Here is a compilation of essays on ‘Biogas’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Biogas’ especially written for school and college students.
Essay on Biogas
Essay Contents:
- Essay on the Introduction to Biogas
- Essay on the Gobar Gas Plant
- Essay on the Biogas Engines
- Essay on the Biogas Digesters
- Essay on the Raw Materials for Biogas Generation
- Essay on the Bio-Gas Applications
- Essay on the Advantages of Biogas
- Essay on the Land Fill Gas Production
1. Essay on the Introduction to Biogas:
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Most organic materials undergo a natural anaerobic digestion in the presence of moisture and absence of oxygen. 60 – 80% of carbon of biomass is converted to a gas called biogas. This contains CH4, CO2, N2 and traces of H2S. The biogas has a heating value of 18.8 to 26.4 MJ/m3. The biogas can be upgraded to a synthetic natural gas (SNG) by removing CO2 and H2S. The heating value of SNG is 37 MJ/m3. One kilogram of dry organic material produces 0.12 to 0.18m3 of methane with energy content of 4.5 to 7 MJ/kg raw materials. A biogas plant is schematically shown in Fig. 6.10.
The various types of biomass can be vegetable waste, animal dung, silt from sewage plant of municipal and industrial effluent water, garbage and vegetable residues, waste from food processing industry. The rate of production of biogas is 0.3 to 0.7 m3 per kg of organic dried mass of animal and vegetable waste. The water vapour and sulphur can be removed from the biogas and cleaned biogas can be used to drive engine for cogeneration plant.
2. Essay on the Gobar Gas Plant:
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Cow-dung is a wonderful waste to meet the fuel and fertilizer requirements in rural areas. With the help of modern technology of anaerobic digestion, the biogas obtained from cow-dung can be effectively used to meet the energy requirements for cooking and heating by direct burning of biogas. This gas can be fed to engines to generate power for lighting, pumping of water, agriculture and small village industries. Of course, spent slurry is a useful by-product with nitrogen content of 1.5 to 2% to be used as good manure.
The cattle population in India is 235 million heads with a dry dung yield of about 170 × 106 tonnes/year. Livestock and indeed human waste have much potential as an energy source via anaerobic digestion. The wastes are treated with the simultaneous generation of methane fuel and retention of nitrogen and other vital plant nutrients in the remaining sludge which can be recycled as a fertilizer.
Biogas generation is a versatile process ranging from small domestic Gobar gas plants catered by a few catties to a much bigger community type plant where relatively large volume of cow-dung is continuously available. These depend greatly on a hot climate and manual labour for its functioning.
Rural Energy Balance:
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In India, more than one lakh biogas plants developed by Khadi and Village Industries Commission are already operating. There is a potential of producing about 22,000 × 106 cubic metres of biogas. The biogas has approximately 65% CH4 and has a heating value of 21 MJ/m3. For a typical village of population 500, the number of cattle would be around 250. The amount of dry dung collected from them is 180 tonnes/year.
This would be sufficient to meet the complete energy requirements of the village population except for two or three months of winter when there will be a shortfall of 20- 40%. However, with further optimization of the anaerobic digestion process this shortage could conceivably be reduced to zero. Given the appropriate innovative technology, and equally important, the willingness to use it, the present quantity of cow-dung can be used to fully meet the energy requirements of rural India.
3. Essay on the Biogas Engines:
The requirement of Indian farmers for engines varies from 3.7 kW to 7.5 kW in vertical high speed and vertical slow speed types all over the country. Normally, the engine runs on an average for 5 hours a day. The biogas engines are essentially diesel engines where air intake is connected to biogas supply. The diesel is required for starting the engine and about 20 percent diesel and 80 per cent biogas are mixed automatically to produce power for running the pump-set.
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The biogas consumption is about 0.46m3/kWh which can be obtained from 13.5 kg of cattle dung, i.e., daily produce of one cattle. The price of a typical 3.7 kW, 1500 rpm biogas engine with centrifugal pump of 100 × 100 mm including, accessories and trolley is about Rs. 6000. It is subsidised by the Government and can be financed by the State Agro Industries, Land Development Banks and all nationalized banks. The cost of a typical gobar gas plant of 85m3 capacity is about one lakh rupees.
