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Coal and biomass cofiring: fundamentals and future trends 119

is no need for continuous biomass supply because the plant can burn coal if biomass is
not available. Biomass cofiring in coal-fired power plants therefore offers significant
advantages: modern coal-fired power plants are highly efficient (>44%), they have
coal supply facilities that also facilitate biomass supply, and they also have advanced
flue gas cleaning equipment, which in some cases may obviate separate cleaning for
biomass. During the last years, different forms of biomass have been co-combusted
in existing coal-fired boilers, where biomass is used as a supplementary fuel to substi-
tute for up to 10% of the coal in terms of energy content. The costs of adapting existing
coal power plants for cofiring biomass are significantly lower than building new dedi-
cated biomass systems (Fernando, 2005).
Relying solely on biomass is risky due to unpredictable feedstock supply because
of the seasonal nature of biomass resources as well as poorly established supply infra-
structure in many parts of the world. Other constraints of generating power solely
from biomass are the low heating values and the fuel’s low bulk densities, which
create the necessity of transporting large amounts of biomass (Agbor et al., 2014).
Biomass cofiring for power generation provides an effective way to overcome these
challenges because cofiring plants have the option to revert to dedicated coal combus-
tion for mitigating the effect of biomass fuel shortages (Karampinis et al., 2014). On
the other hand, the energy use of biomass can add value to the forestry and agriculture
sectors of developing and emerging countries. Likewise, industries such as construc-
tion, manufacturing, food processing, and transportation may be beneficiaries of
cofiring.
Although biomass and coal cofiring provides the benefit of reduction of GHG emis-
sions to the atmosphere, it presents some logistical and performance issues that should
be analyzed, such as the availability of biomass resources, their transport to the power
plant, the different cofiring technologies, as well as the technological and environ-
mental issues associated with biomass cofiring.

5.2 Biomass characterization and properties

The characteristics of the biomass vary widely from one type and category to another
due to their diverse nature. Biomass can also be classified into several categories based
on their properties: woody biomass, herbaceous biomass, straw-derived biomass,
aquatic biomass (kelp, etc.), and wastes (manure, sewage, refuse containing biological
material, etc.). The method of utilizing a particular type of biomass typically depends
on which category it belongs to. The moisture content is a primary deciding factor in
choosing which energy conversion process to use. The aquatic biomass and wastes
generally have the highest moisture content, and they are more suited to be treated
by biochemical methods (fermentation and anaerobic digestion). Woody biomass
has the lowest moisture levels, whereas herbaceous biomass has intermediate values.
Most industrial applications have been focused on thermochemical processes (com-
bustion, gasification, and pyrolysis), which use woody biomass and low-moisture va-
rieties of herbaceous biomass (Madanayake et al., 2017).