Syngas and hydrogen combustion in GT

Syngas and HydrogenCombustion in GT

S.Giammartini

State of art about the useof H2 rich Syngas in GTs, in the prospect ofHydrogen Economy

Syngas

With this acronym we are use to indicate a gas of varying compositionthat can be produced by gasification of coal, biomass, waste or bypetrolchemical / metallurgical industry

Syngas consists mainly of carbon monoxide and hydrogen, and has less than half the energy density of natural gas

Opportunity gases, coming from wastes, petrochemical and metallurgicalindustry, and even more the prospects of the hydrogen economyput in evidence the problem of :

how we can burn these fuels in GTs?

1. Industrial experiences about syngas withlow percentage content of H2 (< 20 %)

Summarythree steps:

2. Syngas with high content of H2 (up to ~ 100%)

3. Future prospects and new advanced technologies


Summary:



Generally, to minimize the high costs of a new project, a low BTU burner isderived from a premixed burner for NG, operated in diffusive mode

two are the elements that can characterize a not convenctional fuel:Low CalorificValue (LHV) and volume ratio H2/CO

For conventional fuels, the effects that phisical/chemical parameters deviation caninduce on GT combustion, are negligible.On the contrary, for non-conventional fuels, effects of H2 content are very significant

About syngas reactivity, the only parameter that we can determine analyticallyis the laminar flame velocity, defined as:

= cinematic viscosity; u = unburned density

From the formula: SL increases if H2 percentage increases, because the density of the mixture can be very low respect to the density of NG.

u

fuelL

v)1(2S += puuc

K=where: (Diffusivity factor)

Future H2-based energy concepts will require 90 100% H2 as fuel,but now it can involve intermediate H2 concentrations

ANSALDO Energia experiencesA tipical modified Low BTU diffusive burner, developed by ANSALDO Energia, is shown in figure (starting from a V94-K)

FuelOil Low BTUFuel

Natural Gas

Air 12

3

5

4

6

Cooling Air Main components are:

1. A diffusive line (1-yellow) feeded with NG, forthe start-up and for going up the power, up toSyngas commutation (change over point);

2. A pilot line (2-orange), with NG, to prevent theextinction;

3. A diagonal swirler (3) for secondarycombustion air;

4. The diffusive low BTU fuel line (4 - green)to feed GT in the power range:change over base load.

6. Primary swirled air

by P.Gobbo - Ansaldo Energia

Respect to the convenctional burner, the low BTU version has enlarged channels topermit the feeding with syngas diluted with steam, to reduce reactivity of fuel and NOxemissions

1

FuelOil Low BTUFuel

Natural Gas

Air 12

3

5

4

6

Cooling AirFuelOil Low BTUFuel

Natural Gas

Air 12

3

5

4

6

Cooling Air At the start up the burner is feeded by NG in the diffusiveLine (1). Power is increased with NG up to the change overpoint (50% of the base load), before to switch at the LowBTU line;

The start up with NG is imposed by the high laminar flamevelocity of H2 (SLH2 ~ 350 cm/s; SL CH4 ~ 43 cm/s),infact low flow rates can determine ignition in zones nearthe internals of the burner

About the practice

During the switch phase (15-20 min), machine is runned with NG (in 1) and Syngas (in 4);

A configuration like this can be easily modified to be adapted at different syngascompositions and characteristics


Effecs of H2 percentace increaseon the syngas flame velocity,and mitigation effects of the dilution with air

by P.Gobbo - Ansaldo EnergiaLambda

S

L

(

c

m

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s

)

NG + 40% H2

NG

SL(NG)

SL(40%H2)

SL(40%H2)~1,5 SL(NG)

2


Effecs of H2 percentace increaseon Flash Back margins in Premixed mode (F-class machine V94-3A)

dp/p (Air Flow Rate)

Flash Back limits

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No Overheating

Risk ofOverheating

40% H2

Enlargement ofthe overheating zone

Pilot feeded with H2 (40% from premixed line + 10% from pilot)reduces stability limits and safety margin on flash back further on

Red lines represent flash back limits in function of H2 %

3

Results

Tests of Flash Back, carried out with mixture of NG + H2 (max 50% vol),put in evidence the following results:

No overheating in diffusive conditions;

In premixed mode safety margin on flash back is very reduced, respectto NG;

Pilot flame feeded with H2 reduces stability limits and safety marginon flash back;

In diffusive mode, no significant effect of H2 on flash back is observed;

An increase of 20 30 % of NOx is evaluated in premixed mode, formixture of 40% vol of H2.


