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Nr. 424: Danish emission inventories for stationary combustion plants. Inventories until 2018

Nielsen, M. 2021. Danish emission inventories for stationary combustion plants. Inventories until 2018. Aarhus University, DCE – Danish Centre for Environment and Energy, 280 pp. Scientific Report No. 424 http://dce2.au.dk/pub/SR424.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 Trans-boundary 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 Com-mission’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 com-pounds (NMVOCs), carbon monoxide (CO), particulate matter (PM), black carbon (BC), ammonia (NH3), heavy metals (HMs), polyclorinated dibenzodioxins and –furans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) 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 (EU ETS).

In the inventory for the year 2018, 74 stationary combustion plants are specified as large point sources. The point sources include large power plants, waste incineration plants, industrial combustion plants and petro-leum refining plants. The fuel consumption of these large point sources corresponds to 51 % 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 2018, the total fuel consumption was 19 % lower than in 1990 and the fossil fuel consumption was 49 % lower than in 1990. The use of coal and oil has decreased whereas the use of natural gas, waste and biomass has increased.

In 2018, stationary combustion accounted for 32.5 % of the national emission of GHGs (including LULUCF) and 42 % of the CO2 emission.

Stationary combustion plants account for more than 50 % of the national emission (2018) for the following pollutants: SO2, PM2.5, BC, the heavy metals As, Cd, Cr, Hg and Se, HCB, PCDD/Fs, PCBs and PAHs. Further-more, the emission from stationary combustion plants accounts for more than 10 % of the national emission for the following pollutants: NOx, NMVOC, CO, TSP, PM10 and the heavy metals 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, CH4 and N2O, SO2, NOx, Hg, Se, HCB and PCBs.

Residential plants is the most important stationary combustion emission source for NMVOCs, CO, NH3, particulate matter, BC, Cd, Cr, Cu, Pb, Zn, PAHs and PCDD/Fs. Wood combustion in residential plants is the predominant emission source.

Industrial plants are the main emission sources for SO2, As and Ni.

CO2 is the most important greenhouse gas accounting for 97.3 % 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 greenhouse gas emission are lower in 2018 than in 1990, CO2 is 54.8 % lower and greenhouse gas emissions are 53.9 % lower. 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. place between 1990 and 2007. Residential wood combustion is a major emission source for NMVOCs, CO, NH3, PM, BC, dioxins (PCDD/Fs), some heavy metals and PAHs. A change of technology (installation of modern stoves and boilers) has caused decreasing emission factors.

The NMVOC emissions from stationary combustion plants has decreased by 10 % from 1990. The emission increased until 2007 and decreased after 2007. 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 CO emission from stationary combustion has decreased 33 % since 1990. The time series for CO from stationary combustion plants follow the time series for CO emission from residential plants. The increase of wood consumption in residential plants in 1999-2007 is reflected in the time series for CO emission. The decreased emission in 2007-2018 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.

The time series for PM emission from stationary combustion plants follows the time series for PM emission from residential plants. The emission of TSP, PM10 and PM2.5 was 1 %, 5 % and 4 % lower in 2018 than in 1990. The PM emissions increased until 2007 and decreased after 2007. The increase until 2007 was caused by the increased wood combustion in residential plants. However, the PM emission factors have decreased for this emission source category due to installation of modern stoves and boilers. The stabilisation of wood consumption in residential plants in 2007-2014 has resulted in a decrease of PM emission from stationary combustion between 2007 and 2014. Residential wood combustion is the main emission source for BC.

The emission of PAHs has decreased since 1990, mainly after 2007. This is also a result of the time series for combustion of wood in residential plants.

Emissions of all heavy metals have decreased considerably (18 % - 92 %) since 1990. Emissions have decreased despite increased incineration of waste. This has been possible due to installation and improved performance of gas cleaning devices in waste incineration plants and also in large power plants, the latter being a further important emission source.

The PCDD/F emissions has decreased 39 % 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 in this source category.

The HCB emission has decreased 79 % since 1990 mainly due to improved flue gas cleaning in waste incineration plants.

The dl-PCB emissions have decreased 63 % 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 interval for the Danish greenhouse gas emission from stationary combustion is estimated to be ±2.3 % and the trend in greenhouse gas emissions is -53.9 % ± 1.0 %-age points.

As part of the EU review of the reported GHG emission data, EU performs for each member state a comparison of Eurostat energy data in terms of TJ with energy data provided in the CRF. The largest differences between the two approaches have been explained. The calorific value (LCV) for coal applied in the Eurostat data are not in agreement with the average LCV for coal applied in the Danish energy statistics. In addition, 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.

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 43 % of the total CO2 emission reported in the Danish emission inventory.

The CH4 emission from stationary combustion was 54 % higher in 2018 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 N2O emission from stationary combustion has increased by 18 % 1990 to 2018. However, fluctuations in emission level due to electricity import/export are considerable.

SO2 emission from stationary combustion plants has decreased by 96 % since 1990. The considerable emission decrease is mainly a result of the reduced emission from public 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 76 % since 1990. The reduced emission is largely a result of the reduced emission from Public 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 2018, the wood consumption in residential plants was 4.6 times the 1990 level. The increase mainly took