Predicting Greenhouse Gas Emissions From Flares - SCS Global ...

Predicting Greenhouse Gas
Emissions from Flares
Matthew Johnson, Ph.D., P.Eng.
Mechanical & Aerospace Engineering
Carleton University

Flaring in Alberta
• Although there have been significant reductions
in previous years, in 2003, 1.4 billion m 3 of gas
were flared or vented in Alberta
(843 million m 3 of solution gas)
(AEUB, ST60B, 2004)

Greenhouse Gas Emissions
• Worldwide an estimated 76 billion m 3 of gas
were flared or vented in 2002
• Significant source of CO 2
equivalent emissions

Project Objective
• Develop a research backed protocol for
estimating greenhouse gas (CO 2 equivalent
emissions) from solution gas flares
– Extend results of previous windtunnel based research
with large parametric data set
– Continue to evolve and improve parametric efficiency
model
• Project is possible because data base of fully-
controlled, parametric experiments exists!

Previous Work
• Research focussed on carbon conversion
efficiency
Mass of Carbon Converted to CO2
η =
Mass of Carbon Originally as Fuel
• Significant progress in quantifying efficiencies of
non-sooting flares under a range of conditions
– Crosswind, Diameter, Exit Velocity, Basic fuel
composition (sweet), Diluent content

Previous Work
• Fuel stripping mechanism identified responsible
for emissions of raw flare gas
• Semi-empirical empirical flare efficiency model developed
(Johnson & Kostiuk, P. Comb. Inst. 2002) and
verified at full scale
⎡
3
LHV mass
= A⋅
exp⎢B
⎢⎣
( ) ( )
1 −η
⋅
∞
⎤
( d )
1/ 3
⎥ ⎥ j o ⎦
gV
U

Efficiency
Model
• Correlation
effectively collapses
widely varied data
(1-η)(LHV mass ) 3 (MJ/kg) 3
• Data includes
n.g. + CO 2
n.g. + N 2
C 3 H 8 + CO 2
C 3 H 8 + N 2
C 2 H 6 + N 2
2 ≤ U ∞ ≤ 17 m/s
0.5 ≤ V j ≤ 4 m/s
12.2 ≤ d o ≤ 49 mm
25000
20000
15000
10000
5000
0
Natural gas based fuel
Propane based fuel
Ethane based fuel
(0.317 X)
Y = 156.4 e
(0.272 X)
Y = 32.06 e
LHVmassCorr-Qorf-2-UgVD13.GRF
0 5 10 15 20 25
U ∞ / (g V j d o ) 1/3

Greenhouse Gases (GHG)
• Kyoto Accord specifically names six gases /
types of gases that contribute to global warming
– carbon dioxide (CO 2 );
– methane (CH 4 );
– nitrous oxide (N 2 O);
– hydrofluorocarbons (HFCs);
– perfluorocarbons (PFCs); and
– sulphur hexafluoride (SF 6 ).
• Climate forcing also occurs from other
substances not yet named in the Kyoto Accord

GHGs Relevant for Flare Emissions
• Principle contributors are carbon dioxide and
methane
• Other species may be relevant based on IPCC
data but do not have accepted GWP values and
are not included in Kyoto Accord:
– CO and particulate matter (Direct climate forcing)
– NOx and SO 2 (Indirect climate forcing)
• In line with Kyoto, consider CO 2 and CH 4 only

Global Warming Potentials (GWPs(
GWPs)
• Relative measure of climate forcing of 1kg of
substance compared to 1kg of CO 2
– Usually defined on a 100 year time horizon
– Established by Intergovernmental Panel on Climate
Change (IPCC)
– Used to make GHG calculations on a CO 2 equivalent
basis
Gas
Lifetime
(years)
Global Warming Potential
(Time horizon in years)
20 yrs 100 yrs 500 yrs
Carbon dioxide CO 2
1 1 1
Methane CH 4
12.0 62 23 7

GHG Calculation Methodology
• First calculate instantaneous rate of CO 2 and
CH 4 emissions
– Must accurately determine split, γ, , between CO and
unburned fuel in emissions
– Existing efficiency model does not provide this
information
– Major part of ongoing work is to develop better
model for this split, γ
– However, data suggest CO is much less important
and γ =0.1 is a reasonable estimate for now

GHG Calculation Methodology
• Calculation of instantaneous GHG emission
1. Given fuel composition and operational parameters
(flare diameter, exit velocity, wind speed), use
parametric model to calculate efficiency (η)(
2. Use fuel composition and modeled CO/fuel split
parameter (γ)(
) to find mass emission rate of CH 4 and
CO
3. Use IPCC global warming potential values to
calculate instantaneous GHG emission
m& equiv
= GWP ⋅m&
+ m&
GHG
CH
4 CH4
CO2

GHG Calculation Methodology
• Must convert instantaneous GHG emission
calculated at one wind speed value to
meaningful “average” value
• Concept of “Yearly Averaged Efficiency” and
“Yearly Averaged GHG Equivalent Emission”
– Possible to develop using parametric data set and
efficiency model

