Greenhouse Gas Emissions

Emissions from Combustion

The use of fossil fuels constitutes the main anthropogenic source of greenhouse gases. Within this, carbon dioxide is the most important contributor; emissions of this gas occur during the combustion process, when the carbon contained in the fuel is combined with oxygen. Because combustion is not always complete, a small quantity of this carbon is emitted as carbon monoxide, methane, and some heavier volatile hydrocarbons. These gases are then oxidized to carbon dioxide in the atmosphere in a period of time than can range from a few days to ten years.

Additionally, oxidation of the nitrogen contained in fuels produces the formation of nitrous oxide and nitrogen oxides; emissions of the latter are closely linked to the air-fuel relation, combustion temperatures, and equipment control mechanisms. The formation of nitrous oxides is not yet well understood.

The level of reliability of greenhouse gas emission estimates is different for carbon dioxide and the rest of the gases. The former can be calculated with greater precision as the emission factors only depend on the carbon content of the fuel, the amount of fuel used and the oxidized fraction. The quantity of carbon in fossil fuels varies significantly by fuel type. Coal contains the greatest amount of carbon per unit of energy, while crude oil and natural gas contain 25% and 50% less than coal, respectively.

Carbon dioxide emission estimates from combustion were based on the two methodologies proposed by the IPCC: Top-Down and Bottom-Up (IPCC/OECD, 1995, vol.3). The Top-Down approach is based on apparent consumption of the different types of primary fuels, and is used to generate total CO2 emissions from combustion. The Bottom-Up method allows the estimation of emissions by sectors, based on final fuel consumption and transformation activities data. Theoretically, the application of these two alternative methods should make no difference in a countryâs total CO2 emission estimate, since the amount of fuel consumed, and hence the amount of carbon oxidized, should be the same in both approaches.

As shown in Table II-2, total CO2 emissions from the energy sector in 1990 were estimated to be 104,335 Gg, based on the Top-Down methodology (as reported in Tables S-1, S-2 and II-1).

However, when the Bottom-Up approach is applied, CO2 emissions resulting from adding the emission estimates by sector reach 94,907 Gg. Thus, the Venezuelan inventory shows a 9% difference between the CO2 emission results obtained from the application of both methodologies. This difference is basically due to the fact that apparent consumption in Top-Down, is 7.6% higher than the corresponding figure for the Bottom-Up (Table II-2), as a result, mainly, of statistic adjustments in the National Energy Balance (MEM,1990). Annex 2 presents a detailed explanation and analysis of Top-Down and Bottom-Up methodologies.

Tables D1-1 and D1-2 in Annex 1, show emission estimates based on the Top-Down methodology and Tables C3-1 and C3-2 summarize results based on the Bottom-Up approach. Emission estimates of the non-CO2 trace gases are less reliable. Since they are originated by incomplete combustion, related emission factors depend on the type of fuel, the technology used, the size and age of the equipment, the operation temperature, the combustion efficiency, the emission control technology, as well as the maintenance and operating conditions.

Greenhouse gas emissions from combustion, based on Bottom-Up method, are shown in Table II-3, and have been classified, according to their origin, in stationary and mobile sources. Stationary sources include all industrial activities and the residential, commercial, service and other sectors, while mobile sources refer to transportation activities. Figure II-4 shows GHG emissions by sector and gas; a logarithmic scale was used due to considerable differences in emission figures of the different gases.

A more detailed analysis for each specific area is provided below in two separate sections: carbon dioxide and other gases.

CARBON DIOXIDE EMISSIONS

Carbon dioxide contributes to nearly one third of the natural greenhouse effect. A continuous increase of its concentration in the atmosphere, produced by antropoghenic activities, has been observed from the beginning of the industrial period. At a global level, since then, the concentration of carbon dioxide has increased by more than 25%, mainly due to the use of fossil fuels.

Venezuela generated 187,820 Gg of carbon dioxide in 1990 . The most important source was energy combustion, which contributed with 104,335 Gg (estimate based on the Top-Down method) or 56% of the total CO2 emissions (Figure II-5).

The emission factors used for the different fuels are those recommended by the IPCC methodology, which are very similar to the National factors estimated by the Venezuelan Oil Research Institute (INTEVEP) except for natural gas, due to variations found on its composition.

