Oxyfuel Research at RWE npower plc. The CRF 2012 Annual Meeting and Combustion Divisional Seminar, 25th April 2012. Gerry Riley and John Smart Presented by Mark Flower RWE npower PAGE 1
Presentation overview Background Highlights from Test Programmes - Oxyfuel UK DTI Project - BOM-COM RFCS - EcoScrub RFCS project - Fuel project (RWE npower project) - Oxygen injection project with BOC Summary RWE npower PAGE 2
Background: What is oxyfuel? > Flue gas is recycled and air is replaced by oxygen > The gas inside the boiler becomes almost nitrogen-free and CO 2 is then removed. Furnace/Boiler Furnace/Boiler Convective Zone Convective Zone Radiative Zone Radiative Zone Recycled O 2 Recycled O 2 Coal Coal Cooler Cooler CO 2 CO 2 CO 2 (non CO 2 (non WWWW WWWW Separation Separation Atmospheric Atmospheric Plant Plant Disposal) Disposal) W W Electro-static Electro-static Precipitator Precipitator Primary Primary H 2 O H 2 O Coal Mill Coal Mill Oxygen Oxygen Air Air Nitrogen Nitrogen Air Separation Plant Air Separation Plant RWE npower PAGE 3
Background – Recycle Ratio Recycled Flue Gas (m RFG ) Wet Dry Recycle Recycle Air ASU Boiler CO 2 - Rich Product (m PFG ) Fuel N 2 H 2 0 M RFG Via FGD RR = ---------------------- M RFG + M PFG RWE npower PAGE 4
Overview of CTF programme CTF Studies Fuel Issues Safety Optimisation Desktop Process Development Studies RWE npower PAGE 5
Overview of CTF programme Safety handling and storage of oxygen and Selection of coals (optimise purchasing) CO 2 CTF Studies Use of biomass Flame detection issues (higher moisture and Furnace slagging CO 2 may affect UV and IR absorption) Furnace Corrosion Safety of mixing oxygen/CO 2 Fouling Fuel Issues Safety Flame stability NO X (chemistry not well understood) Safe switch-over the oxyfuel combustion Heavy metal recycling and ash composition Safety of staff with CO 2 /flue gas leaks etc. Burner design Purging for safety Optimisation Carbon burnout Air leakage Heat transfer (radiative/convective properties) Optimum recycle ratio Air heater design Regulation issue - LCPD limits for Desktop Optimisation of mixing strategy (where to add oxyfuel Process O 2 - PA/SA/TA etc.) Pre-investment issues (upfront Gas recirculation Development parameters) Studies Oil burner operation on oxyfuel Required footprint for retrofit (e.g. air separation unit) Flexibility - start-up/shutdown limited by air separation unit so cold-start on air RWE npower PAGE 6
CTF oxyfuel conversion > Two-stage conversion of the CTF – Phase 1: Stored CO 2 injection – Phase 2: Flue gas recirculation > Why a two-phase strategy? – Rapid start-up with less (though significant) engineering – air ingress – Flexibility – Identify show stoppers or new issues at an early stage – Second stage to quantify full impact of issues such as NO X , slagging, corrosion and trace elements that cannot be fully studied by CO 2 injection alone RWE npower PAGE 7
CTF oxyfuel conversion > Two-stage conversion of the CTF – Phase 1: Stored CO 2 injection – Phase 2: Flue gas recirculation – Cancelled following strategic review > Why a two-phase strategy? – Rapid start-up with less (though significant) engineering – air ingress – Flexibility – Identify show stoppers or new issues at an early stage – Second stage to quantify full impact of issues such as NOX, slagging, corrosion and trace elements that cannot be fully studied by CO2 injection alone – Cancelled following strategic review RWE npower PAGE 8
