Browsing by Author "Ahtila, Olli"

In recent times climate change, decrease of fossil fuels and increase of their price have greatly increased worldwide interest in renewable energy sources. In Finland, there has been a lot of concentration towards forest industry’s secondary produced wood basis biomass, that forest industry uses for its energy production. Forest industry’s waste water cleaning process creates different kinds of sludge, which are either reused or destroyed by burning or transporting to waste treatment plant. Especially reuse of bio sludge is difficult, and waste area placing in the future is impossible or at least economically too expensive. In practice, sludge is treated by burning, and by drying it becomes a bio fuel. The energy use is the best way to destroy waste sludge. Because of the high water consist of the sludge it must be dried before burning. Drying the sludge with secondary energy flow with waste heat from forest industry processes increases energy income from the burning process and replaces the use of fossil fuels. The goal of this research was to find out the most optimal mixture of bark and sludge by changing different drying parameters. The experimental work was started by building a laboratory size fixed bed dryer for the energy technology experiment hall, where drying was studied by blowing heated air through the fuel layer. The dried fuel material was a mixture of bark and sludge, or just bark or sludge at different masses, different percentage mixtures and different temperatures. Making the drying curves was based on weight changes. In the test rig were probes for controlling and setting the temperature as the experiment expected. The temperature and weight changes were recorded to computer during the experiment. The drying experiments showed that sludge-bark mixture dries well, when the percentage of the sludge mass doesn’t increase over 50 %. When the share of sludge is higher, drying is no longer effective, which is due to channelling of the air through the dried fuel material in the fixed bed dryer. When drying the bark, increase of the temperature from 50 °C to 70 °C was much more effective than from 70 °C to 90 °C, the difference in drying time was about doubled.