Economy
& Energy
Year IX -No
60:
February
2006 - March
2007
ISSN 1518-2932
No
60 Em
Português|
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Economy
& Energy |
No
60 Em
Português |
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Analysis of Specific Problems Related to Emissions that Generate the Greenhouse Effect
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Text for Discussion:
Summary 1 – Introduction 2 –Background 3 – Corrections in the Calculation of Emissions from Renewable and Non-Renewable Sources 4 – Treatment of Transformation Centers 4.1 Carbon Balance in Petroleum Refineries 4.2 Carbon Balance in Natural Gas Plants 4.3 Carbon Balance in Coking Plants 4.4 Carbon Balance in Gasification Plants 4.5 Carbon Balance in Alcohol Distilleries 4.6 Carbon Balance in Charcoal Plants 5 – Conclusion 1 – IntroductionThis study surveys the data for the revision of the Carbon Balance, object of the Partnership Contract 13.0020.00/2005 signed between the Economy – e&e – Organization and the Ministry of Science and Technology – MCT. The present article is specifically related to Goal 3 whose proposed activity is the analysis of problems concerning emissions of greenhouse effect gases detected by the carbon balance and other studies conducted by the CGMCT. It is also connected with Goal 5 since it was used a more complete version of the software under development. The following specific problems are examined: a – Problems regarding the inclusion of renewable and non-renewable fuels in the “Other Recoveries” item; b – Problems detected in carbon balance in Transformation Centers. Based on these corrections, the C and CO2 emissions are calculated in the energy use and transformation in Brazil using the bal_eec. Software. This software consolidates the carbon balance and emissions calculations previously carried out by ben_eec and benemis_e[1]. 2 - BackgroundThe methodology used is to account for the primary and secondary fuels that enter in the economic system of a country to satisfy needs generated by human activities (even the non-commercial ones) and the carbon mass that leaves the system. Once introduced in the national economy, the carbon contained in a fossil fuel is emitted to the atmosphere or is retained in some way, for example, in the fuel stock increase, its transformation into a non-energy product or its partial non-oxidized retention in the combustion residues. Report 1 has presented a revision of the technical basis of the Project and of the chronogram (due to the delay involving the transfer of resources) and the following Technical Notes. 1 - Technical Notes № 1: Evaluation of Emissions Using the Extended Top-Down Process for the 1970 - 2004 Period (Goal 1). Published in the Nº 58 issue of this periodical. 2 - Technical Notes № 2: Carbon Content in Biomass Fuel (Goal 3). Published in the Nº 57 issue of this periodical. 3 - Technical Notes № 3: BEN_EEC Program – User’s Manual (Goal 5). In the Carbon Balance calculation carried out in the ambit of the No 01.0065.00-2003 Agreement between e&e and MCT some differences were detected regarding the Extended Top-Down and Bottom – Up approaches and this is the object of the present study. Some differences were also detected between the Carbon Balance and the Initial Inventory of the MCT. Some of them correspond to the difference regarding the inclusion of renewable and non-renewable emissions in the Other Recoveries item. The Other Recoveries item represented in 2005, 5.2% of the quantity involved in the transformation of primary into secondary energy and 0.8% of the final consumption in terms of carbon mass. That is, even though important from the methodological [2] point of view, it is expected that the corrections to be introduced in the present situation will not have an important impact on emissions calculations. The differences found in the transformation centers are more significant in terms of emissions (14% of the carbon mass emitted in 2005) and are also important for the coherence tests on carbon balance were it is expected to establish the carbon mass processed in a transformation center or in sectors where consumption (in terms of BEN) is direct 3 – Corrections in the Calculation of Emissions from Renewable and Non- Renewable SourcesOne of problems found in previous calculations and in the comparison of results of the Carbon Balance Project with other studies is due to the distinction between renewable and non-renewable energy sources. The emitted carbon by renewable sources (fuel) is not incorporated in the atmospheric carbon inventory because it is entirely recycled by biosynthesis if production is