Regarding the degree of oxidation, it is necessary to note that not all carbon is oxidized to CO2 when a fuel is burned, due to inefficiencies of the processes. Consequently, some carbon is not affected by burning or remain as ashes. In accordance to the IPCC recommendations, the following non-oxidized fractions were used: 2% for solid fuels, 1% for liquid fuels, and 0.5% for gases. Additionally, it is important to mention that not all of the fuels provided to industrial processes are burned. In some industries, such as petrochemical and others, they are used as feedstocks to produce different goods.

In some of these cases, such as fertilizers, lubricants, and detergents, the carbon contained in the fuels is rapidly oxidized, when exposed to air. In other cases, on the contrary, the carbon is sequestered by the product for hundreds of years, such as plastics, rubber, formaldehyde, and asphalt. Thus CO2 emission values initially obtained must be adjusted for the amount of sequestered carbon.

Carbon dioxide emissions produced by the energy sector are mainly caused by the use of oil and natural gas. According to Top-Down method, the former generated 52,789 Gg in 1990 while emissions from natural gas were estimated to be 49,669 Gg, which represented 51% and 48% of these emissions, respectively (Figure II-6). Coal represented only 2% of these emissions, since coal consumption in the country is very low. Figure II-6 also shows an opposite relation in the composition of apparent consumption between both sources, oil 47% and natural gas 52%, due to the differences in carbon content in the fuels.

The emission estimates of carbon dioxide by sectors were based on the Bottom-Up methodology. As shown in Figure II-7, the larger amounts of emissions come from the transportation sector (31%), the oil and gas industry (23%) and electricity generation (21%) . Unlike the other gases, the emissions of carbon dioxide are distributed more evenly among the different origin sources, as can be observed in Figure II-4.

All of the emissions generated by transportation are due to the use of oil products while in the manufacture industry and the electricity generation, the emissions are mainly related to the use of gas.

Stationary Sources

In 1990, stationary sources emitted 65,523 Gg of carbon dioxide, mainly from the use of natural gas (55%) and oil (43%) (Figure II-8). The energy consumption data, disaggregated by activity, were obtained from the following sources: the National Energy Balance (MEM 1990), the Energy Survey of the Manufacture Industry (OCEI/MEM, 1990), PDVSA and the Electrical Industry. MENU D2 (Annex1) contains data and GHG emission calculations for stationary sources.

The greatest amount of emissions within the stationary sources corresponds to the energy industry, which generated 41,554 Gg in 1990, coming from the oil and gas production (22,035Gg) and electricity generation (19,519 Gg). The oil and gas industry consumed 192 Pj of fuel in 1990, mainly natural gas (92%). When adding refinery losses, which were particularly high in 1990, the total volume of fuel used in the oil and gas industry reached 342 Pj. The origin of these losses and the corresponding CO2 emissions are uncertain.

In this report, the total amount of refinery losses was assumed to undergo a combustion process; thus CO2 emissions were estimated using the same approach of the other fuels. As a result, 50%of the total CO2 emissions generated by the oil and gas industry is due to refinery losses (Figure II-9). Given the importance of these emissions, in deph studies are needed to determine the origin of refinery losses and their impact on CO2 emissions.

The electricity industry consumed 319 Pj of fuel , distributed as shown in Figure II-10. Thus, most of the emissions from these industries come from natural gas (13,018 Gg) and fuel oil (5,426 Gg). The third most important emitter of carbon dioxide in the stationary sources is the manufacture industry, which generated 18,696 Gg of carbon dioxide; similar to the energy industry, most of the emissions come from the use of natural gas (66%) and oil products (25%). The emission estimates are based on the amount of fuel (290 Pj) burned by the manufacture industry in 1990. Figure II-11 shows the distribution of fuel consumption in this industry. Fuel used for transportation (11 Pj) was not included for emissions estimate in this sector but within the mobile sources.

Manufacture industry also consumes an important amount of fuels (180 Pj) that is used as feedstocks in the production processes (150 Pj) and non energy uses (30 Pj); most of the carbon contained is not released, but remains sequestered in the products. The non-sequestered carbon amount was estimated and added to emissions from combustion.

