Biomass Combustion and Co-firing

Supply and pre-treatment

Supply and pre-treatment

Several types of pre-treatment are being applied in practice to lower
handling, storage, and transportation costs, and to reduce the need to
invest in very complex, robust, and expensive combustion installations.
For example, wood waste from northern Sweden is first pelletised, before
it is transported to combustion installations in the south of the country.
Common pretreatment options are size reduction, compacting, drying, and
washing.

Wheel loaders are often used for
transporting sawdust and bark from long-term storage to the
feeding system of the biomass heating plant (Courtesy of
Stadtwärme Lienz, Austria)

In order to reduce its moisture content, freshly harvested wood is
often left outside for a number of weeks before it is chipped and fed to a
combustion plant.

Herbaceous species such as grain straw are often left in the field and
exposed to weather conditions to reduce the alkali and chlorine contents.
This way, combustion problems related to corrosion and sintering are
reduced. Further fuel drying may be feasible if natural heating sources
(eg solar energy) or waste heat from the combustion plant (eg from flue
gas condensation units) are available.

Solid biofuels are increasingly “tailored” to the respective
application process, using new upgrading methods or technologies. These
can either be applied during or immediately after field production (eg
leaching by rainfall or irrigation), or in a preparatory process prior to
use (eg stationary leaching, use of additives, compaction). The need for
such pretreatment steps depends on transportation distances, fuel prices,
size of the plant, fuel-feeding mechanism applied, combustion and heat
recovering technology applied, materials used, etc.

Schematic diagram of the principle
of a short-term biomass drying process based on pre-heated air from a flue
gas condensation unit

With the growing market for bioenergy systems, analysing and improving
fuel properties becomes increasingly important. This even extends to plant
breeding and variety/clone selection. Genetic engineering, although still
controversial could open up new opportunities for yield and quality
improvement of biofuels.