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No. 279: Danish emission inventories for stationary combustion plants. Inventories until 2015

Nielsen, M., Nielsen, O.-K. & Plejdrup, M.S. 2018. Danish emission inventories for stationary combustion plants. Inventories until 2015. Aarhus University, DCE – Danish Centre for Environment and Energy, 324 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 279 http://dce2.au.dk/pub/SR279.pdf 

Summary

Danish emission inventories are prepared on an annual basis and are reported to the United Nations Framework Convention on Climate Change (UNFCCC or Climate Convention) and to the Kyoto Protocol. Furthermore, a greenhouse gas emission inventory is reported to the European Union (EU) due to the EU – as well as the individual member states – being party to the Climate Convention and the Kyoto Protocol.

Danish emission inventories for non-GHGs are prepared on an annual basis and are reported to the UNECE-Convention on Long-Range Transboundary Air Pollution (LRTAP) and EU Directive 2016/2284 on the reduction of national emissions of certain atmospheric pollutants.

Five pollutants (sulphur dioxide, nitrogen oxides, non-methane volatile organic compounds, ammonia and particulate matter with an aerodynamic diameter below 2.5 µm) are estimated for reporting to the European Commission’s National Emissions Ceiling Directive (NECD).

The inventories include the following pollutants relevant to stationary combustion: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulphur dioxide (SO2), nitrogen oxides (NOx), non-volatile organic compounds (NMVOC), carbon monoxide (CO), particulate matter (PM), black carbon (BC), ammonia (NH3), heavy metals (HMs), polyclorinated dibenzodioxins and –furans (PCDD/F), polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and hexachlorobenzene (HCB).

The inventories for stationary combustion are based on the Danish energy statistics and on a set of emission factors for various source categories, technologies and fuels. Plant specific emissions for large combustion sources are incorporated into the inventories. This report provides detailed background information on the methodology and references for the input data in the inventory - energy statistics and emission factors.

The emission factors are based either on national references or on international guidebooks (EEA, 2016; IPCC, 2006). The majority of the country-specific emission factors are determined from Danish legislation, Danish research reports, or calculations based on plant-specific emission data from a considerable number of large point sources. The plant-specific emission factors are provided by plant operators, e.g. in PRTR data, other annual environmental reports or in the EU Emission Trading Scheme (ETS).

In the inventory for the year 2015, 76 stationary combustion plants are specified as large point sources. The point sources include large power plants, waste incineration plants, industrial combustion plants and petroleum refining plants. The fuel consumption of these large point sources corresponds to 50 % of the overall fuel consumption of stationary combustion.

The fuel consumption for stationary combustion plants has decreased since 1990. However, the fuel consumption fluctuates due to variation in the import/export of electricity from year to year. In 2015, the total fuel consumption was 23 % lower than in 1990 and the fossil fuel consumption was 45 % lower than in 1990. The use of coal and oil has decreased whereas the use of natural gas, waste and biomass has increased.

In 2015, stationary combustion accounted for 37 % of the national emission of GHGs (including Land Use, Land-Use Change and Forestry, LULUCF) and 48 % of the CO2 emission.

Stationary combustion plants account for more than 50 % of the national emission (2015) for the following pollutants: SO2, PM10, PM2.5, BC, the heavy metals As, Cd, Cr, Hg and Se, HCB, PCDD/F and PAH. Furthermore, the emission from stationary combustion plants accounts for more than 10 % of the national emission for the following pollutants: NOx, NMVOC, CO, TSP and the heavy metals Ni, Pb and Zn. Stationary combustion plants account for less than 10 % of the national emission of CH4, N2O, NH3, the heavy metal Cu, and PCB.

Public electricity and heat production is the most important stationary combustion emission source for CO2, N2O, and NOx.

Residential wood combustion and lean-burn gas engines installed in decentralised combined heating and power (CHP) plants are the two largest emission sources for CH4.

Residential plants is the most important stationary combustion emission source for CO, NMVOC, PM, BC, PAH and PCDD/F. Wood combustion in residential plants is the predominant emission source.

The main emission sources for SO2 are industrial plants and public electricity and heat production plants.

Industrial plants, public electricity and heat production plants and residential plants are the main emission sources for the different heavy metals.

CO2 is the most important greenhouse gas accounting for 97.8 % of the greenhouse gas emission (CO2 eq.) from stationary combustion. The greenhouse gas (GHG) emission trend follows the CO2 emission trend closely. Both the CO2 and the total GHG emission were lower in 2015 than in 1990: CO2 by 51.2 % and GHG by 50.5 %. However, fluctuations in the GHG emission level are large. The fluctuations in the time series are mainly a result of electricity import/export but also of outdoor temperature variations from year to year that results in fluctuations in the fuel consumption for space heating.

