L. Douglas Smoot & Robert E. Jackson

Combustion Resources, Inc

Provo, UT

Joseph D. Smith

Systems Analysis and Solutions, LLC

Owasso, OK

IFRC International Pacific RimCombustion Symposium

26-29 September 2010Maui, Hawaii 1

•

Environmental Protection Agency –

Mr. Brian Dickens -

Technical Discussions

–

Financial Support

•

Eastern Research Group, Inc.–

Mr. Paul Buellesbach

•

Technical Review–

Dr. Ahti

Suo-Att

ha

–

Mr. Larry Berg

•

Mr. Scott Smith, Zeeco–

Flare Photograph

2

•

Identify & Quantify Generalized Flare Performance Parameters for Allowing High Flare Combustion Efficiency–

Open, single-stage, steam-assisted flares

–

How do Vent LHV and Flare LHV affect flare performance?–

How much steam can be effectively added to reduce smoke?

–

For various fuels, purge gases

•

Apply Mass and Energy Balances

•

Approach Applicable to other Flare Systems3

4

•

Vent Gas =

•

Flare Gas = vent gas + pilot fuel/air + steam

•

Adiabatic Temperature = maximum temperature of a flare gas –

air mixture

•

Flammability Ratio = volume fraction of fuel in the flare gas –

air mixture (includes steam, purge gas)

•

Lower Heating Value = heat of combustion of a stoichiometric, fuel–air mixture with water vapor product 5

WasteFuel Gas

+ SupplementalFuel Gas

+ PurgeGas

•

Structural–

Diameter

–

Length •

Operational–

Flow Rates:

waste fuel

purge gassupplemental fuel

steam

pilot fuel/air

combustion air•

External–

Wind velocity, ambient air conditions

6

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛++

Δ=

S

S

P

P

F

F

FCFf

MWW

MWW

MWWVol

HWLHV)(

))(()(

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛++

Δ=

S

FS

P

FP

F

FC

MWWW

MWWW

MWVol

H)/()/(1)(

)(

(LHV)f

independent of mass flow rates, flare diameter and height(ΔHC

)F

near-constant for typical hydrocarbons (weight basis)

For small purge flow, value of steam/fuel to maintain (LHV)f

⎟⎠⎞

⎜⎝⎛=⎥

⎦

⎤⎢⎣

⎡−

Δ=⎟⎟

⎠

⎞⎜⎜⎝

⎛≈⎥

⎦

⎤⎢⎣

⎡+ VG

SMWMW

VolLHVMWH

WW

WWW

F

S

F

SCF

F

S

PF

S

)(

Increasing purge flow adds to supplemental fuel requirement 7

Kanary, GlassmanFuel Mol. Weight LHV kcal/g Stoich

vol. % Lean Flam Limit, % stoich. (avg

= 54)

Benzene 78.1 9.56 0.0277 48

1, 3-Butadiene 54.1 10.87 0.0366 54

n-Butane 58.1 10.92 0.0312 58

2-Butene 56.1 10.82 0.0377 53

Cyclohexane 84.2 10.47 0.0227 57

Cyclopentane 70.1 10.56 0.0271 55

n-Decane 142.3 10.56 0.0133 56

Ethane 30.1 11.34 0.0564 53

n-Heptane 100.2 10.62 0.0187 56

n-Hexane 86.2 10.69 0.0216 56

Kerosene 154.0 10.30 --- 53

Methane 16.0 11.95 0.0947 58

n-Nonane 128.3 10.67 0.0147 58

n-Octane 114.2 10.70 0.0165 58

n-Pentane 72.1 10.82 0.0255 55

l-Pentene 70.1 10.75 0.0271 42

Propane 44.1 11.07 0.0402 51

Propene 42.1 10.94 0.0444 54

Toluene 92.1 9.78 0.0227 53

xylene 106.0 10.30 --- 56

Gasoline 73 octane 120.0 10.54 --- ---8

Fuels MethanePropaneButadienen-octane

Purge Gas Mass Flow Rate3 levels

Steam/Vent Gas1, 2.5, 4

Flare Gas LHV50 –

400

9

(Tad

, LHVflare

, LHVvent

, FR)

0

500

1000

1500

2000

2500

3000

3500

4000

0 50 100 150 200 250 300 350 400 450 500

Flare Gas Lower Heating Value (BTU/scf)

Add

iaba

tic F

lam

e Te

mpe

ratu

re (F

)

MethanePropeneButadienen-OctaneLog (all data)

