Choice of method

The choice of method will depend on national circumstances as shown in the decision tree, Figure 3.1. Emissions are estimated from the total fuel requirement, or values derived from estimates of the total fuel requirement, used in the production of NH3. The fuel energy requirement is not accounted for separately. Note that values reported in energy units (or volume units) need to be converted to mass units when estimating emissions.

Methods are classified according to the extent of plant-level data that are available. The Tier 1 method is based on default values and national statistics; the Tier 2 method is based on complete plant-level output data distinguished by fuel input type and process type, and default values; and the Tier 3 method is based entirely on plant-level input data.

The Tier 3 method uses plant-level output data and plant-level fuel input per unit of output to derive the total fuel requirement. Similarly, Tier 3 can also use plant-level emission factors per unit of output provided that the source of these factors is plant-level detailed data on the fuel inputs per unit of output.

TIER 1 METHOD

The Tier 1 method uses ammonia production to derive emissions as follows:

Equation 3.1 CO2 emissions from ammonia production - Tier 1

Where:

ECO2 = emissions of CO2, kg AP = ammonia production, tonnes

FR = fuel requirement per unit of output, GJ/tonne ammonia produced

CCF = carbon content factor of the fuel, kg C/GJ

COF = carbon oxidation factor of the fuel, fraction

RCO2 = CO2 recovered for downstream use (urea production), kg

Ammonia production and emission factors can be obtained from national statistics and the emission factor can be determined from default values shown in Table 3.1. Where no information is available on the fuel type and/or process type, it is good practice to use the highest emission factor shown in Table 3.1. CO2 recovered for downstream use can be estimated from the quantity of urea produced where CO2 is estimated by multiplying urea production by 44/60, the stoichiometric ratio of CO2 to urea. When a deduction is made for CO2 used in urea production it is good practice to ensure that emissions from urea use are included elsewhere in the inventory. If data are not available on urea production it is good practice to assume that CO2 recovered is zero.

TIER 2 METHOD

The initial step is to determine the total fuel requirement. For the Tier 2 method the total fuel requirement for each fuel type is estimated as follows:

Equation 3.2

Total fuel requirement for ammonia production - Tier 2

Where:

TFRi = total fuel requirement for fuel type i, GJ

APij = ammonia production using fuel type i in process type J, tonnes

FRjj = fuel requirement per unit of output for fuel type i in process type J, GJ/tonne ammonia produced

Ammonia production, the fuel type and process type can be obtained from producers, and the fuel requirement per unit of output (FR) can be determined from the default values shown in Table 3.1. Emissions are derived according to Equation 3.3:

Equation 3.3

CO2 emissions from ammonia production - Tier 2 and 3

Where:

ECO2 = emissions of CO2, kg

TFR = total fuel requirement for fuel type i, GJ

CCFi = carbon content factor of the fuel type i, kg C/GJ

COFi = carbon oxidation factor of the fuel type i, fraction

RCO2 = CO2 recovered for downstream use (urea production, CO2 capture and storage (CCS)), kg

When using the Tier 2 method, the C content of the fuel (CCF) and C oxidation factor (COF) may be obtained from the default values shown in Table 3.1 or country specific Energy Sector information. Data on CO2 recovered for urea production and CCS should be obtained from producers.

TIER 3 METHOD

The Tier 3 method requires that the fuel requirement be obtained from producers. The total fuel requirement is the sum of the total fuel requirements reported by each NH3 production plant. That is:

Equation 3.4

Total fuel requirement for ammonia production - Tier 3

Where:

TFRi = total fuel requirement for fuel type i, GJ

TFRin = total fuel requirement for fuel type i used by plant n, GJ

Once data on total fuel requirements are collected and collated, CO2 emissions can be estimated using Equation 3.3. When using the Tier 3 method, it is good practice to obtain information on the CCF and COF from producers or to use country specific energy sector information. As with the Tier 2 method, data on CO2 recovered for urea production (if any) and CCS (if undertaken) should be obtained from producers.

Although data on ammonia production is not used in the calculation under the Tier 3 method it also needs to be collected from producers for reporting purposes.

Box 3.1

CO2 RECOVERED FOR INDUSTRIAL GAS

CO2 recovered for industrial gas applications is not accounted for separately as this is a relatively low volume short term use and it is assumed that all industrial gas carbon will be emitted to the atmosphere in the producing country. For example, industrial CO2 used in freezing applications is assumed to be released in the producing country.

Figure 3.1 Decision tree for estimation of CO2 emissions from ammonia production

Figure 3.1 Decision tree for estimation of CO2 emissions from ammonia production

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for discussion of key categories and use of decision trees.

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