Annex 30 Complementary information to source category 3a Fossil Fuel Power Plants
Overview of recent revisions
Approximately ninety literature sources have been identified in a worldwide search for primary measurement data and emission factors for fossil fuel fired power plants. Investigations included air emissions and releases into residues. The revision of the information related to source group 3 focused on the following aspects:
- Review of existing emission factors
- Review of proposed source categories
- Further information to be included on non- conventional fuels
- Derivation of emission factors for “simple“ technologies
In source category 3a “Fossil fuel power plants”, a new class was introduced and a new dioxin emission factor was proposed to cover releases from peat fired power boilers. The proposed emission factor refers to peat combustion in boilers for heat and/or power production. Peat is used in countries where it is domestically available. As for class 2 covering coal fired power boilers, it should be noted that the use of high-chlorine coal induces higher releases to air, of up to 200 µg TEQ/TJ.
Derivation of emission factors
Release to Air
Releases to air are the predominant vector for fossil fuel combustion. Typically, measured concentrations from large power plants are far below 0.1 ng TEQ/m³; mostly one to two orders of magnitude for solid and liquid fuels. Whereas Dutch data from large coal-fired power plants gave an emission factor of 0.35 μg TEQ/t, German data were between 0.004 and 0.2 μg TEQ/t (0.09 and 7.1 μg TEQ/TJ) and UK data had a median value of 0.14 μg TEQ/t (range: 0.06-0.32 μg TEQ/t). Swiss sources gave mean emission factors of 230 μg TEQ/TJ for coal-fired power plants. German data report between 0.02 and 0.03 μg TEQ/TJ for natural gas-fired boilers (LUA 1997).
The default emission factor for class 1 was derived from values reported between 0.4 and 118 μg TEQ/TJ. For the Toolkit, a median value of 35 μg TEQ/TJ was chosen. Class 2 emission factor was derived from average values reported between 230 (Swiss data from LUA 1997) and 7 μg TEQ/TJ. The reported values vary in a broad range from 3 -100 µg TEQ/TJ and depend highly on fuel quality and power plant technology. The lower end refers to measurements at a coal-fired power plant in Poland with circulating fluidized bed technology (Grochowalski and Konieczynski 2008).
Class 3 emission factor was derived based on McGettigan (2009). Class 4 was derived from average values reported between 1 and 4 μg TEQ/TJ. Class 5 is based from emission measurements taken at two power plants in Estonia firing shale oil, which gave emissions between 2.3 and 24 pg I-TEQ/Nm³ (at 10% O2). The comparatively high concentration of 400 pg I-TEQ/Nm³ (at 10% O2) has not been taken into account when determining the emission factor due to operational problems at the plant (Schleicher et al. 2004a). Class 6 emission factor came from average values reported between 0.5 and 1.5 μg TEQ/TJ (LUA 1997, IFEU 1998, Environment Canada 1999).
Release to Water
No release to water is expected. However, in cases where wet scrubbers are installed and effluents are generated, this release vector needs to be highlighted. Presently, no numeric value can be provided to estimate this release.
Release to Land
No release to land is expected unless untreated residue is directly placed onto or mixed with soil.
Release in Products
The process has no product; thus no release to product occurs.
Release in Residues
There is a scarcity of measured data for PCDD/PCDF concentrations in fly ash and more data will be needed. It can be assumed that the content of PCDD/PCDF in the fly ash increases with the content of unburned carbon and the amount of waste co-fired.
Estonia, where power plants use shale oil as a fuel, PCDD/PCDF have been analyzed in fly ashes from power plants, which were equipped with electrostatic precipitators. The concentrations in these fly ashes ranged from non quantifiable concentrations to 1.66 ng I-TEQ/kg of dry ash (LOQ included for TEQ calculation) (Schleicher et al. 2004a, Roots 2001). The data do not enable determination of emission factor and thus, countries that wish to quantify the releases from the power plants fuelled with shale oil and are equipped with ESPs, may wish to multiply the mean of the above two measurements (= 1.2 g TEQ/t of ESP fly ash) with the mass of fly ash collected from these plants.
To make a preliminary estimate, UK data on PCDD/PCDF in residues from industrial coal combustion can be used (Dyke et al. 1997, EC 1999a). Concentrations in fly ash were 0.23-8.7 ng TEQ/kg ash and grate ash gave 0.02-13.5 ng TEQ/kg. The concentrations in soot were higher (up to 53 ng TEQ/kg). Taking an average ash production rate of 10% and average concentration of 4 ng TEQ/kg ash, an emission factor of 0.4 μg TEQ/t (coal input) (approx. 14 μg TEQ/TJ) was derived.