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Chapter 9
Lignocellulosic Biomass
Anne Rödl
Abstract This paper gives an overview of some important annual and perennial
crops for the provision of lignocellulosic biomass. It describes their cultivation
practices as well as their requirements concerning site characteristics and typical
logistic chains. Information on physical and chemical properties of these different
lignocellulosic biomass plants determining their capability for biokerosene production is presented. Additionally, data on the potential yields and the areas currently
under cultivation are given for each of the described crops.
9.1Introduction
Higher plants, mostly with perennial growth patterns, deposit stabilizing substances
like lignin in their cell walls. Because of this lignified (woody) structural tissue they
are also called lignocellulosic plants. The solid organic matter of such lignocellulosic plants is composed of celluloses, hemicelluloses and lignin in varying composition depending on the species and to some extent also on the site conditions. Such
lignocellulosic biomass is often seen as a promising raw material for the production
of biofuel because it is an abounded source of organic material that is not directly
competing with the markets for food and fodder. Lignocellulosic biomass can also
be supplied from waste streams in forestry and agriculture as well as from industry
or the final consumer (e.g. demolition wood).
Due to these advantages the use of lignocellulosic biomass for biokerosene production is investigated in various countries in the recent years. Mainly the following
conversion pathways have been studied.
• Kerosene can be produced based on pyrolysis oils provided from solid
organic feedstock. Pyrolysis means the heat induced cracking of the organic
A. Rödl (*)
Hamburg University of Technology, Institute of Environmental Technology and Energy
Economics, Hamburg, Germany
e-mail: anne.roedl@tuhh.de
© Springer-Verlag GmbH Germany 2018
M. Kaltschmitt, U. Neuling (eds.), Biokerosene,
DOI 10.1007/978-3-662-53065-8_9
189
190
A. Rödl
macromolecules within an oxygen-free atmosphere providing a gaseous, liquid
and solid phase. The liquids can be further treated within “classical” refinery processes to comply with the kerosene specifications; the most important treatment
processes are dehydration, oligomerization and hydrogenation. This conversion
route is still in an early research state; but lots of research and demonstration
projects are underway [1].
• Fisher-Tropsch (FT)-based kerosene can also be produced from solid biomass.
Within such a route the organic matter is first transferred to a syngas within
a heat induced processes operated with a lack of oxygen within a gas atmosphere, the so called gasification. The provided syngas mainly consisting of
carbon monoxide (CO) and hydrogen (H2) is then used as a source material for a
subsequent chemical synthesis process. This heat induced chemical conversion
is the so called Fisher-Tropsch (FT) synthesis. Here long chain hydrocarbons
are formed from the syngas components. This intermediate or FT-product can
then be further processed into jet fuel via existing refinery processes to meet the
given product specifications. The gasification step of this so called BtL-process
(biomass-to-liquid) has been successfully demonstrated in the Güssing plant in
Austria. Large scale plants for fuel production via the Fischer-Tropsch route
from coal or natural gas are located in South Africa and in the Middle East.
Nevertheless, for biomass this route has not yet been successfully demonstrated
at large scale.
• Biokerosene based on alcohols can also be provided from lignocellulosic
biomass. Here the solid organic matter is firstly converted via an enzymatic
or acidic hydrolysis to sugar molecules. These organic molecules can be used
afterwards as a base material for a “classical” alcoholic fermentation; i.e. the
sugar is converted via biocatalysts (yeast) to alcohol (e.g. ethanol). Afterwards
the alcohol is processed into biokerosene via the so called alcohol-to-jet (AtJ)
processes consisting mainly of the sub-processes dehydration, oligomerization
and hydrogenation. Again, several parts of this route have been demonstrated at
various stages of development but the overall process is still in an early stage and
thus not yet ready for the commercial market.
• A similar conversion pathway from solid biomass to kerosene is based on the
thermo-chemical gasification of solid biomass for the provision of a syngas
similar to that from the BtL-route. This gas can then be used as a raw material
within syngas fermentation (biological conversion) or alcohol synthesis (chemical conversion) in order to produce different types of alcohols (e.g. biobutanol).
These alcohols can then be further transferred into biokerosene via alcohol-to-jet
(AtJ) processes. Like the other pathways this route is not yet available, not even
on a pilot scale.
Due to this various conversion options for biokerosene production lignocelluloses is
an important feedstock for the provision of next generation biofuels. Therefore, this
promising organic resource is described in detail below.
9 Lignocellulosic Biomass191
9.2
Resources and Characteristics
9.2.1Origin
Lignocellulosic resources can be grown on fields or in forests, can be obtained as
by-products from primary (i.e. agricultural forestry) or secondary (i.e. industrial)
production or remain as wastes from the processing of organic material. These different types of resources for lignocellulosic biomass are characterized briefly in the
following.
• Energy crops. Energy crops are cultivated on agricultural fields or in forests in
order to provide biomass solely for energetic use (i.e. typically no other use is
intended). The following criteria can be used to classify energy crops:
–– Annual or perennial crops. Lignocellulosic biomass can be obtained from
annual or perennial plants. Typical for the latter are trees like poplar or
willow that are grown in so called short rotation plantations. Other examples
are perennial grass species (e.g. giant reed) that are grown on intensively or
extensively managed fields. Also annual grasses with huge yields can provide
lignocelluloses.
–– Herbaceous or woody biomass. Energy crops can also be categorized according to its origin from herbaceous or woody biomass. The latter is typically
biomass from trees and shrubs characterized by an obviously wooden structure. Annual and perennial grasses are in general referred to as herbaceous
biomass. This group of plants is characterized by huge variations in particular
related to its chemical composition. Typical for this group are e.g. reed canary
grass or switch grass.
–– Agricultural or forestry production. A further classification of energy crops
can be made according to their production scheme. Agricultural production is
typically intensive with high input (e.g. fertilizer, plant protection agents and
soil preparation) and short production cycles. Forestry production scheme can
be characterized as extensive production with low inputs and long rotation
periods. The latter includes also virgin biomass from natural forests [2]. The
differentiation between these two groups is sometimes not clear.
• By-products. By-products of bio-based products either occur already during
harvest on fields and in forests or during subsequent processing of the biomass
in industry. It is barely impossible to produce marketable goods from any type
of biomass without any by-products. By-products are mostly arising from parts
of the plant that have a supporting function for the usable part of the plant,
e.g. stabilization, protection, attraction etc. In general by-products are not that
parts of plants they have initially been cultivated for. From an economic and
practical point of view it makes a difference where by-products accrue. Collecting them from fields or forests is more complex then separating them from
192
A. Rödl
a production process. Therefore, the following classification of by-products is
suggested.
–– By-products occurring in primary sector (during harvests). Parts of the cultivated plants that are not needed for the production of the final product are
separated during harvest operations and typically remain on the agricultural
field or in the forest. A typical example is the coupled production of grain
and straw. Another example is the co-production of wood saw- or veneer logs
together with branches, stumps and bark.
–– By-products from secondary sector (occurring during processing). Agricultural and forestry commodities are typically further processed within various
downstream industrial upgrading processes in order to receive a merchantable
product. During processing also by-products will occur. Typical examples are
the production of sawdust, slabs, edgings and trimmings etc. in the forest processing industry (e.g. saw mills). Other examples are husks and bran provided
during rice and grain processing. The same is true for the production of sugar
from sugar cane; here bagasse is provided as a by-product.
