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Biogas Biogas – A unique source of renewable energy Biogas clearly promises to resolve both energy problem and the environmental crisis of our modern days.
Bio Gas

Wonders with waste – First and foremost, environmental damage is reduced by using biogas as a fuel for energy.

Recent years have witnessed rapid industrialization for better world and population growth, along with recklessly extravagant consumption of energy. This in turn has triggered enormous increase in energy production based on non‐renewable energy resources such as oil, coal, and natural gas. In order to break the dependence on fossil fuels, much research is underway to find new and efficient ways of energy production from renewable energy sources.

Biogas from Raw Materials Biogas can be produced from regionally available raw materials In several places around the world, communities are already converting cow dung, human waste and kitchen garbage into usable energy.
From waste to Biogas

While thinking about environment and all the problems that we have created regarding pollution, it is time to start thinking about possible solutions. We are now aware of concepts like – Making money with manure, From kitchen waste to Biogas etc. In several places around the world, communities are already converting cow dung, human waste and kitchen garbage into usable energy.

Growing uncertainty about our more traditional energy sources is increasing demand for sustainable energy, not least biogas. Biogas is a renewable energy source, like solar and wind energy. Furthermore, biogas can be produced from regionally available raw materials and recycled waste and is environmentally friendly and easy to produce almost everywhere. Biogas production capacity is directly proportional to the agricultural level of a country. Its ease of production and relatively higher efficiency compared to other renewable energy sources make it particularly important for countries which are not self‐sufficient in energy production.

Flaring Biogas Flaring biogas Biogas is a mixture that is produced by microorganisms during the decomposition of vegetable and animal wastes in an oxygen-free environment.
What is biogas?

The term 'biogas' is commonly used to refer to a gas which has been produced by the biological breakdown of organic matter in the absence of oxygen. Biogas is a mixture that is produced by microorganisms during the decomposition of vegetable and animal wastes in an oxygen‐free environment. It consists of methane (60–70%), carbon dioxide (30–40%) and hydrogen‐sulfide (0–2%).

For its production, plant seeds that are rich in oil (e.g. sunflower), vegetables rich in carbohydrates (e.g. potato, wheat, corn, beet), fiber‐rich plants (e.g. flax), other plant and tree remains (e.g. branches, hay, roots, bark), and animal remains can be utilized as raw material. Municipal and industrial waste can also be utilized on the condition that they are purified from inorganic materials like plastic and glass.

Sunflower and biogas Raw material for biogas production Plant seeds and tree remains can be used as raw material for biogas production.
Anaerobic Digestion

The gases methane, hydrogen and carbon monoxide can be combusted or oxidized with oxygen and the resultant energy release allows biogas to be used as a fuel.

Biogas production technology provides alternate source of energy in rural areas and acts as an appropriate technology that meets the basic need of cooking fuel in rural areas. Using local resources, that is cattle waste and other organic wastes, energy and manure ( nutrient value and can be applied on land) are derived.

Biogas is produced by the action of bacteria on organic material in airless conditions hence the process is also known as anaerobic digestion. The bacteria slowly digest the material (usually animal dung, human wastes and crop residues) and produce a gas which is roughly 60% methane and 40% carbon dioxide.

Methane in biogas Composition of Biogas Biogas is "renewable natural gas" containing approximately 60% methane (CH4) and roughly 40% carbon dioxide and trace amounts of other gases.
Biogas production

Biogas production is a chemical process occurring in stages during which different bacteria act upon the organic matter resulting in the formation of methane and acids. The main factors that influence biogas production are pH (level of acidity) of the feedstock and the temperature. It is well established that a biogas plant works optimally at pH level of 7 or just above (neutral solution) and a temperature of around 35°C. In low temperatures, bacteria activity slows down resulting in substantial decrease in gas generation, ceasing completely below 10°C.