The emission estimates for the industrial sector were done for two digit categories in accordance with the International Standard Industrial Classification of All Economic Activities (ISIC). Additionally, each category was considered separately for the following energy uses: steam generation, direct heat and other uses.

The industrial categories that produce the greatest quantities of emissions are: basic metallic (ISIC 37); food, beverages and tobacco (31); chemicals (35), and non-metallic mineral industries (36), which all together generated 87% of the emissions from the manufacturing sector (Figure II-12). Most emissions from the use of energy comes from steam generation (41%) and direct heat (44%), the rest corresponds to engines, refrigeration, and others.

The residential sector generated 3,678 Gg of carbon dioxide while the commercial, service, and others emitted 572 Gg. Oil products are the main emitter, followed by natural gas. In 1990, these sectors consumed 68 Pj and, as can be seen in Figure II-13, the most commonly fuel used was LPG, which is most frequently used for cooking. Kerosene, mainly used in rural areas, has also a relatively important participation (17%). The energy data were based on the 1990 National Energy Balance. However, consumption of natural gas and LPG had to be estimated separately, as the Energy Balance does not discriminate them by sector. It was asumed that 70% of the domestic natural gas and 90% of LPG are used by the residential sector and the rest by the commercial and service sectors. Figure II-7 presents the emission estimates for these sectors by type of fuel.

Mobile Sources

The 1990 emissions of carbon dioxide from mobile sources were estimated to be 29,384 Gg (Table II-4). As the IPCC methodology recommends that CO2 emissions from bunkers should not be taken into account in the fuel origin country, the mobile sources estimates only considered national emissions.

The data used to estimate emissions from road transport were taken from MEM-RISO, 1993. The quality of the data is rather poor since the country lacks reliable and updated statistics on national automotive fleet. The emission calculations were based on a total fleet of 2.3 millions units; however, this figure, as well as the fleet characteristics used for the emission inventory, were based on assumptions and rough estimates of: number of vehicles by type, fuel consumption, Km-lt specifications, average milage, passengers-Km, and freight-Km. The primary sources were: MEM, 1990; PULIDO,1992 and INTEVEP, 1994.

Figure II-14 contains demand estimates for passenger transportation (PASS-KM) and freight (TN-KM), by type of vehicle and fuel used. Figure II-15 shows fuel consumption estimates for road transportation (392.9 Pj) by type of vehicle, where private vehicles consumed the greatest amount of fuel (39%). It is important to note that the results obtained for fuel consumption in the public transport seems to be low, when considering that in Venezuela, big cities have high densities of vehicules and especially, low fuel use efficiency, mainly due to the fleet age, poor maintenance, and high traffic volume. Reliability of emission estimates depends on the quality of this information.

As was mentioned earlier, CO2 emissions from mobile sources were 29,384 Gg, where gasoline is the most important emitter, with 21,760 Gg (74%), as shown in Figure II-16. Emissions from national transportation are mostly generated by road transportation, 27,404 Gg (93%),whose disaggregation by type of fuel and vehicle is shown in Figure II-17. Emissions from private vehicles are the most important within this sector, with 10,593 Gg of carbon dioxide in 1990, which represented 39% of the total road transport emissions, followed by heavy duty trucks, with 27%. Emissions from public transportation are the least significant, as only they contributed with 14.2%, 3,932 Gg; this amount also seems to be low when considering the primary data problems mentioned above. MENU D3 (Annex 1) contains data and GHG emission calculations for emission results for mobile sources.

EMISSIONS OF OTHER GASES

The other greenhouse gases generated by energy consumption are methane, nitrous oxide, and the photochemical gases from incomplete combustion, such as nitrogen oxides, carbon monoxide and NMVOC. Emissions of these gases vary according to the type of activity where the combustion occurs, and basically depend on the type of fuel; technology, size and age of the equipment; pollution control; maintenance, and operating conditions.

Emissions of non-CO2 GHG gases are calculated separately for stationary sources and mobile sources. Figure II-18 shows that the latter are responsible for most of the emissions. Regarding National GHG estimates, emissions of non-CO2 trace gases from combustion of fossil fuels are significant for nitrogen oxides (87%) and carbon monoxide (46%), the NMVOC emissions are totally generated by mobile sources, since the emissions from other sources were not estimated.

