improving gas turbine fuel flexibility...thermal plasma aka equilibrium plasma spark, arc...

Improving Gas Turbine Fuel Flexibility

Wajid Ali ChishtyProgram 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)

InquiriesNatural GasSyngas

Increasing H2

Incr

easi

ng C

2+

Traditional Variation

High reactivity fuelsChallenge:

“Flashback”

Low reactivity fuelsChallenge: Blowout

Fuel Flexibility Spread

2

Stable Gas Turbine Operational Regime

Blowout

Flashback

Mass flow rate

Equi

vale

nce

ratio

Stoichiometric

Region of stable

operation

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

AnodeCathode

Zone of plasma formation

Zone of plasma formation

VDC

4

PAC - Methodologies

Other efforts to improve blowout

limit

NRC effort to improve flashback limit

Mass flow rate

Equi

vale

nce

ratio

Stoichiometric

Region of stable

operationFlashback

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)

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: uLocal < Su

• Criteria for flashback in the boundary layer :

(Eichler & Sattelmayer, 2011)

= ∂= ≤

∂b

f yF

b wall

S ugy

δ

δ

6

Flashback Sensitivity to Velocity Profile

(Schäfer et al., 2003)

Boundary layer flashback

Flashback through the core flow

7

NRC Experience – Dielectric Barrier Discharge (DBD)

Electrodes Insulation

Dielectric barrier

Ionic wind

Plasma region(volume)

Combustionchamber

Premixer

8

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 = 913Φ = 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

0

0.2

0.4

0.6

0.8

1

1.2

-28 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 28

u (m

/s)

Radial location (mm)u without DBDu with DBD

Control of Boundary Layer Flashback

Flame front

~200 s-1 ~400 s-1

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 speedThe combustion chamber is more fuel-flexible

13

National Research Council Canada

Supporting Gas Turbine Innovation in Canada

Wajid Ali ChishtyProgram Leader at NRC Aerospace

Advanced Biofuel Symposium, Montreal, July 23-24, 2015

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