Biogas is produced from bio degradable wastes through a process called anaerobic digestion. Anaerobic digestion is a naturally occurring process through which organic matter such as manure, feed spills, meat processing wastes and crop residues are stabilized by microorganisms strictly in the absence of air. During this process, some organic compounds are converted to methane (CH4) and carbon dioxide (CO2) gases. This mixture of gases is known as biogas. Like natural gas, biogas can also be used as a fuel in power generators, engines, boilers and burners.

Storing Biogas Specially designed and insulated tanks are used to facilitate the anaerobic digestion process under a controlled atmosphere.
Instrumentation for Biogas Production

In practice, specially designed and insulated tanks are used to facilitate the anaerobic digestion process under a controlled atmosphere. These tanks are known as anaerobic digesters or bio digesters.

The effluent coming out from the digester after the completion of the digestion process is known as digestate. Digestate has nutrient value and can be applied on land like manure. Digestate also has much less odor compared to stored manure. Designing a properly sized digester to obtain the maximum biogas production per unit of digester volume is important in maintaining low capital construction costs.

Metanogens Role of methanogens in biogas Production Methanogens are microorganisms that produce methane as a metabolic byproduct in anerobic conditions.
Operating Parameters

Most anaerobic digesters are operated in the temperature range of 15 to 45°C. The pH of the slurry in the digester is maintained between 6.5 and 7.5. The typical retention time of organic matter in the anaerobic digesters varies from 2 days to 60 days, depending on the type of digester and the concentration of organic matter processed. Carbon‐nitrogen ratio of the feed material is also an important factor and should be in the range of 20:1 to 30:1. For example, cowdung has a C–N ratio of 25:1 and is considered ideal for maximum gas production.

Solid concentration in the feed material is also crucial to ensure sufficient gas production, as well as easy mixing and handling. 8 to 10% of total solids is the normal value required. Cow dung has a solid concentration of about 20% and therefore, it is recommended that dung and water are mixed in a 1:1 ratio to attain the desired level of solids. One kilogram of dung produces about 40 liters of biogas.

Anaerobic Digestion What is the role of bacteria in Biogas production? Biogas is generated when bacteria degrade biological material in the absence of oxygen, in a process known as anaerobic digestion.
Effluents and bacteria

Anaerobic digestion depends on the biological activity of relatively slowly reproducing methanogenic bacteria. These bacteria must be given sufficient time to reproduce, so that they can replace cells lost with the effluent sludge, and adjust their population size to follow fluctuations in organic loading.

If the rate of bacteria lost from the digester with the effluent slurry exceeds the growth rate of the bacteria, the bacterial population in the digester will be"washed out" of the system. (slurry is the liquid discharged from any source. Effluents can genarate from municipalities, industries, farms, ships etc. A viscous, semi–solid mixture of bacteria, virus‐laden organic matter, toxic metals, synthetic organic chemicals, and settled solids removed from domestic and industrial waste is known as sludge waste). This washout is avoided by maintaining a sufficient retention time for solids ensuring that the bacterial cells remain in optimal concentration within the digester. The number of days the feed material is required to remain in the digester to begin gas production is known as Hydraulic Retention Time (HRT) – It is the most important factor in determining the volume of the digester; the larger the retention period, higher the volume.

Biogas Purification Biogas has a clean energy In Biogas purification, pure and high calorific value fuel methane is extracted.
Biogas Purification

Biogas is an economical, renewable and an eco‐friendly fuel. Biogas is produced in an anaerobic digester i.e. a Gobar gas plant. Biogas in its natural self consists of moisture, carbon dioxide, hydrogen sulfide and methane gas. Methane has a high calorific value in its pure stage. Due to the presence of impurities Biogas becomes a very low calorific value fuel and hence finds a very limited application even though it is cheap and easily available.

We have to extract pure and high calorific value fuel methane from low calorific fuel Biogas to make it an Internal Combustion (IC) Engine suitable fuel. Once pure methane is available in suitable quality and quantity it finds a wide range of applications from running an oil engine, driving a motor car engine to operating a gas turbine for rural power generation.

