Economy & Energy
Year IX -No 52:
October - November 2005   
ISSN 1518-2932

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Espirito Santo will turn into Bolivia

Carbon Balance in the Greenhouse Effect Gases Emissions in Energy Use and Transformation in Brazil:

 Analysis of Results and Conclusions.

Text for Discussion:

Alternative to the Additional Protocol of the IAEA Nuclear Safeguards Agreement

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 Article:

Carbon Balance Concerning the Emissions of Greenhouse Effect  in the Energy Use and Transformation in Brazil: Comparison between the Extended Top-Down and Bottom-Up Methodologies – Analysis of Results and Conclusions.

Carlos Feu Alvim, Frida Eidelman and Omar Campos Ferreira

feu@ecen.com, frida@ecen.com, omarecen@pib.com.br

Introduction

The Economy and Energy Organization has made together with the Ministry of Science and Technology a study about carbon balance in the emissions resulting from the use and transformation of energy. The dissemination of the results of this study has been made by the e&e periodical. The following results have already been published:

● Carbon Balance in the Production, Transformation and Use of Energy in Brazil – Methodology and Results of the Top-Bottom Process in the period 1970 – 2002 (e&e N 48).

● Carbon Balance in the Energy Transformation Centers (e&e N 50).

 ● Results corresponding to the adopted accounting process that includes the extended Top-Down approach and the use of coefficients calculated in the national inventory for the period 1990-1994 for estimating emissions from 1970 to 2002 by the Bottom-Up process (e&e Nº 51).

In the present issue the results of both methods are compared and some deviations found are pointed out; they should bring about corrections in the inventory of carbon balance and emissions inventory. Suggestions regarding the corrections are presented and they will be the object of a complementary analysis.

Comparison of Emissions using the two Methods

The benemis program made for calculating emissions permits to obtain synthetic tables grouping energy sources and economical sectors. In the case of the benemis_c_eee version the contained carbon data, emissions using the two processes and their comparison can be obtained for each year.

 Table 1 shows the values of contained carbon without discounting emissions of the main consuming sectors and energy sources grouped by origin[1].

In the following tables the emissions calculated by the Top-Down (Table 2) and Bottom-Up (Table 3) methods are compared in the aggregated form. Table 4 illustrates the procedure used for the comparison: the discrepancies relative to these two methods are indicated by colors with limits fixed by percents of deviations (white for differences below 0.1% or zero values, green, between 0.1% and 10%, yellow, between 10% and 30% and red, above that value). Concerning the aggregated tables, there is an additional difficulty namely the aggregation criterion of fuel by origin. In the case of gases, for example, residential gas had different origins along time and in the usual BEN’s structure it is presented together with coke plant gas. In the program’s present representation by origin it is recorded as mineral gas.

Table1: Carbon Contained in Fuels Used in Gg/year, Year 1990

Table 2: Carbon Emissions in Gg/year (1990) – Top Down Method

Table 3: Emissions by Sector and by Group of Fuels - Year:1990 - Gg /year Bottom-Up

                           (*) Excludes Transformation

Identifying the problems is easier when one examines the difference by fuel and when the accounts have a larger disaggregated form. This will be carried out in what follows. Preliminarily, it should be observed that in Table 4 the red cells for mineral coal identify problems concerning the fuel by origin, mainly gas. Some deviations pointed out for biomass are due to difficulties already detected in transformation.

Figure 1 shows the emissions by sector and by fuel by origin obtained using coefficients obtained in the Bottom-Up process. The Transport Sector is the largest sector responsible for carbon emissions from fossil sources.

The following tables illustrate the results obtained from calculating the carbon balance (year 1990) and are used in the analysis of the existing problems.

The first two tables (Table 5 and Table 6) show the original carbon content in the fuels used in transformation and consumption. In transformation, the negative masses show (as in BEN) the absorption of an energy source that is transformed into another one and recorded as positive input on the same line. For the transformation centers where emissions are not calculated (Petroleum Refineries, Natural Gas Plants, Gasification Plants, Coke Plants, Distilleries and Other Transformations), the “Total” column on the right points out the faults in the carbon balance. Later on, using the results of the following tables it will be possible to complete the carbon balance of the remaining transformation units.

