Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

CO 2 EM IS SI ONS FROM C EM ENT
PRODUC TIONACKNOWLEDGEMENTS
This paper was written by Michael J. Gibbs, Peter Soyka and David Conneely (ICF Incorporated). It wasreviewed by Dina Kruger (USEPA).

ABSTRACT
Cement is an important construction ingredient produced in virtually all countries. Carbon dioxide (CO2) is a byproduct of a chemical conversion process used in the production of clinker, a component of cement, in whichlimestone (CaCO3) is converted to lime (CaO). CO2 is also emitted during cement production by fossil fuelcombustion and is accounted for elsewhere. However, the CO2 from fossil fuels is accounted for elsewhere inemission estimates for fossil fuels. The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories(IPCC Guidelines) provide a general approach to estimate CO2 emissions from clinker production, in which theamount of clinker produced is multiplied by the clinker emission factor.
The IPCC Guidelines recommend two possible methods for calculating the clinker emission factor. The first
method is to use the IPCC default value for the fraction of lime in clinker. The second method is to calculate theaverage lime concentration in clinker by collecting data on clinker production and lime fraction by type. The
IPCC Guidelines state that the difference between the default value and a value based on collected data is
expected to be small. If clinker production data are not available, it is recommended that countries back-calculate
clinker production from the cement data while applying a correction factor for clinker imports/exports. Once anestimate has been derived, emissions can be estimated by means of the clinker emission factor.
The IPCC recommends using clinker data, rather than cement data, to estimate CO2 emissions because CO2 isemitted during clinker production and not during cement production. If clinker is traded internationally, using
cement production data results in a biased emissions estimate because the cement could potentially be produced
from clinker that was made in another country. Although clinker data are the preferred data source, cement data
may be more readily available in some countries. In this case, the recommended approach is to estimate thefraction of clinker in the cement and back-calculate clinker production.
Quality assurance and quality control activities should be implemented at several stages in the emission
estimation process. At the plant level, key activities include internal quality control on production data andemission factors, as well as documenting data and methods for reviewers. The inventory agency must ensure theaccuracy of plant submissions as well as the compiled inventory. It is also responsible for providing
documentation and sufficient information to the United Nations Framework Convention on Climate Change(UNFCCC). One or more types of external review may also be appropriate.

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1
1.1

INTRODUCTION
Nature, magnitude, and distribution of source

Overview of Cement Production
Cement is an important construction ingredient around the world, and as a result, cement production is asignificant source of global carbon dioxide (CO2 ) emissions, making up approximately 2.4 percent of global
CO2 emissions from industrial and energy sources (Marland et al., 1989). Cement is produced in large, capitalintensive production plants generally located near limestone quarries or other raw carbonate mineral sources asthese sources are the principal raw materials used in the cement production process. Because the production
plants are expensive, the number of plants in a country is generally limited (less than 100). Carbon dioxide isemitted as a by-product of clinker production, an intermediate product in cement manufacture, in which calcium
carbonate (CaCO3) is calcinated and converted to lime (CaO), the primary component of cement. CO2 is also
emitted during cement production by fossil fuel combustion. However, the CO2 from fossil fuels is specificallyaccounted for in emission estimates for fossil fuels.
Process Description
Carbon dioxide is released during the production of clinker, a component of cement, in which calcium carbonate(CaCO3) is heated in a rotary kiln to induce a series of complex chemical reactions (IPCC Guidelines).
Specifically, CO2 is released as a by-product during calcination, which occurs in the upper, cooler end of thekiln, or a precalciner, at temperatures of 600-900°C, and results in the conversion of carbonates to oxides. The
simplified stoichiometric relationship is as follows:
CaCO3 + heat  CaO + CO2
At higher temperatures in the lower end of the kiln, the lime (CaO) reacts with silica, aluminum and ironcontaining materials to produce minerals in the clinker, an intermediate product of cement manufacture. The
clinker is then removed from the kiln to cool, ground to a fine powder, and mixed with a small fraction (about
five percent) of gypsum to create the most common form of cement known as Portland cement. Masonry cement
is generally the second most common form of cement. Because masonry cement requires more lime thanPortland cement, masonry cement generally results in additional CO2 emissions.

2
2.1

METHODOLOGICAL ISSUES
Selection of good practice methods

The IPCC Guidelines provide a general approach to estimate CO2 emissions from clinker production, in which
the amount of clinker produced is multiplied by an emission factor. Thus the basic equation to estimate CO2
emissions from clinker production is:
EQUATION 1
Activity/Production Data ● CKD Corrections Factor = CO2 Emissions from Clinker
Where CKD stands for Cement Kiln Dust.
Because masonry cement requires additional lime, the IPCC Guidelines provide an equation, based on masonry
cement production parameters, to estimate CO2 emissions resulting from the additional lime. The equation, andits components, is presented in Box 1.

