The sludgebark and to a certain extent the bark were until a decade ago waste products without any economic value that were thrown away. A number of environmental laws and increcing energy prices have improved the prerequisites for increasing the use of these materials. At Seskarö sawmill they burn the sludgebark and a great deal of the bark in the sawmill furnace. The sludgebark has a number of disadvantages compared to bark during burning. The sludgebark is often wet which means the energy net from burning often gets low. The sludgebark is also often more or less contaminated with stones, sand, snow and other unwanted things.
The overall purpose with this work is to suggest actions to optimize the handling of bark and sludgebark so that the economic benefit for Seskarö sawmill will be maximized. There are a number of different alternatives for machines and actions that will be presented for optimizing the handling of bark and sludgebark. In the report there are also examples given on different refinement alternatives for how to increase the fuel quality of bark and sludgebark.
The work started with an investigation of how the bark was handled at the sawmill. To be able to understand how the bark is handled today, the chief and other relevant staff at the sawmill were interviewed.
A literature study was done to be able to make an estimation of the dry matter losses of the bark caused by storage. An interview/ questionnaire investigation was carried out to about 60 different sawmills to get knowledge about the handling of the sludge bark. Internet was also used to get more information and suggestions of machine alternatives for handling of sludge bark. Calculations were made to make out the most profitable usage and handling methods.
It is common that bark is stored for a long period before combustion. This leads to dry matter losses in the material. There are many factors that make a difference for the storage result. Some of the most important factors are temperature, access to oxygen, nutrients and the moisture content of the bark. In average the dry matter loss is about 3.5 % per month over a six month period. The losses are significantly higher in the beginning of the storage period but later on merge out.
When the sludgebark is gathered at Seskarö sawmill it contains a great deal of twigs, wood pieces, stones and other contaminations. Before the material reaches the furnance the sludgebark must be worked through so it becomes more homogeneous and clean from big stones and metal pieces. Today the sawmill hires an entrepreneur with a Doppstadt DZ 750 kombi that twice a year comes to crush the bark and other wood pieces at the sawmill. Besides this they also rent a siftscoop that sorts the sludgebark. The yearly cost for reprocessing the sludgebark including the machine rental amounts to about 200 000 SEK.
The sludgebark is stored for about 3.5 months leading to significant dry matter losses. This cost due to dry matter losses amounts to about 42 000 SEK per year. One way to diminish the losses is to have a daily reprocessing of the sludgebark with a machine placed at the sawmill. With help from the formula for fixed annual installment the economic result for different machine investments has been calculated. The machine that got the best result was an ALLU SM 4-27. This is a siftscoop that sifts away the bigger stones and metal pieces. This siftscoop is placed on a wheel loader. The annual savings for investing in a ALLU SM 4-27 compared with today’s system for reprocessing the sludgebark amounts to roughly 125 000 SEK.
This report also looks at other bark uses such as soil fertilizer or decontaminator of oil. These alternatives have also been assessed in an investment analysis. They were less profitable than using the bark fore energy.
Summing up, the bark is a resource that ought to be better used at Seskarö sawmill. The bark is getting more and more valuable. There is money to make at finding new markets and customers for the bar...
