The Thermochemical Conversion of Biomass into High-Value Products: Microwave Pyrolysis - The Economic Utilisation of Food Co-Products - page 39

biomass also offers the potential to convert agricultural and municipal waste
into sources of energy. 3 As a solid fuel, biomass can be used in dedicated boilers
or cofired with coal in existing power plants. Direct use is problematic due to
the inherently high oxygen and moisture content, which result in a lower
heating value. This, along with impurities such as chlorine and inorganic
components, has led to problems with uptake of this technology. 4
To overcome this problem a new biorefinery approach was developed to
produce a high-quality drier fuel or energy-densified char that is more suitable
for uptake in the energy sector. Biorefineries are facilities that integrate
conversion processes and equipments to produce fuels, power, and chemicals
from biomass.
At the moment there are two major approaches to convert lignocellulosic
biomass to liquid biofuels: biochemical and thermochemical breakdown (see
Figure 3.1), each of which comes with its own drawbacks. Biochemical
conversion, through the use of enzymes, tends to be slow, requiring a batch-
wise manufacturing process and can only be used to convert cellulose itself. 5 On
the other hand, the process is selective and operates at low temperatures.
Thermochemical treatments tend to be relatively quick and continuous,
involving high temperatures. High temperature initiates a number different
processes resulting in a complex mixture of products with uncontrollable
properties. For practical usage of biofuels they have to meet certain,
controllable criteria. Char has to be grindable, hydrophobic and with as much
energy density (calorific value) as possible. While bio-oils can be seen as a

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3 .

Figure 3.1 Types of biorefinery.