Environmental Engineering Reference
In-Depth Information
Biomass harvest
Herbaceous biomass
Woody biomass
Mowing
Short rotation
Natural forest
Field drying, tedding or raking
Delimbing and debarking
Merging windrows by raking
Baling and bale handling
Chopping
Chipping
Bundling
Densification
Storage and/or transportation
FIGure 7.1
Biomass harvest options and procedures.
and are powered by the tractor power takeoff. Conventional hay mowing leaves the material in a
swath behind the mower, and fresh cut grasses require 3-5 days to dry, depending on crop, soil,
and weather conditions (Srivastava et al. 2006). This swath contains the leaves and the stems of the
plant; the leaves dry faster because of their larger surface area and unprotected outer layer. When
the swath is dried and handled, the leaves will be inherently more brittle and prone to blowing away.
To encourage faster stem-drying, many mowers are now equipped with rubber-coated steel rollers
that crush the stems to allow greater airflow. This conditioning of the stems can speed drying time
to 2-4 days, but it requires an additional energy input of 2-4 kWh/Mg dry matter (DM) (Srivastava
et al. 2006). Conditioning is not required for biomass materials that can be mowed dry such as
corn stover, soybean straw, cereal straw, spring-harvested switchgrass, and cover crops. Popular
in Canadian Prairies, windrowers or swathers, which are equipped with cutter bars, create a crop
windrow in a single pass from dry standing biomass in the field.
7.2.2 f
iEld
d
rying
, t
Edding
, r
aking
,
or
m
Erging
Raking accumulates the mowed swaths into a large windrow or elongated pile that can be fed
into a baler with higher efficiency as compared with a small swath. Tedding is used to achieve
faster drying and a uniform moisture level within a swath. Rakes and tedders can also be used
to invert a swath to encourage faster drying times. A typical rake will cause mass losses of
3-6% because of breaking of the fragile material (Srivastava et al. 2006). More leaves than
stems are lost during the raking or tedding process because of the drier and more brittle nature
of the leaves.
7.2.3 B
aling
and
B
alE
h
andling
The use of balers to densify and contain herbaceous biomass is common on most farms that harvest
dry material. Currently available equipment includes round balers, small square balers, and large
square balers. Round and square balers are equipped with a pick-up header to feed windrowed
