XII Международная студенческая научная конференция Студенческий научный форум - 2020

Biogas technology, the generation of a combustible gas from anaerobic biomass digestion, is a well-known technology. There are already millions of biogas plants in operation throughout the world. Whereas using the gas for direct combustion in household stoves or gas lamps is common, producing electricity from biogas is still relatively rare in most developing countries. In Germany and other industrialised countries, power generation is the main purpose of biogas plants; conversion of biogas to electricity has become a standard technology.

This article will discuss the potentials, obstacles and necessary framework conditions for the utilisation of biogas for small and medium scale electricity generation in developing countries. This article will not address the biogas production process in general but focus uniquely on electricity generation. 

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.)

Theoretically, biogas can be converted directly into electricity by using a fuel cell. However, this process requires very clean gas and expensive fuel cells. Therefore, this option is still a matter for research and is not currently a practical option. The conversion of biogas to electric power by a generator set is much more practical. In contrast to natural gas, biogas is characterized by a high knock resistance and hence can be used in combustion motors with high compression rates.

In most cases, biogas is used as fuel for combustion engines, which convert it to mechanical energy, powering an electric generator to produce electricity. The design of an electric generator is similar to the design of an electric motor. Most generators produce alternating AC electricity; they are therefore also called alternators or dynamos. Appropriate electric generators are available in virtually all countries and in all sizes. The technology is well known and maintenance is simple. In most cases, even universally available 3-phase electric motors can be converted into generators. Technologically far more challenging is the first stage of the generator set: the combustion engine using the biogas as fuel. In theory, biogas can be used as fuel in nearly all types of combustion engines, such as gas engines (Otto motor), diesel engines, gas turbines and Stirling motors etc.

Next, we provide statistics on electricity generation from biofuels from Library of Agency for Renewable resources e. V. [1].

Gross electricity generation 2018 [2].

Stromerzeugung aus Biomasse 2018 [3].

Stromerzeugung aus erneuerbaren Energien 2018 [4].

Biomassestrom in der Direktvermarktung [5].

Economically, electricity from biogas must compete with electricity generation from fossil fuels and other renewable energies such as hydro power. Supporting factors are:

Rising prices of fossil fuels

Low reliability of electricity provision from national grids with persistent risk of power cuts and vulnerability of hydro power to drought.

Inhibiting factors are:

Relatively low prices of fossil fuels

Need to buy high quality components from industrialised countries

Unfavorable conditions for selling electricity

Lack of awareness, capacity and experience preventing the economic operation of infrastructure components.

The economic feasibility of a biogas plant depends on the economic value of the entire range of plant outputs. These are:

Electricity or mechanical power

Biogas

Heat, co-generated by the combustion engine

The sanitation effect with COD and BOD (chemical and biological oxygen demand) reduction in the runoff of agro-industrial settings

Slurry used as fertiliser.

In Germany, power generation from biogas is only profitable due to grid connection and sup-porting feed-in tariffs. By contrast, power generation in Russia to be especially profitable in settings far away from the national grid and other energy sources, as the legal framework conditions and the lack of appropriate feed-in tariffs do not support feeding into the grid. However, in countries such as Russia, the first signs of financial and legal support for the supply of electricity from biogas power plants should appear. Output-oriented support schemes (such as the German EEG) have proved to be more successful than investment-oriented financial support.

Direct subsidies and public financial contributions to installation costs have been crucial for the installation of some pilot plants. However, they have not provided incentives for proper and efficient operation. By contrast, the establishment of appropriate feed-in tariffs stimulates the construction of efficient plants and their continuous and efficient operation.

Through its projects and programmes, German technical cooperation therefore recommends the establishment of guaranteed feed-in price schemes similar to the one in Germany.

However, besides price considerations, there remain many barriers to market penetration and development of the biogas sector:

Lack of awareness of biogas opportunities

High upfront costs for potential assessments and feasibility studies

Lack of access to finance

Lack of local capacity for project design, construction, operation and maintenance

Legal framework conditions that complicate alternative energy production and commercialisation: for example, the right to sell electricity at local level has to be in place.

As long as the national framework conditions are not favourable, electricity generation from biogas will remain limited to a few pilot applications. [1].

References:

Electricity Generation from Biogas [Электронныйресурс]. – Режим доступа: https://energypedia.info/wiki/Electricity_Generation_from_Biogas (дата обращения: 01.03.2019).

Biomassestrom in der Direktvermarktung [Электронныйресурс]. – Режим доступа: https://www.fnr.de/fileadmin/allgemein/pdf/broschueren/basisdaten_bioenergie_2019_web.pdf (дата обращения: 01.03.2019).

Stromerzeugung aus erneuerbaren Energien 2018 [Электронныйресурс]. – Режим доступа: https://www.fnr.de/fileadmin/allgemein/pdf/broschueren/basisdaten_bioenergie_2019_web.pdf (дата обращения: 01.03.2019).

Stromerzeugung aus Biomasse 2018 [Электронныйресурс]. – Режим доступа: https://www.fnr.de/fileadmin/allgemein/pdf/broschueren/basisdaten_bioenergie_2019_web.pdf (дата обращения: 01.03.2019).

Gross electricity generation 2018 [Электронныйресурс]. – Режим доступа: https://www.fnr.de/fileadmin/allgemein/pdf/broschueren/basisdaten_bioenergie_2019_web.pdf (дата обращения: 01.03.2019).

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