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What is biogas?
This is the gas or
actually, a mixture of gases, produced
during the anaerobic (oxygen-free)
digestion of organic matter by various
anaerobic bacteria. Biogas typically
consists of 55 to 70% methane and 45 to 30% carbon
dioxide with small amounts of hydrogen sulphide, water vapour and other
impurities.
The
combustible gas in biogas is methane
which is the same as natural gas. One
standard cubic metre of methane has an
energy content of 35.8 Mj or 9.94 kWh.
Biogas by itself can be used as fuel for
boiling or heating purposes. In large
quantities, it can be used to generate
electricity using a gas engine generator
or a gas turbine. For this purpose,
hydrogen sulphide, which is corrosive, is
first removed using certain
desulphurization equipment. Similarly,
water vapour can be removed by
condensation equipment installed along
the pipeline. For other applications,
such as fuel for NGV vehicles, biogas
can be further upgraded to biomethane
whereby carbon dioxide is also removed.
In a large
landfill, or in a sewage or palm oil
mill effluent pond, anaerobic conditions
can exist whereby biogas is being
produced and emitted into the atmosphere
hence contributing to the global warming
effect. This is because methane is a
highly potent greenhouse gas (GHG),
being 21 times more potent than carbon
dioxide.
What is a biogas plant?
A
biogas plant is built to efficiently
convert organic matter or biomass into
energy (in the form of biogas) using the
anaerobic digestion process. The
substrate (that is, the input organic
matter) used is usually organic waste
material that would otherwise need to be
disposed of. A biogas plant is designed
to maximize the output of biogas from
any organic material or biomass
available in the shortest possible time.
The residue, or digestate, can be
processed into valuable organic
fertilizer. Large biogas plants would
include power generation equipment to
convert the biogas to electricity which
could be sold to the national grid.
A biogas
plant is therefore a most effective
system for biological recycling, besides
contributing to a reduction in carbon
emissions. As an investment, it is not
only profitable but necessary in view of
the inevitable depletion of fossil
fuels. Unlike other methods of treating
organic waste, a biogas plant has the
further advantage of not causing any odour emission problem. This is because
biogas plant digesters are completely
sealed to ensure anaerobic conditions.
Also, biogas plants can be designed to
be as big or as small as required based
on the quantity of substrate available.
With the
appropriate biogas plant technology,
practically all kinds of organic waste
or biomass can be used to produce
biogas, and organic fertilizer. Such
waste material therefore should not be
regarded as waste but as stores of
untapped renewable and sustainable
energy. And biogas plant technology appears to
be the best method to convert such
organic waste into renewable energy.
In
Malaysia, the palm oil industry
generates the largest volume of organic
waste in the form of empty fruit bunches
(EFB), mesocarp fibres, palm kernel
shells and also palm oil mill effluent (POME).
Other major items of organic waste are
the organic fraction of municipal solid
waste (OFMSW), livestock farm manure,
agro-industry processing wastes, sewage
treatment plant sludge, etc. The biogas
potential vary with different types of
organic wastes.
Superior biogas technology
Germany is
the world leader in renewable energy and
has the most advanced biogas technology.
At SP Multitech Renewable Energy Sdn Bhd,
we have a technology transfer agreement
that enable us to build biogas plant
with superior German technology but with
Malaysian pricing.
Wet Fermentation
Anaerobic
digestion biogas plants fall into two
categories. The more common one is the
wet fermentation plants which make use
of steel or concrete tanks as digesters
usually in a two-stage configuration.
The first and smaller tank is for the
initial hydrolysis stage followed by the
acetogenesis and methanogenesis stages
in the second and larger tank. It is a
continuous process and the total tank
capacity is sized according to the total
daily input multiplied by the number of
days of hydraulic retention time
required.
Dry Fermentation
The dry
fermentation anaerobic digestion (DFAD)
technology is a more recent development.
This method is more energy and labour
efficient, and is suitable for
substrates with lower moisture content.
This system consists of a number of
digesters or bio-reactors equipped with
special airtight doors, the number
depending on the expected retention time
required. Each digester is designed to
accommodate one day’s supply of
substrate which is fed each day into the
digesters in sequence. Each digester is
a batch processor but when operated in
sequence, the system is a continuous
process.
The DFAD
biogas technology is particularly
suitable for substrate with lower
moisture such as OFMSW. This technology
could revolutionize the management and
disposal of MSW which is usually sent to
the landfill. Such DFAD plants could be
set up at landfill sites. Then the MSW
received would first sorted out with
the organic portion going to the DFAD
biogas plant to produce biogas and
organic fertilizer. In the sorting
process, recyclable items made of
plastic, glass or metal could be taken
out for sale to recycling companies.
Then, only the inorganic, non-recyclable
items need to go to the landfill,
thereby helping to extend the lifespan
of the landfill site. A big landfill
that has up to 250 tonnes of OFMSW would
have enough biogas to generate up to 3
MW of electrical output.
In both
methods, it is important to monitor and
maintain optimum environment for the
various types of bacteria, especially the
methane-enhancing or methonogenic bacteria, to thrive on.
This is where technological expertise
and knowledge of such bacteria are
required to achieve good overall
results. With technology support from
our German partner, we are confident
that our biogas plants would perform
exceedingly well.
Global effort
There is serious global concern about
global warming caused by emission of GHGs and every country should contribute
to the global effort to reverse the
trend by promoting green or renewable
energy. At SP Multitech Renewable Energy
Sdn Bhd, we intend to play a significant
role in this effort by building as many
biogas plants as possible. We would
consider it a service for the cause of
global environmental protection.
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