EN09 Emissions (CO2, SO2 and NOx) from public electricity and heat production - explanatory indicators

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DPSIR: Driving force

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Electricity and heat production from public thermal power plants is a significant source of both air pollutants and greenhouse gas emissions. Reduction of these power sector emissions is needed to achieve the greenhouse gas emission reductions for the whole society as agreed under the Kyoto Protocol and that of air pollutants as agreed under the NEC directive. Understanding what is driving the trend in emissions from public electricity and heat production can help identify successful policies for reducing the environmental impacts of this sector.

Public electricity and heat production is the most important source of CO2 emissions (around one-third of all CO2 emissions) and is the largest and second largest source respectively of SO2 and NOx emissions (the largest for the latter being transport). There are generally four ways of reducing the environmental pressures from producing a given output of electricity and heat, i.e. not accounting for a reduced demand:

 

1. Increasing the share of non-fossil fuels, as power production from renewable energy sources and nuclear produce no harmful emissions at the point of electricity production (with the exception of thermal renewables that involve combustion, such as certain types of biomass and wastes; and nuclear waste).
2. Increasing the efficiency with which electricity and heat is produced from fossil fuels. Advances in engineering technology and operational procedure have all resulted in improved efficiencies (see EN19). The use of combined heat and power (see EN20) increases efficiencies dramatically as much of the heat produced is used to provide useful energy services at other points of the system
3. Changing the mix of fossil fuels used for electricity and heat production. Coal, lignite and oil all naturally contain significant amounts of carbon, sulphur, nitrogen, which react with oxygen during combustion to form the oxides that cause damage to the environment. Natural gas contains significantly less of these chemicals, thus a switch from coal or lignite to natural gas leads to an environmental improvement.
4. Introducing emissions abatement techniques:
   • Flue gas desulphurisation (FGD) can be fitted to reduce SO2 emissions from the flue gases. There are a wide variety of FGD techniques, of which the most common are wet scrubbers. Wet scrubbers work by using a slurry or solution to absorb SO2, producing an initially wet by-product. Frequently, limestone is used as the sorbent, generating gypsum as a by-product. Other techniques include spray dry scrubbing and regenerative processes. Typically, FGD can achieve SO2 removal of more than 90 %.
   • Combustion modification and flue gas treatment can be used to reduce NOx emissions. One of the most common forms of combustion modification is to use low NOx burners. There are various types of low NOx burner, which can typically reduce NOx emissions by up to 40 %, by controlling the mixing and proportions of fuel and air to reduce the formation of NOx. Flue-gas treatment can also be used to remove NOx from the flue gases.
   • Carbon Capture and Storage may also be an option in the future for reducing CO2 emissions, but the technology has not yet entered the market.

As a result of these measures, the emissions of public power production were reduced between 1990 and 2004 despite a 33% increase in the amount of public electricity and heat produced.

a) CO2 emissions:
Emissions of CO2 from public electricity and heat production in the EU-25 decreased by 1.6 % between 1990 and 2004. However, if the structure of electricity and heat production had remained unchanged from 1990 (i.e. if the shares of input fuels used to produce electricity and heat had remained constant and the efficiency of electricity and heat production also stayed the same), then by 2004 emissions of CO2 would have increased by 33% above their 1990 levels, in line with the additional amount of electricity and heat produced. The relationship between the increase in electricity generation and the actual reduction in emissions during 1990-2004 can be explained by the following factors:

• An improvement in the thermal efficiency of electricity and heat production (see EN19) (e.g. from the closure of old, inefficient power plants and the introduction of new plants based on more efficient combined cycle technologies). During 1990-2004, there was a 15 % reduction in the fossil-fuel input per unit of electricity produced from fossil fuels.
• Changes in the fossil fuel mix used to produce electricity (e.g. fuel switching from coal and lignite to natural gas, see EN27), with much of this being linked to the increased use of the economically attractive gas turbine combined cycle technology and the closure of a number of coal-fired power plants. However, a rise in the price of gas relative to coal in recent years has led to increased utilisation of existing coal plants, and is the primary cause of a rise in emissions from public electricity and heat production from around 1999 onwards (8% increase from 1999 to 2004). There was a 15% reduction in the CO2 emissions per unit of fossil-fuel input during 1990-2004.
• The approximately 2 % lower share of nuclear and renewable energy (including biomass) in 2004 compared to 1990. During 1990-2004, the share of electricity from fossil fuels in total electricity production increased by 2 %. This effect has become more pronounced in recent years with a decrease in hydropower due to low rainfall (EN27), although 2004 saw a return to more average levels of hydropower production.

