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Emission of Greenhouse
Effect Gases by Thermoelectric
Power Plants
(December 1999 Version)

e&e team

This work is part of the study on emission of greenhouse effect gases resulting from the operation of the Brazilian thermoelectric power plants in the period between 1990 and 1997 made for the Brazilian Ministry of Science and Technology and PNUD.

SUPPORT:

Original Proposition (practically maintained)

The study was concentrated on three lines:

• survey of the thermoelectric power plants installed in the country by technology type and evaluation of the fuel used in each one of them (the survey made is not available in electronic media)
• evaluation of the contribution of each type of fuel to the emission of the different greenhouse effect gases (CO2. CO, NOX, N2O, CH4 and NMVOC), according to the respective technology (geographic distribution by state allows for considering the main power plants);(Present report)
• projection of power plants emissions foreseen in ELETROBRÁS' Decennial Expansion Plan. These values are compared to preliminary evaluations of economical reference scenario carried out by e&e using information available from producing companies (under study).

1. Introduction

The generation of electrical energy by thermal power plants is very limited and geographically localized. In Brazil there is a noticeable predominance of hydraulic energy as primary source of electrical energy. Thermoelectric and mineral coal power plants are located close to the mines in the south region.

Figure 1.1 Generation of the public utilities is basically hydraulic, thermal participation is modest and the use of the existing capacity has been subordinated to conjunctures - Data from BEM/MME 1998 (1.1).

As a strategic option, mainly after the 1973 and 1979 petroleum shocks, all priority has been given to hydraulic generation which, albeit renewable, is capital intensive.

Furthermore, fuel is consumed for this purpose with strong regional predominance, noticeable diesel oil in the north and coal in the south. Fuel oil is concentrated in the north and southeast regions and in the latter it is used to supply eventual or seasonal needs of the interconnected net.

Table 1.1: Use of Fuel for Generating Electricity in the Period 1990-1997 TJ/year

On the other hand, plant distribution by state for public use is so specialized that it permits, as it will be noticed, to practically individualize the consumption of the most important plants (coal and fuel oil) by the consumption at the state level.

Figure 1.2 Generation in the public electric power plants by fuel presents a notable concentration by state, fuel oil in AM, RJ and SP states and coal in SC and RG states.

By fuel type, we have the distribution in the period shown the following figure. Coal (4 plants) and fuel oil (3? Plants) represent 71% of fuel consumed and they should be handled in a special way. The diesel oil plants can be handled as a set or as main types.

Figure 1.3 Coal and fuel oil represent 71% of the thermal energy in GJ used in thermal generation in the public power stations (nuclear not included)

Figure 1.4 Participation of fuel oil in CO2 generation sources has been replaced by vapor coal and diesel - Data from BEN/MME 1998.

1.2 Auto-producers

Auto-producers have had an important role in thermoelectric generation and this role has been growing with time as shown in the following figure.

Figure 1.5. Thermoelectric self-producer contributions are almost equivalent to that of public power plants - Data from BEN/MME 1998.

Figure 1.6 In self-producers a much larger variety of fuel is found, mainly fuel locally available or used in cogeneration processes - Data from BEN/MME 1998.

Auto-producers deserve a separate study, due to their importance, the diversity of fuel used and the sectors involved.

2. Public Electrical Power Plants

In December 1997 the installed capacity of the public thermoelectric power plants was the following

Table 2.1 Installed Capacity by System

(*) They correspond to more than 300 localities electrically isolated one from the other.

About 85% of the isolated systems are in the North Region that includes the states of Amazonas, Roraima, Rondônia, Amapá and Acre. The remaining 15% are distributed in the states of Pará, Maranhão, Tocantins, Pernambuco, Bahia, Mato Grosso, Mato Grosso do Sul, Paraná and Rio Grande do Sul.

The thermoelectricity generation percentage by region and by fuel type in December 1997 are the following one:

Table 2.2 Thermoelectricity Generation Percentage by Region and by Fuel Type

3 Coal Thermoelectric Plants

3. General Aspects

Generation using vapor coal is located in 4 power plants associated with mines near to the plants. They are:

The fact that these plants use different types of specific coal differentiated by their calorific power permits using the available data at the state level in order to evaluate with good approximation the emission of each plant. For the first three plants there is a specific study relative to the emissions and that was carried out by JICA/ELETROSUL/CEEE (2.1).

3.2 Emission Parameters

           3.2.1 - Efficiency

The study surveyed for different operation conditions the SO2. NOx and particulate emissions for these plants using fuel with different calorific power and different sulfur content. The study calculated as well the dispersion of the pollutants. Furthermore, operational data such as gas temperature and velocity in the chimney, generated power and quantity of consumed fuel are given. The operational data and the fuel characteristic, namely ash and sulfur content, were supplied by the power plants.

The operational efficiency was inferred for different operation conditions and they are shown in Table 3.2 for the three plants.