in permanent regime. However, when the carbon balance is used as a control instrument regarding adequate emission coefficients, all carbon involved in energy use and transformation should be considered and this demands the separation of the National Energy Balance into the two categories (renewable and non-renewable). The emission coefficients used are also different: it was used the in the case of Other Recoveries the 20.0 tC/TJ factor for the non-renewable sources (as petroleum) and in the case of renewable ones it was used the value of vegetal residues, that is, 29.9 tC/TJ. For most energy sources there is no doubt regarding their origin (renewable or not) both for primary and secondary sources. This is not true for the mentioned item [3], that in most cases is considered as a share of the renewable sources, including in studies carried out by e&e (ref. Carbon Balance Final Report of December 2005). In the case of transformation one can also identify the type of energy source by the products that are generated or by the type of transformation (e.g. refineries transform non-renewable sources). According to information from those responsible for the Energy Balance at MME one should consider that one part of this item is renewable and the other is non-renewable. The “toe” spreadsheet for “accounts” and energy sources from the BEN data was then used, and the different accounts that participate in this energy source were analyzed in order to separate the renewable part. These values and two options for the energy sources were included in the bal_eec program. To feed these values in the energy spreadsheet it was used the Other Non Renewable column available at the extended Balance structure (BEN 49X46) but whose content is zero for all years. The renewable sources were maintained in the original column. The staff responsible for the Energy Balance is working in order to supply definite numbers regarding the share of renewable and non-renewable sources in this item for several years. The approximation adopted here (based on the distribution of the existing years) gives a preliminary estimate. The following criteria were adopted for separating Other Recoveries into renewable and non-renewable sources: · Refineries and Natural Gas Producing Units (non-renewable); · Public Service Power Plants: the source is renewable (wind power) and there is no direct emission (emission coefficient equal to zero); · Autoproducers Power Plants: classification into renewable and non-renewable sources according to Table 3.1, and for the previous and subsequent years average values were considered. It should be noted the presence of sulfur where there is no emission involved (excluded in the emission calculation). However, sulfur was kept in the energy balance in the non-renewable part so that the energy balance calculation remains coherent with BEN’s data; · Industrial Sector: Cement Industry (considered half renewable and half non- renewable), Chemical Industry (considered as non-renewable), Paper and Cellulose Industry (considered as renewable) and Ceramics Industry (considered as renewable); · Gases from Blast Furnaces and Steelworks are non-renewable.
Table 3.1: Distribution of Fuels in the Autoproducers Power Plants Included in the “Other Renewable” item of BEN AUTOPRODUCERS POWER PLANTS ENERGY CONSUMPTION IN ELECTRICITY GENERATION
Source: MME/BEN In Table 3.2 it is shown the distribution of energy sources in “Other Renewable” regarding renewable and non-renewable sources. Table 3.2: Distribution of renewable and non-renewable sources in the Other Recoveries Item for the year 2000
4 – Treatment of Transformation CentersIn the previous evaluation carried out for MCT significant differences in the carbon balance were found and in some cases differences in energy in Transformation Centers. BEN presents the following transformation centers:
Transformation centres can be divided into two groups according to the treatment they get in BEN. In those with (*) the energy consumption is not considered in the transformation centers themselves but rather as energy consumption in the so called “energy sector”. So the energy used in refining is accounted for in the energy sector as consumption of products (refinery gas, fuel oil, etc.). In the case of distilleries, energy consumption from bagasse is also accounted for in the energy sector. Emission calculations for the inventory adopted an analogous procedure. For this reason it includes only emissions associated with electricity power plants and charcoal plants. In the case of carbon balance it must be balanced in all cases when emitted gases are included. This