O 2 settings 72% rr, Total flow 722.64kg/h 65% rr, Total flow 567.69kg/h 68% rr, Total flow 624.70kg/h 75% rr, Total flow 806.57kg/h 70% rr, Total flow 670.91kg/h Sec 16 Sec 567kg/h@28.9%O 2 Sec 412kg/h@38.0% O 2 Sec 470kg/h@33.9%O 2 Sec 650kg/h@25.4% O 2 516kg/h@31.3%O 2 (time: 12:54) (time: 14:36) (time: 14:04) (time: 12:29) (time: 13:27)

Flame Images g • Temperature profiles for different simulated recycle rates under lower O settings lower O 2 settings 65% RR: Sec.f 368kg/h@34.8% 68%RR: Sec.f 62% RR: Sec.f 322kg/h@39.4% 62% RR: Sec.f 322kg/h@39.4% g @ (time: 15:18, 29-10) 422kg/h@30.5% (time: 12:32, 30-10) (time: 15:05, 29-10) 75% RR: Sec.f 600kg/h@22.1% 72% RR: Sec.f 513kg/h@25.5% (time: 13:41, 29-10) (ti 13 41 29 10) ( (time: 14:18, 29-10) ) Note: Images and temperature profiles shown here are 17 averaged for 10 instantaneous readings over about 2 minutes.

Flame oscillation frequency for different recycle ratios and total flows and their comparison to the air-firing (Russian Coal) Air Only Low O2 setting 20 20 18 18 (Hz Root Mid Hz) 16 16 16 16 tion frequency (H tion frequency 14 14 12 12 10 10 8 8 6 6 Oscillat 6 6 Oscillat 4 4 Root Mid 2 2 0 0 High O2 setting 60 65 70 75 80 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 20 20 Recylce ratio (%) R l ti (%) O2 (%) 18 equency (Hz) Root Mid 16 14 Note : 12 1) The data points are average values of 10 instantaneous readings. The “error 10 10 bar” indicates the standard variation of the data. b ” i di t th t d d i ti f th d t Oscillation fre 8 2) Low O 2 %: 22.1(75rr), 25.5(72rr), 32.9(68rr), 34.8(65rr) and 39.4(62rr) 6 3) High O2%: 24.5(75rr), 28.0(72rr), 30.5(68rr), 37.1(65rr) and 41.7(62rr) 4 2 0 0 60 65 70 75 80 18 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 19

Stop Press

Latest results - Wet/Dry comparison Radiative Heat Flux Russian coal B, 18%H2O, 3% O2 550 550 Russian B/Air, 3%O2 - dry x kW/m 2 OF 65% RR - dry 500 OF 72% RR - dry OF 75% RR - dry OF 68% RR - wet 450 OF 72% RR - wet Heat Flux OF 75% RR - wet OF 65% RR - wet 400 350 Radiative 300 250 R 200 0 500 1000 1500 2000 2500 3000 3500 Axial Distance from Burner, mm , 21

Latest results – Wet (8%) / Wet (18%) comparison Radiative Heat Flux Russian coal B, 3% O2 550 550 OF 68% RR, H2O 18% - wet kW/m 2 500 OF 68% RR, H2O 8% - wet 450 450 eat Flux 400 diative He 350 350 300 Rad 250 250 200 0 500 1000 1500 2000 2500 3000 3500 Axial Distance from Burner, mm 22

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 Peak radiative - dry nd Peak radiative - wet convective an 1.2 Convective - dry diative HF Convective - wet Li (P k di ti 1.0 peak rad Normalised c 0.8 0.6 N Oxyfuel operation normalised to Air operation 0.4 60% 65% 70% 75% 80% Effective Recycle ratio 23

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 24

Thank you for your attention. Questions?

Background – Recycle Ratio Recycled Flue Gas (m RFG ) Wet Dry Recycle Recycle Air ASU ASU Boiler CO 2 - Rich Product (m PFG ) Fuel N 2 N 2 H 2 0 M RFG RFG RR = ---------------------- M RFG + M PFG 26