4. Essay on the Biogas Digesters:
Biogas is produced by digestion in the presence of anaerobic organisms in the absence of oxygen at ambient pressure and temperatures of 35 – 70°C. The container in which digestion takes place is known as the digester. The anaerobic digestion consists of enzymatic hydrolysis to breakdown cellulosic biomass into simple compounds, these organic compounds are then broken down into organic acids, and these organic acids are then converted into methane (CH4) and carbon dioxide (CO2).
The efficiency of biogas (CH4 + CO2) generation depends upon the following factors:
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i. Acid formers and methane fermenters must remain in a state of dynamic equilibrium which can be achieved by proper design of digester.
ii. A pH value between 6.5 to 8 must be maintained for best fermentation and normal gas production.
iii. For anaerobic digestion, temperature variation should not be more than 2 to 3°C. Methane bacteria work best at 35 – 38°C.
iv. A specific ratio of carbon to nitrogen (C/N ratio) must be maintained between 25:1 and 30:1 depending upon the raw material used.
v. The water content should be around 90% of the weight of the total contents.
vi. The slurry should be agitated to improve the gas yield.
vii. Loading rate should be optimum. If digester is loaded with too much raw material, acids will accumulate and fermentation will be affected.
Digester Design:
1. There are many shapes of digester tanks used in practice.
2. Two types of covers are used. Fixed cover has low cost and more resistance to corrosion.
Floating type cover has the following advantages:
(i) The danger of mixing oxygen with the gas is less. Therefore, danger of explosive mixture formation is reduced,
(ii) Fresh waste can be added to the tank and slurry can be withdrawn without difficulty while digester is in operation. No special pressure equalising device is required.
(iii) The solids are continuously submerged and there is less problem of floating matter.
Capacity of the Digester:
The capacity of the digester tank can be estimated as follows:
Volume of digester = (Q1 + Q2/2)t
Where Q1= Daily rate of waste added
Q2 = Daily volume of waste after digestion
t = Digestion time in days.
Digestion time to produce good sludge depends upon the temperature in the tank. In winters, the sewage sludge digestion tanks are heated to 35°C.
The following guidelines may be used to fix optimum size of a biogas plant:
i. Daily rate of waste to be digested,
ii. Type of waste,
iii. Period of digestion,
iv. Method of stirring, if any
v. Arrangement for raw waste feeding and discharge of digested slurry,
vi. Climatic conditions,
vii. Mix of raw waste,
viii. Water table and sub-soil conditions,
ix. Type of dome, and
No separate heating and stirring may be used for agriculture waste.
Types of Digesters:
There are numerous types and designs of biogas digesters.
Mainly two types of digesters are used for community biogas generation:
1. KVIC Community-Type Gobar Gas Plant:
The Khadi and Village Industries Commission of India has designed and patented a “Grah Luxmi” Gobar Gas plant. It has been adopted in Indian villages on a large scale.
The digester is pit made of masonry. It has a diameter of 1.2 to 6m and well depth of 3.5 to 6 m. A vertical wall divides the well into two semi-cylindrical compartments.
The partition wall is submerged in the slurry. Cement pipes of 10 cm diameter serve as inlet and outlet pipes. The dung and water are mixed in the ratio of 4:5 in the feed tank and fed to the well.
The digester can hold the raw material for 60 days. When gobar slurry is added, fermented slurry flows out in the outlet tank and collected in a composed pit.
A floating type mild steel drum fits the digester at the top and sinks into the slurry. When gas is generated, the float cover rises and floats freely on the surface of the slurry. A central guide pipe prevents its tilting. The floating drum also acts as gas seal and ensures a gas pressure of 10-15 cm of water gauge. The biogas is tapped from the drum top.
The cost of steel drum is 40% of total plant cost and corrosion of drum demands regular maintenance.
2. Chinese Digester:
In KVIC gobar gas plant, biogas is the main product and manure is a byproduct. Chinese use the digester for manure and biogas as by-product.
It is a fixed dome design and gas is available at variable pressure. It is totally made of masonry. The construction cost may be 40% of KVIC design and it has very little maintenance requirements.
5. Essay on the Raw Materials for Biogas Generation:
Forestary and agricultural residues can be best utilized to generate, electricity or process heat by fluidised bed combustion. These can also be dried and used for gasification. Cow-dung is a wonderful waste for generation of biogas by anaerobic digestion.