Table 4: Comparison of Results of the two Processes.        
 The percent differences are relative to the Bottom-Up data (colors classify the deviations)

Figure 1: Values of carbon emitted by sector and by fuel by origin.

Table 7 presents the emissions obtained through the reconstruction of the Bottom-Up process and Table 8 presents those obtained through the Top-Down process. Table 9 presents the analysis of results and the percent deviations found between the two processes (values relative to the Bottom-Up value).

Table 5 –Carbon Content by Activity and by Energy Source

 (Final Consumption) – Year 1990 – Gg/year

Table 6: Carbon Content by Activity and by Energy Source

– Year 1990 - Gg /year (Transformation)

Table 7: Emissions by Activity and by Energy Source (Final Consumption

and  Transformation) – Bottom-Up Method – Year 1990 - Gg /year

Table 8 Emissions by Activity by Energy Source (Top-Down Method) 

1990 - Gg /year

 
Table 9: Carbon Balance: Comparison Top-Down X Bottom-Up

(values relative to the 2nd)

             The comparison regarding the balance uses the already described colors code. In Table 9 the colors indicate the magnitude of discrepancies between the values calculated by the two approaches. The analysis of the transformation centers could be completed using the collected data.

                Considering that our aim is to make a diagnosis and not a revision of the coefficients, some energy sources were picked up as a help for this purpose. In order to make this analysis easier, we have calculated the relationship between the emission coefficients and the carbon content in the carbon mass conservation of gasoline, firewood and fuel alcohol. We have also picked up the cases of diesel oil and charcoal to allow a comparison with the three fuels identified as those that deserve more attention.

Carbon Balance in Transformation

     The carbon balance results for the transformation centers are shown in Table 10.

Table 10: Carbon Balance in the Transformation Units for the Year1990 calculating the emissions by Bottom-Up and Top-Down Processes

 The emission calculated by the two methodologies is included in Table 10, the carbon balances present satisfactory results for most transformation units. In the autoproducers power plants some important differences were detected in the results of the two methodologies that may be assigned to emissions calculation in the use of “other primary” and tar (see Table 9). In the charcoal plants the emissions are underestimated but the bigger problem seems to be in the Bottom-Up methodology. In an attempt to equate the matter, firewood will be analyzed in what follows as it presents deviations relative to the two methods. The case of distilleries has already been previously commented and there are problems in the carbon mass/ energy coefficients both for alcohol (that will be analyzed in what follows) and the raw material (sugarcane juice and molasses) for which a generic coefficient is applied.

Emission Coefficients and Carbon Conservation

The emission coefficients used by the benemis program utilize the results of the emission calculations carried out by the Bottom-Up process. Since the carbon mass is conserved, these coefficients must have a relationship so that, for example, if an automobile emits less carbon monoxide (CO), the CO2 quantity or other carbon compounds must increase. The relationship regarding the coefficients is shown in the following box.

The relationship between the emission factor and the carbon mass in the fuel will be used in the emission coefficient analysis.

Analysis of Gasoline and Diesel Oil Emissions

Gasoline presents one of the most important discrepancies between carbon emissions evaluated by the two methods. In effect in 1990 the carbon mass calculated by the Bottom-Up method is 8050 Gg while it is 5863 Gg by the Top-Down one, with a 37% difference relative to the result from the second method.

According to BEN, in 1990 we had:

7485 thousand toe of gasoline or 313 thousand TJ and 5922 Gg (or thousand t) of Carbon;

Using the 0.04186 tC/toe and18,9 tC/TJ factors and assuming that 99% of the carbon undergoes oxidation (not retained) we have 5863 Gg of carbon by the Top-Down process.

Gasoline consumption in 1990 in Brazil was 7485 thousand toe (9606 thousand m3), that corresponds to a mass of 7041 thousand t[2]. This mass contains 6125 thousand t (Gg) of C, using the carbon content used previously in the present study [3] that is only 3.4% different from the carbon mass calculated using the IPCC factor.

