PHYSICAL PRETREATMENT OF BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 246

TABLE 8.1 Overview of milling techniques applied for biomass
Milling technique

Main forces Advantages Disadvantages

Ball mills Shear Simple construction Effectiveness for

downsizing to very
small sizes is
relatively low

Compression Easy to operate
Cheap

Relatively high energy
utilization

Vibro energy mills
like ball mill
but with
vibration

Shear More effective in

crystallinity reduction

More expensive than ball
mills Compression

Lower end particle sizes
compared to ball mills

Relatively high specific
energy utilization

More complex
construction

Knife mills (Kratky
and Jirout, 2011)

Shear Used for wide range of

(tough) biomass

Only relatively dry
biomass (<15 wt%
moisture content) Lower specific energy

consumption (compared
to hammer mills)

Hammer mills Compression Cheap as they are standard

equipment (though more
expensive than ball mills)

Relatively high energy
utilization (especially
compared to knife
mills)

Easy to operate

Two-roll mills Compression Easy to operate, simple

construction

Moderately fine
distribution only Some shear

Disk mills and
wet-disk mills

Shear Processes wet streams, so no

drying needed

High specific energy
consumption for
milling process Finely ground product

High shear—
cavitation-based
machines

Cavitation,
shear

Very effective for fine
grinding

Need upstream size
reduction
For smaller feed sizes
only

These three approaches lead to the following equations for energy consumption:

1 1

L 1

Bond E = C B

L p −

p ð Eq : 8 : 2 Þ

:

1
L 2 −

1
L 1

Rittinger : E = C R ð Eq : 8 : 3 Þ

L 2
L 1

ð Eq : 8 : 4 Þ

Kick : E = C K ln