Figure 3.1 Efficiency does not depend on the operation range studied relative to the nominal power. The large units show a larger efficiency

Table 3.1

Efficiencies were not sensitive to operational range 50% above the nominal power. Variations of the coal calorific power were not significant in each unit so that the influence of this factor might be verified. Since they belonged to different batches (different days and different ash and sulfur content) this might be an indication of stability of these characteristics. In different units of the same plant the variation is significant which makes it preferable whenever possible to use directly coal consumption and checking efficiencies through electric generation data.

SO2 , NOx and particulate emissions were specifically studied by JICA. Some contradictory facts could be observed such as values of sulfur emission having mass values superior than those indicated for the fuel. The following graphic illustrates this fact.

Figure 3.2 A systematic difference was detected between the emitted sulfur that was systematically superior to that indicated for coal.

Apparently these are systematic errors in determining the coal sulfur content or emissions (or in our interpretation). It is noticeable, on the other hand, a good relative correlation. The calculated sulfur emission in the referred study are coherently much lower than those measured. It could have been an interpretation error in the sulfur content values that might be, for this plant, related to the carbon mass and not to the fuel. Considering this hypothesis, the correction yields a much more coherent value. Furthermore, the content supplied - 1.9% - is in contrast to that supplied in INFORMATIVO ANUAL DA INDÚSTRIA CARBONÍFERA 1994. Ministério de Minas e Energia for the referred mine. Adopting the hypothesis that the contents refer to the coal without ash one finds emission value (sulfur retention about 23%) and content value - 3.4% that seem more coherent. For the present work we preliminarily adopted values corrected in this way.

Values obtained for the three plants in different measurements in some units in each plant

Figure 3.3 - Declared sulfur contents and sulfur emissions show some apparent incoherence

The parameter mass of S emitted by TJ of burnt fuel permits to directly infer emissions from consumed fuel and when available the sulfur content. In the case of the Candiota plant there is an apparent incoherence between the variation in emissions and the relative stability of sulfur content indicated for the coal. As the methodology used for detecting emissions was adequate for other cases, the reliability of the ore analysis should be verified.

In the table below we indicate the values of the coefficients obtained for sulfur emission. For the Jorge Lacerda Plant we have considered the content values corrected as mentioned above.

In case the sulfur content for the several years should be available, the retention mentioned in the previous item should be used excepting plant's indication about process variations.

NOx emissions were measured by JICA and the following parameters were found for the three plants. These values are given in the table below.

The authors of JICA's work observe that NOx emissions are low due to low temperatures in the boiler. Measurements were carried out in external environmental sampling points relative to the NO2/NOx ratio but as no values for O3 are available it was not possible to model the dispersion. The NO2 indexes observed were lower than the usual ones as well as those for NOx. In the present evaluation we have considered that the indicated default values for the parameters' ratio are maintained.

Note: The relative emission of particulate may indicate incomplete combustion. The material collected in the precipitators (of relatively low efficiency) is re-injected in the boilers. This is an indication that the material was not burnt. An analysis of combustion data may eventually supply data about non- burnt carbon and CO emission. Temporally, a parametric evaluation of these emissions was made.

3.3 Emission comparisons using global and specific parameters

Data of JICAS' study were collected in 1996. For this same year global data by state specifying coal type are available. This practically allows for identifying the quantity of coal consumed by plant as shown in the following tables.

From these parameters one can obtain the emission due to the plant and/or the fuel type by state that, as can be observes, is bi-univocal. In this case the available data permit to estimate performance of the plants.

SO2 Emissions

NOx and N2O Emissions

3. Fuel Oil Plants

3.1 General Aspects

Electricity generation by public plants is limited to the states of Amazonas, São Paulo, Rio de Janeiro, Rio Grande do Sul and Minas Gerais.

The table below summarizes the characteristics of these plants:

Table 3.1 Fuel Oil Thermal Plants

3.2 Fuel Oil Consumption by State

Table 3.2 Fuel Oil Consumption for Electricity Generation in the States in 1000t/year

The results are parametric for the moment. When data concerning the fuel oil used are available the results will have a better precision. It can be noticed that data by state are satisfactory

• Minimal Data Necessary about the Fuel

Calorific Power

Sulfur Content

Composition (C/H ratio is useful)

• Data concerning the plants

Operation scheme with characteristics of main components associated with combustion

Specific emission data for the plants or for similar ones

4. Emission by State

4.1 General Aspects

Parametric tables were elaborated by state and by year and the consumption by fuel type and by year. Multiplying these parameters (as shown for coal) permits to evaluate the emission of each state.

Presently there are some differences concerning fuel type (with subdivisions for coal) and some characteristics already obtained for the main plants (coal). The Excel tables allow for automatic updating the global results.

4.2 Preliminary Results

Some preliminary results are already available. Those for 1997 and 1991 are shown below. The unit is Gg (gigagram).