Therefore, the carbon mass calculated from emissions in the Bottom-Up process (8050 Gg) exceeds that of the gasoline itself. The carbon mass and that of contained carbon (of the gases and the total) are shown in Table 11. The data are compared with those published by the Brazilian Declaration and it differs only in the NMVOC value that should be reevaluated after the MCT supplies the coefficients used here.

Table 11: Gas Emissions and Masses of Contained Carbon for Gasoline (year 1990) and carbon/ implicit energy factor in the emission coefficients used.

The carbon mass/energy factor for gasoline should be 27.1tC/TJ in order to correspond to the emission factor, instead of IPCC’s 18.9 that was adequate for carbon balance in refineries.

The difference found is assigned to a procedure suggested by IPCC where in the case of CO₂ the total carbon mass obtained would be indicated. Even then it seems convenient in the future to avoid this double counting of emissions. It would be prudent, at least, to make explicit the procedure adopted and warn that all emitted carbon mass is considered in the CO₂ emissions. An additional observation is that in a Bottom-Up process it would be expected that emissions would be based on experimental values (in the case, measurements that represent the fleet).

In the future, a modification will be introduced in the benemis program so that one can have emission coherent with the carbon balance (avoiding double counting).

The same emission evaluation was carried out for diesel oil (Table 12). The results were compared with those of the inventory. In the Top-Down methodology the contained carbon (17789 Gg in Table 6) and the carbon emissions (17531 Gg in Table 8) were evaluated and they are not much different from those calculated in the Bottom-Up process (17955 Gg in Table 7).  The calculated fc value (20,7 tC/TJ) is not much different from the value recommended by IPCC (20,2 tC/TJ) as well, and the small difference could be caused by the relative importance of the small emissions that only correspond to 2.3% of the total emission.

Table 12: : Gas Emissions and Masses of Contained Carbon for Diesel Oil (year 1990) and carbon/ implicit energy factor in the emission coefficients used.

Analysis of Firewood Emissions

Firewood is another energy source (besides gasoline and alcohol) in which the carbon monoxide in the emissions is important and its analysis is of interest.

The contained carbon value from the Top-Down method (17210 Gg) is lower than that from the Bottom-Up method (19341 Gg), as in the case of gasoline. However, the coefficients used are less trustworthy than those of gasoline and consequently the calculation of the carbon mass is also less trustworthy. The fc value (25.5 tC/TJ) is lower than that indicated by the IPCC and used in the Top-Down approximation (fc=29.9 tC/TJ). Its calculation is shown in Table 13.

Table 13: Emissions for firewood (year 1990) and calculation of the fc coefficient (carbon mass / energy) corresponding to emissions

Regarding the values for charcoal (Table 14) it has a carbon mass/energy factor compatible with that recommended by IPCC (fc=29,9 tC/TJ) and presents a 2.6% difference in carbon emissions.

Table 14: Emissions for charcoal (year 1990) and calculation of the fc coefficient (carbon mass / energy) corresponding to emissions

Analysis of Alcohol Emissions

In the case of alcohol the carbon mass / energy coefficient in the Top-Down method is incoherent with the value obtained using pure ethanol data. The emission values were transferred to Table 15. The calculated carbon mass in emissions (4333 Gg) exceeds the mass calculated in the Top-Down process (3652 Gg) that must be underestimated due to the C mass/ energy used (14.81 tC/TJ), also underestimated.

However, the carbon mass is coherent with the value expected from the carbon content in ethanol. In fact, the alcohol mass (anhydrous +hydrated) is 9063 thousand t of alcohol that corresponds to about 8900 thousand t of pure ethanol. From the chemical formula of ethanol and from the atomic masses involved we conclude that 24/46 of the ethanol mass is made up of carbon. Therefore we have a mass of approximately 4600 thousand t of this element in alcohol consumption in 1990. This estimate is also coherent with the carbon mass in the emitted gases. That is, in this case the Bottom-Up approximation seems trustworthy and the fc value found (17.9 tC/TJ) is coherent with the expected value for ethanol.

