compounds with the screen overflow and to enrich the biogenic
materials in the underflow (Requirement R 3).
Fig. 2 depicts a mass balance and the average material composition
of the different grain size fractions. Due to the low biogenic
share, the screen overflow is not further processed into fuel. It can
either be burned as RDF (net calorific value approx. 16,000 kJ/kg)
or landfilled. The biogenic enriched screen underflow, instead, will
be further processed as biomass fuel. Therefore the screen underflow
will be screened at 12 mm (S 2) and 3.5 mm (S 3). As a consequence,
three grain size fractions are generated: the grain size
fraction 12–40 mm hereinafter specified as coarse fraction, the
grain size fraction 3.5–12 mm specified as mean fraction and a fine
fraction 0–3.5 mm.
The material 0–40 mm is fine, storied, agglomerated material
which is difficult to screen. Therefore, the flip-flow screen technique
was chosen for screening with a high acceleration. Fig. 3 displays
the composition of the individual grain size fraction of the 0–
40 mm material. Approximately half of the mass is smaller than
12 mm [33]. Due to the fact that it is not possible to reliably differentiate
between biological and fossil material in the