Small-Scale Conversion of Biogas to
Electricity
Dexter Lo, Shierlyn S. Paclijan, Peter Andres Gamones, Xavier
University
Small-Scale Conversion of Biogas to Electricity
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Small-Scale Conversion of Biogas to Electricity
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Contents
1. Concept
2. How it can optimize SSWM
3. Applicability
4. Advantages and Disadvantages
5. References
Small-Scale Conversion of Biogas to Electricity
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1. Concept
Background
Biogas is a mixture of methane, carbon dioxide, water and hydrogen
sulphide produced during the anerobic decomposition of organic
matter.
Biogas is a combustible gas mixture produced during the anaerobic
digestion of organic matter in a biogas reactor.
Composition:
•Methane (65-70%)
•Carbon dioxide (25-30%)
•Varying quantities of water and
hydrogen sulphide
•Other compounds such as ammonia,
hydrogen, nitrogen and carbon
monoxide
(adapted from ASHDEN (2004), TILLEY et al. (2008))
Small-Scale Conversion of Biogas to Electricity
Anaerobic Biogas Reactor
Source: TILLEY et al. (2008)
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1. Concept
Background
Biogas energy may be derived from methane and other combustible
gases. It is considered a renewable form of energy production.
The heating value correlates with the methane content. The methane
in biogas is generally equivalent to 600-800 Btu/ft3 and can be
utilized directly as a heat source or to produce electricity (MDCSEO 2003).
Biogas must be dehumidified and purified before combustion;
otherwise it can damage the gas engine.
In principle the chemical energy of the combustible gases is converted
to mechanical energy in a controlled combustion system.
This mechanical energy then activates a generator to produce
electrical power.
Gas turbines and internal combustion engines are the most common
technologies used in this kind of energy conversion.
Small-Scale Conversion of Biogas to Electricity
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1. Concept
Cogeneration/ Combined Heat and Power (CHP)
The most efficient way of using biogas is in a cogeneration process that
simultaneously generate both electricity and useful heat.
Thermal power plants and heat engines, do not convert all of their thermal
energy into electricity. In most heat engines, a bit more than 50% is lost as
excess heat
By capturing the excess heat, CHP uses heat that would be wasted in a
conventional power plant, potentially reaching an efficiency of up to 89%,
compared with 55% for the best conventional plants (WRAPAI 2009).
The heat output can be reused to run the CHP to produce electricity again.
Byproduct heat at moderate temperatures (100-180°C) can also be used in
absorption chillers for cooling (WRAPAI 2009).
Micro-Cogeneration: less than 5 kWe
(WRAPAI 2009)
Mini-Cogeneration: more than 5 kWe and less than 500 kWe
Small-Scale Conversion of Biogas to Electricity
(WRAPAI 2009).
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1. Concept
Example
Micro CHP in the home.
Small-Scale Conversion of Biogas to Electricity
Source: P. Bance, Ceres Power
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1. Concept
Example
Combined Heat and Power (CHP) unit “micro size” in Germany. Source: GTZ Ecosan
Small-Scale Conversion of Biogas to Electricity
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1. Concept
Technologies Used
Various cogeneration technologies on household level are available.
Micro- and Mini-Cogeneration installations use five different
technologies:
Microturbines
Internal combustion engines
Stirling engines
Closed cycle steam engines
Fuel cells
Micro-CHP based on Stirling engines is considered to be one of the most
cost effective of the so called micro-generation technologies in
abating carbon emissions.
Small-Scale Conversion of Biogas to Electricity
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2. How it can optimize SSWM?
Small-Scale Conversion of Biogas to Electricity can help in optimizing
your local water management and sanitation system and make it more
sustainable by:
Providing an environmental friendly way of energy production by
making use of the energy content of excreta
Having a positive impact on climate change. In fact, the contribution of
a methane molecule (CH4) to the greenhouse effect is 21 times greater
than that of a carbon dioxide molecule (SUSANA 2009). Therefore burning
methane, even though producing CO2, reduces its impact on the
environment.
Providing a source of income generation (if sold back to the grid)
Small-Scale Conversion of Biogas to Electricity
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3. Applicability
This technology is easily adaptable and can be applied at household or
community level. To minimize distribution losses, the reactors should be
installed close to the CHP where the gas can be used.
Biogas cogeneration is also extensively used in rural China, Nepal, Vietnam and
other nations where waste management and industry closely interface.
Micro Cogeneration
Useful for a single house or small business because of the low power output.
The electricity can be used within the home or business or, if permitted by the
grid management, sold back into the electric power grid.
Mini Cogeneration
• Installation is usually more than the micro cogeneration and supplies
electricity for more than one household.
• Mini-CHP has a large role to play in the field of carbon reduction in buildings
where more than 14% of carbon can be saved by 2010 using CHP in buildings
(WRAPAI 2009).
Small-Scale Conversion of Biogas to Electricity
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4. Advantages and Disadvantages
Combined Heat and Power (CHP)
Advantages:
Disadvantages:
• Generation of a renewable,
valuable energy source
•Requires expert design and skilled
construction
• Low operating costs
•Gas production below 15°C, is no
longer economically feasible
• Underground construction
minimizes land use
• Long life span
•High capital costs
•Expert maintenance required
• No/low electrical energy required
• Positive impact on greenhouse gas
emissions
• Increases income by selling back
electric energy to electric power
grid
• On site use of heat
Small-Scale Conversion of Biogas to Electricity
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5. References
COELHO S. T., GONZALEZ VELASQUEZ S. M. S., MARTINS O. S., ABREU F. C. DE (2006): Biogas from Sewage Treatment
used to Electric Energy Generation, by a 30 kW (ISO) Microturbine. Sao Paulo, Brazil: Brazilian Referenze Center on
Biomass (CENBIO)
MDCSEO (2003): Minnesota’s Potential for Electricity Production Using Manure Biogas Resources. Minnesota, USA:
Minnesota Department of Commerce State Energy Office (MDCSEO)
SCHALLER M. (2007): Biogas electricity production hits 17 272GWh a year in Europe. In: Engineer Live, p. 46-49
SUSANA (2009): SuSanA fact sheet 09/2009. Links between sanitation, climate change and renewable energies.
Sustainable Sanitation Alliance (SuSanA)
TILLEY, E., LÜTHI, C., MOREL, A., ZURBRÜGG, C., SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and
Technologies. Switzerland: Swiss Federal Institute of Aquatic Science (EAWAG) & Water Supply and Sanitation
Collaborative Council (WSSCC)
WRAPAI (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research. Australia: Waste Refinery
Australia Project Association Incorporated (WRAPAI)
Small-Scale Conversion of Biogas to Electricity
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