Biomass Electricity: Introduction

November 7, 2018
Biomass Electricity
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Areas Covered
 Biomass definition
 From Biomass to Power process
 Issues arising from the use of Biomass
 Conclusion

November 7, 2018
Bioma
ss
Storag
e
Combustion Exhaus
t
Ash
Turbin
e
Condense
r
Generat
or
Electrici
ty
The photo above shows a Biomass
Plant
BIOMASS
Introduction
Biomass is plant and animal waste that can be
converted to other forms of energy like biofuel,
electricity or even heat. It is a renewable
energy source as wastes will always be
available and well managed forests will always
have trees. Using biomass is considered the
same as going green as rice husks, stalks,
cobs, shells and woody residues are used in
generation of power. This factsheet will look
into at biomass in electricity production and
the related issues concerning biomass power.
BIOMASS ELECTRICITY
Biomass power is electricity produced by
converting biomass into energy.
Biomass(net)=Increase biomass(gross)-
Decrease biomass(gross)
1 tonne of biomass can produce around 1
megawatt-hour of electric power plus carbon
weighing at around 50 kilograms (M, 2009). If
the biomass plant is maintained properly it can
run for over 20 years where the heating
system needs 2-5 hours of maintenance per
week and boiler tube cleaning should be
around 2 times a year. Generally a biomass
electric system consist of fuel storage
equipment, furnace, boiler, pumps, fans, steam
turbine, generator, condenser, cooling tower,
exhaust controls and system controls.
Photo above showing from biomass to electricity process
Converting Biomass to
Electricity
Firstly biomass is stored in
order to maintain a continuous
supply. Biomass is mostly
stored in subterranean, bunker,
or even silo using cranes and
belts. Biomass storage is key as
its availability is dependent on
crop seasonality and this
coupled with availability of
cheaper means of transport
have an effect on the
production at the power plant
(Nasiri, 2014). Production of
biomass power is highly
favoured in tropical countries
where forest growth rate is
often very high. Around 20
acres of land is needed for fuel storage and 10 acres of land for plant producing around 10

November 7, 2018
megawatts electricity units. Biomass used in electricity production is mainly wood by products like
sawdust and tree barks to form pellets or briquettes. Also the bunker stored biomass should be
enough for around four days of operation considering the changes in weather and should be clean so
that dirt is not scoped into the furnace alongside the wood chips.
Biomass like sawdust are usually obtained from wood processing plants and sugarcane residues
come from sugar mills.
Secondly, biomass is fed into a furnace where it is burned to create steam by heating water in a
boiler. If wood chips are used their moisture content should not exceed 30% as chips from freshly fell
trees contain a moisture content of up to 70%.a surge bin is used to control the rate at which biomass
enters the combustor (Marshall, 2010). A fire suppressing system like a temperature sensor is needed
to inhibit fire that can spread through the conveyor or water is used to put off fire.
The emissions from combustion of biomass are controlled by use of exhaust systems like electrostatic
precipitator or even multi-cyclones. Main combustion by products are carbon dioxide and water Also a
system control for nitrogen oxide, sulphur oxide and hydrocarbons must be put in place. The end
products of combustion process are mainly steam, ash and carbon dioxide (CO2). Woody biomass has
a maximum of 5% ash and is periodically removed from the system using augers. Ash produced can
be used compost fertiliser or making bricks used in construction.
Furthermore, the steam (containing heat energy) produced is fed to the turbine rotor using nozzles
hence turning the turbine blades due to its high velocity. Fans are used in removal of fumes that
might be produced in the boiler and in heat distribution in the heating process.in this case the fans
pump air leading to increase in temperatures (Peter, 2010). A fan works better in conditions with
appropriate pressure and temperatures hence there is need for a fan that can withstand high
temperatures and pressure. Later the steam is condensed into water by extracting the latent heat of
vaporisation by making the steam volume reduce to zero and again pumped to the boiler to be used
again. The condenser needs ample supply of water.
Lastly, a generator is used to produce electricity from the energy produced by the turbines using the
rotor and stator. The electric current is a product of the stator where the terminals of the generator
are connected to the metal coil that wounds the solid iron core. The rotor produces a magnetic field
by spinning around the rotor. Semi rotation by the rotor changes the polarity of electricity produced
by the generator. The steam turbine drives the generator producing electrical energy from
mechanical energy that is fed into the high voltage power transmission grid where it is ready for use
by consumers.
Issues surrounding the use of Biomass in Electricity Production
On the Positive Side
Firstly, power produced from biomass is usually
carbon free. Any carbon emitted during the
day to the atmosphere as a result of burning of
biomass is absorbed by plants through
photosynthesis that is,
CO2+2H2O=CH2O+O2+H2O. CO2 absorption rate
is calculated in terms of an acre as follows,
-0.23metric ton C/ year x (44 units CO2/12
units C)= -0.85 metric ton CO2 absorbed per
acre per year This means there is massive
reduction of greenhouse gas emissions to the
atmosphere hence addressing global warming
and climate change. Since CO2 emissions from
biomass are controlled there is 80% reduction
in the CO2 emitted into the atmosphere. The US
emission rate per year of CO2 is calculated as
1640.7lbs CO2/MWh x (4.536 x 10-4 metric
tonnes/lb x 0.001 MWh/kWh = 7.44 x 10-4
metric tons CO2/kWh
Secondly, biomass energy means a cleaner
environment (Joe, 2000). With the current
increase in population there is need for proper
waste management as many waste are usually
littered in oceans and streams. With the use of
biomass in electricity production the garbage
can be put to better use in waste to energy
plants hence reducing land pollution. Annual
change of biomass carbon stocks is calculated
as follows,
Change in CB = Change in CG + CConversion -
Change in CL
Thirdly, with time fossil fuels will be history
only to be read about in history books or
watched in documentaries. Biomass energy
that is usually economically and
environmentally friendly like biodiesel and
ethanol will have to fill in these shoes left by
fossil fuels as biomass is almost everywhere on
the planet.
Also, ash that is a by-product of burning
biomass is used as a fertilizer that is nutrient
rich and organic.
Furthermore, burning of waste means that
there is no need for landfills. Such land can in
turn be used in cultivation of energy crops
instead of being used in waste management.

