Biogas Plant PPT - Agrobotany

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Frequently Asked Question

What is Biogas?

Summary

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Biogas is produced from the anaerobic digestion of organic materials in the presence of moisture and the absence of air.

Biogas is a mixture of methane (CH4 ):55 - 65 %, Carbon dioxide (CO2): 40 - 30%, and H2, H2S, and N2.

The calorific value of biogas ranges from 5000 to 5500 Kcal/Kg.

What is Anaerobic Digestion?

Anaerobic digestion is the decomposition of organic waste into gaseous fuel by bacteria in an oxygen-free environment. The process occurs in 3 stages

1. Hydrolysis

Large molecules are breakdown into smaller sizes by enzymes. which in turn are decomposable by bacteria i.e. cellulolytic bacteria is of two types mesophilic (30°- 40°) and thermophilic (50°-60°). (Eg - Polysaccharides into monosaccharides). Then they are further converted into organic acids (acetate, propionate and butyrate).

2. Acid Formation

In this phase, the organic materials convert into simple acids eg. – volatile fatty acids. Acetic acid is one common by-product of the digestion of fats, starch and proteins, some other acids like butyric acid and propionic acid are also produced.

3. Methane Formation

Methanogenic bacteria react with acetic acid, and with other products to produce methane. Methane-forming bacteria are slow, in about 14 days at 25 °C the digestion will be completed. The remaining indigestible matter is referred to as “slurry”.

What is the Optimum Condition for Biogas Plant?

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Temperature - 30-35°C

pH - 6.8-7.5

C/N ratio - 20-30:1

Solid content - 8-10%

Retention time - 20-50

How many Types of Biogas Plant?

Summary

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A Floating type

B. Fixed type

A. Floating types

This type of Plant, is not underground due floating gas holder hence land Occupied by the plant cannot be used for any other purposes.

1. KVIC-Type (KVIC- Khadi Village Industries Commission)

This mainly consists of a digester (Dept. – 3.5-6.5 m and 1.2 to 1.6 m in diameter) for fermentation and a floating drum for the collection of gas. There is a partition wall in the centre, which divides the digester vertically. The digester is connected to the inlet pipe (by which the dung, is mixed with water (4:5) and loaded into the digester) and outlet pipe ( by which the fermented material will flow out through) by two pipes. One of the main components of the biogas plant is

Gas holder - its cylindrical shaped body is constructed of mild steel sheets and acts as a seal for the gas. The holder fits into the digester like a stopper. When the gas is generated the holes float freely. On the surface of the slurry. A central guide pipe is also provided to prevent the tilting of the holder. The gas pressure varies between 7 to 9 cm of the water column. The cost of the Drum is about 40% of the total cost of the plant.

2. Janat-Type Biogas Plant

This name was introduced by the Gobar Gas Research Station due to its reduced cost. But it's a Chinese-origin design. The main feature of this plant is - no need for steel and any moving structure and maintenance cost is low. This plant can be constructed by some pre-explained precautions and indigenously available building material. This model has higher capacity and longer life than the KVIC-TYPE model. hence its use as a community biogas plant.

This plant consists of a well-underground sort of digester made of cement and bricks. And has a dome-shaped roof which remains underground. Al almost the middle of the digester rectangle shape structures is facing each other and come up to a little above of underground level, acting as inlet and outlet pipes of the plant. A Dome shaped roof is fitted with a pipe on its top which is the gas outlet of the plant. The principle of gas production is the same as KVIC-TYPE but the gas pressure is about 90cm water column which is higher than the KVIC-type plant.

2. Deenbandhu Biogas Plant:

Deenbandh model was developed in 1984, by Action for Food Production (AFPRO). A voluntary organisation, saturated in New Delhi, designed the entire Deenbandh biogas Plant. Their construction cost is less than the KVIC-TYPE model. The cost reduction has been achieved by minimising the surface area by joining the segment of two spheres of different diameters at their base. The holder of deenbandh is a hemispherical fixed-dome type. The dome is made from pre-fabricated reinforced concrete and attached to the digester, which has a curved bottom. The slurry is fed from the mixed tank through an inlet pipe connected to the digester. After Fermentation, the biogas collects inside the dome. The gas is brought out for use through a pipe connected to the top of the dome. And by-product is stored in the outlet chamber and taken out by the hole. In India, about 90% of biogas plants are deenbandh type.

What are the Advantages of Biogas Plant?

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1. Cost of equipment used for making biogas is less and the equipment used is very simple.

2. Waste product obtained from the digester is the best quality fertilizer and gives the best yields.

3. Biogas can be used for lighting, running engines, and farm machines and cooking gas in the kitchen.

4. Distribution of gas has no problems of any gas leakages and fires.

5. Biogas is the best medium for cooking food.

6. Organic feedstocks used in the plants are easily available at all places

What are the Disadvantages of Biogas Plant?

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The biogas product of the biogas plant has to be used at nearby places only. It can not be transported to long-distance places.

Biogas can not be filled in bottles.

Biogas plants required more area.

It can not be established in the Urbana area due lake of the availability of land.

Explain about Basic Pre-requisites of Biogas Plant Installation.

1. The surface or area should be levelled and at a higher elevation than the surrounding areas to avoid a run-off.

2. Soil Should not be too loose of an area.

3. The biogas plant should be nearer to the place of gas use and also near to the place of raw materials production.

4. The groundwater table should not be too high.

5. Adequate supply of water should be available.

6. The plant should get the maximum sunshine during the day.

7. A minimum distance between a plant and a source of water should be 1.5m...

8. Plants should be away from trees to avoid root interference.

9. It should be adequate space for slurry pits.

10. The solid content in slurry should be maintained between 7.5 to 10% for better gas production.

11. C:N of raw materials should be 20-30:1 for good gas production.

What are the Factors Affecting Biogas Production

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1. C:N Ratio

The carbon and nitrogen ratio should be 20-30:1. If it is high so gas production becomes slow.

2. Temperature

The temperature affects the reaction that takes place inside the digester. 30-35°C is optimum for gas production. The gas production will be stopped at 10°c.

3. Loading Rate

The loading rate is defined as the amount of raw material fed to the digester per day per unit volume. If the reactor is overloaded, acid accumulation will be more obviously affecting daily gas production.

4. pH

The pH should be 6.8-7.5. Both the acidic and alkaline nature of slurry affects the activity of microorganisms.

5. Total Solid Content

The TDC of raw material should be 8-10%. It helps in the easy digestion of raw materials and improves gas production.

6. Degree of Mixing

Bacteria in the digester have very limited reach to their food, it is necessary that the slurry is properly mixed and bacteria get their food supply. It is found that slight mixing improves fermentation;

7. Diameter-to-Depth Ratio

Studies reveal that gas production per unit volume of digester capacity was maximum when the diameter-to-depth ratio was in the

range of 0.66 to 1.00.

8. Toxicity:

The high concentration of heavy metals and detergents hurts the gas production rate. Detergents like soap, antibiotics, and organic solvents are toxic to the growth of microbes inside the digester.

Reference:

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