Yhdyskuntajätteen kahden energiahyödyntämistavan eroavuudet ilmastonmuutoksen hillinnän näkökulmasta

Objectives recently set by the EU to mitigate climate change and to reduce waste landfilling, in addition to increased energy prices, have increased attentions to utilise energy content of the waste streams. Waste utilisation to energy can be divided in two common practices. These are combustion in waste-to-energy (WtE) plants and SRF (or REF/RDF) co-firing in power plants with other fuels. In comparison with WtE plants, one advantage of co-firing is higher power to heat ratio. This significantly effect on the overall greenhouse gas (GHG) balances of these practices because the difference in produced electricity is compensated by "marginal production" which often results relatively high CO₂ emissions. On the other hand, the refining process of SRF consumes energy and energy content of the sidestream may not be utilised. In addition, if sidestream will be landfilled it causes methane emissions. In the integrated "Climate action and renewable energy package" of the EU published in January 2008 mandatory emission reduction targets are proposed separately to ETS (Emission Trading Scheme) sector and non-ETS sector. Targets for the non-ETS sector are national and CO₂ emissions from new WtE plants planned to Finland will possible be excluded from the ETS and therefore counted in the non-ETS sector. Electricity and heat from waste combustion, however, usually substitute fuels and emissions in the ETS sector making it more difficult to achieve national targets of the non-ETS sector. In this study, different scenarios to utilise the thermal energy of landfilled municipal solid waste in Finland were assessed. It is difficult to estimate the amount of waste in the future and therefore the present amount and composition were used as default values in the calculations. Uncertainty was estimated for every parameter used in the calculations. The results are presented as probability distributions based on the stochastic modelling. Differences in GHG emissions of the scenarios were hundreds of thousands CO ₂-equivalent tons annually in both the ETS and the non-ETS sectors. In non-ETS sector the differences correspond 3-14% of the non-ETS sector total reduction target set for Finland. Sectors combined it seems that the best scenarios probably reduce GHG emissions from 0.5 up to 1 Mt annually comparing today even if reduced emissions from landfilling are not taken into account. In the worst scenarios GHG emissions from power and heat production may even increase. However, quantitative estimations are not presented for GHG reduction from reduced landfilling due to the fact that amount of considered waste is the same in all scenarios. This results equal reduction in emissions and causes therefore no bias when scenarios are compared. However, emissions from possibly landfilled sidestream of SRF refining process are included to calculations. Mitigation of climate change will require many relatively expensive operations. In the case of waste utilisation, also cost savings in addition to emission reductions can be obtained by optimal recycling of materials and energy. According to the results of this study, waste fractions which could be refined to SRF with a reasonable yield should not, from the climate change mitigation point of view, be incinerated. Higher electricity production and thus greater substitution of fossil fuels is achieved by REF co-firing.