Economy & Energy
Year VIII -No 48:
February - March 2005  
ISSN 1518-2932

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Carbon BALANCE in THE ProduCTION, TransformaTION AND UsE OF EnergY IN BraZil– MetHodologY AND Results Of The "Top-Bottom" PROCESS FROM 1970 TO 2002.

1. Carbon Balance Project.

2. Methodology.

3. Carbon Content in Energy Sources.

    Calculation of the Carbon Content.

    Results for the Contained Carbon.

Carlos Feu Alvim (coordinator)

Frida Eidelman

Omar Campos Ferreira

1. Carbon Balance Project

The Carbon Balance Project, executed by the NGO Economy and Energy – publisher of this periodical - aims at supplying a tool for calculating the carbon balance in the production, transformation and use of energy in Brazil and for calculating the carbon content in the emissions of greenhouse effect gases, and the dissemination of the results in electronic form and printed reports

The objective is to detect – through the simultaneous application of the Top-Down and Bottom-Up techniques – the possible omissions in one of the two approaches that could be due to incoherence of the coefficients used or flaws in the emissions calculation. The principle used is that carbon atoms do not disappear in the fuel use process and in each phase of the process the original quantity of carbon (contained mass) must be the same as that emitted or captured by some process.

The present study, carried out under an agreement with the Ministry of Science and Technology (MCT), has concentrated on the methodology and diagnoses of the deviations found. Suggestions regarding the treatment of the problems and the establishment of a coherent balance will be presented at the conclusion of the present report. The necessary corrections will be made afterwards.

The comparisons made with the inventory data show that these corrections – mainly in the Top-Down process – are quantitatively not relevant. As a consequence, it is possible to obtain the emissions between 1970 and 2000 with a precision equivalent to that of the Brazilian Inventory.

The Final Report was delivered to the Ministry of Science and Technology – MCT and is available in our electronic address http://ecen.com. This article presents in a concise way some of the results obtained. Other results will be presented in the next issues of this periodical.

The period examined is from 1970 to 2000, corresponding to that of the data available at the Brazilian Energy Balance (BEB), published by the Ministry of Mines and Energy[1], when the project was executed and they were used by the present study.

2. Methodology

The Carbon Balance will try to establish an accounting of the net input and output of carbon in the activities concerning energy sources. The scheme is analogous to that adopted by BEB and is shown in Figure 1.

Figure1: Brazilian Energy Balance Scheme. Source: BEB/MME

Strictly speaking, one could make a carbon balance in each of the steps of the scheme above. The present study is concentrated on the centers of energy transformation and consumption. The treatment of the previous steps is certainly of interest for calculating the balance but it would involve data that are not available at BEB. For example, it would be important to know the characteristics of imported petroleum and of that internally produced in order to check the carbon content at the refineries’ input.

The values used in that balance are originally given in natural units that correspond to those used at the origin of information (mass in tones and volume in m3). In some cases, when the sources are grouped, the units are in tones equivalent petroleum (tep) and a special criterion must be established in order to calculate the emissions.

For the input data, it is necessary to evaluate the mass (or volume) of the emitted gases, its carbon content and the mass of this element that is eventually retained. Whenever available, one must also account for the losses provided that they are a real evaluation; when they are a simple record of the accounting differences, the carbon balance will calculate them. The methodology to compile the results was the object of the previous e&e-MCT agreement (ONG Nº 01.0077.00/2003) and is described in the reports presented whose abstract was published in the e&e periodical.[2].

In the methodology adopted, the emissions are calculated multiplying the values relative to the final use of the energy sources and to some transformations, expressed in energy, by coefficients calculated by surveying the inventory of greenhouse effect gases emissions in Brazil[3]. The coefficients used in the years before the period of the inventory calculation are those used for the first year when it was calculated (1990). The coefficients for the years subsequent to 1999 are those corresponding to that year (last year of the inventory).

For hydrocarbons, an approximation for the carbon content by contained energy can be obtained from the difference between the high and low heat values given by BEB. The methodology and its verification for gasoline was shown in the No 43 issue of this periodical (http://ecen.com/eee43/eee43p/ecen_43p.htm) and that of natural gas, in the present issue. The differences between the heat values fundamentally corresponds to the (latent) heat liberated in the condensation of water vapor formed in the combustion of one unit of fuel mass and the heat removed from the condensed water in order to reduce it to the ambient temperature, considered as 25º (540+75 cal/g_water). The difference between the heat values permits to deduce the quantity of water that is formed and consequently the hydrogen contained per unit mass of the fuel. The participation of carbon (in the case of hydrocarbons) is the complement of this participation.

3. Carbon Content in Energy Sources.

The elaboration of carbon balance requires firstly the conversion of BEB's data to carbon mass. The second step is to calculate the emissions that contain carbon.

Both in the carbon content calculation and the emissions evaluation, it is sometimes convenient to have data that are more detailed than that published in BEB's annex pages. It is convenient, for example, to have natural gas as humid and dry gas, hydrated and anhydrous alcohol as well as sugarcane compounds (sugarcane juice, bagasse and molasses) data.