High-end Biogas High–end Biogas purification system Biogas treatment system allows for purification of biogas up to bio-methane condition (complete analog of natural gas with methane concentration in the range of 90-97%).
Purification process

Biogas generated from the digester is allowed to flow through moisture traps. This process drains out the moisture present in the gas. The gas is then allowed to counter flow in a specially designed sulfide extractor. This filter drains out balance moisture along with the present sulfides. Treated gas is pressurized with the help of a primary compressor. The filters mounted drain out any moisture left and oil present post compression.

The pressurized clean gas is then passed through a physical separation device. It is a specially designed modern high pressure combined directional flow device for cleaning Biogas of it high impurities. A measuring device is fitted after the filters to gauge the quantum of clean methane gas collected in the collecting tank. Gaseous fuel generates maximum efficiency when it is injected into a converted IC engine with the desired constant pressure.

Biogas Storage Selection of an appropriate biogas storage system makes a significant contribution to the efficiency and safety of a biogas plant.
How gas is stored?

A wide variety of materials have been used in making biogas storage vessels. Medium and high‐pressure storage vessels are usually constructed of mild steel while low‐pressure storage vessels can be made of steel, concrete and plastics. Each material possesses advantages and disadvantages that the system designer must consider.

The newest reinforced plastics feature polyester fabric which appears to be suitable for flexible digester covers. The delivery pressure required for the final biogas conversion system affects the choice for biogas storage. (Read biodegradable plastic here)

Biogas for Combustion Biogas – fulfilling home needs Biogas can be used readily in all applications designed for natural gas such as direct combustion.
Biogas application

By an approximation, 100 cows will give 1000 Kg of cow dung per day. This in a bio–digester will yield about 40 M3 of Gobar gas. After removing impurities such as CO2, sulfur, moisture etc will yield about 20M3 or 17Kg of pure methane gas. It is only now that, a technology has been developed, enabling the use of this gas from bio–digester. Gober gas is purified of all impurities and moisture. Pure methane gas is then compressed. This compressed Bio–Gas (CBG) is capable of running power plants and vehicles.

Biogas can be used readily in all applications designed for natural gas such as direct combustion including absorption heating and cooling, cooking, space and water heating, drying, and gas turbines. It may also be used in fueling internal combustion engines and fuel cells for production of mechanical work and/or electricity. If cleaned up to adequate standards it may be injected into gas pipelines and provide illumination and steam production. Finally, through a catalytic chemical oxidation, methane can be used in the production of methanol production.

Biogas in Transport Biogas train A biogas–powered train, named Biogaståget Amanda, has been in service in Sweden since 2005.
Biogas in transport

If concentrated and compressed (CBG), it can also be used in vehicle transportation. Compressed biogas is becoming widely used in Sweden, Switzerland, and Germany.

In many countries, biogas is viewed as an environmentally attractive alternative to diesel and gasoline for operating buses and other local transit vehicles. The sound level generated by methane–powdered engines is generally lower than that generated by diesel engines and the exhaust fume emissions are considered lower than the emission from diesel engines, and the emission of nitrogen oxides is very low. Application of biogas in mobile engines requires compression to high pressure gas (>3000 psig) and may be best applied in fleet vehicles.

Thus, Biogas is a well established fuel for cooking and lighting in a number of developing countries. Biogas makes a meaningful contribution to the energy supply and it saves fossil energy, such as coal, oil and gas. It also makes a significant ecological contribution to heat and electricity production. Biogas clearly holds promise to resolve both the energy problem and the environmental crisis of our modern days.

References

  • http://en.wikipedia.org/wiki/Biogas#Applications
  • http://www.fountainmagazine.com/Issue/detail/Biogas-as-a-Clean-Energy
  • http://www.biofuelsassociation.com.au/what-is-biogas-made-from
  • http://biogas.ifas.ufl.edu/uses.asp