VTT Processes

PELLETISATION OF RECOVERED FUEL

Leif Åkers, Ewapower Ab Oy, Launisaarentie 90, FIN-68600 Pietarsaari, Finland tel. + 358 6 322 7200, fax +358 6 322 7201

Ewapower Ab oy was founded in 1996 by waste management companies ASJ and Ekorosk owned by the towns of Vaasa and Pietarsaari and by adjacent municipalities, as well as by the package material manufacturer WalkiWisa owned by UPM-Kymmene Corporation. The task of Ewapower is to process recovered fuel pellets from source-separated commercial and industrial wastes and from household waste of Pietarsaari. The plant manufactures pellets about 30 000 t/a. The pellets are burned in the 120 MW bubbling fluidised-bed boiler of UPM-Kymmene Oyj Wisaforest, substituting for coal, about 2 - 15% of energy.

Qualitative characteristics and variations of recovered fuel pellets manufactured by Ewapower were studied. The combustion-technical quality was determined by systematic sampling. The pellet samples were combined from several single samples. The fuel-technical characteristics of pellets were as follows: calorific value as received 20 - 27 MJ/kg, for dry matter 21 - 28 MJ/kg; moisture content 3 - 10%, and ash content for dry matter 2 - 10%.

Chlorine content is a combustion-technical critical factor of fuel quality. Chlorine contained in the fuel may cause dioxin emissions and hot corrosion on the heat surfaces of the steam boiler. Chlorine is derived mainly from PVC plastics, which contain 20 - 60% chlorine. The analyses carried out indicated that the chlorine content of pellets ranged within large limits, the average being 0.68%. Although the metal and heavy metal contents were on an acceptable level, at certain other plants using recovered fuels especially aluminium has been found to cause deposits on the surfaces of steam pipes in the boiler.

Recovered fuel pellets can be stored and are easy to handle. Dosage and mixing with the main fuel (e.g. wood or peat) is simple and feeding into the boiler proceeds smoothly. Hence, combustion is also easy to control.

On the basis of this project, further studies will be initiated. Research objects are, i .a., development of a removal method for PVC plastics and non-magnetic metals, which would increase the capacity and availability of the pelletisation process, and more efficient utilisation of drying.

A.  Production and quality of recovered fuels, source-separation