Environmental Engineering Reference
In-Depth Information
￿
Feedstock homogenization or smart blending
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Tailoring to a specific feeding system
As this chapter only deals with physical pretreatment, (thermo)chemical treatment is
excluded; pretreatment processes such as torrefaction and steam explosion are dealt
with in Chapters 12 and 13, respectively.
8.2 HARVESTING AND TRANSPORT
The first step in the chain from grown biomass-to-energy conversion is the process of
harvesting. The ratio of the energy content of the biomass for further processing to that
of the energy input (also called the energy ratio balance ) may be significantly
impacted by the harvesting technique, time (due to impact of weather conditions),
and subsequent transportation parameters, such as distance and methods. In this
section, harvesting of woody forest products, agricultural crops, grass, and aquatic
biomass is discussed.
8.2.1 Wood
8.2.1.1 Primary Harvesting During wood harvesting in forestry, either labor-
intensive manual chain sawing is practiced or use is made of a feller buncher, which
is a forestry vehicle made for the purpose of grasping and holding whole trees with a
hydraulically driven system while at the same time cutting them with an inbuilt
chainsaw.
8.2.1.2 Extraction from the Forest When wood has been cut in the forest, it must
be transported to a so-called landing (gathering location); this is done using forwar-
ders . These machines enable the heavy transport of multiple collected logs, stems, and
small trees using a trailer. When wood needs to be harvested from mountainous or
hilly landscapes, cable haulers are used, as vehicles with wheels or tracks cannot
safely move through such steep forests. The cable installation is mounted using a
tractor or truck, both using a tower with drum winch.
Skidders are vehicles aimed at pulling harvested stems or even whole trees to the
landing place. They usually lift biomass from one end, and as a result, soil and stones
may contaminate the harvested material. Once the whole trees and stems have been
delivered to the landing place, processors are used to remove limbs from the stem
wood, cut off tops, and crosscut (also called
) the stem wood to convenient
lengths. The remaining smaller logs are then transport ready for delivery to a sawmill.
For compact, more energy-dense transport, the harvested wood product is usually
baled; the wood is compressed, bundled, and tied together. The energy content of
(forest residues) bales has been reported to be about 2.56 MWh
section
t −1 on a wet basis
with a moisture content of 45 wt% (Van Loo and Koppejan, 2004).
 
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