Annex 33 Complementary information to source category 3d Household Heating and Cooking with Biomass
Overview of recent revisions
In source category 3d “Household heating and cooking with biomass”, the information generated within the pilot project on simple stoves in Mexico is included; the experiment used an indoor high-volume sampler and one continuous sampler, as well as an outdoor sampler. The results of this pilot project, including measurements of PCDD/PCDF, PCB and HCB emissions from four simple stoves using wood as fuel, with limited combustion control and a duct for the evacuation of flue gases, were used to revise and amend emission factors to air and residues. Results obtained suggest daily fluctuations of PCDD/PCDF levels according to the cooking pattern.
Four new classes were added in this category, as follows:
- Straw fired stoves, including all types of residential combustion using herbaceous biomass as a fuel such as straw pellets.
- Charcoal fired stoves, including all types of residential combustion using charcoal as a fuel. Higher emissions may nevertheless occur from barbecuing.
- Open-fire (3-stone) stoves (virgin wood), including residential combustion of wood without control of combustion conditions and without ducts for the evacuation of flue gases. Traditional 3-stone stoves are a typical example.
- Simple stoves (virgin wood) used for cooking with limited combustion control and with a duct for the evacuation of flue gases.
Emission factors for dioxin like PCB, ∑6PCB and HCB are proposed for two classes in this category, i.e. open-fire 3-stone stoves (virgin wood) and simple stoves (virgin wood), based on the results of the project in Mexico (Cardenas et al. 2011).
Table II.33.1 Dioxin-like PCB in WHO 2005 TEQ emission factors for source category 3d Household Heating and Cooking with Biomass
3d Household Heating and Cooking with Biomass Emission Factors (µg TEQ/TJ) Classification Air Water Land Product Residue (ng/kg) 5 Open-fire 3-stone stoves (virgin wood) 0.1 6 Simple stoves (virgin wood) 10 0 0 0.1
Table II.33.2 ∑6PCB emission factors for source category 3d Household Heating and Cooking with Biomass
3d Household Heating and Cooking with Biomass Emission Factors (mg/TJ) Classification Air Water Land Product Residue (ng/kg) 5 Open-fire 3-stone stoves (virgin wood) 6 Simple stoves (virgin wood) 100 0 0 ND
Table II.33.3 HCB emission factors for source category 3d Household Heating and Cooking with Biomass
3d Household Heating and Cooking with Biomass Emission Factors (mg/TJ) Classification Air Water Land Product Residue (ng/kg) 5 Open-fire 3-stone stoves (virgin wood) 200 6 Simple stoves (virgin wood) 10 0 0 200
The resulting emission factors for PCDD/PCDF are relatively low and close to the ones proposed in the 2005 edition of the Toolkit. As for the PCDD/PCDF in ashes, the emission factors derived were lower than the existing ones.
As it is anticipated that the use of simple stoves to substitute open fire in developing countries will increase substantially over the next years, other biomass sources or new types of devices may be considered for further investigation.
Derivation of emission factors
Release to Air
Releases to air are the predominant vector for biomass combustion. The default emission factor for class 1 was derived from mean values reported between 2 and 50 μg TEQ/t of wood burned. The values of 2.4–4.7 μg TEQ/kg as reported in the Austrian study seems to be extraordinarily high. The values of 0.2–0.7 μg TEQ/t as reported in the German study seem to represent the lowest end of the spectrum. So does the Swiss value of 24 ng TEQ/GJ. It is important to note that the values reported for clean biomass combustion are consistently one order of magnitude below the values reported for the combustion of contaminated biomass such as treated and/or painted wood. Thus, an average value of 1.5 μg TEQ/t was chosen for clean biomass where as a value of around 25 μg TEQ/t was used for contaminated biomass. Based on an average heating value of 12–15 MJ/kg for wood, default emission factors of about 100 μg TEQ/TJ can be calculated for clean biomass and 1,500 μg TEQ/TJ for contaminated biomass (LUA 1997, IFEU 1998). LUA (1997) gave emission factors of 50 μg TEQ/t for slightly contaminated and 500 μg TEQ/t for highly PCP-treated wood, which would result in emission factors of 3,300 μg TEQ/TJ and 50,000 μg TEQ/TJ, respectively.
Information on charcoal fired stoves (class 4) is scarce. The proposed value of 100 µg TEQ/ TJ has to be considered as an expert estimate based on Schleicher (2002).
New emission factors for classes 5 and 6 are based on Cardenas et al. (2011).
Release to Water
No release to water is expected.
Release to Land
No release to land is expected unless the combustion takes place directly on the soil. Due to a lack of data, no default emission factor could be derived.
Release in Products
The process has no product; thus no release to product occurs.
Release in Residues
PCDD/PCDF in the ash residue range from a few nanogram to several thousand ng TEQ/kg (or μg TEQ/t, respectively). Combustion of virgin wood will generate lower concentrations in the ash whereas treated wood results in higher concentrations. The mean concentrations determined by Wunderli et al. (1996) will be used in the Toolkit as a first estimate: they determined an average of 1,000 ng I-TEQ/kg of ash generated for contaminated wood and 10 ng I-TEQ/kg of ash generated for clean wood. For peat as a fuel, no TEQ-based results were found. However, a publication by Mehrag and Killkam (2003) found 60.6 ng PCDD/PCDF (tetra-through octachlorinated homologs) per kg of peat ash in a sample from the 19th century. Applying the emission factor of class 2 for peat ash is suggested. Utilization of this factor would not underestimate the release.
The new class 3 emission factor for straw fired stoves is derived from Launhardt (2000). This value refers to the range reported for combustion chamber ash (5-33 ng TEQ/kg). Concentrations in heat exchanger ash are typically higher. With regard to mixed ashes a value at the upper end of the range is proposed. New emission factors for residues are included in classes 5 and 6 based on Cardenas et al. (2011).