Co-Firing of Hydrogen and Natural Gases in Lean Premixed ...guethe/...Cofiring_Alstom.pdf · the...

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CO-FIRING OF HYDROGEN AND NATURAL GASES IN LEAN PREMIXED CONVENTIONAL AND REHEAT BURNERS (ALSTOM GT26)

Torsten Wind Alstom

Baden, Switzerland

Felix Güthe Alstom

Baden, Switzerland

Khawar Syed Alstom

Baden, Switzerland

ABSTRACT Addition of hydrogen (H2), produced from excess

renewable electricity, to natural gas has become a new fuel type

of interest for gas turbines. The addition of hydrogen extends

the existing requirements to widen the fuel flexibility of gas

turbine combustion systems to accommodate natural gases of

varying content of higher hydrocarbons (C2+). The present

paper examines the performance of the EV and SEV burners

used in the sequential combustion system of Alstom’s reheat

engines, which are fired with natural gas containing varying

amounts of hydrogen and higher hydrocarbons. The

performance is evaluated by means of single burner high

pressure testing at full scale and at engine-relevant conditions.

The fuel blends studied introduce variations in Wobbe

index and reactivity. The latter influences, for example, laminar

and turbulent burning velocities, which are significant

parameters for conventional lean premixed burners such as the

EV, and auto-ignition delay times, which is a significant

parameter for reheat burners, such as the SEV. An increase in

fuel reactivity can lead to increased NOx emissions, flashback

sensitivity and flame dynamics. The impact of the fuel blends

and operating parameters, such as flame temperature, on the

combustion performance is studied. Results indicate that

variation of flame temperature of the first burner is an effective

parameter to maintain low NOx emissions as well as offsetting

the impact of fuel reactivity on the auto-ignition delay time of

the downstream reheat burner. The relative impact of hydrogen

and higher hydrocarbons is in agreement with results from

simple reactor and 1D flame analyses. The changes in

combustion behaviour can be compensated by a slightly

extended operation concept of the engine following the

guidelines of the existing C2+ operation concept and will lead

to a widened, safe operational range of Alstom reheat engines

with respect to fuel flexibility without hardware modifications.

INTRODUCTION Due to the progress in installation of sustainable energy

from e.g. wind turbines or solar with unforeseeable power

output, several potential energy carriers are in development.

The use of hydrogen (H2) as energy storage, produced by

electrolysis powered by surplus sustainable energy, gives the

challenge to burn a hydrogen blend natural gas in an Alstom

gas turbine. The existing natural gas infrastructure could be

used for storage of a small amount of hydrogen. The actual

limit of 5 vol.-% in the natural gas pipelines could be extended

to 15 vol.-% in the mid-term [1]. Furthermore a local

electrolysis device with H2 storage is feasible to increase the

sustainable proportion of the fuel within the operational limit of

the local gas turbine. Also fuel gas mixtures from biomass or

coal gasification require higher fuel flexibility regarding H2.

Extensive single burner high pressure tests at full scale

were performed for existing GT26 standard premix and

standard reheat burners (GT26 upgrade 2006 and upgrade 2011

[1]) with 15 to 60 vol.-% H2-doped natural gas. Emissions and

flame instabilities were monitored and several flame position

tests were carried out.

Aspects of fuel flexibility have been highlighted for the

Alstom products and it is perceived as one of the strengths of

the Alstom combustion technology. This has been demonstrated

several times [2][3]. Fuel flexibility as a feature can offer a

competitive advantage.

The limits for allowed fuels are determined by several

factors and several components in the plant.

Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition GT2014

June 16 – 20, 2014, Düsseldorf, Germany

GT2014-25813

1 Copyright © 2014 by Alstom Technologie AG

The fuel has to be brought to the GT and controlled within

the different fuel lines via the fuel distribution system (FDS).

Constraints to the fuels are therefore given by the required

pressure at the combustor, which is given by the pipeline and

might require expensive additional compression. Condensation

of low boiling components has to be avoided. The supply

pressure has to be sufficient to allow flow through the fuel

injectors into the burner with sufficient momentum to allow

good fuel-air mixing.

In the combustor finally the composition of the fuel

determines the chemical reactivity of the fuel in the combustion

process, which, for safety reasons, has to be between the limits

of flashback and blow out. Increased NOx production of H2

containing natural gas flames have been reported before [4].