• Waste. Lignocellulosic biomass is also contained in waste streams. These materials can be classified by the following two criteria.
–– Waste from unprocessed material. This group contains lignocellulosic waste
available as more or less “virgin” material. This means the structure and composition of the lignocellulosic material has not been changed within chemical or physical processes. Examples for this group are the woody fraction of
garden wastes or wastes from landscape management. Additionally untreated
construction wood, demolition wood and other waste wood can be included
in this group.
–– Waste from processed material. A significant amount of the globally traded
lignocellulosic biomass is processed into products where the original structure and composition of the lignocellulosic material has been modified like
for example pulp and paper. At the end of their use phase they are typically
treated as wastes. An example of this group is waste paper like old packing
materials or newspapers.
9.2.2Characteristics
Lignocellulosic biomass is composed of organic macromolecules forming complex
structures. Thus, their molecular and chemical structure is discussed below. Further,
some important impurities are addressed.
The molecular components of lignocellulosic biomass are mainly hemicelluloses, celluloses and lignin [3]. The distribution of these components varies between
different types of plant species. Thus Table 9.1 shows the average share of these
components within different lignocellulosic feedstocks. According to these data the
9 Lignocellulosic Biomass193
Table 9.1 Physical-chemical properties of different lignocellulosic biomass crops (LHV: lower
heating value, SRC: short rotation coppice)
Cellulose
[% dry
basis]
Hemicellulose
[% dry
basis]
Lignin
[% dry
basis]
Ash
[%]
Water
content
[% wet
basis]
LHV
[MJ/kg]
Miscanthus
44–57a
16–30a
8–22a
1–9a
3–49a
15–21a
Reed Canary
Grass
26–39a
17–28a
4–5a
2–13a
7–65a
16–20a
Elephant grass
34b–42c
20b–23c
8c–24b
6a–10c
74a
18a
Common Reed
34d–38e
21e–28d
19d–23e
3–8f
16a
Giant reed
31 –39
21 –35
18 –23
3 –6
h
36–42
14g–15a
Switchgrass
30–45a
21–35a
5–23a
2–10a
8–15a
17–19a
Sugarcane
(bagasse)
34–42
a
29–43
19–21
2–12
6–50
a
17–18a
Wheat (straw)
29–52a
11–39a
8–30a
1–19a
10–17a
15–21a
Corn (stover)
28–51a
19–30a
11–17a
4–10a
5–6a
17–19a
Wood, coniferous
35–83a
8–42a
12–43a
1–6a
0–63a
16–24a
Wood,
broadleaved
28–50
18–39
13–28
0.2–5
3–48
a
15–21a
SRC (poplar,
willow)
35–80a
13–42a
15–32a
0.2–5a
2–50a
17–20a
Crop
a
h
i
a
a
j
h
a
h
j
a
a
a
a
a
14g–15a
a
See Ref[4], bSee Ref. [5], cSee Ref. [6], dSee Ref. [7], eSee Ref. [8], fSee Ref. [9], gSee Ref. [10],
See Ref. [11], iSee Ref. [12], jSee Ref. [13]
h
variations between various types of plants are less pronounced compared to the
differences within one single group.
The most important chemical components in lignocellulosic biomass are carbon
(C), hydrogen (H) and oxygen (O). Typically carbon is contained in woody or herbaceous biomass with 45 to 47 mass-%. Hydrogen contributes with a minor share;
5 to 6 mass-% are characteristic values. Similar to the share of carbon is also the
fraction of oxygen with 40 to 46 mass-% in average. For energetic purposes oxygen
is in most cases an undesired component because it reduces the heating value. Thus
one factor determining the potential to produce high value liquid fuels is the relation
of hydrogen and oxygen to carbon within the virgin organic material. The closer the
hydrogen to carbon ratio to the desired hydrocarbon molecules, the more efficient is
the overall conversion process of the respective biofuel.
Figure 9.1 shows the H/C to O/C ratio of different lignocellulosic biomasses.
According to this graphic biomass crops are characterized by a higher O/C ratio
194
A. Rödl
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Fig. 9.1 H/C to O/C ratio of different lignocellulosic biomasses in comparison to selected fossil
energy carriers
in comparison to fossil fuels. Additionally the energy content of the material is
increasing with decreasing ratios [3].
Apart from carbon, hydrogen and oxygen other elements like nitrogen (N), sulfur
(S), phosphorus (P) and potassium (K) are contained in lignocellulosic biomass.
Due to e.g. poisoning effects on catalysts and toxic emissions these trace elements
are critical for the further processing of the biomass in most of the cases. Additionally they are influencing the ash content negatively. As a very general rule of thumb
it can be stated, the higher the share of trace elements and the ash content the lower
is the energy content of the fuel. Ash might also cause serious operational problems
in thermo-chemical conversion processes.
As a further disturbing substance always moisture is contained in biomass. Water
is typically unwanted from an energetic point of view because it decreases the
heating value. For this reason biomass crops with a low moisture content can typically be converted more efficiently to liquid fuels via thermo-chemical conversion
than biomass with a higher water content [3].
9.3Wood
Wood can be found in perennial plants whose typical structure is produced from
the tissue between wood and bark called the vascular cambium. The cambium is
forming a ring of cell producing tissue in the stem or the root of woody plants. All
9 Lignocellulosic Biomass195
tissue that is produced to the inside of the stem is called wood or xylem and all
tissue produced to the outside is called bast tissue or phloem.
Depending on the species the cambium is producing xylem and phloem continuously or just during periods with favorable conditions (e.g. growing season, rainy
season etc.). In zones with distinct seasons therefore the typical pattern of year rings
occurs. Compared to this wood from tropical tree species show no or just a very
weak formation of year rings due to the year-round balanced growing conditions.
The xylem consist of the water conducting cells tracheids or vessels, fiber cells
for support and parenchyma cells for the storage of reserves. The structure of xylem
varies considerably between the group of gymnosperm and angiosperm plants.
Coniferous trees are belonging to gymnosperm plants. Their wood consists mostly
of tracheides. These are less specialized cells that are acting as water conducting
and supporting cells at the same time. Therefore the wood of gymnosperm does not
have any fiber cells; they show only a few parenchyma cells and often contain resin.
Wood of angiosperm plants mainly consists of vessels but all other elements, like
fiber cells, parenchyma cells and tracheids can also be found.
Broadleaf trees that are belonging to the angiosperm plants, can be classified into
ring porous and diffuse porous trees, according to the arrangement of their vessels.
Ring-porous wood has bigger vessels that can conduct water very fast. These big
vessels are just produced in spring and are arranged circularly in the early wood
of the year ring. They are only functional for one season wherefore the total water
conducting system of ring-porous trees has to regrow in spring. Diffuse porous trees
have smaller vessels which are spread all over the cross section and which are functional for more than one year. Therefore the water-conducting stem section is bigger
in diffuse porous trees than in ring-porous species [14].
With the time older tracheides or vessels of all species are not used for water
transport anymore. So called tyloses block vessels or tracheids and a lot of species
fill them with pigments, tannins or resins which help to prevent fungi or bacteria
attacks and increase the durability of the wood. This so called heartwood mostly
differentiates from the sapwood by a different color and changed wood properties.
