CO2 Emission Factors for Coals

Emission factors are used in greenhouse gas inventories to estimate emissions from coal combustion. In the absence of direct measures, emissions factors are frequently used as a quick, low cost way to estimate emissions values. Coal combustion has been a major contributor to the CO2 flux into the atmosphere. Nearly all of the fuel carbon (99 %) in coal is converted to CO2 during the combustion process. The carbon content is the most important coal parameter which is the measure of the degree of coalification (coal rank). Coalification is the alteration of vegetation to form peat, succeeded by the transformation of peat through lignite, sub-bituminous, bituminous to anthracite coal. During the geochemical or metamorphic stage, the progressive changes that occur within the coal are an increase in the carbon content and a decrease in the hydrogen and oxygen content resulting in a loss of volatiles. Heterogeneous composition of coal causes variation in CO2 emission from different coals. The IPCC (Intergovernmental Panel on Climate Change) has produced guidelines on how to produce emission inventories which includes emission factors. Although 2006 IPCC Guidelines provided the default values specified according to the rank of the coal, the application of country-specific emission factors was recommended when estimating the national greenhouse gas emissions. This paper discusses the differences between country-specific emission factors and default IPCC CO2 emission factors, EF(CO2), for coals. Also, this study estimated EF(CO2) for two different types of coals and peat from B&H, on the basis fuel analyses. Carbon emission factors for coal mainly depend on the carbon content of the fuel and vary with both rank and geographic origin, which supports the idea of provincial variation of carbon emission factors. Also, various other factors, such as content of sulphur, minerals and macerals play an important role and influence EF(CO2) from coal. Carbonate minerals (calcite and siderite) directly contribute CO2 when they decompose during coal combustion. Variations in the maceral content can also influence CO2 emissions; high inertinite contents increase CO2 emissions. Sulphur in coal reduces EF(CO2). Fuel analysis is very important when estimating greenhouse gas emissions and emission factors. In this preliminary study, based on the results of the fuel analysis, CO2 emission factors for coals and peat from Livno, B&H have been calculated. EF(CO2) is defined as the amount of carbon dioxide emission per unit net calorific values of the fuel. Net calorific value (the lower heating value) corresponds to the heat produced by combustion where total water in the combustion products exists as water vapour. The EF(CO2) obtained for sub-bituminous coal, lignite and peat were: 98.7, 109.5, and 147.9 t TJ(-1), respectively, which correspond to the following net calorific values: 20.6, 11.5 and 3.6 MJ kg(-1). The heating value is generally known to increase with the increase in carbon content (this parameter is connected with the degree of coalification, coal age). The other indispensable parameters are hydrogen, which has a positive effect on the net calorific value, and oxygen and water which impact the net calorific value negatively. The differences in net calorific values can be explained in part by the difference of total moisture content among the different fuel types. The CO2 emission factors calculated in this study were compared with those of IPCC. A significant difference was observed for peat (39.5 %), followed by lignite (8.2 %) and sub-bituminous coal (4.3 %).