The IPCC Guidelines outline several approaches for calculating CO2 emissions from zinc production. The choice of a good practice method depends on national circumstances as shown in the decision tree in Figure 4.16. The Tier 3 method may be used if facility-specific measured emissions data are available. Tier 2 method uses country specific emissions factors for both primary and secondary production processes. The Tier 1 method is very simple and it may lead to errors due to its reliance on assumptions rather than actual data. The Tier 1 method calculates emissions from general emission factors applied to a country's total zinc production and is the least rigorous method. This method should only be used when zinc production is not a key category.
The simplest estimation method is to multiply default emission factors by zinc product type (Equation 4.33). When the only data available are national zinc production statistics, it is good practice to use default emission factors. If material specific data are not available to calculate emissions using the Tier 2 methodology, but the process type is known, inventory compilers can calculate emissions using Equation 4.34.
ECo2 = CO2 emissions from zinc production, tonnes Zn = quantity of zinc produced, tonnes
EFdefault = default emission factor, tonnes CO2/tonne zinc produced
Equation 4.34 CO2 emissions from zinc production (Tier 1)
ECO2 = CO2 emissions from zinc production, tonnes
ET= quantity of zinc produced by electro-thermic distillation, tonnes
EFET = emission factor for electro-thermic distillation, tonnes CO2/tonne zinc produced
PM = quantity of zinc produced by pyrometallurgical process (Imperial Smelting Furnace Process) , tonnes
EFPM = emission factor for pyrometallurgical process, tonnes CO2/tonne zinc produced
WK = quantity of zinc produced by Waelz Kiln process, tonnes
EFwk = emission factor for Waelz Kiln process, tonnes CO2/tonne zinc produced
Emission can be calculated using country specific emission factor based on aggregated plant statistics on the use of reducing agents, furnace types and other process materials of interest is developed based on default emission factors applicable to those materials. These data may be available from governmental agencies responsible for manufacturing or energy statistics, business or industry trade associations, or individual zinc companies. Tier 2 is more accurate than Tier 1 because it takes into account the materials and the variety of furnace types used in the zinc sector that contribute to CO2 emissions for a particular country rather than assuming industry-wide practices.
If actual measured CO2 emissions data are available from zinc facilities, these data can be aggregated and used directly to account for national emissions using the Tier 3 method.
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