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

(Ref: Wisniewski & Handelsman 2010)

0 11.5 23.0 34.5 46.0 57.5 65.0 LHV (MJ/kg)

Inquiries Natural Gas Syngas

Increasing H2 Increasing C2 +

Traditional Variation High reactivity fuels Challenge: “Flashback” Low reactivity fuels Challenge: Blowout

Fuel Flexibility Spread

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Stable Gas Turbine Operational Regime

Blowout Flashback

Mass flow rate

Equivalence ratio Stoichiometric

Region of stable

• peration

Flashback limit Blowout limit

High reactivity fuels Low reactivity fuels

3

Plasma Assisted Combustion (PAC)

• Types of plasma discharges
• Thermal Plasma
• aka equilibrium plasma
• spark, arc
• Non-thermal Plasma
• aka non-equilibrium, “silent” plasma
• DC – Corona discharge, Streamer
• AC - Dielectric Barrier Discharge

(DBD)

• Advantages
• Virtually non-intrusive when not in use
• Solid-state - no moving parts
• Simple design
• All electrical - fast response
• Robust

VDC

Corona Discharge DBD

Electrodes Dielectric material Anode Cathode Zone of plasma formation Zone of plasma formation

VDC

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PAC - Methodologies

Other efforts to improve blowout limit NRC effort to improve flashback limit

Mass flow rate Equivalence ratio

Stoichiometric Region of stable

• peration

Flashback Blowout

• Chemical kinetic
• Ignition via thermal plasma
• Initiation of chain branching

reactions through electron excitation via non-thermal plasma

• Hydrodynamic
• Ionic wind/ ionic propulsion

(NRC experience)

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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: uLocal < Su

• Criteria for flashback in the boundary layer :

(Eichler & Sattelmayer, 2011)

=

∂ = ≤ ∂

b

f y F b wall

S u g y

δ

δ

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Flashback Sensitivity to Velocity Profile

(Schäfer et al., 2003)

Boundary layer flashback Flashback through the core flow

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NRC Experience – Dielectric Barrier Discharge (DBD)

Electrodes Insulation Dielectric barrier Ionic wind Plasma region (volume) Combustion chamber Premixer

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Control of Core Flow Flashback

• No DBD actuation
• Application of DBD actuation

Reducing air flow rate leading to flame flashback (a): Stable→ (b): Start flashback→ (c): Flashback

(a) (b) (c)

Φ = 0.843 Φ = 0.893 Φ = 913 Φ = 0.773

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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

• perated at much lower flow

rates

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0.2 0.4 0.6 0.8 1 1.2

• 28
• 24
• 20
• 16
• 12
• 8
• 4

4 8 12 16 20 24 28

u (m/s) Radial location (mm)

u without DBD u with DBD

Control of Boundary Layer Flashback

Flame front ~200 s-1 ~400 s-1

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Improvement in Stability Margin

• DBD actuation delays

flashback to higher equivalence ratios

• For given total flow rates,

the DBD actuation allows to

• perate with mixtures of

much higher flame speed

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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

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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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