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addressing uncertainty in oil and natural gas industry greenhouse

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Comb<strong>in</strong><strong>in</strong>g the fuel usage for the two diesel fired equipment, the total <strong>uncerta<strong>in</strong>ty</strong> <strong>in</strong> the diesel fir<strong>in</strong>g rate<br />

is calculated by apply<strong>in</strong>g Equation 4-4 <strong>and</strong> us<strong>in</strong>g the absolute <strong>uncerta<strong>in</strong>ty</strong> values.<br />

U ( abs) = (U( abs) +U( abs)<br />

2 2<br />

Diesal Fir<strong>in</strong>g Rate Generator Pump<br />

U abs = × × + × × = × Btu yr<br />

6 2 6 2 6<br />

( )<br />

Diesal Fir<strong>in</strong>g Rate<br />

(0.123 2912 10 ) (0.235 77.7 10 ) 356.85 10 /<br />

6<br />

356.85×10 Btu/yr<br />

6<br />

2989.7×10 Btu/yr<br />

( )<br />

Urel ( ) = 100%× = ± 11.9% Btu/yr<br />

Uncerta<strong>in</strong>ty Estimate of CO 2 Emissions from Diesel Combustion:<br />

E<br />

2,989.7×<br />

10 Btu<br />

year<br />

0.0732 tonnes CO<br />

10 Btu<br />

6<br />

2<br />

CO<br />

= × =<br />

2<br />

6<br />

2<br />

219 tonnes CO / yr<br />

The <strong>uncerta<strong>in</strong>ty</strong> <strong>in</strong> the emissions factor is determ<strong>in</strong>ed by eng<strong>in</strong>eer<strong>in</strong>g judgment to be 10%. The total<br />

<strong>uncerta<strong>in</strong>ty</strong> for the CO 2 emissions is then is calculated by apply<strong>in</strong>g Equation 4-6 <strong>and</strong> us<strong>in</strong>g the relative<br />

<strong>uncerta<strong>in</strong>ty</strong> values.<br />

2<br />

( )<br />

U ( rel) = U( rel) +U( rel ) = 11.9 + 10.0 =± 15.6% tonnes CO /yr<br />

2 2 2 2<br />

CO AF EF 2<br />

F.3 Uncerta<strong>in</strong>ty <strong>in</strong> Stationary Combustion Devices – CH 4 , N 2 O, <strong>and</strong> CO 2 e Emissions<br />

In this hypothetical example, CH 4 <strong>and</strong> N 2 O emissions from combustion are calculated us<strong>in</strong>g the fuel-based<br />

emission factors presented <strong>in</strong> the API Compendium. The calculations for CH 4 <strong>and</strong> N 2 O emissions from<br />

combustion are repr<strong>in</strong>ted directly from the API Compendium. Some <strong>uncerta<strong>in</strong>ty</strong> values were assigned as<br />

follows:<br />

• Fuel Consumption for B<strong>oil</strong>ers = ±15% (assigned by expert judgment).<br />

• Heat<strong>in</strong>g Value of Gas Combusted = ±4% (measured <strong>in</strong>dependent of <strong>gas</strong> composition; assigned by<br />

expert judgment here).<br />

• Gas Composition measurement = ±4% (determ<strong>in</strong>ed by analysis of repeat samples us<strong>in</strong>g<br />

techniques from Section 4; assigned by expert judgment here).<br />

• The <strong>uncerta<strong>in</strong>ty</strong> <strong>in</strong> the emissions factor for N 2 O is determ<strong>in</strong>ed by eng<strong>in</strong>eer<strong>in</strong>g judgment to be<br />

+150%,–100%. The <strong>uncerta<strong>in</strong>ty</strong> <strong>in</strong> the emissions factor for methane is 25% based on expert<br />

judgment.<br />

Uncerta<strong>in</strong>ty Estimate of CH 4 <strong>and</strong> N 2 O Emissions from B<strong>oil</strong>ers <strong>and</strong> Heater/Reb<strong>oil</strong>ers:<br />

Natural <strong>gas</strong> emission factors for CH 4 <strong>and</strong> N 2 O are based on the energy consumed by the equipment. This<br />

differs from the CO 2 emission estimates above, which were based on the volume of <strong>natural</strong> <strong>gas</strong> consumed.<br />

So, the fuel usage <strong>in</strong>formation from Table F-2 must first be converted to an energy <strong>in</strong>put basis.<br />

Pilot Version, September 2009 F-7

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