The composition also influences the emissions of the

combustor with respect to NOx and CO emissions, which is

determined by the reactivity via the flame position and the

degree of premixing and eventually the NOx production

chemistry of the fuel itself. While the direct chemical impact on

(prompt) NOx by reaction with the fuel plays a minor role

(except for trace species like fuel bound nitrogen) the flame

shape and position influence the emission noticeably.

The parameters on engine level constraining the fuels are

therefore the dew point of the fuels, the pressure loss between

pipeline and the injector, the jet penetration in the burner as

well as the chemical reactivity in the flames of the

corresponding combustors. The comparison of different fuels

with respect to the pressure requirements is established by the

Wobbe index, which assures that a given injector with a given

pressure drop is capable of delivering a given energy content

through nozzles of given dimensions at given jet penetration.

The Wobbe index therefore contains the energy content and the

density of the fuel.

�� LHV�� ∙ �� °��

Chemical reactivity can be assessed by chemical kinetics

simulations as explained in a later section. The change of

Wobbe index by doping with hydrogen or C2+ is shown in

Figure 2, natural H-gas provides a basis for fuel mixtures,

which were used for high pressure single combustor tests.

NOMENCLATURE C2+ - Higher Hydrocarbons

EV burner - EnVironmental burner

FDS - Fuel distribution system

GT - Gas Turbine

LHVmass MJ/kg Lower Heating Value

p Pa Pressure

PSR - perfectly stirred reactor

PFR - plug flow reactor

PREMIX - premixed laminar flame model

S1R - Staging ratio

SEV - Sequential EnVironmental

SL - Laminar Flame speed

ST - Turbulent Flame speed

T K Temperature

TAT1 °C Temperature After Turbine (High

Pressure)

TAT2 °C Temperature After Turbine (Low

Pressure)

TFM K SEV Burner Inlet Temperature for

fulfilling Flashback margin

THG K Hot Gas Temperature at Combustor

Exit

Tin K Inlet Temperature

VG - Vortex Generator

WI - Wobbe Index

WRL - Wide Range Logic for C2+

ρ kg/m3 density

φ - Equivalence ratio

ALSTOM GT 26 The sequential combustion system of the GT26 gas turbine

consists of primary combustor (EV) with 24 circumferential EV

burners and lances, followed by a turbine and a re-heat

combustor (SEV) with 24 burners and lances. A cross section of

the GT26 gas turbine is shown in Figure 1. The advantage of

the Alstom GT26 gas turbine with its reheat technology

compared to single stage combustion is an additional degree of

freedom balancing the power of the two combustion chambers.

The Alstom GT26 C2+ operation concept utilizes this degree of

freedom to optimize combustion behavior for fuels containing

C2+ [5][6]. Due to the fact that H2 and C2+ have a similar

behavior in terms of reactivity, the C2+ operation concept can

also be applied to H2 fuel mixtures, which will be shown later

in detail.

Figure 1: Alstom GT24/GT26 sequential combustion

system

Part of the fuel is injected within the EV burners into the

swirling air and thoroughly mixed before entering the EV

combustor. The premix flame is stabilized at the exit of each

EV burner by a recirculation zone due to vortex breakdown.

The reaction products from the EV combustor are expanded in

a single stage high-pressure turbine and subsequently enter the

SEV combustor. The temperature at the SEV inlet is defined as

TAT1. The fuel is injected into hot gases in the SEV burner and


well mixed before entering the SEV combustor, which is

operating at auto-igniting conditions not requiring an external

igniter. The fuel amount between both combustors is optimized

for each operating point and approximately equal at full load

with natural gas.

The WI min and WI max limits show the Wobbe Index

range, in which the GT26 can be operated (apart from other

fuel restrictions). The intended H2 doped fuels are within that

Wobbe Index range with and without fuel preheating.

Figure 2: Wobbe Index for H2, C2+, natural gas

mixtures The fuel reactivity is increasing (laminar flame speed,

auto-ignition delay time) with increase of H2 / C2+.