The CH4 emission from stationary combustion was 43 % higher in 2015 than in 1990. The emission increased until 1996 and decreased after 2004. This time series is related to the considerable number of lean-burn gas engines installed in CHP plants in Denmark during the 1990s. The decline in later years is due to structural changes in the Danish electricity market, which means that the fuel consumption in gas engines has been decreasing. The CH4 emission from residential plants has increased since 1990 due to increased combustion of wood in residential plants.

The emission of N2O was 1 % higher in 2015 than in 1990. The fluctuations follow the fluctuations of the fuel consumption, which is a result of import/export of electricity.

SO2 emission from stationary combustion plants has decreased by 95 % since 1990. The considerable emission decrease is mainly a result of the reduced emission from electricity and heat production plants due to installation of desulphurisation technology and the use of fuels with lower sulphur content. These improvements are a result of sulphur tax laws, legislation concerning sulphur content of fuels, emission ceilings for large power plants and lower emission limit values for several plant categories.

The NOx emission from stationary combustion plants has decreased by 77 % since 1990. The reduced emission is largely a result of the reduced emission from electricity and heat production due to installation of low NOx burners, selective catalytic reduction (SCR) units and selective non-catalytic reduction (SNCR) units. The installation of the technical improvements was launched by legislation including emission ceilings for large power plants, lower emission limits for several plant categories and NOx tax laws. The fluctuations in the emission time series follow fluctuations in electricity import/export.

In 2015, the wood consumption in residential plants was 4.2 times the 1990 level. The consumption of wood in residential plants increased between 1990 and 2007. The increased residential wood consumption until 2007 has caused considerable changes in the emission of NMVOC, CO, PM, BC and PAH from stationary combustion due to the fact that residential wood combustion is a major emission source for these pollutants. However, a change of technology (installation of modern stoves) has caused decreasing emission factors.

The CO emission from stationary combustion has decreased 20 % since 1990. The decreased emission in 2007-2015 is a result of implementation of improved residential wood combustion technologies and the fact that the rapid increase of wood consumption until 2007 have stopped. Furthermore, the emission from straw-fired farmhouse boilers has decreased considerably.

The NMVOC emission from stationary combustion plants has decreased by 3 % from 1990. The emission increased until 2007 and decreased between 2007 and 2014. The increased emission is mainly a result of the increasing wood consumption in residential plants and of the increased use of lean-burn gas engines in CHP plants. The decrease in 2007-2014 is a result of lower emission from residential wood combustion and the low number of operation hours for the lean burn gas engines.

The emission of TSP, PM10 and PM2.5 has increased by 20-24 % since 1990 due to the increase of wood combustion in residential plants until 2007. After 2007, the emission has decreased due to installation of modern stoves and boilers with lower emission factors. The time series for BC follows the time series for PM.

The emission of PAHs has increased until 2007 and decreased after 2007. This is also a result of the time series for combustion of wood in residential plants.

All the heavy metal emissions have decreased considerably since 1990 – between 41 % and 91 %. This is a result of the installation and improved performance of gas cleaning devices in waste incineration plants and large power plants.

The PCDD/F emission has decreased 67 % since 1990 mainly due to installation of dioxin filters in waste incineration plants. The emission from residential plants has increased due to increased wood consumption. However, the emission factor for residential wood combustion has decreased due to installation of modern stoves and boilers.

The HCB emission has decreased 80 % since 1990 mainly due to improved flue gas cleaning in waste incineration plants. The emission from residential plants has increased in recent years due to increased wood consumption.

The dioxin like PCB emission has decreased 67 % since 1990. The decrease is mainly a result of the flue gas cleaning devices that have been installed in waste incineration plants for dioxin reduction.

The uncertainty level of the Danish greenhouse gas (GHG) emission from stationary combustion is estimated to be within a range of ±2.2 % and the trend in greenhouse gas emission is -50.5 % ± 1.0 %-age points.

An emission inventory including fuel consumption and CO2 emissions have been estimated based on Eurostat data. The results based on Eurostat data are presented and compared to the Danish emission inventory. The largest differences between the two approaches have been explained.  The fuel consumption for transport between mainland Denmark and Greenland and the Faroe Islands is not included in the reporting to Eurostat whereas it is considered domestic in the Danish emission inventory. This causes a difference for liquid fuels used for aviation and navigation. Some calorific values (LCV) applied in the Eurostat data are inaccurate and not in agreement with the Danish energy statistics. This cause differences for several fuels including a considerable difference for coal.

The verified emission data reported under EU ETS Directive 2003/87/EC have been compared to the Danish emission inventory for GHGs. The verified CO2 emissions add up to 45 % of the total CO2 emission reported in the Danish emission inventory.