Yearly Averaged Efficiency
• Statistical weighted average of efficiency taking
into account widely varying wind conditions
• Provides convenient and meaningful measure of
flare efficiency
where
η =
∞
∫
0
P( U ) η(
U ) dU
∞
P(U ∞ ) = probability distribution
function of wind speed
U ∞ = wind speed
η(U ∞ ) = efficiency of flare as
function of wind speed
∞
∞

Yearly Averaged Efficiency
Relative Frequency
0.30
0.25
0.20
0.15
0.10
0.05
Environment Canada
Hourly Averaged Wind Speed Data
for Edmonton International Airport
(1984-1988)
(1-η)(LHV mass ) 3 (MJ/kg) 3
25000
20000
15000
10000
5000
12.1 mm ≤ do ≤ 49.8 mm
Natural Gas + CO 2 or N 2
Y = 146.5 e (0.1745 X)
0.00
E:\IR-YEG84-88HAVG.GRF
0
LHVmassCorr-NG-Qorf-2-Dia-UgV13D12.GRF
0 2 4 6 8 10 12 14 16 18 20
Hourly Averaged Wind Speed (m/s)
0 5 10 15 20 25 30 35
U ∞ / [(gV j ) 1/3 (d o 1/2 )] (m -1/6 )

Sample GHG Prediction
Calculations

Scenario #1: Mean Solution Gas Flare
• Operating Parameters:
– Q = 246,900 m 3 /yr
– D = 4 inch
– Flare Gas = 95 % Methane, 5 % CO 2
– LHV = 32.2 MJ/m 3
– Flare location: Edmonton (Airport weather data)
• Yearly Averaged Efficiency: 99.4 %
• Annual CO 2 equivalent GHG emission: 477 tonnes

Scenario #2: “Low BTU” Solution
• Operating Parameters:
Gas Flare
– Q = 246,900 m 3 /yr
– D = 4 inch
– Gas = 50 % Methane, 50 % CO 2
– LHV = 16.9 MJ/m 3
– Flare location: Edmonton (Airport weather data)
• Yearly Averaged Efficiency: 78.9 %
• Annual CO 2 equivalent GHG emission: 778 tonnes

Scenario #3: Variable Composition
• Mean Volume
Solution Gas
Flare
Q = 246,900 m 3 /yr
D = 4 inch
Gas = CH 4 / CO 2
Edmonton Airport
weather data
Yearly Averaged Efficiency (%)
100
90
80
70
60
50
246,900 m 3 /yr
4" Diameter Flare
YEG Wind Data
1200
1000
800
600
CO 2 Equivalent GHG Emissions (tonnes)
40
FlareGHGCalc-FuelComp.grf
400
0.4 0.5 0.6 0.7 0.8 0.9 1
CH 4 Fraction in Fuel

Scenario #4: Adding CH 4 to
Mitigate GHG
• Mean Volume
Solution Gas
Flare
Trends vs.
added CH 4
Starting Point:
Q = 246,900 m 3 /yr
D = 4 inch
LHV = 13.55 MJ/m 3
Gas = 0.4 CH 4
, 0.6 CO 2
Yearly Averaged Efficiency (%)
100
90
80
70
60
50
40
Adding CH4 to
raw flare gas
4" Diameter Flare
YEG Wind Data
FlareGHGCalc-AddFuel.grf
0 50000 100000 150000 200000 250000
Added CH 4 (m 3 /year)
1150
1100
1050
1000
950
900
850
CO 2 Equivalent GHG Emissions (tonnes)

Scenario #4: Adding CH 4 to
Mitigate GHG
• Mean Volume
Solution Gas
Flare
Trends vs.
Heating Value of
Flare Gas
Starting Point:
Q = 246,900 m 3 /yr
D = 4 inch
LHV = 13.55 MJ/m 3
Gas = 0.4 CH 4
, 0.6 CO 2
Yearly Averaged Efficiency (%)
100
90
80
70
60
50
40
Adding CH 4 to
raw flare gas
4" Diameter Flare
YEG Wind Data
FlareGHGCalc-AddFuel-LHV.grf
12 16 20 24
Lower Heating Value of Flare Gas (MJ/m 3 )
1150
1100
1050
1000
950
900
850
CO 2 Equivalent GHG Emissions (tonnes)

Conclusions
• It is now possible to define and estimate a
yearly averaged efficiency for a solution gas
flare
– Combines statistical wind speed data with parametric
efficiency model
– Provides a meaningful and rigorous way of assessing
flare performance
– Demonstrates utility of controlled parametric
experiments and modelling

Conclusions
• Outlined preliminary approach to calculate yearly
averaged greenhouse gas equivalent emissions
– Requires more work to accurately segregate CO / CH 4
before being ready for widespread use
– Very useful method for predicting CO 2 equivalent
emissions
– Will permit engineering calculation of “what-if”
scenarios for GHG management and mitigation

Funding Partners