Stability limits and NOx emissions in premixed combustionin function of pilot flame percentage (P/T %) and H2 % content

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Results: Combustion stability, burning NG only, requires pilot flame in DLN burner. The addition of H2 gives a wider flame stability range, and consequently allows to work at very low values of the P/T ratio without any problem.

At P/T level less than 4% the concentration of the NOx emissions fallsFrom G.Benelli et al. ENEL Ricerche

ENEL results

Conclusions

Different experimental campaigns demonstrate the feasibility of burningHydrogen enriched flame within industrial DLN Gas Turbine burners.

A 10% addition in weight of hydrogen allows to operate, using DLNcombustor, at almost full premixed mode with NOx emissions below10 ppm@15%O2


Summary:



Hydrogen Economy

The hydrogen economy founds its appeal on the advantages of this fuel,mainly :

No generation of CO2; SOx; CO; UHC; VOC

Radical solution of the greenhouse effecs

In this scenario it is generally admitted that:

Gas Turbine is one of the most promising prime moversfor H2 applications

Hydrogen-fuelled Gas Turbine

Today Hydrogen is not terra incognita (unknown land) for Gas Turbine:a considerable number of E-class machines are burning H2 actually

Actual experience:- In Spain about 20 Frame 6B, erected in 90s are burning 10 70% H2- In UK a Frame 9E is burning 48-55 % of H2- In Korea a 40 MW GT (Daesan, a petrolchemical complex) is operated withcombustion of over 97% H2

The Daesan plant boastes some records : from september 1997,over 10 years of experience with content of 85-97% of H2 availability has been 96,5%

Always the start up is feeded with NG

~ 40 times ~ 8 times ~ half43

350

H2-air flames: General Considerations

120.650 kJ/kg10.770 kJ/Nm3H250.030 kJ/kg35.500 kJ/Nm3CH4

Mass basisVolume basisLHVH2 is a dual-faced fuel, due toits very low density, respect NG:

Resuming: combustion properties of H2 in Air respect CH4

100% NG

80% H2 100% H2

40% H2

5

0

m

m

exposure time=1 s, f# = 5

exposure time=1 s, f# = 3.4



Effects of increasing H2 percentageAbout swirleddiffusive burner

Results:the increase of H2 percentage, determines the progressive reduction of flamedimensions that means significat reduction of combustion chamberdimensions for burners of new design.

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90 130 170 210 250 290 330 370 410 450 490 530

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0% H210% H230% H2

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Strain parameter, Uair/dburner, 1/s

BLOWOUT

STABLE

The increase of H2 % content has the effect to enlarge the stability region

Swirled burner can be operated at very lean equivalence ratio, and greater Reynolds number (Uair), when fed with fuel mixture of Natural Gas + H2

90% NG +10% H2

80% NG +20% H2

100% NG

( )f air

f air stoich

m mm m

= & && &

Effects of increasing H2 % on flame stability

Diffusive combustionEffects of H2 concentration increase

on the longitudinal profile of the liner temperature

Increase of H2 content

shorter H2 flamehigher local wall temp.

Radiation: absence of soot contributionis compensed by higher H2O

Results: H2 content has effect only in the zone between the dome and the primary holes of dilution.Respect to the case of NG combustion, the maximum of temperature move back towards the dome.This displacement is almost independent from combustion pressure, and mixture composition. After primary combustion zone, T profiles are equivalent, so we can conclude that reduction of soot is belanced by higher H2O radiation From G.Benelli et al. ENEL Ricerche

ENEL experiences

1. Flames Short & Fast: As an effect of very simple chain reaction respect CH4

H2-air flames: Combustion effecs

1. Flame Short & Fast: Very simple chain reaction respect CH4 High diffusivity and reactivity (due to radicals H; OH; ..) :

H2 is 15 times lighter than air, so 3 times more diffusive than air High Flash Back risk at the present no premix combustion technology

is available for GTs

From G.Benelli et al. ENEL Ricerche

H2% increaseproduces shorterand stronger flames


1. Flame Short & Fast: Very simple chain reaction respect CH4 High diffusivity /reactivity of intermediate species / radicals (H; OH; ..)

