How to calculate the biological conversion efficiency of a biogas plant for a certain period?is there any specific equation?

Dear Md. Nurul Islam,

Please read the following text:

Biogas is the gas resulting from an anaerobic digestion process. A biogas plant can convert animal manure, green plants, waste from agro industry and slaughterhouses into combustible gas.

Biogas can be used in similar ways as natural gas in gas stoves, lamps or as fuel for engines. It consists of 50-75% methane, 25-45% carbon dioxide, 2-8% water vapour and traces of O2 N2, NH3 H2 H2S. Compare this with natural gas, which contains 80 to 90% methane. The energy content of the gas depends mainly on its methane content. High methane content is therefore desirable. A certain carbon dioxide and water vapour content is unavoidable, but sulphur content must be minimised - particularly for use in engines. The average calorific value of biogas is about 21-23.5 MJ/m³, so that 1 m³ of biogas corresponds to 0.5-0.6 l diesel fuel or about 6 kWh (FNR, 2009). The biogas yield of a plant depends not only on the type of feedstock, but also on the plant design, fermentation temperature and retention time. Maize silage for example - a common feedstock in Germany - yields about 8 times more biogas per ton than cow manure. In Germany, cow manure and energy crops are the main forms of feedstock. About 2 live-stock units (corresponding to about 2 cows or 12 rearing pigs) plus 1 ha of maize and grass are expected to yield a constant output of about 2 kWel (48kWhel per day. In the South Asian context, ESMAP uses a typical specific input-output relation of about 14 kg of fresh cattle dung (the approximate production of one cow on one day) plus 0.06 l diesel fuel to produce 1kWh electricity.

Gas Production Figures If the daily amount of available dung (fresh weight) is known, gas production per day in warm tropical countries will approximately correspond to the following values:

1 kg cattle dung 40 liters biogas

1 kg buffalo dung 30 liter biogas

1 kg pig dung 60 liter biogas

1 kg chicken droppings 70 liter biogas

If the live weight of all animals whose dung is put into the biogas plant is known, the daily gas production will correspond approximately to the following values:

cattle, buffalo and chicken: 1,5 liters biogas per day per 1 kg live weight

pigs, humans: 30 liters biogas per day per 1 kg weight

For yield ranges and methane contents for 33 different substrates, please see Gas Yields and Methane Contents for Various Substrates.                                                                                                                                   Each kilogram of biodegradable material yields 0.4 m3(400 liters) of gas.

Gas lights consume around 0.1m3(100 liters) of gas in one hour.

Appropriate feedstock for electricity-generating biogas plants is available in adequate quantity in many countries. Small and medium-size biogas plants could provide a considerable contribution to national electricity generation in such countries. However, in comparison to industrialised countries, only very few small and medium sized biogas plants are used for electricity generation in Africa, Latin America and even Asia.

Electricity production from biogas can be a very efficient method for producing electricity from a renewable energy source. However, this applies only if the emerging heat from the power generator can be used in an economically and ecologically sound way. The average calorific value of biogas is about 21-23.5 MJ/m³, meaning that 1 m³ of biogas corresponds to 0.5-0.6 l diesel fuel or an energy content of about 6 kWh. However, due to conversion losses, 1m³ of biogas can be converted only to around 1.7 kWhel. Bigger biogas plants are generally more cost-efficient than smaller ones. However, electricity generation from biogas is a technology appropriate even for relatively small applications in the range of 10-100kW.

Burkard, Thilo (2009): Project cases of Biogas-plants in Kenya. Presentation for Biogas Delegation Trip, Agritechnica 2009. Clearly presented detailed analysis of the technical and economic aspects of 5 biogas power plants in Kenya.

COPEL DISTRIBUIÇÃO S A: VENCEDORES DA CHAMADA PÚBLICA, 2009, 2.p List of winners of a tender to sell electricity to the grid in the state of Paraná, Brazil.

ESMAP (2005) Advancing Bioenergy for Sustainable Development - Guideline for Policy-makers and Investors. Report 300/05.

Fachagentur Nachwachsende Rohstoffe e.V. (FNR) (2009): Biogas Basisdaten Deutschland – Stand: Oktober 2008. 7p. Very short but comprehensive overview of the biogas situation in Germany.

