Annex 10 Complementary information to source category 1b Hazardous Waste 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
Default emission factors are based on the assumption that the waste burned leads to about 3% of fly ash and the PCDD/PCDF release associated with the disposal of bottom ash is negligible in classes 3 and 4. No data exist for classes 1 and 2 for bottom ash concentrations. Also, the removal efficiency of particulate matter increases with the quality of the plant. Class 4 should only be used for highly sophisticated hazardous waste incineration plants in conjunction with a strictly enforced regulatory value of 0.1 ng TEQ/Nm³ (at 11% O2), such as legislated in the European Union. The vast majority of all hazardous waste incineration plants can be assumed to fall into classes 2 and 3. Class 1 should be chosen mainly for very small (< 500 kg/h) and simple furnaces operated in a batch type mode without any APC system attached to the back end, e.g., muffle ovens.
Release to Air
The default emission factor for class 1 was derived from a specific flue gas volume flow rate of about 17,500 Nm³/t of hazardous waste and a concentration of about 2,000 ng TEQ/Nm³.
Class 2 assumes a reduction in the specific flue gas volume flow rate to 15,000 Nm³/t of hazardous waste due to better combustion controls and lower excess air. The PCDD/PCDF concentration drops to 20 ng TEQ/Nm³ (at 11% O2) in this case.
In class 3, the combustion efficiency improves further and the efficiency of the APC system improves resulting in a drop of the PCDD/PCDF concentration to about 1 ng TEQ/Nm³ (at 11% O2). Also, the specific flue gas volume flow rate is reduced to 10,000 Nm³/t HW.
Class 4 represents the current state-of-the-art in HW incineration and APC technology. Thus, only 7,500 Nm³/t HW and a concentration of significantly less than 0.1 ng TEQ/Nm³ (at 11% O2) is realistic (LUA 1997, IFEU 1998, Environment Canada 1999).
PCB emission factors to air have been derived in a measurement campaign in France (Delepine et al. 2011). For class 4, high technology HW incinerators, emission factors in the range of 0.0004-0.237 µg TEQ/ ton of HW incinerated are calculated for dioxin-like PCBs, and between 6 – 154 µg/t of HW incinerated for indicator PCBs.
Release to Water
Releases to water occur when wet scrubbers are employed for the removal of particulate matter and when residue is cooled or washed with water. The amount of PCDD/PCDF released through this vector can best be estimated by using the default emission factors supplied for residue. The maximum actual PCDD/PCDF concentration found in wet scrubber effluent was below 0.15 µg TEQ/t (LUA 1997). Overall, this release vector is not considered to be important for this source type.
Release to Land
No release to land is expected unless untreated residue is directly placed onto or mixed with soil. The concentration released in such cases will be covered under “Release in Residues”.
Release in Products
The process has no product, thus no release to product occurs.
Release in Residues
The amount of fly ash in hazardous waste is typically around 3%. Fly ash also contains unburned carbon of 0.5% (class 4) up to 20% (class 1). Since unburned carbon in the fly ash greatly enhances the adsorption of PCDD/PCDF, the concentration is greatest in class 1. In class 1, PCDD/PCDF was assumed to be around 300,000 ng TEQ/kg fly ash.
In class 2 the concentration drops to 30,000 ng TEQ/kg fly ash due to greatly improved combustion efficiency resulting in a much lower LOI of the fly ash.
Class 3 cuts this value down to 15,000 ng TEQ/kg fly ash based on further improvements.
Class 4 assumes not only high combustion efficiency but also very high collection efficiency, especially of the very small fly ash particles. Combined fly ash and boiler ash from a BAT-compliant hazardous waste incinerator has been determined to have a PCDD/PCDF concentration of 388.2 ng TEQ/kg and a generation rate of about 3 percent. With the inclusion of scrubber sludge, the PCDD/PCDF concentration decreased to 367.8 ng TEQ/kg at the same time the combined generation rate increased to 6.4% (van Caneghem et al. 2010). Bottom ash was generated at a rate of 24.6% and an emission factor of 10 ug TEQ/t waste was derived for bottom ash.