Improving energy use in sawmills : from drying kilns to national impact

Abstract: Increased concern about environmental problems has amplified the public`s interest inenergy usage. The improved subsidies for biomass, together with the rising energy priceshave made biomass a desirable product on the energy market. Energy intensive industries inthe field of wood and biomass now have nowadays an opportunity to decrease energyconsumption and to sell their biomass surplus on the energy market.This Licentiate thesis focuses on strategies to decrease biomass usage in sawmill industriesin order to increase their surplus biomass and increase their profit. This is done throughsystem analysis of sawmill industries in terms of mass and energy flows. The energyanalysis focuses on the drying kiln using psychrometric and thermodynamic relationships.State-of-the-art technologies, available on the market, have been studied to determine theirpossible effect on the total energy usage in the sawmills.This study was undertaken to determine the national use of energy due to sawmills and thepotential magnitude of improvements. Sawmills are important suppliers to the biomassmarket, since medium to large capacity sawmills contribute with 95% of the Swedish annuallumber (sawn boards) production (17.3 Mm3) with a lumber interchange of only 47%. Therest of the timber (unsawn logs) is transformed into biomass through the lumber productionprocesses. An essential part (12%) of the timber is used for supplying heat to the productionprocesses, mainly to the drying process which is the most time and heat consuming processin the sawmill. The main conclusions are that the heat demand for drying lumber in Swedishsawmills was found to be 4.9 TWh per year and the drying process can be made moreeffective by use of state-of-the-art technologies. Hence the internal use of biomass insawmills can be decreased, thereby increasing the biomass that can be sold to the marketand/or to generate heat and/or electricity, resulting in more profitable sawmills and asignificant increased supply of biomass to the market.It was also found that with available state-of-the-art technologies it is possible to recycle theheat in the evacuated air from the dryer, and if the recovered heat is used for heat sinksinside or close to the sawmill a large decrease of the energy usage can be achieved. If thetechnologies are implemented up to 5.56 TWh of equivalent biomass can be saved,depending on the technology, the specific sawmill conditions, kiln settings and dryingsystem operation. However, some of the considered technologies consume a substantialamount of electricity, so the economic benefit should be carefully evaluated.