Friday, January 23, 2009

Emission Factors

Over the last few years I have performed a lot of emission calculations and have found it frustrating that I had to spend hours searching for emission factors. I recently decided to compile a few short tables and carry them with me on a USB stick for easy access. Here they are. All the values can be found on the IPCC’s EFDB site or through a search engine. Different sources may have different values, but they should not be too far off. I cannot recall and reference all the websites I have used, but if I remember correctly, the values are from the late 90’s and early 2000’s. Since I have to do some editing and don’t have much time, I will break up the factors into a couple of posts.

Using the tables

CO2 = (Amount of fuel used) * (Calorific Value) * (Carbon Content) * (Oxidation) * 3.66

Oxidation values are usually given in percentages and are around 98% to 100%. I usually use 99% to be safe. 3.66 comes from the ratio of Carbon to Oxygen in CO2. If you do not understand why you need 3.66, try doing a line calculation and write out all the units. You are calculating the emission with respect to carbon, but don’t forget that you are emitting CO2 and not just C. Chances are you have come across simple conversion factors which take you from Fuel Used to CO2 emitted. The above calculation takes into account a few more factors and may vary slightly from the simple conversion factors. When doing the calculation remember to keep in mind the units.

Calorific Values, Natural gas-based fuels

Fuel

(GJ/kg)

(MMBTU/lb)

Natural Gas

0.051

0.022

Methane

0.0556

0.0239

Ethane

0.0519

0.0223

Propane

0.0504

0.0217

Butane

0.0495

0.0213

Isobutane

0.0495

0.0213

n-Butane

0.0494

0.0213

LNG

0.052

0.022

Carbon Content, Natural gas-based fuels

Fuel

(kg C/GJ)

(Thousand BTU/lb)

Natural Gas

14

33

Methane

13.5

31.3

Ethane

15.4

35.8

Propane

16.2

37.7

Butane

16.7

38.9

Isobutane

16.7

38.9

n-Butane

16.8

38.9

LNG

16

38

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