Choice of method

The decision tree in Figure 2.1 describes good practice in choosing the most appropriate method based on national circumstances. In the Tier 1 method, emissions are based on clinker production estimates inferred from cement production data, correcting for imports and exports of clinker. The estimation of emissions directly from cement production (i.e., applying an emission factor directly to cement production without first estimating clinker production) is not considered to be a good practice method because it does not account for clinker imports and exports.

In Tier 2, emissions are estimated directly from clinker production data (rather than clinker production inferred from cement production) and a national or default emission factor. The Tier 3 approach is a calculation based on the weights and compositions of all carbonate inputs from all raw material and fuel sources, the emission factor(s) for the carbonate(s), and the fraction of calcination achieved. The Tier 3 approach relies on plant specific data. If the inventory compiler considers plant-level data to be unreliable or highly uncertain, then it is good practice to use Tier 2.

Tier 2 and Tier 3 should also include a correction for CKD. Tier 2 includes a correction addition for emissions associated with CKD not recycled to the kiln. Tier 3 also should account for CKD. Unlike the Tier 2 approach, when using Tier 3, emissions attributed to uncalcined CKD not recycled to the kiln should be subtracted from the total emissions estimate.

Should CO2 capture technology be installed and used at a plant, it is good practice to deduct the CO2 captured in a higher tier emissions calculation. The default assumption is that there is no CO2 capture and storage (CCS) taking place. Any methodology taking into account CO2 capture should consider that CO2 emissions captured in the process may be both combustion and process-related. In cases where combustion and process emissions are to be reported separately, e.g. for cement production, inventory compilers should ensure that the same quantities of CO2 are not double counted. In these cases the total amount of CO2 captured should preferably be reported in the corresponding energy combustion and IPPU source categories in proportion to the amounts of CO2 generated in these source categories. For additional information on CO2 capture and storage refer to Volume 3, Section 1.2.2 and for more details on capture and storage to Volume 2, Section 2.3.4.

TIER 1 METHOD: ESTIMATING CLINKER PRODUCTION THROUGH USE OF CEMENT PRODUCTION DATA

As noted above, calculating CO2 emissions directly from cement production (i.e., using a fixed cement-based emission factor) is not consistent with good practice. Instead, in the absence of data on carbonate inputs or national clinker production data, cement production data may be used to estimate clinker production by taking into account the amounts and types of cement produced and their clinker contents and including a correction for clinker imports and exports. Accounting for imports and exports of clinker is an important factor in the estimation of emissions from this source. Emissions from the production of imported clinker should not be included in national emissions estimates as these emissions were produced and accounted for in another country. Similarly, emissions from clinker that is ultimately exported should be factored into national estimates of the country where the clinker is produced. An emission factor for clinker is then applied and the CO2 emissions are calculated according to Equation 2.1.

Equation 2.1

Tier 1: Emissions based on cement production

CO2 Emissions =

Z (Mci • Ccll ) - Im + Ex _ i _

CO2 Emissions = emissions of CO2 from cement production, tonnes Mcl = weight (mass) of cement produced3 of type i, tonnes Cdl = clinker fraction of cement of type i, fraction Im = imports for consumption of clinker, tonnes Ex = exports of clinker, tonnes

EFclc = emission factor for clinker in the particular cement, tonnes CO2/tonne clinker The default clinker emission factor (EFdc) is corrected for CKD.

3 In some statistical compendia production of cement is taken to mean production of cement plus the exports of clinker. If this is the case, it is good practice to subtract clinker exports from the Mci factor in Equation 2.1.

Figure 2.1

Decision tree for estimation of CO2 emissions from cement production

Figure 2.1

Decision tree for estimation of CO2 emissions from cement 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.

Is this a key

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.

TIER 2 METHOD: USE OF CLINKER PRODUCTION DATA

If detailed and complete data (including weights and composition) for carbonate(s) consumed in clinker production are not available (Tier 3), or if a rigorous Tier 3 approach is otherwise deemed impractical, it is good practice to use aggregated plant or national clinker production data and data on the CaO content in clinker, expressed as an emission factor in the following Equation 2.2:

Equation 2.2

Tier 2: Emissions based on clinker production data

CO2 Emissions = Mcl

Where:

CO2 Emissions = emissions of CO2 from cement production, tonnes Mci = weight (mass) of clinker produced, tonnes

EFci = emission factor for clinker, tonnes CO2/tonne clinker (See discussion under Section 2.2.1.2, Choice of Emission Factors, for Tiers 1 and 2 below.) This clinker emission factor (EFcl) is not corrected for CKD.

CFckd = emissions correction factor for CKD, dimensionless (see Equation 2.5)

The Tier 2 approach is based on the following assumptions about the cement industry and clinker production:

1. The majority of hydraulic cement is either portland cement or a similar cement, which requires portland cement clinker;

2. There is a very limited range in the CaO composition of clinker and the MgO content is kept very low;

3. Plants are generally able to control the CaO content of the raw material inputs and of the clinker within close tolerances;

4. Even where the output of clinker is calculated by a plant rather than directly measured, there is generally close agreement between the two determination methods when audits are performed;

5. The CaO content of clinker from a given plant tends not to change significantly over the years;

6. The main source of the CaO for most plants is CaCO3 and, at least at the plant level, any major non-carbonate sources of CaO are readily quantified (see Section 2.2.1.2 below);

7. A 100 percent (or very close to it) calcination factor is achieved for the carbonate inputs for clinker manufacture, including (commonly to a lesser degree) material lost to the system as non-recycled CKD; and

8. Dust collectors at plants capture essentially all of the CKD, although this material is not necessarily recycled to the kiln.

