Table 1. Characteristics of the test chippers.
Type Drum Disc
Make Pezzolato Pezzolato
Model PTH 300 G H880/250
Year 2012 2012
Serial # CI 5240 CI 5389
Weight kg 2320 1460
Knives n° 2 2
Blade offset mm 15 13
Screen mm 50 NA
Piece breaker NA 3 blades, 40 mm
1

Fig. 1. The experimental set up with the PTH 300 G drum chipper.

2

Fig. 2. The experimental set up with the H 880/250 disc chipper.

Table 2. Average time consumption (minutes) per oven-dry tonne chips by chipper and feedstock type.
Feedstock type Disc Drum ∆ Disc (%)
Chestnut stem 6.28a 5.46a 15.0
Poplar branches 10.17b 8.99b 13.1
Poplar logs 6.73a 6.24a 7.9
Poplar mill residue 9.46b 9.46b 0.0
Note: different letters on the average values in the same column indicate statistical significance at the 5 % level; ∆ Disc (%) is the percent increment recorded for the disc chipper, assuming the drum chipper value as the reference base, i.e. ; ∆ Disc (%) = 100 * (Disc – Drum)/Drum.
Table 3. Anova table for time consumption per oven-dry tonne by chipper and feedstock type.
Source DF Type III SS p
Chipper 1 118441.383 0.0535
Feedstock 3 3447703.362 <0.0001
Chipper*Feedstock 3 56431.216 0.6132
Table 4. Average power consumption (kW) when chipping by chipper and feedstock type.
Feedstock type Disc Drum ∆ Disc (%)
Chestnut stem 35.39a 46.26a –23.5
Poplar branches 21.66b 28.83b –24.9
Poplar logs 37.89a 45.99a –17.6
Poplar mill residue 27.92c 34.51c –19.1
Note: different letters on the average values in the same column indicate statistical significance at the 5 % level; ∆ Disc (%) is the percent increment recorded for the disc chipper, assuming the drum chipper value as the reference base, i.e. ; ∆ Disc (%) = 100 * (Disc – Drum)/Drum.
Table 5. Ancova table for average power consumption when chipping by chipper and feedstock type with productivity as covariate.
Source DF Type III SS p
Chipper 1 1239.876 <0.0001
Feedstock 3 1117.873 <0.0001
Chipper*Feedstock 3 49.275 0.2561
Productivity 1 2423.577 <0.0001
Table 6. Consumed energy (MJ) per oven-dry tonne chips by chipper and feedstock type.
Feedstock type Disc Drum ∆ Disc (%)
Chestnut stem 20.80a 24.81a –16.2
Poplar branches 21.38a 25.34a –15.6
Poplar logs 24.95b 28.40b –12.1
Poplar mill residue 26.12b 32.15b –18.8
Note: different letters on the average values in the same column indicate statistical significance at the 5 % level; ∆ Disc (%) is the percent increment recorded for the disc chipper, assuming the drum chipper value as the reference base, i.e. ; ∆ Disc (%) = 100 * (Disc – Drum)/Drum.
Table 7. Anova table for consumed energy per oven-dry tonne by chipper and feedstock type.
Source DF Type III SS p
Chipper 1 575710069.9 <0.0001
Feedstock 3 800329555.6 <0.0001
Chipper*Feedstock 3 29352520.4 0.5779
Table 8. Consumed diesel fuel (L) per oven-dry tonne chips by chipper and feedstock type.
Feedstock type Disc Drum ∆ Disc (%)
Chestnut stem 2.36a 2.73a –13.6
Poplar branches 2.92b 3.35b –12.8
Poplar logs 2.67b 3.21b –16.8
Poplar mill residue 3.11c 3.94c –21.1
Note: different letters on the average values in the same column indicate statistical significance at the 5 % level; ∆ Disc (%) is the percent increment recorded for the disc chipper, assuming the drum chipper value as the reference base, i.e. ; ∆ Disc (%) = 100 * (Disc – Drum)/Drum.
Table 9. Anova table for consumed diesel fuel per oven-dry tonne by chipper and feedstock type.
Source DF Type III SS p
Chipper 1 8.957 <0.0001
Feedstock 3 15.375 <0.0001
Chipper*Feedstock 3 0.924 0.3818
3

Fig. 3. Average chip size distribution for the disc chipper (grey bars) and drum chipper (black bars).

Table 10. Particle size distribution by chipper and feedstock type.
Chipper Disc Drum
  Chestnut logs
>45 mm 0.1 0.1
45–16 mm 3.8 3.4
15.9–8 mm 50.9 43.7
7.9–3 mm 36.4 42.6
<3 mm 8.8 10.2
  Poplar logs
>45 mm 0.0 0.1
45–16 mm 3.8 3.5
15.9–8 mm 63.7 60.5
7.9–3 mm 25.7 27.0
<3 mm 6.8 8.9
  Poplar branches
>45 mm 0.3 0.4
45–16 mm 5.5 5.5
15.9–8 mm 52.7 44.9
7.9–3 mm 32.0 36.5
<3 mm 9.5 12.7
  Sawmill residues
>45 mm 0.5 0.4
45–16 mm 9.6 7.8
15.9–8 mm 62.9 50.5
7.9–3 mm 21.5 31.1
<3 mm 5.6 10.2
Note: data obtained from back-transformation of Arcsine transformed data.
Table 11. Anova table for particle size distribution.
Source DF Type III SS p
>45 mm
Chipper 1 6.502 * 10–5 0.8889
Feedstock 3 0.043 0.0063
Chipper*Feedstock 3 0.001 0.9505
45–16 mm
Chipper 1 0.005 0.1926
Feedstock 3 0.237 <0.0001
Chipper*Feedstock 3 0.004 0.6782
15.9–8 mm
Chipper 1 0.179 <0.0001
Feedstock 3 0.455 <0.0001
Chipper*Feedstock 3 0.031 0.1114
7.9–3 mm
Chipper 1 859.638 <0.0001
Feedstock 3 3730.834 <0.0001
Chipper*Feedstock 3 263.547 0.0529
<3 mm
Chipper 1 0.074 <0.0001
Feedstock 3 0.065 <0.0001
Chipper*Feedstock 3 0.016 0.0458
Note: analysis conducted after arcsine transformation.