Biomass ranks fourth as energy resource on global basis. Biomass is CO2
neutral and contains very little sulfur, hence it does not contribute greatly
to acid-rain problems. Biomass have unique role on a renewable energy
source.While the growing need for sustainable electric power can be met by
other renewables, biomass is our only renewable source of carbon-based fuels
and chemicals. Bioenergy is the word used for energy associated to biomass, and
biofuel is the bioenergy carrier, transporting solar energy stored as chemical
energy. Biofuels can be considered a renewable source of energy as long as they
based on sustainable biomass production.
As Europe is very much the center of the global wood fuel market in general
and the wood pellet/briquette market in particular, it comes as no surprise
that vast majority of big wood fuel producers
of many countries have European countries as their final destination.
With the goal set by the European Union to achieve a 20% share of renewable
energy in the energy mix and a 20% decrease in greenhouse gas emissions by 2020
(DIRECTIVE 2009/28/EC, 2009) it is likely that the increase in EU demand for
bioenergy will accelerate. However, it is also likely that a large share of
future use of bioenergy in Europe will be from biomass of non-European origin
as the resources are unlikely to be cost cost-competitive compared to biomass
to biomass imported from other parts of the world.
Trading wood fuel is always complex due to the biomass itself being both
low in value per volume unit as well as difficult to store and transport as a
result of it being a “living material” and hence susceptible to degradation
from biological processes. Torrefaction is a technology
to improve the quality
of the biomass fuel and is followed
by densification (pelleting
/ briquetting) will
save transportation costs. Torrefaction
has many advantages that overcome some
problems in the wood fuel in general.
The quantities of biomass co-fired in large coal fired and other fossil
fuel-fired power plant boiler have increased fairly dramatically over the past
few years, particularly in Northern Europe but also elsewhere in the world. The
level of co-firing activity worldwide, and the co-firing ratios at specific
plants, are likely to increase further over the next few years.
Biomass materials have significant levels of inorganic matter as impurities,
and many of the practical problems encountered with the combustion of biomass
materials, or the co-combustion of biomass materials with coal and other fossil
fuel, are associated with the nature and behaviour of the biomass ash and the
other inorganic constituents. In practical terms, the ash-related problems in
biomass combustors and boilers, and in plants co-firing biomass with more
conventional fossil fuels, have commonly been associated with:
-The formation of fused or partly fused ash agglomerates and slag deposits
at high temperature within furnaces;
-The formation of bonded ash deposits at lower gas temperatures on the heat
exchange surfaces in the boiler convective sections and elsewhere;
-The accelerated metal wastage of boiler components due to gas-side
corrosion and erosion;
-The formation and emmision of sub-micron aerosols and fumes; and
-The handling and utilization/disposal of ash residues from biomass
combustion plants, and of the mixed ash residues from the co-firing of biomass
in coal-fired boilers.
In very general terms, the nature of the problems and the impact on plant
perfomance depend both on the characteristics of the biomass fuel, i.e.
principally on the ash content and the ash chemistry, and on the design and
operation of the combustion equipment and the boiler. Raw material have
significant role of the densified (pellet/briquette) torrefied biomass quality.
We will choose raw material with low ash content and a high ash melting temperature.
The peat and coal have the higher ash contents, but only a relatively small
portion of the mineral material is in the water and acetate soluble fractions
and is considered to contribute to the formation of the fine ash/aerosol
material. In the case of the biomass materials, the total mineral contents are
lower, but a much higher proportion of the mineral material is considered to
contribute to the formation of the fine ash/aerosol fraction. The ash residue
is normally weighed to provide an estimate of the ash content of the fuel, and
then analysed for the ten major elements present in coal ashes, i.e. SiO2,
Al2O3, Fe2O3, CaO, MgO, TiO, Na2O, K2O3, P2O5 dan SO3.
Usually slagging takes place with biomass fuels containing more than 4% ash
and non-slagging fuels with ash content less than 4%. The ash content of
different types of biomass is an indicator of slagging behaviour of the
biomass. Generally, the greater the ash content, the greater the slagging behaviour.
But this does not mean that biomass with lower ash content will not show any
slagging behaviour. The temperature of combustion temperature, the mineral compostion
of ash and their percentage combined determine the slagging behaviour. If
conditions are favorable, the the degree of slagging will be greater. Minerals
like SiO2, Na2O and K2O3 are more trouble some.
The selection of raw materials is an
important factor for the
production of torrified biomass. High quality torrified biomass need to be produced to meet a variety of industrial
and domestic needs.
Chemical treatment of raw materials can be
made to increasing the quality of raw materials, but it will do if the quality
of raw materials is
not sufficient anymore. Finally
a reliable technology for the production
of torrified biomass absolutely necessary to meet those needs.
