Annex 9 Complementary information to source category 1a Municipal Solid 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
Release to Air
For class 1, the default emission factor of 3,500 µg TEQ/t of waste burned was derived from a flue gas flow rate of about 10,000 Nm³/t MSW and a concentration of 350 ng TEQ/Nm³ (at 11% O2). Emission factors of 3,230 µg TEQ/t have been reported from Switzerland and 5,000 µg TEQ/t from the Netherlands (LUA 1997).
For class 2, it is assumed that the specific flue gas volume is 7,000 Nm³/t MSW, due to better combustion controls and lower excess air and the PCDD/PCDF concentration is reduced to 50 ng TEQ/Nm³ (at 11% O2). Plants of this type may be equipped with an ESP, multi-cyclone and/or a simple scrubber.
In class 3, the combustion efficiency and the efficiency of APC systems are further improved (e.g., ESP and multiple scrubbers, spray-dryer and baghouse or similar combinations) so that the PCDD/PCDF concentration is reduced to about 5 ng TEQ/Nm³ (at 11% O2). Also, the specific flue gas volume is reduced to 6,000 Nm³/t MSW.
Class 4 incinerators are the current state-of-the-art in MSW incineration and are equipped with advanced APC technology (e.g., activated carbon adsorption units or SCR/DeDiox). Thus, only 5,000 Nm³/t MSW and a concentration of less than 0.1 ng TEQ/Nm³ (at 11% O2) will be the norm (LUA 1997, IFEU 1998).
In a study of a Thai municipal solid waste incinerator, the flue gas concentrations at 11% O2 ranged from 0.65 to 3.10 ng I- TEQ/Nm³ with an average of 1.71 ng TEQ/Nm³ (at 11% O2). The concentrations of total PCDD/PCDF (Cl4-Cl8) were between 41.3 and 239 with a mean of 122 ng/Nm³ (at 11% O2) (UNEP 2001, Fiedler et al. 2002). The measured average concentration of 122 ng PCDD/PCDF/m³ is above the Thai standard for municipal waste incinerators of 30 ng/m³; the mean of 1.7 ng TEQ/Nm³ is also above the European standard of 0.1 ng TEQ/m³. The measured emissions would result in an emission factor of 6.1 µg TEQ/t of waste burned. The Toolkit would have classified this incinerator into class 3 and would have given an emission factor of 30 µg TEQ/t. By applying the Toolkit’s default emission factor, the release would have been overestimated by a factor of 5 but would have fallen into the anticipated order of magnitude.
PCB emission factors to air have been determined in a measurement campaign in France (Delepine et al. 2011). For class 4, high technology MSW incinerators, emission factors in the range of 0.004 - 0.017 µg TEQ/ ton of MSW incinerated are calculated for dioxin-like PCBs, and between 2 and 64 µg/t of MSW incinerated for indicator PCBs.
Release to Water
Releases to water may occur when wet scrubbers are employed for the removal of particulate matter or to cool down ashes. In such cases, the amount of PCDD/PCDF released through this vector, can best be estimated using the default emission factors given for residue. Normally, concentrations are in the range of a few pg TEQ/L and the highest PCDD/PCDF concentration reported in a scrubber effluent before removal of particulate matter was below 200 pg TEQ/L. Most of PCDD/PCDF are associated with the particulate matter and are consequently captured in the filter cake or sludge from treatment of the scrubber effluent. For inventorying purposes, these scrubber water treatment residues are included with fly ash.
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
PCDD/PCDF concentrations in fly ash are substantial, while the total mass generated per ton of MSW is typically around 4-9%. PCDD/PCDF concentrations in the bottom ash are rather low, however, the amount of bottom ash generated per ton of MSW is around 19-30% (UNEP 2011b). Fly ash and bottom ash also contain unburned carbon from 1% (class 4) up to 30% (class 1). Since unburned carbon in the ash greatly enhances the formation and adsorption of PCDD/PCDF, the concentration is greatest in class 1; here, 500 ng TEQ/kg was chosen for bottom ash. This value has been extrapolated; it is about 10-fold above the average measured concentrations from European plants in the 1980s.
In class 2 the concentration is assumed to be 30,000 ng TEQ/kg in fly ash and 100 ng TEQ/kg in bottom ash due to greatly improved combustion efficiency resulting in a much lower LOI of the ash.
For class 3, these values are assumed to be lower due to further improvements.
For class 4, high combustion efficiency, and very high collection efficiency, especially of the very small fly ash particles, are assumed. These small particles supply a large adsorption surface for PCDD/PCDF and therefore the overall concentration does not decrease further. Thus, the value for the fly ash is set at 1,000 ng TEQ/kg and the concentration for the bottom ash drops to 5 ng TEQ/kg.