The neatly trimmed logs moving along the production lines at UPM mills spend time in different storage conditions before reaching their destination. They are stored alongside forestry trails and in huge sand field depots. During all this the logs gather a certain amount of sand, stone and pieces of metal to their surface.
In the plywood industry the logs are also soaked in water and following this a certain amount of moist bark waste gathers at the bottom of the soaking pond. This side stream contains 60 to 70 percent water. It is difficult to use in energy production because of its poor fuel value.
"The most troublesome wood side streams are the soaking pond bark and the different varieties of bark from de-barking, they can contain metal, soil and bigger chunks of wood. The moist and partly decomposed bark waste is also a challenge," explains Environment Manager Sanna Kontinen, responsible for developing the recycling methods of bark in the Zero Solid Waste to Landfill project.
Efficient screening methods developed in collaboration with universities
The majority of the sandy and moist wood material can be incinerated in the select UPM mill boilers that can handle the impurities. There are however some qualities of wood waste that contain so much sand and soil that it is not possible or sensible to burn them.
The solution is in more efficient screening and drying. In screening the sand, soil and other impurities are sieved away. The drying improves the fuel value of the waste. A two-year research project with Mikkeli University of Applied Sciences focuses on screening the water and sand from the soaking pond bark.
When the most practical solutions for the drying and screening of the material has been found it is possible to compost the rest of the material and perhaps commercialise it as soil enrichment material. The rest of the bark can then be burnt in boilers.
There are other uses to bark besides burning it. There is however no uniform way to utilise the side stream, only various local applications. In the Zero Solid Waste to Landfill project these applications will be carefully looked at and the best are chosen to act as models for the country-wide modus operandi.
"At UPM Jämsä River Mills the sandy wood-material is screened, the bark burnt and the leftover decomposed bark used in soil enrichment. At UPM Kymi the sandy bark material is used in producing decking material and at UPM Pietarsaari we have a partner that can utilise our sandy bark as an acidic cultivation platform. It is possible to commercialise the sandy bark or to refine the partly decomposed bark to a soil enriching material with plenty of minerals. We just need a partner that can create the market for the product independently. The cost, of course, has to be manageable to UPM," describes Kontinen.