INVESTIGATION OF CHEMICAL REACTIVITY The challenge for the combustion system for highly

reactive fuels can be described and evaluated by chemical

kinetics studies. The chemical reactivity can be assessed by

chemical kinetics simulations, where usually the laminar flame

speed, which takes into account the molecular transport

properties of the fuel, is determined for the premix flame (first

combustor-EV) or the minimum residence time of a perfectly

stirred reactor with heat release (PSR extinction time). To

account for the fuel effects that are investigated here, turbulent

flame speeds are estimated as a measure of reactivity in the

burner as describes elsewhere [11], [12]and [13]. To access

assess the sequential combustor (SEV) of the reheat engine [3]

auto-ignition delay times (from a plug flow reactor- PFR) are

used.

To obtain reliable trends the use of a properly validated

reaction scheme is crucial. This validation has been part of a

research program over several years and has been reported in

[7], [10], [11]. The kinetic mechanism was chosen from

Curran’s group at national university of Gallway (NUIG). For

the current paper version NUIG_54.1 was used. The flame

position of the first combustor of the GT24/GT26 is determined

by the flow field and the chemical reactivity in the turbulent

field. A relative comparison of fuels reactivity can be done

based on the laminar flame speeds as shown in Figure 3 near

GT26/GT24 base load conditions. The flame speeds are

calculated as function of flame temperatures (varying φ) at lean

conditions near GT operation for various model fuels as

indicated.

To take into account the enhanced reactivity of the H2

containing fuels in a turbulent flame the molecular transport

properties of the low Lewis number have to be taken into

account [9]. The correction for turbulence accounts for an

averaged Lewis number effect and has been described in [10].

The data are normalized to natural gas at 1700K. To maintain

an average reactivity of that reference condition (and keep a

similar flame position) the temperature would have to be

adjusted accordingly. The turbulent reactivity is only estimated

here since not all the characteristics of the flow field are

accounted for. The relative difference appears to change more

with fuel reactivity than the laminar flame speed alone.

Validation of the work on turbulent and laminar flame speed is

ongoing [11].

Figure 3: Effect of H2 addition to the normalized

laminar flame speed (top) and turbulent flame speed (middle) and PSR extinction time( bottom) calculated for different flame temperatures and various H2 and

C2+ model fuels as indicated at conditions near GT26 Base load. The reference case is indicated by the red

square.


The flame speeds depend not only on H2 content but also on

the equivalence ratio φ of the mixture of premixed flame. They

are shown in a 3D colormap of φ vs. H2 content in Figure 4 for

hydrogen and natural gas mixtures in terms of turbulent flame

speeds. The red solid lines indicate the maximum flame speed

for given fuel composition. Note that the maximum flame speed

is on the rich side near φ ~1.1 for natural gas (red line) and is

shifting towards higher equivalence ratios for high H2 contents.

The technical challenge is that the highest risk at high reactivity

is at the fuel rich side near the injection, which has to be

considered for evaluation of the flashback risk.

Figure 4: Contour plot of turbulent flame speeds (using NUIG_54_1 mechanism) for natural gas/

hydrogen mixtures (horizontal axis) and different

equivalence ratios φφφφ (vertical axis). The red line indicates the maximum flame speed for each fuel

composition The reactivity of the sequential burner (SEV) is evaluated

by calculating auto-ignition times, as shown in Figure 5. The

relevance of the calculated auto-ignition times to burner

performance within the SEV high pressure data, is

demonstrated by the good match of the measured near

flashback operation points as shown later (Figure 13) for all

tested fuels.

The trends of the SEV reactivity (Figure 5) are very similar

to the trends for the EV (Figure 3) showing the highest

reactivity for 60% H2 and showing C2+ and H2 to have

comparable effects. GT26 operation with higher reactivity fuel

requires a re-balancing of the power from EV to the SEV

combustor. For fuel gas with varying C2+ content, Alstom has

already a good experience with the wide range logic. This

optional GT26 logic allows operation with C2+ content up to

18 vol.-% C2+.

Figure 5: Effect of H2 addition to the normalized auto-

ignition time calculated for various SEV inlet temperatures and various H2 and C2+ model fuels as

indicated at conditions near GT26 Base load.

EXPERIMENTAL SETUP Full scale engine hardware tests at full engine pressure

with H2 co-firing were performed in the high pressure test

facility at DLR Cologne, Germany. For EV and SEV two

different sector test rigs were used to simulate the gas turbine

conditions as close as possible. The air conditions (e.g. pressure

and temperature) at compressor exit of a gas turbine can be

adjusted. Different fuel gas compositions can be mixed before

fuel injection.

