Radiation and Stability of Oxy-Fuel Combustion

Transcription

1 Radiation and Stability of Oxy-Fuel Combustion Mario Ditaranto, Thomas Oppelt, Bård Lode, Inge Saanum International Conference on Sustainable Fossil Fuels for Future Energy July 6 th 1 th, 29, Roma, Italy Acknowledgements to funding partners: StatoilHydro, GE Global Research, Statkraft, Aker Kværner, Shell, TOTAL, ConocoPhillips, ALSTOM, the Research Council of Norway and Gassnova 1

2 Presentation Outline Introduction Challenges in oxy-fuel combustion Experimental set-up and measurement techniques Results Heat radiation profiles Emission spectra Stability behaviour Conclusions 2

3 CO 2 -free Power Generation Cycles Application to gas turbine cycles or boilers 83 % CO 2 15 % H 2 O NG Pressurized oxygen HRSG 2% O 2 1 bar Condenser Condenser 1328 C.4 bar H 2 O CO 2 to compress GT Steamturbine Generator 96 % CO 2 2 % H 2 O 2.1 % O 2 9 % recycle 3

4 Challenges in Oxy-fuel Combustion Years of experience for air-supported combustion Stoichiometric combustion temperature, unburned CO 2 injection/dilution mixing, stability, heat transfer Unusual properties temperature, laminar burning velocity, stability 4

5 Experimental Set-Up 1 mm 3 mm O 2 / CO 2 Plenum CH 4 5

6 Measurement Techniques Radiative heat flux Gas concentration by sampling and analysis Fine wire thermocouple lift off by OH* imaging f abs,g f rad, inc f rad, f T w f r, w f e, w ds Emission spectrometry f mes f cond? s T1 T c f conv f r,sensor f rad, inc f e,g T g f e,sensor Figure 25: Radiative flux measurement - Definition of notations - Figure 24: Heat Flux probe Heat transfers in detail Dfiii f i 6

7 Controlled Conditions in the Chamber Temperature field in gas layer 12 Temp. (K) h = 75 mm h = 14 mm h = 22 mm h = 285 mm h = 33 mm h = 42 mm h = 46 mm h = 535 mm Radius (mm) [O2] (% vol. dry) kW 35% O2 h=1/4 h=2/4 h=3/4 h=4/4 Flame length (mm) kw 2 kw 3 kw 5 kw Radius (mm) O2 in oxidant (% vol.) 7

8 Effect of O 2 on Flame Length Shorter flames 8 High stoichiometric mixture fraction Delayed turbulence transition Flow laminarization Lf (mm) Annular jet velocity (m/s) stoi cond Higher stability quality Central jet velocity (m/s) Higher flame speed 8

9 Radiation from Oxy-Fuel Flames Re = 468 heat flux (kw/m2) 1 Air 8 35% O2 in CO2 4% O2 in CO2 6 5% O2 in CO2 6% O2 in CO2 4 7% O2 in CO height (mm) heat flux (kw/m2) Re = 234 Air 1 35% O2 in CO2 4% O2 in CO2 8 5% O2 in CO2 6 6% O2 in CO2 7% O2 in CO height (mm) As O2 in the oxidant increases: Flames are shorter Peak heat flux increases Less distributed heat flux Higher radiation in the near field More soot is produced in the near field, but is more easily consumed because more oxidant conditions 9

10 Radiation from Oxy-Fuel Flames heat flux (kw/m2) air 1 kw 2 kw 3 kw 5 kw height (mm) As the Re increases Peak heat flux is displaced towards higher relative axial location At higher O2 enrichement peak heat flux tends to be constant It requires 35% O2 in CO2 to behave as air in laminar regime 35% O2 in CO2 7% O2 in CO2 1 1 heat flux (kw/m2) kw 2 kw 3 kw 5 kw heat flux (kw/m2) kw 2 kw 3 kw 5 kw height (mm) height (mm) 1

11 Radiation from Oxy-Fuel Flames The total radiative heat flux increases as O2 enrichement increases truly due to higher soot temperature Qtot (kw/m2) 5 Re = Re = 144 Re = Re = O2 in oxidant (%) 11

12 Spectrometry Results Continuous background emission (soot and broadband CO 2 *) Emission bands of OH* and CH* [OH] (ppm) Φ=1, 3% O2 Φ=1, 4% O2 Φ=1, 6% O2 Φ=1, 8% O X (cm) 12

13 Flame Static Stability h_ lo [mm] 8 Air 21% O2 7 Air 23.4% O2 Data from Ditaranto 6 Data from Kalghatgi Kalghatgis correlation 5 Oxyfuel 34% O2 4 Oxyfuel 38% O2 Oxyfuel 42% O V [m/s] 27-3% of O2 in the CO2 to ensure stabilisaton of a methane flame But, a very high stability is achieved when O2 exceeds 3 % in the mixture h_lo [mm] % O2 Twref=52 (h) 34 % O2 Twref=18(h) 36 % O2 Twref=44 36 % O2 Twref=155(b ) 36 % O2 Twref=34 (h) 38 % O2 Twref=118(l) 38 % O2 Twref= % O2 Twref=5 (l) 38 % O2 Twref=31 (h) 4 % O2 Twref=66 (h) 4 % O2 Twref=96 (h) 4 % O2 Twref=31 (h) 42 % O2 Twref=93 (l) 42 % O2 Twref=5 (h) 42 % O2 Twref=153(l) 44 % O2 Twref=141(l) 44 % O2 Twref=58 (T) 44 % O2 Twref=94 (l) Stabilisation at burner is affected by radiation charateristics of the flame environment V [m/s] 13

14 Conclusions Soot and radiation are expected to be of high importance in oxy-fuel combustion The influence of CO 2 addition in the combustion process has been quantified by comparison with air Stability is very sensitive to the radiative characteristics of the flame environment 14