Forest-Fuel Systems Comparative Analyses in a Life Cycle Perspective

Sammanfattning: Forest fuels can be recovered, stored and handled in several ways and these different ways have different implications for CO2 emissions. In this thesis, comparative analyses were made on different forest-fuel systems. The analyses focused on the recovery and transport systems. Costs, primary energy use, CO2 emissions, storage losses and work environment associated with the use of forest fuel for energy were examined by using systems analysis methodology in a life cycle perspective. The bundle system showed less dry-matter losses and lower costs than the chip system. The difference was mainly due to more efficient forwarding, hauling and large-scale chipping. The potential of allergic reactions by workers did not differ significantly between the systems. In difficult terrain types, the loose material and roadside bundling systems become as economical as the clearcut bundle system. The stump and small roundwood systems showed the greatest increase in costs when the availability of forest fuel decreased. Stumps required the greatest increase in primary energy use. Forest fuels are a limited resource. A key factor is the amount of biomass recovered per hectare. Combined recovery of logging residues, stumps and small roundwood from thinnings from the same forest area give a high potential of reduced net CO2 emissions per hectare of forest land. Compensation fertilization becomes more cost-effective and the primary energy use for ash spreading becomes low – about 0,25‰. The total amount of available forest fuel in Sweden is 66 TWh per year. This would cost 1 billion €2007 to recover and would avoid 6.9 Mtonne carbon if fossil coal were replaced. In southern Sweden almost all forest fuel is obtainable in high-concentration areas where it is easy to recover. When determining potential CO2 emissions avoidance, the transportation distance was found to be less important than the other factors considered in this work. The type of transportation system did not have a significant influence over the CO2 avoided per hectare of forest land. The most important factor analysed here was the type of fossil fuel (coal, oil or natural gas) replaced together with the net amount of biomass recovered per hectare of forest land. Large-scale, long-distance transportation of biofuels from central Sweden has the potential to be cost-effective and also attractive in terms of CO2 emissions. A bundle recovery system meant that more biomass per hectare could be delivered to end-users than a pellet system due to conversion losses when producing pellets.