EV test rig The EV burner of GT26 upgrade 2006 and 2011 consists of

a conical swirler and a long lance. The fuel gas is divided

between two stages, as shown in Figure 6. Stage 1 fuel is

injected through the lance and stage 2 fuel is injected along the

swirler slots. Both stages are continuously in operation, the

ratio is adjusted to ensure flame stability and low emissions.

The flame is stabilized by a recirculation region generated by

vortex breakdown.

Figure 6: Staged EV burner with long lance

Figure 7 shows the single burner high pressure test rig in

flow direction from left to right, in which the EV burner was

tested. Emissions were measured at plane 4. Plane 1 and plane

4 were used for optical access. Pulsations were measured at

plane 2.


Figure 7: EV single burner high pressure test rig;

standard rig instrumentation

SEV test rig The SEV burner and SEV lance are shown in Figure 8.

Two different sets of hardware of GT26 upgrade 2006 and

upgrade 2011 [1] were tested. The combustion products of the

first combustor, mixed with cooling air, enter the burner and

pass through the four delta wing vortex generators (VGs),

which enhance the mixing. The lance is located directly after

the VGs. The fuel is injected perpendicularly, shielded by

carrier air, through four nozzles at the lance tip. The hot gas and

fuel are then premixed in the mixing zone until finally auto-

ignition takes place in the combustion chamber after sudden

expansion.

Figure 8: SEV burner (left), SEV lance (right)

The described hardware was tested in a reheat test rig [1],

shown in Figure 9. A single premix (EV) burner serves as hot

gas generator for the SEV burner, providing the requested SEV

inlet conditions. A transition piece with blockage rods is in

between for decoupling the combustion chambers. These

blockage rods also contain the emission probes, for detection of

the SEV inlet components. The tested SEV burner and SEV

lance are installed after the transition piece. The SEV emissions

are measured at the end of the SEV combustor. Figure 9 shows

the SEV high pressure test rig with flow direction from left to

right.

Figure 9: SEV single burner high pressure test rig

The SEV combustion chamber features an inner and outer

segment like in the gas turbine.

The high pressure test rig was operated at nominal GT26

base and part load conditions and at specific off-design

conditions for flame position testing.

RESULTS The high pressure tests were mainly used to show

influence on NOx and flashback margin for higher reactivity

fuel like H2-doped natural gas and C2+ fuels.

EV single burner high pressure test results The high pressure test showed increased flashback

robustness of EV burner with staged long lance (upgrade 2006

and 2011) to burn high C2+ and H2 co-firing mixtures. No signs

of flashback appeared at base load condition at a pressure level

of 30 bar with a fuel mixture of 45 vol.-% H2 and 55 vol.-%

NG. At part load condition at a pressure level of 16 bar up to 60

vol.-% H2 were tested. Only during one test at off-design

conditions with higher hot gas temperature first flashback

indications occurred. The optical device showed sporadic

flashback but no indication at the burner thermocouples could

be seen. This test showed that flashback risk for up to 30 vol.-%

H2 doped NG for the GT26 is low. Pulsations at idle operation

are reduced by increasing the H2 content in the fuel.

For the hot gas mappings the fuel split of stage 1 and 2 was

adjusted to minimize the NOx emissions for each type of fuel.

The mappings were performed at engine part and base load

conditions. Figure 10 shows the NOx emissions over the hot gas

temperature for different H2, C2+ and natural gas mixtures at

base load conditions. The black curve shows the reference case

with natural gas (7 % C2+). The blue (15% H2, 6% C2+) curves

are below the light grey (18% C2+) curve. This means that the

EV NOx emissions of 15% H2-doped natural gas do not exceed

the NOx emissions of natural gas with 18 % C2+.


Figure 10: EV NOx over TAT1 for different H2, C2+, natural gas mixtures at base load pressure level

Figure 11 shows the interpolation of the required hot gas

temperature reduction to maintain 5 ppm NOx @ 15 % O2

versus the volume fraction of H2 + C2+. Fuel mixtures with up

to 15 vol.-% H2 (6 vol.-% C2+) require less reduction of hot

gas temperature compared to fuel with similar volume

percentages of C2+. Therefore the extension of the Alstom C2+

operation concept (Wide Range Logic / WRL) to H2 (limited to

9 % C2+) can be used to control EV NOx. At volume fractions

of H2 and C2+ higher than 30%, C2+ fuels require less hot gas

temperature reduction compared to H2-doped fuels.