The Ministry of Mines and Energy (MCT) published in 2002 balance data for 49 energy sources and 46 “accounts”[i]. Economy and Energy – NGO made a computer program (in Visual Basic and Excel) called ben_ee, where these data can be obtained in final or equivalent energy, in partial or complete tables. The energy source data can be represented in ton equivalent petroleum (tep) in the concept previously adopted by BEB and in the present one[ii], in Low Heat Value (LHV) and High Heat Value (HHV) and in “natural units” (mass and volume).

As part of the present agreement, the computer program was updated for the available data (1970- 2002) and they are also expressed in carbon content by using coefficients (mass C/energy) for each energy source. The annual data (in energy) are therefore converted to contained carbon and can now also be used for the set of years and generate temporal series.

In another approach that incorporates the Bottom-Up approximation results, the consolidated energy balance results (24 energy sources) and the values calculated by the MCT staff that elaborated the national emissions inventory published in the “Brazilian Communication to the United Nations Framework on Climate Change”[iii], were used to calculate the emission coefficients by energy source in each of the economic sectors presented in the balance (consumption) and transformation centers where there are direct emissions.

Using the above mentioned program denominated ben_eec (equivalent energy and carbon balance in the present version), tables with the carbon content by “account” and by energy source as normally presented in BEB were produced.

Comparing the results of the two methodologies, one can evaluate the validity of the carbon mass/energy coefficients used and the eventual errors or omissions in the inventory calculation. The carbon balance will also permit the extrapolation of emission values in the years before and after the inventory period (1990-1994) with more assurance.

It is hoped that the first set of results will be very similar to that corresponding to the Top-Down calculation recommended by the IPCC. The difference should only be the quantity of carbon retained (in the energy source uses) and in the non-oxidized carbon. In an easy way, it is possible to obtain emission values corresponding to this methodology from the results generated in this program. The program and its manual are available at http://ecen.com

Calculation of the Carbon Content

The ben_eec program presents the high and low heat values supplied by the MME. These values could be used for obtaining the carbon content as shown in Annex 1 of the Final Report. Even though the results for the year 2002 have been promising, some important differences were found. Besides that, as the objective of the present work is to develop a methodology and make a diagnosis, we have opted in the present step to use the same coefficients values used previously for calculating the emissions inventory. For this reason, we have used the coefficients of COPPE’s report to the General Coordination of Climate Change[4] that are, most of them, those values recommended by the IPCC[5]. It should be pointed out that the emissions values found in that reference are those that have been adopted by the already mentioned Brazilian National Communication.

In Table 1 are presented the results of the methodology application based on the heating values and the coefficients used in the present report (actually the same as those of COPPE’s report to the MCT mentioned above).

Table 1: Carbon content using the high and low heating values compared with values based on the IPCC values

Results for the Contained Carbon

The ben_eec program supplies the contained carbon by “account” and by energy source. In Table 2 are given the contained carbon values in the energy sources of the Energy Balance for petroleum and its products (including the liquids from natural gas), for natural gas and for mineral coal and its products. It is also shown the sum of the carbon mass from fossil fuels and that from biomass. The values obtained are compared with the national inventory and they show good agreement.

Table 2: Carbon Content in Energy Sources Used in Brazil from 1970 to 2002

Table 3: Comparison between the Obtained Carbon Content and those of the Brazilian Inventory

Figure 2 represents the evolution of the contained carbon in the energy sources used in Brazil compared with that of the national inventory

Figure 2: Carbon content in the energy sources used in Brazil obtained in the present work compared with data from the National Inventory.

 Figure 3 shows the evolution of the carbon content of energy sources used in Brazil by primary fossil energy and in biomass

Figure 3: Carbon contained in the energy sources for the main fossil fuels and biomass

Table 4 shows data for 1994 using the division shown in BEB’s annexes. Annex 3 of the Final Report contains additional tables for selected years. Tables in this and other formats for additional years can be generated by the program that is annexed to this report.

It is worth while to notice that in the way that the program was made, it can produce almost immediately a Top-Down evaluation of the emissions that contain carbon. The result of such an evaluation is very close to the data corresponding to the line “Gross Internal Offer” of the spreadsheet (49 energy sources) that generated Table 4 (24 energy sources). The program evaluates the quantity of carbon retained in the non-energy uses of the fuels using factors suggested by IPCC and subtracting this quantity from the corresponding item.

More precisely, it would be necessary to use two more lines of the spreadsheet to subsidize the calculations. Using the Non-Energy Final Consumption line, one evaluates the carbon retained in the non-energy uses. The “Total Transformation” line can be used to evaluate an oxidation coefficient in cases where the data “division” used (49X46) has more than one IPCC coefficient. This occurs only in the cases of natural gas (liquids of natural gas and dry gas) and firewood (coal production and other uses).

In Table 5 the results obtained by the Top-Down (COPPE/MCT) process are compared with those calculated here using the carbon content table. It should be noted that the present work has used the same data source used by COPPE for the MCT but the data supplied by the MME are different. Particularly, it is already possible to use here the low heat value (LHV) adopted by BEB for defining the ton equivalent petroleum (tep) which was not available in the previous evaluation.

