Wihersaari, Margareta

VTT Processes, Koivurannantie 1, P.O.Box 1603, FI–40101 JYVÄSKYLÄ, Finland

VTT Publications 564, May 2005, 93 p. + app. 71 p. [in English]
ISBN 951–38–6445–6 (soft back ed.)
ISBN 951–38–6446–4 (PDF edition)

Project: SIHTI Programme, PUUENERGIA Programme

Keywords: greenhouse gases, emissions, energy supply systems, biofuels, bioenergy, biomass production, wood fuels, forest residues, municipal wastes, renewable energy sources

Abstract

Greenhouse gas emission assessments of energy supply systems have traditionally included the CO2 emissions produced as the fuel is burned. A lot of models and calculations for evaluating greenhouse gas emission savings by using bioenergy have been introduced. The approaches often cover a major part or sometimes even the whole energy system. The biofuel production process itself is one piece that is normally covered very briefly or considered insignificant. Unfortunately, this means that the significance of some affecting factors might not have been estimated. The object of the thesis was to study the greenhouse gas balances in connection with the harvesting and production of biofuels and, based on this, evaluate in what situations there is a need to re-evaluate the potentials of greenhouse gas emission savings when using bioenergy for substituting fossil fuels.

Different methodologies were used in the separate evaluations: the philosophy and methodology of industrial ecology was used to analyse the sustainability and material flows of the Finnish forest industry. A simple calculation model was developed for analysing the energy consumption and greenhouse gas emissions for biomass production chains, upgrading of biofuels and production of solid recovered fuels. Emission risks from long-time storage of biofuel and biodegradable material were evaluated as well as changes in forest soil carbon due to harvesting of forest residues. The examination of the biofuel production chains showed that in a favourable situation as much as 97–98% of greenhouse gas emissions for a fossil fuel could be avoided by substituting it with a biofuel. On the other hand the investigation also pointed out that e.g. increasing fuel storage and upgrading activities for biofuels are likely to decrease this percentage remarkably. The main conclusion of the thesis was that the neutrality of greenhouse gas emissions when producing bioenergy should be re-evaluated. The author further suggest that tools and stimulants for keeping the greenhouse gas emission levels in fuel production chains as low as possible should be developed.

Contents

Abstract
Preface
List of original publications
Units and abbreviations
1. Introduction
1.1 Global warming and energy related greenhouse gas emissions
1.2 Renewable energy – a technical measure to reduce the energy related greenhouse gas emissions?
1.3 The contents and objectives of the thesis
2. Methods and materials
3. Aspects on greenhouse gas emissions related to using biofuels for substituting fossil fuels
3.1 Forest fuels as a part of the utilisation of forest biomass
3.2 Energy efficieny and greenhouse gas emissions of biofuel production chains
3.2.1 Forest residue
3.2.2 By products
3.2.3 Biofuel cultivation
3.2.4 Upgrading biofuels
3.2.5 Aspects on substituting fossil fuels with a biofuel
3.3 Potential greenhouse gas emissions from storage of biofuels
3.4 Utilisation of forest residues and the effect on the carbon pool in forest soil
3.5 Aspects on considering municipal waste as a biofuel
3.6 Biomass or municipal waste disposal considered as a base scenario
3.7 Uncertainties of the calculations
4. General discussion
4.1 Discussion of the results
4.2 Further discussion and recommendations
5. Summary
References
Appendices
mega watt hour
nitrous oxide
Forestry
Bark
Order of priority for the results

Figures and Tables

Figure 1. Different ways of generating biomass suitable for biofuel production.

Figure 2. Some studied elements of the forest residue fuel production chains.

Figure 3. The expression “energy balance” used in this thesis refers to the external energy input in proportion to the biofuel output.

Table 1. Parameter values used in model calculations (Table 1 in Paper V).

Figure 4. Flow chart of the soil carbon model. The boxes represent carbon compartments, the arrows carbon fluxes and the text by the arrows parameters controlling the fluxes. The values used for the parameters are shown in Table 1 (Fig. 1 in Paper V).

Figure 5. Various ways of producing wood derived fuels in Finland.

Figure 6. Flows of wooden materials in the Finnish forest industry in 1997 (Fig. 5, Paper I).

Figure 7. The carbon flows in Finnish forest industry in 1997 (Fig. 8 in Paper I).

Figure 9. Flows of base cation nutrients in a forest ecosystem (Fig. 2 in Paper I).

Figure 10. Fuels used and production of electricity, process heat and space heat in the Finnish forest industry in 1997 (Fig. 7 in Paper I).

Table 2. Calculated energy input and GHG emissions for five wood chips production chains in Finland (Table 1, Paper III, modified). The outtake of forest residue is considered to be equal in all chains (100 loose m3 ha-1).

Figure 11. The magnitude of GHG emissions from a full fuel chip production and combustion chain (Fig. 2 in Paper III, modified).

Table 3. Evaluation of energy input and GHG emissions for agricultural by- products. The presented values were calculated for straw and corn in Hungary (Wihersaari 2003, modified).

Table 4. Evaluation of energy input and GHG emissions for energy forestry (poplar) in Hungary (Wihersaari 2003).

Table 5. Evaluation of energy input and greenhouse gas emission evaluations for producing upgraded biofuels in Hungary (Wihersaari 2003, modified).

Table 6. Emission profile of fossil fuels used in Finland (kg per MWhfuel) (Wihersaari 2003).

Table 7. Emission profile of the Hungarian fossil fuels (kg CO2eq MWhfuel-1 (Wihersaari 2003).

Figure 12. The magnitude of GHG emission savings in Hungary when replacing coal with bio-chip, oil with bio-oil and gas with bio-gas. For 'min dom' and 'max dom,' only the domestic emissions are calculated for, for 'min total' and 'max total,' also the emissions abroad are noticed. The unit is kg CO2eq MWhfuel-1 (Wihersaari 2003).

Table 8. Wood derived fuels used as energy in Finland 2002 (Statistics Finland 2003).

Table 9. An evaluation of annually utilised volumes of bark, sawdust and fuel chip in Finland, their typical moisture and energy content and appearing length of storage time.

Figure 13. Simplified temperature behaviour assumed for two types of decomposing forest fuels (Fig. 2 in Paper IV).

Figure 14. A principal estimation of cumulative greenhouse gas emissions for storage of two kinds of fuel chip with different decomposing behaviour. The assumed temperature level inside the storage heap is the same as shown in Fig. 13 (Fig. 3 in Paper IV, modified).

Figure 15. Studied elements of the SRF production chain.

Table 10. An overall estimate of the uncertainty of the estimates made in the thesis.

Figure 16. The magnitude of GHG emissions (kg CO2eq MWh-1) from different parts of a fuel chip production chain ( a)The calculated magnitude of these emissions have to be considered more uncertain than the other.b) Evaluated for a six month storage of chip). (Fig. 2 in Paper III, modified).

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