Contents

Summary

This methodology represents carbon dioxide (CO2) emissions associated with the production of ammonia. The data and calculation methodology is sourced from the Greenhouse Gas Protocol (GHGP) worksheet tool CO2 emissions from the production of ammonia, version 2.0, which is ultimately based on the methodologies described in Volume 3, Chapter 3 - Chemical Industry Emissions of the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.

The calculations provided within this category represent the Tier 1, 2 and 3 approaches of the IPCC guidelines.


The methodology

Emissions model

Ammonia (NH3) is a major industrial chemical used directly as a fertiliser and a refrigerant, as well as in the processes of heat treating and paper pulping, and in the manufacture of nitric acid (and nitric acid ester), nitrates, nitro compounds, explosives of various types, and urea. In addition to the nitrogen (N) component (which is sourced from air), the production of ammonia (NH4) requires a source of hydrogen (H). The predominant source of H employed in the manufacture of ammonia is natural gas (usually methane, CH4), although other hydrocarbons (as well as water, H2O) are less commonly used. H is obtained using a process known as catalytic steam reforming, which is described by the following reaction:

  1. 0.88CH4 + 1.26Air + 1.24H2O → 0.88CO2 + N2 + 3H2

As suggested, a by-product of the process is CO2. Indeed, the production of ammonia represents a significant non-energy-related industrial source of CO2 emissions.

This methodology enables the calculation of ammonia-associated CO2 emissions based on a mass-balance approach which assumes that all feedstock/fuel carbon (C) which enters the production process is emitted as CO2. The quantity of feedstock/fuel C is determined on the basis of (1) the quantity of feedstock/fuel consumed and (2) the carbon content of the feedstock/fuel. This quantity of C is converted into the corresponding quantity of CO2 using the ratio of their relative molecular/atomic masses (i.e. 44/12).

In addition, the methodology can take into account the capture/recovery of CO2 for use in urea production or storage. In this case the quantity of CO2 emitted is adjusted according to the quantity recovered.

This methodology can represent each of the IPCC tier 1, 2 or 3 approaches, depending on the activity data available (see below).

Model data

The rate at which ammonia production produces emissions of CO2 depends on the type of process and type of fuel used. This methodology provides data representing 416 scenarios which are differentiated by their plant type (e.g. modern European plants, mixed age plants), production process (e.g. conventional reforming, partial oxidation) and fuel type (e.g. natural gas, coking coal). Each scenario is represented by default values for:

  • the typical quantity of feedstock/fuel consumed per unit of ammonia produced
  • the typical carbon content of the feedstock/fuel

These values can be specified on facility-specific basis if data is available, however. In addition, the methodology provides conversion factors for quantities of both C and urea into the corresponding quantities of CO2, based on the respective molecular/atomic masses of each.

Activity data required

CO2 emissions are directly proportionate to the quantity of fuel consumed, which therefore must be provided. There are two ways in which this quantity can be specified: (1) the total quantity of fuel consumed can be explicitly specified (on an energetic basis; e.g. GJ); or (2) the quantity of ammonia produced can be specified. In the latter case, the total fuel quantity is determined on the basis of an additional value representing the quantity of fuel required per unit of ammonia (i.e. GJ per kg). This can be provided if facility-specific or national data is available. Otherwise, a default value for the respective production scenario can be used.

The methodology also requires a value for the carbon content of the fuel. This is defined on an energetic basis, i.e. the mass of carbon per unit of energy yielded by the fuel (kg per GJ). Where facility-specific data is not available, the methodology provides default values for each fuel type.

In addition, the completeness of oxidation can be specified, i.e. the fraction of the fuel which is fully combusted. If no facility-specific data is available, combustion is assumed by the methodology to have occurred completely, i.e 100%.

Finally, this methodology can optionally take in to account CO2 which is recovered for storage or urea production. In the case of urea production, the quantity of CO2 can be specified in one of two ways: (1) by specifying the quantity of CO2 recovered explicitly; or (2) by specifying the quantity of urea produced, in which case the corresponding quantity of recovered CO2 is derived using the respective molecular masses of urea and CO2.

Calculation and results

The quantity of C which enters the production process is determined by multiplying the specified quantity of fuel consumed by the values for carbon content and oxidation level. This is converted into the corresponding CO2 quantity using their relative molecular/atomic masses, from which any quantities of CO2 recovered are subtracted.


Additional information

IPCC Tiers

The following combinations of activity data define each of the IPCC tiered approaches:

Tier 1

  • Fuel specified in terms of ammonia production together with default fuel requirement
  • Fuel type is not available. The fuel with the highest emissions factor is used
  • Carbon content and oxidation level are defined using methodology the default value
  • Recovered CO2 specified using urea production data or assumed to be zero if no explicit data is available

Tier 2

  • Fuel specified in terms of ammonia production together with default fuel requirement
  • Each fuel type differentiated and calculated separately
  • Carbon content and oxidation level are defined by either methodology defaults or from facility-specific or national data
  • Recovered CO2 specified where appropriate

Tier 3

  • Each fuel type differentiated and calculated separately
  • Explicit quantities of each fuel type consumed used
  • Carbon content and oxidation level are defined by facility-specific or national data
  • Recovered CO2 specified where appropriate

Urea production

When a deduction is made for CO2 used in urea production, IPCC advise that it is good practice to ensure that emissions from urea use are included elsewhere in an inventory. CO2


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