INTERNATIONAL MARITIME ORGANIZATION
E
IMO
INTERSESSIONAL MEETING OF THE
GREENHOUSE GAS WORKING GROUP
1st session
Agenda item 3
GHG-WG 1/3/1
30 May 2008
ENGLISH ONLY
REVIEW OF THE CO2 OPERATIONAL INDEX
Review of Carbon to CO2 conversion factors
Submitted by International Association of Independent Tanker Owners (INTERTANKO)
SUMMARY
Executive summary:
This document reviews the relevant Carbon to CO2 conversion factors
for three main fuel types used by ships and compares the results with
the equivalent factors in MEPC/Circ.471
Strategic direction:
7.3
High-level action:
7.3.1
Planned output:
7.3.1.3
Action to be taken:
Paragraph 3
Related document:
MEPC/Circ.471
Introduction
1
This document is submitted in accordance with the Guidelines on the Organization and
method of work MSC-MEPC.1/Circ.1 and it suggests corrected values for the Carbon to
Carbon Dioxide (CO2) conversion factors for three main fuel group types used by ships.
2
The current values of Carbon to CO2 conversion factors used in the calculation of the
Vessel’s Operational Index are given in MEPC/Circ.471. They are referenced to the revised 1996
IPCC Guidelines for national GHG inventories. However, these values are “default” figures and
suggested for use when better data is not available. Therefore, INTERTANKO undertook a
review of the Carbon to CO2 conversion factors. The review, calculations and the suggested new
values of these factors are shown in the annex to this document. The review also indicates the
extent to which the new suggested values of Carbon to CO2 conversion factors differ from those
shown in the MEPC/Circ.471.
For reasons of economy, this document is printed in a limited number. Delegates are
kindly asked to bring their copies to meetings and not to request additional copies.
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GHG-WG 1/3/1
-2-
Action requested of the Intersessional Meeting
3
The intersessional meeting is invited to consider the corrected Carbon to CO2 factors
provided by this document and take action as appropriate.
***
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GHG-WG 1/3/1
ANNEX
Page 1
ANNEX
REVISION OF CARBON INDEX AND CO2 CONVERSION FACTORS
IN MEPC/CIRC.471
METHODOLOGY OF ASSESSMENT AND CALCULATION
The amount of CO2 emissions is calculated as a function of the amount of fuel used by ships and
as a function of the pure Carbon content in each fuel type. The bunker fuel oils used by ships are
Marine Diesel/Gas Oil (MDO/MGO), High Sulphur Fuel Oil (HSFO) and Low Sulphur Fuel Oil
(LSFO). The step wise methodology to calculate the Carbon to CO2 conversion factor is as per
MEPC/Circ.471 and is as follows:
Step 1 – Establish the mean molecular structure for the 3 fuel oils used by ship – The Carbon
content on each fuel type is determined to establish the mean molecular structure for each fuel
oil. These are presented in the Table 1 and are based upon reasonable and expert assessed mean
molecular size of the average hydrocarbon content appropriate to each fuel type. The calculations
assume that fuels contain only paraffins and contain no cyclic molecules whose hydrogen/carbon
ratios differ due to their unsaturated status.
Fuel type
MDO/MGO
HSFO/LSFO
Average Molecular structure
C18
C30
Table 1
Within the respective fuel oils, and CO2 as appropriate, the individual atoms and their molecular
weights are shown in Table 2, which are used throughout the calculations.
Hydrocarbon Atoms
Carbon
Hydrogen
Oxygen
Molecular Weight
12.011
1.0
15.9994
Table 2
Step 2 – Establish the Hydrocarbon content in each of the fuels – This is obtained indirectly by
assessing the non-hydrocarbon elements in these fuels (not containing atoms of carbon). The data
for each fuel type is shown in Table 3.
