Mid Sweden University

There are many possible systems for recovering, refining, and transporting logging residues for use as fuel. Here we analyse costs, primary energy and CO2 benefits of various systems for using logging residues locally, nationally or internationally. The recovery systems we consider are a bundle system and a traditional chip system in a Nordic context. We also consider various transport modes and distances, refining the residues into pellets, and replacing different fossil fuels. Compressing of bundles entails costs, but the cost of chipping is greatly reduced if chipping is done on a large scale, providing an overall cost-effective system. The bundle system entails greater primary energy use, but its lower dry-matter losses mean that more biomass per hectare can be extracted from the harvest site. Thus, the potential replacement of fossil fuels per hectare of harvest area is greater with the bundle system than with the chip system. The fuel-cycle reduction of CO2 emissions per harvest area when logging residues replace fossil fuels depends more on the type of fossil fuel replaced, the logging residues recovery system used and the refining of the residues, than on whether the residues are transported to local, national or international end-users. The mode and distance of the transport system has a minor impact on the CO2 emission balance.

There are multiple systems for the collection, processing, and transport of forest residues for use as a fuel. We compare two systems in use in Sweden to analyze differences in fuel cost, CO2 emissions, dry-matter loss, and potential for allergic reactions. We compare a bundle system with the traditional Swedish chip system, and then do an in-depth comparison of a Finnish bundle system with the Swedish bundle system. Bundle systems have lower costs, while the allergic reactions do not differ significantly between the systems. The bundle machine is expensive, but results in high productivity and in an overall cost-effective system. The bundle system has higher primary energy use and CO2 emissions, but the lower dry-matter losses in the bundle system chain give CO2 emissions per delivered MWh almost as low as for the chip system. Also, lower dry-matter losses mean that more biomass per hectare can be extracted from the clear-cut area. This leads to a higher possible substitution of fossil fuels per hectare with the bundle system, and that more CO2 emissions from fossil fuel can be avoided per hectare than in the chip system. The Finnish bundle system with its more effective compressing and forwarding is more cost- and energy-effective than the Swedish bundle system, but Swedish bundle systems can be adapted to be more effective in both aspects.

Here we examine the cost, primary energy use, and net carbon emissions associated with removal and use of forest residues for energy, considering different recovery systems, terrain, forwarding distance and forest productivity. We show the potential recovery of forest fuel for Sweden, its costs and net carbon emissions from primary energy use and avoided fossil carbon emissions. The potential annual net recovery of forest fuel is about 66 TWh, which would cost one billion 2005 to recover and would reduce fossil emissions by 6.9 Mt carbon if coal were replaced. Of the forest fuel, 56% is situated in normal terrain with productivity of >30 t dry-matter ha (-1) and of this, 65% has a forwarding distance of <400 m. In normal terrain with >30 t dry-matter ha (1) the cost increase for the recovery of forest fuel, excluding stumps, is around 4-6% and 8-11% for medium and longer forwarding distances, respectively. The stump and small roundwood systems are less cost-effective at lower forest fuel intensity per area. For systems where loose material is forwarded, less dry-matter per hectare increases costs by 6-7%, while a difficult terrain increases costs by 3-4%. Still, these systems are quite cost-effective. The cost of spreading ash is around 40 2005 ha (-1), while primary energy use for spreading ash in areas where logging residues, stumps, and small roundwood are recovered is about 0.025% of the recovered bioenergy.

In this study, we analysed and compared costs, primary energy use and CO₂ benefits of recovering stumps and small roundwood from thinnings, together with logging residues. Small roundwood, chipped at a terminal or end-user, has a cost comparable to the chip system and a primary energy use comparable to the bundle system used for recovery of logging residues. The small roundwood system with roadside chipping is more expensive. As productivity in the cutting process improves, the small roundwood alternatives become more cost-effective. The stump system has costs in the same range as or lower than the chip and bundle systems. Forestry operations for stump and small roundwood recovery require considerable primary energy, but net recovery per hectare is much greater than for the chip and bundle systems, which means that more fossil fuel can be displaced per hectare of clearcut than with a chip or a bundle system. Stumps and small roundwood from thinnings can become as cost-effective as logging residues in the near future. Furthermore, when stumps and small roundwood from thinnings are also used to replace fossil fuels, the potential CO₂ reduction will be about four times as great as when only logging residues are used with a traditional chip system.

Local, national and international transportation of forest fuels with regard to costs, primary energy use and CO₂ emission was analysed. The main issue was the extent to which both mode and distance of transport affect the monetary cost, CO₂ emission and primary energy use arising from the use of various types of forest residues for energy purpose. Local applications proved the most efficient options of those studied. Chipping of bundles at a terminal, for transport by rail and sea to national or international end-users, has low costs and produces only modest CO₂ emissions. For the pellet options, the cost is about the same as for chipping, but require more primary energy and emit more CO₂. The traditional chipping system is more expensive than the other options. The costs of the international options over a transport distance of 1100 km vary between 21 and 28 €₂₀₀₇/MWh, whereas pellet options cost between 22 and 25 €₂₀₀₇/MWh. The primary energy required for transport of logging residues vis-à-vis pellets falls in the range 4–7% and 2–4%, respectively, of the bio-energy delivered. The primary energy needed to produce pellets gives them a lower fossil fuel substitution rate per hectare, compared with bundle systems. Similarly, for chip systems vis-à-vis bundle systems, the biomass delivered to the conversion plant is reduced by the greater physical dry-matter losses entailed by chipping systems in the forest-fuel chain.

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.