R2 = 0.9816

Flare Gas Lower Heating Value (BTU/scf)

Adi

abat

ic F

lam

e Te

mpe

ratu

re (F

)

10

Purge Gas (1, 2, 3X), Steam/Vent Gas (1, 2, 3)

0

500

1000

1500

2000

2500

3000

3500

4000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Vent Gas Lower Heating Value (BTU/scf)

Add

iaba

tic F

lam

e Te

mpe

ratu

re (F

)

MethanePropeneButadienen-Octane

Vent Gas Lower Heating Value (BTU/scf)

Adi

abat

ic F

lam

e Te

mpe

ratu

re (F

)

11

)]/()/[()]/()/()/[()/()(

PPFF

SSPPFFFv MWWMWW

MWWMWWMWWLHVLHV+

++=

•

Required Vent (LHVv

) Heating Values always greater than flare LHVF

• With no steam, values equal

• Flare temperature does not correlate with vent LHV

12

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Steam/Vent Gas Ratio

Fuel

Flo

w (l

bm/h

r)

MethanePropeneButadienen-Octane

Steam/Vent Gas Ratio

Req

uire

d Fu

el F

low

(lbm

/hr)

13

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300 350 400 450

Flare Gas Lower Heating Value (BTU/scf)

Lim

iting

Ste

am/V

ent G

as R

atio

MethanePropeneButadienen-Octane

Flare Gas Lower Heating Value (BTU/scf)

Max

imum

Ste

am/V

ent G

as R

atio

14

(Without Purge Gas)

•

Fuel –

Air OnlyFuel/(Fuel + Air) = Stoichiometric Ratio

•

Flare Gas –

Air (Combustion Zone Gas)Fuel/(Flare Gas + Air) = Flammability Ratio (FR)m

•

FRm

includes inert diluentsPurge GasCarbon Dioxide (from pilot fuel/air)Steam

15

16

17

Adi

abat

ic F

lam

e Te

mpe

ratu

re (F

)

Mixture Flammability Ratio FRm

For Steam-assisted Flares:•

Flare Operating criteria established via application of mass and

energy balances and hydrocarbon flammability limits

–

Recommended standards not dependant on stack diameter or capacity

–

Flare gas lower heating value (LHV)f

appropriate energy standard for setting flare gas energy level (correlates with adiabatic flame temperature, Tad

)–

Vent gas heating value (LHVg) not appropriate energy standard (low correlation to T

ad)–

Minimum LHVf

(ca. 200 Btu/ft3) required to maintain efficient combustion above lean flammability limit

–

LHVf

values above ~300 Btu/ft3

restrict steam use, S/V mass ratio < 2–

Appears to be a “Maximum Steam/Vent mass ratio”

based on LHVf

–

Fuel requirements to maintain flare gas LHV reach extreme levels

for steam rates above S/V ~ 3/1

–

With negligible purge rate, maximum steam rate can be calculated

directly to maintain LHVf

≥

200 Btu/ft3

•

Recommended Standards for Steam-assisted flares–

200 ≤ LHV(flare gas) ≤ 300 Btu/ft3

– (S/V)max ≤ 3 18

•

Currently, these standards are only applicable to steam- assisted flares

•

Only apply to hydrocarbon fuels (not hydrogen, acetone, ammonia, alcohols)

•

These do not guarantee high combustion/destruction efficiency

•

Applicable to “similar”

waste and supplemental fuels•

Considers “inert”

purge gas

•

Correlation of flare combustion efficiency data required to to establish flare standards

•

Fuel tendencies of soot formation not considered

Generalized Application of this method can reduce or eliminate limitations!

20

Recent Flare Test Data

•

Work by EPA with John Zink and Marathon illustrate applicability of these methods

•

Next few slides were taken from a recent report issued by Marathon Oil Company

Draft -

Enforcement Confidential

Comparison of Recent data t Pohl’s data for 97-98% Combustion Efficiency Points

ED

A11B

A19

MPC TxCity

9/09

Combining Recent Marathon Data with earlier Pohl Data, is there an equation which relates “Exit velocity”

to “Flare Gas

Heating value”

for Combustion Efficiency > 98%?

Pohl & MPC Data

y = 326.2x0.1635

0

100

200

300

400

500

600

700

800

0.1 1 10 100

Exit Velocity (ft/s)

Hea

ting

Valu

e (B

TU/s

cf)

Series1

Pow er (Series1)

What about Flare Flame Shape as effected by wind and Combustion Efficiency?