Since the aim of the present report is not to evaluate the emissions, some small divergences were not entirely elucidated and they may be due to energy source data or to how to group smaller fractions of the energy flux[iv]. The comparison results were encouraging, with average deviations smaller than 1% that are doubtless much smaller than those implicit in the adopted methodology.

Therefore, it is possible to make an evaluation of the emissions in the long 1970-2002 period that is presented in what follows.

Evaluation of Emissions between 1970 and 2002 or the Use of the Top-Bottom Process 

The IPCC methodology was adapted to directly calculate data generated by the ben_eec program. Three lines of the spreadsheet shown in Table 4 were used, namely:

·          Gross Internal Offer

·          Total Transformation

·          Non- Energy Final Consumption

It should be mentioned that the Top-Down methodology starts from the principle that the number of carbon atoms is conserved along the several interactions that finally will result in CO2 emission or of any other gas containing carbon. The IPCC methodology is directed to evaluating the carbon dioxide production.

This methodology consists of accounting for the primary and secondary fuels that enter in the economic system of a country in order to satisfy the needs of human activities (even the non-commercial ones) and that leave the system (retention in materials, net exports and non-oxidation).

Table 4:  Contained Carbon by Type of Fuel and “Account” – Gg/Year 2002

Table 4:  Contained Carbon by Type of Fuel and “Account” – Gg/Year 2002 (suite)

In order to avoid double counting, the raw materials produced or imported as well as the products exported or imported are accounted for; the transformations (of primary into secondary energy) carried out in the country should not be considered, as the carbon has already been computed in the raw material.

The gross internal offer concept actually corresponds to that adopted by IPCC where stock variations and re-injections are accounted for. It excludes as well the production losses that may however be evaluated from the spreadsheet generated by ben_eec.

The retained carbon, accounted for in the Top-Down methodology is that corresponding to the non-energy use. In this type of use carbon is not always retained and the IPCC methodology recommends the use of some coefficients (mass percent) in order to take into account the emission by natural evaporation (and subsequent conversion to CO2 in the atmosphere) or by waste burning or degradation. When they are not supplied, one can use evaluated coefficients based on available information. In the present case we have opted, whenever possible, for the values used in the mentioned COPPE/MCT report. The values used in the reference report were 0.8 for naphtha, 0.5 for lubricants, 0.75 for tar and 0.33 for dry natural gas. For other compounds the value 1 was adopted (all carbon retained). In Table 5 the calculation process is illustrated for the year 1994. [v]

Table 5: Emissions Calculation using the IPCC Top-Down Method  1994 Gg/Year

Table 5: Emissions Calculation using the IPCC Top-Down Method (Suite)

In Table 6 a example of CO2 Emissions calculation using three outputs lines of the carbon content table is shown.

 Table 6: Example of CO2 Emissions Calculation using Output Lines of the Program

In Table 7 the net emissions (carbon content – retained carbon) are shown for the other years separated into fossil fuels and biomass. The values calculated for the national inventory are also compared in Table 8 with those obtained here.

    Table 7: Net Emissions in Gg/year of Carbon

     Table 8: Comparison of Net Carbon Emissions Results (Gg/year)

The fraction of oxidized carbon (that directly, or through degradation of other compounds in the atmosphere, generates CO2) varies according to the fuel. In the adopted methodology (Top-Down) this correction is carried out using a multiplying factor suggested by IPCC. In two cases (firewood for coal production versus firewood for direct burning and dry natural versus liquids from natural gas) there are specific coefficients. From the carbon mass involved in the transformation, one can calculate the participation of firewood in coal production and that of dry natural gas in consumption. The oxidized fraction for firewood and mineral coal can be obtained and the complement is computed in the other use of each energy source. Using the consumption participation share of humid natural gas (raw material) as dry gas (in the example with 71.1% participation share and 99.5% oxidation) and the consumption complement as natural gas liquids (28.9% with 99% oxidation), one estimates an average coefficient for firewood and humid natural gas that is the weighted average between the two original coefficients. This coefficient is recalculated in each year using the participation shares.[vi]

Table 9 shows the annual results obtained here by primary source and for biomass. The results are compared with the values of the National Inventory in Table 10.

Table 9: CO2 Emissions in Gg/year for Brazil

Table 10: Comparison of CO2 Emissions in Gg/year for Brazil calculated in the present work with those of the inventory

Figure 4: CO2 emissions obtained by the Top-Down methodology adapted to the program’s output format.

The agreement between the data obtained here (for the available years) and those of the inventory is very good. It should be pointed out that the calculation routine of the program is completely equivalent to that of IPCC, as demonstrated in Table 5. The small observed differences should be ascribed to the low heat values that in the present approximation are those adopted by BEB and they were not available at the time the inventory was made; there are also small doubts concerning the energy allocations relative to the IPCC methodology. The program developed here is therefore a powerful tool for evaluating the past and projected balances. It can be very useful as well for calculating the inventory of countries that have not made it yet. In future studies, a program that presents graphics and tables for the inventory can be.

References:

Graphic Edition/Edição Gráfica:
MAK
Editoração Eletrônica

Revised/Revisado:
Tuesday, 11 November 2008.