TIER 3 METHOD: USE OF CARBONATE(S) INPUT DATA

Tier 3 is based on the collection of disaggregated data on the types (compositions) and quantities of carbonate(s) consumed to produce clinker, as well as the respective emission factor(s) of the carbonate(s) consumed. Emissions are then calculated using Equation 2.3. The Tier 3 approach includes an adjustment to subtract any uncalcined carbonate within CKD not returned to the kiln. If the CKD is fully calcined, or all of it is returned to the kiln, this CKD correction factor becomes zero. Tier 3 is still considered to be good practice in instances where inventory compilers do not have access to data on uncalcined CKD. However, excluding uncalcined CKD may slightly overestimate emissions.

Limestones and shales (raw materials) also may contain a proportion of organic carbon (kerogen), and other raw materials (e.g., fly ash) may contain carbon residues, which would yield additional CO2 when burned. These emissions typically are not accounted for in the Energy Sector, but, if used extensively, inventory compilers should make an effort to see if they are included in the Energy Sector. Currently, however, too few data exist on the kerogen or carbon contents of non-fuel raw materials for mineral processes to allow a meaningful default value related to the average kerogen content of raw materials to be provided in this chapter. For plant-level raw material-based calculations (Tier 3) where the kerogen content is high (i.e., contributes more than 5 percent of total heat), it is good practice to include the kerogen contribution to emissions.

The Tier 3 approach will likely only be practical for individual plants and countries that have access to detailed plant-level data on the carbonate raw materials. Emissions data collected on the plant level should then be aggregated for purposes of reporting national emissions estimates. It is recognized that frequent calculations of emissions based on direct analysis of carbonates could be burdensome for some plants. As long as detailed chemical analyses of the carbonate inputs are carried out with sufficient frequency to establish a good correlation between the carbonates consumed at the plant level and the resulting clinker production, the clinker output may then be used as a proxy for carbonates for emissions calculations in the intervening periods. That is, a plant may derive a rigorously-constrained emission factor for the plant's clinker, based on periodic calibration to the carbonate inputs.

Equation 2.3

Tier 3: Emissions based on carbonate raw material inputs to the kiln

CO2 Emissions = £(EF •Mi • Fl) -Md .Cd .(1-Fd) . EFd +^(Mk . Xk • EFk)

Emissions from carbonates j v.

Emissions from uncalcined CKD not recycled to the kiln k

Emissions from carbon-bearing non-fuel materials

Where:

CO2 Emissions = emissions of CO2 from cement production, tonnes

EFj = emission factor for the particular carbonate i, tonnes CO2/tonne carbonate (see Table 2.1)

Mj = weight or mass of carbonate i consumed in the kiln, tonnes

Fi = fraction calcination achieved for carbonate i, fractiona

Md = weight or mass of CKD not recycled to the kiln (= 'lost' CKD), tonnes

Cd = weight fraction of original carbonate in the CKD not recycled to the kiln, fractionb

Fd = fraction calcination achieved for CKD not recycled to kiln, fractiona

EFd = emission factor for the uncalcined carbonate in CKD not recycled to the kiln, tonnes CO2/tonne carbonateb

Mk = weight or mass of organic or other carbon-bearing nonfuel raw material k, tonnesc

Xk = fraction of total organic or other carbon in specific nonfuel raw material k, fractionc

EFk = emission factor for kerogen (or other carbon)-bearing nonfuel raw material k, tonnes CO2/tonne carbonatec

Notes on defaults for Equation 2.3:

a: Calcination fraction: In the absence of actual data, it may be assumed that, at the temperatures and residence times achieved in cement (clinker) kilns, the degree of calcination achieved for all material incorporated in the clinker is 100 percent (i.e., Ft = 1.00) or very close to it. For CKD, a Fd of <1.00 is more likely but the data may show high variability and relatively low reliability. In the absence of reliable data for CKD, an assumption of Fd = 1.00 will result in the correction for CKD to equal zero.

b: Because calcium carbonate is overwhelmingly the dominant carbonate in the raw materials, it may be assumed that it makes up 100 percent of the carbonate remaining in the CKD not recycled to the kiln. It is thus acceptable within good practice to set Cd as equal to the calcium carbonate ratio in the raw material feed to the kiln. Likewise, it is acceptable to use the emission factor for calcium carbonate for EFd.

c: The CO2 emissions from non-carbonate carbon (e.g., carbon in kerogen, carbon in fly ash) in the non-fuel raw materials can be ignored (set Mk • Xk • EFk = 0) if the heat contribution from kerogen or other carbon is < 5 percent of total heat (from fuels).

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