study will precisely test the consistency between the amount of carbon that constitutes the “input” and the “output” made up by the emitted carbon-containing gases, by the retained or non-oxidized carbon and, as in the case of transformation, by the products (or wastes) that are generated. In what follows it will be presented the results of the Energy (only graphics) and Carbon(graphics and tables) Balances for the following Transformation Centers: Petroleum Refineries, Natural Gas Plants, Gasification Plants, Coking Plants, Distilleries and Charcoal Plants. Corrections that were considered pertinent were implemented and will be considered in the results. Except for charcoal plants, it is expected that the energy and carbon balances (input x output) are right for each type of center. Calculation is based on the values (Output – Input) that in BEN’s structure that was adopted by the program corresponds to the Total item in the line of each Transformation Center. So an ad-hoc table is built for the account pertaining to the focused Transformation Center. The program is run for all years (from 1970 to 2005) both for energy (toe) and Carbon Mass (Gg of C). The Energy and Carbon Balances Graphics are built using the difference percent values (Total/Input). 4.1 Carbon Balance in Petroleum RefineriesIn the case of Petroleum Refineries the ad-hoc tables are built for the Petroleum Refinery account, with the columns Primary Energy (Petroleum plus Other Non Renewable) – that correspond to Input - and Total (Input -Output). The carbon mass values in Gg (thousand tons) can be seen in Table 4.1. With the percent difference values (Total/Input) is built the Energy and Carbon Balance Graphics in Petroleum Refineries (Figure 4.1) that is shown with the corresponding energy value. TABLE 4.1:Values of Contained Carbon in Gg of Carbon for Petroleum Refineries
Figure 4.1: Energy and Carbon Balance in Petroleum Refineries Energy and Carbon Balances show a similar behavior along the years and a small mass deviation. It seems that an appropriate emission coefficient choice was made and that the different characteristics of the fuel had small influence on carbon balance in petroleum refineries along the years. The fact that carbon balance is negative is compatible with transformation losses that are not recorded in BEN. 4.2 Carbon Balance in Natural Gas PlantsFor the Natural Gas Processing Units (NGPU) liquids are extracted from humid natural gas that condensate at room temperature and it remains dry natural gas composed mainly of methane and ethane. The liquid fractions can be directly incorporated to some products (LPG, Naphtha, etc.) or receive treatment in Natural Gas plants. This seems to be the preferential destination in recent years perhaps because it facilitates the homogeneous characteristics of commercialized products and simplifies the operation of the NGPUs. In Table 4.2 are shown the results of the ad-hoc tables built for the Natural Gas Plants account and the Humid Gas (Input) and Total (Output– Input) columns for carbon mass values. TABLE 4.2: Contained Carbon Values in Gg of Carbon for Natural Gas Plants
Using the percent differences regarding carbon mass (in Gg) and energy (in toe) it was built the Energy and Carbon Balance in Natural Gas Plants (Figure 4.2).
FIGURE 4.2: Energy and Carbon Balance in Natural Gas Plants It can be noticed in Figure 4.2 that from 1995 on there is practically no difference between the energy and carbon balances in spite of the fact that the same emission factor was used for all the years. In the years before 1995 the curves follow exactly the same trend but with a systematic component of the variation. This can be explained by the use of coefficients that are not adequate if natural gas from different origins have been used during this period. The different composition of the liquid products obtained indicates that the humid gas treated in the NGPU had varied compositions as shown in Figure 4.3. The largest percent value of liquids obtained in the first years indicates a more “humid” natural gas (containing a larger liquid fraction) or a smaller liquid extraction in the last years. In this case the conversion coefficient from natural units (m3) to toe should be different for each year. In the same way different coefficients should be used for carbon mass calculation (tC/toe).[4] It can also been seen in Figure 4.2 that there is a trend both for energy and carbon to be negative and not distributed around zero. Systematic negative values indicate losses since systematic positive values certainly involve errors regarding the mass/and or energy coefficients used.