Table15: Emissions for alcohol (year 1990) and calculation of the fc coefficient (carbon mass / energy) corresponding to emissions

• 6. Conclusions

• The Carbon Balance carried out here is an excellent diagnosis tool for Emissions Inventory. The Top-Down and Bottom-Up methodologies are compared allowing an analysis of the results and identification of errors.

• Furthermore, the calculation programs that were developed permit to estimate emissions between 1970 and 2002, extending to five years the results of the inventory (in the energy area) compiled by the MCT (1990 to 1994)

• In the methodological aspect, the highlights were:

• ·          Extension of the Top-Down method to the transformation and consumption centers  in an approximation called Top-Bottom;

• ·          Survey of Carbon and Energy Balance in the transformation centers;

• ·          Demonstration of the correlation existing among the emission coefficients and carbon content and the carbon mass/energy factor;

• ·          Identification and evaluation of the double counting in the  Bottom-Up procedure where the carbon volume of some fuels can be overestimated in up to 30%;

• ·          Methodology for calculating the carbon and hydrogen content in fuels using the low and high heat values of hydrocarbons.

• In the calculation tools we point out:

• ·          A program that calculates emission using the Top-Down process directly from data of an energy source balance extended in a methodology equivalent to that of IPCC. (ben_eec);

• ·          A program that evaluates carbon emissions using energy source data and emission coefficients by type of use of fuel included in BEN (benemis_eee_c);

• ·          A program that supplies the carbon emissions calculated by the two methodologies in the “account” and energy source of BEN and  the differences found in both forms (benemis_eee_c);

• ·          Comparison between the results of the two emission calculation methodologies using summary tables with color codes (benemis_eee_c).

• Concerning the results – that was not the main objective of the study – it should be pointed out:

• ·          Evaluation by the Top-Down process of emissions in the use and transformation of energy between 1970 and 2002;

• ·          Extension of the evaluation of emissions using coefficients taken from the Bottom-Up methodology for the period 1970 to 2002.

• Regarding diagnosis, the following points should be noticed:

• ·          Identification of problems relative to the high and low heat values whose coherence should be revised[4]; the most notorious case  BEN is that of natural gas;

• ·          Carbon balance in some transformation centers show important differences between the input and output carbon mass that are larger for biomass; the most important case (according to the diagnosis) is that concerning the incorrect carbon mass/energy coefficients for alcohol; differences were also detected in the energy balance that may be due to inadequate heat values data;

• ·          Carbon balances show important results for fuels where emissions of other gases containing carbon are larger than CO₂ due to the double counting in the calculation; the largest difference refers to gasoline mainly in years when carbon monoxide was more accentuated;

• ·          Identification of inaccuracy regarding energy allocation by fuel of origin that might influence the emission accounting (biomass X fossil fuels).

• Recommendations for future studies:

• ·          Elaboration of a program (from ben_eec) that can generate graphics and tables for the inventory in the Top-Down methodology;

• ·          Study the carbon content coefficients for biomass, notably in the alcohol and vegetal coal production;

• ·          Analysis of consistency regarding BEN’s high and low heat values  and those from  Petrobrás and other sources;

• ·          Development of procedures for evaluating hydrogen (and carbon) content in a fuel using the difference between the high and low heat values;

• ·          Proposition of a coherent set of emission coefficients and carbon content from the analysis of the carbon and energy sources balance values.

•  

List of Annexes to the MCT Report, available only in Portuguese at the Internet: http://ecen.com

Annex 1: Contained Carbon, Equivalent Energy and Energy Balance 49 X 46 -                
 ben_eec Program- User’s Manual

Annex 2: Tables of Contained Carbon in Fuels in Selected Years

Annex 3: Results Of Carbon Balance in Selected Years

Annex 4: Goal 1 Report of the Carbon Balance Project

Graphic Edition/Edição Gráfica:
MAK
Editoração Eletrônica

Revised/Revisado:
Tuesday, 11 November 2008.