Wood is produced from trees. Latest statistics estimate that 4 billion ha worldwide are covered by trees in forests. This is roughly 30 % of the total land area [15].
Three of the world’s major biomes are dominated by trees. They are listed below.
• The Taiga or boreal forest is dominated by coniferous tree species.
• The deciduous forests are characterized by broad-leafed tree species either mixed
with coniferous species or not. Due to their appearance in the temperate zone, a
major part of the area is characterized by deciduous tree species that shed their
leaves in winter due to a shortage of light and warmth. There are also areas e.g.
in the Mediterranean zone that are characterized by evergreen species.
• The tropical forests are dominated mainly by broad leaved tropical tree species.
They are located in the area around the equator, which is characterized by much
precipitation and balanced temperatures between 20 and 30 °C around the year.
Tropical rainforests have the highest tree species diversity on earth and contain
in general more than half of all animal and plant species [16].
196
A. Rödl
In the following, selected coniferous and broadleaf tree species are described and
most important forest management schemes are presented.
9.3.1 Selected Tree Species
Trees and bushes can be classified into coniferous and broadleaf species. Ginkgo
plants are considered to belong to the gymnosperm plants. They neither belong to
coniferous nor to broadleaf species but form a third division of trees –the Gingkophyta. Only Gingko biloba is still existing as the last species of this archaic division.
Southeastern China is believed to be the last natural home of gingko, while it was
distributed around the globe in the Mesozoic era [17]. Meanwhile it has spread
again around the world because it is very popular as an ornamental plant and as a
city tree because of its tolerance against air pollution [18].
In the following some characteristic and economically significant tree genera that
can be found around the globe are described.
9.3.1.1 Coniferous Species
Conifers are evergreen, needled trees which develop wooden cones containing the
seeds. Coniferous trees can be found around the globe but mostly in the Northern
hemisphere within the boreal and temperate zone. The Southern hemisphere is dominated by Araucariaceae. Within the genus of coniferous trees the tallest (sequoia
sempervirens), thickest (sequoiadendron giganteum) and oldest trees (pinus longaeva) on earth can be found. Coniferous trees are often settling extreme sites
with special environmental conditions, like very low or high temperatures, a short
vegetation period or sites with very dry, nutrient-poor or acid soils. On sites with
average growing conditions deciduous trees are more competitive. Their growth is
straight and mostly monopodial which makes them very attractive for forest and
wood industry.
Pine (Pinus). Pines can be found in about 100 species in the Northern hemisphere.
They often have 2, 3 or 5 evergreen needles on short shoots (Fig. 9.2) [19].
Pines are important timber producers and are often planted in forests, parks or
gardens. Pines tolerate dry and poor soils and are in general quite undemanding. It
can grow on extreme dry but also on extreme wet sites. As a pioneer species pines
demand a lot of light and are therefore suitable for afforestation of poor and dry
sites. Naturally pines are widespread all over North America, Eurasia and native to
low lands and hilly regions. Pines are the characteristic trees of the Polish, Swedish,
Finnish and Russian-Siberian Forests [20]. In the tropics and sub-tropics of Central
America and Asia pines can be found in mountainous regions [21]. In Germany
Pinus sylvestris is the second most tree species in forests and is cultivated on 22 %
9 Lignocellulosic Biomass197
Fig. 9.2 Drawing of pine (left side:
tree, right side: branch with cones;
www.uli-schmidt-paintings.com)
of the wooded area [22]. It reaches heights up to 45 m and develops a strong taproot
that protect it from windthrows.
Pine wood, especially the heartwood, is hard and durable and is widely used
as construction wood, for interior constructions or furniture production [23].
Further it is used for production of Oriented Strand Boards (OSB) and in pulp
and paper industry for obtaining brown pulp and semi-pulp for kraft paper or
paperboard.
Spruce (Picea). 50 species of spruce can be found worldwide and especially on the
Northern hemisphere in the temperate zone. They are evergreen trees (Fig. 9.3) and
belong to the family of pines (Pinacea). Picea abies (Norway spruce) is an important tree species for timber production in Central Europe; it is also is often planted
in forests, parks or gardens [19]. In Germany Norway spruce is the most common
species in forests and is cultivated on 25 % of the wooded area [22]. Naturally
Norway spruce can be found from Scandinavia to the Balkans whereby in Central
Europe preferably the moist mountainous regions from 800 to 2,500 m are settled.
These trees can reach heights up to 60 m but have a relatively shallow root system,
which makes them vulnerable against storm events.
Spruce has a high water demand but is not suitable for waterlogging soils because
of its shallow root system and the danger of windthrows. Nutrient requirements of
spruce are low and soils with pH 4 to 5 are preferred. Further Norway spruce is suffering from warm temperatures and draughts which increases the danger of insect
pests and other diseases [24].
198
A. Rödl
Fig. 9.3 Drawing of spruce (left side: tree, right side: branch with cones; www.uli-schmidt-paintings.com)
The wood is light and bright and has a high strength, elasticity and shrinks only
to a small extent. Because of its good processing properties spruce wood is widely
used as construction wood (doors, windows, floors, roof trusses etc.) or in timber
processing industry for pulp and paper or board production. But also for various
other purposes like music instruments, packaging material, wooden toys etc. spruce
wood is suitable. If spruce wood is impregnated it can also be used outdoors in
landscaping and gardening.
9.3.1.2 Broad-Leaved Species
Broad-leaved trees belong to the group of angiosperms which is a relatively young
group of plants compared to gymnosperms. They distinguish from gymnosperms
because they produce flowers which contain the enclosed ovary. The floral organs
mature to fruits that contain the seeds.
Broad-leaved trees can be deciduous or evergreen. Deciduous trees shed their
leaves during seasons with unfavourable conditions. Leaves are dropped to reduce
transpiration and to prevent their water conducting system of collapsing. Trees in
the temperate zone shed their leaves during the winter when water is frozen in the
soil and cannot be withdrawn, while Mediterranean species shed their leaves in dry
periods. Evergreen trees keep their leaves also during periods with unfavourable
conditions because their structure protect them against water losses.
9 Lignocellulosic Biomass199
Broad-leaved trees can be found in a big variety around the globe. Temperate
deciduous forests are mainly dominated by oaks, beeches, maples and birches. Tropical forests contain a huge variety of broad-leaved species that cannot be described
here in detail. Below just some of the most important tree genera for timber production are characterized.
Oak (Quercus). There are 400 to 600 species of oak spread all over the world
mainly in the Northern hemisphere. There are some species of oak with evergreen
leaves and others which shed their leaves. Typical for all oaks is their characteristic
fruit – the acorn (Fig. 9.4). Oaks grow slowly and can grow very old. They will
reach heights up to 40 m and their roots develop a deep taproot [25].
The largest diversity of oak species occurs in North America while in Germany
mainly two indigenous and one alien species can be found. Indigenous species in
the centre of Europe are Quercus robur (Pedunculated oak) and Quercus petrea
(Sessile oak), while Quercus rubra (Red oak) is imported from North America.
Moreover in warmer regions of Europe small populations of Quercus pubescens
(Downy oak) and Q. cerris (Turkey oak) can be found; but these trees do not have
any commercial relevance.
Oaks are light demanding tree species. Their water demand depends on the
respective species. Q. robur needs more humid and nutrient rich soils than Q. petrea.
