1.2. Problems associated with utilization of agricultural
residues as fuels
Despite the large generation of agricultural residues, the
current level of their utilization as fuel is low. For example,
in Finland, some 4 million tonnes of straw are produced
annually and about 2.2 million tonnes could be potentially
collected and used as a source of energy. However, only 15–
20% is utilized mainly as cattle fodder or baled as fuel, the
rest is either ploughed back into the soil or burnt on the field
[7]. In Kenya, more than 6 millions tonnes of agricultural
residues were produced in 1995 but only 35% was used for
energy production, mainly bagasse in the sugar processing
industries [8]. The level of utilization of agricultural residues
depends on economics and availability of the necessary
technology [3].
Generally, the agricultural residues are produced locally
and often they have a low density. Because of the resulting
high transportation costs it is often uneconomical to use
agricultural residues as the main fuel in big power stations.
The use of biomass residues in small local power stations
has the disadvantage of the specific higher investment costs,
a specific higher need of employees and a lower thermal
efficiency compared with a big power station. An economic
study for Austria showed that small local biomass fired
plants for the production of electrical power are uneconomical
at the moment and that the path of the co-combustion
of biomass with coal in existing or new power stations is the
most economic one [9]. This may also be true for the most
developed countries. For developing countries with lower
costs for personnel, other solutions for the thermochemical
use of agricultural residues may be more economical.
Another important factor which influences the level of
energy usage of agricultural residues is the local availability