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Introduction

Carbon dioxide emissions are produced when carbon-based fuels are burned. National emissions estimates are based on the amounts of fuels used and on the carbon content of fuels.

Fuel combustion is widely dispersed throughout most activities in national economies and a complete record of the quantities of each fuel type consumed in each end-use activity is a considerable task, which some countries have not undertaken. Fortunately, it is possible to obtain a relatively accurate estimate of national CO2 emissions by accounting for the carbon in fuels supplied to the economy. The supply of fuels is simple to record and the statistics are more likely to be available in many countries.

In accounting for fuels supplied14 it is important to distinguish between primary fuels (i.e. fuels which are found in nature such as coal, crude oil, natural gas), and secondary fuels or fuel products, such as gasoline and lubricants, which are derived from primary fuels.

Accounting for carbon is based mainly on the supply of primary fuels and the net quantities of secondary fuels brought into the country.

To calculate supply of fuels to the country necessitates the following data for each fuel and year chosen:

• the amounts of primary fuels produced (production of secondary fuels is excluded);

• the amounts of primary and secondary fuels imported;

• the amounts of primary and secondary fuels exported;

• the amounts of fuel used for international marine bunkers and international aviation (hereafter referred to as bunkers);

• the net increases or decreases in stocks of the fuels.

For each fuel, the production (where appropriate) and imports are added together and the exports, bunkers, and stock changes are subtracted to calculate the apparent consumption of the fuels. In cases where exports of secondary fuels exceed imports or stock increases exceed net imports, negative numbers will result.

The manufacture of secondary fuels is ignored in the main calculation, as the carbon in these fuels has already been accounted for in the supply of primary fuels from which they are derived. However, information on production of some secondary fuel products is required to adjust for carbon stored in these products.

Three other important points influence the accounting methodology:

14. The following discussion excludes all non-carbon energy sources such as nuclear, hydro, geothermal, solar, etc.

• Stored carbon

Not all fuel supplied to an economy is burned for heat energy. Some is used as a raw material (or feedstock) for manufacture of products such as plastics or in a non-energy use (e.g. bitumen for road construction), without oxidation (emissions) of the carbon. This is called stored carbon, and is deducted from the carbon emissions calculation. Estimation of the stored carbon requires data for fuel use by activities using the fuel as raw material.

• International bunker fuels

The procedures given for calculating emissions ensure that emissions from the use of fuels for international marine and air transport are excluded from national emissions totals. However, for information purposes, the quantities and types of fuels delivered and the corresponding emissions from international marine bunkers and international aviation should be separately reported.

• Biomass fuels

In the IPCC methodology, biomass fuels are not included in the CO2 emissions from fuel combustion and are only shown for informational purposes. This is because for CO2 emissions, biomass consumption for fuel is assumed to equal its regrowth. Any departures from this hypothesis are counted within the land use, land use change and forestry module of the 1996 IPCC Guidelines. For this reason, emissions from the burning of biomass for energy are not included in the CO2 emissions from fuel combustion in this publication.

Methodology

The IPCC methodology breaks the calculation of carbon dioxide emissions from fuel combustion into six steps:

Step 1: Estimate apparent fuel consumption in original units

Step 2: Convert to a common energy unit

Step 3: Multiply by emission factors to compute the carbon content

Step 4: Compute carbon stored

Step 5: Correct for carbon unoxidised

Step 6: Convert carbon oxidised to CO2 emissions

Completing Worksheet 1

This section is from the Workbook of the 1996 IPCC Guidelines and provides step-by-step instructions for calculating emissions at the detailed fuels and fuel products level. Worksheet 1 can be consulted at the end of this chapter.

NOTE: The main worksheet allows CO2 emissions from biomass fuels to be calculated but it does not include them in the national total.

1 Apparent consumption is the basis for calculating the carbon supply for the country. To calculate apparent consumption (or total fuel supplied) for each fuel, the following data for primary fuels are entered:

• International bunkers (Column D)

For secondary fuels and products, the only figures entered are:

• International bunkers (Column D)

These allow the overall calculation to account for all consumption.