Stationary Sources

Stationary combustion is an important source of nitrogen oxides, which represented 40% of the national emissions of this gas, in 1990. However, the contribution of stationary sources to the rest of the non-CO2 gases is not significant. Table II-5 presents the emission estimates from stationary combustion by gas and source. Figure II-19 shows that, in general, the main source of emissions is the energy industry (electricity generation and oil and gas industry) followed by the manufacture industry.

Electricity Generation

Electricity generation is the most important source of emissions of nitrogen oxides (41%), within the stationary combustion activities. It is also important for methane (33%) and nitrous oxide (22%). As mentioned earlier, electricity generation plants used 319 Pj of fossil fuel; 77% was used in public plants while the rest in autogeneration by the oil and gas and the manufacture industry. Public electricity generation was mainly performed in steam plants, and, in smaller proportion, in gas turbines simple cycle.

The emission estimates from electricity generation by type of plant and fuel used are presented in Table II-6. Steam plants generate most of the emissions of nitrogen oxides (61%) and nitrous oxide (71%) while gas plants have a greater contribution to methane (93%) and carbon monoxide (60%) emissions. Regarding distribution by type of fuel, natural gas contributes with most of the emissions of all gases, except for nitrous oxide, whose emissions are mainly generated by oil products (71%).

The data used for emission calculation are based on the information provided by MEM, 1990, regarding electrical plants, which was disaggregated by type of plant according to the information obtained from OPSIS, 1994. The data on electricity autogeneration were adjusted with the information used by MEM-RISO, 1993. Due to the lack of all necessary information on the characteristics of autogeneration plants, it was assumed that gas turbines are used, in spite of being aware that the manufacture industry also utilizes steam plants. The emission factors used are provided by Table 1-7 of the IPCC/OECD, 1995, Vol 3.

Oil and Gas Industry

The oil and gas industry consumed in its operations 192 Pj of fuel in 1990; but the total amount of fuel used by this industry reached 342 Pj, due to the refinery losses. In consequence, when these losses are considered, this sector becomes an important source of non- CO2 gases from the combustion of stationary sources: 43% of CH4 and 38% of N2O. For this industry, disaggregated information on fuel uses is not available, thus estimations were based on general emission factors provided by Table 1-17 and 1-18 IPCC /OECD, 1995, vol. 3.

Manufacture Industry

The manufacture industry is the main source of carbon monoxide within stationary sources (74%) and the second most important source of emissions of nitrous oxide and nitrogen oxides, as can be noted in Figure II-19. As mentioned earlier, the manufacture industry consumed 290 Pj of fuel in 1990; Figures II-20 and II-21 present its distribution by fuel type, industry category, and energy uses. The industries with the highest fuel consumption are basic metallic, chemical, non-metallic mineral, and food, beverage, and tobacco industries.

Fuel consumed by the manufacture industry is mainly dedicated to steam generation and direct heat, other uses include engines, refrigeration, air conditioning, and transport. More than 70% of steam generation is found in the food, beverage and tobacco industry and the chemical industry, while the use of direct heat is concentrated in the basic metallic and non-metallic mineral industries.

The information sources for energy consumption were the same as the ones used for CO2 emission estimates. It is important to notice that the emission factors provided in Tables 1-8 and 1-9, IPCC/OECD, 1995, Vol 3, are not sufficiently disaggregated to perform emission estimates with the same levels of details (industry categories and energy use) available for CO2 calculations; and consequently, it was necessary to make some adjustments, not all adequate. Other sources of information will need to be identified in order to develop some national factors, especially for those industries that generate important amounts of emissions.

Emission estimates from the manufacture industry are presented in Table II-7, the industrial categories with the highest emissions are also those with the highest energy consumption, mentioned earlier. These categories all together emit more than 80% of the total emissions generated by the manufacture industry for each gas.

Figure II-22 shows the distribution of emissions by fuel. Natural gas emits most of the methane and nitrogen oxides while oil products, coal, and coke are responsible for most nitrous oxide emissions. Natural gas and bagasse are the main contributors to carbon monoxide emissions. Regarding energy uses, direct heat is the most important source of nitrogen oxides, nitrous oxides, and carbon monoxide, while steam generation is largely responsible for methane emissions.

