Wir schaffen Wissen heute für morgen Increased risk for flashback in case of dynamic operation of gas turbines Yu-Chun Lin 28. August 2013 1 Introduction Pre-combustion CO 2 capture H 2 -rich fuel mixtures 2
Experiments Operation pressure: 20 bar Air flow rate: 750 mn/h 3 Max. Preheat: 823 K 3 Profiles of Flame Front: H 2, Syngas, and CH 4 Fuel Air H 2 P = 5 bar T ad 1750 K Fuel Air Syngas (H 2 -CO 50-50) CH 4 (Natural Gas) Fuel Air 75 mm 290 mm 4
Flashback 5 When the Flame Gets Shorter Flashback? Fuel Air H 2 Φ = 0.50 P = 2.5 bar T 0 = 623 K u 0 = 40 m/s Fuel Air Φ = 0.39 Fuel Air Φ = 0.32 6
Mechanisms of Flashback* 1. Core flow flashback 2. Combustion induced vortex breakdown (CIVB) 3. Combustion instability induced flashback 4. Boundary layer flashback (BLF) *Lieuwen, T., McDonell, V., Santavicca, D., and Sattelmayer, T., 2008, Burner Development and Operability Issues Associated with Steady Flowing Syngas Fired Combustors, Combustion Science and Technology, 180, pp. 1169-1192. 7 Boundary Layer Flashback H 2 -N 2 70-30, P = 10 bar, T 0 = 623 K, u 0 = 40 m/s, Φ ~ 0.3 (a) Typical operation (b) Flame anchoring /Flashback 8
Model for Laminar/Turbulent BLF* Flashback: g f g c Laminar: g f = u/ y = 8 u 0 d -1 g c = 3 S L02 /(2 b 0.5 α) Turbulent: g f = 0.03955 u 1.75 0 ν -0.75 d -0.25 g c =? u(y) g f = ( u/ y) y=0 Flame front g c = velocity/distance Penetration distance Wall of the premixing pipe =? Quenching distance *Lewis, B. and von Elbe, G., 1943, Stability and Structure of Burner Flames, Journal of Chemical Physics, 11, pp. 75-97. 9 S T : Evaluation T 0 = 623 K u 0 = 40 m/s Continuity: ρ 0 A 0 u 0 = ρ 0 A f, averaged S T c = 0.05 0.5 A 0 (d 25 mm) F L <c=0.05> Progress variable (c) approach: c = 0 fresh mixture c = 1 completely burnt gas 10
S T vs. Normalized Flame Length S T, cone = u 0 [1 + 4 (F L <c=0.05> /d) 2 ] -0.5 d F L <c=0.05> 1.0 bar + 2.5 bar 5.0 bar 7.5 bar 10.0 bar Fuel gas: H 2 -N 2 85-15 11 Model for Turbulent BLF Flashback: g f g c Turbulent: g f = 0.03955 u 0 1.75 ν -0.75 d -0.25 g c =? u(y) g f = ( u/ y) y=0 Flame front g c = S T /(Le δ L0 ) Penetration distance Le α/d H2 -N 2 Quenching distance Wall of the premixing pipe 12
g f vs. g c : Predicting the Flashback Limit (1/3) g f, 10.0 bar g f, 7.5 bar g f, 5.0 bar g f, 2.5 bar Fuel gas: H 2 -N 2 85-15 g f = 0.03955 u 0 1.75 ν -0.75 d -0.25 13 g f vs. g c : Predicting the Flashback Limit (2/3) g f, 7.5 bar Flashback! Predicted Φ FB g c = S T /(Le δ L0 ) Le α/d H2 -N 2 Fuel gas: H 2 -N 2 85-15 14
g f vs. g c : Predicting the Flashback Limit (3/3) g f, 10.0 bar g f, 7.5 bar g f, 5.0 bar g c, 10.0 bar g c, 7.5 bar g c, 5.0 bar + g c, 2.5 bar g f, 2.5 bar Predicted Φ FB Fuel gas: H 2 -N 2 85-15 15 Measured Φ FB : Syngas* Flashback! T 0 = 573 K T 0 = 623 K T 0 = 673 K Stable Fuel gas: H 2 -CO 50-50 *Daniele, S., Jansohn, P., and Boulouchos, K., 2010, Flashback Propensity of Syngas Flames at High Pressure: Diagnostic and Control, GT2010-23456, Proceedings of ASME Turbo Expo 2010, Glasgow, UK. 16
Predicted Φ FB : Syngas T 0 = 573 K T 0 = 623 K T 0 = 673 K Stable Fuel gas: H 2 -CO 50-50 17 Φ FB : Syngas, T 0 = 673 K Predicted Measured Fuel gas: H 2 -CO 50-50 18
Φ FB : Syngas, T 0 = 623 K Predicted Measured Fuel gas: H 2 -CO 50-50 19 Φ FB : Syngas, T 0 = 573 K Predicted Measured Fuel gas: H 2 -CO 50-50 20
Measured & Predicted Φ FB : Syngas Predicted, T 0 = 573 K Measured, T 0 = 573 K Predicted, T 0 = 623 K Measured, T 0 = 623 K Predicted, T 0 = 673 K Measured, T 0 = 673 K Fuel gas: H 2 -CO 50-50 21 Predicted Φ FB : Syngas & H 2 -Rich H 2 -CO 50-50 H 2 -N 2 70-30 H 2 -N 2 85-15 H 2 22
Velocity Gradients vs. T ad : Syngas & H 2 -Rich g f, 10.0 bar g c, Syngas, T 0 = 673 K g c, Syngas, T 0 = 623 K g c, Syngas, T 0 = 573 K g c, H 2 g c, H 2 -N 2 85-15 g c, H 2 -N 2 70-30 P = 10 bar 23 Velocity Gradients vs. T ad : CH 4 & H 2 -Rich g f, H 2 -rich g f, CH 4 g c, H 2 -rich H 2 H 2 -N 2 85-15 H 2 -N 2 70-30 CH 4 g f, CH 4 P = 2.5 bar 24
Summary (1/2) One of the concerns about introducing the natural gasfired combined cycle power plants to Switzerland is the accompanying emissions of green house gases. In order to comply with the limits on CO 2 emissions, the carbon capture and sequestration (CCS) techniques have to be implemented. If the carbon capture is done prior to the combustion process, the hydrogen content in the fuel gas is significantly increased ( H 2 -rich ), and this leads to higher propensity of flashback. 25 Summary (2/2) For steady flowing combustors (e.g., gas turbine combustor), the flashback in the turbulent boundary layer is one of the major operational issues when burning these H 2 -rich fuels. An indicator that predicts specifically the occurrence of this flashback mode is developed in PSI, which could be further implemented to qualify various burner designs. 26
Thank you! 27