These three factors interact with each other in a multiplicative way: Actual CO2 emissions reduction = 1.33 (increase in electricity production) X 0.85 (efficiency improvement) X 0.85 (fossil fuel switching) X 1.02 (increase in nuclear and renewable share)3 = 0.98. The combined effect was a reduction of 1.6% in CO2 emissions in 2004 compared to the 1990 level.

Linking the changes in CO2 emissions to specific policies that have been targeted at public electricity and heat production is difficult. Furthermore, a number of the policy measures such as the Directive on renewable electricity (2001/77/EC), the EU Emissions Trading Scheme (2003/87/EC) and the Large Combustion Plant Directive (2001/80/EC) may have had a limited effect in the time series covered (1990-2004). More detailed analysis concerning total energy consumption has been undertaken for Germany and the UK (Fraunhofer Institute, 2001), which suggests that around 60 % of the reductions in total energy-related CO2 emissions in the two countries are the result of special circumstances (unification in Germany which led to the closure of many inefficient, coal-fired power plants and energy market liberalisation in the UK) rather than being directly attributable to the effects of climate-related policies. It is likely that an analysis specifically looking at public power production in the two countries would indicate similar conclusions. However, the impact of new policies, in particular the EU Emissions Trading Scheme, are likely to have a greater influence in the future.

b) SO2 emissions:
Emissions of SO2 from public electricity and heat production in the EU fell by 71% over the period 1990 to 2004. As per CO2 emissions, if the structure of power production had remained unchanged from 1990 then by 2004 emissions of SO2 would have increased by 33% above their 1990 levels, in line with the additional amount of electricity and heat produced. This decoupling of SO2 emissions and electricity and heat production over the period 1990 to 2004 has been due to:

• The introduction of flue gas desulphurisation (FGD) and the use of lower sulphur coal and oil, which led to a 67% reduction compared with 1990 levels.
• The switch in the fuel mix away from coal and oil towards lower sulphur fuels such as natural gas, which led to a 24% reduction.
• Efficiency improvements, which resulted in a 14% reduction.
• The 2% lower share of nuclear and non-thermal renewable energy (i.e. excluding biomass) in 2004 compared to 1990, which actually increased emissions by 3 %.

In a similar manner to CO2 emissions the overall multiplicative impact of these individual influencing factors was a 71% reduction in SO2 emissions in 2004 compared to 1990 levels. The increased utilisation of coal plants has in recent years meant that the decline in SO2 emissions has slowed, although the significant specific reductions being achieved by flue gas desulphurisation mean that SO2 emissions have continued to fall in absolute terms.

c) NOx emissions:
Emissions of NOx from public electricity and heat production in the EU fell by 45% over the period 1990 to 2004. If the structure of power production had remained unchanged from 1990 then by 2004 emissions of NOx would have increased by 33% above their 1990 levels, in line with the additional amount of electricity and heat produced. This decoupling of NOx emissions and electricity and heat production over the period 1990 to 2004 has been due to:

• The introduction of low-NOx combustion technology and flue gas treatment, which led to a 49% reduction.
• Efficiency improvements, which resulted in a 14% reduction.
• The switch in the fuel mix, away from coal and fuel oil towards natural gas, which led to an 8% reduction.
• The lower share of nuclear and non-thermal renewable energy (i.e. excluding biomass) in 2004 compared to 1990, which actually increased emissions by 3%.

The overall effect was a 45% reduction in NOx emissions in 2004 compared to 1990 levels. However NOx emissions stayed at similar levels in the period 2000 to 2004. In a similar manner to that for CO2 emissions, this trend is linked to an increased use of coal and lignite for electricity and heat production from 1999/2000 onwards.