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Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

BOX 1
IPCC METHODS

Masonry Cement Production Data
Masonry cement, in contrast with Portland cement, requires additional lime. To account for this, the IPCC
Guidelines provide an equation, based on masonry cement production parameters, to estimate CO2 emissions
resulting from the additional lime. The equation is illustrated below.
EQUATION 2
CO2 (tons) from CaO added to masonry cement =a ● (all cement production ) ● ((1-1/(1 + b)) ● c) ● 0.785
Where:
a = fraction of all cement produced that is masonry cement (e.g., 0.05-0.2)
b = fraction of weight added to masonry cement by non-plasticiser additives such as lime, slag, andshale (e.g., 0.004, 0.006)
c = fraction of weight of non-plasticiser additives that is lime (e.g., 0.7-0.9)
a ● (all cement production) = masonry cement production((1-1/(1+b)) ● c) = fraction of lime in masonry cement not attributable to clinker((1-1/(1+ b)) ● c) ● 0.785 = an emission factor of CO2 from masonry cement additives

2.2

Emission factors

Estimating emissions generally involves two emission factors: an emission factor for clinker production and anemission factor for Cement Kiln Dust (CKD) production.

2.2.1

Clinker emission factor

The clinker emission factor is the product of the fraction of lime in the clinker multiplied by the ratio of the massof CO2 released per unit of lime. This is illustrated below:
EQUATION 3
EF clinker = fraction CaO ● (44.01 g/mole CO2 / 56.08 g/mole CaO)orEQUATION 4
EF clinker = fraction CaO ● 0.785
The multiplication factor (0.785) is the molecular weight ratio of CO2 to CaO in the raw material mineral calcite (CaCO3), fromwhich most or all of the CaO in clinker is derived. CaO content can show variations by country of origin and facility.
The IPCC Guidelines recommends two possible methods for calculating the emission factor. The Tier 1 method
uses the IPCC default value for the fraction of lime in clinker, which is 64.6 percent. This results in an emission
factor of 0.507 tons of CO2/ton of clinker, as illustrated below:
EQUATION 5
EF clinker = 0.646 ● 0.785 = 0.507
The Tier 2 method is to calculate the average lime concentration in clinker by collecting data on clinker
production and lime fraction by type. The difference between the default value and a value based on collected
data is expected to be small.

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2.3

Activity data

2.3.1

Clinker data

IPCC recommends using clinker data, rather than cement data, to estimate CO2 emissions because CO2 is emitted
during clinker production (not cement production). Also, if clinker is traded internationally, using cement
production data creates biased emission estimates because the cement could potentially be produced from clinker
manufactured in another country. Furthermore, the amount of clinker in other types of cement, such as blended
and natural cement, is highly variable and difficult to estimate.
If cement data are already available and clinker data are not available, the recommended method is to estimate
the fraction of clinker in the cement and back-estimate clinker production. Figure 1 provides a simple decision
aid illustrating preferred methods.
Figure 1

Preferences for selecting the appropriate production
data

Are clinker
production
data available?

No

Is there significant
import or export ofclinker?

No

Are cement
production data
available?

Yes

Yes

No

Yes

Use clinker data

Collect clinker data

Use cement data

Multiply by clinker
emission factor

Multiply by clinker
emission factor

Back-calculate
to estimate
clinker
production

Multiply byclinkeremission factor

2.4

Uncertainty

Parallel to the IPCC sector-specific experts meetings on good practice guidance, the IPCC is completing a
programme of work on emissions inventory uncertainty. This work will result in recommendations to the
UNFCCC on approaches to assessing and managing uncertainty. During the IPCC Inventory Experts Group
Meeting in Paris (October 1998), technical experts in the uncertainty programme came up with a series ofquestions to be answered in the sectoral meetings. Specifically, the sectoral experts meetings should provide
answers to these questions in the individual source context. The questions are listed in the general background paper.

2.5

Completeness

Cement is produced in capital-intensive plants often located near limestone (CaCO3) quarries. The number ofplants is generally low (less than 100) and the plants are easy to locate and monitor, making it highly feasible for178

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Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

countries to collect clinker or cement production data from each plant in the country. To facilitate creating an
up-to-date inventory, countries should monitor imports and exports of clinker.

2.6

Other important issues

2.6.1

Baseline

An emissions baseline is an important component of an inventory programme. Developing a baseline requires
collecting and compiling clinker and CKD production data during or following the baseline period. As mentioned
previously, a complete inventory should include data collected from each plant. Difficulties may arise when:•

Individual plants have not maintained records during the baseline period; or•Individual plants that produced clinker and CKD during the baseline period are no longer in operation.