- H2 is 15 times lighter than air, 3 times more diffusive than air High Flash Back risks at the present no premix combustion technology


2. Very Hot flames: Only a molecule (H2O) as combustion product, per molecule of fuel (H2):

that determines very increased radiation effects on the liner

From M.Moliere GE Energy

4H2-air flames: Combustion effecs

2. Very Hot Flame: Only a molecule of combustion product (H2O) per molecule of fuel (H2) Adiabatic Stoichiometric Comb. Temp. (Tas) of H2 ~ Tas of CH4+150C

Diffusive flame: NOx increases with (adiabatic) combustion temperature DeNOx Steam/Water injection has the effects: (i) to degrade efficiency;

(ii) to amplify the H2O radiative effectsFrom G.Benelli et al. ENEL Ricerche


1. Flame Short & Fast: Very simple chain reaction respect CH4 High diffusivity /reactivity of intermediate species / radicals (H; OH; ..)

- H2 is 15 times lighter than air, 3 times more diffusive than air High Flash Back risks at the present no premix combustion technology


2. Very Hot Flame: Only a molecule of combustion product (H2O) per molecule of fuel (H2) Tas (adiabatic stoichiometric combustion Temperature) of H2 ~ Tas (CH4)+150C

3. Very Stable Combustion: Very large Flammability Range

(LFL = 4% vol UFL = 75% vol)and lower Auto-ignition Temp.


4. Radiative & Aerothermal effects

Enhanced heat transfer with H2O rich hot gas: Produces radiation & convection severe impact on metal temperature

Moreover:An extremely turbulent hot gas (1400 1700 K) impacts the 1 stageturbine nozzles, so they undergo the highest temperature and mechanical stress, partially mitigated by the dilution air and by thecooling air from the 1 stage nozzles

Future prospects about this aspect:

Actual E-class GTs are characterized by Tf = 1100 - 1150 CFuture H2 based power applications will require higher Tf (1300 1400 C)

From M.Moliere GE Energy


SIEMENS ExperiencesIn the last years significant test campaigns have beencompleted. Results indicate that:

Industrial plantsoperating with high H2 %

Generally connectedto gasification

Significantpercentage of H2

TG Siemens/Ansaldo

Resuming

3 are the driving forcesof H2 as fuel

Need to prevent pre-ignitionParticular care for avoiding flash back

These factsdetermine:

To reduce risk of flashbackand NOx emissions

Mixing of fuel and air within shortest possible timeIt is necessaryTo carry out

actionsto promote:

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by SIEMENS

Fuel propertiesconsidered

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by SIEMENS

by SIEMENS

Diffusion or DLN Combustionrespect to the Flash Back risk ( H2 diluted with N2)

Increase dilution and gasvelocity

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Conclusions GTs are well positioned for H2-based generation in the medium / large

power range

Experiences accumulated with E-class GT provides solid milestonesin terms of feasibility / safety / reliability

Diluted H2-mixture (H2-N2) is likely to alleviate most issues:- New combustion chambers or use of available IGCC GT chambers- NOx: as an effect of lower combustion temperature- Safety: in terms of mitigation of high flammability issues- Radiative: lesser H2O content in the combustion gas

Pending aspects exist, expecially for advanced H2-fuelled GTs:- H2 compatibility of materials- Development of Ultra Lean burners, flash back free- Blade material for higher TiT- Global safety policy for H2 storage/transport and leak detection


Summary:


3. Future prospectives and new advanced technologies

Our traditional experiences about combustion, related tonatural events, every day life or techological applications, are relative to two foundamental way to burn: diffusive combustion (> 90% of industrial applications) premixed combustion (tipical of GTs).

High temperature of reactants and low concentrationof oxygen make possible another way:

FLAMELESS COMBUSTION

Flammability limits: temperature effect

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CH4 concentration in mixture with air

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stoichiometry

l Lower (lean) flammabilitylimit

threshold flameless

Fuel in air is flammable within a specific range of concentration (lower and upper limits) underself-ignition temperature.Over the self-ignition (auto-ignition) temperature these limits tend to vanish,and mixture burns anyway even if not necessarily with flame front.

