Nielsen, M., Nielsen, O.-K. & Plejdrup, M. 2014. Danish emission inventories for stationary combustion plants. Inventories until 2011. Aarhus University, DCE – Danish Centre for Environment and Energy, 188 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 102 http://dce2.au.dk/Pub/SR102.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 as well as to the United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution (LRTAP Convention). 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. Four pollutants (sulphur dioxide, nitrogen oxides, non-methane volatile organic compounds and ammonia) are estimated for reporting to the European Commission’s National Emissions Ceiling Directive (NECD).

The annual Danish emission inventories are prepared by the DCE - Danish Centre for Environment and Energy, Aarhus University. The inventories include the following pollutants relevant to stationary combustion: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), sulphur dioxide (SO₂), nitrogen oxides (NO_x), non-volatile organic compounds (NMVOC), carbon monoxide (CO), particulate matter (PM), ammonia (NH₃), heavy metals (HMs), polyclorinated dibenzodioxins and –furans (PCDD/F), polycyclic aromatic hydrocarbons (PAH) and hexachlorobenzene (HCB). In addition to annual national emissions, the report includes emission data for a number of source categories. Every five years[1] the reporting includes data on the geographical distribution of the emissions, a projection of emissions, data and details of the activity data, e.g. fuel consumption – on which the inventories are based.

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 on either national references or on international guidebooks (EEA, 2009; IPCC, 1997). 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 annual environmental reports or in the EU Emission Trading Scheme (ETS).

In the inventory for the year 2011, 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 58 % of the overall fuel consumption of stationary combustion.

In 2011, the total fuel consumption was 4 % lower than in 1990 and the fossil fuel consumption was 23 % lower than in 1990. The use of coal has decreased whereas the use of natural gas and biomass has increased. The fuel consumption for stationary combustion plants fluctuates due to variation in the import/export of electricity from year to year.

Stationary combustion plants account for more than 50 % of the national emission for the following pollutants: SO₂, CO₂, PM₁₀, PM_2.5, the heavy metals As, Cd, 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: NO_x, NMVOC, CO, TSP and the heavy metals Cr, Ni, Pb and Zn. Stationary combustion plants account for less than 10 % of the national emission of CH₄, N₂O, NH₃ and the heavy metal Cu.

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

Lean-burn gas engines installed in decentralised combined heating and power (CHP) plants and combustion of biomass in residential plants are the two largest emission sources for CH₄.

Residential plants is the most important stationary combustion emission source for CO, NMVOC, particulate matter, 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 98.0 % 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 2011 than in 1990: CO₂ by 30 % and GHG by 29 %. 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 consumption for space heating.

The CH₄ emission from stationary combustion has increased by a factor of 2.9 since 1990. This is mainly a result of the considerable number of lean-burn gas engines installed in CHP plants in Denmark during the 1990s. In recent years, the emission has declined. This is due to liberalisation of the Danish electricity market, which means that the fuel consumption in gas engines has decreased. The CH₄ emission from residential plants has increased since 1990 due to increased combustion of wood in residential plants.

The emission of N₂O was 4 % higher in 2011 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 94 % since 1990. The considerable emission decrease is mainly a result of the reduced emission from electricity and heat production due to installation of desulphurisation technology and the use of fuels with lower sulphur content. These improvements are a result of both sulphur tax laws and legislation concerning sulphur content of fuels, emission ceilings for large power plants and emission limits for several plant categories.

The NO_x emission from stationary combustion plants has decreased by 68 % since 1990. The reduced emission is largely a result of the reduced emission from electricity and heat production due to installation of low NO_x 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 and lower emission limits for several plant categories. The fluctuations in the emission time-series follow fluctuations in electricity import/export.

In 2011, the wood consumption in residential plants was 3.7 times the 1990 level. The consumption of wood in residential plants peaked in 2007. The increased residential wood consumption until 2007 has caused considerable changes in the emission of NMVOC, CO, PM 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 increased 5 % since 1990. The increase in CO emission from residential plants is less than the increase in wood consumption because the CO emission factor for wood combustion in residential plants has decreased since 1990. Furthermore, the emission from straw-fired farmhouse boilers has decreased considerably.

The NMVOC emission from stationary combustion plants has increased 14 % since 1990. The increased NMVOC emission is mainly a result of the increasing wood combustion in residential plants and the increased use of lean-burn gas engines. The emission from straw-fired farmhouse boilers has decreased.

The emission of TSP, PM₁₀ and PM_2.5 has increased by 26-30 % since 2000 due to the increase of wood combustion in residential plants. The emission of PAHs has increased by 79-115 % since 1990, also a result of the increased combustion of wood in residential plants.

All the heavy metal emissions have decreased considerably since 1990 – between 76 % and 92 %. This is a result of the installation and improved performance of gas cleaning devices in waste incineration plants and large power plants.

PCDD/F emission has decreased 62 % since 1990 mainly due to installation of dioxin abatement in waste incineration plants that was necessary due to the emission limit included in Danish legislation. However, the emission from residential plants has increased due to the increased wood combustion in the sector.

The uncertainty level of the Danish greenhouse gas (GHG) emission from stationary combustion is estimated to be within a range of ±2.0 % and trend in greenhouse gas emission is -29.1 % ± 1.2 %-age points[2].