Q. robur can even grow on waterlogged and compacted soils.
Especially in North America oaks are important trees for timber industry. In
Germany oak grows on 10 % of the wooded area [22] and is often used for high
quality products like veneers, flooring, furniture and stairs. Oak has a very hard and
durable wood. It is therefore very well suited for the construction of wooden houses,
bridges or ships. In former times oak forests have been used as fuel wood reservoirs
Fig. 9.4 Drawing of oak (left side: tree, right side: branch with acorns; www.uli-schmidt-paintings.com)
200
A. Rödl
and have been managed as coppiced woodland that is regrowing after periodically
cuts. The acorns have been used for breeding pigs and the bark that contains a lot
of tannins has been used for tanning leather. Today oak wood is sought for barrel
production [25].
Beech (Fagus). The genus beech can be found around the globe in the Northern
hemisphere with the greatest diversity in Eastern Asia. To the Southern hemisphere
a similar genus called the southern beeches (Nothofagus) is native. Beeches are
deciduous trees and can reach heights up to 40 m. The fruits called beechnuts are
characteristic for the genus (Fig. 9.5).
Beech forest is the potential natural vegetation of Central European forests.
Beeches prefer a humid, Atlantic climate with nutrient rich, calcareous soils. Too
dry or wet sites are avoided. Due to its shade tolerance they are very competitive
against more light demanding species. They can endure long times in the shade of
older trees awaiting their collapse. After that they start their rapid growth even in
older ages. Beech is an important timber producing tree in Europe and covers for
example 15 % of the wooded area in Germany [22]. Its importance grew in recent
years because of ecological reasons. Forest administrations try to increase the share
of broad-leaved trees in order to improve the soil and biodiversity in monoculture
spruce stands which have been the typical industrial forests within the last 100 years
in most parts of Europe.
Beech wood is bright and very hard but not very resistant against fungi and
decay. Therefore it can only be used for interior constructions, stairs, floors and
Fig. 9.5 Drawing of beech (left side: tree, right side: beechnut; www.uli-schmidt-paintings.com)
9 Lignocellulosic Biomass201
furniture. In the last years experiments with chemically or thermally modified beech
timber have taken place to increase its applicability outdoors. Also the pulp and
paper industry uses small diameter wood assortments of beech and additionally it’s
popular as fuel wood [26].
Eucalyptus. Another important tree for forestry and wood processing industry is
eucalyptus. Almost all of the about 600 species of eucalyptus that is cultivated all
over the world can be found have their origin in Australia. Only a few species stem
from New Guinea, Indonesia or the Philippines. Today eucalyptus is cultivated
mainly in dry tropical and subtropical zones in South America, Africa, India and
the Near East [27]. In 2012 about 14 million ha have been covered with eucalyptus
plantations [28].
Eucalyptus grows fast and has low demands on soil fertility but is very light
demanding. Most of the species are draught resistant, but some species have a very
high water demand. Eucalyptus is used as a fast producer of fuel wood and timber.
Further the leaves contain the well-known oil that is used commercially from some
species. Eucalyptus is not frost tolerant.
Eucalyptus globulus was the first eucalypt species that was introduced in Europe
and North America mainly for timber and pulp production. But also its oil is
extracted. This species growths and spreads very fast and threatens endemic vegetation. It is very water demanding and is considered to lower the water table [28]
which increases the danger of forest fires. Portugal has the largest area of planted
eucalyptus in Europe covering 25 % of the Portuguese forest area [29].
9.3.2 Production Schemes
9.3.2.1Forests
Forests can be classified in primary forests, planted forests and other naturally
regenerated forest [30].
• Primary forests are all forests that are not influenced by any human activities.
• Naturally regenerated forests show clearly visible indications of human activities.
• Planted forests are mainly composed by trees which have been introduced
through planting or seeding.
Most of the natural forests especially in the temperate zone are not existing any
more today; they have been cleared already in ancient times. Only 30 % of all forested area on earth are still primary forests. All other forested land is more or less
influenced by humans. In Europe just 2 % of all forests can be classified as primary
forests and in Germany no single square meter of primary forest exists any more.
While natural forest area declined, planted forest area was increasing between 1990
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A. Rödl
and 2015 [31]. Fertile soils, good growing conditions and a high demand on food
and fodder lead to a large conversion of forested area into agricultural land. Furthermore, due to the high demand on fuel and construction wood the natural forests
have been converted into commercial forests characterized by a controlled cultivation of selected tree species. According to the FAO definition the major forested
area in the temperate zone is dominated by planted forests.
Northern Europe and the mountainous regions are dominated by coniferous forest
with a coverage of 50 to 100 % [32]. Compared to this, South and South-East Europe
is dominated by broadleaved forest [32]. For example in Germany coniferous tree
species still dominate forestry with 57 % of the total forest area. But the share of
broadleaved species increased by 7 % within the last decade [22]. All over, there is a
tendency towards a more nature based forest management in Central Europe which
promotes the introduction of broad leaved tree species and low impact harvesting
regimes avoiding clear cuts.
The harvested logs can be classified into roundwood, industrial roundwood and
pulpwood which are foremost processed in forest industries. Wood assortments
with lower value are often used as fuel wood. Thus there might be a competition on
this type of forest products when it comes to a large scale biokerosene production.
Additionally, these low value assortments are also interesting for other industries,
like biorefineries or biomass fired power plants. Worldwide about 1.2 billion m³ of
coniferous roundwood1 and 2.5 billion m³ of non-coniferous roundwood have been
harvested in 2015 [33].
Wood or tree production is characterized by perennial production cycles and is
therefore different from agricultural production, where the crop is typically produced within one growing season. Forestry is controlling the composition, growth
and quality of forests by different silvicultural interventions. Among these are
•
•
•
•
planting or regeneration,
stand improvements by release cuttings or pruning,
thinning,
final harvest.
In traditionally managed forests (high-growing coppices) all trees in the same
section have more or less the same age and are planted, thinned and harvested at
the same time or within a defined period. Forest clearcutting systems are worldwide
the most common forest management system. But especially in Europe more nature
based, preserving systems are on the rise because of environmental concerns [34].
The idea behind nature based forest management is that the soil is continuously
covered with forest and not periodically bare. This is more advantageous for several
indigenous plant and animal species in the forest, the soil structure and its nutrient
flows.
1
cubic meters underbark (i.e. excluding bark) – see FAO [35]
9 Lignocellulosic Biomass203
Besides, further forest management concepts are common. These are coppices
or mixed coppices. Coppices are mostly used for fuelwood production and have
been common until the middle of the nineteenth century in Central and Southern
Europe. For these forests broadleaved tree species like hazel, chestnut, ash, maple
or hornbeam are used that are able to re-sprout after harvest. Mixed coppices are a
combination of coppiced trees and high trees to meet the demand of fuel- and construction wood at the same time.
9.3.2.2Plantations
Cultivation of fast growing trees on fertile land gains more and more importance
some years ago when agricultural lands have been left abandoned (i.e. set aside
land). But since prices for agricultural goods rise again it became less and less
economic feasible to grow energy crops on fertile land. That’s why for example the
cultivation of short rotation coppice (SRC) stagnates at the moment within Europe.
