Question

Which of the following has the highest calorific value?
a.) Coal gas
b.) Water-gas
c.) Producer gas
d.) Carbon dioxide gas

Answer 1

Hint: Calorific value is the amount of heat energy is released during complete combustion of 1 Kg of a fuel. Calorific value is a property of a substance to produce heat. You can use this to find the correct answer here.

Complete Solution :
To answer this, we must remember that calorific value is the amount of heat released by a unit weight or unit volume of any substance when it is completely combusted.

Now, let’s discuss the gases given to us briefly.
- Firstly, we have coal gas. It is a flammable fuel made from coal. It is produced upon strongly heating coal in absence of air. We know that organic substances are broken down by heating in absence of air. This process is known as dry distillation. Dry distillation of solids gives us gases and dry distillation of coal gives us coal gas.
The calorific value of coal gas is 18 – 20 megajoules per cubic metre.

- Then we have water gas. Water gas consists of a mixture of carbon monoxide and hydrogen. We use it for the removal of carbon monoxide from fuel cell applications. Water gas is named ‘water’ gas due to the involvement of water steam in its preparation. A white hot hard coal or coke is blasted with steam and it produces carbon monoxide and hydrogen.
The calorific value of water gas is around 11 megajoules per cubic metre.

- Next, we have producer gas. Producer gas is a combustible gas and it is manufactured by blowing steam through hot coke or coal so that the fuel is completely gasified. It consists mainly of carbon monoxide and hydrogen along with nitrogen. It might also contain some amount of carbon dioxide. It is mainly used in large industrial furnaces as a fuel.
The calorific value of water gas is around 5.8 megajoules per cubic metre.

- Lastly, we have carbon dioxide gas. It is a chemical compound found in nature which is made up of two oxygen atoms each covalently double bonded to a single carbon atom. Carbon dioxide is a significant greenhouse gas that absorbs heat radiation from Earth's surface which in any case would have left the atmosphere. Its calorific value will be lower than the other gases in the options as they are a mixture of two or more gases.
We can understand from the above discussion that coal gas has the highest calorific value.
So, the correct answer is “Option A”.

Note: The calorific value affects the efficiency of a fuel. Efficiency of a fuel is directly proportional to its calorific value. If a gas has high calorific value, then its efficiency is also high. Calorific value is calculated by several theoretical and experimental means.