Rig modifications > CO 2 injection – Storage tanks for O 2 and CO 2 with mixing and safety systems – Modified system of blowers and SA/TA heaters – Steam boiler – Doping gasses (SO x , NO x ) – Controls and logic interface with existing CTF system RWE npower PAGE 9
Schematic of Once Through Oxy-Fuel System Coal Steam Primary Air Boiler 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 RWE npower PAGE 10
RWEnpower’s OxyFuel facility O 2 , CO 2 and N 2 Storage Vessels RWE npower PAGE 11
RWEnpower’s OxyFuel facility Evaporators RWE npower PAGE 12
RWEnpower’s OxyFuel facility Gas mixers RWE npower PAGE 13
RWEnpower’s OxyFuel facility Gas Heaters RWE npower PAGE 14
RWEnpower’s OxyFuel facility Burner RWE npower PAGE 15
Schematic of CTF Test Furnace RWE npower PAGE 16
BOFCOM Heat Transfer under OxyFuel Firing Conditions RWE npower PAGE 17
Driver for Studying Heat Transfer Distributions – Radiative and Convective • Radiation heat transfer is driven by gas temperature (T 4 ) while convective heat transfer by gas temperature and velocity. • To operate as “air equivalent” the balance between radiative and convective heat transfer has to be found • 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 would be circa 8% by volume). RWE npower PAGE 18
Radiative HT - South African coal – Dry Recycle Furnace Heat Flux Measurements South African coal, Oxyfuel (3% O 2 ) SAcoal/Air - 3% O2 500 Oxyfuel RR 65% Oxyfuel RR 68% 450 Radiative Heat Flux kW/m 2 Oxyfuel RR 70% Oxyfuel RR 72% Oxyfuel RR 75% 400 350 300 250 200 0 500 1000 1500 2000 2500 3000 3500 Axial Distance from Burner, mm RWE npower PAGE 19
IFRF Burner - RR 66%, 38% Inlet O 2 Hot intense flame RWE npower PAGE 20
IFRF Burner – RR 77%; 28% Inlet O 2 Cool Flame RWE npower PAGE 21
Normalised Convective & Radiative Heat Flux Russian Coal - Dry Recycle Dry Oxyfuel Operation Normalised to Air Operation 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 New Build Retrofit Avoid Normalised Radiative and Normalised Adiabatic Measured Peak Radiative Convective Heat Flux Flame Temperature 1.2 data indicates 74% 1.2 Recycle is "Air- equivalent" 1 1 0.8 0.8 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 RWE npower PAGE 22
Oxycoal - Flame Stability Flame Animations (South African Coal) • Images for different simulated recycle rates under low O 2 settings 70% rr, Total flow 656.99kg/h 65% rr, Total flow 554.74kg/h 68% rr, Total flow 615.71kg/h 72% rr, Total flow 709.04kg/h Sec 501kg/h@29.0% O 2 Sec 552kg/h@26.5%O 2 Sec 400kg/h@35.8% O 2 Sec 457kg/h@31.6% (time: 13:14) (time: 12:41) (time: 14:19) (time: 13:44) • 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 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) RWE npower PAGE 23
Flame Images • Temperature profiles for different simulated recycle rates under lower O 2 settings 65% RR: Sec.f 368kg/h@34.8% 68%RR: Sec.f 62% RR: Sec.f 322kg/h@39.4% (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) (time: 14:18, 29-10) Note: Images and temperature profiles shown here are averaged for 10 instantaneous readings over about 2 minutes. RWE npower PAGE 24
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 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 RWE npower PAGE 25
BOFCOM Deposition Studies under OxyFuel Firing Conditions RWE npower PAGE 26
Combustion Test Facility RWE have carried out a series of deposition runs on their pilot scale combustion test facility RWE npower PAGE 27
Bofcom Deposition Data – Russian Coal 2 1300 Furnace Exit Temperature Probe temperature 1200 Temperature Deg C 1100 1000 900 64 66 68 70 72 74 76 Recycle Rate, % RWE npower PAGE 28
Recommend
More recommend