Currently eucalyptus, poplar and willow are typical species for such wood plantations managed with production schemes close to an intensive agricultural production. Globally approximately 95 million ha are covered by such plantation [36].
For example, roughly on 9.2 million ha poplar and willow are planted, of which
3.4 million ha are outside forests in agroforestry systems [36].
Willow plantations can be found in Argentina (56,400 ha), Italy (20,000 ha),
Romania (19,505 ha), Sweden (11,100 ha) and Iran (10,000 ha). Willow plantations
in Europe have been marginal in 2012 with the largest cultivated area in Sweden,
followed by Poland (9,000 ha), the UK (6,000 ha) and Germany (5,000 ha) [37].
Besides Sweden no real commercial willow plantations have been established in
Europe so far [37]. Average yields in Europe are between 4 and 10 t/(ha a) while
willow plantations grow more slowly in the North (on average 4 to 7 t/(ha a)) than
in the South (8 to 10 t/(ha a)) on average of Europe [37].
Worldwide area of planted poplar is bigger than that of willow. Poplar can be
grown in warmer regions than willow. Thirty-five percent of the planted poplar
area is established in agroforestry which amounts on around 2 million ha worldwide [38]. Those plantations can be mainly found in China (7.6 million ha), India
(305,000 ha), France (236,000 ha), Turkey (125,000 ha), Spain (105,000 ha), Italy
(101,430 ha) and Argentina (40,500 ha) [36]. The poplar wood from India and
China is mostly used for wood products like matches or plywood [38]. Italy has
7,000 ha planted poplar plantations with yields up to 25 tDM/(ha a) [39]. On average
yields of planted poplar are lower, ranging between 6 and 12 tDM/(ha a). Globally
growth rates range between 1 and 14 tDM/(ha a) are reported with 6 tDM/(ha a) on
average [36]. The average yield for example in Northern Europe lies between 3 and
5 tDM/(ha a) and might reach 10 to 11 tDM/(ha a) if the plantation is fertilized and
properly weeded [37].
Rotation periods in short rotation plantation are short compared to that in regular
forestry. The trees are harvested every 2 to 4 years depending on the soil fertility, water availability and average ambient temperatures which are influencing
204
A. Rödl
parameter on the increment. On low fertility soils rotations are longer with 5 to 7
years. The plantation can be coppiced 6 to 8 times [40].
Before planting typically herbicide application is needed in some cases to
remove weeds; this is especially true on old pasture land. After that the area
is ploughed. The used planting materials are mostly un-rooted cuttings or rods
where the roots normally develop very quickly. For energy plantation often
10,000 to 15,000 cuttings per ha [41] are planted with mechanical planters
between April to May. Weed control is needed in the first year and can be done
mechanically or by the application of herbicides. Fertilizer application is recommended especially on poor soils and from the second or third growing season
to secure the health of the coppice. Fertilizer demand is modest compared to
“classical” agricultural cash crops because nutrients contained in the leaves are
recycled at the end of each growing season [40]. Harvesting is carried out in the
winter period every 3 to 4 years, on average. The crop can be directly chipped
during harvest or can be harvested as whole shoots with special self-propelled
harvesting machines. Those harvesting machines are typically modified standard
forage harvesters with fixed harvesting heads. The harvested material has to be
transported to the storage facility or has to be stacked at the edge of the field.
Transport of chipped material is mostly carried out with tractors on very short
distances or trucks on longer distances.
After harvesting and transportation the material has to be stored and dried if
it is not used immediately. Whole stem harvesting and bundling can be advantageous if no proper drying facilities are available. This is true because biomass losses
during drying of whole stems are typically lower compared to wood chips if they are
not stored sufficiently ventilated in piles. Chipping is then required after a drying
period. The optimization of storage operations is an important aspect to be considered within the overall biomass supply chain because it determines biomass quality
and operation costs [37].
At the end-of-life the coppice site has to be restored. Stools and roots have to be
removed using a rotovator or forestry mulcher; it is also suggested to kill the crop
by applying a herbicide like glyphosate and sow grass in the following year and wait
until the roots are decaying.
9.3.3 Production and Trade
Production. Wood is an important and valuable good that is traded all over the
globe. Total world production of roundwood reached 3.7 billion m³ in 2015 [42].
Figure 9.6 shows the breakdown of total roundwood production on major producing
countries sort by continents. It should be noticed that the broad category “roundwood” includes coniferous and non-coniferous wood for material use (industrial
roundwood) as well as wood fuel (e.g. for charcoal production). Slightly more
than the half of the globally produced roundwood is used as fuelwood [42, 43]. In
total almost twice as much non-coniferous roundwood as coniferous roundwood
9 Lignocellulosic Biomass205
has been produced worldwide in 2015. Just looking on industrial roundwood production (sawlogs, veneer logs, pulpwood etc.) more coniferous wood is produced
[42].
Major producers of roundwood are the US, India, China, Brazil and Russia. If
Russia is included, Europe produces almost 20 % of the globally provided roundwood. Big timber producing countries in Europe are Sweden (2.0 %), Finland
(1.6 %) and Germany (1.5 %). Most roundwood in total comes from Asia with India
and China as the major players. But this is mainly non-coniferous fuel wood. Fuel
wood production is highest in India, China, Brazil and in African countries. In 2015
India produced 16 % of the global fuel wood and China 9 % [33].
Major producers of industrial roundwood are the US (19 %), Russia (10 %),
China (9 %) and Canada (8 %) followed by Brazil and Sweden (4 %) in 2015 [42].
Consumption. Figure 9.7 shows the breakdown of total roundwood consumption
on major consuming countries sort by continents. The consumption is calculated
from the production plus imports minus exports (see also FAO [35]).
All over global demand on wood for wood products, pulp and paper as well as
wood fuel is strongly increasing especially in the western world [43, 44]. In 2014
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Fig. 9.6 World production (reported as cubic meters in the rough; includes coniferous and non-coniferous wood for charcoal, sawlogs, veneer logs, pulpwood round and split and industrial roundwood) of roundwood in 2015 (3.71 billion m³) (major producing countries by continents; data
obtained from FAO [33])
206
A. Rödl
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Fig. 9.7 Consumption of roundwood in 2015 (3.70 billion m³) (major consuming countries (LAC:
Latin America and Caribbean) by continents; data obtained from FAO [33])
the highest growth of the global wood industries in the last 5 years occurred. Production and consumption of wood-based panels increased in all regions of the world
but mainly in China. Additionally fuel wood consumption increased rapidly on a
global scale. Mainly driven by European consumption also the production of wood
pellets has shown a strong growth. But also production and consumption of wood
pellets in Asia has more than doubled in 2014 compared to the year before [44]; but
all over this market is still on a very low level.
Major consumers of roundwood in total are not differing very much from the
major roundwood producing countries (US, China, India, Brazil and Russia). If
only industrial roundwood is taken into consideration the main consumers are the
US with 19 %, China with 12 %, Russia with 9 %, Brazil with 8 %, Canada with 8 %
and Sweden with 4 % of total world industrial roundwood consumption [42]. China
grew as a consumer of forest products and has overtaken the US recently. China
is also the biggest producer and consumer of paper and wood-based panels [42].
Overall wood fuel consumption increased only slightly in 2014 with the strongest
rises in Europe [42].
