Example Inventory 4 Source Group 3 Power Generation and Heating

Introduction

The purpose of this case study is to illustrate the process of inventory development, update and revision, focusing on a single source group: Power generation and heating. We will consider a hypothetical example of a PCDD/PCDF inventory in country X, and describe the baseline inventory process, its update and revision for this particular source group.

Baseline Inventory

The total share of fuels in indigenous energy production in country X can be broken down as follows: 55% from hard coal, 37% from brown coal and the remaining 8% comes from gas, oil and hydro. Hard coal is thus the basic fossil fuel burned in households not only for heating, but also for cooking.

National activity statistics for the baseline reference year (2001) provide the following consumption figures:

  • hard coal 174,338 TJ
  • lignite 980 TJ
  • high methane natural gas 110,658 TJ
  • nitrified natural gas 16,953 TJ
  • LPG 20,812 TJ
  • light fuel oil 17,496 TJ

By grouping the fuels according to type (solid, liquid, gaseous) we obtain the following figures:

  • coal 175,318 TJ
  • oil 17,496 TJ
  • natural gas 148,423 TJ

3e Household Heating and Cooking with Fossil Fuels

One of the main sources of PCDD/PCDF releases in country X comes from combustion processes in household boilers and furnaces, where commercial fuels are frequently co-combusted with household waste. The municipal and housing sector has a dominant share in PCDD/PCDF emissions, as the main fuel used in this sector is hard coal, with an annual consumption of 9 million tons.

The 2003 Toolkit applies an emission factor for burning of coal in residential heating systems of 70 μg I-TEQ/TJ corresponding to approximately 2 μg I-TEQ/t. The default emission factor was derived from mean values reported between 1.6 and 50 μg I-TEQ/t of coal burned. Several recent measurements indicate that the emission from the residential burning of coal in country X may be much higher.

These results indicate that the emission factor for residential burning of coal - even though the coal is not co-combusted with waste - may be significantly higher than the default emission factor of the Standardized Toolkit. The default emission factor is still used as a medium estimate, but it is estimated that the real average emission factor is likely to be higher rather than lower, and a range of 35-1,000 μg I-TEQ/t will be applied.

The resulting annual releases to air are presented in the table below:

Source category Source Class Activity rate TJ/year EFAir (µg I-TEQ/t) Annual release to air (g TEQ/a)
Medium (Toolkit, 2003)   Range   Medium   Range
Domestic heating and cooking – fossil fuels Coal fired stoves 219,484 70 30-1,000 15 6.6-200
Update of the Inventory

In 2008, new emission factors are published in country X based on specific measurements of emissions from coal fired stoves. These country-specific factors are then used with higher confidence to update the inventory. Activity rates are comparable with those estimated for the baseline year, and are equally derived from national statistics, as in the baseline inventory.

Source category Source Class Activity rate TJ/year EFAir (µg I-TEQ/t)
Country-specific		 Annual release to air (g TEQ/a)
Domestic heating and cooking – fossil fuels Coal fired stoves 200,000 115 23

The results show a slight increase in releases, although activity rates were maintained at relatively constant levels. This is clearly due to applying a different set of emission factors, which were derived to better reflect the national circumstances in country X.

Revision of the Baseline Inventory

The revision of the baseline inventory is thus necessary to ensure consistency of trends in releases over time. In this example, the revision is triggered by scientific findings and developments, allowing country X to re-calculate releases by using an own set of emission factors developed to better reflect national circumstances.

Source category Source Class Activity rate TJ/year EFAir (µg I-TEQ/t)
Country-specific		 Annual release to air (g TEQ/a)
Domestic heating and cooking – fossil fuels Coal fired stoves 219,484 115 25.24

The revised baseline estimates show that indeed a decrease in releases from this major source has happened from 2001 till 2008.

Conclusion

This example shows that when applying own emission factors, through periodic refinement of the methodology to develop the PCDD/PCDF inventory, revisions of the previous inventories are equally needed. Besides changes in the Toolkit methodology through its revision in 2013, better information becoming available at the country level, including through direct measurements of emissions and development of more specific emission factors, is an equally important triggering factor to revise baseline estimates of releases. If the revision of the baseline is not performed, the results obtained for the different reference years are not readily comparable and trends over time cannot be estimated.