Biomass is a collective term which applies to organic matter
which can be converted to energy. Biomass utilization for the production of
power on site within the built environment is a strategy for the mitigation of
CO2. The electricity or power that is produced from biomass fuel is
theoretically carbon cycle neutral.
As an example of how using biomass to provide energy is
carbon cycle neutral the following example is for energy crops.
|
Carbon component of energy crop |
CO2 emission impact |
|
Carbon produced during fuel consumption |
increase |
|
Carbon stored in fuel |
decrease |
|
Carbon stored bellow ground |
decrease |
|
Carbon cycle neutrality |
Net decrease in carbon (carbon sequestration) |
The main biomass sources are: energy crops such as trees,
from biological residues there is waste from agriculture and the forestry
industries as well as municipal resources such as the biomass components of
municipal solid wastes.
The biomass utilization process are: direct combustion of
biomass such as in wood fuels boilers, gasification as well as other chemical
processes.
The most commonly used biomass fuel is that which is derived
from trees, this is commonly termed as wood fuel can take the form of logs,
wood chips or pellets. Wood fuel is
arguably the least expensive renewable energy technology for the generation of
heat. The heat market within the UK is the largest single component in the
energy sector occupying some 45% of the total market. Some 30% of the renewable
energy use is from the burning of wood fuels.
Woof fuel boilers are certainly more technically advanced
than the traditional wood stoves which have been used over the ages for cooking
and space heating.
Log fuels are
perhaps the least versatile of the wood fuels. Modern log boilers offer high
levels of efficiency of around 90% theoretical, real efficiencies will be less.
It is possible to fill most modern log boilers from the top with a days worth
of logs as they operate on the down draught principle. This means that the
boiler is still able to maintain clean combustion. New modern wood chip boilers offer clean and
efficient fuel burning. In order to maintain good clean and efficient fuel
burning is essential that ration of fuel to air known as the fuel air mix is
maintained as the optimal value. Lambda control is one method of achieving
this, the oxygen content of the flue gas is measured and the fuel to air mix is
adjusted accordingly. In many cases the wood chip boiler will be used to supply
a space heating base load. Modern wood chip boilers are quite flexible and are
capable of operating at around 30% of the maximum continuous rating value (MCR)
and are still able to maintain high efficiency and environmental performance.
Pellet fuel is the most versatile and controllable fuel and can be used to
maintain high levels of efficiency. Pellet fuels are probably the most suitable
fuel for small scale applications. Pellet fuels can be burned in the majority
of wood chip boilers or in specifically designed wood chip boilers.
Other types of biomass fuel are currently being used on a
smaller scale such as agricultural wastes and municipal waste. Boilers for
burning of these fuels must be designed to be able to cope with the varying
composition of the fuels and will not be discussed in this web page.