Figure 11: Delta flame temperature for EV NOx over H2

+ C2+ content. Interpolation of required flame temperature reduction for constant NOx of 5 ppm @ 15 % O2 at GT26 base load conditions for different

fuel types

SEV single burner high pressure test results Off-design flame position tests were performed at base

load pressure level for both hardware of upgrade 2006 and

upgrade 2011 [1] with several fuel gas mixtures. The SEV fuel

mass flow was kept constant during that test. The SEV inlet

temperature was set to a lower starting value. The inlet

temperature was increased at a constant rate until critical

conditions were reached; all other parameters were held

constant. The base case of testing was with fuel natural gas. All

other cases were compared to it.

Flashback analysis method: The propensity for SEV flashback is a major concern when

combusting highly reactive fuels. The SEV combustor is

operating at auto-igniting conditions. Shorter auto-ignition

delay times, respectively higher inlet temperatures and the

increase of fuel reactivity shift the flame closer to the burner.

To operate with a constant safety margin the inlet temperature

has to be altered for reactive fuel. An experimental approach to

this is given by the flashback analysis method described here.

For a given fuel the test is started from a safe operating point at

low TAT1 (SEV -Tinlet) using a burner instrumented with

thermocouples. A point of equal reactivity (still with margin to

damaging flashback) is defined by the thermocouple being

influenced by the flame itself. This is approached by raising

TAT1 until the slope of the temperature sensor increases,

indicating the presence and direct heat impact of the flame. The

difference between the smoothened temperature measurement

and the simulated temperature (from a heat balance model) of

the burner exit wall were plotted over time, or equivalently over

the inlet temperature, see Figure 12.

Figure 12: Difference between the smoothened temperature measurement and the simulated

temperature of the burner exit wall as function of SEV inlet temperature for different fuel types during flame

position tests

While increasing TAT1 by a given rate at a certain inlet

temperature the measured values start to deviate from the heat

balance simulation (increases faster than the air temperature),

which shows that heat radiation from the flame influences the

thermocouple at the burner exit. In that case the heat release

zone is expected to be at the burner exit and the flashback

margin is very narrow. The temperature at the difference of

10 K defines the inlet temperature for comparison of flashback

margin (TFM) of the different types of fuel. This temperature is

the basis for the required TAT1 de-rating (with respect to the

base fuel) which is shown below for both SEV hardware types

independently. The tests yield a set of fuel compositions and

operating conditions (TAT1) of comparable reactivity.

To compare this with the theoretical approach a simple 1 D

model is used. The assumption is that the auto ignition time

describes the reactivity sufficiently. The auto-ignition delay


times at TFM, which refers to the same reactivity or to the same

simulated ignition time, were calculated. These auto-ignition

delay times for all fuels (containing H2, C2+) at TFM were

converted into a distance by multiplying by the mean burner

velocity and plotted as probability distribution (Figure 13). All

calculations for all tested fuels fall in a very narrow range

(accuracy of < 10%) and lie close to the measured physical

position of the thermocouple used for the analysis. For

visualization the measured values are plotted on top of a

Gaussian probability distribution.

The procedure proves the relevance and the reliability of

the PFR modeling for flashback safety prediction and NUIG

kinetic model to describe the engine condition. It combines the

experimental approach with a proper kinetic model to predict

engine behavior. The corresponding analysis using the GRI3.0

model was carried out and resulted in very scattered results

(STD +-25% and a total spread of 100%) for the different fuels,

highlighting the importance of proper chemical kinetics basics

to operate the reheat gas turbine.

Figure 13: Histogram of ignition distance calculated from the flashback condition for different fuels and

burner temperature (log spacing) With the experimental verification of the prediction

methodology (using validated kinetics) the operation of the

highly reactive fuels can be adjusted.

