Choice of method for estimating CH4 emissions

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CH4 emissions from incineration and open burning of waste are a result of incomplete combustion. Important factors affecting the emissions are temperature, residence time, and air ratio (i.e., air volume in relation to the waste amount). The CH4 emissions are particularly relevant for open burning, where a large fraction of carbon in the waste is not oxidised. The conditions can vary much, as waste is a very heterogeneous and a low quality fuel with variations in its calorific value.

In large and well-functioning incinerators, CH4 emissions are usually very small. It is good practice to apply the CH4 emission factors provided in Chapter 2, Stationary Combustion, of Volume 2.

Methane can also be generated in the waste bunker of incinerators if there are low oxygen levels and subsequent anaerobic processes in the waste bunker. This is only the case where wastes are wet, stored for long periods and not well agitated. Where the storage area gases are fed into the air supply of the incineration chamber, they will be incinerated and emissions will be reduced to insignificant levels (BREF, 2005).

Figure 5.2 shows the decision tree for CH4 and N2O emissions from the incineration and open burning of waste.

Figure 5.2 Decision Tree for CH4 and N2O emissions from incineration/open-burning of waste

Figure 5.2 Decision Tree for CH4 and N2O emissions from incineration/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.

2. The Tier 1 and Tier 2 methods follow the same approach but differ to the extent country-specific data are applied.

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.

2. The Tier 1 and Tier 2 methods follow the same approach but differ to the extent country-specific data are applied.

The calculation of CH4 emissions is based on the amount of waste incinerated/open-burned and on the related emission factor as shown in Equation 5.4.

Equation 5.4

CH4 emission estimate based on the total amount of waste combusted

Where:

CH4 Emissions = CH4 emissions in inventory year, Gg/yr

IWi

= amount of solid waste of type i incinerated or open-burned, Gg/yr

EFi

= aggregate CH4 emission factor, kg CH4/Gg of waste

10-6

= conversion factor from kilogram to gigagram

i

= category or type of waste incinerated/open-burned, specified as follows:

MSW: municipal solid waste, ISW: industrial solid waste, HW: hazardous waste,

CW: clinical waste, SS: sewage sludge, others (that must be specified)

The amount and composition of waste should be consistent with the activity data used for estimating CO2 emissions from incineration/open burning.

Default emission factors are provided under Section 5.4.2, CH4 emission factors, for incineration and open burning of waste.

If the CH4 emissions from incineration or open burning of waste are key categories, it is good practice to use a higher tier.

Tier 2 is similar to Tier 1 but takes country-specific data into account. Tier 2 also follows Equation 5.4, as Tier 1. Inventory compilers should use country-specific data including activity data, emission factors by waste, technology or management practice.

Countries with a high proportion of open burning or batch-type/semi-continuous incinerators should consider further investigation of CH4 emission factors.

It is good practice to use the Tier 3 method when plant-specific data are available. All incinerators should be considered and their emissions summed.

Figure 5.2 provides a general decision tree for estimating CH4 emissions from incineration and open burning of waste. The best results will be obtained if country-specific or plant-specific CH4 emission factors are available. Information on CH4 from incineration and open burning of waste to satisfy the requirement of Tier 3 method is currently scant.

If detailed monitoring shows that the concentration of a greenhouse gas in the discharge from a combustion process is equal to or less than the concentration of the same gas in the ambient intake air to the combustion process then emissions may be reported as zero. Reporting these emissions as 'negative emissions' would require continuous high-quality monitoring of both the air intake and the atmospheric emissions.

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