Nyhet | 2014-08-08 | 15:06

Characterisation of recovered waste wood for thermal energy production

Raquel Rodríguez Varela, Chemical Engineering, Royal Institute of Technology (KTH).

Abstract

The utilization of recovered waste wood (RWW) have increased its importance in Sweden. These waste wood can be both from Nordic locations and also imported from other countries, such as United Kingdom. As waste wood is contaminated by distinct treatments and it can also contain external objects, its properties are significantly different than in clean woody fuels. Therefore, using recovered waste wood as a solid fuel for thermal energy production is expected to produce important effects on the impacts on the boiler performance.

In order to evaluate the fuel quality of RWW and the influence of the contaminants on its properties, waste and clean woods were compared. Some other evaluations were performed in order to identify the differences among origin and also over the time (from 2000 to 2013), as well as for qualitatively analysing the major pollutant sources in RWW.

Furthermore, both a semi-theoretical and a real plant evaluation of the fuel impacts were performed. Thus, it is possible to compare the potential risks of the fuel impacts to the real environmental boiler performance, including the influence of primary and secondary measures in the plants.

The results of the quality analysis showed that:
• In comparison to clean wood, RWW has a lower moisture content, but higher ash, emission components (N, S and Cl) and heavy metals contents. Recovered waste wood also shows a higher variability on its properties, which is not favourable for an optimum combustion performance
• There is a difference in origin depending on source and pre-treatment like fractioning
• Over the time, waste wood also seems to have diminished its heavy metals content

The contaminant source analysis showed that the major pollutant source in current RWW is the surface-treated wood and that the main pollutant sources in RWW seem to have changed during the last years.

From the impact analysis, it was concluded that the indexes for air emissions should be consider only as a rough guide, as the real impacts on the boiler performance will strongly vary depending on the primary and secondary measures used and their efficiency.

Key words:Recovered waste wood, quality trends, pollutant sources, fuel impacts

Thesis grade: A