9 Lignocellulosic Biomass207
Fig. 9.8 Top five importing and exporting countries of roundwood in 2015 (data obtained from
FAO [33])
In Africa and Latin America wood fuel is used for charcoal production. Charcoal
is used in Africa in urban households for cooking, whereas it is mainly used for
industrial purpose e.g. in steel industry in Brazil [42].
Looking at roundwood trade (Fig. 9.8) the biggest importers are the European
Union (EU28), China and Russia. China is even the world largest importer of
industrial roundwood (40 % of total industrial roundwood imports) followed by
Germany with 6 % [42]. India became the world’s fourth largest importer of industrial roundwood in 2014. Big roundwood exporting nations are Russia and New
Zealand and the EU28. On the other side, Russia, New Zealand and the US are
the largest exporters of industrial roundwood. Latin American or African countries
even cannot be found neither under the top 10 importing nor exporting countries
in 2015 [33].
9.4
Herbaceous Biomass
Similar to the presentation of lignocellulosic biomass from wood below herbaceous
biomass for the provision of lignocellulosic organic matter is discussed. Therefore
selected species are presented and a brief overview on possible production schemes
is given. Table 9.2 gives an overview of the described lignocellulosic biomass crops
and their most important parameters.
208
A. Rödl
Table 9.2 Selected parameters of cultivation and harvest for different lignocellulosic biomass
crops
Crop
Yield
[tDM/(ha a)]
Fertilizer demand
[kgN/(ha a)]
Dry matter
lossesc [%]
Water content
at harvest [%]
Miscanthus
15–25 (8–11)d
50–75
20
15–2
Reed canary
Grass
e
12–13 (UK)
6–8 (Finland)h
100
30
10–15
Elephant grass
10–30 (fertilized)
2–10 (unfert.)f
25–35a
150–300b
n/a
80–90
Common reed
5–10g
–
–
18–20h
Giant reed
25–40
ca. 100
30
36–49j
Switchgrass
8–17e
0–50
20–40k,l
15–20
i
e
j
See Ref. [5], bSee Ref. [7], cDue to harvest after winter, dIn brackets yields on sandy soils in
Germany [45], eSee Ref. [46], fSee Ref. [47], gSee Ref. [48], hSee Ref. [49], iSee Ref. [50], jSee Ref.
[10], kSee Ref. [51], lSee Ref. [52]
a
9.4.1Miscanthus
Miscanthus is a plant family with 20 species indigenous in Africa and East Asia.
It was introduced in Europe as an ornamental plant some 50 years ago. Often the
hybrid version Miscanthus x giganteus is grown [45]. It is a perennial reed and
its above-ground parts die back in winter. Miscanthus belongs to the group of C4plants which have another type of carbon fixation process within photosynthesis
then “normal”, so called, C3-plants that are indigenous in Central and Northern
Europe. This makes these plants more efficient in dry, sunny, warm climates which
results in higher biomass yields than that of “normal” C3-plants. It can reach 4 m
in height within 1 year [45]. The crop propagates through rhizomes but not through
seeds because the hybrid produces infertile seeds. A miscanthus plantation can be
utilized up to 20 years [53].
Currently, miscanthus is cultivated on estimated 30,000 ha in Europe with the
largest share in the UK (20,000 ha), followed by Austria, Switzerland and Germany
[54]. In China an area of 400,000 ha is under cultivation [54].
Miscanthus is planted by 8 to 10 cm rhizome pieces (2 to 4 rhizomes per m²) with
row spacing of about 75 cm. A full soil preparation before planting is required and
weeding is needed especially in the first year. The plantation is first harvested after
2 years with yields from 4 to 7 tDM/(ha a) and as from the third year yields from
10 to 20 tDM/(ha a) can be reached depending on the site conditions. Harvest can be
carried out with maize choppers or balers [45]. Roughly 10 % of the biomass is lost
during harvest [55]. To avoid high water contents within the harvested biomass, harvesting should be carried out in March or early April. Also the content of unwanted
9 Lignocellulosic Biomass209
elements in the biomass is lower if harvest takes place after winter because during
autumn and winter these elements are washed out from the grown biomass. The
disadvantage of such a late harvest is the considerable biomass losses occurring
during winter time. If the material is not used immediately the storage under a roof
is recommended to protect the material re-wetting [56]. Nutrients are removed by
the plant from the upper parts and stored in the roots during winter. This means
nutrients are recirculated by the plant and fertilizer input can be reduced.
The removal of the rhizomes is quite easy because they are shallow and therefore
two treatments by cultivator dries out the rhizome water content in late winter which
then is lower than in autumn.
9.4.2 Common Reed (Phragmites australis)
Phragmites australis or common reed belongs to the family of poacea and can
be found in wetlands around the globe with several sub families. Like the before
described miscanthus it is a perennial grass which reaches up to 4 m in height
and dries back in winter. It spreads aggressively from its root system [57]. Since
common reed grows naturally in reed beds of lakes or slow-running rivers it prefers
basic, nutrient rich and wet soils. There are reported yields up to 30 tDM/(ha a) but
in field trials in Europe only 5 to 10 tDM/(ha a) have been reached [48]. Traditionally
it is used for housing construction, especially for thatching roofs, but also as an
insulating material. Reed for thatching has to be dry and is therefore traditionally
harvested in winter [48]. If reed is used for energy purposes it is also favorable
to harvest in winter when water contents are low. During harvest the material is
chipped and might be pressed to pellets, bails or bulks [48]. Increasingly the standing crop is also used as a natural wastewater treatment facility. In most of the cases
it is not planted but occurs naturally. Köbbing et al. [58] estimated that there might
exist around 20 million ha of common reed in 2013.
9.4.3 Giant Reed (Arundo donax)
Giant reed (Arundo donax) is perceived as an invasive species and spreads in the
tropics and subtropics. In some regions of the US and Australia it has a pest potential. Most important in this respect seems to be the control of spreading. Nevertheless, the potential production of giant reed as an energy crop is discussed widely
[59]. Very high yields from 25 to 40 tDM/(ha a) have been reported [50]. Giant reed
prefers humid soils on the banks of rivers, lakes or swamps but also tolerates drier
conditions once it is established. The harvest can be carried out in autumn or after
the winter [10]. A harvest after winter causes considerable biomass losses during
the winter. After harvest it can easily be stored in the field without any protection.
210
A. Rödl
Storage losses of 10 to 15 % of the total biomass production can occur if the blades
and sheaths are lost [19].
9.4.4 Reed Canary Grass (Phalaris arundinacea)
Reed canary grass (Phalaris arundinacea) is also a perennial grass where the upper
parts of the plant dry back in winter. It is indigenous in temperate zones of Europe,
Asia and North America and an invasive species in wetlands and disturbed areas.
It propagates through seeds and rhizomes and can reach heights of 2 m within one
vegetation period [60]. The grass needs nutrient rich and well ventilated soils. It is
possible to cultivate reed canary grass on wet soils which are flooded 2 to 3 months
per year. Therefore the grass is especially interesting for peatlands renaturation
[61]. The use of the harvested grass from restored peatland sites can help the farmer
to receive an alternative income from former drained agricultural lands.
Stand establishment is realized after soil preparation. About 25 kg/(ha a) are
sowed. Reed canary grass can reach yields of 12 to 13 tDM/(ha a) and the plantation
can be harvested over 10 to 15 years. If harvesting is carried out in early spring
biomass losses of 15 to 26 % have been reported to occur during the winter period.
