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A major part of residues from pulp industry are deposited as waste at high disposal costs. Thispaper summarizes a five-year research project concerning implementation of an industrial,automatic roll-pelletizing method at a heating plant in the city of Kalmar, Sweden and presentsthe visions of the newly initiated research project where pulp industry residues are recycledtogether with wood ash. Also combustion issues are included.

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.

Sustainable whole-tree harvesting practice requires that nutrient removal from the forest is compensated. Wood ashes contain all the nutrients, except for nitrogen, that are found in unburned fuel and can also increase soil pH, which makes ash recycling a natural way to stabilize the nutrient balance and counteract the acidification of forest soils that occurs due to intensive forest management. Several methods for processing ashes into spreadable products have been developed. The aim of this paper is to compare these methods. The study mainly focused on an economic evaluation of production, transportation and the spreading of self-hardened ash, ash pellets and ash granules. Self-hardened ash is generally considered to be the cheapest alternative to manufactured ash products, but these results imply that the most cost effective alternative is ash pellets. Around 27% of total costs could be earned from recycling the ash by producing pellets and 8% if granules are produced instead of self-hardened ash. This partly depends on the higher density of the pellets and granules and a significant reduction in the number of transportation operations. The reduction in transportation operations and diesel consumption also has major environmental benefits. Furthermore, it is more efficient to produce granules and pellets than it is to produce self-hardened ash and it is also easier to produce a reliable product of an appropriate size, shape and texture for a market that has well defined requirements.

Companies that generate a large amount of wood ash will need an industrial process to agglomerate the ash and lower its reactivity, because untreated ash is a dust hazard for workers and is difficu ...

The central heating plant of Kalmar, Sweden produces 200–300 tons wood ash every year. A stabilised material for nutrient recycling is produced by adding water and dolomite to the wood ash and granulating the mixture. Combined mineralogy and chemistry can be used to interpret the transformation processes that occur during hardening and weathering of the granules, thus leading to a possibility to refine the production process and final characteristics of the granules. Mineralogy was separately studied in the wood ash, dolomite, self-hardened wood ash and granules by X-ray diffraction. Magnesium- and calcium-containing minerals are most common in the ash materials in the present study. The amounts of portlandite and calcite present in self-hardened and granulated ash samples are clearly higher than those in the untreated ash, showing that these minerals are formed during the treatments. Additionally, one potassium-containing secondary mineral, syngenite, is formed during the self-hardening of wood ash. Quartz, dolomite and the Fe–K–Mg-silicate in the granules originate from dolomite. The secondary minerals gypsum and calcium silicate hydrate are present in the granules. Portlandite occurs only in control granules in the field study. This suggests that hardening of granules continues in the field and portlandite is transformed into calcite. After up to 3 years on forest soil, the crystalline compounds dolomite, calcite, quartz, ankerite, albite and alumohydrocalcite are present in granules, of which alumohydrocalcite is formed as a secondary mineral in the field. These results suggest that the dissolution of granulated wood ash is strongly delayed compared with untreated wood ash and self-hardened wood ash because of the formation of less soluble compounds during the granulation process.

Use of biofuels in the form of logging residues is increasing in the European countries. This intensive forestry, where entire trees are removed from the felling sites, may contribute to a negative nutrient balance in the forest soil. Recycling of ash from the combustion of clean wood fuel, sometimes in combination with limestone or additives/binders, back into the forest soil could maintain the soil nutrient reservoir intact. Before spreading ash, it is important to determine its contents and, particularly, its decomposition pattern using reliable laboratory leaching tests. In this study, mineralogy and the leaching of Na, Ca, K, Mg, Mn, Al, Cu, Fe, P, and Zn from wood ash pellets and granules, produced both from green liquor sludge and fly ash, are examined by XRD and by subjecting these substances to three different laboratory leaching tests: upflow percolation (CEN/TS 14405), batch leaching (SS-EN12457), and a new Swedish leaching test using a magnetic stirrer. Mineral phases such as quartz, ettringite, calcite, gehlenite, and aphtitalite were identified in the ash granules and in the ash/green liquor sludge granules, by means of XRD. Six additional minerals were detected in the granules of ash only, and another six in the ash/green liquor sludge granules. At L/S 2, the batch leaching test resulted in the highest amounts of elements leached and the upflow percolation test the lowest. At L/S 10, both the batch leaching test and the upflow percolation test resulted in high amounts of elements leached. The batch leaching test at L/S 10 complies quite well with the percolation test and could be suitable for ash/green liquor sludge granule evaluation in daily practice. The magnetic stirrer test seems to underestimate the release potential of elements from granules. The batch test is simple to perform, and has the ability to dissolve 70-80% of the elements with the highest mobility from the materials under study.

Limestone and dolomite powder were tested as binders during wood ash agglomeration on an industrial and a laboratory scale. Two agglomeration methods are compared. Dolomite from Estonia is commonly used as a binder/additive during automatic production of agglomerated wood ash at the central heating plant of Kalmar, Sweden. Swedish limestones from Oland and Ignaberga as well as Swedish dolomite from Glanshammar were used as binders in the production of test agglomerates of wood ash. The chemical and mineralogical composition of the binders as well as of the resulting granules and pellets is presented. The structural, chemical and leaching properties of the hardened ash/binder agglomerates are discussed in relation to their possible environmental impact on forest soil. The environmental acceptance of recycling of agglomerated ashes to forest soils is also discussed in relation to the new recommendations.