Annex 22 Complementary information to source category 2g Zinc Production
Overview of recent revisions
For this source category, class 4 and 5 were merged together to include information on both zinc melting and primary zinc production. New PCDD/PCDF emission factors for residues were identified.
Emission factors for other unintentional POPs than PCDD/PCDF are presented below:
Table III.22.1 PCB emission factors for source category 2g Zinc Production
2g Zinc Production Emission Factors (µg TEQ/t zinc) Classification Air Water Land Product Residue 1 Kiln with no APCS 100 2 Hot briquetting/rotary furnaces, basic dust control; e.g., fabric filters/ESP 2 3 3 Comprehensive pollution controls, e.g., fabric filters with active carbon/DeDiox technology 0.1 4 Zinc melting and primary zinc production 0.001
Table III.22.2 HCB emission factors for source category 2g Zinc Production
2g Zinc Production Emission Factors (µg/t zinc) Classification Air Water Land Product Residue 1 Kiln with no APCS 50,000 2 Hot briquetting/rotary furnaces, basic dust control; e.g., fabric filters/ESP 50,000 3 Comprehensive pollution controls, e.g., fabric filters with active carbon/DeDiox technology 50,000 4 Zinc melting and primary zinc production 1,000
Emission factors for PCB/HCB are provided with:
- A medium level of confidence for classes 1, 2 and 3 (PCB) and classes 3 and 4 (HCB), as emission factors are not based on expert judgment but are not derived from a broad geographical coverage;
- A low level of confidence for class 4 (PCB) and classes 1 and 2 (HCB), as emission factors are based on extrapolations and expert judgment.
Derivation of emission factors
Release to Air
In Germany, emission factors were provided for hot briquetting (63-379 μg TEQ/t zinc with emissions between 89 and 953 ng TEQ/m³, mean = 521 ng TEQ/m³), a rotating cylinder furnace (62.3 μg TEQ/t with emissions between 10 and 335 ng TEQ/m³; mean = 175 ng TEQ/m³) and for zinc melting (typically under 0.1 ng TEQ/m³, LUA 1997).
Although this data set is very limited initial estimations of releases may be obtained by applying the emission factor of 100 μg TEQ/t of zinc produced where hot briquetting or rotary furnaces are used (class 2). Where furnaces are used feeding scrap materials or filter ashes from the steel industry to recover zinc (Japanese data) and with no dust removal an estimated factor of 1,000 μg TEQ/t can be used (class 1). For high technology facilities using comprehensive pollution controls such as fabric filters with lime and active carbon injection an estimated factor of 5 μg TEQ/t can be used (class 3).
Class 1 emission factor has been confirmed by recent data obtained from a Waelz kiln in Taiwan which was not equipped with any APC (3,000 µg TEQ/t, Chi 2009). In addition, the same paper confirmed class 2 emission factor from measurements on a Waelz kiln equipped with a scrubber, a cyclone and a bag filter (101 µg TEQ/t). It also measured an emission factor of 5 µg TEQ/t on a plant equipped with a comprehensive APC (scrubber, cyclone, bag filter and activated carbon injection), confirming class 3 emission factor. Class 3 emission factor was also confirmed by Japanese data (7.1 µg TEQ/t, Iwata et al. 2008).
In Japan, 10 measurements were achieved on different Zn primary melting plants (Iwata et al. 2008). The mean value was 0.11 µg TEQ/t. Former classes 4 and 5 are merged into a new class 4 dedicated to zinc melting and primary zinc production.
The publication from Taiwan mentioned above (Chi et al. 2008) also allows for new PCB emission factors for classes 1 to 3. Class 4 PCB emission factor is derived from Polish data (Grochowalski et al. 2007).
Several Japanese publications (Iwata et al. 2008, Ota et al. 2005, Sakai et al. 2009) provided HCB emission factors for secondary zinc production (classes 1 to 3). Those ranged between 42,000 and 85,000 µg/t. Therefore, an emission factor of 50,000 is proposed for these classes. The same publications also provided emission factors for primary zinc production (1,000 µg/t).
Release to Water
A release may occur if effluents are discharged. The source of any effluent from the process should be noted.
Release to Land
No release to land is expected.
Release in Products
Levels of PCDD/PCDF in refined zinc are not relevant.
Release in Residues
Residues from gas cleaning are expected to contain PCDD/PCDF. Three publications issued in 2009 gave first results focused on PCDD/PCDF levels in residues from secondary zinc production. In China, an emission factor of 0.246 µg TEQ/t zinc was derived (Ba et al. 2009). In South Korea, several plants were investigated without any process and APC description being given and an emission range of 0.02-13 µg TEQ/t zinc was provided. The third one was from a team from Taiwan which measured levels from residues produced by two Waelz kilns (260-1,900 µg TEQ/ t EAF dust). Assuming 2 t EAF dust by ton of produced zinc, this range would correspond to emission factors of 520-3,200 µg TEQ/t zinc.
Therefore an emission factor of 0.02 µg TEQ/t zinc (lower end of Jin et al. 2007 range) is proposed for class 1. For classes 2 and 3, an emission factor of 1 µg TEQ/t zinc is proposed. However, in the specific case of Waelz kilns, emission factors can reach 2,000 µg TEQ/t zinc. The kind of process should therefore be cautiously recorded.