Amounts of all fuels can be expressed in joules (J), megajoules (MJ), gigajoules (GJ), terajoules (TJ) or thousands of tonnes of oil equivalent (ktoe). Solid or liquid fuels can be expressed as thousands of tonnes (kt) and dry natural gas can be expressed as tera-calories (Tcal) or cubic metres (m ).

NOTE: The figure for production of natural gas, used in Worksheet 1, does not include quantities of gas vented, flared or re-injected into the well.

Quantities are expressed in terms of the net calorific values (NCV) of the fuels concerned. NCV is sometimes referred to as the lower heating value (LHV). NCVs are approximately 95% of the gross calorific value (GCV) for liquid fossil, solid fossil and biomass fuels, and 90% of the GCV for natural gas.

2 Apparent consumption is calculated for each fuel using this formula:

Apparent consumption =

Production + Imports - Exports - International bunkers - Stock change

The results are entered in Column F.

Particular attention is given to the algebraic sign of "stock change" as it is entered in Column E. When more fuel is added to stock than is taken from it during the year there is a net stock build and the quantity is entered in Column E with a plus sign. In the converse case (a stock draw) the quantity is entered in Column E with a minus sign.

Step 2 Converting to a common energy unit (TJ)

1 The conversion factor used for each fuel is entered in Column G.

2 The Apparent consumption is multiplied by the relevant conversion factor (NCV or scaling factor) to give apparent consumption in terajoules. The result is entered in Column H.

Table 1 Conversion Factors

Unit

Conversion factor

J, MJ or GJ

Number is divided by the appropriate factor, 1012, 106 or 103 respectively, to convert to TJ.

106 toe

Number is multiplied by the conversion factor, 41868 TJ/106 toe, to convert to TJ.

Tcal

Number is multiplied by the conversion factor, 4.1868 TJ/Tcal.

103 t

The net calorific value of each fuel is used (see Table 2).

Step 1 Estimating apparent fuel consumption

TABLE 2

SELECTED NET CALORIFIC VALUES

Factors (TJ/103 tonnes)

Refined petroleum products

Gasoline

44.8Ü

Jet kerosene

44.59

Other kerosene

44.75

Shale oil

36.ÜÜ

Gas/diesel oil

43.33

Residual fuel oil

4Ü.19

LPG

47.31

Ethane

47.49

Naphtha

45.Ü1

Bitumen

4Ü.19

Lubricants

4Ü.19

Petroleum coke

31.ÜÜ

Refinery feedstocks

44.8Ü

Refinery gas

48.15

Other oil products

4Ü.19

Other products

Coal oils and tars derived from coking coals

28.ÜÜ

Oil shale

9.4Ü

Orimulsion

27.5Ü

NOTE: When converting from 103 t, for anthracite, coking coal, other bituminous coal, sub-bituminous coal and lignite, separate country-specific net calorific values are used for production (Column A), imports (Column B), and exports (Column C). For these fuels, apparent consumption is calculated by converting production, imports, exports, and stock changes to TJ first. For international bunkers (Column D) and stock change (Column E), either a weighted average net calorific value or a factor appropriate to the dominant source of supply is used.

Step 3 Multiplying by carbon emission factors

1 The carbon emission factor (CEF) used to convert apparent consumption into carbon content is entered in Column I.

Table 3 shows the default values used in this publication.

Table 3

CARBON EMISSION FACTORS (CEF)

Fuel

Carbon emission factor (t C/TJ)

LIQUID FOSSIL

Primary fuels

Crude oil

2Ü.Ü

Orimulsion

22.Ü

Natural gas liquids

17.2

Secondary fuels/products

Gasoline

18.9

Jet kerosene

19.5

Other kerosene

19.6

Shale oil

2Ü.Ü

Gas/diesel oil

2Ü.2

Residual fuel oil

21.1

LPG

17.2

Ethane

16.8

Naphtha

(2Ü.Ü) (a)

Bitumen

22.Ü

Lubricants

(2Ü.Ü) (a)

Petroleum coke

27.5

Refinery feedstocks

(2Ü.Ü) (a)

Refinery gas

18.2 (b)

Other oil

(2Ü.Ü) (a)

SOLID FOSSIL

Primary fuels

Anthracite

26.8

Coking coal

25.8

Other bituminous coal

25.8

Sub-bituminous coal

26.2

Lignite

27.6

Oil shale

29.1

Peat

28.9

Secondary fuels/products

BKB & patent fuel

(25.8) (a)

