Improving Gas Turbine Fuel Flexibility Wajid Ali Chishty Program - PowerPoint PPT Presentation

Improving Gas Turbine Fuel Flexibility Wajid Ali Chishty Program Leader at NRC Aerospace Advanced Biofuel Symposium, Montreal, July 23-24, 2015

Fuel Flexibility Spread High reactivity fuels Increasing C 2 + Challenge: Inquiries “Flashback” Natural Gas Syngas Increasing H 2 Traditional Variation 0 11.5 23.0 34.5 46.0 57.5 65.0 LHV (MJ/kg) (Ref: Wisniewski & Handelsman 2010) Low reactivity fuels Challenge: Blowout 2

Stable Gas Turbine Operational Regime High reactivity fuels Region of Equivalence ratio stable Low reactivity fuels operation Stoichiometric Flashback Blowout Mass flow rate Flashback limit Blowout limit 3

Plasma Assisted Combustion (PAC) • Types of plasma discharges  Thermal Plasma Zone of plasma Corona formation  aka equilibrium plasma Discharge  spark, arc  Non-thermal Plasma  aka non-equilibrium, “silent” plasma V DC V DC  DC – Corona discharge, Streamer Cathode Anode  AC - Dielectric Barrier Discharge (DBD) Zone of plasma • Advantages formation DBD  Virtually non-intrusive when not in use  Solid-state - no moving parts  Simple design  All electrical - fast response  Robust Electrodes Dielectric material 4

PAC - Methodologies • Chemical kinetic NRC effort to improve  Ignition via thermal plasma flashback limit  Initiation of chain branching reactions through electron excitation via non-thermal Equivalence ratio Region of plasma stable operation Flashback • Hydrodynamic Stoichiometric  Ionic wind/ ionic propulsion Other efforts to (NRC experience) improve blowout limit Blowout Mass flow rate 5

Flame Flashback Mechanisms • Four types of flashback are recognized:  Boundary layer  Core flow  Combustion instabilities  Combustion Induced Vortex Breakdown (CIVB) • Occurs if the local flow velocity is lower than the flame speed: u Local < S u • Criteria for flashback in the boundary layer : S ∂ u f y = δ = ≤ ∂ g b δ F y b wall (Eichler & Sattelmayer, 2011) 6

Flashback Sensitivity to Velocity Profile Flashback through the core flow Boundary layer flashback (Schäfer et al., 2003) 7

NRC Experience – Dielectric Barrier Discharge (DBD) Combustion chamber Plasma region (volume) Ionic wind Premixer Dielectric barrier Insulation Electrodes 8

Control of Core Flow Flashback • No DBD actuation (b) (c) (a) Reducing air flow rate leading to flame flashback (a): Stable → (b): Start flashback → (c): Flashback • Application of DBD actuation Φ = 0.893 Φ = 0.843 Φ = 913 Φ = 0.773 9

Improvement in Stability Margin • For fixed flow rates of combustible mixture, the burner can be operated with fuels and/or blends of much higher flame speeds • For constant flame speeds, the combustor can be operated at much lower flow rates 10

Control of Boundary Layer Flashback ~200 s -1 ~400 s -1 1.2 1 0.8 u (m/s) 0.6 0.4 0.2 0 -28 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 28 Radial location (mm) u without DBD u with DBD Flame front 11

Improvement in Stability Margin • DBD actuation delays flashback to higher equivalence ratios • For given total flow rates, the DBD actuation allows to operate with mixtures of much higher flame speed 12

Conclusions • The proposed application of DBD:  Increases the velocity gradient at the wall of the premixer  Delays flashback to occurs at higher equivalence ratios and lower flow rates The stable operation regime is extended  Allows the operation with mixtures of higher flame speed The combustion chamber is more fuel-flexible 13

National Research Council Canada Supporting Gas Turbine Innovation in Canada Wajid Ali Chishty Program Leader at NRC Aerospace Advanced Biofuel Symposium, Montreal, July 23-24, 2015

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