Percentage in fuel of non-Hydrocarbon elements
MDO/MGO
HSFO
LSFO
Component type
Sulphur Content
Ash and Metals
Water
Total non-Hydrocarbon elements
0.80%
0.01%
0.20%
1.01%
2.70%
0.15%
0.50%
3.35%
1.00%
0.15%
0.50%
1.65%
Hydrocarbon% (content in fuel)
98.99%
96.65%
98.35%
Table 3
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ANNEX
Page 2
Step 3 – Calculate the Carbon concentration (Carbon %) in the fuel – To determine the Carbon
concentration in the fuel one needs the three elements as given by the following formula:
molecular weight of Carbon content in the fuel
x Hydrocarbon %
average molecular weight of the Hydrocarbon in the fuel
The Hydrocarbon content in each fuel (Hydrocarbon %) is given in Table 3. The molecular
weight of the Carbon in the fuel is calculated with the formula:
Carbon % =
Cn = n x 12.011
where “n” is the number of Carbon atoms in the molecule (i.e. n = 18 for the MDO/MGO
and n = 30 for HSFO and LSFO – see Table 1). As an example for MDO/MGO:
C18 = 18 x 12.011 = 216.2
Based upon the standard chemical equation for paraffins of nCH(n + 2), the molecular weight of
the Hydrocarbon atoms in the fuel is calculated with the formula:
Cn = (n x 12.011) + (n x 2 + 2)
As an example, the Carbon concentration in MDO/MGO is:
Carbon % =
216.2
254.2
x 98.99% = 84.20%
Using the data for each fuel type, one can determine the Carbon concentration (Carbon %) in
each of the fuel type, as given in the Table 4:
MDO/MGO
(C18)
216.20
254.20
98.99%
84.20%
87.50%
Carbon molecular weight
Hydrocarbon average molecular weight
Hydrocarbon content in fuel
Carbon concentration in the fuel
carbon concentration in MEPC Circ. 471
HSFO
(C30)
360.33
422.33
96.65%
82.46%
85.00%
LSFO
(C30)
360.33
422.33
98.35%
83.91%
N/A
Table 4
Step 4 – Calculate the Carbon to CO2 factor (similar for all the individual fuel calculations) – The
Carbon to CO2 factor gives the amount of CO2 generated by one atom of carbon. It is calculated
by the following formula:
Carbon to CO2 factor =
molecular weight of the CO2
molecular weight of Carbon
The molecular weight of the CO2 is = molecular weight of the atom of Carbon + 2 x molecular
weight of the atom of oxygen = 12.011 + 2 x 15.9994 = 44.01
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ANNEX
Page 3
Therefore, the Carbon to CO2 factor is =
44.01
= 3.66
12.011
Step 5 – Calculate the Carbon to CO2 conversion factor for each fuel type. – The conversion
factor is derived by correcting the pure Carbon to CO2 factor for the concentration of Carbon in
each fuel type or:
Carbon to CO2 conversion factor = Carbon to CO2 factor for CO2
x Carbon %
For MDO/MGO the Carbon to CO2 Conversion factor = 3.66 x 0.842 = 3.082.
This means that there would be 3.082 tonnes of CO2 emitted for each tonne of MDO/MGO
fuel combusted.
The calculations run for each fuel type and the results are presented in the Table 5.
MDO/MGO
Carbon to CO2 conversion factor for CO2
Carbon concentration in the fuel
Carbon to CO2 conversion factor for a fuel
carbon concentration in MEPC/Circ. 471
84.20%
3.082
3.206
HSFO
3.66
82.46%
3.021
3.114
LSFO
83.91%
3.075
N/A
Table 5
Conclusion
INTERTANKO would suggest the following Carbon to CO2 conversion factors are used instead
of those now referred to in MEPC/Circ.471.
FUEL TYPE
Marine diesel and marine gas oils (MDO/MGO)
Low Sulphur Fuel Oils (LSFO)
High Sulphur Fuel Oils (HSFO)
Carbon to CO2 conversion factor
3.082
3.075
3.021
___________
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