The waste and dead parts of living organisms (plants and animals) such as wood, straw, cow dung, agricultural wastes and household rubbish are collectively called as bio mass. The bio energy produced by burning or processing of bio-mass is the main source of energy for millions of villagers in India. Bio-mass can be converted into energy by using different methods. One method is to bury the plant and animal wastes in the earth by digging wells. After some time, these waste materials decay to produce methane gas. The second method of obtaining bio energy from bio-mass is to directly burn the bio-mass such as dry cow dung and wood. But the burning of dry cow in the form of fuel is not advisable due to following reasons:
- Burning of cow dung as a fuel produces a lot of smoke which is harmful for human health and cause environmental pollution.
- Burning of cow dung as a fuel destroys useful nutrients present in it.
- Very less amount of heat is produced during burning of cow dung.
- A large amount of ash gets produced as residue after burning of cow dung.
Third method of obtaining energy from bio-mass is to prepare biodiesel. This is done by removing glycerine from vegetable oil. The biodiesel so produced from vegetable oils is then used as diesel fuel.
In spite of these methods, one more method to use bio-mass is to convert one type of fuel into another more useful fuel. For example, wood and cow dung can be converted into more useful fuels called charcoal and bio-gas respectively. The process of conversion of solid biomass into gaseous fuel is called bio mass gasification. Now, we will discuss in detail the methods to convert wood into charcoal and cow dung into biogas. But, before doing so we should know the meaning of destructive distillation. Destructive distillation can be defined as the process of conversion of complex carbon compounds into simple substances by heating strongly in a closed vessel in absence of air.
Destructive Distillation of Wood or Preparation of Charcoal
To prepare charcoal from wood, take two hard glass tubes. In first glass tube, put some pieces of wood and fix it in horizontal position with the help of a stand. In second test tube put some water and fix it in vertical position. Now, set the apparatus with the help of two delivery tubes as shown in fig. 9. Make it sure that the joints are air tight. Now, heat the glass tube containing pieces of wood first gently and then strongly with the help of a burner.
Destructive Distillation Of Wood
After sometime you will find a gas called wood gas is flowing out through second delivery tube. The wood gas is combustible and consists of many gases. You will also find that a black coloured residue called charcoal is left in first glass tube and a black liquid has settled at the bottom of second glass tube containing water.
It should be noted that charcoal burns easily without producing smoke and produces more heat as compared to wood on burning. Due to these reasons charcoal is considered better fuel than wood.
Test Your Understanding and Answer These Questions:
- What is bio mass?
- What is bio mass gasification?
- What is destructive distillation?
- Explain destructive distillation of wood.
- Why burning of cow dung cake is not advisable?
- Why charcoal is considered a better fuel than wood?