Choice of method for estimating CO2 emissions

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The common method for estimating CO2 emissions from incineration and open burning of waste is based on an estimate of the fossil carbon content in the waste combusted, multiplied by the oxidation factor, and converting the product (amount of fossil carbon oxidised) to CO2. The activity data are the waste inputs into the incinerator or the amount of waste open-burned, and the emission factors are based on the oxidised carbon content of the waste that is of fossil origin. Relevant data include the amount and composition of the waste, the dry matter content, the total carbon content, the fossil carbon fraction and the oxidation factor.

The following sections describe the tiers to be applied for the estimation of CO2 emissions from incineration and open burning of waste. The tiers differ to what extent the total amount of waste, the emission factors and parameters used are default (Tier 1), country-specific (Tier 2a, Tier 2b) or plant-specific (Tier 3).

The Tier 1 method is a simple method used when CO2 emissions from incineration/open burning are not a key category. Data on the amount of waste incinerated/open-burned are necessary2. Default data on characteristic parameters (such as dry matter content, carbon content and fossil carbon fraction) for different types of waste (MSW, sewage sludge, industrial waste and other waste such as hazardous and clinical waste) are provided in Table 5.2 in this chapter and Tables 2.3 to 2.6 in Section 2.3, on waste composition in Chapter 2 of this Volume. The calculation of the CO2 emissions is based on an estimate of the amount of waste (wet weight) incinerated or open-burned taking into account the dry matter content, the total carbon content, the fraction of fossil carbon and the oxidation factor. The method based on the total amount of waste combusted is outlined in Equation 5.1, and the method based on the MSW composition is given in Equation 5.2. It is preferable to apply Equation 5.2 for MSW, but if the required MSW data are not available, Equation 5.1 should be used instead.

Equation 5.1

CO2 emission estimate based on the total amount of waste combusted

CO2 Emissions = £ ( SW, • dmt • CFi • FCFi • OFi ) • 44/12

Where:

CO2 Emissions = CO2 emissions in inventory year, Gg/yr

SWi = total amount of solid waste of type i (wet weight) incinerated or open-burned, Gg/yr dmi = dry matter content in the waste (wet weight) incinerated or open-burned, (fraction)

CFi = fraction of carbon in the dry matter (total carbon content), (fraction)

FCFi = fraction of fossil carbon in the total carbon, (fraction)

OFi = oxidation factor, (fraction)

44/12 = conversion factor from C to CO2

i = type of waste incinerated/open-burned specified as follows:

MSW: municipal solid waste (if not estimated using Equation 5.2), ISW: industrial solid waste, SS: sewage sludge, HW: hazardous waste, CW: clinical waste, others (that must be specified)

If the activity data of wastes are available on a dry matter basis, which is preferable, the same equation can be applied without specifying the dry matter content and the wet weight separately. Also if a country has data on the fraction of fossil carbon in the dry matter, it does not need to provide Cf,- and FCF,- separately but instead it should combine them into one component.

For MSW, it is good practice to calculate the CO2 emissions on the basis of waste types/material (such as paper, wood, plastics) in the waste incinerated or open-burned as shown in Equation 5.2.

Equation 5.2

CO2 emission estimate based on the MSW composition

CO2 Emissions = MSW • £ (WF} • dm} • CF} • FCF} • OFj) • 44/12

Where:

CO2 Emissions = CO2 emissions in inventory year, Gg/yr

MSW = total amount of municipal solid waste as wet weight incinerated or open-burned, Gg/yr

WFj = fraction of waste type/material of component j in the MSW (as wet weight incinerated or open-burned)

dmj = dry matter content in the component j of the MSW incinerated or open-burned, (fraction) CFj = fraction of carbon in the dry matter (i.e., carbon content) of component j

The methodology is addressed under Section 5.3, Choice of Activity data, and Chapter 2, Waste Generation, Composition and Management.

FCFj = fraction of fossil carbon in the total carbon of component j OFj = oxidation factor, (fraction) 44/12 = conversion factor from C to CO2

j j = component of the MSW incinerated/open-burned such as paper/cardboard, textiles, food waste, wood, garden (yard) and park waste, disposable nappies, rubber and leather, plastics, metal, glass, other inert waste.

If data by waste type/material are not available, the default values for waste composition given in Section 2.3 Waste composition could be used.

If CO2 emissions from incineration and open burning of waste is a key category, it is good practice to apply a higher tier.

The Tier 2 method is based on country-specific data regarding waste generation, composition and management practices. Here, Equations 5.1 and 5.2 are also applied, as outlined for the Tier 1 method. It is good practice to use the Tier 2 method when CO2 emission from incineration and open burning of waste is a key category or when more detailed data are available or can be gathered.

Tier 2a requires the use of country-specific activity data on the waste composition and default data on other parameters for MSW (Equation 5.2). For other categories of waste, country-specific data on the amounts are required (Equation 5.1). Country-specific MSW composition, even if using default data on other parameters, will reduce uncertainties compared to the use of aggregated MSW statistics.

A Tier 2a method for open burning of waste could incorporate annual surveys on the amounts and the composition of waste burned by households, authorities and companies responsible for the waste management.