In such cases, it may be necessary to estimate baseline clinker and CKD production. Approaches for estimatingproduction figures may include:•

Estimating clinker and CKD production data based on plant production capacity and the utilisation rate; or•

Calculating the estimates using national production data from the baseline period.

If production data are estimated using plant production capacity and plant utilisation rates, care should be taken toaccount for time during which plants are not operating (i.e., down-time).

2.6.2

Cement Kiln Dust (CKD)

CO2 is also emitted during the calcination of cement kiln dust (CKD) in the kiln. CKD is a by-product of the kiln
process and a portion of the CKD is placed back in the kiln and incorporated into the clinker. The remaining
portion is lost – placed in a landfill or used for other purposes. The lost CKD represents additional CO2
emissions not accounted for in the clinker emissions estimate.
The recommended method to estimate the additional CO2 emissions from the lost CKD is to multiply an emission
factor by the amount of lost CKD. However, CKD production data are usually not available. The CO2 from the lost
CKD is generally equivalent to about 2-6 percent of the total CO2 emitted from clinker production. If data are notavailable, it is recommended that countries select a percentage between 2-6 percent and multiply the percentage by
the estimate of CO2 emissions from clinker production. This yields an estimate of CO2 from the lost, calcined CKD.

3REPORTING AND DOCUMENTATION

3.1

Current IPCC reporting guidelines

This section provides information on the current IPCC Guidelines. The IPCC Guidelines are used to guidecountries in the preparation and submissions of annual greenhouse gas emissions inventories to the UNFCCC
Secretariat. The Guidelines establish:•

Standard tables, definitions, units, and time intervals for reporting all types of emissions;•

Necessary documentation to enable comparison of national inventories, including worksheets, major
assumptions, methodological descriptions and enough data to allow a third party to reconstruct the inventory
from national activity data and assumptions, and•An uncertainty assessment.

CO2 emissions from cement production are reported in IPCC Guidelines Volume 1, Table 2: Sectoral Report for
Industrial Processes, which calls for entries for each source for emissions totals of carbon dioxide, methane,
nitrous oxide, precursor gases (NOx, CO, NMVOCs, SO2), HFCs, PFCs, and SF6.
CO2 emissions from cement production are reported under the IPCC category 2A1, which derives from thefollowing classification scheme:

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2:

Industrial processes

2A:

Non-Metallic Mineral Products

2A1:

Cement Production

3.2

Confidential business information

The issue of confidential business information (CBI) may make reporting national inventory in a transparent
manner highly problematic. Countries may need to create confidential tracking and reporting systems, or,alternatively, to report the number of plants with an aggregated national total. If only one plant exists, CO2
emissions from cement production may need to be combined with CO2 emissions from other industrial sources,
because reporting emissions from the one cement plant would release potentially confidential information.

4
4.1

INVENTORY QUALITY
Introduction

Inventory quality assurance and quality control (QA/QC) is a process integral to the development of a credible
inventory. A well-developed and well-implemented quality assurance programme fosters confidence in the final
inventory results regardless of the purpose and goal of the inventory. A successful quality assurance programme
requires internal quality control procedures and an unbiased, external review and audit. The internal QC
activities are designed to ensure accuracy, documentation and transparency. The external review process isdesigned to minimise errors that occur in the preparation of emissions inventories and reduce or eliminate
potential inherent bias. Figure 2 outlines the flow of information and processes followed at each stage of the process.
Figure 2

Inventory QA/QC Process
Cement Plant

Internal QC:

Plant-level measurement and calculations

Documentation:

Plant-level information provided to the government agency, and results of internal QC
Government Agency

Review/QA:

Plant-level inputs

Internal QC:

Compilation of national inventory from plant-level data

Documentation:

Results of compilation and results of QA/QC

Reporting:

Official submission to UNFCCC
External Review

External Review:

External audit, stakeholders, peer and public review of inventory results,
external verification against other data etc.