But on the other hand the water and mineral content decrease considerably over
the winter period which is favorable if the biomass is used energetically [46]. Harvesting machinery depends on the soil conditions. In general harvesters or mowers
with wide tires or crawler track are required [62]. The plant has a higher nitrogen
demand than other C4 plants and fertilizing can be advantageous to stabilize high
yields [46]. High ash contents especially occur on heavy clayey soils with high
silicon contents. The removal of the reed canary plantation is possible by deep
ploughing. Reed canary grass is cultivated on 20,000 ha in Finland and on 7,000 ha
in Sweden [63].
9.4.5 Elephant Grass (Pennisetum purpureum – Napier Grass)
Napier grass (Pennisetum purpureum) is a tropical perennial grass with high yields
[57]. It is also called elephant grass because it is the favorite food of elephants. It
might reach heights up to 3.6 m and is indigenous to subtropical Africa (e.g. Zimbabwe). Elephant grass is a plant with high water requirements and depends on
rainfalls around 1500 mm/a. But this plant tolerates also dry times because of its
deep root system. Apart from that the grass is not tolerant to flooding and also not
frost-resistant. Therefore it only can be cultivated in tropical or subtropical areas.
Full soil preparation is needed before planting of root cuttings. The yield depends
on the water availability, soil fertility and management. Further it should be planted
in fertile soil because yields decline quickly if the plantation is not fertilized sufficiently. Yields between 25 and 35 tDM/(ha a) [5] can be reached in fertilized stands
9 Lignocellulosic Biomass211
but only 2 to 10 tDM/(ha a) are possible without fertilization. More frequent cutting
give less dry matter [47]. At present it is mostly planted for fodder. The young stems
can be fed as hay or pellets [47]. The crop is mostly planted in rows from setts or
cuttings.
9.4.6 Switch Grass (Panicum virgatum)
Switch grass (Panicum virgatum) also belongs to the group of C4 plants and is indigenous in North America. It is also a perennial grass that spreads through its rhizome
system and reaches up to 3 m in height. The grass tolerates drought and prefers warm
temperatures. Therefore it grows in Central Europe only in the summer season.
Before seeding or planting switch grass site preparation is needed. As already mentioned for the other perennial grasses it is also favorable to harvest switch grass after
winter when water and nutrient content is reduced. Fertilize demand depends on the
time of harvest and is less if the grass is harvested after winter. In general switch
grass has relative low requirements for water and fertilizer.
9.5
By-Products and Wastes
Below important by-products typically used for the provision of lignocellulosic
biomass are discussed in detail. Therefore, again a distinction is made between
woody and herbaceous biomass.
9.5.1Wood
Residual Wood from Forests. Wood residues occur from forest operations. After
the harvest of timber, wood from twigs, branches or stumps etc. is often left in the
forests. This wood can be classified into unused coarse wood and non-coarse wood.
• Unused coarse wood are parts of the tree with a diameter above 7 cm including
bark. This wood can originate from strong branches or from the lower parts of
the tree trunk. In general broadleaved trees have naturally a higher share of unusable parts above 7 cm in diameter than coniferous trees.
• The term non-coarse wood denotes woody parts of the tree which have a diameter below 7 cm. That can be smaller branches, twigs etc.
In former times these wood assortments have been left in the forests. Since some
years they are sold partly to private small-scale wood buyers who process them
by themselves and use them as fuel wood. Nevertheless, leaving a certain share of
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A. Rödl
residual wood in the forests is sometimes essential for environmental reasons, like
securing a sufficient nutrient supply or providing a varying habitat for different
animal species.
Since for example in Germany and most likely also in other countries annual
fellings of roundwood are expected to be higher than reported in the official
statistics [64] also the share of residual wood is believed to be underestimated.
For Germany it has been estimated that 3.5 million m³ of non-coarse wood and
3.2 million m³ unused coarse wood have been produced in 2013 [64]. Nevertheless sometimes parts of the unused coarse wood are used for fuel wood. It
might be difficult to use these parts for liquid fuel production because they have
a relative big share of bark, which causes higher contents of extractives, lignin
and suberin, whereas the cellulose content is comparatively low [65]. Nevertheless, a certain share of this residual wood from forests could be used for fuel
production.
Residual Wood from Forest-Based Industry. In forest industries where the
wood is further processed to high-value products wood residues for example occur
from sawmill processes. During these processes (e.g. sawmilling) different residual “products” can be obtained, e.g. sawdust, woodchips, bark, planer shavings.
These resources are mostly untreated. The ash content depends on the share of
the bark relative to the overall mass as well as on the tree species. Most of the
wood processing companies already make use of these residues since they use
them for energy generation for their own processes (e.g. for wood drying) and
thus for internal use. There also exist combined saw mill – pellet, saw mill – fiber
or particle board producing plant concepts. In general it could be expected that
woody resources from these sources are highly sought and therefore only partly
available for other uses.
Waste Wood. The term waste wood is clearly defined in the German “Waste
Wood Directive” (Altholzverordnung) which entered into force in 2003. Hence,
waste woods are used products from massive wood, wood-based panels or other
wooden composites with a share of more than 50 % wood intended for disposal.
The directive further defines four categories that classify waste wood after its
grade of treatment with chemicals or colors. For example, category AI is denoting untreated wood that has been only processed mechanically. While category
AIV is denoting treated wood with wood preserving chemicals and a high pollution load like railway sleepers or poles. Category AII and AIII denote the
respective gradations between these two extremes. According to the mentioned
directive waste wood has to be separated and afterwards used for recycling or
generating energy in approved facilities. Landfilling of these wood resources
is not allowed any more. Waste wood from the category A1 might also be a
suitable resource for biokerosene production, but also one of the smallest fractions of waste wood [66]. Besides, it is also a thought resource in particle board
industry.
9 Lignocellulosic Biomass213
9.5.2 Herbaceous Biomass
Below selected organic mass streams of herbaceous biomass occurring as a by-product are discussed.
Bagasse. Sugarcane bagasse is a fibrous residue that remains when sugar juice is
removed from sugarcane. Sugarcane is a perennial grass and belongs to the family of
poaceae. It originates from New Guinea and the South Pacific but is now cultivated
all around the world in tropical and sub-tropical regions because it does not tolerate temperatures below 15 °C. Major producing countries are Brazil, India, China,
Thailand and Pakistan. Sugarcane can grow on a lot of different soil types but it is
characterized by a high water demand. A new plantation is usually established typically with cuttings. A plantation can be harvested 10 times or even more, depending on the nutrient supply, because the shoots are re-growing. Sugarcane shoots
can be harvested every 9 months in highly intensive cultivation or every 10 to 18
months in more extensive cultivation typically realized in small scale farming [67].
After harvesting leaves, trash and roots have to be removed and the cane has to be
transported quickly to the sugar mill. Harvesting can be carried out manually or
mechanically with cane harvesters. Manual harvesting is still done in many countries and needs skilled workers. In case of high labor costs and high crushing capacities of the mills harvesting is mechanized. In Western or emerging producing countries, like Australia, Brazil, the US or South Africa, sugarcane cultivation is highly
mechanized [68].