Figure 4.3: Percent value of carbon mass obtained from humid natural gas has varied substantially from 1988 on, what justifies the deviation of carbon balance relative to energy balance observed in the previous figure . When the Carbon Balance is calculated according to what is shown in Phase 1 (Ref. 2) each ten years until 2005, one has the values of Table 4.3. In this table it can be observed that in most years the Carbon Balance does not present deviations above the expected value and whenever this occurs the variation could be due to variation ob carbon content in the humid gas that is not reflected in the coefficients used (considered as constant). TABELE 4.3: Carbon Balance in selected years (mass in Gg) for Natural Gas Plants
4.3 Carbon Balance in Coking PlantsIn Coking Plants, metallurgical coal is converted in mineral coal coke (used in steel fabrication) in a distillation process in the absence of oxygen. Gases and liquids are produced as side products and the gases are used as fuel in steelworks including the coking itself, as well as liquids. The gases are recorded in the Balance as coking gas and the liquids as tar. Calculations were carried out with two different emission factors for coking gas and concerning tar, since we have no value suggested by IPCC, the value used in the Initial Inventory was adopted, namely 25.8 tC/TJ. The carbon balance is shown in Table 4.4 and it is compared, in Figure 4.4, with the energy balance. In the case of Coking Plants the input is Metallurgical Coal (National and Imported) and the output is mineral coal coke, coke oven gas and tar. TABLE 4.4: Values of Contained Carbon in Gg of Carbon for Coking Plants
FIGURE 4.4: Energy and Carbon Balance in Coking Plants showing the values calculated with the 29,5 and 13,0 tC/TJ (correction) coefficients for coking plant gas; the corrected carbon balance values practically coincide with those of the energy balance. A similar behavior is found in the Carbon and Energy Balances but the two curves are too distant from each other showing a systematic error due to the use of an emission factor that is not adequate for calculating carbon emission. As there was no factor calculated by e&e for coke oven gas, the value adopted by the Inventory (29,5 tC/TJ) was initially used. IPCC suggest for coke plant gas (in the case of sectorial calculations, as the case here) the13.0 tC/TJ value. This low value (relative to the other energy sources) is justified by the hydrogen that is present in this type of gas. The calculations were then repeated using this value and the corrected curve is presented in Figure 4.4. It should be noticed that in Figure 4.4 the curves follow the same behavior and there still a systematic error (even though much smaller than the previous one) that can be assigned to the energy balance as the behavior of both curves is practically the same. 4.4 Carbon Balance in Gasification PlantsPiped gas for distribution to the network existing in 1970, practically restricted to the cities of Rio de Janeiro and São Paulo, was produced in gasification plants. Between 1970 and 2002 the raw material used in its fabrication changed from the predominant mineral coal (most of it metallurgical) to naphtha (petroleum product) and finally, to natural gas. The availability of natural gas for distribution caused the change of the old network and of consumer’s equipment so that in the last years there was only a residual production in these plants that were deactivated from 2003 on.In Table 4.5 are shown the data from the bal_eec program and in Figure 4.5 the Energy and Carbon Balances for Gasification Plants
FIGURE 4.5: Energy and Carbon Balances in Gasification Plants TABLE 4.5: Values of Contained Carbon in Gg of Carbon for Gasification Plants
When Dry Natural Gas was used together with Naphtha, both curves practically coincide from 1983 to 1994, but subsequently and until 2002 there are large variations even after adjustments of the emission coefficient regarding dry natural gas. These variations are present in both curves and reach 70% which shows that there is some problem concerning energy source data or its interpretation. The low relative importance of these plants in energy consumption and emissions do not justify a great effort to clarify the differences found. 4.5 –Carbon Balance in Alcohol DistilleriesThe emission coefficient previously used for alcohol was 14.8 tC/TJ. According to calculations carried out by e&e and that are part of Report 1 as Technical Note 2 published in the N° 57 issue of this periodical, this coefficient was changed to 18.8 tC/TJ for both Anhydrous and Hydrated Alcohol. As input to Distilleries we have Sugarcane Liquor and Molasses and as output Anhydrous and Hydrated Alcohol. The results obtained by the bal_eec program for the contained carbon balance are presented in Table 4.6. In the Carbon Balance analysis in a alcohol distillery the wastes are combustion gases represented by CO2 , fermentation gas (CO2) and glycerol considered as a representative of carbon compounds rejected as vinhoto. Therefore, a correction was introduced using data regarding carbon content in biomass from Technical Note 2 of Report 1 (see e&e N° 57). The results of this correction are presented in Table 4.7. TABLE 4.6: Values of Contained Carbon in Gg for Distilleries
TABLE 4.7: Values of Carbon in Gg in Distilleries corrected for vinhoto and CO2 from Fermentation
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