Choice of emission factors

Tier 1 method

The Tier 1 method uses default values for CCF, COF and C contained in the product where petroleum coke is used in the estimation. Alternatively, where carbide production is used, the method uses default emission factors shown in Tables 3.7 and 3.8 where relevant. In both cases, the default factor for CaC2 use is applied.

Tier 2 method

As for the Tier 1 method, the Tier 2 method uses default emission factor values except for the amount of C contained in the product, where plant-level data are required.

Tier 3 method

The Tier 3 method requires plant-level data for all variables except for CCF and COF of the petroleum coke where country specific Energy Sector values may be used. This includes plant-level emission factors for lime if it is produced in-house and plant-level emission factors for CaC2 used to produce acetylene for welding applications.

CO2 from silicon carbide production

More carbon is needed in the silicon carbide production process than calculated from a stoichiometric reaction. The excess carbon is oxidised during the process, little is left as ash (Raaness, 1991). Typical default values for Norwegian plants for carbon content in coke are 97 percent and for carbon contained in product, 35 percent. This implies a typical emission factor of 2.3 tonnes CO2/tonne petroleum coke used (IPCC, 1997), or 2.62 tonnes CO2/tonne carbide produced.

CH4 from silicon carbide production

Measurements at Norwegian plants suggest emission factors of 10.2 kg CH4/tonne petroleum coke or 11.6 kg CHVtonne carbide produced (IPCC, 1997).

Table 3.7

Default factors for CO2 and CH4 emissions from silicon carbide production

Process

Emission Factor (tonnes CO2/tonne raw material used)

Emission Factor (kg CH4/tonne raw material used)

Emission Factor (tonnes CO2/tonne carbide produced)

Emission Factor (kg CH4/tonne carbide produced)

Silicon carbide production

2.30

10.2

2.62

11.6

Source: Revised 1996 IPCC National Greenhouse Gas Inventories, Vol.3, p.2.21 (IPCC, 1997)

CO2 from calcium carbide production

Emission factors may be derived from the use of raw materials (petroleum coke) and from carbide production using a mass-balance approach. Limestone used in carbide manufacture contains about 98 percent CaCO3 and is accounted for elsewhere. 1 750 kg limestone (or 950 kg CaO), 640 kg of petroleum coke and 20 kg carbon electrodes are required to produce 1 tonne of carbide.

The default emission factors for estimating emissions are included in Table 3.8.

Table 3.8

Emission factors for CO2 emission from calcium carbide production and use

Process

Default Emission Factor (tonnes CO2/tonne raw material used)

Default Emission Factor (tonnes co2/tonne carbide produced)

Petroleum coke use

1.70

1.090

Use of product

not relevant

1.100

Source: Revised 1996 IPCC National Greenhouse Gas Inventories, Vol.3, p.2.22 (IPCC, 1997)

The theoretical emission factor calculated from a stoichiometric reaction is lower for the petroleum coke step than that shown in the table. Excess carbon is oxidised in the process and the suggested emission factors were calculated from the actual use of raw materials in a Norwegian plant. The emission factor for acetylene use is calculated from the actual (not stoichiometric) carbon content of carbide.

The CO2 emissions may be lowered by utilising the gas when producing dicyanodiamide from carbide (Olsen, 1991).

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