Yields between 150 and 175 t/(ha a) in sub-tropical zone and up to 300 t/(ha a)
depending on the growing season can be realized. In 2014 the worldwide average
fresh cane yield was around 70 t/(ha a) [33]. Information on the dry amount of bagasse
which can be obtained from 1 t of sugarcane varies between 14 and 17 % [69, 70].
Weijde et al. [71] even adopt a dry-matter ratio of 0.6:1 from Kim and Dale [72],
which would result in an average bagasse yield of about 11 tDM/(ha a). An Australian
publication even reports about 30 % wet bagasse from crushed wet sugarcane [73].
Total production of sugarcane worldwide reached 1.9 billion t/a in 2014 [33]. The
crop was cultivated on about 27 million ha. This would mean 266 to 317 million tDM/a
of bagasse have been produced.
Bagasse is already widely used in sugar mills for heat and power provision. But it
is already by now used outside of sugar industry as a resource for co-firing, fodder,
paper production or as raw material for fiberboards or the production of chemicals.
Straw. Straw are leafs and stalks which remain when different agricultural crops
like cereals, oil and fiber crops or legumes are threshed. Usually, straw is left on
the field after harvesting the crop to secure reproduction of the humus layer for a
sustainable nutrient supply.
Typically the amount of straw is related to the main product (e.g. grain). In most
cases with the straw-grain ratio is around 1:1 [74]. Harvest of the grain is mostly
214
A. Rödl
carried out by combined harvesters and the grain is removed by lorries while the
straw remains on the field. In general only 60 % of the totally available straw is
usable [75].
Relatively widespread are wheat, rye and barley straw. Their water content at
harvest is below 20 %, but compared to other bioenergy crops they contain more
ash (5 to 15 %).
A number of possible supply chains for straw exist. Chopped straw can
be c­ ollected and transported lose from the fields but with low bulk densities
between 40 and 65 kg/m³ [74]. A higher density can be reached if the straw is
baled (100 to 150 kg/m³). Highest densities (550 kg/m³) can be reached by pelleting the straw directly on the field.
After e.g. baling the straw on the field it is transported into the temporary storage
facility by a tractor where it is handled with a telescopic handler and is stored there.
After storage it has to be transported to the conversion plant via tractor, lorry or
railway according to the transport distance [76]. The supply chain of biomass provisioning to a conversion plant consists of collecting, pre-conditioning like chipping,
baling etc.), storage and transport [77].
Wheat has been cultivated on 222 million ha in 2014 [33] with an average yield
of 3.3 tDM/(ha a). This would amount to a worldwide amount of 731 million t/a of
wheat straw if a ratio of 1:1 between the grain and the straw is assumed. So far this
resource is only very scarcely used as a renewable resource for heat production –
mainly in Denmark, Austria and Great Britain [78].
Rice Husks. Rice husks are encasing and protecting the rice grains. They are separated from the grains during milling process. About 20 % of the total grain weight
are husks [79]. For long time rice husks have been treated as a waste product and
have been burned or landfilled. Recently rice husks have been recognized as a valuable resource for energetic or material use (e.g. chopsticks, insulating material).
About 741 million t/a of paddy rice have been produced worldwide in 2014 [33].
This would mean an amount of 148 million t/a of rice husks occurred in the same
year. The biggest rice producer was China with around 207 million t/a of paddy rice
in 2014, followed by India with around 157 million t/a and Indonesia with about
71 million t/a of rice [33].
Corn Stover. Corn stover are leaves and stalks from corn (maize) remaining on
the field after harvest of the grains. The straw which was left on the field has to be
collected from the field and to be transported to the conversion site. Straw quality
and dry matter content might worsen when removal from the field is delayed.
Cleaning of the straw before conversion might be required [80]. In Europe about
56 million t/a of maize have been harvested in 2015 [81]. Worldwide 958 million t/a
maize have been produced on about 177 million ha [82, 83]. Main producers in
2015 were China, the US, Brazil and Europe [82]. According to FAOSTAT [33]
the average yield between 2010 and 2013 was about 5.2 t/(ha a). Assuming a cornstraw relation of about 1:1 [84] there would have been a theoretical potential of
9 Lignocellulosic Biomass215
approximately 918 million t of straw. Only 20 to 60 % of the available corn stover
can be harvested sustainably [85]. This would mean a theoretical sustainable potential of 184 to 551 million t/a of available corn stover worldwide. Parts of that are
already used today for animal feed or bedding. Removal of straw from the field
might cause humus balance deficits especially if in the following crop rotation
cereals, root crops or again maize is cultivated on the same field [84].
9.6
Final Considerations
Table 9.3 gives an overview of the yields and currently cultivated area for some of
the previously discussed crops. Reliable data for most of the described perennial
grasses is not available. Mostly there only exist some field trials that amount globally to some thousand ha. Further the table contains calculations of the total potentially harvested amounts of each crop. For this purpose the indicated average yields
have been used. The result gives an idea of the currently globally available amounts
of these crops. The used resources discussed throughout this paper comprise waste
material in the cases of sugarcane, wheat and maize. Wheat and corn straw can be
assumed to equal the displayed harvested amount, because they have a straw-grainratio of approximately 1:1. Sugarcane bagasse will be on average 30 % or less of
Table 9.3 Currently cultivated areas, average yields and potentially harvested amounts of selected
lignocellulosic biomass crops
Cultivated area
[million ha]
Reference
year
Crop yield
[t/(ha a)]
Miscanthus
0.4b
2002
15b
6
Sugarcane
27.18
2014
69.9c
1,900
Wheat
221.6
2014
3.3c
731
Corn (maize)
183.3
2014
5.6
1,027
Rice, paddy
163.2
2014
4.5d
Willow, planted
0.57
2012
5–10
3–6
Willow, outside forests
0.04
2012e
5–10f
0.2–0.4
Poplar, planted
8.6
2012e
6–14g
52–120
Poplar, outside forests
3.2
2012
6–14
19–45
e
e
c
Potentially
harvested amount
[million t/a]a
741
f
g
a
Potential amount if average yields are considered (own calculations) bSee Ref. [3] cWet mass at
harvest according, average according to FAOSTAT [33] dSee Ref. [33] eSee Ref. [36] fDry matter,
average yield according to Hinge and Christou [37] gDry matter, average yield according to FAO
[36]
216
A. Rödl
the totally harvested wet sugarcane biomass and might therefore be estimated on
approximately 570 million t/a. Rice husks make up 20 % of the total harvested
amount of paddy rice. It should be kept in mind that some of this total amount is
already distributed on the market and will not be available to other uses. But the
future distribution of these lignocellulosic resources depends also on market prices
and the “new” customer’s willingness to pay.
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Dr. Anne Rödl is working as a post-doctoral researcher at the Institute of Environmental Technology and Energy Economics (IUE) at Hamburg University of
Technology (TUHH). She received her PhD from the Department of Biology at
Hamburg University and holds a Master of Science in Forestry. After graduating
from her studies she worked for the German Federal Research Institute for Rural
Areas, Forestry and Fisheries. There she investigated the environmental impacts
of wood production from short rotation coppice and wrote her PhD thesis about a
further development of life cycle assessment (LCA) methodology in terms of water
use. After finishing her PhD she joined IUE and inter alia gives lectures in environmental assessment and sustainability management.
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