SEV hardware upgrade 2006: The required TAT1 de-rating for H2, C2+ and natural gas

mixtures, which maintains the flashback margin of reference

natural gas is shown in Figure 14 for SEV hardware upgrade

2006. Up to 30 vol.-% H2 + C2+ the flashback margin is higher

for the same amount of total H2 + C2+, the higher the H2/C2+

ratio. Figure 14 shows the normalized required TAT1 de-rating

for fuel variation based on flashback tests (symbols) and based

on chemical kinetic simulations (curves).

Figure 14: Required TAT1 reduction for fulfilling sufficient flashback margin vs. H2 + C2+ content

(upgrade 2006). Measured de-rating and simulated (NUIG) de-rating, reference natural gas with 7 vol.-%

C2+ The NOx vs. flame temperature curves of different fuel

types and different SEV inlet temperatures are very close

together. NOx emissions of natural gas doped with 15 vol.-% H2

up to 45 vol.-% H2 and also 33 vol. % C2+ are comparable and

40 % higher than the reference case with NG with 6 vol.-%

C2+, see Figure 15.

Figure 15: SEV NOx emissions vs. SEV THG for

different fuel types of GT26 upgrade 2006

SEV hardware upgrade 2011: The flashback margin of upgrade 2011 hardware for

natural gas is already higher than for upgrade 2006 hardware.

Therefore operation with higher TAT1 is possible compared to

upgrade 2006. The entire TAT1 scale is shifted to a higher

temperature. Beside that “bonus” the required TAT1 de-rating

with natural gas as reference is shown in Figure 16. Up to 30

vol.-% H2 + C2+ the flashback margin is higher for the same

amount of total H2 + C2+, the higher the H2/C2+ ratio. Figure

16 shows the normalized required TAT1 de-rating for fuel

variation based on flashback tests (symbols) and based on

chemical kinetic simulations (curves).


Figure 16: Required TAT1 reduction for fulfilling sufficient flashback margin vs. H2 + C2+ content

(upgrade 2011). Measured de-rating and simulated (NUIG) de-rating, reference natural gas with 7 vol.-%

C2+

The effect of 15 vol.-% H2 doping on NOx is small or even

negligible at engine conditions. The compensation of increased

SEV NOx for higher H2 concentration by decreasing the SEV

inlet temperature is limited. An overview of NOx for different

type of fuels and inlet temperatures is given in Figure 17.

Figure 17: SEV NOx emissions vs. SEV THG for

different fuel types of GT26 upgrade 2011

ADAPTION OF GT OPERATION CONCEPT The operation with H2 mixtures should have minimal

impact on performance and emissions. Decrease of TAT1 for

operation with H2 doping is acceptable due to the fact that the

power and efficiency reduction is minor in Alstom’s reheat

engines. Decrease of TAT2 should be avoided due to large

reduction of power output of the gas turbine and the whole

combined cycle power plant. A sufficient flashback margin has

to be guaranteed.

For H2 co-firing up to 30 vol.-% H2 an adapted C2+ Wide

Range Logic [5][6] can be used as conservative operation based

on the fact that up to 30 vol.-% H2+ C2+ the flashback margin

is higher and the NOx is lower for the same amount of H2 +

C2+ the higher the H2/C2+ ratio. This dependency is switched

at around 30 vol.-% H2+ C2+. Limitations for EV and SEV

operation are SEV flashback and overall NOx emissions, the

EV flashback risk can be neglected, as it was described above.

The SEV flashback margin has to be sufficient for all fuel

mixtures. In general fulfilling the NOx emission limit of 15 ppm

@ 15 % O2 is a more stringent requirement than fulfilling a

sufficient flashback margin.

As the same EV burner is installed in GT26 upgrade 2006

and 2011, the operation with EV only is shown below for both

engines. Due to the higher reactivity of H2-doped natural gas,

the effect of piloting is increased and the flame is much more

stable in general, the S1R has to be adapted accordingly. For

doing that, H2 can be weighted as C2+ and the Wide Range

Logic [5][6] for C2+ can be used.

The SEV could be switched on earlier the higher the H2

content due to the fact that part load CO is lower the higher the

H2 content. Two scenarios for the modification of the operation

concept for H2 doped natural gas are possible. Scenario 1 stands

for operation with constant NOx and Scenario 2 for operation

with similar SEV flame position in comparison to the reference

case with natural gas. For operation with SEV on, this section is

divided into GT26 upgrade 2006 and 2011, because of different

hardware used.

