The dead parts of plants and trees, and the waste materials of animals are called biomass. Biomass is called organic matter which is used as a fuel to produce energy. Biomass includes wood, agricultural wastes (crop residues) and cow-dung. Biomass contains chemical energy in the form of carbon compounds. Dried biomass (like wood) is the oldest source of heat energy which is still widely used as a fuel for domestic purposes. Actually, biomass is which solar energy manifests itself. This is because all the plants and trees which provide biomass (like wood) used sun's energy to grow.
Even the animal wastes (like cow-dung) are given by cattle who grew by consuming plant food made with the help of sunlight energy. Since the fuels like wood, agricultural wastes and cow- dung are all plant and animal products, so they are called biomass (or biofuels). Please note that biomass is a renewable source of energy because it is obtained from plants (or animals) which can be produced again and again.
The Case Of And Charcoal
Wood is biomass. When wood is burnt, is produced. So, wood has been used as a fuel for a long time. Wood that is burnt as a fuel is called firewood. Wood is a renewable source of energy. Wood is obtained by cutting down the trees. Now, if we ensure that enough trees are planted in place of cut down trees, then a continuous supply of firewood can be obtained.
The traditional use of wood as a fuel has many disadvantage. For example:
- The burning of wood produces a lot of smoke which pollutes the air, and
- The calorific value (or heat value) of wood is low, being only 17J/g.
Due to improvement in the technology for using the conventional source of energy, wood can be converted into a much better fuel called charcoal. Charcoal can be prepared from wood as follows:
When wood is burnt in a limited supply of air, then water and other volatile material present in it get removed and a black substance 'charcoal' is left behind. Thus, wood minus volatile material is charcoal. Charcoal is mainly carbon (C). Charcoal is mainly used as a fuel for domestic purposes. Charcoal is a Charcoal fuel than wood because of the following reasons:
- Charcoal has a higher calorific value than wood. That is, charcoal produces more heat on burning than an equal mass of wood.for example, the calorific value (heat producing value) or charcoal is higher, being about 33 kilojoules per gram, whereas that of wood is low being only 17 kilojoules per gram.
- Charcoal does not produce smoke while burning whereas wood produces a lot of smoke on burning and pollutes the air.
- Charcoal is a compact fuel which is easy to handle and convenient to use.
Cow- dung is biomass. It is also known as 'cattle dung' or animal dung or just 'dung'. Cow- durning is the 'excreta' of cattle such as cows and buffaloes, etc. Cow dung is usually semi-solid. In our villages, dried cow- dung cakes have been traditionally used as fuel for cooking food. When cow- dung cakes are burnt, they produce heat. This heat is used for cooking food, etc. It is however, not good to burn cow-dung directly as a fuel food, etc. It is, however, not good to burn cow dung directly as a fuel because of the following disadvantages:
- Cow- dung contains important element like nitrogen and phosphorus (called nutrients), which are required by the solid to support crops. So, burning of dung in the form of dung cakes destroy the useful nutrients which can otherwise be used as a manure in agricultural.
- Dung cakes produce a lot of smoke on burning which causes air pollution.
- Dung cakes do not burn completely, they produce a lot ash as residue
- Dung cakes have low calorific value (low heat producing value).
When used in this way, cow- dung gives us a advantage:
- It gives us a clean biogas, and
- The spent dung can be used as a manure.
Biogas is not single gas. It is a mixture of gases. Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide. The major constituent of biogas is methane, which is an extremely good fuel. In fact, biogas contains up to 75 per cent of methane gas which makes it an excellent fuel.
Biogas is produced by the anaerobic degradation of animal wastes like cow-dung (or plant wastes) in the preset of water. This degradation is carried out by anaerobic micro- organisms called anaerobic bacteria in the presence of water but in the absence of oxygen. Cow dung and plant wastes contain a lot of complex carbon compounds like carbohydrates, proteins and fats. The anaerobic bacteria degrade (decompose) theses carbon compounds to form methane gas, which is the main constituent of biomass. Some other gases like carbon compounds to form methane gas, which is the main constituent of biomass. Some other gases like carbon dioxide, hydrogen and hydrogen sulphide are also formed. Cow dung is known as 'gobar' in Hindi. Since biogas is prepared mainly from cow- dung, so biogas is popularly known as 'gobar Gas' in Hindi. Since biogas is prepared mainly from cow- dung, so biogas is popularly known as 'gobar gas' in our villages.
We will now describe a biogas plant which is also known as gobar- gas plant.