Coke oven / gas coke

29.5

Coke oven gas

13.Ü (b)

Blast furnace gas

66.Ü (b)

GASEOUS FOSSIL

Natural gas (dry)

15.3

BIOMASS (c)

Solid biomass

29.9

Liquid biomass

(2Ü.Ü) (a)

Gas biomass

(3Ü.6) (a)

Notes to Table 3

(a) This value is a default value until a fuel specific CEF is determined. For gas biomass, the CEF is based on the assumption that 50% of the carbon in the biomass is converted to methane and 50% is emitted as CO2. The CO2 emissions from biogas should not be included in national inventories. If biogas is released and not combusted, 50% of the carbon content should be included as methane.

(b) For use in the sectoral calculations.

(c) Emissions from the use of biomass for fuel are not shown in this publication.

2 The apparent consumption in TJ (in Column H) is multiplied by the carbon emission factor (in Column I) to give the carbon content in tonnes of C. The result is entered in Column J.

3 The carbon content in tonnes C is divided by 103 to give gigagrammes of carbon. The result is entered in Column K.

1 Estimating fuel quantities

Bitumen and lubricants

Domestic production for bitumen and lubricants is added to the apparent consumption (shown in Column F of the main Worksheet 1) for these products and the sum is entered in Column A of Auxiliary Worksheet 1.

Coal oils and tars

For coking coal, the default assumption is that 6% of the carbon in coking coal consumed is converted to oils and tars. The apparent consumption for coking coal (from Worksheet 1, Column F) is multiplied by 0.06.

Starting with the 2006 edition, the IEA Secretariat has requested coal tar data on its annual coal questionnaire. In cases where this information has been provided, to be consistent with the 1996 IPCC Guidelines, 75% of the part reported as non-energy was considered to be stored and the default 6% of coking coal was not applied.

Natural gas, LPG, ethane, naphtha and gas/diesel oil

The amount of these fuels used as a feedstock for non-energy purposes is entered in Column A.

2 Converting to TJ

The appropriate conversion factors are inserted in Column B of Auxiliary Worksheet 1. The estimated fuel quantities (Column A) are multiplied by the relevant conversion factor to give the estimated fuel quantities in TJ. The result is entered in Column C.

3 Calculating carbon content

The estimated fuel quantities in TJ (Column C of Auxiliary Worksheet 1) are multiplied by the emission factor in tonnes of carbon per terajoule (Column D) to give the carbon content in tonnes of C (Column E). The figures are divided by 103 to express the amount as gigagrammes of carbon. The results are entered in Column F.

4 Calculating actual carbon stored

The carbon content (Column F of Auxiliary Worksheet 1) is multiplied by the fraction of carbon stored (Column G) to give the carbon stored. The result is entered in Column H.

When Auxiliary Worksheet 1 is completed

5 The values for carbon stored for the relevant fuels/ products are entered in Column L of the main Worksheet 1.

6 The values for carbon stored (Column L) are subtracted from carbon content (Column K) to give net carbon emissions. The results are entered in Column M.

Step 5 Correcting for carbon unoxidised

1 The values for fraction of carbon oxidised are entered in Column N of Worksheet 1. Table 4 provides information on typical values measured from various facilities and suggests global default values for solid, liquid and gaseous fuels.

2 Net carbon emissions (Column M) are multiplied by the fraction of carbon oxidised (Column N) and the results are entered in Column O, actual carbon emissions.

Table 4

FRACTION OF CARBON OXIDISED

Coal1

G.98

Oil and oil products

G.99

Gas

G.99S

Peat for electricity generation2

G.99

1 .This figure is a global average but varies for different types

of coal, and can be as low as G.91.

2.The fraction for peat used in households may be much lower.

Step 4 Calculating carbon stored

Step 6 Converting to CO2 emissions

1 Actual carbon emissions (Column O) are multiplied by 44/12 (which is the molecular weight ratio of CO2 to C) to find total carbon dioxide (CO2) emitted from fuel combustion. The results are entered in Column P.

2 The sum is total national emissions of carbon dioxide from fuel combustion. These are the numbers shown for total CO2 emissions from fuel combustion in this publication.

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