Tier 2b requires country-specific data on the amount of waste incinerated/open-burned by waste type (Equation 5.1) or MSW composition (Equation 5.2), dry matter content, carbon content, fossil carbon fraction and oxidation factor, in addition to country-specific waste composition data. If these data are available, an estimate according to Tier 2b will have lower uncertainty than Tier 2a.

A Tier 2b method for open burning of waste could incorporate annual and detailed surveys on the amounts and the composition of waste burned by households, authorities and companies responsible for the waste management described in Tier 2a, with a combined measurement programme for emission factors related to the practices of open burning in the country.

It is good practice to implement those measurement programmes in different periods of the year to allow consideration of all seasons since emission factors depend on the combustion conditions. For example, in some countries where there is a rainy season and open burning is practised, more waste is burned during the dry season because of better burning conditions. Under these circumstances emission factors may vary with season.

In any case, all country-specific methods, activity data and parameters used should be described and justified in a transparent manner. The documentation should include descriptions on any experimental procedures, measurements and analyses made as well as information on atmospheric parameters such as temperature, wind, and rainfall in the case of open burning.

The Tier 3 method utilises plant-specific data to estimate CO2 emissions from waste incineration. It is good practice at this tier level to consider parameters affecting both the fossil carbon content and the oxidation factor. Factors affecting the oxidation factor include:

• type of installation/technology: fixed bed, stoker, fuidised bed, kiln,

• operation mode: continuous, semi-continuous, batch type,

• size of the installation,

• parameters such as the carbon content in the ash.

The total fossil CO2 emissions from waste incineration are calculated as the sum of all plant-specific fossil CO2 emissions. It is good practice to include all waste types and the entire amount incinerated as well as all types of incinerators in the inventory. The estimation is done similarly as in the Tier 1 and Tier 2 methods and at the end, the CO2 emissions from all plants, installations and other subcategories are added up to estimate the total emissions from waste incineration in the country.

The decision tree in Figure 5.1 gives guidance on the choice of method. The choice will depend on the national circumstances and the availability of data. Management practices in the decision tree are related to incineration and open burning.

Figure 5.1 Decision Tree for CO2 emissions from incineration and open burning of waste

Figure 5.1 Decision Tree for CO2 emissions from incineration and open burning of waste

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

1. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

The following Table 5.1 gives an overview on Tier levels at which default values or country-specific data are to be applied for calculating CO2 emissions.

Table 5.1

Overview of data sources of different tier levels

Data sources

Tiers

Total waste amount (W)

Waste fraction (WF): % of each component mainly for MSW

Dry matter content (dm)

Carbon fraction (CF)

Fossil carbon fraction

(FCF)

Oxidation factor (OF)

management-

management-

management-

management-

management-

management-

specific

Tier 2b

country-specific

country-specific

country-specific

country-specific

default / country-specific

default / country-specific

Tier 2a

country-specific

country-specific

default

default

default

default

Tier 1

default / country-specific

default

default

default

default

default

5.2.1.4 CO2 EMISSIONS FROM INCINERATION OF FOSSIL LIQUID WASTE

Fossil liquid waste is here defined as industrial and municipal residues, based on mineral oil, natural gas or other fossil fuels. It includes waste formerly used as solvents and lubricants. It does not include wastewater, unless it is incinerated (e.g., because of a high solvent content). Biogenic liquid waste, e.g., waste oil from food processing, does not need to be accounted for, unless biogenic and fossil oil are mixed and a significant portion of its carbon is of fossil origin.

Fossil liquid waste is here considered as a specific type of waste, for which combustion is a common management practice. In some countries it is not incinerated together with solid waste (e.g., hazardous waste) but treated separately. Fossil liquid waste is in many cases not taken into account in the waste statistics, because in some countries they are not included as part of the main waste streams discussed in Section 5.2.1.1.

Fossil liquid waste is not taken into account in Section 5.2.1.1 to 5.2.1.3 because the equations are not applicable for this type of waste. Unless fossil liquid waste is included in other types of waste (e.g., industrial waste, hazardous waste), the emissions need to be calculated separately. Consistent with the reporting guidance, emissions from incineration of fossil liquid waste are reported in the Energy Volume when it is used for energy purposes.

CO2 emissions from incineration of fossil liquid waste can be estimated using Equation 5.3.

Equation 5.3

CO2 EMISSION FROM INCINERATION OF FOSSIL LIQUID WASTE

Where:

CO2 Emissions = CO2 emissions from incineration of fossil liquid waste, Gg ALi = amount of incinerated fossil liquid waste type i, Gg CLi = carbon content of fossil liquid waste lype i, (fraction)

OFj = oxidation factor for fossil liquid waste type i, (fraction) 44/12 = conversion factor from C to CO2

If the amount of fossil liquid waste is in terms of volume, this should be converted into mass using the density. If no information on the density of fossil liquid waste in the country is available, the default density provided can be used.

Three tiers to estimate the CO2 emissions from incineration of fossil liquid waste are described as:

Tier 1: The default values are provided in Table 5.2.

Tier 2: Country-specific data on amount of fossil liquid waste incinerated, carbon content and country-specific oxidation factor are required at this tier, for each type of fossil liquid waste.

Tier 3: Plant-specific data should be used if available. The required data are the same as for Tier 1 and Tier 2. Estimates should consider all plants incinerating fossil liquid waste as well as the total amount of fossil liquid waste incinerated.

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