Documentation:

Results of external review
UNFCCC Secretariat

External Review:

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Requires standard format and transparency – ensure consistency with otherinventories and external data

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Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

4.2
4.2.1

Internal inventory QA/QC systems
Plant-level activities

Plant-Level Data QC
The personnel at each plant are responsible for determining the QC procedures unique to that plant. Plant data
includes production data, as well as data on the amount of lime and other substances added. Performing QC on
plant data also involves cross-checking the data. Examples include cross-checking the amount that is producedwith the amount that is shipped, or cross-checking the amount of clinker produced with the amount of cement
produced (if cement is produced in the same plant). A QC procedure should also include a written procedure forhow data are collected, records of current and historical plant data and estimates of accuracy and precision.
Plant-Level Documentation
Documentation is a crucial component of the review process, because it enables reviewers to identify mistakes
and suggest improvements. Among others, the following information is needed for the reviewing/auditing agency:•

A detailed description of data collection methods, and•A discussion of potential biases involved in data collection, such as a discussion of possible reasons forincorrect production data. For example, producers may give incorrect data to avoid environmental
regulations or government taxes. If there is potential bias, the discussion should include suggestions on how
to overcome this bias.

In addition, a standardised reporting form is recommended to provide transparent information on production.
Given that data are collected from each production plant, the reporting form should be signed and certified by anappropriate plant representative.

4.2.2

Inventory Agency Level Activities

Inventory Agency Review (QA) of Plant-Level Information
Before accepting plant-level emissions data, the inventory agency should assess plant data, including bothproduction data and data on the amount of lime and other substances added to the clinker if such information isavailable. This review involves close cooperation with plant owners and personnel to ensure that production data
are accurate. The assessment should include a review of records, comparison with historical plant data,
identification of potential bias in the data and recommendations for improvement, such as better data
management methods.
Inventory Agency QC on Compiling National Emissions
In addition to the thorough quality assessment of data discussed above, the inventory agency should ensure thatthe process of aggregating data to develop the national inventory undergoes quality control. This should include:•

Ensuring that all data are included, and•Identifying any anomalies and/or patterns through comparison with industry trends.

Inventory Agency Documentation on Compiling National Emissions
For the CO2 emission inventory for cement production, a QA/QC management plan should address the specificitems required to perform audits and reviews. Examples of the types of information needed for documentationand external audit include:•

A detailed description of the inventory methodology;•

Identification of the required input parameters and the methodology used to obtain these input parameters, and•Frequency of data collection, estimation and results of accuracy and precision determinations.

4.3

External inventory QA/QC systems

External QA activities include a planned system of review and audit procedures conducted by personnel not
actively involved in the inventory development process. The key concept is an independent, objective review to

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assess the effectiveness of the internal QC programme, the quality of the inventory and to reduce or eliminate
any inherent bias in the inventory processes.
Several types of external reviews or audits may be appropriate such as:•

Third party audit
An audit of the documentation and calculations by an accredited organisation, expert or independent third
party ensures that each number is traceable to its origin. Given that much of the information used indeveloping CO2 emission estimates from cement production may be proprietary, a third party audit that
protects confidentiality may be necessary.

•

Expert (peer) review
A detailed peer review would be appropriate when a procedure for determining CO2 emissions is first
adopted or revised; it would not be needed on an annual basis. Such a review is designed to ensure that themethodology accurately represents the plant's particular situation, is as rigorous as possible and that thedata and assumptions reflect the best available information.

•

Stakeholder review
Review by cement producing companies, industrial organisations and government can provide a forum forreview of the methods used.

•

Public review
Some countries make their entire inventory available for public review and comment. This process may
result in a range of comments and issues on a broader level than other review processes.

Confidential Business Information Issues
Reviewing production data involves examining data from each plant. However, given that the plant-levelproduction data are often considered confidential, some producers may be unwilling to release production data,or to have production data released to the public.

5

CONCLUSIONSThe key issues relate to the methodology used to calculate clinker emissions, availability of CKD data as well as
confidentiality. The emissions equation assumes that all CaO in clinker is derived from CaCO3. As noncarbonate sources could be potentially used by manufacturers, possible margins of error from such anassumption should be investigated. Availability of CKD data is usually lacking and the possibility of using
default CKD correctional factors is to be further analysed. The confidential nature of business practices could
also hamper the reporting of a national inventory in a transparent manner. Options could include the developmentof confidential tracking systems or the aggregation of the national total of cement production plants.

REFERENCES
Intergovernmental Panel on Climate Change (IPCC) (1997). Revised 1996 IPCC Guidelines for National
Greenhouse Gas Inventories. Reference Manual (Revised).Vol 3. J.T. Houghton et al., IPCC/OECD/IEA,
Paris, France.
Marland, G., T.A. Boden, R.C. Griffin, S.F. Huang, P. Kanciruk and T.R. Nelson (1989), ). Estimates of CO2
Emissions from Fossil Fuel Burning and Cement Manufacturing, Based on the United Nationals Energy
Statistics and the U.S. Bureau of Mines Cement Manufacturing Data. Report No. #ORNL/CDIAC-25,
Carbon Dioxide Information Analysis Centre, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.

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