November 7, 2018
Lastly, the usage of biomass as an alternative
source of energy to fossil fuels creates room
for stable fuel prices. There will be less
fluctuations if any by reducing monopoly of the
oil producing and exporting countries hence
easing political and global tensions like the
recent conflict between the European Union
and Ukraine and Russia.
On the Negative Side
Firstly, if other emissions like nitrogen oxide,
sulphur oxide and hydrogen chloride escape to
the atmosphere there will be acid rain. This will
cause water and soils to be acidic causing
damages to the ecosystem. (Felipe, 2010)
Secondly biomass plants use an average of
35000 gallons of water per megawatt hour and
this disrupts local water sources.
Thirdly, there is massive deforestation
practices by countries like the USA to grow
energy crops. This means an additional 25% of
greenhouse gases leading to climate change.
The rate crop producing carbon is calculated as
follows,
-33.43 metric tons C/acre/year x (44 units
CO2/12 units C = -122.56 metric tons
CO2/acre/year
Also, if people cut trees at a rate that is higher
than how trees grow promotes deforestation
(Felipe, 2010).
MY TAKE ON THE BIOMASS DEBATE
Biomass power is safer than fossil fuels but not totally safe. But it holds the key to substitute fossils in
future. By 2020 another 3500 biomass plants are to be built worldwide meaning that mankind has
found the value of common waste. In USA alone biomass produces electricity amounting to 50 billion
kilowatt-hours meaning that it has potential if harnessed to its full potential. The benefits of biomass
outweigh its disadvantages. Since the discovery of fire up to date man has harnessed energy derived
from biomass as it is the main source of fuel in developing countries for domestic use. So just like the
sun, it is impossible for all plant life to come to an end on earth. So I believe that biomass is a future
fuel and is here to stay.
References
Darby, T., 2014. What is Biomass Renewable Energy?. New York: s.n.
E, K., 2008. Catalyctic Conversion of Biomass. Paris: Paris Press.
Felipe, S., 2010. Intensive Forestry. California : University of California.
Joe, E., 2000. Future Fossil Fuel Carbon Emission. London: Cambridge University Press.
L, B., 2005. Biomass-Coal Combustion. Chicago: s.n.
Linda, S., 2009. Into A Warming World. New York: NYU publishers.
Marshall, M., 2010. First Generation Biofuels. Chicago: University of Chicago Press.
M, J., 2009. Production of Biomass for Energy. Birmingham: s.n.
Nasiri, M., 2014. Modeling Biomass to Energy. New York: New York University Publishers.
O, G., 2009. Biomass or Fossil Fuel Combustion. California: California University Press.
Peter, A., 2010. Useful Products from Complex Starting Materials. London: s.n.
Tena, S., 2017. Blek Outlook for Forestry Industry. Chicago: University of Chicago Press.