Wood has extensively been used as a fuel in the past but it is composed of very less amount of carbon and many impurities like sulphur, chlorine, silicon and water.
So, its efficiency as a fuel is very less and a large amount of smoke and ash are produced.
However, the fuel efficiency can be increased and smoke reduced if wood is converted into charcoal by removing the volatile impurities and water.
Similarly, in biomass, when cow dung cakes are used as a fuel, a large amount of smoke and ash is generated. But if it is modified the efficiency as a fuel is increased.
BIOGAS PLANT
Biomass:
Biomass is organic matter that is obtained from living organisms such as crop residue, animal waste, forest debris, municipal solid waste, etc.
It is made up of 75% carbon along with hydrogen, nitrogen, oxygen and small amounts of alkali metals, alkaline earth metals and heavy metals.
Biogas:
It refers to the biological breakdown of organic matter in the absence of oxygen.
It is a mixture of gases produced by the anaerobic decomposition of organic matter such as municipal waste, agricultural waste, plant residue, food waste, etc.
The main components are methane, carbon dioxide and a small amount of hydrogen sulphide and moisture.
CONSTRUCTION AND WORKING OF BIOGAS PLANT:
Construction
Digester:
It consists of underground tank T called digester tank which is made of bricks.
The digester is a kind of sealed tank in which there is no air.
It has a dome-shaped roof made of cement and bricks.
Dome of Digester:
The dome of the digester tank acts as a gas holder. There is a gas outlet through a valve at the top of the dome.
On the left side of the digester tank is a sloping inlet chamber and on the right side is a rectangular outlet chamber, both made of cement and bricks.
The inlet chamber is connected to a mixing tank while the outlet tank is connected to the overflow tank.
Working
Cow-dung and water are mixed in equal proportions to prepare the slurry.
This slurry of dung and water is fed into the digester tank.
The digester tank is filled with dung slurry upto the cylindrical level the dome being left free for the collection of biogas.
It takes about 50 to 60 days for the new gas-plant to become operative.
During this period, the cow-dung undergoes degradation by anaerobic bacteria in the presence of water (but absence of oxygen) with the gradual evolution of biogas.
This biogas starts collecting in the dome. As more and more biogas collects in the dome, it exerts pressure on the slurry in the digester.
From the overflow tank, the spent slurry is removed gradually. The spent dung-slurry, left the extraction of biogas, is rich in nitrogen and phosphorus compounds and hence forms good manure.
Methane is the main constituent of bio-gas. Other gases present with it are hydrogen, carbon dioxide Sulphide.
ADVANTAGES OF BIOGAS
Biogas is non – polluting and burns without smoke. So,no harmful gas such as CO2, CO, NO2, and SO2 are evolved.
The slurry produced after the production of biogas is used as manure in fields. The method of disposal is safe and efficient and hence no space is wasted in the form of landfills.
Biogas plants require very little installation cost. It becomes self-sufficient in a span of 3-4 months.
Biogas also provides work opportunity for thousands of people, especially in rural areas.
Biogas is considered as a renewable source ofenergy because the production is dependent on the generation of waste which is an endless process.
DISADVANTAGES OF BIOGAS
It is not economically viable to use biogas on a large scale since it is difficult to enhance the efficiency of biogas,.
It contains many impurities which are difficult to be controlled even after rounds of purification.
Biogas is highly corrosive to the container when compressed, to be used as fuel.
Methane is produced which comes in contact with oxygen and reacts violently to produce carbon dioxide. The highly inflammable nature of methane makes it prone to explosions.
USES OF BIOGAS
Biogas is used as a fuel for cooking food.
Biogas is a good domestic fuel because of the following reasons:
Biogas burns without smoke and hence does not cause air pollution.
Biogas has a high calorific value. That is, biogas produces a large amount of heat per unit mass.
Biogas burns completely without leaving behind any residue (unlike wood, charcoal or coal). So, it is a clean fuel.
There is no storage problem for biogas as it is supplied by pipes directly from the gas plant.