Other raw materials are:
1. Water Hyacinth:
It grows as floating water plant in the rivers and canals. It contains 95 percent water and 5 percent cellulose, lignin, etc. It grows in waste waters thereby cleaning the ponds. It gives about 350-420 litres of biogas per kg of dry weight. It is one of the important sources of biogas production next to animal wastes.
2. Algae:
Algae plants grow in lakes, tanks, etc. The best place for their cultivation is in shallow land ponds. It can be anaerobically fermented to produce methane with a lower calorific value of 15000 kJ/kg of dry algae.
3. Ocean Kelp:
It is a kind of sea weed which grows in the coastal areas and also in the high seas. Yield rates range from 300-500 wet tonnes/acre/year.
4. Grasses:
Some fast growing grasses can also be used for biogas generation. Napier grass, Sudan grass and Bangola grass give the best yield. The cut grass is mixed with water and fed to bio-gas digesters.
6. Essay on the Bio-Gas Applications:
Biogas is a flammable fuel gas with 60 percent methane and rest CO2. Its heating value is about 18 kJ/m3. The gas can be upgraded by removal of CO2 with water scrubbing and the gas with high heating value can be used in I.C. engine.
The main applications of biogas are:
1. Cooking:
There are thousands of homes in rural areas using biogas as fuel for cooking. Low cost burners have been designed for the hot plate.
2. Domestic Lighting and Heating:
The biogas supply from the digester is sent through a rubber hose where a nozzle is used for the lamp and stove. The gas sprays out from the nozzle at a very high velocity and mixes with air drawn into the mixing chamber due to low pressure after the nozzle. The brightness and force of combustion of stove and lamp depend on the biogas pressure. A biogas lamp with a mantle can run for six hours per m3 biogas and give a luminosity of 60 W equivalent of electrical light.
3. I.C. Engines:
Biogas can be directly used in SI engines with suitable modification in the carburetor. However, bio-gas engines are essentially diesel engines.
4. Fuel Cell:
Electricity can be produced by using bio-gas in a fuel cell with air as oxidant. The electrolyte is usually potassium hydroxide.
7. Essay on the Advantages of Biogas:
i. The initial investment is low due to simple plant.
ii. The raw materials for digester can be grown and cultivated like conventional agriculture.
iii. The technology is very suitable for rural areas.
iv. Biogas is locally generated and can be easily distributed for domestic use.
v. The raw material utilization also helps to keep the villages clean.
vi. The by-products like nitrogen rich manure can be used with advantage.
The main disadvantages are requirement of large land areas for cultivation of biomass and difficulties in the distribution of bio-gas as the same cannot be liquefied.
8. Essay on the Land Fill Gas Production:
Solid wastes, or refuse are generated by industrial and domestic processes (garbage). Industrial wastes include paper, wood, metal scraps, and agricultural waste products. Domestic waste products include paper, containers, tin, aluminium, food scraps and sewage. In developed countries the solid waste production can be as high as 1 metric ton per person per year. A typical sample of municipal waste can be as given in table. 6.2.
Some wastes like paper, metals and woods can be recycled for reuse. Much of it can be burned for heating and generating steam for electric power plants. Refuse burning in incinerators has been a wide practice in many parts of the world. The energy potential of refuse is not too great by burning. But refuse has low Sulphur content.
The main problems are the wide assortment of constituents, high moisture content, dangers of explosions due to careless volatile fuel dumping and metal sparks during processing and wide variations in heat content. Therefore, a mixture of solid waste and fossil fuel, with refuse supplying 10 to 20 percent of the heat input to the boilers is being used for power plants. The costs of collection, transportation and processing (removal of ferrous metals and non-combustibles, shredding and hammer milling) have to be considered against its use for land filling.
The land filling yields gas @ 8m3 /annum. The approximate composition of landfill gas is:
CH4 : 59%
CO2 : 40%
N2 : 1%
HC + H2S : Traces
The lower heating value is only 5MJ/m3. In case of large-scale land-fill gas, it can be processed to be used as a substitute for natural gas. In an absorption or membrane separation process, CO2 is removed and the methane content can reach 98%. A gas turbine power plant working on landfill gas is operating on the suburbs of India’s capital. Fig 6.13 shows the layout of a landfill gas plant.