Commercial and Services, Residential, and Others.

The contribution of commercial and services, residential and other sectors to GHG emissions from stationary sources is very limited, except for nitrous oxide as 17% of this gas is generated by these sectors (Figure II-19). Their influence is rather indirect since they have high electricity consumption and, as mentioned earlier, electricity generation is an important source of emissions from stationary combustion. Fuels that are mostly used in these sectors are LPG and natural gas, followed by kerosene, other distillates, and biomass.

The emission estimates were based on MEM, 1990 and the emission factors provided by the IPCC/OECD,1995, Vol 3, in Tables 1-10, 1-11, and 1-18. The emission factors were selected considering the use of gas heaters, propane/butane furnaces, and distillate oil furnaces for the residential sector, while gas boilers, distillate boilers, and propane/butane furnaces were considered for the commercial and service sector. However, the emission factors used do not adjust well to the use of energy in Venezuela, and consequently, it will be necessary to research on more appropriate factors or develop national values.Tables II-8 and II-9 show the emissions estimates for these sectors by type of fuel.

Biomass Burned for Energy

The data available on biomass burned for energy show a very low consumption of this fuel in the country; MEM,1990 reports 0.453 Pj consummed in residential sector as wood and charcoal. Additionaly, the sugar industry burned 5.8 Pj of bagasse for energy. Validation in this area will be necessary in order to ensure the reliability of the data.

Other gases emissions from biomass were estimated for residential and industrial sectors, using the emissions factors in Tables 1-8 and 1-10 of the IPCC/OECD,1995. Results are included in Tables II-7 and II-8.

Mobile Sources

The use of fossil fuel in transportation is the most important source of emissions of the other gases originated by combustion, mainly those generated by incomplete combustion, such as carbon monoxide, methane and NMVOC. All emissions reported of NMVOC correspond to transportation, which generated 249 Gg in 1990, since the emissions from other sources were not estimated.

Mobile sources emitted 1,837 Gg of carbon monoxide and 9.9 Gg of methane, which represented 97% and 78%,respectively, of these gases emissions generated by combustion (Table II-10). The contribution of transport to nitrogen oxides emissions was comparatively less important, with 54% of the total combustion emission of this gas; only 0.4 Gg of nitrous oxide were produced by this source.

As mentioned earlier, the emission estimates of the non-CO2 gases have a high degree of uncertainty as, on one hand, the emission factors depend on a set of variables, usually with no available information, and highly sensitive to variations of any of these variables. On the other hand, due to defficiencies of the automotive fleet data, mentioned in the CO2 chapter.

Some of the variables that affect the emission factors in the transportation sector, are: type of fuel, mode of transportation and type of vehicle, characteristics of ÇoperationÈ (driving cycle), emission controls, age of the fleet, maintenance, travel distances, yield per liter, road conditions, average speed, etc.

The need to manage a wide range of variables and the numerous conditions that could affect the yield of each mobile source category, especially those related to road transport, make very difficult any attempt to generalize the emission characteristics in this area. This is even a very complex problem for countries with much experience in developing national emission inventories and recognized discipline of data gathering and statistics.

As developing national emission factors for the emission inventory of NOx, CO, CH4, and NMVOC was not possible, the calculation was based on some of the factors published in Tables I-20 to I-26 of IPCC/OECD,1994. Vol.3 and information provided by MOBILE4 Model of U.S. EPA. The emission factors taken into consideration corresponded to non-catalytic emission control technology while for diesel heavy duty trucks, it was assumed that the available models do not incorporate any kind of control.

The emissions of the photochemical gases: CO, CH4, and NMVOC, as in the case of CO2, are mainly generated by gasoline vehicles with a contribution, in all cases, of more than 90%. On the other hand, about 60% of both, NOx and N2O emissions is generated by gasoline and the remainder 40% by diesel (Figure II-23).

Table II-11 shows the distribution of the emissions generated by the different types of vehicles for each gas. For NOx and N2O, the highest proportion corresponds to heavy-duty trucks. For the rest of the gases, private vehicles and light-duty trucks account for most of the emissions. Public transport, in all cases, has the lowest contribution to the emissions.

Index    Next
If you have any questions or comments please contact us at VEBHM7SL@IBMMAIL.COM.