Franz, Michael (2009): Zielmarktanalyse (ZMA). Der Markt für Biogas in Kenia. Studie des Projektentwicklungsprogramm Ostafrika im Rahmen der Exportinitiative Erneuerbare Ener-gien des BMWi. Description of the status in Kenya of biogas technology, available local know-how, market potential as well as legal and economic framework conditions. Detailed discussion of a biogas plant at a sisal plantation in Kilifi and lessons learned.

Franz, Michael and Klaus v. Mitzlaff (2009): The Biogas Market in Kenya - Status Quo and Potentials. Presentation for Combined Biogas Business and Study Trip from Kenya and Tan-zania, to Hannover, November 13, 2009. German Technical Cooperation (GTZ).

Grope, Johann (2009): Optimierung eines Biogasanlagenmodells unter Berücksichtigung der spezifischen Rahmenbedingungen Südbrasiliens. Study of DBFZ on behalf of GTZ. 84 p. Describes framework conditions of biogas activities in southern Brazil and current technol-ogy. Develops proposals for optimised biogas technology.

GTZ (2010):

Agro-Industrial Biogas in Kenya – Potentials, Estimates for Tariffs, Policy and Business Recommendations. Study of Deutsches Biomasse Forschungs Zentrum (DBFZ) on behalf of GTZ, Renewable Energy Project Development Programme East Africa. 69p. This comprehensive study documents the high potential for electricity production in Kenya from municipal solid waste and agro-industrial production, especially sisal and coffee produc-tion. About 16% of actual electricity consumption could be covered by electricity from biogas. The costs of different plant types and sizes are calculated. Grid connection and appropriate feed-in-tariffs are identified as the main prerequisites for commercial investment in this sector. The proposed basic feed-in-tariffs are within a price range similar to current levels in Germany (0.10 – 0.2 US$ /kWh el.

GTZ-PURE (2005): Feasibility Study on Biogas from Poultry Droppings in Bangladesh, Pre-pared By Bangladesh Centre for Advanced Studies (BCAS) in collaboration with Energy Consulting Services (ECS), December 28, 2005. Surveys biogas activities in Bangladesh and discusses briefly the possibilities and profitability of electricity generation in Bangladesh.

Mitzlaff, Klaus von (1988): Engines for Biogas. GTZ-GATE /Viehweg. 164p. Documents early approaches of GTZ towards electricity generation from biogas. Describes the essential basics of internal combustion engines and properties of biogas as a fuel for internal combustion engines. Suggests parameters for planning a biogas engine system, with an overview of commercially available systems.

Muchel, H. and H. Zimmermann (1985): Purification of Biogas. GTZ: Aus der Arbeit von GATE, 33p. Viehweg Documents early GTZ approaches towards electricity generation from biogas. Describes the properties and origins of hydrogen sulphide in biogas plants, its effects on the gas-utilisation equipment and methods for removing H2S from biogas.

Practical Action (2009): Small-Scale Bioenergy Initiatives: Brief description and preliminary lessons on livelihood impacts from case studies in Asia, Latin America and Africa. Final re-port, prepared for PISCES and FAO by Practical Action Consulting. Jan. 2009. 135p.

Raninger, Bernhard (2009): Biomass-Waste Management - a contribution to a Low CO2-Circular Economy and an Environmental Sound Urban & Rural Development. Presentation to International Symposium on ‘City Group Development Model’, Changsha, Hunan, China, Dec. 3 to Dec. 4, 2009.

Tomowsky, Arno (2006): GTZ Biogas-experience in Africa. Presentation held at international Workshop on the Biogas Sanitation Initiative for Africa’. Amsterdam, Oct. 2006. Unpublished. A brief summary of lessons learned by GTZ over more than 20 years of biogas activity in Africa.

For further read, please use the following link:

Hoping this will be helpful,

Rafik

Thank you for your kind response.

I have another question sir.

what will be if the plant doesn't feed regularly?

if the feeding rate is once in two or three days, how can I evaluate the plant efficiency?

Dear Md. Nurul Islam,

In this case the efficiency may drop by 40-50%.

Rafik