Environmental Engineering Reference
In-Depth Information
CHAPTER 2
Chemical composition of biomass
Torbjörn A. Lestander
2.1 INTRODUCTION
Biomass is here defined as biological material derived from living (or recently living) plants that
is used as a source of energy; the term also encompasses peat. It is assumed that any biomass
used is harvested sustainably without endangering food security, habitats, or soil conservation.
Biomass is a complex fuel. Its primary components are cellulose, hemicellulose and lignin,
which are the main constituents of the plant cell wall. These species also account for the bulk of
its energy content (calorific value). The non-uniformity and varied sources of biofuels make it
necessary to convert them to standardized solid, liquid, or gaseous fuels.
2.1.1 A new biocarbon era
The world's population has recently passed seven billion (UNFPA 2011) and atmospheric CO 2
levels continue to increase, reaching new all-time peaks, also in 2011 (NOAA 2012). Over the
last decade, cumulative global anthropogenic carbon dioxide (CO 2 ) emissions have increased by
more than 3% annually (Raupach et al ., 2007). More than half a trillion tonnes of CO 2 have been
added to the atmosphere since the onset of industrialization (Allen et al ., 2009). This increases
the risk of rapid changes in the Earth's atmospheric system followed by irreversible climate and
ecosystem change (Solomon et al ., 2009).
Energy conversion plays a key role in sustainable development. As stated in the Kyoto protocol
(UNFCC, 1998), there is a great need for renewable sources of energy to prevent the worst effects
of climate change, which is largely driven by non-neutral carbon dioxide (CO 2 ) emissions to
the atmosphere. Today, renewable energy sources supply only around 16% of the world's total
energy demand (REN21, 2011), even if the use of firewood in the Third World is included. The
development of renewable energy sources also offers a way to reduce dependence on fossil fuels.
As such, there is increasing pressure to shift from fossil fuels to renewable energy sources as a
means of meeting social energy demands. Achieving a shift of this kind will require the rapid
development of novel technologies and methods for the large-scale exploitation of sustainable
and CO 2 -neutral energy sources such as bioenergy.
The amount of biomass used in energy conversion processes such as combustion, co-firing,
torrefaction, pyrolysis and gasification is expected to increase rapidly. Renewables will become
the world's fastest-growing source of energy, causing bioenergy to become one of the fastest
growing energy sectors. For example, the amount of electricity generated frombiomass is expected
to triple within the first quarter of the 21st century (EIA, 2011).
We are currently at the beginning of the industrialized biocarbon era and must develop novel
know-how concerning the pre-treatment, handling, and transportation of biomass from farmland
to industrial facilities, in addition to the new scientific and technical knowledge that will be
needed to develop large-scale biomass-based industrial processes. The development of complex
and integrated processes for exploiting biomass will turn yesterday's unwanted waste into a crucial
resource for sustainable development. To achieve this, it will be necessary to reduce the time spent
between cropping, pretreatment and processing so as to avoid degradation of the organic matter,
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