Chemical composition of biomass - Biomass as Energy Source: Resources, Systems and Applications - page 34

i.e. the development of moulds, bio-contamination, and oxidation. Conservation methods will
have to be developed for species that can only be cropped at certain times of year in order to
overcome microbial degradation of stored biomass and to minimize the spreading of microbes
that are harmful to health.
Industrial usage of bioenergy has increased significantly in recent years and continues to rise.
Sweden and Finland are both global leaders in terms of the extent of their adoption of bioenergy.
Notably, bioenergy recently surpassed oil in Sweden to become the country's largest source of
energy; the government has set a target of having almost 50% of the nation's energy requirements
met by renewable sources, including biomass (which is primarily to be obtained from forest trees;
Energimydigheten, 2011).
In addition to the increased production and usage of chopped or chipped raw biomass for
energy conversion, there has been a significant increase in demand for refined solid biofuels
such as pellets. Europe has around 650 pellet mills with a combined annual output of 9.8 million
tonnes of fuel pellets in 2009. The size of the EU-27 market for fuel pellets is expected to increase
between 10- and 30-fold by 2020 (Sikkema et al ., 2011). Pelletizing of torrefied materials is of
special interest for co-combustion in coal-based combined heat and power plants. The predicted
increases in demand for biofuel will lead to regional shortages of by-products such as sawdust
and shavings that serve as feedstock for pellet production. Thus, if the expansion of the pellet
industry is to be maintained, it will be necessary to identify alternative raw materials for their
production.
2.1.2 The potential of biomass for energy conversion
The exploitation of bioenergy will play a key role in the transition away from fossil fuels, which
currently account for 81% of the world's annual energy turnover (REN21, 2011). Bioenergy is
the renewable energy source whose usage is increasing the most rapidly because it can replace
fossil fuels for heating applications, in power production, and as fuel for vehicles (AEBIOM,
2011; BP, 2011). The world's yearly gross primary production of plants is about 150 Pg C/y (Still
et al ., 2003) but only 0.9-1.5 Pg C/y is currently used for the production of bioenergy (Andres
et al ., 1999; Ludwig et al ., 2003). Calculations performed by Tao et al . (2012a) using the residue-
to-product ratio outlined by Koopmans (1997) and data from the FAOSTAT (2009) suggest that
each year around 2.7-3.5 Pg C/y of agro-crop residues are generated in addition to the 'waste'
biomass produced by forest industries (see Table 2.1). This corresponds to nearly one tonne of
dry biomass per person on the planet. As such, there is considerable potential for exploiting
residual biomass from the agricultural sector for energy production, along with the current usage
of residues and byproducts from forestry.
It is estimated that China and the USA generate around 0.74 and 0.5 Pg (Gt, billion dry
tonnes), respectively, of residual biomass suitable for energy production each year (Lal, 2005;
Liao et al ., 2004; Xie et al ., 2010). However, there is some uncertainty about the total capacity
for biomass production. The US Department of Energy (2011) estimates that the United States'
annual production of energy crops could potentially reach 1.0-1.3 Pg (Gt, billion dry tonnes) by
the year 2035.
Approaches that only consider the energy that can be obtained from biomass are shortsighted,
since it can be used to produce other useful things such as bio-based chemicals and products.
In addition, agro-biomass can often be used for other useful purposes, e.g. as a feed, fertilizer
or feedstock for pulp production. According to Liao et al . (2004), nearly 60% of the biomass
residuals in China could potentially be used in biofuel production. Today, about 2.5 billion people
around the world use biomass as their primary fuel for cooking, especially in developing countries
(IEA, 2009; Mishra and Retherford, 2007). However, there is also substantial on-going misuse of
biomass, with large quantities of material being burned in open fields to remove waste in order to
facilitate the growth of the next season's crop and to clear land for agricultural use, as well as in
so-called back yard burning. In addition to energy losses, these practices also cause air pollution.