Annex 14 Complementary information to source category 1f Waste Wood and Waste Biomass Incineration
Overview of recent revisions
No revisions were made to emission factors in this source category. Additional guidance has been introduced on classifying sources within this category, estimating activity rates, and on data quality aspects.
Derivation of emission factors
Release to Air
In modern facilities, biomass is burned in either stationary or circulating fluidized bed furnaces where the formation of PCDD/PCDF is limited due to good combustion conditions. Such plants would likely have effective pollution control systems, especially removal of particulate matter, which is critical for the operation of circulating fluidized bed furnaces. Other furnace types commonly used are vertical rotary stage or open hearth-type furnaces, grate-type furnaces or muffle-type furnaces.
The default emission factors for all three categories were determined based on reported emission concentrations between 130 µg TEQ/t (Belgian study) and 1 µg TEQ/t (Canadian and Swedish studies). Thus, for class 1 a default emission factor of 100 µg TEQ/t was chosen for those old uncontrolled facilities. Class 2 represents better controlled newer facilities. A default emission factor of 10 µg TEQ/t was assigned to this class. Finally, class 3 with a selected default emission factor of 1 µg TEQ/t includes all the modern facilities for waste wood and biomass combustion (LUA 1997, IFEU 1998, Environment Canada 1999).
Release to Water
PCDD/PCDF concentrations in scrubber effluent from waste wood and waste biomass incinerators are not available.
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
PCDD/PCDF concentration in the ash will be high since the ash usually contains rather high concentrations of unburned carbon. Especially in older furnaces, higher gaseous emissions clearly indicate lower combustion efficiency resulting in higher concentrations of unburned carbon in the fly ash. Thus, high concentrations of PCDD/PCDF in the ash must be expected. Unfortunately, only very limited data from Canada as well as Germany was found indicating a wide range from as high as 23,000 ng TEQ/kg ash to as low as 3.7 ng TEQ/kg of ash. Based on the fact that the total ash concentration in waste wood and biomass averages between 3% and 10%, an average value of 5% was chosen. This leads to a default emission factor of about 1,000 µg TEQ/t for class 1 and 0.2 µg TEQ/t for class 3. For class 2, a medium value was chosen due to lack of data (LUA 1997, IFEU 1998, Environment Canada 1999). In class 1, no APC equipment is used and consequently no fly ash is collected but rather most of it is emitted to the atmosphere with the flue gas. Even though no specific collection device for fly ash is installed and the majority of the fly ash is discharged through the stack, some fly ash is expected to collect in the furnace and the ductwork leading to the stack as well as in the stack itself. Measured data for bottom ash could not be obtained, consequently the default emission factors for residue only consider fly ash.