Upper (rich)flammabilitylimit

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0 1 2 3 4 5Flue recirculation ratioKv

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Self-ignition temperature

combustionstable flameless

stableflamefrontat theburner

No stable flame risk of explosion

Lifted flames

Flameless Combustion

Kv = PdCric / Airinput

Flue recirculation ratio Kv

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Graphic representation of combustion regimes in function of Temp. and Recirc. Factor.4 regions are evident : a zone of convenctional combustion caracterized by a limited mixing with entrained recirculated flue gases a zone of unstable flame, under self-ignition (auto-ignition) temperature (high risk of explosion) a zone of lifted flame, over self-ignition (auto-ignition) temperature; a stable combustion zone, without flame front, caracterized by presence of reactants,hot combustion productsand hot flue gases. Condition for stable combustion is Kv > 2-3

21 17 13 9 5O2 %

Flameless combustion with oil: an evidence

Burner 100kW: BTZ oil; Air 250C;O2% = 21%

Burner 100kW: BTZ oil; Air 500C;O2% = 12%

Ansaldo Caldaie:Gioia del Colle station

No flame front !only IR emissions

Cortesia WS

Comparison between Flame and Flameless combustion

Furnace at 1200 C

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recirculation rate Kv

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self-ignition

no reactionTair = 400 C

T rec flame mode

flameless mode

T adiab

FLAMELESS

In Flame mode, temperature, starting from Tair, goes up witha high gradient, up to the AdiabaticTemperature. (BROWN LINE)

In Flameless mode, temperature goes up very softly, as effect of premixig with flue gases.Above self-ignition temperaturewe have a moderate gradient,up to the adiabatic temperature,suitable of the recirculation rate(GREEN LINE)

In Flameless mode we reduce the maximum of temperaturebecause we dont have flame front !

.Temperature profiles(y = 0 : burner axis)

1200,0

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1300,0

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1450,0

0,00 0,20 0,40 0,60 0,80

furnace axis (x/L)

T

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flox 1250Cflame 1250C

NOx emissions in flue gas

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flameMILD

Temperatureprofiles

NOxemissions

Flameless combustion:some experimental evidences

From the microscopic point of view

In flame we have high gradientsof temperature andconcentration of species(reactants + products ofcombustion)

In flameless mode we can observethe general smoothing of thesequantities

Temperature profiles

fuel gas

preheated air1000 C

FL592B-E

preheated air1000 C

furnace wall

air jet

flue gas

reaction zone

fuel gas

(( (((

(( (((

Traditional

Staged burner

Flameless combustion is obtained:Increasing the entrainment of combustion products .the effects are;Great temperature uniformity

Reduced production of thermal NOx

Limited recirculation (Kv < 1)

Flameless combustion: practical realization

enhanced recirculation (Kv > 3)

How we can realizeFlameless Combustion in GT burner ?

Trapped Vortex Combustion Strategy can be a solution for FlamelessCreate a stable vortex system in a cavity,where fuel and oxidant are injected, mixed and burn with minimum pressure drop

The anchorage of the flame is assured by recirculation of hot combustion products

First cavity Second cavity

Component Volumefraction [%]

H2 40

CH4 9

CO 15

CO2 35

N2 1

Dati

Temperature + velocity maps

Temperature map

CFD simulationsof Syngas combustionin a TV burnerFlameless combustionis stable and anchoredin the first cavity

FLOX Turbogas combustor CFD simulation

CO Mole Fraction

Temperature

A conceptual design, proposed by DLR and WS (Ge)

TV Burner exp. tests

Trapped Vortex seemsto represent a real possibilityto realize Flameless Combustionin Gas Turbines

Thank youfor yorattention !

Syngas and Hydrogen Combustion in GTFlammability limits: temperature effectFlameless CombustionFlameless combustion with oil: an evidence Comparison between Flame and Flameless combustionFlameless combustion: some experimental evidences Flameless combustion: practical realization FLOX Turbogas combustor CFD simulation

Documents

Syngas and hydrogen combustion in GT