Production of fertiliser from wood ash

In 1995, at the central heating plant of Kalmar, Draken, a project aiming to manufacture a granular ash product for nutrient recycling to forest soils instead of depositing it in landfills was started. Prototype equipment for granule manufacturing was developed and built by Kalmar Energi & Miljö in co-operation with Kalmar University College. Production of fertiliser from wood ash comprises aspects of technology, ecology and economy. The composition of granules mostly complies with the requirements of The National Swedish Board of Forestry for nutrient content and heavy metal levels. When constructing an automatic and continuous manufacture process, the on-line measurement of percentage of unburned carbon present in the wood ash is most important for the overall granule properties. Granulation is a more expensive method of treating ash, but granulated ashes give very slow ecological effects and could make ash recycling more acceptable in ecologically sensitive areas.