Operation of GT26 upgrade 2006 GT26 upgrade 2006 operated with 15 vol.-% H2-doped

natural gas (15 vol.-% H2, 6 vol.-% C2+) at design conditions

relates to a SEV NOx increase of about 1.1 g/kg fuel. At the

same time the EV NOx is increased by 0.5 g/kg fuel. For

scenario 1 with constant NOx level compared to the reference

case with natural gas at design conditions the reduction of

TAT1, which is also close to the required flashback margin

(scenario 2).

Operation at constant NOx level with higher H2 content

than 15 vol.-% is not possible with GT26 upgrade 2006 without

reduction of TAT2, and consequently loss of efficiency.

Operation of GT26 upgrade 2011 The SEV NOx of the GT26 upgrade 2011 hardware is

lower compared to the upgrade 2006 hardware. Also the

flashback risk is lower, as described in previous sections. The

flashback margin of 15 % H2-doped natural gas (15% H2, 6 %

C2+) is sufficient already at design conditions, no de-rating

would be required for operation with slightly higher NOx, but

still below 15 ppm -@ 15 % O2. For constant NOx (scenario 1)

compared to the reference case with natural gas a reduction of

EV hot gas temperature is required.

Operation with 30 vol.-% H2-doped natural gas is still

feasible with same gas turbine NOx level compared to the

reference case with natural gas by further reduction of TAT1.


CONCLUSION AND OUTLOOK The combustors of Alstom GT26 upgrade 2011 were tested

successfully with H2, natural gas mixtures. Standard hardware

can be applied for H2 co-firing up to 30 vol.-% H2. The existing

Alstom Wide Range Logic for C2+ operation [5][6] can be

adapted to mixtures of natural gas, C2+ and H2.

GT26 upgrade 2006 can be operated with up to 15 vol.-%

H2-doped natural gas and GT26 upgrade 2011 can be operated

with up to 30 vol.-% H2-doped natural gas without change of

hardware. No reduction of exhaust temperature is required and

therefore the power reduction respectively the loss of efficiency

caused by EV de-rating is minor.

In case of the GT26 upgrade 2011 operation with 15 vol.-

% doped natural gas below the NOx level of 15 ppm @ 15 %

O2 is possible without de-rating of the EV.

A demonstration plant for H2 storage and co-firing of GT26

upgrade 2011 with 30 vol.-% H2 doped natural gas could show

the capability for storage of the excess renewable electricity

and grid stabilization using fast-responding combined cycle

power plant operated with H2-doped natural gas. Further tests

and minor adaptions of gas turbine hardware are required for

operation with up to 45 vol.-% H2-doping. Supporting the EU

2020 target of CO2 reduction, operation with 45 vol.-% H2

based on sustainable energy would result in 20 % reduction of

CO2 emissions. The Wobbe Index of intended H2 doped fuels is

within the specified range of the GT26.

REFERENCES [1] K. M. Düsing, A. Ciani, U. Benz, A. Eroglu, K.

Knapp, „Development of GT24 and GT26 (upgrades

2011) Reheat Combustors, achieving reduced

emissions and increased fuel flexibility”, ASME Turbo

Expo, GT2013-95437.

[2] DVGW “Mit Gas-Innovationen in die Zukunft” (2012)

[3] F. Güthe, J. Hellat, P. Flohr, "The reheat concept: the

proven pathway to ultra-low emissions and high

efficiency and flexibility", Journal of Engineering for

Gas Turbines and Power, 131, 021503 (2009).

[4] Therkelsen, P., Werts, T., McDonell, V. Samuelsen, S.,

Analysis of NOx Formation in a Hydrogen Fueled Gas

Turbine Engine, Paper No. GT2008-50841, ASME

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[5] Oliver Riccius, Richard Smith, Peter Flohr, Felix

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95151, (2013).

[11] A. Morones, S. Ravi, D. Plichta, E. L. Petersen, N.

Donohoe, A. Heufer, H. J. Curran, F. Güthe, T. Wind,

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Turbo Expo, GT2014-26742, (2014).

[12] Beerer D., McDonell V., Therkelsen P. and Cheng,

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GT2012-68216, ASME Turbo Expo 2012,

Copenhagen, Denmark, June 11–15, 2012

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Layer Flashback Limits for Premixed Hydrogen-Air

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